CA2141043A1 - Black glss ceramic from rapid pyrolysis in oxygen-containing atmospheres - Google Patents
Black glss ceramic from rapid pyrolysis in oxygen-containing atmospheresInfo
- Publication number
- CA2141043A1 CA2141043A1 CA002141043A CA2141043A CA2141043A1 CA 2141043 A1 CA2141043 A1 CA 2141043A1 CA 002141043 A CA002141043 A CA 002141043A CA 2141043 A CA2141043 A CA 2141043A CA 2141043 A1 CA2141043 A1 CA 2141043A1
- Authority
- CA
- Canada
- Prior art keywords
- heating
- black glass
- carbon
- carbon atoms
- silicon
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/045—Silicon oxycarbide, oxynitride or oxycarbonitride glasses
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
- C03C10/0009—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing silica as main constituent
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C14/00—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix
- C03C14/002—Glass compositions containing a non-glass component, e.g. compositions containing fibres, filaments, whiskers, platelets, or the like, dispersed in a glass matrix the non-glass component being in the form of fibres, filaments, yarns, felts or woven material
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2214/00—Nature of the non-vitreous component
- C03C2214/02—Fibres; Filaments; Yarns; Felts; Woven material
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2214/00—Nature of the non-vitreous component
- C03C2214/02—Fibres; Filaments; Yarns; Felts; Woven material
- C03C2214/03—Fibres; Filaments; Yarns; Felts; Woven material surface treated, e.g. coated
-
- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C2214/00—Nature of the non-vitreous component
- C03C2214/20—Glass-ceramics matrix
Abstract
A black glass having the empirical formula SiCxOy where x is greater than zero and up to about 2.0 and y is greater than zero and up to about 2.2 is produced from a cyclosiloxane polymer precursor by pyrolysis in the presence of oxygen by heating at a rate exceeding about 5 °C/min.
Description
~ 0 4 3 W094/03405 PCT/US92/06~4 BLACX G~ASS CERAMIC FROM RAPI3 PYROT.YSIS IN OXYGEN-CO~TAINING ATMOSPH~ES
Prior Art The invention relates generally to carbon-containing glass which may be used alone or as a matrix material reinforced with fibers.
In USSN 002,049 a ceramic composition designated "black glass~ is disclosed which has an empirical formula SiCxOy where x ranges from 0.5 to about 2.0 and y ranges from about 0.5 to about 3.0, preferably x ranges from o.s to 1.6 and y ranges from 0.7 - 1.8. That ceramic material has a higher car~on content than prior art materials and is very resistant to high temperatures - up to about 1400-C. It is produced by reacting in the presence of a hydrosilylation catalyst a cyclosiloxane having a vinyl group with a cyclosiloxane having a hydrogen group to form a polymer precursor, which is subsequently pyrolyzed in an inert atmosphere to yield black glass.
The present in~ention involves a new method of pyrolyzing such black glass precursors.
In co-pending application U.S. Ser. No.
07/586,632, it is shown that by including oxygen during the pyrolysis that the carbon content of the black glass can be adjusted to a lower value useful for certain purpo~es. We have now found that if the pyrolysi8 step is carried out rapidly enough that the eff~ct of oxygen can be over~ome and black glass having a high car~on content can be achieved, even if pyrolyzed in the presence of air.
W094/~3405 ~o~3: PCT/US9~/06~ ~
Summarv of t~e Invention A car~on-containing black glass reramLc composition having the empirical formula SiCxOy where x is greater than zero and up to about 2.0, preferably up to about 1.6, and y is greater than zero and up to about 2.2, preferably up to about 1.8, is produced by pyrolyzing certain polymer precursors at a rate exceeding 5-C/min, preferably 50-C~min to lOOO C/min, most preferably above lOO-C/min in the presence of oxygen, preferably in air.
~ The black glass ceramic composition is the = pyrolyzed reaction product of a polymer prepared from (1) a cyclosiloxane monomer having the formula ~ R' = 15 -- (si--O) n I .
R
= 20 where n is an integer from 3 to about 30, R is = hydrogen, and R' is an alkene of from 2 to about 20 car~on atoms in which one vinyl carbon atom is directly bonded to silicon or (2) two or more different cyclosiloxane monomers having th~ formula of tl) where for at least one monomer R is hydrogen and R' is an alkyl ~u~ having from 1 to about 20 carbon atoms and for t~e other monomers R is an alkene from a~out 2 to about 20 carbon atoms in which one vinyl carbon is - directly h~n~e~ to silicon and R' is an alkyl group of = 30 from 1 to about 20 carbon atoms, or (3) cyclosiloxane monomers having the formula of (1) where R and R' are independently salected from hydrogen, an ~lkene of from 2 to about 20 carbon atoms in which one vinyl car~on atom is directly bonded to silicon, or an alkyl group of from 1 to about 20 carbon atoms and at least some of ~ 21410~3 said monomers contain each of said hydrogen, alkene, and alkyl moieties, said polymerization reaction takin~
place in the presence of an effective amount of hydrosilylation catalyst. The polymer product is pyrolyzed by heating in an oxidizing atmosphere at a rate above 5-C/min to a temperature in the range of about 800-C to about 1400-C. The black glass ceramic thus produced retains carbon despite being in an oxidizinq atmosphere. When the heating rate is above lo about 100 C/min~ the black glass ceramic contains substantially the same amount of carbon as produced by pyrolysls in an inert atmosphere.
The black glass may be employed in many forms such as fibers, coatings, films, powders, monoliths, and particularly as a matrix for fiber reinforced composites.
The heating may be carried out using hot combustion gases, radiant energy, or other methods familiar to those skilled in the art. The carbon content may be controlled by adjusting the heating rate, and the oxygen access to the polymer during pyrolysis.
DescriDtion o~ the Preferred ~hodiments ~l~c~ G!~s ~mic Th~ black glass ceramic ha~ an empirical formula sicxoy wherein x is greater than zero and up to about 2.0, prQf~rably up to about 1.6, and y is greater th~n zero and up to about 2.2, preferably up to about 1.8, wher~by the car~on content range~ up to about 40%
by weight. The black glass ceramic i5 the product of the pyrolysis at a rate eXcee~ing S-C/min in an - oxidizing atmosphere to temperatures between about 800-C and about 1400-C of a polymer made from certain siloxane monomers. Preferably, a heating rate of .
a~~
~ 50 C/min to 1ooo C/min is used, most preferably greater = than 100 C/min. The carbon content will be determined generally by the heating rate and the access of oxygen to the polymer precursor during pyrolysis.
~ 5 The polymer precursor of the black glass = ceramic may be prepared by subjecting a mixture containing cyclosiloxanes of from 3 to 30 silicon atoms to a temperature in the range of from about lo-C to about 300-C in the presence of 1-200 wt. ppm of a ~ 10 platinum hydrosilylation catalyst for a time in the = range of from about 1 minute to about 600 minutes. The = polymer formation takes advantage of the fact that a silicon-hydride will react with a silicon-vinyl group = to form a silicon-carbon-carbon-silicon bonded chain, thereby forming a network polymer. For this reason, ~ each cyclosiloxane monomer must contain either a - silicon-hydride bond or a silicon-vinyl bond or both.
~ A silicon-hydride bond refers to a silicon atom bonded = directly to a hydrogen atom and a ~ilicon-vinyl bond refers to a silicon atom bonded directly to an alkene carbon, i.~., it is connected to another carbon atom by = a double bond.
The polymer precursor for the black glass ceramic may be defined generally as the reaction product of (1) a cyclosiloxane monomer having the = formula = R' I
(Si--O) n R
where n is an integer from 3 to 30, R is hydrogen, and = R' is an ~lkDne of from 2 to 20 carbon atoms in which one vinyl carbon atom is directly bonded to silicon or .
W094/03405 ~1 4 ~ O ~ 3 PCT/US92/06644 (2) two or more different cyclosiloxane monomers havlng the formula of (1) where for at least one monomer R is hydrogen and R' is an alkyl group having ~rom 1 to 20 carbon atoms and for the other monomers R is an alkene from a~out 2 to 20 car~on atoms in which one vinyl carbon is directly bonded to silicon and R' is an alkyl group of from 1 to 20 carbon atoms, or (3) cyclosiloxane monomers having the formula of (1) where R and R' are independently selected from hydrogen, an alkene of from 2 to about 20 carbon atoms in which one vinyl car~on atom is directly bonded to silicon, or an alkyl group of from 1 to about 20 carbon atoms and at least some of said monomers contain each of said hydrogen, alkene, and alkyl moieties, said reaction taking place in the presence of an effective amount of hydrosilylation catalyst.
The black glass ceramic may be prepared from a cyclosiloxane polymer precursor wherein both the requisite silicon-hydride bond and the silicon-vinyl bond are present in one molecule, for example, 1,3,5,7-tetravinyl-1,3,5,7-tetrahydro-cyclo-tetrasiloxane. Such monomers may also contain alkyl ~ou~ such a~, for example, 1,3-divinyl-1,5-dihydro-3,5,7,7-tetramethylcyclosiloxane. Alternatively, two or more cyclosiloxane monomers may be polymerized.
Such monomer~ would contain at least either a silicon hydride bond or a silicon-vinyl bond and the ratio of the two types of bonds should be about 1:1, more ~ro~dly about 1:9 to 9:1.
Examples of such cyclo~iloxanes include, but are not limited to:
1,3,5,7-tetramethyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetravinyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetravinyltetraethylcyclotetrasiloxane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, ~ W094/03405 PCT/US92/06~4 ~
1,3,5-trimethyltrivinylcyclotrisiloxane, 1,3,5-trivinyltrihydrocyclotrisiloxane, 1,3,S-trimethyltrihydrocyclotrisiloxane, 1,3,5,7,9-pentavinylpentahydrocyclopentasiloxane, 1,3,5,7,9-pentavinylpentamethylcyclopentasiloxane, 1,1,3,3,5,5,7,7-octavinylcyclotetrasiloxane, = 1,1,3,3,5,5,7,7-octahydrocyclotetrasiloxane, 1,3,5,7,9,11-hexavinylhexamethylcycloh~Yasiloxane, 1,3,5,7,9,11-hexamethylhexahydrocyclohexasiloxane, 1,3,5,7,~,11,13,15,17,19-decavinyldecahydrOcyclodeca-siloxane, 1,3-divinyl-1,5-dihydro-3,5,7,7-tetramethylcyclosiloxane ~ 1,3,5-trivinyl-1,3,5,7,7-= lS pentamethylcyclotetrasiloxane 1,3,5-trihydro-1,3,S,7,7-= pentamethylcyclotetrasiloxane 1,3,S,7,9,11,13,15,17,19,21,23,2S,27,29-pentadeca-vinyl-1,3,5,7,9,11,13,1s,17,19,21,23,25,27,29-pentadecahydrocyclopentadecasiloxane - 1,3,5,7-tetrapropenyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetrapentenyltetrapentylcyclotetrasiloxane and 1,3,5,7,9-pent~Asc-~ylpentapropylcyclopentasiloxane.
~ 25 It will ~e understood by those skilled in the _ art that while the silo~A~9 monomers may be pure ~pecl~s, it will be frequently desirable to use = mi~as of Such monomers, ln which a single species is ominant. M~xture~ in which the tetramers predominate have ~een found particularly useful.
Whilc the rcaction works best if platinum is ~ the hydrosilylation cataly~t, other catalysts such as _ cobalt and manganese carbonyl will perform adequately.
= The catalyst can be dispersed as a solid or can be used as a solution when added to the cyclosiloxane monomer.
.
W094/03405 2l 41 0~ 3 PCT/US92/06644 7 ~
With platinum, about l to 200 wt. ppm, preferably 1 t_ 30 wt. ppm as the metal will be employed as t~e catalyst.
Blac~ glass precursor poly~er may be prepared from either bulk or solution polymerization. In bulk polymerization, neat monomer liquid, i.e., without solvents, reacts to form oligomers or high molecular weight polymers. In bulk polymerization, a solid gel can be formed without entrapping solvent. It is particular1y useful for impregnating porous composites to increase density. Solution polymerization refers to polymerizing monomers in the presence of an unreactive solvent.
When the resin is used in impregnating fibers to form prepreg, it preferably is prepared by solution polymerization. The advantage of solution polymerization is the ease of controlling resin characteristics. It is possible but very d$fficult to produce B-~tage resin suitable for prepregs with consistent characteristics by bulk polymerization.
Soluble resin with the desirable viscosity, tackiness, and flowability suitable for prepregging and laminatin~
can be_ obtained consistently using solution polymerization process. The production of ezsily hand~eable and consistent resin is very critical in ~ ite ~abrication.
E~er~
Where reinforcing fibers are used with the blac~ glas~ ceramic they typically are refractory fibers which are of interest for applications where superior physical properties are needed. They include such materials as boron, silicon carbide, graphite, silica, quartz, S-glass, E-glass, alumina, aluminosilicates, boron nitride, silicon nitride, boron W094/03405 ~ PCT/US92/06644 car~ide, titanium boride, titanium car~ide, zirconium oxide, silicon carbonitride, silicon oxycarbonitride and zirconia-toughened alumina. The fibers may have - various sizes and forms. They may be monofilaments from l ~m to 200 ~m diameter or tows of 200 to 2000 filaments. When used in composites of the invention they may be woven into fabrics, pressed into mats, or unidirectionally aligned with the fibers oriented as desired to obtain the needed physical properties.
lo An important factor in the performance of the black glass composites is the strength of the bond between the fibers and the black glass matrix.
Consequently, where improved m~h~nical strength or toughness is desired, the fibers are provided with a coating which raduces the bonding between the fibers ~ and the blac~ glass matrix. The surface sizings found - on fibers as received or proA~ m~y be removed by solvent wA~ing or heat treatment and the coating applied, which may be of carbon or other materials such as boron nitride and silicon carbide.
= Various methods may be used to apply a car~on = coating, including chemical vapor deposition, solution coating,_ and pyroly~is of organic polymers such as carbon pitch and phenolics. One preferred technique is 2s chemical vapor deposition using decomposition of methane or other hydroc~on~. Another method is pyrolysis Or an organic polymer coating such as phenol-forcaldehyde polymers cros~-linkQd with such agents a~ the monohydrate or sodium salt of paratoluene~u~fonic acid. Still another method uses toluene-solublQ and toluene-insoluble carbon pitch to coat the fibers. Boron nitride and silicon carbide coatings are typically applied by chemical vapor deposition from a gaseous prec~rsor.
,.
..
0 ~ 3 W094/03405 PCT/US92/06~4 Processin~
As previously discussed, the blac~ glass precursor is a polymer. It may be shaped into fibers and com~ined with reinforcing fibers or the black glass precursor may be used in solution for coating or impregnating reinforcing fibers. Various methods will suggest themselves to those skilled in the art for combining the black glass precursor with reinforcing fibers. It would, for example, be feasible to com~ine fibers of the polymer with fibers of the reinforcing material and then to coat the resulting fabric or mat.
Alternatively, the reinforcing fibers could be coated with a solution of the polymer and then formed into the desired shape. Coating may be done by dipping, spraying, brushing, or the like.
In one method, a continuous fiber is coated with a solution of the black glass precursor polymer and then wound on a rotating drum covered with a release film which is easily separated from the coated fibers. After sufficient fiber has been built up on the drum, the process is stopped and the uni-directional fiber mat removed from the drum and dried.
The resulting mat (i.e., "prepreg") then may be cut and ~ ted into the desired shapes.
In a second method, a woven or pressed fabric of the reinforcing fibers is coated with a solution of the black gla~s precursor polymer and then dried to remov~ the solvQnt, after which it may be formed into the desired 5h~pes by procedures which are familiar to thosQ skilled in the art of fabricating structures with the prepreg ~heets. For ~mrle, layers of prepreg sheets may be laid together and pressed into the needed shape. The orientation of the fibers may be chosen to strengthen the composite part in the principal load-bearing directions.
W094/03405 ~ 0 ~3 PCT/US92/06~4 ~ A third method for fabricating the polymer - composite is by resin transfer molding. In resin - transfer molding a mold with the required shape is filled with the desired reinforcement material. The reinforcement could be a preform having a 3-dimensional weave of fibers, a lay-up of fabric plies, a non-woven mat of chopped staple or bundled tows, or assem~lies of whiskers, and such others as are familiar to those skilled in the art. The reinfor~ement - 10 material would be coated with carbon, boron nitride or ~ other appropriate material to insure a weak bond = between matrix and reinforcement in the final composite where improved mechanical strength or toughness is desired. These coatings may be omitted where the end use does not require high tensile strength. The filled mold is injected, preferably under vacuum, with the neat monomer solution with an appropriate amount of = catalyst. The relative amounts of vinyl- and hydro-monomers will be ad~usted to obtain the desired carbon level in t~e pyrolyzed matrix. The low viscosity (<50 centipoise) of the neat monomer solution i exceptionally well suited for resin impregnation of thic~ wal-l and complex shape components.
~ The filled mold is then heated to about = 25 30 C-~50-C for about ~-30 hours as Fequired to cure the monomer solutions to a fully polymerized state. The specific cure cycle is tailored for the geometry and de~ired st~te of cure. For exampLe, thicker wall section require slower cures to prevent uneven curing and exoth~rmic heat build-up. The cure cycle is tailored through control of the amount of catalyst added and the t~me-temperature cyc~e. External pressure may be used during the heating cycle as desired.
q~0~3 W094/03405 i~i PCT/US92/06644 When the component is fully cured, 1t is removed from the mold. In this condition it is equivalent in state to the composite made by lamination and autoclaving of prepreg plies. Further processing consists of the equivalent pyrolysis and impregnation cycles to be described for the laminated components.
Solvents for the blac~ glass precursor polymers include hydrocarbons, such as isooctane, toluene, benzene, and xylene, and ethers, such as tetrahydrofuran, and ketones, etc. Concentration of the prepregging solution may vary from about 10~ to about 70% of resin by weight. Precursor polymer used in impregnating the fibers is usually prepared from solution polymerization of the respective monomers.
Since the precursor polymers do not contain any hydrolyzable functional groups, such as silanol, chlorosilane, or alkoxysilane, the precursor polymer is not water sensitive. No particular precaution is needed to exclude water from the solvent or to control relative h~ ity during processing.
The resin ages very slowly when stored at or below room t~ ~atures as is evident from its shelf lif~ of ~ore than three months at these te~^ratures.
The re~in is stable both in the ~olution or in the 25 ~ey~L~. Prepregs stored in a refrigerator for three month~ have ~een u~ed to make l~minates without any dif~lc~lty. Al~o, resin solutions stored for months havQ been used for making prepreqs ~ c~s6fully.
~arg~ and complex shape composites can be fabric~ted from laminating prepreg~. One method is hand lay-up. S~veral plies of prepregs cut to the desired ~h~re are laid-up to achieve the required thi~ s of the component. Fiber orientation can be tai-lored to give ~Yimll~ strength in the preferred direction. Fibers can be oriented unidirectionally WO94/O~s 2 1 4 1 ~ 4 3`. PCT/US92/06644 [o]~ at go angles [0/90], at 45' angles [0/45 or 4S/90~, and in other combinations as desired. The laid-up plies are then bonded by vacuum compaction before autoclave curing. Another fabrication method is tape laying which uses pre-impregnated ribbons in forming composites. The resin properties can be controlled to provide the desired tac~iness and viscosity in the prepreg for the lay-up procedures.
After the initial bonding of the prepreg plies, the composites are further consolidated and cured by heating to temperatures up to about 250-C
under pressure. In one method, the composited prepreg is placed in a bag, which is then evacuated and the outside of the bag placed under a pre~sure sufficient = 15 to bond the layered prepreg, say up to about 1482 kPa.
~ The re~in can flow into and fill up any voids between = the fibars, forming a void-free ~1 ~n l~minate. The resulting polymer-fiber composite is den~Q and $s ready for conversion of the polymer to black glass ceramic.
= 20 Heating the ~o~o--ite to temperatures from about 800-C up to about 1400-C (pyrolysis) converts the polymer into a black glass ceramic containing ~ essentia~ly only carbon, silicon, and oxygen.
= According to this invention, the carbon content may be variad by ~d~usting the h-at$ng ratQ and the access of oxyg~n to th~ polymer precursor during pyrolysis. It iS charact~ristic of tha bl_ck gla~s prep~red ~y pyrolyzing the cyclosiloxan~s d~cribsd _bove that the r~sulting black gla~s may have a larg~ carbon content, = 30 but it is ~ble to withstand eXposurQ to tsmperatures up = to about 1400-C in air without oxidizing to a = significant d_~Ls-. Pyrolysis i8 u~u_lly csrried out with a heating to the maximum temperature selected, holding at that temperature for a period of time determined by the size of the structure, and then W094/03405 ~1 4 ~0 ~ 3 PCT/US92/06~4 coolin~ to room temperature. When fabricated using appropriate fiber type, volume, and architecture, little bulk shrinkaqe is observed for the blac~ glass composltes and the resulting structure typically has about 70-80% of its theoretical density. Conversion of the polymer to blac~ glass takes place between 430 C
and 950 C.
Since the pyrolyzed composite structure still retains voids, the structure may be increased in density by impregnating with a neat monomer liquid or solution of the black glass precursor polymer. The solution is then gelled by heating to about SO-C-120 C
for a sufficient period of time. Following gelation, the polymer is pyrolyzed as described above. Repeating these steps, it is feasible to increase the density up to about 95S of the theoretical.
PYrol~si 5 Heretofore, as discussed in co-pending U.S.
Patent Application Serial No. 07/586,632, we have believed that including oxygen in the atmosphere during pyrolysis would burn off at least some and up to all of the carb~n, leaving in the extreme case essentially only silica, S~O2. A feature of the black glass ceramic has been that once formed the carbon ~pp~rS to be unreactive w~en later expos~d to oxygen. When a re~uced carbon content was desired, as in co-pending application, U.S. Serial No. 07/586,632, oxygen could b~ i..L~ c~d during pyrolysi~. In a series of Qxp~ri~ents the composition of the pyrolyzed product was varied depending upon the amount of oxygen present in the aL~a_~here as shown in the following ta~le. The heating rate was 2-C/min up to 850-C.
2~41043 .
W094/03405 ` PCT/US92/06644 Product ComPos ition - Car~on, 2 % Wt.% ~ormula O 27 SiC1.370~.03 2 22 SiC1.1s1.w 17 SiCo.s1o1.s5 13 SiC~.7101.69 0.7 SiC0.~02.10 One might conclude, as we previously believed, that oxygen should ~e excluded during pyrolysis if a high car~on content was wanted. This has now been discovered to be only one method of achieving 2 high car~on content and that, in fact, air can be present, provided that the heating proceeds at a rate exceeding about 50-C/min, at which condition the thermal d~ ocition of the polymer precursors ~o~inAtes the oxidation re~ction which would remove carbon.
There are believed to be two re~ctions which the precursor polymers undergo during pyrolysis, namely a decompo~ition:
(1) Precur~or - sic~oy + CH~ + H2 + other hydrocar~ons and an oxidation:
= 2S (2) prQcur~or + 2 ~ S iOz + H20 + C02 + CO + H2 +
other hy~ ~o~ons It appe~rs t~at when the precursors are heated rapidly enough reaction (l) i~ favored and reaction (2) is = 30 slow~d by the need to diffus~ oxygen to the polymer.
Consequently, under proper conditions in the presence of o~e," the precursor polymers can be converted to black glass having a high carbon content. It would follow that one could produce a black glass having the = 35 maximum car~on content, equivalent to pyrolysis in an b~3 inert atmosphere, by heatinq the blac~ glass precursors rapidly so that reaction (1) is favored, or one could adjust the carbon content by using a less rapid heating rate and/or adjusting the oxygen access to the precursor polymer so that some carbon would be lost by reaction t2). We prefer, for convenience and economy, to heat the black glass precursors as rapidly as possible, i.e, above 50- C/min, in air, preferably above about 100-C/min up to 1000-C/min. The heating rate for achieving ~Yi~um carbon content in the black glass ceramic should exceed about 100 C/min, whereupon it is possible to obtain a black glass ceramic having about 27 wt.% carbon.
The amount of carbon in the final black glass produced by rapid pyrolysis also depends on access of oxygen to the precursor polymers via the gas flow rate and on sample size and geometry. It will be understood by those skilled in the art that the desired carbon content can be obtained, for example, by adjusting (1) heating rate, (2) oxygen con~ent of the atmosphere, (3) gas flow rate, (4) sample size, and (5) sample _U~o~ inqs ~e.g, covering the sample to limit the a.~ of oxygen).
Once it is ~&_o~..ized that rapid pyrolysis can y~h~ black glass even in the presence of oxygen, then the procedure can be carried out in variou~ ways, including dire~t application of hot combustion gases, or e%posur~ to radiant energy. Other examples would includ~ las~r h-~ting, RF induction heating, plasma heating, liquid and fluidized bed immersion, microwave hQating, CO~.~ P -tiVQ gas hsating, direct resistance heating and the like.
Direct exposure to flames would be expected to proA~c~ a black glas~ containing high levels of carbon, since the heating would be rapid and oxygen , W094/03405 ~ 4 ~ O ~ 3 PCT/US92/06644 should be present. For general use such a method might be too uncontrolled to provide uniform results.
However, it might be useful for pyrolysis of small areas in a larger piece of black glass material.
~5 Alternatively, since the polymer precursors conYert to -a black glass ceramic, which is resistant to further oxidation they could be used as fire resistant coatings, takinq advantage of the rapid pyrolysis of the invention.
FY~mnle 1 Polvmer Precursor Pre~aration = The cyclosiloxane ha~ing silicon-vinyl bond was poly(vinylmethylcyclosiloxane) tvisi). The - cyclosiloxane with a ~ilicon-hydride bond was lS poly(methylhydrocyclosilox~ne) (HSi). Both _ cyclosiloxanes were mixtures of ~onomers, about 85S by = weight being the cyclotetr mer with the remainder bein~
principally the cyclopentamer and cycloh~Y~mer. A
volume ratio of S9 ViSi/41 HSi was mixed with 22 wt.
ppm of platinum as a platinum-cyclovinylmethylsiloxane complex. 200 mL of the monomer solution was heated at 50-C for 6 hour~ and then gelled and post-cured at = lOO-C foF 2 hour~. ThQ resin produced was poly(methyl methylenecyclosiloxane) (PMMCS). It was hard and dry =25 at room temperature.
E~D1e 2 S~mples of about 80 mg of blac~ glass sors pr~par~d a~ in Example 1 having a particle BiZ~ of 1-2 ~m were placed in a thermogravimetric analy is inS,tru~nt (TGA) (Mettler). Air at the rate of 200 m~/minute was p~ed over the s~mples and the t~mperature was r~ised at a rate of lOO-C/min, SO-C/min, 2S-C~min, 10-~/min, and l-C/min to a temperature of 900-C and then held there for 30 minutes. The results are shown in the following table.
~4~0~3 W094/03405 PCT/US92/06~4 Heating PRODUCT
Rate Color Yield, ~ A~earance Car~on, wt.
1C/min off White 80 Powdery <1 10-C/min Gray 82.3 Glassy <2 5 25-C/min Gray 85 Glassy 6 50-C/min Blac~ 86 Glassy 17 100-C/min 81ack 86 Glassy 24 It will be seen that the car~on content increased as the heating rate was increased and that blac~ glass equivalent in carbon content to black gla~ produced by heating in an inert atmosphere resulted from the highest heating rate. For heating rates below 100-C/min, the TGA results showed that all of the weight loss occurred during the heating period. There was no additional weight loss in the 900-C holding period, indicating that the product was sta~le.
~y~m~ le 3 Two samples were rapidly heated by placing them in a preheated furnace at 860-C in stagnant air.
One sample was a strip of PMMCS resin about 1 mm thick by 2.5 cm x 3.5 cm. The second sample was a 6 cm x 0.5 cm composit~ 2 mm thick in which Nextel- 480 fibers reinforced a PMMCS matrix. The Nextel- 480 composite w~s f brtcatJd by autoclave curing stac~s of B-stage r~in impr,gn ted preprQgs. Both samples were placed on alum~na foam bloc~s, introduced into the 860-C
pr~h~tod furn c~, and left for l hour and 40 minutes.
AftQr r_moving th~ samples and cooling them freely in the air to roo~ temperature measurements were made to determine the n~ture of the products, as given in the following ta~
W O 94/03405 ~ ~ q ~ ~ ~ 3 18 PC~r/US92/06644 U~ --U~ ,_ I
', I
C~
~: n I
s~ ~
-~ U U
~s ~ .
_ ~r o o o o~ ~ _~
~ ~ o o -_~
3 ~
_î o ~o ~n ~ ~ ~ , ~a . .
o o q C Ç
U~ .
0 ~ 3 Again it ran be seen that rapid heating, even in air, can yield a black glass having a high carbon content.
It is estimated that the rate of heating in this experlment was about 300-lOOO C/min.
~Y~le 4 A piece of PMMCS resin prepared as in Example 1 (1 mm x 2.5 cm x 3.5 cm) was placed in an oven preheated to 86~ C, left there for 18 hours in stagnant air, and then cooled to room t~p~rature over 5 hours.
The heating rate was estimated to be about 300-lOOO-C/min. The product had a ~lack color. Elemental an~ly~is of the pyrolyzed material by Leco carbon analysis and atomic absorption of silicon showed that the product contained 24.3 wt.~ carbon and 45.6 wt.
15 si7 icon.
F~Yam~le 5 fCo~n~r~tive) A piece of PMMCS re~in prepared a~ in Example 1 (1 m~ x 2.5 cm x 3.5 cm) was heatQd in stagnant air from room temperature to 850-C over 8 hours and then held at 850-C for 1 hour ~efore cooling to room temperatur~ over 8 hours. The heating r~te was about 1.7-C/mi~. The ~ oduct was white and the yield was 80%. A carbon analysis ~y Leco car~on analyzer showed the ~.od~ct contained only 0.7 wt.% carbon.
~ he r~ults of Example 5 indicate that the rat~ of heating dram~tically affect~ the carbon content ~h~n compar~d with the results of Example 4.
Prior Art The invention relates generally to carbon-containing glass which may be used alone or as a matrix material reinforced with fibers.
In USSN 002,049 a ceramic composition designated "black glass~ is disclosed which has an empirical formula SiCxOy where x ranges from 0.5 to about 2.0 and y ranges from about 0.5 to about 3.0, preferably x ranges from o.s to 1.6 and y ranges from 0.7 - 1.8. That ceramic material has a higher car~on content than prior art materials and is very resistant to high temperatures - up to about 1400-C. It is produced by reacting in the presence of a hydrosilylation catalyst a cyclosiloxane having a vinyl group with a cyclosiloxane having a hydrogen group to form a polymer precursor, which is subsequently pyrolyzed in an inert atmosphere to yield black glass.
The present in~ention involves a new method of pyrolyzing such black glass precursors.
In co-pending application U.S. Ser. No.
07/586,632, it is shown that by including oxygen during the pyrolysis that the carbon content of the black glass can be adjusted to a lower value useful for certain purpo~es. We have now found that if the pyrolysi8 step is carried out rapidly enough that the eff~ct of oxygen can be over~ome and black glass having a high car~on content can be achieved, even if pyrolyzed in the presence of air.
W094/~3405 ~o~3: PCT/US9~/06~ ~
Summarv of t~e Invention A car~on-containing black glass reramLc composition having the empirical formula SiCxOy where x is greater than zero and up to about 2.0, preferably up to about 1.6, and y is greater than zero and up to about 2.2, preferably up to about 1.8, is produced by pyrolyzing certain polymer precursors at a rate exceeding 5-C/min, preferably 50-C~min to lOOO C/min, most preferably above lOO-C/min in the presence of oxygen, preferably in air.
~ The black glass ceramic composition is the = pyrolyzed reaction product of a polymer prepared from (1) a cyclosiloxane monomer having the formula ~ R' = 15 -- (si--O) n I .
R
= 20 where n is an integer from 3 to about 30, R is = hydrogen, and R' is an alkene of from 2 to about 20 car~on atoms in which one vinyl carbon atom is directly bonded to silicon or (2) two or more different cyclosiloxane monomers having th~ formula of tl) where for at least one monomer R is hydrogen and R' is an alkyl ~u~ having from 1 to about 20 carbon atoms and for t~e other monomers R is an alkene from a~out 2 to about 20 carbon atoms in which one vinyl carbon is - directly h~n~e~ to silicon and R' is an alkyl group of = 30 from 1 to about 20 carbon atoms, or (3) cyclosiloxane monomers having the formula of (1) where R and R' are independently salected from hydrogen, an ~lkene of from 2 to about 20 carbon atoms in which one vinyl car~on atom is directly bonded to silicon, or an alkyl group of from 1 to about 20 carbon atoms and at least some of ~ 21410~3 said monomers contain each of said hydrogen, alkene, and alkyl moieties, said polymerization reaction takin~
place in the presence of an effective amount of hydrosilylation catalyst. The polymer product is pyrolyzed by heating in an oxidizing atmosphere at a rate above 5-C/min to a temperature in the range of about 800-C to about 1400-C. The black glass ceramic thus produced retains carbon despite being in an oxidizinq atmosphere. When the heating rate is above lo about 100 C/min~ the black glass ceramic contains substantially the same amount of carbon as produced by pyrolysls in an inert atmosphere.
The black glass may be employed in many forms such as fibers, coatings, films, powders, monoliths, and particularly as a matrix for fiber reinforced composites.
The heating may be carried out using hot combustion gases, radiant energy, or other methods familiar to those skilled in the art. The carbon content may be controlled by adjusting the heating rate, and the oxygen access to the polymer during pyrolysis.
DescriDtion o~ the Preferred ~hodiments ~l~c~ G!~s ~mic Th~ black glass ceramic ha~ an empirical formula sicxoy wherein x is greater than zero and up to about 2.0, prQf~rably up to about 1.6, and y is greater th~n zero and up to about 2.2, preferably up to about 1.8, wher~by the car~on content range~ up to about 40%
by weight. The black glass ceramic i5 the product of the pyrolysis at a rate eXcee~ing S-C/min in an - oxidizing atmosphere to temperatures between about 800-C and about 1400-C of a polymer made from certain siloxane monomers. Preferably, a heating rate of .
a~~
~ 50 C/min to 1ooo C/min is used, most preferably greater = than 100 C/min. The carbon content will be determined generally by the heating rate and the access of oxygen to the polymer precursor during pyrolysis.
~ 5 The polymer precursor of the black glass = ceramic may be prepared by subjecting a mixture containing cyclosiloxanes of from 3 to 30 silicon atoms to a temperature in the range of from about lo-C to about 300-C in the presence of 1-200 wt. ppm of a ~ 10 platinum hydrosilylation catalyst for a time in the = range of from about 1 minute to about 600 minutes. The = polymer formation takes advantage of the fact that a silicon-hydride will react with a silicon-vinyl group = to form a silicon-carbon-carbon-silicon bonded chain, thereby forming a network polymer. For this reason, ~ each cyclosiloxane monomer must contain either a - silicon-hydride bond or a silicon-vinyl bond or both.
~ A silicon-hydride bond refers to a silicon atom bonded = directly to a hydrogen atom and a ~ilicon-vinyl bond refers to a silicon atom bonded directly to an alkene carbon, i.~., it is connected to another carbon atom by = a double bond.
The polymer precursor for the black glass ceramic may be defined generally as the reaction product of (1) a cyclosiloxane monomer having the = formula = R' I
(Si--O) n R
where n is an integer from 3 to 30, R is hydrogen, and = R' is an ~lkDne of from 2 to 20 carbon atoms in which one vinyl carbon atom is directly bonded to silicon or .
W094/03405 ~1 4 ~ O ~ 3 PCT/US92/06644 (2) two or more different cyclosiloxane monomers havlng the formula of (1) where for at least one monomer R is hydrogen and R' is an alkyl group having ~rom 1 to 20 carbon atoms and for the other monomers R is an alkene from a~out 2 to 20 car~on atoms in which one vinyl carbon is directly bonded to silicon and R' is an alkyl group of from 1 to 20 carbon atoms, or (3) cyclosiloxane monomers having the formula of (1) where R and R' are independently selected from hydrogen, an alkene of from 2 to about 20 carbon atoms in which one vinyl car~on atom is directly bonded to silicon, or an alkyl group of from 1 to about 20 carbon atoms and at least some of said monomers contain each of said hydrogen, alkene, and alkyl moieties, said reaction taking place in the presence of an effective amount of hydrosilylation catalyst.
The black glass ceramic may be prepared from a cyclosiloxane polymer precursor wherein both the requisite silicon-hydride bond and the silicon-vinyl bond are present in one molecule, for example, 1,3,5,7-tetravinyl-1,3,5,7-tetrahydro-cyclo-tetrasiloxane. Such monomers may also contain alkyl ~ou~ such a~, for example, 1,3-divinyl-1,5-dihydro-3,5,7,7-tetramethylcyclosiloxane. Alternatively, two or more cyclosiloxane monomers may be polymerized.
Such monomer~ would contain at least either a silicon hydride bond or a silicon-vinyl bond and the ratio of the two types of bonds should be about 1:1, more ~ro~dly about 1:9 to 9:1.
Examples of such cyclo~iloxanes include, but are not limited to:
1,3,5,7-tetramethyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetravinyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetravinyltetraethylcyclotetrasiloxane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, ~ W094/03405 PCT/US92/06~4 ~
1,3,5-trimethyltrivinylcyclotrisiloxane, 1,3,5-trivinyltrihydrocyclotrisiloxane, 1,3,S-trimethyltrihydrocyclotrisiloxane, 1,3,5,7,9-pentavinylpentahydrocyclopentasiloxane, 1,3,5,7,9-pentavinylpentamethylcyclopentasiloxane, 1,1,3,3,5,5,7,7-octavinylcyclotetrasiloxane, = 1,1,3,3,5,5,7,7-octahydrocyclotetrasiloxane, 1,3,5,7,9,11-hexavinylhexamethylcycloh~Yasiloxane, 1,3,5,7,9,11-hexamethylhexahydrocyclohexasiloxane, 1,3,5,7,~,11,13,15,17,19-decavinyldecahydrOcyclodeca-siloxane, 1,3-divinyl-1,5-dihydro-3,5,7,7-tetramethylcyclosiloxane ~ 1,3,5-trivinyl-1,3,5,7,7-= lS pentamethylcyclotetrasiloxane 1,3,5-trihydro-1,3,S,7,7-= pentamethylcyclotetrasiloxane 1,3,S,7,9,11,13,15,17,19,21,23,2S,27,29-pentadeca-vinyl-1,3,5,7,9,11,13,1s,17,19,21,23,25,27,29-pentadecahydrocyclopentadecasiloxane - 1,3,5,7-tetrapropenyltetrahydrocyclotetrasiloxane, 1,3,5,7-tetrapentenyltetrapentylcyclotetrasiloxane and 1,3,5,7,9-pent~Asc-~ylpentapropylcyclopentasiloxane.
~ 25 It will ~e understood by those skilled in the _ art that while the silo~A~9 monomers may be pure ~pecl~s, it will be frequently desirable to use = mi~as of Such monomers, ln which a single species is ominant. M~xture~ in which the tetramers predominate have ~een found particularly useful.
Whilc the rcaction works best if platinum is ~ the hydrosilylation cataly~t, other catalysts such as _ cobalt and manganese carbonyl will perform adequately.
= The catalyst can be dispersed as a solid or can be used as a solution when added to the cyclosiloxane monomer.
.
W094/03405 2l 41 0~ 3 PCT/US92/06644 7 ~
With platinum, about l to 200 wt. ppm, preferably 1 t_ 30 wt. ppm as the metal will be employed as t~e catalyst.
Blac~ glass precursor poly~er may be prepared from either bulk or solution polymerization. In bulk polymerization, neat monomer liquid, i.e., without solvents, reacts to form oligomers or high molecular weight polymers. In bulk polymerization, a solid gel can be formed without entrapping solvent. It is particular1y useful for impregnating porous composites to increase density. Solution polymerization refers to polymerizing monomers in the presence of an unreactive solvent.
When the resin is used in impregnating fibers to form prepreg, it preferably is prepared by solution polymerization. The advantage of solution polymerization is the ease of controlling resin characteristics. It is possible but very d$fficult to produce B-~tage resin suitable for prepregs with consistent characteristics by bulk polymerization.
Soluble resin with the desirable viscosity, tackiness, and flowability suitable for prepregging and laminatin~
can be_ obtained consistently using solution polymerization process. The production of ezsily hand~eable and consistent resin is very critical in ~ ite ~abrication.
E~er~
Where reinforcing fibers are used with the blac~ glas~ ceramic they typically are refractory fibers which are of interest for applications where superior physical properties are needed. They include such materials as boron, silicon carbide, graphite, silica, quartz, S-glass, E-glass, alumina, aluminosilicates, boron nitride, silicon nitride, boron W094/03405 ~ PCT/US92/06644 car~ide, titanium boride, titanium car~ide, zirconium oxide, silicon carbonitride, silicon oxycarbonitride and zirconia-toughened alumina. The fibers may have - various sizes and forms. They may be monofilaments from l ~m to 200 ~m diameter or tows of 200 to 2000 filaments. When used in composites of the invention they may be woven into fabrics, pressed into mats, or unidirectionally aligned with the fibers oriented as desired to obtain the needed physical properties.
lo An important factor in the performance of the black glass composites is the strength of the bond between the fibers and the black glass matrix.
Consequently, where improved m~h~nical strength or toughness is desired, the fibers are provided with a coating which raduces the bonding between the fibers ~ and the blac~ glass matrix. The surface sizings found - on fibers as received or proA~ m~y be removed by solvent wA~ing or heat treatment and the coating applied, which may be of carbon or other materials such as boron nitride and silicon carbide.
= Various methods may be used to apply a car~on = coating, including chemical vapor deposition, solution coating,_ and pyroly~is of organic polymers such as carbon pitch and phenolics. One preferred technique is 2s chemical vapor deposition using decomposition of methane or other hydroc~on~. Another method is pyrolysis Or an organic polymer coating such as phenol-forcaldehyde polymers cros~-linkQd with such agents a~ the monohydrate or sodium salt of paratoluene~u~fonic acid. Still another method uses toluene-solublQ and toluene-insoluble carbon pitch to coat the fibers. Boron nitride and silicon carbide coatings are typically applied by chemical vapor deposition from a gaseous prec~rsor.
,.
..
0 ~ 3 W094/03405 PCT/US92/06~4 Processin~
As previously discussed, the blac~ glass precursor is a polymer. It may be shaped into fibers and com~ined with reinforcing fibers or the black glass precursor may be used in solution for coating or impregnating reinforcing fibers. Various methods will suggest themselves to those skilled in the art for combining the black glass precursor with reinforcing fibers. It would, for example, be feasible to com~ine fibers of the polymer with fibers of the reinforcing material and then to coat the resulting fabric or mat.
Alternatively, the reinforcing fibers could be coated with a solution of the polymer and then formed into the desired shape. Coating may be done by dipping, spraying, brushing, or the like.
In one method, a continuous fiber is coated with a solution of the black glass precursor polymer and then wound on a rotating drum covered with a release film which is easily separated from the coated fibers. After sufficient fiber has been built up on the drum, the process is stopped and the uni-directional fiber mat removed from the drum and dried.
The resulting mat (i.e., "prepreg") then may be cut and ~ ted into the desired shapes.
In a second method, a woven or pressed fabric of the reinforcing fibers is coated with a solution of the black gla~s precursor polymer and then dried to remov~ the solvQnt, after which it may be formed into the desired 5h~pes by procedures which are familiar to thosQ skilled in the art of fabricating structures with the prepreg ~heets. For ~mrle, layers of prepreg sheets may be laid together and pressed into the needed shape. The orientation of the fibers may be chosen to strengthen the composite part in the principal load-bearing directions.
W094/03405 ~ 0 ~3 PCT/US92/06~4 ~ A third method for fabricating the polymer - composite is by resin transfer molding. In resin - transfer molding a mold with the required shape is filled with the desired reinforcement material. The reinforcement could be a preform having a 3-dimensional weave of fibers, a lay-up of fabric plies, a non-woven mat of chopped staple or bundled tows, or assem~lies of whiskers, and such others as are familiar to those skilled in the art. The reinfor~ement - 10 material would be coated with carbon, boron nitride or ~ other appropriate material to insure a weak bond = between matrix and reinforcement in the final composite where improved mechanical strength or toughness is desired. These coatings may be omitted where the end use does not require high tensile strength. The filled mold is injected, preferably under vacuum, with the neat monomer solution with an appropriate amount of = catalyst. The relative amounts of vinyl- and hydro-monomers will be ad~usted to obtain the desired carbon level in t~e pyrolyzed matrix. The low viscosity (<50 centipoise) of the neat monomer solution i exceptionally well suited for resin impregnation of thic~ wal-l and complex shape components.
~ The filled mold is then heated to about = 25 30 C-~50-C for about ~-30 hours as Fequired to cure the monomer solutions to a fully polymerized state. The specific cure cycle is tailored for the geometry and de~ired st~te of cure. For exampLe, thicker wall section require slower cures to prevent uneven curing and exoth~rmic heat build-up. The cure cycle is tailored through control of the amount of catalyst added and the t~me-temperature cyc~e. External pressure may be used during the heating cycle as desired.
q~0~3 W094/03405 i~i PCT/US92/06644 When the component is fully cured, 1t is removed from the mold. In this condition it is equivalent in state to the composite made by lamination and autoclaving of prepreg plies. Further processing consists of the equivalent pyrolysis and impregnation cycles to be described for the laminated components.
Solvents for the blac~ glass precursor polymers include hydrocarbons, such as isooctane, toluene, benzene, and xylene, and ethers, such as tetrahydrofuran, and ketones, etc. Concentration of the prepregging solution may vary from about 10~ to about 70% of resin by weight. Precursor polymer used in impregnating the fibers is usually prepared from solution polymerization of the respective monomers.
Since the precursor polymers do not contain any hydrolyzable functional groups, such as silanol, chlorosilane, or alkoxysilane, the precursor polymer is not water sensitive. No particular precaution is needed to exclude water from the solvent or to control relative h~ ity during processing.
The resin ages very slowly when stored at or below room t~ ~atures as is evident from its shelf lif~ of ~ore than three months at these te~^ratures.
The re~in is stable both in the ~olution or in the 25 ~ey~L~. Prepregs stored in a refrigerator for three month~ have ~een u~ed to make l~minates without any dif~lc~lty. Al~o, resin solutions stored for months havQ been used for making prepreqs ~ c~s6fully.
~arg~ and complex shape composites can be fabric~ted from laminating prepreg~. One method is hand lay-up. S~veral plies of prepregs cut to the desired ~h~re are laid-up to achieve the required thi~ s of the component. Fiber orientation can be tai-lored to give ~Yimll~ strength in the preferred direction. Fibers can be oriented unidirectionally WO94/O~s 2 1 4 1 ~ 4 3`. PCT/US92/06644 [o]~ at go angles [0/90], at 45' angles [0/45 or 4S/90~, and in other combinations as desired. The laid-up plies are then bonded by vacuum compaction before autoclave curing. Another fabrication method is tape laying which uses pre-impregnated ribbons in forming composites. The resin properties can be controlled to provide the desired tac~iness and viscosity in the prepreg for the lay-up procedures.
After the initial bonding of the prepreg plies, the composites are further consolidated and cured by heating to temperatures up to about 250-C
under pressure. In one method, the composited prepreg is placed in a bag, which is then evacuated and the outside of the bag placed under a pre~sure sufficient = 15 to bond the layered prepreg, say up to about 1482 kPa.
~ The re~in can flow into and fill up any voids between = the fibars, forming a void-free ~1 ~n l~minate. The resulting polymer-fiber composite is den~Q and $s ready for conversion of the polymer to black glass ceramic.
= 20 Heating the ~o~o--ite to temperatures from about 800-C up to about 1400-C (pyrolysis) converts the polymer into a black glass ceramic containing ~ essentia~ly only carbon, silicon, and oxygen.
= According to this invention, the carbon content may be variad by ~d~usting the h-at$ng ratQ and the access of oxyg~n to th~ polymer precursor during pyrolysis. It iS charact~ristic of tha bl_ck gla~s prep~red ~y pyrolyzing the cyclosiloxan~s d~cribsd _bove that the r~sulting black gla~s may have a larg~ carbon content, = 30 but it is ~ble to withstand eXposurQ to tsmperatures up = to about 1400-C in air without oxidizing to a = significant d_~Ls-. Pyrolysis i8 u~u_lly csrried out with a heating to the maximum temperature selected, holding at that temperature for a period of time determined by the size of the structure, and then W094/03405 ~1 4 ~0 ~ 3 PCT/US92/06~4 coolin~ to room temperature. When fabricated using appropriate fiber type, volume, and architecture, little bulk shrinkaqe is observed for the blac~ glass composltes and the resulting structure typically has about 70-80% of its theoretical density. Conversion of the polymer to blac~ glass takes place between 430 C
and 950 C.
Since the pyrolyzed composite structure still retains voids, the structure may be increased in density by impregnating with a neat monomer liquid or solution of the black glass precursor polymer. The solution is then gelled by heating to about SO-C-120 C
for a sufficient period of time. Following gelation, the polymer is pyrolyzed as described above. Repeating these steps, it is feasible to increase the density up to about 95S of the theoretical.
PYrol~si 5 Heretofore, as discussed in co-pending U.S.
Patent Application Serial No. 07/586,632, we have believed that including oxygen in the atmosphere during pyrolysis would burn off at least some and up to all of the carb~n, leaving in the extreme case essentially only silica, S~O2. A feature of the black glass ceramic has been that once formed the carbon ~pp~rS to be unreactive w~en later expos~d to oxygen. When a re~uced carbon content was desired, as in co-pending application, U.S. Serial No. 07/586,632, oxygen could b~ i..L~ c~d during pyrolysi~. In a series of Qxp~ri~ents the composition of the pyrolyzed product was varied depending upon the amount of oxygen present in the aL~a_~here as shown in the following ta~le. The heating rate was 2-C/min up to 850-C.
2~41043 .
W094/03405 ` PCT/US92/06644 Product ComPos ition - Car~on, 2 % Wt.% ~ormula O 27 SiC1.370~.03 2 22 SiC1.1s1.w 17 SiCo.s1o1.s5 13 SiC~.7101.69 0.7 SiC0.~02.10 One might conclude, as we previously believed, that oxygen should ~e excluded during pyrolysis if a high car~on content was wanted. This has now been discovered to be only one method of achieving 2 high car~on content and that, in fact, air can be present, provided that the heating proceeds at a rate exceeding about 50-C/min, at which condition the thermal d~ ocition of the polymer precursors ~o~inAtes the oxidation re~ction which would remove carbon.
There are believed to be two re~ctions which the precursor polymers undergo during pyrolysis, namely a decompo~ition:
(1) Precur~or - sic~oy + CH~ + H2 + other hydrocar~ons and an oxidation:
= 2S (2) prQcur~or + 2 ~ S iOz + H20 + C02 + CO + H2 +
other hy~ ~o~ons It appe~rs t~at when the precursors are heated rapidly enough reaction (l) i~ favored and reaction (2) is = 30 slow~d by the need to diffus~ oxygen to the polymer.
Consequently, under proper conditions in the presence of o~e," the precursor polymers can be converted to black glass having a high carbon content. It would follow that one could produce a black glass having the = 35 maximum car~on content, equivalent to pyrolysis in an b~3 inert atmosphere, by heatinq the blac~ glass precursors rapidly so that reaction (1) is favored, or one could adjust the carbon content by using a less rapid heating rate and/or adjusting the oxygen access to the precursor polymer so that some carbon would be lost by reaction t2). We prefer, for convenience and economy, to heat the black glass precursors as rapidly as possible, i.e, above 50- C/min, in air, preferably above about 100-C/min up to 1000-C/min. The heating rate for achieving ~Yi~um carbon content in the black glass ceramic should exceed about 100 C/min, whereupon it is possible to obtain a black glass ceramic having about 27 wt.% carbon.
The amount of carbon in the final black glass produced by rapid pyrolysis also depends on access of oxygen to the precursor polymers via the gas flow rate and on sample size and geometry. It will be understood by those skilled in the art that the desired carbon content can be obtained, for example, by adjusting (1) heating rate, (2) oxygen con~ent of the atmosphere, (3) gas flow rate, (4) sample size, and (5) sample _U~o~ inqs ~e.g, covering the sample to limit the a.~ of oxygen).
Once it is ~&_o~..ized that rapid pyrolysis can y~h~ black glass even in the presence of oxygen, then the procedure can be carried out in variou~ ways, including dire~t application of hot combustion gases, or e%posur~ to radiant energy. Other examples would includ~ las~r h-~ting, RF induction heating, plasma heating, liquid and fluidized bed immersion, microwave hQating, CO~.~ P -tiVQ gas hsating, direct resistance heating and the like.
Direct exposure to flames would be expected to proA~c~ a black glas~ containing high levels of carbon, since the heating would be rapid and oxygen , W094/03405 ~ 4 ~ O ~ 3 PCT/US92/06644 should be present. For general use such a method might be too uncontrolled to provide uniform results.
However, it might be useful for pyrolysis of small areas in a larger piece of black glass material.
~5 Alternatively, since the polymer precursors conYert to -a black glass ceramic, which is resistant to further oxidation they could be used as fire resistant coatings, takinq advantage of the rapid pyrolysis of the invention.
FY~mnle 1 Polvmer Precursor Pre~aration = The cyclosiloxane ha~ing silicon-vinyl bond was poly(vinylmethylcyclosiloxane) tvisi). The - cyclosiloxane with a ~ilicon-hydride bond was lS poly(methylhydrocyclosilox~ne) (HSi). Both _ cyclosiloxanes were mixtures of ~onomers, about 85S by = weight being the cyclotetr mer with the remainder bein~
principally the cyclopentamer and cycloh~Y~mer. A
volume ratio of S9 ViSi/41 HSi was mixed with 22 wt.
ppm of platinum as a platinum-cyclovinylmethylsiloxane complex. 200 mL of the monomer solution was heated at 50-C for 6 hour~ and then gelled and post-cured at = lOO-C foF 2 hour~. ThQ resin produced was poly(methyl methylenecyclosiloxane) (PMMCS). It was hard and dry =25 at room temperature.
E~D1e 2 S~mples of about 80 mg of blac~ glass sors pr~par~d a~ in Example 1 having a particle BiZ~ of 1-2 ~m were placed in a thermogravimetric analy is inS,tru~nt (TGA) (Mettler). Air at the rate of 200 m~/minute was p~ed over the s~mples and the t~mperature was r~ised at a rate of lOO-C/min, SO-C/min, 2S-C~min, 10-~/min, and l-C/min to a temperature of 900-C and then held there for 30 minutes. The results are shown in the following table.
~4~0~3 W094/03405 PCT/US92/06~4 Heating PRODUCT
Rate Color Yield, ~ A~earance Car~on, wt.
1C/min off White 80 Powdery <1 10-C/min Gray 82.3 Glassy <2 5 25-C/min Gray 85 Glassy 6 50-C/min Blac~ 86 Glassy 17 100-C/min 81ack 86 Glassy 24 It will be seen that the car~on content increased as the heating rate was increased and that blac~ glass equivalent in carbon content to black gla~ produced by heating in an inert atmosphere resulted from the highest heating rate. For heating rates below 100-C/min, the TGA results showed that all of the weight loss occurred during the heating period. There was no additional weight loss in the 900-C holding period, indicating that the product was sta~le.
~y~m~ le 3 Two samples were rapidly heated by placing them in a preheated furnace at 860-C in stagnant air.
One sample was a strip of PMMCS resin about 1 mm thick by 2.5 cm x 3.5 cm. The second sample was a 6 cm x 0.5 cm composit~ 2 mm thick in which Nextel- 480 fibers reinforced a PMMCS matrix. The Nextel- 480 composite w~s f brtcatJd by autoclave curing stac~s of B-stage r~in impr,gn ted preprQgs. Both samples were placed on alum~na foam bloc~s, introduced into the 860-C
pr~h~tod furn c~, and left for l hour and 40 minutes.
AftQr r_moving th~ samples and cooling them freely in the air to roo~ temperature measurements were made to determine the n~ture of the products, as given in the following ta~
W O 94/03405 ~ ~ q ~ ~ ~ 3 18 PC~r/US92/06644 U~ --U~ ,_ I
', I
C~
~: n I
s~ ~
-~ U U
~s ~ .
_ ~r o o o o~ ~ _~
~ ~ o o -_~
3 ~
_î o ~o ~n ~ ~ ~ , ~a . .
o o q C Ç
U~ .
0 ~ 3 Again it ran be seen that rapid heating, even in air, can yield a black glass having a high carbon content.
It is estimated that the rate of heating in this experlment was about 300-lOOO C/min.
~Y~le 4 A piece of PMMCS resin prepared as in Example 1 (1 mm x 2.5 cm x 3.5 cm) was placed in an oven preheated to 86~ C, left there for 18 hours in stagnant air, and then cooled to room t~p~rature over 5 hours.
The heating rate was estimated to be about 300-lOOO-C/min. The product had a ~lack color. Elemental an~ly~is of the pyrolyzed material by Leco carbon analysis and atomic absorption of silicon showed that the product contained 24.3 wt.~ carbon and 45.6 wt.
15 si7 icon.
F~Yam~le 5 fCo~n~r~tive) A piece of PMMCS re~in prepared a~ in Example 1 (1 m~ x 2.5 cm x 3.5 cm) was heatQd in stagnant air from room temperature to 850-C over 8 hours and then held at 850-C for 1 hour ~efore cooling to room temperatur~ over 8 hours. The heating r~te was about 1.7-C/mi~. The ~ oduct was white and the yield was 80%. A carbon analysis ~y Leco car~on analyzer showed the ~.od~ct contained only 0.7 wt.% carbon.
~ he r~ults of Example 5 indicate that the rat~ of heating dram~tically affect~ the carbon content ~h~n compar~d with the results of Example 4.
Claims (12)
1. A process for producing a black glass having the formula SiOxOy where x is greater than zero and up to about 2.0 and y is greater than zero and up to about 2.2 wherein a black glass polymer precursor is pyrolyzed to produce a glassy structure by heating in the presence of oxygen at a rate exceeding 5°C/min to a maximum temperature in the range of 800°C to 1400°C wherein the black glass precursor is the pyrolyzed reaction product of a cyclosiloxane monomer having the formula where n is an integer from 3 to 30, R is hydrogen, and R' is an alkene of from 2 to 20 carbon atoms in which one vinyl carbon atom is directly bonded to silicon or (2) two or more different cylosiloxane monomers having the formula of (1) where for at least one monomer R is hydrogen and R' is an alkyl group having from 1 to 20 carbon atoms and for the other monomers R is an alkene from 2 to 20 carbon atoms in which one vinyl carbon is directly bonded to silicon and R' is an alkyl group of from 1 to 20 carbon atoms, or (3) cyclosiloxane monomers having the formula of (1) where R and R' are independently selected from hydrogen, and alkene of from 2 to about 20 carbon atoms in which one vinyl carbon atom is directly bonded to silicon, or an alkyl group of from 1 to about 20 carbon atoms and at least some of said monomers contain each of said hydogen, alkene, and alkyl moieties, said reaction taking place in the presence of an effective amount of hydrosilylation catalyst.
2. The process of Claim 1 wherein said black glass precursor is heated in the presence of air.
3. The process of Claim 1 wherein the heating rate if 50°C/min to 1000°C/min.
4. The process of Claim 3 wherein the heating rate is greater than 100°C/min.
5. The process of Claim 1 wherein the heating is carried out by direct application of hot combustion gases.
6. The process of Claim 1 wherein the heating is carried out by radiant energy.
7. The process of Claim 1 wherein the carbon content is controlled by adjusting the heating rate.
8. The process of Claim 1 wherein the carbon content is controlled by adjusting access of oxygen to said polymer precursor during pyrolysis.
9. The process of Claim 1 wherein the carbon content is controlled by adjusting the rate of gas flowing over said black glass precursor.
10. The process of Claim 1 wherein the heating is carried out by a method selected from the group consisting of laser heating, RF induction heating, plasma heating, liquid and fluidized bed immersion, microwave heating, convective gas heating, and direct resistance heating.
11. The process of Claim 1 wherein the black glass is in a form selected from the group consisting of fibers, coatings, films, powders, monoliths, and fiber-reinforced matrices.
12. The product of the process of any of Claims 1-11.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US68442591A | 1991-04-12 | 1991-04-12 | |
| JP50524592A JP3437572B2 (en) | 1991-02-12 | 1991-12-13 | Improved artificial blood |
| US07/863,481 US5266533A (en) | 1991-04-12 | 1992-04-02 | Black glass ceramic from rapid pyrolysis in oxygen-containing atmospheres |
| PCT/US1992/006644 WO1994003405A1 (en) | 1991-04-12 | 1992-08-07 | Black glass ceramic from rapid pyrolysis in oxygen-containing atmospheres |
| US08/084,397 US5322555A (en) | 1991-04-12 | 1993-06-29 | Fire resistant coating composition |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2141043A1 true CA2141043A1 (en) | 1994-02-17 |
Family
ID=27543485
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002141043A Abandoned CA2141043A1 (en) | 1991-04-12 | 1992-08-07 | Black glss ceramic from rapid pyrolysis in oxygen-containing atmospheres |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US5322555A (en) |
| EP (1) | EP0654016B1 (en) |
| JP (1) | JP2597474B2 (en) |
| CA (1) | CA2141043A1 (en) |
| DE (1) | DE69222953D1 (en) |
| WO (1) | WO1994003405A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3302278B2 (en) * | 1995-12-12 | 2002-07-15 | キヤノン株式会社 | Method of manufacturing electron-emitting device, and method of manufacturing electron source and image forming apparatus using the method |
| US5891518A (en) * | 1997-01-30 | 1999-04-06 | Northrop Grumman Corporation | Carbon fiber-coating produced via precursor/solvent solution |
| US6121169A (en) * | 1998-02-24 | 2000-09-19 | Northrop Grumman Corporation | Porous interfacial coating for fiber reinforced ceramic matrix composites |
| US20020190409A1 (en) * | 2001-06-18 | 2002-12-19 | Burdsall Charles W. | Method for reinforcing ceramic composites and ceramic composites including an improved reinforcement system |
| US11512818B2 (en) | 2020-07-10 | 2022-11-29 | Junming Ding | Multi-mode portable lighting device with novel battery charging unit |
Family Cites Families (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5128494A (en) * | 1985-04-26 | 1992-07-07 | Sri International | Hydridosiloxanes as precursors to ceramic products |
| USRE32107E (en) * | 1982-12-23 | 1986-04-08 | Dow Corning Corporation | Carbon-containing monolithic glasses and ceramics prepared by a sol-gel process |
| DE3338663C1 (en) * | 1983-10-25 | 1985-05-23 | Th. Goldschmidt Ag, 4300 Essen | Organosilicon compounds and textile fiber preparations containing them |
| US4661577A (en) * | 1985-10-01 | 1987-04-28 | General Electric Company | Aminofunctional polysiloxanes |
| JPH0639567B2 (en) * | 1986-05-22 | 1994-05-25 | 東レ・ダウコ−ニング・シリコ−ン株式会社 | Curable organopolysiloxane composition |
| US4719276A (en) * | 1986-10-27 | 1988-01-12 | Dow Corning Corporation | Neutralization of catalyst in polymerization of polydiorganosiloxane |
| US5242866A (en) * | 1987-01-09 | 1993-09-07 | Allied-Signal Inc. | Carbon-containing black glass monoliths |
| US4766191A (en) * | 1987-07-10 | 1988-08-23 | Dow Corning Corporation | Silicone polymer termination |
| GB8905966D0 (en) * | 1989-03-15 | 1989-04-26 | Tsl Group Plc | Improved vitreous silica products |
| US4975794A (en) * | 1989-03-27 | 1990-12-04 | Iomega Corporation | Bernoulli effect transducer coupler |
| US5180694A (en) * | 1989-06-01 | 1993-01-19 | General Electric Company | Silicon-oxy-carbide glass method of preparation and articles |
| US4981820A (en) * | 1989-07-28 | 1991-01-01 | General Electric Company | Cellular silicon-oxy-carbide glass from foamed silicone resins |
| CA2010675A1 (en) * | 1989-06-01 | 1990-12-01 | Gary M. Renlund | Silicon-oxy-carbide glass and articles |
| US5006142A (en) * | 1990-03-28 | 1991-04-09 | The United States Of America As Represented By The United States Department Of Energy | Oxynitride glass production procedure |
| US5043002A (en) * | 1990-08-16 | 1991-08-27 | Corning Incorporated | Method of making fused silica by decomposing siloxanes |
| US5231059A (en) * | 1990-09-21 | 1993-07-27 | Allied-Signal Inc. | Process for preparing black glass using cyclosiloxane precursors |
-
1992
- 1992-08-07 JP JP6505245A patent/JP2597474B2/en not_active Expired - Fee Related
- 1992-08-07 WO PCT/US1992/006644 patent/WO1994003405A1/en active IP Right Grant
- 1992-08-07 CA CA002141043A patent/CA2141043A1/en not_active Abandoned
- 1992-08-07 DE DE69222953T patent/DE69222953D1/en not_active Expired - Lifetime
- 1992-08-07 EP EP92917769A patent/EP0654016B1/en not_active Expired - Lifetime
-
1993
- 1993-06-29 US US08/084,397 patent/US5322555A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0654016B1 (en) | 1997-10-29 |
| JPH07506082A (en) | 1995-07-06 |
| EP0654016A1 (en) | 1995-05-24 |
| JP2597474B2 (en) | 1997-04-09 |
| DE69222953D1 (en) | 1997-12-04 |
| US5322555A (en) | 1994-06-21 |
| WO1994003405A1 (en) | 1994-02-17 |
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