US 3779784 A
A fibrous material is provided which is composed of composite fibers having a number average diameter of up to about 10 microns and an average length/diameter ratio of at least about 5/1. The fibers have a core of alkali metal hexatitanate encapsulated by a shell of rutile TiO2 and are essentially inert to aqueous 5% by weight HF solution. The fibrous material is particularly useful in the reinforcing of plastics.
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Description (OCR text may contain errors)
United States Patent [191 Emslie, deceased COMPOSITE FIBERS OF ALKALI METAL HEXATITANATE AND RUTILE TH);
 Inventor: Robert Steele Emslle. deceased, late of Chadds Ford, Pa. by Jean McPhaul Emslie, administratrix  Assignee: E. l. DuPont de Nemours and Company, Wilmington. Del.
 Filed: Apr. 6, 1972 [2i] Appl. No.: 241,681
 US. Cl. 106/300, l06/308 B  Int. Cl. C091: 1/36  Field of Search 106/300. 308 B  References Cited UNITED STATES PATENTS 3338.677 8/l967 Berry 106/300 l Dec. 18, 1973 3,703.357 ll/l972 Surls et al. l06/300 Primary Examiner-Curtis R. Davis Al!orneyDonald A. Hoes [S 7] ABSTRACT A fibrous material is provided which is composed of composite fibers having a number average diameter of up to about 10 microns and an average length/diameter ratio of at least about 5/1. The fibers have a core of alkali metal hexatitanate encapsulated by a shell of rutile TiO, and are essentially inert to aqueous 5% by weight HF solution. The fibrous material is particularly useful in the reinforcing of plastics.
1 Claim, 1 Drawing Figure l5 MICRONS COMPOSITE FIBERS OF ALKALI METAL HEXATTTANATE AND RUTILE T102 BACKGROUND OF THE INVENTION Water-insoluble, fibrous alkali metal titanates having the formula M O(TiO where M is an alkali metal of atomic number of at least I l, and n is a number of from 4 to 8 and their preparations are disclosed in U.S. Pat. Nos. 2,833,620, Gier et al.; 2,841,470, Berry; 3,328,117, Emslie et al.; and 3,33l,658, Lewis et al.
The preparation of fibrous titanium dioxide is described in U.S. Pat. Nos. 3,0l2,857, Pease; 3,065,091, Russell; 3,24l,928, Pease; and 3,244,481, Berry.
Also mixtures of pigmentary titanium dioxide and fibrous alkali metal titanates are disclosed in U.S. Pat No. 3,484,260, Emslie et al.
These fibrous materials are useful as reinforcing components for plastics, ceramics and cermets. Other uses include insulation materials and additives during paper manufacture.
It is known that fibrous titanates will tend to deteriorate in certain acid atmospheres and that improvements in this and other properties would be desirable.
SUMMARY OF THE INVENTION In accordance with the invention there is provided a fibrous material composed of composite fibers having a number average diameter of up to about 10 microns and an average length/diameter ratio of at least about 5/1, said fibers having a core composition corresponding to the formula wherein M is an alkali metal of atomic number of at ieast 1 1, said core being encapsulated by a shell of rutile TiO thereby rendering the fibers essentially inert to aqueous by weight HF solution.
The individual composite fibers possess the combined strength of the alkali metal hexatitanate and rutile components. In addition they tend to be less expensive to prepare, more dense, and more stable to acid and elevated temperatures than are the alkali metal titanates. It is known, for example, that when ordinary potassium titanate fibers are heated to a temperature over 900 C., they start to lose potassium oxide and some strength. The rutile titanium dioxide shell of the composite fibers of the present invention minimizes the loss of alkali at high temperatures. Since the outer shell of these composite fibers is rutile titanium dioxide, the fibers are characterized by the higher refractive index of titanium dioxide, i.e. the refractive index of rutile TiO is about 2.7] compared to the refractive index of potassium titanate which is about 2.35. This higher refractive index of the composite fibers is important when the fibers are to be used in a system where high opacity is a desired characteristic.
The presence of the alkali metal hexatitanate and rutile TiO components in the composite fibers can be readily confirmed by X-ray analysis techniques as both components are characterized by distinct X-ray diffraction patterns. The existence of the core/shell composite structure is readily confirmed by treating the fibers with a 5% by weight HF solution. A true composite is virtually unaffected by the treatment since rutile TiO is essentially inert to the action of 5% or even HF solution. If the fibers were a homogeneous mixture of alkali metal hexatitanate and rutile TiO or if the alkali metal hexatitanate was otherwise in the shell portion, considerable dissolution and weight loss would occur.
The actual percentage of rutile TiO as a shell about the core of alkali metal hexatitanate is not critical pro vided that the amount be such as to ensure inertness to the action of 5% by weight HF solution. Normally the alkali metal titanate should constitute at least l0% and, preferably at least 50%, by weight of the composite fibers.
The fact that the TiO shell about the alkali metal hexatitanate core is in the rutile crystalline phase serves to distinguish the products of the invention from prior art products in which alkali metal titanate fibers may have been leached with acid to remove a portion of the alkali metal oxide from the surface; i.e. such leaching would not result in a distinct TiO shell of the rutile crystalline phase.
Various processes can be used for preparing the composite fibers. One technique, to be described in Example l hereinafter, involves the preparation of alkali metal titanate fibers in the usual way. This may be accomplished, for example, by calcining a dry blended mixture of anatase TiO alkali metal carbonate and alkali metal halide followed by leaching of the calcined product to remove soluble salts. The resultant alkali metal titanate fibers can then be converted to composite fibers by calcining, for example, at 1,000 C., in the presence of a boronor silicon-containing compound such as Na, 8 0 K B 0 B 0 Na SiO muscovite mica, or feldspar. The composite fibers form directly, apparently as a result of the reaction of the boronor silicon-containing compound with the alkali metal oxide in the surface portion of the alkali metal titanate fibers.
Alternatively, alkali metal titanate fibers may be initially formed by the procedure described above but with the inclusion of one of the aforementioned boronor silicon-containing compounds in the dry blended mix before calcining. This method is illustrated in Example ll hereinafter.
Still a third method, and one which wqll be illustrated in Examples lll through V hereinafter, involves direct formation of the composite fibers from a mixture of an alkali metal hydroxide, titanium oxychloride, and one of the silicaor boron-containing compounds described above. In this case, a salt-gel is formed of the various components, which is calcined at a temperature of 850 C. to 1,050" C. More particularly, the salt-gel is prepared by admixing concentrated aqueous alkali metal hydroxide solution, e.g. KOH or NaOH, and aqueous titanium oxychloride solution (e.g. as prepared from the reaction of TiCl, and ice), the mixing preferably being carried out by means of a high speed, high shear mixer. In the process, one solution is conveniently added to the other in relative amounts such that a pH of at least 9, preferably of l0-l 0.5, is reached, at which point a thick salt-gel is formed. The salt'gel is then cast in a suitable container and, preferably, dried. The resultant porous brick is subsequently calcined at a temperature in the range from 850 C. to L050 C. and then leached, e.g. with water or aqueous liquids, to produce the composite fibers.
Regardless of the method employed, simple leaching of the resultant fibers appears to remove essentially all residual compounds containing boron or silicon. Thus, borates tend to be converted to higher borates in the process and these are generally soluble in the water used as a leaching agent. Where a silicon-containing compound has been employed, the use of an aqueous HP leaching solution may be necessary to remove un' desired silicate byproducts.
The amount of boron or silicon-containing compound that need be so employed will vary depending upon which particular process is selected. Moreover, the amount will affect, at least to some extent, the thickness of the TiO shell which is formed. Too little may result in an unduly thin TiO shell, which in turn may fail to give the requisite inertness to a HF solu' tion. Large quantities of the boronor silicon containing compound will, conversely, tend to produce a relatively thick shell of TiO This is not particularly detrimental, however, except from the standpoint that the economics may be less favorable. In general, it is satisfactory to employ some 5 to 50% by weight of the boronor silicon-containing compound based on the weight of the composite fiber which is formed.
Each of the processes results in a composite fiber in which the titanate is essentially in the hexa-crystalline form. apparently because that species is the most thermally stable species.
The utility of the composite fibers will depend, at least in part, upon their particle size. Smaller size particles, say of 0.1 to 0.6 micron in diameter, are useful for the pigmentation of paper, plastics, fibers and the like. Larger size particles, most commonly of 0.6 to 3 microns in diameter, but occasionally up to microns in diameter, are useful in the reinforcement of plastics or as insulation materials. In general the composite fibers should have aspect ratios, i.e. L/D ratios of at least 5 to l but more preferably to l. Aspect ratios of l00-l,000 to l are not uncommon.
DESCRIPTION OF THE DRAWING FIG. 1 is a photomicrograph at 4,200X of composite t\ Ti,,() rutile fibers prepared by the salt-gel method of Example IV with the incorporation of both gotassium borate and paper pulp in the reaction mixture.
EXAMPLES To illustrate the invention more completely, the following examples are given. These are for purposes of illustration only and are not to be construed as limitalion of the invention.
EXAMPLE I Pigmentary size fibers of potassium titanate are produced by the general procedure described in Emslie et =1l. US. Pat. No. 3,328,l l7 involving the calcination of potassium carbonate, anatase TiO and KCl.
A 04 gr. portion of the potassium titanate fibers are wet mixed with 0.6 gr. of wet ground plate glass (silicate glass). The mixture is then dried and placed in a furnace. The temperature is raised to 900 C. over a period of about 2 hours and kept at that temperature for hour. The product is removed from the furnace, and eached in 5% by weight HF with agitation for 3 days. After settling, decanting the clear liquor, filtering, washing with water and drying, the product is subjected to analysis.
Xray analysis demonstrates that the product is composed of K 'li o and rutile TiO, in a ratio estimated 0 be about if]. Microscopically the fibers are found to have an L/D ratio of about l00:l. They are in the pig mentary range, i.e. with a fiber diameter of about (H to 0.6 microns. The core/shell structure is confirmed by the inertness to 5% by weight HF solution in water.
EXAMPLE II A blend is prepared by micronizing together the following components:
300 grams anatasc TiO, I00 grams K,CCi
200 grams KCl The mixed powder is then added to wet paper pulp I00 grams total weight 20% paper pulp fibers) and rolled in a four liter vessel for l hour. Balls form that are about l2 cm. in diameter and are made up of the paper pulpingredient mixture. These balls are calcined for 2 hours at ],000 C. The composite fibers are then recovered by leaching away the soluble salts with dilute sulfuric acid.
Microscopically the product is found to have an average length of about 10 microns, an average diameter of about 0.1 to 0.2 micron and a surface area of 7.3 M lg. The fibers are found to be composed of a predominately potassium hexatitanate core and an outer rutile TiO shell.
EXAMPLE III Fifty grams of KOH is added to 50 cc. distilled water to prepare a concentrated KOH solution which is then placed in a Waring Blendor along with 15 grams K B O While agitation is maintained, a titanium oxychloride solution (considered to be represented by the formula TiOCI- 'ZHCI) is added until a pH of 10 is reached. The titanium oxychloride solution is prepared by mixing TiCl and ice in a 31'] weight ratio. The amount of titanium oxychloride solution so required is 150 grams.
The salt-gel thus prepared is cast into a glass vessel lined with polytetrafluoroethylene and dried for 4 hours at 200 C. A porous brick is formed which is then calcined for minutes at 900 C.
The calcined brick is leached free of soluble salts by washing with hot distilled water. Fourteen grams of a fibrous product are thereby obtained. X-rays reveal that the product, which has a surface area of 9.5 Mlgn, contains both rutile and potassium hexatitanate. Examined microscopically, the composite fibers are found to have an average diameter of about 0.1 micron and an L/D ratio of about 200.
Five grams of the product is placed in 10% aqueous hydrogen fluoride solution in a polyethylene beaker. After 2 hours of stirring, the fibrous product is recovered, washed with distilled water, and dried. It is found to be essentially unchanged. This demonstrates that the rutile effectively encapsulates a potassium hexatitanate core since it is known that potassium titanate alone would be completely soluble in 10% hydrogen fluoride solution.
EXAMPLE IV The procedure is the same as that of Example III except that 10 grams of wet paper pulp (20% solids) is added to the KOH solution along with the 15 grams of K B O In this case the potassium hexatitanatel'l'iO composite fibers have a surface area of 17 M /gr. and length and diameter dimensions similar to the fibers of Example [11. FIG. 1 is a photomicrograph of the fibers at 4,200x.
EXAMPLE V Fifty grams of KOH is added to 50 cc. distilled water to prepare a concentrated KOH solution. The concentrated KOH solution is placed in a Waring Blendor along with grams of wet paper pulp (20% solids) and 10 grams of a titanium oxychloride solution prepared as in Example Ill. While agitation is maintained, more of the titanium oxychloride solution is added until a pH of 10 is reached, this requiring grams of the solution.
The salt-gel thus prepared is cast and dried as in Example lll. The porous brick thus formed is subsequently calcined for 1 hour at 950 C.
The calcined brick is leached free of soluble salts by washing with hot distilled water. A 10% hydrogen fluoride solution is then used over a period of 2 hours to dissolve away the silicates generated in the calcination step. The treatment otherwise leaves the fibers essentially unchanged.
The recovered composite fibers have a surface area of l5 Mlgr. and X-rays reveal the presence of both rutile and potassium hexatitanate components. The fibers have length and diameter dimensions similar to those of Example Ill.
EXAMPLE VI Composite fibers prepared by the methods described in Examples II and III are tested for their reinforcing strength in a commercial, high density, linear polyeth- FLEX TEST RESULTS Sample Flex Strength-psi Flex Moduluspsi Control No fiber reinforcement 4.500 150,000 Example ll fibers 7,320 1 290 594,000 1* 40,000 Example III fibers 6,450 :2 230 427,000 1 17,000
What is claimed is:
l. A fibrous material composed of composite fibers having a number average diameter of up to about l0 microns and an average length/diameter ratio of at least about Sll, said fibers having a core composition corresponding to the formula wherein M is an alkali metal of atomic number of at least 1 1, said core being encapsulated by a shell of rutile TiO, thereby rendering the fibers essentially inert to aqueous 5% by weight HF solution.
I I I I.