US 3332796 A
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July 25, 1967 Filed June 21, 1962 MAGNETIC VALVE 12 MAGNETIC VALVE C. KOOY PREPARING NICKEL FERRITE SINGLE CRYSTALS 0N A MONOCRYSTALLINE SUBSTRATE 3 She rats-Sheet l NICO B0 CO2 FB O27 MONOCRYSTAL FIG.1
FURNACE INVENTOR GORNELIS KOOY BY i i L I. AG T July 25, 1967 Y c. KOOY 3,332,796
PREPARING NICKEL FERRITE SINGLE CRYSTALS ON A MONOCRYSTALLINE SUBSTRATE Filed June 21, 1962 3 Sheets-Sheet 2 FIG 2 28 2s 21. 22 2'0 fa 1 6 12 1'2 1qNVE-|TOR M0 CORNELIS KOOY BY 2 g AGEN July 25, 1967 C. KOOY 3,332,796
PREPARING NICKEL FERRITE SINGLE CRYSTALS ON A MONOCRYSTALLINB SUBSTRATE Filed June 21, 1962 3 Sheets-Sheet 3 29 --Mo m FIGA 2e 2e 22. 22 2 0 fa 1s 1:. 1'2 1 0 :1
INVENTOR GORNELIS KOOY BY AGENT United States Patent 6 3 Claims. (Cl. 117-21) The invention relates to a method of manufacturing a single crystal body of a compound which is capable of being sintered.
It is known to manufacture single crystal bodies by melting the relative compound and, during cooling, taking such measures that the particles of the solidifying melt arrange in a particular manner with respect to each other. This may occur, for example, by inducing the crystallization in the melt with a cold finger which usually comprises a small seed crystal. It is also known to heat the powder of the compound in question in the flame of an oxyhydrogen blowpipe, the powder being taken along by the inner pipe of the .blowpipe. The powder is caught on a refractory rod and solidifies to form a single crystal body. In these cases, the method is carried out at the melt- .ing temperature of the pure compound. Naturally, the gas atmosphere should be adapted to the equilibrium of the compound at this temperature. In connection with the high melting temperature, this is often hard to realize, as a result of which some compounds decompose entirely at the melting temperature.
Alternatively, methods are known which are carried out at a temperature lower than the melting temperature of the pure compound. The melt contains, in addition to the pure compound, one or more other compounds which are active as fluxes. This method may be used in those cases in which a suitable flux exists for the compound in question. In addition, special measures should be taken to influence the nucleation and to check uncontrolled nucleation.
The invention relates to a particular method which is also carried out below the melting temperature of the pure compound. It is based on the recognition of the fact that a controlled recrystallization takes place if a thin layer of powdered particles is applied on a monocrystalline substratum and sintered.
In the method according to the invention, a layer of at most 2-00 microns, preferably at most 20 microns, of a powder of the compound in question or of substances which form the compound in question on heating having a particle size of at most microns, is provided on a single crystal body and heated to a temperature which lies in the recrystallization temperature range of the compound in question. The method is carried out below the melting temperature since the recrystallization temperature range lies below the melting temperature. The recrystallization temperature range lies between /2 and /3 of the absolute melting temperature. A temperature in this range is sometimes termed Tamman temperature. With this method, the particles of the powder recrystallize according to an ordered pattern as a result of the monocrystalline substrate on which it is provided. The thickness of the layer is at most 200 microns to prevent arbitrary recrystallization from taking place in part of the applied layer. Good results are obtained with a layer thickness of at most 20 microns. The particles of the powder are on the substrate in an arbitrary orientation. The ordered growth turns out to start from those particles of the powder which, as far as the crystal orientation is concerned, are rationally linked with those of the substrate. The particle size of the powder should be at most 5 microns for the powder to be reactive.
So the compound is not applied in an atomic or molecular form but in the form of small crystalline powdered particles. The powder may consist of particles of the compound in question. Then the method according to the invention substantially comes to a recrystallization with a controlled nucleation of the recrystallization nuclei. The powder may also consist of substances which form the compound in question on heating. In this case, both a reaction and an ordered crystallization take place. The powder is applied on a single crystal body. The composition of this body may be equal to that of the body to be manufactured but it may also have a different composition and even a crystal structure which differs from that of the single crystal body to be manufactured. In this latter case, a sufliciently large difference should exist between the interfacial surface energy with respect to the substrate with oriented and non-oriented particles of the powder so as to form recrystallized orientation nuclei. The powder layer may be provided on the substrate in various manners. It may be effected in the form of a suspension, after which the substrate with the suspension layer are heated. It is also possible to provide a thin powder layer immediately on a heated substrate by blowing the powder on it by means of a gas stream.
In this manner, thin monocrystalline layers are formed which can easily be separated from the substrate. To obtain single crystal bodies having a larger thickness, the method according to the invention is repeated several times.
Compounds, of which single crystal bodies can be manufactured by means of the method according to the invention are, for example, BaTiO and NiFe O Since it is very difficult to obtain a single crystal body of NiFe Q, according to a known method, use is made according to the invention of a signal crystal body having a magnetoplumbite structure, for example a body of a composition BaFe O or a single crystal body having a different hexagonal crystal structure, for example a body of a composition BaCo Fe O In order that the invention may readily be carried into effect, it will now be described, by way of example, with reference to the accompanying drawings and the ensuing examples.
FIG. 1 diagrammatically shows an apparatus which may be used in the method according to the invention.
FIGS. 2, 3 and 4 show intensities of an X-ray diffraction pattern of bodies manufactured according to the method according to the invention.
FIG. 5 shows the intensities of an X-ray diffraction pattern of a known body.
EXAMPLE I A mixture of NiCO and Fe O in a ratio of 1:1 was ground for 16 hours in ethyl alcohol in a ball mill and then another 16 hours in a vibrating mill. After drying, a suspension in amyl acetate with approximately 0.25% nitrocellulose was made of the powder. Of this suspension a 20 micron thick layer was coated on the (0001) face of a single crystal body of SrFe O which, after drying, yielded a homogeneously distributed layer of powder particles on the surface of the single crystal body. This was heated in oxygen for 15 minutes at 0 C. Of this product an X-ray diffraction pattern was made which, in addition to the reflections of the basal plane of the SrFe O single crystal, also showned the (111), (222), (333) and so on reflections of the spinel lattice of NiFeO The method was repeated several times. After five times, the X-ray diffraction diagram invariably showed only the (111) reflections of spinel and those of the basal plane of SrFe O from which it appears that the layer of NiFe O formed is monocrystalline or that it has a very pronounced orientation with the (111)-axis parallel to the hexagonal c-axis of the substrate crystal.
EXAMPLE II By means of the apparatus diagrammatically shown in FIGURE 1, small portions of a powdered mixture of NiCO and Fe O in a ratio of 1:1 where applied on the (0001) face of a single crystal body of Baco Fe O which was at a temperature of 1325 C. The tube furnace 1 contains the said single crystal body 2. On the one side, the aluminum oxide tube 3 extends in the furnace so that it nearly touches the single crystal body 2. By means of a connecting limb 4 the tube 3 is connected to the glass tube 5 having two branches. The glass container 6 containing the powder mixture 7 of NiCO and Fe O is provided in the one branch. The tube 8 which comprises a magnetic shutter 9 and a flow meter 10 extends in the vessel 6 in the powder mixture 7. The other branch of the tube 5 comprises a magnetic shutter 11 and a flow meter 12. A stream of oxygen was blown through the tube 8 at a rate of from 5 to 10 liters/ min. which caused eddies in the container 6, as a result of which the powder was more or less fluidized and the smallest particles were conducted into the tube 5 over such a distance that they Were blown on the single crystal body 2 at a rate of from 10 to 15 liters/min. by a stream of oxygen supplied to the other branch of the tube 5. The furnace temperature was 1325 C. By controlling the magnetic shutters, powder was blown on the single crystal body for 2 seconds every 10 minutes. 0.2 to 0.4 mg. of the powder mixture were applied to the surface of the single crystal body which had an area of 0.5 x 0.5 cm. This method was repeated many times. The results are shown in FIGURES 2, 3 and 4 which are X-ray diffraction patterns after 14, 68 and 106 operations respectively. In the figures the intensity I of the reflections of a MoKa radiation is plotted in an arbitrary unit as a function of a deflection angle 20. From the increase of the ratio of the intensities of the (111) spinel reflection and the basal reflections of BaCo Fe O it may be concluded that an ordered spinel layer is formed on the single crystal substrate. The orientation follows from the absence of all reflections other than those of the (111) plane. In FIGURE 4, the peak of the (333) line falls outside the plane of the drawing. For comparison, FIGURE 5 shows the reflections of a body constituting of NiFe O in which the particles are arbitrarily present. Single crystal bodies obtained in this manner and having thicknesses of from 100 to 300 microns could be detached from the substrate.
The same result was obtained in a method in which the mixture of NiCO and Fe O was replaced by a powder of NiFe O which was obtained by heating the powder mixture of NiCO and Fe O at 1000 C. and grinding the reaction product in alcohol in a ball mill for 16 hours and in a vibrating mill for 8 hours and then drying it. I
\rVhat is claimed is:
1. A method of manufacturing a single crystal body of NiFe O comprising the steps of applying a layer of powder NiFe O not exeeding 2:00p. in thickness and composed of particles not exceeding 5 in diameter on a monocrystalline substrate of BaFe O and heating said layer to a temperature between /2 and /3 the absolute melting temperature of NiFe O to thereby recrystallize the particles into a monocrystalline layer.
2. A method of manufacturing a single crystal body of NiFe O comprising the steps, applying a layer of NiFe O powder not exceeding 200p. in thickness and composed of particles not exceeding 5 in thickness on a monocrystalline substrate of BaCo Fe O and heating said layer to a temperature between /2 and /3 the absolute melting temperature of NiFe Og to thereby recrystallize the the particles into a monocrystalline body.
3. A method of manufacturing a single crystal body of NiFe O comprising the steps, applying a layer of NiFe O powder not exceeding 200 in thickness and composed of particles each having a diameter not exceeding 5 1 on a monocrystalline substrate of SrFe O and heating said layer to a temperature between /2 and /3 the absolute melting temperature of NiFe O to thereby recrystallize the particles into a monocrystalline body.
References Cited UNITED STATES PATENTS 2,832,705 4/1958 Seidl 117168 X 3,037,180 5/1962 Linz 25262.3 X 3,047,429 7/1962 Stoller 117215 3,093,517 6/ 1963 Lyons 25262.3 X 3,100,158 8/1963 Lemaire 117215 3,108,072 10/1963 Gutsche 252-62.3 X 3,109,749 11/1963 Di Ricco 1172l5 NORMAN YUDKOFF, Primary Examiner.
MAURICE A. BRINDISI, Examiner.
H. T. CARTER, S. J. EMERY, Assistant Examiners.