3,784,682 United States Patent Office Patented Jan. 8, 1974 feet the true density. That is, by this method only theo- 3,784,682 retical or near theoretical densities can be obtained by DENSIFYING METAL HYDRIDES WITH HIGH making the material quite free from porosity (p. 354). TEMPERATURE AND PRESSURE The true density remains the same. Leonard M. NiebylsM, Birmingham, Mich., assignor to Ethyl Corporation, Richmond, Va. SUMMARY OF THE INVENTION No Drawing. Continuation-in-part of abandoned applica- tion Ser. No. 392,370, Aug. 24, 1964. This application The process of this invention provides a practical Apr. 9,1968, Ser. No. 721,135 method of increasing the true density of hydrides of Int. CI. COlb 6/00, 6/06 metals of Groups II-A, II-B, III-A and III-B of the U.S. CI. 423—645 8 Claims Periodic Table. More specifically, true densities of said 10 metal hydrides may be substantially increased by subject- ing a hydride to superatmospheric pressures at or above ABSTRACT OF THE DISCLOSURE fusion temperatures. When beryllium hydride is subjected A method of increasing the density of a hydride of a to this process, a material having a density of at least metal of Groups II-A, II-B, III-A and III-B of the 0.69 g./cc. is obtained. It may or may not be crystalline. Periodic Table which comprises subjecting a hydride to 15 a pressure of from about 50,000 p.s.i. to about 900,000 DESCRIPTION OF THE PREFERRED p.s.i. at or above the fusion temperature of the hydride; EMBODIMENT i.e., between about 65° C. to about 325° C. Beryllium According to the method of this invention, when a hydride obtained from this process has a density of at 20 metal hydride, such as beryllium hydride, in an amorphous least 0.69 g./cc. form, is subjected to superatmospheric pressures at the fusion temperature or higher, the true density of the hy- This application is a continuation-in-part of my co- dride is increased appreciably over the true density of said pending application Ser. No. 392,370, filed Aug. 24, hydride in its original amorphous form. 1964, now abandoned. 25 The metal hydrides whose densities can be increased according to this invention are hydrides of the elements BACKGROUND OF THE INVENTION of Groups II-A, II-B, III-A and III-B, including the lan- thanum series of rare earth elements; that is, those ele- Metal hydrides find use in many applications. For ex- ments having an atomic number between 58 and 71 inclu- ample, reaction with water allows their use as a ready 30 sive. Thus, among the metal hydrides that can be used means for hydrogen generation. Densification of a metal are the hydrides of the elements of Group II-A of the hydride allows a greater amount of hydrogen to be evolved Periodic Table; that is, beryllium hydride, magnesium hy- per unit volume of hydride. dride, calcium hydride, strontium hydride, and barium Certain metal hydrides, notably beryllium hydride, findhydride . Likewise, the hydride can be zinc hydride, cad- use as rocket fuel components because of their uniquely 35 mium hydride or mercury hydride; that is, a hydride of high specific impulse. However, because beryllium hy- an element of Group II-B of the Periodic Table. Simi- dride, for example, has a relatively low specific density, larly, the hydride of an element of Group III-A of the propellants containing beryllium hydride as a fuel also Periodic Table can be employed. Thus, boron hydride, have a low specific density, resulting in relatively low de- aluminum hydride, gallium hydride, indium hydride, and livered impulse per unit volume. Therefore, increasing 40 thalium hydride can be used. Also, the hydride of an ele- the density of beryllium hydride would aid in producing ment of Group III-B of the Periodic Table can be used; an even greater delivered impulse per unit volume and to wit: scandium hydride, yttrium hydride, lanthanum hy- allow greater flexibility in the construction of rocket dride and the hydrides of elements of the lanthanide and motors. actinide series of rare earth elements; that is, those ele- Beryllium hydride has been synthesized by Coates and 45 ments having atomic numbers from 58 to 71 inclusive. Glockling, J. Chem. Soc. 25-26 (1954), by the pyrolysis Accordingly, cerium hydride, praseodymium hydride, neo- of di-tertiary butyl beryllium etherate and by Head, dymium hydride, promethium hydride, samarium hydride, Holley and Rabideau, J. Am. Chem. Soc. 29, 3687 (1957),europiu m hydride, gadolinium hydride, terbium hydride, using ether-free di-tertiary butyl beryllium. More re- dysprosium hydride, holmium hydride, erbium hydride, cently, a superior product has been obtained by the py-50 thulium hydride, ytterbium hydride, and lutecium hydride rolysis of tertiary butyl beryllium etherate dissolved in a can be used in accordance with this invention. high-boiling inert solvent (co-pending application Ser. No. The hydrides of beryllium and aluminum are preferred 176,865, filed Feb. 26, 1962). However, the beryllium in this invention as they are most susceptible to the proc- hydride products of the above synthetic processes are ess described herein. Beryllium hydride is most highly pre- without exception amorphous in structure, and as a re- 55 ferred as its density is particularly increased by the tech- sult are characterized by a relatively low density, 0.57 3 niques of this invention. to 0.67 gram per cm. , which limits their suitability for The density increase is accomplished by fusing the this application. particles of a hydride. The term "fusing" as used here Methods of increasing the density of a material are means that the particles of a hydride flow into one another known in the metallurgical art. For example, Jones, Fun60- or coalesce forming a coherent structure. The temperature damental Principles of Powder Metallurgy, Edward Ar- at which this takes place is called fusion temperature. nold (Publishers) Ltd., London (1960), in the chapter Definite changes in the physical properties of the ma- on pressing discusses increasing the density of a metal terial take place at the point of fusion. For example, while powder by hot-pressing (pp. 351-355). However, this prior to fusion the amorphous hydride is opaque, at the method increases only the bulk density and does not af- 65 point of fusion, this material becomes clear and trans- 3,781,545 3 4 parent similar to glass. The degree of clarity depends on slurry was filtered, the filter cake washed with hexane or the degree of purity of the hydride. That is, if beryllium petroleum ether and then dried. The products were white hydride is contaminated with beryllium metal or beryllium to a somewhat gray in appearance and had densities of oxide, then the degree of clarity of the fused hydride will from 0.63 to 0.67 g./cc. The following table summarizes be directly proportional to the amount of the impurities g the conditions and results of several runs, since these impurities themselves do not undergo fusion. TABLE I Fusion of the metal hydride is readily accomplished by [Solution pyroiysis] control of the temperature and pressure imposed on the - material. The pressure can be either mechanical, gas pres- Hati0 BeH2> sure or hydrostatic. Gas pressures generally have to be io solvent/ time, Temp., wt! Density, quite a bit higher at any particular temperature than is Bun Solvent PTBBEi mm. ° c. percent g./cc. necessary with mechanical or hydrostatic pressure. Simi- l Dodecane... 3/t 20 195 93.4 0.65 larly, hydrostatic pressures should be somewhat higher g- do"""" 1.5/1 so 195 92!? 0.65 than mechanical pressures. 4=11IIIIIIII-I IdoIIIIIII 1! 5/1 20 210 92! 9 0^63 The greater the pressure, the lower the temperature re- 15 f^SV" 3/1 30 "7-202 90.? a w quired to accomplish fusion of a metal hydide. The reverse 7 do 3/1 60 191-196 93.5 0.0a is also true. However, no fusion can be obtained at the s'lIIIIIIIIIIdoIIIIIII !/i 100 19^200 94.3 o'.es atmospheric pressure or at the room temperature. Thus, a i6riIIIIIIIIIdoIIII-.- 3/1 90 197-200 94.8 0.65 pressure of at least 50,000 p.s.i. and a temperature of at , Di.tert-butyi beryllium etherate. least 65° C. is required to accomplish fusion and the 20 ' -A. refined kerosene with a boiling range or about 200-250° C. increase in density according to the process of this inven- , ... ^ . ,, , ., . ... tion. For beryllium hydride, preferably a pressure of over J? h}s manneTJ flet^yIalummT 75,000 p.s.i. and most preferably over 100,000 p.s.i., and cally decomposed to aluminum hydride Similarly di- a temperature of over 100° G. and most preferably over ,., - . .. , , " 135° C. is employed. 25 Als0' dibutylcadmium is pyrolyticalln y decomposed to The particular temperature-pressure relationship at cadmium hydride, which a particular metal hydride is fused depends on txample 2 several factors, among which are purity of the metal Beryllium hydride was obtained by neat pyroiysis of di- hydride, and origin of the metal hydride; that is, whether tert-butyl beryllium etherate as follows, it was formed pyrolytically or metathetically. Pyrolytically 30 Di-tert-butyl beryllium etherate was added to a vessel and metathetically formed beryllium hydride is generally equipped with heating means, temperature measuring readily fused at a temperature of from 135° to 210° C. means, vacuum creating means and pressure measuring and under a pressure of at least 50,000 p.s.i. means. The vessel was heated and the pressure was In order to pyrolytically prepare a metal hydride, an brought down to 60 mm.