Microcrystalline-to-amorphous metal and/or alloy powders dissolved without protective colloid in organic solvents

BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of finely divided microcrystalline-to-amorphous metal and/or alloy powders or highly dispersed colloids by the reduction of metal salts with alkali metal or alkaline earth metal hydroxides that are kept in solution in organic solvents by means of specific complex-forming agents. What is further claimed is the use of the powders produced according to the invention in powder technology (Ullmanns Encykl. Techn. Chemie, 4th Edition, Vol. 19, p. 563) or as catalysts in a neat or supported form (Ullmanns Encykl. Techn. Chemie, 4th Edition, Vol. 13, p. 517; further: Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 19G, pp. 28 et seq.). The colloids prepared according to the invention may be used to apply the metals in the form of fine cluster particles onto surfaces (J. S. Bradley, E. Hill, M. E. Leonowicz, H. J. Witzke, J. Mol. Catal. 1987, 41, 59 and literature quoted therein) or als homogeneous catalysts (J. P. Picard, J. Dunogues, A. Elyusufi, Synth. Commun. 1984, 14, 95; F. Freeman, J. C. Kappos, J. Am. Chem. Soc. 1985, 107, 6628; W. F. Maier, S. J. Chettle, R. S. Rai, G. Thomas, J. Am. Chem. Soc. 1986, 108, 2608; P. L. Burk, R. L. Pruett, K. K. Campo, J. Mol. Catal. 1985, 33, 1).
More recent methods for the preparation of superfine metal particles consist of metal evaporation (S. C. Davis and K. J. Klabunde, Chem. Rev. 1982, 82, 153-208), electrolytical procedures (N. Ibl, Chem. Ing.-Techn. 1964, 36, 601-609) and the reduction of metal halides with alkali metals (R. D. Rieke, Organometallics 1983, 2, 377) or anthracene-activated magnesium (DE 35 41 633). Further known is the reduction of metal salts with alkali metal borohydrides in an aqueous phase to form metal borides (N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press 1986, p. 190). The coreduction of iron and cobalt salts in water results in the production of a Fe/Co/B alloy having the composition of Fe.sub.44 Co.sub.19 B.sub.37 (J. v. Wonterghem, St. Morup, C.J.W. Koch, St, W. Charles, St. Wells, Nature 1986, 322, 622).
SUMMARY OF THE INVENTION
It was now surprisingly found that metal hydrides of the first or second main groups of the Periodic Table can be employed as reducing agents for metal salts by means of organoboron and/or organogallium complexing agents in an organic phase, whereby metals or metal alloys in powder or colloidal form are obtained which are boride-free and/or gallium-free, respectively.
The advantages of the process according to the invention are constituted by that the reduction process can be very out under very mild conditions (-30.degree. C. to 150.degree. C.) in organic solvents, further by the good separability of the metal or alloy powders from the usually soluble by-products, and by the microcrystallinity of the powder and the fact that the particle size distribution may be controlled as dependent on the reaction temperature. It is a further advantage that colloidal solutions of metals or alloys are obtained under certain conditions (use of donor-metal salt complexes and/or ammoniumtriorgano hydroborates) in ethers or even neat hydrocarbons without an addition of further protective colloids.
PREFERRED EMBODIMENTS
As the metals of the metal salts there are preferably used the elements of the Groups IVA, IB, IIB, VB, VIB, VIIB and VIIIB of the Periodic Table. Examples of metals of said Groups of the Periodic Tables comprise Sn, Cu, Ag. Au, Zn, Cd, Hg, Ta, Cr, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt.
As the metal salts or compounds there are used those which contain either inorganic or organic anions, and preferably those which are solvated in the systems employed as solvents, such as hydroxides, oxides, alcoholates and salts of organic acids. As the reducing agents there are used metal hydrides of the general halides, cyanides, cyanates, thiocyanates as well as formula MH.sub.x (x=1, 2) of the first and/or second Groups of the Periodic Table which have been reacted with a complexing agent having a general formula BR.sub.3, BR.sub.n (OR').sub.3-n or GaR.sub.3, GaRn(OR').sub.3-n, respectively (R, R'=C.sub.1 C.sub.6 -alkyl, phenyl, aralkyl; n=0, 1, 2) (R. Koster in: Methoden der Organischen Chemie (Houben-Weyl-Muller), 4th Edition, Vol. XIII/3b, pp. 798 et seq., Thieme, Stuttgart 1983). All types of organic solvents are suitable for the process according to the invention as far as they do not react themselves with metal hydrides, e.g. ethers, aliphatics, aromatics as well as mixtures of various solvents. The reaction of the metal hydrides with complexing agents for the purpose of solvation in organic solvents may be carried out according to the invention with particular advantage in situ, optionally with the use of a less than stoichiometric amount of complexing agent.
During the reaction of the metal salts, the complexed hydrides are converted into salts of the type M(anion).sub.x (M=cation of ammonium, an alkali metal or an alkaline earth metal; x=1, 2). M-hydroxides, -alcoholates, -cyanides, -cyanates and -thiocyanates will form soluble -ate complexes with the organoboron and organogallium complexing agents, said -ate complex being of the types M[BR.sub.3 (anion)], M[BR.sub.n (OR').sub.3-n (anion)] and M[GaR.sub.3 (anion)], M[GaR.sub.n (OR').sub.3-n (anion)]. Since, by virtue of said -ate complex formation, the reaction products of the hydrides remain in solution, upon completion of the reaction according to the invention the metal or alloy powder may be recovered in the pure state with particular advantage by way of a simple filtration from the clear organic solution. In the course of the reaction according to the invention, M-halides, as a rule, do not form such -ate complexes; however, in many cases after the reaction they remain dissolved in the organic solvent, for example THF. This applies to, more specifically, CsF, LiCl, MgCl.sub.2, LiBr, MgBr.sub.2, LI, NaI and MgI.sub.2. Thus, for facilitating the work-up, in the preparation according to the invention of the metal and alloy powders from the corresponding metal-halogen compounds, the selection of the cation in the hydride is governing. Said cation should be selected so that it forms a halide with the respective halogen which halide is soluble in the organic solvent. Alternatively, M-halides which are precipitated from the organic solvent upon completion of the reaction according to the invention, e.g. NaCl, may be removed from the metal or alloy powder by washing-out, e.g. with water. It is a characteristic feature of the process carried out according to the invention that the organoboron and organogallium complexing agents can be recovered after the reaction either in the free form or by de-complexing the by-products M(anion).sub.x. Reactions of Ni(OH).sub.2 with Na(BEt.sub.3 H) in THF result in the formation of Na(BEt.sub.3 OH) in solution, as is evidenced by the .sup.11 B-NMR spectrum (.sup.11 B signal at 1 ppm). From this -ate complex present in the solution, the complex-forming agent BEt.sub.3 is recovered by hydrolysis using HCl/THF in a yield of 97.6% as is evidenced by analytical gas chromatography (Example 15).

BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described with reference to the accompanying drawings, wherein:
FIGS. 1 and 2 show particle size distributions resulting from different reaction conditions in accordance with the present invention; and
FIGS. 3, 4 and 5 are X-ray diffraction diagrams of different products produced in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION
According to the invention there are obtained powder metals having a particle size of 0.01 .mu.m (Example 11) up to 200 .mu.m (Table 2, No. 46). The particle size distribution may be controlled via the reaction parameters. Upon a given combination of starting materials and solvent, the metal particles obtained according to the invention are the finer, the lower the reaction temperature is. Thus, the reaction of PtCl.sub.2 with Li(BEt.sub.3 H) in THF at 80.degree. C. (Table 2, No. 46) provides a platinum powder which has a relatively wide particle size distribution of from 5 to 100 .mu.m (see FIG. 1). The same reaction at 0 .degree. C. (Table 2, No. 45) provides a platinum powder which has a substantially narrower particle size distribution and marked maximum at 15 .mu.m (see FIG. 2).
FIG. 1
FIG. 2
The metal powders prepared according to the invention are microcrystalline-to-amorphous, as is evident from the X-ray diffraction diagrams thereof. FIG. 3 shows powder X-ray diffractograms measured by means of CoK.sub..alpha. -radiation of Fe powder prepared according to the invention (Table 2, No. 3) before and after a thermal treatment of the sample at 450 .degree. C. The untreated sample shows just one very broad line (FIG. 3a), which furnishes evidence of the presence of microcrystalline to amorphous phases (H. P. Klug, L. E. Alexander, X-ray Diffraction Procedures for Polycrystalline and Amorphous Materials, 2nd Edition, Wiley, New York 1974). After 3 hours of treatment of the sample at 450 .degree. C. a sharp line, due to recrystallization, is observed at a scattering angle 2 .theta. of 52.4.degree. at a lattice spacing of the planes of D=2.03 .ANG. which is characteristic of the face-centered cubic lattice of .alpha.-iron (FIG. 3b).
FIGS. 3a and 3b
A simple co-reduction of salts of different metals or of mixed oxides in accordance with the process of the invention under mild conditions results in the formation of finely divided bi-metal and poly-metal alloys. The co-reduction of FeSO.sub.4 and CoCl.sub.2 with tetrahydroborate in an aqueous solution has been described by J. V. Wonterghem, St. Morup et al. (Nature 1986, 322, 622). The result of said procedure--evidenced by the elemental composition and the saturation magnetization of 89 J T.sup.-1 kg.sup.-1 is a Fe/Co/B alloy having the composition of Fe.sub.44 Co.sub.19 B.sub.37. After annealing said product at 452 .degree. C., the saturation magnetization, although it increases to 166 J T.sup.-1 kg.sup.-1, still remains far below the value to be expected for a Fe.sub.70 Co.sub.30 alloy of 240 J T.sup.-1 kg.sup.-1, which fact the authors attribute to the presence of boron in an alloyed or separate phase. In contrast thereto, the co-reduction according to the invention of FeCl.sub.3 with CoCl.sub.2 (molar ratio of 1: 1; cf. Example Table 5, No. 6) in a THF solution with LiH/BEt.sub.3 provides a boron-free powder of the Fe.sub.50 Co.sub.50, as is proven by the elemental analysis. Evidence for the existence of a microcrystalline-to-amorphous Fe/Co alloy is derived from X-ray diffractograms of the powder obtained according to the invention before and after a thermal treatment (FIG. 4). Prior to the heat treatment, the diffractogram shows only a very broad diffuse line (a) which is characteristic for weakly crystalline to amorphous phases. After the heat treatment (3 hours at 450.degree. C.) a sharp line is observed in the diffractogram (b) at a scattering angle 2 .theta. of 52.7.degree. at a lattice spacing of the planes of D=2.02 .ANG. which is characteristic of a crystallized Fe/Co alloy.
FIG. 4
To furnish evidence of that the alloy formation already takes place in the course of the reduction process according to the invention and is by no means induced afterwards by way of the heat treatment, a 1:1 blend of amorphous Fe and Co powders was measured before and after the heat treatment effected at 450.degree. C. (FIG. 5). The untreated blend again exhibits a diffuse line (a). After 3 hours at 450.degree. C., the pattern develops into the superposition of two sets of lines (b) for body-centered cubic Fe (x) and hexagonal or face-centered cubic Co (o). The comparison of the FIGS. 4 and 5 furnishes evidence of the a microcrystalline-to-amorphous alloy is formed upon the co-reduction according to the invention, which alloy re-crystallizes only upon heat treatment.
FIG. 5
According to the invention, one-phase two- and multi-component systems in a microcrystalline to amorphous form may be produced by freely combining the salts of main group and subgroup elements, non-ferrous metals and/or noble metals. It is also possible according to the invention with a particular advantage by reducing or co-reducing metal salts and/or metal compounds or salt mixtures coated on support materials as far as these will not react with hydroethylborates (e.g. Al.sub.2 O.sub.3, SiO.sub.2 or organic polymers) to produce shell-shaped amorphous metals and/or alloys on supports (Example 14). Amorphous alloys in the pure or supported states are of great technical interest as catalysts.
With a particular advantage there may be obtained according to the invention under certain conditions metals and/or alloys in the form of a colloidal solution in organic solvents without the addition of a protective colloid. The reaction of the salts of non-ferrous metals or noble metals (individually or as mixtures) with the tetraalkylammonium triorgano hydroborates as accessible according to the German Patent Application P 39 01 027.9 at room temperature in THF results in the formation of stable colloidal solutions of the metals which are red when looked through. If the metal salts are employed in the form of donor complexes, then according to the invention the colloidal metals are preparable also with alkali metal or alkaline earth metal triorgano hydroborates in THF or in hydrocarbons (cf. Table 6, Nos. 15, 16, 17).
The invention is further illustrated by way of the following Examples.
EXAMPLE 1
Preparation of nickel powder from Ni(OH) 2 with NaBEt.sub.3 H in THF
5 g (41 mmoles) of NaBEt.sub.3 H dissolved in THF (1 molar) are dropwise added at 23.degree. C. with stirring and under a protective gas to a solution of 1.85 g (20 mmoles) of Ni(OH).sub.2 in 200 ml of THF in a 500 ml flask. After 2 hours the clear reaction solution is separated from the nickel powder, and the latter is washed with 200 ml of each of THF, ethanol, THF and pentane. After drying under high vacuum (10.sup.-3 mbar) , 1.15 g of metal powder are obtained (see Table 1, No. 6).
Metal content of the sample: 94.7 % of Ni
BET surface area: 29.7 m.sup.2 /g
EXAMPLE 2
Preparation of silver powder from AgCN, Ca(BEt.sub.3 H).sub.2 in Diglyme
2.38 g (10 mmoles) of Ca(BEt3H).sub.2 dissolved in Diglyme (1 molar) are added to 1.34 g (10 mmoles) of AgCN in a 500 ml flask under a protective gas, and Diglyme is added to give a working volume of 250 ml. The mixture is stirred at 23.degree. C. for two hours, and the black metal powder is separated from the reaction solution. The silver powder is washed with 200 ml of each of THF, ethanol, THF and pentane and dried under high vacuum (10.sup.-3 mbar). 1.10 g of metal powder are obtained (see Table 1, No. 17).
Metal content of the sample: 89.6 % of Ag
BET surface area: 2.3 m.sup.2 /g
TABLE 1__________________________________________________________________________Reductions of Metal Salts or Metal Compounds ProductsStarting Reaction Conditions Amount Metal Boron Specific BET- Materials Reducing t T Recovered Content Content Surface AreaNo. Metal Salt (mmoles) Agent (mmoles) (h) (.degree.C.) (g) (%) (%) (m.sup.2 /g)__________________________________________________________________________1 Fe(OEt).sub.2 12,0 NaBEt.sub.3 H 30 16 67 0,6 96,8 0,16 62,22 Co0.sup.+ 40,0 NaBEt.sub.3 H.sup.++ 120 16 130 2,40 98,1 -- 79,23 Co(OH).sub.2 20,0 NaBEt.sub.3 H 41 2 23 1,20 94,5 0,40 46,84 Co(OH).sub.2 20,0 NaBEt.sub.3 H 50 16 67 1,09 93,5 1,09 49,85 Co(OEt).sub.2 18,6 NaBEt.sub.3 H 47 16 67 1,16 93,5 0,82 33,26 Co(CN).sub.2 20,0 NaBEt.sub.3 H 100 16 67 1,22 96,5 0,20 52,17 NiO.sup.+ 40,0 NaBEt.sub.3 H.sup.++ 120 16 130 2,46 94,1 0,0 6,58 Ni(OH).sub.2 20,0 NaBEt.sub.3 H 41 2 23 1,15 94,7 0,13 29,79 Ni(OH).sub.2 20,0 NaBEt.sub.3 H 50 16 67 1,13 93,3 0,89 35,710 Ni(OEt).sub.2 16,1 NaBEt.sub.3 H 40 16 67 0,96 91,4 0,58 12,511 Ni(CN).sub.2 18,0 NaBEt.sub.3 H 50 16 67 1,17 89,2 0,63 53,612 Cu0.sup.+ 40,0 NaBEt.sub.3 H.sup.++ 120 16 130 2,37 93,8 0,18 8,613 CuCN 21,3 NaBEt.sub.3 H 26 2 23 1,28 98,7 0,09 18,614 CuCN 20,0 NaBEt.sub.3 H 30 16 67 1,30 94,7 0,0 8,915 CuCN 47,5 LiBEt.sub.3 H 48 2 23 2,83 97,3 0,0 5,116 CuSCN 3,5 NaBEt.sub.3 H 4 2 23 0,23 96,1 0,0 --17 CuSCN 20,0 NaBEt.sub.3 H 30 16 67 1,24 95,0 0,23 2,618 Pd0.sup.+ 12,6 NaBEt.sub.3 H.sup.++ 120 16 130 2,03 95,4 0,24 14,019 Pd(CN).sub.2 10,0 NaBEt.sub.3 H 22 2 23 1,06 86,6 1,57 27,620 Pd(CN).sub.2 10,2 NaBEt.sub.3 H 31 16 67 1,06 95,5 1,38 12,121 Ag.sub.2 0 20 NaBEt.sub.3 H.sup.++ 60 16 20 4,19 97,7 0,10 1,822 AgCN 10 Ca(BEt.sub.3 H).sub.2 * 10 2 23 1,10 89,6 0,20 2,323 AgCN 10 NaBEt.sub.3 H 12 2 23 1,08 90,5 0,20 2,424 AgCN 10 NaBEt.sub.3 H 12 16 67 1,06 86,2 0,19 2,625 Cd(OH).sub.2 20 NaBEt.sub.3 H 50 2 23 2,25 97,9 0,22 --26 Pt0.sub.2 11 NaBEt.sub.3 H 54,9 4 20 2,09 97,5 0,55 --27 Pt(CN).sub.2 5,3 NaBEt.sub.3 H 14 16 67 1,00 87,5 0,93 5,728 AuCN 4,5 NaBEt.sub.3 H 7 2 23 0,87 97,5 0,0 3,029 Hg(CN).sub.2 11,0 NaBEt.sub.3 H 54 2 23 2,18 96,1 1,29 --__________________________________________________________________________ Solvent: THF .sup.+ Autoclave experiment under H.sub.2atmosphere .sup.++ Solvent: Toluene *Solvent: Diglyme
EXAMPLE 3
Preparation of rhenium powder from ReCl.sub.3, LiBEt.sub.3 H in THF
3.8 g (36 mmoles) of LiBEt.sub.3 H dissolved in THF (1 molar) are dropwise added at 23.degree. C. with stirring and under a protective gas to a solution of 2.43 g (8.3 mmoles) of ReCl.sub.3 in 200 ml of THF in a 500 ml flask. After 2 hours the clear reaction solution is separated from the rhenium powder, and the rhenium powder is washed with 200 ml of each of THF, ethanol, THF and pentane. After drying under high vacuum (10.sup.-3 mbar), 1.50 g of metal powder are obtained (see Table 2, No. 36).
Metal content of the sample: 95.4%
BET surface area:82.5 m.sup.2 /g
EXAMPLE 4
Preparation of cobalt powder from LiH, BEt.sub.3 in CoCl.sub.2
0.5 g (63 mmoles) of LiH, 0.62 g (6.3 mmoles) of triethylborane and 250 ml of THF are added to 3.32 g (25.6 mmoles) of CoCl.sub.2 under a protective gas and are refluxed with stirring for 16 hours. After cooling to room temperature, the cobalt powder is separated from the reaction solution and is washed with 200 ml of each of THF, ethanol, THF and pentane. After drying under high vacuum (10.sup.-3 mbar), 1.30 g of metal powder are obtained (see Table 2, No. 10).
Metal content of the sample: 95.8% of Co
BET surface area: 17.2 m.sup.2 /g
EXAMPLE 5
Preparation of tantalum powder from TaC.sub.5 with LiH, BEt.sub.3 in toluene
0.48 g (60 mmoles) of LiH, 0.6 g (6 mmoles) of triethylborane and 250 ml of toluene are added to 3.57 g (10 mmoles) of TaCl.sub.5 under a protective gas and are heated at 80.degree. C. with stirring for 16 hours. After cooling to room temperature, the tantalum powder is separated from the reaction solution and is washed with three times 200 ml of toluene and once with 200 ml of pentane. After drying under high vacuum (10.sup.-3 mbar), 3.87 g of metal powder are obtained (see Table 2, No. 34).
Metal content of the sample: 46.5% of Ta
EXAMPLE 6
Preparation of Na[(Et.sub.2 GaOEt) H]
34.5 g (200 mmoles) of diethylethoxygallium--Et.sub.2 GaOEt--were boiled under reflux in 400 ml of THF with 30.5 g (1270 mmoles) of NaH for four hours. A clear solution is obtained from which excessive NaOH is removed by filtration using a D-4 glass frit.
A 0.45M solution was obtained according to the protolysis with ethanol.
Preparation of palladium powder from PdCl.sub.2 and Na [(Et.sub.2 GaOEt)H]
45 ml (20.25 moles) of the Na[(Et.sub.2 GaOEt)H] solution thus obtained are dropwise added at 40.degree. C. with stirring and under a protective gas to a solution of 1.91 g (10.76 mmoles) of PdCl.sub.2 in 200 ml of THF in a 500 ml flask. After 2 hours the clear reaction solution is separated from the palladium powder, and the palladium powder is washed with two times 200 ml of H.sub.2 O, 200 ml of THF and 200 ml of pentane. After drying under high vacuum (10.sup.-3 mbar), 1.2 g of metal powder are obtained (see Table 2, No. 29).
Metal content of the powder: 92.7% of Pd
TABLE 2__________________________________________________________________________Reduction of Metal Halides ProductsStarting Reaction Conditions Amount Metal Boron Specific BET- Materials (m- Reducing t T Recovered Content Content Surface AreaNo. Metal Salt moles) Agent (mmoles) (h) (.degree.C.) (g) (%) (%) (m.sup.2 /g)__________________________________________________________________________1 CrCl.sub.3 7,4 NaBEt.sub.3 H 30 2 23 0,38 93,3 0,3 186,82 MnCl.sub.2 25,4 LiBEt.sub.3 H 75 1 23 0,8 94,07 0,42 --3 FeCl.sub.3 71,4 LiBEt.sub.3 H 375 2 23 3,70 97,1 0,36 --4 FeCl.sub.3 10,0 NaBEt.sub.3 H 35 2 23 0,61 90,1 0,03 57,15 FeCl.sub.3 10,0 NaBEt.sub.3 H 35 16 67 0,51 81,2 0,20 --6 CoF.sub.2 21 NaBEt.sub.3 H 46 2 23 1,30 94,6 0,0 37,97 CoF.sub.2 19,8 NaBEt.sub.3 H 61 16 67 1,10 96,9 0,0 16,28 CoCl.sub.2 10,0 NaBEt.sub.3 H 25 2 23 0,55 96,7 0,22 33,59 CoCl.sub.2 14,0 NaBEt.sub.3 H 35 16 67 0,83 95,1 0,0 28,110 CoCl.sub.2 25,6 LiH + 63 16 67 1,30 95,8 0,0 17,2 10% BEt.sub.311 CoBr.sub.2 23 LiBEt.sub.3 H 60 2 23 0,80 96,69 0,0 16,012 NiF.sub.2 21 NaBEt.sub.3 H 46 2 23 1,56 71,3 0,0 29,913 NiF.sub.2 28 NaBEt.sub.3 H 85 16 67 1,64 93,9 0,0 53,114 NiCl.sub.2 11 NaBEt.sub.3 H 35 2 23 0,68 92,9 0,17 --15 NiCl.sub.2 14 NaBEt.sub.3 H 42 16 67 0,79 96,9 0,0 46,716 CuF.sub.2 16,1 NaBEt.sub.3 H 40 2 23 1,01 97,6 0,3 7,017 CuCl.sub.2 20,7 LiBEt.sub.3 H 60 2 23 1,24 97,3 0,0 17,818 CuBr.sub.2 18,5 LiBEt.sub.3 H 56 2 23 1,18 94,9 0,0 2,319 CuCl.sub.2 17,5 Na(Et.sub.2 BOMe)H 40 2 23 1,13 94,7 0,1 5,620 ZnCl.sub.2 20 LiBEt.sub.3 H 50 12 67 1,30 97,8 0,0 --21 RuCl.sub.3 11 NaBEt.sub.3 H 37 16 67 1,15 95,2 0,52 98,022 RuCl.sub.3.3H.sub.2 O 10 LiBEt.sub.3 H 35 2 23 0,75 90,7 0,0 22,423 RhCl.sub.3 10 NaBEt.sub.3 H 65 2 23 1,03 98,1 0,10 32,524 RhCl.sub.3 10 NaBEt.sub.3 H 33 2 23 1,04 75,9 0,14 --25 RhCl.sub.3 10 NaBEt.sub.3 H 36 16 67 1,05 94,7 0,37 64,626 RhCl.sub.3 14,2 LiBEt.sub.3 H 50 2 23 1,46 96,1 0,66 29,627 PdCl.sub.2 10 NaBEt.sub.3 H 22 2 23 1,00 96,2 0,18 7,528 PdCl.sub.2 10 NaBEt.sub.3 H 22 16 67 0,91 98,0 0,29 9,629 PdCl.sub.2 10,8 Na(GaEt.sub.2 OEt)H 20 2 40 1,20 92,7 -- --30 AgF 10 NaB(OMe).sub.3 H 6 2 23 1,05 94,1 0,05 --31 AgF 11 NaBEt.sub.3 H 12 2 23 1,07 96,9 0,0 0,232 AgI 4,8 NaBEt.sub.3 H 5 2 23 0,45 95,3 0,02 --33 CdCl.sub.2 11,3 LiBEt.sub.3 H 28,3 2 23 1,16 99,46 0,0 --34 TaCl.sub.5 * 10,0 LiH + 60 16 80 3,87 46,5 0,0 -- 10% BEt.sub.335 RcCl.sub.3 3,0 NaBEt.sub.3 15 2 23 0,51 91,69 0,0 --36 RcCl.sub.3 8,3 LiBEt H 36 2 23 1,50 95,4 0,0 82,537 OsCl.sub.3 5,0 NaBEt.sub.3 20 2 23 0,86 95,8 0,0 73,738 IrCl.sub.3.4H.sub.2 O 10,0 NaBEt.sub.3 H 70 2 23 2,44 77,1 0,16 --39 IrCl.sub.3 10,0 NaBEt.sub.3 H 33 2 23 1,94 95,7 0,24 22,740 IrCl.sub.3 10,0 NaBEt.sub.3 H 35 16 67 2,00 94,9 0,02 42,341 IrCl.sub.3 10,0 KBPr.sub.3 H 35 16 67 1,95 94,7 0,08 33,642 PtCl.sub.2 10,0 NaBEt.sub.3 H 22 2 23 1,85 98,2 0,21 15,943 PtCl.sub.2 10,0 NaBEt.sub.3 H 25 16 67 1,97 95,9 0,34 16,244 PtCl.sub.2 15,0 LiBEt.sub.3 H 40 2 23 2,89 99,2 0,0 --45 PtCl.sub.2 15,0 LiBEt.sub.3 H 40 4 0 2,83 99,0 0,0 --46 PtCl.sub.2 15,0 LiBEt.sub.3 H 40 12 67 2,89 99,03 0,0 --47 PtCl.sub.2 10,0 LiH + 30 12 67 1,92 99,1 -- -- 10% GaEt.sub.2 OEt48 PtCl.sub.2 10,0 LiH + 30 5 67 1,93 98,8 0,0 -- 10% BEt.sub.349 SnCl.sub.2 10,4 LiBEt.sub.3 H 31 2 23 1,04 96,7 0,0 --50 SnBr.sub.2 10,3 LiBEt.sub.3 H 31 2 23 0,95 87,1 0,0 --__________________________________________________________________________ Solvent: THF *Solvent: Toluene
EXAMPLE 7
Preparation of rhodium powder from RhCl.sub.3, NBu.sub.4 (BEt.sub.3 H) in THF
11.6 g (34 mmoles) of NBu.sub.4 (BEt.sub.3 H) dissolved in THF (0.5 molar) are dropwise added at 23.degree. C. with stirring and under a protective gas to a solution of 2.15 g (10.3 mmoles) of RhCl.sub.3 in 200 ml of THF in a 500 ml flask. After eight hours 100 ml of water are dropwise added to the black reaction solution, and then the rhodium powder is separated from the reaction solution. The rhodium powder is washed with 200 ml of each of THF, H.sub.2 O THF and pentane and dried under high vacuum (10.sup.-3 mbar). 1.1 g of metal powder are obtained (see Table 3, No. 4).
Metal content of the sample: 90.6%
BET surface area: 58.8 m.sup.2 /g
TABLE 3__________________________________________________________________________Reductions with NBu.sub.4 (BEt.sub.3 H) Products Reaction Conditions Amount Metal Boron Specific BET- Starting Materials NBu.sub.4 (BEt.sub.3 H) t T Recovered Content Content Surface AreaNo. Metal Salt (mmoles) (mmoles) (h) (.degree.C.) (g) (%) (%) (m.sup.2 /g)__________________________________________________________________________1 FeCl.sub.3 6,3 22 1 40 0,1 95,3 0,2 --2 CoCl.sub.2 11,9 29 1 23 0,39 93,6 0,0 10,53 RuCl.sub.3 8,6 30 8 23 0,9 87,9 1,2 30,04 RhCl.sub.3 10,3 34 8 23 1,1 90,6 0,5 58,85 PdCl.sub.2 10,0 25 8 40 1,0 96,9 1,0 10,86 IrCl.sub.3 6,7 23 8 40 0,96 96,6 0,0 8,17 PtCl.sub.2 10,0 25 8 40 1,37 97,9 0,0 24,1__________________________________________________________________________ Solvent: THF
EXAMPLE 8
Preparation of platinum powder from (NH.sub.3).sub.2 PtCl.sub.2, NaBEt.sub.3 H in THF
3.05 g (25 mmoles) of NaBEt.sub.3 H dissolved in THF (1 molar) are dropwise added at 23.degree. C. with stirring and under a protective gas to a solution of 3.0 g (10 mmoles) of (NH.sub.3).sub.2 PtCl.sub.2 in 200 ml of THF in a 500 ml flask. After 2 hours the clear reaction solution is separated from the platinum powder, and the platinum powder is washed with 200 ml of each of THF, H.sub.2 O, THF and pentane. After drying under high vacuum (10.sup.-3 mbar), 1.95 g of metal powder are obtained (see Table 4, No. 1).
Metal content of the sample: 97.1% of Pt
TABLE 4__________________________________________________________________________Reductions of Organometal Compounds Products Reaction Conditions Amount Metal Boron Starting Materials Reducing t T Recovered Content ContentNo. Metal Salt (mmoles) Agent (mmoles) (h) (.degree.C.) (g) (%) (%)__________________________________________________________________________1 Pt(NH.sub.3).sub.2 Cl.sub.2 10 NaBEt.sub.3 H 25 2 23 1,95 97,1 0,322 Pt(Py).sub.2 Cl.sub.2 2 LiBEt.sub.3 H 5 2 23 0,38 97,1 0,023 Pt(Py).sub.4 Cl.sub.2 2 LiBEt.sub.3 H 5 2 23 0,38 97,5 0,014 CODPtCl.sub.2 10 NaBEt.sub.3 H 25 2 60 1,96 97,9 0,585 CODPtCl.sub.2 10 NaBEt.sub.3 H 25 2 23 1,06 96,9 0,16__________________________________________________________________________ Solvent: THF Py = pyridine COD = cyclooctadiene1,5
EXAMPLE 9
Preparation of a cobalt-platinum alloy from PtCl.sub.2, CoCl.sub.2, LiBEt.sub.3 H in THF
9.54 g (90 mmoles) of LiBEt.sub.3 H dissolved in 90 ml of THF are dropwise added with stirring and under a protective gas to a refluxed solution of 2.04 g (15.7 mmoles) of CoCl.sub.2 and 4.18 g (15.7 mmoles) of PtCl.sub.2 in 260 ml of THF in a 500 ml flask. After seven hours of reaction time the mixture is allowed to cool to 23.degree. C., and the clear reaction solution is separated from the alloy powder, which is washed with 250 ml of each of THF, ethanol, THF and pentane. After drying under high vacuum (10.sup.-3 mbar), 3.96 g of metal alloy powder are obtained (see Table 5, No. 1).
______________________________________Metal content of the sample: 76.3% of Pt, 21.6% of CoBoron content of the sample: 0.0%BET surface area: 18.3 m.sup.2 /gX-ray diffractogrammeasured with CoK.sub..alpha. -radiation and Fe-filter:Peaks of reflections 2 .theta. 55.4.degree. (47.4.degree.)Lattice spacings of planes 1.93 .ANG. (2.23 .ANG.)______________________________________
EXAMPLE 10
Preparation of a iron-cobalt alloy from FeCl.sub.3, CoCl.sub.2, BEt.sub.3, LiH in THF
1.01 g (127 mmoles) of LiH, 1.25 g (12.7 mmoles) of triethylborane and 350 ml of THF are added under a protective gas to 2.97 g (22.9 mmoles) of CoCl.sub.2 and 3.79 g (23.4 mmoles) of FeCl.sub.3 in a 500 ml flask. The mixture is heated at 67.degree. C. for six hours. After cooling to room temperature, the iron cobalt alloy powder is separated from the reaction solution and washed two times with 200 ml of THF each. Then the alloy powder is stirred with 150 ml of THF as well as 100 ml of ethanol until the gas evolution has ceased. The alloy powder is once more washed with 200 ml of each of THF and pentane. After drying under high vacuum (10.sup.-3 mbar), 2.45 g of metal alloy powder are obtained (see Table 5, No. 6).
______________________________________Metal content of the sample: 47.0% of Fe, 4.1% of CoBoron content of the sample: 0.0%BET surface area: 42.0 m.sup.2 /gX-ray diffractogrammeasured with CoK.sub..alpha. -radiation and Fe-filter:Peaks of reflections 2 .theta. 52.7.degree.lattice spacings of planes 2.02 .ANG.______________________________________
EXAMPLE 11
Preparation of a iron-cobalt alloy from FeCl.sub.3, CoCl.sub.2, LiBEt.sub.3 H in THF
A solution of 9.1 g (15.7 mmoles) of FeCl.sub.3 and 3.1 g (24 mmoles) of CoCl.sub.2 in 1.2 liters of THF is dropwise added at 23.degree. C. with stirring and under a protective gas to 150 ml of 1.7M (255 mmoles) solution of LiBEt.sub.3 H in THF. After stirring over night, the iron-cobalt alloy is separated from the clear reaction solution and is washed two times with 250 ml of THF each. Then the alloy powder is stirred with 300 ml of ethanol, followed by stirring with a mixture of 200 ml of ethanol and 200 ml of THF until the gas evolution has ceased. The alloy powder is once more washed two times with 200 ml of THF each. After drying under high vacuum (10.sup.-3 mbar), 5.0 g of metal alloy powder are obtained (see Table 5, No. 7).
______________________________________Metal content of the sample: 54.79% of Fe, 24.45% of CoBoron content of the sample: 0.0%X-ray diffractogrammeasured with CoK.sub..alpha. -radiation and Fe-filter:Peaks of reflections 2 .theta. 52.5.degree. (99.9.degree.)Lattice spacings of planes 2.02 .ANG. (1.17 .ANG.)______________________________________
Particle size determined by raster electron microscopy and X-ray diffractometry: 0.01 to 0.1 .mu.m.
TABLE 5__________________________________________________________________________Co-Reductions for the Preparation of Alloys ProductsStarting Reaction Amount Boron SpecificMaterials Conditions Re- Metal Con- BET-Sur- DIF.sup.a) Metal (m- Reducing t T covered Content tent face Area D.sup.c)No. Salt moles) Agent (mmoles) (h) (.degree.C.) (g) (%) (%) (m.sup.2 /g) 2 .theta..sup.b) (.ANG.) Notes__________________________________________________________________________1 FeCl.sub.3 56 LiBEt.sub.3 H 250 5 23 4,8 Fe: 64,5 0,69 -- 52,7.degree. 2,02 one-phase CoCl.sub.2 27 Co: 31,62 FeCl.sub.3 27 LiBEt.sub.3 H 100 2 23 1,6 Fe: 83,8 0.43 -- -- -- -- CoCl.sub.3 3 Co: 10,63 FeCl.sub.3 56,1 LiBEt.sub.3 H 255 5 23 5,0 Fe: 54,8 0,0 -- 52,5.degree. 2,02 -- CoCl.sub.2 23,9 Co: 24,5 99,9.degree. 1,174 Fe.sub.2 Co0.sub.4 * 21,6 NaBEt.sub.3 H 196 16 120 3,8 Fe: 61,1 0,45 -- 52,5.degree. 2,02 one-phase Co: 30,35 FeCl.sub.3 23,4 LiH + 127 6 67 2,45 Fe: 47,0 0,0 42,0 52,7.degree. 2,02 one-phase CoCl.sub.2 22,9 10% 13 Co: 47,1 micro- BEt.sub.3 crystalline6 Co(OH).sub.2 20 NaBEt.sub.3 H 100 7 67 2,35 Co: 48,3 0,25 -- 51,7.degree. 2,05 one-phase Ni(OH).sub.2 20 Ni: 45,9 micro- crystalline7 Co(CN).sub.2 22,5 NaBEt.sub.3 H 110 7 67 3,0 Co: 42,5 0,08 -- -- -- -- Ni(CN).sub.2 21,7 Ni: 40,38 CoF.sub.2 21,1 NaBEt.sub.3 H 110 7 67 2,61 Co: 46,6 0,11 -- 51,9.degree. 2,05 one-phase NiF.sub.2 22,9 Ni: 48,9 micro- crystalline9 CoCl.sub.2 15,7 LiBEt.sub.3 H 90 7 67 3,96 Co: 21,6 0,0 18,3 55,4.degree. 1,93 one-phase PtCl.sub.2 15,7 Pt: 76,3 47,4.degree. 2,2310 RhCl.sub.3 10 LiBEt.sub.3 H 60 5 67 2,49 Rh: 26,5 0,04 -- 40,2.degree. 2,24 one-phase PtCl.sub.2 10 Pt: 65,5 46,3.degree. 1,9611 RhCl.sub.3 10 LiBEt.sub.3 H 70 5 67 3,00 Rh: 33,5 0,15 -- 42,3.degree. 2,14 one-phase + IrCl.sub.3 10 Ir: 62,5 traces of IrCl.sub.312 PdCl.sub.2 10 LiBEt.sub.3 H 50 5 67 3,02 Pd: 33,6 0,04 -- 40,1.degree. 2,25 one-phase PtCl.sub.2 10 Pt: 63,4 46,3.degree. 1,9613 PtCl.sub.2 10 NaBEt.sub.3 H 75 12 67 3,80 Pt: 50,2 0,15 33,3 40,0.degree. 2,25 one-phase IrCl.sub.3 10 Ir: 48,7 46,5.degree. 1,95 micro- crystalline14 CuCl.sub.2 21,4 LiBEt.sub.3 H 100 4 67 2,56 Cu: 49,6 0,0 2,9 Cu.sub.6 Sn.sub.5 + SnCl.sub.2 16,4 Sn: 47,6 Cu + Sn15 FeCl.sub.3 20 LiBEt.sub.3 H 245 1,5 23 3,65 Fe: 30,18 0,0 -- one-phase CoCl.sub.2 20 Co: 31,45 micro- NiCl.sub.2 20 Ni: 30,96 crystalline__________________________________________________________________________ Solvent: 350 ml of THF .sup.a) Xray diffractogram, measured with CoK.sub..alpha.radiation using Fe filter .sup.b) Maxima of reflection .sup.c) Lattice spacing of the planes *autoclave experiment under H.sub.2atmosphere
EXAMPLE 12
Preparation of a colloidal chromium solution using NBu.sub.4 (BEt.sub.3 H) in THF
1.58 g (10 mmoles) of CrCl.sub.3 and 11.25 g (33 mmoles) of NBu.sub.4 (BEt.sub.3 H) dissolved in THF are dissolved in another 300 ml of THF at 23.degree. C. with stirring and under a protective gas. A colloidal chromium solution is obtained (see Table 6, No. 2).
EXAMPLE 13
Preparation of a colloidal platinum solution from Pt(Py).sub.4 Cl.sub.2 and KBEt.sub.3 H in toluene (Py=pyridine)
0.583 g (1 mmole) of Pt(Py).sub.4 Cl.sub.2 and 0.28 g (2 mmoles) of KBEt.sub.3 H are dissolved in 300 ml of toluene at -20.degree. C. with stirring and under a protective gas. A colloidal platinum solution of dark-red appearance in transparent light is obtained (see Table 6, No. 17).
TABLE 6__________________________________________________________________________Preparation of Colloidal Metal Solutions Reaction Conditions Starting Materials NBu.sub.4 (BEt.sub.3 H) t TNo. Metal Salt (mmoles) (mmoles) (min) (.degree.C.) Solvent (ml)__________________________________________________________________________1 MnCl.sub.2 10 25 20 23 THF 3002 CrCl.sub.3 10 33 20 23 THF 3003 FeCl.sub.3 10 35 20 23 THF 3004 CoF.sub.2 10 25 20 23 THF 3005 CoCl.sub.2 10 25 20 23 THF 3006 NiF.sub.2 10 25 20 23 THF 3007 NiCl.sub.2 10 25 20 23 THF 3008 RuCl.sub.3 1 4 20 23 THF 3009 RhCl.sub.3 1 4 20 23 THF 30010 PdCl.sub.2 1 3 20 23 THF 30011 IrCl.sub.3 1 4 20 23 THF 30012 ReCl.sub.3 1 4 20 23 THF 30013 OsCl.sub.3 1 4 20 23 THF 30014 PtCl.sub.2 1 3 20 23 THF 30015 (COD)PtCl.sub.2 1 3 20 23 THF 15016 Pt(Py).sub.4 Cl.sub.2 1 2,0* 300 -20 THF 15017 Pt(Py).sub.4 Cl.sub.2 1 2,0* 300 -20 Toluene 30018 CoCl.sub.2 /FeCl.sub.3 1/1 6 20 23 THF 300__________________________________________________________________________ *KBEt.sub.3 H Py = pyridine COD = cyclooctadiene1,5
EXAMPLE 14
Preparation of a Fe/Co alloy on an Al.sub.2 O.sub.3 support
11.5 g (70.89 mmoles) of FeCl.sub.3 and 2.3 g (17.7 moles) of CoCl.sub.2 are dissolved in 1 liter of THF. In a wide-necked reagent bottle with a conical shoulder 50 g of Al.sub.2 O.sub.3 (SAS 350 pellets, Rhone Poulenc) are impregnated over night in 335 ml of the above-prepared FeCl.sub.3 /CoCl.sub.2 solution in THF, whereupon the green solution becomes almost completely discolored. The solvent is removed, and the support is dried under high vacuum (10.sup.-3 mbar) for three hours. The impregnation is repeated with another 335 ml of FeCl.sub.3 /CoCl.sub.2 solution, whereby an intensely colored yellow solution is obtained. The solution is removed, and the support is again dried under high vacuum (10.sup.-3 mbar) for three hours. The impregnation is once more carried out with 330 ml FeCl.sub.3 /CoCl.sub.2 solution over night, whereupon no further change in color occurs. The solution is removed and the Al.sub.2 O.sub.3 pellets are treated with 63.6 g (600 mmoles) of LiBEt.sub.3 H in 400 ml of THF at 23.degree. C. for 16 hours, whereby the color of the pellets turns to black. The reaction solution is removed, and the pellets are washed with 300 ml of each of THF, THF/ethanol(2:1), THF and dried under high vacuum (10.sup.-3 mbar) for four hours. Obtained are Al.sub.2 O.sub.3 pellets which have been provided only on the surfaces thereof with a shell-like coating of a Fe/Co alloy.
Elemental analysis: 1.13% of Fe; 0.50% of Co.
EXAMPLE 15
Regeneration of the carrier BEt.sub.3
To the clear reaction solution separated from the nickel powder in Example 1 there are dropwise added 11.7 ml of a 3.5M (41 mmoles) solution of HCl in THF with stirring and under a protective gas within 20 minutes, whereupon, after briefly foaming and slight generation of heat, a white precipitate (NaCl) is formed. The reaction mixture is neutralized with Na.sub.2 CO.sub.3 and filtered through a D-3 glass frit. 222.5 g of a clear filtrate are obtained which, according to analysis by gas chromatography, contains 1.76% (3.92 g=40 mmoles) of BEt.sub.3. Thus, 97.5% of the carrier BEt.sub.3 are recovered, relative to the carrier complex initially employed.
EXAMPLE 16
Regeneration of the carrier BEt.sub.3
To the solution separated in Example 3 there are added 1.62 g (10 mmoles) of FeCl.sub.3. Upon completion of the reaction the solution is distilled. 206 g of a clear distillate are obtained which, according to analysis by gas chromatography, contains 1.63% (3.36 g=34.3 mmoles) of BEt.sub.3. Thus, 95.2% of the carrier BEt.sub.3 are recovered, relative to the carrier complex initially employed.
EXAMPLE 17
Preparation of cobalt powder from CoO with NaBEt.sub.3 H in toluene
In a 250 ml autoclave equipped with a stirrer, 3.0 g (40 mmoles) of CoO and 70 ml of toluene are admixed under a protective gas with 75 ml of an 1.61M NaBEt.sub.3 H solution (120 mmoles in toluene) and heated in an H.sub.2 atmosphere (3 bar) at 130.degree. C. for 16 hours. After cooling to room temperature, the protective gas (H.sub.2) is vented, and a black reaction mixture is discharged. The cobalt powder is separated from the supernatant clear solution and is washed with 200 ml of THF. Then the mixture is stirred with 100 ml of THF as well as 100 ml until the gas evolution has ceased, is washed two more times with 200 ml of THF each and, after 2 hours of drying under high vacuum (10.sup.-3 mbar), 2.4 g of metal powder are obtained (see Table 1, No. 2).
Metal content of the sample: 98.1% of Co
BET surface area: 79.2 m.sup.2 /g
EXAMPLE 18
Preparation of Silver powder from Ag.sub.2 O with NaBEt.sub.3 H in toluene
39 ml of a 1.55M NaBEt.sub.3 H solution (60 mmoles) in toluene are dropwise added at room temperature with stirring and under a protective gas to 4.64 g (20 mmoles) of Ag.sub.2 O and 31 ml of toluene in a 500 ml flask. After 16 hours the reaction solution is separated from silver powder, and the latter is washed with 200 ml of THF. Then the mixture is stirred with 100 ml of THF as well as 100 ml until the gas evolution has ceased, is washed two more times with 200 ml of THF each and, after drying under high vacuum (10.sup.-3 mbar), 4.19 g of metal powder are obtained (see Table 1, No. 21) .
Metal content of the sample: 97.7% of Ag
BET surface area: 71.8 m.sup.2 /g
EXAMPLE 19
Preparation of nickel as a shell-shaped coating on an aluminum support from NiCl.sub.2 .multidot.6H.sub.2 O with LiBEt.sub.3 H in THF
270 g of spherical neutral aluminum oxide are shaken in a solution of 150 g (631.3 mmoles) of NiCl.sub.2 .multidot.6H.sub.2 O in 500 ml of ethanol for 45 minutes, rid of the supernatant and dried under high vacuum (10.sup.-3 mbar) at 250.degree. C. for 24 hours. After cooling, 1 liter of a 1.5M LiBEt.sub.3 solution in THF is added, and after 16 hours of shaking the clear reaction solution is removed. The residue is washed with 1.5 liters of each of THF, THF/ethanol mixture(1:1), THF and, upon drying under high vacuum (10.sup.-3 mbar), a spherical aluminum oxide comprising 2.5% of Ni metal applied in the form of a shell. The Ni-content may be increased, while the shell structure is retained, be repeating the operation.
EXAMPLE 20
Preparation of nickel-impregnated aluminum oxide support from NiCl.sub.2 .multidot.6H.sub.2 O with LiBEt.sub.3 H in THF
270 g of spherical neutral aluminum oxide are impregnated with a solution of 200 g (841.7 mmoles) of NiCl.sub.2 .multidot.6H.sub.2 O in 500 ml of distilled water for 16 hours. After drying under high vacuum (250.degree. C., 24 h), the solid is reacted with LiBEt.sub.3 H in the same manner as described in Example 19. Upon work-up there is obtained a nickel-impregnated aluminum oxide having a nickel content of 4.4%. The nickel content may be increased by repeating the operation.

Number	Name	Date
3180835	Peri	Apr 1965
3814696	Verdone et al.	Jun 1974
4080177	Boyer	Mar 1978
4576725	Miura et al.	Mar 1986
4624797	Wakayama et al.	Nov 1986
4863510	Tamemasa et al.	Sep 1989
4877647	Klabunde	Oct 1989
5034313	Shuman	Jul 1991
5308377	Bonnemann et al.	May 1994

Number	Date	Country
1075601	Mar 1989	JPX
9011858	Oct 1990	WOX

Microcrystalline-to-amorphous metal and/or alloy powders dissolved without protective colloid in organic solvents

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

Priority Claims (1)

Parent Case Info

US Referenced Citations (9)

Foreign Referenced Citations (2)

Divisions (1)