Feb., 1914
T H E J 0 L- R S A L 0 F I S D
r.52' RI .4 L
quite a s vigorous, if not more vigorous, t h a n the corresponding one with ferric oxide. Experiments n-ere t.ried, October, 191 2 , using a standard Goldschmidt Thermit conical welding furnace. I n t o t h i s was charged j-IO lbs. of finely divided C o s 0 4 with t h e theoretical a m o u n t of aluminum, 8A1 = 4.k1203 according t o t h e equation 3C0301 9Co. T h e reaction was started b y lighting a fuse of finely divided aluminum a n d potassium chlorate, rolled in a piece of tissue paper. T h e furnace fired with extreme violence, in every case becoming a n intense white heat. T h e vigor of t h e reaction was so great t h a t t h e lining of t h e furnace, although t h e best alundum-magnesite-cement mixture, n-ould s t a n d u p for only t v o or three charges. T H E METAL-The metal produced in this manner n-as readily tapped from t h e bottom of t h e furnace into iron or sand moulds. I t frequently contained less t h a n 0.1 per cent of aluminum. and, of course, was carbon-free. T h e various metals, chromium, molybdenum. etc., made by t h e Goldschmidt Co. b y this method. as they h a r e come t o us, r u n about 0 . j per cent i n aluminum a n d are carbon-free. c 0 sc L U S I Oss This aluminum reduction method can obriously be used with considerable satisfaction where absoltitely carbon-free metal is required, a n d where a somewhat increased cost is not prohibitive. XIoreover, i t affords a method of preparing cobalt-aluminum alloys a t once by adding a n excess of metallic aluminum. T h e price of crude aluminum, such as might be used for t h i s purpose, is i n t h e neighborhood of I ; cts. per lb. One pound of aluminum \%-ill reduce a n d melt . i n this way a little over t w o pounds of metallic cobalt. Therefore, there is a charge of 1 7 cts. in t h e form of I 11). of metallic aluminum, for t h e power for reducing a n d melting t w o pounds of metallic cobalt. There might, of course, be some return for t h e fused aluminum oside which resulted from t h e process, b u t even allowing liberally for this, the costs are high a s .compared with t h e carbon a n d carbon monoxide methods of reduction described elsewhere in this paper. I t is obvious t h a t t h e heating costs must be high b y t h e aluminum method, for heat is being supplied a t a temperature greater t h a n 2100' C., t h a t is, a t a temperature far in excess of what is required for t h e reduction of t h e oxide a n d t h e melting of t h e metal, a n d with consequent attendant increased losses, due t o conduction a n d radiation.
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ELECTROCHEMICAL AND >fETALLURGICAL S C H O O L OB M I N l i Y G , KISGSTON,
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RESEARCH LABORATORIES
QUEEN'S U N I X 7 E R S I T Y
ONTARIO
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OXIDES OF COBALT' By HERBERT T. KALMUS
T h e following oxides of cobalt have been described in various places throughout t h e literature: C o 2 0 , COO, COSO,, C O 6 0 7 , C O 4 0 5 , CO304, c O , o ~ o , c0203,
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Published by permission of the Director of Mines, Ottawa, Canada. See footnote t o previous article, page 107.
-1 S D E S G I S E E RI AJ-G C H E M I ST R Y
11;
C O ~ ~ OC, o ~ 3, 0 5 ,C o o 2 , and considerable disagreement is t o be found among the statements concerning them. T h e existence of many of these compounds is doubtful, a n d there are but three of t h e m which particularly concern t h e commercial manufacturer of cobalt oxide: Co304, CoeO; and COO. These concern us in the production of metallic cobalt. TTe shall. therefore, describe these three oxides as m-e have observed t h e m in the course of the experiments reported in our previous article, p. 1 0 7 of this issue of THISJ O U R S A L . C 0 B .4L T 0 - C 0 B A L T I C 0 X I D E ,
c 030 .I
T h e ordinary black commercial cobalt oxidc which has been prepared from t h e hydrate, b y calcining in the neighborhood of ; j o o C.?is a mixture of C o 3 0 4 and C o 6 0 7 ,but largely t h e former. There is a n abundance of proof throughout t h e previous paper t h a t this black oxide is lai-gely C o 3 0 4 , of which t h e following m a y be particularly noted: ( a ) The purified cobalt oxide used for hydrogen reduction experiments. making allowance for t h e impurities according t o the analyses, w a s computed t o contain 7 2 . 9 per cent c o b i l t . The hydrogen reduction experiments, using this same oside. showed, n-herever t h e reduction xyas complete, a loss of oxygen amounting t o 2 7 . 0 per cent. A s was s h o w n on p . I I I , this checks m-ith t h e 7 2 . 9 per cent of cobalt, with allowance made for t h e slight impurities. Hencc, this black oxide must be largely Co301>a s m a y bc seen from thc following theoretical percentages: Per ccrit cobalt Co?Oa..
.
CoaOl.. . , . Co,07., , , . . , .
. ,.. .. ..., .
, . coo . . . . . . . . . . . . , ,
. 71 1 . 73.4 , , , . . i5.9 ,, . , , 7 8 . 8 , ,
,
( b ) T h e purified cobalt oxide used for thc carbon monoxide experiments, making allowance for the impurities according t o t h e analysis, was computet1 t o contain 72.9 per cent cobalt. The C O reduction experiments, using this same oxide, whererc'r reduction was complete, showed a loss of oxygen amounting t o 2 7 . 0 per cent. As was shown on pp. I I O and 111, this checks with 7 2 . 9 per cent cobalt, with allow-:ince made for t h e slight impurities. Hence, this black oxide must be largely Co304 according t o the table under ( a ) . -1s a further proof t h a t t h e black oside calcined (c) a t a good red heat is C0~0.3,the following experiment was tried: A pure black hydrate of cobalt was made from electrolytic cobalt by t h e potassium-cobalti-nitrite method. This was calcined t o constant veight a t I O j O C., yielding a chocolate-brown powder, which was uniform under t h e microscope. Several samples of this brown powder were calcined t o constant \\-eight a t 640' C., and in each instance showed a loss of water between I I . 5 per cent a n d I I .8per cent. Therefore, t h e brown powder corresponds very closely t o C0203.HaO. T h e material resulting from these calcinations n-as a black powder identical in appearance under t h e microscope with t h e black cobalt oxide of commerce.
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THE J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
116
A sample of this previously calcined black oxide was calcined a t a red heat t o a constant weight of 0 . 8 3 0 0 gram. T h e same sample was t h e n completely reduced with a mixture of hydrogen a n d carbon monoxide gas a t 900" C., which brought i t t o a constant weight of 0.6063 gram. T h u s , t h e loss in weight was 2 7 . 2 per cent. Except for traces, this material was free from non-reducible substances, so t h a t t h e oxide contained 72.8 per cent cobalt, against 73.4 per cent corresponding theoretically with Co30a. This was checked several times, which substantiates t h e statement t h a t black cobalt oxide is c0304. ( d ) X further experiment was a s follows: Black oxide was brought t o constant weight a t 640' C., a n d immediately thereafter brought t o constant weight by heating t o 1 0 2 0 ' C. This experiment was tried several times and in every instance t h e percentage loss in weight was found t o be very close t o 7 . 1 per cent. The resulting gray.oxide a t 1 0 2 0 ' C. analyzed 79.3 per cent Co, corresponding very well with C O O (78.8 per cent Co). * The theoretical loss in passing from cos04 t o COO is 6 . 6 per cent. As against this, t h e theoretical loss passing from Co304 t o C O ~ O ,would be 3.3 per cent, a n d correspondingly, passing from Co60, t o COO t h e loss would be 3.3 per cent. Thus, there is very little d o u b t b u t t h a t our reduction of t h e black oxide formed at red heat, t o t h e gray a t 1 0 2 0 ' C., corresponds with the transition from Co 0 4 t o C O O . (e) T w o independent samples of brown C0203.&0, calcined t o constant weight a t 640' C., analyzed for cobalt,' respectively, 74.7 per cent a n d 73.8 per cent. This analysis is between c0304 = 73.4 per cent CO a n d C o 6 0 , = 7 j . 9 per cent Co. This black oxide is therefore largely Co304 with some Co6Oi. T h e black hydrated cobalt oxide, a s formed commercially b y precipitation of a chloride or sulfate solution with bleach,* or t h e brown Co203.H20, may be calcined a t a n y temperature between 385' C a n d 910' C., t o yield substantially t h e same product, b u t in practice it is better t o calcine a t a good red temperature, in order t h a t t h e calcination may t a k e place with reasonable speed. T h a t there is a range between 385' C. a n d 910' C.. through which very little oxidation or reduction of t h e black Co304 t a k e s place, is shown by t h e following figures: Starting with C0304. heated t o constant weight &t 38j0 C. t h e loss in weight heating it t o constant weight is
.. . . . . . 0 . 7 per cent . . . . , . 1 . 2 per cent
at 640' C.. . a t 770' C.. . ,
at 860' C. at 910' C.
. .. . ., ,
2 . 4 per cent 2 5 per cent
Just above 910' C., however, t h e reduction begins t o t a k e place very rapidly, a n d t h e black CoaO4 reacts t o become gray COO. Continuing t h e experiment for which t h e figures above are given, we have loss i n weight heating it t o constant weight at 980' C.
. . . . . . 7 . 0 per
cent
T h i s oxide, Co304,shows no trace of being magnetic. 1 1
Including very small amounts of Ni and Fe. See page 107.
T H E OXIDE
Vol. 6 , No.
2
~ 0 ~ 0 ,
C o 6 0 i is not t o be distinguished from C o 3 0 4 either in appearance or in method of preparation; in f a c t , we have not succeeded i n forming a pure oxide of cobalt which analyzed very close t o 75.9 per cent. On t h e other hand, as will be noticed in many places throughout this paper, t h e analyses of t h e material obtained b y calcining a t a red heat are frequently something in excess of 73.4 per cent after making allowance for impurities. TTe, therefore, assume t h a t a certain a m o u n t of C060, accompanies the Co30i. COBALT MONOXIDE,
COO
Cobalt monoxide is t h e stable oxide of cobalt when calcination takes place a t a high temperature, t h a t is, in t h e neighborhood of 1 0 0 0 ' C. It is a gray powder and reacts t o form t h e metal by heating with carbon monoxide gas a t any temperature above 4 j o " C . , or with hydrogen gas a t a n y temperature above 2.50' C. Cobalt monoxide also exists in an allotropic form which is a yellow-green powder. Either t h e yellowgreen or t h e gray cobalt monoxide oxidizes t o c0304, or t o a mixture of C0.104 a n d C060, when heated in t h e air t o a n y temperature between 385' C. a n d 910' C. The yellow-green variety is readily formed by heating Co304 with 2 t o 3% b y weight of C a t temperatures in t h e neighborhood of 900' C. Xumerous analyses of t h e purified gray oxide have been made, which range around t h e theoretical value 78.8 per cent. The following experiment was tried t o prove t h a t yellow-green oxide is a n allotropic form of t h e gray C O O : Black c 0 3 0 4 calcined a t 640' C. t o constant weight was t h e n calcined t o constant C. It lost, thereby, 7 . 1 per weight a t 1 0 2 0 ' cent in weight, a n d t h e product was gray COO. Yellow-green COO, produced by t h e reduction of black Co304 with hydrogen a t 300' C.. was calcined t o constant weight in a i a t 640' C., ga ning, thereby, 6. j per cent in weight a n d becoming black. This experiment, like t h e others, indicates t h a t t h e gray a n d the yellow-green oxides are identical t o within such limits t h a t if t h e yellow-green be C O O , t h e gray cannot depart from it by more t h a n t h e formula Co,,Ozo. Such differences as there are, however. seem t o show uniformly t h a t t h e gray has slightly t h e greater oxygen content of t h e two. A further experiment was performed with t h e yellowgreen oxide as follows: Freshly prepared yellowgreen oxide was reduced t o metal with hydrogen and carbon monoxide gas, a n d brought t o constant weight. During t h e reduction, t h e loss in weight was 2 1 . 5 per cent in one case a n d 21.3 per cent in another, corresponding very well with t h e reduction of COO, t o metallic cobalt which would be 21.3 per cent. Both t h e gray a n d t h e green COO are nonmagnetic, a n d t h e samples of gray prepared b y us, as well a s those obtained from commercial sources, are homogeneous powders under I O O diameters magnification. ELECTROCHEMICAL AND METALLURGICAL RESEARCH LABORATORIES SCHOOL OF MINING,QUEEN'SUNIVERSITY KINGSTON, ONTARIO
