6.

7.

A. K. Shurin, G. Ya. Kozyrsk i i , V. K. Sul 'zhenko, and O. M, Barabash , "H igh - t empera tu r e s t rength of the n i o b i u m - z i r c o n i u m nitr ide eutect ic ," Dokl. Akad. Nauk SSS13, 222, No. 6, 132-134 (1975). I~. Kief fer , " P r e p a r a t i o n and p rope r t i e s of in ters t i t ia l compounds," J. Ins t . Met., 97, No. T-6 , 164-172 (1969).

I ~ E A C T I O N S B E T W E E N F I N E L Y D I V I D E D M O D I F I E D

F E 1 3 1 ~ O M A G N E T I C S A N D O I ~ G A N I C L I Q U I D S

A . G. Z h i g o t s k i i , T . M. S h v e t s , S . I . R a d o s h i n s k a y a , a n d P . I . K a p r i e n k o

UDC 621.762.274

In the cour se of p repa ra t ion and subsequent industr ial opera t ion of m e t a l - p o l y m e r m a t e r i a l s fine meta l powders m a y come into contact with organic liquids of the var ious kinds. Because of the speci f ic e lec t ronic s t ruc tu re of a toms of the i ron-group m e t a l s and conditions under which e lec t ro ly t ic powders a r e produced by the t w o - l a y e r bath method [1], such contact may bring about a pronounced change in the su r face and bulk p rope r t i e s of the powders .

In this a r t i c l e a descr ip t ion is given of the effect of a number of organic liquids on some su r face c h a r - a c t e r i s t i c s and t h e r m a l behavior of e lec t ro ly t ic Fe and F e - C o - N i (60 : 30 : 10) a l loy powders p r e p a r e d by the method descr ibed in [2, 4], where data a r e a lso given on the i r magnet ic p rope r t i e s . The upper l ayer of the e lec t ro ly t ic bath was a 0.5% solution of oleic acid in toluene; during e l ec t ro lys i s oleic acid molecu les a r e adsorbed on the me ta l pa r t i c les [5], which p romotes t he i r f lotation into the upper, organic layer and has a p ro tec t ive effect, prevent ing a tmosphe r i c oxygen f r o m oxidizing the powder.

As organic liquids, the solvents employed in the manufac ture of both the Fe and F e - C o - N i al loy powders and cor responding m e t a l - p o l y m e r m a t e r i a l s and c h a r a c t e r i z e d by different polar i t ies - toluene, acetone, cyelohexanone, ethanol, and E t h y l c e l l o s o l v e - we re used. The solvents , of g rades "eh." ("pure") and "kh.ch." ( "chemica l ly pure") , we re subjected to additional puri f icat ion by app rop r i a t e techniques [6]. t~iaterial e x t r a c - t ion f rom the su r f aces of the powders was studied by the i n t e r f e rome t r i e method. The pa r t i c les of the Fe and F e - C o - N i al loy powders had dendri t ic shapes and coefficients of an i sod iame t ry ranging f r o m 1 : 5 to 1 : 7; the length of the m a j o r axis of the m a j o r i t y of the par t i c les was 1000-2500 ~ (Fig. 1).

Exper imen t s involving t r ea tmen t of the me ta l powders with the organic liquids showed that the amount of oleic acid ex t rac ted f r o m the s u r f ace s of the f e r r o m a g n e t i c s was s t rongly affected by t r e a t m e n t conditions and the po la r i ty of the ex t rac t ing agent. F o r the iron powder, on whose su r face the oleic acid content was, a c - cording to e lementa l ana lyses for ca rbon and hydrogen, 4.1% of the to ta l weight of the powder, the amounts of oleic acid washed off by acetone and ethanol were 2.0 and 2.8%, r e spec t ive ly . Apar t f r o m oleic acid, iron o lea tes , too, could have pas sed into the solution, in the s a m e way as did zinc o lea tes in [7]. T r e a t m e n t of the powders in a Soxhlet appara tus [8] sha rp ly inc reased the amount of oleic acid washed off. While, e.g., in a c e - tone at 50~ the amount of oleic acid washed off was 1.2%, in the Soxhlet appara tus it r o s e to 2%. F r o m the r e su l t s obtained it follows that, for the organic liquids investigated, ex t rac t ing abi l i ty inc reases in the o rde r toluene < acetone < cyclohexanone < ethanol < Ethylcel losolve .

As the different solvents washed off dif ferent amounts of oleic acid, it was suspec ted that the propens i ty of the me ta l for oxidation would be s i m i l a r l y affected. Indeed, for the Fe powder t r e a t m e n t with acetone was found to shift the beginning of the exo the rmic oxidation p roces s toward lower t e m p e r a t u r e s compa red with the s t a r t i n g i r o n powder, the two t e m p e r a t u r e s being 100 and 115~ r e spec t i ve ly (Fig. 2). The d i f ferent ia l t h e r m o g r a v i m e t r i e ana lys i s cu rves for the s ta r t ing and t r e a t ed powders a r e indicative of s tepwise oxidation of the f inely divided f e r romagne t i c s with h i gh - t empe ra tu r e exo the rmic peaks, which probably co r re spond to the decomposi t ion of oleic acid into dialkyl ketones [9].

Although in cyclohexanone and Ethylce l losolve la rge amounts of oleie acid and, in the l a t t e r case , i ron o lea tes we re washed off, the beginning of oxidation of the iron powder was displaced toward higher t e m p e r a t u r e s ,

Inst i tute of Colloid C h e m i s t r y and the C h e m i s t r y of Water , Academy of Sciences of the Ukrainian SSR. T r a n s l a t e d f r o m Poroshkovaya Metal lurgiya, No. 10(214), pp. 52-55, October , 1980. Original a r t i c l e submitted, a f t e r rev is ion , March 1, 1980.

702 0038-5735/80/1910- 0702 $07.50 �9 1981 Plenum Publishing Corpora t ion

Fig. 1. Electron mierographs of particles of fine iron (a) and i r o n - c o b a l t - n i c k e l alloy (b) powders, x 1800.

o

z~T

0 0

0

ao 20

0

I25 175

,e,o 27e 3,ee 4r r, ~

2

5

Fig. 2. Differential thermogravimetrtc analys is curves for fine iron powder: 1) starting powder; 2) treatment with acetone at 50~ 3) treatment with Ethylce l losolve at 50~ 4) treatment with eyclohexanone at 50~

TABLE i

Extracting Trea tment conditions I Ssp' m2/g agent

Iron 41,0

Toluene 50 ~ 49, I ~ 8oxhlet apparatus 52,0

Acetone 50 ~ 50,0 )> Soxhlet apparatus 54,7

Cyclohexanone 50 ~ 50,0 Ethanol 50 ~ 56,3

)> Soxhlet apparatus 58,9 Ethylcellosolve 50 ~ 46,3

I ron - cobalt-- nickel alloy 35,5

Toluene 50 ~ 38,0 Acetone 50 ~ 42,3

Soxhlet apparatus 50,2

703

viz. , 130 and 125~ re spec t ive ly . This was probably due to difficulties in r emova l of molecules of the polar adsorbed solvents which had displaced the oleic acid, resul t ing in the fo rmat ion of a m o r e imperv ious oxide fi lm which slowed down the oxidation of the f e r romagne t i c powder. The oxidiation r a t e of the powder in this case was reduced by a fac tor of 1.7-3.0 and its total weight gain by a fac tor of 2-3 compared with the s ta r t ing iron powder, whose weight gain in the t e m p e r a t u r e range to 500~ amounted to 10%.

Thus, by using organic liquids of different boiling points and intensi t ies of reac t ion with the su r faces of f e r romagne t i c powders in the cou r s e of the l a t t e r ' s p repara t ion or t r ea tmen t , it is poss ible to regula te the i r degree of and p ro tec t ionaga ins t oxidation. These phenomema would be expected to be less pronounced with powdered F e - C o - N i al loys because of t he i r lower iron content and higher r e s i s t a n c e to oxidation [101.

Removal of adsorbed oleic acid by the act ion of the organic solvents on the Fe and F e - C o - N [ al loy powders was accompanied by substant ia l changes in the i r su r face ac t iv i t ies , which mani fes ted t hemse lves in inc reases in the i r speci f ic su r faces Ssp (Table 1) and heats of wetting.

The specif ic sur face Ssp of the F e - C o - N i al loy powder was s m a l l e r than that of the Fe powder. The inc rease in Ssp brought about by t r e a t m e n t with a weakly polar liquid was g r e a t e r for the Fe powder. In the case of a solvent reac t ing v igorous ly with the adsorbed oleic acid through hydrogen bonds or with su r face oleates (ethanol), a l a r g e r amount of the modifying agent was dislodged, resu l t ing in a g r e a t e r inc rease in the specif ic su r face of the powder. However, a f t e r a m o r e v igorous reac t ion of a solvent (Ethylcellosolve), with the probabi l i ty of fo rmat ion of su r face compounds a f t e r the r e m o v a l of the adsorbed oleie acid or o lea tes , the increase in the specif ic su r face of the f e r r o m a g n e t i c powder proved to be less than expected.

The inc rease in the specif ic su r face of the f e r romagne t i c me ta l powders caused by t r e a t m e n t with the organic liquids brought about i nc reases in the i r f ree sur face energ ies . This mani fes ted i tse l f in growth in the heats of wetting of the Fe and F e - C o - N i al loy powders by benzene, as de te rmined f rom integral curves of heat evolution with t ime . The r e su l t s of a c a l o r i m e t r i c study showed that the heat of wetting of the Fe powder (2.6 kJ/l~g) was g r e a t e r than that of the F e - C o - N i al loy powder (2.0 kJ /kg) . T r e a t m e n t with acetone increased the heat of wetting of the Fe powder to 4.3 k J /kg . These data lead to the conclusion that t r e a t m e n t of a fine f e r romagne t i c me ta l powder with an organic liquid is accompanied by an inc rease in its to ta l f ree su r face energy .

L I T E I ~ A T UI~ E C I T E D t

1. E . M . Natanson, Colloidal Metals [in Russian] , Academy of Sciences of the Ukrainian SSI~, Kiev (1959). 2. E . P . Zhelibo, K. A. Aryupina, and E. M. Natanson, " F o r m a t i o n of fine iron powder on the cathode,"

Poroshk . Metall . , No. 2, 14-19 (1973). t 3. T . M . Shvets, L. Yu. tvanova, Z. M. Mel 'nichenko, E. G. Mishehenko, and E. M. Natanson, "Magnetic

p rope r t i e s of fine i r o n - c o b a l t - n i c k e l al loy powders ," Poroshk . Metall . , No. 7, 71-75 (1972). t

4. T . M . Shvets, Z. M. Mel 'niehenko, V. P. Vasilenko, L. Yu. Ivanova, and E. M. Natanson, "Ef fec t of mature of the cathode m a t e r i a l on the p rope r t i e s of the f inely divided i r o n - c o b a l t - n i c k e l al loy," Ukr. Khim. Zh., 3_88, No. 10, 993-996 (1972).

5. E . M . Natanson, Yu. I. Khimehenko, and T. M. Shvets, "Mechanism of the reac t ion of po lymers with colloidal me ta l pa r t i c les at the instant of t he i r fo rmat ion on the cathode," Dokl. Akad. Nauk SSSt~, 158, No. 5, 1162-1165.

6. A. Wei sbe rge r , E. P roskaue r , J. l~iddick, and E. Tuns, Organic Solvents [l~ussian t rans la t ion] , IIL, Moscow (1958).

7. A . V . Uvarov and N. A. Aleksandrova, "Effect of type of pigment and f i l le r on the c h a r a c t e r of the i r reac t ions with organic ac ids ," Lakokrasoehnye Mater . Ikh Pr imenen ie , No. 2, 1-3 (1971).

8. Organicum (Labora tory Manual of Organic Chemis t ry) [l~ussian t ransla t ion] , Vol. 1, Mir, Moscow (1979). 9. B . N . Tyutyunnikov, C h e m i s t r y of Fats [in l~ussian], P ishchevaya P rom. , Moscow (1966).

10. V . J . Liunenbom, "The reac t ion between iron and wa te r in the absence of ozsrgen," J. E l ec t rochem. Soc., 105, No. 6, 322-324 (1958).

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