3.

4.

5.

6.

7.

8.

9.

S. I. Pope l ' , "Kine t ics of sp read ing of mel t s on solid su r f aces and wetting kinet ics ," in: Adhesion of Melts and Braz ing of Mate r ia l s [in Russ ian] , No. 1 (1976), pp. 3-28. Yu. B. Kuz 'ma , N. S. Bilonozhko, and E. M. Nimkovich, "Sys tem l a n t h a n u m - n i c k e l - b o r o n , " Dopovidi Akad. Nauk Ukr. RSR, Ser. A, No. 10, 939-941 (1973). G. F. Stepanchikova and Yu. B. Kuz 'ma , " S y s t e m La- -Co- -B , " Visnik L 'v ivsk . Derzhavn. Univ., Ser. Khim., No. 18, 16-18 (1976). G. V. Samsonov, A. D. Panasyuk, G. K. Kozina, and L. V. D'yakonova, "Contact reac t ion of r e f r a c t o r y compounds with liquid me ta l s , " Poroshk . Metall . , No. 7, 66-70 (1972). G. V. Samsonov, A. D. Panasyuk, and M. S. Borovikova, "Contact r eac t ion between r e f r a c t o r y bor ides and liquid i ron group meta l s , " Poroshk . Metall . , No. 6, 51-57 (1973). V. N. E remenko , N. D. Lesnik, andT. S. Ivanova, "Spread ing kinet ics and contact r eac t ion in an a lumi - n u m - i r o n - g r o u p - m e t a l s y s t e m , " in: Adhesion of Melts and Braz ing of Mate r ia l s [in Russ ian] , No. 1 (1971), pp. 47-50. Yu. V. Naidich, V. M. P e r e v e r t a i l o , and O. B. Loginova, "Adhesion and wetting of graphi te by Group VIII me ta l s , " Izv. Akad. Nauk SSSR, No. 4, 37-41 (1979).

CALORIMETRIC INVESTIGATION OF

OF FINE ELECTROLYTIC POWDERS OF

MAGNETIC MATERIALS WITH ORGANIC

A. G. Zhigotskii, T. M. Shvets, and V. A. Mikhailik

T H E R E A C T I O N S

F E R R O -

S O L V E N T S

UDC 621.762.274

Colloidal e lec t ro ly t i c me ta l powders produced by the t w o - l a y e r bath method [ 1] a r e widely used in in- dus t ry [2]. The speci f ic mode of growth of the i r pa r t i c l e s r e su l t s in the fo rma t ion of an i sod iamet r i c poly- c r y s t a l s c h a r a c t e r i z e d by a cons ide rab le in te rna l s t r e s s , the p r e s e n c e of n u m e r o u s defects of all kinds, a l a rge spec i f ic su r face , and hence a l a rge excess su r f ace energy. However , adsorp t ion of oleie acid, which is employed as a s tabi l iz ing and floating agent, on the su r f aces of growing me ta l pa r t i c l e s d e c r e a s e s the l a t t e r ' s su r f ace energy. Such a change in su r face energy can have a m a r k e d effect on the p r o p e r t i e s of the finely di- vided me ta l s t h e m s e l v e s and a lso on the conditions of product ion and c h a r a c t e r i s t i c s of compos i te m a t e r i a l s obtained f r o m them. Yet at p r e s e n t the re a r e v i r tua l ly no publ ished quanti tat ive data concerning the su r face ene rgy of such m a t e r i a l s . One way of obtaining informat ion of this type is to study the heats of wetting of me ta l powders by liquids of va r ious na tu res .

In this connection, in the p r e s e n t work an inves t igat ion was c a r r i e d out into the wetting of fine Fe and F e - C o - N i al loy powders by three organic s o l v e n t s - benzene, methanol , and n-propanol . Chemical ana lyses for ca rbon and hydrogen r evea led that the powders contained 4.1% of oleic acid re la t ive to the meta l , in the adsorbed s ta te and in the f o r m of su r face o lea tes . To r e m o v e oleic acid phys ica l ly at tached to the meta l s u r - face, the powders were t r ea t ed with ace tone and toluene in a Soxhlet appara tus .

The p a r t i c l e s of the Fe and F e - C o - N i al loy powders were dendri t ic in shape, and had an iso t ropy co- eff icients ranging f r o m 1 : 5 to 1 : 7, the lengths of the i r m a j o r axes being 2000-3000 nm. The specif ic s u r - faces of the powders , de t e rmined ch romatograph ica l ly , were 41.0 and 35.5 m2/g, r espec t ive ly . The conditions of p r e p a r a t i o n of the e lec t ro ly t i c Fe and F e - C o - N i powders were s i m i l a r to those desc r ibed in [3-5] .

The heats of wetting Q of the Fe and F e - C o - N i al loy powders were de t e rmined with a D A K - I - 1 m i - c r o c ~ o r i m e t e r . The a r e a s under wetting t h e r m o g r a m s , which were propor t iona l to the total amounts of heat evolved during the expe r imen t s , were e s t ima ted using an I P - 3 p rec i s ion in tegra to r . Cal ibra t ion with e lec t r i c c u r r e n t showed that one count of the i n t e g r a t o r r e p r e s e n t e d 616 . 10 -i~ kJ. All expe r imen t s were conducted at

30~

Before the determinations of Q of specimens, weighed 0.1-g powder samples were vacuum-treated in

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 . T rans l a t ed f r o m Poroshkovaya Metal lurgiya , No. 3(219), pp. 69-72, March, 1981. Or ig inal a r t i c l e submit ted, a f t e r rev is ion , Sep tember 30, 1980.

210 0038-5735/81/2003-0210507.50 �9 1981 Plenum Publishing Corpora t ion

TABLE 1. Heats of Wetting of Fe and F e - C o - - N i Alloy Pow- de r s by Organic Solvents

Extractant Wettingliqmd 10 ~kg

Iron powder

Acetone Benzene 4,330 Methanol 3,4 I0 n-Propanol 6,640

Toluene Benzene 4,730 Methanol 2,000 n-Propanol 9,170

No treatment Benzene 2,620 n-Propanol 9,550

Iron-cobalt-nickel alloy powder Acetone n-Propanol 5,160 No treatment Benzene 2,020

n-Propanol 5,530

spec ia l capsu les at a t e m p e r a t u r e of 80~ and a res idua l p r e s s u r e of 1.33 N / m 2. The wetting liquids were subjected to drying, as r e c o m m e n d e d in [6], and addit ional pur i f ica t ion [6, 7]. The t h e r m a l effects l inked with the reac t ions between the wetting liquids and meta l powder su r f aces were accompanied by heat evolution r e - sult ing f r o m p r o c e s s e s occu r r ing during the des t ruc t ion of the capsu les with spec imens [6], and it was t h e r e - fo re n e c e s s a r y to a s s e s s the magnitude of this effect. The total t h e r m a l effect due to capsule des t ruc t ion was de te rmined , as de sc r ibed in [8], using capsu les fi l led not with powder but with g lass cy l inders (the f r ee vol - ume of a capsule was 0.170-0.200 cm3). F o r benzene and n-propanol t he rma l ef fec ts of 5.82" 10 -~ and 23.75" 10 .6 kJ, r e spec t ive ly , were recorded . As the absolute magni tudes of the t h e r m a l effects accompanying the wetting of the powders we re equal to, depending on the i r chemica l composi t ion and su r face condition, be tween 0 . 2 . 1 0 - 3 a n d 1 �9 10 -3 kJ , the magni tudes of the c o r r e c t i o n s wouldnot have signif icant ly affected the r e su l t s of wett ing heat m e a s u r e m e n t s .

The values of Q of spec imens were found to be s t rongly affected by the compos i t ion of the powder and na tu res of the ex t r ac t an t and wetting liquid (Table 1). The value of Q of the i ron powder p roved to be l a r g e r than that of the F e - C o - N i al loy powder. This finding can be linked with the specif ic e lec t ron ic s t r u c t u r e of the me ta l s i n v e s t i g a t e d - t rans i t ion me ta l s with unfil led 3d-e lec t ron shel ls . A reac t ion of the d o n o r - a c c e p t o r type between the liquids inves t iga ted and a meta l su r face can take place with the par t i c ipa t ion of unpa i red e l ec t rons of the oxygen a toms of the alcohols and 7r-electrons of benzene molecu les on the one hand and, on the other , of su r f ace me ta l a toms located main ly at c o r n e r s and on edges of c ry s t a l l i t e s of l ea s t coordinat ion number . Under such condit ions, the fo rmat ion is poss ib le of so -ca l l ed "quas inormal covalent l inkage" [9] b e - tween molecu les of adso rbed subs tances and t rans i t ion meta l su r f aces .

Analys is of the data of Table 1 shows that, as a r e su l t of t r e a t m e n t with acetone and toluene, which r e - moved phys ica l ly adsorbed oleie acid and f reed some of the adsorp t ion cen te r s on meta l s u r f a c e s , the s u r - face energ ies of the me ta l s grew, which mani fes ted i t s e l f in i n c r e a s e s in the heats of wetting Q of the powder meta l s by benzene. With n-propan01, however , the opposi te ef fec t was observed , which mus t have been caused by addit ional heat genera t ion as a r e su l t of the reac t ion of the desorbed oleic acid with this solvent .

The c h a r a c t e r of the wetting t h e r m o g r a m s of the powders inves t iga ted (Figs . 1 and 2) shows also that the reac t ions of the organic liquids with the su r f aces of the finely divided meta l s we re ini t ia l ly accompan ied by absorp t ion of heat n e c e s s a r y fo r the r e m o v a l of oleic acid f r o m these s u r f a c e s . This phenomenon was p a r t i c - u l a r ly pronounced with the s ta r t ing powders (Fig. 1), which mani fes ted i t se l f in negat ive effects on the wetting t h e r m o g r a m s in the init ial pe r iods of contact be tween the wetting liquids and powders . Subsequently, heat evolution due to the r eac t ion of molecu les of the liquids with ac t ive su r f ace cen te r s b e c a m e dominant , and pos i t ive overa l l t he rma l ef fec ts were recorded . With the a c e t o n e - p r e t r e a t e d powders (Fig. 2), the con t r ibu- t ion f r o m the above-ment ioned p r o c e s s to the overa l l t h e r m a l effect was much s m a l l e r , and consequent ly no negat ive t he rma l ef fec ts we re detec ted in the init ial pe r iods of the reac t ions .

The data obtained a r e evidence that n -p ropano l r e ac t s with the su r face of a f inely divided me ta l with m o r e in tense heat evolution c o m p a r e d with the o the r wetting l iquids. As a resu l t , i t is m o r e effect ive in r i d - ding a meta l su r face of oleic acid, which m a y be a t tached to meta l by var ious kinds of bond, ranging f r o m the

211

r mW 6,0 ~ 4o

go

I ' 0 1 2 J 4 5

~

d_~ mW

~ rain

0 / 2 J

Fig. 1 Fig. 2

Fig. 1. T h e r m o g r a m s of wetting of Fe powder by n -propanol (1) and of F e - C o - N i al loy powder with n -p ropano l (2) and benzene (3).

Fig. 2. T h e r m o g r a m s of wetting of a c e t o n e - p r e t r e a t e d Fe powder by n -propanol (1) and benzene (2).

Van der Waals reac t ion to the fo rmat ion of meta l l ic o[ea tes . Apa r t f r o m this, n -propanol r e ac t s m o r e s t rongly with act ive e l e c t r o n - a c c e p t o r cen te r s on the su r face of a t rans i t ion meta l than do the o ther so rba te s inves t i - gated. In this case , the contr ibut ion f r o m the reac t ion of hydrocarbon rad ica l s of n -propanol and oleic acid adsorbed on a su r face may be significant.

This c i r c u m s t a n c e as well as a s t r o n g e r assoc ia t ion of molecu les of the f o r m e r , with the fo rmat ion of long chains of H-bonds [9], and hence a weaker reac t ion with a powder explains to a l a rge extent why the heat of wetting Q of an i ron powder by methanol is l e s s c o m p a r e d with n-propanol .

Additional informat ion on the condition of the su r faces of the finely divided f e r romagne t i c m a t e r i a l s in- ves t iga ted may be provided by a compar i son and ana lys i s of the r e su l t s obtained in this work and l i t e r a tu r e data concerning Q of iron and iron oxide powders with many times smaller specific surfaces [ 10, 11]. Values of Q close to those found for the finely divided ferromagnetic materials wetted by n-propanol at compara- tively high values of Q for wetting by benzene may be evidence that large parts of the surfaces of the powders

investigated were covered with hydrocarbon radicals of chemisorbed oleie acid [ 12].

On the other hand, larger values of heat of wetting Q of the ferromagnetic materials by n-propanol com- pared with benzene may point to the existence of parts of surfaces covered with oxide films, which react more vigorously with n-propanol than with a metal surface [ II]. If we assume that the area occupied by one oleic acid molecule is equal to 20.5 ~2 [ 13] and that molecules form a close-packed monomolecular layer on a metal surface, the calculated specific surface of a specimen is 17.5 m2/g, which is one-half the experimentally determined value. This effect will be even more pronounced when the adsorbed oleie acid is unevenly distribu-

ted on a metal surface.

Thus, our investigation into the wetting of electrolytic iron and iron-cobalt-nickel alloy powders by organic solvents of various natures (whose molecules can act as electron donors) has established that the surface energy of finely divided iron is greater than that of the ferrous alloy. The best wetting agent for both powders is n-propyl alcohol, with which the greatest amount of energy is generated, so that its molecules can

effectively dislodge molecules of other adsorbed substances from metal powder surfaces.

It can r easonab ly be a s s u m e d that the wett ing of the su r f aces of f inely divided f e r r o m a g n e t i c m a t e r i a l s by organic liquids involves pa r t i a l desorp t ion of a s u r f a c e - a c t i v e subs tance act ing as a s t ab i l i ze r and reac t ion with act ive me ta l su r face cen te r s exposed during this p r o c e s s as well as with act ive cen te r s in oxidized s u r - face por t ions (which is accompanied by the fo rma t ion of bonds of the d o n o r - a c c e p t o r type) .

212

LITERATURE CITED

1. E.M. Natanson, Colloidal Metals [in Russian], Naukova Dumka, Kiev (1959). 2. E.M. Natanson and Z. R. Ul'berg, Colloidal Metals and Metallic Polymers [in Russian], Naukova

Dumka, Kiev (1971). 3. E.P. Zhelibo, K. A. Aryupina, and E. M. Natanson, "Formation of fine iron powder on the cathode,"

Poroshk. Metall., No. 2, 14-19 (1973). 4. T.M. Shvets, L. Yu. Ivanova, Z. M. Mel'nichenko, E. G. Mishchenko, and E. M. Natanson, "Magnetic

properties of fine iron-cobalt-nickel alloy powders," Poroshk. Metall., No. 7, 71-75 (1972). 5. T.M. Shvets, Z. M. Melrnichenko, V. P. Vasilenko, L. Yu. Ivanova, and E. M. Natanson, "Effect of

cathode materials on the properties of a finely divided iron-cobalt-nickel alloy," Ukr. Khim. Zh., 388, No. 10, 993-996 (1972).

6. S.J.N. Gregg and K. S. Sing, Adsorption, Surface Area and Porosity, Academic Press (1967). 7. A. Weisberger, E. Proskauer, J. Riddick, and E. M. Tuns, Organic Solvents [Russian translation], IL,

Moscow (1958). 8. V . E . Polyakov, I. T. Polyakeva , and Yu. I. Ta ra sev i ch , "Determinat ion of the heats of wetting of d i s -

p e r s e m ine ra l s of smal l specif ic su r face , " Kolloidn. Zh., 3_._88, No. 1, 188-191 (1976). 9. G . C . P imen te l and O. McClellan, Hydrogen Bond [Russ ian t r ans la t ion] , Mir, Moscow (1964).

10. E . H . Allen and R. M. Pate l , "Adsorption of alcohols on finely divided powders ," J . Appl. Chem., 2_~0, No. 6, 165-171 (1970).

11. E . H . Loase r , W. D. Harkins , and S. B. Twiss , "Molecular in te rac t ion between n -p ropy l alcohol and iron o r i ron oxides," J . Phys . Chem., 57.._., No. 6, 591-597 (1953).

12. A . W . Adamson, Phys ica l C h e m i s t r y of Surfaces , Wiley (1976). 13. D. P a t t e r s o n (edi tor ) , P igments : An Introduction into the Phys ica l C h e m i s t r y of P igments [Russian

t rans la t ion] , Khimiya, Leningrad (1971).

RELATIONSHIP BETWEEN THE ELECTRONIC

STRUCTURES AND ELECTROPHYSICAL

PROPERTIES OF NITRIDES

T. V. Andreeva, Yu. M. Goryachev, and B. A. Kovenskaya

UDC 621.762

In this a r t i c l e c o m p a r a b l e calculat ions a r e made of the e lec t ronic s t r u c t u r e s of the n i t r ides of s -p and d e lements [ 1, 2] with the a im of analyzing the fo rma t ion of the i r e l ec t rophys ica l p rope r t i e s , demons t ra t ing d i f fe rences in behav io r between s -p and d s ta tes , and examining the posi t ion of n i t r ides among other c l a s s e s of compound.

In the condensed s ta te the a i t r ides exhibit a b road s p e c t r u m of e lec t rophys ica l p r o p e r t i e s (Table 1), ranging f r o m those c h a r a c t e r i s t i c of d i e l ec t r i c s and semiconduc to r s to those typical of s e m i m e t a l s and meta l s [ 1, 3]. S u c h a va r i e t y of p r o p e r t i e s is linked with d i f fe rences in e lec t ron ic s t ruc tu re between different n i t r ides . A c o m p a r i s o n of the n i t r ides of s - p and d e lements with one another and also with oxides and c a r - bides (Table 1) has shown that the f o r m e r a r e d ie l ec t r i c s obeying the rule of va lence compounds, while the l a t t e r a r e meta l l ike compounds exhibiting deviat ions f r o m s to i eh iome t ry in wide ranges of homogeneity. F o r the n i t r ides of d e lements , the o r d e r of t rans i t ion f r o m s e m i m e t a l s to meta ls and back to s e m i m e t a l s is (ScN, TiC) -* (TIN, VC) ~ (VO, CrNx).

In each group of elements the nitrides occupy, according to properties, an intermediate position between the carbides and oxides. This point is illustrated by Fig. i, showing experimentally determined values, yielded by thermodynamic studies, of energies of atomization of the carbides, nitrides, and oxides of transi- tion elements referred to one atom, Uat. In oxide-nitride-earbide series Uat monotonically grows; the

Inst i tute of Mate r i a l s Science, Academy of Sciences of the Ukrainian SSR. Trans la t ed f r o m Poroshkov- aya Metal lurgiya , No. 3 (219), pp. 73-76, March, 1981. Original a r t i c l e submit ted, a f t e r rev is ion , August 30, 1980.

0038-5735/81/2003-02] 3 $07.50 �9 1981 Plenum Publishing Corpora t ion 2! 3