The vapor pressure and evaporation rate of borides of titanium, zirconium, and chrome; and of strontium and carbides of titanium, zirconium, and chrome, molybdenum silicide; and nitrides of titanium, niobium, and tantalum in a vacuum were studied. It is concluded that all subject compounds evaporate by molecular structures except AlB sub 12' which dissociates, losing the aluminum

Bolgar, A. S.

Samsonov, G. V.

Verkhoglyadova, T. S.

English

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NASA TECHNICAL MEMORANDUM 
VAPOR PRESSURE ANb EVAPORATION RATE OF CERTAIN 
HEAT-RESISTANT COMPOUKDS IN A VACUUM AT 
HIGH TEMPERATURES 
A. S.  Bolgar, T. S. Verkhoglyadova, G. V. Sarsonov 
( D A S A - T U - ~ ~ ~ O ~ ~  o ~ ~ c 3  zs~ssoar ran ~ € 5 -  15436 
SVAPOMTICI BIT& C CBBlAIS  EIIT-61SISSIBI 
COIIPOUIDS I1 A VACGOI AT E l G B  168PESATURBS 
(Iational Aesona~tict  and Scacr Uaclas 
A ~ i s t r a t i o p )  11 p BC A4;/6f A 0 1  CSCL 07D 63/25 17758 
Translation of "Davleniye para i skorost' ispareniya nekotorykh 
tugoplavkikh soyedineniv v vakuure pri vysokikh t-erperaturakh," 
Izvestiva Akaderii Nauk SSSR, Otdeleniye Tekhnicheskikh Nauk, 
Metallurgiyz i Toplivo, no. 1, 1961, p. 142-145. 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 FEBRUARY 1985 
https://ntrs.nasa.gov/search.jsp?R=19850010726 2020-03-20T20:20:52+00:00Z
STANDARD TITLE PACE 
Vapor Pressure and Evaporation R a t e  of Certain 
.S. Verkimglyadova aiid 
Washingtcm, D.C. 20546 
5. h l - t r y  N o h a  
Translation of *Davleniye para i skorost '  ispareniya nekotorykh 
tugoplavkikh soyediyeniy v vakuwne pri vysdrikh temperaturakh , * 
Izvest iya Akademii Nauk SSSR, Otdeleniye T e k h n i ~ h e s k ~ h  Nauk, 
Hetallurgiya i Toplivo. no. 1, 1981. pp- 142-145. 
The vapor pressure and evaporation r a t e  of borides of ti tanium, 
zirconium, and chrome, a s  w e l l  as of strontium and carbides of 
ti tanium, zirconium, and ckrame, molybdenum s i l i c i d e ,  and n i t r i d e s  of 
t i t a n i u m ,  n iob im,  and tantalum i n  a vacuum are studied. It is concluded 
t h a t  a l l  subjec t  compounds evaporate by molecular s t ruc tu res  except 
AlBI2, which d issocia tes ,  losing the  aluminum. 
17. ( (8 ,  W-rds ( ~ c l ~ t e d  by ~uthor(r)) 10. Dirhibution S * ~ * r n u # t  
Heat-resistant ccinpounds, borides, 
VAPOR PRESSURE AND ZVAPORATION RATE OF CERTAIN 
BEAT-RESISTANT COMPOUNDS IN A VACUUM 
AT HIGH TBMPBRATURES 
A. S. Bolgar, T. S. Verkhoglyadova, G. V. Samsonov 
Tht development of high-temperature technology requires /142* 
that we find materials which can be used in a vacuum at high 
temperatures, whose chemical composition does not significantly 
change under these conditions, and which have tbe lowest vapor 
pressures and evaporation rates. 
The most promising materials of this type are heat-resistant 
compounds: borides, carbides, nitrides, and silicides of metals 
in the IV-VI groups in the periodic system (titanium, zirconium, 
hafnium, vanadium, tantalum, chrome, molybdenum, tungsten , as 
well as certain non-metallic heat-resistant compounds, such as 
carbides and nitrides of boron and silicon, and boron-silicon and 
boron-aluminum alloys. However, the behavior of thzse materials 
in a vacuum at high temperatures has not been adequately studied 
and this creates considerable problems in selecting them for 
practical uses. 
Old data on this problem, obtained for nitrides of heat- 
resistant transient metals, is referenced in monographs [1, 2:. 
little has been added to this data in recent years. 
Reference 131 determines rhenium silicide dissociation pressure 
by effusion method, reference f43 tantalum silicide dissociation. 
Data has been obtained on silicon[5] and boron(61 nitride 
dissociation pressure, as well as on the pressure of saturated 
vapors of boron itself[7]. The results of this research, 
presented in table 1, show that tt-zre is virtually no data on the 
most interesting and important classes of heat-resistant 
compounds -- carbides and borides, which have the highest melting 
pointsl81, chemical stability[91, and mechanical strength at high 
*Numbers in the margin indicate pagination of the original. 3 
temperaturesflO]. In particular, Campbell feels that borides of 
transient metals should be considered the most promising 
materials for use as refractories in a vacuum at temperatures 
above 2500'.  
This article reviews vapor pressure and evaporation rate of 
borides of titanium, zirconium, and chrome, as well as of 
strontium and carbides of titaniun, zirconium, and chrome; 
molybdenum silicide, and nitrides of titanium, niobium, and 
tantalum in a vacuum. Evaporation rate was calculated using 
Langmorc's method[l], based on measuring the decrease in weight 
of the subject material over a unit of tine from a unit of 
surface. Vapor pressure was calculated with the formula, 
where is the change in weight, g; a is the accorrodation 
factor, about 1; A is the samp1ens surface, cm2; T - holding 
time, sec, at temperature To, K; M is molecular weight taking 
into account that the molecular weights of the vapor and compound 
are equal, i . e .  it is assumed that there is 30 dissociation. 
This data was then used to calculate evaporation heat. 
The unit for calculating evaporation rate is designed on the 
basis of a retort-type laboratory vacuum furnacefll] and is 
depicted in figure 1. Heater 3, made of molybdenum or tungsten 
wire wound into a 25-rs-diameter coil, is fastened between two 
live, water-cooled contacts, 2 and 6. The heater is protected by 
two small double screens 4 and one large screen 1 made of 
molybdenum plate. The sample, in the form of a pressed pellet, 
is placed into a molybdenum cup 5, attached to a substrate at the 
bottom of live contact 6. This unit could be used for 1143 
experiments at temperatures from 1100 to 1900'. A vacuum was 
provided by a VH-461 initial vacuum pump and a V-15 mercury 
diffusion pump. Temperature was measured with an optical 
pyrometer, taking into account appropriate measuring errors. 
* 
To vacuum pump 
Figure 1. Unit for measuring 
evaporation rate of heat- 
resistant compounds: 
1 - large s c r e e n ;  2 - upper 
electrode; 3 - molybdenum coil; 
4 - small s c r e e n s ;  5 - cup with 
sample; 6 - lower electrode; 
7 - w a t e r - c o o l e d  p l a t e ;  
8 - live contact; 9 trap cooled 
by liquid nitrogen. 
Zigure 2. Vapor pressure of 
heat-resistant compounds as a 
function temperature itvo outer 
curves represent NbC and HfC 
respectively. 
The results are given in table 2 and shown in figure 2. 
Table 3 presents comparative data on the change in chemical 
composition of the samples before and after heating in a vacuum 
at 1700". 
It follows from this data (given the limited accuracy of 
chemical analysisl that none of the compounds except AIBIZ 
undergoes dissociation at the temperatures studied, i-e. 
evaporation takes place in molecular structures. However, since 
mass-spectrometry did not reveal the existence of, for example, 
TiC in a gas phaseill', we can hypothesize that, during heating, 
dissociation takes place in a gas phase on the edge of the 
sample's surface. In other words, the samples' surfaces 
disintegrate with gradual detachment and elimination of molecular 
structures. 
Data in table 2 for hafnium and niobium carbides, as well as 
for strontium hexaboride, was used to set up equations for vapor 
pressures: 
I g  PHfC:mm Hg: = 8.6 - !30 555/T?!1900-200OoC! 
I g  ' N ~ C  *ram Hg' = 1 0 . 6  - i 3 G  666 -Tli1800-2000°C1 
!g PSre :em Hg! = 6.36 - :21 428iTi11500-2000'C) 
6 
Table 1. Equations for Dissociation Pressure for i14$ 
Certain Heat-Resistant Compounds 
Compound 
7 
R* 
RcSi 
RtSir 
f q-& 
T@ 
T&-r 
f*, 
Si& 
BN 
g* *** 
t ion 
-- 
-, 
** r = Gas 
-- - -  -  
Diss3ciation Equa 
- 
-,mt:m,m+sir* 
t f & ~ t r r ) = ~ ! ~ R ~ i , ~ + ~ , r ,  
~S&=RtSi,,isi,,, 
f ~ . iS i (~ ,=~ .~T . ' ~ )+s , , ,  
' ; S T ~ ( , . , - ~ ~ T ~ S ~ , ~ ~ +  Sztr .
1oTJLym=5T.iSi(,, + Sic,, 
'/,f~m)"~~T&..4m)-~i,r, 
Si+&-',,+zx4,, 
28Nd=2B,,+3iqr, 
Bat.) -Bar, 
Table 2. Temperature Relationship between Vapor Pressures 
and Evaporation Rates of the Compounds Studied* 
08- 
ound 
Ti 
Zrc 
Hfc 
5 top line represents evaporation rate, v. 10 , g/cm3. S ~ C ;  thc 
ottom line -- vapor pressure. p* 10 mm Hg. 
These equations can be used to extrapolate approximated /m 
boiling points of 5400, 4500, and 5100°C for HfC, NbC, and SrB6 
respectively. The boiling point of NbC correlates satisfactorily 
with published dataf121. 
Table 3. Change in Chemical Composition of Samples of 
Heat-Resistant Compounds after Heating in a Vacuum at 1700" 
Table 4 presents t h e  ilea- of evaporation of  t h e  subject heat- 
resistant compounds. 
Compound 
Tic 
Z r C  
H f C  
&bC 
Cr3C2 
TieZ 
ZrB2 
CrB2 
T a b l e  4.  Heats of evaporation p of the heat-resistant 
Compounds S t u d i e d  
Metal/#on-metal Ratio 
Before 
Experiment 
i A) 
4.06 
7.63 
15.92 
7.69 
6.50 
2 . 2 1  
4.21 
A I B  0.176 
TiN 3.36 
MoSi, 
- 
1 - 7 2  1.79 
---- .- - 
0.039 
0.990 
1.030 
Compound 
After 
Experiment 
I B )  - 
4.12 
7.62  
16.42 
7.97 
6.44 
2.09 
4.21 
2 . 5 9  
0 
Compound 
Z r B Z  
CrBZ 
A1B12 
T i N  
NbN 
Ta2N 
MoS i 
&-- 
T iC 
Z r C  
HfC 
NbC 
Cr3C2 
B/A 
1.010 
0.999 
1.030 
1.030 
0.995 
0.995 
1.000 
1.080 
.__-__ -___.. 
p ,  Rcal/mole 
-- 
56.4 
41.2 
45.7 
62.3 
91.5 
4 2 . 0  
57.1 
38.08 
52.20 
139.64 
167.00 
44.00 
97.90 
lrb6 1 4 5 . 7 0  TiB2 
Conclusions. 1. Evaporation rates and vapor pressures  for 
several heat-resistant compounds: PIC. Z r C .  BfC. WbC. CrgCp. 
ZiB,, ZrB.?, C r B 2 .  SrB6. A1B12, 
* C 
116, WbE, Ta,E, and HoSi2, were 
C 
calculated with Langmore's method and the evaporation heats of 
these curpounds were determined. 
2. It is shown that, at the temperatures studied. all subject 
compounds evaporate by molecular structures, except 4 l B  which 12- 
dissociates, losrng the aluminum. 
Institute of Hetalloceramics 
and Special Alloys 
Academy of Sciences U S S R  
R E F E R E N C E S  
Deshman, S. Nauchnyye osnovy vakuumnoy tekhniki (Scientific 
Bases for Vacuum Technology), Izdatel'stvo inostrannoy 
literatury, 1950. 
Tekhnika vysokikh temperatur (High- Temperature Technology), 
ed. I. K. Campbell, Izdatel'stvo inostrannoy literatury, 
1959. 
Searcy, A., McNees, R. J . ,  American Chemical Societ-y, 1953, 
75, 1578. 
Vyers, C., Searcy, A. J., American Chemical Societv, 1957, 
79, 527. 
Samsonov, G. V., Silitsidy i ikh ispol'zovaniye v tekhnike 
{Silicides and Their Use in Technology), Izdatel'stvo A& 
UkSSR, Kiev, 1959. 
Samsonov, G. V., Yarkovskiy, L. Ya., Zhigach, A. F., 
Valyashko, M. G., Bor, yego soyedineniya i splavy (Boron, Its 
Campounds and Alloysi, Izdatel'stvo AN UkSSR, Kiev, i 9 6 0 .  
Priselko, Yu. A. Sapozhkov, Yu. A., Tseplyayeva, A. V., 
Measuring Pressure of Saturated Boron Vapc~r, Izvestiva AN 
SSSR, Otdeleniye tekhnicheskikh nauk, Metallurgiys i toplivo, 
1960, No. 1, 234. 
Samsonov, G. V., Umanskiy, Ca. S., Tverdvve soyedineniya 
tugoplavkikh metallov !Solid Compounds of Heat-Resistant 
Metals', Metallurgizdat, 1957. 
Samsonov, G. V., Prospects for Using Heat-Resistant Compounds 
in the Chemical Industry, Khimicheskaya nauka i 
promyshlennost', 1958, No. 6, 807. 
Vereykina, L. I,., Rudenko, V. N., Samsonov, G. V., Study of 
Strength Characteristics of Certain Heat-Resistant Compounds 
by High-Temperature Compression, Zavodskaya laboratoriya, 
1960, No. 5, 620. 
Chupks, W. Berkowitz, J., Giese, C., Tnghram, M. Phys. Chem., 
1958, 62, 5. 
Kiffer, R., Shvartskopf, P., Tverdyye splavy iSolid Alloys), 
Metallurgizdat, 1957. 


Vapor pressure and evaporation rate of certain heat-resistant compounds in a vacuum at high temperatures

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