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17XV International Symposium on Self-Propagating High-Temperature Synthesis
SHS OF TITANIUM-CHROMIUM CARBIDES: INFLUENCE OF GREEN COMPOSITION
O. A. Golosova*", P. A. Miloserdov", V. A. Gorshkov", and O. M. Miloserdova"
aMerzhanov Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, Moscow, 142432 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10048
In the paper, the effect of green mixture composition on combustion parameters and composition of SHS Cr-Ti-C products was studied. In order to prepare titanium-chromium carbides by SHS process, a mixture of chromium oxides CrO3 and Cr2O3 was previously used. However, CrO3 is toxic and low technologic. Therefore, calcium chromates CaCrO4 and CaCr2O7, which are CrO3 stabilized by calcium oxide, were chosen as a chromium-containing additive.
We studied systems based on CaCrO4:
CaCrO4 + Al + C ^ &3C2 + CaO + AhO3 TiO2 + Al + Ca + C ^ TiC + CaO + AhO3
and based on CaCr2O7:
CaCr2O7 + Al + C ^ &3C2 + CaO + AhO3 TiO2 + Al + Ca + C ^ TiC + CaO + AhO3
In experiments, replacing aluminum with calcium for more complete reduction of titanium oxide was carried out.
Calculation of combustion temperature of mixtures depending on the titanium oxide content showed that the combustion temperature of mixture 2 (Fig. 1b) is higher than that of mixture 1 (Fig. 1a). Mixture 2 is also characterized by higher amount of gaseous products. The calculated yield of target product remains practically unchanged.
T K
ad' 3100-,
3000-
2900-
2800-
2700
2600-
2500
20
40 60
a, %
80
(a)
a, % wt.
40
-30
-20
-10
0 100
Td K
3300 3200 3100 3000 2900 2800 2700 2600 2500
20
40a, %60
(b)
a., % wt.
1 '
40
-30
-20
-10
80
100
Fig. 1. Calculated adiabatic combustion temperature (Tad), mass fraction of metallic (ai) ang gaseous (a2) reaction products as a function of a. (a) System 1, (b) system 2. a = (M2/(Mi + M2)) x 100%, where Mi is the mass of mixture based on (a) CaCrO4 and (b) CaCr2O7, M2 is the mass of CaCr2O7.
0
0
0
iSHS 2019
Moscow, Russia
Experiments were carried out using a reactor with V = 3.5 l under an overpressure of argon of 5 MPa. Mixtures were placed in graphite container 40 mm in diameter. Mixture mass was 50 g. Results are presented in Fig. 2.
It is seen that an increase in the titanium oxide fraction leads to a decrease in the burning velocity. The material loss caused by sputtering decreases from 5.8 to 3.5%. The separation of target product from oxide layer in CaCrO4-based mixtures occurs up to a = 10% (Fig. 2a). To expand the phase separation limit, 20 wt % highly exothermic CaO2 + Al additive was added into the mixture. This made it possible to prepare cast product up to a = 30%. In the case of mixtures based on CaCr2O7 (Fig. 2b), cast product is obtained up to a = 40% without the use of highly exothermic additive. The material loss caused by sputtering is slightly reduced from 12 to 10%.
U, mm/s 10-i
98
765
43
10
20
a, %
(a)
30
7, % wt. ' r30
-25
-20
-15
-10
-5
0 40
U, mm/s 2018 161412 100
10
20
a, %
(b)
30
77, % wt. ' 25
-20
-15
-10
40
Fig. 2. Measured values of burning velocity (U), yield of target product (ni), and material loss caused by sputtering (n2) as a function a.
5
0
Conclusions
The use of mixtures based on calcium dichromate improves reaction parameters and phase separation. For mixtures based on calcium chromate, it is necessary to use a highly exothermic additive.
The research was supported by the Russian Foundation for Basic Research (project no. 18-08-00804).
