CC BY
32■SHS 2019 Moscow, Russia
SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF
TITANIUM CARBIDE
T. Ergul", U. Cinarli", M. Bugdayci*A, and A. TuranA
aChemical and Process Engineering Department, Institute of Science, Yalova University,
Yalova, 77200 Turkey
bChemical and Process Engineering Department, Faculty of Engineering, Yalova University,
Yalova, 77200 Turkey *e-mail: mehmet.bugdayci@yalova.edu.tr
DOI: 10.24411/9999-0014A-2019-10037
Titanium carbide synthesis was first performed by Moissan in an electric arc furnace. TiC, which is between the refractory carbides, has become a highly studied material over the last decades because of its perfect combination of high hardness, high melting temperature, good thermal and electrical conductivity. Titanium carbide has a B1 type face centered cubic (FCC) crystal structure. The cage parameter of TiC is 0.432 nm.
TiC shows wide composition range from TiC0.47 to TiC with respect to the Ti/C ratio without changing the structure of FCC. However, its properties change according to Ti/C ratio. In the Ti-C binary phase diagram, hexagonal a-Ti, at low temperatures, and FCC P-Ti at elevated temperatures can dissolve a limited amount of C. TiC has a melting temperature of 3067°C.
Titanium carbide is a ceramic powder which is one of the hardest natural carbides and, it is used in cermets and advanced ceramic tools. Titanium carbide is produced through carbothermic reduction, chemical vapor deposition, direct carburization, mechanical alloying, and self-propagating high temperature synthesis (SHS) methods. Between the methods in question, SHS results in the formation of high purity and nano-size products because of extremely short reaction times. In this process, TiC is produced with less external energy requirement.
In this study, TiC was produced by using SHS method from TiO2, Mg, and C raw materials with respect to Eq. 1. Raw materials were mixed at different stoichiometric ratios as 1.0x and 1.1x for C and from 0.9x to 1.2x for Mg. Powder mixtures were put in a copper crucible. Reactions were started by means of a metal wire which the electricity was passed through. Reactions lasted very fast as a result of the nature of metallothermic reactions. SHS experiments were carried out under air atmosphere.
TiO2 + C + 2Mg ^ TiC + 2MgO (1)
Before the experimental studies, thermochemical simulation studies were carried out by means of HSC Chemistry 6.1 software. Some calculated thermodynamical data (for Eq. 1) can be seen in Table 1. For metallothermic reactions, specific heat is an important parameter showing the self-propagation of reactions. The specific heat value of the reaction (Eq. 1) was calculated as 3152.9 J/g and, it is greater than 2250 j/g. Therefore, it was enough for self-sustainable reaction conditions.
Table 1. Calculated thermodynamical data for Eq.1 (HSC Chemistry 6.1).
AHxn, kJ/mol -442.95
SreactantM, g/mol 140.49
Specific heat, J/g -3152.92
XV International Symposium on Self-Propagating High-Temperature Synthesis
After SHS experiments, an HCl leaching step was conducted to purify TiC and to extract Mg-based impurities of the products out. Following leaching conditions were applied: solid weight of 10 g, solid/liquid ratio of 1/10 and duration of 60 minutes at room temperature. Liquid phase consisted of 23 mL distilled water and 77 mL 37% HCl. Filter cakes were dried at 105 °C for 150 minutes. Dried filter cakes were weighed and, mass loss values, after leaching, were recorded. Weight loss values (with respect to leached solid weights) were given in Fig. 1 for SHS experiments carried out under air atmosphere. As stated in the literature, TiC is not dissolved in HCl acid. Therefore, it was expected to solve all compounds without TiC in products through applied HCl leaching step. For the SHS products of experiments conducted with 1.1x C stoichiometry, filter cake weight were very similar in the experiments carried out with 1.1x and 1.2x Mg stoichiometric ratios. But for 1.0x C stoichiometric ratios, solid weight values decreased with increasing Mg stoichiometric ratios.
l l.i Mg Stoichiometry
Fig. 1. Weight change of filter cakes after HCl leaching in the SHS experiments conducted under air atmosphere.
After SHS and following leaching experiments obtained powders were characterized by using XRD technique. Bruker D8 Advance X-ray diffractometer was used to examine phases formed in powders. These analyses were performed in XRD apparatus at 35 kV and 40 mA conditions, CuXa radiation (1.54060 A) in the range of 10°-90°. Figures 2 and 3 show XRD patterns of selected SHS products in the experiments carried out under air atmosphere. In both patterns, TiC phases were detected after leaching. It was predicted that amount of TiC phase will be enhanced in the experiments which will be carried out under Ar atmosphere to prevent further oxidation
Leached SHS Product
;j mJmJ^jj —JI
SHS Product
........Ai.....—..».... .„..I
40 50 2Theta
Fig. 2. XRD patterns of products in the experiment (TiO2:C:Mg, 1.0-1.0-1.1) under air atmosphere before and after HCl leaching.
Fig. 3. XRD patterns of products in the experiment (TiO2:C:Mg, 1.0-1.1-1.1) under air atmosphere before and after HCl leaching.
ISHS 2019 Moscow, Russia
The present study is an on-going work. Following further studies were planned: SHS experiments under argon atmosphere, optimization of leaching conditions and investigation of effects of mechanical activation on synthesized powders.
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