Metal silicides are similar to metals in electrical conductivity, high temperature performance, oxidation resistance and compatibility with the production process of silicon integrated circuits. Transition metal silicides can be used for low-resistance gate and interwire, schottky gate and resistance contact. Tantalum silicide preparation method includes: the combustion synthesis (combustionsynthesis, CS) or self-propagating high-temperature synthesis, arc melting method, etc. Combustion synthesis or self-propagating high temperature synthesis is a method for the synthesis of intermetallic compounds by the exothermic reaction of an element/compound. It has the advantages of simple equipment, low energy consumption, short synthesis time, etc. Its main disadvantages are fast reaction speed, difficult process control, easy to exist heterogeneous. The combustion synthesis of tantalum silicide requires preheating to initiate the reaction and realize the synthesis. The arc melting process generally requires a long homogenization time, and the loss of silicon due to volatilization may lead to the formation of some heterophases in the melting process. Plasma spraying technology because of its jet temperature as high as 10000 ℃, the jet velocity of 300-400 – m/s, high temperature melting, rapid solidification and the advantages of the near net shape at an organic whole, and the technology is not restricted by the shape or size, easy to implement its short preparation forming process, gradually developed into a kind of new parts forming technology, has been used to the preparation of some parts. The high purity tantalum silicide powder is used as the raw material for the preparation of tantalum silicide powder by plasma spraying technology. Therefore, how to obtain high purity tantalum silicide powder (without heterophase formation) becomes the key.
Tantalum silicide has high melting point, low resistivity, corrosion resistant, high temperature oxidation resistance and silicon, carbon matrix material has excellent properties such as good compatibility, as the grid material, integrated circuit connection lines, high temperature oxidation resistance coating, etc., in the electric heating element, the field of high temperature structure parts and electronic devices more widely research and application. Examples of its application are as follows:
1) to prepare a silicon nitride – tantalum silicide composite ceramic material. The silicon nitride – tantalum silicide composite ceramic material is composed of the following raw materials by weight: 92-98 parts of silicon nitride powder, 12-15 parts of tantalum silicide powder, 3-6 parts of neodymium powder and 2-5 parts of rhodium oxide powder. Preparation of the present invention silicon nitride – tantalum silicide composite ceramic materials, low porosity, the ceramic material products in the process of working long hours can still maintain good mechanical properties, service life is long, in addition, the invention preparation of silicon nitride – tantalum silicide composite ceramic material fracture toughness is high, to meet the market of silicon nitride ceramics performance requirements of the material is increasing day by day.
2) for tantalum silicide coatings, described methods include using particle size range of 10 to 120 microns, the purity is more than 95 wt % of tantalum silicide powder, using vacuum plasma spraying process or low pressure plasma spray process will tantalum silicide powder spraying in the pretreatment of high temperature resistant surface of substrate material, a quick tantalum silicide coatings, parameters of plasma spraying process is as follows: the plasma gas Ar: 30-50 SLPM; Plasma gas H2:8-18 SLPM; Powder carrier gas Ar: 1.5-5slpm; Spraying distance: 100-350mm; Spraying power: 30-58kw; Powder feeding rate: 8-30g·min-1; Spray pressure: 100-800mbar.
3) preparation of a kind of carbon/carbon composite material base of tantalum silicide/silicon carbide coating on the components of tantalum silicide, silicon carbide, silicon and small amounts of transition metal carbides, its preparation when using secondary embedding method in after grinding and polishing of carbon/carbon composites directly embedding deposition of silicon carbide coating surface, and then in the silicon carbide coatings were deposited by the embedding method of carbon/carbon composite material surface deposition coating preparation of tantalum silicide. The invention can effectively utilize the high-temperature oxidation resistance of tantalum silicide, improve the service temperature of carbon/carbon composite materials, fill the gap in the research of carbon/carbon composite based tantalum silicide coating at home and abroad, and lay a foundation for the future use of carbon/carbon composite materials at higher temperature for a long time in this field.
The preparation of TaSi2 powder includes the following steps: -500 mesh silicon powder and -300 mesh tantalum powder are weighed according to the stoichiometric ratio of TaSi2. In order to obtain high purity products, we need to choose high purity silicon powder and tantalum powder, such as 99.95 or 99.99% purity. The combination of -500 mesh silicon powder and -300 mesh tantalum powder is selected to better mix the silicon and tantalum evenly and surround the tantalum particles with silicon particles, which is conducive to the easier contact reaction between the silicon and tantalum in the subsequent steps of combustion synthesis. The stoichiometric ratio is used to obtain the TaSi2 phase. When -200 or -300 mesh silicon powder and tantalum powder are used, it is difficult to obtain complete single-phase TaSi2 phase powder, and a small amount of Ta5Si3 phase is always available. The use of a smaller powder can make the reaction more complete, but this increases the oxygen content of the powder, which in turn impedes the synthesis. The specific steps are as follows: weighing 23.6 grams of -500 mesh silicon powder and 76.4 grams of -300 mesh tantalum powder; Adding NH4Cl powder, which accounts for 0.5 grams of weight of silicon powder and tantalum powder; The powder ball was grinded to a ratio of 8:1 and the grinding time was 12 hours. The powder after ball grinding was put into the silicon carbide crucible and vibrated on the vibration table until the relative density was 40%. The crucible filled with powder was put into the synthesis furnace, vacuumed and filled with argon. The temperature was raised to 650℃ per minute at 20℃. The tantalum silicide synthesis reaction was ignited by tungsten wire electrification. After cooling, zirconia spheres and cans were broken to obtain the final powder products, which were all tantalum silicide phase by XRD detection.