Study On Synthesis Of Ti₂SnC,Ti₂SC Powders And Oxidation Mechanism

A new family of layered ceramic phase MAX(MAX phase,general formula M_n+1AX_n,M is an early transition metal,A is an A-group element and X is either C or N)has attracted much material researchers,because of its the excellent properties of ceramic and metal.The Ti₂SnC and Ti₂SC powders were prepared by self-propagating high-temperature synthesis?SHS?method.The effects of different composition and ratio of different raw materials on the phase composition and microstructure of the composites were studied.The Ti₂SnC was purified by acid.According to the critical conditions introduced by the Semenov's theory of spontaneous ignition,the criterion for evaluating the ignition temperature of the thermal explosion system at a linear heating rate.Applying this criterion,the ignition of the TE synthesis of 2Ti-Sn-C samples at different heating rates were evaluated using non-isothermal DSC.The oxidation behavior of Ti₂SC powder in air atmosphere was studied and its oxidation mechanism was analyzed.The Ti₂SnC powder material was synthesized by self-propagation high-temperature synthesis using Ti/Sn/C powders as raw materials.It can be seen that Ti₂SnC was main phases of the SHS products,with a certain amount of TiC and Sn.When the Sn content increases,the Ti_xSn_y and TiC impurity phases in the material gradually decrease.When the amount of Sn in the raw material is 1.05 mol,the Ti_xSn_y and TiC phases disappear and the lamellar structure of the material becomes more obvious.When the content of Sn is 1.1 mol,the TiC phase appears in the material.Indicating that the appropriate addition of Sn content can promote the synthesis of Ti₂SnC.Meanwhile,the reaction mechanism of 2Ti-Sn-C was studied by DSC curve.According to the critical conditions introduced by the Semenov's theory of spontaneous ignition,the criterion for evaluating the ignition temperature of the thermal explosion system at a linear heating rate.Applying this criterion,the ignition of the TE synthesis of 2Ti-Sn-C samples at different heating rates were evaluated using non-isothermal DSC.And the ignition temperature for isothermal TE is predicted to be602.4?by the multiple linear regression.High-purity Ti₂SnC ceramic powders has been obtained form mixtures of Ti,Sn and Graphite with a mole ratio of 2:1:1 by thermal explosion in vacuum.Indicating that the thermal insulation critical furnace temperature of the 2Ti-Sn-C system obtained by this criterion is true and reliable.While adjusting the molar ratio of Sn in the raw materials,the effects of different raw materials on the phase composition and microstructure were studied.The ternary ceramic Ti₂SC powders were synthesized by self-propagation high-temperature synthesis with different samples from both the Ti-S-C and Ti-S-TiC powder mixtures.The results showed that Ti₂SC was main phase of the product of the Ti-S-C and Ti-S-TiC systems,but a little of TiC and Ti₃S₄ exist in the synthesized sample.The sample only exist Ti₂SC and TiC when the TiC content is 1.05 mol.The reaction mechanism for synthesizing Ti₂SC has been proposed,which implicates that in the Ti-S-C/TiC reaction system,firstly,Ti reacts with S to form Ti-S liquid,then Ti reacts with C to form TiC;liquid Ti-S reacts with TiC to form Ti₂SC.The TiC has been mixed in raw materials which avoid the thermal explosion during Ti₂SC.The isothermal oxidation behavior of Ti₂SC powders synthesized by self-propagation high-temperature synthesis has been investigated at 500-800?in flowing air.The growth of the oxide scales on Ti₂SC from 500?to 800?obeyed a parabolic law.When Ti₂SC was heated in air,it started to oxidize,at 500?.The final product of the Ti₂SC powders oxidized is rutile-Ti O₂ at 800?,and the powders changed from light grey to yellow.The oxidation of product was composed of an outer layer of coarse-grained TiO₂?rutile?,clearly the S and C diffuse out,whether the diffusion is atomic and in the form of SO₂ and CO₂ gas.