Fabrication Of Porous MoAlB Ceramic And Its High Temperature Oxidation Behavior

Based on the current severe environmental issues,filter materials that can withstand higher temperatures are needed to apply in the field of high-temperature flue gas dust removal.The relevant literature shows that Mo Al B can withstand high temperature corrosion at least 1300℃and has excellent mechanical properties.The purpose of this paper is to fabricate porous Mo Al B materials which can be used in harsh environment.The pore structure parameters,mechanical properties and high-temperature oxidation resistance of Mo Al B materials are deeply studied by various characterization methods.We have also explored the effect of Al content on the microstructure of Mo Al B porous ceramics and pore forming mechanism.Besides,the oxidation kinetics,composition of oxide film and oxidation mechanism of Mo Al B porous materials were investigated.The specific contents of the work are as follows:Using Mo/Al/B mixed powders as raw materials in the molar ratio of 1:n:1（n is between 1.4 and 1.9,with each increase of 0.1）,porous Mo Al B ceramic was prepared by activation reaction sintering method.The influence of Al content on the phase composition and pore structure of Mo Al B was discussed by means of phase analysis（XRD）,micro-morphology analysis（SEM）,Archimedes principle and pore size tester,and its reaction mechanism was also explored.On the basis of synthesizing pure Mo Al B,the phase transformation process of porous ceramics Mo Al B at different temperature ranges was analyzed by differential thermal analysis（DSC）and phase analysis（XRD）,and the microstructure and pore structure parameters at different sintering temperature ranges were characterized,with emphasis on the pore-forming mechanism of Mo Al B porous ceramics.Foam Mo Al B ceramics with high porosity and arranged pores were fabricated by freeze casting method,and the effects of different solid contents on pore structure and mechanical properties were analyzed.Additionally,after static oxidation weight gain experiment,the phase transformation,oxide film composition,micro-morphology and pore structure parameters of porous Mo Al B materials at 800～1100℃were systematically studied by using multiple characterization methods such as phase analysis（XRD）,X-ray photoelectron spectroscopy（XPS）,energy spectrum analysis（EDS）,scanning electron microscopy（SEM）and pore size tester,and the oxidation kinetics and oxidation mechanism were emphatically explored.The mechanical properties of Mo Al B porous ceramics were examined by tensile test,and the thermal shock resistance of Mo Al B porous ceramics was also tested.The experimental results show that:（1）Pure MoAlB was successfully fabricated at 1000℃by activation reaction sintering technology according to the molar ratio of Mo/Al/B of 1:1.7:1.（2）The porosity,pore size and permeability of porous Mo Al B ceramics gradually increase with an increasement of Al content,which can effectively regulate the pore structure parameters of porous Mo Al B materials through the control of Al content.（3）Foam Mo Al B ceramics with unique pore structure were successfully prepared by freeze casting.When the solid content is controlled at 12.5～20 vol%,the porosity is limited at 82～88%,and the compressive strength is maintained at 2.8～14.3MPa.（4）Porous Mo Al B has good mechanical properties and is easy to process and shape,and its tensile strength can reach 55.8 MPa at room temperature,and after cyclic oxidation at 1000℃for 50 hours,the tensile strength is 50.6 MPa.（5）The oxidation experiment shows that porous Mo Al B ceramic has excellent oxidation resistance.After50 hours of cyclic oxidation at 1000℃,the oxidation rate of Mo Al B porous materials reaches 37.31 mg²·cm^-4·h^-1,the open porosity is 36.4%,and the air permeability is 72.1m³·m^-2·kpa^-1·h^-1.