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The in situ SiC resistance to oxidation and corrosion resistance studies with corundum -based materials

Author: GuXiaoLei
Tutor: ZhongXiangChong
School: Zhengzhou University
Course: Materials Science
Keywords: in-situ SiC Al2O3 based materials oxidation resistance corrosion resistance
CLC: TQ175.1
Type: Master's thesis
Year: 2009
Downloads: 22
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Abstract

In-situ SiC bonded Al₂O₃ based materials are prepared by using bauxite based corundum （as aggregates）, fused corundum （as fines）, ultra fineα-Al₂O₃ and silicon powder as starting materials and fired at 1450℃in carbon embedded condition. The physical properties, high temperature mechanical properties, oxidation resistance and corrosion resistance have been studied. The effects of SiC, SiAlON and Al addition on the phase composition, microstructure and properties of in-situ SiC bonded corundum based materials have been discussed in this thesis. The results indicated that:（1） When the silicon powder is added into Al₂O₃ based materials, after forming and firing at 1450℃for 3 hours in carbon embedded condition, the specimens are well sintered. Si reacted with CO and N₂ to in-situ formed fibrous or granular SiC and SiAlON. The sintering mechanism of the composites is nonoxides bonded reaction sintering. These composite materials possess high hot temperature strength and good thermal shock resistance, the hot modulus of ruputure （HMOR） at 1400℃is 9～12MPa; the residual strength ratio after one thermal shock atΔT=1100℃（water cooling） is 35～65% and residual strength is 10.8～18.8MPa.（2） On the basis of 2～8% Si addition, 5% SiC and 5% SiAlON addition can increase HMOR and TSR. SiC addition would contribute to increase in TSR noticeably and SiAlON addition would contribute to increase in HMOR. When 5% Si and 1～3% Al are simultaneously addition, HMOR increases noticeably （maximum 21.0MPa） and TSR is relatively good.（3） The in-situ SiC bonded Al₂O₃ baesd materials exhibit good oxidation resistance, and the oxidation resistance performance was improved at 1000℃and 1500℃along with the addition of Si. The oxidation resistance at 1500℃is better than that of at 1000℃, it is because oxidation productions, SiO₂ and Al₂O₃, of non-oxide materials formed dense mullite protective layer at 1500℃, which inhibite the penetration of O₂. On the basis of adding 5% Si, the oxidation resistance would be improved slightly with further addition of Al.（4） The composite materials exhibit good corrosion resistance at 1500℃, the thickness of corrosion layer is less than 2.6mm. On the basis of adding 2～8% Si, the corrosion resistance would be improved obviously with further addition of 5% SiC andβ-SiAlON, because of the increased amount of nonoxide. The thickness of corrosion layer is less than 1.0mm. On the basis of adding 5% Si, the corrosion resistance would be improved slightly with further addition of 1～3% Al. The thickness of corrosion layer is decreases from 2.5mm to 1.9mm.（5） The corrosion mechanism is: SiC and SiAlON reacted with O₂ and the production were SiO₂ and Al₂O₃. CaO reacted with SiO₂ and Al₂O₃ to form CAS2, then the matrix was corroded because the melting point of CAS2 is very low, CaO reacted with Al₂O₃ grains to form CA₆, and the corrosion retarded because of the high melting point of CA₆. Viscosity of slag increased because of CaO consumed quickly, then the corrosion and penetration ability of slag were rapidly decreased. There were certain amount nonoxide materials in the penetration layer, they existed in the hole and blocked the entrance of slag penetrating. With further addition of Si, Al, SiC or SiAlON, nonxides content increases in the matrix, so the corrosion resistance is improved obviously.

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