Takehiko Hirata

Improvement of the corrosion resistance of alumina–chromia ceramic materials in molten slag

Abstract In the previous study, we found out that the corrosion of ceramic materials in molten slag depended strongly on the viscosity of the slag and the basicity gap between the ceramics and the slag. In this study, we propose experimental equation to predict the corrosion rate of a ceramic material in a molten slag as functions of the viscosity and the basicity gap on the basis of the corrosion tests. Cr2O3–Al2O3 ceramic materials were used for the tests in the SiO2–CaO–B2O3 based model molten slag. The obtained experimental equation is as follows: logΔ D=0.18 ∗ log Δ B−0.55 ∗ log η+C where, ΔD is the depth of corrosion (μm), ΔB the basicity gap between the slag and specimen, η the viscosity of slag (Poise). C is the constant that depends on the conditions of the corrosion. The value is 2.7 for the testing temperature of 1573 K, holding time of 3600 s and rotating speed of specimen of 5.2 cm s−1 within this corrosion test.

Sintering behavior of Cr2O3-Al2O3 ceramics

Abstract We investigated the sintering behavior of Cr 2 O 3 –Al 2 O 3 ceramic materials. In our observation of the isothermal shrinkage behavior of Cr 2 O 3 –Al 2 O 3 ceramic, the activation energy of sintering reaction was measured to be 102 kJ/mol, that is, the near value of the activation energy of diffusion of Al ions in Al 2 O 3 single crystal. Therefore the diffusion of cations is believed to control the sintering behavior of this material. With the addition of TiO 2 , (the compound chosen to accelerate the diffusion of cations) to Cr 2 O 3 –Al 2 O 3 , the sintering behavior was accelerated.

Synthesis of β-Si3N4 particles from α-Si3N4 particles

Abstract This report describes an investigation of the synthesis of β-Si 3 N 4 particles from α-Si 3 N 4 particles. The β fraction of Si 3 N 4 particles was found to depend on temperature, heating time, and the type of crucibles in which the Si 3 N 4 particles were heated. When Si 3 N 4 particles were heated in a crucible made of carbon, most α-Si 3 N 4 particles converted to β-Si 3 N 4 after heating at 2000°C for 90 min in an atmosphere of N 2 of 9 kgf/cm 2 . The morphology of the resulting β-Si 3 N 4 particles appeared as a whisker shape. When Si 3 N 4 particles were heated in a crucible made of boron nitride, most α-Si 3 N 4 particles converted to β-Si 3 N 4 after heating at 2000°C for 480min in an atmosphere of N 2 of 9kgf/cm 2 . The resulting morphology was equiaxed. It is suspected that the transformation occurs via the gas phase and is affected by the partial pressure of oxygen in the atmosphere.

Influence of impurities in Al2O3 ceramics on hot corrosion resistance against molten salt

Abstract This report describes an investigation of the influence of impurities of Al2O3 on the hot corrosion resistance against V2O5–Na2SO4 molten salt. Thickness of damage zone in Al2O3 ceramics whose purity is high depends on the holding time linearly. On the other hand, thickness of damage zone in Al2O3 whose purity is relative low depends on square root of holding time. In the impurities, SiO2 affected the corrosion rate of Al2O3 especially. Grain boundaries are suffered from hot corrosion. SiO2 would influence the diffusion rate of corrosive elements through grain boundaries and the corrosion rate.