Okayama Ceramics Research Foundation

This paper describes the formation mechanism of monophasic Al3BC3 powder with hexagonal plate-like morphology using Al, B4C, and C powders in a stoichiometric ratio. For the synthesis of pure Al3BC3 by the conventional solid-state reaction method, it is important to avoid contamination from the starting powders. Thermogravimetry-differential thermal analysis curves and quantitative analysis by inductively coupled plasma-atomic emission spectroscopy revealed that there was no vaporization of the powder mixture during heating up to 1470 °C in a high-purity argon atmosphere. We found that the phases and Al3BC3 particle morphology after heating at 1800 °C strongly depended on the mixing conditions. In the case of a two-step process (remixing and reheating the sample), particles with random morphology were observed. On the other hand, well-faceted Al3BC3 particles were predominantly formed in a one-step process that involved heating after ball-milling for 24 h.

Al4SiC4 is probably used as non-oxide raw material for high-temperature ceramics. Al4SiC4 was synthesized by using starting materials of metal-carbon, metal-oxide- carbon or carbides. In this paper, Al4SiC4 has been synthesized by using oxides (Al2O3 and SiO2) and carbon as starting materials through carbothermal reduction process. The oxidation properties in air and O2 atmosphere by TG method and the stability of the synthesized Al4SiC4 heated in moisture were investigated. Pure Al4SiC4 phase was synthesized when heating the mixture powder of Al2O3, SiO2 and C (C : Al2O3 : SiO2 = 8 : 2 : 0.8, in molar ratio) at 1700°C for 8h in flowing Ar atmosphere. The synthesized Al4SiC4 powder consists of platelet shape grains with size of 68μm length, 35μm width and 1μm thickness. Al4SiC4 obviously oxidized from 800°C when heated in flowing air or O2 atmosphere. When keeping Al4SiC4 powder in moisture, it was not observed to be reacted with water by XRD and SEM analysis.

Self‐repairing function is observed in carbon‐containing refractory such as MgO–C, Al 2 O 3 –C, and so forth. Non‐oxides such as pure metallic, alloys, carbides, and nitrides are intentionally added to the refractory composition to bring about this function. As a basis of the development of a self‐repairing refractory, the self‐repairing mechanism in the carbon‐containing refractory is described.

In order to develop an ideal material for the nozzle used in steel continuous casting process, the hydration resistance of some CaO-containing complex oxides and CaO-NiO solid solutions were investigated systematically. The hydration resistance of the complex oxides was CT >CZ>CS>CF>CB3BTB2 B>CB2BS>>CB2BF>CB3BA>CAB2B>CaO. CT should be a promising material for the nozzle. A large number of fine secondary-NiOss particles were separated from the CaOss crystal grains in CaO-NiO solid solution and improved the hydration resistance.

The hardening mechanism of refractory patching materials with a phosphate binder was investigated by means of 31P static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Ten refractory patching materials were made of refractory powders of SiO2 and fused alumina and five mixed solutions of phosphoric acid and aluminum biphosphate as phosphate binders. 31P static and MAS NMR spectra were measured of five phosphate binders and twenty soft and hard refractory patching materials, respectively, to reveal the local structure around P atoms. The 31P static and MAS NMR spectra revealed that PO4 tetrahedra in the phosphate binders have no P-O-P linkage between PO4 tetrahedra and that as the patching materials become hard, the ratio of PO4 tetrahedra with bridging oxygens increases, respectively. This result suggests that the hardening of the patching materials is caused by the condensation of the phosphate binder. But the ratio of PO4 tetrahedra with bridging oxygens was not enough to form the network by P-O-P linkage between PO4 tetrahedra. On the basis of these results, the hardening mechanism of refractory patching materials with a phosphate binder is proposed.

Al2O3-coated graphite powder was prepared using ethyl acetoacetate aluminium diisopropoxide through the sol-gel method. The fluidity of the Al2O3-coated graphite powder slurry was studied. The apparent viscosity of a 2mass% Al2O3-coated graphite powder slurry was lower than that of a graphite powder slurry in the range of 25-40mass% solid loading. It is concluded that the fluidity of the Al2O3-coated graphite powder slurry depends on the fraction of free water of the slurry, the degree of dispersion and the wettability by water of the Al2O3-coated graphite powder.

強リン酸中でセレンをハロゲン化物として蒸留する分離捕集法を適用し,還元気化/ICP-AESでカルシウム中の微量セレンの定量を試みた.ハロゲン化物によるセレンの蒸留は,リン酸(15w/v%)-ヨウ化水素酸(2.0w/v%)-亜鉛(0.2w/v%)の溶液系に,所定量の試料(0.5mol dm-3塩酸溶液)を加えて行い,留出液を過塩素酸系の溶液に吸収捕集した.更に吸収液中のセレン(VI)を(IV)に予備還元し,ICP-AESで測定した.本法によるセレンの回収率は,セレン0.005μg cm-3のとき99.0%であり,RSDは2.05%(n=8)であった.又,本法を炭酸カルシウム中(Ca:5000μgcm-3)の極微量セレンの定量に応用したところ,共存イオンの影響が小さく,高精度(2.00±0,05ng g-1)で定量(検出限界:0.5ng g-1)できることが明らかとなった.