Takeshi Shiono

On the fracture toughness of polycrystalline alumina measured by SEPB method

Abstract Fracture toughness (KIC) of a polycrystalline alumina was evaluated using a single edge precracked beam (SEPB) method. A Knoop indentation-induced microcrack was introduced into a bend bar specimen, and then a sharp pop-in precrack was developed by applying the bridge loading technique. The precrack length (a/W) was varied by changing the indentation load and/or the support groove width of the anvil. The precracked specimens were fractured by three-point bending under a cross-head speed of 0·5 mm/min at room temperature. KIC values of a polycrystalline alumina were dependent on precrack length for a W . The dependence was discussed in terms of residual stress around the indentation-induced crack and crack mouth opening displacement (CMOD).

Effect of the preparation condition on the properties of titania-silica derived from tetraisopropyl titanate(IV) and tetraethyl orthosilicate

Titania-silica mixed oxide was prepared by hydrolyzing tetraethyl orthosilicate and tetraisopropyl titanate(IV) with a mixture of ethanol and 0.01 N aqueous acetic acid. Surface Ti content, BET surface area, and the number of acid sites increased with an increase in 0.01 N aqueous acetic acid. Thus hydrolysis of both alkoxides occurred simultaneously with a large amount of the acetic acid solution, and there was extensive interaction between TiO2 and SiO2 phases. With small amount of 0.01 N aqueous acetic acid, however, titanium hydroxide was first formed and, then, it was covered with the silica phase produced in a later stage of the hydrolysis. Increase in the acetic acid solution also led to the formation of a large amount of tetrahedral Ti species, which were active for the epoxidation of oct-1-ene usingt-butyl hydroperoxide as an oxidant.

Preparation of Inorganic Consolidated Body Using Aluminium Hydroxide Mechanically Activated by Dry Milling

Aluminium hydroxide (Al(OH)3) was mechanically activated by dry milling. In order to develop an inorganic consolidated material, the structure and reactivity of milled Al(OH)3 were investigated and consolidated bodies were prepared using the reaction between activated Al(OH)3 and a potassium silicate solution. Milling up to 1 h apparently reduced the grain size and promoted amorphization, although milling longer than 2 h did not give a significant physical change. Milled Al(OH)3 directly transformed to χ-Al2O3 around 270°C. The transformation temperature decreased with increasing milling time. The remarkable enhancement of the reactivity was attained. The reactivity of Al(OH)3 milled for 2 h improved 1000 times more than that of as-received Al(OH)3. The preforming paste, prepared with as-received Al(OH)3, could not consolidate at room temperature without drying. On the other hand, for Al(OH)3 milled for 2 h, the preforming paste consolidated in 10 min and the consolidated material showed much better resistance against water than that prepared with as-received Al(OH)3. The possibility of a new inorganic consolidated material was suggested using the reaction between mechanically activated Al(OH)3 and the potassium silicate solution.

Observation of Surface Structure of Kyo-Kawara (Ceramic Material for Roof Component) Fabricated by Traditional Skillful Technique

Kyo-gawara is one of traditional crafts, one of Japanese roof tile made in Kyoto by using traditional techniques. The characteristics of Kyo-gawara is gloss on surface available in “Migaki” process. Migaki process is that craftsman strokes half-dry surface with paddle one by one. Number of products that a craftsman has to finish the process is decided. In previous study, investigation about the relationship between number of times of Migaki process and surface properties of Kyo-gawara cannot be seen [1]. In this study, specimens having different number of time of Migaki process (none, once, twice) were used, surface structure and properties were analyzed, and investigation about the relationship between Migaki process and surface characteristics was performed. Measurement items are surface roughness (Ra), contact angle, water absorption. As a result, surface roughness tended to decrease, and with increase of number of times of Migaki process. From the result of measurement of contact angle and water absorption, it was clarified that Migaki could improve waterproofness.Copyright

Analysis of the bacterial community found in clay wall material used in the construction of traditional Japanese buildings.

Clay wall (also called mud wall in English and tsuchikabe in Japanese) material is used in traditional Japanese buildings. Clay wall material is manufactured by fermenting a mixture of clay, sand, and rice straw. A culture-independent study based on 16s rRNA sequences revealed that Clostridiales of Firmicutes, alpha-, gamma- and delta-proteobacteria of Proteobacteria, and Acidobacterium of Acidobacteria exist in the clay wall material. Of these, we focused on Clostridium and Geobacter and their possible roles in the degradation of the cellulose component of the straw and the reduction of ferric iron in the clay during fermentation.

Optimized method of producing washers of titanium hydride for plasma gun using occluded hydrogen gas

An optimized way of producing washers of titanium hydride for the application to a plasma gun using the occluded gas is presented. The amount of H2 gas (equivalently, gas pressure p) is entirely preadjusted in a gas reservoir of a simple instrument. The temperature T of a furnace is completely feedback controlled. Data show that when p is the order of 1atm, T needs to be higher than about 450°C in order to successfully produce washers of titanium hydride. Results on compressive strength of the loaded washers suggest that an appropriate ratio of atoms of hydrogen to titanium is less than H:Ti∼0.85:1.

Evaluation of Thermal Shock Resistance for Ceramic Materials by Young’s Modulus

When a sudden temperature difference is applied to a brittle material such as ceramics, some cracks will occur in the material and it may fracture in some case. The generated cracks as a fracture origin may cause the strength reduction, so the evaluation of thermal shock resistance is very important for ceramic materials. In the conventional evaluation of the thermal shock resistance (thermal shock fracture temperature, ΔTC), the fracture stress is measured after thermal shock test as a function of temperature difference. For this method, however, many specimens are required to estimate fracture stress by bending test and the variation of the stress is large. In the present study, we tried to specify the temperature of crack initiation by measuring Youngs modulus and fracture stress before and after a thermal shock test with different temperature difference. Polycrystalline alumina with high purity was used for evaluation of thermal shock resistance. The Youngs modulus of all specimens was measured by resonance method. The specimen at the prescribed temperature between 200°C and 600°C, it was quickly put into water to apply thermal shock. The Youngs modulus of specimens after the test was measured and the change in Youngs modulus before and after thermal shock test was evaluated. Further, the specimen after the evaluation was measured the fracture strength. As a result, it was found that Youngs modulus is possible to estimate thermal shock resistance. Further it is also possible to evaluate thermal shock behaviors using only one specimen.

Preparation of Consolidated Body Zeolite from Rice Husk Ash

Rice husks (RHs) are agricultural wastes which include approximately 20 mass% of silica (SiO2). In Thailand, RHs have been applied as fuel for thermal power generation systems and a large amount of ash (Rice husk ash: RHA) was produced. In addition, our research group has reported before that binder-free consolidated zeolite A could be obtained by using SiO2 powder with geopolymer reaction as a humidity conditioning material because zeolite A has been used as desiccant and builder for detergent with low silica content. Moreover, other kind of zeolite with high amount of SiO2 content, such as ZSM-5, was under interest due to its good properties as catalytic activity and a unique pore structure. But, it was not widely utilized because of the difficulty of consolidated body preparation. Therefore, in the present study, the possibility of the usage of RHA as raw materials for consolidated zeolite A and ZSM-5 was investigated for the high-value application of RHA under specific heat treatment condition, molar ratio and preparation technique. After specimens were obtained, XRD analysis and SEM were charactarized for consolidated bodies to confirm cystalline phases and observe microstructure, respectively. Consolidated zeolite A was synthesized with heat treatment above 60°C. The sample heat treated at 60°C for 24 h consisted of homogeneous zeolite A particles with the size smaller than 1 μm. In addition, consolidated ZSM-5 was synthesized with an usual method as TPABr (Tetra propyl ammonium bromide) technique and research method as S.C. (seed crystal) technique. The results showed that although around 10 μm seed crystal was used, around 4~5 μm of ZSM-5 particles were obtained by S.C. technique. This result led to the possibility to use RHA with S.C. technique to synthesize consolidated body and control ZSM-5 particle size.

Fracture Energy and Fracture Toughness of In Situ Calcium Hexaluminate (CA6)-Alumina Monolithic Refractory

One of main raw materials for monolithic refractory is calcium aluminate cement which provides CA6 hexagonal plate-like microstructure with self-toughening properties and fracture resistance. In the present study, in-situ CA6 was formed by using sintered alumina mixing with alumina cement in stoichiometric composition to achieve 100 mass% and 50 mass% of CA6 in alumina monolithic refractory with 2 mass% of silica addition. Samples were fired from 1400-1500°C for 5 h and characterized for physical and mechanical properties. The results showed that both samples could not obtain CA6 content as expected and apparent porosity did not exhibit in the same tendency. However, only proper amount of CA6 content could gain proper amount of apparent porosity which is the main effect of mechanical properties. Especially the formation of CA6 lower than 50 mass% with the presence of low melting phase caused low apparent porosity and led to high fracture toughness and effective fracture energy.

Control of hexagonal plate-like microstructure of in-situ calcium hexaluminate in monolithic refractories

ABSTRACT The self-toughening property of calcium hexaluminate (CaO•6Al2O3, CA6) in engineering ceramics causes a remarkable interest in the in-situ CA6 in monolithic refractory. The determination of significant factors which controls the formation and microstructure of CA6 in monolithic refractory is mainly discussed in this study. Samples were prepared by using calcium aluminate cement and sintered alumina and the chemical composition was fixed at the molar ratio of CaO: Al2O3 = 1:6. In order to evaluate the suitable sintering condition and SiO2 content for CA6 phase formation, the variation of firing temperature and holding time was first modified at 1400–1500°C for 1–5 h. The second factor was done by adding 2–10 mass% of SiO2 into the primary mixture. In comparison, the results were confirmed that high firing temperature at 1500°C provided the highest quantity of CA6 phase and plate-like microstructure. In addition, longer proceeding time contributed to the grain growth of CA6, especially, within 5 h of holding time. SiO2 importantly helped to enhance hexagonal plate-like microstructure due to the ability of ion mobility in low-melting phase of gehlenite but the suitable content of SiO2 should not exceed 2 mass% for the better control ability of CA6 formation and microstructure.