Effects of solute ion and grain size on superplasticity of ZrO2 polycrystals

The deformation of ZrO₂ polycrystals containing 2 to 8 mol% Y₂O₃ or 12 mol% CeO₂ were investigated by uniaxial tension and tensile creep tests at elevated temperatures. It was found that there were two deformation mechanisms. The stress exponent was close to 2 for the finegrained materials (less than 1 m), but the exponent decreased with increasing grain size. This behaviour was analysed using a model based on grain-boundary sliding with diffusion accommodation, in which the diffusion creep controlled by interface-reaction and that controlled by diffusion of cations were incorporated. The diffusion coefficient of cations was greatly affected by the concentration of the solute ions. It was observed that there was a negative correlation between interface-reaction rate and Y₂O₃ concentration.     

Dynamic Evolution of Grain-Boundary Films in Liquid-Phase-Sintered Ultrafine Silicon Carbide Material

Spatially resolved electron energy-loss spectroscopy (EELS) analysis revealed a dynamic evolution of grain-boundary (GB) films in a liquid phase (Al₂O₃–Y₂O₃–CaO) sintered β-SiC, which had been deformed both in tension and in compression. An effective chemical width was measured from the oxygen segregation to GBs. Significant increase of Al content in GB films was correlated to devitrification of amorphous pockets to form YAG during both deformations. This brought Y into and expelled Al from the pockets. The extra Al was pushed into GBs to form alumina-based films. Al-Y interdiffusion between GB films and pockets is related to deformation time, indicating a constant and limited interdiffusion rate. This evolution of GB films demonstrated that the dynamic process equilibrated these intergranular regions and phases. GB sliding and interdiffusion among intergranular regions were common mechanisms for both deformation modes. Fracture was mainly caused by YAG formation.     

An Optically Isolated High‐Performance Servo Network in FA Systems for Total High Productivity

In recent years, the reduction of total cost of ownership (TCO) from system architecture to start‐up, operation and maintenance has risen rapidly with the demand for factory automation (FA). But due to the complexity and combination of functions of machines and devices, and to progress in meeting high‐speed and high‐accuracy demands, networking of controllers and amplifiers has come into use. However, conventional servo networks have had various problems in TCO reduction. The servo network proposed in this paper can obtain position and speed information from counterpart amplifiers in the synchronous control by communication between amplifiers, which is conventionally unattainable. Compared with the conventional system, high‐speed, high‐accuracy operation can be realized with the new synchronous compensation control utilizing data transferred between amplifiers, and improvements in operating productivity were verified with an actual machine. Conventional systems used multiple electrical signals, but the new network realizes optical communication over only a single pair of optical cables using optically isolated circuit technology, and it has also proved effective for increasing productivity in the setup and maintenance.     

Effect of bonding conditions on the bonding strength in an aluminum bonding using ultrasonic vibrations and high-frequency induction heating in an atmosphere

ABSTRACT

The needs of aluminium joints have grown in recent years. However, as aluminium forms strong oxide layers on the surface in an atmosphere, joining of these materials is difficult. This is why we conceived a new atmosphere solid-phase bonding method that uses high-frequency induction heating and ultrasonic vibration. The effects of ultrasonic vibration and bonding conditions on this new bonding method were investigated. As a result, we were able to confirm the efficacy of ultrasonic waves on bonding. The bonding mechanism of new bonding method was also clear.     

Sintering behavior of Al2TiO5 base ceramics and their thermal properties

Sintering behavior of Al₂TiO₅ without and with various additives and the thermal properties of the sintered material—thermal expansion and decomposition—were investigated. The precursors of Al₂TiO₅ powders were prepared by homogeneous precipitation and coprecipitation. Sintering of pure Al₂TiO₅ gave a fine grained-structure at 1300°C, but resulted in large-grained and cracked microstructures at 1400 and 1500°C. Addition of ZrO₂ or BaO gave fine-grained microstructures with a small increase in thermal expansion. Addition of ZrO₂, BaO or ZrSiO₄, especially ZrSiO₄, was effective in suppressing the thermal decomposition of Al₂TiO₅ at 1100°C. ©     

New Insights into Additive Structure Effect on Crystal Agglomeration of L‐Valine

Specific small amounts of amino acids caused agglomeration of L‐valine (L‐Val) crystals during evaporative crystallization from aqueous solutions. The agglomeration of L‐Val occurred only under acidic condition when guest amino acids satisfied several conditions. Only L‐form amino acids that have carboxylic acid groups and sufficiently long alkyl chain in the side‐chains could induce agglomeration of L‐Val. The length of alkyl chain in the side‐chains controls the degree of agglomeration. Data indicated only 0.5 wt % of L‐2‐aminoadipic acid, which has a similar chemical structure to L‐glutamic acid (L‐Glu), produced the large agglomerates > 1000 μm. The particle size was ～ 500 μm when using the same amount of L‐Glu. Based on the results from previous tests and this paper, the whole mechanism for the L‐Val agglomeration in the presence of specific guest amino acids has been revealed.     

GAS PERMEANCE BEHAVIOR AT ELEVATED TEMPERATURE IN MESOPOROUS ANODIC OXIDIZED ALUMINA SYNTHESIZED BY PULSE-SEQUENTIAL VOLTAGE METHOD

Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H₂ permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H₂/N₂ permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H₂/N₂ permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H₂ permeance and the H₂/N₂ permselectivity of the amorphous silica membrane on the block type were 1.1 × 10^?7 mol/m² · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.     

Viable utilization of polycarbonate as a phosgene equivalent illustrated by reactions with alkanedithiols,mercaptoethanol, aminoethanethiol,and aminoethanol: A solution for the issue of carbon resource conservation

Methods for the chemical recycling of polycarbonate (PC) wastes in the forms of bisphenol A (BPA) and cyclic heterocarbonates, such as 1,3‐dithiolan‐2‐one (DTO), 1,3‐dithiane‐2‐one (DTA), and cyclic unsymmetric heterocarbonates, were investigated to prove that PC can be utilized as a phosgene equivalent for industrial purposes. Treatment of PC pellets or waste PC compact discs with 1,2‐ethanedithiol and a catalytic amount of base (e.g., 1.5 mol % NaOH) in dioxane for a short period at 40°C produced DTO and BPA, both in nearly quantitative yields. The reaction could also be carried out in DTO, which saved the use of conventional solvents. Other cyclic heterocarbonates, that is, DTA, 1,3‐oxathiolan‐2‐one, 1,3‐thiazolidine‐2‐one, and N‐methyl‐1,3‐oxazolidine‐2‐one, were prepared in high yields under analogous conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2959–2968, 2003