Hydrothermal Corrosion of Alumina Ceramics

The corrosion behavior and strength degradation of alumina ceramics with 99%, 99.9%, and 99.99% Al₂O₃ were studied in water at 300°C and 8.6 MPa for 1 to 10 d. The weight loss in alumina ceramics was mainly attributed to the dissolution of SiO₂ and Na₂O grain-boundary impurities. Intergranular corrosion proceeded in the alumina ceramics by preferential attack at the grain boundaries. The extent of the strength reduction for corroded alumina ceramics was related to the impurity level in the alumina ceramics.     

TARGET YIELDS AND HYDROGEN CONSUMPTION IN BROWN COAL LIQUEFACTION

A simple mechanistic model for brown coal liquefaction has been developed and used in conjunction with data from PDU operation to examine the factors which contribute to hydrogen consumption. It is found that after allowing for hydrogen generation requirements, the maximum achievable refined product yield from Morwell brown coal ((ssuming a naphtha/middle distillate ratio of 5:6 together with refined product H/C ratios of 1.8 for naphtha and 1.5 for middle distillate) is 46 - 48%, corresponding to a hydrogen consumption of 6.6 - 7.6%. Alternatively, if consideration of hydrogen generation is excluded (as in pilot plant operation), the maximum yield would be around 54%, corresponding to 6.6% net hydrogen consumption. These results suggest that an aim of maximizing product yield by decreasing Cl-C4 gas formation may not be as desirable as at first thought.     

Transient and steady state crack growth kinetics for stress corrosion cracking of a cold worked 316L stainless steel in oxygenated pure water at different temperatures

The stress corrosion cracking (SCC) growth kinetics for a cold worked 316L stainless steel was continuously monitored in high purity water at different temperatures and dissolved oxygen (DO) levels under a K (or K_max) of 30 MPa m^0.5. The total SCC test time was more than 8000 h to make sure the steady state crack growth rate under each test condition could be reached. Crack growth rate (CGR) increases with increasing temperature in the range 110-288 °C. A typical intergranular-cracking mode is identified. Depending on the previous test condition, especially the temperature, three kinds of crack growth kinetics, i.e., increasing with testing time then becoming steady, being constant during the whole period, or decreasing with test time then becoming steady, are identified and discussed. Time-dependent and testing history-dependent crack growth modes were confirmed in two series of tests in 2 ppm DO and 7.5 ppm DO pure water. The apparent activation energies are calculated and compared with other data in different environments under different applied loading levels for understanding the cracking mechanism.     

Preparation of Tubular Silica-Glass Membranes with Thin Silica Layers by Sputtering, Using the Novel Sputtering Apparatus for Tubular Supports

Tubular SiO₂-glass membranes with thin, dense SiO₂layers on porous glass supports were prepared via sputtering, using the novel sputtering apparatus for tubular supports. This apparatus had a holder for tubular supports and a rotation mechanism. The sputtering conditions of the membranes were investigated. A support temperature of 573 K was determined to be the best among the temperatures that were selected in our experiments. Scanning electron microscopy observations showed that the membrane surfaces became smooth as the sputtering time increased and had no cracks. The permeances of helium, nitrogen, and CO₂were measured at a temperature of 373 K. The permeances for the membranes were on the order of 10^-9 molm^-2s^-1Pa^-1 (10^-5 cm³(STP)cm^-2s^-1(cm Hg)^-1). The ratio of the permeances of helium to nitrogen was similar to the theoretical Knudsen value. These values were much lower than the values that were expected from the dense SiO₂glass. This phenomenon was considered to be attributable to the presence of microcracks during the sputtering deposition.     

Nondestructive inspection of thermal barrier coating of gas turbine high temperature components

A thermal barrier coating (TBC) is applied to high‐temperature components in gas turbines, and consists of a ceramic topcoat and a metallic bondcoat. Various kinds of TBC degradation and damage occur in high‐temperature components during service, such as topcoat thinning, topcoat delamination, and formation of a thermally grown oxide (TGO) layer below the topcoat, each of which can be examined using a suitable nondestructive inspection technique. Topcoat thinning can be detected by topcoat thickness measurement using terahertz waves, which are electromagnetic waves in the frequency region between optical and radio waves. The measurement resolution is about 10 μm, which is comparable to microscopic observation of the cross section in destructive inspection. Topcoat delamination can be detected by active thermography, in which the topcoat surface is scanned by a heating laser and the surface temperature distribution is measured by a thermal infrared camera. The combination of temperature peak and residual thermal image detection is effective in eliminating false detection. The TGO layer can be detected using photoluminescence, in which the Cr³⁺ ions included as an impurity in Al₂O₃ are detected. Since delamination tends to occur at locations at which the TGO layer has grown, TGO layer detection provides an effective method to select regions where delamination has occurred or is likely to occur. An inspection flow based on these techniques is proposed, which is expected to aid the establishment of condition‐based maintenance strategies of high‐temperature components. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Study on new GMA welding process with duplex current feeding

Gas metal arc welding (GMAW) under pure argon shielding gas atmosphere (pure argon-GMAW) is suitable to obtain a high-strength and high toughness welded joint. However, it is difficult that pure argon-GMA welding is applied practically welding structure because of arc instability. In order to perform stable pure argon-GMA welding, duplex current feeding GMAW (DCF-GMAW) has been developed. The DCF-GMAW consists of primary GMA welding current and secondary welding current by constant-current power resource. DFC-GMAW can feed larger current near wire tip. This effect makes that weld penetration depth is deeper, weld bead shape is improved using DCF-GMAW.     

Development and characterization of micro-dispersed lacquer

本文利用一种特制的搅拌装置来制备微分散生漆。研究了在不同的搅拌速率和搅拌时间下所获得的生漆微粒子的直径和性能的关系。粒度分布测定表明,经过60分钟且每分钟240转搅拌处理的生漆,其粒子直径分布最窄,平均为0.194微米。凝胶色谱(GPC)分析显示生漆中的寡聚体增加的同时单体的百分含量减少了,意味着在搅拌的过程中发生了聚合反应。另外,微分散生漆的粘度、干燥成膜时间、膜亮度、膜颜色、膜光泽以及耐紫外线等特性也作了深入的探讨。     

Optical and adhesive properties of composite silica-impregnated Ca-α-SiAlON:Eu2+ phosphor films prepared on silica glass substrates

The compaction of a Eu-doped Ca-α-SiAlON phosphor powder was performed by electrophoretic deposition (EPD). The effect on the adhesion and optical properties of the silica precursor as both a binder of the powder and a filler of the air voids were evaluated. The adhesion of the silica impregnated composite film to the silica glass substrate was characterized by the tape test. The improvement of the external quantum efficiency was confirmed from the PL spectra measurement after the silica impregnation. The temperature dependence of the external quantum efficiency was also investigated in order to discuss the advantage of using the silica precursor as a binder for high-brightness LED applications.     

Measurement and correlation of the solid-liquid-gas equilibria for carbon dioxide + normal chain saturated aliphatic hydrocarbon systems

The pressure p-temperature T projections of solid-liquid-gas (S-L-G) three-phase coexistence lines for the carbon dioxide + tetradecanoic acid (C₁₄H₂₈O₂) system, the carbon dioxide + hexadecanoic acid (C₁₆H₃₂O₂) system, and the carbon dioxide + 1-hexadecanol (C₁₆H₃₄O) were measured by the first melting point method in which the initial appearance of the liquid phase was observed. The profiles of the p-T projections of the S-L-G lines for the carbon dioxide + acid systems are similar to each other, the S-L-G equilibria for the carbon dioxide + acid systems are, however, different from that for the carbon dioxide + 1-hexadecanol systems. The experimental p-T projections of the S-L-G lines were also correlated by the Peng-Robinson equation of state and the van der Waals type mixing rules with two binary interaction parameters introduced into attraction term and size terms, respectively. The present model gave good correlation results for all of the experimental S-L-G lines with maximum average absolute relative deviations of 0.075% for the carbon dioxide + tetradecanoic acid system, 0.14% for the carbon dioxide + hexadecanoic acid system and 0.28% for the carbon dioxide + 1-hexadecanol system, respectively.