Reaction joining of SiC ceramics using TiB2-based composites

SiC ceramics were reaction joined in the temperature range of 1450–1800 °C using TiB₂-based composites starting from four types of joining materials, namely Ti–BN, Ti–B₄C, Ti–BN–Al and Ti–B₄C–Si. XRD analysis and microstructure examination were carried out on SiC joints. It is found that the former two joining materials do not yield good bond for SiC ceramics at temperatures up to 1600 °C. However, Ti–BN–Al system results in the connection of SiC substrates at 1450 °C by the formation of TiB₂–AlN composite. Furthermore, nearly dense SiC joints with crack-free interface have been produced from Ti–BN–Al and Ti–B₄C–Si systems at 1800 °C, i.e. joints TBNA80 and TBCS80, whose average bending strengths are measured to be 65 MPa and 142 MPa, respectively. The joining mechanisms involved are also discussed.     

An adaptive extraction of generalized eigensubspace by using exact nested orthogonal complement structure

The contribution of this paper is three-fold: first, we propose a novel scheme for generalized minor subspace extraction by extending an idea of dimension reduction technique. The key of this scheme is the reduction of the problem for extracting the ith (i ≥ 2) minor generalized eigenvector of the original matrix pencil to that for extracting the first minor generalized eigenvector of a matrix pencil of lower dimensionality. The proposed scheme can employ any algorithm capable of estimating the first minor generalized eigenvector. Second, we propose a pair of such iterative algorithms and analyze their convergence properties in the general case where the generalized eigenvalues are not necessarily distinct. Third, by using these algorithms inductively, we present adaptive implementations of the proposed scheme for estimating an orthonormal basis of the generalized minor subspace. Numerical examples show that the proposed adaptive subspace extraction algorithms have better numerical stability than conventional algorithms.     

TWO-CRACK PROPAGATION PATHS IN A FUNCTIONALLY GRADED MATERIAL PLATE SUBJECTED TO THERMAL LOADINGS

Two-crack propagation paths in a ceramic/metal functionally graded material plate (FGP) under one-cycle temperature change of heating and cooling are considered. When the FGP is subjected to thermal shock, a single crack or multiple cracks often initiate on the ceramic surface during the cooling process and propagate in the FGP. Crack paths are influenced by the heating temperature conditions, a compositional profile of the FGP, the fracture toughness, interaction among multiple cracks, and so on. Transient thermal stresses are treated as a linear quasi-static thermoelastic problem for a plane-strain state. The crack paths are treated under fracture mechanics using the finite-element method. The effects of heating temperature conditions, a compositional profile of the FGP, the fracture toughness, and a crack space on the crack propagation pattern are discussed and are shown in figures.     

Development of rapid hygrothermal pasteurization using saturated water vapor

We developed a novel rapid hygrothermal pasteurization (RHP) method using saturated water vapor with a dew point of 100 °C. In the present study, the effects of RHP on microbiological quality and quality attributes such as color changes, firmness and ascorbic acid content on many fresh-cut fruits and vegetables (cabbage, cucumber, carrot, cherry tomato, bell pepper, strawberry, pineapple and melon) were investigated. The RHP was performed within a second by free-falling samples through a cylindrical processing chamber filled with steam. The RHP resulted in a 0.7–2.0 log order reduction in the numbers of naturally inoculated mesophilic bacteria. Furthermore, the RHP induced no significant changes in color and firmness of samples, except on the leafy vegetable, cabbage. Ascorbic acid was also retained approximately 80% and above. These results indicate that the RHP is a clean and effective method for decontaminating mesophilic bacteria on fresh fruits and vegetables with minimal changes in quality.Industrial relevanceIn fresh-cut industry, an effective and risk-free decontamination technology is required for use in place of a conventional method, washing by chlorine that can produce carcinogenic chlorinated by-products. In this study, the rapid hygrothermal pasteurization (RHP) method using saturated water vapor was invented and their ability for applying minimal processing was evaluated. The results showed that RHP, without using chemicals, can reduce microorganism load and preserve quality attributes in many kinds of fresh-cut fruits and vegetables. Therefore, RHP could be used as a novel method, which can be generally applicable to fresh-cut fruits and vegetables in the food industry.     

DRYING AND DEWATERING R&D IN JAPAN

Presently, it has become an urgent and important concern worldwide to reduce the volume of waste and rationally use the waste for electric power generation. Sludge is a dominant part in the family of wastes. Drying of sludge, not only for volume reduction but also for further utilization, is becoming an essential and integral process. On the other hand, as the requirement of new materials production, for example, fine particles of micron or sub-micron scale for advanced materials, some new drying technologies and techniques have emerged. The market-pull may be the direct and active impetus to drying research and development (R&D). In this paper, drying technologies for sludges, fine particles, coatings as well as advanced dewatering are discussed to reflect the “hot” points of drying and dewatering R&D in Japan. And some novel dryers are also presented.     

Simultaneous removal of NO/sub x/, SO/sub x/, and CO/sub 2/ at elevated temperature using a plasma-chemical hybrid process

In previous studies, the authors confirmed that the plasma-chemical combined hybrid process for controlling NO flue gas emission was extremely effective and economical in comparison with the conventional selective catalytic reduction (SCR) system and other technologies. In the present study, we carried out experiments on the simultaneous removal of NO/sub x/ and SO/sub x/ at elevated temperature using the plasma-chemical hybrid process. A series of experiments was performed to quantify all the reaction byproducts such as N/sub 2/O, CO, HNO/sub 2/, HNO/sub 3/, NO/sub 3//sup -/, and SO/sub 4//sup -/ to evaluate the simultaneous NO/sub x/ and SO/sub x/ removal efficiency. The oxidation from NO to NO/sub 2/ without decreasing NO/sub x/ concentration (i.e., minimum reaction byproducts) and with least power consumption is the key for the optimum operation of the plasma reactor. The produced NO/sub 2/ was totally converted to N/sub 2/ and Na/sub 2/SO/sub 4/ with Na/sub 2/SO/sub 3/ or Na/sub 2/S with and without NaOH using the barrier-type packed-bed plasma reactor followed by the packed-column chemical reactor. The NO/sub 2/ reduction was more effective for Na/sub 2/S than Na/sub 2/SO/sub 3/ but produces H/sub 2/S with Na/sub 2/S. For both cases at least five times the stoichiometric amount of chemicals were required for complete NO/sub 2/ reduction. Nearly 100% of NO/sub x/ and SO /sub 2/ and 40% Of CO/sub 2/ simultaneous removal were achieved with less than 5 ppm of N/sub 2/O and CO. The operating cost was less than 1/4 the SCR process. The additional SO/sub 2/ treatment system can be eliminated.     

Determination of potent odorants in apple by headspace gas dilution analysis

Gas chromatography-olfactometry with headspace gas dilution analysis was used to evaluate the odor potencies of volatile compounds in Fuji apple. To improve the resolution of volatile compounds, the dilution analysis was conducted on two types of capillary columns with different polarities. Thirty three and 20 compounds were identified on DB-WAX and DB-5 columns, respectively. Methyl 2-methylbutanoate, isobutyl acetate, ethyl butanoate, ethyl 2-methylbutanoate, isopentyl formate, butyl acetate and hexyl acetate as well as hexanal were important odor contributors in the headspace gas of apple on the basis of high Flavor Dilution (FD) factors. Threshold values-in-air of these compounds were also estimated from the relationships between their FD factors and concentrations. Methyl 2-methylbutanoate and ethyl 2-methylbutanote were considered as the most potent odorants because of their lowest threshold values. In addition, the threshold values-in-air of isopentyl formate, isopentyl acetate and butyl isobutanoate, which have never been reported, were estimated at 0.149, 1.95 and 0.00607 μl/l, respectively.