Fabrication of Elongated α-SiAlON via a Reaction-Bonding Process

A reaction-bonding process, which offers low sintering shrinkage and is a low-cost process, was applied to fabricate Y–α-SiAlON ceramics. The green compacts composed of Si, Y₂O₃, Al₂O₃, and AlN were nitrided and subsequently postsintered. Dense single-phase Y–α-SiAlON with elongated grain morphology could be achieved in the specimen postsintered at 1900°C. The material exhibited high hardness (1850 HV10) and high fracture toughness (5.1 MPa·m^1/2).     

Polysoap-induced polymerization of methyl methacrylate and styrene by poly(sodium alkyl 2-hydroxy-3-methacryloyloxypropyl phosphate)s in water

Summary Poly(sodium alkyl 2-hydroxy-3-methacryloyloxypropyl phosphate)s as polysoap induced the radical polymerization of methyl methacrylate and styrene in the absence of an added radical initiator in water at 80°C. The polysoap having a C₁₄ alkyl group showed the highest activity of all tested groups. The generalized initiation mechanism of the spontaneous polymerization in which the micellar aggregation state participates is discussed.     

Densification behaviour and mechanical properties of pressureless-sintered B4C–CrB2 ceramics

B₄C based ceramics composites with 0–25 mol% CrB₂ were fabricated by pressureless sintering in the temperature range 1850°C to 2030°C. The CrB₂ addition enhanced the densification of B₄C due to the CrB₂–B₄C eutectic liquid phase formation. Both a high strength of 525 MPa and a modest fracture toughness of 3.7 MPa m^1/2 were obtained for the B₄C–20 mol% CrB₂ composite with a high-relative density of 98.1% after sintering at 2030°C. The improvement in fracture toughness is thought to result from the formation of microcracks and the deflection of propagating cracks resulting from the thermal expansion mismatch of CrB₂ and B₄C.     

Surface Finishing of Alumina Ceramics by Means of Abrasive Jet Machining

Abrasive jet machining (AJM) is proposed as a new approach to surface finishing of structural ceramics. The effect of AJM on the material removal behavior of a commercially available alumina ceramic, and its effect on mechanical properties, was characterized and compared with identical material subjected to conventional finishing processes. Conventional grinding of the ceramic resulted in a surface that was dominated by intergranular fracture, whereas, during AJM, impact by the abrasives led to material removal in a manner resembling ductile behavior, and the resulting surface appearance was much smoother. A significant improvement in flexural strength was attained, compared with the strength of both the ground and lapped samples, because of an induced compressive residual stress.     

Melting of Silica up to 7 GPa

Melting relations of SiO₂ were determined up to 7 GPa. The triple point of quartz-coesite-liquid is located at 4.5 GPa and 2450°C. The melting curve of coesite has a steep initial slope (150°C/GPa) and reaches about 2700°C at 7 GPa. Densities of the quenched glasses are also reported.     

Thermo-mechanical stability of porous alumina: effect of sintering parameters

Recently, we proposed a two-step heating schedule involving pulse electric current sintering (PECS), a kind of pressure assisted vacuum sintering, and subsequent post-heat treatment in air to fabricate porous alumina support, using commercially available alumina and carbon powders [J. Mater. Res. 18 (2003) 751]. During pressure assisted vacuum sintering, Al₂O₃–C system of low porosity was obtained and in second stage, i.e. during post-heat treatment in air, carbon particles present in the Al₂O₃–C system burnt out to form highly porous Al₂O₃ support. Following our previous brief study, the effects of sintering parameters such as temperature, pressure, and heating rate on the properties of the porous alumina were investigated. The porosity varied between 28 and 38% depending on the sintering parameters. As desired, the pore size distribution did not change with post-heat treatment temperature and hence the mechanical properties as well. It was concurred from this present study that the sintering parameters of PECS greatly influenced pore characteristics and other properties of porous compacts. We admit that the initial composition ratio of powder mixture (Al₂O₃:C) also plays important role on properties such as porosity, pore size, etc. which is beyond the scope of this present study.     

IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias

Recently, one type of thermal-type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature T_c for stable responsivity to temperature. Electric field induced-type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg_1/3Nb_2/3)O₃ (PMN) and Pb(Sc_1/2Ta_1/2)O₃ (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor. This paper describes the sensor properties of electric field induced-type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high-response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced-type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.     

Application of the independent molecule model to the calculation of free energy and rigid-body motions of water hexamers

The stabilities of five water hexamers (cyclic, boat, book, prism and cage structure) in the gas phase were investigated with the independent molecule model. In this model, the position and orientation of each water molecule within the hexamer are characterized with a translational vector and Eulerian angles, and then each molecule can move freely as a rigid body with respect to the others. Force field energy minimization yielded structures for each hexamer. Normal mode analyses were done on the five hexamers. Hydrogen bond strength in the hexamer decreases in the order: boat, cyclic, book, cage and prism. Hydrogen bond lifetimes also decrease in this order. By estimating the internal energy and the vibrational entropy of rigid-body motions, we determined the temperature dependence of the free energy for each hexamer in the range 100–350 K. Free energy of the hexamers increases in the previously mentioned order also. The most stable hexamer is the boat, and the least stable is the prism. The stabilities of the boat and the cyclic are very similar. The more planar hexamers (cyclic and boat) are more stable than the three-dimensional hexamers (cage and prism). Although the experiments of Liu et al. [Nature 381 (1996) 501] were interpreted in terms of a cage cluster, our calculations indicate boat is more likely.     

Accumulation of benzoic acid in suspension cultured cells of Pinus thunbergii Parl. in response to phenylacetic acid administration

The generation and accumulation of both benzoic acid (BA) and its conjugates were induced in suspension cultured cells of Pinus thunbergii by administering either phenylacetic acid (PA), a toxic metabolite of Bacillus cereus (strain HY-3) accompanying the pine wood nematode, or a lyophilized culture supernatant of this bacterium. BA conjugates reached their maximal levels in quantity two days after the administration and then decreased gradually until the 14th day, while BA increased significantly throughout this period. This pattern is similar to that in 3-year-old pine trees treated with PA, suggesting that the pathological reaction of pine tissues to the PA toxin might be involved in the pathogenesis mechanism for the pine wilt disease.