Synthesis of Compositionally Homogeneous Sr(CuxZn1−x)1/2W1/2O3

A complex perovskite of Sr(Cu _x Zn_{1- x} )_1/2 W_1/2O₃ (SCZW) is synthesized by a new combination of wet and dry processess. Mixed oxides containing Cu²⁺ and Zn²⁺ (CZ) are prepared by the wet process (coprecipitate method). SCZW is obtained by the dry process (mixed-oxide method) from a mixture of CZ, SrCO₃, and WO₃. SCZW has practically no compositional, unlike solid solutions prepared by the conventional dry method. The wet–dry process method is useful because the wet process is applied to only B-site cations having the same valence.     

Fabrication and Microstructure Characterization of Ti3SiC2 Synthesized from Ti/Si/2TiC Powders Using the Pulse Discharge Sintering (PDS) Technique

Ti/Si/2TiC powders were prepared using a mixture method (M) and a mechanical alloying (MA) method to fabricate Ti₃SiC₂ at 1200°–1400°C using a pulse discharge sintering (PDS) technique. The results showed that the Ti₃SiC₂ samples with <5 wt% TiC could be rapidly synthesized from the M powders; however, the TiC content was always >18 wt% in the MA samples. Further sintering of the M powder showed that the purity of Ti₃SiC₂ could be improved to >97 wt% at 1250°–1300°C, which is ∼200°–300°C lower than that of sintered Ti/Si/C and Ti/SiC/C powders using the hot isostatic pressing (HIPing) technique. The microstructure of Ti₃SiC₂ also could be controlled using three types of powders, i.e., fine, coarse, or duplex-grained, within the sintering temperature range. In comparison with Ti/Si/C and Ti/SiC/C mixture powders, it has been suggested that high-purity Ti₃SiC₂ could be rapidly synthesized by sintering the Ti/Si/TiC powder mixture at relatively lower temperature using the PDS technique.     

Characterization of alicyclic polyimides based on cyclobutane ring dianhydride and aromatic diamine

Films of alicyclic polyamic acid and polyimide containing cyclobutane ring in dianhydride moiety and aromatic ring with p- or m-linkages in diamine moiety were characterized by infrared (IR) spectroscopy, dynamic viscoelasticity, differential-scanning calorimetry (DSC), density, and wide-angle X-ray diffraction analyses. Partially and fully imidized polyimides were obtained by varying the imidization temperature, e.g., 150°C, 250°C, and 350°C. It was found from the results of IR spectra, dynamic viscoelasticity, and DSC measurements that the imidization of alicyclic polyamic acid was reduced at about 150°C and needed a higher imidization temperature than aromatic polyamic acid. Alicyclic polyimide with m-linkage in the diamine moiety had a higher density and a much more ordered structure than with p-linkage. © 1994 John Wiley & Sons, Inc.     

Application of pulse discharge sintering (PDS) technique to rapid synthesis of Ti3SiC2 from Ti/Si/C powders

To synthesize Ti₃SiC₂ samples, pulse discharge sintering (PDS) technique was utilized to sinter elemental powders of Ti/Si/C with stoichiometric and off-stoichiometric ratios in a temperature range of 1200–1500 °C. The results showed that high purity Ti₃SiC₂ could not be obtained from the Ti/Si/C powder with molar ratio of 3:1:2, and Ti₃SiC₂ preferred to form at relatively low sintering temperature for a short time. When 5Ti/2Si/3C and 3Ti/1.5Si/2C powders were sintered for 15 min, the TiC content was respectively decreased to 6.4 and 10 wt.% at 1250–1300 °C. The corresponding relative density of the samples sintered from 5Ti/2Si/3C powder was calculated to be as high as 99% at the temperature above 1300 °C. It is suggested that low-temperature rapid synthesis of Ti₃SiC₂ would be possible through the PDS technique, provided that the composition of the starting powders should be adjusted to be off-stoichiometric ratio from 3:1:2.     

Association and physical gelation of ABA triblock copolymer in selective solvent

Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-PtBuA-PMMA) in 1-butanol (PtBuA selective solvent) indicated that PMMA-PtBuA-PMMA chains are molecularly dissolved above 50 °C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and PtBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9-12.0 wt%) revealed that the system was viscous sol state at 60 °C. Drastic increase of shear storage modulus (G′) occurred with decreasing temperature, and at 25 °C, G′ showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G′ indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging PtBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time-temperature superposition along the frequency axis. Just above sol-gel transition concentration (C_gel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging PtBuA chain above C_gel.     

The polymerization and copolymerization of nitroalkyl acrylates and nitroalkyl methacrylates

Nitroalkyl acrylates and methacrylates involving some new compounds were prepared. The homopolymerization of these monomers in toluene and their copolymerization with styrene in acetone were carried out with azobisisobutyronitrile as initiator. The rate of polymerization of the nitroalkyl acrylates showed a correlation with the number of nitro groups situated on the ester side chain. The apparent activation energies of the polymerization were found to be 22.0–27.5 kcal./mole for the nitroalkyl acrylates and about 11.5–13.0 kcal./mole for the nitroalkyl methacrylates. From the reactivity ratios and Q-e values of the copolymerization the following information was obtained. The copolymerization behavior of nitroalkyl acrylates and methacrylates showed an alternating tendency, and these monomers belong to the conjugative monomer groups. On the reactivities of these monomers, the polarity of vinyl group was affected a little by nitro group of ester bond side, and the resonance affected little. These monomers were crosslinked with 2-methyl-2-nitro-1,3-propylene diacrylate. Some of the polymers showed marked improvement in the physical properties of elastomers.     

Reinforcement of polypropylene by cellulose microfibers modified with polydopamine and octadecylamine

Cellulose microfibers (CMFs) having surfaces modified with polydopamine (PDPA) and octadecylamine (ODA) were prepared, and their reinforcing abilities for polypropylene (PP) were investigated. The PDPA coating was made via self-polymerization of dopamine (P-CMF), and subsequent alkylation was conducted by the reaction with ODA (OP-CMF). The modified CMFs exhibited improved dispersibility in the PP matrix due to the reduced hydrophilicity. The OP-CMF/PP composite prepared by batch mixing had a higher tensile modulus compared to that for the pure PP and composites with unmodified CMFs. However, excess alkylation lowered the tensile modulus, and the presence of an optimal degree of alkylation was demonstrated. The CMF/PP-IM composites fabricated by injection molding exhibited improved tensile properties compared to those prepared by batch mixing. Both the tensile modulus and yield stress were increased by increasing the CMF content and improved by the surface modification of the CMFs.     

Steam oxidation resistance of two-layered Ni-Cr and Al APS coating for USC boiler applications

Thermal spray of Ni-Cr and Al coatings was attempted on modified 9Cr-1Mo steel, to evaluate their steam oxidation resistance. Atmospheric plasma spray (APS) coatings of 50Ni-50Cr as undercoat and Al topcoat were attempted with the aim that the pores produced by 50Ni-50Cr undercoat can be filled with Al topcoat during the steam oxidation. The steam oxidized samples evinced the Ni and Cr diffusion towards the Al coating structure and changed the topcoat in to the Ni-Al intermetallics. Though the two-layered coating exhibited an excellent performance against the steam oxidation for the base steel substrate till 3000 h of test, the top layers of the coating underwent significant internal oxidation.     

Impedance-step phenomenon of thin-film GMI element with inclined magnetic stripe domain

An extraordinary impedance-step phenomenon of GMI (giant magnetoimpedance) effect was studied. It is observed for a thin-film GMI element with an inclined magnetic stripe domain. The “inclined stripe domain” means a domain structure that has inclined domain walls against the width direction of the GMI strip. An observation of magnetic domain reveals that a sudden change of domain structure, such as stripe-domain vanishing or occurrence, happens simultaneously with the impedance step. A theoretical consideration, based on the bias-susceptibility model of a single-domain magnetic thin film with uniaxial anisotropy, qualitatively shows that the existence of an inclined stripe domain makes the impedance lower than that characteristic of a single-domain structure.     

IMPROVEMENT OF TYPE IV CRACKING RESISTANCE OF 9Cr HEAT RESISTING STEEL WELDMENT BY BORON ADDITION

Creep lives of high Cr ferritic heat resisting steel weldments decrease due to Type Ⅳ fracture, which occurs as a result of formation and growth of creep voids and cracks on grain boundaries in fine-grained heat affected zone (HAZ). Because boron is considered to suppress the coarsening of grain boundary precipitates and growth of creep voids, we have investigated the effect of boron addition on the creep properties of 9Cr steel weldments. Four kinds of 9Cr3WSCoVNb steels with boron content varying from 4.7×10-5 to 1.8×10-4 and with nitrogen as low as 2.0×10-5 were prepared. The steel plates were welded by gas tungsten arc welding and crept at 923K. It was found that the microstructures of HAZ were quite different from those of conventional high Cr steels such as P91 and P92, namely the fine-grained HAZ did not exist in the present steel weldments. Boron addition also has the effect to suppress coarsening of grain boundary carbides in HAZ during creep. As a result of these phenomena, the welded join