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Softening Temperature (softening + temperature)
Selected AbstractsCrack-Healing Behavior of Liquid-Phase-Sintered Silicon Carbide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Young-Wook Kim Crack-healing behavior of liquid-phase-sintered (LPS) SiC ceramics has been studied as functions of heat-treatment temperature and crack size. Results showed that heat treatment in air could significantly increase the indentation strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the softening temperature of an intergranular phase in each material. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the indentation strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to ,200 ,m. In addition, a simple heat treatment of SiC ceramics sintered with Al2O3,Y2O3,CaO at 1100°C for 1 h in air resulted in even further improvement of the strength, to a value of 1054 MPa (,150% of the value of the unindented strength). Crack closure and rebonding of the crack wake due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in LPS-SiC ceramics. [source] Characterization of gelatin nanofibers electrospun using ethanol/formic acid/water as a solventPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 2 2009Hsin-Chieh Chen Abstract Gelatin nanofibers were prepared via electrospinning using aqueous solutions of formic acid and ethanol as the solvent instead of cytotoxic solvents. The resulting mat was further crosslinked with glutaraldehyde (GTA). The influence of the storing time on the viscosity and gel point of the solution was investigated. The gelatin nanofibers were examined using a field emission scanning electron microscope (FESEM) for the fiber size and morphology. The lowest diameter of gelatin fiber (85,nm, without beads) was achieved when the gelatin concentration was 20,wt% and electrospinning was conducted with a voltage of 20,kV over a distance of 10,cm at ambient temperature. The results from differential scanning calorimetry (DSC) showed that the softening temperature of gelatin nanofibers crosslinked with GTA was elevated. In addition, GTA-crosslinked gelatin nanofibers exhibited cell compatibility for mouse mesangial cells (CRL 1927). Copyright © 2008 John Wiley & Sons, Ltd. [source] Poly(triarylamine): Its synthesis, properties, and blend with polyfluorene for white-light electroluminescenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2007Hung-Yi Lin Abstract A new high-molecular-weight poly(triarylamine), poly[di(1-naphthyl)-4-anisylamine] (PDNAA), was successfully synthesized by oxidative coupling polymerization from di(1-naphthyl)-4-anisylamine (DNAA) with FeCl3 as an oxidant. PDNAA was readily soluble in common organic solvents and could be processed into freestanding films with high thermal decomposition and softening temperatures. Cyclic voltammograms of DNAA and PDNAA exhibited reversible oxidative redox couples at the potentials of 0.85 and 0.85 V, respectively, because of the oxidation of the main-chain triarylamine unit. This suggested that PDNAA is a hole-transporting material with an estimated HOMO level of 5.19 eV. The absorption maximum of a PDNAA film appeared at 370 nm, with an estimated band gap of 2.86 eV from the absorption edge. Unusual multiple photoluminescence maxima were observed at 546 nm, and this suggested its potential application in white-light-emission devices. Nearly white-light-emission devices could be obtained with either a bilayer-structure approach {indium tin oxide/poly(ethylenedioxythiophene):poly(styrene sulfonate)/PDNAA/poly[2,7-(9,9-dihexylfluorene)] (PF)/Ca} or a polymer-blend approach (PF/PDNAA = 95:5). The luminance yield and maximum external quantum efficiency of the light-emitting diode with the PF/PDNAA blend as the emissive layer were 1.29 cd/A and 0.71%, respectively, and were significantly higher than those of the homopolymer. This study suggests that the PDNAA is a versatile material for electronic and optoelectronic applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1727,1736, 2007 [source] Aromatic polybenzoxazoles containing ether,sulfone linkagesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2001Sheng-Huei Hsiao Abstract A series of poly(o -hydroxy amide)s having both ether and sulfone linkages in the main chain were synthesized via the low-temperature solution polycondensation of 4,4,-[sulfonylbis(1,4-phenylene)dioxy]dibenzoyl chloride and 4,4,-[sulfonylbis(2,6-dimethyl-1,4-phenylene)dioxy]dibenzoyl chloride with three bis(o -aminophenol)s including 4,4,-diamino-3,3,-dihydroxybiphenyl, 3,3,-diamino-4,4,-dihydroxybiphenyl, and 2,2-bis(3-diamino-4-hydroxyphenyl)hexafluoropropane. Subsequent thermal cyclodehydration of the poly(o -hydroxy amide)s afforded polyethersulfone benzoxazoles. Most of the poly(o -hydroxy amide)s were soluble in polar organic solvents such as N -methyl-2-pyrrolidone; however, the polybenzoxazoles without the hexafluoroisopropylidene group were organic-insoluble. The polybenzoxazoles exhibited glass-transition temperatures (Tg) in the range of 219,282 °C by DSC and softening temperatures (Ts) of 242,320 °C by thermomechanical analysis. Thermogravimetric analyses indicated that most polybenzoxazoles were stable up to 450 °C in air or nitrogen. The 10% weight loss temperatures were recorded in the ranges of 474,593 °C in air and 478,643 °C in nitrogen. The methyl-substituted polybenzoxazoles had higher Tg's but lower Ts's and initial decomposition temperatures compared with the corresponding unsubstituted polybenzoxazoles. For a comparative purpose, the synthesis and characterization of a series of sulfonyl polybenzoxazoles without the ether group that derived from 4,4,-sulfonyldibenzoyl chloride and bis(o -aminophenol)s were also reported. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2262,2270, 2001 [source] | ||||||||||