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Microstructural Examination (microstructural + examination)
Selected AbstractsEffects of Inulin/Oligofructose on the Thermal Stability and Acid-Induced Gelation of Soy ProteinsJOURNAL OF FOOD SCIENCE, Issue 2 2008Y.-C. Tseng ABSTRACT:, Differential scanning calorimetry (DSC) and dynamic oscillatory shear testing were performed to study the influence of inulin (Raftiline® HP-gel and Raftiline® ST-gel) and oligofructose (Raftilose® P95) on the thermal stability and gelation (using glucono-,-lactone [GDL] as a coagulant) of soy protein isolate (SPI) dispersions. Addition of 10% (w/v) inulin/oligofructose or sucrose increased (P < 0.05) the peak denaturation temperatures (Tm) of 7S and 11S soy proteins in SPI dispersion (5%[w/v], pH 7.0) by an average of 1.9 and 2.3 °C, respectively. GDL induced SPI thermal gelation, and the gel rheology was affected by both the pH decline and the specific temperature of heating. Addition of inulin/oligofructose (8%, w/v) improved the gelling properties of preheated SPI dispersion (8%, w/v) coagulated with GDL, showing 14.4 to 45.6% increase (P < 0.05) in gel rigidity (G, value) at the end of heating (81 °C). Microstructural examination revealed a denser protein cross-linking structure and reduced pore sizes in SPI gels containing inulin/oligofructose. In general, inulin was more capable of improving SPI gelation than oligofructose, suggesting that the degree of fructose polymerization in the fructans was of thermal and rheological importance. [source] Alumina Volatility in Water Vapor at Elevated TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Elizabeth J. Opila The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250° and 1500°C, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 ± 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process. [source] Behavior of Silver and Palladium Mixtures during HeatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Terry Garino The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X-ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high-temperature XRD studies on a commercial 20% palladium material with submicrometer-sized particles indicated that an intermetallic phase, most likely Ag3Pd, formed in air between 300° and 400°C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340°C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525°C. No PdO was detected by XRD at 400°C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375°C. When the material was heated in argon for 1 h at 400°C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5,30 ,m) with palladium particles (1,3 ,m) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium. [source] Investigation on the oxidation behaviour of gamma titanium aluminides coated with thermal barrier coatingsMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 7 2008R. Braun Abstract In the present study, the applicability of thermal barrier coatings (TBCs) on ,-TiAl alloys was investigated. Two alloys with the chemical compositions of Ti-45Al-8Nb-0.2B-0.15C and Ti-45Al-1Cr-6Nb-0.4W-0.2B-0.5C-0.2Si were used. Before TBC deposition, the specimens were pre-oxidised in laboratory air or low partial pressure oxygen atmosphere. Yttria partially stabilised zirconia top coats were then deposited using electron-beam physical vapour deposition (EB-PVD). The oxidation behaviour of the ,-TiAl specimens with TBC was studied by cyclic oxidation testing in air at 850 and 900,°C. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). No spallation of the TBC was observed for pre-oxidised specimens of both alloys when exposed to air at 850,°C for 1100 cycles of 1,h dwell time at high temperature. SEM micrographs of the thermally grown oxide scale revealed outer mixed TiO2/Al2O3 protrusions with a columnar structure. The protrusions contained small particles of zirconia and a low amount of about 0.5 at% zirconium was measured by EDS analysis throughout this outer oxide mixture. The TBCs exhibited excellent adherence on the oxide scale. Intercolumnar gaps and pores in the root area of the TBC were filled with titania and alumina. Below the outer columnar oxide scale, a broad porous zone of predominant titania was observed. The transition region between the oxide scale and substrate consisted of a discontinuous nitride layer intermixed with alumina particles and intermetallic phases rich in niobium formed at the nitride layer/substrate interface. When thermally cycled at 900,°C, the oxide scales on the alloy Ti-45Al-8Nb-0.2B-0.15C pre-oxidised in low partial pressure oxygen spalled off after 540 cycles. For the sample with TBC, spallation was observed after 810 cycles. Failure occurred in the thermally grown oxide near the oxide/nitride layer interface. Microstructural examinations revealed again oxide scales with columnar structure beneath the zirconia top coat and good adherence of the TBC on the thermally grown oxides formed at 900,°C. [source] Effect of Varying Quartz Particle Size and Firing Atmosphere on Densification of Brazilian Clay-Based StonewareJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006G. P. Souza Body mixes for stoneware containing a Brazilian red clay, nepheline syenite, and quartz with two different median particle sizes (,2 and 18 ,m) were fired under oxidizing and reducing atmospheres. The densification behavior was followed by dilatometry simulating the firing schedule, as well as by water absorption, linear shrinkage, and bulk density measurements on as-fired specimens. It was revealed that finer quartz led to interconnected pore closure at 1125°C when fired under an oxidizing atmosphere. Densification was systematically related to the uniformity of the compacts in the unfired state. Phase and microstructural examination by X-ray diffractometry, scanning electron microscopy/energy-dispersive spectroscopy (EDS), and transmission electron microscopy/EDS showed that mullite developed more extensively in the stonewares fired in an oxidizing atmosphere, along with cristobalite and haematite, whereas metallic iron was found in stonewares fired under a reducing atmosphere. [source] Positron annihilation study of recrystallization behaviour in Zr2.5%Nb alloyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009S. Mulki Abstract In CANDU reactors Zr 2.5%Nb alloy is used as pressure tube material due to low neutron absorption cross section, a high resistance to corrosion in water, high strength and good creep resistance. The two phase alloy consists of ,-fcc and ,-bcc. The recrystallization behavior of Zr2.5Nb strongly depends on morphology and distribution of second phase. In this study, the material was deformed to 60% and then was recrystallized in , + , region for different duration (i.e. 2 minutes to 14 days at 700 °C). The recrystallized microstructure was characterized by Orientation Imaging Microscopy (OIM). The evolution of microstructure was examined by Positron Lifetime Spectroscopy and Doppler Broadening measurement for each heat treated samples. Results from positron annihilation studies and other microstructural examination have been used to rationalize the recrystallization aspects, defects and ,-phase distribution. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||