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Phase Evolution (phase + evolution)
Selected AbstractsPhase Evolution in Heat-Treated Si3N4 with Additions of Yb2O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Gang Feng Guo The heat treatment of silicon nitride (Si3N4) ceramics with additions of 8, 12, and 16 wt% Yb2O3 was carried out at different temperatures and the evolution of grain boundary (GB) phase was investigated systematically by X-ray diffraction (XRD) as well as scanning electron and transmission electron microscopic analyses. XRD results reveal that the extent and the ease of GB crystallization increase with increasing the Yb2O3 content, and that high heat-treatment temperatures in general favor crystallization of the quaternary compounds such as the Yb4Si2O7N2 phase. These results provide an insight into the GB phase evolution in the Yb-system Si3N4 ceramics subjected to a postsintering heat treatment. [source] Phase Evolution During Formation of SrAl2O4 from SrCO3 and ,-Al2O3/AlOOHJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2007Yu-Lun Chang Through the execution of experimental investigation, thermogravimetry, X-ray diffractometry, Fourier transform-infrared spectrometry, transmission electron microscopy, and energy-dispersive spectrometry, a variant reaction mechanism model was proposed for the solid-state reaction between SrCO3 and Al2O3/AlOOH for formation of SrAl2O4 material. The solid-state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO3 from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO3 and alumina. Conversely, at temperatures higher than that, the solid-state reaction is dominated by the diffusion of Al3+ ions into the SrCO3 lattice. In this mechanism, two metastable species, hexagonal SrCO3 and hexagonal SrAl2O4, were observed. The activation energies of SrCO3 decomposition in the solid-state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ,130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO3 decomposition decreases to 34 kJ/mol. [source] Effect of CaF2 and CaO Substituted for MgO on the Phase Evolution and Mechanical Properties of K-Fluorrichterite Glass CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Mehdi Mirsaneh Chain silicate glass ceramics based on K-fluorrichterite (KNaCaMg5Si8O22F2, KFR) have potential for use in restorative dentistry and biomedical applications because they may be cast to shape and, when cerammed, have high biaxial flexural strength and fracture toughness. Excess CaO in canasite-based chain silicate compositions is known to enhance their bioactivity. Therefore, two new glass ceramic compositions have been fabricated with 5 mol% CaF2 (Glass A) and 5 mol% CaO (Glass B) substituted for MgO in the KFR formula unit. The phase evolution of Glasses A and B was studied in detail using X-ray diffraction and transmission electron microscopy. In addition, their mechanical properties were assessed. For Glass A, the fracture toughness (FT=2.66±0.02 MPa·m1/2) and biaxial flexural strength (BFS=227.3±24.5 MPa) were optimized for samples heat treated at 900°C for 4 h. In Glass B, however, the best FT (2.08±0.02 MPa·m1/2) and BFS (217.4±4.4 MPa) were obtained at 950°C. In view of their excellent mechanical properties and castability, Glasses A and B are considered potential candidates for fabrication of custom medical devices in restorative dentistry and moderate load-bearing reconstructive bone surgery. [source] ChemInform Abstract: Modeling of the Phase Evolution in Mg1-xAlxB2 (0 < x < 0.5) and Its Experimental Signatures.CHEMINFORM, Issue 44 2009David A. Andersson Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Thermal Shock Performance of Fine Grained Al2O3 Ceramics With TiO2 and ZrO2 Additions for Refractory Applications,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Christos G. Aneziris Abstract Due to zirconia and titania additions carbon-free fine grained alumina ceramics are produced with superior thermal shock performance. The decomposition of Al2TiO5 in the alumina doped matrix dominates during thermal shock attack and leads to higher strengths in comparison to the as sintered samples after thermal shock. EDX, EBSD, and XRD investigations describe the phase evolution before and after quenching the samples from 950 to 1200,°C in water, respectively. [source] Extension of the C18 stationary phase knowledge by using the carotenoid testJOURNAL OF SEPARATION SCIENCE, JSS, Issue 19 2010Eric LesellierArticle first published online: 16 AUG 2010 Abstract The carotenoid test for octadecylsiloxane-bonded stationary phases used in RPLC was developed some years ago. Additional experiments have now been performed with varied stationary phases. The effect of the bonding density and of the pore diameter on steric selectivity, polar surface activity and hydrophobicity was determined by using YMC series (J'Sphere and Pack ODSA). The test was also extended to estimate the phase evolution of several classical or hybrid silicas. The high loading phases were also studied, as well as the fused core silicas. The effect of the particle size reduction on the three previous phase properties was investigated in the goal to determine in which way this parameter could also modify the chemical properties of the phases. [source] A Simple Oxidation Route to Prepare Pseudobrookite from Panzhihua Raw IlmeniteJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Xi Chen A simple oxidation route to prepare pseudobrookite from Panzhihua raw ilmenite was developed. By oxidizing ilmenite concentrate in air for 3 h at 1473 K, a pure pseudobrookite was achieved. The X-ray diffraction studies showed a possible sequence of the phase evolution with temperature, FeTiO3,FeTiO3+Fe2O3+TiO2,Fe2O3+TiO2+Fe2Ti3O9,Fe2O3+TiO2+Fe2TiO5,Fe2TiO5. The sluggish formation reaction of the target product was ascribed to the low heat treatment temperature. During the phase transformation, the extra Ti atoms from FeTiO3 accommodate into the 4c and 8f sites to form the solid solution (Fe,Ti)2TiO5. AC susceptibility determinations indicated that the as-prepared pseudobrookite was an antiferromagnetic compound and performed the typical anisotropic spin glass behaviors. The decreased phase transition temperature of the prepared pseudobrookite from order to disorder meant a high disorder degree. This oxidation route might be useful to the comprehensive utilization of raw ilmenite, especially for Panzhihua ilmenite in Pan-Xi region of China. [source] Molten Salt Synthesis and Characterization of Potassium Polytitanate Ceramic Precursors with Varied TiO2/K2O Molar RatiosJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Tomas Sanchez-Monjaras Semi-crystalline potassium titanates, useful as precursors to produce composite materials and coatings, were synthesized by thermal treatment of powdered TiO2 in molten mixtures of KNO3 and KOH at 450°,550°C. The products obtained had similar structures of laminar crystals, aggregated in particles of about 3 ,m of n=TiO2/K2O molar ratio in the range 2.8,6.0. The value of n could be regulated by the temperature of synthesis, the weight ratio of [KOH]/[KNO3] in the molten salt mixture, and the number of water washing operations. The reduction of the TiO2/K2O molar ratio increased the contents of H2O in the composition of potassium polytitanate, from 5.3 to 11.4 and from 0.2 to 8.6 (wt%) in the adsorbed and structural forms. The thermal treatment of the potassium polytitanate precursors obtained resulted in dehydration and chemical interaction with unreacted TiO2 at 500°,750°C, amorphization at 750°,850°C, crystallization of K2Ti4O9 (in some cases K3Ti8O17) at 850°,1090°C, and crystallization of K2Ti6O13 at temperatures >1090°C. The mechanisms of the structural transformation and phase evolution were considered as a function of the TiO2/K2O molar ratio in the potassium polytitanate. [source] Phase Evolution in Heat-Treated Si3N4 with Additions of Yb2O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Gang Feng Guo The heat treatment of silicon nitride (Si3N4) ceramics with additions of 8, 12, and 16 wt% Yb2O3 was carried out at different temperatures and the evolution of grain boundary (GB) phase was investigated systematically by X-ray diffraction (XRD) as well as scanning electron and transmission electron microscopic analyses. XRD results reveal that the extent and the ease of GB crystallization increase with increasing the Yb2O3 content, and that high heat-treatment temperatures in general favor crystallization of the quaternary compounds such as the Yb4Si2O7N2 phase. These results provide an insight into the GB phase evolution in the Yb-system Si3N4 ceramics subjected to a postsintering heat treatment. [source] Synthesis, Densification, and Phase Evolution Studies of Al2O3,Al2TiO5,TiO2 Nanocomposites and Measurement of Their Electrical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Vikas Somani Alumina,aluminum titanate,titania (Al2O3,Al2TiO5,TiO2) nanocomposites were synthesized using alkoxide precursor solutions. Thermal analysis provided information on phase evolution from the as-synthesized gel with an increase in temperature. Calcination at 700°C led to the formation of an Al2O3,TiO2 nanocomposite, while at a higher temperature (1300°C) an Al2O3,Al2TiO5,TiO2 nanocomposite was formed. The nanocomposites were uniaxially compacted and sintered in a pressureless environment in air to study the densification behavior, grain growth, and phase evolution. The effects of nanosize particles on the crystal structure and densification of the nanocomposite have been discussed. The sintered nanocomposite structures were also characterized for dielectric properties. [source] Analysis of Phase Coexistence in Fe2O3 -Doped 0.2PZN,0.8PZT Ferroelectric Ceramics by Raman Scattering SpectraJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Man-Kang Zhu In this work, we suggested a method to evaluate quantitatively the effect of doping oxide on the phase coexistence of PbZr1,xTixO3 (PZT)-based ceramics through the analysis of the Raman scattering spectra. Theoretically, the degenerated T3u mode in the cubic phase of PZT will transform as A1(3) and E(4) modes in the tetragonal phase or as rhombohedral (R) modes in the rhombohedral phase below the Curie temperature, which set up the theoretical base to study the phase coexistence in ferroelectric materials. Through separation by fitting of the Raman bands, the shifts and intensities of different Raman vibration modes were determined. A calculation equation representing the phase coexistence was put forward based on the theoretical analysis of the degenerated T3u modes. The results showed that a turning point appears at the Fe2O3 addition of 0.3%. The variation in the electrical properties of the Fe2O3 -doped Pb(Zn1/3Nb2/3)O3 (PZN),PZT ceramics also affirmed the turning point of the phase evolution as the addition of Fe2O3. [source] Influence of Diaspore Seeding and Chloride Concentration on the Transformation of "Diasporic" Precursors to CorundumJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2001Richard L. Smith "Diasporic" precursors derived from sols formed by the controlled hydrolysis of aluminum sec-butoxide in the presence of HCl yielded mixtures of corundum and amorphous alumina when calcined between 500° and 800°C. The fraction of corundum in the calcined products depended on the HCl/alkoxide ratio used during hydrolysis and was maximized at 64 wt% when the molar ratio was 1. Precursors formed from sols hydrolyzed in the presence of HNO3 rather than HCl yielded only amorphous products or transition aluminas when treated below 900°C. The corundum yield of the precursors was enhanced when they were seeded with diaspore (,-AlOOH) crystals. Precursors synthesized with an HCl/alkoxide ratio of 1 and seeded with 7.6 × 1016 diaspore seeds/(mol of Al2O3) were transformed to phase-pure corundum within 12 h at 700°C. Based on studies of the phase evolution of the precursors during calcining, it was concluded that the diaspore seeds promoted conversion by acting as corundum nuclei once they decomposed at ,450°C. [source] The effect of experimental conditions on the detection of spermine in cell extracts and tissuesNMR IN BIOMEDICINE, Issue 2 2010Nicholas G. Spencer Abstract The aim of this work was to investigate the effect of experimental conditions on the visibility of polyamines. In solution the chemical shift of the three groups of peaks (at approximately 1.8, 2.1 and 3.1,ppm) were found to be pH dependent. Relaxation times in aqueous solution at pH 7.0, 298,K and 11.74,T were measured to be: putrescine (T1,=,2.49,s, T2,=,2.07,s), spermidine (T1,=,1.27,s, T2,=,1.05,s) and spermine (T1,=,1.02,s, T2,=,0.82,s). Simple spin-echo sequences could not be used to measure T2 as the spins also experience phase evolution from homonuclear coupling which imposes a modulation on the T2 decay curve. This modulation is eliminated by using CPMG sequences with an echo spacing of <500,µs. Relaxation times for spermine in solution in presence of metal ions and protein showed that metal ions had little effect on T2; however, addition of 15,mg/ml bovine serum albumin reduced T2 of spermine (0.41,s at 298,K and 0.19,s at 277,K) but was not as short as the T2 of the polyamine peak in prostatic tissue (0.03,s at 277,K). The MR visibility of polyamines in prostate cell extracts, PC-3 xenograft (intact as well as extracted) and intact human prostatic tissues were investigated. Polyamines were not detected in methanol/chloroform extracts, but were visible in perchloric acid extracts of prostate tumour cells. No polyamines were detected in the HR MAS spectra of three samples of whole PC-3 xenograft tissue studied. In summary, the chemical shift of polyamine species is pH dependent, while protein binding causes peak broadening and reduction in T2. Perchloric acid extraction improves visibility of intracellular polyamines, but whole tissue polyamines are not seen in xenografts without epithelial/ ductal structure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Study on the phase evolution of (Pb,Cu)Sr2(Y,Ca)Cu2Oz (z , 7)PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006T. Maeda Abstract The formation process of (Pb(1+x )/2Cu(1,x )/2)Sr2(Y1,xCax)Cu2Oz is investigated by means of X-ray diffractometory (XRD), thermal analysis and scanning electron microscopy for nominal compositions of x = 0,0.5. It is shown by XRD measurement that nearly single-phase samples are obtained at x = 0,0.4 by firing at 1000 °C in air for only 1 h. In the heating step, the existence of partial melting state slightly below the firing temperature is clearly observed in the results of differential thermal analysis. It is concluded that this causes the extremely rapid formation of this compound. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||