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Sintering Conditions (sintering + condition)
Selected AbstractsNormal Sintering of (K,Na)NbO3 -Based Ceramics: Influence of Sintering Temperature on Densification, Microstructure, and Electrical PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2006Yuhua Zhen Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO3,NaNbO3, KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d33 value of 206 pC/N was obtained for the Li- and Ta-codoped KNN ceramics prepared at 1090°C. [source] Textured Microstructure and Dielectric Properties Relationship of BaNd2Ti5O14 Thick Films Prepared by Electrophoretic DepositionADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Zhi Fu Abstract An alternative approach to tailor the temperature coefficient of permittivity (TC,r) of high Q dielectric BaO,Re2O3,TiO2 (Re: rare earth elements) thick films is presented. 10- to 80-µm-thick BaNd2Ti5O14 (BNT) films are fabricated by electrophoretic deposition on Pt foils under different processing conditions. Observed anisotropic grain growth is facilitated by constrained sintering. The increase of the sintering temperature increases markedly the aspect ratio of the grains, decreases the dielectric permittivity and TC,r changes from ,114 to +12,ppm °C,1. By controlling the sintering temperature, near-zero TC,r, high Q thick films can be fabricated with 45,<,,r,<,70. These findings are of technological relevance since they demonstrate that control of substrate constraint and sintering conditions can be used to control grain anisotropy and thus microwave properties of the BaO,Re2O3,TiO2. The thick films facilitate scaling to small device sizes for high frequency operation. Similar observations are expected in other microwave systems thus opening further technological opportunities. [source] Preparation of a Highly Conductive Al2O3/TiN Interlayer Nanocomposite through Selective Matrix Grain GrowthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Xihai Jin An electroconductive TiN/Al2O3 nanocomposite was prepared by a selective matrix grain growth method, using a powder mixture of submicrosized ,-Al2O3, nanosized ,-Al2O3, and TiN nanoparticles synthesized through an in situ nitridation process. During sintering, a self-concentration of TiN nanoparticles at the matrix grain boundary occurred, as a result of the selective growth of large ,-Al2O3 matrix grains. Under suitable sintering conditions, a typical interlayer nanostructure with a continuous nanosized TiN interlayer was formed along the Al2O3 matrix grain boundary, and the electroconducting behavior of the material was significantly improved. Twelve volume percent TiN/Al2O3 nanocomposite with such an interlayer nanostructure showed an unprecedentedly low resistivity of 8 × 10,3,·cm, which was more than two orders lower than the TiN/Al2O3 nanocomposite without such an interlayer nanostructure. [source] Differential Sintering by Improper Selection of Sintering Parameters during Pulse Electric Current SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004D. Doni Jayaseelan Recently, we reported on the retention of fine-grained micro-structure in Al2O3/3 vol% 3Y-ZrO2 composites using the pulse electric current sintering (PECS) technique. It was demonstrated that a high heating rate is beneficial for the retention of fine grains and homogeneous microstructure. As there are few reports on microstructural inhomogeneity and excessive grain growth in compacts densified by the PECS technique, we carried out a series of experiments on monolithic alumina by varying the sintering parameters and discussed the characteristic results. All specimens that were densified under selective sintering conditions attained high density (,99% of the theoretical density) at 1250°3C in > 5 min. The average fracture strength of monolithic alumina was observed to be 741 ± 25 MPa and the fracture toughness was 2.2 MPa.m <1/2, and these were reasoned out to small grains. However, compacts sintered under very low compaction pressure attained ,92%-93% of the theoretical density, and these specimens had undesirable microstructural inhomogeneity owing to differential sintering. Hence, in the present study, we address the problem of differential sintering. [source] Microstructural Evolution of Calcium-Doped ,-AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Arzu Altay Effect of different calcium doping levels on the microstructure of high-purity ,-alumina was studied as a function of sintering time and temperature using scanning electron microscopy (SEM). Microstructural evolution was related to hypothetical calcium excess at the grain boundaries (,Ca) that was calculated assuming zero solubility of calcium in bulk ,-alumina. Under all sintering conditions, grains were uniform in size and equiaxed for low calcium concentrations (<3 Ca atoms/nm2). The grain morphology became elongated when the calcium concentration at the grain boundaries reached calcium excess of ,Ca= 3,3.5 Ca atoms/nm2 in all samples. The average grain sizes of undoped samples were ,10% larger than the average grain sizes of low-calcium-doped samples. This decrease is believed to be due to solute drag effect of segregated Ca impurities on the grain boundary mobility. For the samples that were sintered at 1500° and 1600°C, slablike abnormally grown grains appeared for critical calcium excess concentrations of ,Ca= 4.5,8 Ca atoms/nm2. With abnormally grown grains a dramatic increase in average grain size was observed. However, when the calcium concentration was increased further, above certain calcium excess concentration depending on sintering temperature, a significant decrease in grain size was observed. In contrast to samples sintered at 1500° and 1600°C, when the samples sintered at 1400°C, although the hypothetical calcium coverage exceeded ,Ca= 11 Ca atoms/nm2, only few grains grew abnormally without significantly affecting the average grain size. Observations clearly indicated that calcium impurities caused elongated (slablike) grain morphology when their excess concentrations reached a critical level at the grain boundaries. [source] Grain Growth of ,-SiAlON in the Calcium-Doped SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Ya-Wen Li Two calcium-doped ,-SiAlON compositions (Ca0.6Si10.2Al1.8,O0.6N15.4 and Ca1.8Si6.6Al5.4O1.8N14.2) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from ,-Si3N4 to ,-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of ,-SiAlON. Elongated ,-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the ,-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the ,-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development. [source] Novel repair method for technical enamels based on sol,gel and sol-dispersion coatings,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008S. Benfer The aim of the work presented here is the development of a novel repair method for technical enamels by using chemical nanotechnology. Good adhesion of coatings requires good wettability of the substrate by the repair solution. This was achieved by different pre-treatments of the steel substrates. Low sintering temperatures of the coatings can be ensured by the use of nanoparticle-based systems. Based on liquid metal alkoxides, a colloidal alumina sol and metal salts homogeneous sols with up to seven enamel compounds were prepared. The sols were brush coated onto plain and partly enamelled steel substrates and sintered in a furnace, by inductive heating or an IR emitter. Thin (single layer,,,1µm) crack-free layers were obtained on nearly all substrates independent of the sintering conditions investigated. The local sintering methods (IR emitter, inductive heating) allow to produce multiple coating systems in short times. Electrochemical impedance spectroscopy (EIS) provides evidence of the protective effect of these layers compared to the bare substrate, but as a result of their chemical composition the layers are not stable in the electrolytic environment for longer times. The thickness of such multiple coatings (20 layers, ,,8 µm) is still small compared to that of a technical enamel. Therefore, sol dispersion systems containing powder particles and sol components are applied on top of the sol,gel layers to increase the thickness of the sintered layers. [source] Electrical transport properties of aliovalent cation-doped CeO2ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Mark C. Pearce Abstract We report the comparative electrical properties of monovalent (Na+), divalent (Ca2+, Sr2+), trivalent (In3+, La3+) and coupled substitution of divalent and trivalent (Ca2+ + Sm3+) cation-doped CeO2. The investigated samples were prepared by solid-state reaction (ceramic) using the corresponding metal oxides and salts in the temperature range 1000,1600 °C in air. Powder X-ray diffraction (PXRD), laser particle size analysis (LPSA), scanning electron microscopy (SEM), and ac impedance spectroscopy measurements were employed for structural, morphology, and electrical characterization. PXRD studies reveal the formation of single-phase cubic fluorite-type structures for all investigated samples except those doped with In3+. The variation of lattice parameters is consistent with ionic radii (IR) of the dopant metal ions, with the exception of Na+ -doped CeO2. Our attempt to substitute In3+ for Ce4+ in CeO2 using both ceramic and wet chemical methods was unsuccessful. Furthermore, diffraction peaks attributed to CeO2 and In2O3 were observed up to sintering conditions of 1600 °C. Among the single-phase compounds investigated, Ce0.85Ca0.05Sm0.1O1.9 exhibits the highest bulk conductivity of 1.3 × 10,3 S/cm at 500 °C with activation energy of 0.64 eV in air. The electrical conductivity data obtained for Ce0.85Ca0.05Sm0.1O1.9 in air and Ar were found to be very similar over the investigated temperature range, indicating the absence of p-electronic conduction in the high oxygen partial pressure (pO2) range which is consistent with literature reported on Sm-doped CeO2. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||