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Hot Pressing (hot + pressing)
Selected AbstractsTranslucent ,-Sialon Ceramics by Hot PressingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004Xinlu Su The single-phase ,-sialon ceramics with high optical transmittance have been prepared by hot pressing. The maximum transmittance reached 65.2% and 52.2% in the infrared wavelength region, 58.5% and 40% in the visible region for the samples 1.0 and 1.5 mm thickness, respectively. The material also exhibited good mechanical properties of high hardness (20 GPa) and better fracture toughness (5.1 MPa·m1/2). Both high optical transmittance and improved toughness of ,-sialon ceramics were attributed to the less-grain-boundary glassy phase and the homogeneous microstructure, which was obtained by a proper process and confirmed by SEM and TEM observation, compared to that prepared by ordinary sintering. It is, therefore, expected that the translucent ,-sialon ceramics could be a promising optical window material. [source] Hot pressing of germanium monochromator crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004S. F. Treviño The method and parameters for vacuum hot pressing of single-crystal germanium, suitable for a large-area double-focusing neutron monochromator, are presented. The square virgin crystals have a mosaic that is less than 0.01° and isotropic. After appropriate pressing at high temperature (1073,K at a pressure of 10.7,MPa) the mosaic becomes anisotropic, about 0.5° in one direction and 0.2° in the other. The distribution of the mosaic widths of the crystals in the two directions are given, together with their composite values. [source] Synthesis and Low Cycle Fatigue Behavior of In-situ Al-based Composite Reinforced with Submicron TiB2 and TiC Particulates,ADVANCED ENGINEERING MATERIALS, Issue 12 2004S.C. Tjong Low cycle fatigue behavior of in-situ aluminum based composite reinforced with submicron TiB2 and TiC particulates was investigated. This novel composite was prepared from the TiO2 -Al-B-C system via reactive hot pressing. The incorporation of carbon into such a system induces the formation of TiC particulate at the expense of brittle Al3Ti phase. The influence of submicron particulate formation on the tensile and fatigue properties of the composite is discussed. [source] Properties of ZrB2 -Reinforced Ternary Composites,ADVANCED ENGINEERING MATERIALS, Issue 9 2004D. Sciti Different amounts of ZrB2 particles are added to a matrix constituted by AlN+SiC for the production of novel electro-conductive composites by hot pressing. The presence of ZrB2 particles makes the composites electro-conductive and improves many relevant mechanical properties, such as toughness, hardness and strength. The new materials can reach a fracture toughness of 4 MPa.m1/2 and strength of 504 MPa at 1400°C. [source] Hot-Pressed Glass Matrix Composites Containing Pyrochlore Phase Particles for Nuclear Waste Encapsulation,ADVANCED ENGINEERING MATERIALS, Issue 7 2003A.R. Boccaccini As alternative immobilization materials for Pu-bearing nuclear waste, lead-containing glass matrix composites with homogeneously distributed lanthanum zirconate pyrochlore particles (up to 30,% by volume) have been developed. Fabrication by hot pressing at the relatively mild temperature of 610,°C leaves the pyrochlore structure of the La zirconate unchanged, which is crucial for the containment of radioactive nuclei. The Figure, an SEM image of a polished sample with 30,% La2Zr2O7, demonstrates the homogeneous particle distribution and absence of pores. [source] Reactive Processing in Ceramic-Based SystemsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2006William G. Fahrenholtz Reactive hot pressing is discussed as a processing method to form ceramic-based materials. Fundamental aspects of thermodynamics such as favorable Gibbs'-free energy changes, phase equilibria, and adiabatic temperature are presented as criteria for determining whether the desired reactions can be used to form dense materials. Two case studies are presented as examples to describe control of microstructure and properties. The fabrication of Al2O3,Nb and ZrB2 are discussed with respect to the three thermodynamic criteria as well as the microstructure and properties of the materials that are produced. [source] Hot pressing of germanium monochromator crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004S. F. Treviño The method and parameters for vacuum hot pressing of single-crystal germanium, suitable for a large-area double-focusing neutron monochromator, are presented. The square virgin crystals have a mosaic that is less than 0.01° and isotropic. After appropriate pressing at high temperature (1073,K at a pressure of 10.7,MPa) the mosaic becomes anisotropic, about 0.5° in one direction and 0.2° in the other. The distribution of the mosaic widths of the crystals in the two directions are given, together with their composite values. [source] Relationship between the crystalline structure and mechanical behavior in isotropic and oriented polyamide 12JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Nadya Dencheva Abstract This study reports on the relationship between the crystalline structure and mechanical behavior of differently processed and annealed polyamide 12 (PA12) samples. Two sets of samples were obtained: isotropic PA12 films prepared by hot pressing and oriented cables prepared by consecutive extrusion and cold drawing. These samples were isothermally annealed in the range of 80,160°C and then subjected to tensile tests at room temperature. A combination of solid-state 13C-NMR and synchrotron wide- and small-angle X-ray scattering was used to obtain reliable structural data from these samples before and after the tensile tests. These structural data were related to the mechanical properties of the respective PA12 samples. Deformation models explaining all the experimental results were suggested for the different PA12 samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Assessment of the dyeing properties of pigments from Monascus purpureusJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2005Diana De Santis Abstract Monascus purpureus C322 was cultivated on well-established production media to yield prevailingly red or orange pigment-rich ethanolic extracts. Once these extracts had been diluted by an overall factor of 50, they were used as such to dye raw wool standard specimens differently premordanted using alum or stannic chloride. Independently of the mordant used, the specimens dyed with the red pigment-rich extracts showed a pale red colour tending to pink, whereas the specimens dyed with the orange pigment-rich extracts exhibited a more definite orange colour. By carrying out a few colourfastness standard tests (manual washing at 40 °C, acid and basic perspiration and hot pressing), stannic chloride-premordanted wool specimens dyed with the red pigment-rich extracts were found to be less resistant to acid and basic perspiration than their orange counterparts. Since the production of the orange pigment-rich ethanolic extracts appeared to be more cost-effective than that of their red counterparts, the former might support the present demand for colorants of natural origin in the textile sector. Copyright © 2005 Society of Chemical Industry [source] Simulation of the Stress-Assisted Densification Behavior of a Powder Compact: Effect of Constitutive LawsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Héctor Camacho-Montes The densification of powders with linear and nonlinear viscous behavior (Scherer and Riedel models) and with power-law-deformation (Khun,McMeeking) behavior was studied under hot pressing and sintering forging conditions. Several numerical experiments, designated cases in this work, were performed to study the effect of (i) the uniaxial stress exerted by the piston and (ii) the rate of the uniaxial stress. The stress state was calculated using the finite-element program ANSYS for each case. Considering the mesoscopic behavior of the powders, densification rates were obtained. The similarities and differences between predictions from the three constitutive models are highlighted. The relationship between the constitutive behavior and the most effective stress state is one of the focuses of this study. For example, we show that under constant stress loading, hot pressing more effectively promotes densification than sinter forging for constitutive behaviors that do not follow the power-law creep. In general, as expected, the increase of uniaxial applied stress and piston velocity favored densification. However, the increase in densification depends strongly on the constitutive law. [source] Sc3+,Lu3+ -Doped ,-SiAlONsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Feng Ye Sc3+ and dual Sc3+,Lu3+ -doped ,-SiAlON compositions were sintered by hot pressing, and the formation behavior, microstructure, and mechanical properties were assessed. It was found that the small cation Sc3+ could not be accommodated into the ,-SiAlON structure alone. The addition of Lu2O3 in the composition induces the Sc3+ cation to enter the ,-SiAlON structure, and leads to the production of ,-SiAlON with an elongated-grain microstructure. Transmission electron microscopy analysis shows that ,-SiAlON grains always contain an ,-Si3N4 core, implicating heterogeneous nucleation to be in present in a mixed lutetium/scandium-doped ,-SiAlON system. [source] Hot Forging of a Textured ,-Sialon CeramicJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Andrew Carman A texture was introduced into an Sm-,-sialon ceramic by hot pressing, such that the c -axis was preferentially oriented normal to the pressing direction. The material was then uniaxially hot forged for up to 60 min, with the forging direction normal to the hot-pressing direction. The texture initially reduced to a one-dimensional preferential orientation in the direction normal to both the hot-pressing and hot-forging directions. Further deformation resulted in a two-dimensional texture normal to the hot-forging direction. The forging process was used to produce a strong one-dimensional texture by alternating between the hot-pressing and hot-forging directions, thereby producing a material with significant anisotropy in its properties. [source] Processing and Properties of TiB2 with MoSi2 Sinter-additive: A First ReportJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006T. S. R. Ch. The densification of non-oxide ceramics like titanium boride (TiB2) has always been a major challenge. The use of metallic binders to obtain a high density in liquid phase-sintered borides is investigated and reported. However, a non-metallic sintering additive needs to be used to obtain dense borides for high-temperature applications. This contribution, for the first time, reports the sintering, microstructure, and properties of TiB2 materials densified using a MoSi2 sinter-additive. The densification experiments were carried out using a hot-pressing and pressureless sintering route. The binderless densification of monolithic TiB2 to 98% theoretical density with 2,5 ,m grain size was achieved by hot pressing at 1800°C for 1 h in vacuum. The addition of 10,20 wt% MoSi2 enables us to achieve 97%,99%,th in the composites at 1700°C under similar hot-pressing conditions. The densification mechanism is dominated by liquid-phase sintering in the presence of TiSi2. In the pressureless sintering route, a maximum of 90%,th is achieved after sintering at 1900°C for 2 h in an (Ar+H2) atmosphere. The hot-pressed TiB2,10 wt% MoSi2 composites exhibit high Vickers hardness (,26,27 GPa) and modest indentation toughness (,4,5 MPa·m1/2). [source] Translucent ,-Sialon Ceramics by Hot PressingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004Xinlu Su The single-phase ,-sialon ceramics with high optical transmittance have been prepared by hot pressing. The maximum transmittance reached 65.2% and 52.2% in the infrared wavelength region, 58.5% and 40% in the visible region for the samples 1.0 and 1.5 mm thickness, respectively. The material also exhibited good mechanical properties of high hardness (20 GPa) and better fracture toughness (5.1 MPa·m1/2). Both high optical transmittance and improved toughness of ,-sialon ceramics were attributed to the less-grain-boundary glassy phase and the homogeneous microstructure, which was obtained by a proper process and confirmed by SEM and TEM observation, compared to that prepared by ordinary sintering. It is, therefore, expected that the translucent ,-sialon ceramics could be a promising optical window material. [source] High-Temperature Resistant Composites in the AlN,SiC,MoSi2 SystemJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Diletta Sciti Two fully dense composites containing AlN, SiC, and MoSi2 in different amounts were produced by hot pressing. Young modulus, hardness, electrical conductivity, and thermal expansion coefficient were measured at room temperature. Strength and toughness were evaluated up to 1300°C in air. According to statistical analysis, the temperature has little or no effect on high-temperature fracture behavior of the composites. These electroconductive materials are suitable for thermomechanical applications at high temperature, the strength being about 600 MPa at 1300°C. [source] Pulsed Electric Current Sintering of Silicon NitrideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Motohiro Suganuma Pulsed electric current sintering (PECS) has been used to densify ,-Si3N4 powder doped with oxide additives of Y2O3 and Al2O3. A full density (>99%) was achieved with virtually no transformation to ,-phase, resulting in a microstructure with fine equiaxed grains. With further holding at the sintering temperature, the ,-to-, phase transformation took place, concurrent with an exaggerated grain growth of a limited number of elongated ,-grains in a fine-grained matrix, leading to a distinct bimodal grain size distribution. The average grain size was found to obey a cubic growth law, indicating that the growth is diffusion-controlled. In contrast, the densification by hot pressing was accompanied by a significant degree of the phase transformation, and the subsequent grain growth gave a broad normal size distribution. The apparent activation energy for the phase transformation was as high as 1000 kJ/mol for PECS, almost twice the value for hot pressing (,500 kJ/mol), thereby causing the retention of ,-phase during the densification by PECS. [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 Method to Prepare Electroconductive Titanium Nitride,Aluminum Oxide NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Jingguo Li A novel method for the preparation of TiN,Al2O3nanocomposites was developed. TiN,Al2O3nanocomposite powders were prepared by the direct nitridation of TiO2,Al2O3nanocomposite powders that were derived from the simultaneous hydrolysis of tetra-butyl titanate and precipitation of aluminum nitrate. Dense sintered bodies of these TiN,Al2O3nanocomposite powders were obtained by hot pressing at 1450°,1650°C and 30 MPa for 60 min. The resistivity of nanocomposite reaches a minimum (1.5 × 10,3,·cm) at 25 vol% TiN additions. The percolation concentration of nanocomposite is ,10 vol% TiN. [source] Exuding Liquid from Grain Boundaries in AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001N. Ravishankar Bicrystals of alumina with anorthite glass in the boundary were prepared by hot pressing. Annealing of the bicrystals leads to the migration of the intergranular liquid to the free surface of the sample. It is proposed that the migration is driven by the difference in the wetting behavior of the free surface and the boundary. [source] Highly efficient bismuth telluride doped p-type Pb0.13Ge0.87Te for thermoelectric applicationsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 6 2007Yaniv Gelbstein Abstract Bi2Te3 doped p-type Pb0.13Ge0.87Te samples were prepared by hot pressing. We report on very high power factor values of ,30 ,W/cm K2 at 500 °C, as were determined from Seebeck coefficient and electrical resistivity measurements. From dilatometric characterization, the phase transition from the low temperature rhombohedral to the high temperature cubic NaCl structures, takes place at 373 °C. This transition is accompanied by a continuous and gradual change of the lattice parameters, as was observed by hot stage XRD, suggesting a good mechanical durability upon thermal cycling and operating in large thermal gradients. Rhombohedral distortion of the cubic NaCl structure of Pb1,xGex Te upon cooling, characterized by changes in the interaxial angle , and the lattice parameter. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal conductivity reduction in fullerene-enriched p-type bismuth telluride compositesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010N. Gothard Abstract We present a systematic study of the effects of fullerene nanoinclusions upon a p-type bismuth,antimony,telluride matrix, where the ultimate goal is maximizing the figure of merit by reducing the thermal conductivity (TC). Nanocomposites consisting of a bismuth,telluride matrix with fullerene inclusions have been prepared both by mechanical mixing and ball milling, with the final consolidation in each case achieved by uniaxial hot pressing. A series of samples was produced with fullerene concentrations ranging from fractional levels to several molar percent, and the effects of the fullerene additions upon the resulting microstructure have been considered. Thermal and electrical transport properties have been measured from 10 to 300,K, and the data are discussed in light of the underlying physical mechanisms. [source] Thermoelectric properties of rapid hot pressed polycrystalline Ag1,xPb18SbTe20 synthesized from doping PbTe nanocrystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Xingliang Xin Abstract Polycrystalline thermoelectric (TE) materials of n-type and with compositions of Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) were prepared by rapid hot pressing from alloy powders, which were obtained by ball milling crystalline ingots. The ingots were synthesized from PbTe nanoparticles, made by solvothermal reactions, and Ag, Sb and Te powders via vacuum-sealed melting in quartz ampoules. Through rapid hot pressing at 748,K for 15,min under 80,MPa, the polycrystalline samples possessed 95% relative densities with the average grain size of 5,µm. The electrical resistivity, Seebeck coefficient and thermal conductivity of the Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) samples were measured in the range from room temperature (RT) to 673,K. The thermal conductivity was dramatically decreased, caused by scattering of phonons from grain boundaries and interfaces. By optimizing the values of carrier concentration and carrier transference, the Ag1,xPb18SbTe20 (x,=,0.2) sample achieved a maximum ZT value of 1.019 at 673,K. [source] Swirl mat, and long discontinuous fiber mat,reinforced polypropylene composites,status and future trendsPOLYMER COMPOSITES, Issue 4 2000J. Karger-Kocsis Polypropylene (PP) composites with glass and natural fiber mat reinforcement (GMT-PP and NMT-PP, respectively) are widely used in different applications, competing with metallic sheets and thermoset polymer composites. Their production occurs via melt impregnation, slurry deposition and various textile architecturing processes that lead to either consolidated or non-consolidated preforms. These preforms are then converted into final parts by hot pressing. The "traditional" GMT-PP composites are nowadays faced with a great challenge because of the introduction of long fiber reinforced thermoplastic (LFT) composites produced on- or off-line. This paper gives a brief survey on the manufacturing, processing, properties and application of GMT and GMT-like systems and it concludes by describing some of the future trends, especially in the fields of material and process developments. [source] Single-walled nanotube bucky paper and nanocompositePOLYMER INTERNATIONAL, Issue 11 2006Jihua Gou Abstract A new processing method for the fabrication of single-walled nanotube (SWNT)-reinforced nanocomposites was developed to achieve uniform dispersion and high composition of the nanotubes in the nanocomposites. In this method, SWNTs were preformed as bucky paper by multi-step dispersion and micro-filtration of a suspension of nanotubes. The nanocomposites were then fabricated by infiltration of diluted epoxy resin through the bucky paper and hot pressing. The wetting of the nanocomposites was examined using scanning electron microscopy and atomic force microscopy. The results showed that the epoxy resin completely penetrated the bucky paper through the nanoporous structures. The results of dynamic mechanical analysis of the nanocomposites showed that the storage moduli of the nanocomposites increased by 200,250%. The tan , curves indicated that the nanotubes had a strong influence on the damping properties of the nanocomposites. This processing technique is an effective method for fabricating nanocomposites with uniform dispersion and high composition of SWNTs. Copyright © 2006 Society of Chemical Industry [source] | ||||||||||||||||||||||||||||