Papers by Keyword: Pressureless Sintering

Abstract: Fluoridated composite Hydroxyapatite biomaterial was prepared by sintering the hydroxyapatite Ca₁₀ (PO₄)₆. (OH)₂[HA] powder with addition of titanium fluoride 30 wt. % -TiF₃ and mixture of iron oxide and aluminum oxide [5 wt. %-Al₂O₃/Fe₂O₃ ; (5/1)]. The pellets were prepared by conventional sol-gel technique. The as-prepared samples were sintered at various temperatures and the effect of different temperature on grain size and mechanical properties has been investigated. The samples were sintered at various temperatures of 1100-1400 °C. After sintering, the sample’s mechanical properties such as compressive strength, bending strength, Vickers hardness were improved to be 49±0.26-103±0.26 MPa, 19.6±0.20-36.2±0.20 MPa, and 7.97±0.16-12.50±0.16 GPa with their grains size 4.76±0.10-17.63±0.10 μm and bulk densities 1.8944-2.2426 g/cm³.

Abstract: The MgTiO₃ and CaTiO₃ powders were synthesized by solid reaction method, and MgTiO₃-CaTiO₃ ceramic was prepared using pressureless sintering method. The experiment prepared MgTiO₃-CaTiO₃ ceramics with high compactness and stable permittivity by the way of changing the mole ratio of MgTiO₃ and CaTiO₃ to investigate the effect of CaTiO₃ on the performances of MgTiO₃-CaTiO₃ ceramics. The results show that Mg₂TiO₄ formed as second phase during sintering. Volume density and dielectric constant of MgTiO₃-CaTiO₃ ceramics with 10%mol CaTiO₃ reach maximum of 3.612g/cm³ and 17.8, respectively, under 1460°C sintering temperature. And for the MgTiO₃-CaTiO₃ ceramics with 5%mol CaTiO₃ the maximum values which are 3.5g/cm³ and 16.6, respectively, appear under 1510°C sintering temperature.

Abstract: In this study, functionally gradient aluminum reinforced by Silicon carbide particles (FGMSiCp/Al) composites are prepared by microwave sintering and pressureless sintering processing. The sintering behaviors, mechanical properties of composites were measured, and microstructure was observed by optical microscope and SEM. The results showed that the density of sintered samples which prepared by microwave sintering were better than that presureless sintering one. The highest density of sintered sample by microwave sintering reached 2.64 g/cm3, the relative density was 95.65%. Whatever preparing process, the mechanical properties of sintered samples were related to the temperature. The distribution of silicon carbide particles is uniform in the aluminum matrix, however, slight agglomeration can be observed. The interface between other layers is not obvious except interface between Al and 5% SiC/Al layer.

Abstract: Boron carbide is an attractive neutron absorbing material used both in Fast Breeder Reactors (FBR) and in Pressurised Water Reactors (PWR) owing to its very high absorption cross section for thermal neutrons, chemical stability and refractory character. In the present paper, ¹⁰B enriched B₄C ceramics are prepared by pressureless sintering at 19602160°C, under argon, using ¹⁰B boron carbide powder as raw material, 18 wt% phenolic resin as sintering aid. In the sintering temperature range, with the increasing of sintering temperature, both the relative density and flexural strength increase linearly, the average particle sizes increase from about 3μm at 1960°C to more than 30μm at 2160°C. The sample sintered at 1960°C has a 91.7% of relative density and 192 MPa of flexural strength and a homogeneous texture with 3-4μm particle size, which are enough for pellet application of reactors.

Abstract: Particle reinforced SiC composites with the addition of TiB2 were fabricated in range of 1750°C to 1950°C by pressureless sintering by utilizing liquid phase with AlN-Y2O3 as sintering additives. The effective of sintering aids in densification, the mechanical properties of sintered sample and the microstructure had been investigated in this paper. The results showed that the best densification behaviors occurred in AlN:Y2O3 at 60 :40%mol ratio not at eutectic point. Adding TiB2 to SiC matrix increase the toughness and decreased the hardness. Microstructure analysis showed that the increasing of toughness was due to the crack deflection with some contribution intergranular fracture mechanism.

Abstract: The processing of boron carbide by pressureless sintering with nano-sized rare-earth compounds additives to obtain dense pellets for use as neutron absorber in fast breeder reactors is investigated. The effect of dysprosium aluminum garnet (DAG) and dysprosium titanate nanopowders on density and mechanical properties was studied. The addition of DAG and dysprosium titanate nanopowders was found to be beneficial in the densification of B₄C powders. B₄C with 5 wt. % of DAG or dysprosium titanate nanopowders, exhibiting bulk density of 2.14g/cm³ and 2.35 g/cm³, could be prepared by pressureless heating at 2120°C and 2160°C.

Abstract: Pressureless sintering to obtain high density boron carbide-titanium diboride composites by in-situ reaction was studied. Pressureless sintering behavior of this material was investigated between 1800-2150 .The effects of composition, sintering temperature and tine were examined. Density up to 98.5% T.D. was reached at 2150. Maximum values of flexural strength (502 MPa), hardness (33 Gpa) and fracture toughnes (4.6 MPa·m^1/2) were observed in the specimens containing 15 vol.% TiB₂.

Abstract: The Si¬₂ON₂-SiC ceramic was fabricated by pressureless sintering method. In this paper we researched the effect of SiC content (50%, 70% and 90%) on the performance of silicon oxynitride bonded silicon carbide ceramics. Through testing and analyzing the SEM, XRD, density and porosity of the final silicon oxynitride bonded silicon carbide ceramic samples, the results show that: changes in SiC content not only affect the bulk density of the composites but also affect the phase composition and the microstructure of fracture surface. The most compactness experimental product is sintered at1500°C containing 50wt% SiC.

Abstract: An Oxide Ceramic-Based Composite in the Al₂o₃-Sio₂-Zro₂ (ASZ) System Was Developed and Investigated Using a Pressureless Sintering Route. the Effect of the Content of each Component and Sintering Temperature upon the Microstructure, Density, Hardness and Strength Was Studied. X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) Were Used to Investigate the Phase Transformation Sequences of the ASZ Composite System. the Flexural Strength Was Measured Using Three-Point Bending Method on a Universal Testing Machine, while the Indentation Fracture (IF) Method Was Used to Determine the Fracture Toughness of the Composite. the Results Showed that, with Varying Zro₂ Content, Keeping the Silica Content Constant and the Alumina as a Matrix, Densification Tends to Decrease as the Content of Zirconia Increases from 20 Wt. % of the Composition. X-Ray Diffraction Peaks Indicated Fully Developed Alumina, Mullite and Zirconia Phases due to Solid-Phase Reaction and Liquid-Phase Sintering of the System. the Experimental Results Also Revealed that, for a Sintering Temperature of 1500°C, the Hardness Value Ranged from 12 Gpa to 14 Gpa and the Flexural Strength Was 420±31MPa.The Fracture Toughness (K_Ic) Was Also Reported to Be between 4.5 and 5.1 Mpa.m^1/2, for Samples Sintered at a Temperature of 14500C.

Abstract: βThe B₄C and phenolic resin were used as sintering additives to study the different β-SiC（cubic silicon carbide) addition to the performance of α-SiC pressureless sintering ceramics in this paper, and the optimum sintering temperature and the best β-SiC addition amount were determined. By XRD, SEM,density testing and other tests showed that, all the β-SiC transform 6Hα-SiC during the sintering process ,the ceramics have a Vickers hardness of 18.04 GPa,a frature toughness of 4.51MPa ,a density of 3.13g/cm³ by adding 15wt% β-SiC powders.