Papers by Keyword: Bend Strength

Abstract: We examined sintering additives for alumina. When using CuO-TiO2-Nb2O5 additive, dense sintered alumina was obtained by firing at 1000°C or below, even though additive content was at most 10 mass%. It is considered that the formation of mixed oxide consists of CuO, TiO2 and Nb2O5 has an important role for low temperature sintering of alumina. Thermal conductivity of the above sample was 15 W/mK, which was the highest value yet reported within LTCC (Low Temperature Co-fired Ceramics) materials.

Abstract: Dense 8mol% yttria-stabilized zirconia (8YSZ) consisting of submicrometer-sized grains was prepared using spark plasma sintering (SPS) along with Al2O3 additives. The starting powder with average particle size of 50nm was densified to 98% of the relative density with short sintering time (5min) at 1200
while preserving a submicrometer grain size. The fracture toughness and bending strength showed maximum values of 2.54MPam1/2 and 380MPa at 2vol% alumina-added 8YSZ, due mainly to the higher relative density and small grain size. The electrical conductivity of 2vol% alumina-added 8YSZ was 0.0278 S/cm at 700
 in airThus, alumina additions in 8YSZ using the SPS method are an effective process to improve the mechanical strength and electrical conductivity.

Abstract: 3Y-TZP/TiNiCo composites have been successfully fabricated by three step heating (dehydrogenation, hydrogen reduction, hot-pressing) of 3Y-TZP /NiO/TiH2/CoO powder mixtures. XRD analysis revealed that TiNi-base intermetallic compounds such as Ni4Ti3, NiTi, Ni3Ti had formed. The bending strength of 3Y-TZP/TiNiCo composites (~650 MPa) were much higher than those of 3Y-TZP monolith (
350 MPa) sintered at the same condition. The electrical resistivity characteristics indicated that 3Y-TZP/30 vol%TiNiCo composites were good electrical conductors. Cobalt addition to TiNi phase influenced on electrical properties of final composites, while their fracture strength was unchanged by the Co addition.

Abstract: Lu2O3 and SiO2 were used as sintering additives and rod-like β-Si3N4 seeds were added to enhance β-Si3N4 grain unidirectional growth. Silicon nitride ceramics were prepared by tape casting and gas pressure sintering
at 1950oC in 10 atm nitrogen atmosphere for 6 h. Compare to the no-seeded Si3N4, the seeded and tape-cast Si3N4 ceramics have obvious anisotropic microstructure and anisotropic properties. When a stress applied along with the grain alignment direction, the bending strength of the seeded and tape-cast Si3N4 at 1500oC was 738 MPa, which was almost the same as its room temperature bending strength. However, the bending strength of the seeded and tape-cast at room temperature was 556 MPa (perpendicular direction); and their thermal conductivity were 67 W/m·K (perpendicular direction) and 83 W/m·K (parallel direction), respectively. The anisotropic properties of the seeded and tape-cast Si3N4 were attributable to the elongated Si3N4 grain alignment.

Abstract: Silicon nitride - silicon carbide nanocomposite has been prepared by an in-situ method that utilizes formation of SiC nanograins by C+ SiO2 carbothermal reduction during the sintering process. The developed C/SiO2 derived nanocomposite consists of a silicon nitride matrix with an average Si3N4 matrix grain diameter of approximately 200 nm with inter- and intra- granular SiC inclusions with sizes of approximately 150 nm and 40 nm, respectively. The mean value of room temperature 4-point bending strength is 670 MPa with the Weibull modulus of 7.5 and indentation fracture toughness of 7.4 MPa.m1/2. The creep behaviour was investigated in bending at temperatures from 1200°C to 1450°C, under stresses ranking from 50 to 150 MPa in air. A significantly enhanced creep resistance was achieved by the incorporation of SiC nanoparticles into the matrix. The inserts machined from this composite have three times longer life time compared to those available on the market.

Abstract: P-type Bi0.5Sb1.5Te3 compounds doped with 3wt% Te were fabricated by spark plasma sintering and their mechanical and thermoelectric properties were investigated. The sintered compounds with the bending strength of more than 50MPa and the figure-of-merit 2.9×10-3/K were obtained by controlling the mixing ratio of large powders (PL) and small powders (PS). Compared with the conventionally prepared single crystal thermoelectric materials, the bending strength was increased up to more than three times and the figure-of-merit Z was similar those of single crystals. It is expected that the mechanical properties could be improved by using hybrid powders without degradation of thermoelectric properties.

Abstract: Silicon nitride ceramics was prepared by tape casting nonaqueous ceramic slurries, laminating the green ceramic tapes, and gas pressure sintering in nitrogen atmosphere. Lu2O3 and SiO2 were used as the sintering additives, and 3 wt.% β-Si3N4 seed was added to enhance β-Si3N4 grain growth unidirectionally. The seeded and tape-cast Si3N4 showed very good high temperature bending strength at 1500oC, when the stress applied along with the grain alignment direction. This was attributable to the formation of a high melting point grain boundary phase and the fibrous Si3N4 grains alignment. After exposure in air at 1500oC for up to 100 h, the oxidation products formed on the Si3N4 surface consist of Lu2Si2O7 and SiO2. The bending strength of the oxidized and tape-cast Si3N4 was degradation, the strength decrease was associated with the formation of new defects on the surface and the interface between the oxide layer and the Si3N4 bulk.

Abstract: A new bioactive bone cement (cGBC) consisting of crystallized MgO-CaO-SiO2-P2O5 glass beads and high-molecular-weight polymethyl methacrylate (hPMMA) has been developed to overcome the degradation seen with a previously reported cement (GBC) consisting of MgO-CaO-SiO2-P2O5-CaF2 glass beads and hPMMA. The purpose of the present study was to evaluate the degradation of cGBC using an in vivo aging test, and to compare the degradation of cGBC with that of GBC. Hardened rectangular specimens (20x4x3mm) were prepared from both cements. Their initial bending strengths were measured using the three-point bending method. GBC and cGBC specimens were then implanted into the dorsal subcutaneous tissue of rats, removed after 6 or 12 months, and tested for bending strength. The initial bending strengths (MPa) of GBC and cGBC were 141.9±1.8 and 144.4±2.4, respectively, while at 6 months they were 109.1±2.6 and 114.1±4.9, and at 12 months they were 109.1±3.2 and 113.1±3.3, respectively. Although the difference in initial bending strengths was not significant, the bending strength of cGBC was significantly higher than that of GBC at 6 and 12 months, indicating that cGBC is more resistant to cement degradation. The bending strengths of both GBC and cGBC decreased significantly from 0 to 6 months but did not change significantly thereafter. Thus, degradation of cGBC and GBC does not appear to continue after 6 months. We believe that cGBC and GBC are strong enough for use under weight-bearing conditions and that their mechanical strength (especially that of cGBC) is retained in vivo.

Abstract: The oxidation behavior of Ca-α-Sialon composites prepared by using the powders of α-Si3N4, AlN, Al2O3 and CaCO3 as the starting materials has been studied, for the composition Ca0.8Si8.8Al3.2O16N14.4 in the temperature range of 1200 to 1400°C for 24 to 96h in an air stream. The bending strength and weight gain of the samples before and after oxidation experiment were measured, and the phases of surfaces of the samples were examined by XRD, the microstructures of sections and surfaces of the samples were observed by SEM. The results show that the weight gain increased and the bending strength decreased as the oxidation time increased, and the oxidation layers contained bar cristobalite and glass phase at 1200°C, bubbles and glass phase at 1300°C, transparent glassy film and the pores at 1400°C, the phases of oxidation layers consisted of cristobalite, CaAl2Si2O8, and glass phase.