Alumina ceramics and cemented carbides are ground by diamond wheel in many cases. And a vertical spindle surface grinding machines with a rotary table are widely used for grinding of these materials. In these type of machine tools, a cup grinding wheels are usually used. Grinding fluid is supplied from the center of the main shaft and spread by a simple centrifugal force conventionally. However, a loading occurs easily in this method. Two supply methods of grinding fluid were developed in order to improve the conventional method. A plate part and a groove part were set separately in the straight cup wheel. As a result, the grinding fluid flowed strongly and the ground chips were removed out effectively. The ground surface roughness of alumina ceramics and cemented carbides in this developed methods were smaller than that of the conventional method. And the loadings were not occurred using developed method even in the case of large depth of cut.
In order to fabricate dense ZrO2-Al2O3 ceramics by pressure-less sintering, three kinds of granules of calcined neutralization co-precipitated 75 mol% ZrO2(2.0 mol%Y2O3)-25 mol%Al2O3 powders added with a small amount of cellulose nanofiber (CNF), i.e., (2, 2, 6, 6-tetramethylpiperidine 1-oxyl)-oxidized (TEMPO) CNF, non-oxidized CNF and polyvinyl alcohol (PVA) were prepared and compacted. Then, they were sintered at 1523 K for 8.64·104 s in air. The granules prepared via the addition of 0.15 mass% TEMPO-CNF revealed a low relative density Dr for powder compacts (43.0%), however, they showed the highest Dr (99.8%) of sintered ceramics with the excellent mechanical properties, i.e., Vickers hardness Hv of 15.4 GPa, fracture toughness KIC of 18.2 MPa·m1/2 and bending strength σb of 882 MPa. These properties are almost the same as those fabricated by pulsed electric-current pressure sintering (PECPS). This might be explained in terms of i) the charged 1st particles induced by TEMPO-oxidized CNF addition could form the nano meter-gap between the primary particles in the granules, and then ii) this nano meter-gap could suppress the particle-sintering at relatively low temperatures, and then much densification at high temperatures could be achieved.
In this study, we investigated sinterabilities and electrical conductivities at 550-900°C of (La0.97M0.03)PO4 (M = Ca, Sr, and Pb) with a monazite structure. It was found that the Pb substitution could improve the sinterability of LaPO4 even at low sintering temperature. Although the Pb-substituted sample exhibited hole conduction at the high-temperature range, protonic conduction became to be observed with decreasing temperature. Compared with the Sr-substituted sample, (La0.97Pb0.03)PO4 showed lower proton conductivity. Taking these results into account, we performed a co-substitution of Sr and Pb for LaPO4 to enhance both the protonic conduction and the sinterability. As a result, it was demonstrated that (La0.94Sr0.03Pb0.03)PO4 had a higher relative density than Sr-substituted ones, and the co-substitution could improve the protonic conduction. It can be considered that the co-substitution is a promising way to prepare dense LaPO4-based protonic conductors.
The titanite-based ceramics with nominal composition CaTi1−xNb4x/5SiO5 (0 ≦ x ≦ 0.2) in which part x of Ti sites are occupied with Nb, showed a remarkable jump of the complex relative permittivity at x = 0.025 compared with that at x = 0 at 110 GHz. Real part increased from 22.5 to 39, and the imaginary part from 4 to 14 (tangent delta from 0.18 to 0.36). Non-reflection condition is fulfilled in both cases when 0 < x < 0.0125, d/λ0 = 0.05 and x = 0.2, d/λ0 = 0.045, where d is thickness of the plate sample and λ0 is the wavelength of incident electromagnetic wave. The dominant dielectric dispersion may occurr due to difference of ionic polarization between Ti4+ and Nb5+ ions relative to O2− ions, which becomes inactive and saturates at x = 0.025. From the measurement of the lattice parameters, a, b, c, and the angle β, characterizing monoclinic crystal structure, this saturation may have close correlation with some structural rearrangement of constituting atoms, Ti and Nb in CaTi1−xNb4x/5SiO5.