In this research, porous W matrixes for dispenser Ba-W cathodes were prepared by metal injection molding (MIM) using W powders with different particle shapes as raw materials. Other than investigating the effect of the powder particle shape on the pore characteristics of the porous W matrix, the influence of the powder particle shape on the emission properties of the Ba-W cathode was also investigated. Irregular W powder particles had higher surface roughness and specific surface area than the spherical W particles, resulting in sinuous pore channels and higher pore-specific surface area in the prepared W matrix. The emission current density of the cathode processed from the irregular powder was thus improved as the level of Ba-O dipoles, covered on the emission surface, was increased. This is due to the high pore-specific surface area offering a high contact area between W and impregants in the cathode.& COPY; 2023 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
The effects of melt-spinning speed ( v=15, 20, 25, 30, 35 m/s) and heat-treatment process on the magnetic properties and microstructure of melt-spun Nd26Pr3FebalCo4Ga0.42B0.92 ribbons were investigated. The ribbons show an obvious orientation when the speed is less than 25 m/s in the free side, and c-axis is perpendicular to the strip surface; the orientation decreases with the increase of melt-spinning speed. The grain can be refined by increasing the melt-spinning speed. When v<25 m/s, the initial magnetization curve shows a one-step magnetization process, and demagnetization curve have good squareness. When v >= 25 m/s, the amorphous phase content increases obviously, the initial magnetization curve changes to two-step magnetization process, and the demagnetization curve collapses obviously. The best magnetic properties B-r=0.80 T, mu H-0(cj)=1.56 T, ( BH)(max)=108.22 kJ/m(3) are obtained under v=25 m/s. After optimum crystallization annealing treatment, the amorphous phase content reduces significantly, all of the magnetic properties of ribbons improve obviously at v <= 25 m/s. Squareness and coercivity increase remarkable at v> 25 m/ s; The ribbon prepared at v=35 m/s possesses the highest coercivity (mu H-0(cj)=2.10 T). The best magnetic properties B-r=0.91 T, mu H-0(cj)=1.82 T, (BH)(max)=141.65 kJ/m(3) are obtained under v= 30 m/s. The microstructure changes along with the thickness direction. The wheel side is composed of amorphous and fine grains, the free side is composed of larger grains. After the heat-treatment, the amorphous phase content is reduced significantly.
The electrical conductivity of binary composite is closely related to the microstructure, and its morphological distribution of composition phase have fractal characteristic. Based on fractal theory and general effective medium（GEM）equations, the conductivity model of binary composite was established, and the relationship between the conductivity of composite and conductivity of component phase and fractal dimensions was determined.And the model was applied to the calculation of the conductivity of three molybdenum-based cermet: Mo-ZrO 2 ,Mo-SiO 2 and Mo-Al 2 O 3 system. The results show that the critical exponent t in the GEM equation has a certain functional relationship with the fractal dimension and tortuosity fractal dimension of the highly conductive phase.The fractal dimension Dfgradually increases with the increasing of the volume fraction, and the tortuosity fractal dimension DTgradually decreases with the increasing of the volume fraction. The calculated results of the conductivity model for the three Mo-based cermet are in good agreement with the experimental results.
The microstructural evolution and high-temperature oxidation behavior of bentonite modified MoSi 2 composite coating prepared by spark plasma sintering were studied. The results show that the composite coating is mainly composed of MoSi 2 phase and a small amount of Mo 5 Si 3 phase, and the addition of bentonite reduces the CTE mismatch between the coating and substrate, thus the composite coating presents a crack-free morphology.During oxidation at 1 500 ℃, the composite coating maintains slow mass gain since a dense and complete layer of SiO 2 forms on the surface during the oxidation process, which inhibits the high-temperature diffusion of oxygen and effectively avoids the further oxidation inside the coating. Compared with single MoSi 2 coating, the oxide scale of the bentonite modified composite coating is thinner with a crack-free morphology, therefore showing relatively better high-temperature oxidation resistance.
Based on the practical demand of raw materials quality control stability, with single particle size graded fused silica powder as the matrix material and zircon as the mineralizer, silica-based ceramic cores were prepared.Excellent high-temperature flexural strength and creep resistance was obtained through doping alumina powders and adjusting the sintering temperature. The effects of alumina and sintering temperature on the high temperature dimensional stability of silica-based ceramic cores were discussed. The results show that the increasing of the alumina amount and the sintering temperature are beneficial to the crystallization of cristobalite and the sintering level of silica-based cores, leading to significantly improves of the creep resistance of silica-based cores, but slightly deteriorates the high-temperature flexural strength. As the alumina doping ratio increases from 0 to 0.3%, the 1 550 ℃/30 min thermal deformation of the ceramic cores is significantly reduced from 3.86 mm to 0.54 mm,while the flexural strength at 1 550 ℃ is decreased from 27.86 MPa to 21.79 MPa. With the increasing of the sintering temperature from 1 180 ℃ to 1 240 ℃, the thermal deformation is reduced from 3.86 mm to 0.47 mm, while the flexural strength at 1 550 ℃ is deteriorated from 27.86 MPa to 19.67 MPa.
