Implementing pressure-assisted flash sintering of ZnO powder without pretreatment by a new experimental configuration is presented. Rapid and energy-concentrated heating of electrode-sample-electrode area by induction heating allows preheating and flash sintering of loose-pack powder in the die with pressure assistance. Using an insulated die enables the current to flow through the sample during flash sintering. ZnO ceramics with a relative density of 95.1% can be achieved in less than 3 min. The whole process includes 104 s of preheating by a low-power induction heating device and 30 s of flash sintering assisted by a pressure of 26 MPa using the pulsed direct current (DC). The process characteristics of pressure-assisted flash sintering using the pulsed DC are discussed. The effect of pressure on densification and grain size is analyzed in detail, and some potential mechanisms are provided. 相似文献
In the present work, Tungsten (W)/oxide dispersion strengthened (ODS) steel joints were fabricated by the direct solid state diffusion bonding (SSDB) technology with a multistage cooling process, and the microstructure and tensile strength of the bonded interfaces and parent materials were experimentally investigated. The results show that W and ODS steel can be successfully bonded at the temperature ranging from 900 °C to 1050 °C, without severe macroscopic deformation or obvious microscopic defects. Reaction layers generated at the bonded interfaces are evolutive with the bonding temperature, result in different fracture locations of the bonded joints. In the joint bonded at 950 °C, a higher interfacial strength of ~ 234.2 MPa is achieved, due to the formation of nano-scale intermetallic compound FeW. Microstructure of W remains stable after all the SSDB processes, while the lath structure of ODS steel is completely broken and transformed into the equiaxed grains, which should be responsible for the deterioration of strength. When the bonding temperature is higher than 950 °C, the pinning effect of precipitates M23C6 and nano-oxide particles on the movement of dislocations is observed.
A new magnetic macroparticle filter design consisting of an off-plane double-bend (OPDB) filter is described. The transport of the vacuum arc plasma through this OPDB filter is investigated using Langmuir and deposition probes. Films of amorphous hard carbon have been deposited using a 90° single bend and the OPDB filter and the macroparticle contents of the films are compared. The experimental results were found to be in good agreement with the simulations results based on an improved drift approximation model. The results demonstrate that OPDB filter has a relatively better transmission efficiency than the 90° single bend filter, lower macroparticle counts and is suitable for preparation of diamond-like carbon coatings with high quality. 相似文献
This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar with some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates. 相似文献