Advanced Materials Research Vols. 97-101

Abstract: α-Al2O3 platelets were successfully synthesized in molten NaCl-KCl salt using the pre-calcined Al(OH)3 powders as starting materials, and the effect of milling medium on the powder characteristics was investigated, with the purpose of obtaining high performance sintered ceramics. When anhydrous alcohol was used as milling medium, the synthesized product at 900°C was porous α-Al2O3 with a small amount of amorphous Al2O3. While deionized water was used, single-phase and dense α-Al2O3 platelets were developed at 900°C. It was related with different solubility of NaCl-KCl salt in anhydrous alcohol and deionized water during milling. When the synthesized α-Al2O3 platelets were used as seeds in sintered ceramics, fracture toughness was developed.

Abstract: High nitrogen nanostructured Fe-17Cr-11Mn-3Mo stainless steel powders were produced by high energy ball milling under a nitrogen atmosphere. It was found with increasing the milling time, the nitrogen contents of the powder mixtures increase linearly up to 1.98 wt pct after 96h, and a linear regression equation, WN = 0.19357 + 0.01887t , has been further established. In addition, with the increased milling time, the crystallite sizes and particle sizes of the powders decrease continuously, the lattice strains and sphericity of the powders increase gradually. After milling 60h, the high nitrogen nanocrystalline stainless steel powders with a fine particle size range of 5~10μm, excellent sphericity and uniform components can be obtained, whose crystallite size is about 5.0nm and lattice strain is about 1.0%. The powders milled for 60h was compacted using spark plasma sintering process at different temperatures. It is found that a fully austenitic high nitrogen stainless steel with almost full densification can be obtained by SPS at 1000°C, whose nitrogen content is 0.82 wt pct.

Abstract: In this paper, the main element is constructed high energy electromagnetic compaction system on the high-energy flat coil. Physical model for analyzing dynamic response of high pulse current was reviewed. Design loading device using high energy electromagnetic technology to suppress powder, consider the exhaust, stripping, loading, positioning and other issues,propose a more reasonable program.The device includes various components of the installation. such as coil, the coil plate, driver, amplifiers, punching first, die, upper and lower fixing plate. The model of device based on Pro/E to facilitate manufacturing.Pressure embryo along the suppression direction has more uniform density distribution.The technology possesses advantagesof the single side forming and directional loading.

Abstract: Aimed principally at increasing the impact velocity of the particle assuming a given circumferential velocity and to achieve collinear collision of particles by a mechanical method with a consideration on energy saving for comminution, a prototype dual cone impact mill was designed and built. This dual cone impact mill mainly consists of two cone disks with the same geometrical dimensions, and the same rotational speeds rotating in opposite directions. There are no grinding media in the dual cone impact mill. The dependence of the comminution effect on two parameters, cone disk speed and air flow rate, was experimentally investigated. The results obtained from grinding quartz and cement clinker indicate that this prototype mill can be used for grinding materials of Mohs hardness up to of 6-7, while achieving mean particle sizes of 10  m.

Abstract: Metal powders behave high strain rate, viscous effect and first hardening then softening deformation characteristics during the forming process of high velocity compaction. The characteristics of high strain rate and viscous effect are described by composite nonlinear viscoelastic body which consists of non-linear spring, linear spring and high strain rate Maxwell element. The deformation characteristics of first hardening then softening can be described by changing the degree of the term of nonlinear spring from greater than 1 to less than 1. Constitutive relation of metal powder in high velocity compaction is established. The degree of the term of nonlinear spring is considered as a function of strain. The function is approximated by linear, quadratic and cubic polynomial and the stress-strain curves are analyzed respectively. Analysis results indicate that the constitutive equation can describe the deformation characteristics of metal powder in high velocity compaction.

Abstract: A new process for manufacturing sintered porous surface tube has been developed. By using this technology, three kinds of sintered porous surface tubes were fabricated, which base material was carbon steel and the sintered layer was bronze powder. And their boiling heat transfer characteristics were investigated experimentally. The experimental results indicated that the boiling heat transfers coefficient and the heat flux of these porous surfaces tubes were increased by 8~14 times and 5~8 times respectively compared with the smooth one. Finally, a new high flux heat exchanger was designed and applied instead of conventional one in a refinery.

Abstract: Iron disilicide（-FeSi2）compounds were synthesized by field-activated pressure assisted synthesis (FAPAS) process, and their thermoelectric properties were measured. Fine microstructure with small pores was obtained in the fabricated samples. The average grain size was approximately 0.3 m. The thermal conductivity in the temperature range of 300-725 K was 3-4 Wm-1K-1, which was considerably lower than that of the same materials synthesized by other methods including SPS process. Lower thermal conductivity provided a higher figure of merit, ZT of 28.50×10-4 in the temperature range of 330-450 K.

Abstract: In this paper, with sodium carbonate as an auxiliary agent in the fly ash, the mixtures were sintered at 880°C for 90 min, then dissolved by different concentrations of sulfuric acid respectively for extracting the hydrated silica. The results show that when the activated ash fly is dissolved by different concentrations of sulfuric acid, the dissolution rates of ash fly increase with the concentration of sulfuric acid increasing. Impurities of aluminum and iron atoms are present in an orderly array of micro-andalusite structure in the generative hydrated silica. When they are dissolved by sulfuric acid for 2%(wt%), the orderly structure is destroyed obviously, and the aluminum and iron atoms are separated out. The purity of hydrated silica can reach 99.9%.

Abstract: In order to explore the micro-torsion mechanism of polarization axis, we studied the microstructure of fused region and taper region of polarization maintaining(PM) fiber devices. Micro crystallizations were observed at the fused region on the fused region and the taper region of polarization maintaining fiber devices with scanning electron microscopy (SEM). The amount and size of the micro crystallizations are increased with decreasing drawing speed and their distribution is asymmetry along the fiber axis. Moreover, micro cracks were observed only at the taper region. The micro cracks became broader and deeper with increasing drawing speed and their distribution is also asymmetry along the fiber axis. The asymmetry of these microstructures is the primary reason that results in micro torsion during the fabrication process of polarization maintaining fiber devices and further deteriorates the optical performance, especially extinction ratio.

Abstract: At present, the surface of computer hard disk substrate has reached atom-scale planarization after chemical mechanical polishing (CMP). Post-CMP cleaning is one of the key factors influencing the CMP performances. During cleaning, cleaning solution and cleaning methods play a key role in cleaning quality and effectiveness. In the present paper, alkylpolyoxyethylene alcohol carboxylic ester (FAC) surfactant was synthesized and its cleaning performances on atom-scale planarization surface of computer hard disk substrate were investigated. Microscope analysis indicated that the prepared detergent containing FAC surfactant exhibited improved cleaning performances compared with the commercial detergent. Further, inductively coupled plasma (ICP) atomic emission spectrometer, auger electron spectrogram (AES) and atomic force microscopy (AFM) analyses after static corrosion test showed that the prepared cleaning solution had lower corrosion to hard disk substrate.