气流循环粉碎法制备Al2O3超细粉的研究

以粗颗粒Al2O3粉为原料,采用气流循环粉碎法制备了d50＜1μm的Al2O3超细粉.按正交表L9(34)安排正交试验,通过方差分析确定了制备Al2O3超细粉的最佳气流循环粉碎条件,并分析了各因素对气流循环粉碎过程的影响程度.不同物料的最佳气流循环粉碎条件应通过实验确定.在本研究的实验条件下,制备Al2O3超细粉的最佳条件为进气压力1.0 MPa,给料压力0.4 MPa,循环时间1.5 h.     

400MPa级超细晶粒钢焊接接头的低温韧性

利用CO2+Ar气体保护焊,分别采用单道焊接和双道焊接工艺对厚度为8 mm的400 MPa级超细晶粒钢钢板进行了焊接,采用系列冲击试验方法对焊接接头的低温韧性进行了研究。试验结果表明,在焊接接头中,焊逢位置低温韧性较差。由于双道焊较小的热输入,减小了焊缝及热影响区组织粗化,其焊接接头的低温韧性好于单道焊,并使热影响区面积变小。     

Ultra-fine particles release from hardcopy devices: sources, real-room measurements and efficiency of filter accessories

The release of ultra-fine particles (UFP, d < 0.1 µm) from hardcopy devices such as laser printers into the indoor environment is currently a topic of high concern. The general emission behavior of a printer can be examined by conducting emission test chamber measurements with particle-counting devices. Chamber experiments with modified laser printers operated without toner or paper also revealed UFP emissions. On the basis of these results we reasonably doubt the opinion that UFPs primarily originate from the toner. Instead, the high-temperature fuser unit is assumed to be one source for ultra-fine particle emission. UFP release typically follows the flow path of the cooling air which may leave the printer casing at various points (e.g. the paper tray). This limits the usability of the commercial filter systems available because the released particles could leave the printer without passing through the filter. Chamber measurements with various filter systems retrofitted to a laser printer demonstrate different efficiencies of UFP reduction. Complementary experiments were carried out in an office room. Here the decay of the particle concentration after a print job was about ten times slower than in the test chamber. A toxicological assessment of the emitted particles requires that their chemical composition be known. Due to the low mass of the released UFPs chemical analysis needs a prior enrichment on a feasible media. Experiments using electrostatic precipitation showed a flame retardant (tri-xylyl phosphate) whose concentration on the media was dependent on the number of pages printed. Whether this compound was particle-bound could not be determined.     

Microstructure and Mechanical Properties of Semi-continuous Equal-channel Angular Extruded Interstitial-free Steel

An innovative method called semi-continuous equal-channel angular extrusion(SC-ECAE)has been developed to produce ultrafine grained steel by inducing severe plastic deformation.In contrast to the external forces that are exerted on specimens in traditional ECAE,the driving forces are applied on the dies in the novel SC-EACE process.Commercial interstitial-free steel sheets with width of 160 mm and thickness of 2 mm were processed repeatedly to various passes at room temperature using this method.The microstructural evolution was characterized using high-resolution electron backscatter diffraction(EBSD),and the mechanical properties were investigated by tensile testing.The EBSD images indicated that the fraction of high-angle boundaries(HABs)began to increase gradually after four passes;after six passes,elongated HAB structures with nearly submicron-scale average spacings were formed.The tensile testing results showed that strengthening was accompanied by a decrease in tensile ductility,but no significant anisotropy was observed.After 10 passes,a final HAB fraction of about 90% and an overall grain size of 0.55μm,yield strength of 638.7 MPa,an ultimate tensile strength(UTS)of 710.3 MPa,and a total elongation of 12.0% were obtained.     

Scalable Parallel Algorithms for Geometric Pattern Recognition

This paper considers a variety of geometric pattern recognition problems on input sets of size n using a coarse grained multicomputer model consisting of p processors with Ω(n/p) local memory each (i.e., Ω(n/p) memory cells of Θ(log n) bits apiece), where the processors are connected to an arbitrary interconnection network. It introduces efficient scalable parallel algorithms for a number of geometric problems including the rectangle finding problem, the maximal equally spaced collinear points problem, and the point set pattern matching problem. All of the algorithms presented are scalable in that they are applicable and efficient over a very wide range of ratios of problem size to number of processors. In addition to the practicality imparted by scalability, these algorithms are easy to implement in that all required communications can be achieved by a small number of calls to standard global routing operations.     

Microstructures and Toughness of Weld Metal of Ultrafine Grained Ferritic Steel by Laser Welding

3 mm thick 400 MPa grade ultrafine grained ferritic steel plates were bead-on-plate welded by CO2 laser with heat input of 120～480 J/mm. The microstructures of the weld metal mainly consist of bainite, which form is lower bainite plates or polygonal ferrite containing quantities of dispersed cementite particles, mixed with a few of low carbon martensite laths or ferrite, depending on the heat input. The hardness and the tensile strength of the weld metal are higher than those of the base metal, and monotonously increase as the heat input decreases. No softened zone exists inheat affected zone (HAZ). Compared with the base metal, although the grains of laser weld are much larger, the toughness of the weld metal is higher within a large range of heat input. Furthermore, as the heat input increases, the toughness of the weld metal rises to a maximum value, at which point the percentage of lower bainite is the highest, and then drops.     

新型油井水泥触变剂的研究与应用

常规油井水泥触变剂常存在触变性不够强、影响施工安全、综合性能欠佳等问题。为此,通过将合成聚合物和超细无机材料以2∶3的比例复配,开发出一种新型油井水泥触变剂BCJ-200S,研究了其应用性能。结果表明,该触变剂可显著提高水泥浆触变性,且温度影响小,90℃加入1.5% BCJ-200S后水泥静浆静置10 min的胶凝强度从2.3 Pa增加到61.0 Pa,静置前后的φ₃₀₀读数分别为206和210,再静置10 min胶凝强度为61.3 Pa,其触变结构可逆性良好,对水泥浆稠化、失水、强度等性能没有产生不良影响;其还可改善水泥石的力学性能,增强水泥石抗破坏能力;另外,配伍性研究结果表明,该触变剂具有良好的现场适应性。其在大港油田官38-22油井进行了首次应用,该井采用12 m3触变水泥浆封堵Ng2出水井段,一次封堵成功,最高挤注压力达16 MPa,钻塞后对封堵层试压8 MPa合格,解决了该井出水难题。      

Corrosion and ion release behavior of ultra-fine grained bulk pure copper fabricated by ECAP in Hanks solution as potential biomaterial for contraception

Ultra-fine grained (UFG) bulk pure copper has been successfully fabricated by equal-channel angular pressing (ECAP), with the grain size about 380 nm after 8 passes. The potentiodynamic polarization results of the ECAP copper specimens tested in Hanks solution revealed that the corrosion current of UFG copper is higher than that of the coarse grained copper. The cupric ion release behaviors of UFG copper immersed in Hanks solution for 30 days only displayed a burst release during the first 3 days (in comparison to the 1-2 months for the conventional Cu) from 115 μg/day to 12.5 μg/day, after which the ion release remained constant and slow. During the immersion experiments, Cu₂O was the only corrosion product found on the surface and it took 10 days or so to form a uniform Cu₂O layer. Uniform corrosive damage on the surface and few localized corrosion is observed. The above results indicate that UFG copper could have high potential as biomedical materials for contraception.     

尼尔森重选在我国石英脉型金矿选矿工艺中的应用

石英脉型金矿是我国重要的金矿工业类型,矿石中金多以自然金的形式存在。尼尔森选矿机是一种高效离心选矿设备,能够有效回收矿石中的自然金,因其富集比高、环境友好等优势,已在我国石英脉型金矿选矿工艺中得到广泛应用。为了尽可能地提高金回收率,尼尔森重选通常与浮选、氰化等工艺联合使用。目前国内研究最多、应用最广泛的是尼尔森重选-浮选工艺和尼尔森重选-全泥氰化工艺,此外,还有少数关于浮选-尼尔森重选工艺和尼尔森重选-无氰提金工艺的研究。在介绍各个工艺流程研究现状的基础上,重点列举了尼尔森重选-浮选工艺和尼尔森重选-全泥氰化工艺的生产实例,基于各工艺优缺点的综合分析,提出尼尔森重选-浮选工艺普遍适用于我国石英脉型金矿。     

Structural Ultrafine Grained Steels Obtained by Advanced Controlled Rolling

Steels with ultrafine grains (lower than 5 μm), which usually known as ultrafine ferrite or ultrafine grained materials, are presently the object of intense research, because of the improvement in resistance and fracture toughness they may reach compared to conventional steels (with grain sizes above this value). It is shown that the forenamed steels designated in the Euronorm EN 10149-2, which are manufactured by advanced techniques of controlled rolling and mainly used in automotive industry, have an ultrafine grain size in the range of 2.5 to 3.5 μm, and with elastic yield stresses higher than 400 MPa. Based on the Morrison-Miller criterion, it is shown that values of the strain-hardening coefficient lower than 0.08 would make the industrial application of these steels unfeasible.