一种新型镍基粉末高温合金挤压工艺研究

针对一种新型粉末高温合金WZ-A3进行了一系列的热挤压工艺试验,探究了挤压温度、挤压速度、挤压比对棒材显微组织的影响以及棒材的整体组织均匀性。结果表明：在恒定挤压速度35 mm/s、挤压比4.7:1条件下,挤压温度为1110 ℃时,合金棒材已发生完全动态再结晶,当挤压温度继续增加,晶粒发生明显长大。在恒定挤压温度1110 ℃、挤压速度35 mm/s条件下,挤压比为2.1:1时,合金再结晶不完全而且存在较多原始颗粒边界;当挤压比增加至4:1~4.7:1时,再结晶程度完全充分,PPB也完全消除。在恒定挤压温度1130 ℃、挤压比4.7:1条件下,在20~50 mm/s范围内随着挤压速度的增加,晶粒呈长大趋势。在挤压温度1110 ℃、挤压速度35 mm/s、挤压比4.7:1条件下整个挤压棒材的组织较为均匀,从棒材头部到尾部,晶粒略微细化,并且棒材边缘的组织较心部和1/2R更细小。     

Biopolymer-assisted green synthesis and characterization of calcium hydroxide nanoparticles

The use of biopolymers in the synthesis of different nanostructures can be a cost effective and eco-friendly approach. In the present study, a facile and “green” sol–gel method was employed for preparing calcium hydroxide nanoparticles (Ca(OH)₂-NPs) in gelatin matrix as a bio-template. Prepared nanoparticles were characterized by different instruments such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), and Fourier transform infrared spectroscopy (FTIR). The PXRD analysis revealed hexagonal Ca(OH)₂-NPs with preferential orientation in (101) reflection plane. They are hexagonal in shape with a mean particle size of approximately 42 nm in thickness. The synthesized Ca(OH)₂-NPs using gelatin were found to be comparable to those obtained from conventional methods using hazardous capping/stabilizing polymeric agents or surfactants and this route can be an excellent alternative for the synthesis of Ca(OH)₂-NPs using biomaterials.     

Microencapsulated Fish Oil Powder Formulation with Improved Resistance to Oil Leakage During Powder Compression

The effects of the addition of pectin to a primary fish oil emulsion stabilized by a heated milk protein–carbohydrate mixture, and heat treatment of emulsion at low pH (with or without the addition of pectin) on the properties of final emulsions (pH 7) and powders (~42 % w/w/fat) prepared from these emulsions were examined. Either the addition of pectin (without the additional heat treatment at pH 3), or additional heat treatment step at pH 3 (with or without pectin) reduced the surface oil and free oil of spray dried powders, and also reduced oil leakage on powder compression. However, the extra heat treatment step at low pH to the emulsion (without pectin) resulted in a greater susceptibility to oxidation of EPA and DHA in the powder. A judicious choice of ingredients for formulating and processing emulsions prior to spray drying enables the application of food‐grade microencapsulated fish oil powders in directly compressible tablet applications.     

烟花圆盘造粒机的设计与造粒工艺研究

研发一种烟花圆盘造粒机,基于粉体成粒理论,通过单因素实验分析黏合剂的雾化压力及流量、供粉速率、料斗喷嘴与出料口距离和抛光时间4个单因素对微丸质量的影响,确定了工艺参数。然后进行了正交实验,在对实验所得造粒样品进行粒度分级的基础上,最终确定了造粒的最佳工艺参数。     

空滤试验系统中的新型给粉机研制

给粉机是滤清器试验测试系统中的试验粉供送装置.能否按照标准和设计要求准确给粉对于滤清器试验有很大影响.根据滤清器试验对加粉的要求设计一种新型的给粉机.使用刮刀从旋转粉盘的沟槽中刮取试验灰,通过调节刮刀插入深度和旋转粉盘的转速来调节给粉速度.机器内部的试验灰和外界空气接触面积小,同时在储粉桶中设计了干燥措施,保证内部试验灰的长久干燥.     

Combined Usage of Sodium Borohydride and Aluminum Powder for High‐performance Hydrogen Generation

The sodium borohydride (NaBH₄)‐based hydrolysis system has received considerable interest as a potential hydrogen source for vehicular application. But its practical application was greatly restricted by the low hydrogen density and high material cost. In the present study, we reported that addition of aluminum (Al) powder is an easy but highly effective way for addressing the problems of the NaBH₄‐based hydrolysis system. The system was composed of alkaline aqueous solution of NaBH₄ and solid powder mixture of Al and Co₂B catalyst. The effects of alkaline concentration, NaBH₄ concentration and Al amount on the hydrogen generation (HG) performance of the system were investigated. Our study showed that there exist a mutual‐promoting mechanism between the hydrolysis reaction of NaBH₄ and the Al/H₂O reaction. As a consequence, this system exhibited distinct advantages over the conventional NaBH₄‐based system in terms of HG rate, fuel conversion, hydrogen density and H₂ production cost. These favourable attributes make the (NaBH₄+Al)/H₂O system attractive for mobile/portable hydrogen source applications.     

Influence of Thermal Treatment on Microstructure and Hardness of Niobium Alloyed PM‐Tool Steel

Abstract

This work describes carbides present in the tool steel containing 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W, prepared by the powder metallurgy (PM) process. The influence of thermal treatment conditions on carbide behavior is investigated. During austenitization, some dissolution of M₇C₃ occurs, while MC carbides are thermally stable. So, the quenched steel is composed of two types of carbides: chromium rich M₇C₃ and niobium rich MC, besides martensite and retained austenite. During tempering of the hardened steel at the temperatures above 480°C, the precipitation of very fine carbides and martensite recovery occur, which results in secondary hardening. Precipitated particles are predominantly vanadium and molybdenum rich MC, M₂C, and M₆C carbides.     

An investigation of density determination methods for porous materials,small samples and particulates

Three new density measurement techniques have been devised and evaluated for the measurement of non-standard objects, namely porous material samples, small solid samples, powders and particulates. Hydrostatic weighing has traditionally been used to determine the density of solid artefacts. This method is not, however, suitable for porous objects since they will adsorb water making weighing in water unstable and possibly detrimental to the material samples. A method, weighing the artefacts in inert gas, has been developed for this application. The density determination of small solid artefacts cannot be achieved by conventional hydrostatic weighing techniques due to limits on the accuracy with which the weight-in-water can be determined. A density gradient column method for such measurements, delivering very low uncertainties, has been developed and evaluated. A liquid pyknometry method has also been investigated as an alternative to traditional helium and mercury pyknometry. The technique offers improved accuracy and a precise determination of thermal coefficient of the sample under test.     

气力输送粉料流量测量的差压－浓度法

本文基于物料稀相气力输送压损比与混和比（ｍ）的比例关系式：　＝１＋ｋ·ｍ提出了一种以气固两相管程总压降（△Ｐｔ）和粉料浓度（βｓ）为测量参数的在线测量气力输送粉料流量的新方法，建立了差压－浓度法粉料流量测量数学模型及格应的测量系统。经实验验证，精度为５％，满足工业应用要求。     

混粉准干式电火花加工介质击穿机理研究

混粉准干式电火花加工以气、液、固三相流作为工作介质,能够有效改善气中加工短路率高、加工效率低的问题。以纯净气体介质的击穿理论为基础,对三相流工作介质的击穿机理进行理论分析,阐明固、液分散相的作用机制。建立混粉准干式电火花加工的极间电场强度表达式,给出三相流中加工的放电间隙计算式,从理论上证明分散相的加入使得混粉准干式电火花加工的放电间隙较气中加工大,指出放电间隙增大是加工效率提高的一个重要原因。进行压缩空气中和三相流介质中的放电加工对比试验。测得两种加工介质中的放电间隙值,试验证实三相流工作介质具有放电间隙增大效果。测得放电电压波形,证实气体连续相中固、液分散相的加入能够降低短路率,提高加工稳定性。