Effect of Powder Particle Size on the Properties and Microstructure of Ti(C,N)-Based Cermet

The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of grains, the one with black cores surrounded by obvious rim structures, and the other whose cores were white with unconspicuous rim structures and adhesive phase. In the cermet made from fine powders, the amount of grains with white cores was much more than that in cermet made from coarse powders. In addition, their properties were also much better.

Powder Size Influence on Tensile Properties and Porosity for PM Ti2AlNb Alloy Prepared by Hot Isostatic Pressing

Pre-alloyed powder of Ti2AlNb alloy was prepared by electrode induction gas atomization method, and the powder was screened into fi ve kinds of powder size distribution. Fully dense Ti2AlNb alloy was prepared by powder metallurgy(PM) using hot isostatic pressing. The properties of pre-alloyed powder and PM Ti2AlNb alloy were tested. Results show that mean grain size of PM Ti2AlNb alloy is infl uenced by powder particle size, but particle size has no signifi cant infl uence on tensile properties. Finer Ti2AlNb powder has low Argon gas bubble ratio and high oxygen content, and poor fl owability of fi ner powder increases the degree of diffculty during degassing. As a result, big pores(> 50 μm) are observed in PM Ti2AlNb alloy prepared by fi ner powder and cause plasticity loss of tensile properties. In order to get a better comprehensive properties of PM Ti2AlNb alloy, powder with an average size(~ 100 μm) is suggested.

Preparation and Characterization on Nano- Sized Barium Titanate Powder Doped with Lanthanum by Sol-Gel Process

The nano-sized BaTiO3:La3+ powders were prepared by sol-gel process using butyl phthalate, barium acetate and lanthanum oxide as raw material, and these samples were tested by means of TG-DTA, XRD and SEM. The results indicate that with the annealing temperature and the doped concentration rising, the powders' particle sizes will increase and decrease respectively. When annealing temperature is 900 ℃ and doped concentration is 7%, the phase is cubic without other phases, and the particle size of power is 43.34 nm.

Preparation of nanosized W/Cu composite powder by sol-gel technique

Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.

Particle Size Distribution,Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

Synthesis and Characterization of Nano-sized Boron Powder Prepared by Plasma Torch

Hydrogen thermal plasma jet was employed to prepare nano-sized boron powder with hydrogen reduction of BCI3. The maximum yield of nano-sized boron powders was about 50% with the operational conditions of H2/BCl3 of 4.5：1, total feed of 4.9 m3/h, and plasma power of 25 kW. The samples were analyzed by X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM）, and inductively coupled plasma - mass spectrometry （ICP-MS）, inductively coupled plasma - atomic emission spectrometry （ICP-AES）, inductive combustion infrared absorption （ICIA） and infrared thermal conductivity of oxygen and nitrogen analyzer （ITCA）. The results show that the boron powders have different crystal structures with higher dispersion and purity. The average diameter is about 50 nm, and the purity is 90.29% or so. This new technology can use simple process to produce high quality boron powders, and is feasible for industrial production.

Synthesis of Neodymium-Doped Yttrium Aluminum Garnet (Nd∶YAG) Nano-Sized Powders by Low Temperature Combustion

The homogeneously dispersed, less agglomerated (Nd0.01Y0.99)3Al5O12 nano-sized powders were synthesized by the low temperature combustion (LCS), using Nd2O3, Y2O3, Al(NO3)3·9H2O, ammonia water and citric acid as starting materials. This method effectively solves the problems caused by solid-state reaction at high temperature and hard agglomerates brought by the chemical precipitation method. The powders were characterized by TG-DTA, XRD, FT-IR, TEM respectively and the photoluminescence (PL) spectra of (Nd0.01Y0.99)3Al5O12 green and sintered ceramic disks were measured. The results show that the forming temperature of YAG crystal phase is 850 ℃ and YAP crystal phase appearing during the calcinations transforms to pure YAG at 1050 ℃. The particle size of the powders synthesized by the LCS is in a range of 20～50 nm depending on the thermal treatment temperatures. The effectively induced cross section (σin) with the value 4.03×10-19 cm2 of (Nd0.01Y0.99)3Al5O12 ceramics is about 44% higher than that of single crystal.

Corrosion resistance of waterborne epoxy coating pigmented by nano-sized aluminium powder on steel

A novel kind of waterborne epoxy coating pigmented by nano-sized aluminium powders on high strength steel was formulated. Several coatings with different pigment volume content (PVC) were prepared. The coating morphology was observed using scanning electron microscopy (SEM), and the electrochemical properties were investigated by electrochemical impedance spectroscopy (EIS). Immersion test and neutral salt spray test were also conducted to investigate the corrosion resistance of the coating. It is demonstrated that the critical pigment volume content (CPVC) value is between 30% and 40%. The coating with PVC of 30% exhibits good corrosion resistance in 3.5% (mass fraction) NaCl solution.

Size effect on compressive strength of reactive powder concrete

In this paper the coefficient and law of the size effect of RPC were studied through experiments and theoretical analysis. The size-effect coefficients for the compressive strength of RPC are deduced through experiments.They indicate that RPC without fiber behaves quite the same as normal or high strength concrete.The size effect on compressive strength is more prominent in RPC containing fiber.Bazant's size effect formula of compressive strength applies to RPC.A formula is given to predict the compressive strength of cubic RPC specimens 100 mm on a side where the fiber dosage ranges from 0-2%.

Effects of Particle Size and Content of Silicon Powder on Strength and Microstructure of Coked Al_2O_3-ZrO_2-C Refractories

Effects of particle size （A：d50 = 336. 9 μm, B：d50 =123.5μm, C： d50=19.5 μm, D： dso=2.21μm） and content （1 wt% , 3 wt% , 5 wt% , 7 wt% ） of silicon powder on cold crushing strength （CCS） , pore size distribution and microstructure of Al2O3 - ZrO2 - C refractories coked at high temperature had been investigated by means of mercury porosimeter, SEM, EDS, tic. The results indicated that particle size and content of silicon powder affected the cold crushing strength of coked specimens. It increased with the addition of silicon powder and its finer particle size. However, it decreased greatly when using too fine silicon powder. The particle size and content of silicon powder also impacted the phase evolution and microstructure of coked specimens, much more β-SiC whiskers constituted network structure and well distributed in specimens with reduction of their slenderness ratios when finer silicon powder was added, corresponding to that, the specimens＇ pore size distribution range became narrower with smaller pore diameter, but β-SiC whiskers were distributed sparsely and the specific pore volume of small pores increased when much finer powder was added. It was worthly mentioned that some nitride could form in specimens with addition of appropriate particle size and content of silicon powder.

Effect of Particle Size and Distribution of Rapidly Quenching NdFeB Magnetic Powder on Magnetic Properties of Polymer-Bonded NdFeB Permanent Magnet

ＰｏｌｙｍｅｒｂｏｎｄｅｄＮｄＦｅＢｐｅｒｍａｎｅｎｔｍａｇｎｅｔ，ｆｉｒｓｔｌｙａｐｐｅａｒｅｄｉｎ１９８０ｓ，ｉｓａｎｅｗｔｙｐｅｏｆｐｅｒｍａｎｅｎｔｍａｇｎｅｔｉｃｃｏｍｐｏｓｉｔｅ，ｗｈｉｃｈｃｏｎｓｉｓｔｓｏｆＮｄＦｅＢｐｅｒｍａｎｅ...

Preparation and characterization of nanometer-sized barium titanate powder by complex-precursor method

A new complex-precursor method was proposed to prepare nanometer-sized BaTiO3 powder. Firstly,Ti2O(O2)2(ta)24-complex ions were prepared by the reaction of H2O2,Ti4+ and ta3-(ta=C6H6O6N3-) with a desirable amount of surface active agent,and then the Ba2Ti2O(O2)2(ta)2·2H2O precursor was obtained by reaction between Ti2O(O2)2(ta)24-and Ba2+. Finally,the precursor was annealed at 800 ℃ for 2 h to obtain BaTiO3 powder. The morphology,the particle size distribution,the purity and the molar ratio of Ba to Ti of BaTiO3 powder were investigated systematically by TEM,XRD,IR,Raman and chemical analysis,respectively. The results show that the BaTiO3 powders with the grain size of about 40 nm have a tetragonal crystalline structure at room temperature and a spherical morphology.

Effect of Slow Cooling in Reducing Pore Size in a Sintered Powder Metallurgical 6061Aluminium Alloy

The usage of powder metallurgy aluminium compacts in lieu of ferrous components in automotives helps to lower vehicle weight. The major drawback in the commercially available press sintered aluminium alloy is porosity which is mainly dependent on the powder metallurgical process parameters such as compaction pressure, sintering temperature and cooling rate after sintering. In this paper the effect of particle size and furnace controlled cooling after sintering on porosity level and micro hardness of an elemental 6061 aluminium alloy has been investigated. Aluminium particle sizes of 20 μm and 150 μm were used. The elemental 6061 aluminium alloy powders are warm compacted at 175 MPa. After sintering for about one hour at 600°C, the aluminium compacts were furnace cooled at the rate of 1°C /min to different temperatures of 500°C, 400°C, 300°C and 200?C. When the cooling temperature after sintering inside the furnace is effected at various temperatures from 600°C to 200°C, for a precipitate hardened aluminium compacts with aluminium particle size of 20 μm, the porosity level reduced by 26% and that for aluminium particle size of 150μm, the porosity level reduced by 23%. Marked improvement in micro hardness value is also observed correspondingly.

Hydrothermal synthesis of boehmites with various particle sizes and transition to α-Al_2O_3 powders by calcination

Boehmite powders with various particle sizes have been prepared by hydrothermal method and the α-Al2O3 powders yielded after subsequent calcination have been studied. Dispersive crystalline boehmite powders of 30-100 nm, 0.4-0.6μm and 1μm in size were obtained respectively by changing the hydrothermal precursors and the pH value of hydrothermal slurry. Calcination of boehmite powders of 30-100 nm at 1250℃ for 1h resulted in the formation of single-phase α-Al2O3 , and the products consisted of vermicular particles. The boehmite powders of 0.4-0.6μm were also fully converted to α-Al2O3 at 1250℃, and the products consisted of plate-like particles with the same size of 0.4-0.6μm. The boehmite powders of 1μm calcined at 1350℃ for 2h were still composed of a little proportions of transition aluminas besides α-Al2O3, and the particles sintered severely. The reaction processes for the formation of crystalline boehmites under hydrothermal conditions and α-Al2O3 powders during calcination have been discussed.

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder Filled Polypropylene

Polypropylene composites of snail shell powder were prepared at filler contents, 0 to 40 wt%. The particle sizes of the snail shell powder investigated were 0.150, 0.30, and 0.42 μm. Talc, of particle size, 0.150 μm was used as the reference filler. The polypropylene composites were prepared in an injection moulding machine and the resulting composites were extruded as sheets. Some mechanical and end-use properties of the prepared composites were determined. Results showed that the snail shell powder improved the tensile modulus, flexural strength, and impact strength of polypropylene and these properties increased with increases in the filler content and decreases in the filler particle size. The elongation at break of the composites was however observed to decrease with increases in the filler content, and particle size. The elongation at break of talc filled polypropylene was zero, an indication of the brittle nature of polypropylene composites of talc. The hardness, water sorption (24-hr) and specific gravity of the composites were found to increase with increases in the filler content, and decreases in the filler particle size. The level of water absorbed by snail shell powder composites of polypropylene is considerably higher than that of talc filled polypropylene. The flame retardant properties of the prepared composites were however found to decrease with increases in the filler content, and particle size. Generally, snail shell powder was found to show greater property improvement over talc in the prepared composites.

粒径对铁皮石斛粉多糖释放及其粉体特性影响

为明确粒径对铁皮石斛(D. officinale)粉中多糖溶出率及其粉体特性的影响,采用中药粉碎机结合球磨仪制备了8种不同粒径的铁皮石斛粉体,研究各粉体样本的粒径分布、比表面积、多糖溶出率、粉体流动性、水合特性、表面微观结构及色差变化。结果表明,[20,200)目粉体中多糖溶出率随粒径减小总体呈上升趋势,但≥200目时溶出率逐渐下降;粉体流动性参数(休止角、滑动角和Carr’s指数)与粒径呈负相关,即粒径越小流动性越差,尤其是[200,250)目较[150,200)目粉体的流动性明显变差;水合特性(WHC、WSC和WSI)随粒径变小先升后降,拐点同样出现在200目前后;色差分析表明,粉体色度参数(L*、a*、b*和ΔE值)也是在[150,200)目与[200,250)目的变化幅度最大。上述结果主要与[200,250)目粉体的比表面积较[150,200)目显著增加(68.1%)有关。综上,[150,200)目(d50=95.6μm)的铁皮石斛粉兼具较好的粉体特性和多糖释放率,同时保证了粉体细度。本研究结果为铁皮石斛的粉体化高效加工及高值化利用提供了理论参考。

饲料中不同蛋黄粉添加量对孔雀鱼繁殖力的影响

本文以孔雀鱼为试验材料,研究了饲料中不同蛋黄粉添加量对孔雀鱼繁殖周期和产仔量的影响。结果表明,饲料中蛋黄粉添加量越高,孔雀鱼繁殖周期越短,处理1(饲喂基础饲料+2%蛋黄粉)、处理2(饲喂基础饲料+4%蛋黄粉)、处理3(饲喂基础饲料+8%蛋黄粉)与CK(饲喂基础饲料)之间差异均显著(P<0.05),但处理1、2、3之间差异不显著(P>0.05);随着饲养时间延长和饲料中蛋黄粉添加量增多,孔雀鱼产仔量增多,处理1、2、3的第3次产仔量均显著高于CK(P<0.05),但处理1、2、3之间差异不显著(P>0.05);处理2的孔雀鱼总产仔量显著高于处理1(P<0.05),虽然处理3的孔雀鱼总产仔量最高,但其与处理2之间差异不显著(P>0.05)。可见,在饲料中添加蛋黄粉可缩短孔雀鱼繁殖周期,提高孔雀鱼产仔量,最适添加量为4%。

负载下活性粉末混凝土钢筋网加固足尺混凝土柱轴压性能试验研究

为提高负载下钢筋混凝土(RC)柱的轴心抗压性能,使用活性粉末混凝土钢筋网(RPCSM)对负载下的RC足尺柱进行加固,设计制作了7根RC方柱试件,其中1根未加固对比柱、1根端部箍筋加密加固柱、2根RPCSM加固柱、3根端部箍筋加密RPCSM加固柱。考虑加固层厚度、钢筋网配筋率和端部箍筋加密对轴心受压RC柱性能的影响,进行了试验研究并分析了各试件的破坏模式、荷载-变形关系和应变变化规律。结果表明:加固柱的承载力提高了2.81~3.82倍;原混凝土柱与RPCSM加固层界面粘结可靠,共同工作良好;随着钢筋网配筋率的提高以及加固层厚度的增加,端部箍筋加密后整体性的提高,承载力和轴向变形能力提高,但延性有所下降。结合规范和破坏机理,给出了承载力计算公式,以促进该加固技术的推广。

非水溶液体系中晶种法制备球形银纳米颗粒

以丙三醇作溶剂,硝酸银为原料,聚乙烯吡咯烷酮(PVP)为分散剂,硼氢化钠为还原剂制备了银纳米晶种;以此银纳米粒子作为初级晶种,以丙三醇作溶剂和还原剂,通过升温提高丙三醇的还原性制备银纳米颗粒。研究分散剂种类、生长液银浓度、晶种加入量对银粉的影响,采用X射线粉末衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)对制备产物的结构、物相、形貌进行表征。结果表明,通过改变条件可以制备出分散性良好、粒径均匀的70nm左右的球形银粉。

丝电爆法制备3D打印金属钽粉的试验研究

针对微米球形钽粉难以制备、粒径不易控制等问题,论文利用丝电爆法成功制备了微米球形钽粉,通过改变初始充电电压、钽丝丝径进行试验,采集丝电爆过程的电压与电流信号,对其机理进行了分析,并表征了所制备的微米钽粉。结果表明:不同丝径下的丝电爆炸过程都经历了五个阶段,丝径为0.4mm钽丝在电爆炸过程中发生了完全气化,而丝径为0.2mm、0.3mm钽丝并未完全气化,处于气液混合的状态;随着初始充电电压的不断增大,一定丝径钽丝上的沉积能量会有不同程度的增加,所制备的微米球形钽粉的平均粒径在逐渐减小;在初始充电电压为10kV时,丝径为0.2mm钽丝所制备的钽粉集中分布在28μm~36μm之间,分布范围较窄,球形度良好,且满足微米级3D打印金属粉的粒径要求。