Preparation of composite particles coated with two kinds of solid powders by semi-chemical recycle method

Polymer microspheres coated with two kinds of solid powders were prepared by the semi-chemical recycle method of waste plastics. Magnetite (Fe₃O₄) and silicon carbide (SiC) were added as solid powders so as to give thermal and electric conductivity and magnetization. Waste expanded polystyrene was used as raw materials of polymer matrix of composite particles. In the experiment, the oil phase dissolving expanded polystyrene was dispersed to form the O/W dispersion in the continuous water phase in which polyvinyl alcohol and magnetite powders were added. And then, silicon carbide powder was added into the O/W dispersion. Composite particles prepared had the structure that a polymer particle was covered with two kinds of solid powders. The amount of each solid powder adhered on the surface of polymer microsphere was strongly affected by an addition time of silicon carbide powder. Furthermore, the gradient adhesion layer due to two solid powders was found to be formed on the surface of polymer microsphere.     

Electrostatic Effects on Dispersion,Transport, and Deposition of Fine Pharmaceutical Powders: Development of an Experimental Method for Quantitative Analysis

Currently, there is no standard method for testing the electrostatic properties of pharmaceutical powders. The objective of this study was to develop a method of characterizing the dispersion, charging, and transport properties of fine powder flowing through tubes of different materials. Powders of known composition and size distribution were dispersed pneumatically and transported through a short section of tubing containing spiral baffle inserts of the same material to simulate powder flow in long sections of horizontal and vertical tubes with bends. The test powder was dispersed using ring jet suction and passed through the baffled tube to a sampling chamber, from which the powder cloud was sampled for particle size and electrostatic charge distribution measurement using an Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) analyzer. Experimental data on the tribocharging and transport properties of different powders are presented along with an explanation of the charging mechanisms. Analyses of particle size and electrostatic charge distributions in real time and on a single particle basis using the E-SPART analyzer coupled with surface structure analyses with XPS and UPS showed that: (1) most powders are charged bipolarly with relatively high charge-to-mass ratio (Q/M) values that would have a strong effect on transport and deposition of powders; and (2) surface structures, particularly adsorbates, influence the work function and tribocharging of powder. Different methods, including plasma treatment, with minimal changes or contamination of the bulk properties of the powders are also suggested. pharmaceutical powders tribocharging dispersion work function charge distributions charge decay plasma treatment     

Electrostatic Effects on Dispersion, Transport, and Deposition of Fine Pharmaceutical Powders: Development of an Experimental Method for Quantitative Analysis

Currently, there is no standard method for testing the electrostatic properties of pharmaceutical powders. The objective of this study was to develop a method of characterizing the dispersion, charging, and transport properties of fine powder flowing through tubes of different materials. Powders of known composition and size distribution were dispersed pneumatically and transported through a short section of tubing containing spiral baffle inserts of the same material to simulate powder flow in long sections of horizontal and vertical tubes with bends. The test powder was dispersed using ring jet suction and passed through the baffled tube to a sampling chamber, from which the powder cloud was sampled for particle size and electrostatic charge distribution measurement using an Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) analyzer. Experimental data on the tribocharging and transport properties of different powders are presented along with an explanation of the charging mechanisms. Analyses of particle size and electrostatic charge distributions in real time and on a single particle basis using the E-SPART analyzer coupled with surface structure analyses with XPS and UPS showed that: (1) most powders are charged bipolarly with relatively high charge-to-mass ratio (Q/M) values that would have a strong effect on transport and deposition of powders; and (2) surface structures, particularly adsorbates, influence the work function and tribocharging of powder. Different methods, including plasma treatment, with minimal changes or contamination of the bulk properties of the powders are also suggested.

pharmaceutical powders tribocharging dispersion work function charge distributions charge decay plasma treatment     

Effects of Powder Velocity and Contact Materials on Tribocharging of Polymer Powders for Powder Coating Applications

Electrostatic powder deposition using corona charging is widely used in a plethora of industrial applications. Disadvantages of this technique are back corona onset and the Faraday penetration limitation. Another method to charge powders is to use tribochargers. Tribocharging depends upon the work function difference between the contacting materials and generates bipolarly charged particles. In this study, acrylic and epoxy powders were fluidized and charged by passing through stainless steel, copper, aluminum, and polycarbonate static mixers, respectively. The particle velocity and powder flow rate were varied to determine their effect on the net charge-to-mass ratio (Q/M) acquired by the powders. The Q/M increased rapidly with velocities between 1.5 to 2.5 m/s and stabilized for higher velocities but decreased with increasing powder flow rate at a constant velocity. The net positive or negative charge on each powder was determined to be dependant on the charger material. The use of an aluminum charger (net negative charge) in combination with a PTFE finger nozzle (net positive charge) resulted in a net powder Q/M of - 0.05 μC/g. The generation of an ion-free powder cloud with high bipolar charge but overall charge density of almost zero is anticipated to provide a better coverage of recessed areas.     

Multi-layered adsorption of 3Y–ZrO2 nanoparticles on polystyrene microsphere

Multi-layered adsorption of 3Y–ZrO₂ nanoparticles on polystyrene (PS) microsphere using layer-by-layer (LBL) assembly technique was investigated. By employing sodium poly (acrylic acid) (PAANa) and polyethylenimine (PEI) to modify the zeta potential of the powders, the heterocoagulation takes place between the coating powders and microspheres substrate and the zirconia coating on the surface of polystyrene spheres was successfully formed. Dense, uniform multi-layered zirconia can be obtained on the surface of polystyrene spheres and the thickness of zirconia coating increased by repeating the coating process. The diameter of the spheres expands to 1.5 μm after the first coating and 1.65 μm after the third coating comparing with the original polystyrene spheres with diameter of 1.4 μm.     

Effect of fabrication method on the structure and properties of a nanostructured nickel-free stainless steel

An ASTM F2581 nanostructured stainless steel was fabricated by two different powder metallurgy routes; Hot Powder Forging (HPF) and Binder Assisted Extrusion (BAE) methods. Their structure and mechanical properties were investigated and compared. In both fabrication methods, the alloy powder was made by using main alloying elements through mechanical alloying, along with the addition of a sintering aid. In the BAE method, a paste was prepared by mixing alloy powders with polymer followed by cold extrusion, polymer removal, and sintering. In the HPF method, the alloy powders were hot forged under high pressure. The structure and the size of the austenite crystallite of the samples were investigated by scanning electron microscopy (SEM), FE-SEM, x-ray diffraction (XRD) and transmission electron microscopy (TEM). It was determined that the samples prepared by the HPF method are generally denser than those made via BAE. The porosities are smaller and almost uniform in size and morphology in the HPF method. Furthermore, microhardness and tensile tests were performed on the samples. The results show that the ductility of BAE samples is higher than the HPF samples. The fracture surface of the BAE sample has deeper dimples, indicating higher ductility for BAE samples. On the other hand, both the hardness and strength of HPF samples are higher than those of the BAE samples. The results show that both methods produced specimens with considerably higher strength and hardness than conventional 316L stainless steel.     

复合级配17-4PH不锈钢粉末电磁先导阀阀芯顶杆组织及其性能

本研究分别以单一气雾化、气雾化∶水气联合雾化=3∶1复合级配17-4PH不锈钢粉末为原材料,采用粉末微注射成形方法制备电磁先导阀阀芯顶杆。对制备得到的电磁先导阀阀芯顶杆的表面质量、微观结构、收缩率及致密度进行测试,并对复合级配粉末阀芯顶杆烧结件进行热处理,分析热处理后样品的硬度以及磨损性能等指标。研究结果表明:复合级配粉末对具有微结构的阀芯顶杆的表面质量、微观结构、收缩率及致密度有着重要的影响。气雾化∶水气联合雾化=3∶1的复合级配17-4PH不锈钢粉末阀芯顶杆注射坯件表面质量相对较好,提高了粉末的烧结活性,烧结样品致密度达到98.86%,收缩率更为均匀,主要组织为马氏体,优于单一气雾化粉末的烧结性能。热处理后阀芯顶杆的组织为马氏体和少量的奥氏体,硬度显著提高,耐磨损性能得到了明显的改善。     

激光快速成形304不锈钢性能及微观组织研究

目的 满足实际生产需求,提高304不锈钢的抗拉强度。方法 在304不锈钢粉末中添加不同质量分数的Ni60AA粉末,采用激光束对粉末进行快速成形,得到不同的试样。通过金相显微镜对不锈钢试样的显微组织进行观察,利用拉力试验机对试样进行抗拉强度测试。结果 随着添加Ni60AA粉末含量的增加,板材试样的抗拉强度呈现出先增大后减小的趋势,当Ni60AA粉末的质量分数为10%时,试样抗拉强度最大,为754~771MPa。结论 添加Ni60AA粉末后,激光快速成形的304不锈钢板材试样微观组织中有部分镍化合物析出,形成强化相,304不锈钢试样的抗拉强度得到很大提高。     

Microstructure and Properties of Laser Surface Alloying 304 Stainless Steel with Si

Silicon was added to the surface of 304 stain-less steel by laser melting the sprayed preplaced Sipowders.The optical microscopy,X-ray diffractionand EPMA were employed to investigate themicrostructure and chemical composition of thelaser surface alloyed layer.The hardness of the al-loyed layer was measured by microhardness testand wear resistance was evaluated by scratch test.Corrosion resistance of laser alloyed sample wasstudied in 1N H_2SO_4+0.1N NaCl and0.5N HCl+0.5N NaCl aqueous solutions.Amicrocrystalline intermetallic compound coatingwith smooth surface and good chemicalhomogeneity without porosity and crack is ob-tained.The hardness is about 720 HV.The wear re-sistance is 2 times better than that of the substrate.The corrosion resistance of the laser alloyed sampleis much better than that of 304 stainless steelsample.     

羧基化聚苯乙烯微球的制备及其自组装行为研究

采用分散聚合法,以乙醇、水为分散介质,苯乙烯为共聚单体,聚乙烯吡咯烷酮（PVP）为稳定剂,AIBN为引发剂,丙烯酸（AA）为功能共聚单体,制备了粒径为100—1000nm羧基化聚苯乙烯微球,研究醇水比、分散剂、引发剂用量对微球粒径及分布的影响,分析微球表面形貌、粒径分布、表面羧基含量,结果表明,胶体晶体是面心立方密排结构,微球单分散性好,表面光滑,球形度好,表面羧基含量最高可达到0．206mmol／g。同时,用垂直沉积法制备出较大范围内呈现高度有序的密排结构聚苯乙烯胶体晶体。     

粉末表面化学镀铜烧结不锈钢的组织和腐蚀行为

研究了不锈钢粉末表面化学镀铜对烧结不锈钢组织和耐蚀性的影响.实验表明,以化学包覆不锈钢粉的形式加入1～5wt%的铜,在1150℃液相烧结时,在烧结不锈钢中,铜元素分布的均匀性以及烧结体的密度比机械混合方式加入铜都有很大提高;同时通过电化学实验表明,化学镀铜方式有利于提高不锈钢烧结体的耐蚀性.     

Coated WC powders by sputtered nanostructured Ni and stainless steel

The efficiency of the powder surface modification depends on their surface characteristics. Sputtering has been revealing an important skill for the coating of powders with metal and metal alloys, with important consequences on the surface properties. However, some modifications in the holder of this particulate substrate have obliged to set up some changes in a non-conventional sputtering system. The aim of the present work is to demonstrate the efficiency of the prototype developed and the influence of deposition parameters in the quality of coated powders; tungsten carbide powders and austenitic stainless steel (SS) and nickel targets have been selected. These types of materials are used in tungsten carbide parts/devices as binders to promote the technological process; as coatings they decrease the interparticle friction reducing the pressure of shape forming as well as the temperature of sintering process.     

具有不同浸润性功能有机表面薄膜的制备

通过开发的有机镀膜技术,选用具有不同功能基团的有机镀液对不锈钢表面进行改性.借助于红外光谱、接触角和表面自由能等测试对有机镀膜处理的不锈钢表面薄膜进行了表征.实验结果表明,经过TTN溶液有机镀膜后,不锈钢表面自由能升高、蒸馏水接触角减小,具有了亲水功能特性;而经过DHN和AF17N溶液有机镀膜处理后,其表面自由能降低、蒸馏水接触角增大,具有良好的疏水功能特性;其中经过AF17N镀液处理后表面自由能最小而接触角最大,即疏水效果最佳.该技术实现了不锈钢表面的亲/疏水表面改性,提供了一种制备具有不同浸润性的有机表面薄膜材料的方法.     

Fabrication and characteristics of porous AISI 304L stainless steels by ceramic powder additions

Abstract

Porous AISI 304L stainless steels were fabricated by a new powder metallurgy technique, based on the addition of oxide based ceramic powders. The mixture of AISI 304L stainless steel powders and oxide based ceramic powders was compacted using a hand press at a pressure of 294 or 490 MPa. The green compacts were sintered at 1150 or 1200°C for 3 h in Ar gas atmosphere. The addition of oxide based ceramic powders into AISI 304L stainless steel powders gave rise to porous AISI 304L stainless steels with fine pores. Also, the addition of the ceramic powders increased the hardness.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

酸洗和热氧化对氮化硅粉料表面特性与浆料流变性能的影响

选用四种商业氮化硅粉料(其中FD1、FD2和M11均由硅粉直接氮化法合成但后处理工艺不同, 而UBE粉的合成采用亚胺基硅热分解法), 系统研究了酸洗和热氧化处理对其表面特性和水基浆料流变特性的影响. 研究表明, 表面基团的种类和数量、可溶性高价反离子浓度以及离子电导率是影响氮化硅粉料在水中分散性能的关键因素. FD1粉料分散性能差的原因是可溶性高价反离子浓度太高, FD2粉料分散性能差的关键是颗粒表面存在Si-O-C-R憎水基团, M11粉料分散性能不好源于离子电导率过大, 而UBE粉料表面的大量Si-O-Si基团是其分散性能差的限制性因素. 经表面改性处理的四种氮化硅水基浆料具有良好的流变特性.     

Investigations on Metal Injection Molding of 316L Stainless Steel

Metal Injection Molding (MIM) was performed with water atomized and gas atomized 316L stainless steel powders and powder blends thereof. Feedstocks were prepared using a thermoplastic binder system and subsequently molded into tensile test specimens. Different debinding procedures and sintering treatments were applied and their influence on carbon content in the product was compared. Chemical decomposition processes of the binder and the influence of powder morphology on debinding and sintering behaviour are discussed. Shrinkage of the MIM-fabricated parts was examined and correlated to the powder characteristics. As a result a procedure is suggested to achieve mechanical properties expected for 316L stainless steel.     

Study on biotribological properties of UHMWPE grafted with MPDSAH

In order to prolong the service life of artificial joints, a zwitterion monomer of MPDSAH ((3-(methacryloylamino)propyl)dimethyl (3-sulfopropyl)ammonium hydroxide) was grafted onto ultra-high molecular weight polyethylene (UHMWPE) powders to construct a brush-like structure by UV irradiation, and then the grafted UHMWPE powders were hot pressed as the bulk materials. The wettability of bulk materials surface with different monomer concentrations was analyzed. The tribological properties of modified UHMWPE bulk materials were investigated under distilled water and saline by sliding against stainless steel ball. The measurement of Fourier-transform infrared (FT-IR) spectroscopy indicates that MPDSAH is successfully grafted onto the surface of UHMWPE powders by UV irradiation. The contact angles of modified UHMWPE are decreased and the surface wettability is effectively improved. The friction coefficient of the modified sample is lower than that of untreated UHMWPE in aqueous lubricants during a long-term friction. With the increase of monomer concentration, the wear rate of grafted UHMWPE decreases gradually in distilled water. The grafting hydrophilic macromolecule polymer is helpful to form a lubricating film of water, which leads to the improvement of the lubricity of UHMWPE.     

Effect of different electrode materials on electrophoretic depositional behavior of yttria-stabilized zirconia powder

The electrophoretic depositional (EPD) behavior of yttria-stabilized zirconia (YSZ) powder with 8 mol% Y₂O₃, which is a common material for oxygen sensors as a solid electrolyte, was investigated on stainless steel and carbon based substrates. Ethanol + HNO₃ based suspensions were used for the EPD experiments, and three different YSZ powders, one commercially available powder and two own-made coprecipitated powders, were deposited. The latter powders were calcined at 900 and 1200 °C, respectively. The concentration of the suspension was 3 g/300 cm³ and a small amount of HNO₃ solution was added as a dispersant. A DC electric field of 100–200 V/15 mm was applied between parallel electrodes. On stainless steel electrodes it was found that the own-made coprecipitated powder calcined at 1200 °C, showing the best deposition properties, whereas the commercial YSZ powder showed the best depositional properties on carbon electrodes. These characteristic depositional behaviors are discussed with regard to the adhesive force between the particles and the different electrodes, and some powder properties, e.g., particle size distribution and packing behavior.A thick, continuous, free-standing YSZ film with a thickness of around 10 μm was successfully obtained after firing the deposit on the carbon electrode in flowing air.     

Fe_3O_4/聚苯乙烯磁性复合微球的制备与应用前景

采用改进的乳液聚合法,制备了磁性Fe3O4为核、苯乙烯和丙烯酸的共聚物为壳的磁性高分子复合微球。在透射电镜下观察磁性微球的粒径在130 nm左右;并用FT-IR、XPS和热失重方法表征了复合微球的组成成分、羧基(-COOH)的含量及所含Fe3O4的百分量。结果表明,微球的粒径分布均匀,大小可控,稳定性好,具有一定的抗溶剂性能,可长时间存放,是纳米磁性高分子聚合物网络的雏形。