Powder mixed electrochemical discharge process for micro machining of C103 niobium alloy

This work demonstrates the viability of the powder-mixed micro-electrochemical discharge machining(PMECDM) process to fabricate micro-holes on C103 niobium-based alloy for high temperature applications.Three processes are involved simultaneously i.e.spark erosion,chemical etching,and abrasive grinding for removal of material while the classical electrochemical discharge machining process involves double actions i.e.spark erosion,and chemical etching.The powder-mixed electrolyte process resulted in rapid material removal along with a better surface finish as compared to the classical microelectrochemical discharge machining(MECDM).Further,the results are optimized through a multiobjective optimization approach and study of the surface topography of the hole wall surface obtained at optimized parameters.In the selected range of experimental parameters,PMECDM shows a higher material removal rate(MRR) and lower surface roughness(R_(a))(MRR:2.8 mg/min and R_(a) of 0.61 μm) as compared to the MECDM process(MRR:2.01 mg/min and corresponding Raof 1.11 μm).A detailed analysis of the results is presented in this paper.

Application Research on Powder Mixed EDM in Rough Machining

Powder Mixed Electric Discharge Machining (PMEDM) has different mechanism from conventional EDM, which can improve the surface roughness and surface quality distinctly and to obtain nearly mirror surface effects. It is a useful finish machining method and is researched and applied by many countries. However there are little research on rough machining of PMEDM. Experiments show that PMEDM machining makes discharge breakdown easier, enlarges the discharge gaps and widens discharge passage, and at last forms even distributed and "large and shadow" shaped etched cavities. Because of much loss of discharge energy in the discharge gaps and reduction of ejecting force on the melted material, the machining efficiency gets lower and the surface roughness gets small in PMEDM machining in comparison with conventional EDM machining. This paper performs experimental research on the machining efficiency and surface roughness of PMEDM in rough machining. The machining efficiency of PMEDM can be highly increased by selecting proper discharge parameters (increasing peak current, reducing pulse width) with approximate surface roughness in comparison with conventional EDM machining. Although PMEDM can improve machining efficiency in rough efficiency, but a series of problems like electrode wear, efficiently separation of machined scraps from the powder mixed working fluid, should be solved before PMEDM machining is really applied in rough machining. Experiments result shows that powder mixed EDM machining can obviously improve machining efficiency at the same surface roughness by selecting proper discharging parameters, and can provide reference accordingly for the application of PMEDM machining technology in rough machining.

EXPERIMENTAL RESEARCH ON CrAl MIXED POWDERS BY MECHANICAL ALLOYING

Thechangesof microstructure, phase? structureand microhardnessof Cr Al mixed powders in the processof mechanical? alloying ( MA) have? beeninvestigated by X ray diffractionanalysis , SEM examination and microstructure testing. The results show that the mi crostructure of Cr Al mixed powderssubjected? to mechanicalalloying for96 hoursexhibits super saturated solid solution of Cr andintermetalliccompound η AlCr2 .

Study on the Evaporation Kinetics of Zinc and Lead in Zn-Pb-Bearing Dust Pellets Mixed with Coal Powder

The study on the evaporation kinetics of zinc and lead in the pellets made of ZnPbbearing dust mixed with carbon ,in nitrogen atmosphere at the temperature range between 1 100 and 1 300 , shows that the reduction temperature has a significant effect on the evaporation rates of zinc and lead and that both the particle size of coal powder and the extra carbon content have no effect on the evaporation rates . The obtained activation energies for the evaporation of zinc and lead are 7942 kJ/mol and 8874kJ/mol respectively. The evaporation rate of zinc is controlled by the reaction between zinc oxide and CO while that of lead is controlled by lead volatilization and the diffusion of gaseous lead through gas boundary layer covering the surface of liquid lead.

Preparation and structure characteristics of nano-Bi_2O_3 powders with mixed crystal structure

The nano-Bi2O3 powders were prepared by a chemical precipitation method with Bi（NO3）3, HNO3 and NaOH as reactants. The structural characteristics and morphology of nano-Bi2O3 powders were investigated by X-ray diffraction and transmission electron microscopy, respectively. The results show that under the optimum condition that 300g/L Bi（NO3）3 reacts at 90℃ for 2h, the Bi2O3 powders with 60nm on the average and 99.5% in purity are obtained. The prepared nano-Bi2O3 powders contain a mixed crystal structure of monoclinic and triclinic instead of traditional structure of monoclinic α-Bi2O3. And the mixed crystal structure is stable in air. The reason for the appearance of the mixed crystal structure may be that the ionic radius ratio of Bi 3+ to O 2- changes easily during the formation of nano-Bi2O3 particles by a chemical precipitation method.

Effect of Recycled Mixed Powder on the Mechanical Properties and Microstructure of Concrete

In this paper,recycled bricks and recycled concrete were applied to prepare eco-friendly recycled mixed powder(RMP)cementitious material,as a supplementary to replace conventional cement for improve the recycling of construction and demolition waste.Based on the effect of cementitious materials on the hydration of silicate cement,the effects of RMP on the workability,mechanical properties and microstructure of recycled mixed powder concrete(RMPC)with the different replacement ratios and the 8:4 and 6:4 mixing ratio of recycled brick powder(RBP)and recycled concrete powder(RCP)were investigated.The results showed that the fluidity of the mix decreased with increasing of the replacement ratio and the mixing ratio of RBP and RCP,but the influence of the fluidity was smaller within 15%replacement ratio.As the replacement ratio increases,the internal pore structure of RMPC tends to be loose and porous,which exhibits a significant pore volume distribution characteristic.The number of large capillaries was considerably increased at replacement ratio of 45%.The 7 d compressive strength of RMPC was slightly lower than that of ordinary concrete.The compressive and splitting tensile strengths of RMPC at 28 d increased by 4.2%and 10.1%,respectively,with increasing curing age at 15%replacement ratio and 6:4 mixing ratio.The RMPC mechanical strengths with RBP and RCP at the mixing ratio of 6:4 was higher than those of 8:2.Finally,a basis for the recycling of RBP and RCP in the construction industry can be provided by the results of this study.

Review to EDM by Using Water and Powder-Mixed Dielectric Fluid

Basically Electrical discharge machining (EDM) is a well-established non-conventional machining process, used for manufacturing geometrically complex or hard and electrically conductive material parts that are extremely difficult-to-cut by other conventional machining processes. Erosion pulse discharge occurs in a small gap between the work piece and the electrode. This removes the unwanted material from the parent metal through melting and vaporizing in presence of dielectric fluid. Performance measures are different for different materials, process parameters as well as for dielectric fluids. Presence of metal partials in dielectric fluid diverts its properties, which reduces the insulating strength of the dielectric fluid and increases the spark gap between the tool and work piece. As a result, the process becomes more stable and metal removal rate (MRR) and surface finish increases. The EDM process is mainly used for making dies, moulds, parts of aerospace, automotive industry and surgical components etc. This paper reviews the research trends in EDM process by using water and powder mixed dielectric as dielectric fluid.

Effect of powder mixing process on the microstructure and thermal conductivity of Al/diamond composites fabricated by spark plasma sintering

Two powder mixing processes, mechanical mixing （MM） and mechanical alloying （MA）, were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering （SPS） to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W.m^-1.K^-1, owing to its having few defects and strong inter-facial bonding.

Fabrication of homogeneously dispersed graphene/Al composites by solution mixing and powder metallurgy

Graphene-reinforced aluminum （AI） matrix composites were successfully prepared via solution mixing and powder metallurgy in this study. The mechanical properties of the composites were studied using microhardness and tensile tests. Compared to the pure Al alloy, the graphene/Al composites showed increased strength and hardness. A tensile strength of 255 MPa was achieved for the graphene/Al com- posite with only 0.3wt% graphene, which has a 25% increase over the tensile strength of the pure Al matrix. Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the morphol- ogies, chemical compositions, and microstructures of the graphene and the graphene/A1 composites. On the basis of fractographic evidence, a relevant fracture mechanism is proposed.

Preparation of Well Dispersed and Ultra-Fine Ce(Zr)O_2 Mixed Oxide by Mechanochemical Processing

Ultra-fine CeO_2-ZrO_2 mixed oxide was successfully synthesized by wet-solid phase mechanochemical processing, Ce_2(CO_3)_3·8H_2O, ZrOCl_2·xH_2O and ammonia were used as reactants. It is found that the crystalline Ce_2(CO_3)_3·8H_2O and ZrOCl_2·xH_2O are changed to amorphous cerium and zirconium hydroxide precursor after milling with ammonia, and Ce_(0.15)Zr_(0.85)O_2 mixed oxide with pure tetragonal phase structure and medium particle size(D_(50))less than 1μm is formed by calcining precursor over 673 K. The XRD patterns indicate that the crystal unite size increases with rising calcining temperature due to crystal growth. However, the particle size and BET surface area of the Ce(Zr)O_2 mixed oxide decreases with rising calcining temperature, which may be attributed to the contract of particles and the vanish of holes inside grains.

Solid liquid Mixed Casting of Al-Si Alloy

The paper presents a novel material preparation technology—Solid liquid mixed casting technology. In the technology, large amounts of homogeneous alloy powder or heterogenous powder with perfect wettability are added into the superheated melt. After strong agitation, the mixed melt can be cast or hot processed. Applying solid liquid mixed casting, three kinds of Al Si alloys were investigated. The results show that, when the mass of powder accession to alloy melt is about 1, the mean size of primary Si in hyper eutectic alloy can be controlled at less than 5 μm; and the mean grain size of α phase in hypo eutectic alloy is less than 10 μm. This technology has the advantage of preparing material with very fine microstructure by fairly simple casting process, and may be a new practicable and valuable metal preparation technology.

Powder Mixing Simulation Using Random Walk Model in Eco-material Preparation

The eco-material composition is not well-distributed in preparation. The eco-material samples were taken for computer image analysis, and its particle numbers and appearance parameters were measured. Based on the mechanism of connective mixing and diffusion, the particles distribution was simulated by a computer using the random walk with Levy flight. The results show that the eco-material microstructure simulated by a computer has an idealized porous structure. The particles distribution has a cluster characteristic that changes with the different size and number of particles in Levy flight trajectory. Each cluster consists of a collection of clusters and shows a structure of self-similar cluster,hence presents a well-defined fractal property. The results obtained from SEM observation are in good agreement with the numerical simulations, and show that the convective mixing presents in the Levy flight walk.

Purity of SiC powders fabricated by coat-mix

Silicon carbide powders were synthesized by the coat-mix process, with phenolic resin and silicon powders as starting materials. The effects of synthetic conditions, including sintering temperature and the molar ratio of resin-derived carbon to silicon on the composition and the purity of the resultant powders were investigated. The results show that a higher sintering temperature and an appropriate molar ratio of resin-derived carbon to silicon are favorable for producing high purity silicon carbide powders. It is found that the silicon carbide content increases slightly with increasing the sintering temperature during the solid-solid reaction. The temperature gradient plays an important role on this trend. When the sintering temperature is raised up to 1500℃, the formation of silicon earbide is based on the liquid-solid reaction, and high purity （99.8wt%） silicon carbide powders can easily be obtained. It can also be found that the optimum molar ratio of resin-derived carbon to silicon is 1：1.

基于高通量测序技术的9种铁线莲属药材混合粉末分子鉴定

目的建立基于高通量测序技术的9种铁线莲属混合粉末分子鉴定方法。方法采用高通量测序技术,对9种铁线莲属药材混合粉末样品中的总DNA经提取,对ITS2片段进行PCR扩增,利用Illumina MiSeq平台对DNA片段进行双端测序,最后采用FLASH、QIIME、GraPhlAn及MEGA 7.0软件对序列进行整理并聚类分析,鉴定混合粉末中的物种。结果混合粉末样品中得到高质量的ITS2序列共496条,铁线莲属物种含有序列72条,比对出棉团铁线莲、女萎铁线莲、短尾铁线莲、灌木铁线莲、单叶铁线莲、黄花铁线莲、粗齿铁线莲等7个物种,未能比对出东北铁线莲和芹叶铁线莲。结论以ITS2作为DNA条形码,采用高通量测序技术,可以鉴定出铁线莲属药材混合样品中的7个物种,为混合药材的鉴定提供依据。

超声混粉电火花加工热力学仿真及表面形貌研究

为了研究超声振动和混粉对电火花加工的影响,基于传热理论,结合超声和混粉特性建立了超声混粉电火花传热模型。基于建立的传热模型对超声混粉电火花加工去除材料过程进行瞬态热力学仿真,并通过实验验证了仿真结果的准确性。通过仿真和实验分析了普通电火花、超声电火花、混粉电火花和超声混粉电火花四种加工方式,结果表明超声混粉电火花加工效率比普通电火花加工效率提高了23%。加入混粉和施加超声可以减少加工表面积碳,提高表面质量;可以使放电凹坑变得更加规则,使表面粗糙度降低。混粉电火花加工相对于普通电火花加工其表面粗糙度平均降低了8.9%,超声混粉电火花表面粗糙度相对于普通电火花平均降低了4.3%。

NH_(4)H_(2)PO_(4)-KHCO_(3)混合粉体对管网甲烷爆炸的抑制特性

在自行搭建的管网实验系统中,将常用于抑制甲烷爆炸的碳酸氢钾KHCO_(3)与磷酸二氢铵NH_(4)H_(2)PO_(4)进行不同比例的混合。选取5种不同的粉体配比,对比单一粉体以及各抑爆工况下各测点的爆炸峰值压力、火焰峰值速度和火焰峰值温度等爆炸特征参数,获得抑制管网甲烷爆炸的最佳工况,并阐述了抑爆机理。结果表明:混合粉体对管网甲烷爆炸的抑制性能优于单一粉体;KHCO_(3)与NH_(4)H_(2)PO_(4)都易受热分解;其中,KHCO_(3)可以在相对较低的温度下迅速完成热解过程,从而吸收更多的反应热,抑爆性能优于NH_(4)H_(2)PO_(4)粉体;混合粉体中,抑爆效果随着KHCO3含量的增加显著提高。在5种混合比例中,当KHCO_(3)与NH_(4)H_(2)PO_(4)质量比为2.0:1.0时,抑爆效果最佳。KHCO_(3)与NH_(4)H_(2)PO_(4)表现出良好的爆炸抑制效果,研究所得结论可为抑制甲烷爆炸研究提供参考。

旋转爆轰发动机内煤粉-氢气两相爆轰流场数值研究

旋转爆轰发动机因其较高的热循环效率在航空航天领域备受关注。为了研究气固混合燃料在空气氛围中的旋转爆轰特性,在圆柱坐标系中建立了气固混合相燃料爆轰理论模型,并基于三维守恒元与求解元方法,对圆盘形燃烧室内的爆轰过程进行三维数值模拟。计算获得了气固混合相旋转爆轰波稳定传播时的流场结构,分析了爆轰流场的热力学参数分布特征、化学反应区分布以及旋转爆轰波后的波系分布特点。研究结果表明,微米级煤粉在氢气辅助作用下可快速反应并支持旋转爆轰波的稳定传播,但因盘形燃烧室的扁平结构特征和非预混喷注方式,导致爆轰波波阵面呈现为不规则的曲面。煤粉和氢气射流穿透空气层的能力差异导致气固混合燃料的化学反应区发生分离,最终以双反应区的爆轰组织形式支持旋转爆轰波稳定传播。旋转爆轰波不规则的曲面结构使其在扁平的燃烧室中发生多次反射,进而在爆轰波后有规律地出现多道反射激波。

工业场地铊、砷污染土壤修复技术研究

研究开发了一种工业场地铊和砷污染土壤修复技术。采用常见的氯化钾、氯化锰、氢氧化钾、膨胀珍珠岩和磷石膏,经过等温等离子体处理等一系列化学反应,制备了一种铁锰基混合粉的修复药剂,该药剂制备过程简单且具有强氧化性和强吸附性。实验结果表明,在修复时间为7 d,修复药剂中氯化锰与氯化铁物质的量比为3∶10,膨胀珍珠岩粉末与氯化铁锰固液比为25∶100,磷石膏与铁锰基混合粉质量比为3∶10的条件下,处理污染土壤,铊、砷的稳定效率分别达到99.21%和99.68%。此外,通过BCR法对土壤中铊、砷的形态分析显示,修复后土壤中铊、砷主要以残渣态存在,显著降低了其对环境的潜在危害。本研究为工业场地重金属污染土壤的修复提供了一种高效、环保的解决方案。

外剥内扎术加内痔柱状缝扎悬吊联合痔科生肌散治疗环状混合痔的临床研究

目的探究外剥内扎术加内痔柱状缝扎悬吊联合痔科生肌散治疗环状混合痔的临床效果和安全性。方法选取2021年1月至2022年8月江苏省无锡市中医院收治的90例环状混合痔患者,采用随机数字表法将其分为对照组(外剥内扎术加内痔柱状缝扎悬吊治疗)和试验组(外剥内扎术加内痔柱状缝扎悬吊联合痔科生肌散治疗),各45例。治疗后1、3、7 d,比较两组肛周疼痛和水肿评分,比较两组治疗前及治疗后2周肛门狭窄情况、血清炎症因子水平,记录两组不良反应发生情况。结果治疗后3、7 d,两组肛周疼痛和水肿评分均低于治疗后1 d,治疗后7 d低于治疗后3 d,试验组治疗后1、3、7 d肛周疼痛和水肿评分低于同期对照组(P<0.05)。试验组肛门狭窄率低于对照组(P<0.05)。治疗后2周,两组肛门功能评分高于治疗前,且试验组高于对照组(P<0.05)。治疗后2周,两组白细胞计数、血清降钙素原水平均低于治疗前,且试验组低于对照组(P<0.05)。试验组不良反应总发生率低于对照组(P<0.05)。结论外剥内扎术加内痔柱状缝扎悬吊联合痔科生肌散治疗环状混合痔的临床效果较好,可在临床上推广使用。

混合钎料对镍基单晶高温合金大间隙钎焊接头组织和性能的影响

【目的】采用一种新型镍基钎料和母材成分一致的高熔点合金粉混合的方法制备出混合钎料,研究了添加的高熔点合金粉的粒径和配比对钎缝微观组织和力学性能的影响。【方法】采用扫描电子显微镜对钎焊接头的析出相、元素分布、微观组织进行了分析,并对钎焊接头的硬度及持久性能进行了测试。【结果】研究表明,接头主要由钎料合金区(FAZ)、界面连接区(IBZ)和扩散影响区(DAZ)三部分组成。钎料合金区主要由M3B2和M8B型硼化物及γ/γ′相组成。界面连接区由γ和γ′沉淀强化相组成。当合金粉粒径为44μm和75μm时,均可得到无缺陷的焊接接头;但当合金粉粒径尺寸达177μm时,钎缝内会形成孔洞缺陷。【结论】随着合金粉比例的提高,接头连接区的显微硬度有所上升。当合金配比由30%到50%,接头的持久寿命由15 h增加至34 h;但进一步提升比例至60%时,接头的持久寿命下降至0.6 h。该文的结果可为实现高温热端零部件的连接和修复工程应用提供理论依据和参考价值。