Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)2-coated Cu2O powder

A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors (MLCC). Spherical ultrafine cuprous oxide (Cu₂O) powder was prepared by glucose reduction of Cu(OH)₂. The Cu₂O particles were coated by Mg(OH)₂ and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tap density, and thermogravimetry (TG). It is found that the shape and size distribution of the copper powder are determined by the Cu₂O powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg(OH)₂ coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm³ and the initial oxidation temperature rises from 125 to 150°C.     

化学气相合成AIN超细粒子过程模型研究

基于化学气相(CVD)合成超细粒子过程的反应、成核、生长和凝并,考虑CVD反应器中的轴向温度分布,建立了CVD反应器中描述超细粒子粒度及分布的一维过程模型。针对AlCl_3-NH_3-N_2体系化学气相合成AlN超细粒子的过程,研究了AlN粒子形成过程特征和操作参数对其粒度及分布的影响。CVD反应器中的轴向温度分布严重影响AlN粒子合成过程中的化学反应速率、成核速率和生长速率;AlN超细粒子的粒度随AlCl_3浓度的减小和总流量的增加而减小,其粒度分布宽度则随总流量的增加而增大。     

AlCl_3-NH_3-N_2体系化学气相淀积AIN超细粒子 Ⅱ.AIN的粒度及分布模型

考虑轴向温度分布和浓度分布,建立了热化学气相淀积反应器中描述粒子粒度及分布的一维反应-凝并模型。研究了AlCl_3-NH_3-N_2体系物系参数和操作参数对AlN超细粒子粒度及分布的影响。温度通过改变反应速率、气体粘度和平均分子自由程等影响AlN粒子的合成,并存在最佳温度分布;随停留时间的增加,AlN粒子粒度增大,几何标准方差GSD减小;反应物浓度升高时,AlN粒子粒度增大,但GSD变化不大。模型化研究结果和实验结果相一致。     

铁磁纳米颗粒系统磁性质对尺寸和各向异性效应的依赖

研究了随机分布颗粒系统的尺寸、各向异性、矫顽力和温度之间的关系.从FexCu1-x,Fe/SiO2,Fe/Al2O3颗粒膜实验结果入手,以Néel-Bron理论和Storner-Wohlfartly模型为依据,建立了描述细磁性颗粒矫顽力Hc与颗粒大小d、热力学温度T的函数关系,并得出在粒径小于dm(=18~20 nm)范围内,矫顽力随着颗粒的尺寸的增加而迅速地增大,而在颗粒尺寸大于这个范围,则按照Hc∝1/d规律变化.       

Characteristics of inclusions in high-Al steel during electroslag remelting process

The characteristics of inclusions in high-Al steel refined by electroslag remelting (ESR) were investigated by image analysis, scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results show that the size of almost all the inclusions observed in ESR ingots is less than 5 μm. Inclusions smaller than 3 μm take nearly 75% of the total inclusions observed in each ingot. Inclusions observed in ESR ingots are pure AlN as dominating precipitates and some fine spherical Al₂O₃ inclusions with a size of 1 μm or less. It is also found that protective gas operation and slag deoxidation treatment during ESR process have significant effects on the number of inclusions smaller than 2 μm but little effects on that of inclusions larger than 2 μm. Thermodynamic calculations show that AlN inclusions are unable to precipitate in the liquid metal pool under the present experimental conditions, while the precipitation of AlN inclusions could take place at the solidifying front due to the microsegregation of Al and N in liquid steel during solidification.     

Influence of particle size and temperature on the dielectric properties of CoFe2O4 nanoparticles

The objective of this study was to establish the dielectric properties of CoFe2O4 nanoparticles with particle sizes that varied from 28.6 to 5.8 nm. CoFe2O4 nanoparticles were synthesized using a chemical coprecipitation method. The particle sizes were calculated accord-ing to the Scherrer formula using X-ray diffraction （XRD） peaks, and the particle size distribution curves were constructed by using field-emission scanning electron microscopy （FESEM） images. The dielectric permittivity and loss tangents of the samples were determined in the frequency range of 1 kHz to 1 MHz and in the temperature range of 300 to 10 K. Both the dielectric permittivity and the loss tangent were found to decrease with increasing frequency and decreasing temperature. For the smallest CoFe2O4 nanoparticle size, the dielectric per-mittivity and loss tangent exhibited their highest and lowest values, respectively. This behavior is very useful for materials used in devices that operate in the microwave or radio frequency ranges.     

低温取向硅钢中第二相粒子的析出行为及热轧组织

研究了不同工艺生产的低温取向硅钢热轧板中第二相粒子的析出行为及其组织。结果表明,热轧板中的析出物除了弥散分布的纳米级球形或椭球形的Mn S、Cu2S外,还观察到与其形貌相似的Si O2、Al N和Si3N4及其复合在一起的复杂化合物。试样中微米级析出物主要为Si O2、Mn S、Cu2S和Al N的复合物,纳米级析出物主要为Al N、Si3N4、Mn S、Cu2S的复合物。热轧板中0.01~0.2μm的析出物数量最多,约占总数的99%。与常规热轧板相比,CSP试样中夹杂物面积密度较小,在大于1μm范围内其平均尺寸较大,会使得后期退火过程中二次再结晶不完整,影响产品磁性能。热轧板在垂直于轧向横截面上组织分布具有很大的差别,其中CSP试样组织相对比较均匀,不利于后续处理工艺中发展完善的二次再结晶织构从而获得良好的磁性能。     

Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds (Al₂CuMg, Al₂Cu, Al₉FeNi, Cu₂FeAl₇, and Al₇Cu₄Ni). After conventional homogenization, Al/Al₂CuMg eutectic phases are dissolved into the matrix, and a small amount of high melting-point eutectic Al/Al₂Cu phases exist in the matrix, resulting in an increase in the starting melting temperature. Under double homogenization, the high melting point Al/Al₂Cu phases are dissolved, and no obvious change is observed for the size and morphology of Al₉FeNi, Cu₂FeAl₇, and Al₇CuaNi compounds.     

Synthesis of nanocrystalline NiCrC alloy feedstock powders for thermal spraying by cryogenic ball milling

Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling (cryomilling) method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy (SEM), laser scattering for particle size analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM). After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr₂O₃ phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.     

Effective antibacterial and phase change PEG/Cu2O@A-HNTs composites for melt-spun difunctional PA6 fiber

Serving as the only defensive line between pathogens and human body, personal protective equipment (PPE) is increasingly attractive among researchers because of their strong antibacterial and temperature control abilities. However, efficient antibacterial properties and regenerative thermal control simultaneously remain unexplored in PPE. Here, one-dimensional halloysite nanotubes (HNTs) modified by acid etch method, are used to synthesis a multifunctional material of PEG/Cu₂O@A-HNTs via in-situ reduction and physical adsorption which serves the above two purposes. PEG/Cu₂O@A-HNTs showed rapid bacterial inactivation and achieved 96.3% bacteriostatic rate against E. coli in only 20 ?min. Meanwhile a broad and complete inactivation spectrum included both E. coli and S. aureus following a series of antibacterial mechanisms. Moreover, adsorption of 70 ?wt% PEG by acid etch HNTs is attributed to the nearly 3 times increased specific surface area compared with native HNTs. This enabled PEG/Cu₂O@A-HNTs to attain a phase change enthalpy of 108.4 ?J/g. In addition, using PEG/Cu₂O@A-HNTs as additives, antibacterial and phase change fiber (APCF) were melt-spun. Their efficiency factor against E. coli and S. aureus was above 99.99%, and retained a temperature control ability for 180s and 272s compared with PA6 fiber in hot and frigid environments respectively.     

Effects of homogenization on the dissolution and precipitation behaviors of intermetallic phase for a Zr and Er containing Al-Zn-Mg-Cu alloy

The effects of homogenization on dissolution and precipitation behaviors of intermetallic phase in a novel Zr and Er containing Al-Zn-Mg-Cu alloy were investigated.In this work,single-stage(SS:475℃/24 h) and doublestage(DS:400℃/12 h+475℃/24 h) homogenization treatments were carried out for the ingots with the heating rates of 300℃/h,50℃/h and 25℃/h,respectively.It was found that Er tended to segregate at the grain boundary in the form of Al_8Cu_4Er,and the formation mechanism was determined to be the eutectic reaction in the front of the solid/liquid interface during solidification.Also,Al_8Cu_4Er phase was detected to possess high melting point(～573.8℃),which fully remained after the homogenization.Meanwhile,a significant impact of heating rate on the dissolution of intermetallic phases for the studied alloy under the DS homogenization was determined,but little impact was observed under the SS homogenization.Morever,the size and distribution of the dispersoids after homogenization were fully analyzed.It was found that slow heating rates was helpful to refine the particles size,and increase the density as well as volume fraction of the precipitation under both SS and DS homogenization.However a higher density and volume fraction of the precipitated particles,and a relatively larger average particle size were gained with DS homogenization.     

Cu2+对好氧颗粒污泥理化特性的影响分析

以普通活性污泥为接种污泥,葡萄糖和乙酸钠为碳源,在SBR反应器中培养好氧颗粒污泥,考察不同质量浓度Cu2+(0 mg/L、1 mg/L、3 mg/L、5 mg/L和10 mg/L)冲击作用对好氧颗粒污泥理化特性的影响。结果表明,随着Cu2+质量浓度从0 mg/L上升至10 mg/L,好氧颗粒污泥的理化特性均受到不同程度的影响。质量浓度为1 mg/L和3 mg/L的Cu2+对COD和NH+4-N的去除率影响较小,而质量浓度为5 mg/L和10 mg/L的Cu2+对COD和NH+4-N的去除率影响较大。随着Cu2+质量浓度的增加,好氧颗粒污泥的丝状菌逐渐增多,污泥浓度不断下降,沉降性能急剧恶化;密实度降低,结构越来越松散,粒径出现两极分化的现象,而且在质量浓度为10 mg/L的Cu2+作用下颗粒污泥解体。     

Microstructural characteristics and mechanical properties of bobbin-tool friction stir welded 2024-T3 aluminum alloy

Cold-rolled 2024-T3 sheet alloy was subjected to bobbin-tool friction stir welding (BTFSW). The microstructural characteristics and mechanical properties of the nugget zone in the as-welded state were investigated. The results show that the equiaxed grain size of BTFSW 2024-T3 alloy decreases from 7.6 to 2.8 μm as the welding speed is increased from 80 to 120 mm/min; in addition, fine grains are generated in the nugget zone and the size distribution is non-uniform. All Al₂CuMg (S') precipitates dissolve into the Al matrix, whereas Mn-rich phases confirmed as T phases (Al₂₀Cu₂Mn₃, Al₆Mn, or Al₃Mn) remain unchanged. The optimized parameters for BTFSW are verified as the rotation speed of 350 r/min and the travel speed of 100 mm/min. The variations in precipitation and dislocation play more important roles than grain size in the nugget zone with respect to influencing the mechanical properties during the BTFSW process. After the BTFSW process, the fracture mode of base material 2024-T3 alloy transforms from ductile rupture to ductile-brittle mixed fracture.     

Synthesis and Largely Enhanced Nonlinear Refraction of Au@Cu<Subscript>2</Subscript>O Core-Shell Nanorods

Au@Cu₂O core-shell nanorods with tunable thickness of Cu₂O shell were synthesized and their linear and nonlinear optical responses were investigated. Two transverse plasmon resonance peaks were observed when the Au nanorods were coated with Cu₂O shells, which were adjusted by the Cu₂O shell thickness. The nonlinear absorption of the Au@Cu₂O nanorods is enhanced by 5 times at the longitudinal plasmon resonance wavelength compared with that of bare Au nanorods. More intriguingly, largely enhanced nonlinear refraction and suppressed nonlinear absorption at the transverse plasmon resonance wavelength were observed in the Au@Cu₂O nanorods. Our findings indicate the existence of strong local field enhancement at the interface between the Au core and the Cu₂O shell, which would provide a promising strategy in designing plasmonic nonlinear nanodevices with good nonlinear figures of merit.     

柠檬酸溶胶凝胶法合成YBa_2Cu_3O_(7-δ)

采用溶胶 凝胶法制备了均匀的YBa2Cu3O7-δ超导细粉·讨论了凝胶的形成过程·配合剂柠檬酸与金属离子结合形成了可溶性的大分子化合物,除水后缩聚反应形成的聚合物长大为小粒子簇,相互连结成连续的三维网络·柠檬酸盐溶液的pH值控制在6 4～6 7之间可防止白色Ba(NO3)2沉淀·溶剂挥发温度宜控制在300℃,使凝胶的形成和自燃过程能在相同温度条件下连续进行·合成YBa2Cu3O7-δ的温度大约在880℃左右,其粉末粒度大约在0 2～1μm之间·     

氮化铝粉末的水解行为研究

研究了亚微米和纳米氮化铝粉末在不同温度下的水解行为,通过测定500nm和40nm的AlN粉末在不同温度水解时pH值随时间的变化,分析了粉末粒度和温度对AlN粉末水解行为的影响,并利用XRD和TEM研究了AlN粉末水解时物相和表面形貌的演变规律.结果表明：AlN粉末的水解速率与温度和粒度相关,并随温度的升高和粒度的减小而加快,XRD表明AlN粉末水解的产物为Al（OH）3和AlOOH,并且常温水解时Al（OH）3占主导,高温水解时AlOOH占主导.TEM显微图表明AlN粉末的水解在粉末表面的台阶上进行.     

Synthesis of Ultrafine AlN Powders in an Al-O-C-N System

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热处理温度对TiO2薄膜光催化活性影响的研究

 采用溶胶-凝胶法及浸渍提拉法,在普通玻璃载玻片上制得了TiO₂薄膜,通过差热分析仪及X射线衍射仪分析了热处理温度对TiO₂的晶型、晶粒大小、孔隙率及薄膜的光催化活性的影响,结果表明存在一个最佳的热处理温度范围,在这一温度范围内薄膜的光催化活性最好.     

二氧化碳分散岩屑机制的模拟试验研究

以东营组实钻岩屑为例,采用模拟试验装置考察井下二氧化碳对岩屑分散机制,并进行岩屑XRD矿物成分和反应液离子成分分析。结果表明:二氧化碳对岩屑粒径影响甚微,地层水长时间浸泡会使岩屑粒径变小,地层水与二氧化碳共存时,岩屑平均粒径先急剧减小,后渐趋稳定,随着温度和压力的升高,岩屑平均粒径逐渐减小;地层水和二氧化碳共存时,东营组岩屑粒径变化的主要是由于二氧化碳促进了岩屑中的黏土矿物分散,缩短了黏土矿物的水化反应时间,同时二氧化碳与水反应生成碳酸,溶解了岩屑中的部分胶结矿物,促进了岩屑粒径的减小。     

Mineral sulphide-lime reactions and effect of CaO/C mole ratio during carbothermic reduction of complex mineral sulphides

Mineral sulphide (MS)-lime (CaO) ion exchange reactions (MS + CaO = MO + CaS) and the effect of CaO/C mole ratio during carbothermic reduction (MS + CaO + C = M + CaS + CO(g)) were investigated for complex froth flotation mineral sulphide concentrates. Phases in the partially and fully reacted samples were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The primary phases during mineral sulphide-lime ion exchange reactions are Fe₃O₄, CaSO₄ Cu₂S, and CaS. A complex liquid phase of Ca₂CuFeO₃S forms during mineral sulphide-lime exchange reactions above 1173 K. The formation mechanisms of Ca₂CuFeO₃S liquid phase are determined by characterising the partially reacted samples. The reduction rate and extent of mineral sulphides in the presence of CaO and C increase with the increase in CaO/C ratio. The metallic phases are surrounded by the CaS rich phase at CaO/C > 1, but the metallic phases and CaS are found as separate phases at CaO/C < 1. Experimental results show that the stoichiometric ratio of carbon should be slightly higher than that of CaO. The reactions between CaO and gangue minerals (SiO₂ and Al₂O₃) are only observed at CaO/C > 1 and the reacted samples are excessively sintered.