Electro/magnetic shielding effectiveness of soft magnetic Fe80Nb6B14 amorphous alloy

Application of the Fe₈₀Nb₆B₁₄ amorphous alloy to electromagnetic shielding was examined in detail using different experimental techniques. For shields made of the optimized (annealing at 700 K/1 h) amorphous ribbons the shielding effectiveness b was measured versus frequency f and shield thickness h. It was shown that for h = 200 μm in the frequency range 2 MHz < f < 15 MHz (the near-zone, electric field) b decreases from 55 dB to 20 dB. In the frequency range 0.2 kHz < f < 10 kHz (the near-zone, magnetic field) b > 20 dB. The best shielding effectiveness, i.e. b > 100 dB was obtained for electromagnetic field in the frequency range 200 MHz < f < 1000 MHz (the far-zone).     

铜粉螺线管线圈磁脉冲致密试验研究

将电磁成形技术用于粉末材料致密，利用螺线管线圈对铜粉进行了致密试验。分析了放电电压、致密次数、加热温度等因素对压坯致密度的影响。试验结果表明增加放电电压、多次放电、对粉末进行预热，均能提高压坯的平均致密度。在压坯轴向上距离中心越远的位置致密度越低，在径向上距离中心越远的位置致密度越高。     

The corrosion of gold and silver coated copper by the thermal degradation products of chloroprene and silicone rubber

The corrosion of gold and silver coatings on copper by the thermal degradation products (100°C) of chloroprene and silicone rubber has been studied by mass-spectrometry, secondary ion mass-spectrometry (SIMS) of interaction products and petrographic analysis of corrosion films. The volatile products of degradation of both organic materials greatly influence the protective coating of gold and silver; the composition of chloroprene rubber is more aggressive and along with decomposition of the protective coating, corrosion leads to the partial removing of the coating with simultaneous corrosion of a copper substrate. Formic acid vapours and chlorine are the most corrosion active components of the atmosphere. These substances produce the unstable gold and silver salts, chlorides and formates, extracting during their degradation fine dispersed crystals of a secondary metal, these being one of the main corrosion products.     

Electromagnetic interference shielding effectiveness of electroless Cu-plated PET fabrics

In order to develop the high quality electromagnetic interference (EMI) shielding textiles for protective clothing, polyester fabrics were electroless copper-plated. Effects of pretreatment conditions such as scouring, etching, and catalyzation on electromagnetic interference shielding effectiveness (EMISE) and physical properties of treated fabrics were investigated.High EMISE of fabrics over the wide range of frequency level were obtained when fabrics were scoured with 0.3% NaOH and 1.0% Triton X-100, and etched with the mixture of HCl/HNO₃ at 25°C for 30 min before activation. We found that KCl was the better catalyst activator than commonly used SnCl₂. EMISE of copper-plated fabrics increased as the concentration of KCl increased up to 1:8 molar ratio of PdCl₂:KCl then decreased with further addition. As the catalyzation temperature increased from 25 to 40°C, the EMISE of copper-plated fabrics increased, whereas their EMISE reduced to about zero when the activation temperature exceeded over 40°C. Physical properties including tensile extension and drape stiffness of copper-plated fabrics are higher than those of the untreated PET, but tensile strength was slightly decreased. By scanning electron microscope (SEM), we found special fracturing behavior of the copper-coated PET fabrics due to the ductility and brittleness of copper film on the PET fabric.     

镀镍石墨粉的电化学性质

利用化学镀方法在石墨粉表面镀覆了一层均匀、完整的金属镍,研究了镀镍石墨粉电极及镀镍石墨粉作为ＭＨ／Ｎｉ电池镍电极导电剂时的电化学性质。实验表明,石墨粉表面镀覆金属镍可增另其电化学活性;用镀镍石墨粉作为电极导电剂时,可以改善镍电极的导电性能,降低电池内阻,提高正极活性物质的利用率,且电池的循环稳定性好,以１Ｃ倍率充放电循环１２０就衰减。     

The stabilization of electrodeposited copper powder

Copper powder was electrodeposited from a solution containing copper sulphate and sulphuric acid. The stability of the powder, as measured by the resistance to oxidation, was assessed over a range of temperatures using a thermal balance. Similar powder was treated with an aqueous solution of benzotriazole, a specific corrosion inhibitor for copper, and also tested. Powder was also deposited from a standard bath containing benzotriazole and the properties of the powder determined. The use of benzotriazole was beneficial in improving the stability of the powder.     

水雾化法制备铜及铜合金粉

介绍了水雾化法制备铜及铜合金粉的研究,结果表明:通过优化设计和工艺参数选择,水雾化原铜粉具有很好的同一性和可控性,松装密度为2.0～2.9 g/cm3,粒径和分布可通过调节工艺参数改变;经氧化还原工艺处理的水雾化铜粉既保持了雾化铜粉良好的流动性,又降低了雾化铜粉的松装密度,达1.3～2.8 g/cm3,并具有良好的压制...     

球形纳米银粉体制备及其表征

采用均匀沉淀和高温热分解相结合的方法制备了纳米银粉体,分析了纳米银粉体形成机理,研究了初始浓度、烧结温度和时间对纳米银粉体粒径和形貌的影响;采用X射线衍射仪、扫描电子显微镜表征了纳米银粉体结构、组成、大小和形貌。结果表明,硝酸银初始浓度0.05 mol/L、烧结温度300℃、烧结2 h,以尿素为pH控制剂,不添加任何其他分散剂条件下可得到分散性好、颗粒均匀,粒径50 nm的球形粉体。     

电解铜粉高速压制成形

研究电解铜粉高速压制成形工艺,探讨冲击能量、压制次数对生坯密度、最大冲击力和脱模力的影响.结果表明:当冲击能量为6 076 J时,试样的生坯密度达到最大,为8.42 g/cm3,相对密度约为95%;当冲击能量相同时,采用两次压制制备的试样的生坯密度较单次压制的高且前者的脱模力较低.高速压制过程中,最大冲击力随冲击能量的增加而逐渐增大,而脱模力较低,仅在45～90 kN之间变化.     

Investigation of corrosion behavior of silver coated brass in acidic solutions

The corrosion behavior of uncoated brass and electrolytically silver coated brass in cyanide solutions such as 0.1 M HCl, 0.1 M H₂SO₄ and 0.1 M H₃PO₄ was investigated by Tafel polarization curves and cyclic voltammetry curves at 1., 24., 48., 72., 96. and 168. hours. The coating efficiency was calculated by current density of corrosion determined from Tafel polarization curves. Surface analysis of coated brass immersed into acidic solution by 168 hours was done. It is concluded that silver coating is very effective to protect the corrosion of brass for a long time.     

银粉和触变剂对低温银浆挥发速率影响的研究

采用不同密度的银粉,改变触变剂类型及含量,以线路复烤前后的电阻值变化率表征银浆的溶剂挥发速率,研究不同条件对银浆溶剂挥发速率的影响。结果表明,低振实密度粉体、有机膨润土、改性聚脲化合物和气相二氧化硅均能快速提高银浆溶剂挥发速率。由振实密度1.6～1.8 g/cm~3的片状银粉、0.25%有机膨润土、0.5%改性聚脲化合物搭配热塑性聚氨酯制备银浆,在150℃×1 min条件下,银浆快速干燥固化,附着力为5B,复烤后电阻变化率3%。     

Composition and morphology of complicated copper oxalate powder

In Cu(Ⅱ)-C2O42--NH3-NH4+-H2O system, complicated copper oxalate powders were synthesized by coordination-precipitation process with ammonium oxalate as precipitating agent. The composition and morphology of the powders were characterized by chemical analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and thermogravimetric and differential thermal analysis (TGA-DTA). The effects of temperature, copper ion concentration and pH value were investigated. The experimental results show that pure copper oxalate hydrate is prepared below a critical pH value of 6.0, whereas the powder turns to be a complicated copper salt combined with NH3 over the pH value. Probable chemical formula, CuC2O4·x(NH3) ·yH2O can be assumed, where x and y relate to experimental conditions. Technological parameters, such as temperature, initial copper concentration and solution pH value, have significant effects on particle size, morphology and dispersion of the powders. Powders with various morphologies, pie shape, spindle shape and rod shape, can be synthesized under certain technological conditions.     

表面活性剂对超细银粉分散性能的影响

在以抗坏血酸为还原剂、银氨配合物为前驱体、PVP为保护剂及表面活性剂为分散剂的液相化学还原体系中制备超细银粉,研究阳离子、阴离子和非离子表面活性剂在银粉制备过程中的防团聚作用和分散作用,并采用扫描电镜(SEM)和X射线衍射等对还原产物进行形貌观察和结构表征.结果表明:表面活性剂的种类对制各样品的纯度、分散性和颗粒大小有着重要的影响,其中阳离子表面活性剂和阴离子表而活性剂的分散效果不明显,非离子表面活性剂的分散效果最好.对吐温(TW)系列分散剂的研究表明:TW相对分子质量的大小对银粉颗粒的分散效果、形貌和大小也有显著影响;采用TW80分散剂可制备出高分散、窄粒级的超细银粉.     

铜基材硝酸银溶液浸镀银的沉积过程

利用电化学方法和场发射扫描电子显微分析方法,对硝酸银溶液中铜基材浸镀银的沉积速率及其沉积物的形貌变化进行研究。结果表明,整个沉积过程可分为外延生长、过渡生长和枝晶生长3个阶段。在不同的沉积阶段,银晶层的沉积速率和形貌也不同。在沉积初期吸附银原子呈现外延生长;在基材表面未被银初晶层覆盖之前,则主要以二维方式沿基材表面铺展：之后,便在初晶层的局部位置以枝晶方式突出生长,最终得到疏松且呈海绵状的银镀层。     

X‐Ray photoelectron spectroscopic investigations of powder coated steel

Polyester powder coatings are used for corrosion protection of different materials. XPS studies were performed in order to characterize such coatings on steel surfaces as a pre‐treatment for following applications like gluing. Different surface treatments by alkaline cleaner, plasma treatment (Plasma Treat® process), and the use of a silicoater (Pyrosil® process) were investigated. In dependence of such treatments, the resulting surfaces are found to be hydrophilic or hydrophobic. Although this behavior can also be investigated by contact‐angle measurements, the aim of our work is the element‐specific characterization of chemical bonding states (speciation).     

紫铜厚大结构件钨极氩弧焊热裂纹形成机理

对紫铜厚大结构件钨极氩弧焊(GTAW)热裂纹形成机理进行了研究.对热裂纹的动态形成过程进行观察和分析,在普罗霍罗夫理论基础上优化了热裂纹形成判据,并建立了基于刚性拘束热裂纹试验的紫铜厚板GTAW有限元模型.结果表明,内部变形率Δε是促使开裂的内因,得到HS201焊缝金属在脆性温度区间内(BTR)的横向拉伸应力及Δε的变化规律,并与其高温延性进行对比,得到不预热工艺下热裂纹产生的原因.为了防止热裂纹的出现,模拟并分析了不同预热温度下HS201焊缝金属的Δε的变化规律,预热温度由500℃降为420℃即可避免热裂纹出现.     

Corrosion of copper and silver plates by volcanic gases

Corrosion products that had been formed on copper and silver plates exposed in Miyake Island, where suffered a volcanic eruption in 2000, were analyzed by X-ray techniques to get better understanding of copper and silver corrosion in harsh environment. The exposure experiment was carried out from September 2004 to April 2005. Many kinds of patina were found on copper such as cuprite (Cu₂O), posnjakite (Cu₄SO₄(OH)₆ · H₂O), brochantite (Cu₄SO₄(OH)₆), antlerite (Cu₃SO₄(OH)₄), and geerite (Cu₈S₅). For silver, silver chloride (AgCl) and silver sulfide (Ag₂S) were formed. Although the volcanic activity had greatly subsided, the atmospheric corrosion of copper and silver plates exposed on Miyake Island was mainly affected by volcanic gases, wet-dry cycles in the environment, and sea-salt aerosols.     

The phototarnishing of silver and copper. Part II

Tarnishing of silver and copper at room temperatures in the presence of CH₃I, HI, CH₃Br, and HBr is caused by absorption of ultraviolet light of appropriate frequency by the growing metal halide scale. No appreciable thermal tarnishing of silver or copper is observed in the presence of these gases at room temperature. The kinetics of the phototarnishing reactions are linear and the rate depends linearly on the incident light intensity. It is concluded that the primary photochemical process is the production in the metal halides of free electrons which then react with adsorbed gas molecules, thereby propagating the reaction.For Part I, see P. T. McTigue and D. J. Young,Aust. J. Chem. 18, 1851 (1965).     

金刚石微粉表面镀覆对线锯的关键作用分析

在分析电镀金刚石线锯工艺流程的基础上,指出了金刚石上砂是电镀线锯最关键的工艺环节.探讨了各种上砂方法及特点,分析了镀覆金刚石微粉对上砂的作用.指出,采用与金刚石形成化合物结合的镀覆金刚石,如镀钛、镀钨、镀钼、镀铬和复合镀的金刚石,有利于高质量金刚石线锯的生产;避免了采用单一镍镀层产生“双极性”效应,导致镍涂层脱落的问题;具有上砂速度快,上砂容易的特点;镍镀层对镀覆金刚石颗粒迅速整体覆盖,镍镀层生长迅速,与镀覆金刚石结合牢固,出刃高;解决了无镀层金刚石以及单一镀镍金刚石与基体结合力差的问题.因此,镀覆金刚石为生产高质量金刚石线锯提供了有力的技术支持.