防止镀银层变色的方法

正镀银层在空气中易变色。在高温、潮湿和有二氧化硫气体的环境中,腐蚀变色更明显。银层变色不仅影响外观,而且会影响导电、导热和焊接性能。简单的防银变色方法可以采用重铬酸盐化学钝化或电化学钝化处理,但效果不甚理想,下列方法较为有效:1)采用脉冲电流镀银。通过改变镀液配方,电镀采用脉冲电源,可以提高阴极电流效率,使镀层孔隙率降低,增加镀层密度,并使镀层中含一定质     

镀银防变色处理

1　前言银为贵金属 ,具有光亮银白色外观和良好的装饰性、导电性、可焊性、反光性及耐蚀性。在航空航天、光学仪器仪表、无线电通讯器材和设备、激光、探照灯、餐具和工艺品等方面经常采用镀银处理。但是银镀层的最大缺点是易与空气中的硫化物作用生成硫化银 ,表面产生黄色、黑色膜层 ,影响产品的外观和反光性能 ,降低导电和钎焊性能。因此 ,解决镀银层抗变色的问题是材料保护方面的重要课题。2　镀银层变色原因(1)银对硫、氧、氯具有很强的亲合力。银在大气中受温度影响在表面形成水膜 ,空气中的氧、硫、氯进入水膜生成难溶的氧化银、硫化…     

镀银层表面变色机理的电子能谱研究 (Ⅱ)光照和Na_2S处理致变色的机理

本文用电子能谱(XPS和AES)研究了不同波长光照射后,镀银层表面膜的组成和状态的变化,结果表明:(1)光波的致变色能力按以下顺序递降2537(?)>3650(?)>日光;(2)同一波长光照射时间越长,变色愈甚;(3)应用俄歇参数方法进行表面元素价态分析,发现2537(?)照射18小时表面约有43%的银为Ag_2O,照射24小时后表面约有18%的银为AgO;(4)XPS测定表明.银层在大气中照射时,表面银先被氧化和氯化,随后氯化物可能转化为Ag_2O,最后Ag_2O被光转化为黑色的超细颗粒的银粒子和AgO.镀银层浸在Na_2S溶液中,然后将一半面积提出液面.让其露在大气中,结果浸在Na_2S液中的部分不变色,露在大气中的部分却变为蓝色.通过Ag(3d)、S(2P)结合能以及M_4VV、M_5VV俄歇峰的测定.证明未变色银表面仍为银,蓝色层则是Ag_2S.因此,镀银层浸入Na_2S溶液后在大气中的变色反应可表示为4Ag+O_2+ZH_2O+2Na_2S→2Ag_2S+4NaOH     

镀银件"白点"、"水雾"的处理

为了保持镀银件良好的工作性能和外观,都必须防变色处理,通常有五、六种处理方法,但化学钝化法用得量多。经化学钝化后银层表面生成一层由Ag2O、Ag2CrO4、Ag2Cr2O7等组成的钝化膜,以隔离银镀层表面与腐蚀介质的接触,从而防止银变色。该工艺单独使用时抗变色很差,若配合其它防变色工艺,效果较理想。     

脉冲电镀银层组织与性能

脉冲电镀银技术具有细化晶粒,孔隙率低,电阻率低的优点。采用脉冲电镀银技术在2A12铝合金基体上制备了银层并进行了镀层组织与性能测试。结果表明,镀银层为单一的面心立方结构,显微硬度为160 HV,银层具有良好的防变色能力与较小的回路电阻。     

装饰性光亮镀银

本文以咖啡壶装饰光亮镀银为例,介绍了餐具和工艺品装饰镀银的工艺过程及工艺要点:1.选择适于基体和表面状态的镀前处理;2.为保证镀层附着强度而进行的预镀铜;3.光亮镀镍添加剂的选择和镀液的维护;4.银的预镀和光亮镀银工艺的选择;5.装饰镀银的防变色处理.     

银层光照和Na_2S处理致变色的机理

本文用电子能谱(XPS 和 AES)研究了不同波长光照射后,镀银层表面膜的组成和状态的变化,结果表明:(1)光波的致变色能力按以下顺序逆降,2537(?)>3650>日光,(2)同一波长光照射时间越长,变色愈甚;(3)应用俄歇参数方法进行表面元素价态分析,发现2537照射18小时表面约有3/7的银为 Ag_2O、照射24小时后表面约有3/17的银为 AgO;(4)XPS 测定表明,银层在大气中照射时,表面银先被氧化和氯化,随后氯化物可能转化为氧化银(Ag_2O),最后氧化银被光转化为黑色的超细颗粒的银粒子。镀银层浸在 Na_2S 溶液中,然后将一半面积提出液面,让其露在液面上的大气中,结果浸在Na_2S 液中的部分不变色,露在大气的部分却变为兰色。通过 Ag(3d)、S(2p)结合能以及M_4VV、M_5VV 俄歇峰的测定,证明未变色银表面仍为银,兰色层则是 Ag_2S。因此,镀银层浸入Na_2S 溶液后在大气中的变色反应可表示为4Ag O_2 2H_2O 2Na_2S→2Ag_2S 4NaOH     

电流密度对无氰镀银层性能的影响

本实验采用硫代硫酸盐体系的镀银液,利用电沉积法在紫铜上制备银层。通过扫描电镜(SEM)、X射线衍射仪(XRD)、电化学工作站、抗硫实验、抗老化实验对镀层微观形貌、晶面取向、晶粒大小、耐蚀性、抗硫性、抗老化性能进行测试。结果表明,当电流密度为0.4 mA·cm-2时,镀层结晶最致密,表面最平整,孔隙率最小,晶面取向为(111),自腐蚀电流密度为70.17 mA·cm-2,自腐蚀电位为-0.2901 V,抗硫性及抗老化性能最优。     

镀(涂)层的后处理工艺 (Ⅲ)

仿金镀层由铜、锌、锡三元或铜、锌二元合金组成，这种合金较活泼，在大气中不太稳定，极易氧化变色，失去美丽的金黄色，故仿金镀层需防变色处理。     

耐热耐蚀性镀银工艺

1　前言由于银和银合金镀层具有优良的低接触电阻和装饰性 ,被广泛应用于连接器接点和半导体引线架以及餐具、乐器等。电子部件用的镀银层是在铜或磷青铜等铜合金带上直接电镀银或银合金 ,然后经冲压加工成ＩＣ引线架等电子部件。镀银件使用中出现的问题有 :(1)电子部件一般使用在机器、汽车发动机内部等温度较高的环境中 ,耐热性不够高 ;(2 )银对于硫化物的耐蚀性差 ,镀银件表面接触电阻就会上升 ,降低可焊性 ;(3)从银层表面渗入的氧扩散到镀层中 ,直至中间镀层或基材 ,使其氧化 ,从而接触电阻上升 ,降低可焊性。针对上述状况 ,本文介绍长…     

Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria

The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm–3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.     

Electrochemical behaviour of chalcopyrite in the presence of silver and Sulfolobus bacteria

The electrochemical behaviour of massive chalcopyrite electrodes has been studied in an acid medium (pH1.5) containing silver ions (0.02gdm?3Ag+) and thermophilic bacteria (68°C). Preliminary tests on particulate electrodes made from graphite, elemental sulfur and Ag2S were included to determine the electrochemical response of reactants (Ag+) and products (S° and Ag2S) associated with the dissolution of chalcopyrite in the presence of silver. Massive chalcopyrite electrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solution and [Ag+]. As well as Ag2S, metallic silver was detected on the chalcopyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopyrite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of the electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two weeks did not improve the surface reactivity. However, in the initial stages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganisms.     

Silver-zinc electrodeposition from a thiourea solution with added EDTA or HEDTA

This paper shows the study of silver-zinc electrodeposition from a thiourea solution with added (ethylenedinitrilo)tetraacetic acid (EDTA), disodium salt and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), trisodium salt. Voltammetric results indicated that silver-zinc alloy can be obtained applying overpotential higher than 0.495 V, in Tu solution containing 1.0 × 10⁻¹ mol L⁻¹ Zn(NO₃)₂ + 2.5 × 10⁻² mol L⁻¹ AgNO₃. This was due to silver(I) ion complexation with thiourea, which shifted the silver deposition potential to more negative value and due to silver-zinc alloy deposition, which occurred at potentials more positive than the potential to zinc deposition alone. EDTA or HEDTA did not significantly affect the silver and zinc deposition potentials, but decreased the current density for silver-zinc deposition. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the silver-zinc deposits showed that the morphology and composition changed as a function of the conditions of deposition, viz, deposition potential (E_d), deposition charge density (q_d) and solution composition (silver, EDTA and HEDTA concentrations). EDS analysis of the deposits showed sulphur (S) incorporated into the silver-zinc deposit, while SEM images showed that this sulphur content seemed to improve the silver-zinc morphology, as did the presence of EDTA and HEDTA in the solution, which enhanced the sulphur incorporation into the silver-zinc deposit. X-ray diffraction (XRD) analysis of the silver-zinc deposit showed that it was amorphous, irrespective of its composition and morphology.     

Kinetic study of Pt nanocrystal deposition on Ag nanowires with clean surfaces via galvanic replacement

ABSTRACT: Without using any templates or surfactants, this study develops a high-yield process to prepare vertical Ag-Pt core-shell nanowires (NWs) by thermally assisted photoreduction of Ag NWs and successive galvanic replacement between Ag and Pt ions. The clean surface of Ag nanowires allows Pt ions to reduce and deposit on it and forms a compact sheath comprising Pt nanocrystals. The core-shell structural feature of the NWs thus produced has been demonstrated via transmission electron microscopy observation and Auger electron spectroscopy elemental analysis. Kinetic analysis suggests that the deposition of Pt is an interface-controlled reaction and is dominated by the oxidative dissolution of Ag atoms. The boundaries in between Pt nanocrystals may act as microchannels for the transport of Ag ions during galvanic replacement reactions.     

Thermodynamic simulation of the composition of mineral compounds upon the gasification of brown coal from the Kansk-Achinsk Basin

The quantitative composition of the products of the gasification (at P = 0.1 MPa and an air excess ratio of 0.3 in a temperature range of 114–1534°C) of brown coal from the Nazarovskoe deposit of the Kansk-Achinsk Basin was calculated using a chemical thermodynamics program [1], the database of which contains the thermodynamic constants of more than 2000 inorganic compounds. The calculation covered the compounds of both trace elements (V, U, Se, Sr, Ag, and Au) and ash-forming elements (Al, Si, Fe, Ca, Mg, K, Na, and S).     

Electrodeposition of Si from organic solvents and studies related to initial stages of Si growth

Electrodeposition of Si on substrates such as Ni, Ag and GC from acetonitrile and tetrahydrofuran containing SiCl₄ and SiHCl₃ as precursors is reported. The deposits readily oxidize on exposure to air but XPS analysis of a deposit with minimum contact with air confirms that elemental Si (2p, 99.5 eV) is electrodeposited. The deposits contained C, O, N and Cl impurities; annealing under argon improved the quality of the deposits. Studies related to initial stages of Si growth using cyclic voltammetry and chronoamperometry suggest that growth occurs via four stages (1) nucleation and localized growth, (2) growth in between islands, (3) growth inhibition and (4) slow growth stage and the growth is inhibited after a layer (∼2 nm) of Si is electrodeposited on the substrate.     

Silver diffusion and mechanism of CaO-MgO-SiO2 glass ceramics in millimeter-wave properties

Glass ceramics have demonstrated excellent millimeter-wave dielectric properties for low-temperature-co-fired-ceramic (LTCC) devices applied in the 5G communication. This study highlights silver (Ag)-diffusion mechanism and millimeter-wave dielectric properties of CaO-MgO-SiO₂ glass ceramics co-fired with Ag electrode near nucleation temperatures. Ag diffusion and elemental inter-diffusion occur during the endothermic-exothermic process near nucleation temperatures (~820 °C), where Ag diffused into the glass-ceramic matrix and resided around the diopside-phase grain boundaries while other metal elements (Zn, Mg, and Al) diffused into the Ag layer. Oxygen ions can flee from the glass-ceramic network above glass transition temperature during the endothermic process and react with the Ag ions to form the Ag-O bonds. The low dielectric dissipation in the millimeter-wave range remains after Ag diffused into the matrix. However, conductivity of Ag-electrode layer decreases at a GHz frequency due to the inter-diffusion elements with lower electric conductivities.     

Synthesis, Characterization of Ag/MCM-41 and the Catalytic Performance for Liquid-phase Oxidation of Cyclohexane

Nano-scale silver supported mesoporous molecular sieve Ag/MCM-41 was directly prepared by one-pot synthesis method. The prepared sample was characterized by XRD, TEM, and N₂ sorption. The results showed that the sample of Ag/MCM-41 had no appreciable incorporation of silver into the mesoporous matrix of MCM-41 with good crystallinity, and silver nanoparticles were dispersed inside or outside of the channels in the mesoporous host. The catalytic performance of the sample for the cyclohexane liquid-phase oxidation into cyclohexanone and cyclohexanol by oxygen in the absence of solvents without inducing agents was investigated. The 83.4% selectivity to cyclohexanol and cyclohexanone at 10.7% conversion of cyclohexane was obtained over Ag/MCM-41 catalyst at 428 K for 3 h. The turn over numbers (TONs) of Ag/MCM-41 was up to 2946. The catalytic activity of Ag/MCM-41 was also compared with Ag/TS-1 as well as Ag/Al₂O₃. The results indicated that Ag/MCM-41 showed superior activity to both Ag/TS-1 and Ag/Al₂O₃. A calcined Ag/MCM-41 was found to be an efficient catalyst for the cyclohexane oxidation into cyclohexanol and cyclohexanone using oxygen as oxidant.     

The interaction of pyrite with solutions containing silver ions

Linear potential sweep voltammetry and X-ray photoelectron spectroscopy have been used to determine the products of the interaction of pyrite with sulphuric acid solutions containing silver ions. Silver sulphide was found to be the principal product for all reaction times. Initially, some sulphur excess (metal deficiency) in the sulphide lattice was associated with the formation of silver sulphide. The presence of elemental silver in addition to silver sulphide after extended reaction times was evident from the characteristics of voltammograms. This elemental silver was not detected by electron spectroscopy because it was formed as crystallites occupying only a very small area of the surface of the silver sulphide-covered pyrite. Silver sulphide was the only surface silver species present on a pyrite surface during acid iron(III) leaching; elemental sulphur was also identified on such surfaces.