Anti‐tarnish treatment of brass for coinage

The anti‐tarnish film was formed on brass for coinage by 1‐phenyl‐5‐mercaptotetrazole (PMTA), which was studied by accelerated corrosion test (metallic coatings‐thioacetamide corrosion test), polarization curves and electrochemical impedance spectroscopy (EIS) in synthetic sweat solution. The accelerated corrosion test showed that PMTA exhibited better anti‐tarnish performance on brass than that of traditional anti‐tarnish agent benzotriazole (BTA). The polarization measurements showed that PMTA could be classified as a mixed inhibitor for it could restrain both anodic and cathodic reactions. EIS measurements indicated that the inhibition efficiency of PMTA on brass was over 98.4% in synthetic sweat solution. All these results showed that PMTA was an excellent anti‐tarnish agent of the brass for coinage, the optimum treating conditions of which were 0.5 gL^?1, pH = 3, 55°C–85°C, 7 min.     

Diffusion and Marker Movements in Beta Brass

Diffusion coefficients and marker movements have been determined in β brass using welded couples. Three different concentration ranges were employed at 750°C, while a fourth concentration range was measured at 500°, 600°, 700°, and 800°C. Marker displacements toward and porosity development in the high zinc side of the couple were observed in all cases. The results were interpreted as favoring a vacancy diffusion mechanism.     

金属锌表面超疏水薄膜的耐蚀及摩擦学性能的表征

目的改善金属锌在海洋环境中的耐蚀及摩擦学性能。方法通过简单的化学刻蚀及自组装技术在金属锌表面制备超疏水薄膜,对薄膜的结构和润湿性进行了表征,研究了超疏水薄膜在模拟海水(3.5%Na Cl溶液)中的耐蚀性能和摩擦学性能。结果经N,N-二甲基甲酰胺水溶液刻蚀后,金属锌表面呈多尺度微纳的Zn O结构,Zn O结构经硬脂酸修饰后,表面呈现出超疏水特性,表面静态接触角达150°,滑动角小于5°。同时发现,在3.5%Na Cl水溶液中,金属锌表面超疏水薄膜具有优异的耐蚀性能,并能够显著降低摩擦和磨损。结论经简单的化学刻蚀及自组装技术可在锌表面构筑超疏水薄膜,薄膜在海洋环境下具有良好的耐蚀、减摩及耐磨性能。     

Inhibitoren der Korrosion 31 (1). Beitrag zur Inhibierung der Korrosion von Zink und Messing

Inhibitors of corrosion 31 (1). Contribution to the inhibition of the corrosion of zinc and brass The following compounds approved as inhibitors of the corrosion of copper are investigated as inhibitors of the corrosion of zinc and brass: 2-aminopyrimidine (A), 5-aminotetrazole monohydrate (B), benzotriazole (C), Kupferron (D), 2-mercaptopyrimidine (E), 2-mercaptothiazoline (F), 2-methyl-4-amino-5-cyanopyrimidine (G), tetrazine-B (H) and 2-amino-3,4,1-dithiazoline-1,5, thione (I). In the presence of the compounds A, B, C, E and G zinc plates are totally corroded in 15 days using standard conditions. With the compounds D, F and H the protective values are 29%, 14% and 39%. A more differentiated information is obtained with acid consumption-time-curves at constant pH using zinc powder. Only the compound C slows down the corrosion. The other compounds enhance the corrosion. In corrosion studies with mixtures of copper and zinc powders the compounds B–I inhibit the corrosion of copper. The acceleration of the corrosion in the presence of compound A was investigated. The corrosion of brass (plate, grain, powder) proceeds with primary removal of zinc. The compounds A, E, F and H are good inhibitors. The inhibition values for brass 64/36 are better than for brass 90/10. The composition of the protecting layers produced on the surface of brass in the presence of the organic inhibitors is determined by X-ray fluorescence measurements. With the inhibitors A, B, E, F and G the content of copper is over 90%, but 80% in the presence of the inhibitors C and H, which delay also the corrosion of zinc. The conception of primary loss of zinc and the subsequent production of a copper-rich copper-inhibitor-protection-layer is confirmed by determining the composition of the precipitations and of the solutions produced during the corrosion of brass.     

Detection of Zinc Diffusion into Tin Coatings on Brass

The corroding potentials, in 0·01 % NaC1 solution, of tin containing small amounts of zinc are initially zinc-like and become tin-like only after immersion in the solution for a time which depends on the zinc content. Potential measurement can be used to detect the diffusion of zinc into tin coatings on brass during flow-brightening or long storage. The small amounts of zinc detected by this means are sufficient to cause, in exposure to copious condensation of moisture, the formation of corrosion products which make soldering more difficult, although they do not affect the soldering of the coating if it is stored normally.     

Room Temperature Adsorptive Removal of Thiophene over Zinc Oxide-Based Adsorbents

This study investigated the room temperature adsorptive removal of thiophene over zinc oxide adsorbents in the presence of hydrogen. The bulk zinc oxide was prepared by precipitation method and calcined at different temperatures in the range of 300-550 °C. Supported zinc oxide was prepared by co-precipitation of 30 wt.% ZnO with alumina and calcined at 550 °C. Properties of the adsorbents were determined by various characterization techniques such as surface area and pore volume analysis, XRD, FESEM, EDX and TPR. The desulfurization process was carried out in a down-flow packed bed reactor at room temperature (30 °C). The BET surface area of bulk zinc oxide adsorbents decreased with the increase in calcination temperature from 300 to 550 °C. The surface area of bulk zinc oxide adsorbents was 30.5 and 14.6 m²/g when calcined at 300 and 550 °C, respectively. The surface are of supported zinc oxide adsorbents was 177 m²/g. The highest average pore size was obtained for bulk ZnO calcined at 550 °C (45 nm) compared to that calcined at 300 °C (42 nm) and supported ZnO (27 nm). The XRD peaks corresponded to the hexagonal structure of zinc oxide. The removal of thiophene was most significant for bulk ZnO calcined at 550 °C. The higher removal efficiency for this adsorbent in spite of lower surface area may be attributed to its higher percentage of larger pores and higher average pore size.     

Die Feuerverzinkung siliziumhaltiger Stähle – Problem und Lösungsmöglichkeiten

Hot dip galvanizing of silicon containing steels – the problem and some attempts to its solution Hot dip galvanizing of silicon containing steels, which are increasingly used today, involves the danger of very thick, poorly adherent, unsightly zinc coatings forming on the steel surface. Quite a number of attempts have been made to prevent this drawback. Chemical surface treatments of the steels to be galvanized did not yield the desired success, whilst mechanical surface treatments by shot blasting gave positive results in certain cases only. Galvanizing in the upper temperature range of conventional working practice (475–485 °C) appears appropriate for steels containing 0.15–0.20% Si, whereas low-temperature galvanizing at 430–440 °C using conventional galvanizing baths should be universally applicable provided that suitable methods are found for pre-heating parts of larger dimensions. Galvanizing with inhibited attack of the zinc caused by small additions of aluminium (less than 0.2%) did not yield coating thicknesses independent of the Si content of the steel. High-temperature galvanizing at more than 530 °C gives satisfactory coatings irrespective of the Si content of the steel; saturation of the galvanizing bath with iron should, however, be avoided. Low-temperature galvanizing at less than 430 °C is possible on principle, provided that the melting point of the zinc is reduced by adding alloying elements such as tin (10–30%), magnesium (3%), or aluminium (4–5%). However, tin is expensive, magnesium deteriorates the wetting properties of the steel, and aluminium requires a very careful pre-treatment, the coatings obtained exhibiting low thicknesses and dependency on the Si content of the steel with iron-saturated baths. Galvanizing with reduced zinc concentrations in zinc-saturated lead baths gave zinc coatings independent of the Si content, while currentless galvanizing in zinc-saturated salt baths was not successful.     

An Investigation of Microstructure and Phase Transformation Behavior of Cu40Zn-1.0 wt.% Ti Brass Via Powder Metallurgy

The effects of Ti addition on phase transformation, precipitation behavior, and microhardness response of Cu40Zn brass were investigated at elevated heat treatment (HT) temperatures using the powder metallurgy method. The volume fraction of the α phase increased with the elevated temperatures, which showed an equal value as that of the β phase at 400 °C, and reached a maximum value of 55.9% at 500 °C. The solid solubility of Ti in Cu40Zn brass matrix decreased as the HT temperature increased. Supersaturated Ti showed high chemical potential for precipitates' reaction in Cu40Zn brass. Lower HT temperature retained higher Ti solid solubility and fine precipitates. The precipitates presented in form of Cu₂TiZn intermetallic compound, distributing uniformly in brass matrix which suppressed the phase and grain growth. After HT at elevated temperature, the precipitates coalesced, grew coarser, and segregated at the primary particle boundaries. The microhardness of the BS40-1.0Ti compact was primarily not only dependent on the solid solubility of Ti, but also dependent on the phase volume fraction of the α and β phases.     

Finite element simulation of sherardising concentration field

ABSTRACT

Sherardising is a surface protection method for obtaining an Fe-Zn coating on a steel surface by thermal diffusion. This paper proposes a model to study the sherardising diffusion process of low carbon steel. The diffusion mathematical model of the zinc coating element is established by the finite element method, which simulates the changes of zinc concentration field with temperature and time in the sherardising process. In the experimental work the sherardised samples were prepared for 2, 6 and 10?h at 375°C and 2, 6 and 8?h at 405°C and 420°C. Each phase’s thickness and the zinc concentration of the sherardising layer were measured by scanning electron microscopy and energy dispersive spectrometry respectively. The results show that the accuracy of the finite element method is verified by the consistency between the simulation results and the experimental results. This model can effectively guide the sherardising process to achieve optimum results.     

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO_2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO_2 content of 4.85 wt% is obtained and high-titanium slag with TiO_2 content of 57.31 wt% and TiO_2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy(SEM) and X-ray diffraction(XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO_2 content is obtained.     

High-Temperature Oxidation Behavior of a Polycrystalline Ti2SnC Ceramic

The isothermal-oxidation behavior of polycrystalline Ti₂SnC at 500–800°C in air has been investigated. The growth of the oxide scale on Ti₂SnC from 500°C to 700°C obeyed a parabolic law, whereas at 800°C it was a two-step parabolic process. Microstructure and composition analysis on the surface and sectioned samples demonstrated that the oxidation of Ti₂SnC was controlled by outward diffusion of titanium and carbon, and inward diffusion of oxygen. As the oxidation continued the oxygen potential in the inner layer was low, and metallic Sn was stable as an interfacial layer between the oxide scale and the Ti₂SnC matrix. This work confirmed the presence of metallic Sn in the oxidized Ti₂SnC and explained why metallic Sn was stable in the oxidized Ti₂SnC sample.     

CuZnAl记忆颗粒对黄铜/锡/黄铜焊点组织与性能影响

研究了不同压力条件下(0.2 N，50 N)瞬时液相键合0.5%亚微米CuZnAl记忆颗粒对黄铜/锡/黄铜焊点组织和性能影响. 发现0.5%亚微米CuZnAl记忆颗粒对界面组织有一定的抑制作用，主要归因于亚微米颗粒的存在减小了元素之间的扩散速率. 另外相对0.2 N压力条件下，50 N压力下由于元素剧烈扩散易于使界面出现大量的空洞，而0.2 N压力界面组织则较为均匀，并且未出现明显的空洞. 力学性能结果表明，添加0.5%亚微米CuZnAl记忆颗粒，焊点的剪切力提高20%~25%. 在0.2 N压力、250 ℃保温10 min，随后200 ℃保温1 100 h可以将黄铜/锡-CuZnAl/黄铜焊点完全转化为金属间化合物，并未发现明显的空洞.     

黄铜化学着色工艺

为了在黄铜基材上室温下获得铁锈色、棕色、枪黑色、仿古绿色膜层,研究了黄铜酸性化学着色工艺.主要讨论前处理、溶液组分、pH值和着色时间等因素对着色膜层质量的影响,并提出工艺维护的措施.研究结果表明:溶液组分是影响化学着色膜颜色的主要因素,使用时要注意控制其含量;适量的添加剂可以提高色膜质量;总之,只有掌握合理的着色工艺参数,才可以得到满意的着色效果.     

Hot mold casting process of ancient East India and Bangladesh

Ancient casting process for production of brass or bronze utensils and icons were made in hot molds using clay molded investment casting or piece mold process, as presumed by archaeologists. Piece mold process is still traditionally practiced in many parts of Eastern India and Bangladesh along with investment casting process. Incidentally, Bengal artisans are more accustomed to piece mold process unlike tribal artisans who practiced investment casting process. This piece mold casting process has been reconstructed to get the idea of metal characteristics in order to investigate ancient casting process of Bengal and Bangladesh. The characterization of ancient archaeo-metal products come to a type of cast Cu-Sn-Zn-Pb type quaternary alloy produced by a slow freezing process. Though these alloys physically differ from the traditional cast alloy of binary Cu-Zn type brass, the physical characteristics are similar to the binary cast alloy character. This investigation throws light on the similarity of the production processes by which ancient artisans probably produced cast metal products.     

Schichtbildung beim Feuerverzinken zwischen 435°C und 620°C in konventionellen Zink‐Schmelzen – eine ganzheitliche Darstellung

Layer formation by hot dip galvanizing between 435°C and 620°C in conventional zinc melts – a general presentation For four typical constructional steels with different Si‐content and enamelling steel the layer growth and the structure of the forming coats is examined as a function of the dipping duration, the melt temperature and the thermal pretreatment. The results are discussed with regard to the experimentally determined hydrogen effusion of the steel. For the temperature range from 435°C to 620°C a pattern is presented, which is applicable for the daily work in the normal and high temperature range.     

Simultaneous extraction of gold and zinc from refractory carbonaceous gold ore by chlorination roasting process

A novel process based on chlorination roasting was proposed to simultaneously recover gold and zinc from refractory carbonaceous gold ore by using NaCl as chlorination agent. The effects of roasting temperature, roasting time and NaCl content on the volatilization rates of gold and zinc were investigated. The reaction mechanism and the phase transition process were also analyzed by means of SEM, EDS and XRD. The results demonstrated that under the optimal conditions of NaCl content of 10%, roasting temperature of 800 °C, roasting time of 4 h and gas flow rate of 1 L/min, the rates of gold and zinc were 92% and 92.56%, respectively. During low-temperature chlorination roasting stage, a certain content of sulfur was beneficial to the chlorination reactions of gold and zinc; and during high-temperature chlorination roasting stage, the crystal structure of vanadium-bearing mica was destroyed, and the vanadium-containing oxides were beneficial to the chlorinating volatilization of gold and zinc. Eventually, the chlorinated volatiles of gold and zinc could be recovered by alkaline solution.     

Metal recovery from stainless steel mill scale by microwave heating

In order to recover metallic components from the mill scale generated in the hot rolling process of stainless steels more efficiently, a carbothermic reduction of the mill scale using microwave heating was carried out. The mixture of the mill scale and graphite particles was heated at a very rapid heating rate of 100°C/min via microwave heating. As a result of this process, self-assembled metallic droplets of 1 mm to 5 mm in diameter were produced in less than 15 min.     

Rasterelektronenmikroskopische Untersuchungen der Heißwasserkorrosion von Zink

Scanning electron microscope study of the hot water corrosion of zinc Experiments in 0.010m sodium sulfate solution have revealed that there is a clear temperature dependence of pitting and general corrosion. At 12 °C cratershaped corrosion is found already after a short time; pit growth is by concentric rings and plate-like corrosion products grow out of the base. At 20 °C there is a scar-type attack with annular shapes being built up by spherical amorphous ZnO. At 40 °C the attack follows the same pattern but corrosion can be recognized already after 5 min; simultaneously, there is an increase of general corrosion, the individual pits being gradually overgrown by amorphous and later plate-like corrosion product. At 50 and 60 °C this type of attack is even more pronounced and is accompanied by the formation of columnar structures. At 70 °C general corrosion predominates and at 80 and 90 °C initial pitting is stopped after a short time, so that general corrosion is practically the only type found here. At 65 °C there is a pronounced corrosion maximum.     

Microstructure and mechanical properties evolution of 65Cu–35Zn brass tube during cyclic rotating—bending process

The cyclic rotating—bending (CRB) processes under different deformation conditions were carried out to refine the microstructure and improve the mechanical properties of the 65Cu—35Zn brass tubes. The microstructure and the mechanical properties in the axial direction of the tubes after the CRB process were studied with the OM, EBSD and conventional tensile test. To obtain the accumulated effective plastic strain of the tube during the CRB process, the FEM simulation was also executed. The results show that the average grain size decreases with the increase of rotation time at RT, and with the decrease of bending angle at 200 °C. With the increase of accumulated effective plastic strain during the CRB process, the reduction rate of average grain size of the brass tube increases, the tensile strength of the brass tube increases in wave shape and the elongation increases first and then sharply decreases.     

The attack of molten zinc on steels

A new technology test method has been developed to determine the attack of molten zinc on different steels. The tests were carried out with low-alloy steels, tool steels and stainless steels. These materials were tested in pure molten zinc and in a zinc alloy containing 4% aluminium. The test temperatures were 400–600 °C. The effect of the superficial oxide layer that protects steel against zinc attack has been investigated and the attack mechanism have been discussed. The relationships between zinc attack, time and temperature have been established for low and high-alloy steels. Small additions of aluminium to the zinc melt have no effect on the attack rate. In a zic melt contaning 4% aluminium the rate of the zinc attack on steel is greatly reduced. In this case the time law is found to be parabolic at 500 °C and linear at 600 °C. In a pure zinc melt the unalloyed steel has a better resistance to zinc attack than tool steel.