Characterisation and properties of powder-rolled porous Ti sheets and IrO2/Ti electrodes

This report investigated synthesis of porous Ti sheets by direct powder rolling followed by vacuum sintering at 1100°C for 1.5?h. Uniform microstructures were observed in the sections longitudinal and transverse to rolling direction in terms of porosity, pore size, gas permeability and filtration efficiency. IrO₂ nanowire arrays were coated onto the powder-rolled porous Ti substrate as an electrode by thermal decomposition. Characterisation results show that the coating mainly exhibited mixture of IrO₂ and α-Ti phases. The coating of IrO₂ nanowire arrays effectively increased the specific surface area of the IrO₂/Ti electrode and reached over 95% of current efficiency. The cyclic voltammetry test of the electrode showed an obvious redox peak due to its increased specific surface area by the porous Ti substrate.     

Effect of additives on sintering response of titanium by powder injection moulding

Abstract

Powder injection moulding is a maturing technology that has proven most useful for the production of complex metallic and ceramic components of modest sizes. Considering the inevitable demand for cost effectiveness in automotive applications, components manufactured from low cost sponge titanium (Ti) powder currently reflect the most advantageous economics among the available Ti powders. This paper describes the net shape fabrication of Ti components and considers the role of iron and zirconium powder additions. Sintering cycle optimisation relied on differential scanning calorimetry to identify a cycle in the 1275–1300°C range for 1–2 h. The sintered material was characterised using tensile and hardness testing and microscopic examinations. The influence of test conditions on densification, microstructure and mechanical properties was analysed.     

Physical simulation of converter steelmaking with powder injection

A water model of top and bottom blown converter with top lance powder injection and bottom tuyere powder injection was established to investigate the powder injection. The results show that the powder penetration ratio under the condition of top lance injection is greater than that under the condition of bottom tuyere powder injection. In both cases, the powder penetration ratio increases with the increase of solid/gas ratio and powder particle size. Powder uniform dispersion time with top lance powder injection is longer than that with bottom tuyere powder injection. Top lance powder injection, lance height of 258?mm, bottom blowing rate of 1·96?Nm³?h^?1 and powder particle size of 0·212–0·380?mm are suggested as the optimum powder injection operation under the experimental condition. The corresponding optimum operation for prototype is top lance powder injection with lance height of 1550?mm, powder size of 1–5?mm and bottom blowing rate of 450?Nm³?h^?1.     

Review of effect of oxygen on room temperature ductility of titanium and titanium alloys

Abstract

Room temperature tensile ductility is an important property of titanium (Ti) and titanium alloys for structural applications. This article reviews the dependency of tensile ductility on oxygen for α-Ti, (α+β)-Ti and β-Ti alloys fabricated via traditional ingot metallurgy (IM), powder metallurgy (PM) and additive manufacturing (AM) or three-dimensional printing methods and recent advances in understanding the effect of oxygen on ductility. Seven mechanisms have been discussed based on case studies of individual titanium materials reported in literature. The dependency of ductility on oxygen is determined by both the composition and microstructure of the titanium alloy. For Ti–6Al–4V (wt-%), as sintered Ti–6Al–4V shows a critical oxygen level of about 0·33 wt-% while additively manufactured Ti–6Al–4V exhibits different critical levels ranging from about 0·22% to well above 0·4% depending on microstructure. Rare earth (RE) elements are effective scavengers of oxygen in titanium materials even just with a small addition (e.g. 0·1 wt-%), irrespective of the manufacturing method (IM, PM and AM). High cycle fatigue experiments revealed no initiation of fatigue cracks from the resulting RE oxide particles over the size range from submicrometres to a few micrometres. A small addition of RE elements offers a practical and affordable approach to mitigating the detrimental effect of oxygen on ductility.     

Density evaluation of powder metallurgy compacts using in situ X-ray radiography

Abstract

The measurement of density in porous materials during mass production process is one of the most important factors in industry. The existing methods for measuring density such as hydrostatic weighing and microscopic examinations have some limitations and some inherent problems associated with them. Recently, processes based on radiography have emerged. This paper deals with the in situ measurement of density of porous materials using X-ray techniques. For this purpose, experiments have been performed at various density levels of powder metallurgy compacts. In situ X-ray radiography was then carried out on samples. A correlation has been made between the film density of radiographic film and the surface density of the compacts. A mathematical relationship was derived between the absorbed X-ray, the film intensity and the compact density. The comparison of values of the experimental data and mathematical relationship reveals 1·6% average discrepancies.     

Pressure leaching of leucoxene concentrate using Ca(OH)<Subscript>2</Subscript>

The results of studying the desiliconization of a leucoxene concentrate using burned lime as a reagent in the presence of NaOH as a catalyst are presented. This process is based on the selective interaction of CaO with the fine silica present in leucoxene grains, which results in the formation of CaSiO₃ at high temperatures and pressures (autoclave process). Experiments are performed on the initial leucoxene concentrate and the products of its beneficiation after magnetizing roasting.     

电解钛氢化脱氢制备超细高纯钛粉工艺

以电解钛为原料,采用氢化、球磨破碎和脱氢的工艺,制备超细高纯钛粉。采用激光衍射粒度分析、SEM及氢和氧元素分析等手段,研究各工艺过程所得的TiH2粉和Ti粉的粒度及其分布、粉末形貌和氧含量的变化趋势。结果表明:电解钛经420℃氢化后,初次球磨得到中位径(D50)为9.81μm的超细TiH2粉,再经600℃保温脱氢,最后经球磨分散得到D50为11.04μm,氧含量为0.48%(质量分数)的不规则形状超细高纯钛粉。在各个工艺过程中,氧含量(质量分数)增加量由低到高依次是TiH2粉脱氢、TiH2球磨制粉、脱氢钛粉球磨和电解钛氢化。     

DSC and FIB/TEM investigation of calcium and yttrium additions in the sintering of magnesium powder

Powder metallurgy can be used to produce near-net-shape magnesium parts and also allows unique chemical compositions to be achieved that can lead to new alloys with novel properties. However, the surface layer formed on the magnesium powders during processing acts as a barrier to diffusion and sintering is less effective. The layer, formed by reactions with the atmosphere, contains oxides, hydroxides and carbonate hydrates of magnesium. To overcome this barrier, small additions of calcium or yttrium metal powders were made to the Mg matrix. The oxides of Ca and Y are thermodynamically more stable than magnesium oxide, and will disrupt the surface layer. The present work reports the results of investigation by differential scanning calorimetry, and focussed ion beam (FIB) microscopy and transmission electron microscopy (TEM), on the effect of calcium and yttrium additions during the sintering of magnesium powder. FIB examination of sintered Mg–1?wt-% Ca show that secondary phases are located along grain boundaries as well as inside porosity, which confirms the characteristic mechanism of magnesium sintering. A TEM specimen made by a FIB liftout process was also examined by TEM and EDS and indicates that the sintering process was successful, with the elemental distribution being as predicted by sintering.     

草酸盐共沉淀法制备Cu-Sn预合金粉末

以CuC12.2H2O,SnCl2.2H2O为原料,草酸为沉淀剂,采用共沉淀-热分解法制备Cu-Sn预合金粉末。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)分别分析前驱体粉末及热分解产物的物相组成和微观形貌,并研究所制备Cu-Sn预合金粉末的粒度和形貌特征。结果表明:共沉淀前驱体为CuC2O4.2H2O和SnC2O4.2H2O的固溶体,采用共沉淀-热分解法制备出的Cu-Sn预合金粉末具有粒度细小、粒度分布窄的特点,其中位径为1.68μm,且该合金粉末对前驱体粉末形貌具有继承性。     

悬浮液进样ICP-AES测定纳米氧化锆中的镁、硅、钙和钛

使用悬浮液进样ICP-AES法测定纳米氧化锆中的镁、硅、钙和钛.样品以Triton X-100溶液作为分散剂,经超声波分散后,在磁力搅拌下动态进样.使用水溶液标准进行校准,不进行基体匹配.实验结果与高压溶样法一致,最终各元素检出限为Mg 0.0008μg/mL,Si 0.028μg/mL,Ca 0.0014μg/mL,Ti 0.013μg/mL,相对标准偏差(RSD)Mg 3.6%,Si 4.1%,Ca 2.8%,Ti 4.3%.     

利用多晶硅切割废料制备SiC粉体

针对目前多晶硅切割废料大量堆积造成环境污染的问题,提出了以多晶硅切割废料为原料,经过盐酸浸出除Fe后,配加活性炭高温反应制备SiC的工艺。首先,对废料成分与碳的反应进行了热力学计算;然后,使用差热分析、X射线衍射和扫描电子显微镜等分析手段,研究了反应温度、反应时间以及废料中的Fe对产物物相组成和形貌的影响。结果表明,切割废料经过酸浸后的主要成分为SiC和Si。碳不能与Fe-Si系合金(FeSi、Fe_5Si_3等)中的Si反应生成SiC,所以为了制备纯度较高的SiC,多晶硅废料反应前必须预先除Fe。当反应温度高于1 400℃时,酸浸后的切割废料与活性炭的反应能够迅速地发生,且反应生成的SiC遗传碳颗粒的形貌。     

溶胶-凝胶法制备纳米稀土镧掺杂钼粉

采用液-液掺杂方式将仲铝酸铵、硝酸镧以及柠檬酸溶液混合,采用溶胶-凝胶法制备纳米稀土镧掺杂钼粉.研究初始溶液pH值和柠檬酸添加量对成胶效果的影响,讨论干凝胶的除胶工艺,分析稀土镧在掺杂铅粉中的存在形式.结果表明:当初始溶液的pH值为1且柠檬酸的添加量为仲钼酸铵质量的1.5倍时,可制备出疏松多孔、网状结构、成胶效果良好的干凝胶.采用直接烧结法在560℃焙烧可将胶体很好地除去,两段还原后得到颗粒为球形且十分均匀的纳米掺杂Mo粉.在掺杂MoO3粉中,镧以La2O3或La-Mo复合氧化物形式存在,稀土颗粒粘附在MoO3颗粒表面.在MoO3的还原过程中La-Mo复合氧化物分解,镧以La2O3的形式存在于Mo粉中.钼粉颗粒尺寸在500 nm左右,掺杂La2O3的尺寸约100nm.     

Conception of a hot forging die out of metal powder equipped with inner cooling channels

Abstract

The main target of this paper is the development of a forging die, made of hot working steel powder, equipped with internal cooling channels. For this purpose a copper rod is embedded inside the green body. Subsequently the copper has to be molten out. Therefore, the suitability of a pressure sintering process and a HIP-process is investigated. The design of the cooling channel is based on numerical simulations of thermal and mechanical stresses within the hot forging die. Furthermore, the study covers the influence of surface contours of the copper tubes (corrugated, plain) on their melting behavior as well as the resulting inner surface of the cooling channel.     

A kinetic model for Ca treatment of Al-killed steels using FactSage macro processing

A kinetic model was developed to investigate the evolution of inclusions during the Ca treatment of Al-killed steels. Evolutions of steel chemistry and inclusion composition in Al-killed Ca-treated steels from previous experimental works were accurately predicted using the current kinetic model. The model was widely used to predict the evolution of inclusions during the Ca treatment of Al-killed steels with varying concentrations of Al, S, O and Ca. During the Ca injection of Al-killed steels, a large number of CaS and CaO inclusions are transiently generated in the Ca-rich zone due to the excessive Ca. Al₂O₃ inclusions are gradually modified to calcium aluminates in the bulk steel with the addition of Ca. The superfluous Ca or S may lead to the formation of solid CaS in the liquid steel.     

Preparation of Ca- Fe oxygen carrier using metallurgical dust

Chemical chain combustion technology is a new combustion technology that achieves efficient and low energy separation for CO2 capture. CaSO4- Fe2O3 oxygen carrier was prepared by sol- gel method from blast furnace slag containing iron, and X- ray diffraction (XRD) and scanning electron microscopy and energy dispersive X- ray (SEM- EDX) were used to characterize the oxygen carrier particles. The results show that the CaSO4- Fe2O3 oxygen carrier prepared from iron metallurgical dust has a mass fraction of 93. 58%, a specific surface area of 10. 37cm2/g and a conversion rate of 67. 47% after reaction?? with coal powder, which has good reactivity. Combined with SEM and EDS analysis, the main cause of the decrease of carrier activity is the accumulation of coal ash during the cycle combustion process, resulting in complex and diversified carrier components, chemical reactions and agglomeration effects, and then carrier activity is reduced.     

喷雾干燥-直接碳化法制备WC-Co复合粉末

在高性能WC-Co的制备中,WC与Co均匀混合和C含量的严格控制具有重要意义。以偏钨酸铵、乙酸钴、重铬酸铵和炭黑为原料,通过喷雾干燥和直接还原碳化法制备WC-Co复合粉末,然后在钼丝炉中通入氢气对前驱体进行还原碳化制备WC-Co复合粉末。对制备好的WC-Co进行总碳含量测定,用X射线衍射进行相分析。研究了喷雾法制备WC复合粉末形貌粒度及碳化温度、碳化时间、配碳量对WC-Co粉末总碳量的影响。结果表明:WC复合粉末为球形粉末,平均颗粒度为50μm;当碳化温度在950℃、碳化时间为3.5h、配碳量为9%时,所得WC-Co复合粉末中WC与Co达到均匀的分布,且其实际总碳含量达到理论总碳量5.79%。     

共沉淀-热分解法制备金刚石工具用预合金粉

研究用共沉淀-热分解法制备金刚石工具胎体用预合金粉,其中包括共沉淀反应pH值、反应温度和热分解反应温度等对粉末收得率和粒度等方面的影响.采用XRD 和SEM对粉末物相组成和形貌进行了分析,同时采用激光衍射粒度分析仪对预合金粉粒度分布进行了分析.研究结果表明:采用共沉淀-热分解法可以制备出良好的预合金化粉末,粉末呈棒状和不规则形状,粉末粒度较细,分布比较均匀、集中;粉末收得率随着共沉淀反应pH 值的增大而提高,在pH 值约等于9.8时达最大值;随着共沉淀反应温度的升高,粉末粒度逐渐增大;随着前驱体热分解反应温度的升高,粉末粒度逐渐增大.     

超声波化学还原法制备超细Ni包覆Cu复合粉工艺研究

采用化学镀法以预制的Cu粉为基体,制备出了超细Ni包覆Cu复合粉体.研究了超声波对Ni包覆Cu复合粉体的转化率、包覆效果及分散性的影响.用SEM、EDS及XRD分析样品的微观形貌、成分及物相组成.结果表明:在超声条件下,获得了分散性较好的Ni包覆Cu复合粉体;不同超声条件下制备的Ni包覆Cu复合粉体中Cu、Ni含量无明...     

固液界面反应法制备针状草酸钴粉体

以钴粉和草酸(H2C2O4)为原料,采用固液界面反应法制备针状草酸钴(Co2C2O4·2H2O)粉体.用扫描电镜(SEM)、X射线衍射仪(XRD)和激光粒度仪对粉体进行表征,研究反应温度、钴粉浓度、草酸与钴粉的计量比以及无机酸的种类和用量对草酸钴粉体的形貌和长径比的影响.结果表明,反应温度为30℃时草酸钴粉体多为颗粒状...     

Densification and deformation during uniaxial cold compaction of stainless steel powder with different particle size

The behaviour of austenitic stainless steel powder column during uniaxial cold compaction was investigated in this work. Powders with different particle size were compacted to the same green density in a hydraulic press, also providing different H/D ratios in order to account for the influence of geometry. The analysis of the data continuously recorded by the press allowed distinguishing the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model for densification was proposed, considering both density and increase in density versus the applied pressure. The trend of reversible and permanent deformations versus the applied pressure was evaluated, also proposing an analytical model. The comparison between the densification curves and the curves of permanent deformation allowed highlighting the physical meaning of the model describing the increase in density for the different particle size.