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An Overview of Tungsten Toxicity
Published in Debasis Bagchi, Manashi Bagchi, Metal Toxicology Handbook, 2020
Ola Wasel, Jennifer L. Freeman
Tungsten (W) is a transition metal with an atomic number of 74, a molecular weight of 183.84, and belongs to Group VIB of the periodic table. Tungsten is present naturally in rocks and minerals. Tungsten is not present in a pure form, but it is naturally combined with other metals.1 The most common forms of tungsten that are used in industrial applications are wolframite and scheelite.1 Tungsten has the highest melting point and highest tensile strength at a temperature of over 1,665°C compared to all other metals.2 Tungsten has several oxidation states: 0, +2, +3, +4, +5, and +6. The physical and chemical properties of tungsten compounds vary based on the oxidation state (Table 24.1). Tungsten is used in the forms of tungsten carbide, metallic tungsten, tungsten chemicals, and tungsten alloy in many different applications (Figure 24.1).1,3
Lighting
Published in Dorin O. Neacşu, Automotive Power Systems, 2020
Concerning its construction, a tungsten filament is placed in a vacuum and heated to incandescence by an electric current at a temperature of about 2,300°C. Tungsten is a heavy metallic element and has the symbol W, its atomic number is 74, and its melting temperature is 3,410°C. The tungsten filament is wound into a spiral to get more length of thin wire into a small space. Improved bulbs are filled with gas instead of a vacuum, most typically argon. This allows the tungsten filament to work at a higher temperature without failing and therefore produces a whiter light. Argon bulbs produce about 17 lm/W compared with a vacuum bulb, which will produce about 11 lm/W only.
Predicting Thermal Conductivity of Metallic Glasses and Their Nanocomposites
Published in Sumit Sharma, Metallic Glass–Based Nanocomposites, 2019
Tungsten has the highest melting point among other known metals, and its remarkable mechanical properties, high density, and high thermal conductivity make it, as well as its alloy-based composites, a candidate for high-temperature and structural applications. Moreover, to exploit metallic glasses for high-temperature applications, their crystallization temperature should be enhanced to resist any phase changes during operations, and thus tungsten is a refractory alloying element used to improve glass-forming ability and crystallization temperature. Moreover, it is practically difficult to form bulky glass systems containing refractory metals by casting, melting, and quick solidification techniques. However, studies has been carried out to investigate the fabrication of multicomponent Ti40.6Cu15.4Ni8.5Al5.5W30 bulk metallic glasses with higher thermal stability using a mechanical alloying method, in which a solid-state reaction process is carried out using a low-energy ball-milling method, to form homogenous glassy powder, and then, by a spark plasma sintering approach, this powder is transformed into bulk metallic glasses. Furthermore, the powder obtained after 200 hours of milling process as a product consists of high thermal stability and is specified by 90 K for the supercooled liquid region and 827 K for the crystallization temperature. The metallic glasses obtained as a product consist of enhanced microhardness and high thermal stability [31].
Enhanced flotation of Pb(II)-activated wolframite using a novel collector
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Jing Qi, Sheng Liu, Xianyang Qiu, Guangyi Liu
As a strategic key metal, tungsten has been widely used in national defense and modern manufacturing(Ilhan et al. 2013; Kupka and Rudolph 2018). Wolframite ((Fe, Mn)WO4) is a critical mineral resource for tungsten production (Habashi 2008; Martins 2014; Martins and Amarante 2013; Suri 2001). For the coarse particle wolframite, the gravity and magnetic separation are two main approaches to their enrichment and recovery (Meng, Feng and Ou 2017; Pandey et al. 2001; Sreenivas et al. 2004; Yang et al. 2016). While, wolframite is brittle, and to liberate it through crushing and grinding will produce plenty of fine particles, which have to be separated and enriched by froth flotation (Ai et al. 2017; Medvedev, Korshunov, and Khavskii 1995; Meng et al. 2015). Wolframite exhibits a certain hydrophilicity, to froth flotation, the first step is to hydrophobize it by collectors. Fatty acids, hydroxamic acids, and their derivatives are common collectors for wolframite flotation (Deng et al. 2015; Hu, Wang and Xu 1997; Meng et al. 2015; Yang 2018). Nowadays, the combination scheme of benzohydroxamic acid (BHA) collector and Pb(NO3)2 activator has been considered as a high-effective approach to float out of fine wolframite particles, which was successfully applied in Shizhuyuan Mine of China to replace the classical ‘‘Petrov’s process’’ (Han et al. 2017). The approach significantly increased the flotation recovery of tungsten in the wolframite concentrates to about 70%. Nevertheless, it still has enough space for promoting the recovery of fine wolframite particles.
Improving tribological properties of TC4 strengthened by tungsten using ESA
Published in Surface Engineering, 2022
Ziyue Qi, Song Zhao, Xiaowen Qi, Yu Dong
Various materials are used for surface strengthening, such as carbon, nickel, tungsten, etc. Tungsten is a kind of metal material with a high melting point at 3410°C, high hardness (i.e. Vickers hardness: 3.43 GPa), good corrosion resistance and stable chemical properties for diverse part manufacturing. Tungsten-strengthened layers are also often implemented to enhance the wear resistance of components, as evidenced by wear-resistant layers for high-speed cutting tools [29]. It is well known that tungsten-strengthened layers possess excellent wear resistance and friction reduction performance. For example, Zhang et al. [29] manufactured wear-resistant tungsten strengthened layers with the lowest friction coefficient in range of 0.1–0.2 on the 1020 steel surfaces. Such results are ascribed to material attributes of high hardness and high failure resistance for tungsten strengthened layers. Notwithstanding that many methods [30–32] have been mentioned for preparing tungsten-strengthened layers, it has been rarely seen for such a layer preparation on the surfaces of titanium alloys via ESA.
Microstructural characterisation of borided binary Fe–W alloys
Published in Surface Engineering, 2018
The addition of tungsten in steels improves hardness, creep resistance and long-term stability of steels at high temperatures. In addition, tungsten is one of the most important carbide forming elements. It lowers the eutectoid point to lower carbon concentrations and increases the amount of undissolved carbide content in hardened steel [26]. Currently tungsten is used in high-speed steels, cold work tool steels, plastic mould steels, hot work tool steels and valve steels with the amount of 0.5–20 wt-%.