Tungsten

The mechanical properties of chemical vapour deposited tungsten (W-CVD) on Ti/TiN adhesion bilayers have been studied. Rapid thermal annealing (RTA) of the Ti/TiN bilayers has been found to strongly affect subsequentIy deposited W films. The stress in W is reduced as a consequence of the RTA treatment of Ti/TiN, and the stress reduction is especially pronounced for thin W films. However. the stress in the Ti/TiN bilayers deposited at 300 or 550 "C increases substantially after the RTA treatment at 650 °C, leading to appreciable increase in the total stress of the whole Ti/TiN/W stack. The nucleation deposition of W on the annealed Ti/TiN is somewhat hindered. The retardation of W growth on annealed Ti/TiN is discussed in terms of thermodynamics and classical nucleation theory in conjunction with the reduction of the interracial impurities (i.e. fluorine and oxygen) as a result of the RTA of Ti/TiN [A., as well as the evolution of the W film texture with the W '~hickness.

Aluminum-Silicon thin film (85 at. % of Al and 15 at. % of Si) was deposited on 304 stainless steel substrate by PVD evaporation process and compared with piston skirt samples of Al-Si eutectic alloy (silicon composition varied from 11.7% to 14.5%). Another thin film of Ti-W-N (70 at. % of Ti and 30 at. % of W) was deposited on the first by PVD sputtering process. The first film showed a maximum hardness value of about 8.3 GPa. The thickness of the film was about 1.2 μm. The second film showed a maximum hardness value of about 17.2 GPa with a columnar structure having elements with diameter between 50 and 400 nm. The thickness of the film was about 1 μm. XRD results showed that the two films had amorphous form, however Al and Si picks had been observed. Tungsten oxide WO3 (1 1 0) pick was also observed at the Ti-W-N film. Raman spectroscopy showed that Ti-W-N film is mainly composed of oxides (Tungsten oxide WO3 , Titanium dioxide TiO2 and Aluminum oxide Al2O3) and Titanium nitride TiN. Tribological tests on the Ti-W-N film showed significant results compared to piston skirt samples made of Al-Si alloy. The friction coefficient values were approximately 6 times lower (from μ≈0.52 for reference piston skirt samples to μ≈0.08 for coated sample).

The present study aims the characterization of W-Sn mineralization at Vale Pião deposit, searching for potential geochemical and mineralogical pathfinders useful in mineral exploration. Vale Pião was exploited in the past for both metals, recording a significant production between the 40s and 60s of the XX century. The sampling focused on a set of drill holes conducted in the 1980s by the SFM (Serviço de Fomento Mineiro) in the area of the former mine, with the intention of valuing the Góis region, namely for W and Sn. The samples selection was based on the intervals where the highest W and Sn grades were obtained, mainly in mineralized lodes and breccias and/or where effects related to hydrothermal alteration processes were observed. It was noted that the occurrence of scheelite was dominant over wolframite, with rare cassiterite. In this study three styles of mineralization were recognized: breccias, quartz lodes and aplites. Four types of quartz lodes (I, II, III and IV) were identified and classified, from the oldest to the most recent, with increasing diversity in terms of mineral association. Only the types III and IV of quartz lodes show mineralization, predominantly in W (scheelite and wolframite); however, it is in breccias that this mineralization reaches greater relevance (scheelite >> wolframite). The mineral infillings of breccia fractures are variable, as well as the nature of the clasts that supports them. The compositional and mineralogical variability observed in the quartz lodes and breccias, suggest a polyphasic and long-lived development path.
It was identified an aplite with cassiterite, scheelite and wolframite mineralization, which suggests proximity to a hidden granite, that can be related to the genesis of the Vale do Pião ore-forming system. In all these structures 3 depositional stages were recognized: an initial one where the main silicates, the mineral phases bearing W and Sn and arsenopyrite were generated. The following stage corresponds to the main sulphide stage, traced by abundant sphalerite, pyrite and pyrrhotite, followed by chalcopyrite. The final stage includes mostly the precipitation of the Au-Ag, Bi (-Te) and Pb, mineral phases. The overlapping of the Au-Ag event on the W-Sn event is observed in several samples, namely in breccias.
Based on X-ray fluorescence and electron microprobe data, significant variations in concentration were observed in major, minor and trace elements incorporated in several minerals, such as scheelite, wolframite, rutile and biotite. The similar bimodal distribution in Zr observed in tungstates distinguishes two generations of scheelite and wolframite and can indicate that both precipitate from a similar hydrothermal fluid variably enriched in Zr. Several rutile analyses, hosted in metassediments, show WO3 and SnO2 values above 2 wt % in, suggesting  that these can be used as proxies to the main mineralizing event. The presence of F in phyllosilicates, mainly in biotite, where higher F contents are verified, may be related to the transport of metals, such as W and Sn, by fluoride complexes. Chloritization, tourmalinization and biotitization correspond to common hydrothermal alteration phenomena closely related to the earliest event that originated scheelite, wolframite and cassiterite, and to the subsequent event, where sulphides were formed. A later Bi-Au-Ag-Te-Pb stage, characterized by the association of electrum ± maldonite + native bismuth + bismuthinite ± joseite ± protojoseite + galena, was identified in breccias and in type IV quartz veins. This mineral assemblage is particularly common in arsenopyrite rich samples.

Key-words: W-Sn-Au, Scheelite, Vale Pião, Geochemistry, Metallogenesis

The necessity of technology and reliance on computer devices is leading people to do whatever it takes to acquire the necessary resources in order to sustain the manufacture and use of computer devices such as mobile phones, tablets, etc. The scarcity of the conflict raw materials known as the 3TG (Tantalum, Tungsten, Tin, and Gold) used in computer manufacture has led to human atrocities and illegal trades of the minerals. To mitigate the issue, the so called Dodd-Frank Act requiring tech companies to audit their supply chains in the United States was enacted by the former president Barack Obama in the year 2010. However, only a handful of companies were able to fully audit their supply chains. This paper therefore addresses the need of a strategy for tech companies’ management and administration to legitimately acquire raw materials without contributing to atrocities, and affecting their companies on financial and legal matters.

The performance ofTi.3W.7 and Nb thin films as diffusion barriers for Au was investigated by Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES). The films were sputter deposited in Ar:N2 (70:30 vol%) or pure Ar on amorphous Si02. They were annealed in air at temperatures ranging from 250·C up to 750·C for several hours. In-depth profiles revealed an onset of oxidation of the barriers at 520·C for Nb and 600·C for TiW. Barrier oxidation and extensive diffusion could be correlated. Distinct diffusion behavior as a function of temperature was established between TiW and Nb. A Nb multilayer structure was found to provide the best reliability as the barrier and as the adhesion layer.

First-principles calculations were used in determining the binding and trapping properties of hydrogen to point defects in tungsten. Hydrogen zero-point vibrations were taken into account. It was concluded that the monovacancy can hold up to five hydrogen atoms at room temperature. The hydrogen was found to distort the self-interstitial atom configuration geometry. The interaction of hydrogen with the transmutation reaction impurities Re and Os were studied. It was found that the substitutional Re and Os have a negligible effect on the hydrogen trapping whereas the interstitial Os may increase the hydrogen inventory in tungsten.

Since its discovery, tungsten, a transition element of Group VIb of the Periodic Table of Elements, and its compounds have been considered environmentally benign. Its presence in biological and drinking water samples in Fallon, Nevada, an acute lymphocytic leukemia cluster struck community has alarmed public health, environmental and regulatory agencies. Tungsten, a metal of extraordinary properties that make it hardly substitutable, is considered an essential commodity with a wide variety of uses stretching from household necessities to highly specialized applications. This work is undertaken in order to explore aspects of environmental behavior of tungsten and its compounds. Occurrence data in terrestrial, atmospheric, aquatic and biotic systems are presented. Various aspects of environmental chemistry, fate transport across environmental interfaces and toxicology are discussed with the objective of identifying knowledge gaps and outlining directions for future research.

Abstract. This paper reports results of a research project related to the development of geopolymeric binder using mineral waste mud from the Portuguese tungsten mine Panasqueira. Abrasion and acid resistance of two ordinary Portland cement (OPC) strength class concrete mixtures (C20/25 and C30/37) and several tungsten mine waste mud (TMWM) geopolymeric binder mixtures was evaluated. Acid resistance was performed by submitting samples to solutions of sulphuric acid, nitric acid and chloridric acid, results of weight loss are reported. Abrasion resistance was assessed by the mass loss of cubic specimens when submitted to 1000 rotations with the Los Angeles apparatus test machine. This study indicates that TMWM geopolymeric binders possess higher acid and abrasion resistance than OPC based concrete mixtures.

The electrochromic properties of mesoporous tungsten oxide are described and compared to standard sol±gel ®lms of WO 3. The block copolymer template used in the synthesis was removed by solvent extraction and calcination methods, leading to mesoporous tungsten oxides which range from amorphous to crystalline depending on the removal treatment. The pores are not ordered but do exhibit a fairly regular diameter with an average size of 4 to 5 nm. The mesoporous tungsten oxides exhibit a well behaved electrochromic response and their electrochemical and optical reversibilities are better than those of the analogous sol±gel ®lm. In addition, the mesoporous ®lms exhibit higher rates for coloration and bleaching. The high surface area of these materials is responsible for this behavior and also leads to multiple peaks in the voltammetric scans.

A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the potential development was given for obtaining accurate formation and migration energies for point defects, making the potential useful in atomic scale simulations of point and extended defects. The potential was used to calculate binding energies and trapping distances for vacancies in vacancy clusters and the recombination radius for self-interstitial atom and monovacancy.

Information on tungsten ecotoxicology is very limited. Moreover, it is an even larger lack of information linking tungsten environmental speciation and environmental effects. Soluble tungsten compounds can be released into the environment after corrosion and dissolution of tungsten containing alloys and minerals. Tungsten aquatic chemistry is quite complicated; tungsten anions may polymerize (depending upon concentration and aquatic geochemistry) in aquatic systems at environmentally relevant pHs. However, our present knowledge of tungsten toxicological effects is entirely based on the data obtained in experiments with monotungstates. Here we report experimental results demonstrating that polytungstates are significantly more toxic than monotungstates. Toxicological effects of sodium tungstate and metatungstate have been examined in the standard OECD toxicological tests for Daphnia, algae and earthworms. LD50 and EC50 values for sodium tungstate are more than 10 times larger than those for sodium metatungstate, when expressed in terms of tungsten concentration. This difference increases 12-fold more when LD50 and EC50 are expressed in terms of molecular concentrations. These toxicity patterns have also been observed in the experiment with laboratory aquatic ecosystems. At the ecosystem level, mono-and polytungstates also affect the nitrogen cycle. These findings stress the need for further studies of both environmental speciation of tungsten and toxicity of different tungsten compounds.