Transformation/dissolution characterization of tungsten and tungsten compounds for aquatic hazard classification
The transformation/dissolution protocol (T/DP) for metals and sparingly soluble metal compounds was applied to determine the transformation/dissolution (T/D) characteristics of yellow tungsten trioxide, WO3; blue tungsten oxide, WOx, x taken as 2.9; tungsten disulphide, WS2; tungsten metal, W; 3 samples of tungsten carbide, WC; sodium tungstate, Na2WO4 · 2H2O; ammonium paratungstate (APT), (NH4)10(H2W12O42) · 4H2O; and ammonium metatungstate (AMT) (NH4)6(H2W12O40) · 3H2O. The T/D data were used to derive aquatic hazard classification outcomes under the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) and European Union Classification, Labelling and Packaging of Substances and Mixtures (EU CLP) schemes by comparing the data with selected acute and chronic ecotoxicity reference values (ERVs) of 31 and 3.37 mg W/L, respectively. In addition to the concentration of total dissolved tungsten (W), the T/D solutions were analyzed for the concentration of the tungstate anion, because speciation can be an important factor in establishing the ecotoxicity of dissolved metals. Results show that the tungstate anion was the predominant W‐bearing species in solution for all substances examined at pH 6 and 8.5. It was found that the 100 mg/L loadings of both the yellow WO3 and the blue WOx exceeded the 31 mg/L acute ERV, so they would classify as Acute 3‐Chronic 3 under the UN GHS scheme but they would not classify under the EU CLP. An effect of pH on the reactivity of the W metal was observed with 3% and 16% W dissolution at pH 6 and 8.5, respectively. Tungsten metal would not classify under either the UN GHS or EU CLP schemes nor would the WS2. The WCs were the least reactive in terms of the 1% or less dissolution of the contained W at pH 6. A critical surface area for WC was calculated. The sodium tungstate, APT and the AMT all yielded, at pH 8.5, total dissolved W concentrations that would result in UN GHS Acute 3‐Chronic 3 classifications. Integr Environ Assess Manag 2018;14:498–508. © 2018 Her Majesty the Queen in Right of Canada. Integrated Environmental Assessment and Management © 2018 SETAC
Acute and Chronic Effects of Sodium Tungstate on an Aquatic Invertebrate (Daphnia magna), Green Alga (Pseudokirchneriella subcapitata), and Zebrafish (Danio rerio)
Although aquatic toxicity data exists for tungstate substances, insufficient data of high quality and relevancy are available for conducting an adequate risk assessment. Therefore, a series of acute and chronic toxicity tests with sodium tungstate (Na2WO4) were conducted on an aquatic invertebrate (Daphnia magna), green alga (Pseudokirchneriella subcapitata), and zebrafish (Danio rerio). Collectively, the data from these studies suggest that sodium tungstate exhibits a relatively low toxicity to these taxa under these test conditions. All studies were conducted in the same laboratory under good laboratory practice standards using Organisation for Economic Co-operation and Development guidelines with the same stock of test material and the same analytical methods. All results are reported as mg W/L. The following toxicity values were based on mean measured concentrations. For D. magna, the 21 day test no-observable effect concentration (NOEC) was 25.9 mg W/L, and the 48-h median effective concentration (EC50) from the acute test was >95.5 mg W/L (the highest concentration tested). The P. subcapitata test yielded an ErC50 of 31 mg W/L. A 38-day test with zebrafish resulted in an NOEC ≥5.74 mg W/L with no effects at any concentration. The 96-h LC50 from the acute test with zebrafish was >106 mg W/L. The results of the current acute study for daphnids and fish are consistent with published literature, whereas the algae results are different from previously reported values. Transformation/dissolution (T/D) studies, which were conducted according to United Nations Globally Harmonized System of Classification and Labelling of Chemicals protocol, confirmed that the WO4−2 anion accounted for most of the tungsten in solution. For classification purposes, the algae ecotoxity reference value was then compared with T/D data and would not classify Na2WO4 as an aquatic toxicant under the European Union Classification, Labelling and Packaging scheme.
Selective etching of InP in NaF solution
Abstract The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [0 1 1] and [ 0 1 ¯ 1 ], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [1 1 1]B and [ 1 1 ¯ 1 ¯ ]B. Both are due to the selective etching of F− ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III–V compound semiconductors for photonic band gap materials.