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
A New Approach to the Hazard Classification of Alloys Based on Transformation/Dissolution
ABSTRACT Most of the metals produced for commercial application enter into service as alloys which, together with metals and all other chemicals in commerce, are subject to a hazard identification and classification initiative now being implemented in a number of jurisdictions worldwide, including the European Union Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) initiative, effective 1 June 2007. This initiative has considerable implications for environmental protection and market access. While a method for the hazard identification and classification of metals is available in the recently developed United Nations (UN) guidance document on the Globally Harmonized System of Hazard Classification and Labelling (GHS), an approach for alloys has yet to be formulated. Within the GHS, a transformation/dissolution protocol (T/DP) for metals and sparingly soluble metal compounds is provided as a standard laboratory method for measuring the rate and extent of the release of metals into aqueous media from metal-bearing substances. By comparison with ecotoxicity reference data, T/D data can be used to derive UN GHS classification proposals. In this study we applied the T/DP for the 1st time to several economically important metals and alloys: iron powder, nickel powder, copper powder, and the alloys Fe–2Cu–0.6C (copper = 2%, carbon = 0.6%), Fe–2Ni–0.6C, Stainless Steel 304, Monel, brass, Inconel, and nickel–silver. The iron and copper powders and the iron and nickel powders had been sintered to produce the Fe–2Me–0.6C (Me = copper or nickel) alloys which made them essentially resistant to reaction with the aqueous media, so they would not classify under the GHS, although their component copper and nickel metal powders would. Forming a protective passivating film, chromium in the Stainless Steel 304 and Inconel alloys protected them from reaction with the aqueous media, so that their metal releases were minimal and would not result in GHS classification. For the other alloys, we developed a new critical surface area–toxic units (CSA-TU) approach to derive their GHS classification proposals. The CSA-TU approach can be readily applied to other multicomponent alloy systems, without the need to arbitrarily select a particular component among several as the determinant of toxicity. This paper shows how regulatory obligations, such as those mandated by REACH, can be met with a laboratory-based CSA-TU method for deriving hazard classification proposals for alloys, linking to attendant environmental protection management decisions. Drawing on T/D data derived from laboratory testing of the alloy itself, the CSA-TU approach can be applied to establish scientifically defensible decisions on hazard classification proposals for an alloy of interest. The resulting decisions can then be incorporated into environmental management measures in such jurisdictions as the European Union. Based on an approach developed specifically for alloys, the hazard classification decisions can be regarded as relevant, credible, and protective of the environment. Since alloys are usually more resistant to chemical attack than their components, this approach is a considerable improvement over the possibility provided for in the GHS of calculating a hazard classification level for an alloy from the classification levels of its components.
Physical Processes in Inorganic Scintillators
BASIC PRINCIPLES AND PROCESSES Physical Mechanism of Scintillation Creation of Electron Hole Pairs Excitation and Emission of Luminescence Centers Scintillation Materials Halides Oxides and Oxide Systems Chalcogenides Glasses Interaction of Ionizing Radiation with Scintillators High Energy Photons Charged Particles Neutral Particles General Characteristics of Inorganic Scintillators Light Yield Duration of Scintillation Pulse Afterglow Temperature Response Optical Properties Radiation Hardness Density Emission Spectra Mechanical and Chemical Properties Physical Parameters Cost Consideration Scintillator Requirements in Various Applications High Energy Physics Intermediate Energy Physics Positron Emission Tomography Gamma Spectroscopy Energy Resolution Intrinsic Scintillator Resolution Nonproportional Response Time Resolution Low Energy Quanta and Electrons CONVERSION OF ELECTRONIC EXCITATIONS IN SOLIDS Charge Carrier Behaviors Delta Rays Secondaries Excitation of Luminescence Centers Effect of Ionization Density Energy Losses Simple Phenomenological Model Plasmon Model Polaron Model Scintillation Yield Spectra Vacuum Ultraviolet Region Ultrasoft X-Rays X-Rays Gamma Rays Heavy Ionizing Particles INTRINSIC LUMINESCENCE OF INORGANIC SCINTILLATORS Excitonic Luminescence Alkali Halide Crystals Alkaline-Earth Fluorides Ternary Halide Compounds Excitonic-Like Luminescence Cesium Iodide Tungstate and Molybdate Phosphors Core-to-Valence Transitions First Evidence for Radiative Core-to-Valence Transitions Excitation Spectra Emission Spectra Experiment Theory Luminescence Kinetics Experimental Theoretical Investigations Temperature Dependence of Luminescence Parameters Conditions of Detection Prospects for Research EXTRINSIC LUMINESCENCE OF INORGANIC SCINTILLATORS Thallium-Activated Halide Scintillators Crystals with NaCl-Type Structure Crystals with CsCl-Type Structure Other Thallium-Based and Thallium-Doped Crystals Crystals Containing Other ns2 Ions Bismuth Germanate (BGO) Sodium-Activated Cesium Iodide Rare-Earth-Activated Crystals General Considerations Europium-Activated Crystals Cerium-Activated Compounds Preliminary Comments LaF3-CeF3 Systems Cerium Chloride Barium Fluoride Gadolinium-Containing Crystals Lu- and Y-Containing Crystals Nd- and Pr-Activated Crystals DEFECT FORMATION BY IONIZING RADIATION Effect on Scintillator Characteristics Mechanisms of Defect Formation Efficiency of Defect Production Geometrical Factor Separation between F and H Centers Temperature Dependence of Production Efficiency Role of Halogen Ion Impurities Effect of Cation Impurities Formation Time of F-H Pairs Closing Comments References Index