14. Gas-phase transport: Tatar/Gannon and van Leeuwen

The formation of a volatile Cr(VI) species at a hot chromium source, its deposition on cooler fibres and the formation of a calcium or sodium chromate are distinct reaction steps. They can occur side by side or in succession. The statement that Cr(VI) also forms without calcium-containing insulation material must therefore be distinguished from the question of what role such an insulation material plays in the binding, quantity and chemical form of the deposited chromium. [11, 35-37]

Tatar investigates chromium oxyhydroxide from a hot steel source and its interaction with spatially separated, cooler aluminosilicate fibres. The proposed esterification concerns chromate-containing surface bonds at aluminium/silicon centres; it is not to be equated with evidence of calcium or sodium chromate. The reaction sequence is derived from XPS findings and the literature. Cr(VI) itself was determined analytically. [35]

If Tatar is cited as evidence that insulation chemistry is fundamentally irrelevant to Cr(VI) deposits, this goes beyond the matter investigated. The work shows a formation and transport pathway without a necessary calcium contribution at the hot source. It invalidates neither Sayano's direct interface evidence nor a subsequent reaction with calcium/sodium components. [11, 35]

Van Leeuwen explicitly takes up Tatar/Gannon and compares quartz, aluminium oxide and two alkaline earth silicate (AES) fibres. All four materials collect Cr(VI). The two AES samples show higher absolute Cr(VI) concentrations in the digestion solutions examined than the quartz and aluminium oxide samples. However, the proportion of Cr(VI) in total chromium does not increase equally in every sample: the individual values in Table II permit a more precise statement than a general description of consistently higher Cr(VI) proportions for AES. [36]

Values according to Table II; percentages calculated from the published individual values and rounded. These are concentrations in digestion solutions, not air concentrations or directly mg/kg of insulation material. Different fibre geometries and sample positions must be taken into account when comparing quantities. [36]

Using FactSage, the authors model the reaction of the condensing chromium species with the oxide components and describe CaCrO₄ as an important possible Cr(VI) carrier of the calcium-containing fibres. This complements gas-phase transport mechanistically. However, the study does not replace the direct XRD phase evidence from Sayano's contact test. Chemically, CaCrO₄ is a Cr(VI) chromate; CaCr₂O₄, by contrast, contains Cr(III). Deviating formula notations in individual passages must be checked on the basis of the oxidation state. [11, 36]

For the transfer to plants, the test conditions must be taken into account: Tatar uses highly humidified air; van Leeuwen approximately 3 vol.% water. Both pass a directed gas flow through a tube with a hot source and downstream fibre samples. Van Leeuwen's experiment runs at local atmospheric pressure, not in a high-pressure steam reactor. The publication states 800 °C in the abstract and, in the methods section, a calibration of the furnace centre to 850 °C. The experiments explain reaction possibilities; their quantities cannot be transferred directly to freely exposed external engine insulation. [35, 36]

European manufacturers' association as client: ECFIA and Montana State University

Tatar and van Leeuwen work within the same American research group at Montana State University; Paul Gannon is involved in both publications. Van Leeuwen's dissertation of May 2024 explicitly states on page 2 that the research originated from a request by ECFIA, the association of European high-temperature insulation wool manufacturers. The aim was to investigate claims by competitors that their products reduced or prevented Cr(VI) formation. The acknowledgements on page iii name partial funding by ECFIA industry partners. [35-37]

This documents that Cr(VI) formation on high-temperature insulation wools was known as an issue within the European manufacturers' association; the occasion was competitors' claims regarding the reduction or prevention of Cr(VI) formation. The dissertation and the later publication are overlapping results of the same research context, not mutually independent confirmations. The funding statement here relates to the dissertation project; it is not presented without further ado as specific funding of each individual publication. [36, 37]

This gives rise to a precise question: which results were communicated to the participating industry partners and when, and how were they incorporated into product information and application-related warnings? The scientific result must be assessed on the basis of its methods and data, independently of this communication question.