{"id":5322,"date":"2025-01-21T22:09:07","date_gmt":"2025-01-21T21:09:07","guid":{"rendered":"https:\/\/seefbv.com\/en\/?post_type=docs&p=5322"},"modified":"2026-06-23T13:17:50","modified_gmt":"2026-06-23T11:17:50","password":"","slug":"cr-vi-formation-in-insulation-high-temperatures","status":"publish","type":"docs","link":"https:\/\/seefbv.com\/en\/docs\/cr-vi-formation-in-insulation-high-temperatures\/","title":{"rendered":"2. The formation of Cr(VI) in insulation at high temperatures"},"content":{"rendered":"

In industrial high-temperature applications, metals such as stainless steel (SS) and lower-chromium alloys are frequently insulated with materials containing alkali and\/or alkaline earth metal oxides, particularly calcium: stone wool, glass wool, glass fibre blankets, needle-felt mats, microporous insulation, or calcium silicate. Some materials, such as AES wool or microporous insulation products, are processed into blanket form. Calcium-free microporous insulation materials often incorporate calcium-bearing glass fibre fabric coatings (e.g. E-glass), which, like directly applied AES mats, can bring chromium into contact with alkali or alkaline earth metal ions. These materials are used in sectors such as combined heat and power (CHP), engines, shipping, trucks and buses, as well as in the energy sector, turbine installations, incinerators, the process industry, and other applications where metal and insulation are exposed to elevated temperatures over extended periods. Under certain conditions, chromate compounds<\/strong> can form, i.e. Cr(VI). These chromate compounds are carcinogenic substances that can pose serious risks to human health and the environment. This article explains how Cr(VI) forms<\/strong>, what role insulation plays, at what temperatures the risk increases, and why it is important to remain alert even at lower temperatures<\/strong>.<\/p>\n

Two mechanisms of Cr(VI) formation: solid phase and gas phase<\/h2>\n

Based on recent studies (including Sayano et al. 2015 and Van Leeuwen et al. 2024), we distinguish two separate but partly overlapping mechanisms<\/strong> by which Cr(VI) can form in or on insulation material:<\/p>\n

1. Solid-state reaction at the interface with the metal<\/h3>\n

When chromium-bearing steels are in prolonged contact with calcium- or sodium-containing insulation materials<\/strong>, Cr can diffuse out of the steel surface. A Cr(III) oxide layer (chromium(III) oxide, Cr\u2082O\u2083) forms at the surface, which is then further oxidised to Cr(VI) under the influence of oxygen and metal oxides such as calcium oxide (CaO) or sodium oxide (Na\u2082O)<\/strong>.<\/p>\n

For example:<\/p>\n