Chromium (VI) compounds
Chromates
Calcium chromate
Sodium chromate
Chromium (VI) and its compounds (chromates) are carcinogenic, partly mutagenic, reprotoxic and completely environmentally harmful dangerous substances classified in the following hazardous substance classes:
Chromium (VI) as chromium trioxide (CrO3) (EC No. 606-053-1; CAS 18540-29-9)
H317 – may cause skin irritation
H350 – carcinogen 1B
H400 Very toxic to aquatic organisms
H410 – very toxic to aquatic organisms with long-term effects
Chromium (VI) as calcium chromate (CaCrO4) (EC No. 237-366-8; CAS 13765-19-0)
H302 – harmful if swallowed
H350 – carcinogen 1B
H400 Very toxic to aquatic organisms
H410 – very toxic to aquatic organisms with long-term effects
Source:https://echa.europa.eu/de/information-on-chemicals/cl-inventory-database/-/discli/details/52650
Chromium (VI) as sodium chromate (CrNa2O4) (EC No. 231-889-5; CAS 18540-29-9)
H330 – Danger to life if inhaled
H350 – carcinogen 1B
H340 – mutagenic 1B
H360 FD – repro 1B - May impair fertility. May harm the unborn child.
H400 Very toxic to aquatic organisms
H410 – very toxic to aquatic organisms with long-term effects
Chromium (VI) and its compounds therefore all belong to the category of so-called “KMR pollutants” (carcinogenic, mutagenic and/or reprotoxic), but above all they are uniformly classified as carcinogen 1B!
The chromate experts inform you
What are chromates?
Chromium (VI) compounds
Chromates are Salts the Chromic acid (H2CrO4). The chromateanion CrO42− has a yellow color and a tetrahedral structure.
(Source:https://www.chemie.de/lexikon/Chromate.html)
Hexavalent chromium compounds such as chromates are oxidations of chromium and are the result of a thermochemical reaction of several elements.
The chromates described on this website, such as calcium or sodium chromate, are formed thermochemically through a combination of chromium (III) oxide [Cr2O3], an alkali metal oxide (sodium oxide [NaO]) or alkaline earth metal oxide (calcium oxide [CaO]) at temperatures between approx. 250 °C and approx. 800°C and the presence of oxygen [O2].
The higher the chromium (III) content and the higher the (earth) alkali metal content and the higher the temperature, the higher the rate of so-called “high oxidation” of chromium (III) to chromium (VI).
CHROMATES AT WORK
Calcium chromate in textile insulation of combined heat and power plant engines
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Insulation materials used today contain alkali or alkaline earth metals, especially calcium or sodium.
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Internal combustion engines (operated with gas, diesel/petrol or hydrogen), turbines (operated with gas or steam, sometimes also with hydrogen) or other components (pipes, exhaust system components, etc.) of energy-generating systems are made of stainless steel with chromium alloys.
The operating temperature of energy-generating systems can be up to 750°C. Therefore, the majority of systems are “insulated”, i.e. insulated with at least one layer of “insulation” (containing alkali and/or alkaline earth metals), but often also with multiple layers (heat storage, heat protection, energy saving).
We refer to energy-generating systems as combined heat and power plants, combined heat and power plants (combined heat and power), among others in the biogas sector, but also local power plants, waste incineration plants and also nuclear power plants.
In Germany alone, for example, B. more than 10,000 biogas plants are operated!
If the insulating materials containing (earth) alkali metals come into contact with the hot parts containing chromium, calcium oxide or sodium oxide is released, particularly through vibration and thermal stress (abrasion, wear), and meets chromium oxides of the stainless steel alloys at high operating temperatures.
Over time, calcium or sodium chromate is formed, which settles as a fine yellow powder between the inner surface of the insulation material and the surface of the hot part, or swirls around the system area due to thermals.
For a long time, the yellow dust was mistakenly thought to be sulfur deposits. But we now know that these are chromium (VI) compounds such as calcium or sodium chromate!
Calcium chromate is also created by using calcium-containing assembly pastes or sealing materials on chrome-containing screws, nuts and flange connections!
