Chromium (VI) compounds
Chromates
Calcium chromate
Sodium chromate
Chromium (VI) and its compounds (chromates) are carcinogenic hazardous substances, some of them also mutagenic and toxic to reproduction, and all of them harmful to the environment, classified in the following hazard classes:
Chromium (VI) as chromium trioxide (CrO3) (EC No. 606-053-1; CAS 18540-29-9)
H317 - may cause skin irritation
H350 - carcinogenic 1B
H400 - very toxic to aquatic life
H410 - very toxic to aquatic life with long-lasting effects
Chromium (VI) as calcium chromate (CaCrO4) (EC No. 237-366-8; CAS 13765-19-0)
H302 - harmful if swallowed
H350 - carcinogenic 1B
H400 - very toxic to aquatic life
H410 - very toxic to aquatic life with long-lasting 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 - fatal if inhaled
H350 - carcinogenic 1B
H340 - mutagenic 1B
H360 FD - repro 1B - May damage fertility. May damage the unborn child.
H400 - very toxic to aquatic life
H410 - very toxic to aquatic life with long-lasting effects
Chromium (VI) and its compounds therefore all belong to the category of so-called "CMR substances" (carcinogenic, mutagenic and/or toxic to reproduction), but above all they are uniformly classified as carcinogenic 1B!
The Chromate Experts inform
What are chromates?
Chromium (VI) compounds
Chromates are salts of chromic acid (H2CrO4). The chromate anion CrO42− has a yellow color and a tetrahedral structure.
(Source: https://www.chemie.de/lexikon/Chromate.html)
Hexavalent chromium compounds such as chromates are oxidation products 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 an alkaline earth metal oxide (calcium oxide [CaO]) at temperatures between approx. 250°C and approx. 800°C and in the presence of oxygen [O2].
The higher the chromium(III) content, the higher the alkali or alkaline earth metal content and the higher the temperature, the higher the rate of the so-called “high oxidation” of chromium(III) to chromium(VI).
CHROMATES AT THE WORKPLACE
Calcium chromate in textile insulation of CHP plant engines
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Insulation materials used today contain alkali or alkaline earth metals, in particular calcium or sodium.
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Internal combustion engines (running on gas, diesel/gasoline or hydrogen), turbines (running on gas or steam, in some cases also on hydrogen) and other parts (pipes, exhaust system components, etc.) of power-generating plants are made of stainless steels with chromium alloys.
The operating temperature of power-generating plants can reach up to 750°C. For this reason, most of these plants are "insulated", i.e. covered with at least one layer of "insulation" (containing alkali and/or alkaline earth metals), but often with multi-layer insulation (heat retention, heat protection, energy saving).
By power-generating plants we mean CHP plants and cogeneration plants (combined heat and power), among others in the biogas sector, but also local power stations, waste incineration plants and even nuclear power plants.
In Germany alone, for example, more than 10,000 biogas plants are in operation!
When the insulation materials containing alkali or alkaline earth metals come into contact with the chromium-containing hot parts, calcium oxide or sodium oxide is released, in particular through vibration and thermal stress (abrasion, wear), and meets the chromium oxides of the stainless steel alloys at high operating temperatures.
Over time, calcium or sodium chromate forms, which settles as a fine yellow powder between the inner surface of the insulation and the surface of the hot part, or is swirled around the plant area by thermal currents.
For a long time, the yellow dusts were mistakenly thought to be sulfur deposits. But we now know that they are chromium (VI) compounds such as calcium or sodium chromate!
Calcium chromate is also formed when calcium-containing assembly pastes or sealing materials are used on chromium-containing bolts, nuts and flange connections!
