Chrome orange
Chemical compound and inorganic pigment
From Wikipedia, the free encyclopedia
Chrome orange is a mixed oxide with the chemical formula Pb2CrO5. It has found use as a pigment.
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| Names | |
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Other names
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| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.038.476 |
| EC Number |
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PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties[1] | |
| CrO5Pb2 | |
| Molar mass | 546.4 g·mol−1 |
| Appearance | red solid |
| Density | 6.63 g/cm3 |
| Melting point | 920 °C (1,690 °F; 1,190 K) |
| insoluble | |
| Solubility | soluble in acids, alkalis |
| Structure[2] | |
| monoclinic | |
| c2/m | |
a = 14.018 Å, b = 5.683 Å, c = 7.143 Å α = 90°, β = 115.23°, γ = 90° | |
Lattice volume (V) |
514.8 Å3 |
Formula units (Z) |
4 units per cell |
| Thermochemistry[3] | |
Gibbs free energy (ΔfG⦵) |
-1161.3 kJ/mol |
| Hazards | |
| GHS labelling:[1] | |
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| Danger | |
| H302, H332, H360, H373, H410 | |
| P203, P260, P264, P270, P271, P273, P280, P301+P317, P304+P340, P317, P318, P319, P330, P391, P405, P501 | |
Threshold limit value (TLV) |
0.0002 mg/m3, 0.0005 mg/m3 (STEL) |
| NIOSH (US health exposure limits):[1] | |
IDLH (Immediate danger) |
100.0 mg/m3 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Properties
Visible light activity up to 550 nanometers has been recorded.[4]
Synthesis
Pb2CrO5 can be made by treating a lead(II) salt with an alkaline solution of a chromate or by treating chrome yellow (PbCrO4) with strongly basic solution.[5]
It can also be synthesized using a gas-liquid precipitation process.[6] Changing the pH controls whether PbCrO4 or Pb2CrO5 is created.[6]
Nanomaterial
Orthorhombic nanocrystals can be selectively synthesized by a room temperature solution reaction.[7]
Using a microwave-assisted ionic liquid (MAIL) method, bundle and rod-like nanocrystals of Pb2CrO5 are formed.[8] In basic solution, single-crystalline Pb2CrO5 could be formed by heating lead acetate and potassium dichromate with microwave radiation for only 10 minutes at 90 °C.[8] The MAIL process is simple, fast, and does not employ surfactants.[8] The presence of hydroxide changes the phase that is formed. Using NaOH, monoclinic Pb2CrO5 is formed.[8] The bundle and rod-shaped structures are sensitive to electron beam irradiation, which will turn them into many small particles.[8]
Pigment
In a catalog published c. 1835, Winsor and Newton paint company identify ten synthetic pathways for producing chrome orange, also called deep yellow.[9] Chrome orange is made of PbCrO4 mixed with basic lead chromate (Pb2CrO5).[9] It has been described as a "yellowish red or sometimes a beautiful deep red" in alkaline conditions.[9] A deep yellow can be created using PbCrO4 and lead sulfate.[9] There are ten synthetic methods for preparing deep chrome yellow (that made with Pb2CrO5), which require a chromate source, a basic lead source, additives, and a sulfate source.[9] Controlling the pH was Winsor and Newton's method for creating pigments from the pale yellow to the deep chrome orange.[9] The resulting product has a high stability to light, which is always coveted by artists and collectors.[9]
Use as a pigment
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Chrome orange can range in color from light to deep orange and is no longer in production as a pigment.[12] It has also been known as Derby red, Persian red, and Victoria red.[12] It was first recorded as a pigment in 1809 and was perfect for some impressionist painters in the nineteenth century. The yellow-orange pigment of the boat in Renoir's 1879 painting, The Seine at Asnières (The Skiff) at the National Gallery, London.[12] Chrome orange was used extensively in Frederic Leighton's Flaming June (1895; Museo de Arte de Ponce).[10]
History
The natural mineral crocoite was discovered in 1797 by Louis Vauquelin and chrome orange was synthesized as a pigment for the first time in 1809.[12] Pb2CrO5 is found in mineral form as phoenicochroite, which is a monoclinic, red, translucent mineral found in various places across the world, including Russia, the US, and Chile.[13]