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Hub AI
Chromium hydride AI simulator
(@Chromium hydride_simulator)
Hub AI
Chromium hydride AI simulator
(@Chromium hydride_simulator)
Chromium hydride
Chromium hydrides are compounds of chromium and hydrogen, and possibly other elements. Intermetallic compounds with not-quite-stoichometric quantities of hydrogen exist, as well as highly reactive molecules. When present at low concentrations, hydrogen and certain other elements alloyed with chromium act as softening agents that enables the movement of dislocations that otherwise not occur in the crystal lattices of chromium atoms.
The hydrogen in typical chromium hydride alloys may contribute only a few hundred parts per million in weight at ambient temperatures. Varying the amount of hydrogen and other alloying elements, and their form in the chromium hydride either as solute elements, or as precipitated phases, expedites the movement of dislocations in chromium, and thus controls qualities such as the hardness, ductility, and tensile strength of the resulting chromium hydride.
Even in the narrow range of concentrations that make up chromium hydride, mixtures of hydrogen and chromium can form a number of different structures, with very different properties. Understanding such properties is essential to making quality chromium hydride. At room temperature, the most stable form of pure chromium is the body-centered cubic (BCC) structure α-chromium. It is a fairly hard metal that can dissolve only a small concentration of hydrogen.
It can occur as a dull brown or dark grey solid in two different crystalline forms: face-centered cubic with formula CrH~2 or a close packed hexagonal solid with formula CrH~1. Chromium hydride is important in chrome plating, being an intermediate in the formation of the chromium plate.
An apparent unusual allotrope of chromium in a hexagonal crystal form was investigated by Ollard and Bradley by X-ray crystallography; however they failed to notice that it contained hydrogen. The hexagonal close packed crystalline substance they discovered actually contains CrHx with x between 0.5 and 1. The lattice for the hexagonal form had unit cell dimensions a=0.271 nm and c=0.441 nm. The crystal form has been described as anti-NiAs structure and is known as the β-phase. Also known as ε-CrH, the space group is Fm3m with hydrogen only in octahedral sites.
A face-centered cubic (fcc) phase of chromium hydride can also be produced when chromium is electrodeposited. Cloyd A. Snavely used chromate in sugar syrup cooled to about 5 °C and with a current density of 1290 amperes per square meter. The unit cell dimension in the material was 0.386 nm. The material is brittle and easily decomposed by heat. The composition is CrHx, with x between 1 and 2. For current density above 1800 amps per square meter and at low temperatures, the hexagonal close-packed form was made, but if the current was lower or the temperature was higher, then regular body-centered cubic chromium metal was deposited. The condition for preferring the formation of face-centered cubic chromium hydride is a high pH. The fcc form of CrH has hydrogen atoms in octahedral sites in the P63/mmc spacegroup.
Face-centered cubic CrH had the composition CrH1.7. But in theory it would be CrH2 if the substance was pure and all the tetrahedral sites were occupied by hydrogen atoms. The solid substance CrH2 appears as a dull grey or brown colour. Its surface is easily scratched, but that is due to the brittleness of the hydride.
Face-centered cubic chromium hydride also forms temporarily when chromium metal is etched with hydrochloric acid.
Chromium hydride
Chromium hydrides are compounds of chromium and hydrogen, and possibly other elements. Intermetallic compounds with not-quite-stoichometric quantities of hydrogen exist, as well as highly reactive molecules. When present at low concentrations, hydrogen and certain other elements alloyed with chromium act as softening agents that enables the movement of dislocations that otherwise not occur in the crystal lattices of chromium atoms.
The hydrogen in typical chromium hydride alloys may contribute only a few hundred parts per million in weight at ambient temperatures. Varying the amount of hydrogen and other alloying elements, and their form in the chromium hydride either as solute elements, or as precipitated phases, expedites the movement of dislocations in chromium, and thus controls qualities such as the hardness, ductility, and tensile strength of the resulting chromium hydride.
Even in the narrow range of concentrations that make up chromium hydride, mixtures of hydrogen and chromium can form a number of different structures, with very different properties. Understanding such properties is essential to making quality chromium hydride. At room temperature, the most stable form of pure chromium is the body-centered cubic (BCC) structure α-chromium. It is a fairly hard metal that can dissolve only a small concentration of hydrogen.
It can occur as a dull brown or dark grey solid in two different crystalline forms: face-centered cubic with formula CrH~2 or a close packed hexagonal solid with formula CrH~1. Chromium hydride is important in chrome plating, being an intermediate in the formation of the chromium plate.
An apparent unusual allotrope of chromium in a hexagonal crystal form was investigated by Ollard and Bradley by X-ray crystallography; however they failed to notice that it contained hydrogen. The hexagonal close packed crystalline substance they discovered actually contains CrHx with x between 0.5 and 1. The lattice for the hexagonal form had unit cell dimensions a=0.271 nm and c=0.441 nm. The crystal form has been described as anti-NiAs structure and is known as the β-phase. Also known as ε-CrH, the space group is Fm3m with hydrogen only in octahedral sites.
A face-centered cubic (fcc) phase of chromium hydride can also be produced when chromium is electrodeposited. Cloyd A. Snavely used chromate in sugar syrup cooled to about 5 °C and with a current density of 1290 amperes per square meter. The unit cell dimension in the material was 0.386 nm. The material is brittle and easily decomposed by heat. The composition is CrHx, with x between 1 and 2. For current density above 1800 amps per square meter and at low temperatures, the hexagonal close-packed form was made, but if the current was lower or the temperature was higher, then regular body-centered cubic chromium metal was deposited. The condition for preferring the formation of face-centered cubic chromium hydride is a high pH. The fcc form of CrH has hydrogen atoms in octahedral sites in the P63/mmc spacegroup.
Face-centered cubic CrH had the composition CrH1.7. But in theory it would be CrH2 if the substance was pure and all the tetrahedral sites were occupied by hydrogen atoms. The solid substance CrH2 appears as a dull grey or brown colour. Its surface is easily scratched, but that is due to the brittleness of the hydride.
Face-centered cubic chromium hydride also forms temporarily when chromium metal is etched with hydrochloric acid.