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Ammonium dichromate
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Ammonium dichromate
Ammonium dichromate is an inorganic compound with the formula (NH4)2Cr2O7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions.
Ammonium dichromate is used in demonstrations of tabletop "volcanoes". However, this demonstration has become unpopular due to concerns about the compound's carcinogenic nature. It has been used in pyrotechnics and in the early days of photography. It is also used in holography.
At standard temperature and pressure, the compound exists as orange, acidic crystals soluble in water and ethanol. It is formed by the action of chromic acid on ammonium hydroxide with subsequent crystallisation.[page needed]
The (NH4)2Cr2O7 crystal (C2/c, z = 4) contains a single type of ammonium ion, at sites of symmetry C1(2,3). Each NH+4 centre is surrounded irregularly by eight oxygen atoms at N−O distances ranging from ca. 2.83 to 3.17 Å, typical of hydrogen bonds.
It has been used in pyrotechnics as part of a conversion coating method for magnesium powder. It may also be used when a dichromate compatible with ammonium perchlorate (NH4ClO4) is needed; potassium dichromate (K2Cr2O7) is commonly used, but reacts with ammonium perchlorate over time to form potassium perchlorate and ammonium dichromate. This mixture occupies 5% more volume than the original K2Cr2O7 + NH4ClO4 mixture and leads to eventual cracking of stars and consolidated compositions.
It was used in a composition in the early 20th century in a combination firework called a serpent's nest to produce the green grass (or nest) from which a separately made pharaoh's serpent or black snake composition emerged.
In holography, it has been used since the 1960s to sensitize dichromated gelatins or other materials on which to expose a hologram. This method has the advantage of being low cost, using relatively common materials, and only requiring isopropyl alcohol for development, but the gelatins created with these methods are sensitive to humidty. Potassium dichromate is also used for this purpose.
It was used in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst.[page needed] It is also used as a mordant for dyeing pigments, in manufacturing of alizarin, chrome alum, leather tanning and oil purification.[page needed]
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Ammonium dichromate
Ammonium dichromate is an inorganic compound with the formula (NH4)2Cr2O7. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions.
Ammonium dichromate is used in demonstrations of tabletop "volcanoes". However, this demonstration has become unpopular due to concerns about the compound's carcinogenic nature. It has been used in pyrotechnics and in the early days of photography. It is also used in holography.
At standard temperature and pressure, the compound exists as orange, acidic crystals soluble in water and ethanol. It is formed by the action of chromic acid on ammonium hydroxide with subsequent crystallisation.[page needed]
The (NH4)2Cr2O7 crystal (C2/c, z = 4) contains a single type of ammonium ion, at sites of symmetry C1(2,3). Each NH+4 centre is surrounded irregularly by eight oxygen atoms at N−O distances ranging from ca. 2.83 to 3.17 Å, typical of hydrogen bonds.
It has been used in pyrotechnics as part of a conversion coating method for magnesium powder. It may also be used when a dichromate compatible with ammonium perchlorate (NH4ClO4) is needed; potassium dichromate (K2Cr2O7) is commonly used, but reacts with ammonium perchlorate over time to form potassium perchlorate and ammonium dichromate. This mixture occupies 5% more volume than the original K2Cr2O7 + NH4ClO4 mixture and leads to eventual cracking of stars and consolidated compositions.
It was used in a composition in the early 20th century in a combination firework called a serpent's nest to produce the green grass (or nest) from which a separately made pharaoh's serpent or black snake composition emerged.
In holography, it has been used since the 1960s to sensitize dichromated gelatins or other materials on which to expose a hologram. This method has the advantage of being low cost, using relatively common materials, and only requiring isopropyl alcohol for development, but the gelatins created with these methods are sensitive to humidty. Potassium dichromate is also used for this purpose.
It was used in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst.[page needed] It is also used as a mordant for dyeing pigments, in manufacturing of alizarin, chrome alum, leather tanning and oil purification.[page needed]
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