Zinc phosphate
Encyclopedia
Zinc phosphate is an inorganic
chemical compound
used as a corrosion
resistant coating on metal
surfaces either as part of an electroplating
process or applied as a primer
pigment
(see also red lead
). Zinc phosphate coats better on a crystalline structure than bare metal, so a seeding agent is often used as a pre-treatment. One common agent is sodium pyrophosphate
.
Natural forms of zinc phosphate include minerals hopeite
and parahopeite, Zn3(PO4)2·4H2O. A somewhat similar mineral is natural hydrous zinc phosphate called tarbuttite, Zn2(PO4)(OH). Both are known from oxidation zones of Zn ore beds and were formed through oxidation of sphalerite
by the presence of phosphate-rich solutions. The anhydrous form has not yet been found naturally.
Zinc phosphate is formed from zinc phosphate cement and used in dentistry
. Zinc phosphate dental cement
is one of the oldest and widely used cements, and is commonly used for luting
permanent metal restorations and as a base for dental restoration
s.
Zinc phosphate cement is used for cementation of inlay
s, crowns
, bridges
, and orthodontic appliances and occasionally as a temporary restoration
. It is prepared by mixing zinc oxide
and magnesium oxide
powders with a liquid consisting principally of phosphoric acid
, water, and buffers
. It is the standard cement to measure against. It has the longest track record of use in dentistry. It is still commonly used; however, resin-modified glass ionomer cement
s are more convenient and stronger when used in a dental setting.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
used as a corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
resistant coating on metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
surfaces either as part of an electroplating
Electroplating
Electroplating is a plating process in which metal ions in a solution are moved by an electric field to coat an electrode. The process uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal...
process or applied as a primer
Primer (paint)
A primer is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted.-When primers are used:...
pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
(see also red lead
Red lead
Lead tetroxide, also called minium, red lead or triplumbic tetroxide, is a bright red or orange crystalline or amorphous pigment. Chemically, red lead is lead tetroxide, Pb3O4, or 2PbO·PbO2....
). Zinc phosphate coats better on a crystalline structure than bare metal, so a seeding agent is often used as a pre-treatment. One common agent is sodium pyrophosphate
Sodium pyrophosphate
Tetrasodium pyrophosphate, also called sodium pyrophosphate, tetrasodium phosphate or TSPP, is a colorless transparent crystalline chemical compound with the formula Na4P2O7. It contains the pyrophosphate ion and sodium cation. Toxicity is approximately twice that of table salt when ingested...
.
Natural forms of zinc phosphate include minerals hopeite
Hopeite
Hopeite is a hydrated zinc phosphate with formula: Zn32·4H2O. It is a rare mineral used mainly as a collectors specimen.Hopeite crystallizes in the orthorhombic system with prismatic, vitreous white to yellow crystals...
and parahopeite, Zn3(PO4)2·4H2O. A somewhat similar mineral is natural hydrous zinc phosphate called tarbuttite, Zn2(PO4)(OH). Both are known from oxidation zones of Zn ore beds and were formed through oxidation of sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
by the presence of phosphate-rich solutions. The anhydrous form has not yet been found naturally.
Zinc phosphate is formed from zinc phosphate cement and used in dentistry
Dentistry
Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...
. Zinc phosphate dental cement
Dental cement
Dental cements are hard, brittle materials formed by mixing powder and liquid together. They are either resin cements or acid-base cements. In the latter the powder is a basic metal oxide or silicate and the liquid is acidic. An acid base reaction occurs with the formation of a metal salt which...
is one of the oldest and widely used cements, and is commonly used for luting
Luting agent
In dentistry, a luting agent is a viscous material placed between tooth structure and a prosthesis, that hardens through chemical reactions to firmly attach the prosthesis to the tooth structure.-Cements as luting agents:...
permanent metal restorations and as a base for dental restoration
Dental restoration
A dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the...
s.
Zinc phosphate cement is used for cementation of inlay
Inlay
Inlay is a decorative technique of inserting pieces of contrasting, often coloured materials into depressions in a base object to form patterns or pictures that normally are flush with the matrix. In a wood matrix, inlays commonly use wood veneers, but other materials like shells, mother-of-pearl,...
s, crowns
Crown (dentistry)
A crown is a type of dental restoration which completely caps or encircles a tooth or dental implant. Crowns are often needed when a large cavity threatens the ongoing health of a tooth. They are typically bonded to the tooth using a dental cement. Crowns can be made from many materials, which...
, bridges
Bridge (dentistry)
A bridge, also known as a fixed partial denture, is a dental restoration used to replace a missing tooth by joining permanently to adjacent teeth or dental implants....
, and orthodontic appliances and occasionally as a temporary restoration
Temporary restoration
Temporary restoration is a temporary filling of prepared tooth until permanent restoration is carried out. It is used to cover the prepared part of the tooth, in order to maintain the occlusal space and the contact points, and insulation of the pulpal tissues and maintenance of the periodontal...
. It is prepared by mixing zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...
and magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
powders with a liquid consisting principally of phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...
, water, and buffers
Buffer solution
A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are used as a...
. It is the standard cement to measure against. It has the longest track record of use in dentistry. It is still commonly used; however, resin-modified glass ionomer cement
Glass ionomer cement
A Glass Ionomer Cement is a dental restorative material used in dentistry for filling teeth and luting cements. These materials are based on the reaction of silicate glass powder and polyalkenoic acid...
s are more convenient and stronger when used in a dental setting.