Tin(IV) oxide, also known as stannic oxide, is the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

SnO₂. The mineral form of SnO₂ is called

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...

, and this is the main ore of tin. With many other names, this

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

of tin is an important material in tin chemistry. It is a colourless,

diamagnetic Diamagnetism is the property of materials that are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagn ...

, amphoteric solid.

Structure

Tin(IV) oxide crystallises with the

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest refractive indices at vis ...

structure. As such the tin atoms are six coordinate and the oxygen atoms three coordinate. SnO₂ is usually regarded as an oxygen-deficient

n-type semiconductor N-type, N type or Type N may refer to: * N-type semiconductor is a key material in the manufacture of transistors and integrated circuits * An N-type connector is a threaded RF connector used to join coaxial cables * The MG N-type Magnette was p ...

. Hydrous forms of SnO₂ have been described as stannic acid. Such materials appear to be hydrated particles of SnO₂ where the composition reflects the particle size.

Preparation

Tin(IV) oxide occurs naturally. Synthetic tin(IV) oxide is produced by burning tin metal in air. Annual production is in the range of 10 kilotons. SnO₂ is reduced industrially to the metal with carbon in a

reverberatory furnace A reverberatory furnace is a metallurgy, metallurgical or process Metallurgical furnace, furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is use ...

at 1200–1300 °C.

Reactions

The reaction from tin(IV) oxide with hot

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

is practiced on a large scale as this carbothermal reduction is used to obtain tin metal from its ores: : Some other reactions relevant to purifying tin from its ores are: : : SnO₂ converts to the monoxide at 1500 °C: : SnO₂ is insoluble in water. It dissolves in sulfuric acid and in molten sodium hydroxide. It is not amphoteric. Like rutile, it is not attacked by solutions of acid or base. Dissolution of SnO₂ in sulfuric acid gives the sulfate: :SnO₂ + 2 H₂SO₄ → Sn(SO₄)₂ + 2 H₂O The latter compound can add additional

hydrogen sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

ligands to give hexahydrogensulfatostannic acid. SnO₂ dissolves in molten alkali to give " stannates," with the nominal formula Na₂SnO₃. Dissolving the solidified SnO₂/NaOH melt in water gives Na₂ n(OH)₆ "preparing salt," which is used in the dye industry.

Uses

In conjunction with vanadium oxide, it is used as a catalyst for the oxidation of aromatic compounds in the synthesis of

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

s and acid anhydrides.

Ceramic glazes

SnO₂ is used as pigment in the manufacture of glasses, enamels and

ceramic glaze Ceramic glaze, or simply glaze, is a glassy coating on ceramics. It is used for decoration, to ensure the item is impermeable to liquids and to minimize the adherence of pollutants. Glazing renders earthenware impermeable to water, sealing th ...

s. Thousands of tons of SnO₂ are produced annually for this application. Pure SnO₂ gives a milky white colour; other colours are achieved when mixed with other metallic oxides e.g. V₂O₅ yellow; Cr₂O₃ pink; and Sb₂O₅ grey blue. This use probably led to the discovery of the pigment

lead-tin-yellow Lead-tin yellow is a yellow pigment, of historical importance in oil painting, sometimes called the "Yellow of the Old Masters" because of the frequency with which it was used by those famous painters. Nomenclature The name lead-tin yellow is ...

, which was produced using tin(IV) oxide as a compound.Hermann Kühn, 1967, "Blei-Zinn-Gelb und seine Verwendung in der Malerei", ''Farbe und Lack'' 73: 938-949 The use of tin(IV) oxide has been particularly common in glazes for

earthenware Earthenware is glazed or unglazed Vitrification#Ceramics, nonvitreous pottery that has normally been fired below . Basic earthenware, often called terracotta, absorbs liquids such as water. However, earthenware can be made impervious to liquids ...

, sanitaryware and wall tiles; see the articles tin-glazing and

Tin-glazed pottery Tin-glazed pottery is earthenware covered in lead glaze with added tin oxide which is white, shiny and opaque (see tin-glazing for the chemistry); usually this provides a background for brightly painted decoration. It has been important in I ...

. Tin oxide remains in suspension in vitreous matrix of the fired glazes, and, with its high refractive index being sufficiently different from the matrix, light is scattered, and hence increases the opacity of the glaze. The degree of dissolution increases with the firing temperature, and hence the extent of opacity diminishes. Although dependent on the other constituents the solubility of tin oxide in glaze melts is generally low. Its solubility is increased by Na₂O, K₂O and B₂O₃, and reduced by CaO, BaO, ZnO, Al₂O₃, and to a limited extent PbO.

Glass coatings

SnO₂ coatings are valued as transparent conducting oxides (TCOs). Like other TCOs, SnO₂ has significant

electrical conductivity Electrical resistivity (also called volume resistivity or specific electrical resistance) is a fundamental specific property of a material that measures its electrical resistance or how strongly it resists electric current. A low resistivity in ...

but is transparent, an unusual combination of properties. Windows coated with SnO₂ also reflect

infrared radiation Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

, which is relevant to temperature control for smart windows. Coatings can be applied using

chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (electro ...

, vapour deposition techniques that employ SnCl₄ or organotin trihalides e.g.

butyltin trichloride Monobutyltin trichloride, also known as MBTC, is an organotin compound. It is a colorless oil that is soluble in organic solvents. Relative to other organotin compounds, MBTC is obscure and not widely used. Applications Glass coating Monobutylt ...

as the volatile agent. This technique is used to coat glass bottles with a thin (<0.1 μm) layer of SnO₂, which helps to adhere a subsequent, protective polymer coating such as polyethylene to the glass. Thicker layers doped with Sb or F ions are electrically conducting and used in electroluminescent devices and photovoltaics.

Gas sensing

SnO₂ has been evaluated as sensors of combustible gases including

carbon monoxide detector A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas to prevent carbon monoxide poisoning. In the late 1990s, Underwriters Laboratories changed the definition of a single station CO dete ...

s. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a

combustible A combustible material is a material that can burn (i.e., sustain a flame) in air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort a ...

gas the

electrical resistivity Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

drops.

Historical uses

This oxide of tin has been utilized as a mordant in the dyeing process since ancient Egypt. A German by the name of Kuster first introduced its use to London in 1533 and by means of it alone, the color scarlet was produced there. Thomas Mortimer, ''A General Dictionary of Commerce, Trade, and Manufactures'' (1810)
Dying or Dyeing
Tin(IV) oxide for this use is sometimes called as "putty powder"''Inorganic & Theoretical chemistry'', F. Sherwood Taylor, Heineman, 6th Edition (1942) or "jeweler's putty".

Polishing

Tin(IV) oxide can be used as a polishing powder, sometimes in mixtures also with lead oxide, for polishing glass, jewelry, marble and silver.