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

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

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 that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

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

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 An extrinsic semiconductor is one that has been '' doped''; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it differen ...

. 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 metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is used here in a generic sense of ''re ...

at 1200–1300 °C.

Amphoterism

Although SnO₂ is insoluble in water, it is amphoteric, dissolving in base and acid.''Inorganic & Theoretical chemistry'', F. Sherwood Taylor, Heineman, 6th Edition (1942) "Stannic acid" refers to hydrated tin (IV) oxide, SnO₂, which is also called "stannic oxide." Tin oxides dissolve in acids. Halogen acids attack SnO₂ to give hexahalostannates, such as nI₆sup>2−. One report describes reacting a sample in refluxing HI for many hours. :SnO₂ + 6 HI → H₂SnI₆ + 2 H₂O Similarly, SnO₂ dissolves in sulfuric acid to give the sulfate: :SnO₂ + 2 H₂SO₄ → Sn(SO₄)₂ + 2 H₂O SnO₂ dissolves in strong bases to give "

stannate In chemistry the term stannate refers to compounds of tin (Sn). Stannic acid (Sn(OH)4), the formal precursor to stannates, does not exist and is actually a hydrate of SnO2. The term is also used in naming conventions as a suffix; for example the ...

s," 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 R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...

s and acid anhydrides.

Ceramic glazes

Tin(IV) oxide has long been used as an

opacifier An opacifier is a substance added to a material in order to make the ensuing system opaque. An example of a chemical opacifier is titanium dioxide (TiO2), which is used as an opacifier in paints, in paper, and in plastics. It has very high refract ...

and as a white colorant in

ceramic glaze Ceramic glaze is an impervious layer or coating of a vitreous substance which has been fused to a pottery body through firing. Glaze can serve to color, decorate or waterproof an item. Glazing renders earthenware vessels suitable for holding ...

s.’The Glazer’s Book’ – 2nd edition. ''A.B.Searle.The Technical Press Limited.'' London. 1935. This has 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 ...

, 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 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 by coating it with a c ...

, sanitaryware and wall tiles; see the articles

tin-glazing Tin-glazing is the process of giving tin-glazed pottery items a ceramic glaze that is white, glossy and opaque, which is normally applied to red or buff earthenware. Tin-glaze is plain lead glaze with a small amount of tin oxide added.Caiger-Smith, ...

and Tin-glazed pottery. 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. SnO₂ has been used as pigment in the manufacture of glasses, enamels and ceramic glazes. 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.

Dyes

This oxide of tin has been utilized as a

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

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.

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. Tin(IV) oxide for this use is sometimes called as "putty powder" or "jeweler's putty".

Glass coatings

SnO₂ 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 (subst ...

, vapour deposition techniques that employ SnCl₄ or organotin trihalides e.g. butyltin trichloride 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 is used in 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 d ...

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 something that can burn (i.e., ''combust'') in air. A combustible material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable mat ...

gas the electrical resistivity drops. Room temperature gas sensors are also being developed using reduced graphene oxide-SnO₂ composites(e.g. for ethanol detection). Doping with various compounds has been investigated (e.g. with CuO). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage

varistor A varistor is an electronic component with an electrical resistance that varies with the applied voltage. Also known as a voltage-dependent resistor (VDR), it has a nonlinear, non- ohmic current–voltage characteristic that is similar to that ...

s. Tin(IV) oxide can be doped with the oxides of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...