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 chemist ...
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 betwee ...
SnO
2. The mineral form of SnO
2 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 t ...
, 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 structure. As such the tin atoms are six coordinate and the oxygen atoms three coordinate.
SnO
2 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 different ...
.
Hydrous forms of SnO
2 have been described as stannic acid. Such materials appear to be hydrated particles of SnO
2 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.
SnO
2 is reduced industrially to the metal with carbon in a
reverberatory furnace at 1200–1300 °C.
Amphoterism
Although SnO
2 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, SnO
2, which is also called "stannic oxide."
Tin oxides dissolve in acids. Halogen acids attack SnO
2 to give hexahalostannates, such as
6">nI6sup>2−. One report describes reacting a sample in refluxing
HI for many hours.
:SnO
2 + 6 HI → H
2SnI
6 + 2 H
2O
Similarly, SnO
2 dissolves in sulfuric acid to give the sulfate:
:SnO
2 + 2 H
2SO
4 → Sn(SO
4)
2 + 2 H
2O
SnO
2 dissolves in strong bases to give "
stannates," with the nominal formula
Na2SnO3.
Dissolving the solidified SnO
2/NaOH melt in water gives Na
2 6">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. Carboxylic ...
s and acid anhydrides.
Ceramic glazes
Tin(IV) oxide has long been used as an
opacifier 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, 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 ce ...
, sanitaryware and wall tiles; see the articles
tin-glazing 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
Opacity or opaque may refer to:
* Impediments to (especially, visible) light:
** Opacities, absorption coefficients
** Opacity (optics), property or degree of blocking the transmission of light
* Metaphors derived from literal optics:
** In lingu ...
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 Na
2O, K
2O and B
2O
3, and reduced by CaO, BaO, ZnO, Al
2O
3, and to a limited extent PbO.
SnO
2 has been used as pigment in the manufacture of glasses, enamels and ceramic glazes. Pure SnO
2 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 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 (substra ...
, 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 is used in sensors of combustible gases including carbon monoxide detectors. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible 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
Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite. It is ...
). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage varistors. Tin(IV) oxide can be doped with the oxides of iron or manganese.
References
Further reading
* Technical discussion of how SnO2:F is used in low-emissivity (low-E) windows. The report includes reflectance and transmittance spectra.
* Information on chemical safety and exposure limits
{{DEFAULTSORT:Tin (IV) oxide
Oxides
Tin(IV) compounds
Semiconductor materials