Tin dioxide
Encyclopedia
Tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

 dioxide
is the inorganic compound
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,...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 SnO2. The mineral form of SnO2 is called cassiterite
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...

, and this is the main ore of tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

. With many other names (see infobox), this oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

 of tin is the most important raw material in tin chemistry. This colourless, diamagnetic solid is amphoteric.

Structure

It crystallises with the rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...

 structure, wherein 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 semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....

. Hydrous forms of SnO2 have been described in the past as stannic acids, although such materials appear to be hydrated particles of SnO2 where the composition reflects the particle size.

Preparation

Tin dioxide occurs naturally but is purified by reduction to the metal followed by burning tin in air. Annual production is in the range of 10 kilotons. SnO2 is reduced industrially to the metal with carbon in a reverbatory furnace at 1200-1300 °C.

Amphoterism

Although SnO2 is insoluble in water, it is an amphoteric oxide, although cassiterite ore has been described as difficult to dissolve in acids and alkalis. "Stannic acid" refers to hydrated tin dioxide, SnO2, which is also called "stannic hydroxide."

Tin oxides dissolve in acids. Halogen acids attack SnO2 to give hexahalostannates, such as [SnI6]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 base to give "stannates," with the nominal formula Na2SnO3. Dissolving the solidified SnO2/NaOH melt in water gives Na2[Sn(OH)6]2, "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
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s and acid anhydrides.

Tin dioxide has long been used as an opacifier
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 tin dioxide , which is used to opacify ceramic glazes and milk glass; bone ash is also used....

 and as a white colorant in ceramic glaze
Ceramic glaze
Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...

s. Its use has been particular common in glazes for earthenware
Earthenware
Earthenware is a common ceramic material, which is used extensively for pottery tableware and decorative objects.-Types of earthenware:Although body formulations vary between countries and even between individual makers, a generic composition is 25% ball clay, 28% kaolin, 32% quartz, and 15%...

, sanitaryware and wall tiles; see the articles tin-glazing
Tin-glazing
Tin-glazing is the process of giving ceramic items a tin-based glaze which is white, glossy and opaque, normally applied to red or buff earthenware. The opacity and whiteness of tin glaze make it valued by its ability to decorate with colour....

 and Tin-glazed pottery
Tin-glazed pottery
Tin-glazed pottery is a majolica pottery covered in glaze containing tin oxide which is white, shiny and opaque. The pottery body is usually made of red or buff colored earthenware and the white glaze was often used to imitate Chinese porcelain...

. 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 (optics)
Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

 of the glaze. The degree of dissolution increases with the firing temperature, and hence the extent of opacity diminishes. Although dependant on the other constituents the solubility of tin oxide in glaze melts is generally low. Its solubility is increased by Na2, K2 and B2O3, and reduced by CaO, BaO, ZnO, Al2O3, and to a limited extent PbO.

SnO2 wires are commonly used as the detecting element in carbon monoxide detector
Carbon monoxide detector
A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide gas in order to prevent carbon monoxide poisoning. CO is a colorless and odorless compound produced by incomplete combustion. It is often referred to as the "silent killer" because it is...

s.

SnO2 coatings can be applied using chemical vapor deposition
Chemical vapor deposition
Chemical vapor deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films. In a typical CVD process, the wafer is exposed to one or more volatile precursors, which react and/or...

, vapour deposition techniques that employ SnCl4
Tin(IV) chloride
Tin chloride, also known as tin tetrachloride or stannic chloride is a chemical compound with the formula SnCl4.At room temperature it is a colourless liquid, which fumes on contact with air, giving a stinging odor...

 or organotin trihalides e.g. butyltin trichloride
Butyltin trichloride
Butyltin trichloride is an organotin compound....

 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.
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
Vanadium(V) oxide
Vanadium oxide is the chemical compound with the formula V2O5. Commonly known as vanadium pentoxide, this brown/yellow solid is the most stable and common compound of vanadium. Upon heating it reversibly loses oxygen...

 yellow; Cr2O3
Chromium(III) oxide
Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.-Structure and properties:...

 pink; and Sb2O5
Antimony pentoxide
Antimony pentoxide is a chemical compound of antimony and oxygen. It always occurs in hydrated form, Sb2O5·nH2O. It contains antimony in the +5 oxidation state.-Structure:...

 grey blue.
SnO2 has been used as a polishing powder and is sometimes known as "putty powder",
SnO2 is used in sensors of combustible gases
Gas detector
A gas detector is a device which detects the presence of various gases within an area, usually as part of a safety system. This type of equipment is used to detect a gas leak and interface with a control system so a process can be automatically shut down...

. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible
Combustibility
Combustibility is a measure of how easily a substance will set on fire, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored. Special precautions are usually required for substances that are easily combustible...

 gas the electrical resistivity drops.
Doping with various compounds has been investigated (e.g. with CuO
Copper(II) oxide
Copper oxide or cupric oxide is the higher oxide of copper. As a mineral, it is known as tenorite.-Chemistry:It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen...

 ). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage varistor
Varistor
A varistor is an electronic component with a "diode-like" nonlinear current–voltage characteristic. The name is a portmanteau of variable resistor...

s.
Tin dioxide can be doped into the oxides of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 or manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK