Tungsten trioxide
Encyclopedia
Tungsten oxide, also known as tungsten trioxide or tungstic anhydride, WO3, is a chemical compound containing oxygen
and the transition metal tungsten
. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkali
s to produce WO3. Further reaction with carbon
or hydrogen
gas reduces tungsten trioxide to the pure metal.
Tungsten(VI) oxide occurs naturally in form of hydrate
s, which include minerals: tungstite
WO3·H2O, meymacite WO3·2H2O and hydrotungstite (of same composition as meymacite, however sometimes written as H2WO4). These minerals are rare to very rare secondary tungsten minerals.
was the first to recognize a new element in the naturally occurring mineral, wolframite
. Tungsten was originally known as wolfram, explaining the choice of "W" for its elemental symbol. Swedish chemist Carl Wilhelm Scheele
contributed to its discovery as well with his studies on the mineral scheelite
.
In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and sodium tungstate
. He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.
, is allowed to react with HCl
to produce tungstic acid
, which decomposes to WO3 and water at high temperatures.
Another common way to synthesize WO3 is by calcination
of ammonium paratungstate
(APT) under oxidizing conditions:
10[H2W12O42]•4H2O → 12 WO3 + 10 NH3 + 11 H2O
P21/n.
s for x-ray
screen phosphor
s, for fireproofing
fabrics and in gas sensors. Due to its rich yellow color, WO3 is also used as a pigment in ceramics and paints.
In recent years, tungsten trioxide has been employed in the production of electrochromic windows, or smart windows
. These windows are electrically switchable glass that change light transmission properties with an applied voltage. This allows the user to tint their windows, changing the amount of heat or light passing through.
2010- AIST
reports a quantum yield of 19 % in photocatalytic water splitting
with a caesium-enhanced tungsten oxide photocatalyst.
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and the transition metal tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
s to produce WO3. Further reaction with carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
or hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas reduces tungsten trioxide to the pure metal.
- 2 WO3 + 3 C + heat → 2 W + 3 CO2
- WO3 + 3 H2 + heat → W + 3 H2O
Tungsten(VI) oxide occurs naturally in form of hydrate
Hydrate
Hydrate is a term used in inorganic chemistry and organic chemistry to indicate that a substance contains water. The chemical state of the water varies widely between hydrates, some of which were so labeled before their chemical structure was understood....
s, which include minerals: tungstite
Tungstite
Tungstite is a hydrous tungsten oxide mineral with formula: WO3·H2O. It is a secondary mineral formed by the weathering of other tungsten containing minerals. It crystallizes in the orthorhombic system in translucent yellow to yellow green masses...
WO3·H2O, meymacite WO3·2H2O and hydrotungstite (of same composition as meymacite, however sometimes written as H2WO4). These minerals are rare to very rare secondary tungsten minerals.
History
Tungsten has a rich history dating back to its discovery during the 18th century. Peter WoulfePeter Woulfe
Peter Woulfe was an Irish chemist and mineralogist. He first had the idea that wolframite might contain a previously undiscovered element .In 1779, Woulfe reported the formation of a yellow dye when indigo was treated with nitric acid...
was the first to recognize a new element in the naturally occurring mineral, wolframite
Wolframite
Wolframite WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite and huebernite . Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite is found in quartz veins and pegmatites associated with granitic intrusives...
. Tungsten was originally known as wolfram, explaining the choice of "W" for its elemental symbol. Swedish chemist Carl Wilhelm Scheele
Carl Wilhelm Scheele
Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
contributed to its discovery as well with his studies on the mineral scheelite
Scheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...
.
In 1841, a chemist named Robert Oxland gave the first procedures for preparing tungsten trioxide and sodium tungstate
Sodium tungstate
Sodium tungstate, Na2WO4, a tungstate of sodium, is useful as a source of tungsten. It is prepared from tungsten ores used to manufacture tungsten by reducing it....
. He was granted patents for his work soon after, and is considered to be the founder of systematic tungsten chemistry.
Preparation
Tungsten trioxide can be prepared in several different ways. CaWO4, or scheeliteScheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...
, is allowed to react with HCl
HCL
HCL or HCl can stand for:* Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia* Hardware compatibility list...
to produce tungstic acid
Tungstic acid
Tungstic acid refers to hydrated forms of tungsten trioxide, WO3.The simplest form, the monohydrate, is WO3.H2O, the dihydrate WO3.2H2O is also known. The solid state structure of WO3.H2O consists of layers of octahedrally coordinated WO5 units where 4 vertices are shared. the dihydrate has the...
, which decomposes to WO3 and water at high temperatures.
- CaWO4 + 2 HCl → CaCl2 + H2WO4
- H2WO4 + heat → H2O + WO3
Another common way to synthesize WO3 is by calcination
Calcination
Calcination is a thermal treatment process applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials...
of ammonium paratungstate
Ammonium paratungstate
Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, with the chemical formula 10·5H2O.Ammonium paratungstate is produced separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3,...
(APT) under oxidizing conditions:
10[H2W12O42]•4H2O → 12 WO3 + 10 NH3 + 11 H2O
Structure
The crystal structure of tungsten trioxide is temperature dependent. It is tetragonal at temperatures above 740 °C, orthorhombic from 330 to 740 °C, monoclinic from 17 to 330 °C, and triclinic from -50 to 17 °C. The most common structure of WO3 is monoclinic with space groupSpace group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
P21/n.
Uses
Tungsten trioxide is used for many purposes in everyday life. It is frequently used in industry to manufacture tungstateTungstate
In chemistry a tungstate is a compound that contains an oxoanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is WO42−, "orthotungstate"...
s for x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
screen phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
s, for fireproofing
Fireproofing
Fireproofing, a passive fire protection measure, refers to the act of making materials or structures more resistant to fire, or to those materials themselves, or the act of applying such materials. Applying a certification listed fireproofing system to certain structures allows these to have a...
fabrics and in gas sensors. Due to its rich yellow color, WO3 is also used as a pigment in ceramics and paints.
In recent years, tungsten trioxide has been employed in the production of electrochromic windows, or smart windows
Smart windows
Smart glass, EGlass, or switchable glass, also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied.Certain types of smart glass can allow users...
. These windows are electrically switchable glass that change light transmission properties with an applied voltage. This allows the user to tint their windows, changing the amount of heat or light passing through.
2010- AIST
National Institute of Advanced Industrial Science and Technology
The , or AIST, is a Japanese research facility headquartered in Tokyo, and most of the workforce is located in Tsukuba Science City, Ibaraki, and in several cities throughout Japan. The institute is managed to integrate scientific and engineering knowledge to address socio-economic needs...
reports a quantum yield of 19 % in photocatalytic water splitting
Photocatalytic water splitting
Photocatalytic water splitting is the term for the production of hydrogen and oxygen from water by directly utilizing the energy from light. Hydrogen fuel production has gained increasing attention as oil and other nonrenewable fuels become increasingly depleted and expensive...
with a caesium-enhanced tungsten oxide photocatalyst.