Tantalum pentoxide
Encyclopedia
Tantalum pentoxide is Ta2O5, also known as tantalum
(V) oxide. Both orthorhombic and hexagonal
phases are known. Ta2O5 is a high refractive index
, low absorption material useful for coatings in the near-UV
to IR
spectra regions; it decomposes only at temperatures >1470 °C.
was obtained from minerals taken from pegmatite
(an igneous rock associated with tantalite
or columbite
) at Ytterby
, Sweden, and Kimoto, Finland. The microlite-pyrochlore mineral series is also a source of tantalum oxide. Microlite
contains approximately 70% of tantalum oxide, and pyrochlore
contains approximately 10%.
into the slurry and adding the stoichiometric quantity of potassium fluoride
to yield a salt. The salts can be separated by a liquid-liquid extraction process, using various ketone
s as the liquids.
(NbTa)2O6 + 6NaOH → Ta2O5·7H2O + Nb2O5·7H2O
Or,
Once K2TaF7 has been isolated, Ta can be extracted by the electrolysis of molten K2TaF7. This pure form of tantalum is then exposed to oxygen at temperatures above 1000 degrees Celsius, to form Ta2O5.
It can also be synthesized by hydrolysis
of its alkoxide
:
s in automotive electronics
, cell phones, and pagers, electronic circuitry; thin-film components; and high-speed tools. In the 1990s, there was a very strong interest to do research on tantalum oxide as a high-k dielectric
for DRAM
capacitor applications. For example, Elpida Memory
(a Japanese company making DRAM) has put in a strong effort to improve ultrathin tantalum oxide films for DRAM applications. Subsequently in the 2000s, this strong interest has dropped very significantly. It is being used in on-chip MIM capacitors for RF CMOS integrated circuits. Due to its high index of refraction, Ta2O5 has been utilized in the fabrication of the glass
of many photographic lens
es.
in a sealed glass tube in a high pressure steel reaction vessel.
Ta2O5 can be reduced several different ways, including the use of metallic reductants such as calcium and aluminum.
These reactions can be further modified to yield pure tantalum via stoichiometry, thermal control and electrolysis.
Materials to avoid when dealing with tantalum pentoxide are strong oxidizing agent
s, chlorine trifluoride
, bromine monofluoride, lithium
and acid
s.
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...
(V) oxide. Both orthorhombic and hexagonal
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
phases are known. Ta2O5 is a high refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
, low absorption material useful for coatings in the near-UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
to IR
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectra regions; it decomposes only at temperatures >1470 °C.
History
The metal oxide discovered by Anders Gustaf EkebergAnders Gustaf Ekeberg
Anders Gustaf Ekeberg was a Swedish chemist who discovered tantalum in 1802. He was notably deaf...
was obtained from minerals taken from pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
(an igneous rock associated with tantalite
Tantalite
Tantalite, [2O6], is a mineral group that is close to columbite. The two are often grouped together as a semi-singular mineral called coltan or "columbite-tantalite" in many mineral guides. However, tantalite has a much greater specific gravity than columbite...
or columbite
Columbite
Columbite, also called niobite, niobite-tantalite and columbate [2O6], is a black mineral group that is an ore of niobium and tantalum. It has a submetallic luster and a high density and is a niobate of iron and manganese, containing tantalate of iron. This mineral group was first found in Haddam,...
) at Ytterby
Ytterby
Ytterby is a village on the Swedish island of Resarö, in Vaxholm Municipality in the Stockholm archipelago.The name of the village means "outer village", implying that its location is its most noteworthy feature....
, Sweden, and Kimoto, Finland. The microlite-pyrochlore mineral series is also a source of tantalum oxide. Microlite
Microlite
Microlite is a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine 2Ta2O6. Microlite is a mineral in the pyrochlore group that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a...
contains approximately 70% of tantalum oxide, and pyrochlore
Pyrochlore
Pyrochlore 2Nb2O6 is a solid solution between the niobium end member , and the tantalum end member .-Occurrence:...
contains approximately 10%.
Synthesis
There are several methods available for the synthesis of tantalum oxide. One method involves isolating tantalum pentoxide by crushing a concentrate of the mineral columbite-tantalite and fusing the powdered mineral with sodium hydroxide to give a slurry of mixed insoluble niobic and tantalic acids. The mixed acids are dissolved by passing anhydrous hydrofluoric acidHydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
into the slurry and adding the stoichiometric quantity of potassium fluoride
Potassium fluoride
Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali metal halide and occurs naturally as the rare mineral carobbiite...
to yield a salt. The salts can be separated by a liquid-liquid extraction process, using various ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s as the liquids.
(NbTa)2O6 + 6NaOH → Ta2O5·7H2O + Nb2O5·7H2O
- ½Ta2O5·7H2O + ½Nb2O5·7H2O + 16KF → K2TaF7 + K2NbF7 + 2HF + 12KOH
Or,
- ½Ta2O5 + ½Nb2O5 + 4KF + 10HF → K2TaF7 + K2NbF7 + 5H2O
Once K2TaF7 has been isolated, Ta can be extracted by the electrolysis of molten K2TaF7. This pure form of tantalum is then exposed to oxygen at temperatures above 1000 degrees Celsius, to form Ta2O5.
It can also be synthesized by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of its alkoxide
Alkoxide
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...
:
-
- 2 Ta(OCH2CH3)5 + 5 H2O → Ta2O5 + 10 HOCH2CH3
Use
Ta2O5 is used to make capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s in automotive electronics
Automotive electronics
Automotive electronics are the electronics used in the automobiles.It includes body electronics, in car entertainment, carputers, chassis electronics and telematics.Automotive electronics...
, cell phones, and pagers, electronic circuitry; thin-film components; and high-speed tools. In the 1990s, there was a very strong interest to do research on tantalum oxide as a high-k dielectric
High-k Dielectric
The term high-κ dielectric refers to a material with a high dielectric constant κ used in semiconductor manufacturing processes which replaces the silicon dioxide gate dielectric...
for DRAM
Dram
Dram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
capacitor applications. For example, Elpida Memory
Elpida Memory
is a corporation established in 1999 that develops, designs, manufactures and sells dynamic random-access memory products. It is also a semiconductor foundry. With headquarters in Yaesu, Chūō, Tokyo, Japan, it was formed under the name NEC Hitachi Memory in 1999 by the merger of the Hitachi, Ltd....
(a Japanese company making DRAM) has put in a strong effort to improve ultrathin tantalum oxide films for DRAM applications. Subsequently in the 2000s, this strong interest has dropped very significantly. It is being used in on-chip MIM capacitors for RF CMOS integrated circuits. Due to its high index of refraction, Ta2O5 has been utilized in the fabrication of the glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
of many photographic lens
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
es.
Reactions
Ta2O5 can be chlorinated to become TaCl5 by heating a mixture of tantalum pentoxide and carbon tetrachlorideCarbon tetrachloride
Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
in a sealed glass tube in a high pressure steel reaction vessel.
- Ta2O5 + 5CCl4 → 2TaCl5 + 5COCl2
Ta2O5 can be reduced several different ways, including the use of metallic reductants such as calcium and aluminum.
- Ta2O5 + 2Al → Al2O3 + TaO2 + Ta
- Ta2O5 + Ca → CaO + TaO4 + Ta
These reactions can be further modified to yield pure tantalum via stoichiometry, thermal control and electrolysis.
Materials to avoid when dealing with tantalum pentoxide are strong oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
s, chlorine trifluoride
Chlorine trifluoride
Chlorine trifluoride is an interhalogen compound with the formula ClF3. This colourless, poisonous, corrosive and very reactive gas condenses to a pale-greenish yellow liquid, the form in which it is most often sold...
, bromine monofluoride, lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
and acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s.