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Titanium dioxide
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Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. It is noteworthy for its wide range of applications, from paint to sunscreen to food colouring when it is given the E number E171.
nium dioxide occurs in nature as the well-known naturally occurring minerals rutile, anatase and brookite, additionally two high pressure forms, the monoclinic baddeleyite form and the orthorhombic a-PbO2 form have been found at the Ries crater in Bavaria.
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Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called titanium white, Pigment White 6, or CI 77891. It is noteworthy for its wide range of applications, from paint to sunscreen to food colouring when it is given the E number E171.
Occurrence
Titanium dioxide occurs in nature as the well-known naturally occurring minerals rutile, anatase and brookite, additionally two high pressure forms, the monoclinic baddeleyite form and the orthorhombic a-PbO2 form have been found at the Ries crater in Bavaria. The most common form is rutile, which is also the most stable form. Anatase and brookite both convert to rutile upon heating. Rutile, anatase and brookite all contain six coordinate titanium. Additionally there are three metastable forms produced synthetically and five high pressure forms:
The naturally occurring oxides can be mined and serve as a source for commercial titanium. The metal can also be mined from other minerals such as ilmenite or leucoxene ores, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present in them.
Spectral lines from titanium oxide are prominent in class M stars, which are cool enough to allow molecules of this chemical to form.
Titanium Dioxide can be found in most of the leading skin/face products.
Production
Crude titanium dioxide is purified via titanium tetrachloride in the chloride process. In this process, the crude ore (containing at least 90% TiO2) is reduced with carbon, oxidized with chlorine to give titanium tetrachloride. This titanium tetrachloride is distilled, and re-oxidized with oxygen to give pure titanium dioxide.
Another widely used process utilizes ilmenite as the titanium dioxide source, which is digested in sulfuric acid. The by-product iron(II) sulfate is crystallized and filtered-off to yield only the titanium salt in the digestion solution, which is processed further to give pure titanium dioxide. Another method for upgrading ilmenite is called the Becher Process.
Applications
Pigment
Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index (n = 2.7), in which it is surpassed only by a few other materials. Approximately 4 million tons of pigmentary TiO2 are consumed annually worldwide. When deposited as a thin film, its refractive index and colour make it an excellent reflective optical coating for dielectric mirrors and some gemstones, for example "mystic fire topaz". TiO2 is also an effective opacifier in powder form, where it is employed as a pigment to provide whiteness and opacity to products such as paints, coatings, plastics, papers, inks, foods, medicines (i.e. pills and tablets) as well as most toothpastes. Opacity is improved by optimal sizing of the titanium dioxide particles.
Used as a white food colouring, it has E number E171. Titanium dioxide is often used to whiten skim milk; this has been shown statistically to increase skim milk's palatability.
In cosmetic and skin care products, titanium dioxide is used both as a pigment and a thickener. It is also used as a tattoo pigment and styptic pencils.
This pigment is used extensively in plastics and other applications for its UV resistant properties where it acts as a UV absorber, efficiently transforming destructive UV light energy into heat.
In ceramic glazes titanium dioxide acts as an opacifier and seeds crystal formation.
In almost every sunscreen with a physical blocker, titanium dioxide is found because of its high refractive index, its strong UV light absorbing capabilities and its resistance to discolouration under ultraviolet light. This advantage enhances its stability and ability to protect the skin from ultraviolet light. Sunscreens designed for infants or people with sensitive skin are often based on titanium dioxide and/or zinc oxide, as these mineral UV blockers are less likely to cause skin irritation than chemical UV absorber ingredients, such as avobenzone.
As a photocatalyst
Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet light. Recently it has been found that titanium dioxide, when spiked with nitrogen ions, or doped with metal oxide like tungsten trioxide, is also a photocatalyst under visible and UV light. The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly. Titanium dioxide is thus added to paints, cements, windows, tiles, or other products for sterilizing, deodorizing and anti-fouling properties and is also used as a hydrolysis catalyst. It is also used in the Graetzel cell, a type of chemical solar cell.
The photocatalytic properties of titanium dioxide were discovered by Akira Fujishima in 1972 . The process on the surface of the titanium dioxide was called the Honda-Fujishima effect .
Titanium dioxide has potential for use in energy production: as a photocatalyst, it can
- carry out hydrolysis; i.e., break water into hydrogen and oxygen. Were the hydrogen collected, it could be used as a fuel. The efficiency of this process can be greatly improved by doping the oxide with carbon, as described in "Carbon-doped titanium dioxide is an effective photocatalyst" .
- produce electricity when in nanoparticle form. Research suggests that by using these nanoparticles to form the pixels of a screen, they generate electricity when transparent and under the influence of light. If subjected to electricity on the other hand, the nanoparticles blacken, forming the basic characteristics of a LCD screen. According to creator Zoran Radivojevic, Nokia has already built a functional 200-by-200-pixel monochromatic screen which is energetically self-sufficient.
In 1995 the Research Institute of Toto Ltd. discovered the superhydrophilicity phenomenon for glass coated with titanium dioxide and exposed to sun light. A discovery by Professor Fujishima and his group This resulted in the development of self-cleaning glass and anti-fogging coatings.
TiO2 incorporated into outdoor building materials, such as paving stones in noxer blocks or paints, can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides .
A photocatalytic cement that uses titanium dioxide as a primary component, produced by Italcementi Group, was included in Time's Top 50 Inventions of 2008 .
For wastewater remediation
TiO2 offers great potential as an industrial technology for detoxification or remediation of wastewater due to several factors.
- The process occurs under ambient conditions very slowly, direct UV light exposure increases the rate of reaction.
- The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided.
- Oxidation of the substrates to CO2 is complete.
- The photocatalyst is inexpensive and has a high turnover.
- TiO2 can be supported on suitable reactor substrates.
Other applications
It is also used in resistance-type lambda probes (a type of oxygen sensor).
Titanium dioxide is also used in some pain relievers, such as tylenol and rite aid brand aspirin
Titanium dioxide is what allows osseointegration between an artificial medical implant and bone.
Titanium dioxide in solution or suspension can be used to cleave protein that contains the amino acid proline at the site where proline is present. This breakthrough in cost-effective protein splitting took place at Arizona State University in 2006.
Titanium dioxide on silica is being developed as a form of odor control in cat litter. The purchased photocatalyst is vastly cheaper than the purchased silica beads, per usage, and prolongs their effective odor-eliminating life substantially.
Titanium dioxide is also used as a material in the memristor, a new electronic circuit element.
It can be employed for solar energy conversion based on dye, polymer, or quantum dot sensitized nanocrystalline TiO2 solar cells using conjugated polymers as solid electrolytes .
It has also been recently incorporated as a photocatalyst into dental bleaching products. It allows the use of decreased concentrations of hydrogen peroxide in the bleaching agent, thus claimed to achieve similar bleaching effects with less side effects (e.g.:transient sensitivity, change in tooth surface topography, etc ...)
It is also used by film and television companies as a substitute for snow when filming scenes which require a winter setting.
Titanium oxide is also used as a semiconductor.
Historical uses
The Vinland map, the map of America ("Vinland") that was allegedly drawn during mid-15th century based on data from the Viking Age, has been declared a forgery on the basis that its ink contains traces of the TiO2-form anatase; TiO2 was not synthetically produced before the 1920s. In 1992, a counter-claim was made that the compound can be formed from ancient ink.
Titanium dioxide white paint was used to paint the Saturn V rocket, which is so far the only rocket that has sent astronauts to the moon. In 2002, a spectral analysis of J002E3, a celestial object, showed that it had titanium dioxide on it, giving evidence it may be a Saturn V S-IVB.
See also
External links
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