Rutile

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Rutile
Specific gravity
4.23 increasing with Nb–Ta content
Optical propertiesUniaxial (+)
Refractive indexnω = 2.613, nε = 2.909 (589 nm)
Birefringence0.296 (589 nm)
PleochroismWeak to distinct brownish red-green-yellow
DispersionStrong
FusibilityFusible in alkali carbonates
SolubilityInsoluble in acids
Common impuritiesFe, Nb, Ta
Other characteristicsStrongly anisotropic
References[2][3][4][5]

Rutile is an

polymorphs of TiO2 are known, including anatase, akaogiite, and brookite
.

Rutile has one of the highest

visible wavelengths of any known crystal and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of certain optical elements, especially polarization optics, for longer visible and infrared wavelengths up to about 4.5 micrometres. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum
.

Rutile derives its name from the Latin rutilus ('red'), in reference to the deep red color observed in some specimens when viewed by transmitted light. Rutile was first described in 1803 by Abraham Gottlob Werner using specimens obtained in Horcajuelo de la Sierra, Madrid (Spain),[6] which is consequently the type locality.

Occurrence

Rutile output in 2005

Rutile is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks.

metastable phases of anatase or brookite.[7] Consequently, the transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three main polymorphs, it is generally the primary titanium-bearing phase in most high-pressure metamorphic rocks, chiefly eclogites
.

Rutile in quartz

Within the igneous environment, rutile is a common accessory mineral in plutonic igneous rocks, though it is also found occasionally in extrusive igneous rocks, particularly those such as kimberlites and lamproites that have deep mantle sources. Anatase and brookite are found in the igneous environment, particularly as products of autogenic alteration during the cooling of plutonic rocks; anatase is also found in placer deposits sourced from primary rutile.

Graubünden, Switzerland. In 2005 the Republic of Sierra Leone in West Africa
had a production capacity of 23% of the world's annual rutile supply, which rose to approximately 30% in 2008.

Crystal structure

The unit cell of rutile. Ti atoms are gray; O atoms are red.
A ball-and-stick chemical model of a rutile crystal
Extended crystal structure of rutile

Rutile has a tetragonal unit cell, with unit cell parameters a = b = 4.584 Å, and c = 2.953 Å. [8] The titanium cations have a coordination number of 6, meaning they are surrounded by an octahedron of 6 oxygen atoms. The oxygen anions have a coordination number of 3, resulting in a trigonal planar coordination. Rutile also shows a screw axis when its octahedra are viewed sequentially.[9] When formed under reducing conditions, oxygen vacancies can occur, coupled to Ti3+ centers.[10] Hydrogen can enter these gaps, existing as an individual vacancy occupant (pairing as a hydrogen ion) or creating a hydroxide group with an adjacent oxygen.[10]

Rutile crystals are most commonly observed to exhibit a prismatic or acicular

nanowires and abnormal grain growth
phenomena of this phase.

Application

Acicular crystals of rutile protruding from a quartz crystal

In large enough quantities in beach sands, rutile forms an important constituent of

titanium metal
.

Finely powdered rutile is a brilliant white pigment and is used in paints, plastics, paper, foods, and other applications that call for a bright white color. Titanium dioxide pigment is the single greatest use of titanium worldwide. Nanoscale particles of rutile are transparent to visible light but are highly effective in the absorption of ultraviolet radiation (sunscreen). The UV absorption of nano-sized rutile particles is blue-shifted compared to bulk rutile so that higher-energy UV light is absorbed by the nanoparticles. Hence, they are used in sunscreens to protect against UV-induced skin damage.

Small rutile needles present in

asterism. Asteriated gems are known as "star" gems. Star sapphires, star rubies
, and other star gems are highly sought after and are generally more valuable than their normal counterparts.

Rutile is widely used as a welding electrode covering. It is also used as a part of the ZTR index, which classifies highly weathered sediments.

Semiconductor

Rutile, as a large band-gap semiconductor, has in recent decades been the subject of significant research towards applications as a functional oxide for applications in photocatalysis and dilute magnetism.[11] Research efforts typically utilize small quantities of synthetic rutile rather than mineral-deposit derived materials.

Synthetic rutile

Synthetic rutile was first produced in 1948 and is sold under a variety of names. It can be produced from the titanium ore

Mohs hardness scale
.

As the result of growing research interest in the

dopants
to impart improved photocatalytic activity through improved photo-generated charge carrier separation, altered electronic band structures and improved surface reactivity.

See also

References

  1. S2CID 235729616
    .
  2. ^ Handbook of Mineralogy.
  3. ^ Webmineral data.
  4. ^ Mindat.org.
  5. ISBN 0-471-80580-7
    .
  6. ^ Calvo, Miguel (2009). Minerales y Minas de España. Vol. IV. Óxidos e hidróxidos (in Spanish). Madrid, Spain: Escuela Técnica Superior de Ingenieros de Minas de Madrid. Fundación Gómez Pardo. p. 237.
  7. ^ Hanaor, D. A. H.; Assadi, M. H. N.; Li, S.; Yu, A.; Sorrell, C. C. (2012). "Ab initio study of phase stability in doped TiO2". Computational Mechanics. 50 (2): 185–94.
    S2CID 95958719
    .
  8. ^
    S2CID 94096447
    .
  9. ^ "Rutile Structure", Steven Dutch, Natural and Applied Sciences, University of Wisconsin – Green Bay.
  10. ^
    S2CID 238860345
    .
  11. ^ Magnetism in titanium dioxide polymorphs J. Applied Physics

External links

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