Uses

Today, rutile is used for four main purposes. These include the production of titanium dioxide pigment, the production of titanium metal, flux coatings and finally as mineral specimens and gemstones on the precious stone market. The most important of these by far is for the production of titanium dioxide white pigment.

Titanium Dioxide Pigment

Heavy metals have often been used for pigmentation. Traditionally, white pigments were made with white lead and zinc oxide. Then, during the 1940’s a stable rutile form of titanium dioxide became available, resulting in a new pigment. This new titanium dioxide pigment, with a reflectivity higher than diamond, had unparalleled whiteness. It was also non-poisonous, opaque and slow-drying in oil.

These days titanium dioxide white pigment is used in paints and plastics, high quality paper, rubber, ceramics (e.g. porcelain), fabric, soap, cosmetics, toothpaste, false teeth, and even some foods (e.g. tumeric). It is also used in sun screening products (e.g. sun cream) due to its ability to reflect ultra violet light.

Production of Titanium dioxide pigment from Rutile

The titanium dioxide pigment is extracted directly from rutile, which contains 92 – 96 % TiO₂. This is done by calcining a mixture of rutile, coke and chlorine to form gaseous titanium tetrachloride (TiCl₄).

TiO₂(s) [impure] + C(s) + 2Cl₂(g) TiCl₄(g) + CO₂(g)

The titanium tetrachloride is then condensed to a liquid and the impurities separated as solids. It is then reheated to a gas and mixed with hot oxygen to form very fine crystalline rutile (raw white pigment).

TiCl₄(g) + O₂(g) TiO₂(s) + 2Cl₂(g)

The displaced chlorine gas can be recycled and thus is a catalyst. This process is known as the Chloride process.

About 92 % of the world’s titanium minerals are used to make titanium dioxide pigment and the three largest manufactures of it are Du Pont (in France), Millennium (in the U.S.A) and Tioxide (in Britain).

Titanium Metal

The Reverend William Gregor discovered metallic titanium in 1791. He recognised the presence of the new element (now know as titanium) in menasanite, a mineral named after Menaccan in Cornwall.

Several years later, Klaproth, a German chemist, rediscovered the element in the ore rutile. Although the pure elemental metal was not isolated until 1910, when Matthew Hunter heated titanium tetrachloride with sodium in a steel bomb at 700 – 800^oC.

During the 1950’s titanium began to come into use as a structural material, stimulated initially by aircraft applications. The metal became valued for its high strength, light weight and corrosion resistance and thus its use increased rapidly.

Today, titanium metal is used to form surgical pieces such as heart pacemakers, artificial limbs and joints, or as a lightweight metal for aircraft and spacecraft components. It is also used as an alloying metal, as when combined with carbon, in the manufacture of stainless and heat-resistant steels, it improves their welding qualities and corrosion resistance.

Titanium is the fourth most abundant metallic element in the earth’s crust and occurs primarily as an oxide ore, of which the most commercially important is rutile.

Production of Titanium Metal from Rutile

Titanium is produced by the Kroll process, which involves chlorinating rutile to titanium tetrachloride (as in the pigment process) and then reducing it to a titanium sponge using molten magnesium.

TiO₂(s) [impure] + C(s) + 2Cl₂(g) TiCl₄(g) + CO₂(g)

TiCl₄(g) + 2Mg(l) Ti(s) + 2MgCl₂(g)

Finally, the sponge is consolidated into ingots in an electric furnace.

Only 3 % of the world’s titanium minerals are used to make titanium metal.

Flux Coating

Improved electric welding rods are produced by the use of coatings containing rutile. This is due to the fact that it stabilises the electronic arc and reduces the viscosity of the slag formed during welding.

Mineral Specimens and Gemstones

Rutile is of major importance to the gemstone market in the form of microscopic inclusions in quartz, tourmaline, ruby, sapphire and other gemstones. These inclusions can produce effects such as cats eyes and asterisms (stars), a phenomenon known as chattoyancy.

One of the most common types of stone produced by inclusions of golden rutile is called rutilated quartz, a semi-precious stone. Here, the golden needles of rutile, called Venus hairs, are arranged in clear quartz in what are sometimes breathtaking patterns, each arrangement being individual.

Rutilated quartz is formed when rutile and quartz crystals are cooled together from high temperatures. This is because at high temperatures and pressures, n(SiO₂) – n(TiO₂) lie in a stable state. As the temperature cools and the pressure eases, the two separate with rutile crystals being trapped inside the quartz.

Rutile also forms its own interesting and beautiful mineral specimens. This is mainly due to the ease with which it undergoes twinning (see Crystal Structure of Rutile). Rutile crystals often form as cyclic twins, comprised of six or even eight “twins”, arranged in a circle. Another common form is a rutile star, which is the formation of crystals of rutile in a six-rayed orientation, as seen below.