Titanium dioxide: from black sand to white pigment

How did titanium go from saving sailors to saving your skin?

Titanium has taken off in recent years. The rust-resistant, light, tough metal forms the bulletproof cocoon that surrounds the pilots of the Air Force's A-10 Warthog. Golfers pay more than $1,000 to swing clubs made from less than a pound of element 22. Bicycles with titanium frames cost anywhere from $3,000 to $7,000 or more.

Despite the recent surge in sales of titanium metal products, the big bucks in titanium are in its more humble use — white pigment. Every year, a half-dozen global companies produce titanium dioxide (TiO2) pigment; they sell the pigment at just under $1 per pound to a global market valued at an estimated $8 billion, many times the market for titanium metal. Paint, plastic, paper makers, and even food processors, buy four million tons of white pigment. And more than 2 million of those 4 million tons are mixed into paints and coatings.

Most people who pick up a gallon of paint notice that it weighs more than a gallon of water. Part of the difference is that the average gallon of paint contains 1.5 lb of white pigment, which has a density twice that of water. TiO2 is also the most expensive of the major ingredients in the can. Part of the price of premium paint is more and better white pigment.
Why so much white pigment? Because it’s the white pigment in paint that hides the wall. When one coat covers, it’s not the color of the paint, but the white pigment. The mechanism is simple. TiO2 pigment particles are like small tuned antennae for reflecting visible light. Light hitting TiO2 particles bounces back. In fact, no other common compound is better at bouncing beams of light than TiO2. The intense white of TiO2 is the reason that coloring a gallon of paint takes just a few drops of color to make an eye-popping pink or a beautiful blue. Very little color goes a long way on a very white base.

In fact, whether in paint, paper or plastics, the ideal manufacturing process disperses the pigment particles evenly, making a mixture that reflects light as efficiently as possible. Ideally, the pigment particles are like chocolate chips in a well-made batch of cookies, distributed evenly throughout the batter. So there are no cookies with clumps of chips nor any with a few lonely chips in a great big cookie.

Although TiO2 is the intensely white commercial compound, the raw material for white pigment is black sand. If that seems ironic, it is — literally. Iron and other impurities give naturally occurring titanium oxides a black cast that gives dark hues to beaches from Norway to Brazil to South Africa to Western Australia. As a result, many titanium product facilities are located at or near ports large enough to unload ocean-going barges of black sand.

Pigment plants take in barges of black sand and react the naturally occurring compound with chlorine, forming titanium tetrachloride, an intermediate that can be made into either white pigment or titanium metal. Although titanium oxides are inert, titanium tetrachloride reacts violently on contact with water, forming a white cloud of pigment and hydrochloric acid. While dangerous, many sailors in World War II owe their lives to this strange reaction. Ships attacked by bombers and Kamakazi planes used smoke to mask their position, but as a last resort would break carefully stored titanium tetrachloride containers in the water, forming an acidic cloud that hurt the eyes and throats of sailors, but was much healthier than direct hits by bombs and torpedoes. The white cloud could completely obscure a ship, making accurate attack impossible.

Paints and coatings make up nearly 60% of the white pigment market. Plastics — everything from white trash bags to vinyl siding — is second place with about 25% of the market. Paper consumes less than 10% of TiO2 used as pigment. But the final few percent are the most fun. If food is white, it’s either butterfat or TiO2. Scan the label of non-dairy coffee creamer, diet cream soups and sauces, or bright white dessert toppings and you are likely to see TiO2. White pigment is also responsible for the vivid white color of crème doughnuts and, on a smaller scale, the tiny little m’s on the M&Ms. TiO2 is the only coloring that will show up in such small quantities.

To add one final irony to this colorful tale, when TiO2 particles are ground to about half the 0.25-µm size that makes white pigment, the result is a very effective reflector of ultraviolet rays. This smaller size particle is actually invisible, reflecting no light at all. So when you put white-colored UV cream on your face and arms at the beach, the real UV protection is as transparent as a clean window. The makers have to add white pigment to the UV protection cream to give it color. From black to white to invisible and back to white again, the chemical compound remains the same — TiO2.

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This article was originally published under the title "We're History" in the June 2005 edition of Chemical Engineering Progress magazine. This article was prepared by Neil Gussman, communications manager for the Chemical Heritage Foundation.