What is titanium dioxide, and what are its properties?
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Titanium dioxide is one of the most essential inorganic materials modern industry consumes. It is widely used in the contemporary world and is the primary commercial product of the titanium production sector. How is titanium dioxide manufactured and utilized? We will discuss it in this article along with other relevant aspects.
Pure titanium dioxide (TiO2) is a colorless, crystalline solid substance. When heated, its crystals turn yellow, and upon cooling, they regain their colorless appearance.
Modifications of titanium dioxide include:
Titanium dioxide is produced in two forms: rutile (R-type) and anatase (A-type).
It scatters light approximately 30% better than anatase, and it has better hiding power (the ability of titanium dioxide to cover the color of the painted surface).
Rutile titanium dioxide is preferred in paints, coatings, plastics, and cosmetics production.
It is less resistant to atmospheric conditions than rutile and provides less protection against UV radiation. Anatase pigments find their application in producing paper, rubber, and soap.
Traditionally, the vast majority (about 95%) of all produced titanium dioxide is used in making paints and coatings.
The leading role of titanium dioxide among white pigments is predetermined by its high level of quality. This product is characterized by its ability to disperse, as well as its thermal and chemical resistance, whitening capability, resistance to atmospheric conditions, high refractive index, and more. These properties depend on the size of raw material particles and are significantly enhanced by their nanostructuring.
In the paint and coatings industry, the primary function of TiO2 is to impart paints with a white color and brightness and to enhance hiding power. It also protects against harmful ultraviolet rays and prevents film aging and yellowing of painted surfaces.
Titanium dioxide is a stable substance (the most stable one among all known white pigments). It is non-volatile and insoluble in acids, alkalis, and solutions under normal conditions.
Titanium dioxide is amphoteric, meaning it has basic and acidic properties (although it reacts with concentrated acids). It demonstrates high chemical stability towards various compounds, including those that may be toxic and present in the environment. Due to its inertness, titanium dioxide is non-toxic and generally considered a very safe substance. It can come into contact with packaged products and even be used as a food coloring in certain concentrations.
It may even enter the body as an aerosol through inhalation or ingestion. It is non-flammable.
Specific properties of titanium dioxide make it indispensable in various industries, contributing to the rapid growth of the global titanium dioxide market.
World Market of Titanium Dioxide Pigment Production.
There is a high demand for titanium dioxide in the global market, which is expected to continue growing. Additionally, there is a constant increase in the worldwide need for inorganic pigments. According to experts&#; estimates, in recent years, titanium dioxide pigment accounted for 65-70% of the total consumption of inorganic pigments and over 90% of the consumption of white pigments.
In , the titanium dioxide market was estimated to be more than 6 million tons, and it is projected that from to , the market will demonstrate an average annual growth rate of over 6%. In the short term, the rapidly growing demand from the paint and coatings industry will be the primary driver of titanium dioxide market growth.
Titanium dioxide pigment is produced in 15 countries, with 33% of production capacity located in the USA. Additionally, almost 40% of production is in China, Ukraine, Germany, the United Kingdom, Finland, Saudi Arabia, Japan, France, Australia, and other countries.
The global titanium dioxide production distribution is as follows:
China has the largest titanium dioxide production capacity, producing approximately 3 million tons annually.
The largest world producers are the following companies: DuPont Titanium Technologies (USA), National Titanium Dioxide Co., Ltd. Cristal (Saudi Arabia), Huntsman Pigments (USA), Tronox, Inc. (USA), Kronos Worldwide, Inc. (USA), Sachtleben Chemie GmbH (Germany; Rockwood Holdings own 100% of the shares), Ishihara Sangyo Kaisha, Ltd. (Japan).
A crucial aspect of the titanium dioxide manufacturing process is the supply of high-quality titanium ore. Despite titanium being one of Earth&#;s most abundant chemical elements, it occurs in deficient natural concentrations. Therefore, to establish an adequate supply of titanium ore capable of meeting the economic demands of TiO2 production, it is essential to implement rational methods of extraction and refinement of this mineral.
Read more about titanium ore mining and processing.
The primary raw material in the titanium dioxide production process is ilmenite concentrate (FeTiO3), produced by mining and processing. Ilmenite is an ore that, from a chemical perspective, is a mixture of oxides, the majority of which are titanium and iron oxides.
The second most significant raw material for the tio2 manufacturing process is titanium slag, containing 75-90% TiO2 and 5-7% FeO.
Read also our article on titanium slag production process.
Natural and synthetic rutile, as well as ore fines, have secondary importance.
Applications of titanium dioxide.
Due to its very high whiteness and fine particle size, titanium dioxide has found wide application as a white pigment in the paint and coatings industry. Among its advantages are non-toxicity, high optical properties (ability to scatter light), availability, chemical inertness, resistance to atmospheric conditions, and more. Gone are the days when paints were made using zinc or lead-containing white pigments.
It is the primary industry using titanium dioxide pigment. But not the last one.
TiO2 is widely used as a white pigment in the pulp and paper industry for producing synthetic fibers, rubber products, plastics, heat-resistant and optical glass, ceramic dielectrics, etc.
Applications of titanium dioxide other than pigment production are as follows:
Titanium dioxide, with a chemical purity of 99.%, is used in producing optical fiber products, medical equipment, and the radio-electronic industry. In manufacturing ultra-pure glasses, titanium dioxide serves as a purity reference.
For matting twisted fibre.
For protection against ultraviolet radiation in sunblock creams, for higher whitening effect of toothpastes, soaps, etc.
For higher whitening effect in products, for protection of product package color (plastics) against ultraviolet radiation.
For higher whitening effect in pharma products.
To increase weather resistance of coatings.
Photocatalyst and inert ceramic base material for active components.
Titanium dioxide nanopowders are used for air purification in cities, in producing nanofiber paper based on TiO2, in hydrogen energy, etc.
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Coating of welding electrodes and coatings of casting molds.
Technologies of titanium dioxide production
In global practice, high-dispersion titanium dioxide pigment is produced by the sulfate (sulfuric acid) and chloride methods.
The sulfate method is based on the decomposition of ilmenite concentrates containing 45-56% TiO2 or titanium slags with a content of 75-80% TiO2, with subsequent conversion of titanium sulfates into dioxide.
The chloride method involves the chlorination of natural rutile concentrates, synthetic rutile, or titanium slags with a TiO2 content of 85% and higher, as well as special slags that have undergone additional processing and contain over 92% TiO2.
Considering specific features of both processes of the TiO2 production process, the primary criterion for choosing between the sulfate and chloride methods is the possibility of providing raw materials of the appropriate quality and environmental-related issues.
Both methods make it possible to obtain high-quality products with identical properties.
The approximate distribution of production technologies among manufacturers worldwide is 45% by the sulfate method and 55% by the chloride method.
The sulfate method was applied in industry in to produce the anatase form of titanium dioxide and later, in , for production of the rutile form. In this method, the initial raw material &#; ilmenite concentrate or titanium slag &#; is dissolved in sulfuric acid, resulting in titanium, iron, and other metal sulfate solutions. Then, basic TiO2 with the necessary particle size is formed after a series of technological transformations, including chemical reduction, purification, precipitation, washing, and calcination. The crystal structure (anatase or rutile form) is controlled during nucleation and calcination.
The equation describes the sulfate method of the titanium dioxide process:
FeTiO3 + 2H2SO4 &#; TiOSO4 + FeSO4 + 2H2O TiOSO4 + H2O &#; TiO2 + H2SO4.
The chloride method was invented in to produce the rutile form of TiO2.
The chloride method converts rutile (natural or synthetic) or titanium slag into titanium tetrachloride (TiCl4) through chlorination in the presence of petroleum coke. Any resulting impurities of other metal chlorides are subsequently removed. The following equation describes the chloride method for obtaining TiO2:
2FeTiO3 + 7CI2 + &#;&#; &#; 2TiCI4 + 2FeCI3 + 3CO2TiCI4 + O2 &#; TiO2 + 2CI2.
The most crucial operation in TiO2 production by the chloride method is the combustion of titanium tetrachloride. It is carried out at temperatures between 900-°C with burners of a particular design.
The titanium tetrachloride combustion reaction is as follows:
TiCl4 + O2= TiO2 + 2&#;12.
The released chlorine can be returned to the production process to obtain titanium tetrachloride.
Titanium pigments obtained by combustion of titanium tetrachloride may contain up to 0.6% adsorbed chlorine. The aqueous suspension of such a product has a pH of less than 7 and is unsuitable for producing paints. Desorption of chlorine from the pigment can be achieved by heating it at temperatures 300-900 °C. The chlorine concentration is reduced to 0.1% in this process. Such a product is suitable for manufacturing paints and enamels but requires surface treatment with silicon and aluminum compounds to obtain higher-quality pigments.
The chloride method is selective and demanding in terms of raw materials. Due to the use of chlorine and high temperatures, it requires corrosion-resistant equipment.
In both technological processes &#; sulfate and chloride &#; the intermediate products are accumulations of TiO2 crystals of pigment size, which need to be separated (ground) to achieve optimal optical characteristics.
Depending on the end-user requirements, various processing methods are used to modify TiO2, including sedimentation of oxides of silicon, aluminum, zirconium, or zinc onto the surface of pigment fractions.
Particular processing methods may be used to optimize operational characteristics for specific applications utilizing oxides in aqueous or anhydrous environments or various combinations thereof. Additionally, organic additives can be introduced by multiple methods to enhance particular characteristics of the pigment.
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Modern methods of additional processing of titanium dioxide pigment.
Practically, there are hardly any industrially produced pigments made of pure TiO2. Most of them undergo inorganic and, in some cases, organic treatment applied to the surface of TiO2 particles through sedimentation, mechanical mixing, or some other method.
Such surface treatment methods improve one or even several operational properties of the pigment, including ease of dispersion, resistance to atmospheric influences, or color stability.
A universal surface treatment method for obtaining a pigment suitable for any practical application has yet to be found. Therefore, the goal of ongoing research is to continue developing new grades of TiO2 that would meet the constantly changing requirements of modern industry.
Titanium dioxide production is a fascinating scientific and technical research and innovation area. Recently, a technology for producing TiO2 has been developed in which ammonium fluoride is used as the primary reagent and is safer than sulfuric acid. Besides, this reagent can be reused, leading to a reduction in waste. One disadvantage of the fluoride technology is that it results in a coarser-dispersed pigment powder compared to the chloride method.
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Conclusions
Author of the article: Larisa Sokol
Hey all, just wondering if there&#;s anyone else out there that&#;s successfully used a titanium oxide-alcohol solution to laser engrave white tiles and if so: What kind of mixture/solution do you use? I&#;ve been using 70% isopropyl with water soluable TiO2 powder but have struggled to find a mixture that works consistently.
Currently I&#;ve been mixing roughly 1oz of iso with between 1.5 and 3 grams of TiO2 but can&#;t find a sweet spot. 1.5 requires a lot of coats and can still leave under-coated streaks that you can see in the engraved image. 3+ Grams seems almost too much, there&#;s visible detail loss and when the tile is washed there are details that literally get washed away.
Anyone else doing it this way, what are your ratios/mixtures?
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