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What is titanium dioxide?

What is titanium dioxide?

Titanium dioxide (chemical formula: TiO2, white solid or powder like amphoteric oxide, molecular weight: 79.9), is a white inorganic pigment, with non-toxic, the best opacity, the best whiteness and brightness, is considered to be the best white pigment in the world today. Titanium white has strong adhesion and is not easy to change chemically. It is always white. Widely used in coatings, plastics, paper, printing ink, chemical fiber, rubber, cosmetics and other industries. Its melting point is very high, and it is also used to make refractory glass, glaze, enamel, clay, high temperature resistant experimental utensils, etc.
At the same time, titanium dioxide has a better UV masking effect. It is often used as sunscreen to blend into textile fibers, and ultrafine titanium dioxide powder is also added into sunscreen cream to make sunscreen cosmetics.

Titanium dioxide can be obtained from rutile by acid decomposition or titanium tetrachloride decomposition. Titanium dioxide has stable properties and is widely used as white pigment in paint. It has good covering ability, similar to lead white, but not black like lead white; it has the same durability as zinc white. Titanium dioxide is also used as a matting agent for enamel, which can produce a very bright, hard and acid resistant enamel cover.

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Titanium dioxide is generally divided into anatase (type A for short) and rutile (type R for short).

Physical property

Relative density: among the commonly used white pigments, titanium dioxide has the lowest relative density. Among the white pigments of the same quality, titanium dioxide has the largest surface area and the highest pigment volume.

Name of pigment
Anatase titanium dioxide
Rutile titanium dioxide
Plate titanium dioxide

Dielectric constant: titanium dioxide has excellent electrical properties due to its high dielectric constant. In the determination of some physical properties of titanium dioxide, the crystal direction of titanium dioxide crystal should be considered. For example, the dielectric constant of rutile type varies with the direction of the crystal. When it is parallel to the c axis, the measured dielectric constant is 180, when it is at right angles to the axis, it is 90, and the average value of the powder is 114. The dielectric constant of anatase titanium dioxide is only 48.
Conductivity: titanium dioxide has the properties of semiconductor. Its conductivity increases rapidly with the rise of temperature, and it is also very sensitive to hypoxia. For example, rutile titanium dioxide is still an electrical insulator at 20 ℃, but its conductivity increases 107 times when heated to 420 ℃. The conductivity of TiO2 is less than 10-10s / cm according to the chemical composition, but the conductivity of TiO2 is as high as 10-1s / cm. The dielectric constant and semiconductor properties of rutile titanium dioxide are very important to the electronic industry, which uses the above characteristics to produce electronic components such as ceramic capacitors.
Hardness: according to the scale of 10 points of Mohs hardness, rutile titanium dioxide is 6-6.5, anatase titanium dioxide is 5.5-6.0, so in chemical fiber extinction, anatase type is used to avoid abrasion of spinneret hole.

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Crystal structure of rutile
Melting point and boiling point: because anatase and anatase titanium dioxide will change to rutile at high temperature, the melting point and boiling point of anatase and anatase titanium dioxide do not exist. Only rutile titanium dioxide has melting point and boiling point. The melting point of rutile titanium dioxide is 1850 ℃, the melting point in air is (1830 ± 15) ℃, and the melting point in oxygen enriched is 1879 ℃. The melting point is related to the purity of titanium dioxide. The boiling point of rutile titanium dioxide is (3200 ± 300) k, and titanium dioxide is slightly volatile at this high temperature.
Although titanium dioxide has hydrophilicity, its hygroscopicity is not very strong, and rutile type is smaller than anatase type.

  • The hygroscopicity of titanium dioxide is related to its surface area, which is large and high.
  • The hygroscopicity of titanium dioxide is also related to its surface treatment and properties.

Thermal stability:
Titanium dioxide is a kind of material with good thermal stability, the general dosage is 0.01% – 0.12%.
Physical structure: rutile type, anatase type; crystal system, tetragonal system.
Lattice constants: a-axis 0.458, c-axis 0.795, a-axis 0.378, c-axis 0.949

  • A axis: 7.19X10-6 2.88~10-6
  • C axis: 9.94X10-6 6.44~10-6

Chemical property

Barium metatitanate is formed from molten barium carbonate (barium chloride or sodium carbonate is added as auxiliary solvent):

  • TiO2+BaCO3=BaTiO3+CO2↑

Insoluble in water or dilute sulfuric acid, but soluble in hot concentrated sulfuric acid or molten potassium bisulfate:

  • TiO2+H2SO4=TiOSO4+H2O

Although the solution of titanium dioxide dissolved in hot concentrated sulfuric acid is acidic, it can also be hydrolyzed when heated and boiled to obtain the hydrated titanium dioxide (β – titanic acid) insoluble in acid and alkali. If alkali is added to the newly prepared titanium hydrochloric acid solution, fresh hydrated titanium dioxide (α – titanic acid) can be obtained. The reaction activity of α – titanic acid is higher than that of β – titanic acid, and it can be dissolved in dilute acid and concentrated alkali. After dissolving in the concentrated sodium hydroxide solution, the hydrated titanate with the formula of Na2TiO3 · H2O can be separated out from the solution.
The gaseous titanium tetrachloride can be prepared by pressing titanium dioxide and carbon powder into a group, coking and heating to 1070-1170k.

  • TiO2+2Cl2+2C=TiCl4↑+2CO↑

This reaction is very important for titanium extraction. Magnesium or sodium can reduce titanium tetrachloride easily.
Titanium dioxide can also be used to produce titanium tetrachloride by the reaction of titanium dioxide with such chlorination reagents as CoCl2 (phosgene), SOCl2 (dichlorosulfoxide), CHCl3 (trichloromethane), CCl4 (carbon tetrachloride)

  • TiO2 + CCl4 = TiCl4 ↑ + 2co2 ↑ (the reaction is completed at 770k)

Surface properties

Surface super hydrophilicity

The results show that the super hydrophilicity of TiO2 surface is due to the change of its surface structure. Under UV irradiation, TiO2 valence band electrons are excited to the conduction band, electrons and holes migrate to TiO2 surface, and electron hole pairs are generated on the surface, electrons react with Ti, holes react with surface bridging oxygen ions, forming positive trivalent titanium ions and oxygen holes respectively. At this time, the hydrolytic dissociation in the air is adsorbed in the oxygen vacancy and becomes the chemically adsorbed water (surface hydroxyl). The chemically adsorbed water can further adsorb the water in the air and form a physical adsorption layer.

Surface hydroxyl

Compared with other semi-metallic materials, the polarity of Ti-O bond in TiO2 is larger, and the water adsorbed on the surface dissociates due to polarization, which is easy to form hydroxyl. The surface hydroxyl can improve the performance of TiO2 as adsorbent and various monomers, and provide convenience for surface modification.

Surface acidity and basicity

When TiO2 is modified, Al, Si, Zn and other oxides are often added. When Al or Si oxides exist alone, there is no obvious acid-base property. However, when TiO2 is combined with TiO2, it shows strong acid-base property and can be used to prepare solid superacid.

Surface electricity

TiO2 particles in liquid (especially polar) media will form a diffusion double electric layer because of the opposite charge adsorbed by the surface charge, which increases the effective diameter of the particles. When the particles are close to each other, they repel each other because of the same charge, which is conducive to the stability of the dispersion system. For example, the surface of TiO2 coated with Al2O3 has positive charge, while TiO2 treated with SiO2 has negative charge.

Preparation method

Gas phase oxidation

Gas phase oxidation at 923k-1023k with dry oxygen:

  • TiCl4+O2=TiO2+2Cl2

Sulfuric acid method

Firstly, the soluble sulfate was prepared by the reaction of milled ilmenite and sulfuric acid (concentration ≥ 80%, temperature 343k-353k) under the condition of continuous air and stirring

  • FeTiO3+H2SO4=TiOSO4+FeSO4+2H2O

Because the reaction is exothermic, the temperature can reach 473k when the reaction is violent.
When preparing titanium dioxide, the key step is to hydrolyze titanium liquid:

  • TiOSO4+2H2O=TiO2·H2O↓+H2SO4

The concentration of titanium solution and the temperature of acidity will affect the hydrolysis reaction. The lower the concentration is, the lower the acidity is, and the higher the temperature is, the easier the reaction will occur. In order to increase the temperature, the reaction is often carried out under pressure, which can also make the precipitated particles closer, so that the product has better physical properties.

Determination of titanium content in preparation of titanium dioxide

In the process of determination, aluminum is added to the titanium liquid first, and Ti (IV) is reduced to Ti3 +. The reduction ability of Ti3 + is stronger than that of SN2 +, it can reduce Fe3 +. Therefore, KSCN is used as indicator in determination, and Ti3 + is titrated with standard Fe3 + solution. During titration, when Fe3 + ion is slightly excessive, blood red [fescn] 2 + will be generated, and then the titration end point will be reached.
TiO2 pigment is extracted from the raw feedstock with either sulfuric acid or chlorine. The chlorine process is the more advanced technology and is generally regarded as having a lower cost structure than the sulfate process. While the chlorine process has a higher raw ore cost due to using purer feedstock, the sulfate process has higher labor, waste and environmental liability costs. The chloride process is generally preferred for the major end uses in paint and plastics, and about two thirds of global capacity utilizes chloride.

The overall chemistry of the two processes can be represented as:

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Comparison of the two processes for the manufacture of titanium dioxide.
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TiO2 industry

The global titanium dioxide industry has gravitated towards the Asia-Pacific region. In terms of supply, the titanium dioxide capacity of China has surpassed that of the US and hit more than 2 million tonnes, making China the world’s largest titanium dioxide producer. In 2011, the titanium dioxide output of China surged by 23.10% year-on-year to 1.812 million tonnes. Apart from the new capacity of 350,000 tonnes contributed by DuPont, any increase in titanium dioxide capacity is expected to come mainly from China in the future.
The industry has been plagued with overcapacity since the 1990s. TiO2 pricing in real terms fell close to 50% between 1990 and 2009. Due to the high fixed cost structure of the business, in periods of overcapacity producers cut prices in a desperate attempt to use up excess capacity.
The last two decades have been marginally profitable at best for TiO2 producers, with plants often running at breakeven. However, overcapacity has persisted, in part due to the large environmental liabilities associated with decommissioning a TiO2 plant.
TiO2 demand underwent a rare sequential decline in 2008-9, dipping by 8% globally and 16% in Western markets over those two years. Several producers responded by permanently shuttering higher cost plants constituting 7% of worldwide capacity. Additionally, many producers temporarily idled plants due to weak demand. These shutdowns, coupled with a rise in demand due to inventory restocking in the global recovery, led to tightening supply and sharply rising prices starting in the back half of 2009. Prices have risen consistently since then, with price increases for the third and fourth quarters of 2011 already announced by the major producers. While there is no uniformly agreed price index for the industry, based on industry data and public company reports prices have risen about 40% in the past year.
The major question on the supply side is China. Ti Insight estimates that there are currently between 60 and 80 TiO2 plants in China with about 1 million mt of capacity, which is almost entirely sulfate capacity. Chinese producers have announced some significant capacity expansions, but there are doubts as to whether those plants will actually get built let alone whether they will actually run at their stated capacity. (DuPont has had a Chinese plant project stuck in the early planning stages since 2005.) Ti Insight estimates that China will add 770,000 mt of capacity by 2015. The consensus confirmed by both industry consultants and TiO2 buyers is that Chinese production is generally regarded as suitable only for lower-end markets and is not a substantial threat to Western producers at the present time. The sulfate process produces a lower quality base pigment than chloride. While sulfate TiO2 can be finished in a way that makes it comparable in quality to chloride, the finishing process is proprietary to each producer and the Chinese are not up to Western standards in that area. Only the top five producers possess chlorine technology and it is assumed the Chinese producers will have a tough time replicating it even if they attempt to do so. And even with the anticipated Chinese capacity expansions the total supply CAGR is only 3% through to 2015. That will probably just about keep up with demand growth.

Application area

Industrial application

Titanium dioxide is an important white pigment and porcelain glaze. Used in paint, ink, plastic, rubber, paper, chemical fiber, watercolor pigment and other industries.
Titanium dioxide is the most white thing in the world. One gram of titanium dioxide can paint an area of more than 450 square centimeters white. It is 5 times whiter than the common white pigment – lithopone, so it is the best pigment for preparing white paint. Titanium dioxide, used as pigment in the world, is up to several hundred thousand tons a year. Titanium dioxide can be added to paper to make the paper white and opaque, and the effect is 10 times greater than other substances. Therefore, banknote paper and art paper should be added with titanium dioxide.
In order to lighten the color of plastics and soften the luster of rayon, titanium dioxide is sometimes added.
In rubber industry, titanium dioxide is also used as filler of white rubber.
The photochemical properties of semiconductor titanium dioxide have made it possible to be used in many fields, such as air, water and fluid purification. Photocatalysts doped with carbon or other heteroatoms can also be used in sealed spaces or regions with scattering light sources. When they are used in coatings on buildings, pedestrian slabs, concrete walls or roof tiles, they can significantly increase the decomposition of air pollutants such as nitrogen oxides, aromatics and aldehydes.
In addition, it is widely used in the production of sunscreen, non-toxic, harmless to human body.

Ultrafine titanium dioxide has excellent UV shielding and transparency. It is widely used in cosmetics, wood protection, food packaging plastics, durable household films, man-made and natural fibers, transparent coatings. The special optical effect in the metallic flash coating makes it get attention and application in the high-grade car paint.

Food application

The U.S. Food and drug administration stipulates that titanium dioxide can be used as all food white elements, and the maximum use amount is 1g / kg sec. 73.575 titanium dioxide. Titanium dioxide, a pigment additive, can be safely used in general coloring food, and shall comply with the following regulations:

  • (1) The amount of titanium dioxide should not exceed 1% of the weight of food.
  • (2) According to the special standards published in article 401 of the decree, coloring food that cannot be used shall not be used unless there are similar standards allowing the addition of pigments.
  • (3) For coloring food, titanium dioxide, the pigment additive for food, can contain appropriate diluent as a safe pigment additive, as follows: silicon dioxide, as a dispersant, does not contain more than 2%.

Product adaptations: preserved fruits, jelly, fried foods, cocoa products, chocolate, chocolate products, hard candy, polished candy, gum based candy, puffed food, confectionery, chocolate products, coating, mayonnaise, salad dressing, jam, solid drink, konjac gel food, etc.

Environmental protection

Purifying air

Titanium dioxide, as the catalyst of photocatalyst pigment, is not only a kind of environmental safety cleaner, but also can save energy and protect environmental resources.
Early Japanese and British scientists applied titanium dioxide to the surface of pavers on urban roads to clean the air. Titanium dioxide can be mixed with asphalt to reduce pollutants in the air. When the car passes by, the concrete or asphalt containing titanium dioxide can purify the air and eliminate 25% to 45% of nitrogen oxides in the vehicle emissions. When titanium dioxide is coated on the concrete surface, the effect of cleaning air is also significant.

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The picture shows titanium dioxide under electron microscope

Cooling the earth

In May 2012, British scientists put forward a bold idea that they can cool the earth by spraying enough titanium dioxide into the stratosphere to reflect the sun’s light, which can effectively offset various adverse climate factors caused by global warming.
Because titanium dioxide can effectively reflect the direct sunlight, and its properties are stable, it has good covering ability, such as spraying in the stratosphere can play a long-term role. British scientists have proposed that the chemical can be brought into the stratosphere by high-altitude balloons, and then released. Once titanium dioxide is evenly distributed in the stratosphere, it can effectively reflect the sun’s light, thus cooling the earth.
Peter Davidson, a chemical engineer and President of Davidson technology, a British consulting firm, is in charge of the project. He said that only 3 million tons of titanium dioxide needed to be transported to the stratosphere can form a 1mm thick protective layer in the stratosphere, which can play a huge role – enough to offset twice the current carbon dioxide content in the atmosphere The greenhouse effect.

Sunscreen cosmetics

Because ultraviolet radiation has great harm to the human body, the developed countries have paid more attention to the research and development of sunscreen products in recent years, and have launched a variety of anti ultraviolet fiber, plastic, film, coating, and sun protection cream, foundation, lipstick, mousse, cream and other anti sun cosmetics. In recent years, China has also increased the research and production of sunscreen cosmetics.

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But in the past, most sunscreens were benzophenone, o-aminobenzophenone, salicylate, p-aminobenzoic acid, cinnamate and other organic compounds, so they were unstable, short-lived, and had large side effects, with certain toxicity and irritation. If they were added too much, they would produce chemical allergy, and even lead to skin cancer. As an inorganic component, nano titanium dioxide has excellent chemical stability, thermal stability, non migration, strong achromatic and covering power, low corrosiveness, good dispersibility, non-toxic, tasteless, non irritant, safe use, and also has the function of sterilization and deodorization. What’s more, as mentioned before, nano titanium dioxide can not only absorb ultraviolet rays, but also emit and scatter ultraviolet rays, so it has strong anti ultraviolet ability. Compared with the same dose of organic anti ultraviolet agent, its absorption peak in the ultraviolet region is higher; In addition, nano titanium dioxide can block the ultraviolet rays in the middle and long wave regions, unlike organic anti UV agents, which can only block the ultraviolet rays in the middle or long wave regions. In particular, due to its fine particles, high transparency of the finished product, it can pass through visible light, and the skin whiteness is natural when adding cosmetics. It overcomes the shortcomings of some organic or pigment grade titanium dioxide opaque, which makes the skin present unnatural pale. Because of this, nano titanium dioxide has been widely valued and gradually replaced by some organic anti UV agents, and become a physical shielding anti UV agent with superior performance in today’s sun protection cosmetics.
With the improvement of people’s living standards and the intensification of international competition, the research and development of safe and efficient sunscreen cosmetics will gradually increase. Nowadays, sunscreen cosmetics market in developed countries has shown strong vitality. From 1999 to 2000, the annual sales volume of the United States has reached 737 million US dollars, 765 million US dollars, and that of the United Kingdom has reached 245 million US dollars, 270 million US dollars. In recent years, the annual sales volume of the United States has increased by 20% and 10% respectively, and the consumption of nano titanium dioxide has also increased greatly year by year. The annual demand of nano titanium dioxide in UV resistant cosmetics in Japan is more than 1000t, and the consumption in textile, plastic and rubber products is more.
From the development trend of sunscreen cosmetics, one is inorganic sunscreen instead of organic sunscreen, the other is bionic sunscreen. The latter is more expensive and difficult to popularize nowadays. The former is of moderate price and superior sunscreen performance, so it is generally accepted. Especially nano titanium dioxide, because of its superior performance and application prospect, has a good development momentum and market potential.
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