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Physical and chemical properties of titanium dioxide

wallpapers Tech 2020-07-21
Titanium dioxide (chemical formula: TiO₂, white stable or powdered amphoteric oxide, molecular weight: 79.9, is a white inorganic pigment with non-toxic, best opacity, best whiteness, and brightness, and is considered to be the world’s A white pigment with the best performance. Titanium dioxide has strong adhesion, is not easy to undergo chemical changes, and is always white. It is widely used in coatings, plastics, papermaking, printing inks, synthetic fibers, rubber, cosmetics, and other industries. Its melting point is very high and is also used to make refractory glass, glaze, enamel, clay, and high-temperature experimental utensils.
At the same time, titanium dioxide has an excellent UV-shielding effect and is often incorporated into textile fibers as a sunscreen. Ultra-fine titanium dioxide powder is also added to sunscreen cream to make sunscreen cosmetics.

Titanium dioxide can be extracted by acid decomposition of rutile, or be obtained by decomposition of titanium tetrachloride. Titanium dioxide has stable properties and is used in large quantities as a white pigment in paint. It has excellent hiding power and is similar to lead white, but does not turn black like lead white; it has the same durability as zinc white. Titanium dioxide is also a matting agent for enamel, which can produce a very bright, hard, and acid-resistant enamel finish.

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

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

Dielectric constant: due to the high dielectric constant of titanium dioxide, it has excellent electrical properties. When determining specific physical properties of titanium dioxide, the crystal orientation of the titanium dioxide crystal should be considered. For example, the dielectric constant of the rutile type varies with the direction of the glass. When it is parallel to the C axis, the measured dielectric constant is 180, when it is at right angles to this axis, it is 90, and its average powder value is 114. The dielectric constant of anatase titanium dioxide is relatively low, only 48.

Electrical conductivity: Titanium dioxide has the properties of a semiconductor. Its electrical conductivity increases rapidly with the rise of temperature, and it is also susceptible to hypoxia. For example, rutile titanium dioxide is still an electrical insulator at 20°C, but when heated to 420°C, its electrical conductivity increases by 107 times. Slightly reducing the oxygen content will have an extraordinary impact on its conductivity. According to the chemical composition of titanium dioxide (TiO2), the conductivity is <10-10s/cm, while the conductivity of TiO1.9995 is as high as 10-1s/cm. The dielectric constant and semiconductor properties of rutile titanium dioxide are fundamental to the electronics industry, using the above characteristics to produce electronic components such as ceramic capacitors.
Hardness: On a scale of 10 on the Mohs hardness scale, rutile titanium dioxide is 6-6.5, anatase titanium dioxide is 5.5-6.0, so anatase is used in chemical fiber matting to avoid abrasion of the spinneret.

Melting point and boiling point: Since both anatase and brookite type titanium dioxide will transform into rutile type at high temperature, the melting point and boiling point of brookite type and anatase type titanium dioxide do not exist. Only rutile titanium dioxide has a melting point and boiling point. The melting point of rutile titanium dioxide is 1850°C, the melting point in the air (1830±15)°C, and the melting point in oxygen enrichment is 1879°C. 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.

Hygroscopicity:

Although titanium dioxide is hydrophilic, it is not very hygroscopic, and the rutile type is smaller than the anatase type.
The hygroscopicity of titanium dioxide has a special relationship with the size of its surface area. The surface area is large, and the hygroscopicity is high.

The hygroscopicity of titanium dioxide is also related to surface treatment and properties.

Chemical properties

Generate barium metal titanate with molten barium carbonate (add barium chloride or sodium carbonate as auxiliary solvent):
TiO2+BaCO3=BaTiO3+CO2↑

Insoluble in water or dilute sulfuric acid, but soluble in hot concentrated sulfuric acid or molten potassium hydrogen sulfate:
TiO2+H2SO4=TiOSO4+H2O

Although the solution obtained by dissolving titanium dioxide in hot concentrated sulfuric acid is acidic, it can be hydrolyzed when heated and boiled to get hydrated titanium dioxide (β-type titanic acid) which is insoluble in acids and alkalis. If alkali is added to the newly prepared titanium hydrochloric acid solution, freshly hydrated titanium dioxide (α-type titanic acid) is obtained, higher reactivity than β-type titanic acid and can be dissolved in dilute acid and concentrated alkali. After being disbanded in concentrated sodium hydroxide solution, the hydrated titanate with chemical formula Na2TiO3·H2O can be precipitated.

Titanium dioxide and carbon powder are pressed into a mass and coked and heated to 1070-1170K to prepare gaseous titanium tetrachloride.
TiO2+2Cl2+2C=TiCl4↑+2CO↑

This reaction is significant for the extraction of titanium. Magnesium or sodium can quickly reduce titanium tetrachloride.

The reaction of titanium dioxide with COCl2 (phosgene), SOCl2 (thionyl chloride), CHCl3 (trichloromethane), CCl4 (carbon tetrachloride) and other chlorinating reagents can also be used to prepare titanium tetrachloride:
TiO2+CCl4=TiCl4↑+2CO2↑(The reaction is completed at 770K)

Surface properties

1. Super hydrophilic surface

It is believed that the super-hydrophilicity of the TiO2 surface is due to the change of its surface structure under light conditions. Under ultraviolet light irradiation, TiO2 valence band electrons are excited to the conduction band, electrons and holes migrate to the TiO2 surface, generating electron-hole pairs on the surface, particles react with Ti, and holes react with surface bridge oxygen ions to form respectively Positive trivalent titanium ions and oxygen vacancies. At this time, the hydrolysis in the air is adsorbed in the oxygen vacancies and becomes chemically adsorbed water (surface hydroxyl groups). The chemically adsorbed water can further adsorb the moisture in the air to form a physical adsorption layer.

2. Surface hydroxyl

Compared with the metal oxides of other semiconductor semi-metal materials, the Ti-O bond in TiO2 is more polar. The water adsorbed on the surface is dissociated due to polarization, and hydroxyl groups are easily formed. This surface hydroxyl group can improve the performance of TiO2 as an adsorbent and various monomers, and provide convenience for surface modification.

3. Surface acidity and alkalinity

TiO2 is often added with Al, Si, Zn, and other oxides when it is modified. Al or Si oxides have no apparent acidity or basicity when they exist alone, but when combined with TiO2, they exhibit firm acidity and basicity and can prepare solid superacids.

4. Surface electrical properties

TiO2 particles in the liquid (especially polar) medium will absorb opposite charges due to the load on the surface to form a diffused electric double layer, which increases the effective diameter of the particles. When the particles are close to each other, each has the same charge. Repulsion is conducive to the stability of the dispersion system. For example, the surface of TiO2 coated with Al2O3 has a positive charge, while the TiO2 treated with SiO2 has a negative charge.

Trunnano is one of the largest titanium dioxide producers in the world. There are titanium dioxide powders and photocatalyst products in various particle sizes. If necessary, please contact Dr. Leo. Email: brad@ihpa.net.