Titanium dioxide is an inorganic compound with the chemical formula of TiOtwoIt is a white solid or powder amphoteric oxide with a molecular weight of 79.866. It has non-toxic, the best opacity, the best whiteness and brightness, and is considered to be a white pigment with the best performance in the world today.Titanium dioxide has strong adhesion, is not easy to cause chemical changes, and is always white.It is widely used in coating, plastic, paper making, printing ink, chemical fiber, rubber, cosmetics and other industries.Its melting point is very high, and it is also used to make fire-resistant glass, glaze, enamel, clay, high-temperature experimental utensils, etc.Titanium dioxide can be extracted from rutile by acid decomposition or obtained from titanium tetrachloride decomposition.There are three allotropes of titanium dioxide in nature: rutile, anatase and plate titanium, and there are also several synthetic crystal forms.
On October 27, 2017, the list of carcinogens published by the International Agency for Research on Cancer of the World Health Organization (WHO) was preliminarily sorted out for reference, and titanium dioxide was included in the list of Category 2B carcinogens.[3]
Among the commonly used white pigments, titanium dioxide has the smallest relative density. Among white pigments of the same quality, titanium dioxide has the largest surface area and the highest pigment volume.
Pigment name
Density/(g/cm ³)
anatase titanium dioxide
3.8~3.9
Rutile titanium dioxide
4.2~4.3
Plate titanium dioxide
4.12~4.23
Dielectric constant
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Because of its high dielectric constant, titanium dioxide has excellent electrical properties.When determining some physical properties of titanium dioxide, the crystallization 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 this axis, it is 90, and the average value of its powder is 114.The dielectric constant of anatase titanium dioxide is only 48.
conductivity
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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 ℃.Slightly reducing the oxygen content will have a special impact on its conductivitytwo）Conductivity<10-10s/cm，And TiOone point nine nine nine fiveThe conductivity of is up to 10-1s/cm。The dielectric constant and semiconductor properties of rutile titanium dioxide are very important for the electronic industry, which uses these characteristics to produce electronic components such as ceramic capacitors.
Rutile crystal structure
hardness
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According to the Mohs hardness scale of 10 points, the rutile type titanium dioxide is 6~6.5, and the anatase type titanium dioxide is 5.5~6.0. Therefore, the anatase type is used in chemical fiber matting to avoid abrasion of the spinneret hole.
Melting and boiling points
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Since both anatase and anatase titanium dioxide will transform into rutile at high temperature, the melting point and boiling point of both anatase and anatase titanium dioxide do not actually exist.Only rutile titanium dioxide has a melting point and a 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 air is 1879 ℃. The melting point is related to the purity of titanium dioxide.The boiling point of rutile titanium dioxide is (3200 ± 300) K. At this high temperature, titanium dioxide is slightly volatile.
Hygroscopicity
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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 has high hygroscopicity.
The hygroscopicity of titanium dioxide is also related to surface treatment and properties.
thermal stability
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Titanium dioxide belongs to the material with good thermal stability, and the general dosage is 0.01%~0.12%.
3. Although the solution of titanium dioxide dissolved in hot concentrated sulfuric acid is acidic, it can be hydrolyzed when heated and boiled to obtain acid and alkali insoluble titanium dioxidehydrous titanium dioxide (beta titanic acid).If alkali is added to the newly prepared titanium hydrochloric acid solution, fresh hydrated titanium dioxide (α - titanic acid) can be obtained. Its reaction activity is greater than that of β - titanic acid, and it can be dissolved in dilute acid and concentrated alkali.After dissolving in concentrated sodium hydroxide solution, the chemical formula Na can be separated from the solutiontwoTiOthree·HtwoO hydrated titanate.
4. Titanium dioxide and carbon powder are pressed into clusters, and then heated to 1070-1170K to produce gaseousTitanium tetrachloride。
TiOtwo+CClfour=TiClfour↑+2COtwo↑ (The reaction is completed at 770K)[2]
Surface properties
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1. Superhydrophilicity of surface
It is believed that under light conditions, TiOtwoThe super hydrophilicity of the surface results from the change of its surface structure.Under ultraviolet light, TiOtwoThe valence band electrons are excited to the conduction band, and the electrons and holes are directed to TiOtwoSurface migration generates electron hole pairs on the surface, electrons react with Ti, and holes react with surface bridge oxygen ions to form positive trivalent titanium ions and oxygen vacancies respectively.At this time, the hydrolytic dissociation in the air is adsorbed in the oxygen vacancy and becomes the chemisorbed water, which can further adsorb the water in the air and form a physical adsorption layer.
2. Surface hydroxyl
Compared with metal oxides of other semiconductor semi metal materials, TiOtwoThe polarity of Ti-O bond is large, and the water adsorbed on the surface is easily dissociated due to polarization, so hydroxyl groups are easily formed.This surface hydroxyl can improve TiOtwoAs adsorbent and various monomer properties, it provides convenience for surface modification.
3. Surface acidity and alkalinity
TiOtwoAl, Si, Zn and other oxides are often added in the modification. When Al or Si oxides exist alone, they have no obvious acid-base property, but they are similar to TiOtwoThe composite shows strong acidity and alkalinity, and can be used to prepare solid superacid.
4. Surface electricity
TiOtwoThe particles in the liquid (especially polar) medium will absorb opposite charges due to the surface charges and form a diffusion double electric layer, which will increase the effective diameter of particles. When particles are close to each other, they will repel each other due to the same charges, which is conducive to the stability of the dispersion system.As per AltwoOthreeCoated TiOtwoThe surface has positive charge, and SiOtwoTiO processedtwoIt is negatively charged.
Calculate chemical data
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Reference value for drainage parameter calculation (XlogP): None
Number of hydrogen bond donors: 0
Number of hydrogen bond receptors: 2
Number of rotatable chemical bonds: 0
Number of tautomers: 0
Topological molecular polar surface area: 34.1
Number of heavy atoms: 3
Surface charge: 0
Complexity: 18.3
Number of isotope atoms: 0
Determine the number of atomic structure centers: 0
Number of uncertain atomic structure centers: 0
Determine the number of chemical bond structure centers: 0
Number of uncertain chemical bond structure centers: 0
Number of covalent bond units: 1[1]
application area
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Industrial applications
Titanium dioxide is an important white pigment and porcelain glaze.Used in paint, ink, plastic, rubber, paper making, chemical fiber, watercolor pigment and other industries.
Titanium dioxide is the whitest thing in the world. One gram of titanium dioxide can paint an area of more than 450 square centimeters white.It is five times whiter than the common white pigment lithopone, so it is the best pigment for white paint.The titanium dioxide used as pigment in the world is more than several hundred thousand tons a year.Titanium dioxide can be added to paper to make it white and opaque, and the effect is 10 times larger than that of other substances. Therefore, titanium dioxide should be added to banknote paper and art paper[5]。
In order to lighten the color of plastics and soften the luster of rayon, titanium dioxide is sometimes added.
In the rubber industry, titanium dioxide is also used as filler of white rubber.
The photochemical properties of semiconductor titanium dioxide have enabled it 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 areas with scattering light sources.When 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, aromatic hydrocarbons and aldehydes.
Ultrafine titanium dioxide has excellent UV light shielding and transparency.It is widely used in cosmetics, wood protection, food packaging plastics, durable household films, artificial fibers and natural fibers, transparent coatings.Because of its special optical effect in metallic flash coatings, it has been valued and applied in premium car coatings.
Titanium dioxide is a semiconductor with small particle size, large specific surface area, loose porosity and rough surface. It is widely used in photoanode materials of dye-sensitized solar cells. Most researchers take titanium dioxide as the prototype, and modify it by hydrothermal method, electrospinning method and other methods, while using metal materialsPhotoanode with excellent performance is prepared by doping reaction of inorganic substances, which is used to assemble dye-sensitized solar cells[9]。
Titanium dioxide can effectively prevent the wanton growth of microorganisms with the help of photocatalysis, thereby reducing the amount of environmental harmful ingredients.The antibacterial mechanism is that titanium dioxide is activated by light, the electron hole pair interacts with oxygen molecules and hydroxyl ions, stimulates free radicals, causes chain reaction, destroys bacterial proteins, and achieves sterilization effect[4]。
Food application
The US Food and Drug Administration stipulates that titanium dioxide can be used as a white pigment in all foods, with the maximum dosage of 1g/kg.Titanium dioxide, the pigment additive, can be safely used in general colored food, subject to the following provisions:
(1) The amount of titanium dioxide shall not exceed 1% of the weight of food.
(2) Colored food shall not be used according to the special standards published in Article 401 of the decree, unless there are similar standards that allow the addition of pigments.
(3) For colored food, edible pigment additive titanium dioxide can contain appropriate diluent as a safe pigment additive, as follows: silicon dioxide, as a dispersant additive, does not exceed 2%.
Product adaptation: cold fruits, jelly, fried food, cocoa products, chocolate, chocolate products, hard candy, polishing candy, gum based candy, puffed food, candy chocolate product coating, mayonnaise, salad jam, jam, solid drinks, konjac gel food, etc.
environmental protection
Purified air
Titanium dioxide, as the catalyst of light paint pigments, is not only an environmentally safe cleaner, but also can save energy and protect environmental resources[8]。
Early Japanese and British scientists coated titanium dioxide on the pavement stone surface of urban roads to clean the road air.Titanium dioxide can be mixed with asphalt to reduce pollutants in the air.When vehicles pass by, concrete or asphalt containing titanium dioxide can purify the air and eliminate 25% to 45% of nitrogen oxides in vehicle emissions.When titanium dioxide is coated on the concrete surface, the air cleaning effect is also remarkable[7]。
Cool the Earth
In May 2012, British scientists put forward a bold idea. They believed that the goal of cooling the earth could be achieved by spraying enough titanium dioxide into the stratosphere to reflect sunlight, which could effectively offset various adverse climate factors caused by global warming.
Since titanium dioxide can effectively reflect direct sunlight, and its properties are stable, it has a good covering ability. If it is sprayed in the stratosphere, it can play a long-term role.British scientists proposed that high-altitude balloons could be used to bring this chemical into the stratosphere and then release it. Once titanium dioxide is evenly distributed in the earth's stratosphere, it can effectively reflect sunlight, thus cooling the earth.
Peter Davidson, president of Davidson Technology, a British consulting company, and a chemical engineer, is in charge of the project. He said that just by transporting 3 million tons of titanium dioxide to the Earth's stratosphere, a protective layer with a thickness of 1 mm can be formed in the Earth's stratosphere,But it can play a huge role - enough to offset the greenhouse effect caused by twice the current carbon dioxide content in the atmosphere.
Sunscreen cosmetics
Due to the great harm of ultraviolet rays to human body, developed countries have paid more attention to the research and development of sunscreen products in recent years, and have successively launched a variety of anti ultraviolet fibers, plastics, films, coatings, as well as sunscreen cream, foundation, lipstick, mousse, baking cream and other anti sun cosmetics.In recent years, China has also increased the research and production of sunscreen cosmetics[6]。
However, in the past, most sunscreens were benzophenones, o-aminobenzones, salicylates, p-aminobenzoic acids, cinnamates and other organic compounds, so they were unstable, short in life, and had large side effects. They had certain toxicity and irritation. If they were added too much, they would cause chemical allergy, and even skin cancer.As an inorganic component, nanometer titanium dioxide has excellent chemical stability, thermal stability, non migration, strong achromatic power, covering power, low corrosivity, good dispersibility, non-toxic, tasteless, non irritating, safe to use, and also has the function of sterilization and deodorization.More importantly, as mentioned above, nano titanium dioxide can not only absorb ultraviolet light, but also emit and scatter ultraviolet light, 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;Moreover, nano titanium dioxide has a blocking effect on the ultraviolet rays in the medium wave and long wave regions, unlike the organic anti ultraviolet agent, which only has a shielding effect on the ultraviolet rays in the medium wave and long wave regions.Especially because of its fine particles, high transparency of the finished product, and its ability to pass through visible light, the skin whiteness is natural when adding cosmetics, which overcomes the disadvantage that some organic substances or pigment grade titanium dioxide are opaque, making the skin appear unnatural pale.Because of this, nanometer titanium dioxide was soon widely valued and gradually replaced some organic anti ultraviolet agents, becoming a physical shielding anti ultraviolet 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, the sunscreen cosmetics market in developed countries has shown strong vitality.From 1999 to 2000, the annual sales volume of the United States reached $737 million and $765 million respectively, and that of the United Kingdom reached $245 million and $270 million. In recent years, the sales volume has increased at a rate of more than 20% and 10% respectively, and the consumption of nano titanium dioxide has also increased significantly year by year.The annual demand of nano titanium dioxide in anti ultraviolet cosmetics in Japan is more than 1000t, and the consumption in textile, plastic and rubber products is even greater.
From the perspective of the development trend of sunscreen cosmetics, firstly, inorganic sunscreen agents replace organic sunscreen agents, and secondly, bionic sunscreen.The latter is expensive and difficult to promote nowadays. The former is affordable and has excellent sunscreen performance, so it is generally optimistic.In particular, nano titanium dioxide has a good development momentum and market potential due to its superior performance and application prospects.[1]、
Sunscreen mechanism
According to the different wavelengths, the ultraviolet ray can be divided into short wave region 190 ～ 280nm, medium wave region 280 ～ 320nm, and long wave region 320 ～ 400nm.The ultraviolet ray energy in the short wave area is the highest, but it is blocked when passing through the ozone layer. Therefore, the ultraviolet rays in the medium wave area and the long wave area are generally harmful to the human body.
The strong UV resistance of titanium dioxide is due to its high refractive index and high photo activity.Its anti ultraviolet ability and mechanism are related to its particle size: when the particle size is large, the barrier to ultraviolet light is mainly reflection and scattering, and it is effective for ultraviolet light in both medium wave area and long wave area.The sun protection mechanism is simple covering, which belongs to general physical sun protection, and the sun protection ability is weak;With the decrease of particle size, light can pass through the particle surface of titanium dioxide, and the reflection and scattering of ultraviolet light in the long wave area are not obvious, while the absorption of ultraviolet light in the medium wave area is significantly enhanced.Its sunscreen mechanism is to absorb ultraviolet rays, mainly ultraviolet rays in the middle wave area.It can be seen that the sunscreen mechanism of titanium dioxide to different wavelengths of ultraviolet light is different. The barrier to ultraviolet light in the long wave area is mainly scattering, and the barrier to ultraviolet light in the medium wave area is mainly absorption.
Due to its small particle size and high activity, nanometer titanium dioxide can not only reflect and scatter ultraviolet light, but also absorb ultraviolet light, so it has a stronger barrier ability to ultraviolet light.
The absorption mechanism of titanium dioxide to ultraviolet light may be that the electronic structure of nano titanium dioxide is composed of conduction bands formed by valence electron bands and empty orbitsBand gap width(about 3.2eV) The light with high energy is absorbed, so that the electrons in the valence band are excited to the conduction band. As a result, the valence electron band is short of electrons and holes occur, forming an electron hole pair that is easy to move and has strong activity.On the one hand, such electron hole pairs can recombine with each other when various redox reactions occur, releasing energy in the form of heat or fluorescence; on the other hand, they can dissociate into free holes and free electrons that freely migrate to the lattice surface or other reaction sites in the lattice, and are immediately captured by surface groups.Normally, titanium dioxide will activate the surface water to produce surface hydroxyl groups to capture free holes and form hydroxyl radicals, and free electrons will soon combine with absorbed oxygen to produce superoxide radicals, which will also kill surrounding bacteria and viruses.It can be seen that ultraviolet radiation, surface water activation degree and oxygen absorption rate are the three basic conditions of titanium dioxide photo activity.It is precisely because nano titanium dioxide will produceFree radical, which will accelerate the aging of the skin and cause harm to the skin.Therefore, when using nano titanium dioxide as a sunscreen, we should start with weakening or eliminating the three basic conditions to weaken or eliminate its photoactivity, thereby reducing its harmfulness.
classification
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Class I: Titanium dioxide is dry ground and untreated. Class I titanium dioxide has low surface area and low oil absorption value.
Class II: Class I titanium dioxide is treated and wet ground to remove large particles, and coated with 4% silicon aluminum. It has the lowest surface area and the lowest oil absorption value.
Class III: typical ultra-fine coating grade, with organic coating.
Class IV: large coverage, which can be divided into Ⅳ a and Ⅳ b, with the coverage between 5% and 10%.Ⅳ b is mainly used in titanium dioxide with high addition, because its opacity is better than Ⅳ a[12]。
performance
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Rutile type absorbs more radiation energy at high energy (shorter wavelength) than anatase type. In other words, for rutile type titanium dioxide, in the UV wavelength range (350-400nm) with strong lethality, its reflectivity to ultraviolet light is far lower than anatase type titanium dioxide. In this case, it shares much less ultraviolet light on surrounding film-forming materials, resins, etc,The service life of these organics is long, which is why the weather resistance of rutile titanium dioxide is better than that of anatase titanium dioxide[11]。
performance
Type I
Type II
Type III
Type IV
Type a b
TiOtwo%(Minimum)
ninety-seven
ninety-three
ninety-two
ninety-one
eighty-two
Density/(g/cm ³)
four point two zero
four point zero five
four point zero five
four
three point seven zero
Surface area/(m ²/g)
6.6-7.7
12.0-12.8
11.0-18.0
seventeen point seven
twenty-eight point eight
Oil absorption value/(g/100g titanium dioxide)
fifteen
nineteen
15-19
twenty-four
thirty
Water content/(g/100g titanium dioxide)
forty
thirty
thirty
thirty-five
fifty-five
% Clad (Al/Si)
nothing
three point five
three point six
four point nine
thirteen
Dispersity
high
secondary
secondary
high
low
security information
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Safety terminology
S2：Keep out of reach of children.
Keep out of the reach of children.
S25：Avoid contact with eyes.
Avoid eye contact
S26：In case of contact with eyes， rinse immediately with plenty of water and seek medical advice.
In case of contact with eyes, please immediately flush with plenty of water and seek medical advice.
S36/37：Wear suitable protective clothing and gloves.
Wear appropriate protective clothing and gloves[10]。
Risk terminology
R10：Flammable.
Flammable.
R20/21/22：Harmful by inhalation，in contact with skin and if swallowed.
Harmful by inhalation, skin contact and if swallowed.
R36/37/38：Irritating to eyes，respiratory system and skin.
Irritating to eyes, respiratory system and skin[10]。
