Barium titanate (Barium titanate) molecular formula BaTi03, relative molecular mass 233.21.



1. Product performance



Barium titanate, also known as barium metatatate, white crystalline powder, there are four different crystal types: higher than 120℃, stable is cubic crystal shape; At 5 ~ 120℃, the tetragonal type is stable. At 5 ~ 90℃, the rhombic crystal is stable. Below 90℃, the rhombic hexahedral type is stable. Barium titanate is soluble in concentrated hydrochloric acid and hydrofluoric acid, but not soluble in water or alkali solution. The melting point is 1625℃, the density is 6.08g/cm3, and the dielectric constant is very high.



2. Production methods



(1) There are usually two solid-state methods. One is the barium carbonate method. Barium carbonate reacts with titanium dioxide at high temperature to produce barium titanate and carbon dioxide.



Write BaC03 + TiO2 - BaTi03 + CO2



Another method is to take barium nitrate as raw material, react with titanium dioxide at high temperature to produce barium titanate and nitrous oxide.



Ba (NO3) 2 + TiO2 - BaTi03 + N2O5 write



Because the by-product of solid phase method is gas phase and easy to be separated from the product, it is often used in the preparation of reagent grade or high purity barium titanate.



(2) Carbonate precipitation method USES TiC14, BaCO3 and ammonium bicarbonate as main raw materials. The process is to prepare a certain concentration of TiC14 solution and mix it with BaC03 slurry according to the equal molar ratio. Coprecipitates of metatitic acid and barium carbonate are formed by adding to the mixture of NH4HCO3 and NH3 at room temperature.



TiC14 HCL + H2O - TiOCl2 + 2



BaC03 + 2 hc1 - write BaC12 + H2O + CO2



TiOC12 + BaC12 + 4 nh4hco3 - H2Ti03 + BaC03 left + H2O + 3 + 4 nh4cl our fleet to write



The obtained coprecipitates were filtered and washed, and the impurities (C1-) in the precipitation were removed, and then dried and crushed. Then, BaTiO3 powder is obtained by calcination at a temperature lower than 1000℃ for 2 ~ 3h. The purity of the product can generally reach 99.5% and the average particle size is less than lum.



Ammonium carbonate can also be used instead of ammonium bicarbonate as a precipitator with a similar production process.



(3) Barium hydroxide hydrothermal method: The raw material containing barium is barium hydroxide, and the raw material containing titanium is titanium tetrachloride (TiC14), titanium dichlorooxide and titanium sulfate. The production process is divided into two steps. The first step is hydrolysis of TiCI, TiOCl2 or TiOSO4 to prepare Ti02·xH20. Hydrolysis can be carried out at room temperature or under heating conditions. After hydrolysis, impurities such as C1- or S042- embedded in the sediment can be removed by filtration and washing; The second step is to mix Ti02·xH2O with Ba(OH)2 solution, react under certain pressure and temperature, and get BaTi03, which is then filtered, washed and dried to get the finished product.



(4) Oxalic acid method the production process of this method is that TiC14, BaC03 (or BaC12) and H2C204 are prepared into a solution of certain concentration. After purification and removal of Sr, Ca, Mg and other impurities, TiC14 solution is mixed with the amount of BaCl2 solution and other substances, heated to about 70℃, and then H2C204 solution is added, the amount of which is 2 times of the amount of barium (measured by the amount of substances). At a temperature of 70℃ or so, stir and mix for 3 ~ 5h to produce barium oxalate precipitation.







After 3-5h reaction to obtain the above precipitation, liquid-solid separation is carried out through filtration, and the sediment is washed to remove the impurities such as chlorine ion and so on. The sediment is then dried and sent to the tunnel kiln for calcining. The calcining temperature is controlled at 900 ~ 920℃ and the calcining time is 2 ~ 3h.







The calcined products were screened out by barium titanate. This method is widely used at present.



(5) Alcohol salt method, also known as organic method, with barium alcohol and titanium alcohol as raw materials.



One method is to dissolve the titanium alcohol and barium alcohol in an organic solvent at an equal molar ratio, and then pass the mixture into the atomizer together with combustion gas (such as oxygen or air) for ignition and combustion. At this time, the titanium alcohol and barium alcohol decompose and react to produce barium titanate.







BaTi03 was prepared by this method. The particle size of the product could be controlled by the concentration of titanium alcohol and barium alcohol in the raw liquid. The average particle size was within the range of 0.01 ~ 0.2um. The purity can reach 99.9%.



The other method is alcohol-brine hydrolysis, in which BaTi03 is prepared by hydrolysis of a mixture of barium diisopropanol and titanium tetratert-pentanol. The technological process is to stir the amount of the above two kinds of alcohol solution and other substances mixed, then refluxed mixing, hydrolysis in pure water, then BaTi03 precipitation can be obtained. After the precipitation was separated, washed and dried, the high purity ultrafine BaTi03 powder was obtained.



Ba (OC3H7) 2 + H2O + 2 c3h7oh - BaO



Ti (OC5H11) 4 + 4 + 2 h20 - Ti02 c5h  11 oh



BaO + Ti02 - BaTi03



The purity of BaTiO3 obtained by this method is 99.99%. Granularity is also very fine, average granularity 0. Lum.



Using Ti02 (98% purity) and Ba(OH)2·8H20 (98% purity) as raw materials and catechol as coordination agent, the (NH)2 [Ti(C6H402) 3] ·2H2O was first prepared and then converted into barium salt, and then calcined to obtain BaTi03. Because of pyrocatechol on titanium (Ⅳ) has a strong coordination ability, accurate and easy control, molar ratio of Ba/Ti so generated BaTi03 has high purity, small size, good uniformity and lower sintering temperature. The main chemical reactions in the preparation process are as follows:



3C6H6O2+6NH3·H2O+Ti(SO4)2→ (NH4)2 [Ti(C6H402)3] ·2H20↓+2(NH4)2S04+4H2O



(NH4)2[Ti(C6H402)3] ·2H20+Ba(OH)2·8H20→Ba[Ti(C6H402)3] ·3H20+2NH3↑+9H20







This method can be used to prepare high purity ultrafine barium titanate for electronic industry.



3. The process flow



(1) solid phase method



Barium carbonate method













(2) Carbonate precipitation method







(3) Barium hydroxide hydrothermal method







(4) Oxalic acid precipitation method







(5) alkoxide







(6) Pyrocatechol titanium-barium method







4. Technology formula







5. The production process



(1) Solid phase method



Barium carbonate method. Equal mole of BaC03 and TiO2 were put into an organic ball mill made of polyethylene and other materials. Agate ball and pure water were added in proportion and mixed by wet ball mill. The purpose of ball mill is to mix two kinds of materials evenly. Second, grind the material to a certain particle size.



Attention should be paid to the lining of the ball mill and the selection of ball material in the mixture, as far as possible without mixing harmful impurities. The shape of the ball mill and its speed directly affect the mixing and grinding efficiency. The grinding efficiency decreases with the increase of time, so it is limited to improve the mixing effect by prolonging the ball grinding time. Generally, the ball grinding time is controlled in the range of 24 ~ 36h. The ratio of material, ball and water is generally 1:2:2. Specific operation, according to the water absorption of the material, paste viscosity of the above proportion to make some appropriate adjustment, in order to achieve a better mixing effect.



In industrial scale production, it is unavoidable to mix with iron and other harmful impurities when mixing, which can be removed by iron removal equipment. For example, by passing the ball ground slurry through a large electromagnet, the scrap iron in the slurry will be adsorbed on the magnetic steel grid and removed.



After the ball grinding iron pulp through the filter (or pressure filter) dehydration sent to dry, drying can be carried out in a drying box, can also use a large drying equipment with a blower. After drying, the material is calcined in the tunnel kiln. The calcination temperature is generally controlled within the range of 1250 ~ 1300℃ and maintained at this temperature for 2.5 ~ 3.5h. The key link of this method is to control the calcining temperature and time of tunnel kiln, which has great influence on the product quality.



The product BaTi03 obtained by calcination needs to be ground before powder can be obtained.



The method is simple and easy to operate, and the cost is low. However, the disadvantage is that it must rely on mechanical crushing, and the crushing for a long time will often make the material seriously polluted. At the same time, because the material is not easy to mix evenly, the reaction is also difficult to carry out very thoroughly. Therefore, the purity of BaTi03 produced by this method is low, which is generally about 98.5%; The particle size is also large, and the average particle size of the powder is generally about 2 um.



Laboratory method: 9.0g titanium dioxide and 23.6g barium carbonate were put into 50mL platinum crucible, and then covered with 66g anhydrous potassium fluoride. At the beginning, without cover, slowly heat, make the material melt. The lid was then tightly closed and kept at 1,160 ℃ for 12h, then cooled at 25℃ per hour and cooled to 900℃. A flux was added and slowly cooled to room temperature. The reaction material was immersed in hot water and barium titanate was extracted.



Barium nitrate method. Mix titanium dioxide and barium nitrate in equal quantities and heat them slowly at 500 ~ 600℃ for 3h. Then the material was crushed and burned at 1000℃ to obtain higher purity barium titanate.



(2) The carbonate precipitation method USES metataric acid as raw material and ammonium carbonate as precipitant.



First, the metatonic acid was purified and the impurities were removed to obtain the high purity metatonic acid. Then the pulping was carried out, and the appropriate temperature was controlled during the pulping process. Soluble barium salt [such as BaC12,Ba(N03)2] and precipitant (NH4)2CO3 were added slowly, and mixed and stirred for 1-2h. After the complete precipitation reaction, filter and wash to remove impurities in the sediment. The sediment is then dried, crushed and then calcined. The calcination temperature is controlled within the range of 900 ~ 960℃. After calcination for 2 ~ 3h, BaTi03 powder is obtained. The purity of BaTi03 was 99.7% and the average particle size was 0.4um.



(3) The pressure and temperature used in the hydrothermal method with barium hydroxide are different. For example, the pressure used in Switzerland is 2 ~ 50MPa and the temperature is 200 ~ 370℃. In Japan, the pressure is 0.5mpa and the temperature is about 150℃. The pressure used in Denmark is 30 ~ 60MPa and the temperature is 380 ~ 450℃. High pressure and temperature can improve the reaction rate and shorten the reaction time. But there are also atmospheric pressure, the temperature is the boiling temperature of the reaction material. The reaction time of atmospheric hydrothermal method is long, and the reaction can only be completed by about l0h under the condition of intense stirring. The particle size of BaTi03 prepared by hydrothermal method is generally very small, but the purity of the product is often not very ideal. The main reason is that Ba(OH)2 is easy to absorb C02 in the air and partly produces BaCO3, thus affecting the purity of the product. To prevent the formation of BaCO3, the operation can be protected by nitrogen. The product can also be washed and separated with dilute acetic acid solution to remove BaC03, and then washed and dried with pure water, so that the product purity can reach 99.5% or above.



(4) Barium carbonate is reacted with hydrochloric acid to form barium chloride solution by oxalate precipitation. TiC14 and oxalic acid were respectively dissolved in water to form solutions, and the three solutions were refined. After the mixture of BaCl2 and TiCl4 solution, 2mol of oxalic acid solution was added at 70 ~ 100℃ to precipitate barium oxalate, which was filtered, washed to Cl- free and dried. The barium titanate product was calcined, screened and packed in the furnace at 700 ~ 1000℃.



(5) The alkali-salt method dissolves titanium alcohol and barium alcohol in organic solvents, respectively, and then passes this mixture with air (or oxygen) into the atomizer for ignition and combustion. The heat generated breaks down titanium alcohol and barium alcohol, and the barium and titanium react directly to form very fine single crystal BaTi03. The particle size can be controlled by the concentration of the raw material and the crystal shape by the calcination temperature.



(6) The pyrocatechol titanium-barium method adds titanium dioxide to a certain amount of concentrated sulfuric acid and ammonium sulfate solution, and heats it to dissolve it. After cooling to room temperature will add it to the ammonia solution of catechol, solution of pH control in the range of 12 ~ 13, almost completely into the titanium rust-colored catechol and titanium (Ⅳ) ammonium acid precipitation. After filtration, the obtained precipitation was dissolved in appropriate amount of water, heated to 70℃, and Ba(OH)2 solution was added while stirring. The quantity ratio of ba-Ti in the material is controlled at about 1:1. Join Ba (OH) 2 solution, namely generated brown catechol and titanium (Ⅳ) barium acid precipitation. After filtering, washing and drying, the satins were burned at 800℃ for about 4h, and then the product BaTi03 was obtained.



The BaTiO3 produced by this method has a purity of 99.96%, the average particle size of the powder is less than 0.2um, and the sintering temperature is about 1250℃. Compared with the solid phase production of BaTi03, the sintering temperature can be reduced by 60-100 ℃.



6. Product standards



(1) Industrial Specifications (Electronic Industry)



Content (BaTi03) ≥ 99.88%.



Particle size: 0.01 ~ 0.2um







(2) Fuji series product Specifications (Japan)







7. Product use



The permittivity of BaTi03 is about 1700, and it can be increased to more than 20000 by doping. Its insulation performance is good, the room temperature when the resistivity is more than 1012 Ω / cm, but if the BaTi03 adding trace amounts of rare earth elements, the resistivity can be down to about 10-2 ~ 104 Ω / cm. At the same time, if the temperature exceeds the Curie temperature of the material, its resistivity in the temperature range of tens of degrees Celsius can increase by 3 ~ 10 orders of magnitude, that is, PTC effect. When BaTi03 under the action of direct current field; There is a persistent polarization effect below 120℃ at the Curie point. The polarized BaTi03 has ferroelectric and piezoelectric properties. Because of the above electrical properties, barium titanate has become an important raw material for many electronic components.



Barium titanate is mainly used in the manufacture of high dielectric ceramic capacitors, laminated ceramic dielectric vessels and positive temperature coefficient thermistor (or PTC thermistor) and other electronic components.



Semiconductor ceramics can be prepared by adding trace rare earth oxides to high purity BaTi03. The characteristic of semiconductor ceramics is that their electrical conductivity varies with the environment. For example, resistance changes when temperature or voltage changes, or when they are exposed to certain gases or moisture. Therefore, semiconductor ceramics are widely used as sensor materials, used to make thermistors and other electronic components.