Process Optimization Of Hydrothermal Synthesis Of Strontium Titanate And Its Mechanism

Strontium titanate is a perovskite oxide with white cubic crystal.It is widely used in electronic ceramics and other fields.It has the advantages of high dielectric constant,low loss and good thermal stability.Because of its excellent piezoelectric,ferroelectric properties and is widely used in the fields of electronic,ceramic and mechanical industries.Band gap of SrTiO3 is 3.2 eV,high band gap,good photocatalytic activity and excellent redox catalytic activity,SrTiO3 has attracted extensive attention in the field of photocatalysis.The conventional synthesis of SrTiO3 is by solid-state reaction between SrCO3 and TiO2 at high temperature,which requires high temperature calcination.The powders obtained with this method usually have serious agglomeration,large particle size,considerable impurity,and irregular particle morphologies,which are not suitable for neither photocatalytic applications nor the processing of dense ceramics with submicron or nanoparticles.In recent years,many wet-chemical methods to synthesize SrTiO3 perovskite ceramic materials,including sol-gel method,combustion method,solution-precipitation method,solvothermal method,hydrothermal routes and mechanochemical method.Among them,hydrothermal synthesis does not require annealing treatment to improve crystallinity,and it has the advantages of short process,easy operation,and controllable product specifications.In this paper,SrTiOnanopowders were synthesized by one-step hydrothermal method using cheap and readily available anatase titanium dioxide(TiO2)as titanium source and strontium hydroxide octahydrate(Sr(OH)2·8H2O)as strontium source.Through single factor and multi-factor orthogonal experiments,the effects of process parameters such as reaction temperature,reaction time,alkaline medium concentration,reactant concentration,Sr/Ti molar ratio and oleic acid addition concentration on product size,crystal structure,morphology,grain size,yield,purity and agglomeration were systematically investigated.The products with regular morphology,narrow particle size distribution,high purity and good dispersion were synthesized.The mechanism of synthesis was explored.The main conclusions are as follows:Firstly,regulation of product morphology:the products showed agglomeration,the agglomeration of SrTiO3 nanoparticles are weakened by the addition of oleic acid and dispersion increased.When the oleic acid concentration is 3 vol.%,the product has regular morphology,uniform grain size and good dispersibility.Secondly,regulation of product purity:within the experimental range,with the increase of reaction temperature and alkaline medium concentration,the purity of the SrTiO3 products are increased,and the concentration of the reactants has little effect on the purity of the product.when the molar ratio of Sr/Ti is 1.25 and 1.00,the peak of TiO2 is present in the product;When the molar ratio of/Ti is 0.75 and 0.5,there is no impurity peak in the product,which is pure SrTiO3,but the crystallinity deteriorates under Sr/Ti molar ratio is 0.5.Pure SrTiO3 can be synthesized under the concentration of reactant is 0.752 mol/L,the concentration of NaOH solution is 25 mol/L,the reaction time is 20 h,the Sr/Ti molar retio is 0.75 and the reaction temperature is 150 ?.Thirdly,the result shows that the particle size of SrTiO3 nanoparticles increases with the increase of reaction temperature,Sr/Ti molar ratio,alkaline medium concentration,reaction temperature and reaction time.The particle size measured by laser particle size analyzer mainly distributes in the range of 0.1-1 ?m.The particle size distribution range is the narrowest when the reaction temperature is 200 ?,the molar ratio of Sr/Ti is 1,the reaction time is 30 h,the concentration of reactant is 0.752 mol/L,the concentration of NaOH solution is 25 mol/L,and the concentration of oleic acid is 3 vol.%,the size is around 0.1 ?m.Fourthly,regulation of microstructure:within the experimental range,with the increase of reaction time and Sr/Ti molar ratio,the grain size of SrTiO3 nanoparticles tends to increase.The grain size of SrTiO3 nanoparticles is mainly distributed between 35-65 nm calculated by Scherrer formula.The products synthesized are perovskite cubic SrTiOnanoparticles with uniform size and regular morphology.Fifthly,synthesis mechanism research:the influence of oleic acid,reaction time and Sr/Ti mole ratio on microstructures of SrTi03 nanoparticles can be explained by interparticle force,Ostwald Ripening and crystal nucleation,respectively.The reaction mechanism of this experiment is consistent with the dissolution-precipitation reaction mechanism.