Study On Microwave Dielectric Properties And Heating Behavior Of Titanic Acid And Its Mixture

The sulfuric acid method is the mainstream process for the production of Ti O₂ in China,and the calcination decomposition of metatitanic acid is one of the key links.However,the conventional calcination of metatitanic acid has some problems,such as insufficient calcination,high consumption and low efficiency,long crystal transformation time of Ti O₂ and insufficient transformation.As a new type of green heating method,microwave has the characteristics of internal heating and bulk heating.Titanium dioxide and titanium carbide can not only induce the temperature rise of metatitanic acid,but also provide the nucleation seed of metatitanic acid calcination and accelerate the growth of crystal nucleus.Therefore,it is of great significance to study the microwave absorption properties of metatitanic acid and its mixtures,screen suitable inducers to improve microwave absorption properties,promote the transformation of Ti O₂ crystal form,and accelerate the nucleation and growth of Ti O₂ for the preparation of high-grade rutile Ti O₂（R-Ti O₂）by microwave calcination of metatitanic acid.In this paper,the microwave dielectric properties of metatitanic acid,metatitanic acid-R-Ti O₂,and metatitanic acid-titanium carbide（Ti C）mixture were systematically studied by the microwave resonant cavity perturbation method.Simultaneously,the electromagnetic reflection loss（RL）of metatitanic acid and its mixture was calculated based on the transmission line theory.The heating behavior in the microwave field and the crystal transformation process of Ti O₂ were explored.R-Ti O₂ was prepared by microwave high-temperature calcination.The specific research results are as follows:（1）Microwave dielectric properties and heating behavior of metatitanic acid and R-Ti O₂mixture.The relative dielectric constant of the mixture of metatitanic acid and R-Ti O₂ is proportional to the apparent density of the material.When the apparent density is 0.475 g/cm³,the dielectric loss factor reaches the maximum value,and the dielectric properties are the best.The high-temperature dielectric parameters of the mixture decreased due to the dehydration process of metatitanic acid at 20-500°C.Between 500-900°C,the change of the dielectric constant of the mixture is relatively stable,and the desulfurization reaction of metatitanic acid is mainly carried out in this stage.Finally,the 20%R-Ti O₂ mixture began to crystal transition at about 950°C,and its microwave dielectric properties were slightly improved compared to metatitanic acid.The heating rate of metatitanic acid and mixture in microwave field is positively correlated with microwave output power.It is negatively correlated with the amount of material.At the same time,the heating rate increases with the increase of the proportion of R-type Ti O₂additive.（2）Microwave dielectric properties and heating behavior of metatitanic acid-titanium carbide mixture.When the apparent density of the material increases to 0.55g/cm³,the optimal dielectric properties can be obtained.In the whole temperature range（20-1000°C）,the mixture material has excellent microwave response ability compared with metatitanic acid raw material.The material temperature is lower than 500°C,the dielectric properties of metatitanic acid are poor due to dehydration reaction.When the temperature range is between 500-800°C,the dielectric properties are relatively stable;when the temperature is higher than 850°C,the dielectric properties of the mixture are significantly enhanced,which is mainly related to the Ti O₂ phase transition reaction induced by additives at high temperature and the conductivity.It shows that titanium carbide additives can effectively promote the phase transformation reaction of Ti O₂ and accelerate the nucleation and growth of Ti O₂ grains when microwave heating metatitanic acid-titanium carbide mixture.（3）Preparation of Ti O₂ by microwave calcination of metatitanic acid and its mixture.The phase transition reaction of Ti O₂ occurs at 950°C for the metatitanic acid-20%R-type Ti O₂ mixture.When the calcination temperature is further increased to 1000°C,the prepared Ti O₂ is a two-phase structure of anatase phase and rutile phase.The XRD diffraction peak of R-Ti O₂ appeared at 850°C in the metatitanic acid-9%Ti C mixture.When the calcination temperature was 1000°C,the superlattice diffraction peak of the prepared Ti O₂ was completely matched with the pure R-Ti O₂ phase.Therefore,compared with the addition of R-Ti O₂,Ti C is more suitable for microwave calcination of metatitanic acid to prepare rutile Ti O₂ inducer.