Effect Of Physically Doped Silicon On High Temperature Phase Transition Of Titanium Dioxide

Titanium dioxide is widely used in various fields because of its good chemical and physical properties.However,there are three crystal forms of titanium dioxide: anatase,rutile and plate titanium.Anatase and rutile are the most widely used.However,the properties of anatase and rutile are different.In order to obtain different crystal forms of titanium dioxide for production use.How to control the crystal structure of anatase and rutile is particularly important.The amorphous titanium dioxide can be transformed into anatase when heated to a certain temperature.The crystalline transition temperature is about 200 ~400 C.The transition temperature from anatase to rutile is about 500 ~700 C.The crystalline transition temperature is affected by precursors,heating rate,atmosphere and dopants.It was found that doped silica inhibited and promoted the crystalline transformation of titanium dioxide from anatase to rutile.In situ XRD and DTA were used to study the real-time phase and phase transition temperature of titanium with different silicon content in situ at high temperature to find out the effect of silicon content on the temperature point of crystal transformation of titanium dioxide.Meanwhile,the mechanism of the effect of physically doped silicon on phase transition of titanium dioxide was revealed by FTIR analysis and the change of elemental orbital peak and phase of XPS.This paper draws the following conclusions:1)Different physical doping amount of silicon inhibits the phase transition from amorphous to anatase.The mechanism is that the doping of silicon refines the grain size of titanium dioxide,thus inhibiting the transformation of titanium dioxide from amorphous to anatase.2)The real-time phase transition from anatase to rutile is accelerated and then suppressed with the increase of silicon doping,and the critical value of the transition is 7.5% of silicon content.3)The results of Ritveld full spectrum fitting refined crystal structure analysis of high temperature in situ diffraction patterns show that the lattice constants a,b and c of titaniumdioxide with silicon addition are smaller than those without silicon addition.The lattice distortion will occur when silicon ions displace titanium ions in the lattice of titanium dioxide,which hinders the transformation of titanium dioxide from anatase to rutile.However,the substitution solid solution formed by substitution of titanium ions in titanium dioxide lattice by silicon ions has a certain solid solubility.When the silicon content exceeds a certain amount,silicon will become the crystalline core of rutile titanium dioxide,which will reduce the nucleation energy and promote phase transformation.4)FTIR and XPS analysis were carried out on silicon-doped titanium dioxide.FTIR analysis showed that the peak of Si-O-Si shifted after doping silicon,which may be that silicon ions entered the lattice of titanium dioxide.Then,it was found by XPS analysis that Ti-O-Si was produced in the phase transformation process of silicon-doped titanium dioxide.It was verified again that there was a substitution solid solution formed by silicon ion replacing titanium ion in the lattice of titanium dioxide in the phase transformation process of titanium dioxide from anatase to rutile.5)The real-time percentage of anatase and rutile during phase transformation was calculated by Rietveld full-spectrum fitting method with 5%,7.5% and 10% titanium dioxide doped,and the effect of holding time on the crystal transformation was investigated.The experimental results show that the percentage of rutile does not always increase with the extension of holding time,but tends to an extreme value after a certain holding time.And with the increase of insulation temperature,this extreme value increases in turn.