Light-colored Conductive TiO₂ With Fiber Shape:Controllable Synthesis And Coating Application

Conductive TiO₂ whiskers is one of the functional TiO₂ material,which possess multiple advantages of high whiteness,excellent electrical conductivity,low percolation threshold and strong stability.In recent years,as a novel light-colored conductive filler,it is widely explored and used in the area of microelectronic technology with conductive or antistatic requirement,such as conductive coating,chemical fiber,paper,ink,and etc.However,there are few reports on the production and sales of related products in China due to the lack of preparation technology of TiO₂ whiskers,let lone meeting the domestic demand.In this work,potassium titanate(K₂Ti_n O_2n+1,1?n?8)whiskers were prepared with the method of calcination,in which nano TiO₂ paticle was used as titantium source.Then,high-purity TiO₂ whiskers with controlled crystalline phase and morphology could be obtained through K⁺/H⁺exchange and calcination of dehydration.Based on that,co-precipitation was applied to assist the process of antimony doped tin oxide?ATO?loading enabling the efficient synthesis of light-colored ATO@TiO₂whiskers with core-shell structure.At last,obtained conductive whiskers were introduced into waterborne polyurethane?WPU?emulsion to prepare the conductive paint for the surface coating of the polyester fabrics.At the same time,it is necessary that the performance of the homemade ATO@TiO₂ conductive whiskers should be compared with that of the current commercial conductive TiO₂ product to prove it prominent properties and prospect of industrialization.The main research content and conclusions are as follows:?1?Anatase nano TiO₂?particle,200±50 nm?was used as titantium source and uniformly mixed with K₂CO₃ solution.Thermogravimetric analysis?TG?was performed on the mixture of TiO₂-K₂CO₃?Ti/K=3?at 50-1000?to determine the reaction temperature range,and the phase components of calcined products within these temperature ranges were discussed to predict the reaction mechanism of the blends at high temperatures.Also,VLS theory was used to explain the growth process and phenomena of whisker crystal.The results shown that the whole reaction and growth process of the K₂Ti₄O₉ whisker was in accordance with the"melt induced growth model",during which potassium rich liquid?K₂O?and intermediates of various titanates were generated.These oriented eutectic whiskers are continuously melted to induce the whisker to grow along the axial direction and finally shape.?2?Based on the special layered structure of the K₂Ti₄O₉ whisker,by controlling the hydration ratio?m?H₂O?/m?K₂Ti₄O₉??and pH value of the reaction system,the complete K⁺/H⁺exchange can be achieved to prepare the high purity hydrated titanic acid?TiO₂·xH₂O?whisker.The experimental results shown that the K⁺replacement rate of>99%can be realized by repeating the ion exchange reaction process for four times with the hydration ratio of 20,20,10 and 10 when the pH is 1.5-2.The results of the kinetic model fitting analysis of hydration process shown that the ion exchange process can be described by quasi-second-order kinetic equation,which included multiple steps such as adsorption,internal and external liquid film diffusion,and the rate control step is chemical reaction process.?3?The high purity TiO₂·xH₂O whisker was used as the raw material,and the controlled crystalline phase and morphology were taken as the optimization targets to investigate the influence of calcining process on the morphology and properties of the whisker.TiO₂ whiskers with different crystalline phase and no defects in morphology were prepared by adjusting the calcination temperature.Meanwhile,the variation of whisker morphology is described based on the analysis results.In addition,nano-TiO₂ gel was added in the calcination process to improve the quality,so as to promote the crystal transformation and adjust the morphology at the same time.The process of high temperature heat treatment enabled the porous TiO₂·xH₂O whisker rearrangement or even recombination of single crystal unit,resulting in the continuous change of whisker morphology and even the transformation of crystal phase.The higher the temperature,the shorter the length and the larger the diameter.Complete anatase and rutile TiO₂whiskers were obtained at 700?and 1100?respectively.However,from the perspective of whisker yield with complete morphology,the former remained above 95%,while the latter was largely damaged and could not be used.Although the morphology was improved to some extent by the doping and calcination of nano TiO₂ gel,and the crystal transformation temperature was reduced,the damage rate was still more than 50%,so the calcination process of rutile TiO₂ whisker needed further research?4?The traditional liquid phase co-precipitation coating process was optimized.On one hand,sodium hsametaphosphate?SHMP?was used for the pretreatment of TiO₂ whisker to improve the dispersion of the carrier and increase the active points on the whisker surface through the adsorption of PO^3-group,thus providing a guarantee for efficient coating process.On the other hand,the orthogonal experiment was used to optimize the four parameters?coating ratio?mSnO₂/mTiO₂?,doping ratio?mSb₂O₅/mSnO₂?,water bath ratio?mTiO₂/mH₂O?and calcination temperature?of the coating process by taking the surface resistivity and whiteness of the whisker as the optimization.Experimental data shown that whiteness and surface resistivity are contradictory optimization indexes,which cannot be optimized together.From the perspective of usability and raw material saving,suitable optimization processes were selected as coating ratio of 25 wt%,doping ratio of 10 wt%,bath ratio of 1:10 and calcination temperature of 500?.In this process,the obtained ATO@TiO₂ conductive whiskers possessed the resistivity of 200±25?,and whiteness value of 78±1.The results of whisker morphology shown that the optimized coating process significantly weakens the particle sensation on the whisker surface,and the extinction effect of TiO₂ significantly improved the whiteness of the conductive whisker.The crystal phase and surface element analysis of whiskers proved that Sb⁵⁺is successfully doped into the SnO₂ crystal lattice.At last,the oil absorption value of ATO@TiO₂ conductive whisker was tested.The homemade product is 56.3±5 g/100g,which had obvious advantages over the traditional carbon black conductive powder and was also close to the commercial-grade conductive TiO₂ products in the market.?5?The homemade ATO@TiO₂ conductive whiskers were uniformly blended with WPU to prepare conductive coating.Conductive/antistatic polyester fiber coated fabric was prepared by coating finishing.At the same time,comparison samples of three commercial grade conductive titanium whites were made.Compared with particle type conductive fillers?>40 wt%?,one-dimensional conductive fillers form a complex conductive network through line-to-line connection,thus fabrics owing a lower percolation threshold?7-12 wt%?.Through experimental analysis:homemade ATO@TiO₂ conductive whisker possess a threshold of 12 wt%,after 50microns coating fabric surface resistance was less than 10⁶?,and whiteness value was 77.Also,the coated fabric still maintained a stable charge escape ability after a long time of washing,lighting and heat treatment.