Preparation Of TiO_x (x?1) Precursor And Study On Preparation Of Porous Titanium By Calcium Thermal Reduction

As a kind of metal material,porous titanium with pore structure has been widely used in biomedicine due to its similar mechanical properties and good biocompatibility with bone.The paper is based on the current research status of porous titanium,and based on the experiment which has been carried out on the preparation of titanium powder by calcium vapor reduction of titanium dioxide,proposing a new method for preparing porous titanium by calcium reduction of porous Ti O_x?x?1?precursor.Ti powder and Ti O₂ powder was used as main matrix constituent,PVA was binder,and Ammonium Carbonate was space holder.Then,the materials were mixed with a mixer and these mixtures were pressed to green sample.The sintering process was put in a vacuum tube furnace under high-purity argon atmosphere.The precursor was placed in a vacuum tank for calcium vapor and molten salt reduction,respectively,and the by-products produced by reduction are removed by acid leaching and vacuum sintering,thereby preparing porous titanium.The molar ratio of titanium powder to titanium dioxide(n _Ti/n _{Ti O2})was 1.0,1.2,and 1.4,and the amount of space holder was10%,20%,30%,40%,and 50%.The results of porous Ti O_x?x?1?precursors synthesis experiments as follow:?1?Precursors with good pore structure can be prepared by this method.The SEM and mercury porosimetry show that the pore size of the precursor shows a gradient distribution.The pore size ranges from a few microns to several hundred microns,and the maximum porosity of the precursor is 75?80%;?2?The main phase of the precursor is Ti O at n _Ti/n _{Ti O2}=1.2.The conditions for synthesis of porous Ti O_x?x?1?precursors were:the ratio is n _Ti/n _{Ti O},temperature is 1450°C,holding time?16h high purity argon atmosphere.Calcium vapor reduction uses calcium as the reducing agent;molten salt reduction uses calcium chloride as the molten salt,and calcium as the reducing agent.The acid leaching process uses hydrochloric acid and acetic acid.The results of calcium vapor reduction experiments as follow:?a?As the precursor porosity increases,the reduction degree is better.However,the structure is easy to collapse after leaching The,the precursor with a larger ratio of n _Ti/n _{Ti O2} has a lower impurity content in the leached product.The reduction products obtained from dry-mixed precursors have poor structural connectivity.With the increase of the reduction time,the porosity of the leached product decreased significantly.Therefore,the optimal conditions for the calcium vapor reduction process as followed:the porosity is55?70%,wet mixing,the ratio is n _Ti/n _{Ti O2}?1.2,and the holding time is more than 36h.?2?The strength of the leached product obtained by the reduction of molten salt is better than calcium vapor reduction.When the mass ratio of calcium chloride to the precursor(M_{Ca Cl2}/M_precursor)exceeds 5,it is more conducive to the reaction.When the mass ratio of calcium to the precursor exceeds 3 times,the deoxidation of the precursor is significantly improved.As the reaction temperature and reaction time increase,the deoxidation of the precursor becomes better.Therefore,the optimal conditions for the molten salt reduction were:the M_{Ca Cl2}/M_precursor is more than 5times,the M_Ca/M_precursor is more than 3?4 times,and the reaction temperature is1113K?1273K,reaction time is more than 36h.?3?The reduced leaching product has multi-gradient pore structure:?3?The reduced leaching product has a pore structure with a gradient distribution:macropores?pore diameter?100?150?m?,micropores?small pores?5?20?m?and mesopores?20?150?m?.Compared with the leached product,the porous titanium after vacuum sintering has lower impurities and a single phase.Vacuum sintering promotes the growth of titanium particles and strengthens the titanium skeleton.However,the pores are shrinked on the surface and inside of the porous titanium after sintering,reducing the porosity to about 50%.