Synthesis And Properties Of Nano Silicocarnotite Powders With Ultrasound-assisted Precipitation Method

It has been proved that silicon-substituted calcium phosphate ceramics possess superior degradability and bone regeneration to HA ceramics,regarding as promising materials for bone regeneration,while the synthesis of single-phase nanocrystallized high Si-containing calcium phosphate is still a challenge.In the present work,a novel and facile aqueous precipitation method assisted with ultrasonic irradiation was adopted firstly to synthesis a single-phase nanocrystallized calcium silicophosphate?Ca₅?PO₄?₂SiO₄,CPS?biomaterial.The effects of different ultrasound-assisted conditions?ultrasonic intensity and ultrasonic time?on the phase,chemical composition,crystallinity and micro morphology of the precursors,as well as on the calcination temperature and particle size of CPS powders were studied,and the relevant mechanism was further discussed.Then,the in vitro bioactivity,osteogenic activity and sinterability of synthesized nanocrystallized CPS were studied in details.Results showed that:?1?Ultrasonic treatment could change the structure of precursors from short rods to fusiform-like structures assembled with fine polycrystalline apatite,and significantly improve the dispersion of precursors.At the same calcination temperature,the content and size of CPS powders would increase with the addition of ultrasonic intensity and time,severally.The phase forming temperature of CPS decreased from 1350?to 1000?under the condition of 350 W for 60 min,and the CPS powder with an average grain size of 84 nm was synthesized successfully;?2?The synthesis mechanism of nano CPS is as follows:the hydroxyl and part of PO₄^3-tetrahedron in HA could be replaced by SiO₄^4-tetrahedron in CPS precursor to form high silicon-containing apatite with hydroxyl vacancy,and ultrasonic treatment could improve the dispersion of precursor and the uniformity of element distribution,thus reducing the phase forming temperature of CPS and preventing particles growing together during the calcination;?3?Comparing with micro CPS and HA powders,nanocrystallized CPS powders showed better apatite deposition ability in vitro,good cytocompatibility,higher ALP expression,and could upregulate the expression of bone formation related genes Runx-2,Bsp and Col-I to achieve better osteogenic activity;?4?The estimated activation energy Q value for CPS grain growth was about255.46 KJ/mol,when the temperature was lower than 1150?,the densification process was mainly dominated by grain boundary diffusion,while when the temperature rose higher,the sintering process was mainly controlled by volume diffusion,which caused rapid grain growth and inhibited the densification process;?5?The grain growth process could be effectively suppressed via two step sintering?TSS?method along with the increase of density,the best TSS sintering schedule for CPS ceramics was:T₁=1200°C without dwelling and T₂=1050°C with the dwelling time of 30 h,and the mean grain size and relative density of CPS ceramics were 0.42?m and 98.4%,respectively.Comparing with the samples of conventional sintering,the grain size of TSS case was smaller and distributed much uniform,and the mechanical strength was also enhanced.