Controllable Preparation Of BaSO₄ Nanodispersions For Transparent X-ray Shielding Nanaocomposite Films

Barium sulfate(BaSO4)nanocrystals as important functional materials have attracted considerable research interests,due to their special properties,such as high whiteness,acid and alkali resistance,non-toxicity,low price,X-rays reflectivity and absorption.However,most of BaSO4 nanocrystals prepared by traditional technologies are nanopowders with broad size distribution and poor dispersibility,which may greatly limit their applications.Therefore,the controllable preparation of highly dispersed nano-barium sulfate is very important.To the best of our knowledge,the synthesis of BaSO4 nanodispersions with wide applications was rarely reported.Here,we firstly present a novel and efficient method to prepare transparent and stable BaSO4 nanodispersions with a particle size of less than 20 nm using a precipitation method in a rotating packed bed(RPB),followed by a modification treatment.The effects of various process factors were explored to obtain the optimal reaction conditions.Furtermore,the X-ray shielding properties of the dispersions in the nanocomposites were investigated.The main research contents and results of the thesis are as follows.1.High-gravity one-step precipitation method without any modification was used to prepare nano-BaSO4 which can be stably dispersed in ethylene glycol to form a transparent dispersion.The effects of various factors on the preparation of BaSO4 nanoparticles were investigated.The optimal conditions were obtainedas follows.Pure methanol was the reaction system,the reaction temperature was 60?,the initial concentration was 0.06 mol/L,and the speed of the RPB was 2500 rpm.BaSO4 nanoparticles with an average particle size of 13 nm were prepared under the optimal conditions.Compared with conventional stirred tank(STR),the product prepared by using RPB has a smaller particle size and a narrower particle size distribution.And the reaction time can be significantly reduced from 20 min to 18 s.2.High-gravity one-step precipitation with surface modification was used to prepare nano-BaSO4 which can be stably dispersed in ethanol and water to form transparent dispersions.The effects of various factors on the preparation of BaSO4 nano-particles were investigated.The optimal conditions were obtained as follows.Stearic acid was used as the modifier,and the addition amount was 30 wt.%.Modification temperature was 60? and modification time was 3 h.The rotation speed of the RPB was 2500 rpm,the feed flow ratio was 1:1 and the feed rate was 300 mL/min.BaSO4 nano-particles with an average particle size of 10 nm were prepared under the optimal conditions.Compared with the conventional STR,the product prepared by using RPB has a smaller average particle size and a narrower size distribution,and the reaction time can be significantly reduced.3.Based on the preparation technology of nano-BaSO4 ethanol dispersion,the secondary surface modification was used to prepare nano-BaSO4 which can be stably monodispersed in weak polar media such as cyclohexane,toluene,THF,chloroform,n-hexane,and n-sunane to form a transparent dispersion.The effects of various technological factors on the preparation of BaSO4 nano-particles were explored.The optimal conditions were achieved.Sodium oleate was used as the second modifier,and the addition amount was 30 wt.%.The modification temperature was 60? and the modification time was 3 h.The initial concentration of the solution was 0.06 mol/L and the rotating speed of RPB was 2500 rpm.BaSO4 nano-particles with an average particle size of 12 nm were prepared under the above conditions.Compared with conventional STR,the product prepared by using RPB has a smaller average particle size and a narrower particle size distribution.4.The transparent BaSO4-PVB nanocomposite films with X-ray shielding function can be easily fabricated through the direct solution blending technique.When the addition amount of BaSO4 is 30%,the as-formed film was still transparent,and the light transmittance at 555 nm is 75.1%.The nanocomposited film has good X-ray shielding performances.The HVL of the composite film with the 30%amount of nano-BaSO4 is 0.11cm and the TVL is 0.38cm when the tube voltage is 55kV.The X-ray shielding performance gradually improves as the BaSO4 content in composite increases.