Preparation,Modification And Stability Regulation Of Hemihydrate Calcium Sulfate Whiskers

The hemihydrate calcium sulfate whisker?CaSO₄·0.5H₂O,or HCSW?is a fibrous monocrystal of calcium sulfate.As a new inorganic chemical product,it was widely used in the fields of insulation,refractory and toughness ceramic because of its especial structure and excellent properties.However,the presence of active sites on surface of the whisker made the whisker in a thermodynamically unstable state,and easily hydrated into short,coarse-grained dihydrate calcium sulfate in the air,thus losing its unique physical and mechanical properties,and excellent chemistry stability.Therefore,it was of great significance to investigate the relations between the structure and properties of whisker and its composites.In this thesis,it was necessary to study the preparation method of HCSW,adjust the hydrophobicity of whiskers through surface modification and study the method of improving the compatibility between whiskers and organic matrix.First,the hydrothermal synthesis of HCSW was studied in this thesis,and the effect of diol additives on the morphology and stability of whiskers was investigated.It was found that the concentration and type of glycols were the key factors of controlling the stability of HCSW.When the triethylene glycol was used as an additive,with the concentration of 18.8×10^-3 mol·L^-1 and the reaction time of 4.5 h,the HCSW could keep thin and long in air for 7days.The HCSW had good water resistance was due to the fact that the-OH on the glycol was adsorbed on the surface of the HCSW instead of the-OH in the H₂O molecule.However,if the carbon chain length of diols was too long and the concentration of diols was too high,the adsorption capacity might be reduced due to repulsion between each other.Then,the surface modification of HCSW was studied in this thesis.The first and second modification of HCSW with KH570 and TMPMP were studied,respectively.It was found that the surface contact angle of HCSW first modified with KH570?HCSW-KH570?increased from 0^o to 36.61^o.The data of contact angle measurements showed that the surface hydrophilic property of HCSW-KH570 was significantly reduced.And The surface contact angle of HCSW second modified with TMPMP?HCSW-KH570-SH?increased from 36.61°to 91.66°.The result showed that the HCSW surface was changed after twice coating,and the property of surface variated from hydrophile to hydrophobic.At this time,the modified HCSW could keep thin and long in air more than 15 days.Finally,the application of HCSW in silicone rubber?DPS?was studied.The results showed that HCSW had remarkable reinforcement on DPS,and its mechanical properties such as tensile strength and elongation at break firstly increased and then decreased with the increase of HCSW dosage.After the whiskers were surface-modified with KH570 and TMPMP,a stable chemical bond was formed on the surface between DPS and the whiskers,and the reinforcing effect was better and the resistance to the medium was increased.When the whisker addition amount was 5%,the tensile strength,elongation at break,and 100%definite stress of HCSW-KH570-SH/DPS composite were 0.876Mpa,253%and 0.61MPa,respectively.