Preparation And Properties Of Gypsum Whisker Reinforced Gypsum Matrix Composites

Natural gypsum resources have been exhausted by excessive exploitation in China.The accumulation of industrial by-product gypsum not only occupies a large amount of land,but also brings great damage to the ecological environment.How to turn waste gypsum into treasure and realize high added value is the starting point and end point of this paper.In this paper,gypsum whiskers were prepared by hydrothermal method from industrial by-product gypsum.In order to avoid the problem of water absorption,inorganic modifiers were used to modify the surface of the whiskers.Finally,the modified whiskers were added into the gypsum matrix,and the properties of the by-product gypsum matrix were enhanced by using the modified whiskers.Through a series of experiments,the whiskers were micro-tested,the basic properties of gypsum matrix composites were tested,and the micro-morphology and phase composition were tested.The main contents are as follows:(1)In the study of preparing calcium sulfate whiskers from desulfurized gypsum,the temperature and holding time were taken as variables.The results showed that with the increase of experimental temperature,the whiskers gradually changed from plate-columnar to strip-like,and the maximum aspect ratio was about 36 at 120 C.With the increase of holding time,the whiskers gradually changed from plate-columnar to strip-like,then from strip-like to short-columnar,and the holding time was 35 minutes.The ratio is about 36.(2)In the study of preparing calcium sulfate whiskers with phosphogypsum,orthogonal experiments were designed to explore the optimal conditions for preparing calcium sulfate whiskers.Through visual analysis and variance analysis,the optimalconditions were obtained as follows: temperature 130 C,heat preservation 30 min,rotational speed 50 r/min,concentration 5%.(3)The volume ratio of composite modified media and the types of modifiers are significant factors affecting the modification process.The solubility of modifiers in composite media directly affects the properties of the final surface modified product layer.When 15% sodium fluoride or sodium alginate is added,the volume ratio of composite medium is 29:1 and the modification time is 5 minutes,the solubility of modified calcium sulfate hemihydrate whisker in water decreases and the crystal structure and properties remain stable.(4)With the increase of calcium sulfate whisker content,the setting time of the three kinds of gypsum matrix composites is shortened,and the porosity decreases first and then increases.When the content of calcium sulfate whisker is 15%,the mechanical properties of natural gypsum matrix composites are the best.The flexural strength and compressive strength of natural gypsum matrix composites are 31.6%and 10.7% higher than those of blank samples,respectively.The mechanical properties of desulfurization gypsum matrix composites are the best when the content of calcium sulfate is 10%,and the compressive strength of the composites is 18.5%higher than that of the blank samples.When the content of calcium sulfate whisker is15%,the mechanical properties of phosphogypsum matrix composites are the best,and the flexural strength is 98.3% higher than that of blank samples.