Preparation Of Calcium Sulfate Nanowhiskers And The Study On Process Conditions

In this dissertation, calcium sulfate nanowhiskers are synthesized via extraction crystallization and room temperature acidification under mild conditions. Through the condition of single factor experiment investigation and determine the appropriate synthetic process conditions, and makes a tentative discussion on the crystallization process of nano-CSW, main content summary is as follows:(1) By the room temperature acidification method, CaSO4·2H2O nanowhiskers were synthesized on a large scale in ethanol-water solvent, using calcium chloride and concentrated sulfuric acid as raw materials, cetyl trimethyl ammonium bromide (CTAB) as crystal control agent. The as-prepared samples were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM). The optimized synthesis conditions were obtained as follows:CTAB dosage of 0.02g,150mL of ethanol-water solvent,98% sulfuric acid addition amount 2mL, stirring speed 250 r/min, the reaction temperature 25 ℃, initial concentration of calcium chloride 0.045mol/L, ethanol-water ratio 2:1 and the reaction time 30min. The as-prepared CaSO4·2H2O nanowhiskers under the optimized conditions were uniform in size with the diameter about 200nm and the aspect ratio about 30.(2) CaSO4·2H2O nanowhiskers were synthesized on a large scale by a simple extractive crystallization route, using CaSO4·2H2O as raw materials, absolute ethanol as the extractive crystallization agent. The as-prepared samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The obtained optimum synthetic conditions were as follows:the extractive crystallization temperature was 20℃, the initial concentration of CaSO4·2H2O was 0.015mol/L, the aging time was 0 min, and the initial system pH value was 7. The results indicated that the prepared CaSO4·2H2O nanowhiskers were uniform in size with the diameter about 50nm and length up to 1500 nm.(3) After a preliminary study on the crystallization process of calcium sulfate, the possible formation process of CaSO4·2H2O nanowhiskers and flake-shaped nanostructure could be described as:The crystallization process of calcium sulfate is firstly formed calcium sulfate whisker by screw dislocation, the newly formed calcium sulfate nanowhiskers to get close to each other and then arrange side by side, thus finally forming the flake-shaped nanostructure. By controlling the synthetic conditions, we can terminate the crystal growth process before the whiskers combine into flakes, and synthesize large-aspect and size-uniform CaSO4·2H2O nanowhiskers on a large scale.(4) Ag2SO4 nanoparticles were synthesized by extractive crystallization, using Ag2SO4 as raw materials, absolute ethanol as the extractive crystallization agent. XRD、 TEM are used to characterize morphology and crystal form of as-prepared Ag2SO4 nanoparticles. The obtained optimum synthetic conditions were as follows: the initial concentration of Ag2SO4 was 0.0032mol/L, the extractive crystallization temperature was 20 ℃, the aging time was 0 min. The results indicate that the Ag2SO4 nanoparticles were uniform in size and the particle size is about 20nm, shows that extraction crystallization method can be applied to preparation of other nanomaterials.