Synthesis On Nano-sized Hydroxyapatite By Neutralization

Phoschemical industry, which is composed of phosphate and compound fertilizer as well as fine phosphorous chemicals, mainly aims at phosphorus resources for processing. And the refine technology is further developed in the future of this field. The Hydroxyapatite (HAP) is emerging as a kind of fine phosphorus chemical products in recent years, which has been used in many ways, such as the suspension polymerization dispersant, fluorescent material, biological material as well as ceramic. As a new kind of inorganic suspension polymerization dispersant, HAP is the most widely used in the suspension polymerization of petrochemical industry. It can make the polymerization process stable, the pressure and temperature more smooth, and can prolong the period of cleaning kettle. In brief, HAP can improve the appearance quality and transparency of the product, and enhance the grade of the product.At present, the HAP with high quality is mainly from imports. The HAP at home makes from suspension polymerization, and it has some drawbacks in the appearance, particle size distribution of resin products. Recent studies show that the activity of HAP dispersant for suspension polymerization is proportional to its specific surface area. Nanoparticle of HAP could improve the dispersion cativity because of its large specific surface area. When HAP particle size reaches to nanometer level, the HAP particles are liable to agglomerate, which can affect resin products injection molding. Increasing the size of the particles for reducing their agglomeration, however, can lower surface activity and influence its dispersion activity. In order to resolve the contradiction between the nanocrystallization of HAP dispersant and its dispersing property, a kind of effective synthetic method and surface treatment must be choosed, as a result, this method can be used to prepare nano-sized HAP particles with large specific surface area and high surface activity.An acid-base neutralization was adopted using phosphoric acid and calcium oxide as starting materials to prepare HAP dispersants for suspension polymerization. The principle of this synthesis technique that is easy to handle is simple, raw materials are cheap and easily-accessible, and the controllable preparation on some properties of particles can be achieved by means of strictly controlling reaction conditions. In this paper, the effects of the process conditions, including the Ca/P of raw materials, the pH value of the reaction system, temperature of reaction, aging time, as well as SDBS addition amount on the structure, chemical composition, grain size and partical size distribution of the HAP products were researched in detail, and the process conditions were optimized by using orthogonal design method. The samples were characterized by laser particle size analyzer, X-ray diffraction instrument, chemical analysis and so on. In order to improve the grain size and the aggregation of Hydroxyapatite powders, different modifiers are used to perform the surface modification of HAP powders to obtain nano-sized particles. The influences of modifiers types, modification time as well as surfactant dosages are investigated. The results were listed as follows:(1) The crystal structure of the prepared HAP is same to Ca10(PO4)6(OH)2.(2) When the control indicators are Ca/P of the HAP products, the optimum process conditions are Ca/P of raw materials1.77, SDBS addition amount1.5mL, temperature of reaction45℃and the pH value of the reaction system11.When the control indicators are grain size and partical size distribution of the HAP products, the optimum process conditions are Ca/P of raw materials1.57, SDBS addition amount1.5mL, temperature of reaction45℃and the pH value of the reaction system9.When the control indicators are the yield of the HAP products, the optimum process conditions are Ca/P of raw materials1.67, SDBS addition amount1.0mL, temperature of reaction55℃and the pH value of the reaction system9. Under the optimum process conditions the experiment for verification is done. It validates the correctness and feasibility of the design method further.(3) All the indicators of the prepared HAP under the optimum process conditions are in line with the ministerial standard HG/T3583-2009, of which the average particle diameter is significantly higher than the standard HG/T3583-2009.(4) As a single modifier, C6H8O7is the best, and scanning electron microscope (SEM) analysis reveals that the size of HAP powders with C6H8O7decreases significantly. Further study under laser particle size analyzer demonstrates that the average size of HAP powders is70nm or so. When C6H8O7and SDBS as the compound modifier are used, it turns out a better consequence. If the modifier is added before acid-base neutralization reaction, the effect of modification is noteworthy and the optimum content of modified agents is4%. The activation index and sedimentation volume of optimal modified products is94%and2.4mL/g, respectively.