Preparation, Characterization And Application Of ASNS

In recent years, the design and controllable constructing of core-shell composite particles have become the focus of a study on a new materials and surface science. Various types of core-shell particles have emerged, especially, the shell material such as silica. Because such particles with core-shell structure often exhibit superior physicochemical properties (e.g. mechanical,chemical,electrical,magnetic and optical) to their single component counterparts, moreover, coating expensive shells on the inexpensive cores materials can lower the cost of the functional materials . With white external appearance,hydrated silicon dioxide has the similar function of reinforcing ability in rubber to carbon,so it is usally called white carbon black .For its low density,high specific surface area, fine dispersion,superior stability , reinforcing ability,thickening property and thixotropy inereasing etc.Silica has been one kind of important inorganic fillers, and widely used in many fields, such as rubber , plastic,medicine, pigment ,toothpaste and daily chemical industry. Thus, under the "particle design" new ideas,to attempts to regard amorphous SiO₂ as shell materials,regard CaCO₃ partiele as core materials to prepare a kind of new-type silica-gel filler, to explored the green synthetic process of silica, to produce a new type of silica (the amorphous silica with novel particle structure is called ASNS) as substitute for it's existing products in some applications. It is the production process of ASNS that reduced the consumption of traditional raw materials of sodium silicate and acid by more than 90 percent, and reduced significantly the cost of washing and drying of products, and met basically the requirement of green chemistry and atom economy .We put forward a novel, rapid, reliable new method on determining the coated effect of calcium carbonate coated with amorphous silicon dioxide. It had practical application value for new measurement techniques of this core-shell material to guide the preparation of calcium carbonate @ silica,and to determine optimum conditions,and to definite technical index of a new product,and to establish enterprise standard. The main work of this dissertation are summed up as follows:1. In this paper we summarized and analyzed the basic characteristics, preparation method, formation mechanism, characterization methods and main application of core-shell particles. Which is of certain guiding significance for studying the preparation, structural performace and coating mechanism of core-shell composite materials.2. We tested and compared physicochemical properties (including the appearance , pH value, heat rate of weight loss, water absorption , sulphate content, the apparent density )of three kinds of silica using for toothpaste abrasives produced by three different manufacturers.3. The technology of coating SiO₂ on the surface of CaCO₃ particles was studied by heterogeneous nucleation method. The influences of the solution concentration of Na2SiO₃ , the pH value, temperature of the system, the dispersion of CaCO₃ particles, blending way and adding rate were made a thorough analysis. The coating mechanism was studied through thermodynamics and dynamics.4. Studying on interaction of methylene blue(MB) in aqueous solution and silica, The effects of initial mass concentration of MB,adsorption time, temperature,pH value,salt on the MB adsorption of silical were also investigated. Experimental results have shown that increasing initial mass concentration of MB favors the adsorption while the acidic pH , temperature and salt go against the adsorption.It was found that the absorbance of visible light of methylene blue(MB) solution decreased at high pH beeause of hydrolysis or forming dimmer of MB. On the basis of this finding,we proposed that there were two reasons for the increasing removal of MB onto silica with the increasing pH value : One was the increasing negative charge on the silica surface with pH increasing and the other was the hydrolysis or dimmer forming of MB which causing the removal increase. As MB is one of the most popular dyes for characterization of various adsorbents, this finding may be also taken as reference to other adsorption system studies.5. The adsorption effect of the aqueous solution of methylene blue on calcium carbonate has been investigated. Experimental results have shown that no adsorption of methylene blue on calcium carbonate occurred. Therefore, according to different adsorption performances distinguishing between silica and calcium carbonate.6.The determination of the coating quantity and coating ratio of CaCO₃/SiO₂ core-shell particles by methylene blue spectrophotometric method. This rapid, simple, direct and accurate determination method has important reference value to guide the production of core-shell particles.