MECHANOCHEMICAL HYDROPHOBIZATION OF MONOAMMONIUM PHOSPHATE
Abstract
Here, we investigated the influence of mechanical treatment on hydrophobization of monoammonium phosphate (MAP) with organosilicon liquid and silicon dioxide in order to obtain the main component of multipurpose fire extinguishing powders. We estimated hydrophobic properties of mixtures of various compositions. Based on the obtained results, the optimal content of hydrophobizing agents for obtaining monoammonium phosphate with the best hydrophobic properties was established. It is shown that the use of only organosilicon liquid for mechanochemical hydrophobization of MAP is not enough to achieve required values for water repellency, tendency to aggregation, bulk density and particle size distribution. According to GOST R 53280.4-2009, the ability to repel water (powders should not completely absorb water droplets) should be at least 120 min; the tendency to caking (mass of the formed aggregates) should not exceed 2% of the total mass of the sample; the apparent density of uncompacted and compacted powders should be at least 700 and 1000 kg/m3, respectively. It was found that in order to achieve the specified parameters, the mechanochemical hydrophobization of monoammonium phosphate should include modification of the mixture which contains 95 wt. % ammonium phosphate, 4.5 wt. % silicon dioxide and 0.5 wt. % hydrophobizing organosilicon liquid (HOL) in a mill with shock-shear loading at an input energy of 100-110 J/g. The absence of moisture in the raw material (preliminary drying of MAP particles) allows us to obtain a finer-grained product with a low tendency to moisture absorption. The process of mechanochemical hydrophobization of MAP can be described in the following way. During grinding hydrophobized silicon dioxide covers the particles of monoammonium phosphate, resulting in blocking active centers of adsorption and creating a structural and mechanical barrier that prevents particle aggregation.
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