Microemulstion synthesis of powders of water-soluble energy-saturated salts

Abstract

769Microemulsion (micellar) synthesis is a popular method and is widely used for preparing nanoparticles of metals [1], oxides [2], and sparingly soluble salts [3,4]. The advantages of this method include: (1) the ease of synthesis; (2) a narrow particle size distribution function of the product; (3) a feasibility of preparing particles of complex composition, multilayered, hybrid, and other types of particles [5]; and (4) a good knowledge of the micellar and microemulsion struc ture. Unfortunately, there only few studies directed to the preparation of nanoparticles of water soluble salts by the microemulsion method. For example, Co(NO 3 ) 2 , CaCl 2 , Na 2 HPO 4 , and Cu(NO 3 ) 2 nanopar ticles have been prepared in a solid phase concentrate in an AOT matrix (sodium di(2 ethylhexyl)sulfosucci nate) via distilling off the solvent (heptane) and water [6,7].Meanwhile, studies of microemulsion synthesis as applied to prepare powders and liquid hydrophobic concentrates of nanoparticles of water soluble energy intensive salts seem to be very promising for both sci ence and application. For example, reverse emulsions of supersaturated ammonium nitrate solutions [8,9] in diesel fuel have almost substituted for TNT con taining industrial explosives [10-13].Our goal here was to study the possibility of prepar ing powders of water soluble salts in reverse micro emulsions of oxyethylated surfactant Tergitol NP 4. EXPERIMENTALReagents The micelle forming surfactant used was oxyethy lated nonylphenol with an average oxyethylation number of four, namely, Tergitol NP 4 (from Dow Chemical). A micellar solution contained 0.25 mol/L Tergitol NP 4 in n decane. The organic solvents used were pure grade n decane and N,N dimethylforma mide (DMF) and high purity grade heptane and ace tone. The initial reagents used were concentrated nitric acid (high purity grade, 16.2 mol/L), concentrated aqueous ammonia (high purity grade, 10.8 mol/L), KOH, and NaBH 4 (both of pure grade), NH 4 NO 3 (pure for analysis grade), and KNO 3 (chemically pure grade). Structural Study of Microemulsions and PowdersThe limiting solubilization capacity V s /V o (the vol ume ratio of an aqueous solubilizate solution to a sol ubilizate containing micellar solution) of a micro emulsion system with respect to aqueous solutions of reagents and salts was determined by serial injections of small volumes of the aqueous phase. The cloud point was detected visually and spectrophotometri cally by an abrupt increase in the absorbance of the solution. Measurements were carried out on a Shi madzu 1700 spectrophotometer using quartz cells (l = 1 cm); the reference solution was a "dry" micellar solution.Microemulsions with initial reagents were structur ally studied by photon correlation spectroscopy and Abstract-The feasibility of preparing energy saturated salts (NH 4 NO 3 , KNO 3 , and NaBH 4 ) in powders with various particle sizes in microemulsion systems based on oxyethylated surfactant Tergitol NP 4 has been demonstrated. Powders were isolated by destroying microemulsio...

Reactivity in combustion process for expanded graphites: influence of dimensional effect

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