MAINTAINING STABLE NANODISPERSED CERIUM OXIDE FOR HEAT TRANSFER PROCESSES
The introduction of heat carriers progressive types causes the productivity of heat exchange systems to increase. One of the challenges in thermal applied applications is the search for heat carriers that will provide revolutionary indicators of thermal conductivity and stability over time, thereby increasing the order of the heat transfer processes efficiency magnitude. The paper describes the creation of stable colloidal solutions using cerium oxide and organic stabilizers to provide better heat exchange performance compared to true solutions. Cerium oxide colloids were obtained by precipitation of the oxide from an aqueous solution of cerium nitrate with an aqueous ammonia solution in the presence of a polymer under vigorous stirring at room temperature. A number of cerium oxide nanosized dispersions, stabilized with polyvinylpyrrolidone, with a particle size of 1–10 nm were obtained. The content of CeO2 in the obtained dispersions was 1.72.10–3, 5.15.10–3, 8.6.10–3, 1.21.10–2, 1.72.10–2 % at a polymer content of 1.10–3 mol/l, the pH of the dispersions was 8–9. Electron microscopic images of the obtained nanodispersions showed a colloidal particles narrow distribution and cerium oxide nanoparticles in size. Colloidal particles are macromolecular tangles of polyvinylpyrrolidone with oxide nanoparticles strung in them. A volume of 20–50 nm organic matrix contains 10–40 particles of 1–10 nm cerium oxide. The particle size distributions of the dispersions established by the photon-correlation spectroscopy method have two areas of maxima for each sample. The first maximum for the dispersions of all investigated concentrations refers to particles with a diameter of 5–6 nm, which, in our opinion, are particles of cerium oxide, both in polymer beads and probably free from the stabilizer. Another maximum, depending on the sample, is observed at 30–70 nm or 100–300 nm, and relates to colloidal particles of PVP with cerium oxide encapsulated particles. The static stability of the cerium oxide obtained nanodispersions with polyvinylpyrolidone for two years under standard conditions is comparable to the true polymer solution. It is proposed by the method of UV spectroscopy to control the reproducibility of the obtaining materials technology. Tests of the thermal conductivity of the obtained 1.72.10–3 % stable cerium oxide nanodispersion were performed at 50 °C relative to distilled water with a thermal conductivity coefficient of 0.65 W/(m·deg). We found an increase in the coefficient for nanodispersions by 4–6 %, which is a significant value for dilute solutions. Ref. 15, Fig. 4 .
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