Al2O3/TiO2 hybrid nanofluids thermal conductivity

Journal of Thermal Analysis and Calorimetry - This research deals with experimental studies on thermal conductivity variation of Al2O3 and TiO2 hybrid nanofluids with water as the base fluid. In...     

Pumping power and heat transfer efficiency evaluation on Al2O3, TiO2 and SiO2 single and hybrid water-based nanofluids for energy application

Journal of Thermal Analysis and Calorimetry - Nanofluids are new heat transfer fluids obtained by suspending different nanoparticles in a base fluid. This research deals with a complex numerical...     

Thermal conductivity of Al2O3/water nanofluids

A considerable number of studies can be found on the thermal conductivity of nanofluids in which Al₂O₃ nanoparticles are used as additives. In the present study, the aim is to measure the thermal conductivity of very narrow Al₂O₃ nanoparticles with the size of 5 nm suspended in water. The thermal conductivity of nanofluids with concentrations up to 5 % is measured in a temperature range between 26 and 55 °C. Using the experimental data, a correlation is presented as a function of the temperature and volume fraction of nanoparticles. Finally, a sensitivity analysis is performed to assess the sensitivity of thermal conductivity of nanofluids to increase the particle loading at different temperatures. The sensitivity analysis reveals that at a given concentration, the sensitivity of thermal conductivity to particle loading increases when the temperature increases.     

ZrO2和Al2O3在金红石型TiO2表面的包覆研究

以(NaPO3)6为分散剂,用化学沉积法对金红石型TiO2进行了锆、铝氧化物包膜。研究了包覆过程中,TiO2的分散、ZrO2和Al2O3用量、反应pH值以及时间对二氧化钛的亨特白度(Wh)和光泽度(L)的影响,并采用扫描电镜(SEM)、透射电镜(TEM)、X光电子能谱(XPS)和沉降性试验对包覆前后的二氧化钛进行了表征,得到包锆、包铝氧化物的优化工艺条件。研究了二氧化钛表面包锆、铝氧化物的包覆机理和表面结构。经过其表面包膜处理,二氧化钛的颜料性能得到明显改善。     

A critical analysis of clustering phenomenon in Al2O3 nanofluids

Journal of Thermal Analysis and Calorimetry - In the present work, an investigation on the relationship between clustering phenomenon and thermal conductivity of nanofluids is presented....     

Thermal conductivity and specific heat capacity measurements of Al2O3 nanofluids

Thermal conductivities and specific heat capacities of nanoparticles of Al₂O₃ dispersed in water and ethylene glycol as a function of the particle volume fraction and at temperatures between 298 and 338 K were measured. The steady-state coaxial cylinders method, using a C80D microcalorimeter (Setaram, France) equipped with special calorimetric vessels, was used for the thermal conductivities measurements. The heat capacities were measured with a Micro DSC II microcalorimeter (Setaram, France) with batch cells designed in our laboratory and the “scanning or continuous method.” The Hamilton–Crosser model properly accounts for the thermal conductivity of the studied nanofluids. Assuming that the nanoparticles and the base fluid are in thermal equilibrium, the experimental specific heat capacities of nanofluids are correctly justified.     

Experimental investigation and prediction of the thermal conductivity of water-based oxide nanofluids with low volume fractions

Journal of Thermal Analysis and Calorimetry - Although there are already many models for prediction of the thermal conductivity of nanoparticle suspension, most of them only consider the cases for...     

Improving stability and thermal properties of TiO2-based nanofluids for concentrating solar energy using two methods of preparation

Journal of Thermal Analysis and Calorimetry - Nanofluids are considered a promising alternative to the classic fluids used in heat transfer processes. One interesting application of nanofluids is...     

Study of properties of Al2O3 and TiO2 supported palladium catalysts in reactions of tetrachloromethane hydrogenation

Properties of Al₂O₃- and TuO₂-supported palladium catalysts modified with calcium oxide were studied. Catalyst samples 2% Pd/CaO-TiO₂ and 2% Pd/CaO-Al₂O₃ were examined by the methods of temperature-programmed reduction in a flow of hydrogen, temperature-programmed desorption of ammonia and carbon(IV) oxide, and X-ray diffraction analysis.     

Reaction of silanes in supercritical CO2 with TiO2 and Al2O3

Infrared spectroscopy was used to investigate the reaction of silanes with TiO2 and Al2O3 using supercritical CO2 (Sc-CO2) as a solvent. It was found that contact of Sc-CO2 with TiO2 leads to partial removal of the water layer and to the formation of carbonate, bicarbonate, and carboxylate species on the surface. Although these carbonate species are weakly bound to the TiO2 surface and can be removed by a N2 purge, they poison the surface, resulting in a lower level of reaction of silanes with TiO2. Specifically, the amount of hexamethyldisilazane adsorbed on TiO2 is about 10% of the value obtained when the reaction is performed from the gas phase. This is not unique to TiO2, as the formation of carbonate species also occurs upon contact of Al2O3 with Sc-CO2 and this leads to a lower level of reaction with hexamethyldisilazane. This is in contrast to reactions of silanes on SiO2 where Sc-CO2 has several advantages over conventional gaseous or nonaqueous methods. As a result, caution needs to be applied when using Sc-CO2 as a solvent for silanization reactions on oxides other than SiO2.     

Intrinsic viscosity of SiO2, Al2O3 and TiO2 aqueous suspensions

The viscosity of dilute suspensions of several metal oxides (SiO2, Al2O3 and TiO2) was measured at different pH values. The intrinsic viscosity, [eta], was derived from the concentration dependence of the viscosity. This magnitude was pH-dependent. A correlation with the shape of the kinetic unity has been proposed.     

Influence of long-term aqueous exposure on surface properties of plasma-sprayed oxides Cr2O3 and Cr2O3-25 wt% TiO2

The influence of water exposure on the surface properties of plasma-sprayed Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) was studied. It was shown that both plasma-sprayed materials contained Cr(VI) hydrous oxide phases, which dissolved rapidly at the beginning of water exposure. The dissolution continued slowly during the whole water exposure time. The Cr(VI) dissolution was accompanied by a rapid increase in surface IEP value. Both Cr(2)O(3) and Cr(2)O(3)-25 wt% TiO(2) showed similar dissolution, zeta potential, and surface oxidation states. Thus the addition of TiO(2) did not influence the surface properties of the plasma-sprayed Cr(2)O(3).     

电化学合成TiO2/Al2O3复合粉体

以四氯化钛和六水三氯化铝为原料,采用电化学方法制备了TiO2/Al2O3复合粉体.以XRD对粉体进行表征发现,以电解TiCl4和AlCl3的混合溶液得到的粉体中,氧化铝主要分布在颗粒的表面.分别电解TiCl4与AlCl3的水溶液,待成胶后再混合而得到的粉体中,两种成分布比较均匀.对复合粉体进行高温处理,在500℃可以得到R-TiO2/γ-Al2O3的复合粉体,而在950℃可以得到R-mO2/α-舢2哂的复合粉体,在1200℃可以得到ALiO5复合陶瓷粉.     

Al2O3涂敷TiO2纳米晶粒的制备及其抗絮凝性研究

纳米材料特异性能的开发与利用,是当今纳米材料科学研究中的热点之一.国外新近报道了[1～3]TiO2纳米晶粒在光学增益体系中的一种新应用.据报道,将TiO2纳米晶粒散布到染料罗丹明过氯酸盐的甲醇溶液中,在Nd:YAG 532 nm激光激发下,产生出奇特的光学现象:发射光纯度极高,波长宽度为2～3 nm,发射峰幅度成10倍地放大,激发能量有明确的阈值,且为各向同性发射.     

Synthesis and formation mechanism of TiO2/Al2O3 nanobelts by electrospinning

Poly(vinyl pyrrolidone) (PVP)/[Ti(SO₄)₂ + Al(NO₃)₃] composite nanobelts were prepared via electrospinning technology, and TiO₂/Al₂O₃ nanobelts were fabricated by calcination of the prepared composite nanobelts. The samples were characterized by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). XRD results show that the composite nanobelts were amorphous in structure, and pure phase TiO₂/Al₂O₃ nanobelts were obtained by calcination of the relevant composite nanobelts at 950°C for 8 h. SEM analysis indicates that the surface of as-prepared composite nanobelts was smooth, the widths of the composite fibers were in narrow range, and the mean width was ca. 8.9 ± 2.1 μm, thickness was about 255 nm, and there is no cross-linking among nanobelts. The width of TiO₂/Al₂O₃ nanobelts was ca. 1.3 ± 0.1 μm and the thickness was about 105 nm. TG-DTA analysis reveals that the N,N-dimethylformamide (DMF), organic compounds and inorganic salts in the composite nanobelts were decomposed and volatilized totally, and the weight of the sample kept constant when sintering temperature was above 900°C, and the total weight loss percentage was 81%. FTIR analysis manifests that crystalline TiO₂/Al₂O₃ nanobelts were formed at 950°C. The possible formation mechanism of the TiO₂/Al₂O₃ nanobelts was preliminarily discussed.