Azmi Zakaria

Measuring Nanofluid Thermal Diffusivity and Thermal Effusivity: The Reliability of the Photopyroelectric Technique

It is important to study nanofluids to understand their extraordinary thermal properties and how the size, concentration and agglomeration of the nanoparticles affect those properties. Photopyroelectric (PPE) technique has been well established in the use of non-destructive measurement of thermal diffusivity and thermal effusivity, by using polyvinylidene fluoride (PVDF) films as sensitive pyroelectric sensors in thermally thick conditions instead of using very thick ceramic sensors. There have been two proposed practical configurations for the PPE technique, the back and the front PPE configurations, to obtain both the thermal diffusivity and effusivity, which are suitable thermal parameters of materials. This PPE technique involves the measurement of thermal waves in the sample due to absorption of optical radiation, by placing a pyroelectric sensor in thermal contact with the sample. This chapter provides a review of the back and the front PPE configurations to determine the thermal diffusivity and effusivity of nanofluids, sample preparation techniques using high-amplitude ultrasonic dispersion and data analysis for metal oxide-based nanofluid materials.

Effect of Co3O4 doping and sintering temperature on optical energy band gap properties in Zn-Bi-Ti-O varistor ceramics

It is necessary to investigate the electronic states of ceramic based ZnO vasristor and effect of doped impurities at different concentration. Band gap (Eg) of the ceramic (99-x) mol% ZnO+0.5u2005mol% Bi2O3+0.5u2005mol% TiO2+ xCo3O4 where x = 0, 0.2, 0.4, 0.6 and 0.8u2005mol%, were determined using UV-Vis spectrophotometer. The samples were prepared via solid-state route and sintered at the sintering temperature at 1110, 1140 and 1170 °C for 45 and 90u2005min in open air. At no doping of Co3O4, the values of Eg are 2.991 ± 0.001, 2.989 ± 0.001 eV for 45 and 90u2005min sintering time; respectively. Eg was decreased to 2.368 ± 0.002 and 2.352 ± 0.001 eV at 0.8u2005mol% Co3O4 for 45 and 90u2005min sintering time; respectively. XRD analysis indicates that two main phases existed at all concentrations which are ZnO and secondary phases, Bi12TiO20, Zn2Ti3O8, ZnCo2O4 and Co3Ti3O. Relative density decreases with the addition of Co3O4 compared to that of undoped at all doping level. When Co3O4 is added in the ceramics, relative density increases with the increase of doping level at both 45 and 90u2005min sintering time. The variation of sintering temperatures and XRD findings of steepness factor are correlated with the UV-Vis spectrophotometer results of based ZnO varistor doped with Co3O4 due to the growth of interface states.It is necessary to investigate the electronic states of ceramic based ZnO vasristor and effect of doped impurities at different concentration. Band gap (Eg) of the ceramic (99-x) mol% ZnO+0.5u2005mol% Bi2O3+0.5u2005mol% TiO2+ xCo3O4 where x = 0, 0.2, 0.4, 0.6 and 0.8u2005mol%, were determined using UV-Vis spectrophotometer. The samples were prepared via solid-state route and sintered at the sintering temperature at 1110, 1140 and 1170 °C for 45 and 90u2005min in open air. At no doping of Co3O4, the values of Eg are 2.991 ± 0.001, 2.989 ± 0.001 eV for 45 and 90u2005min sintering time; respectively. Eg was decreased to 2.368 ± 0.002 and 2.352 ± 0.001 eV at 0.8u2005mol% Co3O4 for 45 and 90u2005min sintering time; respectively. XRD analysis indicates that two main phases existed at all concentrations which are ZnO and secondary phases, Bi12TiO20, Zn2Ti3O8, ZnCo2O4 and Co3Ti3O. Relative density decreases with the addition of Co3O4 compared to that of undoped at all doping level. When Co3O4 is added in the ceramics, relative density incre...

Camera flash heating of a three-layer solid composite: An approximate solution

Camera flash heating and the subsequent thermal wave propagation in a solid composite material is studied using the Laplace transform technique. Full-field rear surface temperature for a single-layer, two-layer and three-layer solid composites are obtained directly from the Laplace transform conversion tables as opposed to the tedious inversion process by integral transform method. This is achieved by first expressing the hyperbolic-transcendental equation in terms of negative exponentials of square root of sα and expanded same in a series by the binomial theorem. Electrophoretic deposition (EPD) and dip coating processes were used to prepare three-layer solid composites consisting ZnO/Cu/ZnO and starch/Al/starch respectively. About 0.5ml of deionized water enclosed within an air-tight aluminium container serves as the third three layer sample (AL/water/AL). Thermal diffusivity experiments were carried out on all the three samples prepared. Using Scaled Levenberg-Marquardt algorithm, the approximate tempe...

Fabrication and modification of chemical deposited nanocrystalline cadmium sulphide thin film in presence of impurity

Tin Doped Cadmium sulphide CdS:Sn thin films were prepared by growth solution technique on commercial glass. The films were annealed in air, at 300δC, for 45 minutes. The effects of Sn doping on the structural and optical properties of CdS thin films were investigated. The resistivity decreased to order of 102Ω-cm in Sn doped film. X-ray diffraction analysis showed that the doped films have a preferred orientation along (111) plane. It was found to have a better transmission of light in doped films than undoped one. Consequently, the results indicate that Sn doped CdS is a suitable material in window layer of CdTe and CIGS solar cell application.