Papers by Author: M.Z.A. Yahya

Abstract: Polymer electrolytes consist of poly(vinylidene fluoride –hexafluoropropylene) (PVDF-HFP) and lithium trifluoromethanesulfonate, LiTf (LiCF3SO3) were prepared by dissolving in dimethylformamide (DMF) using solution casting method and further dried in vacuum oven. The conductivity of each sample was investigated using electrochemical impedance spectroscopy (EIS) method. The samples were measured in two different environments viz. in humidity chamber (40% RH; 27°C) and at ambient condition (~60% RH; 27°C). The maximum conductivity obtained for the samples in humidity chamber was 8.05 × 10-5 S/cm with addition of 35 wt% of LiTf. Meanwhile, the highest conducting samples (with addition of 45 wt% of LiTf) exhibited the ambient condition temperature of 1.11 ×10-4 S/cm. Further increased salt concentration from the optimize concentration values has reduced the conductivity of the polymer electrolyte. Dielectric permittivity studies revealed that samples showed the non-Debye behaviors

Abstract: The optical and electronic structures of poly (N-carbazole) (PVK) blend with poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) and polyvinylpyrrolidone (PVP) in the same composition were investigated. Polymer coating was carried out using doctor blade technique on a glass substrate. Uv-vis and photoluminescence spectrum revealed that there are significant different results obtained between PVK, PVK:PVP and PVK:PVDF-HFP. The electronic parameters such as absorption edge (Ee), allowed direct bandgap (Ed), allowed indirect bandgap (Ei) and Urbach edge (Eu) were calculated by using Tauc/Davis-Mott Model. The value of Ee and Ed for PVK and PVK:PVDF-HFP almost same but there was significant different value between Eu and Ei.

Abstract: A study was conducted on the effects of surface pre-treatment with 3- aminopropyltriethoxysilane (3-APS) on the water absorption and adhesion behaviour of two commercial alkyd and epoxy polyamide organic coatings on mild steel and glass substrates. The results indicated that using 3-APS as surface pre-treatment prior to coating resulted in a significant reduction of total water absorption for alkyd on both mild steel and glass substrate. Subsequently ile adhesion of alkyd is enhanced on both pre-treated mild steel and glass substrate. However 3-APS pre-treatment of mild steel increases water absorption of epoxy and lowers its adhesion strength. While 3-APS pre-treatment of glass reduces water absorption of epoxy and subsequently enhances the overall wet adhesion. These data are consistent with the known adsorption behaviour of 3-APS to steel, i.e. as an easily hydrolysed hydrogen-bond to the amine group, rather than as the more stable metal-oxide-silicon bond.

Abstract: Films of chitosan polymer doped with lithium acetate dihydrate (LiOAc.2H2O) and placticized with oleic acid (OA) and palmitic acid (PA) were prepared by the solution cast technique. The film containing 40.0 wt. % LiOAc and 10.0 wt. % of OA exhibit a room temperature conductivity of ~ 10-5 S cm-1 and the film containing 41.0 wt. % LiOAc and 7.7 wt. % of PA has conductivity ~ 10-6 S cm-1. The plot of ln(sT) versus 103/T for the highest conducting samples obey an Arrhenian relationship in the temperature range between 300 and 363 K implying that the conductivity is thermally assisted. FTIR spectroscopy and XRD techniques have been used for the complexation studies. The LiNiCoO2/chitosan-LiOAc-OA/MCMB electrochemical cell could be charged to a voltage of 4.2 V.

Abstract: The objective of this paper is to show that annealing lithiated transition metal oxide (LTMO) precursors obtained by the sol-gel method at insufficiently high temperatures may not produce the intended pure cathode active materials required in lithium batteries. In this work, LiMn1.5Ni0.5O4 which is a potential cathode active material in the 5 V-class is prepared by the solgel method. The precursor material was obtained when the solid gel was dried and heated at different temperatures in the range between 200 °C and 900 °C for 4 hours. It was observed that on heating the precursor material at least at 500 °C for 4 hours the material produced was LiMn1.5Ni0.5O4 in the present form as proven by the x-ray diffractogram (XRD). On heating at temperatures below this, the formation of LiMn1.5Ni0.5O4 was uncomplete and at temperatures above 500 °C the intensity of the peak at 2q = 18° decreases. The noise level also increased at temperatures above 500 °C.