W. M. Daud

Dielectric and ultrasonic properties of rubber wood. Effect of moisture content grain direction and frequency

Dielectric properties of rubber wood have been studied at low and microwave frequencies with different moisture content and grain direction. The ultrasonic properties were studied with pulsed longitudinal waves of frequency 45 kHz, Two anisotropic directions have been considered for this study — parallel and perpendicular to grain. The low frequencies were of 0.01, 0.1, L0, 10 and 100 Hz and microwave frequencies were of 1, 2.45, 6, 8, 10, 14 and 17 GHz. The moisture content affected the dielectric constant and dielectric loss factor both at low and microwave frequencies? The moisture content above 30% showed little influence on dielectric properties whereas it increases linearly from 0 to 30% in both the grain directions at low frequencies. A continuous increase of dielectric properties was obtained with the increase of moisture content at microwave frequencies and the trend becomes concave upward. Dielectric properties increase as the frequencies increase except dielectric loss factor at microwave frequencies where reverse trends were observed. Little change of dielectric loss factor was obtained at frequencies above 6 GHz. The parallel to grain direction showed higher dielectric constant and dielectric loss factor compared to perpendicular to grain direction. This dielectric anisotropy of wood may be attributed due to the microscopic, macroscopic molecular as well as chemical constituents of wood. Ultrasonic properties were also affected considerably by the moisture content and grain direction. The dried wood showed higher ultrasonic velocity and elastic stiffness constant compared to green wood. The parallel to grain direction exhibits higher ultrasonic velocity and elastic stiffness constant than perpendicular to grain.ZusammenfassungDie dielektrischen Eigenschaften von Hevea brasiliensis wurden bei niedriger und Mikrowellenfrequenz sowie unterschiedlichen Feuchten und Faserrrichtungen untersucht. Die Ultraschalleigenschaften wurden mit gepulsten Longitudinalwellen von 45 kHz bestimmt. Beide Bestimmungen erfolgten parallel und senkrecht zur Faser. Als niedrige Frequenzen wurden 0,01, 0,1, 1,0, 10 und 100 Hz eingesetzt, im Mikrowellenbereich 1, 2, 4, 5, 6, 8, 10, 14 und 17 GHz. Die Feuchte beeinflußt die Dielektrizitätskonstante und den Verlustfaktor in beiden Frequenzbereichen. Zwischen 0 und 30% Feuchte steigt die Dielektrizitätskonstante bei niedrigen Frequenzen linear

Optical Properties of Ternary TeO2-B2O3-ZnO Glass System

A series of ternary tellurite based glasses [(TeO2)70 (B203)30]100–x [ZnO]x glasses with different compositions of ZnO (x= 5 to 30 wt.% in steps of 5 wt.%) have been synthesized by melt quenching method. The role of ZnO to the glasses structure was studied by IR spectroscopy. FTIR spectra revealed broad, weak and strong absorption bands in the investigated range of wavenumber from 280–4000 cm−1 which associated with their corresponding bond modes of vibration and the glass structure. The indirect optical band gap and the direct optical band gap are in the range 2.08–3.12 and 1.54–2.36 eV, respectively. A decrease in the values of energy band gap Eg may come down to the reason that the non-bridging oxygen ion content increases with increasing ZnO content and shifting the band edge to lower energies. The optical band gap and Urbach energies were calculated from the absorption spectra measured between 190 and 900 nm at room temperature. The refractive index, n of the glasses change from 1.84–2.00 while the molar refractivities decrease from 13.06 to 12.00 with the increase of ZnO in mol%.

Dielectric study of electrolyzed rubber

Rubber was produced by placing rubber latex between two electrodes between which an external voltage was maintained. The thickness of the rubber deposited on the anode was measured as a function of time of electrolysis, voltage applied across the electrodes and distance between the electrodes. Based on the observed dielectric responses of rubber obtained through the electrolysis process, an electrical model of conductance and complex capacitance elements linked in parallel is proposed, indicating the additive nature of the individual responses in the system. Electrical representation of rubber obtained by simple drying however showed two different models. Natural rubber was found to have all the elements connected in parallel while that of vulcanized rubber was found to have a series connection of a pair of parallel connected conductance and capacitance elements.