Microwave Dielectric Properties of Hevea Rubber Latex in the Temperature Range of -30°C to 50°C

The dielectric properties of hevea rubber latex were measured at selected microwave frequencies over the temperature range of -30°C to 50°C. The measurements were made on latex concentrate, fresh latex and diluted fresh latex by using an open-ended coaxial-line probe and an automated network analyser. There is a steep increase in the dielectric constant of about one order and dielectric loss factor of about two orders as the phase of latex changes from solid to liquid. The effect of temperature on the ionic conductivity at 0.2 GHz and dipole orientation at 2.6 GHz and above can be clearly seen in these studies. It was found that, the frequency around 10 GHz is a suitable operating frequency for microwave latexometer as dielectric properties are fairly independent of the temperature

Penentuan Struktur Permukaan dengan Menggunakan Kaedah Kapasitans

This work describes a method to obtain surface microtopography of a material by scanning its capacitance. Capacitance was measured by the three terminal method with the core of a coaxial cable used as the measuring probe while the shielding wire acted as the guard electrode to eliminate the fringing field effect. From our results, we found that good image resolution is best obtained if the medium used has a high dielectric constant than the sample

Spektroskopi Impedans Getah Asli Terepoksida (SMR5 dan ENR25)

Kertas ini melaporkan pengukuran spektroskopi impedans getah asli terepoksida yang dilakukan dengan menggunakan spektrometer dielektrik pada suhu 303, 313, 333, 353 dan 373 K dalam julat frekuensi 10-2 ke 106 Hz. Hasil eksperimen menunjukkan bahawa frekuensi santaian atau cirian bagi Z", komponen maya impedans, bertambah dengan penambahan suhu. Model rangkaian litar setara (Re) yang dicadangkan di dalam kajian ini adalah bersetuju dengan data uji kaji yang diperoleh untuk julat frekuensi 10-2 - 106 Hz

Recent development in spinel cobaltites for supercapacitor application

Precious metal oxides exhibit impressive characteristics that caught worldwide attention due to their promising capacitive performance, excellent electrochemical stability and low resistance, and these metal oxides have been extensively employed in supercapacitor application. This type of supercapacitors is known as redox supercapacitors or pseudocapacitors which applied faradaic process in storing energy in their systems. Thus, new materials with impressive electrochemical performance are highly demanded. In this aspect, cobaltite system with spinel structure has been the subject of intense research due to its established applications in electrochemistry. Besides, carbonaceous materials like activated carbons, carbon nanotubes, graphites, graphenes and fullerenes utilize electric double-layer capacitance whereby energy is stored by charge separation at an electrode/electrolyte interface. With greater development conducted on metal oxides and carbonaceous materials for supercapacitor application, introduction of hybrid and composite electrodes comprise of these two types of materials have been well received

Optical absorption spectrum of Cu2O-CaO-P2O5 glasses

Homogeneous CaO–P2O5 and Cu2O–CaO–P2O5 glasses were prepared using a melt-quenched method under controlled conditions. The binary glasses were found to be colourless and transparent while the ternary glasses changed from light green to dark green as the Cu2O content increased. From the absorption edge studies, the values of the optical band gap, Eopt and Urbach energy, ΔE were evaluated. The position of the absorption edge and hence the optical band gap were found to depend on the glass composition. Analysis of the optical band gap shows that for the binary glasses, the value increases as the content of CaO decreases, while for the ternary glasses, the value of the optical band gap increases as the content of the Cu2O decreases. The density of the glasses was also measured and was found to increase with the increase in CaO and Cu2O contents

Dielectric permittivity of nickel ferrites at microwave frequencies 1 MHz to 1.8 GHz

NiFe2O4 prepared via the sol–gel technique were pre-sintered at 900 °C and synthesized at different sintering temperatures from 1,000 °C to 1,200 °C at 100 °C intervals. The samples were characterized for microwave dielectric properties. These samples were measured using Agilent Impedance/Material Analyzer at frequencies 1 MHz to 1.8 GHz. Results showed a decrease in the dielectric constant and loss factor with frequency except at the turning point, around 150 MHz, where the loss factor showed a gradual increase. However, both the dielectric constant and loss factor increase with increasing sintering temperature. The grain size and density also increased with increasing sintering temperature, but the porosity and grain boundary density showed a decrease

Synthesis and electrochemical properties of nanostructured nickel–cobalt oxides as supercapacitor electrodes in aqueous media

Co-precipitation method was adopted in the preparation of nickel–cobalt oxides for potential application in supercapacitors. The formation of spinel nickel–cobalt oxide, NiCo2O4 started below 400 °C as confirmed by X-ray diffraction analysis. Pure phase nickel cobaltite with cation ratio of 1:2 (Ni:Co) was obtained at calcination temperature of 400 °C. The spinel phase decomposed gradually until 700 °C. The calcination time for the formation of NiCo2O4 was found to be between 2 to 4 h. The particle size of the prepared sample studied by transmission electron microscopy showed a value of 9.47 nm. The electrochemical properties of the metal oxide were measured in various acidic, neutral and alkaline electrolyte systems (1.0 M HCl, 1.0 M KCl and 1.0 M KOH) by employment of cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. Ideal capacitor behaviour with the largest operating voltage of 1.0 V and good electrochemical stability were observed in NiCo2O4 using neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest surface redox activity in 1.0 M KOH alkaline electrolyte but showed the lowest electrochemical performance in acidic electrolyte. At the current density of 0.5 A g−1, 1.0 M HCl, 1.0 M KCl and 1.0 M KOH gave specific capacitance values of 3.8, 41.9 and 249.8 F g−1 respectively

Synthesis and elastic behaviour of borate glass doped with high tellurite content

A systematic series of quality binary glass system of (x)TeO2)-(1-x)B2O3 with x = 60 to 80 (wt. %) were successfully synthesized by the rapid quenching method. The densities of each glass samples were determined using Archimedes method with acetone as a floatation medium. The molar volume have been estimated and analyzed for borate glasses doped with tellurite. Ultrasonics methods have been used to study the elastic properties of TeO2B2O3 glasses where the sound wave velocities have been measured in each glass samples at a frequency of 15 MHz and at room temperature. The velocities, both longitudinal and transverse, increase linearly with increasing of TeO2 content in a borate glass network. Their elastic moduli such as longitudinal, Young's, bulk and shear modulus have been calculated as a function of TeO2 concentration. Poisson's ratio and Debye temperature were also found to increase nonlinearly with TeO2 concentration. The glass transition temperature were determined by the differential thermogravimetric analysis at heating rate of 20 K min-1. However the glass transition temperature (Tg) slowly decrease as more tellurite is added into the borate glass network. © 2006 Asian Network for Scientific Information