Dielectric Properties of Hevea Rubber Latex

The dielectric properties of Hevea Rubber Latex have not been thoroughly investigated and are, therefore, not well understood. It is a biological product with a complex composition. A typical composition of freshly tapped natural rubber is made up of 50-80% water, 18-45% rubber hydrocarbon and 2-5% non-rubber constituents. The basic components of non-rubber constituent are proteins, lipids, quebrachitol and inorganic salts. Measurements of the dielectric properties at various moisture contents and temperature s -20 to -60°C in the lowfrequency region of 10⁻² to 10⁶ Hz were done using the Dielectric Spectrometer. The results of the measurement in the low-frequency region are expressed using the dielectric response model. For Hevea rubber latex, three distinct responses have been indicated. These are the real relative permittivity at high frequency ɛ(∞), the loss peak response ɛip and the conductance G. The total losses are conductive losses which arise due to the conducting phases found in latex, and dipolar losses which appear as loss peak responses due to the relaxation of the water molecules. The relaxation peak is shifted to a higher frequency as water content in the latex decreases and as temperature increases. This phenomenon could be due to the difference in the mechanism of polarisation relating to ion and the polarisation relating to ice. The activation energy for latex concentrate is l.66 eV while for fresh latex 2.34 eV. Ice has a non-constant activation process. This is due to the existence of two activation processes. The first activation process gives an activation energy of 0.51 eV whilst the second activation process results in a much lower activation energy. The high activation energy for fresh latex as compared to ice could be due to latex particles being bonded by the water molecules which needs more energy to dissociate. In the microwave region of 0.2 to 20 GHz, dielectric measurements were done using an open-ended coaxial sensor and an automated network analyser at various moisture contents and temperatures from -30 to 50°C. Experimental results in the microwave region show that in the liquid state a conductive loss due water molecules. However, at 10 GHz there is a good relationship between the dielectric properties of hevea latex and moisture content and is almost unaffected by the non-rubber constituents, presevatives and temperature Therefore, 10 GHz is the most suitable frequency for the analysis and design of the microwave moisture meter or latexometer There is a steep increase in the real relative permIttivity of about one order of magnitude and dielectric loss factor of about two orders as the phase of latex changes from solid to liquid

Dielectric properties of strontium titanate in the 1 MHz to 1.5 GHz frequency regions

Strontium Titanate, SrTiO3 samples were prepared using the conventional solid state reaction method. SrTiO3 samples were sintered at 1100°C, 1200°C, and 1300°C. XRD was used to determine the crystalline structure of the samples. The AFM showed the grain size was significantly increased with an increase in sintering temperatures. The dielectric properties of the sample were measured using Agilent 4291B Impedance/material Analyzer in the sub-microwave region in the frequency range 1 MHz to 1.5 GHz at room temperature. The dielectric constant and the average grain size were found to be the highest for the SrTiO3 sample sintered at 1200°C. Hence, greatest dielectric polarization occurred in the sample with the largest grain size

Simultaneous analysis of conductivity and concentration of saline solutions and sea water at microwave frequencies from dielectric investigation.

Prediction of conductivity and concentration of saline solutions and sea water are calculated from dielectric spectra at microwave frequencies of 2 GHz and 5 GHz respectively. The calculation is based on two different previously published empirical models relating to conductivity and concentration. An empirical relationship is established and is used to find corrected calculated conductivity and concentration. The expected results are verified with standard measurement where correlation coefficient of given is 0.98 and above. The data is useful as tools for quality indication of liquid samples

Microwave dielectric characterization of hevea rubber latex at 2.6, 10 and 18 GHz

Dielectric properties of natural rubber Hevea brasiliensis latex were measured at frequencies 0.2 to 20 GHz, at temperatures of 2, 15, 25, 35, and 50°C and around 30-98% moisture content. Measurements were done using open-ended coaxial line sensor and automated network analyzer. As expected, results showed that dielectric constant increased with increasing moisture. From 0.2 to 2.6 GHz, the losses were governed by conductive losses but for frequencies greater than 2.6 GHz, these were mainly due to dipolar losses. The former is due to conducting phases in hevea latex, while the latter is mainly governed by the orientation of water molecules. The results were analyzed at 2.6, 10, and 18 GHz, respectively. These were then compared with the values predicted by the dielectric mixture equations recommended by Weiner, Bruggeman and Kraszewski. All the measured values were found to be within the Weiner's boundaries and close to the upper limit of Weiner's model. It is also close to the predicted values of Bruggeman's model with a/b = 0.1. All the models including Kraszewski are suitable for predicting the dielectric properties of hevea latex for frequencies 2.6 to 18 GHz, moisture content 30 to 98% and temperatures 2 to 50°C

Monitoring microwave dielectric properties during transesterification reaction for palm biodiesel production

Microwave energy offers a fast method to produce biodiesel with advantages of enhancing the reaction rate and improving the reaction separation. The dielectric properties at frequency range from 0.2 GHz to 20 GHz of a mixture during transesterification reaction which are used for producing palm biodiesel were presented. The monitoring was done by placing a dielectric probe at the upper level and lower level of the mixture to measure the dielectric properties during the formation of biodiesel and glycerin respectively. In the transesterification reaction, the mixture consisting of vegetable oil, methanol and sodium hydroxide was heated at a constant temperature of about 45-50 o C and stirred for homogeneity. Results of the measurement over the frequency range showed drastic changes on the dielectric properties in the first 3 minutes of the reaction and after 3 minutes, the dielectric properties slowly decreased and approached the dielectric properties of biodiesel or glycerin. This study gives valuable information on the optimum mixing time for microwave transesterification reaction. These properties could be used to estimate absorbed power by the mixture for application in microwave transesterification process as dielectric loss of the mixture changed from 20 to about 0.5 as the transesterification reaction was completed

Bianchi type III string cosmological models for perfect fluid distribution in general relativity

Some geometrical aspects of Bianchi type III space‐time are investigated. This is followed by the study of Bianchi type III string cosmological models with perfect fluid distribution of matter

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

Conductivity analysis of Bi4Ti3O12 ferroelectric ceramic: a comprehensive study from the dynamic aspects of hopping conduction

Objectives: We focus solely on a comprehensive conductivity analysis of Bi4Ti3O12 ceramic, in a bid to bring seminal ideas for dielectric components, in particular frequency and temperature ranges. Methods/Statistical Analysis: The synthesis of Bi4Ti3O12 ceramic is based on a mechanical activation method. The following sintering at 1273 K ascertains the Bi4Ti3O12 appears to be of single phase crystallizes in orthorhombic form, whose conductivity is determined from the dielectric function in the context of Kramers-Kronig relation on which of this is measured in the frequency domain at varying temperatures. The evaluation of conductivity data is mainly in terms of activation energy. Findings: We find that the separately discussed dc and ac conductivities in similar manner are best isolated into two distinct temperature regions. Charge transport by hopping to the target localized states is the relevant conduction mechanism in bringing insights into the dynamic responses. Variable range and small polaron hopping models associated with the adiabatic small polaron are the decent choices, each of which explaining the dc conductions in these temperature regions. The former involves distant hops, whereas the latter denotes as nearest-neighbour hopping. The percolation treatments applied in the dc conductivity yield promising results if different percolation expressions are used. The correlation between dc and ac conductions for each temperature is irrefutably made through the Barton-Nakajima-Namikawa fitting. In frequency dependence ac regions, the thermally activated hopping carriers are transported in a correlated to a random manner between preferred sites. Performing a Summerfield ac scaling in these temperature regions leads to different scenarios in view of time-temperature superposition principle. Applications/Improvements: Further experiments are encouraged to support the hopping conduction mechanisms from another aspect in order to prompt the use as energy storage function in the electromagnetic application

Dielectric properties of strontium titanate filled mullite composites in microwave region

This research was designed to form better dielectric composite material using one steady state dielectric with a good dielectric material. Distinct dielectric composite was successfully produced using locally sourced kaolinite clay. The samples were made using kaolinite as the base matrix and Strontium Titanate (ST) added in varying ratios. Strontium Titanate were synthesized via solid‐state reaction using Strontium Carbonate and rutile Titanium (IV) Oxide with sintering at 1300 °C. Local white kaolinite was used to fuse the barium titanate material in varying weight ratios. The powders were dry‐mixed and made into pellets for calcination at 1000 °C. The dielectric measurements were carried out using the HP 4291B Impedance Analyzer dielectric setup. Three samples were prepared, namely 10%ST, 20%ST and 30%ST. The dielectric measurements were carried out at room temperature. Microwave region measurements showed steady state and linear dielectric relaxation ranging from 7 in the control sample and dropping down to 5 in 30%ST. The responses indicate linear relation between ST addition and microwave region dielectric permittivity

Bianchi type III string cosmological models for perfect fluid distribution in general relativity

Some geometrical aspects of Bianchi type III space‐time are investigated. This is followed by the study of Bianchi type III string cosmological models with perfect fluid distribution of matter