Zainal Arifin Ahmad

Wideband dielectric resonator antenna for C-Band application

Two segment rectangular dielectric resonator antenna of high permittivity (epsivr = 30) ceramic material was design and fabricated at C-band. The antenna was fed with 50Omega microstrip transmission line. In this design, both dielectric resonators (DRs) are separated with metal plate which acting as shorting post. The length of the two DRs is 7.7 mm and 2.2 mm respectively. The optimum distance from the port was chosen at 17.195 mm. The simulated result shows this type of antenna produces wide bandwidth and omni-directional radiation pattern. The simulated gain was 5.5 dB. The result shows the potentiality of this antenna to be used in the wireless communication.

Nanoscale Investigation of Nb-Doped CaCu3Ti4O12 Grains

CaCu3Ti4O12 (CCTO) is a promising material for microelectronic and microwave device applications due to its unique properties that posses high dielectric constant in the wide temperature range. In this work, atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses were applied for nanoscale imaging of Nb-doped CCTO grains. The Nb-doped CCTO pellets (CaCu3Ti4-xNbxO12+x/2; x = 0, 0.01, 0.03, 0.05, 0.1) were prepared via solid state reaction method and thermally etched at 940°C for an hour. From AFM and SEM images found that tiny bumped as well as terrace type domains are distributed within a grain. The domain size is ranging from 20 to 180 nm measured by AFM. The existence of domains on grain will produce grain boundary and domain boundary resistance inside CCTO. Both domain and grain resistance are believed to strongly influence the electrical properties of CCTO.

Influence of binder in iron matrix composites

The ability to use iron and its alloys as the matrix material in composite systems is of great importance because it is the most widely used metallic material with a variety of commercially available steel grades [1]. The aim of this study is to investigate the influence of binder in particulate iron based metal matrix composites. There are four types of binder that were used in this study; Stearic Acid, Gummi Arabisch, Polyvinyl alcohol 15000 MW and Polyvinyl alcohol 22000 MW. Six different weight percentage of each binder was prepared to produce the composite materials using powder metallurgy (P/M) route; consists of dry mixing, uniaxially compacting at 750 MPa and vacuum sintering at 1100° C for two hours. Their characterization included a study of density, porosity, hardness and microstructure. Results indicate that MMC was affected by the binder and stearic acid as a binder produced better properties of the composite.

Synthesize CCTO Using Different Mixing Media

In recent years, there has been an increasing interest on high dielectric constant that have significant applications in electronic devices. Dielectric materials have many technological applications such as capacitors, resonators and filters. High dielectric ceramic capacitors based perovskite oxides are necessary for modern electronic devices and are found to be suitable for a wide range of applications. Subramanian et al. discovered the high dielectric constant of CaCu3Ti4O12 (CCTO) ~ 10,000 at room temperature. CCTO has the cubic perovskite crystal structure and high dielectric constant of ~ 104 up to 105 at radio frequency and good temperature stability over a wide temperature range [1,2]. These properties were desired for various microelectronic applications. With the high dielectric constant, the material can store more charge and the values make CCTO an attractive material for ultra-high energy density capacitors. However, this properties can be accomplished if single phase of CCTO is formed. Many research have been done recently on the synthesis of the cubic perovskite CCTO and many techniques are working such as sol-gel route [3], combustion techniques [4], molten salt process [5] and etc., but this technique is difficult and complex process during sample preparation.

Porous Ceramic Supports Prepared from Porcelain Mixture

The present paper reports the polymeric sponge method of porous ceramic supports from porcelain mixtures. In this work, polyurethane (PU) foam with three different pore sizes have been selected, which are 100 ppi and 120 ppi as a substrate (support) and 10 ppi as an intermediate layer (catalyst support). In addition, the tubular support shape is selected, which its provide mechanical strength to intermediate layer and membrane layer to withstand the stress induced by the pressure applied over the whole supports. Tubular configuration has been produced by polymeric sponge method. The foam with 120 ppi has a positive effect on the porosity ratio of supports compared to those prepared from 100 ppi. Moreover, the influence of the sintering temperature on the total porosity, average pore size and compressive strength of supports has been investigated.

Characterization of metakaolin treated at different calcination temperatures

This paper presents the characterization of chemical and physical properties of metakaolin obtained via calcination of kaolin at three different temperatures (650˚C, 750˚C and 850˚C) in comparison to that of pure or non-calcined kaolin. Chemical compositions and content of amorphous compound of the resulting metakaolin were assessed with the aid of X-ray fluorescence (XRF), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Particle size analyser was used to study the physical properties of the resulting metakaolin produced in the laboratory from purified kaolin, in order to compare their properties. In thermally activated products, the calcination regimes have an important influence on the properties and long-term durability performance of the cementitious matrices. Further, the evaluation of amorphous material (glassy phase) of the metakaolin was undertaken. The results of chemical compositions for metakaolin using XRF technique showed that the composition of the major oxides (Si O2 + Al2O3 + Fe2O3) was 94.86%, 97.93% and 95.30% for metakaolin treated at a temperatures of 650˚C, 750˚C and 850˚C, respectively. The XRD patterns show that some ingredients are insoluble for the three different temperatures of metakaolin that peaks at 2θ (between 17˚and 27˚). The percentage of SiO2 as glassy phase from the total weight of the metakaolin at 650˚C, 750˚C and 850˚C is 36.79%, 41.57% and 39.24%, while, the total percentages of amorphous compounds (glassy phase) are 79.41%, 81.86% and 82.17%, respectively. The specific gravity of the metakaolin is 2.6. Hence, the calcination temperatures influence the chemical compositions as well as the content of amorphous compound in the metakaolin, which will affect the reactivity of the metakaolin.This paper presents the characterization of chemical and physical properties of metakaolin obtained via calcination of kaolin at three different temperatures (650˚C, 750˚C and 850˚C) in comparison to that of pure or non-calcined kaolin. Chemical compositions and content of amorphous compound of the resulting metakaolin were assessed with the aid of X-ray fluorescence (XRF), X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Particle size analyser was used to study the physical properties of the resulting metakaolin produced in the laboratory from purified kaolin, in order to compare their properties. In thermally activated products, the calcination regimes have an important influence on the properties and long-term durability performance of the cementitious matrices. Further, the evaluation of amorphous material (glassy phase) of the metakaolin was undertaken. The results of chemical compositions for metakaolin using XRF technique showed that the composition of the major oxides (S...

Study on Conversion Time of Brushite to Monetite via Hydrothermal Method

The aim of this research is to identify the optimum conversion time of brushite to monetite. Obtaining optimum conversion time is important to reduce energy consumption and time for cost saving. The presence of distilled water in brushite powder with assistant of temperature and pressure for 45 min under hydrothermal treatment yielded to monetite. The constant temperature at 160 °C with 15, 30, 45 and 60 min for treatment times was used to execute the synthesis of monetite. The treatment times were extended until 2, 6 and 8 h to determine the transformation of phase. The XRD and SEM analysis were used for phase and morphology identifications. The XRD result at 45 min treatment time showed monetite peaks appeared greatly as compared to pure brushite. Whereas, the SEM results showed the existent of polygonal morphology that may referred to the monetite phase. The results obtained in this study conclude that at 45 min treatment time is the optimum conversion time from brushite to monetite

Improvement of Porous Porcelain through Glaze Coating

The dip coating procedure led to accumulation of coating particles at the coating solution and substrate interface. After sintered, frit dissolution implied an occurrence of liquid phase sintering. Simultaneous improvement of surface morphology and bulk density was evident. The significant appearance of cracks and roughed surface of plain porcelain was revolved into crack free and smoother exterior following the dip-coating and sintering process. The surface was properly glazed. This led to enhanced body densification, and sealing of apparent micropores. At the same time, the deposited coating reduced the amounts of open cells and surface defects, which caused reduction in porosity and increment of bulk density.