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Mariamma Mathew

Bio: Mariamma Mathew is an academic researcher from Vikram Sarabhai Space Centre. The author has contributed to research in topics: Hydrophobic silica & Aerogel. The author has an hindex of 1, co-authored 5 publications receiving 10 citations.

Papers
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TL;DR: NicNickel-cobalt ferrite (NCF) without Sn-dopant and with (x = 0 to 0.1%), (Ni 0.7Co 0.4+ d) have been synthesized through solid-state route.
Abstract: Nickel-cobalt ferrite (NCF) without Sn-dopant and with (x = 0 to 0.1%), (Ni0.7Co0.3)(Fe2–xSnx)O4+ d, have been synthesized through solid-state route. Calcination of oxides at 900°C yielded spinel p...

9 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of ceramization heat treatment conditions on phase constitution and microstructures were analyzed using XRD and HRSEM respectively, and the optimum heat treatment condition for achieving uniformly distributed fluorophlogopite phase essential for machinability and at the same time, magnesium aluminum silicate phase for increasing the hardness, was presented.
Abstract: Mica containing glass-ceramic is prepared by crystallizing magnesium alumino silicate glass between 600°C and 1100°C without the use of any additives or nucleating agents. Effects of ceramization heat treatment conditions on phase constitution and microstructures are analyzed using XRD and HRSEM respectively. Developed glass-ceramics have been analyzed for its microhardness and machinability. Optimum heat treatment condition for achieving uniformly distributed fluorophlogopite phase essential for machinability, and at the same time, magnesium aluminum silicate phase for increasing the hardness, is presented.

3 citations

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TL;DR: In this paper, the dielectric properties have been measured near 4GHz by standard rod resonator methods using cylindrical specimens, and it is possible to further improve the Qf of these ceramics by controlling the processing.
Abstract: BaTi4O9(BT4), has dielectric constant (er)≈36 and unloaded Q-factor (Qf) >35,000GHz, but has temperature coefficient of frequency (τf~16-20ppm/°C). Ba2Ti9O20(B2T9), very near to BT4 in the BaO-TiO2 phase diagram, has er~38, Qf~35,000GHz and τf 97.5%). XRD analysis has confirmed the BaTi4O9 phase formation along with secondary phases. FeSEM microstructures show liquid phase assisted sintering leading to fused grains and exaggerated grain growth. The dielectric properties have been measured near 4GHz by standard rod resonator methods using cylindrical specimens. The ceramics have er36.5−38, τf 17THz. It is possible to further improve the Qf of these ceramics by controlling the processing.

1 citations

Journal ArticleDOI
TL;DR: In this paper, the results of measurement of permittivities and results of silica beads and silica aerogels have been presented for the 20 Hz-1 MHz range and less than 1.6 at 1 MHz.
Abstract: Materials with relative permittivity or dielectric constant near to that of air (er~1) are known as ‘ultra-low k’ materials. They find a number of applications in inter-connects of micro-electronic circuits, antennae, high-speed communication substrates etc. Among the inorganic materials, porous silica is the widely studied candidate. Porous silica can be of many types depending upon the extent of porosity and size and connectivity of pores. This paper presents the details of measurement of permittivities and the results of silica beads and silica aerogels. Silica beads, prepared by microwave heating of silica gels, are spherical beads of average 1mm size. Hydrophobic silica aerogels, prepared by ambient pressure drying of silica gels, are irregular chunks of 5-10 mm size. Both are potential bulk fill insulation materials and hence the permittivity can be measured as an aggregate filling a definite volume. The permittivities of these have been measured upto 1 MHz by 3-terminal method using a precision LCR meter and a powder-paste cell as per ASTM-D150-11. The er values of silica aerogels and silica beads in 20 Hz-1 MHz range could be measured and are less than 1.6 at 1 MHz.

1 citations

Journal ArticleDOI
TL;DR: In this article, high surface area (570 m2/g), low density (0.07 g/cm3) and contact angle (1-3 mm) are characterized for silica aerogel granules.
Abstract: Silica aerogels have been prepared through sol-gel process by polymerization of TEOS in the presence of NH4F and NH4OH as catalysts. The solvent present in the gel is replaced by ethanol followed by a non-polar solvent such as n-hexane prior to solvent modification step. Gels are made hydrophobic by treating them with HMDZ to prevent rupture during drying, which has been confirmed by FTIR. Gels are then washed and dried carefully in a PID controlled oven at atmospheric pressure. The ageing duration and solvent exchange combinations are optimized to yield crack-free gels prior to drying. Aerogels are characterized for density, specific surface area, pore volume, pore size, thermal stability and contact angle. Hydrophobic, high surface area (570 m2/g), low density (0.07 g/cm3) silica aerogels are synthesized by using optimized mole ratio of precursors and catalysts. Silica aerogel granules (1-3 mm) as well as monoliths (Ф~35 mm) could be produced through ambient pressure drying of gels.

1 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the effect of rare earth lanthanum metal on the structural, physical-chemical, morphological, thermal and overall properties of Ni-Co ferrites has been evaluated.

21 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to use the Deanship for Scientific Research (Project application No. 2020-164-IRMC), which is supported by the US Department of Defense.
Abstract: This work is supported by Deanship for Scientific Research (Project application No. 2020-164-IRMC).

13 citations

Journal ArticleDOI
TL;DR: In this paper , the electrical and dielectric properties of NiCoGaFe-MSF at temperatures ranging from 20 to 120 °C were systematically studied as a result of 3D graphical drawing of the data obtained from an impedance analyzer.

7 citations

Journal ArticleDOI
12 Apr 2021
TL;DR: In this paper, the impact of V5+ substitution on the structural, magnetic, dielectric and electrical properties of Ni-Zn-Co ferrites has been studied.
Abstract: We have investigated the Vanadium- (V) substituted Ni–Zn–Co ferrites where the samples are prepared using the solid-state reaction technique. The impact of V5+ substitution on the structural, magnetic, dielectric and electrical properties of Ni–Zn–Co ferrites has been studied. The XRD analysis confirms the formation of a single-phase cubic spinel structure. The lattice constants have been calculated both theoretically and experimentally along with other structural parameters such as bulk density, x-ray density and porosity. The FESEM images are studied for analyzing the surface morphology. FTIR measurement confirms spinel structure formation. The saturation magnetization (M s), coercive field (H c) and Bohr magnet on (μ B) are calculated from the obtained M-H loops. The temperature-dependent permeability is studied to obtain the Curie temperature. The frequency and the composition dependence of permeability are also analyzed. Frequency dependent dielectric behavior and ac resistivity are also investigated. An inverse relationship is observed between the composition dependent dielectric constant and ac resistivity. The obtained results such as the electrical resistivity, dielectric constants and magnetic properties suggest the appropriateness of the studied ferrites in microwave device applications.

7 citations

Journal ArticleDOI
TL;DR: In this paper, high-temperature alkali fusion was applied to extract the Si, Al and Fe in the tailings so as to maximize recovery of valuable elements, which could be attributed to the presence of iron oxide.
Abstract: Silica-based aerogel composite was prepared adopting sol–gel technique combined with atmospheric drying method utilizing waste environmentally hazardous iron tailings. High-temperature alkali fusion was applied to extract the Si, Al and Fe in the tailings so as to maximize recovery of valuable elements. The SiO2-Al2O3 (SA) and SiO2-Al2O3-Fe2O3 (SAF) aerogel composites were subjected to assess its adsorption capacity for macromolecules, utilizing methylene blue (MB) as the adsorbate. The specific surface areas of the SA and SAF aerogel were estimated to be 922.03 m2/g and 683.84 m2/g. The equilibrium adsorption capacity for MB was estimated to be 318.47 mg/g and 334.44 mg/g, respectively. Although the specific surface area of SAF was lower than SA, it offered higher MB adsorption capacity which could be attributed to the presence of iron oxide. The results promised utilization of iron tailing generated aerogel composite as a potential adsorbent for separation of high molecular weight compounds.

5 citations