69 research outputs found
Thermal conductivity of refractory glass fibres
In the present study, the current international
standards and corresponding apparatus for measuring the
thermal conductivity of refractory glass fibre products have
been reviewed. Refractory glass fibres are normally produced
in the form of low-density needled mats. A major
issue with thermal conductivity measurements of these
materials is lack of reproducibility in the test results due to
transformation of the test material during the test. Also
needled mats are inherently inhomogeneous, and this poses
additional problems. To be able to compare the various
methods of thermal conductivity measurement, a refractory
reference material was designed which is capable of
withstanding maximum test temperatures (1673 K) with
minimum transformation. The thermal conductivity of this
reference material was then measured using various
methods according to the different standards surveyed. In
order to compare different materials, samples have been
acquired from major refractory glass fibre manufacturers
and the results have been compared against the newly
introduced reference material. Materials manufactured by
melt spinning, melt blowing and sol–gel have been studied,
and results compared with literature values
Microstructural and Mössbauer properties of low temperature synthesized Ni-Cd-Al ferrite nanoparticles
We report the influence of Al3+ doping on the microstructural and Mössbauer properties of ferrite nanoparticles of basic composition Ni0.2Cd0.3Fe2.5 - xAlxO4 (0.0 ≤ x ≤ 0.5) prepared through simple sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray, transmission electron microscopy (TEM), Fourier transformation infrared (FTIR), and Mössbauer spectroscopy techniques were used to investigate the structural, chemical, and Mössbauer properties of the grown nanoparticles. XRD results confirm that all the samples are single-phase cubic spinel in structure excluding the presence of any secondary phase corresponding to any structure. SEM micrographs show the synthesized nanoparticles are agglomerated but spherical in shape. The average crystallite size of the grown nanoparticles was calculated through Scherrer formula and confirmed by TEM and was found between 2 and 8 nm (± 1). FTIR results show the presence of two vibrational bands corresponding to tetrahedral and octahedral sites. Mössbauer spectroscopy shows that all the samples exhibit superparamagnetism, and the quadrupole interaction increases with the substitution of Al3+ ions
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