Mohammad A. Al-Eshaikh

Effect of Optimum Parameters Setting on Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy is very attractive analytical method owing to many advantages, but it is complicated by the matrix effect due to complex nature of the laser–sample and plasma–particles interaction processes. For more precise and accurate analysis results, this effect must be reduced to a minimum. The approach used in this study to reduce the matrix effect was based on the selection of the optimum parameters of the system using pure element standards, followed by data processing and various normalization techniques. The copper alloys were selected for this study knowing that these materials are particularly difficult to be analyzed by laser-induced breakdown spectroscopy due to large differences in the physical properties of the metal constituents. But the accuracy improvements obtained by the proposed approach are encouraging to generalize it to other similar materials. Eighteen reference standards of copper alloys were measured to construct the calibration curves after optimum parameter settings. The coefficients of determination, R 2, obtained from the calibration curves of most elements present in copper alloys were close to 1 (0.99). The validation of this approach was verified by extra reference standards measurement, which gives relative measurement errors varying from about 1–8% according to the inverse level of the element concentration.

Effect of Uniform Dispersion of Single-Wall Carbon Nanotubes on the Thermoelectric Properties of BiSbTe-Based Nanocomposites

Thermoelectric properties of BiSbTe-based bulk nanocomposites by incorporation of single-wall carbon nanotubes (SWCNTs) in different (0.0, 0.5, 1.0 and 1.5) vol.% were investigated from 300 K to 500 K. SWCNTs were uniformly dispersed in BiSbTe via a combination of ultra-sonication, magnetic stirring and mild ball milling. Fine BiSbTe powder was formed by crushing and ball milling the lumps in an inert environment. The composites demonstrate grain boundary structures exhibiting a three-dimensional network of one-dimensional flexible SWCNTs in BiSbTe bulks. The homogenous distribution of SWCNTs in BiSbTe drastically changes the transport properties of the composites. At 0.5 vol.% of SWCNTs, the effective thermal conductivity decreases suggesting the increased phonon scattering. Meanwhile, at 1.0 vol.% and 1.5 vol.%, the conductivities of the composites somehow increases attributed to homogenous distribution of SWCNTs in the BiSbTe matrix. The increased electrical resistivity with the addition of SWCNTs implies the enhanced scattering of carriers at the grain boundaries and SWCNTs/BiSbTe interfaces. The dimensionless figure of merit somewhat decreases with the addition of 0.5 vol.% SWCNTs. The results suggest that the figure of merit can be improved by optimizing the SWCNT composition below 0.5 vol.% by adequately tailoring the thermoelectric transport.

Processing and Thermal Properties of Multiwall Carbon Nanotube/Bismuth Antimony Telluride Composites for Nuclear Energy Applications

In this work the effects of ball milling and carbon nanotubes incorporation on the thermal conductivities of the bulk BiSbTe composites were evaluated. The coarse BiSbTe particles were obtained by crushing BiSbTe lumps and subsequently high energy ball milling was employed in an inert environment to form the fine BiSbTe powder. Multiwall carbon nanotubes in different (0.0, 0.5 and 1.5) vol. % were uniformly mixed in the BiSbTe powder through a combination of ultra-sonication and ball milling, and then processed by rapid high frequency induction heated sintering (HFIHS) to achieve fully dense nanocomposite. Thermal diffusivity of the composites was evaluated and heat capacity was approximated using Pyrocerarm as a reference material. The effect of carbon nanotubes inclusion and BiSbTe particle size reduction on the thermal conductivity was studied from 300 to 500 K. The results show a significant reduction in the thermal conductivity due to the enhanced thermal boundary interface resistance correlated with the fine microstructure/nanostructure in the composites as compared to pristine bulk bismuth antimony telluride.

Analysis of allyl diglycol carbonate by laser induced-breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been used to identify the impurities in the allyl diglycol carbonate, which is used as a charged particle track recording material in solid-state nuclear track detectors. Impurities of magnesium, calcium, sodium and silicon are detected. Plasma parameters such as temperature and electron density are also calculated at optimized conditions in air and argon atmosphere using the silicon lines. The temperature of the LIBS plasma produced in argon atmosphere was higher than the temperature of the LIBS plasma produced in air. Variation in the emission intensity of the carbon I line (247.8561 nm) with respect to acquisition delay and laser power is also studied. It is found that the intensities of Ca and Na lines from LIBS spectra were enhanced 30–40 times in an argon atmosphere as compared to air. Hence LIBS in an argon atmosphere can be used for better identification of impurities in plastics.