Kaleem Ahmad

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.

Characterization and analysis of nanostructured CdO thin film using LIBS technique

Nanostructured thin films of cadmium oxide (CdO) have been synthesized using sol-gel technique on slide glass substrates. Thickness of the film is about 250 nm with average grain sizes of CdO in the range of 93-250 nm. Laser induced breakdown spectroscopy (LIBS) is used to investigate the synthesized CdO thin film. We have investigated LIBS spectrum of CdO thin film in air atmosphere using Spectrolaser-7000 system with 100 mJ fundamental laser beam from Nd:YaG laser and varied delay times from 200 ns to 2 microseconds. Many atomic and ionic lines of Cd were resolved and the variation with the delay time was studied. The plasma parameters have also been studied for Cd 508.58 nm. It is found that plasma cooled very fast after 500 ns as compared to the bulk material. The later showed that the recombination processes are growing very fast with time for nanostructured CdO thin film.

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.

Qualitative analysis of dental nano-composite restorative material using laser induced breakdown spectroscopy and EDS analysis

We have presented Analysis of UV irradiated dental nanocomposites restorative materials using laser-induced breakdown spectroscopy (LIBS). Samples of the materials are irradiated with UV light using 3M ESPE Elipar FreeLight2 Source. LIBS spectra of the samples are recorded using fundamental beam from Q-Switched Nd: YAG laser in conjunction with MS257 Spectrograph (Oriel instrument) equipped with Andor iStar ICCD camera. The emission spectra of these samples have been recorded as a function of laser irradiance. Traces of Titanium, Silicon, Aluminum, Strontium, Zirconium, Sodium and Calcium are detected in these samples. The elemental composition is found to be quite similar but the relative abundance of Zr and Si is higher in more UV exposed material. The samples have also been analyzed with SEM EDS for comparison.

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.

Electrospun semiconducting nanofibers as an attractive material for renewable energy applications

The energy demand of the Kingdom of Saudi Arabia has significantly increased in the last several years and anticipated to be tripled by 2030. This energy hike is caused by high population growth, greater urbanization, and rapidly growing industrialization across the country. Despite the largest oil exporter and producer in the world, the Kingdom has planned to develop sustainable energy technologies to cater the significant portion of the growing energy needs through renewable resources. Nanotechnology provides novel solutions to harvest renewable energy through advanced technologies. In particular, semiconducting nanofiberous materials produced by the simple electrospinning are becoming promising candidates to solve the energy issues. This work highlights the fabrication and characterization of electrospun zinc oxide nanofibers. These types of materials have wide applications in energy devices such as fuel cell, dye-sensitized solar cell, Li-Ion batteries and super capacitors.