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Mozafari M.,Oklahoma State University | Mozafari M.,Amirkabir University of Technology | Moztarzadeh F.,Amirkabir University of Technology | Vashaee D.,Helmerich Advanced Technology Research Center | Tayebi L.,Amirkabir University of Technology
2012 IEEE Green Technologies Conference | Year: 2012

In this research, lead sulfide (PbS) nanocrystals were synthesized via a simple, effective and green method. Then, the effects of heat-treatment at different temperatures on the PbS nanocrystals were investigated. In addition, the average crystallite size using Scherrer's formula, and lattice constant using Bragg's equation were calculated and compared with the standard value. The obtained results showed that an increase in the heat-treatment temperature from 250 to 450°C brought a significant increase in the average crystallite size D of PbS nanocrystals from 13.16 nm to 32.90 nm. The thermal stability of nanocrystals determines the possibility of using these materials in devices operating under conditions above room temperature. It suggests that an increase in the thermal stability extends the temperature range of practical applications. However, an increase in the operating temperature can lead to structural and phase transformations. © 2012 IEEE.

Shahini A.,Helmerich Advanced Technology Research Center | Smith B.J.,Oklahoma State University | Ricci J.L.,New York University | Vashaee D.,Helmerich Advanced Technology Research Center | Tayebi L.,Oklahoma State University
International Journal of Nanomedicine | Year: 2014

Bone healing can be significantly expedited by applying electrical stimuli in the injured region. Therefore, a three-dimensional (3D) ceramic conductive tissue engineering scaffold for large bone defects that can locally deliver the electrical stimuli is highly desired. In the present study, 3D conductive scaffolds were prepared by employing a biocompatible conductive polymer, ie, poly(3,4-ethylenedioxythiophene) poly(4-styrene sulfonate) (PEDOT:PSS), in the optimized nanocomposite of gelatin and bioactive glass. For in vitro analysis, adult human mesenchymal stem cells were seeded in the scaffolds. Material characterizations using hydrogen-1 nuclear magnetic resonance, in vitro degradation, as well as thermal and mechanical analysis showed that incorporation of PEDOT:PSS increased the physiochemical stability of the composite, resulting in improved mechanical properties and biodegradation resistance. The outcomes indicate that PEDOT:PSS and polypeptide chains have close interaction, most likely by forming salt bridges between arginine side chains and sulfonate groups. The morphology of the scaffolds and cultured human mesenchymal stem cells were observed and analyzed via scanning electron microscope, micro-computed tomography, and confocal fluorescent microscope. Increasing the concentration of the conductive polymer in the scaffold enhanced the cell viability, indicating the improved microstructure of the scaffolds or boosted electrical signaling among cells. These results show that these conductive scaffolds are not only structurally more favorable for bone tissue engineering, but also can be a step forward in combining the tissue engineering techniques with the method of enhancing the bone healing by electrical stimuli. © 2014 Shahini et al.

Zamanipour Z.,Helmerich Advanced Technology Research Center | Vashaee D.,Helmerich Advanced Technology Research Center
2012 IEEE Green Technologies Conference | Year: 2012

We report the enhancement of thermoelectric power factor in composite of SiGe-CrSi 2. P-type SiGe- CrSi 2 was synthesized by mechanical alloying and sintering method. In order to achieve nanocrystalline structure composite powder was prepared by high energy ball milling. Prepared powders were sintered at different press conditions to optimize for maximum power factor. The crystal structure and phase formation of SiGe and CrSi 2 alloys in the composite were investigated using x- ray diffraction analysis. The electrical conductivity, Seebeck coefficient and thermal conductivity of sintered samples were measured from room temperature to 850°C. The result shows about 50% improvement in thermoelectric power factor of SiGe-CrSi 2 compared to SiGe alloy. © 2012 IEEE.

Shabafrooz V.,Helmerich Advanced Technology Research Center | Mozafari M.,Helmerich Advanced Technology Research Center | Vashaee D.,Oklahoma State University | Tayebi L.,Helmerich Advanced Technology Research Center | Tayebi L.,Oklahoma State University
Journal of Nanoscience and Nanotechnology | Year: 2014

Electrospinning is a widely used technique to produce continuous polymeric fibers ranging from 2 nm to several micrometers. This technique is not only employed in research laboratories, but it is also increasingly being applied in different industrial fields in the last few decades as a highly versatile and cost-effective technology. Compared to conventional techniques for fiber fabrication, electrospinning can fabricate fibers in a more desirable size (e.g., nanoscale). Nanofibers are generated by the application of a strong electric field on polymer solution. Over the years, more than 200 polymers have been electrospun for various applications. In this review, our aim was to present an overview of the electrospinning technique and its potential applications. We covered the basic principles of the electrospinning technique and parameters which significantly affect the fiber morphology. The most recent work on electrospinning nanofibers for blending polymers, filtration, energy, sensing and biomedical applications was also presented in this review. Copyright © 2014 American Scientific Publishers All rights reserved.

Tayebi L.,Helmerich Advanced Technology Research Center | Zamanipour Z.,Helmerich Advanced Technology Research Center | Mozafari M.,Helmerich Advanced Technology Research Center | Norouzzadeh P.,Helmerich Advanced Technology Research Center | And 3 more authors.
2012 IEEE Green Technologies Conference | Year: 2012

Nearly 60% of the world's energy is wasted as heat. Thermoelectric materials can play an important role in green energy harvesting with their ability to convert waste heat into electricity. In this report, thermal and thermoelectric properties of p- type nanostructured silicon germanium (SiGe) as an important high temperature thermoelectric material was studied and compared with those of crystalline SiGe. The materials were synthesized via mechanical alloying and sintering approach. The different synthesis procedures resulted in two different conformation of SiGe. The first one was in nanostructure configuration and the other was in crystalline configuration containing large grains. Thermal and thermoelectric properties of both configurations were investigated in this manuscript. Although, differential thermal analysis (DTA) did not show significant differences between the thermal characteristics of nanostructured and crystalline SiGe, there were major changes in their thermoelectric properties. The nanostructured SiGe had lower electrical conductivity owing to the large scattering rate of electron at the grain boundaries. However, the lower mobility was accompanied by small thermal conductivity in nanostructured SiGe. The Seeback coefficient was grown in nanostructured SiGe as a result of lower carrier concentration. Considering the influence of all these factors, the nanostructured SiGe was thermoelectrically preferred as the figure-of-merit was increased specially at high temperatures. © 2012 IEEE.

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