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    Nanoparticle silicalite-1 crystallization from clear solutions: nucleation
    (Elsevier Science Bv, 2009) Tokay, Begüm; Erdem-Şenatalar, Ayşe; Schueth, Ferdi; Thompson, Robert W.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882
    Despite much effort spent by various research groups, there remain many aspects of nanoparticle silicalite-1 crystallization from clear solutions which require further investigation. In order to shed light, especially on the nucleation of silicalite-1, particle growth at 100 degrees C from several starting compositions known to yield colloidal silicalite-1, which have been studied previously by other researchers using various techniques, was followed in this study by laser light scattering using scattering angles of 90 degrees and 173 degrees, and zeta potential and pH measurements. Crystallinity was monitored by X-ray diffraction, Fourier transform infrared analysis and transmission electron microscopy. Thermogravimetric analyses and density measurements were also used to characterize the products obtained at various times during the syntheses. The results demonstrate that the distinct time of sudden jump in the effective diameter of the nanoparticles in solution, as observed more clearly by using the back-scattering device, and which marks the beginning of the constant linear growth rate of the particles, corresponds to the nucleation of the silicalite-1 crystal structure. This time was also shown to coincide with the exo-endo thermal switch time of the reaction mechanism, which has been observed previously by another research group. Nucleation was accompanied by an aggregation of a population of smaller particles, as indicated by the broadening of the particle size distribution, and the variation of the pH and zeta potential values during synthesis.
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    Resistive hydrogen sensors based on nanostructured metals and metal alloys
    (Amer Scientific Publishers, 2013) N/A; Department of Electrical and Electronics Engineering; Kılınç, Necmettin; Researcher; Department of Electrical and Electronics Engineering; College of Engineering; 59959
    Hydrogen (H-2), as a renewable energy source, has numerous applications such as chemical production, fuel cell technology, rocket engines, fuel for cars etc. The detection of H-2 is so important in safety issue due to the flammable and explosive properties of H-2 gas, in a H-2 source for leak detection and in H-2 production process because of real-time quantitative analysis of production. This paper reviews resistive type H-2 sensor based on palladium (Pd), platinum (Pt) and their alloy nano-structures in the forms of thin films, nanoporous films, nanowires, nanoparticles, nanotubes, etc. The sensing mechanism of the nanostructured Pd and Pt resistive sensor is discussed in separated section. Nanostructured Pd sensors show a decrease or an increase in their resistance towards H-2 gas depending on continuity of the nanostructure and will be examined in two parts: discontinuous (nano-gap based) and continuous Pd and Pd alloy nanostructure sensors. on the contrary to Pd nanostructure sensor, nanostructured Pt sensors require oxygen (O-2) to operate. There are limited numbers of publications about nanostructured Pt and Pt alloy sensors, so further investigation are needed to well understand sensing mechanism of the Pt sensors.