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Najdeno v: ključnih besedah
Ključne besede: PHOTOTHERMAL-DEFLECTION SPECTROSCOPY, THERMAL DIFFUSIVITY, soil, soil aggregates
Objavljeno: 30.08.2017; Ogledov: 3384; Prenosov: 0
Polno besedilo (12,87 MB)

Opis: In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.
Najdeno v: ključnih besedah
Ključne besede: graphene nanoplatelets, thermal diffusivity, thermal conductivity, photothermal spectrometry
Objavljeno: 30.11.2021; Ogledov: 1062; Prenosov: 57
Polno besedilo (0,00 KB)
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Opis: Natural pyrrhotites have gained significant attention due to their interesting electronic, antimicrobial, and chemical properties. The present work attempts to explore the morphology-induced modifications in the thermal characteristics of natural pyrrhotite due to ageing. The morphological, elemental, structure, optical, and thermal characterisations help in understanding the effect of ageing. The effects of five years of ageing of the sample are (i) Field Emission Scanning Electron Microscopic analysis reveals a morphological transformation from flakes to agglomerated powder, (ii) elemental analyses suggest the ageing induced compositional modification (iii) the Tauc plot analysis shows a bandgap energy modification from 1.46 eV to 1.92 eV, (iv) X-ray Diffraction (XRD), Fourier Transform Infrared, and X-ray photoelectron spectroscopic studies affirm the formation of oxy-hydroxides (v) the XRD data indicates an increase of dislocation density, and (vi) Photoluminescence study shows a deep violet emission evidenced through the CIE plot. The study by the thermal lens technique shows a lowering of thermal diffusivity study by 23%, due to the morphological modifications, adsorbed/chemisorbed hydroxyl groups, and the formation of secondary compounds due to oxidation and weathering. The phonon boundary scattering, weathering induced smaller grain size, reduced phonon mean free path, and point defects also account for the lowering of the thermal diffusivity value and thereby influencing its properties.
Najdeno v: ključnih besedah
Ključne besede: pyrrhotite, thermal diffusivity, thermal lens, ageing, morphology
Objavljeno: 30.06.2022; Ogledov: 497; Prenosov: 3
Polno besedilo (1,82 MB)
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Opis: The thermodynamics of the seed matter after imbibition is highly significant as the growth and germination involve complex biochemical exergonic process. The germination of seed and compositional variation of the seed matter has always been a fascinating field of research. The present work unveils the thermodynamics associated with the changing thermal diffusivity of the seed matter through the green technology-based single-beam thermal lens technique. Investigations are carried out in Vigna radiata seeds, germinating in media with and without carbon allotropes, through various spectroscopic techniques. The morphology of the soot and carbon allotropes is understood from the field emission scanning electron microscope images. The thermal lens study throws light into the energy trapping nature of the seed matter of the seed growing in carbon allotropic media which facilitates biosynthesis. The observed increased rate of growth of the seed is substantiated through the ultraviolet–visible–near-infrared (NIR), Fourier transform infrared, and photoluminescence (PL) spectroscopic analyses. The NIR and PL studies also reveal the formation of chlorophyll molecule during germination. Thus, the study suggests a mechanism for tuning the thermal diffusivity of the seed matter as to trap the biochemical energy to facilitate the further biosynthesis and thereby to enhance the growth rate.
Najdeno v: ključnih besedah
Ključne besede: seed matter, thermal diffusivity, thermal lens, carbon nanoparticle, soot
Objavljeno: 04.07.2022; Ogledov: 470; Prenosov: 0
Polno besedilo (2,68 MB)

Opis: The photothermal phenomenon has emerged as a potential tool for the nondestructive evaluation of thermal and optical properties of materials. Thermal analysis of drugs is an unavoidable part of preformulation study, as temperature variations can induce structural changes of the constituents of drugs. Techniques based on photothermal phenomena are highly sensitive, as only the absorbed radiation contributes to the signal. Periodic illumination and subsequent nonradiative de-excitation generate thermal lens signals of various types within and around the sample. Variation of thermal diffusivity with a concentration of the commonly used drug terbutaline is studied through the single-beam thermal lens technique. The ultraviolet–visible spectrum of the drug shows strong absorption around 500 nm, which suggests the possible wavelengths that can be used for the study. It is found that concentration of the drug in liquid form decides its thermal stability, as its thermal diffusivity varies with concentration. The study gives information about the optimum value for the concentration of the drug noted above for which the chance of thermal stability is high.
Najdeno v: ključnih besedah
Ključne besede: thermal lens, thermal diffusivity, pharmacology, drug
Objavljeno: 30.06.2022; Ogledov: 479; Prenosov: 0
Polno besedilo (1,47 MB)