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Esters of 4-nitrocinnamic acids and 4-halogene-4’-hydroxyazobenzenes – synthesis, mesogenic and optical studies
摘要： Six new compounds were synthesized that have no alkyl chains in their structure: 4-nitrocinnonates of 4-hydroxyazobenzene, 4-nitro-4'-hydroxyazobenzene, 4-fluoro-4'-hydroxyazobenzene, 4-chloro-4'-hydroxyazobenzene, 4-bromo-4'-hydroxyazobenzene, and 4-iodo-4'-hydroxyazobenzene. Using the polarizing microscopy and differential scanning calorimetry, enthalpies and temperatures of phase transitions were determined. All investigated compounds have an enantiotropic nematic phase. These compounds proved to be extremely thermally stable. Thermal decomposition was observed in temperatures above 300°C. Investigated compounds contain two different chromophore groups (i.e. azo and ethene moieties), which influenced the complex trans–cis isomerization processes of both groups (three time-separated processes were observed). It was shown that the presence of the ethene group significantly shifts the π-π* band towards higher energies. The substituent polarity in the azo group also affected the energy of this absorption band. A weak luminescence effect was observed in the 4-nitrocinnonates of 4-hydroxyazobenzene compound.
关键词： nematic,luminescence,Azobenzenes,trans–cis isomerization,polarizing microscopy,DSC calorimetry
更新于2025-09-23 15:23:52
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Thermal oxidative decomposition estimation combining TGA and DSC as optimization targets for PMMA
摘要： Thermal analysis techniques play a key role to determine and characterize solid phase thermal decomposition. In this sense, Simultaneous Thermal Analysis (STA, i.e. TGA and DSC tests carried out simultaneously) are widely employed, since it provides information about how mass is lost and energy released while the temperature of the sample increases. Fire computer models combined with methods numerical methods are widely used to represent the results from tests and to achieve the values of the kinetic and thermal parameters. Previous works looked forward achieving those parameters using, as unique optimization target, the mass loss curve (TGA) or its derivative (DTGA). As the study of heat release rate is a decisive element to characterize the material properly, most recent works were adding additional measures. These extra measurements concern the heat transfer and the energy required or released during temperature programmed heating, such as heat rate release, heat of gasification, or the surface temperatures of the samples. The information about the energy is provided by the Differential Scanning Calorimetry curve (DSC). Despite of the employment of the information provided by the DSC, this information usually is not used as a target to approach the DSC simulated curve to the experimental one as TGA does. Based on the lack of use of the DSC curve as numerical approaching process to set the kinetic properties, we decide to explore the possibility of adding this as a new target in the process. Therefore, kinetic and thermal properties might be achieved fitting experimental and simulated curves simultaneously, which should allow us to take into account the decomposition process and their energy released. Results obtained in the present work reveal the major challenge of getting a set of parameters, which can fit DSC curve. The level of accuracy reached when only TGA is utilized as target to approach is higher than the level of accuracy of DSC curve. This fact makes increase the value of the errors when both curves are used as targets to approach. In other words, an approach to both curves simultaneously cannot be directly made. With this consideration in mind, this paper proposes an alternative methodology in order to fit TGA curve considering the optimization of the DSC curve. The methodology proposed in the present work is applied to the analysis of poly(methyl methacrylate) (PMMA).
关键词： DSC,numerical methods,TGA,CFD,Thermal decomposition,PMMA,optimization methods,solid phase chemistry
更新于2025-09-23 15:23:52
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Exploration of structural, vibrational and spectroscopic properties of self-activated orthorhombic double molybdate RbEu(MoO4)2 with isolated MoO4 units
摘要： RbEu(MoO4)2 is synthesized by the two-step solid state reaction method. The crystal structure of RbEu(MoO4)2 is defined by Rietveld analysis in space group Pbcn with cell parameters a=5.13502(5), b=18.8581(2) and c=8.12849(7) ?, V=787.13(1) ?3, Z=4 (RB=0.86%). This molybdate possesses its phase transition at 817 K and melts at 1250K. The Raman spectra were measured with the excitation at l =1064 and 514.5nm. The photoluminescence spectrum is evaluated under the excitation at 514.5nm. The absolute domination of hypersensitive 5D0(cid:1)7F2 transition is observed. The ultranarrow 5D0(cid:1)7F0 transition in RbEu(MoO4)2 is positioned at 580.2nm being 0.2nm blue shifted, with respect to that in Eu2(MoO4)3.
关键词： Rietveld refinement,rubidium europium molybdate,Raman luminescence,solid state reaction,DSC
更新于2025-09-23 15:23:52
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Formation of Composite Polyaniline and Graphene Oxide by Physical Mixture Method
摘要： The development of polyaniline and graphene oxide composites aims to join the unique properties of each material for aerospace applications. The present paper demonstrates an easy and quick method, compared to the ones found in the literature, to obtain a composite made with polyaniline doped with dodecylbenzenesulfonic acid, a combination commonly called polyaniline, and graphene oxide. Nowadays, the most common studied methods are electrochemistry and in situ chemical polymerization. Differently from these methods, the films were obtained by a physical mixture of equimolar suspension of graphene oxide (4 mg/mL) with 3 concentrations of polyaniline powder: 25; 50 and 75%, being compared to pure graphene oxide and polyaniline. The morphology and structure behavior of all the films were studied, besides the bonding nature between both materials. The films were analyzed by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The apparent interaction between graphene oxide corrugated sheets and polyaniline grains was verified by scanning electron microscopy images. It can be noticed, as the concentration of polyaniline increases, that more polymer was entrapped. To prove the formation of polyaniline/graphene oxide composite, X-ray diffraction and Fourier transform infrared spectroscopy techniques demonstrated the changes on graphene oxide crystallographic plans and on the chemical bonding between polyaniline and graphene oxide, suggesting an interaction between polyaniline and graphene oxide, especially in the composite with 50% polyaniline/50% graphene oxide. Differential scanning calorimetry was used to highlight this effect through the increase in thermal stability. The method of physical mixture was efficient to obtain the polyaniline/graphene oxide composites.
关键词： Structure,DSC,FT-IR,Morphology,Polyaniline,Graphene oxide
更新于2025-09-23 15:22:29
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[IEEE 2017 International Renewable and Sustainable Energy Conference (IRSEC) - Tangier (2017.12.4-2017.12.7)] 2017 International Renewable and Sustainable Energy Conference (IRSEC) - Mapping of the Composition of Soils Naturally Deposited on PV Modules Anywhere in Morocco
摘要： This article constitutes a preliminary phase for the performance of a national cartography of the composition of soils naturally deposited on photovoltaic modules installed in sites of different climates. To do this, a climatic zoning of Morocco according to the De Martonne index was adopted in order to select representative sites concerned with the collection of samples. For the moment, four samples have been collected in Rabat, Errachidia, Agadir and Oujda. These samples were prepared and analyzed. Several analyzes were carried out to determine the physical, chemical and mineralogical composition of these samples. The mineralogical composition was determined via X-Ray Diffraction (XRD) and X-Ray Fluorescence analysis (XF), while characterization of the physical and chemical composition was identified using Differential Scanning Calorimetry (DSC) and Spectroscopy Infrared (IR). The results show the existence of the same abundant constituents namely: Quartz, Calcite, Dolomite, Kaolinite whose percentages differ from a climate to another.
关键词： Soils,Quartz,Calcite,Differential Scanning Calorimetry (DSC),Kaolinite,Climatic zoning,Infrared spectroscopy (IR),X-Ray Diffraction,Photovoltaic modules,Dolomite,Cartography,X-Ray Fluorescence
更新于2025-09-23 15:22:29
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Microstructural interpretation of charge transport dynamics of chemically derived ZnCo2O4 under mechanical milling
摘要： In this work, milling effect on chemically synthesized nanocrystalline Zinc Cobaltite (ZnCo2O4) has been investigated and we report how the structural and electrical properties vary with the milling span. Phase pure ZnCo2O4 has been successfully synthesized via simple and cost-effective co-precipitation method and then it has been milled for one, four and eight hours respectively. XRD confirms formation of single phase cubic structure for both milled and unmilled nano-powders. Different microstructural parameters has been estimated from Rietveld analysis, which shows particle size reduction from ~29.64 nm for unmilled sample to ~18.13 nm for eight hour milled sample. TGA-DSC curve of as prepared sample shows good temperature stability that helps to estimate the appropriate sintering temperature for the samples. TEM analysis also gives values of grain size in agreement with Reitveld analysis. Frequency dependent ac conductivity curve obeys universal Jonscher power law and temperature dependence of frequency exponent is explained by small polaron transaction. Comparable activation energies from hopping mechanism and relaxation process indicates similar transport mechanism. Superimposed scaling spectra obeys TTSP principle. AC conductivity increases with frequency as a result of hopping of the charge carriers. Smaller particles with reduced strain gives enhanced conductivity as well as enhanced value of hopping frequency. This further suggests creation of excess charge carriers in milled samples. Cole-Cole plot shows non-Debye type behavior of the samples. The dielectric loss factor increases with lowering of particle size since smaller grains contributes to faster charge conduction.
关键词： TGA-DSC,Mechanical milling,Electrical characterisation,dielectric loss factor,Microstructure
更新于2025-09-23 15:22:29
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Electrical and Electromagnetic Interference (EMI) shielding properties of hexagonal boron nitride nanoparticles reinforced polyvinylidene fluoride nanocomposite films
摘要： The hexagonal boron nitride nanoparticles (h-BNNPs) reinforced flexible polyvinylidene fluoride (PVDF) nanocomposite films were prepared via a simple and versatile solution casting method. The morphological, thermal and electrical properties of h-BNNPs/PVDF nanocomposite films were elucidated. The electromagnetic interference (EMI) shielding properties of prepared nanocomposite films were investigated in the X-band frequency regime (8–12 GHz). The EMI shielding effectiveness (SE) was increased from 1 dB for the PVDF film to 11.21 dB for the h-BNNPs/PVDF nanocomposite film containing 25 wt% h-BNNPs loading. The results suggest that h-BNNPs/PVDF nanocomposite films can be used as lightweight and low-cost EMI shielding materials.
关键词： Hexagonal boron nitride,PVDF,SEM,EMI shielding,DSC,electrical properties
更新于2025-09-23 15:21:21
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Laser-Induced Voltage of Oil Shale during Retorting
摘要： In this study, a 248 nm laser was used to analyze oil shale at di?erent pyrolysis temperatures. An induced voltage was obtained when the ultraviolet laser irradiated the oil shale surface. The laser-induced voltage (LIV) peak decreases with temperatures below 200 °C, increases with temperatures in the range 200?400 °C, and then decreases above 400 °C. The critical temperatures of 200 and 400 °C corresponded well with the points conformed using thermogravimetry and di?erential scanning calorimetry (TGA-DSC), gas chromatography and gas chromatography coupled (TG-FTIR-MS), and scanning electron microscopy (SEM). Our research suggested that an LIV method could be applied to the analysis of the oil shale pyrolysis process.
关键词： oil shale,TGA-DSC,TG-FTIR-MS,pyrolysis,laser-induced voltage,SEM
更新于2025-09-23 15:19:57
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Characterization of form-stable phase-change material for solar photovoltaic cooling
摘要： Solar PV panel cooling is essential to achieve maximum efficiency of PV modules. Phase-change material (PCM) is one of the prominent options to cool the panel and reduce the temperature, since PCMs have low thermal conductivity. Expanded graphite particles are used to enrich the structure and stability as well as to increase the thermal properties. In the present research work, polyethylene glycol (PEG) 1000 is used as a base material and expanded graphite for inclusive particle. A novel form-stable PEG1000/EG composite PCM mixture is prepared, using impregnation and dispersion method. Expanded graphite and PEG1000/EG sample phase compositions are investigated, using X-ray diffraction technique. No new peak is identified in the composite PCM sample. The surface morphology and structure of EG and PEG1000/EG are investigated, using scanning electron microscopy (SEM). Chemical stability analysis is done by Fourier-transform infrared spectroscopy. Thermal properties of the prepared composite PCMs are analysed by differential scanning calorimetry, thermogravimetric analysis (TGA) and KD2 pro analyser. Results show that addition of EG in various propositions (5%, 10% and 15%) enhances the thermal conductivity of PCM samples from 0.3654 to 1.7866 W mK?1, while melting point and latent heat of fusion of PCM samples are getting reduced. TGA thermographs are used to investigate the thermal stability of the composite PCM samples. TGA curves show that loss of mass happens above the operating temperature, and it is varied with different mass ratios of EG. Characterization of the prepared composite PCM samples is compared and found that PEG1000-85%/EG-15% is the best form-stable PCM, suitable for cooling the solar PV panel as well as to improve the electrical efficiency coupled with a decrease of temperature in the range of 35 °C to 40 °C.
关键词： PEG1000 PCM material,Solar PV cooling,Expanded graphite,Thermal storage,DSC,Characterization
更新于2025-09-23 15:19:57
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Thermophysical Properties of Silicon-Carbide-Based Ceramic Composite Materials Obtained by Spark Plasma Sintering (SPS)
摘要： The factors influencing the thermal conductivity of SiC-based ceramic composite materials obtained by the spark plasma sintering technology with relative density 99% and B4C, AlN, Si3N4, Y2O3, Al2O3, and HfB2 as additives are examined. The thermophysical properties were determined in the temperature range 20 – 1300°C: specific heat, thermal diffusivity, and thermal conductivity of composites. The thermal diffusivity and specific heat were measured by the laser-spark method. The measurements of specific heat are supplemented by measurements performed with a DSC and adiabatic calorimeter. The thermal conductivity is calculated using data on the thermal diffusivity, specific heat, and density.
关键词： laser flash method,specific heat,adiabatic calorimeter,thermal conductivity,ceramic composite materials,thermal diffusivity,thermophysical properties,differential scanning calorimetry (DSC)
更新于2025-09-19 17:15:36