• Energy Research

The TG-DTG and DTA study of dipositive platinum(II)complexes of the general formula [Pt(L-L)(dppmS(2))](ClO(4))(2), where dppmS(2) = Ph(2)P(S)CH(2)P(S)Ph(2) and L-L = dppm (Ph(2)PCH(2)PPh(2)), dppe (Ph(2)PCH(2)CH(2)PPh(2)), and dppp (Ph(2)PCH(2)CH(2)CH(2)PPh(2)), were studied by thermogravimetric analysis from ambient temperature to 1000 degrees C in nitrogen atmosphere. The decomposition occurred in one stage for [Pt(L-L)dppmS(2)](ClO(4))(2), [Pt(L-L)dpppS(2)](ClO(4))(2) and [Pt(L-L)dppmS(2)](ClO(4))(2) complexes. The values of activation energy, E, frequency factor, A, reaction order, n, entropy change, Delta S(not equal), enthalpy change, Delta H(not equal), and Gibss free energy change, Delta G(not equal), of the thermal decomposition were calculated by means of Coats-Redfern method (CR), MacCallum-Tanner method (MC) and van Krevelen method (vK). The activation energy values obtained by CR, MC and vK methods were in good agreement with each other. WOS: 000263044000001

Temperature and size dependence of photoluminescence (PL) of nano-silicon embedded in SiO2 matrix samples were studied. In these measurements, four samples with deferent implantation dose showed their similar tendency. Their nano-structure was investigated by high resolution electron microscopy (HREM) and selected area diffraction (SAD) which confirmed that only those prepared with the higher Si implantation dose formed crystal nano-silicon. The further analysis of the dependence of thermal activation energy on the PL emission energy demonstrates their different behaviors. This leads to an optical method to detect the crystal nano-silicon through comparing their thermal activation energy with the Calcott model, a model that implies the emission from nanocrystallites. Furthermore, the appearance of thermal activation energy in amorphous nano-silicon is discussed in the light of recombination mode of localized carriers through the band-tail state.

Thermal fading (TF) is an important characteristic in choosing appropriate thermoluminescence (TL) materials for particular applications. TF is the process of reducing the capability of producing the response due to radiation exposure. The fading rate of LiF based thermoluminescent (TL) material depends on many experimental parameters such as storage temperature, readout mechanism, annealing and radiation type or time based on the storage time before or after radiation. The general aim of the present work is to investigate if the activation energy E, frequency factor s, maximum temperature, Tm and concentration, n values evaluated from the experimental thermal fading rates glow–curves through a computerized glow–curve deconvolution analysis (CGCD), can simulate the thermal fading glow-curves using a phenomenological model for LiF:Mg, Ti.

The TG-DTG and DTA study of dipositive palladium(II) complexes of the general formula [Pt(L-L)(dppmS(2))1(ClO4)(2), where dppmS(2) = Ph2P(S)CH2P(S)Ph-2 and L-L = dppm (Ph2PCH2PPh2), dppe (Ph2PCH2CH2PPh2) and dppp (Ph2PCH2CH2CH2PPh2), were studied by thermogravimetric analysis from ambient temperature to 1273 K in nitrogen atmosphere. The decomposition occurred in one stage for all complexes. The values of activation energy, E, frequency factor, A, reaction order, n, entropy change, Delta S-not equal, enthalpy change, Delta H-not equal and Gibss free energy, Delta G(not equal) of the thermal decomposition were calculated by means of Coats-Redfern (CR), MacCallum-Tanner (MC) and Horowitz-Metzger (HM) methods. The activation energy value obtained by CR, MC and HM methods were in good agreement with each other. WOS: 000259602200028

Julia code for solar thermal simulations included in "Energy Modeling of Solar Water Heating Systems with On-Off Control and Thermally Stratified Storage Using a Fast Computation Algorithm"

The thermal energy consumption for heating objects is one of the main parameters deciding their technical and structural solution. Reducing energy consumption is realized in various ways. The most used method is passive thermal protection, that is, increasing the thermal insulation parameters of the envelope constructions and optimizing the operation of the technical equipment of the buildings. There are also methods of active thermal protection to reduce heat leakage through non-transparent parts of the building envelope. Active thermal protection (ATP) is a dynamic process that applies primarily to building structures with integrated energetically active elements that fulfill one or more functions in mutually exclusive operating modes of energy systems and heat sources, such as thermal barriers (TB), large-scale heating/cooling, long-term heat/cool storage, capturing solar energy, and energy from the surroundings or even recovering heat in the cold season or cold in the warm season and other combinations. The research area focuses on analyzing active thermal protection’s energy potential. The methodology is based on a parametric study of dynamic thermal resistance (DTR), and heat flows to the interior and exterior from ATP for the investigated envelope of the experimental house EB2020 made of aerated concrete blocks. Such constructions generally show a consistently high DTR of 11.8 to 30.8 ((m2·K)/W) at a low mean heat transfer temperature of 10 to 16 °C, corresponding to the thermal insulation of 300 to 1000 mm. In the case of ATP storage heating with an average temperature of the heat-carrying substance of 30 °C, the heat flow into the interior of the investigated structure would be only 2.31 W/m2. Therefore, they are only suitable for a thermal barrier and heat/cold accumulation. Based on the synthesis and induction of analogical forms of the results of previous research into recommendations for the design of individual energy functions of ATP for perimeter structures of buildings, we present heat flows to the interior/exterior when changing the material of the layers towards the interior from ATP and describe possible variants of the development of building structures with integrated energetically active elements.

The kinetics of oxidation process of realgar and orpiment natural mineral mixture was studied under non-isothermal conditions. The proposed reaction mechanism and chemical transformation investigated by SEM-EDX, XRD and thermal analysis, are discussed. Using mathematical modeling on results obtained during analysis in non-isothermal conditions, activation energy of this process was determined.

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Technological progress is needed to develop renewable energies. Improvements should be especially focused on the energy storage element to help correct the mismatch between energy supply and demand. In concentrated solar power (CSP) plants, ordinary concrete made of Portland cement (PC) has been proven to be a good thermal energy storage (TES) medium. However, the substantial environmental impact of PC manufacturing makes it necessary to develop new materials. Thus, in this work, alternative alkali-activated mortars (AAM) and hybrid materials (HM) have been developed using blast furnace slag to replace PC. This has been done in order to study their stability at high temperature (up to 500 ºC) and their viability to operate as TES, undergoing thermal cycles between 200 ºC and 400 ºC, as they would in CSP technologies. Studying the mechanical and thermal properties after the thermal treatments has revealed that the alternative materials offer improved mechanical properties as well as very good thermal conductivity and storage capacity values. In particular, the best results in terms of mechanical properties were achieved by the AAM system, where the compressive strength value is increased with respect to the reference PC sample by 195% after exposure to 500°C and by almost 97% after 20 thermal cycles between 200°C and 400°C. Furthermore, in terms of thermal properties, the AAM system showed a 31% increase in thermal conductivity after thermal exposure compared to PC. In addition, both AAM and HM systems demonstrated substantial improvements in specific heat and thermal storage capacity, outperforming PC by up to 46% during CSP-like thermal cycles. These promising results open new doors to the study of these alternative materials, such as TES, as they are more suitable than PC from an operational point of view.