Search Results (10)

The problem of intensification of the melt crystal growth process has been analyzed using CdTe as an actual material. Numerical simulation of 100 mm diameter CdTe crystal growth using the VGF technique has been carried out. The heat–mass transfer was controlled by introducing low-frequency oscillating baffle into the melt, which is a so-called axial vibrational control (AVC) technique. The baffle configuration has been optimized to destroy solid “tails”, which were formed near the crucible walls at high cooling rates due to the low thermoconductivity and the corresponding latent heat. Analysis of CdTe homogeneity range showed that during fast crystal cooling, Te micro precipitations were formed, resulting from the decay of oversaturated Cd-rich nonstoichiometric solid solution during the Bridgman crystal growth technique. After full crystallization, a VGF-grown CdTe crystal stays inside the phase field of the high-temperature wurtzite polymorph. This makes it possible to go through the polymorph transition without Te micro-precipitating using the advantages of the VGF-specific feature of very slow cooling. Full article

The increase in economic activities and the industrialization of countries have caused the growth of pollution created by waste and sewage. In particular, the textile industry produces large amounts of liquid contaminants due to the large amounts of water employed during the production of fabrics. In addition, dyes are another category of organic compound used in many industries, such as pharmaceuticals and rubber making. The presence of limitations in physico-chemical methods for the degradation of various dyes has stimulated the interest of researchers worldwide. One of the most economical ways is the use of photocatalytic decomposition under UV light radiation by green nanoparticles (NPs). In recent years, various metal NPs have been made using the green method that is cost-effective, eco-friendly, safe, and simple. Selenium (Se) is a crucial semiconductor metal that is widely utilized for its outstanding photovoltaic and optoelectronic attributes. Due to the excellent physical characteristics of Se, such as thermo-conductivity, anisotropy, and high photoconductivity, it has been used for removing various organic dyes. Hence, green SeNPs have attracted much attention in the catalytic decomposition process. The current review focuses on providing comprehensive studies concerning the degradation or reduction of various organic dyes through green SeNPs as an effective and efficient method and their mechanisms. It highlights the importance of utilizing green chemistry and catalytic properties. The aim is to benefit researchers from both academic and industrial backgrounds. Full article

The heat produced during tooth preparation could be a source of damage for dental pulp, and many variables are involved in this process. The aim of this in vitro study was to evaluate whether the different degrees of wear of the diamond burs significantly influenced the temperature changes in the pulp chamber during tangential veneer preparation. The sample comprised 30 intact permanent monoradicular teeth, randomly assigned to three study groups of 10 teeth each, of which 5 had the pulp tissue preserved and 5 had thermoconductive paste in the pulp chamber. For prosthetic preparation, we used new burs in the first group, burs at their fifth use in the second group, and burs at their eighth use for the third group. The pulp chamber temperature was evaluated at the start, after one minute, and after three minutes of preparation, using a k-type thermocouple. The results of the three-way ANOVA and Tukey post hoc comparisons showed a highly significant effect of the time of measurement, while the pulp condition and the degree of wear of the burs had no effect. In conclusion, the different degrees of wear of conventional diamond burs do not produce statistically significant different changes in the pulp chamber temperature. Full article

In miniaturized and integrated electronic devices, thermal potential and fire hazards caused by heat diffusion require an efficient thermal management system with versatile electronic packaging equipment. The flame retardancy was endowed on the surface of carbon nitride after thermal etching (CNNS) containing piperazine pyrophosphate (PPAP) by hydrogen bonding, and the obtained nanosheet was defined as PPAP-CNNS. During solution blending and program-controlled curing, PPAP-CNNS was used as a multifunctional filler to fabricate highly thermoconductive and fire retardant epoxy resin (EP) composites. In line with expectations, the resultant EP composites containing 7 wt% PPAP-CNNS had an exceptional thermal conductivity (TC) of 1.1 W·m⁻¹K⁻¹, which was 4.8 times higher than pure EP. Simultaneously, there was a sharp drop in the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) compared to pure EP. These reductions were, respectively, 63.7%, 54.2%, 17.9%, and 57.2%. The addition of PPAP-CNNS increased the specific surface area, which increased the heat conduction routes, and also the shape of the compact and solid char layer during burning, protecting the underlying polymer. These improvements to dispersion and surface functionalization were made possible by the compound. These results indicate that the preparation of integrated multi-functional resin described in this study has a wide application. Full article

This paper describes the preparation of new PEG₆₀₀₀–silica-MWCNTs composites as shape-stabilized phase change materials (ssPCMs) for application in latent heat storage. An innovative method was employed to obtain the new organic–inorganic hybrid materials, in which both a part of the PEG chains, used as the phase change material, and a part of the hydroxyl functionalized multiwall carbon nanotubes (MWCNTs-OH), used as thermo-conductive fillers, were covalently connected by newly formed urethane bonds to the in-situ-generated silica matrix. The study’s main aim was to investigate the optimal amount of PEG₆₀₀₀ that can be added to the fixed sol–gel reaction mixture so that no leakage of PEG occurs after repeated heating–cooling cycles. The findings show that the optimum PEG₆₀₀₀/NCOTEOS molar ratio was 2/1 (~91.5% PEG₆₀₀₀), because both the connected and free PEG chains interacted strongly with the in-situ-generated silica matrix to form a shape-stabilized material while preserving high phase-transition enthalpies (~153 J/G). Morphological and structural findings obtained by SEM, X-ray and Raman techniques indicated a distribution of the silica component in the amorphous phase (~27% for the optimum composition) located among the crystalline lamellae built by the folded chains of the PEG component. This composite maintained good chemical stability after a 450-cycle thermal test and had a good storage efficiency (~84%). Full article

Improvement of the thermal conductivity of encapsulant material using doping filler is an important requirement for electronic device packaging. We proposed a simple method for determining the thermal characteristics of composite material that can help save time, increase research performance, and reduce the cost of buying testing equipment. Based on the theory of Fourier law, a general 3D model is simplified into a 2D model, which can then be applied to calculate the thermal conductivity of the tested sample. The temperature distribution inside the sample is simulated by the finite element method using MATLAB software; this is a simple and useful option for researchers who conduct studies on thermal conduction. In addition, an experimental setup is proposed to help determine the extent of thermal conductivity improvement in a sample with doping filler compared to a bare sample. This method is helpful for research on optoelectronics packaging, which relates to the enhancement of thermal conductivity composite material. Full article

The development of highly thermally conductive composites with excellent electrical insulation has attracted extensive attention, which is of great significance to solve the increasingly severe heat concentration issue of electronic equipment. Herein, we report a new strategy to prepare boron nitride nanosheets (BNNSs) via an ion-assisted liquid-phase exfoliation method. Then, silver nanoparticle (AgNP) modified BNNS (BNNS@Ag) was obtained by in situ reduction properties. The exfoliation yield of BNNS was approximately 50% via the ion-assisted liquid-phase exfoliation method. Subsequently, aramid nanofiber (ANF)/BNNS@Ag composites were prepared by vacuum filtration. Owing to the “brick-and-mortar” structure formed inside the composite and the adhesion of AgNP, the interfacial thermal resistance was effectively reduced. Therefore, the in-plane thermal conductivity of ANF/BNNS@Ag composites was as high as 11.51 W m⁻¹ K⁻¹, which was 233.27% higher than that of pure ANF (3.45 W m⁻¹ K⁻¹). The addition of BNNS@Ag maintained tensile properties (tensile strength of 129.14 MPa). Moreover, the ANF/BNNS@Ag films also had good dielectric properties and the dielectric constant was below 2.5 (10³ Hz). Hence, the ANF/BNNS@Ag composite shows excellent thermal management performance, and the electrical insulation and mechanical properties of the matrix are retained, indicating its potential application prospects in high pressure and high temperature application environments. Full article

In this work, the effect of the addition of boron nitride (BN) fillers in a thiol-cycloaliphatic epoxy formulation has been investigated. Calorimetric studies put into evidence that the kinetics of the curing has been scarcely affected and that the addition of particles does not affect the final structure of the network. Rheologic studies have shown the increase in the viscoelastic properties on adding the filler and allow the percolation threshold to be calculated, which was found to be 35.5%. The use of BN agglomerates of bigger size increases notably the viscosity of the formulation. Glass transition temperatures are not affected by the filler added, but Young’s modulus and hardness have been notably enhanced. Thermal conductivity of the composites prepared shows a linear increase with the proportion of BN particle sheets added, reaching a maximum of 0.97 W/K·m. The addition of 80 μm agglomerates, allowed to increase this value until 1.75 W/K·m. Full article

In this paper, the thermoelectric properties of In₂O₃-based materials in comparison with other thermoelectric materials are considered. It is shown that nanostructured In₂O₃ Sn-based oxides are promising for thermoelectric applications at moderate temperatures. Due to the nanostructure, specific surface properties of In₂O₃ and filtering effects, it is possible to significantly reduce the thermal conductivity and achieve an efficiency of thermoelectric conversion inaccessible to bulk materials. It is also shown that a specific surface state at the intergrain boundary, optimal for maximizing the filtering effect, can be achieved through (1) the engineering of grain boundary parameters, (2) controlling the composition of the surrounding atmosphere, and (3) selecting the appropriate operating temperature. Full article

The structure and the maximal nonlinear optical (NLO) susceptibility χ⁽²⁾ are tabulated for more 700 acentric binary oxides, 220 crystals of simple, binary and complex borates and for the same set of 110 carbonates, tartrates, formates, oxalates, acetates and fluoride-carbonates used in ultraviolet and deep ultraviolet optoelectronics. According to the chemical formula, the structural symbols of these crystals have been plotted on the plane of two minimal oxide bond lengths (OBL). It is shown that acentric crystals are positioned on such plane inside the vertical, horizontal and slope intersected ellipses of “acentricity”. The oxide and borate crystals with moderate NLO susceptibility are found in the central parts of these ellipses intersection and, with low susceptibility, on top, at the bottom and border of the ellipses rosette. The nonpolar fluoride-carbonate crystals with high NLO susceptibility are found in the curve-side rhombic parts of the slope ellipse of “acentricity”. The unmonotonous fuzzy dependence “χ⁽²⁾” on the OBL of these crystals is observed, and their clear-cut taxonomy on compounds with π– or σ–oxide bonds is also established. It is shown that the correlations of χ⁽²⁾ with other acentric properties are nonlinear for the whole set of the oxide crystals having their clear maximum at a certain value of the piezoelectric or electro-optic coefficient. The correlation “hardness–thermoconductivity-fusibility” is plotted for oxide crystals, part of which is used at the creation of self-frequency-doubling solid state lasers. Full article