Initial Temperature Research Articles

Cycloaliphatic epoxy-functionalized polydimethylsiloxanes for comprehensive modifications of epoxy thermosets

Polydimethylsiloxane (PDMS) are known as a class of efficient modifiers for epoxy thermosets, but the simultaneous improvement in thermal stability, thermomechanical and mechanical properties remain a challenge. Herein, we report a cycloaliphatic epoxy-functionalized polydimethylsiloxane (PDMS-CE) with a designed epoxy value for comprehensive modifications of diglycidyl ether of bisphenol A (DGEBA)/methylhexahydrophthalic anhydride (MeHHPA) thermosets. Compared to neat epoxy thermoset, the 4 wt% PDMS-CE modified epoxy thermoset showed a 79 %, 120 % and 503 % increase in flexural strength, impact strength and fracture toughness, respectively, as well as a slight increase in the initial thermal decomposition temperature (Td5%) and glass transition temperature (Tg), and a desirable decrease in the dielectric constant and water absorption rate. This comprehensive modification performance was caused by the combined effects of crosslinking density improvement, rigid cycloaliphatic structure, as well as the flexible PDMS chains.

Water Entry of a Heated Axisymmetric Vertical Cylinder

The computational model that is able to estimate the temperature distribution inside a solid specimen during the film boiling phase of immersion quenching (water entry) process has been presented in this paper. It is based on the prescribed initial temperatures of the solid specimen and the liquid quenchant. In addition, the turbulence effects have to be considered using the assumed turbulence kinetic energy value, i.e., the “frozen turbulence” approach, that remains constant thorough the simulation. The studied material is nickel alloy, Inconel 600, for which extensive experimental data are available. The work has been carried out using ANSYS Fluent computational fluid dynamics software and the methods for solution of Stefan problem by Eulerian two fluid VOF model. A satisfactory agreement between the experimental and the calculated data has been achieved, yielding thereby the computationally obtained data that fit to a great extent the prescribed error band of ±10% during the estimated film boiling phase of the immersion quenching process itself. It was, however, found that the temperature calculated in the center of a specimen fits this error band until reaching somewhere t < 6 s due to low presumed turbulence level in the domain. In addition, the explosion of the vapor phase after the body reaches the free surface of the quenchant has also been successfully tracked using the numerical simulation model proposed herein. The major novelty of the present research lies in the fact that a moving boundary problem has been successfully resolved in conjunction with, to a great extent, basic-principle-based heat and mass transfer in a turbulent flow conjugate heat transfer (CHT) numerical simulation using moderate computational resources.

Effect of local carbide formation behavior on repair weld liquation cracking susceptibility for long-term-serviced 247LC superalloy

This study assessed the liquation cracking temperature range (LCTR) for 247LC superalloy repair welds subjected to long-term and high-temperature exposure. To achieve this, the exposed specimens underwent simulations at 1273 K for 500, 1000, 3000, and 5000 h to replicate the long-term service conditions of gas turbines. Spot-Varestraint testing was employed to quantitatively measure LCTR variations. The metallurgical mechanism of the evaluated LCTR in the exposed 247LC superalloys was elucidated by analyzing the microstructural characteristics at the liquation cracking surface and performing thermodynamic calculations. The LCTR was evaluated to be 410 K for specimens exposed for 500 h, 440 K for 1000 h, 385 K for 3000 h, and 610 K for 5000 h. This indicates that the liquation cracking susceptibility of the repaired weld heat-affected zone significantly increased during the long-term service of the 247LC superalloy. After 5000 h of exposure, the formation of fine MC, M6C, and M23C6 carbides on the liquation cracking surface was characterized using transmission electron microscopy. The welding metallurgical mechanism underlying the severe liquation cracking susceptibility can be attributed to the fractions of MC (liquation initiation temperature: 1125–1356 K) and M6C (liquation initiation temperature: 1390–1420 K), which have lower liquation initiation temperatures than the solidus of the 247LC alloy (1530 K). Notably, the area fraction of MC and M6C increased during 5000 h of exposure, which led to an increase in LCTR from 410 K to 610 K.

Collisional cooling in confined gases at cryogenic temperatures: Time dependent near-wall accumulation and gas dynamics

The heat transfer characteristics of a confined gas are often quantified by anisotropic thermal conductivity and are affected by near-wall accumulation. However, in non-equilibrium conditions, where gas and walls are at different temperatures, transport coefficients, and state variables become dynamic, thus offering an interesting aspect of heat transfer, which is investigated in the present work. Here, we focus on the cooling of confined He by collisions with cold metal walls at cryogenic temperatures (30 - 150 K) in pristine and mixed states with a secondary gas at atmospheric pressure. The effects of wall temperature (Tw), type, and mass (m⁎) of the secondary gas on the cooling rate constant (k) and subsequently on the near-wall accumulation of He are investigated through non-equilibrium molecular dynamics simulations. The cooling curves of the confined gases are found to obey Newton's law of cooling. To probe the cooling process further, the temporal evolution of the near-wall accumulation is analyzed and found to be significant for lower Tw, which, in turn, promotes heat transfer at the interface through gas-wall and gas-gas collisions. In a gaseous mixture, such accumulations are found to be smaller for a heavier secondary gas, which leads to the inhibition of gas-wall collisions. Furthermore, the kinetic energy transfer between He and a considerably heavier gas particle is inefficient, resulting in the slower cooling of He, as observed in He-Ne and He-Ar mixtures. The quantity k is additionally affected by the interaction strength and thermal conductivity of the secondary gas, including the initial temperature difference between the wall and the gas (ΔT). The results of this study find their applications in the fields of microelectronics and microplasmas.

Rapid adsorptive removal of eosin yellow and methyl orange using zeolite Y

In this study, zeolite Y was synthesised using a novel method. The heat generated from the reaction of H2SO4 with metakaolin was used as a heat source instead of applying external heat for the dealuminated process. The synthesised zeolite Y produced was analysed by scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS) and Brunauer–Emmett–Teller (BET). Zeolite Y synthesis was mesoporous because of its pore diameter (30.53 nm), as shown in the BET results. Surface area and pore size decrease after adsorption due to dye deposition on the adsorbent’s surface. FTIR has bonds like O–H, C–H, –CH3, and –COOH responsible for adsorption. The maximum adsorption capacity of eosin yellow (EY) and methyl orange (MO) on to zeolite Y by the Langmuir isotherm was 52.91 mg/g and 20.62 mg/g respectively, at pH 2.5 and 8 for EY and MO dye. The batch adsorption studies were conducted, and the influence of different parameters (i.e., adsorbent dose, adsorption time, initial dye concentration, pH and temperature) was investigated. Experimental data were analysed by two linear model equations (Langmuir and Freundlich isotherms), and it was found that the Langmuir isotherm model best describes the adsorption data for methyl orange and Freundlich isotherm for eosin yellow, respectively. Adsorption rate constants were determined using linear pseudo-first-order and pseudo-second-order. The results showed that MO and EY dye adsorption onto zeolite Y followed a pseudo-second-order kinetic model. Thermodynamic studies show that adsorption was an exothermic reaction (enthalpy < 0) and feasible ((Gibbsfreeenergy)<0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(Gibbs free energy)<0$$\\end{document}) at various temperatures under investigation.

Hyperelastic constitutive relations for soft elastomers with thermally-induced residual stress

Residual stress widely exists in soft materials. Besides growth, inhomogeneous thermal expansion is also a primary cause of residual stress. However, establishing a proper hyperelastic constitutive relation is a great challenge since the existing theories cannot capture the change of underlying mechanical responses triggered by temperature variations. In this paper, a general hyperelastic constitutive relation for soft elastomers with thermally-induced residual stress is developed. We first reveal the initial temperature dependence of conventional thermoelastic models. This property attributes the alteration of the underlying thermoelastic response to free thermal expansions. Then, a compatibility-broken curvature compensation (CBCC) framework is established based on finite thermoelasticity. It generates a free thermal expansion to eliminate the Riemannian curvatures of the virtual stress-free configuration derived from the isothermal stress release. Such a mechanism indicates the non-local effect of the residual stress, which fundamentally modifies the traditional view that invariant formulations cover all the possible functional dependence of residual stress. Also, the obtained governing equations are similar to Einstein field equations of the general theory of relativity. This similarity may deeply imply a standard mechanism concerning the curvature compensation leading to residual stress genesis. We finally conduct comparative analyses of the spherically symmetric and axisymmetric problems between the current constitutive relation and the existing models. The influences of adopting distinct residual stresses, the performance of the non-local effect, and the availability of the new constitutive relation are investigated in detail. This framework can shed some light on the constitutive modeling of soft materials.

Effect of water-cooling shock on heat production performance of enhanced geothermal systems

ABSTRACT The heat extraction process of the Enhanced Geothermal System (EGS) faces the problem of mechanical property degradation caused by artificial cracks and surrounding rock caused by water-cooling shock. However, there are few studies considering the effect of water-cooling shock on fracture deformation and heat production performance. Therefore, a comprehensive numerical model considering water-cooling shock was established to simulate the heat extraction process of EGS. Four different scenarios were designed to analyze the influence of water-cooling shock on the heat production performance of EGS. The sensitivity analysis of several important variables affecting fracture aperture and heat production performance is carried out. The results show that compared with EGS without considering water-cooling shock, the heat extraction performance of EGS considering water-cooling shock is more reasonable. For a reservoir with an initial temperature of 300°C, the decrease of production temperature after 40 years is 3.35°C. Water-cooling shock changes the fracture aperture by degrading the elastic modulus of rocks and fractures, which affects the heat production performance of EGS. The decrease of fracture elastic modulus means that the fracture aperture increases under the same injection water pressure and confining pressure. The decrease of elastic modulus of bedrock leads to the decrease of stress sensitivity index, which inhibits the expansion of fracture aperture. Comprehensively considering water-cooling shock on reservoirs and fractures will more reasonably predict the heat production performance of EGS.

Properties and performance of Ni(II) doped magnetic Fe3O4@mesoporous SiO2/UiO-66 synthesized by an ultrasound assisted method for potential adsorbent of methyl orange: Kinetic, isotherm and thermodynamic studies

Ni(II) doped magnetic Fe3O4@mesoporous SiO2/UiO-66 composite (FSUNi(x)) was synthesized by ultrasound methods for methyl orange (MO) adsorption. Ultrasound irradiation caused the in situ growth of Ni on Fe3O4 @mesoporous SiO2/UiO-66 composite. Ni enhanced the surface area and porosity of composites due to the substitution of Zr in UiO-66 with Ni, which generates defects. The SEM and TEM analysis exhibited the Fe3O4 @mesoporous SiO2 core of ∼324 nm diameter, coated with a Ni-UiO-66 shell of ∼ 23 nm thickness. At 10% nickel doping, FSUNi(10) composites showed high surface area, large pore diameter, excellent adsorption capacity, and high magnetic properties (8.16 emu/g) that achieved rapid recovery in 20 s. The influence of contact time (1–120 min), dye concentration (25–350 mg/L), pH of the initial solution (2−13), adsorption temperature (30–50 °C), and ionic strength (0–3 g/L) on the adsorption capacity were determined to understand the kinetic and thermodynamic of adsorption. The maximum adsorption capacity increased from 200.803 to 256.410 mg/g with increasing temperature from 30° to 50°C, and adsorption reached optimum capacity at pH 4. According to isothermal and kinetic analyses, adsorption follows the Langmuir isotherm model and the pseudo second order kinetic model. Based on the Langmuir isotherm model, the maximum adsorption capacities of UiO-66 and FSUNi(10) were determined at 182.815 and 200.803 mg/g, respectively. Thermodynamic analysis revealed the spontaneous and endothermic adsorption of MO dye on FSUNi(10). FSUNi(10) showed high adsorption capacity after three regeneration cycles, which can be a potential magnetic adsorbent for wastewater treatment.

The evolution process and degradation model of permafrost in the Source Area of the Yellow River on the Qinghai-Tibet Plateau since the Little Ice Age

Permafrost degradation is currently receiving as much attention as global warming. Permafrost evolution is a particularly slow process, making it impossible to examine the entire process by observation. Based on the heat conduction theory, in this study, a nonlinear numerical model for the entire process of permafrost evolution was developed with consideration of phase transition. The numerical simulation model was used to retrospectively analyse the evolution process and degradation pattern of permafrost in Tangchama beach-land in the Source Area of the Yellow River (SAYR) from 1400 to 2100; this analysis was performed using ice core inversion results obtained from the Qinghai-Tibet Plateau since the Little Ice Age and various future climate change scenarios from the IPCC Fifth Assessment Report. The simulation results showed that: 1) since 1900, permafrost temperatures have substantially increased, exceeding the range of change between 1400 and 1900; under the RCP2.6, RCP6.0 and RCP8.5 scenarios, permafrost will degrade and disappear in the next 100 years, and the degradation rate will subsequently accelerate. 2) The permafrost table steadily goes downward at first, and the onset of fast permafrost degradation is signalled by the appearance of a residual thawed layer at a depth of 3–4 m. The permafrost layer then gradually thins out as the permafrost table rapidly descends and the permafrost base slowly ascends. The permafrost will fully deteriorate and vanish once the permafrost table and the permafrost base bounds overlap. 3) Due to permafrost degradation, the ground temperature curve can be divided into the following stages: uniform gradient stage, C-type stage, zero-gradient type stage and phase transition stage. The four stages of the “permafrost life cycle” are initial temperature warming, continuous temperature rising, residual thawed layer, and final permafrost disappearance.

Numerical simulation of multi-array spray cooling for hot rolled seamless steel pipes

Spray cooling technology is an efficient cooling method. In the industrial application, the large area cooling requires the multi-nozzle spray design. Reasonable selection of nozzle array form is particularly important. Therefore, the simulation is applied in this study to investigate the effect of the nozzle array on the spray cooling of steel pipes after the model is validated. A steel pipe with a diameter of 140 mm, a wall thickness of 20 mm, and a length of 350 mm is employed as the research object, with an initial temperature of 900 °C. The scheme has four options for double spray spacing: OLR = −15 %, 0 %, 15 %, and 30 %. The results show that when the OLR grows, the cooling area gradually diminishes, and the cooling area's average temperature and average surface heat flux fall and subsequently increase. When OLR=30 %, the best cooling zone shape is obtained. The minimum average temperature, 231 °C, is obtained when OLR = 15 %. After comprehensive analysis, the ideal spray spacing range is found at OLR = 15 %∼30 %. In order to study the nozzle array, spray nozzles are arranged in multiple rows according to OLR = 30 %. This study also explores the strategies of unidirectional inclined spray and opposite inclined spray for lessening the area of the hot spot. There are six nozzle array arrangements in total. By comparing the results, it is discovered that the inclined spray increases the cooling area and accelerates the surface cooling of steel pipes. Under the side-by-side unidirectional inclined spray and the staggered unidirectional inclined spray, the cooling areas are 146,868 mm2 and 142,914 mm2 respectively, the average temperatures are 157.09 °C and 154.28 °C respectively. It is indicated that side-by-side inclined spray and staggered inclined spray are the better nozzle array arrangement to obtain the maximum cooling efficiency.

Preparation of Mg-Mg2Ni/C composite and its excellent hydrogen storage properties

Magnesium hydride (MgH2) is a promising hydrogen storage material with high weight and volume hydrogen capacity. However, higher operating temperature and reversible hydrogen capacity decay inhibit its wide application. To address these issues, Mg-Mg2Ni/C was obtained by ball milling magnesium and nickel-Metal Organic Framework (Ni-MOF), and following calcinations. Initial dehydrogenation temperature of the composite is 530 K, 70 K lower than that of MgH2, and the apparent activation energy of the composite is 77.6 ± 2.1 kJ/mol, which is only 50% of MgH2. At 423 K, the hydrogen capacity of the composite is about 6 wt% within 3600 s, and keeps unchanged after ten cycles. The carbon material introduced by Ni-MOF inhibits the agglomeration of Mg, and Mg2Ni/Mg2NiH4 acts as a “hydrogen pump” in de/hydrogenation process. The carbon coating and “hydrogen pump” lead to the improvement of the ab/desorption kinetics and cycling stability. This attempt paves a potential way to achieve high performance Mg-based composite hydrogen storage materials.

Learning stiff chemical kinetics using extended deep neural operators

We utilize neural operators to learn the solution propagator for challenging systems of differential equations that are representative of stiff chemical kinetics. Specifically, we apply the deep operator network (DeepONet) along with its extensions, such as the autoencoder-based DeepONet and the newly proposed Partition-of-Unity (PoU-) DeepONet to study a range of examples, including the ROBERS problem with three species, the POLLU problem with 25 species, pure kinetics of a skeletal model for CO/H2 burning of syngas, which contains 11 species and 21 reactions and finally, a temporally developing planar CO/H2 jet flame (turbulent flame) using the same syngas mechanism. We have demonstrated the advantages of the proposed approach through these numerical examples. Specifically, to train the DeepONet for the syngas model, we solve the skeletal kinetic model for different initial conditions. In the first case, we parameterize the initial conditions based on equivalence ratios and initial temperature values. In the second case, we perform a direct numerical simulation of a two-dimensional temporally developing CO/H2 jet flame with integrated chemistry modeling as a source of training data for the solution propagator. Then, we initialize the kinetic model by the thermochemical states visited by a subset of grid points at different time snapshots. Stiff chemical kinetics are computationally expensive to solve, thus, this work aims to develop a neural operator-based surrogate model to efficiently solve stiff chemical kinetics. The operator, once trained offline, can accurately integrate the thermochemical state for arbitrarily large time advancements, leading to significant computational gains compared to stiff integration schemes.

A wide ranging experimental and kinetic modeling study of TMEDA pyrolysis and oxidation

Traditional liquid propellants like unsymmetrical dimethylhydrazine include several issues, such as toxicity, short storage time and preservation difficulty at low temperatures. For this reason, exploring green and stable propellant fuels is imperative in the development of propellants. Tetramethyl ethylenediamine (TMEDA) is considered to be a promising green propellant fuel with high specific impulse, non-toxicity, and long-term storage stability. Thus, investigating the combustion characteristics of TMEDA and constructing a detailed chemical kinetic mechanism are of fundamental importance in describing its combustion in computational fluid simulation. For this work, ignition delay times of TMEDA were measured in a shock tube at equivalent ratios of 0.5, 1.0 and 2.0, at pressures of 2, 10, and 20 bar, and in the temperature range of 870–1500 K with fixed fuel concentration at 2 %. After the reflected shock at 990–1500 K, the pyrolysis products of 2000 and 5000 ppm TMEDA in Argon were also measured at 5 and 10 bar conditions in a single pulse shock tube. In addition, laminar flame speeds of TMEDA were measured at initial pressures of 1 bar, initial temperatures of 333 and 353 K, and equivalence ratios ranging from 0.8 to 1.5 in a constant volume reactor. The experimental results were simulated using a detailed TMEDA kinetic mechanism. Reaction path analysis and sensitivity analysis were provided to clarify the chemical kinetics of TMEDA oxidation and pyrolysis. The current work provides new experimental data and fundamental analyses for understanding the oxidation and pyrolysis characteristics of TMEDA, and sheds light on optimal directions for future models.

Heat transfer characterizations of water flow through a single fracture with integrating water dissolution effects for the Enhanced Geothermal Systems

The Enhanced Geothermal Systems (EGS) is the technology that generates connected fracture networks in the Hot Dry Rock (HDR) reservoir with the application of water as the working fluid for hydraulic fracturing and geothermal energy production. A good understanding of water flow behaviors in the single fracture is critically important because connected fracture networks are composed of individual fractures. It should be noticed that the dissolution reaction between the reservoir rock and the working fluid (water) will change the fracture surface directly and consequently affect the mass and heat transfer process of water through the rock fracture in the HDR reservoir. In this study, the heat transfer process of water flow in the single fracture by considering dissolution reactions between water and fracture surfaces of reservoir rock have been investigated under high pressure and temperature conditions. The experiments of dissolution reaction and convective heat transfer have been performed separately for different temperature conditions with the rock sample of 0.2 mm fracture aperture. The influences of reaction duration, mass flow rates and initial temperature have been presented and analyzed. It is found that mass flow rates and temperature have significant effects on measured temperature of fracture surfaces. The effects of dissolution reaction on fracture surface morphology exists but it is extremely small for heat transfer. Based on experimental and simulation data, a modified correlation that integrates reaction duration, mass flow rates and changes of thermophysical properties has been proposed and its maximum error that compares with experimental results is less than 7%. The results of this study provided an accurate correlation for simulations and characterizations of the Hot Dry Rock reservoirs, which is of great importance for geothermal energy production and optimization.

Application of biodrying with hot air aeration system to process solid waste into rdf

Biodrying is a promising method to process municipal solid waste (MSW) while generating refuse-derived fuel (RDF) output. Recent developments in the process of generating refuse-derived fuel (RDF) have led to a renewed interest in minimal pretreatment processes. Although extensive research has been carried out, one of the most significant current discussions about generating refuse-derived fuel (RDF) using biodrying methods is that it has taken a long time to process. The biodrying method using air from the atmosphere takes 21 days to convert solid waste into RDF. As a result of this, Biodrying processes need to be accelerated by flowing hot air into the biodrying reactor. The aim of this study is to analyze the biodrying process temperature profile with a hot air aeration system. The methodological approach taken in this study is to circulate the hot air that comes from the combustion of wood charcoal. Hot air is discharged into solid waste that is inserted into the biodrying reactor. The temperature and concentration of solid wastewater are analyzed every 15 minutes. The results of this study show that the initial MSW temperature of the front reactor was 40o C and that of the rear reactor was 31o C.In the first 15 minutes until 60 minutes, the temperature shows an increase. The MSW temperature of the front reactor was 47o C, and the rear reactor was 35o C.At the 30th minute of the front reactor, it was 63o C, the rear reactor was 61o C; at the 45th minute of the front reactor, it was 81o C, the rear reactor was 73o C; and at the 60th minute of the front reactor, it was 80o C, the rear reactor was 79oC. These findings have significant implications for the understanding of how circulate the hot air aeration system works well.

Global strong solutions to full compressible magnetohydrodynamic system with vacuum in 3D exterior domains

This paper investigates the full compressible magnetohydrodynamic system in three-dimensional exterior domains. For the initial-boundary-value problem of this system with slip boundary condition for the velocity, adiabatic one for the temperature, and perfect one for the magnetic field, we establish the global existence and uniqueness of strong solutions, under the condition that the initial data are of small energy but possibly large oscillations, where the initial density and temperature are both allowed to vanish. Moreover, the large-time behavior of the strong solutions is also shown.

P/N/Si‐containing synergistic flame retardants endowing lignin‐based epoxy resin with good flame retardancy, mechanical properties and heat resistance

AbstractBiobased epoxy resins are gaining attention as a renewable alternative to petroleum‐based resins. However, their inherent flammability requires flame‐retardant treatment. In this study, hexaphenoxycyclotriphosphazene (HPCP) and various synergists were utilized to improve the flame retardancy of lignin‐based epoxy resin (EP‐L). Results showed that (3‐aminopropyl)triethoxysilane (APTES) had the most effective synergistic effect for HPCP to form a P/N/Si‐containing system, resulting in a compact crosslinked char layer. Upon the incorporation of HPCP and APTES (6∶1, 12 wt% of EP mass) into EP, a V‐0 classification was achieved in the UL‐94 vertical burning assessment, with a limiting oxygen index of 33.6% and a 47.77% decrease in the peak of heat release rate. This system minimally influenced the tensile strength of the composite (a 16.51% reduction), and maximumly increased its initial degradation temperature by 83 °C, compared with EP‐L. © 2023 Society of Industrial Chemistry.

Use of hydroxyapatite powder derived from green mussel shell wastes for coating on AISI 316L

This study aimed to determine the effect of preheating AISI 316L metal substrate on the adhesion strength of the hydroxyapatite (HA) layer derived from green mussel shell waste deposit by the flame spray method. The deposition experiment was carried out in a spray gun with a distance of 10 mm with preheat of 200°C, 400°C, and 600°C. A sample without preheating was also a comparison. An optical microscope was for assessing the thickness and uniformity of the HA surface layer. The adhesion strength of the coatings followed the ASTM D4541 Standard. As a result, the adhesion strength of the HA coating increases with increasing preheat temperature. However, using Image-J software, at an initial heating temperature of 600 °C, the adhesion strength of the coating changed from adhesion- to adhesion-cohesive strength, leading to an increase in coating strength noted. The result can add knowledge to understanding the flame spray method for the HA-coated from green mussel shell waste on AISI 316L. The results obtained can increase knowledge to understand the method of flame spraying on HA-coated green mussel shell waste on AISI 316L. Preheat temperature, spray gun shooting distance, HA powder release, oxygen gas pressure, and LPG gas pressure can be used as references.

Optimisation of the Technological Parameters of the Ecological Milk Cooling Plant

The aim of this paper is to optimize the technological parameters of the ecological milk cooling plant with the application of natural cold, which ensures a significant increase in energy efficiency at collection points in the Republic of Moldova. The proposed plant captures the natural cold and stores it in the insulated cold accumulator without the use of freons, which is then used for cooling milk. In order to achieve the goal, the mathematical model of the intermediate refrigerant cooling process using renewable energy was developed in the paper. Based on the requirements imposed on the technological process as well as the developed mathematical model, it was determined that for cooling the intermediate refrigerant from the initial temperature of +140C to +40C, at the ambient temperature of +20C, 34.25 times more equivalent volume of air is required.

Multicolor tunable emission through energy transfer in Dy3+/Ho3+ co-doped CaTiO3 phosphors with high thermal stability for solid state lighting applications

The exploration of multicolor emitting phosphors with single phase is extremely important for n-UV chip excited LED/WLED’s and multicolor display devices. In this paper, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials have been synthesized by solid state reaction method at 1473 K. The synthesized materials were characterized by XRD, FE-SEM, EDX, FTIR, PL and lifetime measurements. The PL emission spectra of Dy3+ doped CaTiO3 phosphors give intense blue and yellow emissions under UV excitation, while the PL emission spectra of Ho3+ doped CaTiO3 phosphor show intense green emission under UV/blue excitations. Further, to get the multicolor emission including white light, Dy3+ and Ho3+ were co-doped simultaneously in CaTiO3 host. It is found that alongwith colored and white light emissions, it also shows energy transfer from Dy3+ to Ho3+ with 367 nm and from Ho3+ to Dy3+ under 362 nm excitations. The energy transfer efficiency is found to be 67.76% and 69.39% for CaTiO3:4Dy3+/3Ho3+ and CaTiO3:3Ho3+/5Dy3+ phosphors, respectively. The CIE color coordinates, CCT and color purity of the phosphors have been calculated, which show color tunability from whitish to deep green via greenish yellow color. The lifetime of 4F9/2 level of Dy3+ ion and 5S2 level of Ho3+ ion is decreased in presence of Ho3+ and Dy3+ ions, respectively. This is due to energy transfer from Dy3+ to Ho3+ ions and vice versa. A temperature dependent photoluminescence studied of CaTiO3:4Dy3+/2Ho3+ phosphor show a high thermal stability (82% at 423 K of initial temperature 303 K) in the temperature range 303–483 K with activation energy 0.17 eV. The PLQY are 30%, 33% and 35% for CaTiO3:4Dy3+, CaTiO3:4Dy3+/2Ho3+ and CaTiO3:3Ho3+ phosphors, respectively. Hence, Dy3+, Ho3+ singly doped and Dy3+/Ho3+ co-doped CaTiO3 phosphor materials can be used in the field of single matrix perovskite color tunable phosphors which may be used in multicolor display devices, n-UV chip excited LED/WLED’s and photodynamic therapy for the cancer treatment.