Heat Preservation Time Research Articles

Growth behavior of aluminum borate whiskers on zirconia toughened alumina (ZTA) particle surface

In this work, B4C-covered zirconia-toughened alumina (ZTA) particles are prepared and oxidised at 1050 °C for different times (0, 2, 4, and 8 h) in air. The X-ray diffraction and electron probe micro-analysis results show that the covering layer is mainly composed of oxide B2O3 intermetallics, residual B4C particles, and Al18B4O33 whiskers. The scanning electron microscopy results show that the growth of Al18B4O33 whiskers on the ZTA particles enhances with increasing heat preservation time; the optimum holding time is determined to be 8 h Al2O3 in the ZTA particles diffuse into the covering layer and combine with B2O3 to form Al18B4O33 whiskers; the Al18B4O33 whiskers grow via the liquid-solid mechanism.

Effect of High Temperature Annealing on Crystal Structure and Electrical Properties of Multicrystalline Silicon by the Metallurgical Method

The defects of dislocations and grain boundaries (GBs) could significantly reduce the electrical properties of multicrystalline silicon (mc-Si) solar cells. In this manuscript, the influence of crystal defects on the electrical properties of mc-Si was investigated, aims to carry out the research about the influence of crystal defects on the electrical properties of mc-Si. Purified metallurgical grade N type mc-Si ingot was obtained with the method of vacuum directional solidification technique by employing industrial production ingot furnace. The variations in grain boundaries and dislocations were characterized by electron backscatter diffraction (EBSD), and their effects on the electrical properties of mc-Si before and after annealing at different heat insulating time were investigated. Experimental results showed that high temperature annealing process could significantly improve the electrical properties of mc-Si, the minority carrier lifetime was improved from 0.599 μs to 0.770 μs after 10 h insulation, with a significant increase of 28.61%. Experimental results indicated that high temperature annealing process could significantly eliminate the crystal defects of multicrystalline silicon. The crystal defects was eliminated more obviously with prolonged heat preservation time. When treated by high temperature annealing, the proportion of small angle grain boundaries in the same region can be increased by as high as 13.45%. Moreover, the whole grain sizes of partly region of silicon wafer could be increased by 20000μm2, increased by 15.89% compared with the original grain sizes. Based on the experiment phenomena, we attributed the improvement in the electrical properties of mc-Si to the elimination of dislocations, increased grain sizes and migration of GBs.

Grain Growth Model of Ultra-Fine Grain AZ80 Magnesium Alloy Multi-Directionally Forged During the Isothermal Heating Process

This paper takes the ultra-fine grain AZ80 magnesium alloy multi-directionally forged as the research object. We observe its heating behavior at 673 K with an optical microscope, analyze the grain size distribution, and the change of average grain size and hardness with different heating time, study the effect of heating time on the grain size change of ultra-fine grain AZ80 magnesium alloy, deduce and verify the grain growth model of ultra-fine grain AZ80 magnesium alloy during its heating process. The research results show that the 24-pass multi-directional forging can make ultra-fine grain AZ80 magnesium alloy of an average grain size of 0.73 μm. When ultra-fine grain AZ80 magnesium alloy is isothermally heated at 673K, its average grain size grows continuously as time extends. Its average grain size and hardness fall into two stages as the heating time changes, namely rapid grain growth stage and stable grain growth stage. If the heat preservation time is less than 300 s, the average grain size grows rapidly as temperature rises; When the heat preservation time reaches 300 s, the grain growth speed will be stable. A grain growth model is established for AZ80 magnesium alloy, which is D2.8932 = D02.8932 + 4.09086 × 10-3t1.6284 under the conditions of isothermal heating, whose computed result well coincides with the measured value.

Effect of semi-continuous replacements of compost materials after inoculation on the performance of heat preservation of low temperature composting

Development of cold-adapted microbial agent is an efficient approach for composting in low temperature. The study was conducted to evaluate the effect of semi-continuous replacements of compost materials after inoculation (SRMI) on the heat preservation of low temperature composting derived from chicken manure. Results revealed that SRMI could significantly improve the heat preservation of the pile, although the time of start-up in two inoculation groups was approximately the same. Due to the increase in the number of replacements of materials led to the changes in microbial community structures and enzyme activity. Non-metric multidimensional and colorimetric methods indicated that microbial community structures and enzyme activity was completely different in SRMI. Structural equation model was constructed by key factors involved in diversity of the microbial community, enzyme activity, temperature and bio-heat generation. In summary, SRMI decidedly increase the heat preservation time of the pile and start-up efficiency of the low temperature composting.

Effect of heat preservation time on the micro morphology and field emission properties of La-doped SiC nanowires

Lanthanum doped SiC nanowires (La-doped SiC NWs) were prepared using the chemical vapor reaction technique at different heat preservation times.

Experimental study on thermal properties and thermal performance of eutectic hydrated salts/expanded perlite form-stable phase change materials for passive solar energy utilization

A novel composite phase change material (PCM) used as exterior and interior envelop materials for passive solar energy utilization was synthesized and investigated in this paper. Eutectic hydrated salt (EHS) consisted sodium carbonate decahydrate (SCD) and disodium hydrogen phosphate dodecahydrate (DHPD) with a mass ratio of 5:5 was prepared as the PCM with its phase change temperature of 26.94 °C and phase change enthalpy of 198.44 J/g while three different kinds of expanded perlites (EPs) were pretreated as supporting materials. According to the results of leakage tests and volume enthalpy, 70%EHS/EP2 was chosen as the form-stable phase change materials (FSPCM) to fabricate phase change insulation panels. The thermal conductivity with different temperature of 70%EHS/EP2 was measured and the maximum was 0.44 W/(m K) when the testing temperature was 25 °C. In addition, the heat storage and release results of 70%EHS/EP2 indicated that there was no supercooling. The thermogravimetric analysis and thermal cycling tests were performed and the results indicated that 70%EHS/EP2 had a good thermal stability and reliability. The heat transfer properties of EP panel and 70%EHS/EP2 phase change panel were tested and the results showed 70%EHS/EP2 phase change panel could remarkably decrease the maximum temperature during the melting process and obviously prolong the time of heat preservation in the cooling process which contributed to its good thermal control performance.

Effects of preparation parameters on low temperature formation of TiO2 photocatalysts

The wastewater containing organic pollutants is becoming a worldwide public health issue. Photocatalysis is a promising technology for the degradation of various organic compounds in wastewater treatment and environmental pollution reduction. Most photocatalysts cannot be widely applied due to their poor photo-response in the visible light region, complexity in preparation and difficulty in recycling. Here, we suggest a facile and modified sol–gel method to synthesize TiO2 nanoparticles at a low temperature. X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and UV–Vis diffuse reflectance spectra were used to investigate the effects of temperature, heat preservation time, and water amount on the crystal structure, the morphologies, and the properties of the samples. That the sample with ratio of the Ti/H2O mol at 1:3 and dried at 180 °C for 6 h showed the most satisfying photocatalytic activity. The average size of this obtained sample was 4.6 nm, the specific surface area was 241.3817 m2/g, and the band gap was 1.84 eV. The reaction rate constant for the methylene orange degradation under visible light irradiation reached 0.09713 min−1 after 60 min.

Thermal management of standby battery for outdoor base station based on the semiconductor thermoelectric device and phase change materials

In order to extend the life span of standby battery for outdoor base station, a semiconductor thermoelectric device/phase change materials (PCMs) coupled battery thermal management system (BTMS), as well as the three-dimensional model of 48 V 80 Ah battery pack, was designed in this paper. The effect of various influencing factors, especially semiconductor thermoelectric device arrangement, temperature range of thermal management, cooling and heating power was investigated numerically. The results showed that the semiconductor thermoelectric devices were arranged at two flanks of minimum size direction could effectively improve the uniformity of battery module temperature field and prolong the heat preservation process. When the temperature difference between upper or lower limit of thermal management temperature range and the phase change temperature of PCMs (TPCM) was no more than 5 K, the maximum temperature difference (ΔTmax) of battery module during the cooling or heating process was lower than 5 K. Both the best choice of cooling and heating power was 200 W. What’s more, after 1 C discharging and 0.5 C charging process, the maximum temperature (Tmax) of battery module was restrained under the 312 K. During continuous cooling and heat preservation cycle, the cooling time and heat preservation time was about 14 h and 4.15 days, respectively, when the average ambient temperature was 323 K. The simulation results will be useful for the design of PCMs based battery thermal management system for outdoor base station battery.

The effect of heat preservation time on the electrochemical properties of LiFePO4

LiFePO4 was prepared via high temperature solid-state method at different heat preservation time. XRD and SEM was used to test the structure and morphology of LiFePO4. Land 2001 was used to test the electrochemical performance of LiFePO4. The results illustrated that well-crystallized LiFePO4 composite with homogeneous small particles was obtained by XRD and SEM. And the optimum heat preservation time was 4 hour. From charge/discharge test, it can be seen that at 0.2C, LiFePO4 has initial discharge capacities of 159.1mAh/g at the heat preservation time 4 hour. From the rate capacity, it can be seen that the discharge capacity was of optimum sample remains above 99% after 200 cycles.

Volatilization behaviors of molybdenum and sulfur in vacuum decomposition of molybdenite concentrate

Thermodynamic calculation, ab initio molecular dynamics (AIMD) and vacuum decomposition experiments were performed to study the volatilization behaviors of Mo and S from molybdenite concentrate by vacuum decomposition. In thermodynamic calculation, starting decomposition temperatures of reactions were calculated, and saturated vapor pressures of Mo, S and MoS2 were also analyzed. In AIMD, geometries of the S n (n≤8), Mo m (m≤8) and Mo m S n (m+n≤8) clusters have been optimized using density functional theory (DFT) with generalized gradient approximation (GGA). And these clusters were simulated in DFT with Cambridge Sequential Total Energy Package (CASTEP) code of Material Studio software. Structures and stabilities of these clusters before and after molecular dynamics simulations were discussed, and diffusion coefficients were also calculated. In vacuum decomposition experiments, relationship between heat preservation time and volatilization rate of Mo and S was obtained, while the constant temperature and chamber pressure were 1823 K and 5–35 Pa, respectively. Above all, both the theoretical and experimental results showed that volatilization behaviors of Mo and S during vacuum decomposition process of molybdenite concentrate were as follows: Mo could partly evaporate into the condensate in the form of clusters, and S could easily evaporate into the condensate.

Low-temperature synthesis of nanocrystalline ZrC coatings on flake graphite by molten salts

A novel molten salt synthetic route has been developed to prepare nanocrystalline zirconium carbide (ZrC) coatings on flake graphite at 900°C, using Zr powder and flake graphite as the source materials in a static argon atmosphere, along with molten salts as the media. The effects of different molten salt media, the sintered temperature, and the heat preservation time on the phase and microstructure of the synthetic materials were investigated. The ZrC coatings formed on the flake graphite were uniform and composed of nanosized particles (30–50nm). With an increase in the reaction temperature, the ZrC nanosized particles were more denser, and the heat preservation time and thickness of the ZrC coating also increased accordingly. Electron microscopy was used to observe the ZrC coatings on the flake graphite, indicating that a “template mechanism” played an important role during the molten salt synthesis.

Deposition of titanium coating on SiC fiber by chemical vapor deposition with Ti-I2 system

Titanium coating was prepared on SiC fiber using titanium-iodine (Ti-I2) mixture by hot-wall chemical vapor deposition. Thermodynamic analysis and experimental observation were carried out in this work. The thermodynamic analysis of the reactions in the Ti-I2 system indicates that Ti and I2 raw powder materials transform to titanium coating as follows: Ti+I2 → (TiI2, TiI3), and (TiI2, TiI3) → Ti. In theory, the conversions of TiI3 and TiI2 reach the maximum when Ti:I2 is 1:1.5, while in actual experiment that reached the maximum when Ti:I2 was 1:2, as there existed the waste of I2 due to sublimation. Typical deposited coating is relatively flat and uniform. However, as SiC is prone to react with Ti at high temperatures, the obtained coating contained some Si and C elements except for Ti. So the coating was not a pure Ti coating but contained some carbides and silicides. Deposition rate of the coating increased with the increase of temperature. The deposited thickness increased with the increase of heat preservation time, and achieved the maximum thickness at 90min.

Optimization of curing process for polymer-matrix composites based on orthogonal experimental method

In this paper, the orthogonal experimental method was carried out to optimize the curing process of aeronautical composite X850/T800 in autoclave process. Four important curing parameters including curing pressure, heating rate, curing temperature and heat preservation time were taken into account, and sixteen samples were fabricated to study the effects of the four parameters mentioned above on the curing quality by interlaminar properties test and microstructure analysis. The interlaminar properties and the interfacial bonding quality of these samples were studied by the short-beam three points bending test and scanning electron microscopy, respectively. Results revealed that the optimal curing process of X850/T800 composite laminate should be as follows: curing pressure of 0.6 MPa, heating rate of 1.5 °C/min, curing temperature of 160 °C, and heat preservation time of 120 min.

Thermodynamic analysis and experimental rules of vacuum decomposition of molybdenite concentrate

Vacuum decomposition process of molybdenite concentrate was investigated under pressure of 5–35 Pa for 15–120 min at the temperature range 1473 K–1973 K. The theoretical and experimental results showed that Gibbs free energy of vacuum decomposition reactions and evaporation rate of pure sulfur provided the theoretical calculation basis for temperature and heat preservation time selection in vacuum decomposition experiments of molybdenite concentrate. Melting points and saturated vapor pressures of pure substances and compounds predicted the evaporation behavior of impurity elements and its compounds during the experimental process. Both Cu and Fe could partly evaporate into condensate and Cu had better evaporation ability than Fe. MoO3 could easily and Al2O3, SiO2 could partly evaporate into the condensate. Kilo-scale experiment was performed based on the small experiments and its results showed that the Mo content of molybdenum metal product was 92.38% and the S content of sulfur product was 96.28%, and the molybdenum recovery rate reached to 95.94%. Both the theoretical and experimental results proved that it was feasible to produce crude molybdenum and sulfur from molybdenite concentrate through vacuum decomposition.

Influence of Process Conditions on the Structure and Hydraulic Activity of Air-Cooling Blast Furnace Slag

Using the industrial limestone, fly ash and pure chemical reagents as raw materials, the blast furnace slag was prepared by the fast air-cooled method. Using orthogonal experiment method, the influence of process conditions such as heating rate, heat preservation time of the blast furnace slag in hearth, discharge temperature of slag and cooling speed on the glass content and hydraulic activity of blast furnace slag were studied, the main influence factors and the optimal process conditions of blast furnace slag were determined. The results showed that the discharge temperature of slag was the key factor influencing on the glass content of granulated blast furnace slag. The impact degree of all process conditions on the glass content of granulated blast furnace slag accord with the following sequence: discharge temperature of slag > heat preservation time > heating rate > cooling rate. And heat preservation time and cooling rate were the key factors influencing 28 days activity index of blast furnace slag, the impact sequence of all process conditions on the 28 days activity index of granulated blast furnace slag was as follows: heat preservation time > cooling rate > discharge temperature of slag > heating rate. This study also optimized the process conditions of granulated blast furnace slag for different indicators.

Microstructure evolution and grain refining performance of new green kind of Al–5Ti–C master alloy

Al–5Ti–C alloy was prepared and the microstructure evolution during the remelting process and its grain refinement performance toward pure aluminium were investigated. The results show that Al–5Ti–C alloy with a more uniform microstructure was successfully prepared, and it was composed of Al, TiAl3 and TiC. At a remelting temperature of 730°C, with the increase in heat preservation time of remelted melt, the originally dispersed TiC was aggregated and pushed toward grain boundaries by α-Al, while TiAl3 dissoluted, aggregated and grew. At a temperature of 1000°C, with the increase in heat preservation time, not only TiC aggregated, but also the size and morphology of TiAl3 were changed significantly as well, the TiAl3 turning in morphology from lump-like or strip-like into coarse needle-like and flake-like grains. The grain refinement experiments show that Al–5Ti–C and remelted Al–5Ti–C master alloy have good grain refining performances.

Process analysis and mechanism investigation of low temperature synthesis of nanoscale calcium hexaboride powder.

The synthesis of nanoscale CaB6 powder via the low temperature chemical reaction of Calcium chloride (CaCl2) with Sodium Borohyride (NaBH4) in vacuum has been investigated in this study. The reaction temperature was determined by differential scanning calorimetry and thermogravimetric analysis (DSC and TG). Crystallization process was provided through studying the influence of heat preservation time on the crystal particles morphologies in vacuum. X-ray diffraction (XRD) was used to investigate the phase and structure of CaB6. The characterization for microstructure was performed by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The elemental analysis was conducted by X-ray photoelectron spectroscopy (XPS). It is concluded that CaB6 nanoparticles can be successfully prepared under low temperature at 500 degrees C. The results showed that in vacuum, 2 hours heat preservation time is enough for the reaction to complete at this temperature. The average size of crystal grains is 25.1 nm with high crystallinity and cubic shaped, which particles size is at the range of 20-100 nm. Longer heat preservation time more than 2 hours will make CaB6 particles connected together to form hard aggregations, that is the sintering process occurred under this temperature. However, the crystal grain size changed unobviously accompanying the holding time prolong due to the high chemical stability of CaB6. The atomic ratio of B to Ca is 5.37:1, less than but close to its stoichiometric ratio 6:1. The synthesis process and mechanism were investigated in this paper.

Heat Preservation Time on the Properties of Red Mud Lightweight Insulation Brick

The red mud lightweight insulation brick was prepared by the sintering process as red mud, fly ash, bentonite as the main raw material, adding a certain amount of pore forming agent and fluxing agent. The sintering heat preservation time of red mud insulation brick on the properties was studied. The red mud lightweight insulation brick damage fracture microstructure was analyzed using scanning electron microscope (SEM) and the sintering mechanism was discussed preliminarily. The results show that with sintering temperature of 1100°C heating for 180 minutes, the performance of thermal insulation brick is better. When the heat preservation time extends to continue, the performances of sample remain stable basically.

Removing chlorine of CuCl residue from zinc hydrometallurgy by microwave roasting

Most Zn hydrometallurgy factories adopt Cu2SO4 as a dechlorination reagent from zinc solution nowadays, thus much CuCl residue is produced. The existing process of treating this residue is washing with water or sodium carbonate solution, which would cause a lot of troubles to water treatment and waste discharge. A method of microwave roasting was adopted for dechlorination of CuCl residue. A 1.5 kW microwave roasting equipment with dust collection and tail gas adsorption systems was set up and applied during the experiment. By investigating the effect of temperature, heat preservation time, moisture content of raw material and grain size of samples on the dechlorination, the optimal experimental condition is obtained. When the samples with 2% moisture and <150 μm grain size are microwave roasted at 400 °C for 2 h, the Cl content turns from 14.27% to 1.35% and the dechlorination rate is as high as 90%, while that with conventional heating is only 60%–80%. The phase change of the roasting process investigated with X-ray diffraction verifies that CuCl in CuCl residue is removed by being transformed into CuO.

Influence factors of photocatalytic activity of the filter media modified by TiO2

The gangue filter media was modified by the titanium dioxide (TiO2) through the liquid phase deposition method. Some influence factors of photocatalytic activity were investigated, including the mole ratio of initial solution, the water bath temperature, the deposition time, the calcination temperature, and the heat preservation time of calcination. The morphology of the film was examined by SEM, EDS, and crystallite structure by X-Ray Diffraction (XRD). The SEM, EDS, and XRD data showed that new TiO2 crystal was found in the modified filter media. And the specific surface area of the modified filter media greatly increased. By the orthogonal experiment, the optimum parameters of modification were (NH4)2TiF6:H3BO3=1:2, water bath temperature of 80?C, deposition time of 5h, calcination temperature of 500?C, and 1h heat preservation time of calcination. Under above conditions, the heavy nitrogen wastewater of 1589.94 mg/L COD and 18750 times chroma was treated by the modified filter media. After 1h catalytic reaction, the decolorization rate and COD removal rate reached 65.89% and 47.87%, respectively.