Heat Preservation Time Research Articles

Research on Leaching Cesium from Medium and Low Pollucite Concentrates by the Sulfuric Acid Process

Abstract With the sharp decrease in high-grade pollucite resources, medium and low grade pollucite concentrate will become the main raw material for extracting cesium in the future. The main process conditions for leaching cesium from medium- and low grade pollucite concentrate by the sulfuric acid process were studied, and the effects of the ratio of leaching liquid to solid, leaching time, leaching temperature and of leaching liquid on the leaching rate of cesium were investigated. The results show that CsAl(SO4)2·3H2O is formed from 2Cs2O·2Al2O3·9SiO2·H2O after the medium and low grade pollucite concentrates are leached by sulfuric acid. The optimum conditions for the leaching process were as follows: the concentration of sulfuric acid was approximately 3.5 mol/L, L/S≈2, the leaching temperature was 120 °C, the heat preservation time was 2.0 h, and the leaching rate of cesium exceeded 93%. The leaching residue was washed and discarded, and the leaching solution was recycled three times and then concentrated to precipitate alum. The [Cs] in the mother liquor resulting from CsAl(SO4)2·3H2O crystallization ranged from 1 g/L to 1.28 g/L, and the [Al] ranged from 0.29 g/L to 0.33 g/L, which could be recycled for leaching.

Effect of Post-Weld heat treatment on residual stress in deck-rib double-side welded joints and process optimization

Post-weld heat treatment (PWHT) is expected to release the welding residual stress (WRS) of deck-rib double-side welded joints in orthotropic steel decks (OSDs). In this paper, the WRS distribution of deck-rib double-side welded joints before and after PWHT is evaluated by hole drilling method and numerical simulation, and the effect of PWHT parameters on WRS relaxation is further compared, and reasonable parameters are suggested. Based on the principle of WRS relaxation by PWHT, the feasibility of secondary continuous PWHT was explored. The results show that PWHT can effectively release the WRS and make the distribution more uniform. Extending the heat preservation time and increasing the temperature can release more WRS, and the heating and cooling rate has little influence on the WRS, so it is recommended to use the specified maximum value. The effect of secondary continuous PWHT is slight, and it is not recommended for use.

Effects of Curing Defects in Adhesive Layers on Carbon Fiber-Quartz Fiber Bonded Joint Performance.

Due to their mechanical load-bearing and functional wave transmission, adhesively bonded joints of carbon fiber-quartz fiber composites have been widely used in the new generation of stealth aviation equipment. However, the curing defects, caused by deviations between the process environment and the setting parameters, directly affect the service performance of the joint during the curing cycle. Therefore, the thermophysical parameter evolution of adhesive films was analyzed via dynamic DSC (differential scanning calorimeter), isothermal DSC and TGA (thermal gravimetric analyzer) tests. The various prefabricating defects within the adhesive layer were used to systematically simulate the impacts of void defects on the tensile properties, and orthogonal tests were designed to clarify the effects of the curing process parameters on the joints' bonding performance. The results demonstrate that the J-116 B adhesive film starts to cure at a temperature of 160 °C and gradually forms a three-dimensional mesh-bearing structure. Furthermore, a bonding interface between the J-116 B adhesive film and the components to be connected is generated. When the curing temperature exceeds 200 °C, both the adhesive film and the resin matrix thermally degrade the molecular structure. The adhesive strength weakens with an increasing defect area ratio and number, remaining more sensitive to triangle, edge and penetration defects. By affecting the molecular structure of the adhesive film, the curing temperature has a significant impact on the bonding properties; when the curing degree is ensured, the curing pressure directly impacts the adhesive's performance by influencing the morphology, number and distribution of voids. Conversely, the heating rate and heat preservation time have minimal effects on the bonding performance.

Probing into the optimum preparation and the chemical durability of Sr0.5Zr2(PO4)3-SmPO4 dual-phase ceramics for nuclear waste forms via in-situ synthesis

In this work, Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics were prepared via in-situ synthesis process, which is a potential novel nuclear waste form for immobilizing the fission product 90Sr and the trivalent actinide radionuclides in high-level waste (HLW). And the preparation technology, microstructure and chemical durability of Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics were systematically investigated. It was confirmed that the optimum microwave-sintering temperature (1050 °C) and heat preservation time (1.5 h) is estimated by Archimedes method. Besides, the as-prepared samples that were consisted of strontium zirconium phosphate (SrZP) and monazite showed the remarkable densification, in which the two crystalline phases were intermixed well with each other. Meanwhile, the formation and evolution of microstructure was also consistent with the variational rule of Sr0·5Zr2(PO4)3/SmPO4, indicating that there was not mutual reaction during the in-situ synthesis process. The PCT and MCC-1 experimental results demonstrated that the elemental normalized leaching rates of tested samples are all at a low level (LRSr∼10−4 g‧m−2‧d−1, LRZr∼10−8-10−6 g‧m−2‧d−1, LRSm∼10−7-10−5 g‧m−2‧d−1 and LRP∼10−4 g‧m−2‧d−1). It is indicated that Sr0·5Zr2(PO4)3-SmPO4 dual-phase ceramics possesses excellent chemical durability for HLW disposal.

CBN‐reinforced Al2O3–Ti(C,N) composites with high toughness sintered under oscillatory pressure

AbstractHigh‐toughness Al2O3–Ti(C,N) composites reinforced by cBN particles were prepared by the new oscillating pressure sintering technique. The density, phase, and microstructure evolution of the Al2O3–Ti(C,N)‐cBN composites sintered at different temperatures were studied, and their effects on the mechanical properties were investigated. The results show that when the sintering temperature increases from 1300 to 1500°C, the heat preservation time shortens, whereas the density and interface bonding strength of the composites increase. In addition, cBN particles can play the role of crack bridging and be pulled out when the composites fracture, improving the toughness of the Al2O3–Ti(C,N)–cBN composites. However, when the sintering temperature further rises to 1600°C, a new phase of TiB2 forms, and the solid solubility of C and N in Ti(C,N) increases, leading to a decrease in density and mechanical properties. As a result, when the Al2O3–Ti(C,N)–cBN composite is sintered at 1500°C, its mechanical properties reach the maximum values of 21.5 GPa, 5.7 MPa m1/2, and 731 MPa for hardness, fracture toughness, and flexural strength, respectively.

Numerical and experimental investigation of an automatic brazing vacuum seal system for Mars soil sample return

The successful retrieval of samples from Mars stands as a pivotal objective for future scientific exploration. The Martian environment presents numerous challenges for preserving the hermeticity of collected samples. An automatic brazing vacuum seal system (ABVSS) is investigated to enhance the sealing performance of the Mars soil sample container. After certain adaptive enhancements, the ABVSS can be applied in the Mars, minor planet, comet or other extraterrestrial soil sample return projects. The ABVSS comprises a cylindrical container, an annular knife edge on a cylindrical lid, a pre-welded indium alloy annulus, and a heating plate. This study examines the influence of brazing temperature through numerical and experimental investigations. Besides, coating materials, brazing temperature and heat preservation time experiments are conducted to assess the impact of wettability and element diffusion on the leakage and sealing reliability of the ABVSS. The results obtained demonstrate that the theoretical simulation results are consistent with the experimental ones. Once indium is melted completely, the ABVSS reaches a minimum temperature of 155.91 °C. The minimum temperature, exceeding 125 °C, effectively autoclaves the container, thereby ensuring compliance with planetary protection regulations. Furthermore, silver, with its higher melting temperature and lower wetting angle, emerges as the optimal electroplating material for enhancing sealing reliability. The optimal leakage rate of 4.3 × 10−5 Pa m3/s is achieved at room temperature with a brazing temperature of 250 °C and a heat preservation time of 20 min.

Experimental study and simulation analysis of thermal-vibratory stress relief treatment of Al-Cu-Mg alloy plate

The considerable uneven residual stress (RS) induced by the quenching process of aluminum (Al) alloys causes dimensional instability and deformation. RS relief is essential to enhance the performance of the Al alloys. Thermal vibration stress relief (TVSR), which integrates conventional thermal stress relief (TSR) and vibration stress relief (VSR), has been shown to effectively reduce and homogenize the RS of Al alloys. To date, the detailed processes and mechanisms of TVSR have yet to be studied. Therefore, TVSR experiments considering the coupling rules of TSR and VSR were conducted on the Al-Cu-Mg alloy. Coupled creep-mechanical finite element (FE) models considering the heat preservation time, vibration time, and vibration sequence was devised to predict the residual stress evolution during TVSR treatment. The TVSR simulation results are in good agreement with the experimental results. The results show that TVSR treatment with a heat preservation time of 110 min followed by vibration for 10 min had the optimal stress relief effect, with a stress relief rate 81.7 % higher than that of TSR. Different TVSR processes had little impact on the Vickers hardness and metallographic structure. The TVSR treatment mechanism was also analyzed.

Study on the Technology of Preparing Ceramsite from Coal Gangue

China's coal resources are extremely rich, and the degree of coal mining is high. During the formation of coal, a large amount of coal gangue will be produced, which not only accumulates land and wastes resources, but may also cause natural disasters such as fires. In this paper, coal gangue is used as the main raw material, and a certain amount of kaolin, steel slag and other auxiliary materials are added to prepare coal gangue ceramsite through a high-temperature sintering process. The research results show that as the sintering temperature increases, the porosity of the ceramsite decreases first. After increasing, the water absorption rate of ceramsite also decreases first and then increases with the increase of the firing temperature, while the compressive strength first decreases and then increases with the increase of temperature. With the increase of the holding time, the porosity of the ceramsite first decreases and then increases. The water absorption rate of the ceramsite also first decreases and then increases with the increase of the firing temperature, while the compressive strength decreases first and then increases with the increase of the temperature. Elevated. With the increase of coal gangue content, the porosity of ceramsite gradually decreases, the water absorption rate of ceramsite also gradually decreases, and the compressive strength gradually increases with the increase of coal gangue content. The optimization can be obtained, the coal gangue content (mass fraction) is 100%, the calcination process system is 1200°C, and the heat preservation time is 60min as the better parameters. At this time, the compressive strength is 29.57MPa and the porosity is 4.36%.

Study on Building Energy Saving Effect and Thermal Response of Roof Greening in Extremely Hot Weather

As the main living space and carrier of the population, cities and buildings have become more seriously affected by changes in global environment in recent years. The deteriorating living environment has brought about the quality of survival of the population, the government’s administrative management, and the sustainable development of the environment. This article has found that green roofs on urban environmental management and building energy consumption have found that green roofs can have an important impact on urban environmental management. In extreme weather events, green roof has a maximum cooling effect of 26℃ in the daytime, and its warming effect at night has been suppressed to a certain extent; the heat preservation time of the green roof can be up to 17 hours after the superposition of precipitation weather incidents, and its heat preservation effect is positively related to the temperature in the daytime. The green roof can reduce the energy consumption of the building by 106W/ ㎡/d in the extreme weather incident, while its energy -saving effect is reduced to 45W/m2/d after superimposing the precipitation meteorological incident.

Preparation of hierarchical porous microspheres composite phase change material for thermal energy storage concrete in buildings

Phase change materials with high latent heat significantly reduce building energy consumption. However, the serious leakage issue, low thermal conductivity, and the poor photothermal response utterly hinder their wide application in architecture. We reported an effective strategy for constructing hierarchical porous composite microspheres (PCN) through spray drying, calcination, and acid activation, using palygorskite (Pal) as the raw material. PCN presented a spherical hierarchical porous structure constructed by crosslinking Pal nanofibers and cellulose nanocrystals in a particular proportion. Paraffin-PCN (P-PCN) composite phase change materials (PCMs) with high shape stability, excellent photothermal conversion ability and latent heat storage capacity were synthesized. The heat preservation time of the P-PCN natural cooling from 35 °C to 30 °C is approximately twice that of the P-Pal. The P-PCN indicates obvious advantages in building thermal management, with the melting enthalpy promoted to 130.2 J/g. Further, the P-PCN-based building materials (P-PCN-B) with the P-PCN and the building aggregate maintain superior light-thermal energy conversion and thermal properties after multiple cycles. The P-PCN-B indicates outstanding mechanical properties (compression strength reaching 14.2 MPa) and flame-retarded properties. This work provides an innovative design strategy for developing multifunctional intelligent energy storage concrete and paves the way for the sustainable utilization of energy storage materials.

Preparation of sludge-corn stalk biochar and its enhanced anaerobic fermentation

In order to realize efficient utilization of stalk and sludge, mixed biochar was prepared from corn stalk and sludge to optimize the characteristics of anaerobic fermentation gas production. The mixed biochar was prepared under different carbonization temperature, raw material ratio, heat preservation time and heating rate, and was added to anaerobic fermentation as a supplement, the relationship between the physicochemical properties of biochar and anaerobic fermentation performance was investigated. The findings revealed that methane production up to 269.23 mL/g VS when the carbonization temperature was 600 °C, the ratio of raw materials was 1:1, the holding time was 90 min and the heating rate was 10 °C/min, and compared with the addition of pure sludge, pure corn stalk and blank control group, the cumulative methane production increased by 36.13%, 37.32% and 47.1% respectively. The biochar's particular surface area and pore structure only affect methane production in a certain range. The link between the characteristics of carbon materials and the generation of methane through anaerobic fermentation is further studied using the theoretical framework provided by this study.

A manta-ray-inspired bionic curing mold for autoclave process of composite manufacturing

The temperature distribution of the mold is directly linked to the manufacturing quality of the composite component. In this paper, a bionic mold based on the analysis of a manta ray in swimming is developed to improve the thermal performance of the mold during the autoclave curing process. The bionic mold has fewer frames and better air permeability, and the mold weight is decreased by 42.95% while the stiffness is proved to satisfy the requirement. The model of the autoclave curing process which is verified by experiments is established to carry out the thermal analysis of the mold. Results show that the air velocity in the mold is increased with the bionic design, which can reduce not only the maximum temperature difference of the mold plate (−30.35%) but also the percentage of low-temperature areas. Besides, the heating rate and the heat preservation time of the mold are also improved.

Vacuum pyrolysis of ammonium paratungstate: Study on reaction mechanism and morphology changes of product

At present, tungsten oxide is mainly produced by atmospheric decomposition of ammonium paratungstate (APT), which usually causes uneven particle size and morphology. In this paper, non-agglomerated tungsten oxide was prepared by vacuum pyrolysis (vacuum pressure is about 20 Pa) of APT. The vacuumpyrolysis mechanism and characterization changes of APT were investigated. The results showed that the pyrolysis of APT in a vacuum could be divided into five main stages based on thermal effect, crystallization water removing (25−170 °C), ammonia removing (170−250 °C), (NH4)6.84H3.16[H2W12O42] dissociation (250−390 °C), hexagonal ammonium tungsten bronze and WO3 part reduction (390−500 °C), h-WO3 crystal transformation (500−600 °C). The effects of pyrolysis temperature, heating rate, and holding time on the morphology and particle size of products were further studied. With increasing temperature, the particle size of the products decreased, and there was no agglomeration. Coarse tungsten oxide (62.43 μm) was obtained at a temperature increase rate of 1 °C/min. The shorter heat preservation time (10 min) was more conducive to the preparation of fine tungsten oxide (32.41 μm). The crystal morphology during APT decomposition into tungsten oxide was "hereditary". Compared with atmospheric decomposition, the vacuum environment is conducive to the preparation of narrow tungsten oxide products.

Fractionation Behaviors of Walnut Shell Bio-Oil Components Under Atmospheric Distillation

In this study, walnut shell bio-oil was separated into aqueous phase and oil phase, which were subjected to atmospheric distillation, accompanied by changes of heating temperature and heat preservation time. The fractionation behaviors of various components were investigated by analyzing the distillate collected independently at each temperature in stages. In distillation experiments on oil phase bio-oil (OPB), phenols fractionated in large quantities in the temperature range of 280-320 °C were the main component of oil phase fraction, of which the overwhelming majority were phenol as well as its congeners and guaiacol as well as its congeners. Changing the temperature program had a significant effect on the separation of these two compounds, and the relative concentrations of both were increased by 468 wt. % and 139 wt. %, respectively, when comparing OPB. Experimental data on the distillation of aqueous phase bio-oil (APB) revealed that the fractions were enriched with compounds such as acetic acid and guaiacol in a directional manner, whereas the large amount of water distillation and heating temperature higher than 140°C were two necessary conditions for the coking of aqueous phase bio-oil. Summary of distillation behaviors for various high-value compounds provides guidance for process design and scale-up utilization.

A graphite enclosure assisted synthesis of high-quality patterned graphene on 6H–SiC by ion implantation

Synthesis of high-quality graphene on insulating/semiconducting substrate is important in the development of future graphene-based electronic device technology. In this paper, an approach of ion implantation followed by annealing in a graphite enclosure was used to directly produce high-quality patterned graphene on 6H–SiC. Specifically, 5 keV argon ions were implanted in single-crystal 6H–SiC followed by thermal annealing in a graphite enclosure to synthesize graphene using the graphite enclosure as a carbon source. After annealing, carbon atoms, coming from graphite enclosure and SiC itself, migrate to the substrate surface and self-assemble into graphene. In contrast with present graphene production techniques, our approach requires a significantly lower temperature of ∼1100 °C and avoids the use of a large amount of gases, hydrogen etching and transfer process. Moreover, in this approach, patterned graphene can be synthesized by precisely controlling the growth site. To understand the growth mechanism, a brief model based on the influence of ion implantation, heat preservation time and graphite enclosure was established. Our work has established a convenient and economical approach of graphene production and expects to spark more interest in graphene-based electronic devices.

Bauxite free iron rich calcium sulfoaluminate cement: Preparation, hydration and properties

For the preparation of calcium sulfoaluminate (CSA) cement without bauxite, the iron rich CSA cement was prepared by the partial substitution of Al for Fe in C4A3s-. Besides, the hydration and properties of iron rich CSA cement were investigated. Raw meal proportioning shows that iron rich CSA cement clinker can be prepared without bauxite when the x value of C4A3-xFxs- exceeds 0.7. Results demonstrate that the iron rich CSA cement clinker can be prepared at 1175–1225 °C with the heat preservation time of 10 min. With the rise of Fe2O3 content in the raw meal, the C4A3s- content of iron rich CSA cement clinker lowers down, more C4AF and C2F forms, more c-C4A3s- forms at the expense of o-C4A3s-, and the crystal size of C4A3s- becomes smaller. For the iron rich CSA cement, the setting time is prolonged and the expansion rate lowers down with the rise of Fe2O3 content. For the compressive strengths, the iron rich CSA cements are lower than that of CSA cement at early hydration age. However, the compressive strength of iron rich CSA cement exceeds that of CSA cement at 90 d. Therefore, it is available to prepare bauxite-free iron rich CSA cement with high late age strength.

Preparation and Mechanical Properties of ZK61-Y Magnesium Alloy Wheel Hub via Liquid Forging—Isothermal Forging Process

A ZK61-Y magnesium (Mg) alloy wheel hub was prepared via liquid forging—isothermal forging process. The effects of Y-element contents on the microstructure and mechanical properties of liquid forging blanks were investigated. The formation order of the second phase was I-phase (Mg3Zn6Y) → W-phase (Mg3Zn3Y2) → Z-phase (Mg12ZnY) with the increase of the Y-element content. Meanwhile, the I-phase and Z-phase formed in the liquid forging process were beneficial to the grain refinement. The numerical simulation of the isothermal forging process was carried out to analyze the effects of forming temperature on the temperature and stress field in the forming parts using the software Deform-3D. Isothermal forging experiments and post heat treatments were conducted. The influence of isothermal forging temperature, heat treatment temperature and preservation time on the microstructure and mechanical properties of the forming parts were also studied. The dynamic recrystallization (DRX), second-phase hardening, and work hardening account for the improvement of properties after the isothermal forging process. The forming part forged at 380 °C displayed the outstanding properties. The elongation, yield strength, and ultimate tensile strength were 18.5%, 150 MPa and 315 MPa, respectively. The samples displayed an increased elongation and decreased strength after heat treatments. The 520 °C—1 h sample possessed the best mechanical properties, the elongation was 25.5%, the yield stress was 125 MPa and the ultimate tensile strength was 282 MPa. This can be ascribed to the recrystallization and the elimination of working hardening. Meanwhile, the second phase transformation (I-phase → W-phase → Mg2Y + MgZn2), dissolution, and decomposition can be observed, as well.

Evolution and Evaluation of Duplex Grain of As-cast 30Cr2Ni4MoV Steel during Heat Treatment

As the main microstructure flaw of heavy forging, duplex grain (the grain size is non-uniform) may result in producing a reject. In this paper, the influences of heat treatment temperature and isothermal holding time on the duplex grains evolutions of as-cast 30Cr2Ni4MoV steel were studied using optical microscope and scanning electron microscope aided with XRD and EDS. It is shown that the globular austenite grains appear at 750 °C and the austenite grains in the regions rich in C, Cr, Ni, and Mo are smaller than that in other regions. Duplex grains appear in the heating process. Moreover, in the isothermal heat treatment process, grains with different grain size number also developed at all of the temperatures performed in the study. But the distribution of the grains with different sizes cannot be evaluated precisely using proper method commonly used now. On the basis of analysis of the sizes of the duplex grains, a new approach for evaluating the level of the mixture of different size grains was proposed, the result obtained are consistent with the experimental results. The microstructure of 30Cr2Ni4MoV could be more uniform by increasing the temperature and extending the heat-preservation time.

Modelling the Elements Reaction–Diffusion Behavior on Interface of Ti/Al2O3 Composite Prepared by Hot Pressing Sintering

Element reaction–diffusion of Ti/Al2O3 composite which was fabricated at various sintering temperatures, holding times, and a sintering pressure of 30 MPa has been discussed in the present research. Results show that the thickness of the reaction layer of the Ti-Al2O3 interface was increased in exponential form in correspondence with the increase of the sintering temperature. Furthermore, according to analysis, the relationship between the thickness of the interface reaction layer, sintering temperature, and heat preservation time acquiring the kinetic equation of interfacial reaction of Ti/Al2O3 composite was d = 182.5exp(−6.6 × 104/RT)t0.48 by linear fitting.

Recycling of metals (Ga, In, As and Ag) from waste light-emitting diodes in sub/supercritical ethanol

In this study, waste light-emitting diodes (LEDs) containing gallium (Ga), indium (In), arsenic (As) and silver (Ag) were used as the research objects. The theoretical and experimental research were done on the recycling of Ga, In, As and Ag in LEDs. Firstly, anhydrous ethanol as solvent is beneficial for the separation of the surface mounted LED support and the colorless transparent encapsulation material containing LED chip and silver line. The optimum experimental conditions are as follows, 250 °C heating temperature, 200 ml anhydrous ethanol (7.5 MPa autogenous pressure) and 90 min heat preservation time. The separation efficiency is the highest in the experimental range, about 82.32%. The subcritical water-ethanol mixture is beneficial to the degradation of colorless transparent packaging resin at the preferential conditions of 300 °C heating temperature, 60% water in the water-ethanol mixture and 240 min heat preservation time, the recovery of Ga, In, As and Ag can reach 93.10%, 85.72%, 93.79% and 99.99%, respectively. This study can provide a high efficiency and environmentally friendly method to recycle the metals from waste LEDs.