Influence Of Thermal Shock Research Articles

Study on mechanical properties of ZnO/Si interface under thermal shock

Influence of thermal shock on ZnO/Si interfacial mechanical properties was studied through experiments, molecular dynamics simulations and machine learning prediction. ZnO films were deposited onto silicon wafers by radio frequency magnetron sputtering and then suffered different times of thermal shock. The experimental results show the adhesion strength of ZnO/Si interface is relatively stable under thermal shock. XRD and simulation illustrate the interfacial reactions of Si based films could experience strong interaction through Si, Zn and O atoms located at ZnO/Si interface during thermal shock, which could explain the stability of the interface. The machine learning prediction indicates the mechanical properties of ZnO/Si interface are still relatively stable after more thermal shocks. The obtained conclusions are hoped to be helpful for the understanding of ZnO/Si properties under thermal load and to guide the design of related devices in energy field.

Thermal shock effects on the microstructure and mechanical properties of iron-based composites reinforced by in-situ Fe2B/FeB ceramic phases

Recently, high-temperature composites reinforced with in-situ phases have been developed as a new class of composites for harsh environments. The behaviour of these composites under sudden heating and cooling conditions is greatly influenced by the type and fraction of components. The aim of this study is to investigate the microstructural properties and mechanical response of iron based composites after thermal shock cycling. The fabrication process involved in-situ powder metallurgy (IPM) sintering of Fe–B4C starting powders. The samples were subjected to thermal shock with a constant temperature differences (ΔT: 600 °C) and varied cycles (N: 1–50). Comparison of microstructural changes and mechanical behaviour before and after thermal shock has been carried out. The boron atoms released from the initial B4C generated diffusion zones in the matrix dominated by iron boride phases (Fe2B/FeB). An effective matrix-reinforcement interface has been created by in-situ powder metallurgy, where boride phases are almost homogeneously distributed in the iron matrix. While the hardness of the composites was significantly developed by the Fe2B/FeB phases, the addition of B4C resulted in a reduction in the coefficient of thermal expansion (CTE). The in-situ phases contributed in the minimisation of the coefficient mismatch by balancing the thermal expansion coefficients between iron and the initial B4C. Under the influence of thermal shock, microcracks and then macrocracks formed on the sample surfaces, increasing in width and depth with thermal cycles. This resulted in accelerated fracture damage under post-thermal loading. Both the impact and flexural strengths of the samples were significantly reduced as the number of thermal cycles increased. Although the 20% B4C reinforced composite provided maximum hardness, it showed poor resistance to thermal loading. The best results for mechanical loads were achieved by the 5% B4C reinforced composite, which showed no cracks even after 50 thermal cycling.

Thermal behavior of minerals in shale and its influence on evolution of gas-flow channels under thermal shock

Thermal shock-induced damage can significantly enhance the connectivity of the rock's fracture network. Thermal Enhanced Recovery (TER) technology holds promising potential for application in shale gas production. Nevertheless, there is still a lack of direct experimental studies focusing on the evolution of shale's gas-flow channels and the mechanism of thermal fracturing in shale under the influence of thermal shock. In this study, we initially investigated the impact of thermal shock on various minerals in shale through X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) imaging, and examined the mass and heat variation with temperature using Thermogravimetry-Differential Scanning Calorimetry (TG-DSC) testing. Subsequently, we assessed the alterations in shale's internal structure due to thermal shock through low-temperature gas (N2) adsorption (LTGA) analysis, and observed the distribution and expansion patterns of shale fractures under thermal shock using computed tomography (CT). Finally, we evaluated the changes in shale permeability before and after thermal shock. The findings indicate that quartz, feldspar, and clay exhibit relatively stable behavior in shale under thermal shock, whereas carbonate and pyrite are prone to crack. Under the combined influence of mineral cracking and thermal stress, the internal pore structure of shale tends to enlarge in size while reducing in surface area. The substantial decrease in pore specific surface area highlights the considerable reduction in gas adsorption capacity. Furthermore, fractures expand along the bedding planes as surface fractures. The expansion of pores and fractures promotes the formation of primary gas-flow channels. In addition, the aforementioned test results demonstrate a high level of consistency, specifically highlighting a distinct threshold temperature (500 °C) for the alteration of various physical parameters of shale during thermal shock. This study is anticipated to offer insights into the implementation of TER technology in the oil and gas industry.

THE USE OF CERAMIC FILTERS IN THE SMELTING OF WORKPIECES FROM HEAT-RESISTANT ALLOYS

To improve the operational characteristics of gas turbine engine blades, it is necessary to use new methods of cleaning and refining metal. Melt filtration is an effective way to improve casting quality.According to the conducted analyses, it was determined that the amount of conditioned waste generated during the smelting of products reaches 27% of the mass of the spent charge, and non-conditioned waste rejected during LUMMA control is 23%. The results of the statistical analysis show that the total amount of waste generated during the smelting of gas turbine blades is, on average, 60–70% of the weight of the loaded charge.The purpose of the work is to create a new composition of the ceramic mixture for the production of high-strength filters, as well as the development of technology for the production of gas turbine parts using them.The analysis was performed on samples of heat-resistant corrosion-resistant alloy CM88Y. The alloy for research was melted from the primary charge on the UPPF-3M foundry unit. As a result of the work carried out, a new rational composition of the mixture for the manufacture of ceramics was created, which allows to increase the characteristics of strength and heat resistance. An instruction was created for the manufacture of ceramic filters at machine-building enterprises. To eliminate damage to ceramic rods in blades under the influence of thermal shock, improved systems for filtering metal in a liquid state and filling ceramic molds are proposed. Uniform temperature distribution across the cross-section of the casting also reduces the number of defective products.

Influence of thermal shock on the performance of B-staged epoxy bond coat for orthotropic steel bridge pavements

B-staged epoxy bond coat (BEBC) has been widely applied as a waterproof adhesive layer in the pavements of orthotropic steel bridges. During its application, the uncured BEBC layer was first paved on the surface of the steel deck or the bituminous surfacing and hot bituminous mixture would be constructed until the BEBC layer became touch-dry. In this paper, the impacts of thermal shock on the degree of cure (DOC), pull-off strength, hydrophilicity, glass transition temperature (Tg), damping performance, thermal stability and mechanical behaviors of the touch-dry BEBC were investigated. Thermal shock greatly increased the DOC of the touch-dry BEBC and the touch-dry BEBC turned to be nearly fully cured after the thermal shock at a higher temperature. The pull-off strength of the touch-dry BEBC was remarkably improved by the thermal shock. After the thermal shock at 160 °C, the pull-off strengths at room temperature and at 60 °C of the touch-dry BEBC were increased by 584% and 914%, respectively. After the thermal shock, the contact angle of the touch-dry BEBC was greatly increased and the hydrophilicity of the touch-dry BEBC was converted to hydrophobicity. Thermal shock significantly increased the Tg of the touch-dry BEBC. Furthermore, the Tg of thermally shocked BEBCs slightly increased in the temperature. Thermal shock improved the damping performance of the fully cured BEBC. The tensile strength and toughness of the touch-dry BEBC were greatly improved by the thermal shock. However, thermal shock lowered the elongation at break of touch-dry BEBC. In the case of thermally shocked BEBCs, the temperature had a limited effect on the tensile strength, while the elongation at break increased in the temperature. The fracture energy first decreased in the temperature and increased after 150 °C. Maximum fracture energy appeared at 160 °C. After the thermal shock, the tensile strength of the touch-dry BEBC was increased by as much as 3-fold. The fracture energy of the BEBC thermally shocked at 160 °C was 182% greater than that of the touch-dry BEBC.

Mechanical test of granite with multiple water\u2013thermal cycles

To study the influence of thermal shock caused by water-cooling on the physical and mechanical properties of high-temperature granite, granite was subjected to an increasing number of high-temperature (300 °C) water-cooling and thermal shock treatment cycles, and static mechanical experiments were carried out on the treated granite. The results support the following conclusions: (1) thermal shock causes an increase in the number and size of the pores and cracks within the granite; thus, its volume expands, density decreases, water absorption rate increases, and P-wave velocity decreases. (2) With an increase in the number of thermal shocks, both the compressive strength and tensile strength of the granite decrease, and there is a linear relationship between the compressive strength and tensile strength. (3) With an increase in the number of thermal shocks, the plasticity of the granite increases and its resistance to deformation weakens, which is manifested as a decrease in both the compressive modulus and tensile modulus of the granite. After 15 cycles of thermal shock, the compressive elastic modulus and tensile modulus of the granite decreased by 25.18% and 46.76%, respectively. (4) The m and s values of the damaged granite were calculated based on the Hoek–Brown empirical criterion, and it was found that both of these parameters decrease with the increase in the number of thermal shocks. The calculation results can provide a reference for engineering rock mass failure.

Culex quinquefasciatus Say larva adapts to temperature shock through changes in protein turn over and amino acid catabolism

Exposure of Culex quinquefasciatus larvae to hypothermia or hyperthermia in relation to ecological temperature has resulted in alteration of enzyme activities related to maintenance of free amino acid pool and protein degradation. Sudden changes in water temperature have led to elevation of protein content particularly in molecular weight between 66 and 97.4 kDa. MALDI TOF analysis revealed the presence of putative uncharacterized protein and Phospholipase A2 activating protein in larvae subjected to 40°C for 1 hour which was not found in control and other temperature treated larvae. These proteins may be playing a role in survival of larvae at higher temperatures. Thermal shock has resulted in channeling of free amino acids for protein synthesis and elevation of amino acid catabolism through increased deamination and altered transamination, which resulted in a sharp decrease in free amino acid pool. Inhibition of Leucine amino peptidase and elevation of Cathepsin D, under the influence of thermal shock may be an adaptive response of larvae to prevent unnecessary degradation of protein and at the same time facilitated rapid internal re-organization which may accelerate pupation. Elevated activity of Phenol oxidase and its co-stimulator Trypsin –like Serine protease, along with increased expression of Phospholipase A2 activating protein is a well co-ordinated defense mechanism leading to increased immune response in stressed state. This study assumes significance because variation in environmental conditions such as global warming and their impact on mosquito physiology can influence efficiency of disease vector.

Influence of thermal shock and environment temperature on mechanical properties of C/SiC/GH783 joint brazed with Cu-Ti + Mo

The carbon reinforced silicon carbide ceramic matrix composites (C/SiC) were brazed to Fe-Ni-Co superalloy (GH783) with Cu-Ti + Mo solder under vacuum at 1000 °C. The influence of thermal shock (in air at 800 °C) and environment temperature on mechanical properties of the joint were investigated. The joint between C/SiC composites and GH783 was dense, crack free, and was comprised of reaction layer, stress relief layer, plastoelastic layer, and diffusion layer. Thermal shock damage and oxidative damage were both existing after the thermal shock. Therefore, the flexural strength of the joint decreased dramatically with the increase of thermal shock times. After 5, 10, and 15 times of thermal shock, the flexural strength of the joint decreased to 42.9, 22.7, and 9.7% of the initial strength, respectively. The flexural strength of the joint decreased dramatically with the increase of environment temperature because of the thermal mismatch between C/SiC and the interface reaction layer. The flexural strength of the joint at 600, 800, and 900 °C was decreased to 60, 39, and 29% of that at room temperature, respectively.

Abnormal thermal shock behavior in electrical conductivity of Ti2SnC

Some ternary carbide and nitride ceramics have been demonstrated to exhibit abnormal thermal shock behavior in mechanical properties. However, the influence of thermal shock on other properties is not clear. This work reports on the influence of thermal shock on electrical conductivity of Ti2SnC as a representative member of ternary carbides. Abnormal change in electrical conductivity was first demonstrated during quenching Ti2SnC in water at 500–800°C. The residual electrical conductivity of the quenched Ti2SnC gradually decreased with increasing temperature, but abnormally increased after quenching at 600°C. The microstructure of surface cracks was characterized. The main mechanism for the abnormal electrical conductivity recovery is that some narrow branching cracks are filled by metallic Sn precipitating from Ti2SnC.

Influence of thermal shock on fouling of smooth, rough and finned tubes

Deposits of salts and extraneous materials occur during water desalination by heating, forming an insulating layer, which is known as fouling. Fouling reduces the rate of heat transfer between the heating medium and the water, subsequently decreases the desalination efficiency gradually and sometimes can lead to operation failure. The thermal shock is a fouling mitigation technique in water desalination units, which could be due to sudden decrease or increase in the heat transfer process. The objective of this research is to study the removal of fouling layers by the thermal shock in case of (i) smooth tubes, (ii) rough tubes and (iii) finned-rough tubes. It has been found that it is possible to remove the fouling layer by the thermal shock technique in case of smooth and rough tubes, but not in case of finned tubes. The thermal shock blows off the fouling layer in case of plain tubes, and the fouling process resumes after the thermal shock without any delays, i.e. no more induction period. Fins assist the sticking of crystals to the heat exchanger tubes and prevent its removal by thermal shock. Fins act as a heat sink during the thermal shock, which reduces the dissipation of heat to the surrounding water, i.e. cooling of the tubes, and prevent cracking of the fouling layer.

Effect of thermal shock on a membrane-type transducer

Results from theoretical and experimental studies of the effect of thermal shock on membrane-type transducers are presented. It is shown that the thickness of the membrane, its rigid center, and sealing exert a powerful effect on the gradient of the temperature field measured along the radius of the membrane. Recommendations intended to reduce the influence of thermal shock on a transducer are given.

The influence of thermal shock and pre-sprouting of seed potatoes on formation of some yield structure elements

For earlier potato yield formation we used pre-sprouting and thermal treatment which both add to the physiological age of potato. At the same time, pre-sprouting is a very time- and energy-consuming procedure. We investigated if thermal treatment could replace pre-sprouting and how it affects the growth and development of potato haulms and tubers. For that purpose an experiment was conducted in 2000–2002 to examine the opportunities for growing potatoes by using different methods of pre-planting treatment of seed tubers. Early, middle and late maturing potato varieties (two Estonian varieties and one Latvian) were used, each being subdivided into three variant categories: untreated, thermal shock and pre-sprouting. The experiment indicated that one or the other of thermal shock or pre-sprouting shortened the time to emergence by up to 10 days. With pre-sprouting, the formation of tubers started as soon as 45 days after planting and with thermal shock 50 days after planting, i.e., 5–10 days earlier than in the untreated variant. Thermal shock of seed tubers had the greatest effect on the number of tubers per plant, while pre-sprouting increased the average weight of tubers. Both pre-sprouting and thermal shock had a strong effect on the weight of the haulms in varieties with a longer growth period.

Influence of SiC particles on mechanical properties of Mg based composite

AZ91 magnesium alloy reinforced with different sizes of SiC particulates has been fabricated using powder metallurgy route. Mechanical properties of the specimens have been studied. Yield and ultimate tensile stresses show a decrease with the increase in the size of SiC particulates. The influence of thermal shock between 400°C and 30°C on the mechanical properties was also investigated. The results show a decrease in yield stress and elongation to fracture with the number of thermal shock cycles.