Thermal Shock Conditions Research Articles

Oxidation kinetics of steels utilized for production of exhaust tips for vehicle mufflers under thermal shock conditions

Oxidation kinetics of steels utilized for production of exhaust tips for vehicle mufflers under thermal shock conditions

Fracture energy of mullite ceramic heat storage material under thermal shock conditions

Based on an engineering application background of mullite ceramic regenerative materials, the fracture energy of mullite ceramic materials was tested using a three point bending experiment combined with the method of rupture work under thermal shock conditions. The variations of fracture energy, along with temperature changes and the depth of crack as well as their relationship with fracture toughness and energy release rate, were discussed in this paper. The results indicated that fracture energy and the depth of crack have a linear relationship. Within the scope of the studied temperature (800°C), the fracture energy reached a higher value at ΔT 400°C and a lower value at ΔT 600°C. With the temperature variations, the fracture toughness, fracture energy and energy release rate follow the same law, and the energy release rate of the ceramic was about 30–45% of the fracture energy.

High temperature oxidation of NiCrAlY, nanocrystalline and enamel-metal nano-composite coatings under thermal shock

Thermal shock behavior of the NiCrAlY coating, the nanocrystalline coating with the same composition of the alloy substrate, and the enamel-metal nano-composite coating is investigated. All the three coatings perform well under thermal shock in air. When thermal shock is conducted in water, cracks nucleate at surface, grow in oxide scale and some of them penetrate into the underlying NiCrAlY or nanocrystalline coatings. For the enamel composite coating, its mass gain after thermal shock is the lowest among the three coatings with no cracks developing at surface. It performs better than the two metallic coatings do in thermal shock conditions.

Evaluation of coupling approaches for thermomechanical simulations

Many problems of interest, particularly in the nuclear engineering field, involve coupling between the thermal and mechanical response of an engineered system. The strength of the two-way feedback between the thermal and mechanical solution fields can vary significantly depending on the problem. Contact problems exhibit a particularly high degree of two-way feedback between those fields. This paper describes and demonstrates the application of a flexible simulation environment that permits the solution of coupled physics problems using either a tightly coupled approach or a loosely coupled approach. In the tight coupling approach, Newton iterations include the coupling effects between all physics, while in the loosely coupled approach, the individual physics models are solved independently, and fixed-point iterations are performed until the coupled system is converged. These approaches are applied to simple demonstration problems and to realistic nuclear engineering applications. The demonstration problems consist of single and multi-domain thermomechanics with and without thermal and mechanical contact. Simulations of a reactor pressure vessel under pressurized thermal shock conditions and a simulation of light water reactor fuel are also presented. Problems that include thermal and mechanical contact, such as the contact between the fuel and cladding in the fuel simulation, exhibit much stronger two-way feedback between the thermal and mechanical solutions, and as a result, are better solved using a tight coupling strategy.

Nitrogen species in few-layer graphene produced by thermal exfoliation of fluorinated graphite intercalation compounds

Few-layer graphene materials have been produced by decomposition of fluorinated graphite intercalated with acetonitrile (CH3CN) or isopropylamine ((CH3)2CHNH2) in the conditions of thermal shock. Electronic structure of the samples before and after exfoliation was studied using near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy. Analysis of the spectroscopic data revealed the same set of nitrogen species in both exfoliation products that indicates decomposition of the intercalated molecules to the atomic state. Most of the nitrogen atoms were incorporated at the edges of graphene layers in pyridinic and protonated nitrogen forms. A difference in the electrochemical performance of the graphene materials was related with the exfoliation degree and the defect density in the graphene layers. Schematic representation of a process of thermal exfoliation of acetonitrile-intercalated fluorinated graphite.

Experimental investigation of thermal shock effects on carbon–carbon composites

In this paper, both compressive properties and oxidation behavior of pristine and thermal shock exposed 2D C/C composite specimens were examined. Pristine test specimens were exposed to thermal shock conditions with temperatures ranging from400°C to 1000°C in an oxidizing environment, followed by compression tests on pristine and thermal shock exposed specimens to obtain their compressive responses. The experimental results showed that 2D C/C composite compressive stiffness and strength decreased with increasing thermal shock temperature. Also, upon exposure to thermal shock, the stress–strain response displayed a non-linear behavior prior to failure as compared to the pristine C/C composite that failed in a brittle manner. Furthermore, it was observed by microstructural analysis that at low temperatures, i.e., 400°C, the oxidation attack was uniform through the interior of the composite. On the other hand, at moderate temperatures, i.e., 600°C, oxidation occurred rigorously at the surface of the composite. At high temperatures, i.e., above 600°C, the specimens experienced the two aforementioned oxidation mechanisms. Therefore, it was concluded that carbon matrix degraded rapidly when exposed to thermal shock conditions in oxidizing environments and protective coating is required to maintain the quality of the composite under such conditions.

Regulation of biofilm formation by Pseudomonas chlororaphis in an in vitro system

The mutants of Pseudomonas chlororaphis 449 with completely or partially suppressed accumulation of N-acyl homoserine lactones exhibited the absence or a pronounced decrease of their capacity for stimulation of biofilm growth in the presence of azithromycin. Biofilms of the wild type strain preformed in the presence of the stimulatory azithromycin concentrations exhibited more intense staining with a polysaccharide-specific dye 1,9-dimethyl methylene blue (DMMB) and were more resistant to heat shock. These findings indicate accumulation of the structural matrix polysaccharides, which play a protective role under the conditions of thermal shock. Extremely low azithromycin concentrations (0.001-0.01 μg/mL) inhibit biofilm formation by P. chlororaphis 449 and P. chlororaphis 66 with suppression of the synthesis of DMMB-staining polysaccharides.

OS11-4 Development of Dual Beam Laser Speckle Strain Gauge for in Situ Damage Evaluation of Coatings under Thermal Shock Conditions(Characterization and Inspection of Coatings,OS11 Reliability of heat resisting alloys and coatings,STRENGTH OF MATERIALS)

OS11-4 Development of Dual Beam Laser Speckle Strain Gauge for in Situ Damage Evaluation of Coatings under Thermal Shock Conditions(Characterization and Inspection of Coatings,OS11 Reliability of heat resisting alloys and coatings,STRENGTH OF MATERIALS)

Fracture Features of Mullite Ceramic Regenerative Material under Thermal Shock Condition

For study the damage characteristic of the mullite heat storage ceramic under thermal shock condition, mechanical properties of mullite have been investigated. Under the different cooling mediums (room temperature water, boiling water, air), single and five cycles thermal shock conditions, The article studied the variation of flexural strength and fracture toughness along with temperature. The result show that with the increase of heat transfer coefficient of cooling medium, the bending strength of ceramic decreased. In the 600°C,the ceramic have a maximum bending strength and a minimum fracture toughness. The fracture toughness of precrack specimen is lower than that of non-precrack specimen on the whole. Both Precrack ceramic and non-precrack ceramic have a maximum fracture toughness at 400°C. The study of this paper provides a theoretical basis for the better predicting fracture damage and service life of heat storage ceramic.

Thermal shock behaviors of YSZ thick thermal barrier coatings fabricated by suspension and atmospheric plasma spraying

Thick thermal barrier coating (TTBC) having segmentation-crack structure is favorable to its durability under severe thermal shock conditions. The present study reports the results of a comparative study on the thermal shock behavior of yttria-stabilized zirconia (YSZ) TTBCs with the segmentation-crack structure fabricated using axial suspension plasma spraying (ASPS) and atmospheric plasma spraying (APS) processes, respectively. The evolution of the microstructures, the phase composition and the failure behavior of both TTBCs before and after the thermal shock tests were investigated. Microstructure analysis showed that both the APS and ASPS coatings possessed typical segmentation cracks in the through-thickness direction, the measured segmentation crack densities (Ds) of the APS and ASPS YSZ top coat were about 2.5 cracks mm−1 and 4 cracks mm−1, respectively. The microstructure analysis also showed an evenly spaced horizontal crack structure for the ASPS coating instead of the large columnar and eliminated splats boundaries structure for the APS coating. During thermal shock cycling, the spallation life of the ASPS TTBCs was improved by a factor of about 2 compared with that of APS coatings. Failure of the APS coatings is due to the fringe segments spallation, but in addition to the fringe segments spallation, a different center segment pull-out spallation can also be detected in the ASPS coatings.

Evaluation of Ceramic Composite Wedge for High Speed Combustor Applications

Ultra high temperature ceramic based Zirconium composite “Wedge” was fabricated with suitable dimensions required for high speed combustor using centrifugal thermit process. The wedges are normally used in the application of the ‘flame holding’ and ‘fuel injection’ of the combustor. The basic requirement of the wedge is that it has to have a very high thermal shock resistance along with near erosion free control surface in un-cooled conditions. Also it has to withstand ultra high temperatures of the order of 2000K under extreme heat flux of 10 MW/m2 and high velocity of gas injection. Wedge shaped strut was machined with special techniques to get the required shape. It was fastened inside the water cooled rectangular duct using tungsten carbide dowel pins. The wedge was tested at the High Speed Combustor Test Facility (HSCTF), with the air flow conditions of 5bar pressure and with an average temperature of 1900K. The flow velocity was at Mach number 2 for the duration of 20seconds. Experiments were repeated many times with the same inlet flow conditions. Thermal shock conditions were created by abruptly bringing down the flow temperature from 1900K to 300K with in short duration of 5seconds. The strut was intact even after several repeated tests except for oxidation coating. The mechanical properties and microstructure characteristics of fuel strut specimens after the combustor test have been investigated and compared with just fabricated material before the test. X-ray radiography also corroborates the flaw less condition of the strut. These results have been discussed in light of the integrity and surface micro structure mechanisms involved in the evaluation process.

A shape-deformable and thermally stable solid-state electrolyte based on a plastic crystal composite polymer electrolyte for flexible/safer lithium-ion batteries

A solid-state electrolyte with reliable electrochemical performance, mechanical robustness and safety features is strongly pursued to facilitate the progress of flexible batteries. Here, we demonstrate a shape-deformable and thermally stable plastic crystal composite polymer electrolyte (denoted as “PC-CPE”) as a new class of solid-state electrolyte to achieve this challenging goal. The PC-CPE is composed of UV (ultraviolet)-cured ethoxylated trimethylolpropane triacrylate (ETPTA) macromer/close-packed Al2O3 nanoparticles (acting as the mechanical framework) and succinonitrile-mediated plastic crystal electrolyte (serving as the ionic transport channel). This chemical/structural uniqueness of the PC-CPE brings remarkable improvement in mechanical flexibility and thermal stability, as compared to conventional carbonate-based liquid electrolytes that are fluidic and volatile. In addition, the PC-CPE precursor mixture (i.e., prior to UV irradiation) with well-adjusted rheological properties, via collaboration with a UV-assisted imprint lithography technique, produces the micropatterned PC-CPE with tunable dimensions. Notably, the cell incorporating the self-standing PC-CPE, which acts as a thermally stable electrolyte and also a separator membrane, maintains stable charge/discharge behavior even after exposure to thermal shock condition (=130 °C/0.5 h), while a control cell assembled with a carbonate-based liquid electrolyte and a polyethylene separator membrane loses electrochemical activity.

Environmental Effects on Thermal Properties of PEI/Glass Fiber Composite Materials

The aim of this study was to investigate the effects of hygrothermal exposure, ultraviolet (UV) radiation, salt spray and thermal shock aging on the thermomechanical behavior of glass fiber reinforced by poly (ether-imide) (PEI) composites. Dynamic mechanical (DMA) and Thermomechanical (TMA) analyses have been performed on the aged PEI composites after being submitted to the climatic chambers. Additional techniques have been used to characterize the laminates, such as optical microscopy and infrared spectroscopy (FT-IR) in order to evaluate possible structural changes in these materials. Slight changes were observed both in glass transition temperature and in thermal expansion coefficient as a result from the environmental conditioning used (hygrothermal, salt spray, UV radiation and thermal shock conditioning). Thus, when exposed to these conditions, PEI/glass fiber laminates maintain its compromise with the performance component.

Membrane fluidity of halophilic ectoine-secreting bacteria related to osmotic and thermal treatment

In response to sudden decrease in osmotic pressure, halophilic microorganisms secrete their accumulated osmolytes. This specific stress response, combined with physiochemical responses to the altered environment, influence the membrane properties and integrity of cells, with consequent effects on growth and yields in bioprocesses, such as bacterial milking. The aim of this study was to investigate changes in membrane fluidity and integrity induced by environmental stress in ectoine-secreting organisms. The halophilic ectoine-producing strains Alkalibacillus haloalkaliphilus and Chromohalobacter salexigens were treated hypo- and hyper-osmotically at several temperatures. The steady-state anisotropy of fluorescently labeled cells was measured, and membrane integrity assessed by flow cytometry and ectoine distribution. Strong osmotic downshocks slightly increased the fluidity of the bacterial membranes. As the temperature increased, the increasing membrane fluidity encouraged more ectoine release under the same osmotic shock conditions. On the other hand, combined shock treatments increased the number of disintegrated cells. From the ectoine release and membrane integrity measurements under coupled thermal and osmotic shock conditions, we could optimize the secretion conditions for both bacteria.

Thermal Shock Corrosion of Valve Steels Utilized in Automobile Industry

The high-temperature corrosion behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil, containing different concentrations of bio-components (5 and 10 wt%) has been studied under thermal shock conditions. It was found that the addition of bio-components decreased the corrosion resistance of steels investigated. It was also found that the X33CrNiMn23-8 steel containing the highest chromium concentration, behaved in the investigated atmospheres much better than three remaining steels due to the formation of highly protective chromia scale.

The Influence of Yttrium on Kinetics and Mechanism of Chromia Scale Growth on Fe-Cr-Ni Base Steels

The influence of yttrium on the corrosion resistance of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil containing 10 wt. % of biocomponents has been studied at 1173 K under thermal shock conditions. These experiments have been carried out by rapid heating of the studied materials up to 1173 K and after two hours cooling down to room temperature. These thermal shocks have been repeated hundreds of times, determining after every shock the mass changes of the corroded samples. It has been found that small amount of yttrium deposited on the steel surface using electrochemical treatment considerably improves the scale adherence and consequently corrosion resistance in the case of X33CrNiMn23-8 steel, containing the highest chromium concentration.

Effects of temperature on the nitric oxide-dependent modulation of the Frank–Starling mechanism: the fish heart as a case study

The Frank–Starling law is a fundamental property of the vertebrate myocardium which allows, when the end-diastolic volume increases, that the consequent stretch of the myocardial fibers generates a more forceful contraction. It has been shown that in the eel (Anguilla anguilla) heart, nitric oxide (NO) exerts a direct myocardial relaxant effect, increasing the sensitivity of the Frank–Starling response (Garofalo et al., 2009). With the use of isolated working heart preparations, this study investigated the relationship between NO modulation of Frank–Starling response and temperature challenges in the eel. The results showed that while, in long-term acclimated fish (spring animals perfused at 20°C and winter animals perfused at 10°C) the inhibition of NO production by L-N5 (1-iminoethyl)ornithine (L-NIO) significantly reduced the Frank–Starling response, under thermal shock conditions (spring animals perfused at 10 or 15°C and winter animals perfused at 15 or 20°C) L-NIO treatment resulted without effect. Western blotting analysis revealed a decrease of peNOS and pAkt expressions in samples subjected to thermal shock. Moreover, an increase in Hsp90 protein levels was observed under heat thermal stress. Together, these data suggest that the NO synthase/NO-dependent modulation of the Frank–Starling mechanism in fish is sensitive to thermal stress.

Corrosion of Valve Steels in Combustion Gases of Diesel Engines under Thermal Shock Conditions

The corrosion behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil, containing different bio-component concentrations of (5 and 10 wt. %) has been studied under thermal shock conditions. It has been found that the addition of bio-components to the fuel oil decreases the corrosion resistance of all steels under investigation, this effect being the stronger, the higher was the concentration of bio-component addition. It has been shown, that in spite of bio-component addition, the X33CrNiMn23-8 steel containing the highest chromium concentration, behaved much better than three remaining steels due to the formation of the highly protective chromia scale.

Influence of Type of Material on Performance of Hydraulic Components in Thermal Shock Conditions

During the start-up of a hydraulic system in low ambient temperatures an incorrect operation may occur. The principles and conditions of safely operating hydraulic driven machines and devices are essential to designers and operators. For this reason the author of this article has conducted a series of tests on hydraulic components and systems in thermal shock conditions (cooled-down components were supplied with hot working medium). In such conditions, the initial parameters of the hydraulic components and systems determine their correct operation. During the start-up of a hydraulic system in thermal shock conditions, elements of hydraulic components warm up in a non-uniform way, due to various material properties and shapes of parts. Differences in clearances between elements and may lead to the faulty performance of hydraulic components and machine break-down. The selection of appropriate materials for various hydraulic component parts should increase machine safety during start-up in thermal shock conditions.

Carbamide peroxide gel stability under different temperature conditions: is manipulated formulation an option?

Nowadays the use of gel containing carbamide peroxide (CP) prepared in Pharmacy is a normal practice in the population. However, the quality of this product is questionable concerning its stability. The aim of this study is was to synthesize and to analyze this drug alone or associated to Carbopol gel through analytical methodology compatible with the routine of the Pharmacies. The reaction between urea and hydrogen peroxide was carried out at different resting times: 24 hours (CP 24 powder) and 48 hours (CP48 powder) after the mixture. Both products were associated with Carbopol 940® gel 1.5% (G) generating G24 and G48 samples. The stability of powders (CP24 e CP48) and the formulations (G24 and G48) were evaluated as a function of time (15, 40 and 45 days) and thermal variation (refrigeration: 8 °C±1; thermal shock 32 °C±1 /8 °C±1; stove: 32 °C±1), using a standard titration method. As a result, only under refrigeration the CP24 and CP48 contents remained stable during the period of 45 days. An interesting finding was that G24 and G48 presented greater stability for at least 45-days under refrigeration and thermal shock conditions, and up to 30 days under stove conditions. The results for the G24 and G48 were slightly higher than those obtained for the control. Therefore, we were able to conclude that association with Carbopol 940® Gel 1.5 % provided greater CP stability and that manipulated formulations containing CP may be viable for use in a period of 45 days under refrigeration conditions. The titration proved to be an effective technique for the analysis of CP with or without Carbopol 940® gel 1.5%.