Cyclic Heating Conditions Research Articles

Effect of hollow glass microspheres (HGM) on improving self-heating capability of cement composites exposed to various deterioration conditions

Cement-based self-heating composites play a crucial role in addressing the need for intelligent road and pavement systems capable of efficient de-icing in severe weather conditions. However, the self-heating capability of these composites can be adversely affected by various deteriorating factors such as water ingress, nitric and sulfuric attacks, and freeze-thaw conditions. In this study, we propose the use of hollow glass microspheres (HGM) to enhance the self-heating capability of cement composites exposed to such deteriorating conditions. The initial investigation focused on observing the effects of HGM incorporation on changes in compressive strength, electrical conductivity, and thermal conductivity. Subsequently, the self-heating capability of these composites was systematically examined under cyclic heating conditions following exposure to deterioration factors. Microstructural analysis, including mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM), was conducted. The results indicated that the inclusion of HGM can effectively safeguard the conductive networks from external solutions, thereby preventing potential disconnection of these networks. Consequently, the incorporation of HGM is anticipated to enhance both the electrical stability and self-heating capability of cement composites exposed to diverse deteriorating conditions.

Impact of silica aerogel addition on the electrical and piezo-resistive sensing stability of CNT-embedded cement-based sensors exposed to varied environments

This study investigated the effects of adding silica aerogel on the electrical and piezo-resistive sensing stability of cement-based sensors exposed to varied environments. Cement-based sensors were fabricated using 50% cement and 50% fly ash as binder material, and 0.5% carbon nanotube (CNT) as conductive filler. Three different contents of silica aerogel (0, 0.25, and 0.5% by binder mass) were added, and the samples were exposed to different moisture states and varied environments, including water ingress and cyclic heating conditions, to observe their electrical stability. Results showed that the addition of silica aerogel with super-hydrophobic and low thermal conductivity properties mitigated the disturbances of the CNT particles from the water ingress and cyclic heating conditions, improving the electrical stability. Based on the long-term sensing result, the authors observed the electrical stability when the maximum compressive loading is applied to the samples. The observation showed that the proper addition of silica aerogel improved the long-term sensing stability, while excessive amounts induced agglomerates, affecting long-term sensing stability. From the experimental results, it can be said that the silica aerogel with super hydrophobic and low thermal conductivity properties can be a solution for improving the electrical and piezo-resistive sensing stability of cement-based sensors exposed to various environmental conditions.

On the thermal stability and performance evaluation of Si doped transition metal nitride/oxide nanolayered multilayer-based spectrally selective absorber for high-temperature photothermal applications

Developing an absorber coating with high absorptance (α) in the solar spectrum region and low thermal emittance (ε) in the infrared region for concentrated solar power (CSP) applications, operating at temperatures >400 °C, is still a great challenge. Herein, we describe a multilayer solar selective coating on stainless steel 304 (SS 304) substrates with α of 0.954 and ε of 0.07. The multilayer solar selective coating consists of: (1) tungsten (W) infrared reflector layer, (2) titanium aluminum nitride (TiAlN) absorber layer, (3) titanium aluminum silicon nitride (TiAlSiN) absorber layer, (4) titanium aluminum silicon oxy-nitride (TiAlSiON) semi-absorber layer and (5) titanium aluminum silicon oxide (TiAlSiO) anti-reflection layer. The compositions of the individual layers have been selected in such a way that they easily form protective layers of Al2O3, TiO2 and SiO2 on the coating surface when exposed to high temperature in air. Further, addition of Si in different layers not only improves the thermal stability but also helps in densifying the microstructure of the layers. Moreover, the presence of multilayer structure hinders the formation of pinholes and pores along with columnar microstructure, a typical characteristic of the sputter deposited transition metal nitrides and oxides. This unique coating design, thus, leads to high spectral selectivity (α/ε) of 13.6 on SS 304 substrate along with thermal stability up to 600 °C for 1000 h in vacuum under cyclic heating conditions. These properties of the developed solar absorber coating demonstrate its suitability for evacuated receiver tubes in CSP plants.

Study of structure features and properties of thermodifusion heat resistant coatings on copper

The article presents data on the features of the structure and properties of heat-resistant layers obtained by thermal diffusion aluminization and siliconization of copper (grade M1) in powder saturating media. The phase composition of the diffusion layers has been investigated, in particular, it has been established that, as a result of aluminization, a heterogeneous structure of the diffusion layer is formed with the participation of Cu3Al and Cu9Al4 aluminides. The data on heat resistance under test conditions with a total duration of 25 hours and a temperature of 800 °C are given. Tests have shown that the best protective properties are possessed by aluminized diffusion layers, which are characterized by a higher sink rate against high-temperature oxidation and cyclic heating conditions. According to the results of the analysis of the microstructures before and after oxidation, the features of the protective action and destruction of the aluminized and silicified diffusion layers were noted. On aluminized specimens, during heat resistance tests, the layer thickness grows deep into the specimen and the aluminum concentration gradually redistributes. For siliconized diffusion layers, a loss of continuity of the protective layer by peeling off sections (swelling) and the appearance of focal of layer corrosion with a test duration of more than 15 h were noted.

Effects of silica aerogel inclusion on the stability of heat generation and heat-dependent electrical characteristics of cementitious composites with CNT

The present study investigated the effects of silica aerogel inclusion on the stability of heat generation and heat-dependent electrical characteristics of cementitious composites with carbon nanotube (CNT). The heat generation and heat-dependent electrical characteristics of the specimens were explored under the monotonic and cyclic heating conditions and they were discussed in terms of compressive strength and SEM test results. The test results indicated that the addition of the silica aerogel improved the stability of heat generation and changes in the electrical resistivity of up to 63% and 68%, respectively, upon 20 cycles of the heating tests. The enhancement in the electrical properties is attributed to the fact that the incorporated silica aerogel mitigated the re-distribution of CNT particles due to hydration reaction during the heating process, which in turn improved the stability of heat generation and heat-dependent electrical characteristics of the cementitious composites.

Effect of Composition on Designed Tandem Absorber to Achieve Selective Properties for High Temperature Solar Thermal Applications

We have designed a tandem absorber comprising of five layers namely:TiAlC / TiAlCN / TiAlSiCN / TiAlSiCO / TiAlSiO on stainless steel substrate by DC unbalanced magnetron sputtering system.Tandem absorber shows a high absorptance of 0.961 with an emittance of 0.15 by careful optimization of flow rates and thicknesses of the individual layers. Further, the detailed effects of reactive gas flow rates and thicknesses of each individual layers on the optical properties were studied. Growth rate and thicknesses of each individual layers of the tandem absorber were studied by cross-section FESEM images. The tandem absorber shows long term thermal stability when annealed in vacuum at 600°C for more than 750 h under cyclic heating conditions, indicating suitability of the tandem absorber for solar thermal high temperature applications.

Experimental investigation of thermal characteristics of lithium ion battery using phase change materials combined with metallic foams and fins

Phase change materials are of great interest in energy storage and energy management applications due to their high latent heat and excellent cycling stability. In this paper, the thermal characteristics of phase change materials (PCM) for thermal management of cylindrical 18650 lithium-ion battery (LIB) were experimentally investigated. A commercial paraffin wax with a melting temperaturerange between 47 - 53.8oC was used in this study. A metal cylinder with a heater was used to emulate the heat generation from a battery, which was surrounded with the paraffin PCM and containted in a metal housing. The experiment was conducted in an environmental test chamber with controlled ambient temperatures and power inputs. Both the battery temperature and the housing wall temperature were measured during steady-state heating and cyclic heating conditions. Since PCM has low thermal conductivity, thermal enhancement techniques were investigated by adding metal foams (MFs) or combining metallic foam and fins into the PCM to enhance the thermal conductivity. The battery temperatures were measured for all the cases and the results were analyzed and discussed.

Effect of Cold Working on Hot Corrosion Behavior of 9 Cr–1 Mo Ferritic Steel in 75 wt% Na2SO4 + 25 wt% K2SO4 Molten Salt Environment at 900 °C

The hot corrosion behavior of as received (0 %), 10, 30 and 50 % cold rolled T-91 (9 Cr–1 Mo) ferritic steels has been studied in salt 75 wt% Na2SO4 + 25 wt% K2SO4 atmosphere under cyclic heating conditions at a temperature of 900 °C for 50 cycles. Each cycle consisted of 1 h heating at 900 °C followed by 20 min of cooling in air. Oxidation kinetics was studied using thermogravimetric technique by recording the weight gain at the end of each cycle. Oxidation kinetics of cold rolled sample with 10 and 50 % reduction followed parabolic rate law while cold-worked with 30 % showed accelerated rate of weight gain compared to the other cold worked samples as well as un-worked sample. 30 % cold worked sample in salt atmosphere was fully oxidized after 50 cycles and only fragmented thick scale remained. X-ray diffraction and scanning electron microscopy were utilized for characterizing the oxide layer. Cold rolled steel sample with 10 % was found to be more oxidation resistant compared to other cases.

OS0523 クロスプライCFRP積層板の繰り返し温度変動下の非主軸クリープ変形挙動

OS0523 クロスプライCFRP積層板の繰り返し温度変動下の非主軸クリープ変形挙動

Influence of superficial CeO2 coating on high temperature oxidation behavior of Ti–6Al–4V

The effect of superficial CeO2 coating on the oxidation behavior of Ti–6Al–4V has been studied under isothermal and cyclic heating conditions in the temperature range of 923–1223K in dry air. During the early periods of exposure, the oxide scale grows obeying near linear followed by near parabolic kinetics and consists of alternate layers of α-Al2O3 and TiO2. The mass gain of the uncoated alloys is found to be two times higher than that of the coated one in the temperature range of 923–1123K up to 36h of exposure. The scale composition on the bare or coated alloy is found to depend both on the temperature and on the time of exposure. During cyclic exposure, the scale suffers spallation for both the bare and the coated alloy, which has been attributed to insufficient plasticity of the scale.

Testing of Neutron-Irradiated Plasma Facing Components

In order to study degradation effects of neutrons on plasma-facing materials and joints, actively-cooled CFC monoblock mock-ups were irradiated in the High Flux Reactor in Petten up to 0.35 dpa at 350 and 750°C. Later, these samples were tested by means of an electron beam facility under static and cyclic heating conditions. The heat removal efficiency and the thermal fatigue behavior of these samples were compared to those of corresponding non-irradiated samples. A significant increase of surface temperature was observed for all CFC samples, due to a reduced thermal conductivity of the materials after neutron irradiation. This effect is less distinctive for samples irradiated at the higher temperature. Long term fatigue tests with 1000 heating cycles at 15 MW/m2 did not create any failure of the plasma-facing material or the bond layer of the tested mock-ups.

Thermal Fatigue Testing of Actively Cooled Divertor Mock-Ups after Neutron Irradiation

In order to study degradation effects of neutrons on plasma-facing materials and joints, actively-cooled beryllium and CFC samples were irradiated in the High Flux Reactor in Petten up to 0.35 dpa at 350 and 700°C. Later, these samples were tested by means of an electron beam facility under static and cyclic heating conditions. The heat removal efficiency and the thermal fatigue behavior of these samples were compared to those of corresponding non-irradiated samples. A significant increase of surface temperature was observed for all samples, due to a reduced thermal conductivity of the CFC materials after neutron irradiation. This effect is less distinctive for samples irradiated at the higher temperature. Long term fatigue tests with 1000 heating cycles at 15 MW/m2 did not create any failure of the plasma-facing material or the bond layer of the tested mock-ups. Similar experiments have been performed with brazed beryllium-copper mock-ups. Flat tile mock-ups with an S65 C armor on a CuCrZr heat sink were loaded up to 1000 cycles at a power density of 7 MW/m2 without detachment of tiles.

Tensile ductility and fracture of superplastic Aluminum-SiC composites under thermal cycling conditions

The tensile and fracture creep behavior of aluminum-SiC composites has been evaluated under isothermal and cyclic heating conditions. The true strain to fracture under thermal cycling conditions is shown to decrease linearly with the logarithm of the applied stress. This trend is unexpected since the strain rate sensitivity exponent, m, is high (typical of superplastic materials) and constant over the range of stresses studied. The results obtained are explained by a fracture mechanics model in which the crack size increases by a strain-induced mechanism. The results are compared with similar behavior obtained in superplastic ceramics.

Corrosion resistance of ceramic-coated stainless steel in a Br 2O 2Ar atmosphere

Coatings of SiC TiC compositional graded film (FGM), m-HfO 2 and c-HfO 2 films on stainless steel (SUS304) plates have been investigated as candidate materials for ‘UT-3’ which is an effective process of hydrogen production through thermochemical decomposition of water. Changing the source gas concentration leads to composition control in TiC-SiC composite films. Cracks in the films could not be avoided in either the TiC-coated SUS304 nor the SiC-TiC double layer-coated SUS304. However the SiC TiC FGM-coated SUS304 had no cracks. Corrosion of the TiC and SiC-20 mol%TiC double-layer-coated SUS304 in the Br 2-O 2-Ar atmosphere was mainly caused by oxidation of the TiC film and SUS304. The SiC TiC FGM-coated SUS304 showed superior corrosion resistance in isothermal and cyclic heating conditions. m-HfO 2 and c-HfO 2 (7·1–44·5 mol% Y 2O 3) were attained by the changing of Y(DPM) 3 gas concentration. XRD measurement shows the monoclinic and cubic HfO 2. Both plate-like and columnar texture in the m-HfO 2 and c-HfO 2 films were observed. m-HfO 2, in which columnar texture, coated SUS304 showed the excellent corrosion resistance in Br 2O 2Ar atmosphere under heat cyclic conditions. This is thought to be due to the effects of columnar texture on the thermal stress relaxation, and of the excellent corrosion resistance of the m-HfO 2.

Structural Ablative Plastics

Abstract Laminated reinforced plastics using carbon or silica fabrics and phenolic resins are widely used for ablative liners of rocket nozzles and for other applications requiring protection of structural elements in a high thermal environment. Under cyclic heating conditions, the phenolic resin chars, thereby providing ablation cooling; on cool-down, cracks and/or delaminations result in the majority of applications. On a reheat cycle, as in a multistart engine or other pulsed environment, a burn-through or other catastrophic failure may occur in the cracked areas.

MISCO MS

Abstract MISCO MS is a highly alloyed heat and corrosion resisting steel recommended for castings subjected to cyclic heating conditions. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as creep. It also includes information on high temperature performance and corrosion resistance as well as casting, heat treating, and machining. Filing Code: SS-95. Producer or source: Michigan-Standard Alloy Casting Company.