High-temperature Mechanism Research Articles

374 Mechanism of continuous high ambient temperature affecting meat quality of finishing pigs

This study investigated the effect of high ambient temperature on meat quality and its mechanism in finishing pigs. All pigs received the same wheat–soybean meal diet. Twenty-four Landrace × Large White pigs (60 kg BW) were assigned to 3 groups—those fed ad libitum at 22°C, those fed ad libitum at 35°C, and those fed at 22°C, but fed the amount consumed by those kept at 35°C—and the experiment lasted for 30 d. Feed intake, weight gain, and intramuscular fat content of pigs were reduced, both directly by high temperature and indirectly through reduced feed intake. Transcriptome analysis showed that downregulated genes caused by feed restriction were mainly involved in muscle contraction, muscle development, and muscle system process or differentiation and that upregulated genes were mainly involved in response to nutrient levels or extracellular stimulus. Downregulated genes caused by high temperature were mainly involved in muscle structure and development, energy, or catabolic metabolism, whereas upregulated genes were mainly involved in DNA or protein damage or recombination, cell cycle process or biogenesis, stress response, or immune response. The mechanisms by which high temperature and reduced feed intake affected meat quality were not completely consistent. Apart from its effects of reducing feed intake, a direct effect of high temperature on meat quality also was involved in negatively regulating cell cycle, stimulating protein, DNA damage and cell apoptosis, and heat stress response. Based on this work, microRNA profiles were analyzed and the integrated analysis of microRNA–mRNA expression levels highlighted an inverse correlation between microRNA and their putative target genes, which further verified the negative effects of high ambient temperatures on feed intake and BW gain in finishing pigs. The results in this study indicate that high temperature decreased energy metabolism and muscle tissue development and increased DNA damage or stress response through regulating microRNA and their targets genes.

High-temperature corrosion mechanism of YSZ coatings subject to calcium–magnesium–aluminosilicate (CMAS) deposits: First-principles calculations

To study the degradation mechanism of yttria-stabilized zirconia (YSZ) coatings by CMAS glass attack at high temperature, density functional theory is used to calculate the energy of CMAS/YSZ(111) system. Over 1513K, the diffusion coefficients of atoms in CMAS are larger than those in YSZ (111) and the diffusion process of (Ca↔Y) and (Si↔Y) occurs, which induced to the formation of a sandwich structure and YSZ depleting in yttrium, allowing tetragonal to monoclinic phase transition of zirconia. The cracking and peeling off of the coating is attributed to the change of YSZ volume and the thermal stress.

Columnar-to-Equiaxed Transition and Equiaxed Grain Alignment in Directionally Solidified Ni3Al Alloy Under an Axial Magnetic Field

The effect of an axial magnetic field on the solidification structure in directionally solidified Ni-21.5Al-0.4Zr-0.1B (at. pct) alloy was investigated. The experimental results indicated that the application of a high magnetic field caused the deformation of dendrites and the occurrence of columnar-to-equiaxed transition (CET). The magnetic field tended to orient the 〈001〉 crystal direction of the equiaxed grains along the magnetic field direction. The bulk solidification experiment under a high magnetic field showed that the crystal exhibited magnetic crystalline anisotropy. Further, the thermoelectric (TE) magnetic force and TE magnetic convention were analyzed by three-dimensional (3-D) numerical simulations. The results showed that the maximum value of TE magnetic force localized in the vicinity of the secondary dendrite arm root, which should be responsible for the dendrite break and CET. Based on the high-temperature creep mechanism, a simple model was proposed to describe the magnetic field intensity needed for CET: $$ B \ge kG^{ - 1.5} R^{1.25} $$ . The model is in good agreement with the experiment results. The experimental results should be attributed to the combined action of TE magnetic effects and the magnetic moment.

Cyclopentane combustion. Part II. Ignition delay measurements and mechanism validation

This study reports cyclopentane ignition delay measurements over a wide range of conditions. The measurements were obtained using two shock tubes and a rapid compression machine, and were used to test a detailed low- and high-temperature mechanism of cyclopentane oxidation that was presented in part I of this study (Al Rashidi et al., 2017). The ignition delay times of cyclopentane/air mixtures were measured over the temperature range of 650–1350K at pressures of 20 and 40atm and equivalence ratios of 0.5, 1.0 and 2.0. The ignition delay times simulated using the detailed chemical kinetic model of cyclopentane oxidation show very good agreement with the experimental measurements, as well as with the cyclopentane ignition and flame speed data available in the literature. The agreement is significantly improved compared to previous models developed and investigated at higher temperatures. Reaction path and sensitivity analyses were performed to provide insights into the ignition-controlling chemistry at low, intermediate and high temperatures. The results obtained in this study confirm that cycloalkanes are less reactive than their non-cyclic counterparts. Moreover, cyclopentane, a high octane number and high octane sensitivity fuel, exhibits minimal low-temperature chemistry and is considerably less reactive than cyclohexane. This study presents the first experimental low-temperature ignition delay data of cyclopentane, a potential fuel-blending component of particular interest due to its desirable antiknock characteristics.

Recent Advances and Current Status of the Characteristic of Deposits on Heating Surfaces from Heating Biomass-fired Boiler

Biomass direct combustion for electricity is the most widely applied and developed biomass conversion and utilization technology, but due to the high content of alkali metals, it will cause deposition and high temperature corrosion of heating surfaces in boiler during biomass combustion, thus reduces the efficiency and influences the long-time safe operation of the boiler. Alkali metals problem especially deposition and high temperature corrosion is urgently need to be solved. A review of literature indicates ash deposition and high temperature corrosion of heating surfaces in biomass-fired boilers, combined engineering practice with experimental study, explored the mechanism of deposition build-up and high temperature.

Design of 3-electrode system for in situ monitoring direct methanol fuel cells during long-time running test at high temperature

To understand the effect mechanisms of long-time running and high operation temperature on performance of the direct methanol fuel cell (DMFC) more clearly and directly, in this paper, a new design of 3-electrode system with a solution-type salt bridge has been developed to distinguish the integral polarization into anodic and cathodic polarizations at various temperatures and explore the attenuation mechanism by in situ monitoring the potential of anode during long-time running process at 80°C, for the first time. The results indicate that the optimized 3-electrode system consists of a standard calomel electrode (SCE) and a solution-type salt bridge placed in the anode hole filled by 0.5molL−1 H2SO4 solution. By utilization of the 3-electrode system, the effect mechanisms of the running temperature and time on electrochemical parameters of the DMFC have been found: (1) The increasing operation temperature improves cathodic performance more significantly than that of anode; (2) the attenuation of fuel cell performance mainly comes from that of anode during the 20-h running test at 80°C, resulting from the sharp drop of electrochemical active surface area of anode. More important, the new 3-electrode system has simplified the detection equipment and reduced the operating difficulty in a practical application for DMFCs, resulting in its portability.

Mechanisms of severe sliding abrasion of single phase steels at elevated temperatures: Influence of lattice structure and microstructural parameters

Due to the complex influence of elevated temperatures on the characteristics of a tribological system, severe high temperature sliding abrasion of single phase metals is a unique type of wear. The mechanisms of high temperature sliding abrasion (indentation and grooving of metallic surfaces) are strongly governed by the temperature-dependent interaction between the bulk metal and the abrasive during the wear process. This interaction can be correlated with the metal physical and microstructural parameters of the worn metal, which consequently greatly influence abrasive wear processes.In this context, the present study deals with the influence of microstructural aspects of single phase steels on the mechanisms of high temperature abrasion. Investigations focus on the aspects of abrasion by performing high temperature hardness and sliding wear experiments (two-body, ceramic counter body) on bcc and fcc steels. Results confirm a clear lattice-structure dependence of the abrasion behavior of steels. Major differences exist in the stability of the mechanical and tribological properties of the bcc and fcc materials investigated. Hardness and work hardening of bcc steels decrease above 500°C, leading to non-stationary wear. In contrast, fcc steels show a steady decrease of mechanical properties, avoiding instabilities. Accordingly, wear experiments and investigations of the wear scars (surface and subsurface regions) show a higher wear resistance and more favorable mechanisms of high temperature abrasion of fcc steels (e.g. pronounced micro-ploughing). Further, the microstructural elements of fcc steels high temperature abrasion resistance are investigated in more detail using X-ray diffraction. Microstructural analysis using diffraction-line broadening (Rietveld analysis) is used to determine the degree of plastic deformation (microstrain) and the phase fraction of α′-martensite of the austenitic wear scars. These parameters are related to the present mechanisms of abrasion, explaining the high temperature wear properties of fcc steels.

Raman and X-ray diffraction studies of superconducting FeTe1−xSex compounds

Iron-based superconducting layered compounds have the second highest transition temperature after cuprate superconductors. Their discovery is a milestone in the history of high-temperature superconductivity and will have profound implications for high-temperature superconducting mechanism as well as industrial applications. We have measured X-ray diffraction and Raman spectra of poly-crystalline FeTe1−xSex samples with x = 0.0, 0.5 and 1 at room temperature. X-ray profile of FeTe and FeTe0.5Se0.5 confirmed the primitive tetragonal unit cell. FeSe is found to be in double phase with tetragonal phase (about 66.62%) and orthorhombic (33.38%). A1g and B1g phonon modes were observed in Raman spectra. At room temperature, these lines are located at 95 and 130 cm−1 for FeTe, 93 and 129 cm-1 for FeTe0.5Se0.5 and 93 and 129 cm-1 for FeSe samples.

Characterization and high-temperature degradation mechanism of continuous silicon nitride fibers

Amorphous silicon nitride fibers were characterized with respect to their chemical and phase compositions. The high-temperature behavior of the fibers was investigated in N2 and Ar at temperatures ranging from 1350 to 1600 °C through tensile tests, pore volume analysis, elemental analysis, weight loss, X-ray diffraction, and scanning electron microscopy to elucidate the effects of the atmosphere on the fiber degradation mechanism. The fibers demonstrated better high-temperature stability in N2 instead of Ar. In particular, the fibers heat-treated in N2 at 1450 °C retained 43% of their original strength (0.64 GPa), while the fiber strength was completely lost in Ar at the same temperature. The primary reason for the strength degradation of the amorphous fibers was the expanding nanopores before the formation of the large Si3N4 grains. However, a catastrophic decrease in strength was due to the drastic thermal decomposition of SiNxOy and crystallization of Si3N4 grains, influenced by N2 pressure. Thermodynamic considerations were additionally applied to estimate the decomposition and carbothermal decomposition of crystalline Si3N4, thereby explaining the significant discrepancy of crystallization transformation at 1600 °C under different atmospheres.

High Temperature Coupling of IR Inactive CC Mode in Complementary Metal Oxide Semiconductor Metamaterial Structure

High temperature (up to 400 °C) coupling of infrared (IR) inactive >CC< mode is reported in complementary metal oxide semiconductor (CMOS)‐compatible refractory metamaterial filter and absorber structure by leveraging the carbon defects in tetraethyl orthosilicate obtained plasma enhanced chemical vapor deposition SiO2 thin film. Here, the role of strain gradient induced dipole moment in high stress configuration on the activation of otherwise inactive >CC< vibration at IR is confirmed. The unusual suppression of the transition is also observed in the absorber structure when the cavity mode strongly overlaps with it. Finally, 14 times better modulation of resonance spectrum is reported by such coupling in absorber configuration that supports thin film interference. The numerical and analytical study of the effect is found to be qualitatively in agreement with the experimental results. The study can set new paths toward more efficient design of spectrally selective thermophotovoltaic energy emitter at mid‐IR and novel mechanism for high temperature sensing on the ubiquitous CMOS platform.

Fabrication of ZnO nanowire-silicon pyramid hierarchical structure, and its self-cleaning

The transmittance diminishment of solar cells, caused by dust accumulation is higher than 52.54% every year (2006 Energ. Convers. Manage. 47 3192), which greatly reduces their overall efficiencies of power conversion. Any other strategy for improving the photovoltaic device cannot compensate for this loss caused by the dust. However, this critical issue has not received much attention. In this work, a kind of self-cleaning coating consisting of ZnO nanowire-silicon pyramid hierarchical structures is proposed to overcome the dust accumulation on the photovoltaic device. The principle of designing this self-cleaning is based on the Cassie-Baxter theory. Both the micron size effect for superhydrophobicity and the performance of anti-reflection of light of the substrate should be retained, which are the requirements of application of solar cell. The pyramid-like silicon (named silicon pyramid, hereafter) is fabricated by simple chemical etching. The effects of isopropanol, KOH, etching time, and etching temperature on the morphology of the silicon pyramid are investigated by using systematic statistical design and analysis method, to obtain the best distribution and size of the silicon pyramid. In the systematic statistical design and analysis method, the pick-the-winner rule is adopted. Eventually, we find that the optimized conditions for etching silicon pyramid (according the requirements of self-clean) are as follows: etching time is 60 min, etching temperature is 95℃, and mixture is 80 mL DI water, 2.9598 g KOH and 20 mL isopropanol. Moreover, ZnO nanowire-silicon pyramid hierarchical structures for the application of photovoltaic device are successfully hydrothermally grown on the substrate of silicon pyramid for the first time. The obtained self-cleaning coating consists of ZnO nanowire (with a diameter of 136 nm) and silicon pyramid (with a size of 8-11 m). The surface of this coating possesses superhydrophobic properties, i.e., a water contact angle of 154 and a contact angle hysteresis of less than 10, after being modified by heptadecafluorodecyltrimethoxysilane. Also, our obtained ZnO nanowire-silicon pyramid hierarchical structures have quite a good performance of anti-reflection, which appear gray in the normal environment. And the mechanism for it is postulated. Importantly, some new phenomena, such as high temperature improving the growth of silicon pyramid, are also revealed. Besides, the physical mechanism for high temperature improving the growth of silicon pyramid and anisotropic etching of silicon substrate is discussed. It is indicated that the anisotropic behavior is attributed to small difference in energy level (being a function of the crystal orientation) between the back-bond surface states. The method we proposed to achieve self-cleaning coating is versatile, reliable and low-cost, which is also compatible with contemporary micro-and nano-fabrication processes.

Investigation of high-temperature charge transport mechanism in Al–Gd2O3–Al-based metal–insulator–metal (MIM) structure

In this paper, the charge conduction mechanism at high temperature in Al–Gd2O3 (MIM) structure has been investigated by performing temperature-dependent current–voltage measurements in the temperature range 280–390 K. MIM structure is realized by electron beam evaporation system where thin films of Gd2O3 (40, 60 and 80 nm) and Al metal on both sides of dielectric film were deposited on glass substrate. The possibility of different transport mechanisms has been testified by plotting various graphs. The nonlinear behavior of LnV versus LnI and V 1/2 versus LnV/I graphs ruled out the possibility of space-charge-limited conduction (SCLC) and Poole–Frenkel mechanism in Al–Gd2O3–Al MIM structure. The straight lines LnI–V 1/2 graphs at various temperatures confirmed that Schottky emission is the dominant transport mechanism in Al–Gd2O3–Al structure. The calculated values of field barrier lowering coefficient at different measurement temperatures were in good agreement with the theoretical prediction confirming conduction is via Schottky emission. The field-dependent Ln(I/T 2) versus 1000/T plots were obeyed a linear relationship according to Schottky emission theory. Furthermore, the dielectric thickness dependence room-temperature current–voltage characteristics of Al–Gd2O3–Al MIM structure were showed strong dependence of current on dielectric film thickness according to Schottky emission theory of conduction current.

Hybrid graphene/geopolymeric cement as a superionic conductor for structural health monitoring applications

In this paper, we demonstrate for the first time a novel hybrid superionic long gauge sensor for structural health monitoring applications. The sensor consists of two graphene electrodes and a superionic conductor film made entirely of fly ash geopolymeric material. The sensor employs ion hopping as a conduction mechanism for high precision temperature and tensile strain sensing in structures. The design, fabrication and characterization of the sensor are presented. The temperature and strain sensing mechanisms of the sensor are also discussed. The experimental results revealed that the crystal structure of the superionic film is a 3D sodium-poly(sialate-siloxo) framework, with a room temperature ionic conductivity between 1.54 × 10−2 and 1.72 × 10−2 S m−1 and, activation energy of 0.156 eV, which supports the notion that ion hopping is the main conduction mechanism for the sensor. The sensor showed high sensitivity to both temperature and tensile strain. The sensor exhibited temperature sensitivity as high as 21.5 kΩ °C−1 and tensile strain sensitivity (i.e., gauge factor) as high as 358. The proposed sensor is relatively inexpensive and can easily be manufactured with long gauges to measure temperature and bulk strains in structures. With further development and characterization, the sensor can be retrofitted onto existing structures such as bridges, buildings, pipelines and wind turbines to monitor their structural integrity.

Effect of high temperature on immune response of grass carp (Ctenopharyngodon idellus) by transcriptome analysis

Exposure to high temperature is an inherent feature of grass carp culture in southern China and juvenile grass carps are predisposed to infectious disease in this condition. To understand how high temperature impacts the immune response to pathogens in grass carp, the transcriptomic profiles of the spleens from immune injected grass carp groups undergoing heat stress and normal temperature were investigated. An average of 72 million clean reads per library was obtained, and approximate 80% of these genes were successfully mapped to the reference genome. A total of 2287 up-regulated and 1068 down-regulated genes were identified. 10 immune-related categories involving 90 differently expressed genes were scrutinized. Expression patterns of 18 differentially expressed genes involving in immune response were validated by quantitative real-time RT-PCR. These results provide further significant insights into the influence mechanism of high temperature to immune response in grass carp.

High temperature mechanics of nanomoulded amorphous metals

High temperature mechanics of nanomoulded amorphous metals was investigated by in situ nanomechanical testing. Nanopillars of Pd43Cu27Ni10P20 metallic glass were synthesized by thermoplastic forming and their stress–strain response was obtained concurrent with direct observation of their deformation behaviour. This allowed the measurement of mechanical behaviour from nanopillars and the corresponding bulk substrate with identical thermal history. A rise in elastic modulus was seen with increase in temperature for both the nanopillars and substrate, which was explained by diffusive rearrangement of atomic-scale viscoelastic units. The results provide fundamental insights into structural rearrangement in metallic glasses.

Dynamic strain ageing in iron alloys: The shielding effect of carbon

Dynamic strain ageing in iron due to various interstitial (carbon) and substitutional (nickel, silicon, chromium, aluminum) solute atoms has been studied by in situ straining in a transmission electron microscope. The effect of carbon in solid solution is characterized by two different carbon-dislocation interactions in the jerky flow and serrated flow temperature domains, and by a low mobility of screw dislocations controlled by a “high-temperature Peierls mechanism”. Substitutional atoms in solid solution can either move the domain of dynamic strain ageing to higher temperatures or not, depending on their chemical affinity for carbon. The results are interpreted by a shielding effect of mobile carbon atoms, inhibiting the interaction between dislocations and substitutional solute atoms.

(Invited) Plasma-Based Technology for Mass Production of Graphene and Other 2D Layered Materials

Arc discharge plasma is as one of the most practical and efficient methods to synthesize various carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene with minimal defects and large yield. This is achieved due to the relatively high synthesis temperature and eco-friendly growth mechanism. Moreover, by introducing a magnetic field during synthesis process, large-scale graphene and high-purity SWCNT can be obtained in one step. In addition, the yield of graphene can be controlled by external parameters, such as the type and pressure of buffer gas, the temperature of substrate, and plasma density and temperature. Bulk graphene (graphene platelets, flakes) is usually characterized by several layer (2-20 nm) graphene pieces having characteristics sizes of about microns to ten microns. Currently, the main method for synthesis of bulk graphene is chemical exfoliation, where chemicals are utilized to separate the graphene sheets from the piece of graphite. Current production capability are quite limited and estimated to be around several tens of tons of material annually worldwide. This work is focused on development of novel highly efficient and low cost plasma-based method for graphene production in industrial quantities characterized by exceptional product properties. The synthesis is based on utilization of arc discharge supported by ablation of anode material at atmospheric pressures. Pure carbon anode (several millimeters in diameter) and arc current in the range 50-100A were utilized for the synthesis. The graphene was synthesized on the metal substrate and was mechanically remove using metallic brush immediately after the synthesis. The synthesized samples were characterized using SEM, TEM and Raman spectroscopy. Typical size of the graphene platelets was found to be about several microns. The graphene platelets down to ~2 layers were obtained. We present state-of-the-art experimental data on various attempts to employ the arc plasma technique for the graphene synthesis and consider growth mechanisms including precipitation, surface-catalyzed processes and a substrate-independent approach. The potential of arc synthesis for the growth of other types of 2D materials and future prospects are discussed.

Interfacial microstructure and high-temperature strength in silicon nitride/nickel-based superalloy bonding

Reliable Si3N4/nickel-based superalloy joints were obtained by partial transient liquid phase bonding with a Ni/Cu/Ti multi-interlayer. The flexural strengths of the joints were investigated at elevated temperatures. The maximum high-temperature bending strength of 115 MPa was achieved when the joint was tested at 1073 K. Microstructures and compositions of the joints after high-temperature testing were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy (TEM). A reaction layer with a thickness of about 3 μm was developed at the interface. The TEM results revealed a fine grain microstructure in the reaction layer of the joint after undergoing bending test at 1073 K. Cu-rich precipitates are observed in the fine-grained reaction layer by TEM. In addition, the high-temperature fracture mechanism of the joints was discussed. The fractures of the joints at room temperature exhibited a brittle fracture characteristic, while plastic deformation of the interlayers in the joint occurred at elevated temperatures.

High-temperature behavior and degradation mechanism of SiC fibers annealed in Ar and N2 atmospheres

The thermal and mechanical stability of SiC fibers at elevated temperature is an important property for the practical application of SiC fiber-reinforced ceramic matrix composites and is related to the heat-treating atmosphere. In this study, the high-temperature behavior of KD SiC fibers with low oxygen content was investigated in both Ar and N2 at temperatures from 1400 to 1800 °C through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, resistivity measurements, and tensile tests in order to understand the effects of atmospheres on the degradation of the fibers. The results show that high-temperature treatment caused more severe strength degradation in Ar than in N2. In particular, the fibers heat treated in N2 at 1700 °C retained a relatively high strength of 1.52 GPa, 60 % of their original strength, while the fiber strength was completely lost after heat treatment in Ar. Fiber strength degradation was mainly caused by a combination of crystal growth and surface flaws. The formation of huge grains and porosity in the fiber surfaces, owing to the thermal decomposition of the SiC x O y N z and SiC x O y phases, significantly degraded the strength for fibers heat treated in Ar. However, the suppressing effect of N2 on the decomposition of the SiC x O y N z phase in the fiber surfaces and nitrided case on the decomposition of the SiC x O y phase in the fiber cores, led to higher SiC fiber temperature stability in N2 rather than Ar.

High-temperature Erosive Wear Characteristics and Mechanism of High Chromium Cast Iron

High-temperature Erosive Wear Characteristics and Mechanism of High Chromium Cast Iron