Tested Temperature Range Research Articles

Thermal shock resistance of rare-earth doped in-situ SiAlON reinforced h-BN matrix ceramics under vacuum thermal cycling

Abstract In-situ SiAlON reinforced BN-matrix ceramics were prepared by hot pressing sintering, and the effects of different rare earth oxides on the thermal shock resistance of the materials were investigated. The effects of rare earth oxides on the phase composition, microstructure, bending strength, thermal properties and thermal shock resistance of the composites were studied. The results show that the phase composition and bending strength of ceramics with different rare earth oxides had no obvious change. However, the influence on the thermal expansion coefficient of the material was notable. The thermal expansion coefficient of the ceramics with CeO2 increased by 24.6% compared with Sm2O3 in the test temperature range. After 50 cycles of thermal shock at Δt = 1150 °C, the residual strength of ceramics with CeO2 was down to 157.1 MPa, decreased by 40.6% compared with the one tested in room temperature. And the Sm2O3-added ceramics reduced by 34.7%–167.1 MPa after thermal shock. The decrease of the residual strength of ceramics is mainly caused by the internal stress generated by the mismatch between the growth of quartz and SiAlON phase in the matrix and the thermal expansion coefficient of the matrix. However, no macro cracks were observed on the surface of the samples after thermal shock.

Poly(lactic acid)/cellulose nanocrystal composites via the Pickering emulsion approach: Rheological, thermal and mechanical properties

The use of nanocellulose is an attractive method to improve the characteristics of biodegradable polymers, but its effects are often affected by uneven dispersion. In this work, cellulose nanocrystals (CNCs) were evenly dispersed into poly(lactic acid) (PLA) via the Pickering emulsion approach. The PLA/CNC composites prepared were studied by rheological, thermal as well as mechanical measurements. Changes in the rheological characteristics of the composites showed that CNC promoted the transition of the composites from fluid to solid-like behavior at high temperatures. The introduction of 5 wt% CNC improved the crystallinity of PLA considerably and increased the onset temperature of crystallization by about 10 °C. The storage modulus of the composites increased throughout the entire temperature range of testing. Flexural modulus was improved considerably. All the results indicated that the Pickering emulsion approach improved the dispersion of CNC in the PLA matrix and CNC improved efficiently most properties of PLA.

Comparative study of Shot creep of single-phase titanium alloys in air and neutral gas environment on the test temperature in range from 673 to 1323 K

The paper presents the results of comparative studies of short-term creep in tensile tests of the VT1-0 commercially pure titanium (analogue Grade 2 according to ASTM A485) and the VT5-1 alloy (analogue Grade 6 according to ASTM B265) in air and argon. Tests by the Dorn’s method were carried out in a gas-tight chamber under constant pressure. The specimens were heated by passing alternating current. Empirical coefficients are determined in power dependences of the creep rate and the conventional creep strength on test temperature in the range from 673 to 1323 K for argon and air environment and nominal stress ranging between 4.45 and 9.36 MPa. It is found that heating in argon environment, as compared to heating in air, decreases the rate of short-term creep and increases creep strength at identical nominal stresses in the entire range of test temperatures. Calculations demonstrate that the energy of the activation of short-term creep does not depend on test conditions. This indicates that the deformation mechanism is unchanged.

DMA, EIS and thermal fatigue of organic coatings

The importance of temperature variations on coatings aging is well known. The aim of this paper is to evidence how aging kinetic, monitored by EIS, can be complemented by dynamic mechanical analyses to access susceptibility of high performance corrosion protective composite coatings, designed for harsh conditions, when subjected to temperature variations, proposing methodology to aid in the selection criteria. Five coatings provided by recognized brands were submitted to corrosion tests with immersion and temperature cycling or shocking. The range of testing temperatures included the so-called humid Tg obtained by Arrhenius-type plot of low frequency impedance modulus. Different aging kinetics were evidenced by EIS for the coatings. Pull-off adhesion measurements complemented by SEM indicated loss of cohesion with cracks and voids nucleation at filler-matrix interfaces as one important feature of the coatings with more accelerated thermal aging kinetics. The irreversibility of impedance on Arrhenius-type plot, follows the thermal stress, but does not predict performance of the coatings. On the other hand, associating EIS with mechanical dynamic analyses allows understanding susceptibility to thermal aging, by considering the coatings viscoelastic properties measured within the range of testing temperatures. The input given by DMA testifies to the importance of having this technique included in coatings assessment protocols whenever temperature variations are in context. With this, one can not only better understand the behavior of the coatings, but also get clues to develop products with even better performance.

High-temperature compressive properties and tribological behaviour of Mo2NiB2–Ni cermets

The present work investigated the high-temperature compressive strength and tribological behaviours of Mo 2 NiB 2 –Ni cermets from 25 to 900 °C. Mo 2 NiB 2 –Ni cermets with four different Ni additions were first fabricated successfully and then tested. The results show that cermets with Ni/B 1.1 have the best compressive strength of 531.8 MPa at 900 °C and superior strength retention at high temperature. With the best high-temperature compressive strength, Mo 2 NiB 2 –Ni cermets with Ni/B 1.1 are used as pins with Si 3 N 4 disks in a tribological test. The wear rate of Mo 2 NiB 2 –Ni cermets gradually increases as the temperature increases from 25 to 900 °C, while the friction coefficient shows the opposite trend. Within the entire testing temperature range, the friction coefficient decreases, and the minimum friction coefficient is obtained at 900 °C. The decline of the friction coefficient is attributed to the self-lubricating oxidation tribolayer covering the worn surface. Moreover, the dominant wear mechanism changes from abrasive wear to oxidation wear as the temperature exceeds 600 °C.

Effects of sintering temperature on microstructure and thermoelectric properties of Ce-filled Fe4Sb12 skutterudites

The improvement of thermoelectric properties of p-type iron-based skutterudites is limited due to the present of more iron-rich impurity phases induced by the inherent structural instability of Fe-containing skutterudites. How to reduce the content of the impurity phase in p-type Fe-based skutterudites is a key to obtain high ZT value. Ce1.25Fe4Sb12 materials with different sintering temperatures (723 K, 773 K, 798 K, 823 K and 848 K) have been prepared by a traditional melting-quenching-annealing process coupled with spark plasma sintering (SPS) technique. The results of XRD and EPMA analysis indicate that all the SPSed samples consist of the main skutterudite phase and impurity phases of FeSb2, Sb, CeSb2 and oxides of Ce and Sb. Compared with other SPSed samples, the SPS-773 K sample has the best thermoelectric properties due to the relatively fewer impurity phases, a large number of micro-nanoscale particles at the grain boundary and more voids. The SPS-773 K sample shows the largest ZT value over the entire test temperature range due to the higher power factor and lower lattice thermal conductivity. The maximum ZT value reaches 0.81 at 800 K. This indicates that thermoelectric properties of Ce-filled Fe4Sb12 skutterudite materials can be effectively improved by reducing impurity phases induced by the optimization of the sintering temperature.

Rapid larval growth is costly for post-metamorphic thermal performance in a Great Barrier Reef fish

Most marine fish species disperse during a planktonic larval stage where individuals exhibit variation in pelagic duration, growth rate and settlement size. Extreme predation risk is predicted to select for rapid growth rates and decreased pelagic duration as a strategy for increasing survival to settlement. How larval traits affect post-metamorphic performance, however, has been a contentious topic over the past 50 yrs. Some studies suggest that larval traits have carry-over effects to later life stages, where larval traits can be positively or negatively correlated with post-metamorphic performance. For example, individuals with rapid larval growth rates may settle at larger sizes and have faster post-metamorphic locomotion than slow-growing individuals. Alternatively, trade-offs between life stages might exist, where rapid larval growth rate may be negatively correlated with post-metamorphic locomotion, potentially due to energetic resource allocation trade-offs. In addition, other studies suggest that larval traits are decoupled from later life stages to allow for a transition in morphology and habitat. We tested how Bathygobius cocosensis hatch size, larval growth rates, settlement size and pelagic duration correlated with post-metamorphic thermal performance of burst swimming speed, routine metabolic rate and critical thermal maximum. We found that larval growth rate was negatively correlated with juvenile routine metabolic rate and burst swimming speed across a range of test temperatures. That is, fast-growing larvae had slower burst swimming speeds and lower routine metabolic rates across temperature as juveniles compared to slower-growing larvae. We also found that hatch size and pelagic larval duration were not correlated with post-metamorphic performance. Thus, we provide evidence both for larval traits having carry-over effects on later life stages and also for larval traits being decoupled with thermal performance post-metamorphosis. This is the first study to show that rapid larval growth rate is costly for post-metamorphic thermal performance.

Modelling of expansion ratio and half-life of foamed bitumen using gene expression programming

ABSTRACT A typical foamed bituminous mixture design process involves production and evaluation of foamed bitumen over a range of foaming temperatures and water contents. Such a process of elaborate testing (over a range of temperatures and water contents) is a time- and resource-consuming exercise. This work presents a novel gene expression programming-based approach to predict the expansion ratio and half-life of foamed bitumen. To develop these predictive models, a database that consists of foamed bitumen characteristics (i.e. expansion ratio and half-life) and physico-chemical properties of bitumen was developed using six distinct binders (of different viscosity grades). Initially, all binders were tested for their physical properties and chemical composition. Furthermore, foamed bitumen characteristics of these binders were measured over the range of test temperatures (110°C to 200°C) and water contents (2% to 11%). The final database consisted of 166 observations (arising out of different combinations of 6 binder types, 6 water contents, and 8 test temperatures and an average of 3 replicates for each condition). Expressions to predict foamed bitumen characteristics have been developed based on temperature, water content, viscosity, and chemical composition using this database through the gene expression programming technique. The numerical values of goodness of fit parameters indicated that models based on physical properties are able to predict expansion ratio and half-life with reasonable accuracy. Furthermore, the use of information regarding chemical composition along with physical properties improved the accuracy of predictive models significantly. These expressions can be used to identify the feasible range of test conditions for the production of foamed bitumen before actual testing is commenced.

On the bonding between glass and PVB in laminated glass

In blast protective design, laminated glass is used to facilitate the safety of building occupants. Laminated glass provides its safety through the maintenance of the bond between the glass and the interlayer, and also through the deformation of the interlayer. The amount of deformation is related to the stretching of the interlayer, which is related to the amount of adhesion between the glass and the interlayer. An experimental and modelling study has been performed on the bond between the glass and the interlayer at different testing rates and temperatures. Tensile tests on cracked laminated glass and pure PVB were performed. These tests were coupled with fracture mechanics methods to calculate a bond fracture toughness. This bond fracture toughness was used to develop a finite element model to predict the separation between the glass and the interlayer. From the experimental studies it was found that the adhesion between the glass and the interlayer is temperature independent in the range of 20 °C–60 °C at a constant testing rate. In contrast, at a constant temperature, the adhesion was found to be loading rate dependent. The finite element model developed has shown for the first time good consistency with experimental data for a wide range of testing rates and temperatures.

Enhanced High-Temperature DC Dielectric Performance of Crosslinked Polyethylene with a Polystyrene Pinning Structure.

In this paper, we propose a method on improving direct current (DC) dielectric performance by designing a polystyrene (PS) pinning crosslinked polyethylene (XLPE) for the application of insulation materials on high voltage direct current (HVDC) extruded cable. Electrical experimental results show that the addition of PS (1–5 phr, parts per hundreds of resin) can significantly reduce DC conductivity and increase DC breakdown strength of XLPE in the test temperature range of 30–90 °C. Microstructure investigation shows PS distributed as particles could participate in the formation of a crosslinking network with the help of a crosslinking agent, thus forming a polymer pinning structure at the interface between XLPE and PS. It is believed that such a special design strengthens the structure of XLPE, which leads to the improved DC dielectric performance at elevated temperatures. Our findings may contribute a new solution for developing HVDC cable insulation materials.

The fatigue fracture characteristics of the bond zone of aluminum matrix composites (Al-12Si/ABOw) with Al-12Si alloys

The strain controlled low-cycle fatigue (LCF) test of the bond zone of aluminum matrix composites (Al-12Si/ABOw) with Al-12Si alloys was carried out with the test temperature range from 25 °C to 350 °C. The cyclic mechanical response characteristics of material at different test temperatures were analyzed. The microstructural evolution process and fracture mechanism of three characteristic fracture models were studied through SEM observation. The influence of temperatures and load magnitudes on fatigue behaviors were also discussed. The results showed that, the cyclic stress responses of the material exhibited cyclic hardening under low-cycle fatigue loading at 25 °C, and the crack occurred at the casting defects in the composite part first, resulting in a flat fracture surface with both composite part and Al-12Si alloy part. When the temperature raised to 200 °C, the cyclic stress response of the material would show out slight cyclic hardening at beginning stage and distinct cyclic softening during later stage. The casting defects in the composite would no longer be the prior crack source, and the crack would initiate at the large-sized primary Si particles nearby the bond zone which led to a fracture surface with the bond zone shape under low-cycle fatigue loading at 200 °C. With the continued increasing of temperature to 350 °C, the cyclic stress responses of the material showed the characteristics of continuous softening, and the fatigue crack generated at the primary Si phases in the Al-12Si alloy part, which caused the specimens fractured at the unreinforced Al-12Si alloy parts with a fracture surface like common aluminum alloy fracture under high temperature. There was one point had to be mentioned that when the magnitude of cyclic strain loadings (△ε/2) was larger than 0.003, the failure mode would be the fracture of the unreinforced Ai-12Si alloy part at any temperature due to the prior fracture of Al-12Si matrix alloy under relatively high loadings. Microstructure observation indicated that the fatigue fracture features of the material transformed from hard-brittle to soft-ductile gradually with the change of test temperatures from 25 °C to 350 °C.

Development of heat- and wear-resistant nanocomposite copper powder based material and technique of its obtaining used for plungers of die-casting machines

This paper presents the chemical composition, technology of manufacture and the basic properties of the nanocomposite Cu-Al-C-O copper powder based material for plungers of die - casting machines developed by the authors. The technology is based on the method of reactionary mechanical alloying in the attritor, which provides the formation of a dispersion-strengthened subgrain structure of the material containing strengthening particles γ-Al2O3 with an average size of 39±7 nm.Its recrystallization temperature is 1000 ± 20 °C, and the hardness in the test temperature range of (20-800 °C) exceeds the hardness of standard bronzes, in particular, CuBe2NiTi, CuAl10Fe4Ni4 and CuAl10Fe3Mn2, widely used in plungers of such foundry equipment. The developed material has a low wear intensity (3.20 ± 0.85)·10−11 and, in contrast to the above bronzes, it can be used at an extremely high (up to 115 MPa) pressure between the plunger and the steel pressing chamber.

Effect of Temperature and Solvent on the Structure of Amide Cavitands

AbstractConformational changes of amide cavitands A–C were investigated at varied temperatures and in several solvents. While cavitands A and B, with comparatively smaller substituents such as Et and iPr, were always in vase conformation in non‐polar solvents such as CDCl3, CD2Cl2, (D8)THF, and C6D6, their thermoswitching (vase to kite) was observed in polar solvents such as (D7)DMF and (D6)DMSO or in the presence of acid (TFA) and H‐bonding inhibitor (TFE). Intra‐ and interannular H‐bonds of A and B were clearly observed by low‐temperature 1H‐NMR spectra in CDCl3. No conformational change of cavitand C with bigger substituent (tBu) was observed under any tested temperature range and in polar or non‐polar solvents; C was always in the kite conformation.

Phase stability and transport characteristics of (ZrO2)1-x(Sc2O3)x(СeO2)y and (ZrO2)1-x-y-z(Sc2O3)x(СeO2)y(Y2O3)z solid solution crystals

Phase stability and transport characteristics of (ZrO2)1-x(Sc2O3)x(СeO2)y (x = 0.08–0.10; y = 0.005–0.015) and (ZrO2)1-x-y-z(Sc2O3)x(СeO2)y(Y2O3)z (x = 0.08–0.10; y = 0.005–0.010; z = 0.005–0.020) melt-grown crystals have been studied after air heat treatment at 1000 °C for 400 h.Annealing of the (ZrO2)1-x(Sc2O3)x(СeO2)y crystals caused the formation of a rhombohedral phase and reduced the electrical conductivity of the specimens in the entire test temperature range. Yttrium co-doping of the (ZrO2)1-x(Sc2O3)x(СeO2)y crystals stabilized the cubic phase for some compositions. In two-phase (ZrO2)1-x-y-z(Sc2O3)x(СeO2)y(Y2O3)z crystals containing a cubic and a tetragonal phases exhibited conductivity degradation. Annealing of cubic crystals caused the formation of the t'` phase and increased their conductivity.

Experimental and theoretical study on an air-source heat pump water heater for northern China in cold winter: Effects of environment temperature and switch of operating modes

Because of the urgent need of environment protection and energy saving, Chinese government has proposed ‘coal-to-electricity’ policy in north China to use air-source heat pump for space heating. Therefore, a cascade heat pump working at −20 °C and providing 75 °C hot water is studied in this work to match original cast iron radiator in cold climate in north China, which was seldom reported. It is also able to provide hot water for industrial and commercial use and work under single-stage mode in summertime. An experimental prototype of the cascade heat pump is designed and set up. Experimental results show COP of the cascade heat pump system can remain 1.69 at environment temperature as low as −21 °C and the COP is around 2 for most of the tested cases. In the tested temperature range, heating capacity varies from 11.32 to 18.93 kW, and discharge temperature varies from 93.95 to 91.42 °C. Thus, the cascade heat pump reveals good energy saving potential and can work stably demonstrating the feasibility to supply high-temperature water for space heating in coal-to-electricity retrofit. To study the switch between cascade and single-stage modes, computational models of the heat pump are established, validated with experimental data. The results imply cascade mode should be switched to single-stage mode when ambient temperature is higher than 20 °C, taking into account the COP, heating capacity, and discharge temperature. The studied system and results can be also used in other cold weather worldwide to help save energy.

Structural, Magnetic, and Giant Dielectric Properties of Gd Substituted CuFeO2 Composites

To study the effects of structural modulation by doping rare earth element on the magnetic and dielectric properties, CuFe1-xGdxO2 (0 ≤ x ≤ 0.2) samples are synthesized using the solid-state reaction method. The XRD and SEM results show that a small amount of Gd3+ ions (x ≤ 0.07) effectively occupies the Fe3+ site and promotes the grain growth of the CuFeO2 system. Judging from the magnetic property measurements, the samples (x = 0, 0.01) undergo two successive magnetic transitions. Further increase of x, the magnetic transition of the samples (x ≥ 0.07) has not been detected in the testing temperature range. The magnetization hysteresis loops show that all of the samples have weak ferromagnetic properties, and the saturation magnetization is obviously enhanced with increasing x. Most interestingly, the dielectric measurements suggests that CuFeO2 samples exhibit a giant dielectric constant (eγ~104), and eγ is obviously improved (~ 4.0 × 104) using the proper Gd content. The dielectric properties are explained using the internal barrier layer capacitance model (IBLC).

Research of thermal protection characteristics for circuit breakers considering nonlinear electro-thermal-structural coupling

Thermal protection is designed in the circuit breaker to interrupt current flow when fault current is detected. To investigate the thermal protection characteristics, a nonlinear electro-thermal-structural model considering the nonlinearities of bimetal deformations have been developed. The coefficients of thermal expansion (CTE) have been measured at different temperatures. Measurement results show that the CTE of thermal sensitive layer of bimetal demonstrates temperature-dependent variation when subjected to different temperatures. The CTE increases from 13.2 ppm/°C at 20 °C to 25.3 ppm/°C at 380 °C, which is equivalent to 91.7% variation in the tested temperature range. Based on the CTE measurements, three different overload protection tests have been conducted according to the requirements of IEC 60898 standard. Simulation results show that the protection unit can be effectively triggered within specified time range under different testing conditions. Comparisons between simulations and experiments show that model predictions with linear CTE assumption only describe expansions at specified temperature. When temperature changes with time, the proposed nonlinear simulation framework is capable to prediction both deformations and temperature changes with higher accuracy.

Tensile behaviors of thermal aged HTPB propellant at low temperatures under dynamic loading

With the purpose of further investigating the influence of aging on the tensile behaviors of hydroxyl-terminated polybutadiene (HTPB) propellant at low temperatures under dynamic loading, uniaxial tensile stress responses of thermal accelerated aged propellant samples at different temperatures (223–298 K) and strain rates ( $0.40\mbox{--}42.86~\mbox{s}^{-1}$ ) were obtained through the use of a new INSTRON testing machine. And scanning electron microscope (SEM) was employed to analyze the microscopic damage of HTPB propellant under the test conditions. Test results indicate that aging can significantly affect the characteristics of the stress-strain curves, mechanical properties and fracture mechanisms of HTPB propellant at low temperatures under dynamic loading. There are three regions in the tensile stress-strain curves of aged propellant when deforming at lower temperatures and the highest strain rate, however, there are five ones for unaged propellant. At lower temperatures and higher strain rates, the strain at maximum tensile stress of the propellant decreases more obviously after aging. Moreover, the variation of mechanical parameters for HTPB propellant with aging time are highly complex due to the occurrence of oxidative cross-linking during aging and the distinct changes of the fracture mechanisms. These variation were reasonably well described with linear model and the improved exponential model in this investigation. The fracture mechanism of aged propellant can change from dewetting, matrix tearing and AP particle fracture to only AP particle fracture with increasing strain rate for the entire test temperature range, and the strain rate for this transition is all at $4.00\mbox{--}14.29~\mbox{s}^{-1}$ . In addition, the microscopic damage of HTPB propellant becomes more severe with the thermal aging time rising, however, this effect is weaker at higher strain rates after long-time thermal aging. Finally, the master curves of typical mechanical parameters for aged HTPB propellant were constructed according to the time-temperature superposition principle (TTSP).

Wireless passive separated LC temperature sensor based on high-temperature co-fired ceramic operating up to 1500 °C

This paper presents a wireless passive resonant temperature sensor based on high-temperature co-fired ceramic (HTCC) and platinum conductive metal, which has a new structure that separates inductors and capacitors, allowing the sensor’s maximum operating temperature to reach 1500 °C. In the temperature range of 43 °C–1500 °C, the resonant frequency of the sensor is extracted and the fitting curve between the frequency and temperature is obtained to demarcate the sensor. The average sensitivity of the sensor can be calculated as 6.7562 kHz °C−1 over the entire test temperature range. In addition, it was found that the maximum relative error of the sensor was only 0.24% via a repeatability experiment, and the hysteresis of the sensor mentioned in this paper is significantly reduced. Moreover, the signal intensity of the sensor mentioned in this paper and the traditional LC sensor are compared in experiments. The experimental results show that the proposed sensor has strong signal readability and meets the requirements of high-temperature testing.

The disparate data problem: The calibration of creep laws across test type and stress, temperature, and time scales

Creep data exists in a diaspora. It is not always available in the regime (short, intermediate-, and long-term) or form (minimum-creep-strain-rate, creep deformation, stress-rupture, etc.) of interest. This is particularly true for new alloys where the time-to-qualification can take between 10 and 20 years. For new alloys, extrapolation is performed using short-term creep data. When incorporating the uncertainty of the creep data, the probability distribution in extrapolations expands with time; eventually leading to unrealistic predictions. Standards recommend that extrapolation should not exceed three times the duration of the longest experiment. For example, a creep deformation model calibrated using short-term creep deformation data (e.g. 103 h) is highly unlikely to generate realistic creep deformation predictions near 105 h. This study proposes integrating disparate creep data in the calibration process of continuum damage mechanics based constitutive laws that are capable of simultaneously predicting minimum-creep-strain-rate, stress-rupture, deformation, and damage. It is hypothesized that cross-calibrating CDM constitutive models to any and every form of available creep data (across test type, stress range, and temperature range) will lead to more reliable extrapolations. This is demonstrated by integrating minimum-creep-strain-rate, stress-rupture, and short-/intermediate-term creep deformation data into the calibration process of two CDM constitutive models. Successful extrapolations are performed for minimum-creep-strain-rate, stress-rupture, and creep deformation. In addition, the approach facilitates the development of creep design maps that can be used for material selection and design and to compare the interpolation and extrapolation ability of the existing creep models.