Thermal Conductivity of Magnesium Alloys in the Temperature Range from −125 °C to 400 °C

Magnesium alloys have been widely used in recent years as lightweight structural materials in the manufacturing of automobiles, airplanes, and portable computers. Magnesium alloys have extremely low density (as low as 1738 kg · m^?3) and high rigidity, which makes them suitable for such applications. In this study, the thermal conductivity of two different magnesium alloys made by twin-roll casting was investigated using the laser-flash technique and differential scanning calorimetry for thermal diffusivity and specific heat capacity measurements, respectively. The thermal diffusivity of the magnesium alloys, AZ31 and AZ61, was measured over the temperature range from ?125 °C to 400 °C. The alloys AZ31 and AZ61 are composed of magnesium, aluminum, and zinc. The thermal conductivity gradually increased with temperature. The densities of AZ31 and AZ61 were 1754 kg · m^?3 and 1777 kg · m^?3, respectively. The thermal conductivity of AZ31 was about 25 % higher than that of AZ61, and this is attributed to the amount of precipitation.     

Influence of Drop Growth Rate and Size on the Interfacial Tension of Triton X-100 Solutions as a Function of Pressure and Temperature

The interfacial tension (IFT) between decane and aqueous solutions of Triton X-100 was determined by the pendant-drop technique, and the effects of the temperature, pressure, surfactant concentration, droplet growth rate, and size were studied. Three aqueous solutions of surfactant were used (0.48 × 10^?4 mol · L^?1, 0.96 × 10^?4 mol · L^?1, 1.43 × 10^?4 mol · L^?1), and the experiments were performed at (2, 3, and 4) MPa and at (30, 40, and 50) °C. As expected, the alkane drop changed its shape, and the IFT of the system decreased as the surfactant adsorbed onto the interface, until the drop finally separates from the capillary, in a maximum time of 2120 s. According to the results, the influence of temperature on the IFT is inversely proportional to the surfactant concentration, because when the concentration increases, the temperature has little effect on it. It was also noticed that the effect of pressure on the IFT at lower surfactant concentrations is less significant than at higher concentrations. When the temperature decreases, the pressure reduces its effect on the IFT, as occurs with systems at 30 °C. The droplet growth rate does not significantly affect the IFT value, while its size does; therefore, when transient studies are carried out, it is required to control the drop size.     

Comparison of Fenitrothion and Trifluralin Adsorption on Organo-Zeolites and Activated Carbon. Part I: Pesticides Adsorption Isotherms on Adsorbents

In the past decades, natural zeolites have found a important role in adsorption applications due to their local availability and low cost preparation. In this study, surface of natural zeolite sample was modified by using cationic surfactants in order to investigate its adsorption capacity to remove pesticides from wastewater. Data obtained from adsorption studies on organo-zeolites were compared with data obtained from those on activated carbon. To determine the adsorption process and properties, the effects of various operating parameters, pH of the solution (3–11), initial concentration of pesticides (5–20 mg · L^?1), contact time (10–350 min), and temperature (25–55°C) were investigated in a batch adsorption technique. According to results, the adsorbed amount of fenitrothion on three different adsorbents decreased whereas those of trifluralin on the adsorbents increased with increasing temperature. Langmuir and Freundlich adsorption models were applied to experimental equilibrium data of pesticide adsorption depending on temperature. The data obtained from adsorption isotherms for organo-zeolites and activated carbon were well fitted to the Freundlich model at all temperatures.     

Influence of solution rate and substrate temperature on the properties of lead iodide films deposited by spray pyrolysis

Polycrystalline lead iodide (PbI₂) thin films have been deposited by spray pyrolysis method using N,N-dimethylformamide (DMF) as solvent as a function of several deposition parameters. DMF is used as an alternative to water due to the larger solubility limit of PbI₂ in this solvent. In this work, the solution rate during the deposition time of 3 h was varied in the range of 0.11 cm³/min up to 0.30 cm³/min. A growth rate varying from 19 Å s^?1 up to 47 Å s^?1 was obtained as a function of solution rate. Dark current as a function of temperature for the final films reveals that for larger solution rates smaller values of electrical resistivity is obtained. For a solution rate of 0.30 cm³/min, an electrical transport activation energy (E _a) of about 0.65 eV was measured for the whole temperature range. On the other hand, for the sample deposited with a solution rate of 0.11 cm³/min, two main transport mechanisms can be observed with an activation energy of about 1.23 eV for temperatures above 50 °C. The effect of substrate temperature is also discussed. Samples were deposited in the temperature range of 170 °C up to 250 °C with a fixed solution rate of 0.16 cm³/min. In addition, the films were exposed to X-ray irradiation in the mammography diagnosis region, using a molybdenum (Mo) anode and a peak tube potential between 26 and 36 kV (equivalent photon energies between 10 keV and 15 keV).     

A Cryostat for Automated mK-Level Thermometer Calibrations from ?202??��C to 250?��C

The National Measurement Institute of Australia (NMIA) has developed a vacuum cryostat capable of calibrating precision electronic thermometers with a transfer error less than 2 mK over the range from ?202 °C to 250 °C. The calibration of precision temperature measurement probes such as platinum resistance thermometers is usually performed in circulated fluid baths to achieve mK-level calibration uncertainties, and requires the use of several baths to cover the commonly used range of ?80 °C to 250°C. Below ?80 °C, dry-well systems cooled by liquid nitrogen are available down to ?196 °C, but achieve poor uniformity and stability. The increased use of cryogenic preservation in the biomedical area has seen an increase in demand for precision calibration of electronic thermometer systems, in particular, down to a few degrees below the boiling point of nitrogen (?196 °C). This has prompted NMIA to develop a new design of a dry-well calibrator, based around a 380 mm long, 50 mm diameter, oxygen-free copper block insulated by gold-plated radiation and guard shields. Temperatures down to ?202 °C are achieved by controlling the flow of liquid nitrogen through a restricting orifice into an evacuated heat exchanger. Computer control of the nitrogen flow and of several immersion heaters achieve a temperature stability of a few mK at all temperatures over the operational range, requiring typically 60 min to equilibrate at each new setpoint. Radiative transfer limits operation to 250 °C where the uniformity is 0.5 mK · cm^?1 (and becoming negligible at lower temperatures). A significant design innovation is the thermometer entry region, which has a purge system to keep the wells free of condensed moisture or atmospheric gases without the need for a seal. As the block is only 50 mm from the face of the cryostat, thermometers as short as 250 mm can be calibrated. The system is now in regular use at NMIA providing fully automated calibrations of precison temperature measurement systems without the need to use multiple temperature enclosures.     

High temperature impedance spectroscopy of barium stannate, BaSnO3

Polycrystalline powder of BaSnO₃ was prepared at 1300 °C using a high-temperature solid-state reaction technique. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with lattice parameter: a = (4·1158 ± 0·0003) Å. The synthesized powder was characterized using X-ray diffraction (XRD) scanning electron micrographs, energy dispersive X-ray analysis, differential thermal analysis, thermogravimetric analysis and Fourier transform infrared techniques. Electrical properties were studied using a.c. impedance spectroscopy technique in the temperature range of 50–650 °C and frequency range of 10 Hz–13 MHz. The complex impedance plots at temperature ≥ 300 °C show that total impedance is due to the contributions of grains, grain boundaries and electrode. Resistance of these contributions has been determined. Variation of these resistances with temperature shows the presence of two different regions with different slopes. The nature of variation for the above three resistances, in both the temperature regions confirms that conducting species (phases) responsible for grain, grain boundaries and electrode are the same. Based on the value of activation energy, it is proposed that conduction via hopping of doubly ionized oxygen vacancies (V $_{\rm{o}}^{\bullet\bullet})$ is taking place in the temperature region of 300–450 °C, whereas in the temperature region of 450–650 °C, hopping of proton, i.e. OH^??? ions occurs.     

Influence of Particle Size and Heating Rate on Decomposition of BC Dry Chemical Fire Extinguishing Powders

Pyrolysis of BC dry chemical fire extinguishing powders which are useful for Class “B” and Class “C” fires was conducted on a thermogravimetric analyzer with sample loading of 10–25 mg under dynamic air atmosphere. The effect of particle sizes (medium value 48.99, 27.24, 4.93 µm) and heating rates (10, 15, and 20°C min^?1) were examined. The pyrolysis kinetics of the samples was analyzed using a distribution activation energy model. It was found that the decomposition temperature decreased and the pyrolysis rate increased after the samples were milled. The agglomeration of particles during production did not have an appreciable influence on the pyrolysis process of the samples in our experimental conditions. The activation energy value was 77.13?219.78 kJ · mol^?1, 58.18?288.67 kJ · mol^?1, and 44.59?209.17 kJ · mol^?1 for the powder of particle size 48.99, 27.24, 4.93 µm. We should use micro powder in fire extinguishing.     

Evolution of the pozzolanic activity of a thermally treated zeolite

Zeolites generally show pozzolanic activity due to their structural characteristics. The utilisation of pozzolans as additions to cements results in added technical advantages of the construction materials. In this study, the pozzolanic activity of a thermally treated natural mordenite-type zeolite from the Palmarito open-air deposit (Cuba) was evaluated with respect to a non-treated zeolite. Initially, a thermal treatment of the zeolite was performed at different temperatures within the range 300–1000 °C for 5 h in order to evaluate the better temperature of treatment. Afterwards, the pozzolanic activity was determined for each temperature after 7 days of reaction with a saturated Ca(OH)₂ solution that simulates the release of lime from ordinary Portland cement during the hydration reaction. The higher pozzolanic activity was achieved with the thermal treatment performed at 300 °C. Therefore, a further study studied the evolution of the mineralogical phases produced during pozzolanic reaction up to 90 days, carried out with the zeolite treated at that temperature. Consumption of Ca²⁺ in solution and formation of C–S–H-like phases with low Ca/Si ratio were experimentally observed as the main pozzolanic products. The thermodynamic study confirms high reactivity of the zeolite at short-term and chemical stability of the reaction products after 28 days. The zeolite thermally treated at 300 °C confirmed an increase in the pozzolanic activity with respect to the non-treated zeolite.     

Study on a novel energetic cocrystal of TNT/TNB

A new energetic cocrystal of TNT/TNB was obtained by evaporating ethanol at room temperature over a period of 3 days. It is found that the donor–acceptor π–π interaction, p–π interaction, and C–H···O hydrogen bond interaction are dominant in the formation of the cocrystal. In this work, physicochemical characteristics of cocrystal have also been studied using several methods: Optical Microscopy, Powder X-ray Diffraction, Single Crystal X-ray Diffraction and differential scanning calorimetry. It is shown that TNT and TNB molecules cocrystallize in a monoclinic system with space group P2₁/c and cell parameters a = 20.4570(8) Å, b = 6.1222(2) Å, c = 15.1635(6) Å, β = 110.091(4)°, and Z = 4. The cocrystal has a crystal density of 1.640 g cm^?3 and H₅₀ (50 % explosion characteristics of drop height) of 112.2 cm, which is higher than that of TNT (100 cm), TNB (77.8 cm) and most of the other explosives. The result shows that co-crystallization may help to improve the performance of TNT and TNB.     

Thermal Characteristics of a Sealed Glass-Water Heat Pipe from 0?��C to 60?��C

Investigations into the thermal characteristics of glass-water heat pipes from 0 °C to 60 °C were carried out at the National Institute of Metrology (NIM), China. In this paper, studies on a glass-water heat pipe with four thermometer wells are described. The experimental results indicated that the temperature stability and uniformity of the thermometer well of the glass-water heat pipes are within several tenths of a millikelvin when the heat pipes are immersed in a constant-temperature liquid bath, since they have a highly effective thermal conductivity. They are able to maintain a constant temperature by the absorption or liberation of the latent heat of evaporation to attenuate temperature fluctuations of the surroundings. Also, above 0 °C to 30 °C, the temperature stability of the thermometer well of the glass-water heat pipe is better than 0.1 mK for approximately 16 h. The maximum temperature differences among the thermometer wells are less than 5.5 mK when the water heat pipes operate in the range from 0 °C to 60 °C. Therefore, water heat pipes are very promising to improve the performance of liquid baths and to accurately calibrate thermometers by comparison.     

Adsorption of Thorium from Aqueous Solution using Nanoporous Adsorbents: Effect of Contact Time,pH, Initial Concentration,and Temperature

Nanoporous silicates MCM-41 have been prepared using different surfactants such as cetyltrimethylammonium bromide (C₁₆TAB) and dodecyltrimethylammonium bromide (C₁₂TAB) as template. The adsorbents are characterized using powder x-ray diffraction, nitrogen adsorption-desorption isotherm data, scanning electron microscopy, and transmission electron microscopy. The thorium sorption was studied as a function of shaking time, pH, initial concentration, and temperature. The sorption of thorium at the determined optimum conditions follows Langmuir and Freundlich isotherms. The results show that the nanoporous MCM-41 synthesized by C₁₂TAB has more adsorption capacity than the MCM-41 synthesized by C₁₆TAB (77.6 µmol · g^?1 vs. 52.1 µmol · g^?1) at 25°C. Th(IV) adsorption onto nanoporous adsorbents was very fast process and therefore, this adsorbent is suitable for column separation. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were found to be 47.76 KJ · mol^?1, 196.21 J · mol^?1 · K^?1, and 19.00 KJ · mol^?1, respectively (at 298 K). The positive value ΔH° suggested the endothermic nature of adsorption and negative ΔG° indicates the feasibility and spontaneity of the adsorption process.     

Martensitic transformation behaviour of non-equilibrium heat treated Ni50·9Ti49·1 alloys

Abstract

Ni50·9Ti49·1 specimens were heat treated using a thermal simulator. The martensitic transformation behaviours of selected areas of the thermal simulating treated specimens were studied with resistivity temperature measurements. In the thermal simulating process specimens were heated by a large electric current to a given peak temperature (400, 500, 600, 800, 900 or 1100°C respectively) and immediately water cooled to room temperature. As the two ends of a NiTi alloy specimen were fixed in copper jigs, unequal heat treatment effect areas were formed in the specimen segments near its two ends. In the unequal area of an 800°C thermal simulating treated sample, a wide transformation temperature range phenomena appeared. The experimental results indicate that non-equilibrium heat treatment proves to be an effective method to fabricate transformation temperature gradient shape memory materials.     

Measurement of the Diffusion Coefficient of Water in RP-3 and RP-5 Jet Fuels Using Digital Holography Interferometry

The diffusion coefficient of water in jet fuel was measured employing double-exposure digital holographic interferometry to clarify the diffusion process and make the aircraft fuel system safe. The experimental method and apparatus are introduced in detail, and the digital image processing program is coded in MATLAB according to the theory of the Fourier transform. At temperatures ranging from 278.15 K to 333.15 K in intervals of 5 K, the diffusion coefficient of water in RP-3 and RP-5 jet fuels ranges from 2.6967?×?10 ^?10 m²·s^?1 to 8.7332?×?10 ^?10 m²·s^?1 and from 2.3517?×?10 ^?10 m²·s^?1 to 8.0099?×?10^?10 m²·s^?1, respectively. The relationship between the measured diffusion coefficient and temperature can be well fitted by the Arrhenius law. The diffusion coefficient of water in RP-3 jet fuel is higher than that of water in RP-5 jet fuel at the same temperature. Furthermore, the viscosities of the two jet fuels were measured and found to be expressible in the form of the Arrhenius equation. The relationship among the diffusion coefficient, viscosity and temperature is analyzed according to the classic prediction model, namely the Stokes–Einstein correlation, and this correlation is further revised via experimental data to obtain a more accurate predication result.     

Plastic flow and microstructural evolution in Ti–6Al–2Zr–1Mo–1V alloys during hot deformation

Abstract

The hot deformation behaviour and microstructural evolution in Ti–6Al–2Zr–1Mo–1V alloys have been studied using isothermal hot compression tests. The processing map was developed at a true strain of 0·7 in the temperature range 750–950°C and strain rate range 0·001–10 s^?1. The corresponding microstructures were characterised by means of a metallurgical microscope. Globularisation of lamellae occurring to a greater extent in the range 780–880°C and 0·001–0·01 s^?1 had a peak power dissipation efficiency of 58% at about 850°C and 0·001 s^?1. The specimens deformed in 750–880°C and 0·01–10 s^?1 showed an instability region of processing map, whereas the specimens deformed in 880–950°C and 1–10 s^?1 indicated three kinds of flow instabilities, i.e. macro shear cracks, prior beta boundary cracks and flow localisation bands.     

Microstructure evolution of ZK40 magnesium alloy during high strain rate compression deformation at elevated temperatures

Abstract

Microstructure evolution of the homogenised ZK40 magnesium alloy was investigated during compression in the temperature range of 250–400°C and at the strain rate range of 0·01–50 s^?1. At a higher strain rate (?10 s^?1), dynamic recrystallisation developed extensively at grain boundaries and twins, resulting in a more homogeneous microstructure than the other conditions. The hot deformation characteristics of ZK40 exhibited an abnormal relationship with the strain rate, i.e., the hot workability increased with increasing the strain rate. However, the dynamic recrystallisation grain size was almost the same with increasing the temperature at the strain rate of 10 s^?1, while it increased obviously at the strain rates of 20 and 50 s^?1. Therefore, hot deformation at the strain rate of 10 s^?1 and temperature range of 250–400°C was desirable and feasible for the ZK40 alloy.     

Preparation of forsterite-based glass ceramics for LTCC from potassium feldspar

A forsterite-based glass ceramic material has been developed from potassium feldspar for low temperature co-fired ceramics (LTCC). The crystalline phases and microstructure of forsterite-based glass ceramics were investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The results show only forsterite was formed in temperature range 900–1,050 °C, and sapphirine was formed in temperature range 1,080–1,100 °C. The glass compact could be well densified at 950 °C, and full densification samples were obtained in temperature range 1,000–1,050 °C. The physical properties including dielectric properties, bending strength and thermal expansion of the specimens were also evaluated. The dielectric constants are in the range 7.00–8.25 and dielectric loss is below 0.01 in the frequency range 1–10 MHz. The specimens obtained in temperature range 950–1,100 °C are of high bending strength (69–106 MPa). The linear coefficient of thermal expansion of the specimen sintered at 1,080 °C is 9.76 × 10^?6 K^?1. All of these qualify the forsterite-based glass ceramic for further investigation as a candidate suitable for applications in LTCC field.     

Yield strength anomaly and dynamic strain ageing behaviour of recently developed advanced ultra-supercritical boiler grade wrought Ni-based superalloy IN 740H

The yield strength anomaly (YSA) and dynamic strain ageing (DSA) behaviour of advanced ultra-supercritical boiler grade wrought nickel-based superalloy IN 740H is studied by conducting tensile tests in temperature range 28–930°C and by employing strain rates 1 × 10^?2, 1 × 10^?3, 1 × 10^?4 and 1 × 10^?5 s^?1 followed by extensive electron microscopic examination. Increase in yield strength accompanied by impairment of ductility indicates that YSA exists in alloy IN 740H in temperature range of 650–760°C. The electron microscopic observation confirms that YSA is due to pinning of dislocations by γ′ precipitates and shearing of γ′ precipitates in IN 740H. DSA is observed in the temperature range of 200–500°C and is predominant at 300°C. The nature of serrated plastic flow due to DSA is dependent on the temperature and strain rate.     

Low-temperature sintered pollucite ceramic from geopolymer precursor using synthetic metakaolin

In this article, pollucite ceramic with high relative density and low coefficient of thermal expansion (CTE) was prepared from Cs-based geopolymer using synthetic metakaolin. Crystallization and sintering behavior of the Cs-based geopolymer together with thermal expansion behavior of the resulted pollucite ceramic were investigated. On heating at 1200 °C for 2 h, the amorphous Cs-based geopolymer completely crystallized into pollucite based on crystal nucleation and growth mechanism. Selected area diffraction analysis and XRD results confirmed the resulted pollucite ceramic at room temperature was pseudo-cubic phase with superlattice structure. Compared with Cs-based geopolymer using natural metakaolin, geopolymer using synthetic metakaolin in this article showed a much lower viscous sintering temperature range, which started at 800 °C, reached a maximum value of ?7.47 × 10^?4/°C at 1121.9 °C, and ended at 1200 °C. Cesium volatilization appeared only when temperature was above 1250 °C. Therefore, densified pollucite ceramic can be prepared from Cs-based geopolymer using synthetic metakaolin without cesium volatilization. Abnormal thermal shrinkage of pollucite ceramic was observed at temperature range from 25.3 to 54.6 °C because of pseudo-cubic to cubic phase transition, and its average CTE was 2.8 × 10^?6/°C from 25 to 1200 °C.     

Effect of telmperature and strain rate on tensile behaviour of M250 maraging steel

Abstract

The effect of temperature and strain rate on the 0·2% yield strength, ultimate tensile strength, and percentage elongation of M250 maraging steel was investigated under uniaxial tensile conditions in the temperature range from 25 (room temperature) to 550°C and strain rate range 10^?4–10^?1 S^?l. Up to 400°C the steel shows essentially strain rate insensitive behaviour with a gradual decrease in the 0·2% yield strength and ultimate tensile strength. The elongation remains constant at all strain rates up to 300°C. Fractographic analysis indicates that the increasing strain rate induces strain constraint resulting in an increased dimple size. An elongated structure was observed at temperatures above 400°C. X-ray diffraction reveals the presence of reverted austenite in the specimens tested at 550°C.

MST/3263