Peak In Temperature Range Research Articles

A novel Ho 36Dy 20Al 24Co 20 bulk metallic glass with large magnetocaloric effect

A new heavy rare-earth-based Ho 36Dy 20Al 24Co 20 bulk metallic glass (BMG) has been prepared by a copper mold casting. A maximum magnetic entropy change of 11.77 J/kg K has been measured in Ho 36Dy 20Al 24Co 20 bulk metallic glass under a magnetic field of 5 Tesla, which is larger than that of the early reported Ho-based bulk metallic glass Ho 30Y 26Al 24Co 20. The half-maximum temperature range of the entropy change peak is as large as 40 K, leading to a superior refrigerant capacity to those of the Gd 5Si 2Ge 2 and Gd 5Si 2Ge 1.9Fe 0.1 crystalline compounds. The excellent magnetocaloric effect together with the unique properties of metallic glass makes this alloy a promising candidate for a magnetic refrigerant in the temperature range below 50 K.

Thermal stability and magnetocaloric properties of GdDyAlCo bulk metallic glasses

Gd 56− x Dy x Al 24Co 20 ( x = 16, 20 and 22) bulk metallic glasses (BMGs) alloys with a diameter of 2, 3 and 3 mm, respectively, were prepared by using copper mold casting. These alloys exhibit higher values of the glass transition temperature, crystallization temperature, and activation energy of the glass transition and crystallization, compared with those of other known rare-earth-based BMGs. A maximum magnetic entropy changes of 15.78 J/(kg K) is obtained in Gd 40Dy 16Al 24Co 20, which is the maximal among all the bulk metallic glasses, and is much larger than those of the known crystalline magnetic refrigerant compound Gd 5Si 2Ge 1.9Fe 0.1 and pure Gd metal. All the three BMG alloys have a broader temperature range of the entropy change peak, resulting in larger refrigerate capacities (RC) than those of conventional crystalline materials. The excellent magnetocaloric properties combining with high thermal stability make them an attractive candidate for magnetic refrigerants in the temperature range of 20–100 K.

Influence of thermal damage on physical properties of a granite rock: Porosity, permeability and ultrasonic wave evolutions

In this paper, parameters for characterization of connected porosity and overall damage in the thermally-cracked rock of granite in order to assess, respectively, its transport properties and its mechanical strength are identified and quantified. Samples were heated to a range of peak temperatures up to 600 °C at ambient pressure. Characterizations were made by measurement of porosity, gas permeability, velocity and attenuation of ultrasonic waves. Our study confirms the strong influence of thermal damage on physical properties, and shows clearly the potential of the above techniques in connection with this type of damage. Typically, we show that the porosity measurement only informs about open porosity, which is distributed and available at rock surface, whereas the gas permeability measurement characterizes the connected porosity. As for the ultrasonic wave propagation, it is sensitive to overall damage in the material. Nevertheless, we observed that the three techniques are complementary and similarly describe the rock behavior in each stage of heat treatment; they show a good consistency between them.

Nonisothermal crystallization and melting behavior of a luminescent conjugated polymer, poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene)

AbstractThe nonisothermal crystallization kinetics of a luminescent conjugated polymer, poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene) (PF6OC10) with three different molecular weights was investigated by differential scanning calorimetry under different cooling rates from the melt. With increasing molecular weight of PF6OC10, the temperature range of crystallization peak steadily became narrower and shifted to higher temperature region and the crystallization rate increased. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC10. Although the Avrami method did not effectively describe the nonisothermal crystallization kinetics of PF6OC10 for overall process, it was valid for describing the early stage of crystallization with an Avrami exponent n of about 3. The combined method proposed in our previous report was able to satisfactorily describe the nonisothermal crystallization behavior of PF6OC10. The crystallization activation energies determined by Kissinger, Takhor, and Augis‐Bennett models were comparable. The melting temperature of PF6OC10 increased with increasing molecular weight. For low‐molecular‐weight sample, PF6OC10 showed the characteristic of double melting phenomenon. The interval between the two melting peaks decreased with increasing molecular weight, and only one melting peak was observed for the high‐molecular‐weight sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 976–987, 2007

Acoustic emission studies of low thermal expansion aluminum-titanate ceramics strengthened by compounding mullite

Mullite (Mu) with high strength was compounded into aluminum-titanate (AT) ceramics with low thermal expansion to increase their strength. For the AT–Mu system composites, thermal contraction and expansion and acoustic emission (AE) event count rate were measured during cooling using the AE technique and the characteristics of AT–Mu composites were evaluated. The expansion due to microcracking in the range of AE count peak temperatures to room temperature was obtained and the crack volume was estimated from the expansion by cracking. A linear relation with a very high correlation ( r = 0.993) was observed between bending strength and crack volume at room temperature. From the linear plot, the bending strength at crack-free temperature in the best AT–Mu composite was shown to be 130 MP.

The thermal history of equilibrated ordinary chondrites and the relationship between textural maturity and temperature

The compositions and textures of phases in eleven equilibrated ordinary chondrites from the H, L, and LL groups spanning petrographic types 4–6 were studied and used to constrain the thermal histories of their parent bodies. Based on Fe–Mg exchange between olivine and spinel, average equilibration temperatures for type 4–6 chondrites encompass a small range, 586–777 °C, relative to what is commonly assumed for peak temperatures (600–950 °C). The maximum temperatures recorded by individual chondrites, which are minima relative to peak metamorphic temperatures, increase subtly but systematically with metamorphic type and are tightly clustered for H4-6 (733–754 °C) and LL4-6 (670–777 °C). For the Ls, Ausson (L5) records a higher maximum olivine–spinel temperature (761 °C) than does the L4 chondrite Saratov (673 °C) or the L6 chondrite Glatton (712 °C). Our data combined with olivine–spinel equilibration temperatures calculated for other equilibrated ordinary chondrites using mineral compositions from the literature demonstrate that, in general, type 4 chondrites within each chemical group record temperatures lower than or equal to those of types 5–6 chondrites. For H chondrites, the olivine–spinel closure temperature is a function of spinel grain size, such that larger grains, abundant in types 5–6 chondrites, record temperatures of ∼740 °C or more while smaller grains, rare in types 5–6 but abundant in type 4 chondrites, record lower temperatures. Olivine–spinel temperatures in the type 6 chondrites Guareña and Glatton are consistent with rapid (50–100 °C/Myr) cooling from high temperatures in the ordinary chondrite parent bodies. With one exception (∼500 °C/Myr), olivine–spinel data for St.-Séverin (LL6) are consistent with similar cooling rates. Cooling rates of order 100 °C/Myr at ∼750 °C for type 6 chondrites are considerably higher than previously determined cooling rates for lower temperatures (⩽550 °C) based on metallography, fission tracks, and geochronology. For H chondrites, current thermal models of an “onion shell” parent body are inconsistent with a small range of peak temperatures based on olivine–spinel and two pyroxene thermometry combined with a wide dispersion of cooling rates at low temperatures. Equilibrated chondrites may have sampled regions near a major transition in physical properties such as near the base of a regolith pile.

Simulation of Electron Transport in InGaAs/AlGaAs HEMTs Using an Electrothermal Monte Carlo Method

The electrothermal simulator developed in this work uses an iterative procedure that self-consistently couples a Monte Carlo electronic trajectory simulation with a fast Fourier series solution of the heat diffusion equation. Results presented in this paper are obtained from the simulation of In0.15Ga0.85As/Al 0.28Ga0.72As HEMTs. The negative differential output conductance (thermal droop) is observed in the electrothermal I ds-Vds characteristics of the simulated devices. Temperature profiles across the simulated region corresponding to different heat generation distributions are shown to be nonuniform with peak temperature and temperature range values dependent upon the device bias. The microscopic details of charge transport are studied, and the relationship between the thermal droop and the microscopic velocity properties is analyzed. The reduction in the length of the semiconductor die is shown to affect the peak temperature values without significantly altering the temperature range. The distribution of heat generation across the devices is simulated using a microscopic level count of phonon emission and absorption events and compared with that obtained using the current density-electric field (JmiddotE) dot product. The J middot E calculation was found to overestimate the local heat generation in the most electrically active regions of the device

Studies on softening of heat-affected zone of pulsed-current GMA welded Al–Zn–Mg alloy

Studies on the softening behavior of the 7005 alloy by means of real welding experiments and heat-affected zone (HAZ) simulation have been conducted. Softening in the HAZ is found to occur above a peak temperature of about 200 °C. It was found that the heat-affected zone of the alloys can be divided into two sub-zones according to their different mechanism of softening: the dissolution zone and the overageing zone. The dissolution zone is characterised by dissolution of precipitates and covers the peak temperature range above 380 °C. The overageing zone is characterised by growth of precipitates and covers the peak temperature range between 230 and 380 °C. The hardness in the heat-affected zone can be recovered by post-weld heat treatment, especially in the dissolution zone. Artificial ageing is more effective than natural ageing considering the recovery of the hardness.

Evidence for Mio-Pliocene retrograde monazite in the Lesser Himalaya, far western Nepal

A multichronometric study involving 40Ar/39Ar and 208Pb/232Th ion-microprobe dating was performed on the two northernmost windows of Lesser Himalayan rocks in far western Nepal. Both regions were sampled for their monazite-rich series. Metamorphic peak temperatures range from 540°C to 370°C. In the highest-grade rocks (Tmax ∼ 540°C), 40Ar/39Ar chronology on hornblende, biotite and muscovite gives ages of 12.9 ± 1.9 Ma, 8.9–11.7 Ma and 4.8 ± 0.4 Ma, respectively. Monazite grains yield two different 208Pb/232Th age populations of 9.3–11.4 Ma and 3.3–5.8 Ma range, respectively. The oldest monazites are found in garnet-rich samples whereas the youngest monazite grains texturally replace allanite in sample retrogressed under greenschist-facies conditions. The lowest-grade sample (Tmax ∼ 370°C) bears also young monazites at 9.0 ± 1.0 Ma, as replacement products of allanite. The chronological results as well as the clear textural relationships between allanite and monazite (which furthermore show identical REE patterns) indicate a monazite growth at the expense of allanite at low temperature (< 370°C) during exhumation. This study shows that young Mio-Pliocene Himalayan monazite should not be considered systematically as a prograde or metamorphic-peak mineral.

Isothermal Bias of the "Filter Ratio" Method for Observations of Multithermal Plasma

An early result from the Transition Region and Coronal Explorer (TRACE) was that the EUV filter ratios for many narrow coronal loops (widths of a few arcseconds) were found to cluster within the small range 0.50-1.70, as functions of position along loop length. The most common interpretation is that the temperature along the loop is in fact nearly constant with a value between 1.1 and 1.3 MK. This interpretation has resulted in a class of TRACE loop models with heating close to the footpoints. We analyze the filter ratio method to show that the constant TRACE 195 A/173 A ratios can be reproduced by multithermal differential emission measures (DEMs) along the line of sight over a wide range of peak temperatures, so long as the distribution is relatively flat and spans the temperature response of both channels. Furthermore, in the limit of flat (i.e., very multithermal) DEMs, the filter ratio method is biased toward the ratio of the integrals of the temperature response functions. This result is general to any measurement of intensity ratios that are formed over a nonzero temperature range (e.g., narrow passbands and ion emission lines).

Softening characteristics in ultra-narrow gap GMA welded joints of ultra-fine grained steel

When a 800 MPa grade ultra-fine grained steel with ferrite grains less than 1 μm and dispersed fine cementite is welded, fine ferrite grains are coarsened resulting in remarkable softening in the heat affected zone (HAZ). The peak temperature at an arbitrary location in HAZ during welding was calculated by heat conduction analysis and the effect of welding thermal history on the microstructure of the UFG steel HAZ was examined by microscopic observation. Softening as a result of ferrite grain coarsening was observed in the region where the peak temperature reaches between 920 and 1300 K for the ultra-fine grained steel with an Ac1 temperature of 980 K and Ac3 of 1150 K. The formation of martensite–austenite constituents started as a second phase above the Ac1 temperature and they curbed HAZ softening in the peak temperature range between 1000 and 1250 K.

Chondrule textures and precursor grain size: an experimental study

Chondrule formation appears to have been a major event in the early solar system, but chondrule properties do not allow us to distinguish between several possible formation mechanisms. The physical nature of the precursors, especially grain size, must affect the textures of the chondrules they yield when heated. We melted precursors of different grain sizes, including extremely fine-grained crystalline aggregates analogous to nebular condensates, to see whether objects resembling most natural chondrules can be crystallized. With one-minute heating and moderate cooling rates, the grain size of the charges depends directly on the grain size of the starting material, for temperatures up to very close to the liquidus temperature. A single rapid heating of condensate-like material thus produces very fine-grained chondrules, like dark-zoned chondrules, for a very wide range of peak temperatures. It is incapable of generating the observed textural distribution of chondrules, which are predominantly porphyritic. The simplest model for chondrules, a single heating of unmodified condensate material, therefore appears unrealistic. Coarse-grained chondrules might be formed from fine-grained precursors by extended heating with evaporation leading to coarsening, or by multiple reheating events, with higher temperatures in subsequent events. Otherwise an origin from annealed condensates, planetary rocks, or by condensation of liquid and crystals is required.

超狭開先アーク溶接における超細粒鋼熱影響部の特性―超細粒鋼溶接熱影響部の軟化域とミクロ組織（第１報）―

800 MPa high strength steel with a low carbon equivalent has been developed by means of refining ferrite grains. In the welded joints of the 800 MPa steel with ultra-fine ferrite grains (less than 1 μm) and dispersed fine cementite particles, fine ferrite grains coarsen due to the welding heat input, and then remarkable softening occurs in the heat-affected zone. For the ultra-fine grained steel (UFG steel), ultra-narrow gap gas metal arc (UNG) welding was utilized as a low heat input welding process. By the UNG welding process with the cooling time from 1073 K to 773 K of about 4.5 sec, the width of the softened region in the heat-affected zone (HAZ) of the ultra-fine grained steel can be minimized to below 2 mm. In order to clarify the softening behavior in the HAZ of UFG steel, the effect of welding thermal cycle on the microstructures of UFG steel was discussed on both the HAZ of the welded joint of UNG welding and its synthetic HAZ, and the results were also compared with the HAZ of SM490 steel. The peak temperature at each point of HAZ was estimated from thermal conduction theory and the measured data. Slightly coarsened ultra-fine ferrites (fine grain A) and larger polygonal ferrites (fine grain B) can be observed in the regions of the peak temperatures from 920 K to Ac3 (1150 K). It was found that the softening in the HAZ of UFG steel occurs within the peak temperature range of about 920 K (below Ac1=980 K) to 1300 K, and the softening in the regions of the peak temperatures from 920 K to 990 K is dependent on the grain size of the larger polygonal ferrite grains (fine grain B). M-A constituents begin to form when the peak temperature exceeds Ac1, and its volume fraction increases with the peak temperature. As second hard phase, M-A constituents restrain the softening of the HAZ in the peak temperature range from about 1000 K to 1250 K. It is known from the results that the hardness in the HAZ has the lowest value at the peak temperature of 1100 K.

フェライト系高温用鋼溶接熱影響部のクリープ強度低下現象と組織変化−フェライト系高温用鋼のＨＡＺ軟化機構（第１報）−

The effect of chromium content on creep rupture strength and microstructural change at high temperature service was investigated to clarify the mechanism of deterioration of creep rupture strength in Heat Affected Zone (HAZ) of heat resistant ferritic steel. Simulated weld thermal cycles, a temperature range from 1103 to 1473 K, were applied to test specimens machined from 2% Cr-1.5% W-V, Nb ferritic steel plates. After heat treatment at 1013 K for 1.8 ks, simulating Post Weld Heat Treatment (PWHT), creep rupture strength were evaluated at 923 K with the applied stress of 98 MPa and various microstructural examinations were carried out. In 2% Cr steel as well as 10% Cr steel shown in previous report, creep rupture strength was deteriorated in HAZ heated in the peak temperature range of 1173-1273 K, and that HAZ after creep test had the lower density of fine particle mainly consisting of MX type carbo-nitride less than 0.1 μm in diameter effective for dispersion strengthening as compared in base metal. However, a degree of deterioration of creep rupture strength in HAZ was smaller in 2% Cr steel than in 10% Cr steel. The growth rate of fine particles such as M23C6 type carbide and MX type carbo-nitride was lower in HAZ of 2% Cr steel compared with in that of 10% Cr steel. The growth of fine MX in 2% Cr HAZ was confirmed in accordance with the Ostwald ripening dominated by chromium diffusion as well as 10% Cr HAZ. The growth rate in the Ostwald ripening was described as a function of chromium content which increased as the increase of chromium content. As results, the mechanism of deterioration of creep rupture strength suggested in HAZ of 10% Cr steel, which the partial dissolution of carbide during weld thermal cycle could accelerate Ostwald ripening, was confirmed to have the universal validity to that in HAZ of 2% Cr steel.

Effects of Ca-based additives on desulfurization during coal pyrolysis

The effects of different Ca-based additives on the sulfur removal of coals during pyrolysis up to 900 °C have been studied in a fixed-bed reactor. It was found that Ca(OH) 2 and CaO were quite effective to capture the sulfur-containing gases, 95% of the sulfur evolved from untreated coal was retained in the char by the use of additives. Both the tar yield and the sulfur content of the tar decreased with addition of Ca-based additives. The effect of Ca(OH) 2 was better than that of CaO due to its higher activity, but CaCO 3 had little effect because of its higher decomposition temperature (−900 °C) than the peak temperature range (400–500 °C) of sulfur-containing gases emission. There is remarkable sulfur retention effect with Ca(OH) 2 prepared by impregnation and ultrasonic treatment due to the higher dispersion in coal particles than by simple mechanical mixing. The ultrasonic treatment is the best method with regard to the lowest SO 2 release during the char combustion. XRD results showed that the sulfur captured by Ca-based additives during pyrolysis turned into CaS. FeS detected in pyrolysis char without additives disappeared in chars with additives, which indicated that CaO could react with FeS through solid-solid reaction. When the chars with calcium-additives were burned in fixed bed reactor, they gave out less SO 2 than the raw coal added with same additives. The best total desulfurization efficiency could reach to about 85%.

Physical aging of glassy normal and waxy rice starches: effect of aging temperature on glass transition and enthalpy relaxation

Effect of physical aging at different temperatures ( T a) on the amorphous transitions of normal and waxy rice starches has been investigated using differential scanning calorimetry (DSC). Glass transition temperature ( T g) increased, but ΔC p at the T g decreased, as the difference ( T g− T a) between T g and T a increased, because the molecular mobility was reduced as the aging temperature was farther from T g. The extent of relaxation was analyzed by determining the limiting relaxation enthalpy (Δ H ∞) at various aging temperatures. The Δ H ∞ versus T g− T a revealed the two different roles by kinetic and thermodynamic controls for the relaxation. When T g− T a was low (0∼30 °C), Δ H ∞ increased with T g− T a, whereas when T g− T a was high (above 30 °C), it decreased with T g− T a. At a constant T g− T a, the residual moisture raised Δ H ∞ due to plasticization effect. The effect of aging temperature on the relaxation temperature range was opposite to that on Δ H ∞, and the peak range became narrower as the moisture content increased. The Δ H ∞ and peak temperature range were different between normal and waxy rice starches. The normal rice starch had a higher Δ H ∞ and a narrower peak temperature range than did waxy rice starch.

Quality assessment of medicinal cod-liver, edible and technical fish oils based on derivative thermogravimetry data

The quality of medicinal cod-liver, edible and technical fish oils was evaluated on the basis of chemical and thermal analyses. The most substantial chemical variables, viz. density, refractive index as well as saponification, iodine and acid numbers were determined. The two groups of thermal variables were determined based on TG and DTG curves of the thermal decomposition of studied fish oils. The onset and end temperatures as well as successive mass losses were read from the TG curves, whereas the temperature range of peak, peak temperature, peak height and peak width at a half of peak height were read from the DTG curves. To find the relation between the chemical and the TG and DTG variables, regression and principal component (PCA) analyses were applied. Good linear relations were found between a majority of chemical and thermal variables. The results of PCA indicate that the TG and DTG techniques are very useful to determine the degree of deterioration of fish oil samples.

Isothermal crystallization behavior and melting characteristics of injection sample of nucleated polypropylene

The isothermal crystallization behavior and melting characteristics of pure polypropylene (PP) and PPs nucleated with a phosphate nucleating agent (A) and a sorbitol derivative (D) have been studied by differential scanning calorimetry (DSC). Compared with pure PP, nucleated PPs show a shorter half-times of crystallization. Dependence of crystallization rate of nucleated PP on the crystallization temperature is stronger than that of pure PP at the higher crystallization temperature, whereas the opposite results are obtained at the lower crystallization temperature. Addition of nucleating agent shifts the temperature at the deviation from the baseline of DSC melting curve, T, and the temperature at the completion of melting, T, to higher temperatures, indicating that nucleated PPs exhibit a higher perfection of PP crystals. A shoulder peak in the high temperature range of melting peak of nucleated PP and a wider low temperature region in the melting peak of pure PP are observed. Obviously, PP and nucleated PPs form different distribution of crystal perfection in the isothermal crystallization process. According to the half-time of crystallization, nucleating agent A is more effective than D. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2547–2553, 2000

Mechanism of chemical sputtering of graphite under high flux deuterium bombardment

Chemical sputtering of graphite materials (isotropic graphite and carbon fiber composite) was studied by irradiation of 5 keV D 3 + beam with a flux up to 4×10 21 m −2 s −1 , which is more than one order magnitude higher than previous low flux beam experiments (< 10 20 m −2 s −1) . The chemical sputtering yield was obtained from measurements of the released methane signal with a quadrupole mass analyser. It was found that the methane yield at peak temperatures is almost independent of flux from 5×10 20 to 4×10 21 m −2 s −1 . Peak temperatures range between 900 and 1000 K, which is higher than those of the previous low flux experiments (<900 K, <10 20 m −2 s −1) . By comparing our experimental results with calculation results based on Roth's model, the annealing effect of radiation damage to prevent methyl group formation appears to be unimportant.

Isothermal crystallization behavior and melting characteristics of injection sample of nucleated polypropylene

The isothermal crystallization behavior and melting characteristics of pure polypropylene (PP) and PPs nucleated with a phosphate nucleating agent (A) and a sorbitol derivative (D) have been studied by differential scanning calorimetry (DSC). Compared with pure PP, nucleated PPs show a shorter half-times of crystallization. Dependence of crystallization rate of nucleated PP on the crystallization temperature is stronger than that of pure PP at the higher crystallization temperature, whereas the opposite results are obtained at the lower crystallization temperature. Addition of nucleating agent shifts the temperature at the deviation from the baseline of DSC melting curve, T, and the temperature at the completion of melting, T, to higher temperatures, indicating that nucleated PPs exhibit a higher perfection of PP crystals. A shoulder peak in the high temperature range of melting peak of nucleated PP and a wider low temperature region in the melting peak of pure PP are observed. Obviously, PP and nucleated PPs form different distribution of crystal perfection in the isothermal crystallization process. According to the half-time of crystallization, nucleating agent A is more effective than D. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2547–2553, 2000