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CN 21-1315/TG
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      28 November 2007, Volume 23 Issue 06 Previous Issue    Next Issue
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    Research Articles
    Synthesis, Microstructure, and Property of Cr2AlC
    Zhijun LIN, Yanchun ZHOU, Meishuan LI
    J. Mater. Sci. Technol., 2007, 23 (06): 721-746. 
    Abstract   HTML   PDF (22736KB)
    Cr2AlC is an unusual layered ternary ceramic that combines the merits of both metals and ceramics. The salient properties of Cr2AlC are strongly related to its bonding characteristics and microstructures. Synthesis, microstructure, and property of Cr2AlC are reviewed in this paper. First, theoretical calculations and physical properties are introduced. Then, the processing of Cr2AlC ceramic in both bulk form and thin films and their basic mechanical properties are summarized. Atomic-scale characterizations of Cr2AlC, as well as the microstructural relationships among Cr2AlC, Al8Cr5, and AlCr2 were achieved using a series of transmission electron microscopy (TEM) techniques. Moreover, high-temperature oxidation and hot corrosion behaviors of Cr2AlC were investigated by means of thermogravimetric analysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and TEM. Mechanism of the excellent high-temperature corrosion resistance of Cr2AlC is discussed based on systematic microstructural analyses. Finally, concise conclusions are drawn.
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    Mechanical Properties, Damage and Fracture Mechanisms of Bulk Metallic Glass Materials
    Zhefeng ZHANG, Fufa WU, Guo HE, J.Eckert
    J. Mater. Sci. Technol., 2007, 23 (06): 747-767. 
    Abstract   HTML   PDF (10781KB)
    The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses (BMGs) and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.
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    Hydrochloric Acid-Promoted Synthesis of cBN via Hydrothermal Route
    Haihui JIANG, Kai LI, Ligang GAI, Qilong WANG, Deliang CUI, Minhua JIANG
    J. Mater. Sci. Technol., 2007, 23 (06): 768-770. 
    Abstract   HTML   PDF (406KB)
    Single phase crystalline cubic boron nitride (cBN) with high yield was prepared by hydrothermal route at low temperature, using hydrochloric acid (HCl) as the promoter. The promotion effect of HCl on the synthesis of cBN is briefly discussed.
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    Dynamic Plastic Deformation (DPD): A Novel Technique for Synthesizing Bulk Nanostructured Metals
    Nairong TAO, Ke LU
    J. Mater. Sci. Technol., 2007, 23 (06): 771-774. 
    Abstract   HTML   PDF (582KB)
    While some superior properties of nanostructured materials (with structural scales below 100 nm) have attracted numerous interests of material scientists, technique development for synthesizing nanostructured metals and alloys in 3-dimensional (3D) bulk forms is still challenging despite of extensive investigations over decades. Here we report a novel synthesis technique for bulk nanostructured metals based on plastic deformation at high Zener-Hollomon parameters (high strain rates or low temperatures), i.e., dynamic plastic deformation (DPD). The basic concept behind this approach will be addressed together with a few examples to demonstrate the capability and characteristics of this method. Perspectives and future developments of this technique will be highlighted.
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    Dynamic Recrystallization of a Cr-Ni-Mo-Cu-Ti-V Precipitation Hardenable Stainless Steel
    A.Momeni, A.Shokuhfar, S.M.Abbasi
    J. Mater. Sci. Technol., 2007, 23 (06): 775-778. 
    Abstract   HTML   PDF (2841KB)
    In this research, the dynamic recrystallization (DRX) behavior of an as-cast precipitation hardenable (PH) stainless steel was investigated by conducting hot compression tests at temperatures between 950–1150oC and under strain rates of 0.001–1 s-1. The flow stress curves show that the DRX is responsible for flow softening during hot compression. The effects of temperature and strain rate on the strain and stress corresponding to peak point (ξp and θp) of flow curve were analyzed individually. It is realized that, they increase with strain rate and decrease with temperature. The relationship between Zener-Hollomon parameter (Z) and ξp was investigated and the equation ofξp =4.3×10-4Z0.14 was proposed. The strain for the maximum rate of DRX (ξmax) was determined under different deformation conditions. Therefore, it is realized that it increases with Z parameter and vise versa. On the basis of obtained results, the equation ofξmax =9.5×10-4Z0.12 was proposed.
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    Mechanical Properties of V-, Nb-, and Ti-bearing As-cast Microalloyed Steels
    J.Rassizadehghani, H.Najafi, M.Emamy, G.Eslami-Saeen
    J. Mater. Sci. Technol., 2007, 23 (06): 779-784. 
    Abstract   HTML   PDF (1658KB)
    The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indicated that good combinations of strength and ductility could be achieved by V and Nb additions. While the yield strength and UTS (ultimate tensile strength) increased up to the range of 378–435 MPa and 579–596 MPa, respectively in the microalloyed heats, their total elongation ranged from 18% to 23%. The presence of Ti, however, led to some reduction in the strength. Microstructural studies including scanning electron microscopy (SEM) and optical microscopy revealed that coarse TiN particles were responsible for this behavior. The Charpy impact values of all compositions indicated that microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that the increase in the hardness of coarse ferrite grains due to the precipitation hardening is the main reason for brittle fracture.
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    Improvement of Intergranular Stress Corrosion Crack Susceptibility of Austenite Stainless Steel through Grain Boundary Engineering
    Weizhong JIN, Sen YANG, Hiroyuki KOKAWA, Zhanjie WANG, Yutaka S.Sato
    J. Mater. Sci. Technol., 2007, 23 (06): 785-789. 
    Abstract   HTML   PDF (1372KB)
    Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.
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    Microstructures and Mechanical Properties of Si-Al-Mn TRIP Steel with Niobium
    Zhengyou TANG, Hua DING, Linxiu DU, Long LI
    J. Mater. Sci. Technol., 2007, 23 (06): 790-794. 
    Abstract   HTML   PDF (907KB)
    Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10-2 to 10-4 s-1, the volume fraction of transformed martensite from retained austenite, as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400oC. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.
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    Phase and Microstructure Analysis of Cu-Cr-Zr Alloys
    Huaqing LI, Shuisheng XIE, Xujun MI, Pengyue WU
    J. Mater. Sci. Technol., 2007, 23 (06): 795-800. 
    Abstract   HTML   PDF (2449KB)
    Phases of Cu-(0.4%–2.0%) Cr-(0.05%–0.16%) Zr alloys were analyzed in both as cast and deformed state. Solute-rich clusters of Cr, which was supposed to form during aging treatment, were observed in as cast state; along with the morphology character, corresponding preferential orientation of Cr phase in as cast state was also investigated. Precipitates were observed to distribute in the matrix with a bimodal distribution, viz. coarse precipitates with dimension larger than several hundred nanometers and fine precipitates with size of 2– 10 nm. Three types of intermetallics, the common compound of Cu51Zr14, correspondingly infrequent Cu5Zr and rare Cu8Zr3, were characterized in different samples.
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    Energy Dissipation and Apparent Viscosity of Semi-solid Metal during Rheological Processes Part II: Apparent Viscosity
    Wen LIU, Shuming XING, Peiwei BAO, Milan ZHANG, Liming XIAO
    J. Mater. Sci. Technol., 2007, 23 (06): 801-805. 
    Abstract   HTML   PDF (1127KB)
    This study investigated the rheological properties of semi-solid metal. An analytical model of apparent viscosity was built up based on analysis of energy dissipation during rheological processes such as slurry preparing, delivering and model filling. The rheological properties of SSM (semi-solid metal) slurry was described by an analytical model in terms of microstructural parameters, which consist of effective solid fraction, particle size and shape, and flow parameters such as mean velocity, fluctuant velocity and relative velocity between liquid and solid phase. The model was verified in the experiment of A356 alloys with a coaxial double-bucket rheometer. And the maximum relative error between the theoretical value and measured one is less than 10%. The results of experiment and theoretical calculation also indicate that the microstructural parameters and flow parameters are two major factors that affect the apparent viscosity of semi-solid alloys, and fluctuant velocity and relative velocity between liquid and solid phase are the key factors to distinguish between steady and transient rheological properties.
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    Effects of High Magnetic Field on Solidification and Corrosion Behaviors of Magnesium Alloy
    Canfeng FANG, Xingguo ZHANG, Hai HAO, Shouhua JI, Junze JIN
    J. Mater. Sci. Technol., 2007, 23 (06): 806-810. 
    Abstract   HTML   PDF (2535KB)
    The solidification behaviors of AZ61 magnesium alloy under a high magnetic field were studied. The corrosion property of AZ61 alloy was investigated in a solution of 3.5 mol/L NaCl by measuring electrochemical polarization. The results show that the high magnetic field can refine microstructure and benefit aluminum transfer. The crystal of α-Mg is induced to orient with their c-axis parallel to the magnetic field. The corrosion studies indicate that different crystal plane of magnesium has different corrosion property. The passivating films on the a- and b-planes have higher corrosion resistance than that on the c-plane. Aligned structure affects the corrosion property of AZ61 magnesium alloy.
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    Solderability of Electrodeposited Fe-Ni Alloys with Eutectic SnAgCu Solder
    Jianjun GUO, Lei ZHANG, Aiping XIAN, J.K.Shang
    J. Mater. Sci. Technol., 2007, 23 (06): 811-816. 
    Abstract   HTML   PDF (1043KB)
    Solderabilities of electrodeposited Fe-Ni alloys with SnAgCu solder were examined by wetting balance measurements and compared to those of pure Ni and pure Fe platings. Excellent solderability was found on the Ni-52Fe plating as both the wetting force and kinetics approached or exceeded those on the pure Ni. However, upon further increase in Fe content to 75 at. pct, the solderability of the alloy was severely degraded even though it was still better than that of the pure Fe plating. X-ray photoelectron spectroscopy showed that such a strong dependence of solderability on Fe content is related to the much thinner, incomplete oxide coverage of Ni-rich plating surface.
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    Effect of Welding Parameters on Dilution and Weld Bead Geometry in Cladding
    M.Nouri, A.Abdollah-zadeh, F.Malek
    J. Mater. Sci. Technol., 2007, 23 (06): 817-822. 
    Abstract   HTML   PDF (2428KB)
    The effect of pulsed gas metal arc welding (GMAW) variables on the dilution and weld bead geometry in cladding X65 pipeline steel with 316L stainless steel was studied. Using a full factorial method, a series of experiments were carried out to know the effect of wire feed rate, welding speed, distance between gas nozzle and plate, and the vertical angle of welding on dilution and weld bead geometry. The findings indicate that the dilution of weld metal and its dimension i.e. width, height and depth increase with the feed rate, but the contact angle of the bead decreases first and then increases. Meantime, welding speed has an opposite effect except for dilution. There is an interaction effect between welding parameters at the contact angle. The results also show forehand welding or decreasing electrode extension decrease the angle of contact. Finally, a mathematical model is contrived to highlight the relationship between welding variables with dilution and weld bead geometry.
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    A Novel Duplex Low-temperature Chromizing Process at 500oC
    Huiliang CAO, Cuilan WU, Jiangwen LIU, Chengping LUO, Ganfeng ZOU
    J. Mater. Sci. Technol., 2007, 23 (06): 823-827. 
    Abstract   HTML   PDF (720KB)
    An optimized low-temperature chromizing process at 500oC was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive dposition and diffusion (TRD) chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It was found that the chromizing speed at 500oC was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1μm in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500oC for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.
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    Density and Mechanical Properties of Aluminum Lost Foam Casting by Pressurization during Solidification
    Bokhyun KANG, Yongsun KIM, Kiyoung KIM, Gueserb CHO, Kyeonghwan CHOE, Kyongwhoan LEE
    J. Mater. Sci. Technol., 2007, 23 (06): 828-832. 
    Abstract   HTML   PDF (933KB)
    Porosity is thought to be severe in aluminum alloy castings produced by lost foam process due to the pyrolysis of the polystyrene foam pattern during pouring, which results in detrimental effect in mechanical property. The slow solidification rate promotes the formation of gassing pin holes, and relative weakness of the thermal gradients can cause micro-shrinkage if the outline of the part complicates feeding in the lost foam casting. One of the methods to eliminate the porosity is to apply high pressure to the molten metal like an isostatic forging during solidification. Fundamental experiments were carried out to evaluate the effect of the external pressure on the porosity and mechanical properties of A356.2 alloy bar in the lost foam casting. Solidification time and porosity decreased with increasing the applied pressure during solidification. Applying external pressure was effective in decreasing the porosity and increasing the elongation of the lost foam casting.
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    Piezoelectric Properties of (Na0.5K0.5-xLix)NbO3 Ceramics
    Peng QI, Jinfeng WANG, Baoquan MING, Juan DU, Xinghua LIANG, Limei ZHENG
    J. Mater. Sci. Technol., 2007, 23 (06): 833-836. 
    Abstract   HTML   PDF (1191KB)
    Lead-free piezoelectric ceramics (Na0.5K0.5-xLix)NbO3 (x=0.057–0.066) were synthesized by an ordinary sintering technique. Substituting Li for K can lead to structural distortion, which improves the Curie temperature (TC) greatly. By adding appropriate LiNbO3 content, piezoelectric constant d33 values reach 202–212 pC/N. Electromechanical coefficients of the planar mode reach 44.4%–46.8%. The dielectric loss is below 2.6%, which is much lower than reported (about 50%). The TC of (Na0.5K0.5-xLix)NbO3 (x=0.057–0.066) is in the range of 490–510oC, at least 70oC higher than that of pure (Na0.5K0.5)NbO3 ceramics. The results show that (Na0.5K0.5-xLix)NbO3 ceramic is a kind of good lead-free high-temperature piezoelectric material.
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    Processing of Ceramic Based Nanocomposite Using α-Al2O3 Powder and FeCl2 Solution as Starting Materials
    Mohamed M.EL-Sayed Seleman
    J. Mater. Sci. Technol., 2007, 23 (06): 837-842. 
    Abstract   HTML   PDF (840KB)
    Alumina-iron nanocomposite powders were prepared by a two-step process. In the first step, α-Al2O3-FeCl2 powder mixture was formed by mixing α-Al2O3 powders with FeCl2 solution followed by drying. In the second step, the FeCl2 in the dry power mixture was selectively reduced to iron particles. A reduction temperature of 750oC for 15 min in dry H2 was chosen based on the thermodynamic calculations. The concentration of iron in FeCl2 solution was calculated to be 20 vol. pct in the final composite. Two techniques were used to produce composite bulk materials. The Al2O3nanocomposite powders were divided to two batches. The first batch of the produced mixture was hot pressed at 1400oC and 27 MPa for 30 min in a graphite die. To study the effect of oxygen on the Al2O3/Fe interface bonding and mechanical properties of the composite, the second batch was heat treated in air at 700oC for 20 min to partially oxidize the iron particles before hot pressing. Characterization of the composites was undertaken by conventional density measurements, X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe micro analysis (EPMA). The suggested processing route (mixing, reduction and hot pressing) produces ceramic-metal nanocomposite much tougher than the pure Al2O3. The fracture strength of the produced Al2O3/Fe nanocomposite is nearly twice that of the pure Al2O3. The presence of spinel phase, FeAl2O4, as thick layer around the Fe particles in the Al2O3 matrix has a detrimental effect on interfacial bonding between Fe and Al2O3 and the fracture properties of the composite.
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    Effect of ZrSiO4 on the Friction Performance of Automotive Brake Friction Materials
    Mustafa BOZ, Adem KURT
    J. Mater. Sci. Technol., 2007, 23 (06): 843-850. 
    Abstract   HTML   PDF (4837KB)
    Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy (SEM), and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820oC. Density of the final samples decreased with increasing the amount of reinforcing elements (ZrSiO4) before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements (ZrSiO4). With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0, 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4showed abrasive wear behaviour, increasing the amount of ZrSiO4resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4showed the best results.
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    Lamellar Spacing Selection in Regular Eutectic Solidification at Low Velocity
    Guanghui MENG, Xin LIN, Weidong HUANG
    J. Mater. Sci. Technol., 2007, 23 (06): 851-854. 
    Abstract   HTML   PDF (412KB)
    Based on the Jackson and Hunt’s analysis, the selection of lamellar spacing in regular eutectics was reexamined at low velocity. The isothermal assumption was released and the effective interface undercooling was determined by the weighted average of the eutectic phases. It is found that the lamellar spacing minimized the effective interface undercooling depends only on the intrinsic characteristics of a given system at a fixed velocity. In addition, the selection of lamellar spacing is related to the relationship between the average interfacial undercoolings of the eutectic phases and the lamellar spacing. The selected lamellar spacing obviously deviated from that predicted by the Jackson and Hunt’s analysis if the variation of the average interfacial undercoolings of the solid phases with the lamellar spacing was markedly different at a constant growth rate.
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    Growth, Structural and Microhardness Studies on New Semiorganic Single Crystals of Calcium Para Nitrophenolate Dihydrate
    C.Vesta, R.Uthrakumar, C.Justin Raj, A.Jonie Varjula, J.Mary Linet, S.Jerome Das
    J. Mater. Sci. Technol., 2007, 23 (06): 855-859. 
    Abstract   HTML   PDF (643KB)
    Good quality crystals of calcium p-nitrophenolate (NPCa) were grown from saturated solution by slow evaporation method. The crystal structure analysis and the molecular arrangement of these crystals were determined using X-ray diffraction (XRD). From single crystal XRD studies, NPCa is found to be crystallized in the monoclinic system with a space group P21/n. The functional groups of the material were confirmed qualitatively by FTIR (Fourier transform infrared spectroscopy) spectral analysis. Optical absorption studies reveal the absorption region and microhardness studies were carried out to confirm the mechanical behaviour of the crystals.
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    High Temperature Thermal Physical Properties of High-alumina Fibrous Insulation
    Boming ZHANG, Shuyuan ZHAO, Xiaodong HE, Shanyi DU
    J. Mater. Sci. Technol., 2007, 23 (06): 860-864. 
    Abstract   HTML   PDF (700KB)
    The thermal properties of high-alumina fibrous insulation which filled in metallic thermal protection system were investigated. The effective thermal conductivities of the fibrous insulation were measured under an atmospheric pressure from 10-2 to 105 Pa. In addition, the changes of the specific heat and Rosseland mean extinction coefficient were experimentally determined under various surrounding temperatures up to 973 K. The spectral extinction coefficients were obtained from transmittance data in the wavelength range of 2.5– 25 μm using Beer’s law. Rosseland mean extinction coefficients as a function of temperature were calculated based on spectral extinction coefficients at various temperatures. The results show that thermal conductivities of the sample increase with increasing temperature and pressure. Specific heat increases as temperature increases, which shows that the capacity of heat absorption increases gradually with temperature. Rosseland mean extinction coefficients of the sample decrease firstly and then increase with increasing the temperature.
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ISSN: 1005-0302
CN: 21-1315/TG
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