Investigation on the Formation Mechanism of Ordered Carbide (FeMn)_3AlC in the Al Added Twinning-Induced Plasticity Steels

The spinodal composition zone in Al added Fe-Mn-Al-C twinning-induced plasticity(TWIP) steels can be determined by contents of Al and C and aging temperature together, based on the thermodynamic analysis. Precipitation of ordered(FeMn)_3AlC carbide by the mechanism of spinodal decomposition occurs in the C-rich and Al-rich zone with low aging temperature. Increase of aging temperature shrinks spinodal composition zone to the high Al and C contents. As a result, the precipitation of(FeMn)_3AlC carbide alters from spinodal decomposition to classical nucleation-growth manner gradually. Further calculation indicates that the diffusion of Al can play a key role in determining the growth rate of(FeMn)_3AlC carbide at high aging temperature.     

Fe-30Mn-11Al-1C合金的调幅分解

通过金相、XRD、透射电镜和显微硬度,分析了Fe-30Mn-11A1-1C合金在450～750℃温度区间时效的组织和硬度的变化规律,研究结果表明时效温度低于450℃奥氏体难以析出第二相,其硬度变化也不大;在550～750℃时效2h,奥氏体晶内产生调幅分解,晶界析出Fe3Al,电镜可观察到典型的调幅结构,随时效温度升高调幅结构波长变大;在650℃经2h时效,有βMn析出;调幅分解及析出相都可以提高合金硬度,但析出物粗化使硬度明显降低．     

Study on Oxidation Activity of CuCeZrO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Doped with K for Diesel Engine Particles in NO/O<Subscript>2</Subscript>

CuCeZrO_x and KCuCeZrO_x catalysts were synthesized and coated on the blank diesel particulate filter (DPF) substrate and a particulate matter (PM) loading apparatus was used for soot loading. The catalytic performances of soot oxidation were evaluated by temperature programmed combustion (TPC) test and characterization tests were conducted to investigate the physicochemical properties of the catalysts. The reaction mechanism in the oxidation process was analyzed with diffuse reflectance infrared Fourier transform spectroscopy. The results demonstrated that CuCeZrO_x catalyst exhibited high activities of soot oxidation at low temperature and the best results have been attained with Cu_0.9Ce_0.05Zr_0.05O_x over which the maximum soot oxidation rate decreased to 410 °C. Characterization tests have shown that catalysts containing 90% Cu have uniformly distributed grains and small particle sizes, which provide excellent oxidation activity by providing more active sites and forming a good bond between the catalyst and the soot. The low-temperature oxidation activity of soot could be further optimized due to the excellent elevated NO’s conversion rate by partially substituting Cu with K. The maximum particle oxidation rate can be easily realized at such a low temperature as 347°C.     

Research on reduction of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> by biomass sawdust

The research on biomass reduction of Fe₂O₃ was carried out by using sawdust as reductant. The direct reducing agents in the biomass magnetization process were determined by comparing various biomass pyrolysis products with the reduction degree (divalent iron content in total iron), reduction temperature range and valence change of Fe₂O₃ in the reduction process. The microstructure variation of Fe₂O₃ at different stages was also analyzed by scanning electron microscopy (SEM). Nonisothermal thermogravimetric analysis (TGA) was applied to explore the thermal reduction process. The results show that the direct reducing substances in the biomass reaction with Fe₂O₃ are H₂ and bio-oil, and the reduction process can be divided into two steps: biomass pyrolyzing to release H₂ and bio-oil, and reductive volatiles reacting with Fe₂O₃. The two steps are relatively independent. The kinetic of the reduction reaction follows a first-order reaction kinetic model, with 88.99 kJ/mol activation energy and 9.55 × 10⁸ min^?1 frequency factor.     

Catalytic Combustion of Lean Methane Assisted by Electric Field over Pd/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Catalysts at Low Temperature

A series of Pd/Co₃O₄ catalysts were prepared by Self-Propagating High-Temperature Synthesis (SHS) method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co₃O₄ catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co₃O₄ catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature-programmed reduction (H₂-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS), the mechanism of catalytic oxidation of CH₄ over Pd/Co₃O₄ catalysts in electric field was proposed. The catalytic combustion of CH₄ occurs only when the temperature is higher than 250 °C normally, but when electric field was applied, the whole process of CH₄ oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co₃O₄ to release the lattice oxygen, resulting in the increase of PdO_x and the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH₄. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.     

Research on electron beam welding of in situ TiB<Subscript>2p</Subscript>/ZL101 composite

Electron beam welding of in situ TiB_2p reinforced aluminum composites was studied. The results show that no obvious pores or cracks is presented in the weld seam. The grains in the weld seam are remarkably refined and TiB₂ particles distribute much more homogeneously than that in base metal. The hardness values of fusion zone and heat affected zone (HAZ) are both increased in comparison with that of base metal. There are no interface reactions between TiB₂ particle and Al matrix. This results supply the evidence that the novel TiB_2p reinforced aluminum composites can be well joined with the electron beam welding.     

Evolving mechanism of eutectic carbide in as-cast AISI M2 high-speed steel at elevated temperature

AbstractThe evolution in type,size and shape of carbides in as-cast American Iron and Steel Institute(AISI) M2 high-speed steel before and after annealing were investigated.The micromechanism which was responsible for those changes was also analyzed and discussed.At the initial stage of reheating,metastable M2C-type carbide decomposed continuously.M6C-type carbide nucleated at the interface of M2C/γfirstly and grow from surface to center.Then MC-type carbide nucleated at both surface of M6C/M6C and inner of M6C.With the increasing decomposition of the metastable M2C-type carbide,the rod-shaped construction of eutectic carbide began necking,fracturing and spheroidizing gradually.Held enough time or reheated at higher temperature,particle-shaped product aggregated and grew up apparently,while secondary carbide precipitated in cell and grew up less sig- nificantly than the former.Based on the above microstructural observation,the thermodynamic mechanism for decomposition of M2C carbide,for spheroidization of products,and for the growth of particles were analyzed.The rate equations of carbides evolution were derived,too.It shows that the evolving rate is controlled by diffusion coefficients of alloy atoms,morphology of eutectic carbides and heating temperature.     

TiCx／Fe（Al，Ti）复合材料的常压制备及性能

通过原位反应常压烧结法制备了一种新型的TiCx／Fe（Al,Ti）复合材料,并对Ti3AlC2与Fe的原位反应途径及制备工艺和性能进行了研究,结果表明,Ti3AlG从760℃附近就开始与Fe初步发生原位反应,生成TiCY相．随着烧结温度达到1100℃,Ti3A1G相的衍射峰完全消失,随着温度继续升高到1400℃的烧结温度范围内,所生成的复合材料物相均保持为TiG和Fe（A1,Ti）固溶体不变．反应后,原料中微米尺寸的Ti3AlG颗粒分裂成尺寸约500nm左右的片状小颗粒,各小颗粒与Fe基体紧密连接的．而复合材料的力学性能随着Ti,～C2的体积含量发生变化,当Ti3AlG含量达到时20％,复合材料抗弯强度达到最大为266MPa．     

Combustion optimization model for NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> reduction with an improved particle swarm optimization

Abstract: This paper focuses on the combustion optimization to cut down NO _x emission with a new strategy. Firstly, orthogonal experimental design (OED) and chaotic sequences are introduced to improve the performance of particle swarm optimization (PSO). Then, a predicting model for NO _x emission is established on support vector machine (SVM) whose parameters are optimized by the improved PSO. Afterwards, a new optimization model considering coal quantity and air quantity along with the traditional optimization variables is established. At last, the operating parameters are optimized by the improved PSO to cut down the NO _x emission. An application on 600MW unit shows that the new optimization model can cut down NO _x emission effectively and maintain the load balance well. The NO _x emission optimized by the improved PSO is lowest among some state-of-the-art intelligent algorithms. This study can provide important guides for the low NO _x combustion in the power plant.     

Formation of nanometer coherent structures during spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys

The nanometer coherent structure evolution of spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys is investigated by the microscopic phase field kinetic model. The results show that the concentration and long-range order parameters all continuously change towards to their equilibrium values during phase transformation. With the increase of elastic interaction energy, the anisotropy along [01] or [10] elastic soft direction is more obvious and the time reaching equilibrium state is also shortened. According to the results, the formation of nanometer coherent structures during phase transformation is composed of the initial decreasing stage of order degree stage, the incubation stage, the continuous increasing stage of concentration order parameter and long-range order parameter, and the later stable stage. The spinodal decomposition and ordering is interaction; the initial ordering stage is a necessary condition of the coexistence phase transformation. The nanometer coherent structures are not found to grow during the whole phase transformation. The simulation results are in accordance with the results in experiment obtained by the aging treatment in Fe-24Al alloys.     

Coupled heat and mass transfer analysis of NH<Subscript>3</Subscript>-H<Subscript>2</Subscript>O falling film absorption on inner tube surface with low solution flow rates

NH₃-H₂O falling film absorption usually takes place with low solution flow rate in real absorption refrigeration system. An experimental study of inner vertical absorption is carried out for the consideration of air-cooling absorber. Variable working conditions are tested to evaluate the heat and mass transfer performances.The traditional evaluation method based on log-mean-temperature（concentration） difference is criticized for its lack of theoretical basis while simultaneous heat and mass transfer process occurs. A new method proposed by Kim and Infante Ferreira is modified to evaluate the experimental results with reasonable assumptions. The method is based on the derivation of coupled heat and mass transfer differential equations of NH₃-H₂O absorption process.The analysis of the same experimental data shows that the new method realizes better consistency with smaller error, especially in heat transfer aspect. Heat and mass transfer performance is enhanced with the increase of solution Reynolds number. Sub-cooling of inlet weak solution also has positive influence on the absorption process,which should be evaluated by the new method correctly. Two correlations are developed to evaluate both Nusselt and Sherwood numbers for the design of air-cooling absorber.     

Scale-invariant occupancy of phase space and additivity of nonextensive entropy <Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">q</Emphasis></Subscript>

Phase space can be constructed for N equal and distinguishable binary subsystems which are correlated in a scale-invariant manner. In the paper, correlation coefficient and reduced probability are introduced to characterize the scale-invariant correlated binary subsystems. Probabilistic sets for the correlated binary subsystems satisfy Leibnitz triangle rule in the sense that the marginal probabilities of N-system are equal to the joint probabilities of the (N −1)-system. For entropic index q ≠ 1, nonextensive entropy S _q is shown to be additive in the scale-invariant occupation of phase space.     

Monte Carlo simulation of B2-L2<Subscript>1</Subscript> ordering transitions in Au-Cu-Al alloy systems

The B2-L2₁ ordering transitions in Au-Cu-Al shape-memory alloys are studied by the Monte Carlo exchange simulations, where a set of the first, the second and the third nearest-neighbor mixing potentials for Cu-Al in the Au-Cu-Al alloys are calculated from first principals using the Connolly-Williams methods. To ensure the phase stability of the β-Au-Cu-Al, the investigation includes the range of compositions Au₂Cu_1−x Al_1+x (−0.15 ⩽ x ⩽ 0.15). The B2-L2₁ transition temperatures are predicted, and are in agreement with the experimental results. The atomic ordering around vacancy of the L2₁ structure is further discussed.     

Effect of oil shale on Na+ solidification of red mud-fly ash cementitious material

Red mud-fly ash based cementitious material mixed with different contents of oil shale calcined at 700°C is investigated in this paper. The effect of active Si and Al content on the solidification of Na⁺ during the hydration process is determined by using X-ray diffraction (XRD), ²⁷Al and ²⁹Si magic-angle-spinning nuclear magnetic resonance (MAS-NMR), infrared (IR), scanning electronic microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is shown that the content of oil shale has a remarkable effect on the solidified content of Na⁺. The hydration process generates a highly reactive intermediate gel phase formed by co-polymerisation of individual alumina and silicate species. This kind of gel is primarily considered as 3D framework of SiO₄ and AlO₄ tetrahedra interlinked by the shared oxygen atoms randomly. The negative charges and four-coordinated Al inside the network are mainly charge-balanced by Na⁺. The solidifying mechanism of Na⁺ is greatly attributed to the forming of this kind of gel.     

Numerical simulation of thermal and iron ore reduction conditions in pre-reduction shaft furnace based on reducing gas composition and temperature

Based on the principles of mass, momentum and heat transfers between the reducing gas and the iron ore solid, a two-dimensional mathematical model for above two phases is established to study the influences of reducing gas composition on thermal and reduction conditions in pre-reduction shaft furnace with the temperature ranging from 1 023 to 1 223K. Due to the strong endothermic effect of iron ore reduction participated by hydrogen (H₂), increasing the ratio of carbon monoxide (CO) to H₂ enlarges high temperature zone under present calculation conditions, thus improves reduction efficiency inside the furnace. In addition, replacing of the reducing gas with an appropriate proportion of nitrogen (N₂) featuring the same temperature has a potential to reduce fuel consumption by as much as 6.5% while the products of similar quality are yielded.     

Recycling of aluminum from fibre metal laminates

Recycling of aluminum alloy scrap obtained from delaminated fibre metal laminates (FMLs) was studied through high temperature refining in the presence of a salt flux. The aluminum alloy scrap contains approximately mass fraction w(Cu) = 4.4%, w(Mg) = 1.1% and w(Mn) = 0.6% (2024 aluminum alloy). The main objective of this research is to obtain a high metal yield, while maintaining its original alloy compositions. The work focuses on the metal yield and quality of recycled Al alloy under different refining conditions. The NaCl-KCl salt system was selected as the major components of flux in the Al alloy recycling. Two different flux compositions were employed at NaCl to KCl mass ratios of 44:56 and 70:30 respectively, based on either the eutectic composition, or the European preference. Different additives were introduced into the NaCl-KCl system to study the effect of flux component on recycling result. Although burning and oxidation loss of the alloying elements during re-melting and refining take place as the drawbacks of conventional refining process, the problems can be solved to a large extent by using an appropriate salt flux. Experimental results indicate that Mg in the alloy gets lost when adding cryolite in the NaCl-KCl salt system, though the metal yield can reach as high as 98%. However, by adding w(MgF₂) = 5% into the NaCl-KCl salt system (instead of using cryolite) all alloying elements were well controlled to its original composition with a metal yield of almost 98%.     

Friction and wear performances of hot filament chemical vapor deposition multilayer diamond films coated on silicon carbide under water lubrication

Tribological properties of chemical vapor deposition (CVD) diamond films greatly affect its application in the mechanical field. In this paper, a novel multilayer structure is proposed, with which multilayer diamond films are deposited on silicon carbide by hot filament CVD (HFCVD) method. The different micrometric diamond grains are produced by adjusting deposition parameters. The as-deposited multilayer diamond films are characterized by scanning electron microscope (SEM) and white-light interferometry. The friction tests performed on a reciprocating ball-on-plate tribometer suggest that silicon carbide presents the friction coefficient of 0.400 for dry sliding against silicon nitride (Si₃N₄) ceramic counterface. With the water lubrication, the corresponding friction coefficients of silicon carbide and as-deposited multilayer diamond films further reduce to 0.193 and 0.051, respectively. The worn surfaces indicate that multilayer diamond films exhibit considerably high wear resistance.     

Thermodynamic analyse on equilibrium precipitation phases and composition design of Al-Zn-Mg-Cu alloys

The solidification paths of Al-Zn-Mg-Cu alloys and its precipitation behavior are analyzed using software package JMatPro 6.0 for material property simulation of Al-base alloys. The microstructures of the experimental alloys are analyzed; the experimental results of microstructural analysis are in agreement with the thermodynamic prediction. Through orthogonal experimental method, this paper designs the composition of Al-Zn-Mg-Cu alloys by studying the variation of ?? (MgZn₂) phase, S (Al₂CuMg) phase, T (AlZnMgCu) phase amount and precipitation temperatures with different Zn, Mg and Cu contents. It is found that with the optimum mass fraction of Zn of 6.7%, Mg of 2.2%?C2.5% and Cu of 1.6%?C2.0%, the mass fraction of ?? phase can be up to 8.7%?C9.22% and that of S phase and T phase can be lower than 0.5%.     

Photothermal effect for Fe3O4 nanoparticles contained in micelles induced by near-infrared light

Near infrared (NIR) light induced photothermal effect for Fe₃O₄ nanoparticles, contained in Pluronic F127 micelles, has been studied and it exhibits high photothermal converting efficiency. Heat is found to be rapidly generated in micelles containing Fe₃O₄ nanoparticles by NIR laser irradiation. Upon irradiation at 808 nm light and with mass concentration of Fe₃O₄ nanoparticles in 4 g/L, the micelle temperature increase is higher than 34°C for 10min irradiation. The maximum temperature of micelles containing Fe₃O₄ nanoparticles in 4 g/L reaches 62°C.     

Phase transitions relating to the pozzolanic activity of electrolytic manganese residue during calcination

Electrolytic manganese residue（EMR） is generated from electrolytic manganese metal（EMM） industry, and its disposal is currently a serious problem in China.The EMR were calcined in the interval 100—900℃to enhance their pozzolanic activity and characterized by the differential thermal analysis-thermogravimetry（TGDTA）, X-ray diffraction（XRD）,infra-red（IR） and chemical analysis techniques with the aim to correlate phase transitions and structural features with the pozzolanic activity of calcined EMR.Prom the phase analysis and compressive strength results,it is found that the EMR calcined within 700—800℃had the best pozzolanic activity due to the decomposition of poorly-crystallized CaSO₄ under the reducing ambient created by the decomposition of（NH₄）₂SO₄.The appearance of reactive CaO mainly contributes to the good pozzolanic activity of EMR calcined within 700—800℃.The crystallinity of Mn₃CO₄ increases leading an unfavourable effect on the pozzolanic behaviour of EMR calcined at 900℃.The developed pozzolanic material containing 30%（mass fraction） EMR possesses compressive strength properties at a level similar to 42.5^# normal Portland cement,in the range of 41.5—50.5 MPa.Besides,leaching results show that EMR blend cement pastes have excellent effect on the solidification of heavy metals.