Effect of addition temperature on dispersion behavior and grain refinement efficiency of MgO introduced into Mg alloy

The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematically studied by microstructure characterization,thermodynamic calculation,and analysis of solidification curves.The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgOp addition temperature is increased from 720 to 810℃,exhibiting a minimum value of 136μm at 780℃.The improved grain refinement efficiency with increasing MgOp addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgOp and Mg melt.Furthermore,a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.

微晶玻璃陶瓷复合材料的研制

采用与基体相匹配的微晶玻璃配方,合理的晶核化温度制度和一次烧成工艺,制备出具有微晶玻璃性能和装饰效果的微晶玻璃陶瓷复合装饰材料。

Kinetic nucleation of primary α(Al) dendrites in Al-7%Si-Mg cast alloys with Ce and Sr additions

Nucleation of dendritic primaryα（Al） phase with addition of element Ce and Sr in hypoeutectic Al-7%Si-Mg cast alloy was investigated by using differential scanning calorimetry （DSC） and scanning electron microscopy. DSC results were used to calculate the activation energy and nucleation work of primaryα（Al） phase. The results show that the values of activation energy and nucleation work are decreased and the nucleation frequency is increased with the additions of Ce and Sr to the alloys. Moreover, the grain size of dendriticα（Al） phase is well refined, and the nucleation temperatures of primaryα（Al） dendrites are decreased with the additions of Ce and Sr. The effects of elements Ce and Sr additions on kinetic nucleation of primary α（Al） phases were also discussed in hypoeutectic Al-7%Si-Mg cast alloy.

Grain refining mechanism of Al-3B master alloy on hypoeutectic Al-Si alloys

Al-3B master alloy is a kind of efficient grain refiner for hypoeutectic Al-Si alloys. Experiments were carried out to evaluate the effect of undissolved AlB2 particles in Al-3B master alloy on the grain refinement of Al-7Si. It is found that the number and the settlement of AlB2 particles in the melt all have effect on the grain refining efficiency. On the basis of experiments and theoretical analysis, a new grain refinement mechanism was proposed to explain the grain refinement action of Al-3B on hypoeutectic Al-Si alloys. The formation of ＇Al-AlB2＇ shell structure is the direct reason for grain refinement and the undissolved AlB2 particles is the indirect nucleating base for subsequent α（Al） phase.

Migration behavior of solidification nuclei in pure Al melt under effect of electric current pulse

A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.

Improving in plasticity of orthorhombic Ti_2AlNb-based alloys sheet by high density electropulsing

In order to optimize the ductility of orthorhombic Ti2AlNb-based alloys sheet,Ti22Al27Nb sheet was treated by high density electropulsing（J max =6.80 7.09 kA/mm2,tp =110 μs） under ambient condition.Microstructures were observed by SEM,and the tensile properties were also studied using uniaxial tension tests.The experimental results show that electropulsing can refine the microstructures of Ti22Al27Nb sheets.The specimen with the fine and homogeneous microstructures has good plasticity,and its elongation reaches 19.4%.The mechanism about the effect of electropulsing treatment on the microstructure of Ti22Al27Nb sheets was discussed.It was thought that the increase in nucleation rate during phase transformation and a very short treating time were regarded as the main reasons of producing smaller grains and increase in the plasticity by electropulsing.

高浓度镁对KCl浮选的影响(第一部分):实验室试验

在由巴西CVRD公司Taquari Vassouras矿山钾盐矿石制备的盐水溶液中进行了粗粒KCl浮选试验,以确定在高浓度Mg2+存在时,钾盐的可浮性。在将Mg2+添加到盐水中时,会产生细粒盐沉淀物,它们主要由NaCl(90%以上)组成,但也有KCl存在。将Mg2+添加到浮选给矿中会在粗粒KCl表面上产生NaCl和KCl细粒晶核。这种表面细粒晶体在粗粒KCl表面上的晶核化可以提高粗粒KCl的浮选回收率。但是,盐水中的细粒晶体沉淀物(主要是NaCl,也有一些KCl)会与粗粒KCl竞争吸附捕收剂,使粗粒KCl的可浮性降低。在捕收剂添加前,将这些沉淀物除去,就可大幅度增加粗粒KCl对捕收剂的吸附量,从而大幅度提高粗粒KCl的浮选回收率。

高浓度镁对KCl浮选的影响(第二部分):选矿厂试验

在巴西阿拉卡茹的CVRD公司Taquari Vassouras矿山选矿厂中,随着矿浆在浮选回路中的流动,有几个原因影响着粗粒KCl的回收。矿石中光卤石含量的提高会促使细粒NaCl和KCl晶体在粗粒KCl上的沉积。这种作用似乎能稍稍增强粗粒KCl的疏水性,因而会提高粗粒KCl的浮选回收率。随着矿浆中Mg2+浓度的提高,矿浆中细粒NaCl和KCl沉淀物数量开始增加。在这些细粒NaCl晶体表面上有KCl包体存在,同样的,在细粒KCl晶体表面上有NaCl包体存在。它们吸附捕收剂,从而降低了粗粒KCl给矿的疏水性和浮选回收率。为了使粗粒KCl表面上有足够多的捕收剂所覆盖,使其保持很好的可浮性,在捕收剂添加前将细粒沉淀物除去是相当重要的。

电解铝液直接生产超薄箔坯料的熔体质量控制

针对电解铝液直接铸轧坯生产超薄铝箔坯料过程中所存在的质量缺陷,结合铸轧法生产铝箔坯料所采用电解铝液的特点,全面分析了生产过程中铝合金熔体处理工艺对熔体质量的影响因素,并研究制定了相应的铝熔体处理措施。有效改善了熔体质量,消除/减少了电解铝液生产超薄铝箔坯料的质量问题,实现了低成本、高效率、高品质、稳定生产超薄箔坯料的目标。

Studies on the Mechanism of Primary Nucleation of Ciprofloxacin Hydrochloride Monohydrate

A general expression for the relationship between induction periodand supersaturation was developed based on polynuclear approach.Different mechanism of primary nucleation in solution can beillustrated by the expression. The results of induction perioddetermined by laser scattering method shows that the crystallizationof ciprofloxacin hydrochloride monohydrate in water/ethanol oraqueous solution is by the mechanism of primary nucleation followedby one-dimensional diffusion growth, and then on-dimensionalcontinuous or 'birth and spread' growth on crystal face. The growthmechanism on the crystal face is affected by temperature and solvent.

Grain refinement of Mg−Al binary alloys inoculated by in-situ oxidation

Utilizing oxide inclusion to induce heterogeneous nucleation event is an available method to achieve grain refinement.In this study,Mg−Al binary alloys were refined by inoculation of in-situ oxidation process.Results show that MgO and MgAl_(2)O_(4) phases are primary oxide products for Mg−xAl alloys inoculated by in-situ oxidation.For pure Mg and Mg−1Al alloy,MgO is the only oxide product.MgAl_(2)O_(4) is another oxide product for Mg−xAl alloy as Al content increases to 3 wt.%.For Mg−3Al alloy,average grain size significantly decreases from 1135 to 237μm,with a high grain refining ratio of 79.1%.Both MgO and MgAl_(2)O_(4) possess nucleating potency forα-Mg grain.MgAl_(2)O_(4) exhibits a higher nucleating potency due to the lower misfit withα-Mg.The grain refinement of Mg−xAl alloys inoculated by in-situ oxidation process is attributed to heterogeneous nucleation events ofα-Mg grains on MgO or MgAl_(2)O_(4) particles.

Effect of trace boron on grain refinement of commercially pure aluminum by Al-5Ti-1B

The effect of boron content on grain refinement of commercially pure aluminum by Al-5Ti-1B was quantitatively assessed.When the boron content is less than 0.03 wt.%,the refining performance of Al-5Ti-1B gradually is weakened as the boron content increases,which is attributed to the reaction of boron with the Al_(3)Ti interlayer on TiB_(2)and the consumption of solute Ti.On the contrary,when the boron content exceeds 0.03 wt.%,the refining performance of Al-5Ti-1B gradually recovers with increasing boron content,which is related to the formation of primary AlB_(2)particles that provide additional nucleant substrates.

Effect of the CaF_2-fraction in the glass-ceramic with abrasion resistance on crystallization

Investigated the effect of an addition of CaF2 on the crystallization of a glass-ceramic with abrasion resistance. X-ray diffraction, differential thermal analysis and scanning electron microscopy were used to determine the effect. The results showed that a suitable addition of CaF2 promoted crystallization by forming an interme- diate crystalline phase. CaF2 can decrease the temperature and active energy of the base-glass for crystallization. When 4 mass-% of CaF2-fraction is added in the glass, the crystallization temperature and active energy is 936 ℃and 172.75 kJ/mol respectively. When CaF2 is increased to 6 mass-%, the temperature and active energy decrease to 890 ℃ and 88.81 kJ/mol. CaF2 is an efficient nucleating agent for the glass-ceramics with abrasion resistant, the optimal content of CaF2 is about 6 mass-%.

Crystal Structure of Binuclear Oxomolybdenum(V), [Fe(H_2O)_6][Mo_2O_4(EDTA)]·5H_2O

The reduction of an aqueous solution of sodium molybdate by iron powder at low pH value (～0.83), in the presence of ethylenediaminetetraacetate (EDTA) ligand, gives the title compound [Fe(H 2O) 6][Mo 2O 4(EDTA)]·5H 2O 1, which was characterized by elemental analysis, IR and X ray single crystal diffraction techniques. Compound 1 crystallizes in monoclinic system, space group P2 1/c, C 10 H 34 N 2FeMo 2O 23 , M r=798.12, a=8.781(1), b=14.081(1), c=21.353(1) , β= 92\^688(1)°, V = 2637.2(3) 3, Z = 4, D c = 2.010 g·cm -3 , μ = 1.579 mm -1 , F (000)=1608, the final R =0.0530 and wR =0.1271 for 3312 observed reflections. The binuclear oxomolybdenum(V) anion and the six coordinated Fe(II) cation are linked to infinite three dimensional network through several hydrogen bonds towards different directions between crystal waters, Fe(II) cation and Mo(V) anion.

Accurate electrical resistance measurement of the crystallization kinetics of amorphous alloys

An accurate four-line ac electrical resistance measurement (ERM)apparatus was developed. By using the ERM the crystallization kinetics of amorphous Ni80P20, FeZr2, Fe86B14 alloys were investigated. The experimental results show that the ERM can identify the early stage of crystallization in amorphous alloys. The ERM detects a crystallization temperature range obviously wider than the DSC does, indicating that the ERM is more sensitive to the structure evolution in crystallization. For the eutectic or polymorphic crystallization, three distinct processes can be identified from the measured resistance variation: (i) crystal nucleation, (ii) subsequent growth of crystal nuclei, and (iii) coarsening of the crystallites. In the early stage of the primary crystallization, the ERM results reflect the nucleation information as well.

Directing nucleation and growth kinetics in solution-processed hybrid perovskite thin-films

A heightened understanding of nucleation and growth mechanisms is paramount if effective solution processing of organic-inorganic perovskite thin-films for optoelectronic applications is to be achieved. Many fabri- cation techniques have been utilized previously to develop high-performance perovskite layers but there remains an absence of a unifying model that describes accurately the formation of these materials from solution. The present study provides a thorough analysis of nucleation and growth kinetics underpinning the development of hybrid organic-in- organic perovskite thin-films. Through precise control of the perovskite growth conditions the spacing of heteroge- neous nucleation sites was varied successfully from several hundred nanometers to several hundred microns. The crystalline regions surrounding these nuclei were found to comprise clusters of highly-oriented crystal domains exceed- ing 100 pm in diameter. However, no beneficial correlation was found between the size of these well-oriented grain-clus- ters and the optoelectronic performance. The formation of the perovskite microstructure features characteristics of both classical and non-classical growth mechanisms. The insights into perovskite thin-film growth developed by the present study provide clear implications for the development of future hybrid perovskite microstructures.

Melting kinetics of bulk SiC using molecular dynamics simulation

The melting kinetics of bulk SiC is studied by using classical molecular dynamics simulation.The mean square displacement,diffusion coefficient,Lindemann index and non-Gaussian parameter are used to analyze the melt nucleation and macrokinetics in the melting process.Melting occurs when the superheated crystal spontaneously generates many Lindemann particles in which they coalesce together to form melt nucleation inside the crystal.The melting process is similar to the solidification process,but also experiences three processes such as nucleation,growth and relaxation.The melting process can be divided into premelting,accelerated melting and relaxation stages.Using the sectional method can properly reflect the kinetic characteristics of the melting process.