全尾砂料浆磁化絮凝沉降特性

为了提高全尾砂料浆(CTR)的絮凝沉降指标,将磁化处理技术引入到全尾砂料浆沉降试验中,分析自然沉降、磁化沉降、絮凝沉降和磁化絮凝沉降4种条件下全尾砂料浆沉降速度和底流质量浓度的变化特性,探索磁化处理在全尾砂料浆絮凝沉降中的作用机理。结果表明:与未经磁化处理的全尾砂料浆相比,磁化处理后的全尾砂料浆沉降指标达到饱和时,PAC添加量节约40%;相同PAC添加量下,磁化处理后的全尾砂料浆沉降速度提高18~55 cm/h、底流浓度提高约0.8%~2.0%。全尾砂料浆磁化絮凝沉降的最优条件为:磁感应强度0.2 T,料浆速度2 m/s,磁化时间2 min,PAC添加量30 g/t;适合磁化处理条件下,对全尾砂料浆进行磁化处理可明显提高其沉降指标。     

基于响应面法外场作用下全尾砂浓密沉降试验

为提高全尾砂料浆浓密沉降的质量浓度,将超声波引入全尾砂料浆浓密沉降试验中。利用MATLAB模拟超声波在全尾砂料浆中的指向性,进而选取出超声波频率范围。采用Design-Expert软件设计,并分析不同条件下超声波对全尾砂料浆最终质量浓度的影响,以及各因素之间的耦合关系,进而优化超声波作用条件。结果表明:当超声波频率为20~40 kHz时,在砂仓中传播指向性较好;超声波外场作用能显著提高全尾砂料浆的最终质量浓度,当全尾砂自然沉降19.77 min后,施加频率20.02 kHz、功率50 W的超声波为最优作用条件,全尾砂料浆最终质量浓度可达77.51%,比自然沉降的最终质量浓度提高4.60%;在合适的超声场条件下,超声波在提高全尾砂料浆的最终质量浓度具有明显优越性。     

聚羧酸减水剂对超细全尾砂膏体性能的影响

针对超细全尾砂-水泥胶结膏体充填料浆黏性大、和易性差,其满足充填输送要求时充填体强度低的问题,通过不同掺量聚羧酸高效减水剂对膏体料浆流动度、坍落、泌水率及其充填体抗压强度影响的试验研究,并借助XRD能谱分析和电镜扫描(SEM)方法,从微观角度揭示减水剂提到充填体强度机理。结果表明:掺量0.5%(质量分数)的聚羧酸高效减水剂可使质量分数为70%~76%膏体充填料浆的流动度、坍落度有效增加;料浆泌水率明显提高,但不会发生严重离析;充填体微观上水泥水化凝胶更多,尾砂颗粒因水化凝胶"包裹"作用形成更大的晶体颗粒,且颗粒分布更为均匀、孔隙更小、结构更为致密,宏观上初期/长期强度显著提高,最高达50%;同时,减水剂掺量小于0.5%为"安全掺量",对充填体强度不会造成劣化影响。     

全尾砂絮凝沉降的影响因素

全尾砂絮凝沉降过程是膏体充填工艺的重要环节。为考察多因素耦合条件下尾砂絮凝沉降规律,开展全尾砂静态絮凝沉降实验,应用Design-Expert软件分析并筛选影响全尾砂絮凝沉降的重要因素,探究单位面积处理量最大时各重要影响因素的最优值。结果表明:不同影响因素耦合条件下,各絮凝沉降曲线形态基本一致,呈现先迅速下降后趋于水平的趋势。影响絮凝沉降的重要因素为尾砂入料浓度、絮凝剂用量、絮凝剂溶液浓度,其最优值分别为16.02%、28.35 g/t、0.1541%,此时单位面积固体处理量最大,为3.04 t/(m2·h)。     

减水剂对细粒级尾砂膏体流变性的影响

为提高非胶结细粒级尾砂膏体的流动性能,探究不同减水剂对细粒级尾砂膏体料浆流动性的影响,以及絮凝剂对减水剂作用的影响,采用流变仪进行了不同类型、不同用量下减水剂对料浆静态屈服应力的影响实验,通过对比实验和理论分析,解释减水剂的影响机理。结果表明：絮凝剂在常规用量下对尾砂料浆的流动性和减水剂作用效果均具有抑制作用;无机盐类和木质素类减水剂均可显著减小料浆静态屈服应力,同等用量下三聚磷酸钠改善流动性的效果最好;聚羧酸系减水剂在一定用量范围内将增大料浆静态屈服应力,随着用量进一步增加,减水剂将减小料浆静态屈服应力从而改善流动性。最后从聚羧酸分子特性出发,分析不同用量下其改善与降低细粒级尾砂膏体流动性的作用机理。     

基于结构参数的超细尾砂充填料浆双变量流变模型及应用

超细尾砂已成为金属矿山充填处理的最大宗固体废料,流变模型是刻画超细尾砂料浆流动特性及确定管输参数的主要依据.基于超细颗粒絮凝结构形成机制,引入结构参数来描述超细尾砂料浆剪切响应过程.采用旋转黏度计对某矿山质量分数72％、74％、76％和水泥添加量240、260 kg/m3的超细尾砂充填料浆进行24组不同剪切强度下的流变...     

膏体充填中絮凝条件对絮团结构及固液分离效率的影响

尾砂浓密中絮团结构与絮凝效果随絮凝条件变化发生改变,对浓密机内沉降区固液分离效率产生影响,但现有研究少有基于尾砂絮团结构分析絮凝条件产生的影响。为此,本文采用管道絮凝方式,对不同絮凝条件下形成的尾砂絮团结构高清获取,分析絮团等效直径以及絮团分形维数随之变化的规律,并对絮凝后的上清液浊度以及絮团沉降速度开展研究。结果发现,阴离子型聚丙烯酰胺与尾砂颗粒形成的絮团结构最大,絮凝剂单耗、尾砂进料浓度、絮凝剂浓度和流体剪切梯度G对絮团等效直径、絮团分形维数、上清液浊度以及絮团沉降速度产生重要影响。絮凝剂单耗在90～105 g/t、尾砂进料浓度在25%～30%、絮凝剂浓度小于1/10000、流体剪切梯度30～50 s^-1时形成的絮团等效直径超过1000μm、絮团分形维数在1.64～1.68之间、絮团沉降速度均超过9 m/min、浓密机模型内上清液浊度低于50 mg/L,絮团沉降速度加快能够提升浓密机内沉降区固液分离效率,该结论为膏体充填实际生产中控制絮凝条件参数提供了价值参考。     

稳态浓密机全尾砂脱水规律物理模拟

结合沉降和压滤实验研究浓密机内全压力范围下尾砂脱水性能,考察网状结构形成体积分数、压缩屈服应力、干涉沉降系数等参数的变化规律。结果表明:网状结构形成体积分数随絮凝剂单耗增加先升高后降低,单耗20 g/t时网状结构形成体积分数达到最大值;压缩屈服应力随体积分数变化呈幂和指数增长,在低压力区域,絮凝剂单耗对底流体积分数影响较大,在高压力区域,絮凝剂作用逐渐弱化;干涉沉降系数随体积分数变化呈幂增长,在低压力区域,絮凝剂单耗对料浆渗透性影响较大,单耗80 g/t时渗透性良好,在高压力区域,絮凝剂单耗对料浆渗透性影响逐渐弱化。实验范围内,膏体料浆存在脱水拐点,其体积分数为38%～42%。     

全尾砂充填膏体固-流转换阶段的流变行为

全尾砂充填膏体具有多尺度、高浓度颗粒悬浮液的特征,传统黏塑性流变模型是否适应于膏体的流变行为是需要研究的重要问题。本文从传统H-B流体对全尾砂膏体的适应性研究入手,首先建立H-B流体的适应性约束条件,选择适宜多尺度、高浓度膏体的流变测量系统与数据转换方法,采用控制剪切速率(CSR)、控制剪切应力(CSS)两种流变测量模式,开展全尾砂膏体流动曲线测量实验。结果表明:流动曲线在CSR测量模式下具有负斜率现象、CSS测量模式下具有剪切条带现象。传统H-B流体在对应阶段内不再适应于全尾砂膏体流变模型,存在固、流态共存的固-流转换阶段,其范围受临界剪切速率■控制,正比于全尾砂膏体的质量浓度。依据全尾砂膏体出现固-流转换阶段的特征,提出工程流变问题应依据临界剪切速率■区别对待,以及膏体充填流变问题中不同剪切速率范围内全尾砂膏体流变模型的合理形式。     

全尾砂静动态絮凝沉降特性

全尾砂絮凝沉降技术是矿山充填工艺的核心环节.为研究全尾砂静态絮凝沉降特性规律,以进料质量分数、絮凝剂单耗为影响因素,以固体通量为评价指标,采用混合均匀试验方案,开展全尾砂静态絮凝沉降试验,建立全尾砂絮凝沉降固体通量模型,获得最优匹配参数.在此基础上,开展全尾砂动态絮凝沉降试验,研究剪切作用和给料速率对底流质量分数的影响...     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.