超声沉淀法制备纳米A12O3粉体

将超声辐射应用于以硫酸铝铵(NH4Al(SO4)2*12H2O )和碳酸氢铵(NH4HCO3)为原料的沉淀法制备Al2O3纳米粉体的化学反应工艺过程, 制备了粒径为12 nm的α-Al2O3纳米粉体.通过SEM、TEM等分析手段研究了超声辐射对前驱体NH4Al(OH)2CO3沉淀物及最终粉体尺寸、形貌及其团聚行为的影响, 并探讨了其作用机理.结果表明 超声辐射由于其自身的空化作用不仅细化了前驱体颗粒、抑制了其间的团聚, 而且延缓了其向凝胶的转变过程, 从而有效地细化α-Al2O3颗粒, 但过高的频率却易导致颗粒间的进一步聚合.     

超声对湿化学法制备Al2O3纳米粉的影响

采用湿化学法在超声场中制备了纳米α-Al2O3粉体,研究了超声辐射作用下前驱体颗粒的成核、长大过程,探索了超声作用下Al2O3晶型的转变.结果表明超声能量能加速前驱体的形核,超声分散可控制晶核的长大和团聚,在超声技术处理下可制备粒径仅为20 nm的NH4A1(OH)2CO3超细前驱体,这一前驱体经8 h陈化后,再经1150℃高温煅烧20 min,可制备得到粒径约为10 nm的α-A1203粉体;研究还发现高频率超声辐射可提高α相Al2O3粉体的结晶度.     

超声场中溶胶凝胶法制备纳米氧化铝粉体的研究

近年来，超声空化处理已被证明是一种制备纳米材料十分有效的技术，当将超声空化作用应用于溶胶凝胶法制备纳米粉体过程时，将为防止团聚体的生成创造一个独特的条件。本文以六次甲基四胺为沉淀剂，研究了超声场下溶胶凝胶法制备纳米Al2O3粉体的工艺，对产物进行了扫描电镜（SEM），X射线衍射（XRD）分析及粒度分析。实验结果表明，超声波的引入可显著提高粉体的性能。超声处理过的前驱体在1100℃煅烧2小时制得了团聚少，平均粒径在30nm左右的α-Al2O3粉体。超声波的辐射作用有利于纳米α—Al2O3粉体的制备，它的作用主要体现在防止胶粒之间的团聚和长大，及破碎团聚体的作用上。     

共沉淀法制备YAG纳米粉体中团聚的研究

分别在NH4HCO3、氨水溶液中滴加NH4Al(SO4)2和Y(NO3)3的混合溶液,共沉淀生成YAG的前驱体.通过对YAG前驱体组成和结构的表征来讨论2种沉淀剂对前驱体团聚的影响,并且通过对2种前驱体热处理过程中YAG相形成的反应历程分析,来解释最终生成YAG粉体的形貌、尺寸及团聚状态.结果表明,使用氨水作为沉淀剂,生成的YAG粉体团聚严重;使用碳酸盐作为沉淀剂形成的前驱体虽然也有一定程度的团聚,但最终生成分散性好、尺寸较小的YAG纳米粉体.     

碳酸铝铵热分解法制备超细氧化铝粉体

以分析纯的NH4Al(SO4)2和NH4HCO3为原料,选择合适的溶液浓度、分散剂及pH值,在合适的工艺条件下,得到NH4Al(OH)2CO3前驱体化合物.前驱体在1100℃下煅烧1h,得到粒径为80～100nm的超细α-Al2O3,Al2O3颗粒基本上呈球形,粒度均匀.研究了溶液浓度、分散剂及pH值对前驱体化合物颗粒细度的影响,用XRD法对前驱体化合物及其煅烧产物进行了表征,并研究了热处理过程中的相变化,对Al2O3多晶转变与热处理温度之间的关系进行了讨论.用SEM对Al2O3粉体的形貌、大小进行了表征.该方法工艺简单,原料易得便宜,综合成本较低,易实现工业化生产.     

表面活性剂对超声喷雾法制备的纳米羟基磷灰石粉体性能影响

在常温常压下,以硝酸钙(Ca(NO3)2·4H2O)和磷酸氢二铵((NH4)2HPO4)为原料,分别将其作为钙与磷的先驱体,运用超声喷雾法特种工艺技术制备羟基磷灰石(HAP)纳米粉体。探讨在制备工艺过程中添加柠檬酸、甘氨酸、葡萄糖和TX-104种表面活性剂对制备的羟基磷灰石纳米粉体的分散性能、粒度、均匀性及形貌等的影响情况。结果表明,所有表面活性剂的加入对粉体的产物相没有影响,但对制备出的纳米羟基磷灰石粉体的分散效果均有一定的影响,在本反应体系中当甘氨酸适量加入时,对纳米羟基磷灰石粉体能起到很好的分散作用;而等量柠檬酸的加入反而加剧了纳米HAP颗粒的团聚。从扫描电镜照片看出,在未加活性剂时,HAP大多呈现椭圆的、30～40nm的颗粒;加入甘氨酸后,有利于HAP颗粒的细化与均匀,而葡萄糖与TX-10的加入则使粒度变大,并易造成局部团聚。并从物化基本原理出发初步探讨与解释上述表面活性剂对HAP产物所造成影响的原因。     

碳酸铝铵热解法制备超细Al2O3

以Al2(SO4)3与(NH4)2CO3为原料,采用液相沉淀法,制备出前驱物碳酸铝铵(AACH),并烧结得到Al2O3粉末。通过分析前驱物的热重曲线,确定了前驱物的高温分解过程;并结合对前驱物在不同烧结温度下所得产物XRD图谱的分析,确定了前驱物的高温相变过程为:AACH→AlOOH→Al2O3(无定型)→γ-Al2O3→θ-Al2O3→α-Al2O3。同时,干燥方式对超细Al2O3分散性的影响在本文中也进行了研究。     

Al2O3和ZrO2纳米粉体悬浮液稳定性研究

获得均匀分散的纳米粉体悬浮液是制备高性能纳米复合陶瓷材料的关键一步.选用纳米粉Al2O3和纳米粉ZrO2,采用单一的空间位阻稳定机制,以PEG为分散剂,以无水乙醇为分散介质,分别制备了1%(体积分数,下同)的Al2O3和ZrO2无水乙醇悬浮液.通过添加不同分子量的PEG,调节PEG的添加量及悬浮液的pH值,并辅以沉降实验,最终得到了最佳分散条件下的高分散、高稳定的Al2O3和ZrO2无水乙醇悬浮液.TEM观察发现:ZrO2悬浮液中颗粒彼此分开,无明显的颗粒团聚现象.这说明该分散工艺能很好地破坏颗粒间的团聚现象,避免颗粒间的聚集沉淀,具有良好的分散效果.     

稀土增强Al2O3掺杂钼基复合粉体的制备

采用溶胶-凝胶法制备了稀土掺杂Al2O3增强钼基复合材料的粉体,研究了在La2O3与Al2O3在不同掺杂量对粉体的影响。结果表明:采用溶胶凝胶法制得La2O3/Al2O3/Mo混合粉体的平均粒径为1～2μm。Al2O3对粉体的均匀性、颗粒分布、粒径大小有一定的影响,Al2O3添加量的增加对粉体的团聚有分散作用。当Al2O3含量为15vol%、La2O3添加量小于2.5%时,La2O3对粉体粒径无明显细化作用。     

超声化学原位合成Al2O3（p）/Al纳米复合材料的组织及其机理（英文）

采用超声化学原位反应,以Al-K2ZrF6-Na2B4O7为反应体系,制备Al2O3(p)/Al纳米复合材料。利用扫描电镜和透射电镜,研究高能超声对复合材料组织和颗粒收得率的影响及加入K2ZrF6对反应过程以及增强颗粒与铝基体的界面的影响。X射线衍射(XRD)、扫描电镜(SEM)与透射电镜(TEM)结果表明:所制备的复合材料增强颗粒为Al2O3,Al2O3颗粒在基体中分布均匀,其形貌为近球形,尺寸20~100nm,界面干净且无界面产物。利用经过二次开发的Image-J软件对Al2O3颗粒收得率进行分析,结果表明,Al2O3颗粒收得率随着超声功率的增大呈现出先增大后减小的变化规律。当超声功率达到0.4kW时,颗粒分布最好且数量最多。并对其反应机理也进行了探讨。     

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).     

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.     

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.     

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.