影响草酸钴分解速度及钴粉粒度的因素

讨论了草酸钴分解的实验室研究及生产过程中,影响分解速度的主要因素及两者的差别。认为对物料的传热是生产过程中的主要控制因素,由于料层中温度梯度的存在,影响到物料床中不同层次分解的钴粉聚集长大过程。     

分步球磨碳热法制备Ti(C,N)复合粉末工艺

以钛铁矿为原料,采用分步球磨后碳热还原法,进行Ti(C,N)复合粉末的制备,并对Ti(C,N)复合粉末的粒径、形貌、物相组成和烧结性能进行测试与分析。结果表明:Ti(C,N)复合粉末粒径为2~5μm,呈正态分布,由Ti(C,N)和α-Fe组成。试验制备Ti(C,N)复合粉末烧结体的抗弯强度达到商业Ti(C,N)粉末烧结体的98%、断裂韧性达到商业Ti(C,N)粉末烧结体的110%。     

球磨时间对W-30Cu复合粉末中W晶粒度及烧结致密化行为的影响

研究了高能球磨时间对W-30Cu复合粉末晶粒度及烧结行为的影响.结果表明,当球磨时间从16h提高到33h时,复合粉的晶粒度由25nm减小到10nm,并发生机械合金化现象;在温度为1275℃烧结60min,经18h高能球磨的复合粉末烧结就可以达到全致密.研究还发现,高能球磨W-30Cu复合粉末具有较好的热稳定性,经950℃退火处理,晶粒尺寸没有发生异常长大现象;经烧结材料的硬度明显高于普通的W-30Cu复合材料.经1 275℃烧结30 min后合金其晶粒尺寸在300～550 nm.     

表面活性剂在超细硬质合金球磨工艺中的作用及研究进展

针对高能球磨法制备超细硬质合金混合料的新技术,简述了在球磨介质中添加表面活性剂的作用及作用机理,总结了表面活性剂在硬质合金球磨工艺中的研究现状,并提出了今后的研究方向。     

由氢还原草酸钴和氧化钴制取金属钴粉的物理性能

在400—580℃温度范围内用氢气将草酸钴和氧化钴还原为金属钴粉,研究了原料粒度和还原温度对钴粉粒度、比表面、松装密度和摇实密度的影响,讨论了还原期间在不同原料表面上发生的局部化学反应机理。结果表明,用草酸钴可制得具有费氏粒度0.5μm、BET 比表面400000cm~2/cm~3的极细钴粉,得自草酸钴的钴粉还具有易于研磨的脆性多孔结构。对于形成多孔产物相的固体物质的分解和还原反应,作者推出了产物核心粒度的计算式。D=1.96(V′/V~p)~(1/2)(G/N)~(1/3)=1.96(V′/V~p)~(1/2)·A·e~(-(E_g-E_(?))/(3RT))     

邦德棒磨功指数算式中G_(rp),P_i和P_(80)间关系的研究

采用三种不同类型矿石对邦自律由功指数算式中Grp，Pi和P80间的关系进行了研究，结果表明：Grp=k1·pi，Pi=k2·P80因此，只要准确地做一次标准律启功指数试验，就能用Grp，Pi和P80间的关系计算出其它任意自矿位瘦的律后功指数；同时利用Pi=k2·P80的关系为测定要求的磨矿位度律启功指数时如何确定试验筛子提供依据．     

Author Index,Powder Metallurgy and Metal Ceramics,Volume 39, Numbers 1-12, 2000 (A translation of Poroshkovaya Metallurgiya)

Powder Metallurgy and Metal Ceramics -     

Author Index,Powder Metallurgy and Metal Ceramics,Volume 39, Numbers 1-12, 2000 (A translation of Poroshkovaya Metallurgiya)

Powder Metallurgy and Metal Ceramics -     

Tables of Contents,Powder Metallurgy and Metal Ceramics,Volume 39, Numbers 1-12, 2000 (A translation of Poroshkovaya Metallurgiya)

Powder Metallurgy and Metal Ceramics -     

Tables of Contents,Powder Metallurgy and Metal Ceramics,Volume 39, Numbers 1-12, 2000 (A translation of Poroshkovaya Metallurgiya)

Powder Metallurgy and Metal Ceramics -     

The diffusion of hydrogen in liquid Ni,Cu, Ag,and Sn

The rates of absorption of hydrogen in stagnant liquid Ni, Cu, Ag, and Sn have been measured using 1) an unsteady-state gas-liquid metal diffusion cell technique similar to that used by El-Tayeb and Parlee for iron and 2) a steady-state diffusion cell technique recently developed in this laboratory. The rates of absorption are considered to be controlled by diffusion in the liquid. On this basis the chemical diffusion coefficients of hydrogen (D _H) in liquid Ni, Cu, and Ag, calculated from the rate data, can be described by:D _H ^Ni =7.47×10^?3 exp(?8550±1114/RT) cm²/secD _H ^Cu =10.91×10^?3 exp(?2148±349/RT) cm²/secD _H ^Ag =4.54×10^?2 exp(?1359±207/RT) cm²/sec In the above equations, the uncertainty in the activation energy (Q _H) corresponds to the 90 pct confidence level. No reliable Arrhenius equation could be obtained forD _H ^Sn , but theD _H values in tin are greater than for the other three metals. The following interesting and possibly significant correlations are observed betweenD _H,Q _H, and the hydrogen solubility (S _H):D _H ^Ni <D _H ^Fe <D _H ^Cu <D _H ^Ag <D _H ^Sn , andQ _H ^Ni >Q _H ^Fe >Q _H ^Cu >Q _H ^Ag , andS _H ^Ni >S _H ^Fe >S _H ^Cu >S _H ^Ag >S _H ^Sn .     

On the Comparison of Graphene and Multi-Wall Carbon Nanotubes as Reinforcements in Aluminum Alloy AA2219 Processed by Ball Milling and Spark Plasma Sintering

Aluminum alloy AA2219-Graphene/MWCNT composites with near theoretical density have been successfully processed through high energy ball milling followed by spark plasma sintering. Effectiveness of varying content of Graphene and MWCNT as reinforcements was studied on different aspects of processing of the composites. The particle size increased during milling due to agglomeration but presence of reinforcement restricted the agglomeration process. Significant change in particle size of milled composite powders was not observed for the type (Graphene/MWCNT) or content (0.5–2 wt%) of the reinforcements. The increase of reinforcement (Graphene/MWCNT) content above 0.5 wt% resulted in lower hardness for spark plasma sintered composites. Further, both AA2219-Graphene and AA2219-MWCNT composites revealed similar hardness values. Finally, different aspects of processing (mechanical alloying, densification) and characterization (microstructure, hardness, electrical conductivity) revealed similar results irrespective of type of reinforcement i.e. Graphene or MWCNT.     

Variations in the composition dependence of the activity coefficient in terminal solid solutions of Ag−Zn,Ag−Cd,and Cu−Zn

The vapor pressure of zinc and cadmium over moderately dilute solutions of α Ag?Zn, α Ag?Cd, and α Cu?Zn was measured. An isothermal equilibrium technique was used, which was believed to give vapor pressures with relatively small error. Temperature coefficients of the vapor pressure were not measured. The purpose was to determine, with greater precision than has been obtained previously, the composition-dependence of the excess Gibbs free energy of the solute. It was found that the excess Gibbs free energy attains a minimum value in α Ag?Zn and α Cu?Zn, and there is a corresponding change ind In γCd/dx _Cd, although it does not go to zero, in α Ag?Cd. Such minima do not violate thermodynamic criteria for phase stability, but have not been reported previously.     

Kinetic Analysis of Isothermal Decomposition Process of Zinc Leach Residue in an Inert Atmosphere. The Estimation of the Apparent Activation Energy Distribution

Thermal decomposition of zinc leach residue has been studied in a tubular furnace under a constant nitrogen gas flowing, at four different operating temperatures (600°C, 750°C, 950°C, and 1150°C). Using a detailed kinetic analysis, it was shown that the investigated process can be described by a two-parameter autocatalytic ?esták–Berggren reaction model. It was noted that the apparent activation energy values E_a increase progressively with a degree of conversion, accompanied by the appearance of a convex Arrhenius dependence. This behavior is a characteristic of a system of parallel competing reactions. It was concluded that the investigated isothermal decomposition process is characterized by unusually very low preexponential factor and low values of the apparent activation energy. Based on the derived density distribution function of E_a values, it was concluded that the isothermal decomposition process probably occurs through four reaction steps, where each step is characterized by one parallel reaction.     

M. Yu. Bal'shin, A Founder in the Science of Powder Consolidation

The collection of analytical and experimental data makes it possible to consider the existence of three common scientific principles for solid body consolidation to be proved. One of them, the identity principle, formulates the degree of generality between properties and the behavior of a porous, consolidating or consolidated body, and a normal body; two others, i.e. the principle of self-regulation and the transmission principle, formulate features of the properties and behavior of powder bodies. The identity principle may be formulated as follows. The properties and behavior of any compact element of a porous body are the same as for the substance of a compact pore-free body with the condition of an identical chemical composition, degree of strain hardening, and test conditions. The self-regulation principle may be formulated as follows. During consolidation there are processes of non-self-regulation (intraparticle, consolidating, increasing and fixing the contacts and equilibrium) loading deformation and self-regulating (intraparticle, deconsolidating, reducing and breaking contacts and body equilibrium) unloading deformation; non-self-regulation consolidating deformation increases, and self-regulation deconsolidating deformation reduces compaction resistance; flow of particles substance is intermediate in nature between entirely continuous and entirely localized flow in contact areas. The greater the degree of consolidation, the lower is the level of self-regulation for its processes. The transmission principle may be formulated as follows. Consolidating stresses applied to a consolidating self-regulating body are transmitted by their elastic balancing in a continuous critical zone lying entirely within the solid phase of a body with equally large interparticle (contact) and intraparticle (critical) sections normal to the loading direction. These stresses and elastic loading are only transmitted through fixed, and not through broken, contact sections at this instant of consolidation, and consequently through fixed critical sections in a fixed critical zone.     

Activity Dependent Brain Plasticity: Does Singing Increase the Volume of a Song System Nucleus? Theoretical Comment on Sartor and Ball (2005).

The avian telencephalic song system, including nucleus high vocal center (HVC), is an important model for the study of brain plasticity. J. J. Sartor and G. F. Ball (2004) asked whether song activity itself could increase HVC volume (see record 2005-01705-022). They report that male starlings that sang more, motivated by gaining possession of a nest box in competition with another male, had larger HVCs than males that sang less. These results are suggestive but correlational. A more direct experimental approach will be required to establish that HVC size is activity dependent. Their experiment is an important first step, however. The song activity hypothesis merits continued investigation because of its potential to produce unique insights into naturally occurring brain plasticity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rod outer segment maintenance is enhanced in the presence of bFGF, CNTF and GDNF

We employed a morphological assay of outer segment collapse to determine if growth factors or other supplements directly affect dissociated rod photoreceptors in vitro. The morphological changes in outer segments were correlated with the light responsiveness of rods. Time-lapse video microscopy was used to observe the collapse of rod outer segments from isolated single cells and small clumps of cells. A consistent pattern of outer segment collapse into the inner segment was observed, yielding a convenient assay of the effects of neurotrophic factors on photoreceptor functional maintenance. The functional state of rods, defined as light-responsiveness, was measured with suction electrode recordings and matched with the various stages of outer segment collapse. Ciliary neurotrophic factor (CNTF) and glial cell-line-derived neurotrophic factor (GDNF) at a high concentration, yielded statistically significant improvements in rat outer segment survival times. Basic fibroblast growth factor (bFGF), which rescues photoreceptors in several rodent models of retinal degeneration, produced a significant increase in survival time in the presence of the cofactor heparin. In 4 out of 10 cases using human tisue, bFGF also yielded a significant increase in survival times. When brain-derived neurotrophic factor (BDNF) was applied to rat rods, outer segment survival times did not change. Outer segments collapsed more quickly when either pigment epithelial cell derived factor (PEDF) or sugar N-acetyl D-galactosamine (NAD-gal) were present. Our results show that rod photoreceptors can respond to bFGF, GDNF and CNTF in vitro and provide evidence for a direct effect of these neurotrophic factors on rods. The rapid collapse of isolated photoreceptors in this model provides a convenient means for testing various neurotrophic agents and the induced cellular responses.     

Thermochemistry of binary alloys of transition metals: The Me-Ti,Me-Zr,and Me-Hf(Me = Ag,Au) systems

The standard enthalpies of formation of congruently melting intermetallic compounds in the (Ag, Au)-(Ti, Zr, Hf) binary systems were determined by high-temperature direct synthesis calorimetry at 1473 ± 2 K. The enthalpies of mixing for the liquid alloys in the same systems have been measured by the same technique in the range of compositions available for experiments at 1473 ± 2 K. The results obtained are compared with estimated values from Miedema’s semiempirical model.