1Cr13钢在氯化钠溶液中闭塞区的化学和电化学变化及加速腐蚀效应

利用模拟闭塞电池测出“1Cr3钢/Cl~-”体系闭塞区不同阶段的化学变化,并在不同阶段的模拟闭塞区溶液中测1Cr13钢的腐蚀串和极化曲线等,绘制出描述该体系闭塞电池腐蚀行为的实验电位/pH图。由“腐蚀率/pH”曲线和电位/pH图都表明该体系存在一个闭塞电池加速腐蚀的临界pH值。约为3.7。当闭塞区溶液的pH值降到临界值以下时,1Cr13钢孔底或缝尖的腐蚀率骤增。其原因是闭塞区内发生了“钝态/活态”转变,并开始放氢反应。     

Structural and magnetic properties of C15 HoMn2 hydrides

Powder samples of cubic HoMn₂H_x hydrides, with 0 ≤ x ≤ 4.3, have been investigated by X-ray diffraction and AC/DC magnetometry as a function of temperature and external magnetic field. Hydrogen is demonstrated to strongly modify structural and magnetic properties. X-ray studies revealed many structural transformations placed at low temperatures. In particular, a transformation from the cubic to the monoclinic structure was detected, which so far has not been reported for other cubic RMn₂H_x (R - rare earth or Yttrium) compounds. The structural transformations are reflected in the magnetic behavior. The change in ordering temperatures implies a very strong relationship between the magnetic interactions and the Mn-Mn distance modified at hydrogen absorption. Tentative magnetic and structural phase diagrams are proposed. The presented results are compared with the properties of other cubic and hexagonal RMn₂H_x hydrides.     

First-principles study of nickel-silicides ordered phases

We present a study of nickel-silicides ordered alloys by means of first-principles calculations. Emphasis was put on the phases (low and high temperatures) identified in the binary phase diagram, namely: Ni₃Si-β₁, -β₂, and -β₃, Ni₃₁Si₁₂-γ, Ni₂Si-δ, -θ, Ni₃Si₂-?, NiSi-MnP and NiSi₂-α. In addition, some common structures are computed for information: L1₂, D0₃ and D0₂₂. The simulations reproduce with a high accuracy lattice parameters and formation energies of main experimental structures, except for β₂ and β₃. Our results clarify the crystallographic nature of the γ structure, and the comparison of experimental Raman spectra and vibrational calculations will help experimentalists to identify without ambiguity NiSi₃ structures.     

Investigation on the isothermal section of the Gd-Ni-Y ternary system at 773 K

The isothermal section of the phase diagram of the Gd-Ni-Y ternary system at 773 K was investigated by means of X-ray powder diffraction, metallographic analysis and scanning electron microscopy with energy dispersive analysis. The isothermal section consists of 12 single-phase regions, 15 two-phase regions and 4 three-phase regions. Six pairs of corresponding compounds in the Gd-Ni and Y-Ni systems, i.e., Gd₂Ni₁₇ and Y₂Ni₁₇, GdNi₅ and YNi₅, Gd₂Ni₇ and Y₂Ni₇, GdNi₃ and YNi₃, GdNi₂ and YNi₂, Gd₃Ni and Y₃Ni and metals Gd and Y form a continuous series of solid solutions, respectively. At 773 K, the maximum solubilities of Gd in YNi and Y in GdNi were about 20 at.% Gd and 8 at.% Y, respectively. No solubility of Gd in YNi₄ and Y in GdNi₄ was observed.     

Burn threshold prediction for High Efficiency Deep Grinding

Burn threshold diagrams are useful for the prediction of thermally induced grinding damage and were originally developed to describe the conventional shallow cut grinding regime. With the development of new high stock removal grinding processes such as High Efficiency Deep Grinding (HEDG), the prevention of thermal damage to the workpiece is of particular concern. The principle of HEDG is based around the change in thermal characteristics of the grinding process at high Peclet numbers, whereby less heat is partitioned to the workpiece. Conventional burn threshold diagrams are valid for Peclet numbers below 50, well below the values expected in HEDG. This study presents a modified approach to the construction of burn threshold diagrams which takes account of the change in thermal partitioning with Peclet number. The approach has been validated through grinding trials over a range of specific material removal rates.     

X-ray diffraction and dielectric studies across morphotropic phase boundary in (1 − x) [Pb(Mg0.5W0.5)O3]-xPbTiO3 ceramics

We present here the results of comprehensive X-ray diffraction and dielectric studies on several compositions of (1 − x)[Pb(Mg_0.5W_0.5)O₃]-xPbTiO₃ (PMW-xPT) solid solution across the morphotropic phase boundary. Rietveld analysis of the powder X-ray diffraction data reveals cubic (space group Fm3m) structure of PMW-xPT ceramics for the compositions with x ≤ 0.42, tetragonal (space group P4mm) structure for the compositions with x ≥ 0.72 and coexistence of the tetragonal and cubic phases for the intermediate compositions (0.46 ≤ x ≤ 0.68). Temperature dependence of the dielectric permittivity above room temperature exhibits diffuse nature of phase transitions for the compositions in the cubic and two phase region while the compositions with tetragonal structure at room temperature exhibit sharp ferroelectric to paraelectric phase transition. The PMW-xPT compositions with coexistence of tetragonal and cubic phases at room temperature exhibit two anomalies in the temperature dependence of the dielectric permittivity above room temperature. Using results of structural and dielectric studies a partial phase diagram of PMW-xPT ceramics is also presented.     

锑掺杂二氧化锡固溶体形成作用机制研究

采用化学共沉淀法制备了Sn1-xSbxO2(x=0~1)固溶体,用XRD、TG-DTA和XPS手段分析了该类固溶体的物相组成,并根据分析的结果绘制了固相线下相图,重点考察了Sn1-xSbxO2(x=0~1)固溶体的形成作用机制。结果表明:在600~1000℃退火温度下,Sn0.95Sb0.05O2固溶体只有四方金红石型SnO2物相的存在,锑主要以Sb5+的形式进入SnO2晶格内形成有限固溶体,而Sn0.6Sb0.4O2和Sn0.2Sb0.8O2固溶体分别在700和800℃出现了斜方白安矿型Sb2O4和四方金红石型SnO2分相;固相线下Sn1-xSbxO2(x=0~1)固溶体相图分为3个区域:四方SnO2单相区,SnO2+Sb2O4两相区和斜方Sb2O4单相区,四方SnO2单相区是(Sn,Sb)O2ss固溶体(Sb3+或Sb5+进入SnO2晶格内,并达到饱和)。(Sn,Sb)O2ss固溶体可作为导电性好和耐腐蚀的半导体材料。     

基于Windows的华中世纪星数控系统PLC编程系统设计

华中世纪星数控系统采用“内装型”PLC,在DOS环境下使用C语言对其进行编程,这种编程方法没有采用Windows操作系统的方便和快捷,而且使用C语言编程同使用传统的梯形图编程相比,对编程人员的技术水平要求高,不便推广使用.针对该问题,开发基于Windows操作环境的数控系统PLC编程系统,主要介绍该编程系统的整体设计及梯形图元件基类的设计.     

Effect of nickel ion from autoclave material on oxidation behaviour of 304 stainless steel in oxygenated high temperature water

Characteristics of the oxide films formed on 304 stainless steel exposed to 290 °C oxygenated water in a nickel-lined autoclave were examined. The oxides evolve from dominating irregularly shaped hematite to faceted spinels with increasing immersion time. The surface layer of oxide film is first Cr-enriched and then Ni-enriched as immersion time increases. The oxides nucleate by solid-state reactions with selective dissolution of Fe and Ni, and then grow up through precipitation of cations from solution. Nickel ions dissolved from the nickel lining could promote the stability of NiFe₂O₄ spinel and influence the oxidation behaviour of 304 stainless steel significantly.     

测定钢板成形极限的三种方法与应用比对

近邻破裂点离线测量法是成形极限试验用来观察成形极限应变的最常用方法。随着光学视频技术在成形试验中的应用,通过测量网格临界破裂时应变的临界破裂点原位测量法,以及ISO12004标准中新推荐的破裂区截面线拟合法,均已进入到成形极限的测量领域。这两种测定成形极限的新方法弥补了紧邻破裂点测量法带来的近似效应和误差,极大提高了成形极限曲线的可信度。文章运用3种不同的方法,对一种高强度冷成形用钢进行成形试验,测定其在近似平面应变状态下的成形极限,并对结果进行比较。