Molten salt synthesis and optical properties of Eu3+, Dy3+or Nd3+ doped NiNb2O6 columbite-type phosphors

Pure, Eu³⁺, Dy³⁺ or Nd³⁺-doped NiNb₂O₆ powders have been prepared by a molten salt synthesis method by using Li₂SO₄–Na₂SO₄ salt mixture as a flux at relatively low temperatures as compared to the solid state reaction method. X-ray diffraction patterns of pure NiNb₂O₆ samples indicated an orthorhombic single phase. For Eu³⁺-doped NiNb₂O₆ samples, the luminescence of Eu³⁺ was observed at 615 nm as red emission while Dy³⁺-doped NiNb₂O₆ showed yellow emission at 577 nm and Nd³⁺ doped sample exhibited a typical emission at 1064 nm varying with the Eu³⁺ or Nd³⁺ doping concentrations. These luminescence characteristics of the doped samples may be attributed to the energy transfer between rare earth ions and NiO₆ octahedral groups in the columbite structure.     

砂轮约束磨粒喷射精密光整加工外圆表面分形维数的研究

应用分形维数与Ra、Rq及支撑长度率的关系对磨削表面和磨粒喷射精密光整加工表面进行研究。试验在MB1332A外圆磨床上完成,加工试样为Ra=0.6 μm左右的45#钢,加工表面形貌和微观几何参数用扫描电子显微镜(SEM)和Micromesvre 2表面轮廓仪测量。试验结果表明：分形维数与Rq呈线性关系可以较好的评价机械加工表面微观形貌的几何结构,以弥补传统的粗糙度评定参数的不足;分形维数值D与支承长度率曲线的变化规律一致,在研究表面接触和磨损中,可用分形维数代替支承长度率曲线。     

Prediction of Carbon Concentration and Ferrite Volume Fraction of Hot-Rolled Steel Strip During Laminar Cooling

A phase transformation model was presented for predicting the phase fraction transformed and the carbon concentration in austenite for austenite to ferrite transformation during laminar cooling on run-out table in hot rolling strip mill. In this model, the parameter k in Avrami equation was developed for carbon steels. The wide range of chemical composition, the primary austenite grain size, and the retained strain were taken into account. It can be used to predict the ferrite volume fraction and the carbon concentration in austenite of hot-rolled steel strip during laminar cooling on run-out table. The coiling temperature controlling model was also presented to calculate the temperature of steel strip. The transformation kinetics of austenite to ferrite and the evolution of carbon concentration in austenite at different temperatures during cooling were investigated in the hot rolled Q235B strip for thickness of 9.35, 6.4, and 3.2mm. The ferrite volume fraction along the length of the strip was also calculated. The calculated ferrite volume fraction was compared with the log data from hot strip mill and the calculated results were in agreement with the experimental ones. The present study is a part of the prediction of the mechanical properties of hot-rolled steel strip, and it has already been used on-line and off-line in the hot strip mill.     

含Nb低碳FB钢组织与扩孔性能的研究

 通过TMCP试验,研究了不同Nb含量低碳FB钢的微观组织和扩孔性能。试验结果表明,随着终轧温度或卷取温度的降低,试验钢强度提高,而扩孔性能降低。随着Nb含量的增加,试验钢的抗拉强度与扩孔性能明显改善。当终轧温度控制在860 ℃,冷却中间温度在710 ℃,卷取温度在450 ℃时,Nb的质量分数约为0.02%的试验钢的铁素体晶粒尺寸细化到6.3 μm,抗拉强度达到570 MPa,扩孔率为91%左右,获得了良好的综合性能。     

Modeling on Dendrite Growth of Medium Carbon Steel during Continuous Casting

Dendrite growth is an important phenomenon during steel solidification. In the current paper, a numerical method was used to analyse and calculate the dendrite tip radius, dendrite growth velocity, liquid concentration, temperature gradient, cooling rate, secondary dendrite arm spacing, and the dendrite tip temperature in front of the solid/liquid (S/L) interface for the solidification process of medium carbon steels during continuous casting. The current model was well validated by published models and measurement data. The results show that in the continuous casting process, the dendrite growth rate is dominated by the casting speed. Dendrite growth rate, liquid concentration at the S/L interface, temperature gradient and cooling rate decrease with proceeding solidification and solid shell thickness growth, while other parameters such as dendrite tip radius, secondary dendrite arm spacing, and dendrite tip temperature in front of the S/L interface become larger with solidification progress and solid shell thickness growth. Parametric investigations were carried out. The effects of the stability coefficient, temperature gradient and casting speed on the micro‐structural parameters were discussed. Under the same conditions, higher casting speed promotes coarser secondary dendrite arm spacing and enlarges the dendrite tip radius, while decreasing temperature gradient, reducing the dendrite growth rate and making the solute distribute more uniform.     

（PEO）_（16）LiClO_4-NaY电解质薄膜的显微组织特征与离子导电性能

采用溶液浇铸法制备了（PEO）16LiClO4-xwt.%NaY（x=0,5,8,12,15,20,35）全固态复合聚合物电解质（CPE）薄膜.通过X射线衍射技术、扫描电镜和交流阻抗方法研究了NaY对（PEO）16LiClO4电解质体系结晶度、显微组织特征与离子导电性能的影响.结果表明,添加适量NaY可通过Lewis酸...     

大掺量矿物掺合料混凝土早期抗裂性能研究

通过平板开裂试验对大掺量(50%)矿物掺合料混凝土的早期开裂性能进行了研究。试验结果表明:随着胶凝材料用量的增大,混凝土试块的单位开裂面积变大,且裂缝的面积增长速率提高;混凝土的养护及成型方式对大掺量矿物掺合料混凝土的早期抗裂性能有很大的影响。     

基于LabVIEW和OPC技术的气体爆炸测试系统开发

开发了一套用于检测气体爆炸特性参数的爆炸测试系统.硬件系统由参数测试装置和视频记录设备构成.软件系统为一套用作控制和数据采集的分布式测控系统,主要采用LabVIEW 8.6开发而成,具有界面友好、操作容易和高度自动化等特点.现场设备的控制逻辑由PLC来实现,LabVIEW应用程序和硬件设备的通讯采用OPC技术来实现.该...     

冒口对钢锭凝固过程固相转变影响的数值模拟

通过自建模型模拟研究了冒口材质和高度对大钢锭凝固过程中固相转变的影响。结果表明:钢锭凝固过程中,锭模及底座附近的钢液发生相转变的速率较快且固液共存区宽度较窄,而冒口附近的钢液发生固相转变的速率较慢且糊状区较宽。相比于传统的黏土砖,轻质砖和绝热板均有助于改善冒口的保温性能,且均可减缓冒口外表面温度上升的速率。冒口高于钢液上表面部分高度的变化对于钢锭凝固过程中冒口附近钢液相转变速率的影响较小。     

Characterization of the structure of TiB2/TiC nanocomposite powders fabricated by high-energy ball milling

TiB₂/TiC nanocomposite powders were successfully prepared by high-energy ball milling of the powder mixtures of Ti and B₄C. X-ray diffraction analysis showed that the TiC phase was not produced until the milling time was up to 24 h and only a minimal amount of TiB₂ was generated, even after 48 h of milling. The critical grain size of Ti milled for the reaction between Ti and B₄C was 31.2 nm. Transmission electron microscopy clearly indicated that the resulting powder mixture obtained after milling for 48 h and annealing at 800 °C for 30 min was composed of nanosized TiC and TiB₂ particles.