Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.     

ICP-AES法测定金属镝中钽

利用钽不溶于酸的性质与稀土分离，用焦硫酸钾熔融，酒石酸浸取，制得被测溶液，采用ICP-AES测定其中钽量，结果令人满意。     

Investigation of the initial stage of borating tantalum

The results of investigation of initial stage of the tantalum borating as well as the effect of oxygen and hydrogen on it are presented. The scheme of the initial stage of tantalum boron saturation is proposed.     

五氧化二钽薄膜的制备及其I-U特性

本文利用脉冲直流反应磁控溅射的方法制备了五氧化二钽 (Ta2 O5)薄膜 ,俄歇电子能谱仪测试了薄膜的成分含量 ,椭偏仪测试了Ta2 O5薄膜的厚度和折射率 ,XRD分析了薄膜的晶体结构 ,并且分别研究了氧气含量、基底温度等成膜工艺对薄膜的影响。研究结果表明薄膜的成分主要是由氧气含量决定的。利用金属 绝缘体 (介质膜 ) 金属 (MIM)结构初步对Ta2 O5薄膜进行了电学性能的测试 :皮安电流电压源测试了薄膜的I U特性 ,制备出的薄膜折射率在 2 1～ 2 2 ,MIM的I U特性曲线显示了较好的对称性和低的漏电流密度     

用离子束混合及快速热处理方法形成钽的硅化物

本文描述用离子束透过钽金属膜进行混合和快速热处理方法来形成钽的硅化物.用溅射方法在P型硅衬底上淀积一层金属钽,然后用砷离子束透过钽金属模进行混合,采用快速热处理后形成了平整的硅化钽薄层.使用厚度为500埃的钽金属膜,得到钽的硅化物薄层电阻为5.5Ω/□.研究了砷离子能量、剂量及钽膜厚度对钽的硅化物薄层电阻的影响.用透射电镜和台阶仪对所形成的硅化钽进行了分析和厚度测量.     

Surface Preparation of Tantalum for Encapsulation and Adhesive Bonding

A number of methods of surface preparation of tantalum for encapsulation in silicone rubber and for structural adhesive bonding were explored. The only ones which could be generally useful were boiling for 24 hours in distilled water (28% improvement) or boiling for 4 hours in 20% sodium hydroxide solution followed by boiling for 2 hours in dilute hydrochloric acid (34% improvement). An alternative, which could sometimes be used, was heating in air for at least 2 hours at 100°C.     

Electrochemical impedance characteristics of Ta/Cu contact regions in polishing slurries used for chemical mechanical planarization of Ta and Cu: considerations of galvanic corrosion

The contact areas between Cu and Ta of a Cu interconnect can be susceptible to galvanic corrosion during chemical mechanical planarization (CMP) in polishing slurries capable of supporting ionic conduction. In the present work, we probe this effect at a partially Cu-covered Ta disk, by combining electrochemical impedance spectroscopy with potentiodynamic polarization and galvanic current measurements in two slurry solutions commonly used in CMP of Ta and Cu. The results of these measurements are compared with those for a Cu disk and a (Cu-free) Ta disk. The impedance data for the Cu-decorated Ta sample show negative impedance values at certain regions of the impedance spectra, whereas the individual Cu and Ta electrodes are free of this effect. The results are examined and explained from considerations of galvanic corrosion at the Ta/Cu bordering regions in contact with the slurry liquid.     

Prediction of stable high-pressure structures of tantalum nitride TaN2

Structure searches based on a combination of first-principles calculations and a particle swarm optimization technique unravel two new stable high-pressure structures (C2/m and Cmce) for TaN₂. The structural features, mechanical properties, formation enthalpies, electronic structure, and phase diagram of TaN₂ are fully investigated. Being mechanically and dynamically stable, the two phases could be made metastable experimentally at ambient conditions.     

Temperature stability of thin anodic oxide films in metal/insulator/metal structures: A comparison between tantalum and aluminium oxide

The dielectric breakdown of thin (d = 3–4 nm) aluminium and tantalum oxide films was investigated by means of current voltage plots in metal/insulator/metal systems. Dielectric breakdown field strengths, E_DB, of 0.6 GV m^− 1 were found for both oxide types at room temperature. Differences appear in the temperature dependence of E_DB. Tantalum oxide films show an unchanged breakdown behaviour for temperatures up to 420 K while aluminium oxide films lose already 80% of their E_DB value in the same temperature range. Time-resolved investigations of the electric breakdown revealed intermediate states of both oxide types which were stable for several ms being characterized by an enhanced tunnel current. The breakdown voltage clearly scales with the oxide thickness for both oxide types.     

Kinetics of Reaction between Iron Ore Fines and Coal or Char Fines

Iron ore fines and coal fines can be made to react to produce direct reduced iron (DRI) fines. There are three ways to achieve the reactions, namely, (a) using homogeneous mixtures, (b) arranging the ore and coal fines in separate but adjacent layers and (c) by fluidizing a mixture of iron ore fines and coal fines by air. This paper mainly discusses the work done by the author and his coworkers on the kinetic aspects of reactions in such systems.