High-temperature oxidation studies of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel

The high-temperature oxidation behavior of cold-sprayed Ni-20Cr and Ni-50Cr coatings on SAE 213-T22 boiler steel has been investigated at 900 °C in air under cyclic heating and cooling conditions for 50 cycles. The kinetics of oxidation of coated and bare boiler steel has been established with the help of weight change measurements. It was observed that all the coated and bare steels obeyed parabolic rate law of oxidation. X-ray diffraction, FE-SEM/EDAX and X-ray mapping techniques were used to analyse the oxidation products of the coated and uncoated boiler steel. The uncoated steel suffered corrosion in the form of intense spalling and peeling of its oxide scale, which was perhaps due to the formation of unprotective Fe₂O₃ oxide scale. Both the coatings showed better resistance to the air oxidation as compared to the uncoated steel. The Ni-50Cr coating was found to be more protective than the Ni-20Cr-coated steel. The formation of oxides and spinels of nickel and chromium may be contributing to the development of air oxidation resistance in the coatings.     

Analysis of dual melting behavior in cold-crystallized poly(ether diphenyl ether metaketone)

By focusing on cold-crystallized poly(ether diphenyl ether metaketone) (PEKm), a more in-depth understanding of the nature of the crystalline morphology has been gained, which may lead to thorough mechanisms for interpreting the observed thermal behavior in PEKm. Apparently, cold-crystallized PEKm containing initially only a single P1 crystal can exhibit dual melting peaks (300 and 320 °C), with the second high-melting peak corresponding to the P2 crystal that was subsequently formed via P1 melting/repacking during the scan. However, dual morphism (preexisting P1 and P2 crystals) could be intentionally introduced into PEKm if it was cold-crystallized at temperature schemes of decreasing order. The P1 and P2 crystals possess the same unit cells (orthorhombic) and thus they differ only in the lamellae populations. The dual lamellar morphism in this PEKm sample also exhibited similar dual melting peaks during scanning, which correspond to melting of the individual P1 and P2 in a sequential order. This study has thus provided important clues in and shed new light on the interpretation of multiple melting with respect to polymorphism in polymers. Relationships between the low-melting and high-melting lamellae in cold-crystallized polyketone polymer have been thoroughly explored. Received: 9 January 2001/Accepted: 3 February 2001     

Direct mercury determination in aqueous slurries of environmental and biological samples by cold vapour generation-electrothermal atomic absorption spectrometry

Direct cold vapour generation from aqueous slurries of environmental (marine sediment, soil, coal) and biological (human hair, seafood) samples have been developed using a batch mode generation system coupled with electrothermal atomic absorption spectroscopy. The effects of several variables affecting the cold vapour generation efficiency from solid particles (hydrochloric acid and sodium tetrahydroborate concentrations, argon flow rate, acid solution volume and mean particle size) have been evaluated using a Plackett-Burman experimental design. In addition, variables affecting cold vapour trapping and atomisation efficiency on Ir-treated graphite tubes (trapping and atomisation temperatures and trapping time) have been also investigated. Atomisation and trapping temperatures, trapping time and hydrochloric acid concentration were the significant variables. The 2²+star and 2³+star central composite designs have been used to obtain optimum values of the variables selected. The accuracy of methods have been verified by using several certified reference materials (PACS-1, GBW-07410, NIST-1632c, CRM-397 and DORM-2). A characteristic mass of 390 pg were achieved. The detection limits of methods were in the range of 40-600 ng g⁻¹. A particle size less than 50 μm is adequate to obtain total cold vapour generation of Hg content in the aqueous slurry particles.     

动态冷原子吸收法快速测定地球化学样品中微量汞

本文介绍了动态冷原子吸收法快速测定地球化学样品中微量汞的方法。本文研究采用了新型的汞蒸气发生器，并对气泡的干扰进行了研究。线性范围为0.2-12ng/mL，标准回收率为97％－106％，相对标准偏差为3.6%，相关系数为0.9997，试验结果表明此方法简便、快速、准确。     

Correlation spectroscopy as a tool for detecting losses of ligand elements in laser welding of aluminium alloys

The plasma plume induced during laser welding of metals is a mixture of metal vapour, coming from the vaporised weld pool surface and shielding gas. The influence of the shielding gas on the welded joints quality is not yet well understood and very few investigations, to the best of our knowledge, were addressed to study its role in case of welding of aluminium–magnesium alloys. In this paper we present a study of the dynamics of plasma plume produced in laser welding of 5xxx aluminium alloys by means of correlation spectroscopy. By our results we can correlate the influence of the welding speed, in case of ineffective gas shielding, to the loss of alloying elements. Finally, the results obtained are consistent with the EDX analysis performed in post-processing on the welded joints.     

CO_2焊接短路过渡过程的动态分析─短路液桥的动态变化与力学测算

ＣＯ＿２气体保护焊接是一种高效、节能和低成本的焊接方法，在钢结构焊接生产中得到了广泛的应用。但也存在着诸如：金属飞溅、焊缝成形较差等问题，要解决这些问题，必须首先对ＣＯ＿２焊接过程的电弧形态以及熔滴变化情况从理论上深入分析研究。本文以高速摄影与光线示波器同步进行拍摄，记录了ＣＯ＿２悍接短路过渡中熔滴的长大、缩颈、脱落的全过程以及相对应的电流电压波形。利用影片数据分析处理系统对所得影片及记录波形进行了分析处理，得到了熔滴过渡形成金属液桥爆断瞬间的最大电流值及所受合力的大小。从理论上更进一步研究了短路过渡的机理，建立了短路过渡的模型，这对正确调节焊接工艺规范，保证焊接质量具有重大的指导意义，研究结果表明：在常规短路过渡ＣＯ＿２焊接中，抑制飞溅是提高ＣＯ＿２焊接质量的关键，利用焊接规范来调节短路频率和短路峰值电流是抑制飞溅的主要途径。     

An experimental study on the keyhole shapes in laser deep penetration welding

In this paper, the laser spot diameter and its intensity distribution are measured with a scanning pinhole, and the keyhole shapes are observed using a specially designed setup in laser deep penetration welding of glass GG17. Based on the above experimental results, the effects of the following factors on the keyhole shapes are studied: the laser spot diameter and its intensity distribution, defocus, welding speed and inverse Bremsstrahlung absorption of the plasma.     

非线性工作状态压电换能器匹配技术

针对压电换能器在大功率下存在复杂非线性而导致匹配参数难以优化的问题,以大功率超声金属焊接为例,通过采集测试焊接过程换能器两端电压的幅值与频率,建立换能器反谐振电阻与驱动电压有效值、频率之间的数学模型;提出基于反谐振电阻模型的最优功率匹配方法,推导了匹配电感电容的计算公式。最后实验验证了数学模型的准确性,且当换能器输入功率在最优功率附近时,匹配网络电能传输效率最高。     

多层金属爆炸焊接复板飞行姿态的计算方法

在两层金属爆炸焊接复板飞行姿态的理论计算基础上，运用质量守恒、动量守恒定理和契特公式推导了多层金属爆炸接复板飞行姿态的理论计算模型，经过实验验证，该计算模型和实验相符合，对于多层金属爆炸焊接工艺参数的设计具有很高的使用价值。     

双金属爆炸焊接上限

本文根据热传导理论给出了爆炸焊接时双金属结合区附近的温度场解析解。并利用该解初步研究了双金属的爆炸焊接上限。