钨铼热电偶的失效分析

笔者采用热力学计算和实验检测(EDS)相结合的方法,探讨了钨铼热电偶在氮气、高温含碳环境中可能发生的反应以及反应进行的条件.研究表明,在高温时,氮气、石墨、石英砂、钨铼之间发生复杂的化学反应是导致钨铼热电偶失效的主要原因;在装配过程中不宜用SiC做钨铼热电偶的绝缘材料,应避免石墨、石英砂、钨铼之间的交叉污染.     

钨铼热电偶的研究,开发及应用

简述了钨铼热电偶的特点、消耗型钨铼热电偶的发展及日本对国产钨铼热电偶的检定结果。探讨了钨铼合金的高温氧化行为，实体型抗氧化钨铼热电偶的研制、应用及存在的问题。结果表明：用抗氧化钨铁热电偶部分取代S型热电偶，用于工业过程温度检测是可行的。     

抗氧化钨铼热电偶的制造工艺与分析

主要介绍一种抗氧化钨铼热电偶的制造工艺,该工艺利用石英玻璃抽真空充惰性气体使钨铼热电偶丝处于惰性气体中,极大提高了钨铼热电偶的使用寿命。有色冶金行业各种各样的高温窑温度大多在1000℃～1300℃之间,每年要消耗大量的热电偶。由于近期贵金属铂铑热电偶的价格又连续暴涨,冶金行业迫切需要一种廉价热电偶来替代贵金属铂铑热电偶。我们在长期从事热工仪表工作中通过对优     

钨铼热电偶在钼冶金高温烧结中的应用

针对目前钼冶金高温侥结炉的测温现状，讨论了使用钨铼热电偶测温代替传统的光学高温计测显的优点，并对比了几种作为钨铼热电偶的二次仪表的特性，以供人们在使用中选择。     

钨铼快速热电偶的实用化趋势

本文回顾了我国钨铼热电偶的发展历史,阐述了钨铼热电偶的优点,指出在我国钨铼快速热电偶已具备在更大范围内实用化的条件。最后,为了推动钨铼热电偶的实用化,提出了三点建议。     

石墨化电炉接触式快速测温试验

1 简介石墨化电炉测温,常用热电偶、光学高温计或光电温度计,通过插入电炉内的石墨测温管,并采用氮气保护办法来测取炉温数据(注)。但是,由于石墨化电炉内产生含游离碳烟气,这种气体在光谱的红外线部分,有强的吸收带,所以使测量结果的误差偏大。为此,上海碳素厂与鹰潭市稀有金属合金厂经过多次讨论,签定了《关于石墨化电炉接触式快速测温试验协议》,即用钨铼热电偶直接接触快速测量石墨化电炉的温度。     

W-5%Re/W-26%Re钨铼偶丝氧化行为

为了解钨铼热电偶丝在空气中的氧化过程、氧化产物成分、氧化膜生长情况,进行了DSC/TG、XRD、SEM等实验.通过填充惰性物质、脱氧、造氢、密封等实体化技术对钨铼热电偶进行了防氧化保护,利用SEM观察了保护后的钨铼偶丝的形貌.结果表明:在空气中,钨铼偶丝高温氧化产物主要为WO3;W-5%Re偶丝873℃时已经可以观察到氧化,W-26%Re的氧化温度可低至681℃;钨铼偶丝氧化层开裂并呈放射状生长,不能形成保护性氧化膜;经防护后的钨铼偶丝断面保持完整,未出现明显氧化膜.     

从钼精矿焙烧烟气中回收铼工业试验总结

前言铼是高熔点稀散金属,它在化工、冶金、国防尖端科学方面占有非常重要的地位。铼具有很高的电子发射性能,广泛应用于无线电、电视和真空技术中;铼具有很高的熔点,是一种重要的高温仪表材料;铼和铼的合金还可以作电子管元件和超高温加热器以蒸发金属;钨铼热电偶具有高的热电动势,可测2600℃甚至2800℃;铼在火箭导弹上用作高温涂层;宇宙飞船用的仪器和高温部件,如热屏蔽,电孤放电,电接触都需铼;铼还     

高温钼丝炉炉温测量与控制

在有还原性介质的高温加热炉中测温，用钢铑热电偶容易被腐蚀，用辐射高温计易受周围环境影响。本文阐述了在上述情况下用普通钨铼热电偶直接连续测取0～1600℃高温的关键技术问题．同时提出了在冷热态电阻比极低的情况下，如何用简易可行的方法一例如电流反馈法或电压有效值反馈法，实现软启动的问题，给出了具体的控制方案及电路图。     

从钼精矿焙烧烟气中回收铼工业试验总结

1.前言铼是高熔点稀散金属,它在化工、冶金、国防尖端科学方面占有非常重要的地位。铼具有很高的电子发射性能,广泛应用于无线电、电视和真空技术中;铼具有很高的熔点,是一种重要的高温仪表材料;铼和铼的合金还可以作电子管元件和超高温加热以蒸发金属;钨铼热电偶具有高的热电动势,可测2600℃甚至2800℃;铼在火箭导弹上用作高温涂层;宇宙飞船用的仪器和高温部件,如热屏蔽,电弧放电,电接触都需铼;铼还用来增强钨钼合金的高温性能并延长其寿命;铼金属、盐类及氧化物可做氢化及去氢工艺过程的优良催化剂。因而世界上近年来的产量供不应求。     

Boron and boron carbide coatings by vapor deposition

The Bureau of Mines investigated the formation of boron and boron-carbide coatings by vaporphase reactions. Optimum parameters were determined for hydrogen reduction of boron trichloride and for the formation of boron-carbide coatings on graphite by reaction with the deposited boron. At 1300°C, about 85 pct of the boron was deposited. Tungsten substrates did not react with the boron deposit; other substrates reacted to various extents. The hydrogen reduction of boron tribromide was briefly investigated. Boron carbide was deposited at 1300°C by adding methane to the boron trichloride-hydrogen feed gas. The chemical composition of the vapor-deposited boron carbide approximated B₄C. A method of etching B₄C was developed to study its microstructure. When boron was deposited on graphite at 1500°C, very hard, uniform, strongly adherent coatings of B₄C were formed that might be useful in applications such as rocket nozzles and chemical reaction and processing vessels.     

陶瓷材料AIN及TiCN中氧、氮的测定

本文介绍了采用LECO TC-136氧/氮测定仪测定陶瓷材料AIN,TiCN中氧及氮的惰气熔融脉冲加热法。该法用Ni-Sn作助熔剂,用“高温”型石墨坩埚提取气体。Al_2O_3及TiO_2中氧回收率分别是100.1％和98％,氮的分析值与化学法比较是满意的。     

Simultaneous reduction nitridation for the synthesis of tungsten nitrides from Ni–W–O precursors

Abstract

Tungsten nitrides were synthesised from NiO–WO₃ and NiWO₄ precursors at 973–1273 K in a flow of H₂–N₂ gas mixture. The reduction–nitridation reactions were carried out isothermally in fluidised bed reactor, and the off-gas from the reactions was continuously analysed by gas chromatography. The effect of reaction temperature and precursor composition on the rate of formation of Ni–W nitrides was studied. The different phases developed during the reduction–nitridation reactions were identified by X-ray diffraction analysis technique. The morphology and the grain structure of the precursors were examined by SEM, and the elemental composition in the structure was analysed by electron dispersive spectrometry. The results showed that the reduction of Ni–W–O precursors proceeded in a stepwise manner (NiWO₄→Ni–WO₃→Ni–WO₂→Ni–W). Tungsten nitrides (WN and WN₂) were formed from the reaction of the freshly reduced W metal with N₂ gas and WN was the predominant phase detected at higher temperatures. The reaction mechanisms were elucidated from the apparent activation energy values and the application of different formulations derived from the gas–solid reaction model at early and later stages of reactions. It was concluded that the interfacial chemical reaction is the rate determining step at initial stages, while a combined effect of gaseous diffusion and interfacial chemical reaction controlled the reaction at later stages. At final stages, the nitridation reactions contributed to the reaction mechanism leading to produce tungsten nitrides.     

惰气熔融-热导法测定碳化钽粉中氮

对惰气熔融-热导法测定碳化钽粉中氮量的分析方法进行了研究。针对碳化钽粉难熔的特点,对石墨坩埚类型、镍助熔剂、石墨粉用量和样品量等测试条件进行了优选。确定的最佳分析方法为,称取0.10～0.12 g样品于0.35 g镍囊中,投入装有0.03 g石墨粉的高温型石墨坩埚中进行测定,分析功率为5.2 kW。用钢标样确定氮工作曲线的校正系数,氮的加标回收率在94%～108%之间。采用本方法测定了2个碳化钽粉中氮量,测定值与GB/T 15076.13-1994(蒸馏分离－奈斯勒试剂分光光度法)吻合,相对标准偏差(n=8)≤3.0 %。     

Solubility of nitrogen and carbon in CaO-Al2O3 melts in the presence of graphite

CaO-Al₂O₃ slags were melted in graphite crucibles under N₂-CO-Ar gas mixtures at 1600°C. The contents of total nitrogen, cyanide and total carbon of the slags were determined by chemical analyses of quenched samples taken by suction from the melt. The nitrogen is present in the melt as nitride N^3- ion and cyanide CN^-1 ion, and carbon as cyanide and carbide C_2- ion. The equilibrium constants for the respective reactions were evaluated. It is found that the nitride capacity of the melt decreases whereas the cyanide and carbide capacities increase with increasing CaO/Al₂O₃ ratio.     

Rate of reactions between carbon dioxide and graphite

Solid graphite rods have been oxidized at temperatures between 1020 and 1510 °C using CO₂ containing gases. The activation energy was found to be 270 kJ/mol in the temperature range from 1020 to 1170 °C where the reaction is chemically controlled. At higher temperatures the reaction is controlled by external mass transfer of CO₂ with an activation energy of 86 kJ/mol. The shift from chemical to mass transfer control depends on the CO₂ pressure and the gas flow behaviour. Since per mol of carbon consumed one net mol of gas is produced, there is a net gas flow away from the graphite surface. This makes the transport of CO₂ to the surface more difficult, retarding the rate at high temperatures.     

Volatilisation problems in the measurement of mould fluxes crystallisation by hot thermocouple technique

Since it is first verified that saturating the room temperature quartz tube with fluoride gas is not effective for inhibiting the NaF volatilization, the effects of fluorides volatilization on crystallization properties of mold fluxes are studied under the open condition of hot thermocouple technique. The volatilization ratio is analyzed by sintering the mold fluxes at an appropriate temperature to weigh the sample accurately. The results show that, at high holding temperatures (1400 - 1500°C), with the increase of fluoride losses and proportion of SiF₄ in the volatiles, the initial crystallization temperature, crystalline fraction, and relative crystallization rate reduced, which leads to the whole C curve shift to the bottom-right. At low holding temperatures (1300°C), the initial crystallization temperature increases with the increase of fluoride losses, and the crystallization could begin during the holding stage. Therefore, it is infeasible to study the crystallization behavior of mold fluxes using hot thermocouple technique.     

Temperature-Dependent Multi-Scale Pore Evolution and Nitrogen Diffusion in Nuclear Graphite

Two- and three-dimensional pore evolutions along with nitrogen diffusion behavior in nuclear graphite were studied using thermogravimetric analysis, X-ray computed tomography, scanning electron microscopy, and the Brunauer-Emmett-Teller method. Calculated nitrogen diffusion activation energy was approximately 2.5 kJ·mol⁻¹. Stable weight loss of graphite specimens increased with temperature, primarily due to more escaped nitrogen from the graphite matrix. Fewer nano-pores and more micro-pores were formed because of the nano-pore coalescence. At 873 K (600 °C), graphite microstructure evolution might be induced by temperature and mild oxidation. Before being placed into high temperature gas-cooled reactors (HTGRs), porous nuclear graphite should be subjected to vacuum at 573 K to 673 K (300 °C to 400 °C) to minimize ¹⁴N in the pores and ¹⁴C generated during operation of HTGRs.

     

Dissolution kinetics of particulate graphite injected into iron/carbon melts

An experimental investigation was undertaken to study the kinetics of graphite dissolution in gasstirred iron/carbon melts. Laboratory apparatus was developed to allow the injection of closely sized graphite into the bottom of a 1 kg scale reactor with nitrogen as a carrier gas. The effects of gas flow, particle loading, particle size, bath sulfur, and temperature on the rate of dissolution were assessed. It was found under the experimental conditions used that the graphite dissolution rate kept pace with the injection rate up to approximately 85 pct of carbon saturation, except when sulfur is present in the bath, in which case the dissolution rate is retarded. Modeling the rate of graphite particle dissolution supports the experimental results in that particle dissolution occurs quickly and under mass transport limitations. Computer generated gas-stirred flow field diagrams for the experimental reactor indicate that conditions exist for particle entrainment in the bath, and hence complete contact with the melt at all times during dissolution. formerly Experimental Scientist, CSIRO, Division of Mineral Engineering