废旧钴酸锂材料选择性硫化过程转化行为研究

废旧LiCoO2电池资源化利用对缓解我国锂钴资源短缺具有重要意义。分析硫磺气体选择性硫化LiCoO2的热力学过程,探讨温度、硫磺量、总压力、添加剂等因素对LiCoO2硫化转化行为和物相转变规律。结果表明,在温度≤600 ℃条件下,调节气氛的氧分压P(O2)和硫磺分压P(S2)可调控Li-Co-S-O体系不同物相的稳定区域,实现LiCoO2选择性硫化和产物调控,且避免SO2等气体的产生。降低体系总压P可降低选择性硫化LiCoO2的反应温度,添加固体碳、铁和氧化铁等将显著影响硫化产物中锂和钴的存在形式。添加FeS2或SO2气体可代替S2气体的硫化作用,对硫化产物中锂和钴的稳定存在形式没有明显影响。气体选择性硫化LiCoO2试验结果验证了计算结果,LiCoO2硫化增重初期SO2利用率约为75%。     

Pt-Al涂层在两种熔盐中的高温热腐蚀行为

采用表面涂盐法研究了镍基高温合金上Pt-Al涂层在Na2SO4和Na2SO4+NaCl两种熔盐中的高温热腐蚀行为.结果表明,在Na2SO4熔盐中,Pt-Al涂层具有很好的抗热腐蚀性能,表面只生成一层致密的氧化膜.在Na2SO4+NaCl混合熔盐中,它的抗热蚀性下降,涂层发生了内氧化和内硫化,并且内层NiAl相的腐蚀比外层富Pt相的更严重     

The attack of Co-Cr alloys by Ar-SO2 atmospheres

Cobalt alloys containing up to 25% chromium have been exposed to Ar-10% SO₂ atmospheres at temperatures between 600 and 1000° C. The results show that, although an increase in chromium content leads to a reduction in the reaction rate, even to negligible rates in the cases of the higher chromium contents, all of the alloys are eventually subjected to rapid attack at more or less longer times, depending on the chromium content. The mechanism of the reaction appears to involve the formation of a more or less protective oxide layer which is eventually penetrated by sulfur. The sulfur forms chromium sulfides at the metal-scale interface, removing the chromium from solution and causing an expansion that cracks the protective scale, allowing both the ingress of gas and the formation of rapidly growing cobalt compounds. The process occurs rapidly with Co-5% Cr alloys, whereas, only the initial sulfur penetration is observed with Co-25% Cr alloys during the time scale of the investigation. The penetration of sulfur is thought to occur as a molecular gas species permeating through the scale down physical defects.     

Sulfidation properties of an Fe-23.4Cr-18.6Al alloy at temperatures 1073 and 1173 K in H2S-H2 atmospheres of sulfur at pressures 104-10−5 Pa

An investigation is reported on the sulfidation properties of an Fe-23.4Cr-18.6Al(at.%) alloy at 1073 and 1173 K in H₂S-H₂ atmospheres, 10⁴ > P_{S 2} 10⁵Pa. The sulfidation kinetics exhibited an early transient period before onset of parabolic kinetics. Values of the parabolic sulfidation rate constants increased by as much as 10⁵ from their smallest values at low sulfur pressures, P_{S 2} 10^–4 Pa, to maximum values at sulfur pressures P_{S 2} 10² Pa. Multilayered scales were formed, the number and types of layers dependent on sulfur pressure. A fully developed scale at sulfur pressures P_{S 2} > 10^–3 Pa.     

Hot corrosion: a modification of reactants causing degradation

Abstract

It has been conjectured that if sulfur in the fuel is removed, engine materials will cease to experience attack from hot corrosion since the fuel sulfur has been viewed as the primary source that has caused hot corrosion and sulfidation. Hot corrosion has been defined as an accelerated degradation process that is generally considered to involve deposition of corrosive species (e.g. sulfates) from the surrounding environment (e.g. combustion gas) to the surface of hot components, followed by subsequent destruction of the protective oxide scale. Most papers in the literature since the 1970s consider sodium sulfate as the single salt causing hot corrosion. There has been a push to remove fuel sulfur content to less than 15 ppm. However, sulfur species may still enter the combustion chamber via air intake or with seawater entrained in the air through the air intake of the ship. Seawater contains, in addition to sodium sulfate, magnesium, calcium, and potassium salts. Additionally, sulfate speciation and the content of atmospheric particulate matter (PM) varies considerably around the world and in some places, such as China and India, high PM seems to cause an increased risk of deposit-induced hot corrosion due to atmospheric pollutants rather than a combustion process (i.e. sulfur impurity in the fuel). The increasing operating temperatures of turbine engines and activities within regions of the world that have relatively high pollutant (PM, SO₂, C, Ca, etc.) levels are working conjointly to cause previously unobserved forms of high-temperature corrosion. This paper will cover some of our revised understanding of hot corrosion and consider other possible contaminants that could further complicate our understanding of hot corrosion.     

The sulfidation behavior of Co-Mo alloys containing various ternary additions

The sulfidation behavior of Co-Mo-X alloys, where X is Al, Cr, Mn, or Ti, has been studied over the temperature range 600 or 700°C to 900°C in 10^–2 atm. sulfur vapor to determine the effectiveness of the various ternary elements at reducing the sulfidation rate relative to Co-Mo alloys. For comparative purposes, each ternary alloy contained a constant atomic proportion (i.e., 55Co, 20Mo, and 25X). All of the alloys were multiphase, and sulfidized to form complex, multilayered scales. The scales usually consisted of an outer layer of cobalt sulfide, an intermediate layer that contained primarily the ternaryelement sulfide, and an inner layer which was heterophasic. Usually, each phase within the multiphase alloy sulfidized independently of one another. In the region of the alloy/scale interface there was often a narrow band of fine porosity (transitional band) together with fine precipitates that separated the inner sulfide from the base alloy. It was found that Al and Cr improved the sulfidation resistance of the Co-Mo binary alloy, whereas Mn had the opposite effect. The Ti-containing alloy underwent a mixed sulfidation/oxidation process, so that its kinetics were inapplicable. Aluminum was found to exert the most beneficial effect. The sulfidation behavior of Co-Mo-Al alloys containing a range of Al concentrations was studied at both 700 and 900°C. It was found that for Al to be effective, a sufficient amount of the spinel, Al_0.55Mo₂S₄, had to form within the inner portion of the scale.     

The corrosion behavior of Ni-Nb alloys in a mixed gas of H2-H2O-H2S

The corrosion behavior of Ni-Nb alloys containing up to 40 wt.% Nb was studied over the temperature range of 550–800°C in a mixed H₂/H₂O/H₂S gas. The scales formed on all alloys were multilayered. The outer scale was single-phase Ni₃S₂, while the structure and constitution of the inner scale depended on alloy composition and reaction conditions. Internal oxidation has been found in Ni-20Nb and Ni-30Nb, external oxidation has been observed on Ni-34Nb. Platinum markers were located at the interface between the outer scale and inner scale. The decrease in corrosion rate with increasing Nb content may be attributed to the presence of increasing amounts of Ni-Nb double sulfides as well as to the presence of Nb₂O₅ in the inner region of the scale.     

The corrosion of Fe-Mo alloys in H2/H2O/H2S atmospheres

The corrosion of Fe-Mo alloys containing up to 40 wt.% Mo was studied over the temperature range 600–980C in a H₂/H₂O/H₂S mixture having a sulfur pressure of 10^–5 atm. and an oxygen pressure of 10^–20 atm. at 850C. All alloys were two-phase, consisting of an Fe-rich solid solution and an intermetallic compound, Fe₃Mo₂. The scales formed on Fe-Mo alloys were bilayered, consisting of an outer layer of iron sulfide (FeS) and of a complex inner layer whose composition and microstructure were a function of the reaction temperature and of the Mo content of the alloys. No oxides formed under any conditions. The corrosion kinetics followed the parabolic rate law at all temperatures. The addition of Mo caused only a slight decrease of the corrosion rate. Platinum markers were always located at the interface between the inner and outer scales, indicating that outer scale growth was primarily due to outward diffusion of iron, while the inner scale growth had a contribution from inward diffusion of sulfur.     

高温时效对310不锈钢硫化行为的影响

研究了高温时效前后的310不锈钢样品在气氛总压为1 05Pa，2.3%SO2/S2/8.8%N2气氛中600℃下的高温硫腐蚀行为.利用金相、扫描电镜/ 能谱及Ｘ射线衍射等分析其腐蚀形貌、成分及结构.结果表明：经时效处理的310不锈钢比未 时效处理者腐蚀严重，前者以晶间腐蚀为主，后者以均匀腐蚀为主.310不锈钢于700℃，100 00 h时效后在晶界大量析出σ相，使晶界附近贫Cr，降低了其抗硫腐蚀性能.     

Kinetics and mechanisms of the oxidation of chromium in H2-H2O-H2S gas mixtures

The oxidation of pure chromium in H₂-H₂O-H₂S gas mixtures was studied as a function of gas composition at 900°C. Oxidation kinetics were measured using a thermogravimetric apparatus, and the oxidation products were characterized using scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). Chromia scales formed when the H₂O/H₂S ratio was about 10 or greater. Scales that comprised a mixture of Cr₂O₃ and chromium sulfides formed when the H₂O/H₂S ratio was about 3, even though Cr₂O₃ was the thermodynamically stable phase under these conditions; i.e., a kinetic boundary exists for pure chromium in H₂-H₂O-H₂S gas mixtures. The transition from chromia scale formation to the formation of scales containing both oxide and sulfide with a change in gas composition (decrease in the H₂O/H₂S ratio) is associated with an inhibition of the overgrowth of growing, metastable sulfide nuclei by the thermodynamically stable Cr₂O₂ phase. Presulfidation experiments confirmed that metastable chromium sulfide can continue to grow after H₂O is added to the gas phase when the H₂O/H₂S ratio in the gas phase is less than a critical value at the temperature of interest.