Fe-15Ce合金的氧化-硫化腐蚀

研究了Fe-15Ce合金及纯Fe、纯Ce在600和700℃下H 2-H2S-CO2中的腐蚀行为.Fe-15Ce合金的腐蚀速度比纯Fe慢但比纯Ce快得多.腐蚀后合 金表面形成多层的腐蚀产物膜,最外层是基体金属的硫化物（FeS）,中间层为两种金属化 合物组成的混合区,最内层为Ce在O和S作用下的内腐蚀区.合金中15 mass%的Ce不足以阻止 基体金属的硫化,这主要与Ce在Fe中有限的溶解度及合金中存在富Ce相有关.     

Fe-15Ce合金的高温硫化腐蚀

研究了含15wt%Ce的Fe-Ce合金在600～800℃、H2-H2S气氛中的硫化行为,其硫的分压为10-3Pa.结果表明,Fe-15Ce合金的腐蚀速度比纯Fe慢,但比纯Ce快得多,随温度升高其腐蚀速度加快.该合金硫化后形成复杂的腐蚀产物膜,最外层为纯Fe的硫化物层,其下为Ce的硫化物与Fe的硫化物的混合物层;内层为Ce的内硫化区,与之相邻的基体金属层中没有贫Ce现象发生.Ce不能从合金的腐蚀区中向外扩散,而是在腐蚀区内原位地形成Ce的硫化物与Fe的硫化物的混合物.与纯Fe相比,尽管Fe-Ce合金的腐蚀速     

H2-H2O气氛下富Cr合金氧化行为研究进展

随着工业的发展,富Cr合金在H2-H2O气氛下的氧化行为越来越常见.与空气等氧化性气氛相比,在H2-H2O气氛中,富Cr合金形成的氧化膜的抗剥落性能、形貌、合金的氧化速率以及活性元素对其影响等都有较大区别,本文从以上几个方面综述了H2-H2O气氛下富Cr合金氧化行为的研究进展.     

Fe-Si合金在600℃不同气氛中的腐蚀

研究了Fe-5Si,Fe-9Si和Fe-13Si合金在600℃下H2-CO2和H2-CO2-H2S两种气氛中的腐蚀行为。结果表明:在两种气氛中,3种合金的腐蚀均遵循近似抛物线规律;并且合金在含S和不含S气氛中的抛物线速率常数数量级分别为10-8和10-10g2·cm-4·s-1。在H2-CO2气氛中合金氧化膜由Fe的氧化物外层、Fe与Si的混合氧化物内层及Si的内氧化区组成;在H2-CO2-H2S气氛中则由层状的FeS外层和FeS+SiO2混合内层组成。两种气氛中合金均没有生成连续的SiO2外氧化膜。气氛中S的加入使合金表面生成了大量的FeS,FeS中较高的离子缺陷浓度为Fe2+向外扩散提供了通道,从而明显增大了合金的腐蚀速率。Si氧化物的生成提高了Fe在两种气氛中的耐腐蚀性。     

Co-15Ce合金在800℃不同硫压下的硫化

研究了含15wt%Ce的Co-Ce合金在800℃、H2-H2S气体中的硫化腐蚀行为,硫分压分别为10-2Pa及10-3Pa.Co-15Ce合金在800℃硫压为10-2Pa时的腐蚀速度很快,几乎与纯Co相当,而在硫压为10-3Pa时,因其硫压在硫化钴的平衡分解压之下,故其腐蚀速度很慢.该合金硫化腐蚀后形成复杂的腐蚀产物膜,在硫压为10-2Pa时其腐蚀产物膜的最外层为纯Co的硫化物层,其下为Ce的硫化物与Co的硫化物的混合物层,内层为Ce的硫化物与金属Co的混合物层;在硫压为10-3Pa时其腐蚀产物膜仅为Ce     

Fe-Y合金在600～800℃H_2-CO_2-H_2S中的腐蚀

研究了纯Fe、纯Y、Fe-15Y和Fe-30Y合金在600～800℃高硫压(10-3Pa)-低氧压(10-19Pa于600℃或10-15Pa于700℃和800℃)混合气中的腐蚀行为.Y在600℃和700℃发生加速腐蚀,但在800℃形成的腐蚀膜有保护性.加入Y能够降低合金的腐蚀速率,但在所有条件下,合金都形成FeS最外层膜、由两金属的化合物组成的中间层和由α-Fe和Y的硫氧化物的细微混合物所组成内硫化-氧化区.Fe似以相当高的速率穿过中间层形成FeS外层.在合金/氧化膜界面内侧不产生Y的贫化现象.从Y在Fe     

Fe-25Cr-9Mn三元合金高温硫化特性

研究了Fe-25Cr-9Mn合金在800℃、10-3─1Pa硫分压的H2-H2S混合气体中的硫化行为,并与Fe-25Cr合金进行了对比。结果表明:Mn的加入提高了Fe-25Cr合金的抗硫化性能,但作用并不显著。在Fe-25Cr-9Mn合金的多层结构硫化层中形成了较厚且独立的α-(Mn.Fe)S层,但它并没有效地阻挡Fe2+和Cr3+向外的扩散。文中讨论了这种现象的原因以及硫化层分层对铁铬合金硫化行为的影响。     

还原性气氛中HCl和H2S导致Fe-Cr合金在700℃的加速失效

研究了Fe-8Cr,Fe-12Cr和Fe-18Cr合金在700℃含氯和两种硫含量还原性气氛中的腐蚀行为.气氛中H2S含量增加导致合金发生加速腐蚀,尤其造成Fe-18Cr合金表面氧化铬膜退化.合金的加速腐蚀与膜中生成的硫化物和氯化物密切相关.合金的腐蚀速率随其Cr含量的升高而降低.通过计算气氛中平衡时的氯势、氧势、硫势预测了合金与气氛可能发生的反应,并解释了腐蚀机制.     

四元Fe-Cu-Ni-Al合金900℃下的恒温及循环氧化行为

研究了Fe-65Cu-15Ni-5Al和Fe-45Cu-15Ni-5Al两种四元合金在900℃的恒温和循环氧化行为。在恒温氧化条件下,Fe-65Cu-15Ni-5Al合金的氧化速率低于Fe-45Cu-15Ni-5Al合金的;Fe-65Cu-15Ni-5Al合金的氧化动力学前期符合抛物线规律,后期为线性规律,Fe-45Cu-15Ni-5Al合金的氧化动力学符合抛物线规律。然而,在循环氧化条件下,Fe-65Cu-15Ni-5Al合金的氧化速率却高于Fe-45Cu-15Ni-5Al合金的。两种合金在恒温及循环氧化条件下,最外层都形成了以CuO为主的厚氧化层,中间层由Fe、Ni和Al的氧化物以及它们之间形成的复合氧化物组成。除了Fe-65Cu-15Ni-5Al合金在恒温条件下不发生内氧化外,其余情况内层都有不连续的Al2O3层形成,Al_2O_3层内侧发生了Al的内氧化。由于在循环氧化条件下,内层的Al2O3层在应力作用下容易破裂,富铜的Fe-65Cu-15Ni-5Al合金腐蚀速率大大高于Fe-45Cu-15Ni-5Al合金的。但是在恒温氧化条件下,富铜的Fe-65Cu-15Ni-5Al合金α相中的Al含量已达到形成保护性外氧化膜所需的临界浓度,因而比Fe-45Cu-15Ni-5Al合金具有更好的抗高温氧化能力。     

Co-15wt?合金在600℃10~(-8)atm S_2中的腐蚀

研究了含15wt％Ce的Co-15Ce合金及纯Ce、纯Co在600℃、H_2-H_2S中的腐蚀行为,介质的硫分压为10~(-8)atm。结果表明,Co-15Ce合金的腐蚀速度比纯Co慢得多,但高于纯Ce。Co-15Ce合金腐蚀后形成复杂的腐蚀产物膜,最外层为纯Co的硫化物层,其下为Ce的硫化物与Co的硫化物的混合物层,内层为Ce的硫化物与金属Co的混合物。15％Ce不足以阻止基体金属Co的硫化腐蚀,这可能与Ce在Co中有限的溶解度及富Ce第二相的出现有关。     

High temperature corrosion of Fe-Cr-Mn-alloys in H2-H2S and H2-H2O-H2S gas mixtures

The sulfidation of Fe-20% Cr-30% Mn, Fe-25%Cr-20%Mn and Fe-25% Cr was studied at 700°C in H₂-H₂S and the oxidation and sulfidation in H₂-H₂O-H₂S after preoxidation in H₂-H₂O. The sulfidation rate is strongly increased for the Mn-containing alloys, layers of (Mn,Cr)S and (Mn,Fe)Cr₂S₄ are formed. Also the oxidation rate is enhanced compared to Fe-25% Cr by formation of MnCr₂O₄ instead of Cr₂O₃. The sulfidation after preoxidation leads to internal and external sulfidation of the Mn-containing alloys. With increasing oxygen pressure p(O₂) = 10^?26…10^?22 atm. of the H₂-H₂O-H₂S mixtures the sulfidation is suppressed, for the higher oxygen pressure 10^?23 and 10^?22 atm. fast oxidation prevails under formation of MnCr₂O₄. Manganese cannot increase the sulfidation resistance of alloys, in spite of the stability and low degree of disorder of its sulfide, since the mixed sulfide (Mn,Cr)S is formed which has a high degree of disorder, high diffusivities and high growth rate according to the doping effect of trivalent Cr³⁺.     

Co-15wt%Y合金的高温硫化-氧化腐蚀

为检验添加钇对纯钴耐高温－低氧混合气腐蚀的影响,研究了Ｃｏ－１５ｗｔ％Ｙ合金在６００￣７００℃ＣＨ２－ＣＯ２混合气中的腐蚀。合金腐蚀后形成多层结构的腐３蚀产物膜,最外层是单一的硫化钴,中间层为由两金属化合物组成的混合物层。最内层是同氧和硫引起的钇的内腐蚀区。在钇含量达到１５ｗｔ％的条件下未发生钇的选择性外硫化／氧化,这与钇在基体金属中有限的固溶度和合金中出现富钇金属间化合物有关。     

Removal of Boron in Silicon by H2-H2O Gas Mixtures

The removal of boron in pure silicon by gas mixtures has been examined in the laboratory. Water-vapor-saturated hydrogen was used to remove boron doped in electronic-grade silicon in a vacuum frequency furnace. Boron concentrations in silicon were reduced from 52?ppm initially to 0.7?ppm and 3.4?ppm at 1450°C and 1500°C, respectively, after blowing a H₂-3.2%H₂O gas mixture for 180?min. The experimental results indicate that the boron removal as a function of gas-blowing time follows the law of exponential decay. After 99% of the boron is removed, approximately 90% of the silicon can be recovered. In order to better understand the gaseous refining mechanism, the quantum chemical coupled cluster with single and double excitations and a perturbative treatment of triple excitations method was used to accurately predict the enthalpy and entropy of formation of the HBO molecule. A simple refining model was then used to describe the boron refining process. This model can be used to optimize the refining efficiency.     

The corrosion behavior of Co-Mo alloys in H2-H2O-H2S environments

The corrosion behavior of Co alloyed with up to 40 wt.% Mo alloys was studied in H₂-H₂O-H₂S gas mixtures over the temperature range between 600C and 900C. The parabolic rate constants for corrosion decreased with increasing amounts of Mo. The compositions of all gas atmospheres fall in the sulfide(s stability region of the ternary M-O-S phase diagrams at all temperatures investigated. All the corrosion scales were composed of sulfides, while no oxide was detected. The sulfide scales formed were duplex at all temperatures except at 900C. The outer layer consisted primarily of cobalt sulfide, while the inner layer was complex and heterophasic, the phases formed being highly composition dependent. MoS₂ predominated in the inner layer for all alloys. However, a metallic Mo layer was formed in the innermost layer of Co-40 Mo. Activation energies were different for all alloys, increasing with increasing Mo content. Identical kinetics were observed for Co-30Mo corroded at 700–800C. A Chevrel-phase Co_1.62Mo₆S₈ was present in scales formed on the samples exhibiting the temperature-independent kinetics. A possible model in which Co_1.62Mo₆S₈ forms preferentially in H₂-containing mixed gas is suggested. Alloys corroded at 900C formed a lamellar-structure scale which contained Co and CoMo₂S₄ layers perpendicular to the alloy surface. A eutectoid decomposition of an unknown Co-Mo sulfide may be responsible for the presence of the lamellar structure.     

High temperature sulfidation of Fe-Mn alloys and Mn in H2-H2S

The sulfidation behaviour of a range of Fe-Mn alloys and pure Mn were studied at 973 K, 1073 K, and 1173 K in H₂-H₂S atmospheres at constant pS₂ or constant pH₂S/pH₂. The sulfidation kinetics were parabolic in most cases, but two different diffusion processes affect the kinetics. In the sulfidation of the Fe-Mn alloys at 973 K and 1073 K, the diffusion of manganese atoms in the alloy is the rate-determining step and an interlocked scale/alloy interface is observed. At 1173 K there is a transition to rate-control by the diffusion of manganese in the sulfide scale connected with transition from rugged to a planar scale/alloy interface.     

The scaling of a Fe-20Cr alloy in H2-H2O-H2S mixtures

The scaling of an Fe-20Cr alloy has been studied in H₂-H₂O-H₂S mixtures between 973 and 1223 K. According to a simplified phase diagram, Cr₂O₃ and FeS should be the thermodynamically stable compounds in the gas mixtures chosen. The reaction followed a mixed rate law between linear and parabolic, indicating that the reaction rate at the scale-gas interface was comparable with the diffusion rate in the scale. At a constant H₂/H₂S ratio the scaling rate initially decreased slightly with increasing water-vapor pressure. A further increase of the water-vapor pressure resulted in localized sulfide formation, while the other parts of the surface were covered with a Cr₂O₃ film. Only Cr₂O₃ formed above a critical water-vapor content. Three zones could be distinguished when a sulfide scale is formed. The outer zone consisted of practically pure FeS; the intermediate zone was a solid solution of (Fe,Cr)S, partially decomposed to FeCr₂S₄ and metal during cooling; and the inner zone contained small Cr₂O₃ inclusions in an (Fe,Cr)S matrix.     

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.     

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.     

The first-class reciprocal quaternary system H3PO4-K2SO4-K3PO4-H2SO4-H2O application to fertilizer fabrication problems

The first-class reciprocal quaternary system H₃PO₄-K₂SO₄-K_3PO₄-H₂SO₄-H₂O has been carefully investigated at 25 and 75°C. Representations have been given using the Jänecke coordinates. Using the established diagrams as a base, a procedure is proposed for preparing specific fertilizers containing potassium and phosphate ions by reacting phosphate rock with aqueous solutions of KHSO₄, addition of calculated amounts of water to the reaction mixture, elimination of an insoluble products, and programmed water evaporation.