Sulfide Scale Research Articles

Sulphidation of copper-nickel alloys—II. Scale growth kinetics

The growth rates of the individual layers in sulphide scales on Cu-Ni alloys have been studied in order to attempt to determine the controlling processes. Parabolic kinetics are obeyed by each layer in scales on Cu−20% Ni and Cu−50% at 718 K. The variations in the layer growth rates with alloy composition at 718 K and the variations for Cu−50% Ni between 653 K and 770 K are also assessed. The growth rate of the outer, CuS, layer decreases with increasing temperature, essentially because of its decreasing thermodynamic stability. The variation of the growth rate of each phase with alloy composition and temperature is interpreted in terms of cation diffusion, growth of both copper and nickel sulphides apparently being controlled by ionic diffusion across the NiS layer. The effects of alloy-scale separation on both scale morphologies and layer growth rates are examined.

Studies of the kinetics of nickel sulfidation in H2S-H2 mixtures in the temperature range 450–600°C

The reaction between pure nickel and H2S-H2 mixtures containing 1–65% H2S has been studied over the temperature range 450–600°C. The sulfidation of nickel in the temperature range 560–600°C has been found to follow a linear rate law at low concentrations of H2S and a parabolic rate law at higher concentrations (10% and 65% H2S); X-ray examination of the scale formed on the metal showed it to be almost entirely β-Ni3S2. On the basis of the kinetics and marker studies it can be concluded that the sulfide scale on nickel is formed by the outward transport of the metal and the inward transport of sulfur. In the temperature range 450–500°C the sulfidation of nickel follows a parabolic rate law. In mixtures containing 10% H2S the scale formed contains voids, the occurrence of which is connected with formation of Ni7S6. It has also been shown that the rate of transport through the Ni3S2 layer has an essential influence on the formation of a continuous layer of Ni7S6. Marker studies have shown that both nickel and sulfur appear to be mobile in β′-Ni3S2.

ニッケル単結晶上における初期硫化被膜の成長

The initial growth of nickel-sulphide formed on the (100), (110) and (111) planes of single crystals in low-pressure H2S and H2-H2S atmospheres was studied by electron microscopy. Sulphidation was carried out at 100 to 500°C.Main results are as follows:(1) The sulphide formed on the specimen was heazlewoodite Ni3S2.(2) Increasing of thickness of sulphide scale, lowering of sulphidation temperature and increasing of H2S pressure led crystals of sulphide to disorientation.(3) At low temperatures (≤300°C) the direction of Ni3S2 [1\bar101] was perpendicular to the surface of the nickel crystal at an early stage, consisting of a combination of two kinds of orientations equivalent and symmetrical to each other. This was explained on the assumption that the chemisorbed layer formed on a clean surface of Ni is the immediate substrate for the growth of Ni3S2. But this relationship at an early stage disappeared as the sulphide scale grew.(4) At high temperatures (≥400°C) the above relationship didn’t appear and the plane of Ni3S2 (00·1) was parallel to the surface of Ni.

Cation Distributions in the Ferrous Sulfide Scales Formed on Binary Iron Alloys

Cation Distributions in the Ferrous Sulfide Scales Formed on Binary Iron Alloys

The Transport of Chromium in Cr2 O 3 Scales in Sulfidizing Environments

The diffusivity of chromium in scales formed during the oxidation of chromium at 900°–1000°C appears to increase by several orders of magnitude when an initially present oxide scale is exposed to sulfur‐bearing atmospheres at low oxygen partial pressure. As a result chromium sulfide scales grow on both sides of the preexisting oxide layer. The transition from oxidation to sulfidation corresponds to a change from parabolic to linear weight gain, indicating that the sulfide growth is controlled by a constant rate of supply of chromium through the oxide to the outer oxide‐sulfide interface, under fixed experimental conditions. The sulfidation rate increases with sulfur partial pressure, indicating that chromium transport in the oxide is affected by changes in the defect structure of induced by the presence of sulfur. A model is proposed in which sulfur enters the oxide as an electron donor, thereby increasing the concentration of chromium vacancies and interstitials.

The effects of molybdenum additions to nickel-chromium alloys on their sulfidation properties

The effect of molybdenum additions to γ-phase Ni-Cr on the reaction of the alloys with H2/H2S atmospheres at 700°C has been investigated. The effect is to reduce the rate of internal sulfidation of the alloys, diminish greatly the extent of liquid sulfide formation and slow the growth rate of external solid sulfide scale. The first two effects are thermodynamic in origin whilst the last effect is due to favorable doping of Cr2S3 and to the formation within a Cr3S4 scale of MoS2 precipitates which partially block outward metal diffusion.

The oxidation of nickel-chromium alloys in atmospheres containing sulphur dioxide

The simultaneous attack of oxygen and sulphur on a range of Ni Cr alloys containing 2–30%Cr has been investigated between 500 and 790°C in Ar-10% SO 2 atmospheres. Reaction kinetics were followed using an automatic recording balance and scale structures were examined by metallography, scanning electron microscopy and microprobe analysis. Compared with pure Ni, the addition of up to 5%Cr at 500°C, or 15%Cr at 700°C, has little effect on kinetics. At higher Cr levels (8–10% at 550°C or 15–20% at 700°C) initial protective behaviour is followed by a period of rapid attack. Even with Cr contents as high as 30% the protection shown is not as good as in the absence of sulphur from the atmosphere. The failure to form protective oxides is thought to be due primarily to the penetration of initially formed Cr 2O 3 scales by sulphur, possibly by solution and diffusion, leading to the formation of duplex (oxide + sulphide) scales which grow rapidly by nickel ion migration.

The Preferred Orientation of the Ferrous Sulfide Scale on Pure Iron at 700°C

The Preferred Orientation of the Ferrous Sulfide Scale on Pure Iron at 700°C

High-temperature corrosion of low Cr-Fe alloys in sulfur vapor

The sulfidation behavior of low Cr-Fe alloys was studied over the range of 700–900°C under 1 atm of pure sulfur vapor. Sulfidation of alloys with 3.7 and 7.4 wt.% Cr does not follow the parabolic rate law at 750–800° C, although for other alloy compositions and temperatures it obeys that law. Sulfide scales consisted of a three-layer structure. The outer layer was FeS, but the inner and intermediate layers contained FeS, FeCr2S4, and Cr3S4, their relative amounts and morphologies depending on the corrosion temperature and alloy composition. Increasing Cr contents resulted in a change in the morphology of FeCr2S4 from dispersed particles to a thick layer. Ultimately, FeCr2S4 was displaced by Cr3S4. The formation of FeCr2S4 and the scale growth mechanism are discussed also.

Sulphidation of Cu and Cu-Ni alloys in H 2S/argon mixture

The sulphidation of cold-worked Cu and annealed Cu and Cu-Ni alloys containing 10 and 50wt.%Ni, has been studied in dry H 2S/argon (1 : 20) mixture at 500°C for the cold-worked, and in the range 320–500°C for the annealed samples. The reaction kinetics were linear in all tests. The rate of sulphidation decreased with increasing amount of cold work. The scale on annealed sample showed considerable blister formation and grain growth which were appreciably less on samples with increasing cold work. There was no blister formation on alloys. From combined techniques of X-ray powder and diffractometry, the sulphide scale on Cu was found to be mainly Cu 2S, while that on the alloys a thick scale of Ni 3S 2 was associated with a thin layer of Cu 2S. Of the two alloys, Cu-10%Ni sulphidized faster than Cu-50%Ni at all temperatures. The activation energy of sulphidation of annealed Cu was about 74 kJ/mole compared with 40 kJ/mole for the alloy. The dissociation of the adsorbed gas at the gas/scale interface is considered to be the rate-controlling process for the linear kinetics.

The Effect of Sulfur Pressure on the Iron Sulfide Scale Growth at Elevated Temperature

The Effect of Sulfur Pressure on the Iron Sulfide Scale Growth at Elevated Temperature

Organic polysulphides in town gas: I. The corrosion problem

AbstractBlockage of small‐bore copper tubing in gas appliances has sometimes arisen from the presence of copper sulphide scale formed by attack on the copper by organic sulphur compounds in the gas. The sulphur compounds responsible for this attack which occurs at atmospheric temperatures, are identified as organic polysulphides, probably the lower aliphatic trisulphides and tetrasulphides, formed from mercaptans and elemental sulphur. Such reactions are shown to occur under the influence of a base catalyst such as lime, and under the conditions existing in the iron‐oxide purifying plants used to remove hydrogen sulphide from fuel gases; mercaptans are present in the gas, and sulphur in the purifying material.A colorimetric test using piperidine has been developed for determining organic polysulphides in fuel gases at concentrations below 1 part/million v/v.Some comments are given on the relevance of polysulphide formation and corrosion to the distribution of North Sea natural gas.

Mechanism of Sulfidation of Nickel‐Chromium Alloys at 700°C as Inferred from Inert and Radioactive Marker Techniques

Sulfidation experiments have been carried out on a Ni‐20 w/o Cr alloy using platinum markers and the tracer S35 to elucidate the transport mechanism for the diffusion‐controlled formation of the duplex sulfide scale. It is concluded that outward diffusion of nickel and chromium accounts entirely for the growth of both layers. Chromium sulfide, being more stable than nickel sulfide, is formed by decomposition of the latter at the boundary between the two layers. This process is compensated for by a rapid growth of nickel sulfide at the gas‐scale interface. It has been unequivocally demonstrated that sulfur diffusion does not contribute significantly to scale growth.

Kinetics and Morphological Development of the Sulfide Scale on a Nickel‐20 w/o Chromium Alloy in Hydrogen Sulfide‐Hydrogen Atmospheres at 700°C

The sulfldation kinetics of a Ni‐20 w/o (weight per cent) Cr alloy exposed to hydrogen sulfide‐hydrogen atmospheres at 700°C have been determined as a function of the sulfur pressure. The morphology and phase composition of the duplex sulfide scale formed as a corrosion product have been investigated. The kinetics appear to be controlled by diffusion of the reactants through the scale. No significant dependence of the parabolic rate constant on the sulfur pressure has been determined within the wide range . A correlation is presented for the growth kinetics and the structural features of the nickel and chromium sulfide constituents of the scales with the ternary nickel‐chromium‐sulfur phase diagram.

On the mechanism of sulphide scale formation on iron

Specimens of iron with various dimensions and degrees of purity were sulphurized in sulphur vapour at atmospheric pressure at 710°C. After reaction for 25 min radioactive sulphur in the form of a small tablet was added, and the reaction was continued for a given period of time. The specimens were sectioned for metallographic study and autoradiograph exposure. It has been shown that the process of the scale growth can be different in different parts of the same specimen depending on the local conditions of scale shrinking. Both single or double layer scale can be formed, the formation of the latter being possible both with and without the transport of sulphur from outside.

Effect of Inhibitors on Protective Properties Of Iron Sulfide Scale

Abstract It has been found that the deposition of iron sulfide scale can be altered considerably by addition of certain chemicals, e.g., formaldehyde, to aqueous system containing hydrogen sulfide. These chemicals modify the sulfide scale structure to render it an effective barrier to corrosion.

Kinetics and Mechanism of Nickel‐Sulfur Reaction

Kinetics and mechanism of the reaction between nickel and sulfur vapors were investigated in the temperature range 480°–640°C under atmospheric pressure. The sulfurization of nickel has been found to follow, under these conditions, the parabolic rate law. The activation energy of this process amounts to 22 kcal/mole. The examination of x‐ray patterns of the scale formed on the surface of the metal has demonstrated that this scale layer is composed almost entirely of . Morphologic investigations show that the scale is composed of two distinct layers. The outer layer, constituting the main part of the whole scale, is compact, polycrystalline, and exhibits an ordered growth texture. The inner layer is porous and does not exhibit any growth texture. The investigations carried out with the aid of the radioactive sulfur isotope 35S have demonstrated that the sulfide scale on nickel is formed exclusively by the outward diffusion of the metal.The confrontation of experimental data with the results obtained by Dravnieks (1) leads to the assumption that the mechanism of the sulfide scale formation on nickel does not depend on the state of aggregation of the oxidizing medium.

不銹鋼製硫黄製錬釜内壁に生成する硫化物スケールに関する研究

不銹鋼製硫黄製錬釜内壁に生成する硫化物スケールに関する研究

鋳鉄製硫黄製錬釜内壁に生成する硫化物スケールに関する研究

We investigated the sulfide scale formed upon the inside wall of ordinary cast-iron pots for sulfur-smelting. Upon microscopic observation of the sections (about 26 mm thick) and chemical and X-ray analysis at various positions of the scale, we obtained the following results: (1) The scale was mainly composed of pyrrhotite and Si was distributed all over the scale, but C was retained in the inner part as graphite. (2) The S content in the pyrrhotite determined by X-ray analysis was found in good agreement with that from chemical method, and rapidly decreased toward the sulfide/metal interface. (3) Cr seemingly moves toward the outer layer of the scale when its content is small. (4) Si as well as Fe and S were distributed periodically with identical intervals in the scale. But these phenomena may be attributed to another mechanism considered from the practical conditions.

Colorimetric estimation based upon a silver sulfide scale and use of the ring oven technique: H. Weisz, M.B. Celap, and V. Almažan, Mikrochim. Acta, 1959, 36–43

Colorimetric estimation based upon a silver sulfide scale and use of the ring oven technique: H. Weisz, M.B. Celap, and V. Almažan, Mikrochim. Acta, 1959, 36–43