Catastrophic Corrosion Research Articles

ChemInform Abstract: CHEMICAL REACTIONS INVOLVED IN THE INITIATION OF HOT CORROSION OF B‐1900 AND NASA‐TRW VIA

AbstractDie Ni‐Basis‐Legierungen B‐1900 und NASA‐TRW VIA werden bei 900°C voroxidiert, mit Na2 S04 beschichtet und ebenfalls bei 900°Korrosionstests durchgeführt.

The hot corrosion of cobalt-base alloys in a modified Dean's rig - III. CoCrMo alloys

A range of CoCrMo alloys have been exposed at 900°C to salt-bearing atmospheres in a modified Dean's rig. The atmosphere consisted of air containing vapours of, respectively, Na 2SO 4, NaSO 4 + NaO, and Na 2SO 4 + NaCl. Both isothermal and 24-h cyclic exposures were used. In general, the presence of molybdenum in the Cr 2O 3-forming alloys caused accelerated and sometimes catastrophic corrosion. The influence of 2.5 Mo addition to the alloys was observed to be minimal. The presence of 10% Mo in the CoO-forming alloys caused acidic fluxing in the pure Na 2SO 4, while the basic salt caused sulphidation corrosion.

Hot Corrosion of Nimonic 105 in Sodium Sulfate-Sodium Chloride Melts

Abstract The corrosion behavior of Nimonic 105 in molten Na2SO4, NaCl, and mixtures of these two salts, at 900 C, in laboratory air and under O2 + SO2/SO3 atmospheres has been evaluated by potentiodynamic, potential decay, and free corrosion potential measurements. In addition, the corrosion products were examined using several electron-optical techniques, and by other analytical methods. Pure Na2SO4 in air did not seem to be very corrosive towards Nimonic 105. Addition of NaCl to the molten Na2SO4 resulted in increased dissolution of Nimonic 105, which was in general nonuniform, alloy constituents nickel and cobalt dissolving more than others. Evidence of internal attack and enhancement of dissolution of the Ni alloy by SO3 was significant only when the corrosion conditions were prolonged. In pure NaCl, catastrophic corrosion occurs, which has been attributed to the depletion, dissolution, and vaporization of some alloy species.

The corrosion behaviour of iron in hydrogen chloride gas and gas mixtures of hydrogen chloride and oxygen at high temperatures

Catastrophic corrosion of iron by oxychlorination in hydrogen chloride gas containing 0–75 vol. % oxygen at 300–800°C has been investigated mainly by means of measurements of weight loss and the amount of sublimates. In pure hydrogen chloride gas, the corrosion behaviour was determined by the formation and sublimation of ferrous chloride. Addition of oxygen to hydrogen chloride gas greatly accelerated corrosion of iron due to the formation and sublimation of a low melting point volatile ferric chloride by oxychlorination reactions.

High‐temperature corrosion of NiCrAl alloy in oxygen‐chlorine mixtures

AbstractIn order to decrease the attack of chlorine in O2Cl2N2 mixtures to NiCr alloys at high temperatures, the corrosion of a preoxidized Ni 20 Cr 4 Al alloy was investigated in N2O2 mixtures with 5 to 150 torr O2 and 20 torr Cl2 at 800°. For the generation of a protective layer of Al2O3 both the untreated and Al evaporated alloy sample was preoxidized in a H220 torr H2O atmosphere at 900° C. As was found, the catastrophic corrosion by Cl2 in a N2Cl2 gas mixture with 20 torr Cl2 could not be prevented by an Al2O3 layer. However, in the simultaneous presence of an oxygen content in the corroding gas mixture not lower than 10 torr, the attack of chlorine could be drastically decreased. The presence of 50 torr Cl2 postulates an oxygen pressure which is technically unrealistic. Since the formed oxide layer spalled off during the cooling period, the Ni 20 Cr 4 Al alloy cannot be used as material for cyclic oxidation. To what extent ThO2 particles dispersed in the alloy can prevent a spalling effect of the oxid film is at present an open question.

The corrosion of carbon steel by wet elemental sulphur

The corrosion behaviour of carbon steel in wet elemental sulphur under both aerobic and anaerobic conditions is reported. The corrosion reaction was studied as a function of the initial pH of the system and the particle size of sulphur. Catastrophic corrosion is observed after an induction period which is found to be a function of the initial pH of the system, the particle size of the sulphur and the presence or absence of oxygen. Corrosion potential measurements suggest that the observed catastrophic corrosion process is subject to catalysis of the cathodic reaction. A possible mechanism for the corrosion reaction is discussed.

Oxidation and hot corrosion of nickel-based alloys containing molybdenum

The oxidation of Ni-15% CrMo alloys has been studied at 900°C in flowing and static oxygen atmospheres. In flowing atmospheres, molybdenum has no effect: all the alloys oxidize in a protective manner. However, in static atmospheres the oxidation rate of alloys with > 3% Mo eventually accelerates, and catastrophic destruction of the alloy takes place. Under these circumstances a molybdenum-rich oxide layer is detected adjacent to the alloy. When specimens are coated with Na 2SO 4 prior to oxidation, alloys containing > 3% Mo again suffer catastrophic degradation, in either flowing or static atmospheres, and again a molybdenum-rich oxide layer is observed. This suggests that the principal role of the salt coating is to prevent the escape of MoO 3 to the atmosphere. The morphology of the attack in the rapid propagation region is very similar to that obtained in pre-sulphidation/oxidation experiments in the absence of salt and that particular aspect of the reaction is not greatly affected by molybdenum; the aluminium content is more important in determining the nature of the propagation. Attack similar to that exhibited by molybdenum-containing alloys can be obtained with Ni-15%Cr binary alloys in the presence of MoO 3 vapour in the atmosphere, and this might suggest that the MoO 3 reacted with the Na 2SO 4 to produce an acid (SO 3-rich) salt, leading to acidic fluxing. However, very similar types of attack were obtained when Na 2MoO 4 was added to the Na 2SO 4, and this should not have affected the acidity of the salt at all. These experiments suggest that acidic fluxing may not be important in the hot corrosion of alloys of this type (molybdenum-containing) and that when catastrophic corrosion is observed, its initiation is probably due to the formation of a molybdenum-rich oxide layer, molten during the reaction. There appears to be a threshold molybdenum content below which attack does not occur, and this seems insensitive to an increase in the chromium content from 15 to 25%.

The Effects of Lead on the Hot Corrosion of Nickel‐Base Alloys

Lead is often found as a trace impurity in fuels used in gas turbines. In addition, lead salts may form on hot superalloy parts during turbine operation in contaminated urban environments. An experimental and thermodynamic study of hot corrosion of nickel‐base alloys at 900°C, in the presence of small concentrations of lead salts, has shown that these contaminants can be very deleterious to alloy corrosion resistance. reduces the corrosion resistance of Ni‐Cr and Ni‐Al alloys by complexing normally protective scale to form and which are soluble in the sulfate melt. is a more aggressive contaminant than , and concentrations of 1 mole per cent in the salt condensate can result in catastrophic corrosion rates with Ni‐Cr alloys.

酸化鉛による鉄基2元合金の高温腐食

It has already been recognized by many researchers that lead oxides , the combustion products of tetraethyl lead, cause high temperature catastrophic corrosion of engine exhaust valves and ignition plugs. But most of the studies on them relate to the reactions in the molten state of PbO.The present investigation was carried out on the effects of heating atmosphere and alloying elements on the high temperature corrosion of Fe and its binary alloys by solid PbO in the temperature range 700°∼850°C i.e. below the melting point of PbO.The results of the experiments are summarized as follows:(1) The catastrophic corrosion of Fe and Fe alloys caused by PbO powder was especially prominent at temperature above 770°C in both air (an oxidizing atmosphere) and argon gas (a reduced oxygen atmosphere).(2) The effect of some alloying elements on the corrosion resistance of Fe was determined; the alloying elements improving the corrosion resistance were Cr and Ni, and those decreasing especially in a reduced oxygen atmosphere were Al and Si.

Catastrophic grain boundary corrosion in a Cr-Fe alloy

Catastrophic grain boundary corrosion in a Cr-Fe alloy

Materials Problems Associated With Uncooled Rocket Nozzles

Abstract A brief discussion is given of thermal shock, erosion, and catastrophic corrosion problems connected with uncooled rocket nozzles used with solid fuels. This is followed by a description of materials and methods used to meet these problems. A small oxygen-hydrogen rocket motor was used to screen materials. Slip cast fused silica was used as a base material and erosion and corrosion resistance was provided in the throat area with arc-sprayed coatings or shells. Fabrication and evaluation techniques used are described as are forming methods and test results. 7.2

Topic of the Month—Catastrophic Corrosion Resulting From Vanadium Pentoxide in Fuel Oil Ash

Catastrophic corrosion resulting from burning fuel oils containing very small concentrations of vanadium is described. Experiments are outlined in which the effects of contamination of fuel oil ash by vanadium and other materials is evaluated after test samples are exposed for varying periods of time at high temperatures. Relative merits of nickel-rich versus nickel-free alloys is mentioned as are experiments involving additives to fuel. Molecular structure of vanadium porphyrin is illustrated and sources of fuel oil containing greatest concentration are listed. 10 references.