In the hierarchical approach of constitutive modelling, the damage accumulation and resulting strain-softening behavior of geologic materials can be modelled by introducing a concept of damage evaluation. The damage accumulation and softening behavior are affected by the size of specimens. A series of uniaxial tests on cylindrical specimens of a simulated rock were performed. The effect of specimen size on the parameters of the damage model were investigated by using the test results. The empirical results show that the damage parameters can be related to a characteristic dimension, which was expressed in terms of length and diameter of the specimen.

No description available.

No description available.

The Electrochemical Noise Method (ENM) monitors the small potential and current fluctuations that occur naturally in electrochemical cells. It is the least intrusive of all electrochemical techniques in common use. This work uses the Electrochemical Noise Method to investigate the corrosion protection afforded by organic coatings. A parameter called Noise Resistance (Rn) is derived from an Ohm law relationship using the potential noise (Vn) and current noise (In) values. The noise on the current and potential data sets is calculated as the standard deviation value. The work is divided into three areas. The first looked at coating systems in the intact state on the substrate. In general this part of the work has corroborated previous work where Rn values of >l x 10^7 ohms-cm^2 indicated protection of the substrate, correlating with DC resistance values of the coating. The second area of work investigated scribed coatings on the substrate. An important property of organic anti-corrosive coatings is the ability to protect the substrate at a break in the coating. In the scribed work the level of protection afforded at exposed metal by the coating was related to the Noise Resistance value. The third area of this investigation looked at novel ENM techniques to investigate organic coatings. Detached intact coatings were examined in a “U” tube test cell that can be used to simulate different conditions that may be encountered in service. Also a new technique was devised for obtaining ENM data from corrosion cells, this does not require the two separate substrate elements necessary for the more established methodology. The new technique has been called the Single Substrate (SS) technique to reflect this useful property. The technique could be used for in-situ monitoring of structures and it could be adapted for investigation of other situations such as reinforcement bars in concrete

The thermodynamic properties of chloride, nitrate and nitrite AFm hydrates have been determined. Investigations of solid solutions and thermodynamic calculations on the influence of these anions on mineralogical changes in cement paste were performed and compared with experiments. To calculate volume changes, densities of principal crystalline phases occurring in cement were critically assessed and tabulated, in some cases with addition of new data. Database was obtained by calculating densities from crystallographic data and unit cell contents. In hydrated cements, anion sites in AFm phase are potentially occupied by OH, SO₄ and CO₃ ions. C1, NO₃ or NO₂ ions readily displace hydroxide, sulfate and carbonate in the AFm structures. Nitrates and nitrites do not have ability to displace chloride from the Friedel’s salt (C1-AFm) though. The binding power of AFm for nitrite/nitrate/chloride was calculated and confirmed experimentally at 25°C. It was observed that presence of chloride, nitrate or nitrite alters the AFm/Aft balance and thereby affect the specific volume of paste solids. It was found that the success of nitrite as a corrosion inhibitor for protection of embedded steel arises from its “smart” behaviour. AFm normally stores and sequesters nitrite. If chloride ingress occurs in service, the AFm undergoes ion exchange, gaining chloride and forming Friedel’s salt, while releasing soluble nitrite ions to the pore fluid. As a result, the aqueous ratio of [NO₂^-]/[C1^-] increases and remains within the passivation range for steel.

No description available.

The stability of Haynes 230 and Hastelloy C-276 nickel alloys exposed to high temperature molten salt with trace contaminants (i.e., water and oxygen) is found to be acceptable for using these metals to house anaerobic MgCl2-KCl and NaCl-KCl-ZnCl2 molten salts at 800oC. The corrosion rate determined by gravimetric tests range from -98 µm/year to 20. 13 µm/year at 800˚C. The corrosion rate is estimated to be 16.14 µm/year for Haynes 230 and 10.03 µm/year for Hastelloy C-276 based on the weight loss and surface area of the coupons when the coupons of Haynes 230 and Hastelloy C-276 alloys are immersed in molten MgCl2-KCl salt in sealed quartz containers and left in an oven at a temperature of 800˚C up to 16 days. The corrosion rate is estimated to be -20.46 µm/year for Haynes 230 and -7.36 µm/year for Hastelloy C-276 based on the weight loss and surface area of the coupons when the alloys are immersed in molten NaCl-KCl-ZnCl2 salt in sealed quartz containers and left in an oven at 800˚C up to 56 days. The corrosion rate of the alloys are well below the DOE requirement of 50 µm/year for the alloys in molten chloride salts to be considered acceptably stable. Ultimate tensile strength (UTS) after immersion of Haynes 230 and Hastelloy C-276 in molten salt ranged from 634 MPa to 860 MPa. The UTS of Haynes 230 is estimated to be 642 MPa after exposure to NaCl-KCl-ZnCl2 for 4 weeks at 800˚c and 841 MPa after exposure to MgCl2-KCl for 4 weeks at 800˚c compared to an untreated sample which achieved a UTS of 851 MPa. Likewise, the UTS of Hastelloy C-276 is estimated to be 692 MPa after exposure to NaCl-KCl-ZnCl2 for 4 weeks at 800˚c and 842 MPa after exposure to MgCl2-KCl for 4 weeks at 800˚c compared to an untreated sample which achieved a UTS of 830 MPa. Molten chloride salts, such as NaCl-KCl-ZnCl2 and KCl-MgCl2, are pretreated by heating and bubbling dry Argon gas in the salt in order to remove oxygen and water and thereby reduce the corrosion of metal containers of molten salt. Monitoring the relative humidity and percent oxygen of the exhaust gas during the sparging of dry Argon at 240 sccm into 150 g of molten chloride salt at 500˚C for NaCl-KCl-ZnCl2 and 700˚C for KCl-MgCl2 allows an estimation time to reach a low level of oxygen and water in the salt and to estimate the amount of oxygen and water removed. Results show water is more difficult to remove than oxygen from the salt. Ten minutes of sparging with dry argon brings oxygen content of exhuast gas to<0.1% O2. Approximately fifty minutes of sparging leaves the exhaust gas only containing<0.7% RH. The total moles of oxygen removed from the salts are estimated to be 0.0043 moles for molten NaCl-KCl-ZnCl2 and 0.0076 moles for KCl-MgCl2. The total moles of water removed from the NaCl-KCl-ZnCl2 salt is estimated to be 0.016108379 moles and 0.002321214 moles from molten KCl-MgCl2.

This thesis describes experiments made to test the corrosion inhibition of quaternary amines on steel.

Magnesium alloys exhibit desirable properties for use in transportation technology. In particular, the low density and high specific strength of these alloys is of interest to the aerospace community. However, the concerns of flammability and susceptibility to corrosion have limited the use of magnesium alloys within the aircraft cabin. This work studies a magnesium alloy containing rare earth elements designed to increase resistance to ignition while lowering rate of corrosion. The microstructure of the alloy was documented using scanning electron microscopy. Specimens underwent salt spray testing and the corrosion products were examined using energy dispersive spectroscopy.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1994 / A quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. The basis for quantitative description involves conducting a voltage balance over the galvanic couple. The contributions to the voltage balance include the galvanic couple cell emf, kinetic descriptions of the anodic and cathodic half reactions, the voltage characteristics 'of mineral-mineral contacts and solution voltage losses. The rates of the anodic and cathodic half' reactions were modelled by the Butler-Volmer equation and ti1ediffusion equation. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. TIle galvanic couples were constructed. as rotating ring disc electrodes and hence electrolyte voltage losses were negligible. Three galvanic couples, copper-platinum, copper-pyrite and galena-pyrite, were electrochemically characterised under different conditions of ferric concentration, electrode rotation rate and temperature. The effect of illumination on the anodic dissolution of galena was investigated. The electrochemical model is in good agreement with experimentally measured galvanic currents. Galvanic interaction is a dynamic function and various models are developed which account for dynamic behaviour in galvanic cells. / MT2017