Signo T. Reis

Ground coat enamels for low carbon steel that contain silica as a mill addition have been developed to study the changes of their properties. Acid-resistant commercial enamel where silica addition was varied from 0 to 10.0 wt % was used for this investigation. The effects of the addition on the corrosion resistance, thermal properties, electrical properties, and mechanical adherence of the enamel to low carbon steel were studied. The corrosion resistance of the steel enameled coupons was tested using a salt spray (fog) apparatus for time periods reaching 168 h at room temperature. It was found that, although the density was not affected, the adherence decreased with an increase in silica content. As expected, the silica addition decreased the coefficient of thermal expansion, which is directly related to the increasing stress between the glass and steel in accordance with the adherence results. A mill addition of 7.5 wt% of silica to the samples was sufficient to obtain adequate enamel adherence and good corrosion resistance. Furthermore, the addition of silica influenced the electrical conductivity and dielectric permittivity measurements at room temperature and the conductivity measured in a wide frequency range (1 Hz–1 MHz). The dielectric permittivity measured at 1 MHz showed decrease after the addition of up to 7.5 wt% of silica.

This paper presents the first report on the corrosion resistance of pipeline steel with damaged enamel coating and cathodic protection in 3.5 wt % NaCl solution. In particular, dual cells are set up to separate the solution in contact with the damaged and intact enamel coating areas, to produce a local corrosion resistance measurement for the first time. Enamel-coated steel samples, with two levels of cathodic protection, are tested to investigate their impedance by electrochemical impedance spectroscopy (EIS) and their cathodic current demand by a potentiostatic test. Due to its glass transition temperature, the enamel-coated pipeline can be operated on at temperatures up to 400 °C. The electrochemical tests show that cathodic protection (CP) can decelerate the degradation process of intact coating and delay the electrochemical reactions at the enamel-steel interface. However, CP has little effect on the performance of coating once damaged and can prevent the exposed steel from corrosion around the damaged site, as verified by visual inspections. Scanning electron microscopy (SEM) indicated no delamination at the damaged enamel–steel interface due to their chemical bond.

This paper reports a study and discusses the role of Fe ions in the inhibition of corrosion of iron phosphate glasses. The structure of the 40Fe ₂ O ₃ –60P ₂ O ₅ (mol%) glass, having a confirmed dissolution rate in aqueous solution at 90°C superior to borosilicate glasses, was investigated. Samples were crystallized at characteristic temperatures defined by differential thermal analysis and analyzed by X‐ray diffraction. Crystalline phases of Fe ₂ Fe[P ₂ O ₇ ] ₂ and Fe ₄ [P ₂ O ₇ ] ₃ were detected. The hyperfine parameters from the Mössbauer spectrum indicate that both Fe ²⁺ and Fe ³⁺ ions are in octahedral coordination, and 18% of the Fe ³⁺ ions in the starting batch are reduced to Fe ²⁺ ions after melting. The broad and symmetric spectra centered in g≈2.0 from the EPR measurements indicate the presence of two or more Fe interacting ions occupying sites of relatively high local symmetry.