High-temperature corrosion behavior of TP91, C22 alloy and C22 based on laser coatings in simulated reducing corrosion environment

To explore corrosion characteristics of TP91, C22 alloy and C22 laser coatings in reducing environment caused by low-nitrogen combustion at 500°C-600°C, a synthetic corrosive medium containing 0.2 vol. % H2S-0.1 vol. % O2-N2 were selected. Results showed that the order of corrosion resistance is: C22 laser coatings>C22 alloy>TP91. 550°C was the limit corrosion temperature for C22 alloy and C22 laser coatings. The reason for the strong corrosion resistance of C22 alloy and C22 laser coatings is that a dense layer of Cr-rich corrosion products due to the is produced in the inner layer, thus protecting the matrix from direct corrosion by corrosive gas. Finer grains before corrosion tests and the formation of dense Cr2O3 inner layers in much speedier process were the main reasons for the best corrosion resistance of C22 laser coatings.

Corrosion Behavior of Thermal Seamless Carbon Steel Boiler Pipes

The current study was absorbed on corrosion of ASTM A106 grade B -02 seamless carbon steel boiler pipes. Beyond corrosion experiments in corrosive medium with varying pH values, the weight lost in addition to corrosion rate (m.p.y) values were computed. The weight loss of boiler tube specimens exposed to corrosive liquid was shown to rise as the exposure period of the specimens increased. The results of the microstructure imaging showed that a de-carburized film of 240 µm thickness was shaped on the fireside of the pipe boiler, with ferrite and a few phases of pearlite. On the water lateral side, it was revealed that boiler pipe failure begins with small rust particles that expand to greater sizes and form scales that are displaced from the boiler pipe's surface. On the surfaces of the boiler pipe water side, several pits with crevice corrosion were observed. The corrosion amounts were discovered to decrease when the specimens' exposure time to corrosive environments and hydrogen ion concentration contents increased (pH). The findings of mechanical characteristic values such as hardness, yield strength, and tensile strength revealed that the waterside had higher values than the fireside, while the middle of the pipe had reasonable values. The findings also demonstrated that at low pH values, a tiny size of rust was created on the boiler tube specimen surface. However, at high pH values of corrosive medium, big sizes of corrosion rust were observed on the specimen surfaces.

Analysis of graphene oxide as an anticorrosive film in metallic materials

Corrosion is an electrochemical or chemical process that causes the deterioration of materials, especially metallic ones, thereby leading to unpredictable negative consequences. The application of anti-corrosive coatings constitutes a means of minimizing such corrosive effects once these coatings act as barriers between the substrate and the corrosive medium. Graphene oxide is a material that has gained notoriety due to its properties, abundance and to the fact that it is environmental friendly. The work we developed aimed to apply a graphene oxide solution on a metallic substrate in order to verify its applicability as an anticorrosive film. For this purpose, the production of the precursor solution was carried out; the application of the solution was accomplished by the dip-coating technique; then, the immersion test in aqueous corrosive medium followed and the characterization by confocal microscopy was performed. The results showed that there was adhesion of the film to the substrate and that it remained insoluble. As a protective layer for anticorrosion coating, the film responded partially well to this study’s proposed objectives because, though it did not manage to slow down the corrosive process, it did minimize the formation of spot corrosion, a more aggressive form of corrosion.

In Vitro Ion Release of Wires in Removable Orthodontic Appliances

Various orthodontic wire compositions and configurations are present on the market for removable appliances; however, there have still been only few studies focusing on the effect of resin color and additives such as glitter on corrosion of metallic wires under different conditions. Thus, the aim of the study was to compare concentrations of released ions (aluminium, chromium, nickel) in a corrosive medium under three different conditions: non-loaded wires, loaded wires, and non-loaded wires treated with Kukis® cleaning tablets. Six different wires made of three types of steel alloy were embedded in PMMA resin leaving one centimetre of each wire emerging from the resin to come into contact with the corrosive medium. Glitter particles were added to half of the produced test specimens. For the unloaded test series, five specimens of each group were covered in a petri dish with 50 mL of corrosive medium (pH 2.3) following EN-ISO 10271 for seven days at 37 °C. The wires for the mechanically loaded test specimens overlapped the resin by 5 cm and were clamped into a time-switched electric drive for a defined period of time before the samples were taken after a testing time of 7 days. In the third group, unloaded test specimens were transferred from their petri dishes into the prepared Kukis® solution every 24 h before being stored in the corrosive medium. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the specific ions in the corrosive solution. Statistical analysis showed that the mechanical loading of all wires could significantly raise the diffusion of ions into the corrosive medium. The colour of the resin did not affect the concentration of the released ions. The Kukis® cleaning tabs could not lower the corrosion of the tested metals, as some of the wires were corroded even more using the brace cleanser. Glitter-containing test specimens showed significantly higher amounts of aluminium. Mechanical loading as well as the presence of glitter particles in the resin significantly affected ion concentrations.

On the Influence of Internal and External Factors on the Processes of Corrosion-Mechanical Fracture of High-Strength Low-Alloy Steels

The article studies the influence of internal and external factors on the process of corrosion-mechanical fracture. It is shown that depending on the conditions of hydrogen charging (temperature and chemical composition of the corrosive medium, type of polarization), the mechanical properties of low-alloy steels change dramatically during the initial period of the experiment. With further increase in the holding time in a corrosive medium without polarization, there is no significant change in mechanical properties. It was found that an increase in the level of applied tensile stresses leads to a reduction in the incubation period of microcracks during hydrogen cracking. It was found that the sensitivity of low alloy steels to cracking is largely determined by the relaxation ability of the structure-the relaxation of residual peak micro-stresses localized at the grain boundaries and substructure boundaries reduces the sensitivity to corrosion-mechanical fracture.