Corrosion and Materials Degradation

This study investigated the effects of Nb additions on the microstructure, hardness, and high-temperature oxidation behaviour of mechanically alloyed and spark-plasma-sintered Ti–48Al–2Cr–xNb alloys containing 1–5 at.% Nb. The aim was to clarify the role of Nb in phase evolution, strengthening, and oxidation protection, and to identify factors that limit its effectiveness. Following mechanical alloying and consolidation at 950 °C, the alloys exhibited predominantly globular γ-TiAl/α₂-Ti₃Al microstructures with localized Nb enrichment. Relative densities remained below 92%, indicating that residual porosity was a significant processing-related factor. The alloy containing 5 at.% Nb exhibited the highest hardness, consistent with Nb-induced solid-solution strengthening and changes in phase constitution. Isothermal oxidation was assessed by measuring weight gain per unit area after exposure at 700 °C for 400 h and at 900 °C for 200 h. At 900 °C, the alloys formed stratified scales consisting primarily of an outer TiO₂-rich layer and an underlying Al₂O₃-rich region. NbO₂ was detected in selected samples; however, no continuous, protective Nb₂O₅-rich scale formed. Preferential TiO₂ growth, together with cracking, exfoliation, and spallation, hindered the formation of a fully protective alumina barrier. At 700 °C, exposure for 400 h produced a substantially thinner, non-adherent oxide scale, consistent with the slower oxidation kinetics at lower temperatures. Consequently, increasing the Nb content did not result in a monotonic improvement in oxidation resistance. Overall, Nb enhanced hardness and influenced phase stability but did not, by itself, overcome the oxidation limitations of TiAl. Its effectiveness depends on densification, Al activity, microstructural homogeneity, and scale adhesion.

Elevated temperature corrosion inhibition has posed significant challenges to carbon steel wellbores. This study proposes bis-Mannich bases (BM)/Mannich-based imidazoline quaternary ammonium salt (MIQ) composite inhibitors with synergistic multiple adsorption, whose performance is evaluated in 0.5 M HCl over a temperature range of 343–423 K and in simulated full-wellbore conditions. The results show that each single inhibitor loses effectiveness above 393 K. By contrast, the BM/MIQ composites act as a mixed-type inhibitor that maintains an inhibition efficiency of 99.6% even at 423 K in 0.5 M HCl and 92.6% in simulated bottom-wellbore conditions, demonstrating excellent inhibition performance under high-temperature conditions. The adsorption process is spontaneous and dominated by chemisorption at elevated temperatures (ΔG < −40 kJ/mol) and follows Langmuir isotherm kinetics. Quantum chemical calculations reveal a synergistic electron transfer interaction between the highest occupied molecular orbital (HOMO) of BM and the lowest unoccupied molecular orbital (LUMO) of MIQ, which plays a key role in enhancing the adsorption stability of the composite system.

Startup delays can leave sulfur-deposit-prone gathering nodes below a prescribed dispersant concentration despite adequate steady dosing. This study combines archived characterization, a conditional experimental mixing comparison and transport calculations for sour gas-gathering systems. Active-flux conservation, route retention and delayed startup response yield finite-deadline dose bounds and a coverage deficit integral (CDI). Twenty solids show local sulfur fractions of 3.71–58.00 wt.%, and 11 of 13 diffraction patterns match orthorhombic S₈. Six calendar-date water pairs show total-sulfur ratios of 8.20–47.96, interpreted descriptively. Six chloride/bromide comparisons from formulation–water blends deviate by −11.1 to +0.7% from an unfitted ideal-dilution benchmark. This check assumes additive volumes, a volume-concentration basis and zero formulation background. Under prescribed transport conditions, 12 h coverage requires 28.84 L/d at nominal inputs and 63.30 L/d over the rectangular parameter set. A 60 L/d cap reaches the illustrative 50 mg/L threshold after 13.00 h in the worst combination. Variable-flow and reversible-storage alternatives test structural sensitivity. CDI summarizes delivery shortfall without establishing a damage response. The experimental comparison concerns conservative ion mixing; field dosing and corrosion predictions require separate active-residual and material-response calibration.