Investigating the Stress Corrosion Cracking (SCC) Susceptibility of Ti-6Al-4V Alloys Fabricated by Electron Beam Melting in Deep-Sea Environment

The stress corrosion cracking (SCC) susceptibility of electron beam melted Ti-6Al-4V alloy (ET) was compared with the conventional wrought alloy (WT). The electrochemical and slow strain rate tensile (SSRT) tests, as well as surface analysis, were conducted under simulated shallow and deep-sea environment. Under shallow conditions, the SCC susceptibility of both alloys was almost the same because of consistent passivation and re-passivation performance of the passivating film. However, under deep-sea conditions, SCC susceptibility of ET was higher than that of WT due to stronger textured-like surface that appeared on ET alloy, where early developed passive film broke down, demonstrating lower passivation and re-passivation rate.

Corrosion Behavior on Titanium Alloys as OCTG in Oil Fields

Titanium alloys have been taken as Oil Country Tubular Goods (OCTG) owing to their higher strength, and better corrosion resistance, but there are some problems in their application process. The corrosion types of titanium alloys were emphatically discussed, and corrosion mechanism was analyzed in this paper. The results showed that the main corrosion type of titanium alloys in hydrochloric acid was pitting, and the surface roughness of titanium alloys could affect it. The critical current density of titanium alloys in phosphoric acid was closely related to temperature and phosphoric acid concentration. The passivation of titanium alloys could be carried out by the growing oxide film at low current density, to achieve the higher stability of passivating film in the concentrated sulfuric acid. Titanium alloys suffered from more serious corrosion in the CO2-containing completion fluid environment than that in the CO2-containing formation water environment. H2S would cause electrochemical corrosion and stress corrosion of titanium alloy pipe, leading to hydrogen embrittlement and even cracking of OCTG. Passivating film was the key to corrosion resistance of titanium alloys, and its composition would change with the depth of the film, presenting N-type. The dynamic corrosion of titanium alloys was mainly controlled by charge transfer.

Formation Process of the Passivating Products from Arsenopyrite Bioleaching by Acidithiobacillus ferrooxidans in 9K Culture Medium

Arsenopyrite is a common sulphide mineral occurring in deposits of gold ore that makes the extraction of gold difficult and, thus, pre-treatment is necessary prior to gold leaching. Bioleaching pre-treatment of arsenopyrite has drawn significant attention owing to its environmental friendliness, low cost and simple operation. A critical impedance of bioleaching to its large-scale industrial application is the slow leaching kinetics. Various passivating products on the surface of arsenopyrite have been found to limit the bioleaching process. This paper reports results from an in-depth investigation into the formation process of passivating products from arsenopyrite bioleaching by Acidithiobacillus ferrooxidans in 9K culture medium including bioleaching experiments and physicochemical analyses of the materials as well as thermodynamic analyses of the leaching system. The results of phase transformation and morphological change of the solid products suggest that the passivation occurring in the bioleaching of arsenopyrite is largely attributed to an initially formed passivating film consisting mainly of realgar (As2S2), orpiment (As2S3) and elemental sulphur (S0) on the arsenopyrite surface. Based on the results, the paper also proposes possible passivation mechanisms to allow for a better understanding on the passivation behaviour of the bioleaching of arsenopyrite.

Optimization of EUV Reticle Cleaning by Evaluation of Chemistries on Wafer-Based Mimic Test Structures

In order to evaluate the effect of repeated cleaning on EUV reticles, specifically, on the etched Mo/Si multilayer, wafer-based test structures with a mimic of this etched Mo/Si multilayer (“black-border”) were fabricated. The resistance of Mo and Si towards alkaline chemistries was tested and quantified using these test structures. The initial passivating film on Mo seems to play a role in delaying the Mo to further oxidize and dissolve in alkaline solutions. For the cleaning times used (minutes) the Mo surface, and thus the black-border edges, will probably stay passivated by that protective oxide in alkaline solution (pH 11), with no or only very limited Mo loss. Stirring and the amount of oxygen or other oxidizing species like H2O2 in solution could increase the oxidation rate of the Mo and/or Mo oxides into soluble Mo(VI) species.

Comparative study of corrosion and tribocorrosion resistance of some biomaterials

ABSTRACTCorrosion and tribocorrosion tests have been conducted on titanium, Ti-6Al-4V and Ti-10Zr-10Nb-5Ta alloys. The experiments have been conducted in four different electrolytes: NaCl solution, Ringer’s solution, phosphate buffered saline solution (PBS) with and without an addition of bovine serum albumin (BSA).The electrochemical study showed that, whatever the electrolyte, the passivating film formed on Ti-10Zr-10Nb-5Ta surface is more stable than those obtained on the surface of titanium or Ti-6Al-4V alloy. In addition, Ti-10Zr-10Nb-5Ta presents a better resistance to corrosion. In PBS solution, open circuit potential (OCP) moved to more positive value in comparison with results obtained in NaCl and Ringer’s solutions, whereas addition of BSA moved OCP value towards more negative potential indicating a detrimental effect.Tribocorrosion tests have been conducted at OCP when sliding against an alumina ball. Friction coefficient, current and volume of material removal at the end of tests have been measured and the results discussed. The influence of the presence of proteins molecules has been particularly analyzed.