H.B. Liu

Characterisation of soil/pipe interface at a pipeline failure after 36 years of service under impressed current cathodic protection

Abstract Study on corrosion behaviour of buried pipeline in saline soil is presented, the pipeline is protected by coating and impressed current cathodic protection system. In this work, spectrometric and spectroscopic techniques were used to characterise the pipe/coating/soil interfaces. The results show the coating/pipe interface forms corrosion products including the following phases: magnetite, goethite, akaganeite and hematite. However, the main phases found at coating/soil interface are magnetite and ferric ion. The behavior is consistent with the corrosion of carbon steel in soil with oxygen and chloride ion. The reaction paths are proposed under the conditions of deteriorated coating, cathodic protection, saline soil and seasonal fluctuations.

Stability and phase transition of sodium nanoclusters

Abstract In this work, structural transformation and some thermodynamic processes of sodium nanoclusters were studied using classic molecular dynamics simulation and density functional theory calculation. These sodium nanoclusters cover cuboctahedra, amorphous, and multi-twinned particles ranging from a few nanometers to tens of nanometers in size. The simulation results indicate different stability regions for different structures and small differences of both melting point and boiling point for all types of clusters. Amorphous transition and Frank–Kasp polyhedron transition from the rounded bcc cluster were observed on the ground state, and also surprising heat capacity curves of amorphous clusters under study were found at regions near the melting.

Structural characteristics and thermal stability of bimetallic Cu-Ru nanocluster

Classical molecular dynamics simulations were used to study the structural characteristics and thermodynamic stability of Cu-Ru nanoclusters of most common structural variants like decahedra, icosahedra and cuboctahedra. As a result, it is found that the three types of structures have consistent stability orders from the point of view of bimetallic elemental distributions. The Ru-core/Cu-shell structures and the eutectic-like structures are more stable than solid solution and Cu-core/Ru-shell. The formation energies of bimetallic clusters are consistently positive, which shows that they are not thermodynamically stable. All clusters including the unstable Cu-core/Ru-shell and solid solution clusters, and the relatively stable Ru-core/Cu-shell transform into eutectic-like cluster during heating process. Additionally, the large difference in melting point between pure Cu and pure Ru cause the Cu part in the formed eutectic-like clusters melt first and escape forming separate cluster in the further heating process.

Assessment on external corrosion rates for API pipeline steels exposed to acidic sand-clay soil

Purpose The purpose of this paper is to study the susceptibility to corrosion processes of X60, X65 and X70 steels immersed in sand-clay soil with pH 3.0, using electrochemical techniques, scanning electron microscopy (SEM), energy dispersive spectroscopy and X-ray diffraction (XRD). Design/methodology/approach Natural acidic soil sample was collected as close as possible to buried pipes (1.2 m in depth) in a Right of Way from south of Mexico. Both steels and soil were characterized through SEM and XRD. Then, open circuit potential was recorded for all steels exposed to soil at different exposure times. Thus, the electrochemical impedance spectroscopy (EIS) was traced, and anodic polarization curves were obtained. Findings The steel corrosion processes started when the active sites were exposed to natural acidic soil. However, corrosion rates decreased for three steels as immersion time increased, obtaining the highest corrosion rate for X60 steel (0.46 mm/year for 5 h). This behavior could be attributed to corrosion products obtained at different exposure times. While, 5 h after removing corrosion products, X65 steel was more susceptible to corrosion (1.29 mm/year), which was corroborated with EIS analysis. Thus, corrosion products for the three steels exposed to natural acidic soil depended on different microstructures, percentage of pearlite and ferrite phases, in which different corrosion processes could occur. Therefore, the active sites for carbon steel surfaces could be passivated with corrosion products. Practical implications The paper identifies the any implication for the research. Originality/value Some anodic peaks could be caused by metallic dissolution and was recorded using high positive polarization (high field of perturbation). In addition, the inductive effects and diffusion process were interpreted at low frequency ranges using EIS. According to X-ray diffraction (XRD), acidic soil had Muscovite containing aluminum and iron phases that were able to generate hydrogen proton at the presence of water; it might be promoted at the beginning of deterioration on low carbon steels. Steel surface cleaning after removing corrosion products was considered to study the possible diffusion phenomena on damaged steel surfaces using EIS.

Insights Into Oxygen Adsorption on Ag-Cu Nanocluster as an Oxidation Catalyst by Ab Initio Atomistic Thermodynamics.

To understand the catalytic activity of Ag-Cu cluster as catalyst of ethylene oxidation, bare Ag and Cu and Ag core/Cu12 shell and Cu core/Ag12 shell are built and optimized by density functional theory calculations incorporating the effect of the atmospheric environment. Consequently different oxygen adsorption sites on the cluster are considered: top site of the shell atoms, bridge site of the shell atoms and hollow site of the shell atoms. For each adsorption site, a few coverages are considered, both oxygen-rich condition and oxygen-poor condition. The phase diagrams of oxygen and 13-atom Ag-Cu clusters are finally determined. The pressure-temperature phase diagrams are determined for the oxygen and 13-atom Ag-Cu clusters, which reveal important insights into this system and its catalytic properties. The phase diagrams of oxygen and 13-atom Ag-Cu clusters are finally determined. The results predict the most stable phase: structure and adsorption of oxygen at certain temperature and certain pressure. Under oxygen-poor condition, the cluster structures are most likely to be changed. This information must be helpful to understand the catalytic process of Ag-Cu cluster as catalyst of ethylene oxidation.