Corrosion Types of Magnesium Alloys

Magnesium (Mg) alloys are susceptible to corrosion in aggressive environments. Corrosion of Mg alloys depends greatly on their composition and microstructure (grain size, the size, shape and distribution of second phases), post-processing and media. In most cases, localized corrosion, such as pitting corrosion and filiform corrosion, generally occurs due to microgalvanic corrosion between the intermetallic compounds and their neighboring α-Mg matrix. However, open literature reported that several corrosion morphologies, that is, intergranular corrosion (IGC) and exfoliation corrosion (EFC), cannot appear on Mg alloys. In this chapter, all typical corrosion modes of Mg alloys and influencing factors are introduced, including general corrosion, galvanic corrosion, pitting corrosion, filiform corrosion, IGC, EFC, stress corrosion cracking (SCC), corrosion fatigue (CF) and so on. The focus is laid on pitting corrosion and EFC. Corrosion mechanisms of Mg alloys are also discussed

Toksičnost aromatskih ketona za stanice kvasca i ubrzanje njihove redukcije primjenom adsorpcijskih smola

Asymmetric reduction of the prochiral aromatic ketone catalyzed by yeast cells is one of the most promising routes to produce its corresponding enantiopure aromatic alcohol, but the space-time yield does not meet people’s expectations. Therefore, the toxicity of aromatic ketone and aromatic alcohol to the yeast cell is investigated in this work. It has been found that the aromatic compounds are poisonous to the yeast cell. The activity of yeast cell decreases steeply when the concentration of acetophenone (ACP) is higher than 30.0 mmol/L. Asymmetric reduction of acetophenone to chiral S-α-phenylethyl alcohol (PEA) catalyzed by the yeast cell was chosen as the model reaction to study in detail the promotion effect of the introduction of the resin adsorption on the asymmetric reduction reaction. The resin acts as the substrate reservoir and product extraction agent in situ. It has been shown that this reaction could be remarkably improved with this technique when the appropriate kind of resin is applied. The enantioselectivity and yield are acceptable even though the initial ACP concentration reaches 72.2 mmol/L.Asimetrična redukcija prokiralnih aromatskih ketona, katalizirana stanicama kvasca, obećavajuća je metoda proizvodnje enantiomerno čistih aromatskih alkohola, no iskorištenje reakcije ne zadovoljava današnje potrebe. U radu je utvrđena toksičnost aromatskih ketona i alkohola za stanice kvasca. Aktivnost stanica kvasca naglo se smanjila pri koncentracijama acetofenona većim od 30 mmol/L. Kao model reakcije za detaljno ispitivanje pozitivnog učinka uvođenja adsorpcijskih smola odabrana je asimetrična redukcija acetofenona u kiralni S-α-feniletilni alkohol, katalizirana stanicama kvasca. Utvrđeno je da smola djeluje kao rezervoar supstrata i agens za ekstrakciju proizvoda in situ. Tako se odvijanje reakcije može znatno poboljšati uvođenjem prikladne smole. Enantioselektivnost i prinos su zadovoljavajući iako je početna koncentracija acetofenona dosegla čak 72,2 mmol/L

Biodegradation behavior of micro-arc oxidation coating on magnesium alloy-from a protein perspective

Protein exerts a critical influence on the degradation behavior of absorbable magnesium (Mg)-based implants. However, the interaction mechanism between protein and a micro-arc oxidation (MAO) coating on Mg alloys remains unclear. Hereby, a MAO coating was fabricated on AZ31 Mg alloy. And its degradation behavior in phosphate buffer saline (PBS) containing bovine serum albumin (BSA) was investigated and compared with that of the uncoated alloy. Surface morphologies and chemical compositions were studied using Field-emission scanning electron microscope (FE-SEM), Fourier transform infrared spectrophotometer (FT-IR) and X-ray diffraction (XRD). The degradation behavior of the bare Mg alloy and its MAO coating was studied through electrochemical and hydrogen evolution tests. Cytotoxicity assay was applied to evaluate the biocompatibility of Mg alloy substrate and MAO coating. Results indicated that the presence of BSA decreased the degradation rate of Mg alloy substrate because BSA (RCH(NH2)COO‾) molecules combined with Mg2+ ions to form (RCH(NH2)COO)2Mg and thus inhibited the dissolution of Mg(OH)2 by impeding the attack of Cl‾ ions. In the case of MAO coated Mg alloy, the adsorption of BSA on MAO coating and the formation of (RCH(NH2)COO)2Mg exhibited a synergistic effect and enhanced the corrosion resistance of the coated alloy significantly. Furthermore, cell bioactive assay suggested that the MAO coating had good viability for MG63 cells due to its high surface area

Fingerprint and multi-component quantitative analyses for quality evaluation of Rhizoma coptidis steamed with rice wine

Purpose: To establish a method for the simultaneous determination of multi-components of Rhizoma coptidis steamed with rice wine (RCRW), and to provide a reference for assessing its standard of quality. Method: Chromatographic separation was performed on a high performance liquid chromatography (HPLC) system to determine the characteristic fingerprint of RCRW. The mobile phase consisted of acetonitrile (A) and 0.1 % trifluoroacetic acid (B), with gradients of B as follows: 15 - 20 % from 0 – 30 min; 20 - 25 % from 30 - 50 min; 25 - 35 % for 50 - 60 min, and 35 % for 60 - 70 min. Results: In the multiple reaction monitoring mode, eight components of RCRW were isolated by HPLCphoto-diode array (PDA) method. A fingerprint of the RCRW was established and 8 peaks were calibrated. The method was further validated in terms of linearity (R2 > 0.9993), precision (relative standard deviation, RSD < 1.51 %); repeatability (RSD < 2.98 %) and stability (RSD < 1.93 %). Mean recovery rate ranged from 96.2 to 103.8 %, while RSD values ranged from 0.92 to 2.88 %. Conclusion: These results show that HPLC-PDA method is accurate and feasible, and that they provide a reference for further comprehensive and effective quality control of RCRW

Corrosion resistance of Mg-Al-LDH steam coating on AZ80 Mg alloy: Effects of citric acid pretreatment and intermetallic compounds

In this study, the effects of intermetallic compounds (Mg17Al12 and Al8Mn5) on the Mg-Al layered double hydroxide (LDH) formation mechanism and corrosion behavior of an in-situ LDH/Mg(OH)2 steam coatings on AZ80 Mg alloy were investigated. Citric acid (CA) was used to activate the alloy surface during the pretreatment process. The alloy was first pretreated with CA and then subjected to a hydrothermal process using ultrapure water to produce Mg-Al-LDH/Mg(OH)2 steam coating. The effect of different time of acid pretreatment on the activation of the intermetallic compounds was investigated. The microstructure and elemental composition of the obtained coatings were analyzed using FE-SEM, EDS, XRD and FT-IR. The corrosion resistance of the coated samples was evaluated using different techniques, i.e., potentiodynamic polarization (PDP), electrochemical impedance spectrum (EIS) and hydrogen evolution test. The results indicated that the CA pretreatment significantly influenced the activity of the alloy surface by exposing the intermetallic compounds. The surface area fraction of Mg17Al12 and Al8Mn5 phases on the surface of the alloy was significantly higher after the CA pretreatment, and thus promoted the growth of the subsequent Mg-Al-LDH coatings. The CA pretreatment for 30 s resulted in a denser and thicker LDH coating. Increase in the CA pretreatment time significantly led to the improvement in corrosion resistance of the coated AZ80 alloy. The corrosion current density of the coated alloy was lower by three orders of magnitude as compared to the uncoated alloy

Influence of intermetallic Al-Mn particles on in-situ steam Mg-Al-LDH coating on AZ31 magnesium alloy

The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide (Mg-Al-CO32--LDH) steam coating on AZ31 Mg alloy was investigated. The alloy was pretreated with H3PO4, HCl, HNO3 or citric acid (CA), followed by hydrothermal treatment, for the fabrication of Mg-Al-LDH coating. The microstructure, composition and corrosion resistance of the coated samples were investigated. The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment, which promotes the growth of the Mg-Al-LDH steam coating. Further, the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings. The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy

An innovative EEG-based emotion recognition using a single channel-specific feature from the brain rhythm code method.

Efficiently recognizing emotions is a critical pursuit in brain–computer interface (BCI), as it has many applications for intelligent healthcare services. In this work, an innovative approach inspired by the genetic code in bioinformatics, which utilizes brain rhythm code features consisting of δ, θ, α, β, or γ, is proposed for electroencephalography (EEG)-based emotion recognition. These features are first extracted from the sequencing technique. After evaluating them using four conventional machine learning classifiers, an optimal channel-specific feature that produces the highest accuracy in each emotional case is identified, so emotion recognition through minimal data is realized. By doing so, the complexity of emotion recognition can be significantly reduced, making it more achievable for practical hardware setups. The best classification accuracies achieved for the DEAP and MAHNOB datasets range from 83–92%, and for the SEED dataset, it is 78%. The experimental results are impressive, considering the minimal data employed. Further investigation of the optimal features shows that their representative channels are primarily on the frontal region, and associated rhythmic characteristics are typical of multiple kinds. Additionally, individual differences are found, as the optimal feature varies with subjects. Compared to previous studies, this work provides insights into designing portable devices, as only one electrode is appropriate to generate satisfactory performances. Consequently, it would advance the understanding of brain rhythms, which offers an innovative solution for classifying EEG signals in diverse BCI applications, including emotion recognition

In vitro degradation and biocompatibility of vitamin C loaded Ca-P coating on a magnesium alloy for bioimplant applications

Molecular recognition was utilized to fabricate bioinspired calcium phosphate (Ca-P) coating on bioabsorbable magnesium alloys through small biomolecules such as Vitamin C (VC). Ca-P and VC hybrid coating (Ca-PVC) was successfully fabricated on AZ31 Mg alloy. The surface morphology and chemical composition of the coatings were investigated using SEM, XRD, and FTIR together with XPS. The results showed that the Ca-PVC coating was composed of bamboo leaf-like Ca-P particles with a thickness of about three times that of the Ca-P coating. The surface roughness of the Ca-PVC coating (1.12 ± 0.12 µm) was lower than that (3.14 ± 1.93 µm) of Ca-P coating, suggesting the formation of refined Ca-P particles resulting from the VC addition. The corrosion resistance of the coated samples was characterized via electrochemical polarization, impedance spectroscopy, and immersion hydrogen evolution tests. The cell toxicity of the coated samples was evaluated utilizing mouse MC3T3-E1 pre-osteoblasts. The charge transfer resistance (Rct) of the Ca-PVC coated alloy increased as compared to the bare and Ca-P coated alloy samples. The Ca-PVC coated alloy exhibited minimal corrosion current density (1.36 × 10−6 A cm−2), which is one order of magnitude lower in comparison to that of the Ca-P coated alloy. These results confirm that VC addition greatly enhanced the coating resistance on AZ31 Mg alloy. It was also noticed that the Ca-PVC coated samples rapidly induced the formation of apatite after immersion in Hank's solution. VC was mainly transformed to L-Threonic acid, which facilitated the nucleation process of the Ca-PVC coating and significantly increased the thickness, density, and bonding strength of the coating. With enhanced corrosion resistance property and excellent biocompatibility, Ca-PVC coating has great potential for application in biodegradable Mg-based alloys

Advances in bioorganic molecules inspired degradation and surface modifications on Mg and its alloys

Mg alloys possess biodegradability, suitable mechanical properties, and biocompatibility, which make them possible to be used as biodegradable implants. However, the uncontrollable degradation of Mg alloys limits their general applications. In addition to the factors from the metallic materials themselves, like alloy compositions, heat treatment process and microstructure, some external factors, relating to the test/service environment, also affect the degradation rate of Mg alloys, such as inorganic salts, bioorganic small molecules, bioorganic macromolecules. The influence of bioorganic molecules on Mg corrosion and its protection has attracted more and more attentions. In this work, the cutting-edge advances in the influence of bioorganic molecules (i.e., protein, glucose, amino acids, vitamins and polypeptide) and their coupling effect on Mg degradation and the formation of protection coatings were reviewed. The research orientations of biomedical Mg alloys in exploring degradation mechanisms in vitro were proposed, and the impact of bioorganic molecules on the protective approaches were also explored

Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-matter Interactions

Van der Waals (vdW) solids, as a new type of artificial materials that consist of alternating layers bonded by weak interactions, have shed light on fascinating optoelectronic device concepts. As a result, a large variety of vdW devices have been engineered via layer-by-layer stacking of two-dimensional materials, although shadowed by the difficulties of fabrication. Alternatively, direct growth of vdW solids has proven as a scalable and swift way, highlighted by the successful synthesis of graphene/h-BN and transition metal dichalcogenides (TMDs) vertical heterostructures from controlled vapor deposition. Here, we realize high-quality organic and inorganic vdW solids, using methylammonium lead halide (CH3NH3PbI3) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids behave dramatically different in light emission. Our studies demonstrate that h-BN monolayer is a great complement to organic perovskite for preserving its original optical properties. As a result, organic/h-BN vdW solid arrays are patterned for red light emitting. This work paves the way for designing unprecedented vdW solids with great potential for a wide spectrum of applications in optoelectronics