Effect of excimer laser surface melting on the microstructure and corrosion performance of the die cast AZ91D magnesium alloy

Excimer laser surface melting (LSM) of the die cast AZ91D alloy has been investigated in terms of microstructure and corrosion behaviour. Excimer LSM of the alloy resulted in a highly homogeneous and refined melted microstructure, which improved the corrosion resistance of the alloy. The latter was associated with the large dissolution of intermetallic phases and the enrichment of aluminium within the melted layer. An increased number of laser pulses resulted in thicker melted layers, but also in enhanced porosity and the formation of micro-cracks at the overlapping area. Both factors diminished the corrosion resistance of the laser-treated alloy.     

On the inhibition of mild steel corrosion by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol

The corrosion inhibition of mild steel in a 2.5 M H₂SO₄ solution by 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT) was studied at different temperatures, utilising open circuit potential, potentiodynamic and impedance measurements. The results indicate that APTT performed as an excellent mixed-type inhibitor for mild steel corrosion in a 2.5 M H₂SO₄ solution and that the inhibition efficiencies increased with the inhibitor concentration but decreased proportionally with temperature. The kinetic and thermodynamic parameters for adsorption of APTT on the mild steel surface were calculated. A chemisorption mechanism of APTT molecules on the mild steel surface was proposed based on the thermodynamic adsorption parameters.     

Corrosion behaviour of intermetallic aluminide coatings on nitrogen-containing austenitic stainless steels

The present work reports the effect of aluminide layers on the aqueous corrosion behaviour of four different 316L stainless steels containing various nitrogen contents (0.015%, 0.1%, 0.2% and 0.56% N). Diffusion annealed aluminide layers are generated over the surface by heat treatment of the aluminium precoated alloys at 750 °C for 25 h in nitrogen atmosphere. X-ray diffraction patterns of the surface modified samples showed the presence of AlN, Al₁₃Fe₄ and FeAl₂ phases. Diffusion of aluminum into the alloy, and the formation of AlN by the reaction of aluminium with matrix nitrogen, was identified using secondary ion mass spectrometry (SIMS). The nitrogen peak in the diffused layer was found to increase with increasing nitrogen content of the base alloy. SEM observation of cross-sectionally mounted alloys showed the presence of spherical AlN phase in addition to iron aluminide intermetallic phases. The role of such a composite surface layer containing intermetallic aluminides and nitride on the corrosion resistance of austenitic stainless steels in 0.5 M NaCl and 0.5 M sulphuric acid is discussed in greater detail based on open circuit potential (OCP)–time measurements, potentiodynamic polarisation studies and electrochemical impedance spectroscopy (EIS) investigations. The aluminide layered alloy with 0.1% N content showed better corrosion performance. The presence of nitrogen was found to have a positive effect in enhancing the hardness of the composite layer. Role of matrix nitrogen on the microstructure and microchemical distribution at the surface, and its role on corrosion resistance in acidic and chloride media are discussed in detail.     

Chemical and electrochemical studies of the inhibition performance of hydro-alcoholic extract of used coffee grounds (HECG) for the corrosion of C38 steel in 1M hydrochloric acid

The corrosion protection of C38 steel in 1M HCl solution with hydro-alcoholic used coffee grounds extract (HECG) was studied using measurements of hydrogen gas evolution, potentiodynamic polarization and electrochemical impedance spectroscopy. This work revealed that the HECG studied acts as a mixed type inhibitor. It has also been shown that the corrosion inhibition efficiency (IE) increases with increasing extract concentration, an IE value of 97.4% was reached with 2 g/L HECG. The inhibitory action of the inhibitor was mainly due to the adsorption of HECG molecules on the C38 steel surface. The studies have shown that HECG adsorbs on the C38 steel surface according to Langmuir's isotherm, with a standard free energy (ΔG⁰_ads) of −18,477 KJ mol⁻¹, which means that HECG delays the corrosion process by physical adsorption. The scanning electron microscope (SEM) study confirmed that corrosion inhibition of C38 steel occurs by adsorption of inhibiting molecules on the metal surface. These results show that the HECG can be used as an excellent corrosion inhibitor for C38 steel in a hydrochloric acid medium.     

Feasibility of using pulsed electric fields to modify biomacromolecules: A review

BackgroundThe challenges encountered in the utilisation of biomacromolecules as functional ingredients can be overcome through modification of their structural elements. Recently, researchers have shown an increased interest in the usage of non-thermal or chemical free modification techniques to improve the stability and function of primary ingredients in the food, biomedical and pharmaceutical applications. This has led to the investigations of pulsed electric fields (PEF) technology as an alternative technique for enhancing modification of chemical reactions and microstructure of biomacromolecules.Scope and approachThe goal of this paper was to conduct a systematic review on the effect of PEF on the functional properties of proteins, polysaccharides and their blends, focusing on the configurational and conformational modifications in the microstructure due to the application of micro/millisecond electric field.Key findings and conclusionsPEF has potential to modify the microstructure and functional properties of biomacromolecules. PEF–induced modifications follow two primary mechanisms, i.e. electrochemical reactions and polarisation of the structural moieties. Critical PEF treatment intensity (E_C) is required for the onset of the microstructural changes in biomacromolecules. These changes are influenced by the settings and configuration of the PEF equipment, product characteristics (molecular weight, pH, conductivity) and system temperature. If properly managed, PEF treatment and subsequently the changes in molecular properties (i.e. molecular disintegration and network formation) could be tailored for the production of superior micro-/nano-structured products for various applications.     

Effect of DC Biasing Field on the Dielectric Properties of High Field Treated SrTiO3 Single Crystals

Dielectric constant (K) and loss (Tan) of strontium titanate single crystals subjected to high electric fields (10 KV/cm, AC or DC) were measured as a function of frequency (10² to 10⁷ Hz). These properties were also studied as a function of time at 10³ Hz immediately after the high field treatment. The value of K and tan of the field-treated samples attained a steady value after 20 hours. Measurements of K and Tan as a function of time and frequency under small DC biasing fields (200 V/cm) were taken. The values of K and tan of the high field-treated samples decreased with time and frequencies; however under a DC biasing field, K increases slightly up to 10 minutes and then decreases slowly with time to a steady value. The inversion temperature (T_i) at different frequencies get reduced with high field treatment. However, the application of small DC-biasing field increased the T_i value with the increase of biasing field strength. On the other hand, activation energy increased with high field and decreased with biasing field. The effect of high DC field treatment on SrTiO₃ single crystal exhibits more prominent changes in K, tan , T_i and activation energy than that of high AC field treated samples.     

Tuning electrical properties of BaTiO3 with iron modification

BaTiO₃ plays an important role in advanced functional devices owing to its fascinating properties. Though it is an excellent ferroelectric material, its magnetism can be switchable via suitable modification. In this report, we have studied iron-modified BaTiO₃, which has been prepared using cost-effective high-temperature solid-state reaction techniques. The Fe-modified BaTiO₃ maintains its crystallinity in the tetragonal phase with P4mm space group with a slight variation of tetragonality ratio to 1.002 from 1.008 of BaTiO₃ of the identical synthesis method. This is confirmed by Rietveld refinement. Field emission scanning electron microscopy (FESEM) and EDX (energy dispersive X-rays) spectrum along with an elemental mapping analysis has provided the feature of the Fe-modifed BaTiO₃. Atomic force microscope (AFM) has been employed to get the detailed surface topology (2D and 3D) and surface roughness of the developed systems. This deformation caused by the incorporation of Fe significantly modifies the electrical properties of barium titanate. The ferroelectric-paraelectric phase transition temperature (T_c) of Fe-modified BaTiO₃ has been diffused and shifted to 300 °C from 120 °C of pure BaTiO₃, suggesting the materials for the high-temperature capacitive application. The room temperature M-H hysteresis of Fe-modified BaTiO₃ indicates the ferromagnetism developed in the BaTiO₃ with the introduction of Fe. The ac conductivity is in the order of 10⁻⁴ Ω⁻¹cm⁻¹, and its frequency response obeys Jonscher's power law. Different charge carriers are responsible for diverse conduction processes in different temperature ranges confirmed by the Arrhenius plot. Impedance spectroscopy studies reveal the existence of NTCR characteristics of the developed system. Well defined ferroelectric hysteresis loop indicates the existence of ferroelectricity in the developed system. The analysis of various electrical parameters has provided information on the material's dielectric relaxation and conduction mechanisms for possible application in functional devices.