Synergistic effects of formaldehyde and alcoholic extract of plant leaves for protection of N80 steel in 15%HCl

Abstract

The synergistic effects of formaldehyde and an alcoholic extract of plant leaves have been studied by weight loss measurements at temperatures up to 363 K using various concentration ratios of the two inhibitors to protect N80 steel against corrosion in 15% hydrochloric acid. The inhibition efficiency was found to decrease with increasing temperature for all except two of the various concentration ratios that were studied. After identifying these two most promising mixtures, their corrosion prevention effects for N80 steel in hydrochloric acid were studied in more detail by weight loss and potentiostatic polarisation measurements. The corrosion rate of the steel was decreased by the presence of small additions of the inhibitors. The extent of decrease was found to depend on the nature of the corrosion inhibitor and its concentration. The inhibition efficiencies of the two plant based inhibitor mixtures were compared with those of two commercially available oil industry corrosion inhibitors. In all cases the adsorption of the inhibitors on the steel appeared to follow the Frumkin or Langmuir adsorption isotherm. The inhibition efficiencies of the two plant based inhibitors and the two commercial inhibitors were evaluated at a concentration level of 0.8% for temperatures in the range 303 K to 363 K) and exposure times of between 1 h and 24 h. Thermodynamic parameters including the free energy of adsorption, activation energy, enthalpy and entropy were calculated in both the absence and presence of inhibitors. Potentiostatic polarisation tests have revealed that inhibitors are primarily of the anodic type.     

Effect of La2O3 Particles on the Oxidation of Electrodeposited Nickel Films

Electrodeposited Ni-La₂O₃composite films with nanometer-sizeLa₂O₃ oxide inclusions werefabricated by the codeposition of nickel withLa₂O₃ particles. The comparativeoxidation behavior in air at 900 and 1000°C of nickel coated with theNi-La₂O₃ composite and films withand without nickel-plating was studied by TGA, AE,SEM/EDX, EPMA, and TEM/EDX. In general, theNi-La₂O₃ composite-coated nickelhad the slowest rate and the best resistance tothermal cycling. AE tests revealed that cracking eventsin NiO scales on Ni-La₂O₃composite-coated nickel was significantly reduced incomparison to that of the scale on nickel-coated nickel during thermalcycling at 900°C. SEM investigation showed that theLa₂O₃-free NiO scale was composedof outer coarse columnar grains and inner equiaxed ones.By contrast, the scale on the Ni-La₂O₃composite-coated nickel consisted of only fine equiaxedNiO grains. The scale on theLa₂O₃-free samples wascharacterized by cracks that originated at thescale-substrate interface and spanned the scale thickness. By contrast,no scale cracks formed at theLa₂O₃-doped NiO scale-substrateinterface, but small voids were created at the triplepoints of the grain boundaries of NiO. In the La₂O₃-doped NiOscale, segregation of La ions to the NiO grainboundaries near the scale-surface was observed by EDXmicroanalyses in the TEM. It is believed that the Laions segregated at the grain boundaries of NiO led to an increase in thecohesion between nickel oxides and in a reduction of thescaling rate and the formation of scale with fineequiaxed crystal structure by blocking the outward and lateral growth of scale. The latter was dueto the predominant outward diffusion of nickel along NiOgrain boundaries being inhibited effectively by thesegregated La ions. The mechanism of the effect of the added La₂O₃particles on the nickel electrodeposits is discussed indetail.     

Corrosion Behavior of Ti60 Alloy Coated with a Solid NaCl Deposit in O2 Plus Water Vapor at 500-700°C

The corrosion behavior of Ti60 has been studiedin oxygen containing water vapor at500-700^°C, with and without a solid NaCldeposit on the surface. No measurable corrosion of theTi60 alloy was observed in atmospheres without NaCl.Corrosion of Ti60 was accelerated in the presence ofNaCl because of the formation of a nonprotectiveTiO₂ oxide scale; the corrosion of Ti60 issignificantly aggravated due to the synergistic effect ofNaCl and water vapor. When the temperature was increasedup to the melting point of NaCl, the corrosion of Ti60coated with NaCl both in air-NaCl and inO₂-NaCl plus water vapor became more severe. Amechanism to explain the effect of water vapor and NaClon the corrosion of Ti60 is proposed.     

Selective use of rubber toughening to optimize lap-joint strength

This paper introduces a novel approach to increasing the lap joint strength, different from the traditional methods of either increasing the lap joint area or altering the joint geometry. This is accomplished by the selective use of rubber toughening in epoxy to optimize lap joint strength. This was accomplished in three stages. In the first stage an adduct was prepared, this was used to make bulk tensile specimens to calculate the bulk properties for various concentrations of rubber, i.e. 0, 10, and 20 parts per hundred parts of resin (epoxy). In the second stage finite element models were developed using the bulk properties previously obtained. Interfacial stresses were used to access the trends obtained by the selective use of rubber toughening at different locations of the overlap in different configurations. The modeling of adhesive joints was done using ALGOR 2-D, linear and nonlinear finite element analyses (FEA). In the third stage, tensile shear tests conducted on the lap joints validated the trends from the finite element models. Finite element modeling and meshing of the lap joints having 25.4 and 50.8 mm adhesive overlap lengths were completed. Different configurations of rubber toughened and untoughened adhesive were tried in these two overlaps. The validation was done by lap joint tests conducted on an Instron mechanical tester coupled with an extensometer. Comparable strengths were obtained for completely toughened overlap and the configuration where only the edges of the adhesive overlap were toughened and the region in-between was untoughened. Also, the nonlinear FEA was shown to represent the experimental results more closely than the linear approach.     

Stress corrosion cracking behaviour of 2091 Al—Li alloy in sulphate and chloride containing solutions

Abstract

The stress corrosion cracking resistance of 2091 Al—Li alloy in underaged, and in peak aged condition was investigated in chloride solutions with or without sulphate addition using both the static load technique and the slow strain rate technique. It is shown that the underaged material is more resistant than peak aged material. Sulphate additions to chloride solutions increase the stress corrosion cracking susceptibility. Metallographic cross-section observations show the simultaneous occurrence of other kinds of corrosion: generalised. corrosion, pitting corrosion, intergranular corrosion, and exfoliation corrosion. It appears that stress corrosion cracking susceptibility increases as the extent of intergranular corrosion decreases.     

CAPTURE EFFECT OF ELECTRORHEOLOGICAL SUSPENSIONS IN FLOW FIELD

According to the results of experiments and theoretical analysis,a phenomenon called “capture effect” is put forward,which could be used to describe the particles dynamic behavior of electrorheological (ER) suspensions. Then a “structure-force” mathematical model is established to explain this effect based on electrostatic energy density equation. The analysis results show that the dynamic coupling process of ER suspensions under an external electric filed is the function not only of the electric intensity,but also of the dielectric properties and the structure form.     

X-Ray Diffraction Study of Oxide Scales Formed at High Temperatures on AISI 304 Stainless Steel After Cerium Deposition

High-resolution X-ray diffraction has been usedto characterize the structure of oxide scales grownduring oxidation at 1173 K of cerium-modified stainlesssteels. The oxide scales consist of a mixture of Fe₂O₃ andCr₂O₃, as well as spinels. Severaloxidation treatments prior to cerium deposition havebeen applied. New phases, which are cerium-related,appear, depending on the preoxidation treatment. Bycomparing these results with previous ones onlanthanum-modified AISI 304 stainless steel, somepossible explanations for the reactive-element effectare proposed.     

Ferrite to austenite reverse transformation process in B containing 9%Cr heat resistant steel HAZ

Abstract

Creep properties of the high Cr heat resistant steel welded joint can be improved by adding B due to prevention of the grain refinement in heat affected zone (HAZ). In the present study, phase transformation behaviour of the B steel HAZ has been investigated to understand suppression mechanism of the grain refinement. During reverse transformation, fine austenite was formed through diffusional transformation at the prior austenite grain boundary in the first stage, and then coarse austenite was formed at the same location of the original austenite. The volume fraction of the fine austenite increased with increasing perk temperature of the weld thermal cycle. This phenomenon can be explained if the coarse austenite contains high density of dislocations. Clear surface relief was observed during the reverse transformation by a confocal laser microscope. These results indicate that martensitic or displacive reverse transformation takes place during welding and it prevents the grain refinement in HAZ.     

Comparison between mechanochemical effect on die cast and extruded magnesium alloys

Abstract

The mechanochemical effect (MCE) of several magnesium based alloys, obtained by both die casting and extrusion methods, was studied by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The mechanochemical behaviour of each alloy was evaluated as a function of die cast parameter, environment, and alloy composition. Electrochemical tests were performed in a buffer solution of sodium tetraborate, (Na₂B₄O₇) with and without magnesium hydroxide (Mg(OH)₂). The MCE was correlated with the microstructure of the Mg alloys.     

Effect of nish rolling temperature on static recrystallisation in hot bands of electrical steel containing 1·3% silicon

Abstract

The effect of the finish rolling temperature (FRT) on recrystallisation behaviour in hot bands of an electrical steel containing 1·3%Si was investigated. Four sequential passes of hot rolling were carried out on the 1·3%Si electrical steel, with finish rolling temperatures ranging from 980 to 700°C, followed by isothermal annealing at 720°C. The experimental results showed that when Ar ₁ <FRT <Ar ₃, fine equiaxed subgrains formed at the boundaries between deformed and non-deformed grains in a necklacelike arrangement, and strain induced boundary migration (SIBM) was the main mechanism corresponding to the formation of recrystallisation nuclei for steels finish rolled below Ar ₁. However, the study also demonstrated that when FRT <(Ar ₁­100 K), a second nucleation mechanism, i.e. subgrain growth, became active in recrystallisation, this resulted in an increase of nucleus density. Steels in which SIBM was the dominant mechanism of recrystallisation possessed the largest grain size, and strongest textures with major component {100}〈110〉.