Abstract:The electrochemical and corrosion behaviour of a surface is extremely complicated and depends on various chemical, physical and mechanical factors. In this study the effect of different surface roughnesses on the corrosion resistance of nickel in 0.5 M sulphuric acid was investigated. Open circuit potential, corrosion current density, polarization resistance and corrosion rate were measured for surfaces polished with different grits (120, 240, 400, 600 and 1200) of silicon carbide papers. The surface roughness… Show more
“…In contrast, as can be seen in Figure 2(b), a different corrosion behaviour and a reverse trend was observed in the case of nickel Figure 2: Dependence of i corr on surface finish of (a) mild steel and (b) nickel. in 0.5 M H 2 SO 4 solution on surfaces with different unidirectional roughnesses [6]. As can be seen in previous work done by the authors, by increasing the roughness of nickel surface from sample G1200 to G60, the polarization curves shifted toward higher corrosion current densities which mean higher corrosion rates [12].…”
“…The same effect was also observed for the effect of roughness on corrosion rate for AE44 Mg alloy before [7]. In both cases the metal has no ability to form a passive layer but in the case of other metals which form a passive layer, a reverse trend was observed [1][2][3][4][5][6]. As it is shown in Figure 1, polarization curves rise to parallel and it is clear that both cathodic and anodic branches show a lower current density indicating that the hydrogen evolution reaction is activation controlled [10,11].…”
“…This is a general trend seen for corrosion of metals with no ability to form a passive layer [7,8]. This trend is in opposite direction compared to nickel (Figure 4(b)) and aluminum with ability to form a protective passive film [3,6]. A reverse trend was also reported by Li and Li [2] for Cu in a 3.5% NaCl solution which was expected.…”
Section: Relationship Between Corrosion Rate and Roughnessmentioning
confidence: 51%
“…Last column in this table is a list of SiC particle size on grinding papers. Nickel also showed an increase in roughness parameters after corrosion which is an indication of the formation of deeper grooves (on rougher surfaces where there is more corrosion) and passive layer (on all surfaces especially smoother surfaces) [6,12]. …”
Section: Roughness Measurementmentioning
confidence: 99%
“…Such a trend was observed for copper, nickel, aluminium, stainless steel, magnesium and titanium alloys [1][2][3][4][5][6]. In all cases the effect of creating different roughnesses were investigated on both localized and general corrosion performance of the alloys.…”
Unidirectional surface roughness of varying magnitudes were created on both nickel and mild steel by grinding on SiC papers with grit sizes from G60 (roughest) to G1200 (smoothest) and the corrosion resistance in 0.5M H 2 SO 4 solution was determined using a potentiodynamic polarization technique. A different trend of corrosion rate versus roughness was seen for the active-passive metal (nickel) and non-active-passive metal (mild steel). For nickel there was an increase in corrosion rate with increasing roughness, whereas for mild steel the corrosion rate decreased with increasing surface roughness. Furthermore, through a detailed examination of the surface before and after corrosion using techniques including profilometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it was established that different corrosion mechanisms were operative for nickel and mild steel. For both metals, the smaller grit sizes produced a rougher surface with wider and deeper grooves. In the case of nickel, the higher roughness provided a greater contact area between the corrosive medium and metal and there was trapping of the corrosive ions in the deep grooves. Both of these factors would lead to an increase in corrosion rate. Also, for the smoother nickel surfaces, it is easier to form a stable passive film. For mild steel, which does not form a passive film, corrosion rates are generally much higher than for nickel. For the rougher surfaces with the deeper grooves, the corrosion product, FeSO4, can fill the grooves thereby acting as a barrier to further ingress of the corrosive ions to the un-corroded metal.
“…In contrast, as can be seen in Figure 2(b), a different corrosion behaviour and a reverse trend was observed in the case of nickel Figure 2: Dependence of i corr on surface finish of (a) mild steel and (b) nickel. in 0.5 M H 2 SO 4 solution on surfaces with different unidirectional roughnesses [6]. As can be seen in previous work done by the authors, by increasing the roughness of nickel surface from sample G1200 to G60, the polarization curves shifted toward higher corrosion current densities which mean higher corrosion rates [12].…”
“…The same effect was also observed for the effect of roughness on corrosion rate for AE44 Mg alloy before [7]. In both cases the metal has no ability to form a passive layer but in the case of other metals which form a passive layer, a reverse trend was observed [1][2][3][4][5][6]. As it is shown in Figure 1, polarization curves rise to parallel and it is clear that both cathodic and anodic branches show a lower current density indicating that the hydrogen evolution reaction is activation controlled [10,11].…”
“…This is a general trend seen for corrosion of metals with no ability to form a passive layer [7,8]. This trend is in opposite direction compared to nickel (Figure 4(b)) and aluminum with ability to form a protective passive film [3,6]. A reverse trend was also reported by Li and Li [2] for Cu in a 3.5% NaCl solution which was expected.…”
Section: Relationship Between Corrosion Rate and Roughnessmentioning
confidence: 51%
“…Last column in this table is a list of SiC particle size on grinding papers. Nickel also showed an increase in roughness parameters after corrosion which is an indication of the formation of deeper grooves (on rougher surfaces where there is more corrosion) and passive layer (on all surfaces especially smoother surfaces) [6,12]. …”
Section: Roughness Measurementmentioning
confidence: 99%
“…Such a trend was observed for copper, nickel, aluminium, stainless steel, magnesium and titanium alloys [1][2][3][4][5][6]. In all cases the effect of creating different roughnesses were investigated on both localized and general corrosion performance of the alloys.…”
Unidirectional surface roughness of varying magnitudes were created on both nickel and mild steel by grinding on SiC papers with grit sizes from G60 (roughest) to G1200 (smoothest) and the corrosion resistance in 0.5M H 2 SO 4 solution was determined using a potentiodynamic polarization technique. A different trend of corrosion rate versus roughness was seen for the active-passive metal (nickel) and non-active-passive metal (mild steel). For nickel there was an increase in corrosion rate with increasing roughness, whereas for mild steel the corrosion rate decreased with increasing surface roughness. Furthermore, through a detailed examination of the surface before and after corrosion using techniques including profilometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it was established that different corrosion mechanisms were operative for nickel and mild steel. For both metals, the smaller grit sizes produced a rougher surface with wider and deeper grooves. In the case of nickel, the higher roughness provided a greater contact area between the corrosive medium and metal and there was trapping of the corrosive ions in the deep grooves. Both of these factors would lead to an increase in corrosion rate. Also, for the smoother nickel surfaces, it is easier to form a stable passive film. For mild steel, which does not form a passive film, corrosion rates are generally much higher than for nickel. For the rougher surfaces with the deeper grooves, the corrosion product, FeSO4, can fill the grooves thereby acting as a barrier to further ingress of the corrosive ions to the un-corroded metal.
In this work, transient thermal response and ablation behavior of liquid silicone rubber composites containing fluxing/ceramic forming fillers were investigated under different heat flows using an oxyacetylene flame. The results indicated that the introduction of zinc borate (ZB) and aluminum oxide (Al2O3) effectively reduced the temperature at various depths of the samples, and they improved the thermal insulation properties and lowered pyrolysis rates. The above finding was attributed to the heat absorption arising from water release and melt filling as well as the vitrified reaction of solid melt due to the decomposition of ZB. Besides, the melting and exfoliation of Al2O3 and the formation of aluminum silicate (Al2SiO5) caused heat absorption effect. Additionally, the mass ablation rates and line ablation rates increased with rising heat flows coupling with a decrease of compressive strength of the char layers. In a nutshell, the effect of adding ZB/Al2O3 on the thermal insulation behavior of epoxy‐modified vinyl silicone rubber (EMVSR) composites under different heat flows was elucidtaed. This work served as a reference for the design and preparation of flexible ablative materials for thermal protection applications.
This study investigated the effectiveness of titania (TiO 2) as a reinforcing phase in the hydroxyapatite (HAP) coating and silica (SiO 2) single layer as a bond coat between the TiO 2-reinforced hydroxyapatite (TiO 2 /HAP) top layer and 316L stainless steel (316L SS) substrate on the corrosion resistance and mechanical properties of the underlying 316L SS metallic implant. Single layer of SiO 2 film was first deposited on 316L SS substrate and studied separately. Water contact angle measurements, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrophotometer analysis were used to evaluate the hydroxyl group reactivity at the SiO 2 outer surface. The microstructural and morphological results showed that the reinforcement of HAP coating with TiO 2 and SiO 2 reduced the crystallite size and the roughness surface. Indeed, the deposition of 50 vol pct TiO 2-reinforced hydroxyapatite layer enhanced the hardness and the elastic modulus of the HAP coating, and the introduction of SiO 2 inner layer on the surface of the 316L SS allowed the improvement of the bonding strength and the corrosion resistance as confirmed by scratch studies, nanoindentation, and cyclic voltammetry tests.
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