Search results for " Corrosion"

Behavior of Calcium Phosphate–Chitosan–Collagen Composite Coating on AISI 304 for Orthopedic Applications

2022

Calcium phosphate/chitosan/collagen composite coating on AISI 304 stainless steel was investigated. Coatings were realized by galvanic coupling that occurs without an external power supply because it begins with the coupling between two metals with different standard electrochemical potentials. The process consists of the co-deposition of the three components with the calcium phosphate crystals incorporated into the polymeric composite of chitosan and collagen. Physical-chemical characterizations of the samples were executed to evaluate morphology and chemical composition. Morphological analyses have shown that the surface of the stainless steel is covered by the deposit, which has a very r…

La torre del Tempo: il punto di vista del chimico

2013

L’obiettivo del presente lavoro è stato quello di valutare la tipologia di lega metallica, il suo degrado e la tipologia di vernice dell’opera in ferro policroma “La Torre del Tempo” di E. Tadini. A tale scopo sono state effettuate delle misure di Microscopia Ottica, Diffrattometria a raggi X, Spettroscopia micro-Raman e Spettroscopia NMR. The goal of this study was to evaluate the type and the of conservation state of the metal alloy and the type of varnish of samples coming from “La Torre del Tempo” E. Tadini. The samples were characterized by Optical Microscopy, X-ray Diffractometry, micro-Raman Spectroscopy and NMR spectroscopy.

Volcanic SiO2-cristobalite: A natural product of chemical vapor deposition

2020

Abstract Cristobalite is a low-pressure, high-temperature SiO2 polymorph that occurs as a metastable phase in many geologic settings, including as crystals deposited from vapor within the pores of volcanic rocks. Such vapor-phase cristobalite (VPC) has been inferred to result from silica redistribution by acidic volcanic gases but a precise mechanism for its formation has not been established. We address this by investigating the composition and structure of VPC deposited on plagioclase substrates within a rhyolite lava flow, at the micrometer to nanometer scale. The VPC contains impurities of the form [AlO4/Na+]0—coupled substitution of Al3+ charge-balanced by interstitial Na+—which are ty…

The effect of Ag, Pb and Bi impurities on grain boundary sliding and intergranular decohesion in Copper

2016

We investigate the changes in grain boundary sliding (GBS) and intergranular decohesion in copper (Cu), due to the inclusion of bismuth (Bi), lead (Pb) and silver (Ag) substitutional impurity atoms at a $\Sigma$5 (0 1 2) symmetric tilt grain boundary (GB), using a first-principles concurrent multiscale approach. We first study the segregation behavior of the impurities by determining the impurity segregation energy in the vicinity of the GB. We find that the energetically preferred sites are on the GB plane. We investigate the intergranular decohesion of Cu by Bi and Pb impurities and compare this to the effect of Ag impurities by considering the work of separation, $W_s$ and the tensile st…

Liner Poliolefinici nella produzione di canalizzazioni e manufatti in calcestruzzo

2009

Shear and flexural strength of corroded R.C. beams

2016

Simplified equations aimed at evaluating the flexural and shear capacity of corroded R.C. beams are presented and discussed in this paper, with reference to ordinary beams reinforced both longitudinally (with same-size bars) and transversely (with stirrups). A model is developed to take care of diffused and localised corrosion (pitting corrosion), concrete decay in compression and bond-strength decay at concrete-reinforcement interface. A fairly innovative contribution of this study is the introduction into the proposed equations of the main parameters governing the corrosion processes. The proposed approach is simple and effective, and may be adopted in the assessment of many damaged struc…

Effect of Molybdate on Corrosion Performance of Oxide Coating Produced on 7075 Al Alloy Using PEO

2022

In this research, plasma electrolytic oxidation (PEO) coatings were prepared on 7075 Al alloy in a silicate-based solution with Na2MoO4 additive using a unipolar waveform at constant current density. The coatings displayed micro-pores, micro-cracks, pancake-like and crater-like features, and also solidified molten oxide particles on the surface. The coatings were majorly composed of Al2O3 (γ, δ, and α), SiO2 (amorphous), and MoO3 phases, which confirms the incorporation of molybdenum in the case of additive-containing coatings. Molybdenum species were transported through cracks, channels, and micropores, as the ready access pathways into the coating and partly sealed the c…

Predictive Model for Cut-Edge Corrosion of Galvanized Steels

2006

A numerical model for the electrochemical behavior of cut-edge of galvanized steels is proposed. Some experimental data of current densities above cut-edge immersed in a 0.03M NaCl solution have been measured, using a scanning vibrating electrode technique, and compared with some simulated ones. A good fit has been obtained. The model geometry has been modified by decreasing the electrolyte thickness in order to tend towards an atmospheric corrosion case; such situation that is not easily accessible by electrochemical studies. Three regions can be distinguished according to the efficiency of the galvanic coupling to protect steel.

The Effect of Electrolytic Solution Composition on the Structure, Corrosion, and Wear Resistance of PEO Coatings on AZ31 Magnesium Alloy

2020

Plasma electrolytic oxidation coatings were prepared in aluminate, phosphate, and silicate-based electrolytic solutions using a soft-sparking regime in a multi-frequency stepped process to compare the structure, corrosion, and wear characteristics of the obtained coatings on AZ31 magnesium alloy. The XRD results indicated that all coatings consist of MgO and MgF2, while specific products such as Mg2SiO4, MgSiO3, Mg2P2O7, and MgAl2O4 were also present in specimens based on the selected solution. Surface morphology of the obtained coatings was strongly affected by the electrolyte composition. Aluminate-containing coating showed volcano-like, nodular particles and craters distributed over the …

Composition and corrosion phases of Etruscan Bronzes from Villanovan Age

2008

A neutron diffraction (ND) and neutron tomography (NT) study of laminated ancient bronzes was performed at the ISIS (Rutherford Appleton Laboratory, UK) neutron source and at the BENSC reactor (Hahn-Meitner Institut, Germany). The samples are part of an 8th century BC Etruscan collection discovered in the necropolises of Osteria-Poggio Mengarelli and Cavalupo in the Vulci area (Viterbo, Italy). The study allowed us to derive-in a totally non-destructive manner-information related to the main composition of the objects, possible presence of alterations and their nature, crusts and inclusions, as well as structure of the bulk. The presence of some components is linked to a variety of question…