Surfaces Of Metal Specimens Research Articles

Characteristics of Si (C,N) Silicon Carbonitride Layers on the Surface of Ni-Cr Alloys Used in Dental Prosthetics.

Chromium- and cobalt-based alloys, as well as chrome-nickel steels, are most used in dental prosthetics. Unfortunately, these alloys, especially nickel-based alloys, can cause allergic reactions. A disadvantage of these alloys is also insufficient corrosion resistance. To improve the properties of these alloys, amorphous Si (C,N) coatings were deposited on the surfaces of metal specimens. This paper characterizes coatings of silicon carbide nitrides, deposited by the magnetron sputtering method on the surface of nickel-chromium alloys used in dental prosthetics. Depending on the deposition parameters, coatings with varying carbon to nitrogen ratios were obtained. The study analyzed their structure and chemical and phase composition. In addition, a study of surface wettability and surface roughness was performed. Based on the results obtained, it was found that amorphous coatings of Si (C,N) type with thicknesses of 2 to 4.5 µm were obtained. All obtained coatings increase the value of surface free energy. The study showed that Si (C,N)-type films can be used in dental prosthetics as protective coatings.

Evaluation of metal-ceramic bond characteristics of three dental Co-Cr alloys prepared with different fabrication techniques

Statement of problemLimited information is available regarding the metal-ceramic bond strength of dental Co-Cr alloys fabricated by casting (CAST), computer numerical control (CNC) milling, and selective laser melting (SLM). PurposeThe purpose of this in vitro study was to evaluate the metal-ceramic bond characteristics of 3 dental Co-Cr alloys fabricated by casting, computer numerical control milling, and selective laser melting techniques using the 3-point bend test (International Organization for Standardization [ISO] standard 9693). Material and methodsForty-five specimens (25×3×0.5 mm) made of dental Co-Cr alloys were prepared by CAST, CNC milling, and SLM techniques. The morphology of the oxidation surface of metal specimens was evaluated by scanning electron microscopy (SEM). After porcelain application, the interfacial characterization was evaluated by SEM equipped with energy-dispersive spectrometry (EDS) analysis, and the metal-ceramic bond strength was assessed with the 3-point bend test. Failure type and elemental composition on the debonding interface were assessed by SEM/EDS. The bond strength was statistically analyzed by 1-way ANOVA and Tukey honest significant difference test (α=.05). ResultsThe oxidation surfaces of the CAST, CNC, and SLM groups were different. They were porous in the CAST group but compact and irregular in the CNC and SLM groups. The metal-ceramic interfaces of the SLM and CNC groups showed excellent combination compared with those of the CAST group. The bond strength was 37.7 ±6.5 MPa for CAST, 43.3 ±9.2 MPa for CNC, and 46.8 ±5.1 MPa for the SLM group. Statistically significant differences were found among the 3 groups tested (P=.028). The debonding surfaces of all specimens exhibited cohesive failure mode. ConclusionsThe oxidation surface morphologies and thicknesses of dental Co-Cr alloys are dependent on the different fabrication techniques used. The bond strength of all 3 groups exceed the minimum acceptable value of 25 MPa recommended by ISO 9693; hence, dental Co-Cr alloy fabricated with the SLM techniques could be a promising alternative for metal ceramic restorations.

The influence of temperature on the inhibition of carbon steel corrosion in acidic lignin

Purpose– This paper aims to investigate the influence of temperature and lignin concentration on the inhibition of carbon steel corrosion in 1 M HCl.Design/methodology/approach– Weight loss corrosion tests were performed at different temperatures in the range of 30-70°C (303-343 K).Findings– It was found that the corrosion inhibition efficiency (IE) of lignin on the carbon steel decreased when the temperature was increased from 60 to 70°C. However, at lower temperatures ranging from 30 to 50°C, the IE improved, due to occurrence of lignin adsorption on the surface of metal specimens. The IE was higher with increasing lignin concentration, thus reducing the weight loss of the carbon steel. The adsorption phenomenon involved exothermic processes because the value of enthalpy of adsorption (ΔH°ads) < 0 and Gibbs free energy of adsorption (ΔG°ads) were less negative with increase in temperature. The entropy of adsorption (ΔS°ads) had negative values, representing the decrease in disorder of adsorption. The adsorption of lignin on the carbon steel surface in 1 M HCl was comprehensive, as deduced from kinetic and thermodynamic parameters. However, physisorption was the major contributor in the inhibition mechanism. The inhibitive features of carbon steel surfaces showed less damage once the steel was treated in lignin, as evident from macroscopy images.Practical implications– The use of lignin as an acid corrosion inhibitor at high temperature is practical in metal surface treatment process.Social implications– The use of organic compounds gives an advantage to the environment, universal health and save cost, as the compounds can be found in nature.Originality/value– Lignin can act as a flexible corrosion inhibitor within the temperature range of 30-70°C in 1 M HCl because it exhibits comprehensive adsorption (i.e. a combination of both physisorption and chemisorption) at specific concentrations.

Smart corrosion sensing phenanthroline modified alkyd coatings

Abstract Alkyd resin was chemically modified with 1,10-phenanthroline-5-amine and characterized by Fourier transform infrared (FTIR) and 13C Nuclear magnetic resonance (13C NMR) spectroscopy. The complex forming ability of phenanthroline modified alkyd resin with Fe2+ ions was studied by UV–Visible spectroscopy. Mixture of Fe2+ solution and modified alkyd resin showed new absorption bands in UV–Visible spectroscopy confirmed the formation of modified alkyd resin-Fe(II) complex. Corrosion sensing property of modified alkyd coating was evaluated by immersing the coated mild steel specimens in 3.5% NaCl solution. Color change was observed in the coating due to onset of corrosion at metal-coating interface. Electrochemical impedance spectroscopy (EIS) was used for correlating the polarization resistance (Rp) of coating with color change. Scanning electron microscopic (SEM) analysis on the surface of metal specimens indicated that the point of color change was the corrosion site. Results revealed that phenanthroline modified alkyd resin can be used in corrosion sensing coating formulations.

Detection of microflaws in metals via investigation of acoustic fields

Distributions of acoustic fields on the surfaces of metal specimens with different degrees of microdamage are measured with a Doppler laser interferometer. Various methods are used for digital data processing for extracting useful information against a noise background. Specific features of the acoustic-field structure are analyzed as functions of the presence and parameters of microflaws in the specimens under study.

Single-step phase-shifting speckle interferometry

We propose a simplified technology of recording and processing speckle interferograms with phase shift that does not require the calibration of the phase-shifting devices and allows one to use the minimum possible number of images. We present the data on the verification of the algorithms and the results of experiments aimed at the investigation of the displacements of the surfaces of metal specimens and performed according to the proposed technology.

ChemInform Abstract: ELECTROCHEMICAL OXYGEN REDUCTION ON OXIDE CATALYSTS

AbstractKinetik und Mechanismus der elektrochemischen Sauerstoffreduktion an Ni‐ und Co‐oxiden (durch thermische oder elektrochemische Oxidation) sowie die Einflüsse der Katalysatornatur und von adsorbiertem Sauerstoff werden durch potentiodynamische und Ring‐Scheibenelektroden‐Methoden untersucht.

Electrochemical oxygen reduction on oxide catalysts

The process of oxygen electroreduction and adsorption in alkaline medium on nickel and cobalt oxides has been studied by the potentiodynamic and the disc-ring electrode methods. The oxide films were formed on the surface of metal specimens by thermal or electrochemical oxidation.After oxidation, the surface was examined by X-ray diffraction and electron diffraction. It was found that, depending on the oxidation conditions, simple or complex oxides are formed on the surface of metal specimens. Nickel and Cobalt oxide films obtained by thermal oxidation at t ° ⩽300°C are more active than pure metals. The oxides of spinel structure Co 3 O 4 and NiCo 2 O 4 have an optimum activity. It is shown that oxygen adsorbed during the heat treatment of the specimens accelerates the process of the molecular oxygen reduction. On the oxides of spinel structure the oxygen reduction reaction proceeds to OH − , whereas on simple nickel oxides the final product of oxygen reduction is HO − 2 .

An electron microscope study of stainless steel deformed in fatigue and simple tension

Abstract A technique is described whereby the surface of metal specimens can be examined by transmission electron microscopy. The original specimens are thinned by electropolishing from one side; thus the surfaoe contours, e.g. slip steps, are preserved on one of the surfaces. It is shown that dislocations are revealed associated with the surface slip lines; the step heights and surface oontours such as those of fatigue striations are observed at a high magnification due to a taper section effect.

Thermal Etching of Silver

NUMEROUS workers have observed that polished surfaces of metal specimens frequently develop an etched appearance when the specimens are heated in atmospheres with which chemical reactions would not be expected. Two types of etching effect have been recorded : (a) the formation of grooves at the grain boundaries, and (b) the development, on the surfaces of crystal grains, of striations which change their direction at grain and twin boundaries. In some cases the boundary grooves form when there are no striations, but when striations appear the boundaries invariably develop grooves. Rosenhain and Ewen1, heating silver, copper and zinc in vacuo, observed boundary grooves, and on heating silver in air both grooves and striations. Together with Day and Austin2, who observed grain boundary grooves in many different types of steel heated in hydrogen, they explained the development of grooves as being due to the preferential evaporation of metal from the grain boundaries. Carpenter and Elam3 observed the development of lines at the grain boundaries of an antimonytin alloy (1½ per cent antimony), and said that the lines were really differences of level and were only produced on cooling. Rawdon and Berglund4 observed striations on iron heated in hydrogen and attributed them to slight volatilization of the polished surface. Johnson5, heating tungsten in nitrogen and argon, observed striations in wires carrying direct current, which he ascribed to the migration of positive tungsten atom-cores over the surface under the action of the electric field. Elam6 found that when copper was heated in vacuo, striations only appeared when cuprous oxide was present, and explained their appearance as being due to the differential oxidation of the copper along certain crystallographic planes followed by the evaporation of the oxide. Gwathmey and Benton7, heating a spherical single crystal of copper in air at 0.3 mm. pressure, found that fine striations appeared which seemed to be due to the development of specific crystallographic planes in the surface. These striations were diminished when the specimen was heated in hydrogen at atmospheric pressure. Boas and Honeycombe8 reported the occurrence of striations and boundary lines in specimens of tin, zinc and cadmium, heated and cooled through a number of cycles. They suggested that the anisotropic expansion of the grains of these non-cubic metals caused plastic deformation in a randomly orientated aggregate and that the striations were slip lines.