Enamel Coatings Research Articles

Bioinspired Anti-demineralization Enamel Coating for Orthodontics

White spot lesions and enamel cracks are the 2 most prominent diseases that occur after orthodontic treatment and are caused by enamel demineralization from accumulated bacterial biofilms and/or enamel damage caused by the removal of residual adhesive after bracket debonding. Inspired by the self-assembled amelogenin nanoribbons in enamel, we developed an enamel coating with a self-assembling antimicrobial peptide, D-GL13K, to simultaneously reduce demineralization and residual adhesive. The self-assembled amphiphilic nanoribbons significantly increased the hydrophobicity of the etched enamel, which reduced the permeability of the coated enamel surfaces as desired. The antimicrobial activity of this coating was evaluated against Streptococcus mutans by colony-forming unit counting and live/dead assays. The anti-demineralization effect was demonstrated by the reduced demineralization depth analyzed by optical coherence tomography and the increased Vickers hardness. The coatings did not reduce the shear bond strength but significantly reduced the adhesive remnant index score. This bioinspired enamel coating may provide a new strategy for preventing white spot lesions and enamel cracks after orthodontic treatment.

Silver-based vitreous enamel coatings: Assessment of their antimicrobial activity towards Escherichia coli and Staphylococcus aureus before and after surface degradation

Porcelain enamel coatings are silica-based inorganic coatings, which are successfully applied to different kind of metallic substrates in applications where high chemical resistance and corrosion protection are needed. In addition, these coatings meet very modern criteria of durability and environmental sustainability. For this reason, they could be a valid solution for application in healthcare settings and public spaces, where cleaning and disinfection are frequently required. The possibility to produce durable antibacterial enamel coatings would broaden their application areas and represent a possible solution to address the spread of pathogens in many public spaces. The main of this work is to develop innovative antibacterial enamel coatings with the addition of silver-based additives (AgNO3) and test their antibacterial efficacy in operando conditions (i.e., after chemical and mechanical degradation) by exploiting antibacterial assays according to the ISO 22196:2011 standard. Three different sample types will be taken under consideration: the reference sample, and the sample with the addition of 1 wt% AgNO3, and the sample with the addition of 2 wt% AgNO3. The surface properties and the microstructure of the samples will be deeply investigated by surface sensitive techniques, optical microscopy, and electron microscopy observations. The antimicrobial efficacy of these samples will be tested against Escherichia coli and Staphylococcus aureus both before and after chemical/physiochemical degradation.

Abrasion behavior and functional properties of composite vitreous enamel coatings fabricated with the addition of 316L stainless steel flakes

Vitreous enamels are a type of inorganic coating used to protect metals from corrosion and weathering. Their durability is mainly determined by the resistance of the surface to mechanical stresses and damages. It is therefore crucial to improve enamel’s mechanical properties since the brittleness of the glassy matrix can lead to catastrophic failure of the coating. The purpose of this study is to investigate the possibility of improving the abrasion resistance of enamel coatings by adding 316L stainless-steel flakes, used as a second ductile toughening additive. The abrasion resistance of the coatings has been studied by using the P.E.I. abrasion test, coupled with Electrochemical Impedance Spectroscopy (EIS) measurements, and SEM observations. The abrasion mechanisms were investigated thoroughly, and the influence of the additive on the functional properties of the coating was taken under consideration. The stainless steel flakes proved useful in improving the coating’s abrasion resistance without compromising other functional properties.

Excellent hot-corrosion and thermal-shock resistance of metal-enamel composite coating on martensitic stainless steel enabled by interface engineering

Hot corrosion and thermal shock behaviors of nano-nickel enamel composite coatings on martensitic stainless steel at 650 °C were investigated, and compared with pure enamel coatings. Both enamel coating and composite coating can protect the steel from the corrosion of NaCl-Na2SO4 eutectic molten salt. However, the enamel coating suffers serious spallation during thermal cycles. Thermal shock resistance of enamel coating is largely improved by adding nano-nickel, as nickel particles not only hinder the rapid expansion of cracks through deflection and branching mechanism, but also act as repair capsules to build bridges for the viscous flow of enamel to heal crack.

Microstructure evolution and fracture behavior of heat treated enamel coating: Experiment and finite element analysis

The enamel coating (CaO-BaO-MgO-SiO 2 -Al 2 O 3 ) is prepared and performed isothermal oxidation at 900 °C. With the increase of oxidation time, the microstructure and phase evolution of enamel coating are analyzed. Meanwhile, the fracture toughness of heat treated enamel coatings are characterized using the micro-cantilever bending method. The experimental result indicates that the heat treatment can promote the precipitation of oval crystal particles from the enamel itself. With increase of crystallinity, the fracture toughness of heat treated enamel coatings increases from 2.35 to 4.20 MPa·m 1/2 . In addition, finite element method (FEM) with inserting global cohesive elements is adopted to estimate the fracture of micro-cantilever for enamel including elliptical crystals. Both load-displacement curves and failure modes from FEM analyses agree well with those from experiments. Meanwhile, the fracture mechanisms including crack deflection, crack bridging, intergranular and transgranular fracture of the enamel can be revealed. • With the increase of oxidation time, the microstructure evolution and phase of enamel coating are analyzed. • The crystallization of SiO 2 -Al 2 O 3 -CaO-BaO-MgO based enamel coating can improve its fracture toughness. • Finite element method (FEM) with inserting global cohesive elements can simulate the authentic fracture process of enamel coating including crystals. And, this method aids in understanding the fracture behavior of glass-ceramic coating.

Patterns of coloring with ionic dyes of the base glass matrix and enamel coatings in the system R2O–ВаО–ZnO–Al2O3–В2О3–TiO2–SiO2

The paper presents the study on the identification of patterns of coloring of a basic glass matrix and enamel coatings based on it in the system R2O–ВаО–ZnO–Al2O3–В2О3–TiO2–SiO2 by a number of ionic dyes. Regardless of the dye content, ionic dyes give the same color tone to both glasses and coatings based on these glasses as follows: CuO (1.0–3.0 wt.%) =489–494 nm (blue-green), Fe2O3 (0.5–2.0 wt.%) =575–585 nm (yellow), K2Cr2O7 (0.5–2.0 wt.%) =570–576 nm (yellow-green), CoO (0.5–1.0 wt.%) =441–463 nm (blue-violet), and NiO (0.5–1.0 wt.%) glass=559'–571' nm, coatings=598–629 nm (brown). It is shown that according to the degree of color intensity of glasses and coatings based on them, the dyes are arranged in the following sequence: CoO>NiO>CuO>K2Cr2O7>Fe2O3.. The research was conducted using a special computer program COLOR GLASS. The established patterns are used in the development of lead-free glass enamels for jewelry and decorative products.

Problems with Surface Protection of Welded Joints by Vitreous Enamel Coating

This work deals with the application of a vitreous enamel coating on welded joints, whereas vitreous enamel being intentionally applied in high thicknesses. As a base material, we used low-carbon steel Kosmalt E 300 T. Two different processes were chosen for pre-treatment-chemical and mechanical. The resulting enamel coating consisted of two successively applied layers of base and cover enamel coating. The thickness and microhardness of the coating were measured. The metallographic analysis was also performed on selected samples. The results show that the high thickness of the enamel coating significantly impairs the useful properties of the product.

Development of Compositions of New Enamel Coatings with Various Operational and Decorative Properties to Protect Steel Architectural and Construction Panels

Metal enameling is widely used in construction, which differs enameled products from other building materials: the ability to obtain a variety of colors and surfaces; resistance of the surface under the influence of the atmosphere and sunlight; high corrosion resistance; light weight, lightness and quick installation; fire resistance; ease of cleaning; the possibility of mechanizing the manufacture of parts in serial production. The authors of the article have developed the compositions of enamel coatings and investigated their aesthetic and consumer and technical and operational properties. Also, three compositions of new enamel coatings for architectural and construction panels have been developed and enamel coatings of various colors, including pastel colors, have been obtained on their basis.

Silicon nitride modified enamel coatings enable high thermal shock and corrosion resistances for steel protection

Vitreous enamel is a durable inorganic material that has been extensively used in our daily life for decoration and protection of the metallic substrates. It guarantees optimal corrosion protection to the covered substrates, but, on the other side, the brittle nature of its matrix highly limits its application. Here new enamel coatings were synthesized by adding silicon nitride with the contents of 0, 1.5, 2.5, 3.5, 5, and 7.5 wt%. Scanning electron microscope (SEM), X-ray diffraction (XRD), micro indentation, impact, thermal shock, and potentiodynamic polarization tests were conducted to evaluate the microstructure and engineering properties of the studied enamel coatings. Results showed that the addition of silicon nitride leads to a high internal porosity of the enamel coating, which consequently improves the resistances against cracking under indentation and impact loads. Especially, the silicon nitride modified enamel coatings were found to survive more than 100 cycles of thermal shocks. Despite the porosity rising, the addition of silicon nitride enhanced the corrosion resistance of enamel coatings at early immersion age, and all enamel coatings kept around 10 times lower corrosion rate than that of the uncoated steel at later immersion age. The findings of this work may provide a solution to steel protection against harsh high-temperature exposure and corrosive environments.

Initial Corrosion Characteristics of Enamel Coated Carbon Steel in Hot Tap Water

Initial Corrosion Characteristics of Enamel Coated Carbon Steel in Hot Tap Water

Corrosion of the WC-12Co and enamel coatings in liquid Zn-55Al alloy at 640 °C

Corrosion behavior of the WC-12Co and enamel coatings in liquid Zn-55Al alloy is investigated comparatively. Serious corrosion consumes over 40 μm of the WC-12Co coating after 100 h immersion. Co dissolution occurs firstly by forming Zn-Co solid solution and then intermetallic compounds. WC is decarburized and reacts with Al to form WAl5 at high temperature. The enamel coating suffers quite slight corrosion. Porous γ-Al2O3 layer develops at surface, which then reacts with the enamel to form a continuous CaAl4O7 interlayer that prevents the further invasion of Al and provides the high corrosion resistance.

Porcelain Enamel Coatings

Porcelain enamel is an inorganic-type coating, which is applied to metals or glass for both decorative and functional purposes. This coating is a silica-based solidified glass mass obtained by high-temperature firing (temperature can range between 450 and 1200 °C depending on the substrate). Porcelain enamel coatings differ from ceramic coatings mainly by their glass structure and dilatation coefficient, and from organic paints mainly by the inorganic nature of the matrix and the chemical bond that exists between the coating and the substrate.

Evaluation of Glass Coatings with Various Silica Content Corrosion in a 0.5 M HCl Water Solution

Two enamel coatings with a high and a low silica content were prepared on 35CrMo steels via vacuum firing. Their corrosion behavior in a 0.5 M HCl solution including corrosion kinetics, microstructures and electrochemistry performance were studied in comparison with uncoated steels. The results show that catastrophic corrosion occurred for uncoated steels while enamel coatings significantly decreased the corrosion rate. Enamel coatings with a high silica content exhibited the best corrosion resistance against hydrochloric acid due to their highly connected silicate network, which inhibited the leaching process of alkali metals in the acid solution. The corrosion inhibition efficiency for enamel containing a high silica content reached a maximum of 94.3%.

The influence of the size of corundum particles on the properties of chemically resistant porcelain enamels

Porcelain enamels are silica-based inorganic coatings, which are successfully applied to different kind of metallic substrates in applications where high chemical resistance and corrosion protection are needed. The main weakness of enamel coatings is represented by the glassy and brittle nature of the matrix: therefore, it is necessary to find some solutions to address this issue effectively and improve their resistance to abrasion. Some recent papers about the production of composite enamels with Al2O3 particles showed that a high concentration of corundum particles (10–20 wt%) could improve the abrasion resistance of these coatings. This work is focused on studying the influence of micro and macro sized corundum particles on the abrasion and chemical resistance of composite enamel coatings. The Al2O3 particles are added in 20 wt % concentration and the firing treatment is optimized for every sample type. The coatings topography and morphology are mainly characterized by scanning electron microscopy measurements and Energy Dispersive X-ray (EDX) microanalysis. The abrasion resistance of the coatings is evaluated by P.E.I. abrasion test. Mass loss and roughness measurements are used to assess the coatings surface properties during the mechanical damage; in addition, Electrochemical Impedance Spectroscopy (EIS) measurements and electron microscopy observations are carried out after 5000 P E.I. abrasion cycles to evaluate the decrease of the coatings protection properties due to mechanical damage. Finally, the coatings chemical resistance is evaluated by exposure to an aggressive fog with the presence of SO2 (Kesternich test), simulating an industrial environment. The addition of macro sized alumina particles leads to an improvement of the coating abrasion resistance, without a loss in the protection properties. Differently, the addition of micro sized alumina particles produces an increase of the coating surface roughness and results to have detrimental effects on the behaviour of the coating in aggressive environments.

Functional Protective Coatings for Steel Architectural Construction Panels

Currently, enameled steel products are becoming very popular in construction, since they have a number of valuable properties that noticeably distinguish enameled architectural and construction panels against the background of other facing building materials. Also, extremely urgent is the problem of obtaining glass enamel coatings for architectural and construction panels with high properties. In the work, glass-crystalline enamel coatings in the system R2O–RO–B2O3–Al2O3–SiO2–TiO2–P2O2–F- were studied, the features of their formation on facing steel panels were revealed. The physicochemical and aesthetic-consumer properties of the developed enamel coatings have been investigated. The influence of the chemical composition of titanium-containing glass and the crystallization process on the whiteness index of white coating glass-crystalline enamels and the characteristic color shade was studied using a spectrophotometric method using an RGB color measurement model. This method made it possible to accurately determine the shades of the obtained glass-crystalline enamel coatings for steel.

Protective and decorative properties of titanium glass enamels

It is known that enamel coatings with enhanced protective and decorative properties can be fabricated on the basis of boron-silicate glass frits with an increased content of TiO2 in their composition. Opacity and white color of enamel coatings are due to their crystallization at firing temperatures. Titanium glass enamels are not pure white visually, and show yellow and blue shades depending on their chemical composition. The purpose of this work was to establish the influence of basic components on the water resistance and color characteristics of titanium enamel coatings. Our experimental study was focused on the glass frits with the chemical composition described by the generalized formula (76–n–m)SiO2nB2O3mNa2O24MexOy, where MexOy is the total content of TiO2, ZrO2, Al2O3, MgO, СaO, P2O5, and K2O. It was found that the glass frits with the following content of basic components (mol.%): Na2O 12–13, K2O 3, B2O3 10–11, SiO2 49–51 demonstrated the highest water-resistant properties. The color characteristics of titanium enamel coatings prepared on the basis of the mentioned glass frits differ significantly from the reference white light A; the titanium enamel coatings under consideration have a yellow-green tint. The highest deviations of the enamel coating color purity and color tone from a standard of white color were observed when increasing the Na2O content in the glass frits composition at the expense of SiO2. The color of titanium coatings with the highest water resistance has a deviation from the standard of white color within 4–6%.

Study of Lower Temperature–Sintered Enamel Coating on Steel Bars: Effect of Coating Cycles

AbstractEnamel coating is a novel type of coating for the corrosion protection of reinforcement in concrete. Recently, improved enamel coating was achieved using low-temperature sintering. This stu...

Phase Structure and Corrosion Resistance of Multilayer Low-Temperature Sintered Chemically Reactive Enamel Coatings

AbstractThe phase structure and corrosion resistance of uncoated, pure enamel-, double-enamel- and triple-enamel-coated hot-rolled plain steel bars were investigated by X-ray diffraction (XRD), las...

Influence of graphene addition on the mechanical and surface properties of vitreous enamel coatings

Vitreous enamel is a very interesting coating for both aesthetical and technical purposes. The deposition of enamel coatings can be exploited on different materials, such as steel, cast iron and aluminium alloys, and it allows to greatly improve their mechanical, chemical, corrosion and thermal protection properties. Despite their high hardness, enamel coatings show limited abrasion resistance, mainly due to their vitreous nature and brittle behaviour. Recently, many studies tried to improve the abrasion resistance of enamel coatings through the modification of frit composition or through the addition of mill additives or hard particles. Another possible option to address the limited mechanical properties of enamel coatings could be represented by the use of graphene, as it has self-lubricating properties. Different concentrations of graphene flakes (0.25 wt.%, 0.50 wt.% and 1.00 wt.%) were added to the frit to study their influence on the enamel abrasion resistance. The performances of modified enamels were assessed exploiting mass loss, gloss and roughness measurements after different abrasion cycles, and microscopy investigations were carried out in order to evaluate the damage mechanism. Electrochemical Impedance Spectroscopy measurements were carried out in order to assess the protection properties and the produced defectiveness of the coating. An improvement of the coating abrasion resistance was obtained introducing 0.25 wt.% graphene inside the enamel matrix, although a loss of aesthetical properties was observed.

Oxidation protection of enamel coated Ni based superalloys: Microstructure and interfacial reaction

We study the oxidation of SiO2-Al2O3-CaO-BaO-MgO based enamel coated Ni based superalloy at 900°C and find that the enamel coatings are highly capable of protecting the Ni based superalloy from oxidation. During the oxidation, the complicated composition crystals precipitated in enamel lead to two linear variation stages of oxidation weight gain. Moreover, the increased roughness of the superalloy interface due to oxidative attack and the immersion of the enamel coating in superalloy should increase the interface bonding strength. Finally, oxidations of Al, Ti and Cr from superalloy dominates the interfacial reactions.