Enamel Coatings Research Articles

Polydisperse dry compositions for slip enameling of thin-sheet steel

The particulars of obtaining polydisperse dry compositions for slip enameling of low-carbon steel are examined. The effect of the deflocculant xanthum gum on the technological and rheological properties of slips and the quality of enamel coatings are investigated.

環境保全に配慮した焼付け塗装仕様の検討 その１４ 各種塗装仕様に対する屋外暴露試験による評価

環境保全に配慮した焼付け塗装仕様の検討 その１４ 各種塗装仕様に対する屋外暴露試験による評価

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

In this study, the corrosion process of enamel-coated deformed rebar completely immersed in 3.5 wt.% NaCl solution was evaluated over a period of 84 days by EIS testing. Three types of enamel coating were investigated: pure enamel, 50/50 enamel coating, and double enamel. Surface condition of the enamel coatings that were intentionally damaged prior to corrosion tests was visually examined at different immersion times. After 84 days of testing, the damaged coating areas were characterized by SEM, and the corrosion products on and adjacent to the damaged areas were collected and analyzed by XRD. Corrosion initiated at the damaged locations with no undercutting of the coating observed. The 50/50 enamel coating had the least corrosion resistance, due to its interconnected pore structure, and prior damage drastically reduced the corrosion resistance of pure and double enamel coated rebar.

Functional Corrosion-Resistant Enamel Coatings and Their Adherence Strength

Functional corrosion-resistant glass enamel coatings make it possible to protect inner surface of oil pipelines in extreme operating conditions. The aim of this study is to propose competitive fluorine-free coatings for energy-effective direct-on enameling technology of pipes. The enamel coatings were applied on the steel surface by the slip method (coatings thickness 450 μm). Their physicochemical and production parameters were defined. The strong adhesion of synthesized enamels to the steel substrate has been achieved by using of the complex adherence promoter, containing optimal quantity of CoO and CuO oxides. The coatings forming mechanism on steel substrate by flexible regime 1 coat–1 firing have been studied. It is established that high level of the coating adhesion is the result of a complex heterogeneous interaction of metal with oxide melt, dissolution and diffusion processes and, as a consequence, intermediate layer formation at the phases boundary during melting (770–780 ◦C). As a result of conducted research, obtained nonnickel rust-resistant glass enamels have been accepted for production of steel pipes with enameled surface.

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

Corrosion Behavior of Enamel Coated Steel Rebar by EIS

Effect of chemically reactive enamel coating on bonding strength at steel/mortar interface

In this study, 84 mortar cylinders, each with one steel rod embedded at its center, were tested in tension to characterize the bonding strength at the steel/mortar interface. The effects of different enamel coatings on the steel rods and the mortar curing time were investigated. The bond strength between a smooth steel rod and mortar can be increased by as much as seven times when the rod is coated with a mixture of 50% (by weight) enamel and 50% calcium silicate (CS) particles. This increase in bond strength is due to the increased surface roughness of the coating and chemical bonding of the embedded CS particles to the surrounding mortar. Uncoated smooth and roughened steel rods and rods coated with pure enamel could be pulled cleanly out of the mortar cylinders, whereas the cylinders split when rods coated with reactive enamels containing CS particles were removed. The failure loads of rods coated with reactive enamels increase with concrete aging time, with a maximum load reached up to at least 97 days, whereas the failure loads of uncoated rods decreased slightly after 28 days of curing.

Powder electrostatic enamelling of household appliances

Principles and practices of contemporary resource and energy saving technology of powder electrostatic application (POESTA)of vitreous enamel coatings are described. Its technological, economic and ecological advantages over slip enamelling in household appliances manufacture are discussed. We develop the principles of synthesis of special glass frits with high electric resistivity for POESTA and discuss the results of studies aimed at the development and industrial implementation of ground, direct-on and coloured cover enamels for household appliances and direct-on thermally resistant chemically durable coatings with antibacterial effect for protection of inner tanks of water heaters. Finally, we describe the development of compositions for easy-to-clean, catalytic and pyrolytic coatings.

Study on the Failure Mechanism of Enamel Coatings in HAZ

Because the enamel coatings has excellent ageing resistance and anti-corrosion performance, the service life of pipeline with enamel coatings as protective layer can be increased remarkably comparing with the ones with organic coatings. But when the pipeline is welded, the high temperature of welding arc will do harm to the bonding strength of the enamel coating and the base metal because of the differences of thermo-physical properties between them. In order to study the failure mechanism of enamel coating in the heat affected zone, the stress changing process of enamel/steel was studied through numerical simulation and the interface of enamel/steel was studied by welding thermal simulation technology. The results show that the weakness parts of the welded joints are the imperfect normalized zone and overheated zone. In the imperfect normalized zone, the micro-cracks generate at the interface of enamel/steel because high stress occurred and some coatings fused incompletely because of short staying time at high temperature that induced micro-cracks in the enamel coating under high welding stress, so it was one of the dangerous zones of HAZ. Because high tensile stress formed during cooling that was dangerous to the brittle enamel coating, the bond layer of enamel/steel was damaged by high temperature of welding and the pores generated at the interface of enamel/steel, the coatings of overheated zone could be pulled off from the base metal easily that caused the steel exposed to the corrosion medium directly without the protection of enamel coating, so it was another dangerous zone of HAZ. Keywords: enamel coating; numerical simulation; welding thermal simulation; failure mechanism; HAZ

Enamel coatings based on slag wastes from heat and electric power plants

The possibility of manufacturing a protective corrosion-resistant enamel coatings that are based on slag wastes from heat and electric power plants and intended for oil steel pipes has been considered. A number of compositions of glass-slag-enamel coatings have been developed. The prepared samples have been tested for strength of adhesion to metal, chemical resistance, and corrosion resistance. It has been demonstrated that the synthesized protective corrosion-resistant glass-slag coatings satisfy all the specified requirements.

Effect of P2O5 addition on Li2TiO3 crystallization with opacification of white single-layer glass enamel coatings

The mutual effect of the components of enamel on its whiteness is examined. Effect of P 2 O 5 on the process of opacification of white single-layer enamels is studied. It is established that Li 2 TiO 3 plays the main role in the mechanism of crystallization.

Specific features of the resource-saving technology of functional single-layer composite enamel coatings for steel

The compositions of single-layer low-melting white enamels with a decreased (no higher than 720°C) firing temperature without toxic and expensive components have been developed. The mechanisms of formation of the developed single-layer low-melting enamels on a steel preliminarily treated by means of deposition of copper, nickel, and zinc films through electroplating, as well as by boronizing, have been investigated.

Use of titanium dioxide for the development of antibacterial glass enamel coatings

It is shown that titanium dioxide is useful for developing antibacterial glass enamel coatings. Antibacterial powder (filler) was synthesized on the basis of hydroxyapatite modified with titanium oxide, and its phase composition was investigated. It was established that the composite glass enamel coatings studied are characterized by a substantial antibacterial and antifungal effect from 70 to 90% with synthesized inorganic filler content from 1 to 5% with Ti4 + /(Ti 4+ + Ca 2+ ) ratio equal ratio 0.04 - 0.07.

A Particular Instability of Unilaterally Supported Thin Plates Under Transversal Load: Effect of the Residual Stresses Induced by Vitreous Enameling

Abstract: Simply supported rectangular thin plates under transversal load, concentrated at the centre of the plate, can show a particular kind of instability at one or two edges depending on their dimensions. If only small displacements are considered, the problem is one of pure bending and instability does not occur; on the contrary this instability is induced by the compressive membrane stresses due to large displacements. Vitreous enamel coatings, generally used to improve anti corrosion properties, increment the load value required to induce the instability by inducing residual tensile stresses on the plate. This paper compares and discusses experimental tests on steel and enamelled steel plates and the results obtained by a non linear numerical model taking into account residual stresses. By both experimental and numerical analysis it was possible to conclude that the presence of residual stresses caused an increment of the values of force and work at which the instability took place with respect to the case where residual stresses were not present.

Enamel microarchitecture of a tribosphenic molar

The tribosphenic molar is a dental apomorphy of mammals and the molar type from which all derived types originated. Its enamel coat is expected to be ancestral: a thin, evenly distributed layer of radial prismatic enamel. In the bat Myotis myotis, we reinvestigated the 3D architecture of the dental enamel using serial sectioning combined with scanning electron microscopy analyses, biometrics of enamel prisms and crystallites, and X-ray diffraction. We found distinct heterotopies in enamel thickness (thick enamel on the convex sides of the crests, thin on the concave ones), angularity of enamel prisms, and in distribution of particular enamel types (prismatic, interprismatic, aprismatic) and demonstrated structural relations of these heterotopies to the cusp and crest organization of the tribosphenic molar. X-ray diffraction demonstrated that the crystallites composing the enamel are actually the aggregates of much smaller primary crystallites. The differences among particular enamel types in degree of crystallite aggregation and the variation in structural microstrain of the primary crystallites (depending upon the duration and the mechanical context of mineralization) represent factors not fully understood as yet that may contribute to the complexity of enamel microarchitecture in a significant way.

Antibacterial composite glass coatings for protecting special-purpose steel panels

It is confirmed that glass enamel coatings are promising for antibacterial protection of steel panels. A methodological approach is developed for obtaining antibacterial composite glass coatings. A glass matrix with a programmed structure, bactericide nanopowders of zinc phosphate, and composite glass coatings based on them have been obtained on the basis of the system R2O – RO – TiO2 – P2O5 – SiO2. The composition of a coating with the maximum antibacterial effect with respect to E. Coli bacteria is determined.

Teeth: Among Nature's Most Durable Biocomposites

This paper addresses the durability of natural teeth from a materials perspective. Teeth are depicted as smart biocomposites, highly resistant to cumulative deformation and fracture. Favorable morphological features of teeth at both macroscopic and microscopic levels contribute to an innate damage tolerance. Damage modes are activated readily within the brittle enamel coat but are contained from spreading catastrophically into the vulnerable tooth interior in sustained occlusal loading. Although tooth enamel contains a multitude of microstructural defects that can act as sources of fracture, substantial overloads are required to drive any developing cracks to ultimate failure—nature's strategy is to contain damage rather than avoid it. Tests on model glass-shell systems simulating the basic elements of the tooth enamel/dentin layer structure help to identify important damage modes. Fracture and deformation mechanics provide a basis for analyzing critical conditions for each mode, in terms of characteristic tooth dimensions and materials properties. Comparative tests on extracted human and animal teeth confirm the validity of the model test approach and point to new research directions. Implications in biomechanics, especially as they relate to dentistry and anthropology, are outlined.

Morphology and fracture of enamel

This study examines the inter-relation between enamel morphology and crack resistance by sectioning extracted human molars after loading to fracture. Cracks appear to initiate from tufts, hypocalcified defects at the enamel–dentin junction, and grow longitudinally around the enamel coat to produce failure. Microindentation corner cracks placed next to the tufts in the sections deflect along the tuft interfaces and occasionally penetrate into the adjacent enamel. Although they constitute weak interfaces, the tufts are nevertheless filled with organic matter, and appear to be stabilized against easy extension by self-healing, as well as by mutual stress-shielding and decussation, accounting at least in part for the capacity of tooth enamel to survive high functional forces.

Spectral selectivity of composite enamel coatings on 321 stainless steel

Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments embedded in a borosilicate-glass matrix were deposited on 321 stainless steel using screen-printing techniques and characterized using total reflectance over the spectral range of 200 nm to 25 μm. The composite coatings exhibited moderate spectral selectivity and excellent thermal stability at 450 °C. Solar absorptance ( α) ranged from 0.82 to 0.90 and calculated thermal emittance at 500 °C ( ε) ranged from 0.46 to 0.79. Both depended on coating thickness and pigment volume concentrations. As an example, the highest solar selectivity was measured in a 0.9 μm coating with α and ε (500 °C) being 0.82 and 0.46, respectively.

Vitreous Enamel Coating on Steel Substrates

Vitreous enamel is a glassy coating formed on a metal substrate by firing at temperatures above 800 °C. The quality of vitreous enamel coating depends on the pre-treatment of the steel substrate surface and the quality of enamel slip. The main aim of this study was to characterize the composition of the steel substrate surface after firing with double finish, to explain the effect of steel substrate surface pre-treatment (blasting, acid pickling) on forming the phase interface of the steel substrate – vitreous coating system, and on its final microhardness, fracture strength and the adhesive properties of the coating. To achieve these aims, the following experimental methods were used: Mössbauer spectroscopy, X-ray diffraction, electron analyzer, and EDAX. Based on the chemical composition of the initial enamel slip and the firing technology, the metal - enamel system interface exhibited various ratios of layers of magnetite, hematite, nonstoichiometric wüstite, and crystals of faylite. The measuring results indicate that the quality and age of enamel slip influences the brittle fracture properties of vitreous enamel coating.

A simple model for enamel fracture from margin cracks

We present results of in situ fracture tests on extracted human molar teeth showing failure by margin cracking. The teeth are mounted into an epoxy base and loaded with a rod indenter capped with a Teflon insert, as representative of food modulus. In situ observations of cracks extending longitudinally upward from the cervical margins are recorded in real time with a video camera. The cracks appear above some threshold and grow steadily within the enamel coat toward the occlusal surface in a configuration reminiscent of channel-like cracks in brittle films. Substantially higher loading is required to delaminate the enamel from the dentin, attesting to the resilience of the tooth structure. A simplistic fracture mechanics analysis is applied to determine the critical load relation for traversal of the margin crack along the full length of the side wall. The capacity of any given tooth to resist failure by margin cracking is predicted to increase with greater enamel thickness and cuspal radius. Implications in relation to dentistry and evolutionary biology are briefly considered.