Papers by Keyword: Adhesion

Abstract: Coatings deposited by detonation spraying equipment CCDS2000 using alumina powder are studied. CCDS2000 is characterized by a computer control system, robot compatible spraying unit (gun barrel), a portable chiller, two powder feeders, and other peculiar properties. This installation allows to deposit coatings on complex shape surfaces and thin-walled parts under optimal conditions. Studies of the coating properties included measurements of coating microstructure, porosity, microhardness, adhesion, cohesion, abrasive and erosive wear, and dielectric properties (specific resistivity and dielectric strength). The detonation sprayed coatings have an adhesion of 60-70 MPa, cohesion of 100 MPa, microhardness of 1500 HV₁₀₀, porosity of about 1% (measured on microsections of coatings using OLYMPUS Stream Image Analysis software). Impregnation of coatings with silicone oil showed that the real open porosity of coatings is up to 6%. Dielectric strength of the ceramic layer with the thickness of 200 μm exceeds 30 kV/mm. Specific resistivity depends on atmospheric humidity and when the relative humidity is less than 60%, the specific resistivity is greater than 10¹³ Ω·cm.

Abstract: A density functional theory (DFT) is used to investigate the energetics of an epoxy resin adhere on a tin oxide and a hydroxylated-alumina surface within a supercell approach. Self—consistent geometry optimization is performed for models of adhesion interface, which is comprised of a fragment of epoxy resin and hydroxylated-Al₂O₃ (001), and SnO2(001) and (110) surface. The epoxy resin studied was simplified fragment based on diglycidyl ether of bisphenol A (DGEBA). It is found that the distance between the resin and the surface where the adhesion force is maximized is substantially the same for all models. Analysis of the energy-distance plot reveals that the fragment of DGEBA molecule adhere most strongly to the SnO₂(001) surface, suggesting that the adhesion force is induced by van der Waals (vdW) interaction.

Abstract: Glass ionomer cement (GIC) is the most commonly used restoration material because of biocompatible material. GIC is restoration material that can be attached to enamel either to dentin physicochemically. The adhesion properties of teeth to restoration have an effect on marginal adaptation. This causes different attachment values. An alternative difference in attachment can be achieved by adding bioactive glass silica material to glass ionomer cement. The formation of hydroxyapatite can be occurred by bioactive glass silica between the tooth surfaces and the restoration materials and it is been expected to reduce microleakage rates. The purpose of this study was to seen the effect of adding 5% silica nanoparticles from sea sand to the GIC on microleakage rates. In this study, silica was synthesized from sea sand by using coprecipitation method. Specimens were 20 maxillary premolars were classified into two groups which were applied GIC (n=10) and silica 5% modified GIC as restorations (n=10). The specimens were immersed in 5% methylene blue solution for 24 hours, then were observed under stereomicroscope and SEM. There were a difference score microleakage and mean value of distance between silica 5% modified GIC with enamel and dentin had smaller distance, as compared to GIC.

Abstract: The paper presents the results of a study of the protective properties of composite coatings obtained on AMg3 aluminum alloy by plasma electrolytic oxidation (PEO) and subsequent modification of formed oxide layer with superdispersed polytetrafluoroethylene (SPTFE) from a suspension based on isopropyl alcohol. The incorporation of fluoropolymer decreased the porosity of base PEO-coating more than one order of magnitude. Formed composite layers increased wearproof of the samples by more than two orders of magnitude in comparison with PEO-coating. Additionally, polymer-containing coatings has higher adhesion compared to substrate. Formed composite layers possess superhydrophobic properties: contact angle attains 155°.

Abstract: Geckos can run swiftly on various surfaces, is not only related to the micro-nanostructure of their setae, but also related to the charged keratin in biological tissues of epidermis. Many gecko-inspired structural materials have been developed in order to obtain desired adhesion property. Much research has been done to improve their adhesion by changing chemical composition and optimizing micro-nanostructure, but little research has been done on the effect of surface charge. Therefore, this study aims to investigate the effect of surface charge on the adhesion of gecko-inspired materials, and to explore a new way to improve their adhesion performance. In this work, the dry adhesive materials made of polyvinylsiloxane (PVS) with mushroom-shaped pillars were polarized under high voltage. The results showed that polarized samples with the mushroom-shaped pillars facing the positive electrode have more negative charge, and the adhesion was improved a lot with increasing charge.

Abstract: The features of obtaining carbon plastics and specific solutions to problems associated with the compatibility of an inorganic filler and a polymer matrix, the formation of adhesive contact of carbon fillers due to the formation of chemical bonds, mechanical adhesions, local stresses and defects at the phase boundary are considered. Successful solutions are presented that provide high adhesive strength between the filler and the polymer matrix.

Abstract: In this work we studied the effect of surface treatment of PET films, which are widely used in food packaging, on the adhesion value of ink layers based on polyvinyl chloride. To give high barrier properties to packaging laminates, the films used in their structure are coated with a nanolayer of aluminum oxide (AlOx). However, these films have a disadvantage associated with the low adhesion of adhesive and ink layers to the AlOx nanolayer. To eliminate this disadvantage, aluminium oxide nanolayer is additionally coated with various polymer coatings. In this work we studied the effect of a polyacrylic coating applied on top of an AlOx layer on improving the adhesion of ink layers. For PET films used in food packaging, optical and surface properties are also important. In this regard, additionally we measured surface free energy, coefficient of friction, and optical properties of the studied PET films. We also highlight the relationship of contact angles of wetting and the work of adhesion for the printing ink with the measured adhesion of ink layers.

Abstract: In the article the effect of fillers of various chemical nature on the corrosion resistance of polyester powder coatings in terms of flaking widths and corrosion expansion widths in accordance with DSTU ISO 4628-8: 2012 was reviewed. According to the results of studies, the effectiveness of the use of fillers to increase the corrosion resistance of the powder coating varies depending on the average particle size and crystalline form of the filler was found. As a rule, in order to receive a powder coating based decorative coating you should apply only one layer of paint, while liquid coatings require applying several layers; this increases the time of coating production. The powder coating can be easily utilized and recycled, thus the economic feasibility of production increases.

Abstract: Ti-based coating has been used for biomaterials to improve biocompatibility, mechanical and corrosion properties. Each coating shows unique performance depending on a variety of factors such as coating microstructure and properties as well as in-service conditions. In this study, the microstructure, surface topography, hardness, adhesion and corrosion properties of Ti and TiN films on stainless steel 316L coated by cathodic arc physical vapor deposition process (PVD) were studied. The results showed that the surface roughness of 316L increased after being coated with Ti and TiN film as evidenced by the numerous particles and voids observed on the surface of both films. The hardness of 316L coated with Ti and TiN was increased by approximately 50% and 85%, respectively. Ti and TiN coated samples showed good adhesion strength with the first critical load (LC1) of approximately 10N and 15N, respectively. However, the types of film failure for Ti and TiN were found to be different. Partial delamination with a high degree of plastic deformation was observed for Ti coating, whereas surface cracks were found for TiN coating. This finding is likely attributable to the difference in flow resistance and the amount of particles and voids observed. All samples showed a stable passive region during 7 days of immersion in Ringer’s solution. Ti film showed better corrosion resistance than TiN, which may have been caused by the effect of more voids on TiN surfaces formed by PVD coating.

Abstract: Nowadays, thermal spray coatings are used to enhance mechanical properties of the material. One of the technologies used to produce thermal spray coating is HVOF spray technology. This is the most advanced and modern technology which has been widely used in the industry due to its flexibility and ability to create coatings with better adhesion in comparison with other thermal spray methods. This article presents some empirical findings from applying the 67Ni18Cr5Si4B alloy powder coating onto C 45 steel shaft by HVOF spray technology. It also analyzes the influence of some technological parameters on the adhesion of the coating. As a result, the parameters of HVOF spray technology are obtained suitable for recovering worn axis-sized workpieces.