Effects of Surface Preparation on the Corrosion Behavior of Mild Steel

Surface preparation of engineering materials is necessary for preventing corrosion and subsequent failure of materials in service. There are different methods of surface preparations that can affect engineering materials in different ways. This study investigated the effect of surface preparation on the corrosion behavior of zinc sprayed and unsprayed mild steel. Quantitative analysis and potentiodynamic polarization techniques were used to evaluate the immersed samples of different surface preparations. The results indicated that the least corrosion rate was observed for the uncoated sample prepared with CC1200 grit paper at 0.041 mpy and successive samples in the order of CC220 grit paper at 0.047 mpy < P60 grit paper at 0.052 mpy < filing at 0.064 mpy and grinding at 0.074 mpy after 42-days of immersion. The prepared samples that were further coated with zinc spray demonstrated a similar trend. The sample prepared with CC1200 grit paper and further coated with zinc spray exhibited the lowest corrosion rate of 1.35 x 10-9 mpy. Potentiodynamic polarization results further suggested that the same behavior was observed in the quantitative analysis.

Intensification of heat transfer during pool boiling of nitrogen on surfaces with capillary-porous coatings produced by 3D-printing

The study of heat transfer, critical heat fluxes (CHF) and evaporation dynamics at pool boiling of nitrogen at atmospheric and low pressures in a stationary heat generation regimes was performed. The two flat cooper heaters with porous coatings of various structural parameters obtained by additive 3D-printing as well as smooth one were used as working surfaces. According to obtained results such coatings significantly effect on pool boiling increasing up to six times the heat transfer coefficients (HTC) in comparison with uncoated sample. For all investigated heaters and pressures, visualization of boiling was performed using a video camera from which data on the bubble departure diameters and estimates of the active nucleation site density were obtained.

Corrosion and Wear performances analysis of PVD CrMoN/Cr Coatings

Tools coated CrN based alloys are currently used in several industries for machining and manufacturing, but present severe wear, limiting their service life. Seeking an alternative, three CrMoN monolayers (~1µm in thickness) coatings with varying in the Mo percentage content were elaborated using the RF magnetron co-sputtering method. These coatings were evaluated and compared with the alloy currently used (CrN) by electrochemical tests in NaCl solution (stationary and no stationary method) and sliding wear tests (ball-on-disc configuration) performed at room temperature. The results indicate that the samples coated with CrMoN presented better performance against wear and corrosion than the uncoated sample. Among the coatings, the labeled C1 (27 % Mo) showed the best corrosion resistance as it presents a positive corrosion potential Ecorr. However, the best wear resistance (lowest coefficient of friction) was shown by coating labeled C4 (33 % Mo). All of the tested specimens underwent abrasive wear in addition to adhesive wear.

Optimizing the layer thickness of sol–gel-derived TiO2 coating on polyetheretherketone

Sol–gel-derived TiO2 coatings have been confirmed to effectively promote bone-bonding behavior on polyetheretherketone (PEEK) surfaces; however, the optimal layer thickness to maximize the osseointegration and adhesive performance has not been yet determined. In this study, we applied sol–gel-derived TiO2 coatings with different layer thicknesses (40 and 120 nm) on PEEK implants to determine the effects of layer thickness on the surface characteristics, adhesive strength, and bone bonding capabilities (including histological osseointegration). The surface analysis results of both coated implants indicated no significant differences concerning the water contact angle, layer adhesion strength, and apatite formation ability in a simulated body fluid. Additionally, the in vivo biomechanical tests revealed a higher bone-bonding strength for both coated PEEK implants (compared with that of the uncoated sample). It was thus concluded that the factor of layer thickness marginally influences the bioactive advantages attained by sol–gel-derived TiO2 coatings on PEEK surfaces, highlighting the significant versatility and clinical availability of this coating technology.

Effect of Mono- and Bilayer Coating of Nanofibrillated Cellulose, its Modification, and Shellac on Properties of Molded Pulps

A molded pulp is increasingly used as eco-packaging, but it has poor water resistance. Therefore, surface coating is common to perform on pulp or paper packaging to overcome this shortcoming. In this study, the bagasse (BG) molded pulp sheets were mono-and bilayer coated with nanofibrillated cellulose (NFC), modified NFC (mNFC), and shellac (S) by using a spin coating technique. Surface morphology, surface wettability, water absorption, and mechanical properties of the coated sheet samples were evaluated and compared to the uncoated sample. It was found that mNFC could effectively provide an even and complete coverage coating layer on the BG-based sheet (BG/mNFC), thanks to the partially substituted ester groups. On the contrary, NFC could not be coated evenly on the BG-based sheet surface (BG/NFC) due to its tendency towards agglomeration. The homogeneity of surface obtained from the first layer coating by NFC or mNFC affected the surface quality of the second layer coating by shellac. As a result, the BG/mNFC/S bilayer coated sample showed the smoothest surface and also the highest water resistance confirmed by SEM, contact angle measurement, and water absorption results. Furthermore, the tensile properties of both bilayer coated samples (BG/NFC/S and BG/mNFC/S) were significantly improved (p<0.05) as compared to the uncoated BG sample. This results suggested that the current bilayer coating system is very promising for advancing the performance of molded pulps in novel packaging uses.

Development of Antibacterial, Antioxidant, and UV-Barrier Chitosan Film Incorporated with Piper betle Linn Oil as Active Biodegradable Packaging Material

This study aims to introduce the antibacterial and antioxidant activities of the Piper betle Linn oil (PBLO) into chitosan film (pCS), named as pCS-PBLO film. The morphology, structure, and properties of the pCS-PBLO film, along with the PBLO concentration between 0.4% and 1.2% (v/v), were determined. The film surface became rough and heterogeneous with the addition of PBLO, which directly influenced on mechanical strength of the resultant film. The addition of the PBLO did not affect thermal stability but significant effect on flexibility and mobility of the film. Importantly, the film enhanced the UV-protective property and antioxidant activity as incorporated-PBLO. Moreover, the resulting film revealed the great inhibition efficiency against the negative-gram (E. coli, P. aeruginosa, and S. typhi) and positive-gram (S. aureus) bacteria based on phenolic compounds, such as the acetyleugenol, eugenol, 4-allyl-1,2-diacetoxybenzen, and chavicol acetate in PBLO components. In particular, the pCS-PBLO film may extend the shelf life of king oranges up to two weeks at 25 °C that is longer as compared to the uncoated sample and coated with chitosan alone. These results suggest that the pCS-PBLO film can be used as environmental-friendly and effective food packaging material in the future.

MAGNETRON SPUTTERED NANOCRYSTALLINE TiN THIN FILMS AND CORROSION PROPERTIES

In this report, TiN nanocrystalline thin films were deposited on glass and Ti-6Al-4V substrates using a DC-magnetron sputtering technique. The TiN films were sputtered using a pure Ti target (99.9%) with 40W of power in Ar/N2 gas mixture atmosphere. The structure of the TiN films was characterized by X-Ray diffraction, as prepared films exhibited a (200) preferred orientation, while film annealed at 500 °C shows the (111), (200) and (311). Polycrystalline, cubic, (111)-orientated TiN films were produced by annealing temperature of 500 °C. The effect of deposited temperature on the microstructural morphologies of the thin films was studied by Field Emission Scanning Electron Microscope (FESEM). The particle size of the sputtered TiN films ranged from 50 to 70 nm and was strongly influenced by annealing temperatures, the morphology of the films deposited before and after annealing has a characteristic agglomeration of particles. Potentiodynamic polarization analysis of the TiN films confirms the inverse relationship between polarization resistance and corrosion current. The biocorrosion measurements for TiN films deposited on the Ti-6Al-4V substrate in 3.5% NaCl solution have also been obtained. Clear improvement in the corrosion resistance was observed rather than for untreated, especially for thermally annealed (500 oC) TiN/Ti-6Al-4V samples. The corrosion rate was 0.1458 mm/y for the uncoated sample, while 2.68510-4 mm/y for TiN/Ti-6Al-4V in samples after annealing. The average corrosion potential calculated was - 0.117 V. The results confirmed that coated alloys with 500 °C thermally treated exhibited a better electrochemical behavior compare with uncoated and non-thermally treated alloys possibly due to the better cohesion degree of the coatings.

Corrosion Protection of A36 Steel with SnO2 Nanoparticles Integrated into SiO2 Coatings

Tin oxide (SnO2) nanoparticles were successfully added to silicon oxide (SiO2) coatings deposited on A36 steel by the sol-gel and dip-coating methods. These coatings were developed to improve the performance of corrosion protection of steel in a 3 wt % NaCl solution. The effects of modifying the SnO2 particle concentration from 0–7.5 vol % were investigated by polarization resistance, Tafel linear polarization, and electrochemical impedance spectroscopy (EIS). The formation of protective barriers and their corrosion inhibition abilities were demonstrated. It was found by electrochemical studies that all of the coated samples presented higher corrosion resistances compared with an uncoated sample, indicating a generally beneficial effect from the incorporation of the nanoparticles. Furthermore, it was established that the relationship between the SnO2 content and the corrosion inhibition had parabolic behaviour, with an optimum SnO2 concentration of 2.5 vol %. EIS showed that the modified coatings improved barrier properties. The resistance for all of the samples was increased compared with the bare steel. The corrosion rate measurements highlighted the corrosion inhibition effect of SnO2 nanoparticles, and the Tafel polarization curves demonstrated a decrease in system dissolution reactions at the optimal nanoparticle concentration.

Study of the Properties of Qxide Coatings Formed on Titanium by Plasma Electrolytic Oxidation Method

The development of the modern industry requires to develop high-performance, environmentally friendly methods for the production of light structural material surface coatings. The use of products and structures made of titanium and its alloys with high wear resistance and corrosion resistance prevails in many industries, in particular in the aerospace industry, shipbuilding, and transport engineering. Nowadays, the application of the plasma electrolytic oxidation method, a promising metal surface treatment method, is of increasing interest. Besides this method is called microarc oxidation. The objective of this work is to study the properties of oxide coatings obtained on titanium alloys under the influence of rapid pulsed effects of the plasma electrolytic oxidation process. Oxide composite coatings were obtained in various electrolyte solutions in this work. Oxide coatings are characterized by high wear resistance. It has been established in tribological tests that the wear resistance of the coating is increased by 2–15 times compared with an uncoated sample. The friction coefficient curves obtained for coated samples show that there is no destruction of the coating to the base. The breaking-in area is marked in the curves. The friction surfaces are adjusted to each other and go to a stable friction mode. The latter results in the friction coefficient decrease and wear rate decrease.

Characterization of Nano-Scale Hydroxyapatite Coating Synthesized from Eggshells Through Hydrothermal Reaction on Commercially Pure Titanium

Commercially pure titanium (c.p. Ti) is often used in biomedical implants, but its surface cannot usually combine with the living bone. A coating of hydroxyapatite (HA) on the surface of titanium implants provides excellent mechanical properties and has good biological activity and biocompatibility. For optimal osteocompatibility, the structure, size, and composition of HA crystals should be closer to those of biological apatite. Our results show that the surface of c.p. Ti was entirely covered by rod-like HA nanoparticles after alkali treatment and subsequent hydrothermal treatment at 150 °C for 48 h. Nano-sized apatite aggregates began to nucleate on HA-coated c.p. Ti surfaces after immersion in simulated body fluid (SBF) for 6 h, while no obvious precipitation was found on the uncoated sample. Higher apatite-forming ability (bioactivity) could be acquired by the samples after HA coating. The HA coating featured bone-like nanostructure, high crystallinity, and carbonate substitution. It can be expected that HA coatings synthesized from eggshells on c.p. Ti through a hydrothermal reaction could be used in dental implant applications in the future.