Synthesis of hybrid silica sol–gel coatings containing Zn particles on carbon steel and Al/Zn coated carbon steel

Owing to increasing interest of coatings applied on low alloy steel and galvanised metal plates and their applications, this work presents the study of the process requirements to be fulfilled in order to coat these metals with an hybrid silica coatings containing Zn particles. The main idea was to combine the “barrier” effect of the hybrid silica coatings with the “active protection” effect of the zinc particles inside the coatings. Sol–gel parameters, Zn particles content and suspension stability have been studied. EMPHOS ES 21, an electrostatic dispersant, has been used to obtain stabilised suspensions. Thick, adherent and crack-free coatings containing 10% Zn particles were prepared by dip-coating on carbon steel and Al/Zn coated carbon steel substrates. The applied coating seems to improve corrosion protection of the two metal substrates, and this effect is more noticeable in the case of the Al/Zn system because of the combination of the complementary corrosion protection properties of both coatings.     

Measurement of adhesion of thin evaporated films on glass substrates by means of the direct pull method

The so-called “direct pull method” is applied to the measurement of adhesion of vacuum-deposited thin film coatings on glass substrates. The results obtained by this method are influenced by errors in alignment of the experimental set-up and by non-uniformities of the cement films used to pull the coatings off the substrate. These effects are analysed. Results are presented for films of zinc sulphide, cryolite and silver deposited on BK7 glass substrates. The forces of adhesion on ion-bombarded substrates in these cases are found to be 430 kp/cm², 540 kp/cm² and 230 kp/cm² respectively.     

Natural Antimicrobial – Containing EVOH Coatings on PP and PET Films: Functional and Active Property Characterization

Natural antimicrobials are currently being tested by many researchers for active packaging applications as a response to consumer demands for safer food products. In previous work, several packaging materials consisting of ethylene vinyl alcohol (EVOH)‐coated polypropylene (PP) films containing essential oils or their constituents as active agents were successfully developed and tested for antimicrobial activity. In this work, selected films from those materials, namely EVOH coatings with carvacrol, citral, marjoram essential oil, or cinnamon bark essential oil, on PP and polyethylene terephthalate (PET) substrates, were subjected to diverse physicochemical analyses in order to assess their suitability for food packaging applications. Concretely, the investigated properties were the stability of EVOH coatings on PP and PET substrates, the retainability of EVOH matrices for active compounds, the mechanical, optical, surface and barrier properties of the final active films and the effects of a matrix modification based on the addition of bentonite nanoclay on the performance of PP/EVOH active packages studied in actual working conditions. Results showed that the application of corona discharge followed by a polyethyleneimine‐based primer was the best anchorage treatment available to stabilize EVOH coatings on PP and PET substrates. Furthermore, they demonstrated that the retention of active agents into EVOH matrices ranged from low to moderate, depending on the embedded substance, and that their presence into an EVOH coating in the final multilayer films did not noticeably affect their mechanical, optical or barrier properties, although it considerably improved their wettability. They also indicated that the inclusion of bentonite nanoparticles into their carrier layers substantially enhanced the performance of the final packages, while maintaining or slightly improving their other physical properties. Hence, as a conclusion, all the assayed multilayer films were considered perfectly valid for food packaging applications, and the incorporation of bentonite nanoclay to their carrier layers was also highly recommended. Copyright © 2014 John Wiley & Sons, Ltd.     

Funktionelle Beschichtungen auf Basis anorganischer Nanosole

Functional coatings on basis of inorganic nanosols The controlled hydrolysis of silicon or metal alkoxides produces nanoparticulate oxide sols which condense to thin transparent gel films on any substrates after coating and drying (so‐called “sol‐gel process”). The co‐hydrolysis and co‐condensation of different alkoxides (chemical modification) as well as the embedding of different additives (physical modification) offers almost unlimited possibilities to vary the properties of nanosols and, therefore, also of the resulting coatings, and to adapt them to the purpose intended. By coating of flexible substrates like textiles, papers or polymer foils it is possible to combine the material protecting functions of the inorganic oxide layer with new functional qualities, e. g. modification of surface energy and charge, alteration of the optical properties, realization of biocompatible and bioactive properties.     

Self-assembly of organic acid molecules on the metal oxide surface of a cupronickel alloy

Corrosion of the metal oxide surface of cupronickel (CuNi) alloys is a problem in applications such as household water pipes, industrial pipelines, and marine vessels. On other substrates, thin films have been used as barriers to corrosion. Here, the formation of self-assembled monolayers (SAMs) on the CuNi metal oxide surface has been investigated. Stable, well-ordered SAMs of octadecylphosphonic acid (ODPA) and 16-phosphonohexadecanoic acid (COOH-PA) were formed on the metal oxide surface of CuNi foils (55% Cu/45% Ni) using a solution deposition method. The ODPA modified surfaces could be used to provide a non-reactive barrier that inhibits corrosion of the CuNi metal oxide surface. Meanwhile, COOH-PA films could be used for further surface reactions such as surface initiated polymerization, in which polymer coatings are grown directly from a well-ordered film. Film-modified surfaces were characterized using diffuse reflectance infrared Fourier transform spectroscopy, contact angle analysis, and matrix assisted laser desorption ionization time of flight mass spectrometry. The ability of the films to inhibit corrosion by limiting oxidation of the CuNi surface was assessed using cyclic voltammetry.     

Evaluation of corrosion resistance of diamond-like carbon films deposited onto AISI 4340 steel

The corrosion resistance of amorphous diamond-like carbon (DLC) coatings deposited by radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique on AISI 4340 steel substrates was evaluated under saline (5% NaCl) and acid (1700 ppm H₂SO₄) atmospheres. The corrosion process was investigated by surface characterization and electrochemical methods, such as potentiostatic polarization and electrochemical impedance spectroscopy (EIS). DLC coatings effectively protected the substrate after 48 h in a salt fog chamber and after the first Kesternich cycle. For comparison, under the same conditions, titanium nitride (TiN) coatings did not protect the substrate even for 2 h of saline exposure and even for the first Kesternich cycle. Although the DLC coatings resisted well to the corrosive action of the aggressive media, nucleation and growth of homogenous and micro-sized pinholes uniformly distributed on DLC coatings were observed as a result of the corrosion processes. The observed results suggest that the development of techniques which would reduce the porosity of the DLC films could promote further improvement on their corrosion protection ability.     

Effect of substrate surface conditions and impact velocity of sprayed particles on coatings produced by plasma spraying

In high temperature plasma spraying, surface conditions of the substrate and the impact velocity of sprayed particles are particularly important in the consideration of factors influencing the resultant coatings. In this study an induction plasma torch was used to spray aluminum, tungsten and nickel particles onto flat (111) single-crystal silicon substrates with different surface preparations. In addition to experiments with silicon substrates with clean surfaces and substrates with previously evaporated aluminum over oxide coatings, oxide films and water vapor, hydraulic oil and grease contaminant films were used to investigate the influence of these surface conditions on adhesion formation. The impact velocity of the sprayed particles was controlled by controlling the speed of a centrifugal disc on which the substrate was installed to traverse the plasma effluent.Scanning electron microscopy was used extensively to characterize features of the particle-substrate interaction and to compare the individual behaviors of the metal particles used. Microcavitations and dislocations resulting from the plastic deformation of the substrate were revealed by the successive use of a metal and a special dislocation etchant.     

Mechanical properties optimization of tungsten nitride thin films grown by reactive sputtering and laser ablation

Transition metal nitrides coatings are used as protective coatings against wear and corrosion. Their mechanical properties can be tailored by tuning the nitrogen content during film synthesis. The relationship between thin film preparation conditions and mechanical properties for tungsten nitride films is not as well understood as other transition metal nitrides, like titanium nitride. We report the synthesis of tungsten nitride films grown by reactive sputtering and laser ablation in the ambient of N₂ or N₂/Ar mixture at various pressures on stainless steel substrates at 400  C. The composition of the films was determined by XPS. The optimal mechanical properties were found by nanoindentation based on the determination of the proper deposition conditions. As nitrogen pressure was increased during processing, the stoichiometry and hardness changed from W₉N to W₄N and 30.8-38.7 GPa, respectively, for films deposited by reactive sputtering, and from W₆N to W₂N and 19.5-27.7 GPa, respectively, for those deposited by laser ablation.     

Direct CVD Growth of Graphene on Traditional Glass: Methods and Mechanisms

Chemical vapor deposition (CVD) on catalytic metal surfaces is considered to be the most effective way to obtain large‐area, high‐quality graphene films. For practical applications, a transfer process from metal catalysts to target substrates (e.g., poly(ethylene terephthalate) (PET), glass, and SiO₂/Si) is unavoidable and severely degrades the quality of graphene. In particular, the direct growth of graphene on glass can avoid the tedious transfer process and endow traditional glass with prominent electrical and thermal conductivities. Such a combination of graphene and glass creates a new type of glass, the so‐called “super graphene glass,” which has attracted great interest from the viewpoints of both fundamental research and daily‐life applications. In the last few years, great progress has been achieved in pursuit of this goal. Here, these growth methods as well as the specific growth mechanisms of graphene on glass surfaces are summarized. The typical techniques developed include direct thermal CVD growth, molten‐bed CVD growth, metal‐catalyst‐assisted growth, and plasma‐enhanced growth. Emphasis is placed on the strategy of growth corresponding to the different natures of glass substrates. A comprehensive understanding of graphene growth on nonmetal glass substrates and the latest status of “super graphene glass” production are provided.     

Effect of microstructure on corrosion behavior of TiN hard coatings produced by a modified two-grid attachment magnetron sputtering process

The introduction of an electrically biased two-grid attachment inside a conventional physical vapor deposition process system produces a reactive coating deposition and increases the metal ion-to-neutral ratio in the plasma, resulting in denser and smoother films.The corrosion behavior of titanium nitride (TiN) coatings was investigated by electrochemical methods, such as potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in deaerated 3.5% NaCl solution. Electrochemical tests were used to evaluate the effect of microstructure on the corrosion behavior of TiN coatings exposed to a corrosive environment. The crystal structure of the coatings was examined by X-ray diffractometry and the microstructure of the coatings was investigated by scanning electron microscopy.In the potentiodynamic polarization test and EIS measurement, the corrosion current density of TiN deposited by the modified two-grid attachment magnetron sputtering process was lower than for TiN deposited by conventional magnetron type and also presented higher charge-transfer resistance values during 240 h total immersion time. The modified process promotes the grain refinement, which yields lower porosity.     

Dünne ITO‐Schichten als leitfähige,transparente Elektroden. Thin films of ITO as conductive,transparent electrodes

This article deals with materials science aspects of In₂O₃:Sn (“ITO”) coatings and with the process technology of variants of sputtering used to obtain thin films with properties desired for specific applications. As an example, antistatic and antireflective coatings of monitor tubes are presented. The influence of sputter parameters such as substrate temperature, plasma excitation mode, sputter pressure and oxygen partial pressure on the quality of the films is discussed. It is shown how application‐oriented basic research helps to obtain recipes for materials design. Two basic aspects are discussed in more detail: the influence of an oxygen surplus in the films on microstructure and electrical properties and the correlation of electrical and optical parameters of the films.     

Comparison of their electrical,optical, and electrochemical properties of as-grown plasma polymerized organic thin films by PECVD

Plasma polymerized organic thin films have been deposited on Si(100), glass and metal substrates at 25∼100 °C using thiophene and toluene precursors by plasma enhanced CVD method. In order to compare physical and electrochemical properties of the as-grown thin films, the effect of the RF (13.56 MHz) plasma power in the range of 30∼100 W and the deposition temperature on the corrosion protection efficiency and optical property were mainly studied in this work. Corrosion protection efficiency (P_k), which is one of important factors for corrosion protection in the interlayer dielectrics of microelectronic devices application, provided an increasing tendency with increasing RF power. The highest P_k value of plasma polymerized toluene film (85.27% at 70 W) was higher than that of the plasma polymerized thiophene film (65.17% at 100 W). The result of contact angle measurement showed that the plasma polymerized toluene films have more hydrophobicity than that of the plasma polymerized thiophene films.     

Hybrid plasma CVD of diamond-like carbon (DLC) at low temperatures

Diamond-like carbon coatings have been deposited onto various substrates at 100–150°C using a hybrid plasma assisted chemical vapour deposition technique activated by radio frequency at 13.56 MHz. The coatings have been characterized using a number of techniques including scanning electron microscopy, Raman spectroscopy, thermoanalysis and pin-on-disc wear testing. Results show the films to be diamond like, with the addition of nitrogen (prior to deposition) promoting the formation of crystallites. In addition the condition and type of substrate have been found to have a strong influence on the structural characteristics of the deposited diamond-like films. SEM analysis of diamond-like carbon coatings deposited onto metal matrix composite materials such as Si-Al MMC is reported. The hybrid CVD technology enabled films to be deposited evenly onto the porous MMC structure. Commercially manufactured drills, coated with DLC and titanium nitride (TiN), have been compared to examine their cutting wear resistance characteristics. This revised version was published online in November 2006 with corrections to the Cover Date.     

Plasma-sprayed self-sealing ceramic coatings: Materials chemistry and high temperature protective properties

The principal theoretical and experimental data relating to the structure and the protective action of self-sealing ceramic coatings (SSCCs) used to prevent non-aqueous corrosion phenomena (T ? 900 K) on metallic surfaces in chemically aggressive environments (oxidation, carburization, nitridation, sulphidation, attack by molten metals etc.) are reviewed. The plasma spray process used to deposit SSCCs is described and some of their properties are summarized. The results obtained in an investigation of the protective efficiency of SSCCs on Incoloy 825 and titanium substrates, which are particularly susceptible to metal dusting and oxidation-nitridation corrosion phenomena, are reported. It is hoped that the work described in this paper will stimulate new approaches to the development and characterization of these novel protective coatings as it is necessary to optimize the prevention of non-aqueous corrosion in many applications.     

Antibacterial Properties and Corrosion Resistance of Nitrogen-doped TiO_2 Coatings on Stainless Steel

The Nitrogen-doped TiO2 (N-TiO2) coatings were fabricated on 304 austenitic stainless steel (SS) substrates by oxidation of titanium nitride coatings,which were prepared by plasma surface alloying technique.Microstructural investigation,corrosion tests and antibacterial tests were conducted to study the properties of N-TiO2 coatings.Composition analysis shows that the SS substrates were shielded by the N-TiO2 coatings entirely.The N-TiO2 coatings are anatase in structure as characterized by X-ray diffraction.The corrosion properties of N-TiO2 coated SS samples in Hanks’ solution were investigated by a series of tests.The electrochemical measurements indicate that the corrosion potential positively shifts from 0.275 V for untrated SS to 0.267 V for N-TiO2,while the corrosion current density decreases from 1.3×105 A/cm to 4.1×10 6 A/cm2.The corrosion resistance obtained by fitting the impedance spectra also reveals that the N-TiO2 coatings provide good protection for SS substrate against corrosion in Hanks’ solution.Electrochemistry noise tests indicate that the N-TiO2 coatings effectively retard the local pitting and crevice corrosion of the SS substrate.The results of the antibacterial test reveal that N-TiO2 coatings give 304 austenitic SS an excellent antibacterial property.     

Cultivation of human fibroblasts and multipotent mesenchymal stromal cells on mesoporous silica and mixed metal oxide films

The application of mesoporous silica and silica–titania-mixed metal oxide films prepared via sol–gel processing as substrates for cell growth was investigated. A deliberate tailoring of the chemical composition of the porous substrates with different Si:Ti ratios was achieved by using a single-source precursor based on a titanium-coordinated alkoxysilane, resulting in mesoporous silica–titania films with hydrophilic surfaces. The different coatings were investigated with respect to their applicability in the cultivation of human cells such as human fibroblasts and multipotent mesenchymal stromal cells. It was found that they promoted cell adhesion and proliferation of human fibroblasts up to a period of 14 days. After 2 weeks only single apoptotic cells could be detected on silica–titania mixed oxide films in contrast to a somewhat higher amount on silica coatings. Furthermore, none of the films inhibited osteogenic differentiation of multipotent mesenchymal stromal cells.     

Fabrication of unbacked ultra-thin films of beryllium and other metals

A method is given for preparing ultra-thin unbacked metal films by evaporating the metal onto rock-salt platelets coated with a thin layer of a soluble thermoplastic resin. Beryllium films have been made with thickness ranging from 0.2 to 0.5 μm and free from “optical” pinholes. The beryllium was rapidly and continuously evaporated from a tungsten crucible with very little corrosion of the crucible. Deposition rates of 100 nm s^-1 were achieved with a source-to-substrate distance of 140 mm.     

The effect of bismuth on the structure of zinc hot-dip galvanized coatings

Low carbon steel substrates were galvanized in molten zinc containing 0.0, 0.5, 1.0 and 2.0 wt.% bismuth. The as-cast coatings were examined with optical microscopy, scanning electron microscopy and X-ray diffraction. From the above investigation it was deduced that Bi addition does not affect the morphology of the galvanized coatings with regard to the “traditional” galvanized coatings, although it is mainly accumulated in the eta phase and in the upper part of the zeta phase in the form of inclusions. However these inclusions could accelerate the coating corrosion because Bi is cathodic to Zn. Furthermore the thickness of the galvanized coatings is reduced when Bi is added.     

On the properties of plasma-sprayed oxide and metal-oxide coatings

Alumina (with 3% TiO₂), zirconia (with 13% Y₂O₃) and powder mixtures of zirconia (with 13% Y₂O₃) and molybdenum (in the proportions 70%:30% and 30%:70%) were plasma sprayed under standard conditions onto several steel substrates. Intermediate Ni-Cr metal layers were used.The adhesive strength of the coatings under static and dynamic stress and the thermal shock resistance were tested as well as the wear and corrosion resistance, the porosity and other properties of these oxide and oxide-metal compound layers. In all the tests the number of samples tested was sufficient for reliable average results to be determined.Resistance against friction and against abrasion, sometimes in combination with corrosion, can be controlled by the use of pure oxide layers or, depending on the type of chemical reactions and mechanical behaviour, of oxide-molybdenum compounds. Some theoretical aspects of the behaviour of the coatings tested will be discussed.A knowledge of the mechanical, thermal and corrosion behaviour of the sprayed layers and the interfaces enables selections for practical use. The results reported are part of an industry-sponsored test program for industrial applications of plasma-sprayed coatings.     

Corrosion behavior of nanolayered TiN/NbN multilayer coatings prepared by reactive direct current magnetron sputtering process

TiN, NbN and TiN/NbN multilayer coatings were deposited on tool steel substrates using a reactive DC magnetron sputtering process. The coatings were characterized using X-ray diffraction, nanoindentation, atomic force microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray analysis. The corrosion behavior of TiN/NbN multilayer coatings was studied in 0.5 M HCl and 0.5 M NaCl solutions using potentiodynamic polarization and compared with single layered TiN and NbN coatings. Approximately 1.5 μm thick coatings of TiN, NbN and TiN/NbN multilayers showed good corrosion protection of the tool steel substrate and multilayer coatings performed better than single layered coatings. The corrosion behavior of the multilayers improved with total number of interfaces in the coatings. In order to conclusively demonstrate the positive effect of layering, corrosion behavior of 40-layer TiN/NbN multilayers was studied at lower coating thicknesses (32–200 nm) and compared with single layer TiN coatings of similar thicknesses. The polarization data and SEM studies of these coatings indicated that the corrosion behavior improved with coating thickness and multilayers showed better corrosion resistance as compared to the single layer coatings. Other studies such as intrinsic corrosion, effects of Ti interlayer and post-deposition annealing on the corrosion behavior of the multilayer coatings are also presented in this paper. The results of this study demonstrate that nanolayered multilayers can effectively improve the corrosion behavior of transition metal nitride hard coatings.