Crystalline Coatings Research Articles

Preparation of zeolite a coatings on copper plates by using the substrate heating method

The substrate heating method was used to grow zeolite 4A coatings on copper plates. The reaction mixture was kept at 25o C, while the plate was heated to a higher temperature. In some of the synthesis experiments performed, the reaction mixture was circulated in the system. The coatings prepared were characterized by X-ray diffraction and scanning electron microscopy. It was demonstrated that crystalline and pure zeolite 4A coatings could be formed on copper by using the substrate heating method from a highly alkaline solution, in which dissolution and oxidation of the copper plates took place. A coating with about 310 µm mass equivalent thickness could be grown on copper after 72 h of synthesis. The thickness decreased when circulation was applied. Compared to coatings previously prepared on stainless steel plates under similar experimental conditions, thicker coatings were grown on copper. It is possible that the roughened surface of copper in the highly alkaline reaction mixture provided a higher number of nucleation sites.

Influence of Crystal Structure, Morphology and Sodium Ion on the Photocatalytic Reactivity of Spray Deposited Titanium Dioxide Film

In this paper, three types of titanium dioxide structures (anatase, heated amorphous and amorphous) from peroxo titanium complex were deposited on glass and wafer substrates by spraying technique. Influences of crystal structure, morphology and sodium ion on UV induced hydrophilicity were studied. X-ray diffraction revealed that crystalline anatase coatings are extremely hydrophilic (<10°) under UV irradiation (indoor) while the amorphous coatings are still hydrophobic on both glass and wafer substrate with contact angles as high as 70º. When amorphous coating was heated at 450°C, its structure was converted into crystalline anatase, and hence its UV induced hydrophilicity behavior on wafer substrate became similar to that of anatase. However, this UV induced hydrophilicity was inhibited on heated glass (450°C), suggesting that sodium ions in the glass might be responsible for the differences between silicon wafer and glass. With increasing coating thickness, such inhibition effect was reduced, but the hydrophilicity still could not reach the level of anatase. After 6 months of outdoor exposure, water contact angle for amorphous, heated amorphous and anatase were 61°, 26.6° and 12.1°, respectively. Also, X-ray diffraction suggested that amorphous is not converted into anatase after long period of UV exposure, although coating morphologies are changed based on Scanning Electron Microscopic observation. It is concluded that the crystal structure, coating morphology and sodium ion concentration have key impact on the photocatalytic properties on glass substrate.

Thixocasting Steel Hand Tools using Al2O3-coated Steel and Molybdenum Dies

Forging is state-of-the-art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high-strength forging steels are used to provide cavity-free components with high mechanical load capacity. Moreover, forging is a cost-effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near-net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel size 17 combination spanners were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi-solid state. Cast parts were heat-treated to enhance the components' toughness, which was subsequently measured by Charpy impact and tensile tests.

Influence of Phosphate Concentration on Plasma Electrolytic Oxidation of AZ80 Magnesium Alloy in Alkaline Aluminate Solution

Plasma electrolytic oxidation of AZ80 magnesium alloy in alkaline aluminate electrolytes develops MgAl 2 O 4 -based highly crystalline oxide coatings with the morphology changing largely with phosphate concentration in electrolyte. The thickness of the coatings increases with phosphate concentration from 5 μm in phosphate-free electrolyte to ∼70μm in the electrolyte containing 0.1 mol·dm -3 phosphate after anodizing for 900 s. The formation of the latter thick coating is associated with intense sparking during anodizing. The thick coatings formed in the electrolytes containing 0.075 and 0.1 mol·dm -3 phosphate are highly cracked. In contrast, the coating formed in the electrolyte containing 0.05 mol·dm -3 phosphate is relatively uniform, showing the highest corrosion protection in 0.5 mol·dm -3 NaCl solution. The coatings consist of two layers, comprising an outer thick layer with high concentration of aluminum and an inner thin magnesium-rich layer.

Polycrystalline coating of hydroxyapatite on TiAl6V4 implant material grown at lower substrate temperatures by hydrothermal annealing after pulsed laser deposition

Hydroxyapatite (HA) is a bioactive ceramic material that mimics the mineral composition of natural bone. This material does not possess acceptable mechanical properties for use as a bulk biomaterial; however, it does demonstrate significant potential for use as a coating on metallic orthopaedic and dental prostheses. Pulsed laser deposition (PLD) of thin films of HA on TiAl6V4 have shown crystalline coatings to be obtained at temperatures of the order of 350-500 degrees C. This condition of high substrate temperature promoted the oxidation of the substrate surface prior to the growth of the HA layer and the oxidation layer degraded the adhesion of the coating to the substrate. In this study, thin films of HA were deposited on TiAl6V4 alloy at a lower temperature of 200 degrees C by PLD and crystallized by a hydrothermal treatment at 100 degrees C. The film was subjected to mechanical as well as cell viability tests in vitro. The thickness, roughness, crystallanity, composition ratio, adhesive strength, and cell adhesion of the film suggest the application of this technique for producing bioactive implants.

Effect of Catalytic Crystalline Waterproof Coatings on Steel Reinforcement Corrosion of Concrete

Catalytic crystalline waterproof coatings (CCWC) can penetrate into pores and cracks of concrete and catalyze reaction to increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate the effect of CCWC on corrosion of concrete. The test results of water impermeability, chloride permeability and potential clearly showed that CCWC could stop water and any soluble salts from penetrating the concrete to cause corrosion. Moreover, results of the secondary impermeability test and SEM micrographs indicated that the active compound could work for a longer term and endow the cement-based materials with self-healing function, which make concrete more compacted. Therefore, it was concluded that CCWC is very effective to protect the steel from corrosion in concrete.

Confined-Plume Chemical Deposition: Rapid Synthesis of Crystalline Coatings of Known Hard or Superhard Materials on Inorganic or Organic Supports by Resonant IR Decomposition of Molecular Precursors

A one-step process for preparing microcrystalline coatings of known superhard, very hard, or ultraincompressible ceramic compositions on either inorganic or organic supports is reported. Midinfrared pulsed-laser irradiation of preceramic chemical precursors layered between IR-transmissive hard/soft supports under temporal and spatial confinement at a laser wavelength resonant with a precursor vibrational band gives one-step deposition of crystalline ceramic coatings without incurring noticeable collateral thermal damage to the support material. Reaction plume formation at the precursor/laser beam interface initiates confined-plume, chemical deposition (CPCD) of crystalline ceramic product. Continuous ceramic coatings are produced by rastering the laser beam over a sample specimen. CPCD processing of the Re-B single-source precursor, (B(3)H(8))Re(CO)(4), the dual-source mixtures, Ru(3)(CO)(12)/B(10)H(14) or W(CO)(6)/B(10)H(14), and the boron/carbon single-source precursor, o-B(10)C(2)H(12), confined between Si wafer or NaCl plates gives microcrystalline deposits of ReB(2), RuB(2), WB(4), or B(4)C, respectively. CPCD processing of Kevlar fabric wetted by (B(3)H(8))Re(CO)(4) produces an oriented, microcrystalline coating of ReB(2) on the Kevlar fabric without incurring noticeable thermal damage of the polymer support. Similarly, microcrystalline coatings of ReB(2) can be formed on IR-transmissive IR2, Teflon, or Ultralene polymer films.

Structural, electrochemical and optical comparisons of tungsten oxide coatings derived from tungsten powder-based sols

Tungsten trioxide (WO 3) electrochromic coatings have been formed on indium tin oxide-coated glass substrates by aqueous routes. Coating sols are obtained by dissolving tungsten powder in acetylated (APTA) or plain peroxotungstic acid (PTA) solutions. The structural evolution and electrochromic performance of the coatings as a function of calcination temperature (250 °C and 400 °C) have been reported. Differential scanning calorimetry and X-ray diffraction have shown that amorphous WO 3 films are formed after calcination at 250 °C for both processing routes; however, the coatings that calcined at 400 °C were crystalline in both cases. The calcination temperature-dependent crystallinity of the coatings results in differences in optical properties of the coatings. Higher coloration efficiencies can be achieved with amorphous coatings than could be seen in the crystalline coatings. The transmittance values (at 800 nm) in the colored state are 35% and 56% for 250 °C and 400 °C-calcined coatings, respectively. The electrochemical properties are more significantly influenced by the method of sol preparation. The ion storage capacities designating the electrochemical properties are found in the range of 1.62–2.74 × 10 − 3 (mC cm − 2 ) for APTA coatings; and 0.35–1.62 × 10 − 3 (mC cm − 2 ) for PTA coatings. As a result, a correlation between the microstructure and the electrochromic performance has been established.

Protective YSZ-based thin films deposited by RF magnetron sputtering

Protective Zr(Y)O 2− δ -based films sputter-deposited onto apatite-type lanthanum silicate ceramics were appraised for potential applications in solid oxide fuel cells with silicate-based solid electrolytes, where the performance may suffer from surface decomposition processes in reducing atmospheres. Dense and crystalline coatings were deposited using radio-frequency magnetron sputtering from an yttria-stabilized zirconia target. On the basis of microstructural analysis and profile measurements, a sputtering power of 300 W was selected in order to achieve deposition rates in the range 0.50–0.75 μm/h. The surface morphology studies using an atomic force microscope revealed typical film structures with small (<50 nm) grains. The polarization of model electrochemical cells with cermet anodes comprising Ni, yttria-stabilized zirconia and Ce 0.8Gd 0.2O 2− δ (50:30:20 wt.%), deposited onto the protective zirconia films, was found quite similar to that of copper–zirconia cermets without interlayers, suggesting that the electrochemical reaction is essentially governed by the oxygen anion transfer from zirconia phase and/or hydrogen oxidation in the vicinity of zirconia film surface.

Structure and morphology of TiB 2 duplex coatings deposited over X40 CrMoV 5-1-1 steel by DC magnetron sputtering

The deposition of titanium diboride (TiB 2) films over tool steel substrates (AISI H13 premium/EN X40 CrMoV 5-1-1) is being investigated due to its excellent corrosion resistance and chemical stability against liquid aluminium. The use of nitrided steels as substrates for TiB 2 deposition may contribute to increase its adhesion and the overall steel resistance in applications such as forging, extrusion and die casting of aluminium. Duplex coatings were obtained by the PVD deposition of TiB 2 films over heat treated and nitrided steel using non-reactive DC magnetron sputtering from a TiB 2 target, varying the substrate bias voltage. Well structured and crystalline TiB 2 films were obtained for the selected deposition conditions, the best crystalline coatings being obtained for the positively biased substrates. Selected films produced over die-casting pins at a bias voltage of +50 V were tested for resistance to liquid aluminium soldering by immersion tests, and compared with the nitrided steel. The duplex TiB 2 coating has a much larger chemical resistance to attack by molten aluminium alloy than the just nitrided steel. Where there is soldering, steel is rapidly attacked and a complex Al–Fe–Si intermetallic forms.

Investigation of boundary conditions for biomimetic HA deposition on titanium oxide surfaces

To improve the clinical outcome of metal implants, i.e. earlier loading and reduction of the incidence of revision surgery, better bone bonding ability is wanted. One method to achieve this is to change the surface chemistry to give a surface that facilitates bone bonding in vivo, i.e. a bioactive surface. Crystalline titanium oxide has recently been proven to be bioactive in vitro and is an interesting option to the more common hydroxylapatite (HA) coatings on implants. A materials possible in vitro bioactivity is tested through soaking in simulated body fluid and studies of possible HA formation on the surface. For bioactive materials, the formed HA layer can also be used as a coating. The aim of the current paper is to investigate some boundary conditions for HA formation on crystalline titanium oxide surfaces regarding influence from coating thickness, soaking time and soaking temperature. The influence from soaking time and temperature on the HA growth were investigated on oxidised Ti samples, (24 h at 800 degrees C) resulting in a rutile surface structure. The oxidised samples were tested at three temperatures (4, 37 and 65 degrees C) and four times (1 h, 1 day, 1 week and 4 weeks). The influence from titanium coating thickness on the HA growth was investigated via depositing thin films of crystalline titanium dioxide on Ti plates using a reactive magnetron sputtering process. Four different PVD runs with coating thicknesses between 19 and 74 nm were tested. The soaking temperature had an effect on the HA formation and growth on both rutile surfaces and native oxide on Ti substrates. Higher temperatures lead to easier formation of HA. It was even possible, at 65 degrees C, to grow HA on native titanium oxide from soaking in PBS. The coating quality was better for HA formed at 65 degrees C compared to 37 degrees C. All PVD-coatings showed HA growth after 1 week in PBS at 37 degrees C, thus even very thin coatings of crystalline titanium oxide coatings are bioactive.

Pulsed laser deposition of hydroxyapatite thin films on Ti–6Al–4V: Effect of heat treatment on structure and properties

Hydroxyapatite (HA) is an attractive biomaterial that has been widely used as a coating for dental and orthopedic metal implants. In this work, HA coatings were deposited on Ti–6Al–4V substrates by laser ablation of HA targets with a KrF excimer laser. Deposition was performed at ambient temperature under different working pressures that varied from 10 −4 to 10 −1 torr of oxygen. The as-deposited films were amorphous. They were annealed at 290–310 °C in ambient air in order to restore the crystalline structure of HA. The coatings morphology, composition and structure were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction techniques. Mechanical and adhesive properties were examined using nanoindentation and scratch tests, respectively. The stability of the HA coatings was tested under simulated physiological conditions. This study reveals that the combination of pulsed laser deposition and post-deposition annealing at 300 °C have the potential to produce pure, adherent, crystalline HA coatings, which show no dissolution in a simulated body fluid.

High-Velocity Oxy-Fuel (HVOF) Suspension Spraying of Mullite Coatings

Mullite coatings (3Al2O3 · 2SiO2) were deposited by suspension thermal spraying of micron-sized (D50 = 1.8 μm) feedstock powders, using a high-velocity oxy-fuel gun (HVOF) operated on propylene (DJ-2700) and hydrogen fuels (DJ-2600). The liquid carrier employed in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to coatings with low porosity and fine and homogeneous porosity distribution, making this process potentially suitable for creating thin layers with low gas permeability. In-flight particle states were measured for a number of spray conditions of varying fuel-to-oxygen ratios and standoff distances and related to the resulting microstructure, stoichiometry, phase composition (EDS, SEM, XRD), and hardness (VHN 300g•f) of the coatings. In an attempt to retain the crystalline phase in the coatings, HVOF operating conditions were varied to limit in-flight particle melting. However, fully crystalline coatings were only obtained by gradually heating the coating during deposition to temperatures above 400 °C.

Shaping potentialities of aluminum nitride polymeric precursors: Preparation of thin coatings and 1D nanostructures in liquid phase

The present paper is focused on the synthesis of a series of poly[ N-(alkylimino)alanes] of the type [HAlNR] n as preceramic polymers for the preparation of aluminum nitride (AlN). Polymers were characterized by means of Fourier transform infrared spectra (FT-IR), liquid-state 1H and 13C NMR spectrometry and elemental analyses. The polymers were prepared in different physical states going from viscous liquid to solid (soluble and/or fusible) compounds with the decrease of the carbon content in the polymer chain. Such properties offer potentialities in the preparation of complex forms of ceramics including thin coatings and 1D nanostructures. AlN thin coatings and 1D nanostructures were obtained from a solution of poly[ N-(isopropylimino)alane] in toluene followed by heat-treatment in flowing ammonia up to 1000 °C resulting in a ceramic yield of 50.6%. Subsequent heat-treatment to 1800 °C in flowing nitrogen allowed the production of crystalline AlN coatings and nanorods identified by Raman spectrometry and X-ray diffraction.

Effect of post-deposition heat treatment on mechanical properties of thermally sprayed hydroxyapatite coating

This paper mainly deals with the inner microstructure and mechanical performance of plasma sprayed hydroxyapatite (HA) coatings before and after heat treatment. The electron probe microanlyser shows that some regions with different contrasts exist in the as-sprayed coatings. Under the back scattering electron (BSE) model, the origin particles of HA are well melted, and there are the more inhomogeneites in the as-sprayed coatings. Heat treatment can eliminate the regions with different contrasts and improve the crystallinity of the coatings. Some coatings were immersed into 50 mL deionised water under constant 37°C condition for 20 days. After the immersion in the deionised water, new layers with dot like precipitates formed on the surface of the as-sprayed coatings and the inhomogeneities were eliminated. For as-sprayed coatings, the amount of precipitates on the surface of low crystalline coatings is larger than that of high crystalline coatings. For post-heat treated coatings, there are no other phases but β-Ca2P2O7 precipitates along the cracks paths. The shear strength of as-sprayed coatings of low crystallinity is higher than that of high crystalline coatings. In this paper, post-heat treatment can improve the shear strength of coarse coatings but decrease that of fine coatings.

Liquid Precursor Plasma Spraying of Functional Materials: A Case Study for Yttrium Aluminum Garnet (YAG)

RF precursor plasma spray synthesis (RFPPS) is an innovative and rapid technique to deposit functional oxide coatings by starting from liquid inorganic precursors and directly producing ceramic coatings. RFPPS offers excellent opportunities in exploring the nonequilibrium phase evolution during plasma spraying of molecularly mixed precursors to form multicomponent oxides. A detailed discussion of progress, critical issues and consideration in precursor development, RF plasma spraying, coating development, and phase evolution of yttrium aluminum garnet (YAG) is presented as a case study. Appropriate selection of precursors and proper tuning of spray parameters resulted in amorphous or crystalline coatings in the as-sprayed condition. YAG phase selection has also been investigated using a discrete, low-density combinatorial synthesis approach.

Mechanical and Thermal Transport Properties of Suspension Thermal-Sprayed Alumina-Zirconia Composite Coatings

Micro-laminates and nanocomposites of Al2O3 and ZrO2 can potentially exhibit higher hardness and fracture toughness and lower thermal conductivity than alumina or zirconia alone. The potential of these improvements for abrasion protection and thermal barrier coatings is generating considerable interest in developing techniques for producing these functional coatings with optimized microstructures. Al2O3-ZrO2 composite coatings were deposited by suspension thermal spraying (APS and HVOF) of submicron feedstock powders. The liquid carrier employed in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to unique and novel fine-scaled microstructures. The suspensions were injected internally using a Mettech Axial III plasma torch and a Sulzer-Metco DJ-2700 HVOF gun. The different spray processes induced a variety of structures ranging from finely segregated ceramic laminates to highly alloyed amorphous composites. Mechanisms leading to these structures are related to the feedstock size and in-flight particle states upon their impact. Mechanical and thermal transport properties of the coatings were compared. Compositionally segregated crystalline coatings, obtained by plasma spraying, showed the highest hardness of up to 1125 VHN3 N, as well as the highest abrasion wear resistance (following ASTM G65). The HVOF coating exhibited the highest erosion wear resistance (following ASTM G75), which was related to the toughening effect of small dispersed zirconia particles in the alumina-zirconia-alloyed matrix. This microstructure also exhibited the lowest thermal diffusivity, which is explained by the amorphous phase content and limited particle bonding, generating local thermal resistances within the structure.

Thermal Stability of Thin Film Corundum‐Type Solid Solutions of (Al1–xCrx)2O3 Synthesized Under Low‐Temperature Non‐Equilibrium Conditions

A novel cathodic arc evaporation process operated in pure oxygen forms corundum-type micro-crystalline structures at temperatures below 600°C. Thermally stable crystalline solid solutions of corundum-type (Al1–xCrx)2Oy have been prepared with this method for x ≥ 0.3 at non-equilibrium conditions. The stability in (Al,Cr)2O3 phases can be explained by their degree of crystallinity and ordering within the structure. The applied processing method results in highly crystalline coatings of pure α-(Al1–xCrx)2Oy. With increasing fabrication temperature (maximum 600°), more stable phases are obtained showing no metal site splitting in the atomic structure.

Técnica alternativa para obter recobrimentos de hidroxiapatita

Este trabalho propõe a deposição química de vapor assistida por chama como uma técnica alternativa para a obtenção de recobrimentos cristalinos de hidroxiapatita sobre substratos metálicos de aço inoxidável 316L. Esta é uma técnica recente, apresentando um enorme potencial na deposição de óxidos, principalmente pelo baixo custo de equipamentos e precursores. Neste trabalho, acetato de cálcio e fosfato de amônio, diluídos em etanol, foram utilizados como sais precursores. A razão molar Ca/P na solução precursora foi de 1,66, equivalente à da hidroxiapatita biológica. Os parâmetros de deposição variados foram: temperatura do substrato (500 e 550 ºC), fluxo da solução precursora (4, 8 e 12 mL/min) e tempo de deposição (5, 10 e 20 min). Os recobrimentos obtidos foram porosos, variando a espessura entre 66 e 757 µm em função dos parâmetros de deposição. Análises por difração de raios X identificaram a fase majoritária hidroxiapatita e indícios de fosfato tricálcico. Por espectroscopia de infravermelho foi possível identificar carbonatos, bem como os grupos hidroxila e fosfato, característicos da hidroxiapatita.

Alternative technique for hydroxyapatite coatings

Flame Assisted Chemical Vapor Deposition (FACVD), a novel technique that shows an enormous potential in porous oxides deposition, was employed for the first time aiming to obtain hydroxyapatite (HA) coatings on 316 L stainless steel metallic substrates. Calcium acetate and ammonium phosphate diluted in ethanol were employed as precursor salts. A Ca/P molar ratio of 1.66 was employed in precursor solution, which is equivalent to stoichiometric hydroxyapatite. A porous coating, formed by an open and interconnected network, was observed by scanning electronic microscopy (SEM) and associated with homogenous reactions. Thickness of hydroxyapatite coating was 412 ± 3 μm. X-ray diffraction (XRD) analysis indicated the presence of crystalline coatings, mainly constituted by hydroxyapatite phase and traces of tricalcium phosphate (β-TCP). Carbonate in the hydroxyapatite coatings was identified by Fourier transform-infrared (FTIR) spectroscopy.