Solution Precursor Plasma Spray Process Research Articles

Cost-effective superhydrophobic ZnO films with adjustable wetting behaviors deposited via solution precursor plasma spray process

In this work, ZnO films featuring hierarchical micron−/nanometer-sized structures were deposited for adjusting wettability by a simple solution precursor plasma spray (SPPS) process using cost-effective zinc acetate solution. The effects of solution flow rate on the surface microstructures, surface roughness, crystalline orientation, and wetting behaviors of the films were investigated comprehensively. The results showed that high solution flow rate facilitated the formation of apparent hierarchical surface structures featuring more uniformly-distributed micron-sized protrusions and higher surface roughness. The increase of solution flow rate also promoted the crystalline growth along the non-polar (100) plane. With the solution flow rate increasing from 10 ml/min to 40 ml/min, the synergy of the surface structures and crystalline growth orientation resulted in a sharp decrease of the surface energy of the films from ~74.4 mJ/m2 to ~12.6 mJ/m2 and a dramatic elevation of water contact angles from ~130° to ~155°. The wetting states of different films were elucidated by correlating the wetting behaviors with the surface structures. The SPPS-deposited ZnO films showed high adhesion to water droplets, similar to the wetting behaviors of the petal effect, which could be used as a “mechanical hand” for non-loss microdroplet transfer. The work shows that SPPS represents a promising method to deposit cost-effective superhydrophobic films with adjustable wetting behaviors.

Effect of feedstock solution concentration on the spectroscopic and electrical transport properties of thermal plasma synthesized ZnO nanoparticles

The structural, optical, spectroscopic, and electrical transport properties of zinc oxide (ZnO) nanoparticles prepared using the solution precursor plasma spray (SPPS) technique were investigated for different feedstock solution concentrations such as 1-mol and 4-mol. Rietveld refined powder X-ray diffraction and Raman spectra reveal that the prepared ZnO crystallizes in a hexagonal wurtzite structure with no secondary phase. The crystallite sizes for 1-mol and 4-mol samples are 27.5 nm and 31.3 nm, respectively. Analysis of UV–vis spectra shows that ZnO's band gap has increased from 3.19 eV to 3.23 eV as the mole concentration has increased. The spherical nature and nano size of the ZnO are confirmed by the pictures obtained using field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM). The presence of elements zinc and oxygen in the Zn2+ and O2− ionic states are revealed by X-ray photoelectron spectroscopy (XPS). Electrical study demonstrates that the initial mole concentration of ZnO powder affected both its electrical conductivity and dielectric constant. The activation energy value of electrical conductivity for 1-mol and 4-mol is 0.661 eV and 0.552 eV, respectively. The impedance analysis shows the electrode effect for the 1-mol sample whereas it is not observed for the 4-mol sample, which is further confirmed by modulus analysis. The presence of defect in the 1-mol sample results in a lower conductivity (3.68 × 10−12 S/cm at 1 Hz) than the 4-mol sample. The comprehensive analysis confirms that the structural, spectroscopic and electrical properties of the ZnO nanoparticle can be tunable to meet demand by changing the feedstock mole concentration in the SPPS process.

Hydrocarbon-induced reversible wetting behaviors of hierarchically-structured yttrium oxide coatings

Yttrium oxide is considerably used in protective coatings and functional films in the industry, while the wettability of yttrium oxide surfaces is seldom investigated. In this work, yttrium oxide coatings were deposited via solution precursor plasma spray process using yttrium nitrate solution as feedstock. The phase composition, microstructures, surface topographies, wetting behaviors, and surface compositions of coatings after different post-deposition treatments were characterized comprehensively. The as-sprayed coatings showed dual-scale hierarchical surface structures which were composed of nanometer-sized particles and splats superimposed on micron-sized columnar structures. The as-sprayed coatings were superhydrophilic, whereas they became superhydrophobic after vacuum treatment, exhibiting water contact angles larger than 160°, roll-off angles smaller than 5°, and complete water droplet rebound behaviors. The superhydrophobic coatings also showed high durability in harsh environments which were corroborated by the self-cleaning test, water flushing, and immersion test. The superhydrophobic coatings became superhydrophilic rapidly after high temperature treatment or Ar-plasma treatment, while the coatings regained superhydrophobicity after another vacuum treatment, showing reversible wetting behaviors. The investigations on the surface compositions of coatings with different wettability were conducted, indicating hydrocarbon adsorption on the surface in vacuum treatment and desorption during high temperature treatment or Ar-plasma treatment induced the reversible wetting behaviors.

Effect of Solution Precursor on Microstructure and High-Temperature Properties of the Thermal Barrier Coating Made by Solution Precursor Plasma Spray (SPPS) Process

Effect of Solution Precursor on Microstructure and High-Temperature Properties of the Thermal Barrier Coating Made by Solution Precursor Plasma Spray (SPPS) Process

Hot corrosion behavior of hybrid double-layered LZ/LZC + YSZ thermal barrier coatings made using powder and solution precursor feedstock

Lanthanum zirconate (La2Zr2O7; LZ) and cerium doped lanthanum zirconate (La2(Zr0.7Ce0.3)2O7; LZC) has gained immense attention as thermal barrier coating (TBC) materials because of their superior thermophysical properties, high-temperature phase stability and chemical inertness than yttria-stabilized zirconia (YSZ). In the present study, LZ and LZC double-layered TBCs are prepared by solution precursor plasma spray process (SPPS) as a top layer over the atmospheric plasma sprayed YSZ coatings, and their hot corrosion behavior is studied. The as-deposited SPPS coatings exhibited single phases, and the microstructural morphologies reveal a hierarchically structured surface with vertically cracked microstructure. Exposure to the high temperature corrosion process results in damage of the morphology and microstructure within the SPPS layer by forming lanthanum vanadate (LaVO4) and lanthanum cerium vanadate ((LaCe)VO4) in LZ and LZC coatings, respectively, while leaching out zirconia (ZrO2). In the case of conventional YSZ, the corrosive salts infiltrate entirely through the coating and result in complete densification and associated phase changes. While combining the above aspects, the hybrid double-layered architecture of LZ/YSZ and LZC/YSZ coatings can be beneficial to protect the underlying YSZ layer against the detrimental infiltration of molten corrosive salt.

Effect of CMAS viscosity on the infiltration depth in thermal barrier coatings of different microstructures

Calcium magnesium aluminum silicate (CMAS) is one of the leading concerns for the gas turbine industry. The effects of CMAS viscosity and the coating microstructure on CMAS infiltration depth were explored by conducting a time dependent interaction study. Three CMAS compositions were used from literature, and their viscosities predicted through FactSage viscosity module were drastically different. The interaction was carried out on three different TBCs synthesized using the solution precursor plasma spray process (SPPS): two of the TBCs were made of yttrium aluminum garnet (YAG) having different microstructures that promote different modes of CMAS infiltration, and one TBC was made of gadolinium zirconate (GZO). All samples had stress relieving vertical cracks and different intensities of horizontally banded porosity, (inter pass boundaries IPBs). A concentration of 100 mg/cm2 of CMAS was applied on the TBCs which were then subjected to a 5-minute interaction at 1300 °C. Samples were analyzed using scanning electron microscopy (SEM), electron dispersive X-ray spectroscopy (EDXS), and transmission electron microscopy (TEM). Low viscosity CMAS readily penetrated the TBCs while more viscous CMAS showed less penetration. The depth of CMAS infiltration depended on the coating microstructure. In the YAG with IPBs, the CMAS spread horizontally in the IPBs before infiltrating deeper, resulting in reduced infiltration depth compared to other samples in spite of having wider vertical cracks. TEM and EDXS analysis were performed to investigate the phases present in the CMAS-TBC interaction region in YAG. Two regions were chosen, the top TBC surface in direct contact with the sea of CMAS, and the region at the CMAS penetration ended within the coating. The results showed that no secondary phases like apatite were observed in YAG, thus it can be concluded that the arrest of CMAS happened solely because of CMAS viscosity and the short infiltration time.

Deposition of Zinc Oxide Coatings on Wood Surfaces Using the Solution Precursor Plasma Spraying Process

In the present work, the solution precursor plasma spray (SPPS) process was used to deposit zinc oxide (ZnO) coatings on wood surfaces using zinc nitrate solution as precursor to improve the hydrophobicity and the color stability of European beech wood under exposure to ultraviolet (UV) light. The surface morphology and topography of the wood samples and the coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The formation of ZnO was detected with the help of X-ray photoelectron spectroscopy (XPS) and by Fourier transform infrared (FTIR) spectroscopy. The FTIR spectra of the coated samples showed the typical Zn–O band at 445 cm−1. According to the XPS analysis, the coatings consist of two different Zn-containing species: ZnO and Zn(OH)2. Variation of the deposition parameters showed that the most significant parameters affecting the microstructure of the coating were the solution concentration, the deposition scan speed, and carrier gas flow rate. The wettability behaviors of the coated wood were evaluated by measuring the water contact angle (WCA). The coatings that completely covered the wood substrates showed hydrophobic behaviors. UV-protection of wood surfaces after an artificial UV light irradiation was evaluated by color measurements and FTIR spectroscopy. The ZnO-coated wood surfaces were more resistant to color change during UV radiation exposure. The total color change decreased up to 60%. Additionally, the FTIR spectra showed that the wood surfaces coated with ZnO had more stability. The carbonyl groups formation and C=C-bonds consumption were significantly lower.

Volcanic ash infiltration resistance of new-generation thermal barrier coatings at 1150 °C

The recent developments in advanced materials for thermal barrier coatings (TBCs) have put thrust towards the progress of new materials due to their superior performance over the state-of-the-art yttria-stabilized zirconia (YSZ). Lanthanum cerate (La2Ce2O7, LC) is one of the promising candidates used against the infiltration of calcium magnesium alumino-silicate (CMAS) melt. For a highly efficient low thermally conductive material, gadolinium oxide doped lanthanum cerate ((La0.9Gd0.1)2Ce2O7, Gd-LC) was synthesized as a new aspirant. Deposits of atmospheric plasma sprayed (APS) LC, Gd-LC coatings were generated, and their interactions against the infiltration of volcanic ash were studied. Both the coatings formed the apatite phase interaction layer, with a considerable quantity of anorthite and spinel phases. On comparison, Gd-LC showed significantly more resistance than LC coatings because of the presence of Gd apatite in Gd-LC coatings. Further, we developed Gd-LC single layer, double-layer, and composite hybrid coatings by employing APS and solution precursor plasma spraying process (SPPS). Phase evolution and microstructural features were studied and are discussed in detail.

Control of the hydrophobicity of rare earth oxide coatings deposited by solution precursor plasma spray by hydrocarbon adsorption

The basis of the hydrophobicity of lanthanide rare earth oxides (REOs) has been the subject of considerable debate. To explore this question, the wetting behaviors and surface compositions of hierarchically-structured Yb2O3 (one of the REOs) coatings and non-REO Al2O3 coatings deposited via solution precursor plasma spray process were investigated in this work. The Yb2O3 coatings were subjected to a number of post-deposition treatments including vacuum (1−15 Pa) treatment, Ar-plasma treatment, heat treatment (400 °C), long-time air exposure and ultra-high vacuum (1 × 10−7 Pa) treatment. Subsequent characterization showed that different post-deposition treatments resulted in different wetting behavior for the Yb2O3 coatings which correlated with the content of hydrocarbon on the surface. Yb2O3 coatings exhibited reversible transitions between superhydrophobicity after vacuum treatment and superhydrophilicity after Ar-plasma or heat treatment, linked to hydrocarbon adsorption onto and desorption from the surface. Yb2O3 coatings after long-time air exposure and ultra-high vacuum treatment both remained hydrophilic and showed a smaller hydrocarbon content than coatings after vacuum treatment. Al2O3 coatings with hierarchical surface structures similar to the Yb2O3 coatings showed an increase in WCA to only ∼17° after the same vacuum treatment, indicating the REO has a much higher affinity for hydrocarbon adsorption than Al2O3, and that the content of hydrocarbon adsorbed on the surface of the REO determined the wetting behavior.

Ytterbium Silicate Environmental Barrier Coatings Deposited Using the Solution-Based Precursor Plasma Spray

Gas turbine efficiency can be improved by increasing the operating temperature and by reducing the need for cooling air, both of which are enabled by higher temperature materials. Silicon carbide based ceramic matrix composites (CMCs) have shown promise for achieving higher temperatures. However, to survive in the high-temperature high-humidity combustion environment, environmental barrier coatings (EBCs) are essential to limit silicon loss of CMCs and its associated damage. Atmospheric plasma spray (APS) is a popular process for making such coatings. In this work, an alternative deposition process is explored, specifically the solution precursor plasma spray (SPPS), where it will be shown for ytterbium monosilicate EBCs that such process directly deposits thin (< 50 μm), dense and crystalline EBC topcoats without annealing of amorphous phases as is needed in the APS process. In addition, the SPPS process allows for quick compensation of system-specific element loss observed in both SPPS and APS processes. Finally, the secondary phase present in EBCs are much smaller in size for the SPPS process and hence less likely to produce cracking compared to APS EBCs.

Vertical grain and columnar structured Ba(Mg1/3Ta2/3)O3 thermal barrier coating deposited by solution precursor plasma spray

Thermal barrier coatings (TBC) with a lamellar structure are more susceptible to erosion than fully dense ceramics and electron beam physical vapor deposited (EB-PVD) coatings. This paper presents a distinctive structure of Ba(Mg1/3Ta2/3)O3 (BMT) with a columnar-oriented appearance and vertical grain nature, which was deposited by plasma spray rather than EB-PVD. Indeed, a radio frequency solution precursor plasma spray (RF SPPS) process was adopted for the coating deposition. The morphology and elemental composition of the vertical grains are analyzed first. With the assistance of optical emission spectroscopy (OES), the formation mechanism of the vertical grains is discussed in detail. In addition, a new TBC system designed for niobium alloy is proposed in this paper. Owing to its high thermal expansion coefficient and unique vertical grain structure, BMT has been considered as the most promising insulation material candidate in this TBC system.

In vitro studies of solution precursor plasma-sprayed copper-doped hydroxyapatite coatings with increasing copper content.

In this present study, in vitro characterization on bioactivity and biocompatibility of the copper-doped hydroxyapatite (Cu-HA) coatings deposited onto Ti6Al4V alloy with increasing copper content obtained using solution precursor plasma spray process were evaluated under simulated body fluid (SBF) and cytotoxicity tests. The growth of flake-like structures was observed at the coatings' surface after 7 days of immersion in SBF. Elemental composition analysis showed a calcium-deficient carbonate-containing apatite for the grown layer. Broadening of the HA peaks were also observed in the X-ray diffraction patterns and infrared absorption spectra of the immersed coatings associated with the possible formation of an amorphous layer at the surface of the coatings. Copper incorporation does not alter the bioactivity of HA but only slowed down for 10 mol% copper content. Cytotoxicity evaluation using MTT assays showed that 3 mol% Cu-HA coating was not toxic under in vitro characterizations.

From lotus effect to petal effect: Tuning the water adhesion of non-wetting rare earth oxide coatings

A facile post-deposition plasma treatment was developed to tune the wetting behavior of Yb2O3 coatings deposited via the solution precursor plasma spray process. The as-deposited coatings exhibited the lotus effect after vacuum treatment, with a water contact angle of ∼162° and a roll-off angle of ∼5°, due to the hierarchical columnar microstructure. When the plasma torch was scanned over the coatings as a post-deposition treatment, the rough top surfaces of the columns present in the as-deposited coatings became smooth, and the coatings then exhibited the petal effect, with a water contact angle of ∼150° to ∼130° and high, tunable adhesion to water. Analysis of the surface compositions showed that after vacuum treatment hydrocarbon adsorption on the as-deposited coatings and plasma-treated coatings was very similar. A mathematical model correlating surface structures with wetting behaviors was developed to elucidate the transition from the lotus effect to the petal effect.

Heterostructured metal oxides-ZnO nanorods films prepared by SPPS route for photodegradation applications

This work presents the first preparation using the Solution Precursor Plasma Spray process of heterostructured films associating ZnO nanorods (NRs) and various metal oxides (CuO, Fe2O3 and Co3O4) by Solution Precursor Plasma Spray process. These CuO/ZnO, Fe2O3/ZnO and Co3O4/ZnO films exhibit hierarchically chocolate sticks-like, dandelion-like or chrysanthemum-like surface morphologies. These heterostructures were confirmed by SEM, XRD, EDS and Raman analyses. The bandgaps of heterostructured films are narrower than that of pure ZnO. The CuO/ZnO film exhibits the highest photocatalytic activity both under UV and visible light irradiation for the degradation of the Orange II dye due to the homogenous distribution of CuO at the surface of ZnO. The high photocatalytic performances originate from the increased visible light absorption and from the effective separation of charge carriers in CuO/ZnO films compared to ZnO NRs.

Experimental investigation of the relationship between thermal barrier coating structured porosity and homogeneous charge compression ignition engine combustion

Heat transfer has a profound influence on homogeneous charge compression ignition combustion. When a thermal barrier coating is applied to the combustion chamber, the insulating effect magnifies the wall temperature swing, decreasing heat transfer during combustion. This enables improvements in both thermal and combustion efficiency without the detrimental impacts of intake charge heating. Increasing the temperature swing requires coatings with lower thermal conductivity and heat capacity. A promising avenue for simultaneously decreasing both thermal conductivity and capacity is to increase the porosity fraction. A proprietary solution precursor plasma spray process enables discrete organization of the porosity structure, called inter-pass boundaries, which in turn produces a step-reduction in thermal conductivity for a given porosity level. In this investigation, yttria-stabilized zirconia is used to create four different thermal barrier coatings to study the potential of structured porosity as means of improving the “temperature swing” behavior in a homogeneous charge compression ignition engine. The baseline coating is “dense YSZ,” applied using a standard air-plasma spray process. Next, significant reductions of the thermal conductivity are achieved by utilizing the solution precursor plasma spray process to create inter-pass boundaries with a moderate overall porosity. Performance, efficiency, and emissions are compared against both a baseline configuration with a metal piston and an air-plasma spray “dense YSZ” coating. Experiments are carried out in a single-cylinder gasoline homogeneous charge compression ignition engine with exhaust re-induction. Experiments indicate that incorporating structured porosity into thermal barrier coatings produces tangible gains in combustion and thermal efficiencies. However, there is an upper limit to porosity levels acceptable for homogeneous charge compression ignition engine application because an elevated porosity fraction leads to excessive surface roughness and undesirable fuel interactions. Comparison of the coatings showed the best results with coating thickness of up to 150 µm. Thicker coatings led to slower surface temperature response and attenuated swing temperature magnitude.

Thermal decomposition and crystallization behavior of double rare-earth co-doped SrZrO3 precursor used in the solution precursor plasma spray process

A double rare-earth (Yb/Gd) co-doped SrZrO3 [Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05] thermal barrier coating (TBC) was prepared by the solution precursor plasma spray (SPPS) using an aqueous solution precursor of nitrates [Sr(NO3)2, Gd(NO3)3·6H2O, Yb(NO3)3·6H2O] and zirconium acetate [Zr(C2H3O2)4]. The thermal decomposition and crystallization process of the solution precursor powders calcined at elevated temperature (~1400 °C) were studied and characterized by X-ray diffraction (XRD) and synchronous thermal analyzer coupled with Fourier transform infrared spectroscopy and quadrupole mass spectrometry (STA/FTIR/QMS) methods. Zr(C2H3O2)4 precursor decomposed into ZrO2, CH3COCH3 and CO2 firstly, followed by decomposition of hydrated nitrate. ZrO2 reacted with SrO (Yb2O3, Gd2O3) and CO2 to generate Yb/Gd co-doped SrZrO3 and SrCO3 simultaneously. SrCO3 decomposed into SrO again at higher temperature, which reacted with ZrO2 to form SrZrO3. The Sr1.1(Zr0.9Yb0.05Gd0.05)O3.05 coating was characterized as single phase with interpass boundary (IPB) structure, nano- and micrometer porosity, and through-thickness vertical cracks, analysed by XRD and the scanning electron microscope (SEM). The average grain size of the coating was calculated to be ~30 nm by Scherrer formula.

Plasma current effects on the microstructure of solution precursor plasma spray YSZ coatings

The Solution Precursor Plasma Spray (SPPS) process has been used for obtaining Zirconia coatings as Thermal Barrier Coatings (TBCs). In this study an in house developed Zirconyle nitratesolution precursor plasma spray setup has been used. In this process the coating is built up by horizontal and vertical passes of the plasma torch across the substrate. The microstructural characterizations of coatings were carried out by scanning electron microscope (SEM) and X-ray diffraction (XRD). Significant effect of plasma current has been observed on the zirconia coatings.

Preparation, Deposition and Characterization of Solution Precursor

The Solution Precursor Plasma Spray (SPPS) process has been used for Thermal Barrier Coatings (TBCs). In this work Zirconyle nitrate is used as solution precursor. It has prepared in house for plasma spray. The prepared solution has successfully deposited on the substrate by SPPS process.The deposited coatings were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD).

Development of photocatalytically active heterostructured MnO/ZnO and CuO/ZnO films via solution precursor plasma spray process

Heterostructured ZnO photocatalysts for the degradation of organic pollutant are mainly synthesized by conventional chemical methods, suffering from long duration, multi-steps, and post-treatment of the powder-formed catalysts after usage. In this paper, Solution Precursor Plasma Spray (SPPS) process is demonstrated to be a fast and efficient method for the one-step preparation of MnO/ZnO and CuO/ZnO heterostructured films for photocatalytic applications. The ratios between MnO or CuO and ZnO materials in the films were easily adjusted by varying the molar ratio of Mn(OAc)2 or Cu(OAc)2 relative to Zn(OAc)2 during the SPPS synthesis. To optimize the microstructure of selected CuO/ZnO films, two alternative spraying patterns were also developed. The modified films (Cu20-ZnO-A and Cu20-ZnO-B) were partly composed of nanorods (NRs) instead of conventional irregular particles. The MnO/ZnO and CuO/ZnO films exhibit narrower bandgap than pure ZnO films. The photocatalytic performances of the ZnO based films were evaluated for the degradation of the Orange II dye. Cu20-ZnO and Cu20-ZnO-B films exhibit the highest degradation efficiency under UV light and visible light, respectively. For example, the SPPS deposited Cu20/ZnO films could almost remove 90% of Orange II within 3 h of UV light irradiation. Moreover, this study not only reveals that SPPS is of high potential for the deposition of heterostructured metal oxide films in rapid one-step, but also points out an efficient spraying strategy for adjusting the nanostructured morphologies in these films.

One-step synthesis and deposition of ZnFe2O4 related composite films via SPPS route for photodegradation application

Binary spinel-type metal oxides (AB2O4) related materials, including ferrites (AFe2O4), are attractive photocatalysts thanks to their excellent visible light response for the photodegradation of organic pollutants. Currently, these materials are synthesized via conventional chemical routes suffering from long preparation duration and multistep. Moreover, the photocatalysts are obtained as nano-powders from conventional chemical routes would introduce another drawback for their recycling and reuse. From an industrial perspective, it is desirable to develop an efficient and facile synthesis process to produce photocatalysts in a non-dispersible form. Herein, we demonstrate that the solution precursor plasma spray (SPPS) process is a single-step method for depositing photocatalytically active zinc ferrite-based films within several minutes. The influence of the precursor ratio on the microstructures and phase compositions of the ZnFe2O4 films was investigated by XRD and Raman analyses. In addition, two optimized ZnFe2O4 films were prepared by increasing the ZnO loading and tailoring injection pattern of the precursor solution. The surface morphologies and optical bandgap were also determined by SEM and UV–visible spectroscopy. The photocatalytic activities of the ZnFe2O4 films were evaluated through the degradation of the Orange II dye and of tetracycline hydrochloride under UV or visible light irradiation. The results show that compositional ratios and composition distribution of the ZnFe2O4 films prepared via SPPS played a key role on the photocatalytic activity. The SPPS route was demonstrated to be a promising method for the synthesis and the deposition of metal oxide (i.e. perovskite type and spinel type) films within a single-step for functional applications.