Solution Precursor Plasma Spray Research Articles

Facile One-Step Route for the Development of in Situ Cocatalyst-Modified Ti3+ Self-Doped TiO2 for Improved Visible-Light Photocatalytic Activity.

Development of visible-light-driven photocatalysts by employing a relatively simple, efficient, and cost-effective one-step process is essential for commercial applications. Herein, we report for the first time the synthesis of in situ Cu-ion modified Ti3+ self-doped rutile TiO2 by such a facile one-step solution precursor plasma spray (SPPS) process using a water-soluble titanium precursor. In the SPPS process, Ti3+ self-doping on Ti4+ of rutile TiO2 is found to take place because of electron transfer from the created oxygen vacancies to Ti4+-ions. In situ Cu modification of the above Ti3+ self-doped rutile TiO2 by additionally introducing a Cu solution into plasma plume is also demonstrated. While the Ti3+ self-doping induces broad absorption in the visible-light region, the addition of Cu ion leads to even broader absorption in the visible region owing to resulting synergistic properties. The above materials were evaluated for various self-cleaning photocatalytic applications under visible-light illumination. Cu-ion modified Ti3+ self-doped rutile TiO2 is noted to exhibit a remarkably enhanced visible-light activity in comparison with Ti3+ self-doped rutile TiO2, with the latter itself outperforming commercial TiO2 photocatalysts, thereby suggesting the suitability of the material for indoor applications. The broad visible-light absorption by Ti3+ self-doping, the holes with strong oxidation power generated in the valence band, and electrons in Ti3+ isolated states that are effectively separated into the high reductive sites of Cu ions upon visible-light irradiation, accounts for improved photocatalytic activity. Moreover, the synthesis process (SPPS) provides a valuable alternative to orthodox multistep processes for the preparation of such visible-light-driven photocatalysts.

Processing Parameter Effects and Thermal Properties of Y2Si2O7 Nanostructured Environmental Barrier Coatings Synthesized by Solution Precursor Induction Plasma Spraying

The solution precursor plasma spray process, in which a solution of metal salts is axially injected into an induction thermal plasma, is suitable for deposition of nanostructured environmental barrier coatings. The effects of main processing parameters, namely the solution precursor concentration, spraying distance, reactor pressure, and atomization gas flow rate, have been analyzed using D-optimal design of experiments regarding the deposition rate and coating porosity responses. Among these four parameters, the solution precursor concentration had the greatest influent on the coating structure, followed by the spraying distance and reactor pressure, and finally the atomization gas flow rate with a small contribution. It is pointed out that the species that impact on the substrate are agglomerates of nanoparticles. The equivalent thermal conductivity of selected coatings was computed from experimental temperature evolution curves obtained by laser flash thermal diffusivity analysis, using two methods: a multilayer finite-element model with optimization, and a multilayer thermal diffusion model. The results of the two models agree, with coatings exhibiting low thermal conductivity between 0.7 and 1 W/(m K) at 800 °C.

Microstructure and Polarization Studies on Interlayer Free La0.65Sr0.3Co0.2Fe0.8O3–δ Cathodes Fabricated on Yttria Stabilized Zirconia by Solution Precursor Plasma Spraying

AbstractNano‐structured cathodes of La0.65Sr0.3Co0.2Fe0.8O3–δ (LSCF) are fabricated by solution precursor plasma spraying (SPPS) on yttria stabilized zirconia (YSZ) electrolytes (LSCF‐SPPS‐YSZ). Phase pure LSCF is obtained at all plasma power. Performances of LSCF‐SPPS‐YSZ cathodes are compared with conventionally prepared LSCF cathodes on YSZ (LSCF‐C‐YSZ) and gadolinium doped ceria (GDC) (LSCF‐C‐GDC) electrolytes. High Rp is observed in the LSCF‐C‐YSZ (∼42 Ohm cm2 at 700 °C) followed by LSCF‐C‐GDC (Rp ∼ 1.5 Ohm cm2 at 700 °C) cathodes. Performance of the LSCF‐SPPS‐YSZ cathodes (Rp ∼ 0.1 Ohm cm2 at 700 °C) is found to be even superior to the performance of LSCF‐C‐GDC cathodes. High performance in LSCF‐SPPS‐YSZ cathodes is attributed to its nano‐structure and absence of any interfacial insulating phase which may be attributed to the low temperature at the interaction point of LSCF and YSZ and low interaction time between LSCF and YSZ during SPPS process. In the time scale of 100 h, no change in the polarization resistances is observed at 750 °C. Based on the literature and from the present studies it can be stated that SOFC with YSZ electrolyte and LSCF‐SPPS‐YSZ cathode can be operated at 750 °C for a longer duration of time and good performance can probably be achieved.

Suspension and precursor solution plasma spraying by means of synchronous injection in a pulsed arc plasma

Research has led to the development of nanostructured coatings by suspension plasma spraying (SPS) or solution precursor plasma spraying (SPPS). Both techniques open a new way to applications in the field of microelectronic devices. However, a better control of plasma/material interactions is necessary. Mono-electrode DC plasma torches indeed generate strongly fluctuating plasma that modifies the thermal and dynamic transfers to the injected suspension droplet, resulting in an inhomogeneous treatment of the latter. This directly influences the texture and microstructure of deposits and subsequently their properties. Efforts to understand the origins of these instabilities have been made and have led to propose a new approach, i.e. an alternative to instabilities attenuations: the reinforcement and modulation of the instabilities. The adjustment of process parameters has allowed obtaining a pulsed laminar plasma and a modulation of its properties. This device is synchronized with an ink-jet print head to reproduce the same conditions of plasma/material interaction for each injected droplet. A home-made DC torch was made. His power of 1kW is well below the standard torches (~30kW for commercial torches) but is well adapted to the flow rate that can be delivered by the print head. This low powered home-made DC torch is used and operates with pure nitrogen as plasma forming gas. Aluminum nitrate aqueous solutions and TiO2 suspensions are injected. The objectives of this work are firstly to characterize this pulsed plasma and its interactions with droplets to facilitate the understanding of heat and dynamics transfers. They are analyzed by time-resolved imaging and optical emission spectroscopy. Secondly, coatings are characterized by SEM, TEM and DRX analysis.

Superhydrophobic Ceramic Coatings by Solution Precursor Plasma Spray.

This work presents a novel coating technique to manufacture ceramic superhydrophobic coatings rapidly and economically. A rare earth oxide (REO) was selected as the coating material due to its hydrophobic nature, chemical inertness, high temperature stability, and good mechanical properties, and deposited on stainless steel substrates by solution precursor plasma spray (SPPS). The effects of various spraying conditions including standoff distance, torch power, number of torch passes, types of solvent and plasma velocity were investigated. The as-sprayed coating demonstrated a hierarchically structured surface topography, which closely resembles superhydrophobic surfaces found in nature. The water contact angle on the SPPS superhydrophobic coating was up to 65% higher than on smooth REO surfaces.

Characterization of Thermal Barrier Coatings Produced by Various Thermal Spray Techniques Using Solid Powder, Suspension, and Solution Precursor Feedstock Material

Use of a liquid feedstock in thermal spraying (an alternative to the conventional solid powder feedstock) is receiving an increasing level of interest due to its capability to produce the advanced submicrometer/nanostructured coatings. Suspension plasma spraying (SPS) and solution precursor plasma spraying (SPPS) are those advanced thermal spraying techniques which help to feed this liquid feedstock. These techniques have shown to produce better performance thermal barrier coatings (TBCs) than conventional thermal spraying. In this work, a comparative study was performed between SPS‐ and SPPS‐sprayed TBCs which then were also compared with the conventional atmospheric plasma‐sprayed (APS) TBCs. Experimental characterization included SEM, porosity analysis using weight difference by water infiltration, thermal conductivity measurements using laser flash analysis, and lifetime assessment using thermo‐cyclic fatigue test. It was concluded that SPS coatings can produce a microstructure with columnar type features (intermediary between the columnar and vertically cracked microstructure), whereas SPPS can produce vertically cracked microstructure. It was also shown that SPS coatings with particle size in suspension (D50) <3 μm were highly porous with lower thermal conductivity than SPPS and APS coatings. Furthermore, SPS coatings have also shown a relatively better thermal cyclic fatigue lifetime than SPPS.

Lithium Iron Phosphate Powders and Coatings Obtained by Means of Inductively Coupled Thermal Plasma

Lithium-ion batteries have high energy efficiency and good cycling life and are considered as one of the best energy storage device for hybrid and/or electrical vehicle. Still, several problems must be solved prior to a broad adoption by the automotive industry: energy density, safety, and costs. To enhance both energy density and safety, the current study aims at depositing binder-free cathode materials using inductively coupled thermal plasma. In a first step, lithium iron phosphate (LiFePO4) powders are synthesized in an inductively coupled thermal plasma reactor and dispersed in a conventional polyvinylidene fluoride (PVDF) binder. Then, binder-free LiFePO4 coatings are directly deposited onto nickel current collectors by solution precursor plasma spraying (SPPS). The morphology, microstructure, and composition of the synthesized LiFePO4 powders and coatings are fully characterized by electronic microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS). Quantifying Li with XPS requires the substitution of iron with manganese in the SPPS precursors (LiMPO4, where M = Fe or Mn). The plasma-derived cathodes (with and without PVDF binder) are assembled in button cells and tested. Under optimized plasma conditions, cyclic voltammetry shows that the electrochemical reversibility of plasma-derived cathodes is improved over that of conventional sol-gel-derived LiFePO4 cathodes.

Effect of SPPS Process Parameters on In-Flight Particle Generation and Splat Formation to Achieve Pure α-Al2O3 Coatings

The present paper describes the role of process conditions in developing phase-pure α-Al2O3 coatings using solution precursor plasma spraying. Different precursor combinations were employed and two ...

Preliminary study of hydroxyapatite coatings synthesis using solution precursor plasma spraying

The liquid precursors of calcium hydroxide and diammonium hydrogen phosphate were injected into the plasma jet generated by the SG-100 torch to synthesize the hydroxyapatite (HA) coatings. Three operational deposition process parameters, namely: (i) electric power, (ii) spray distance, and (iii) scan speed were varied. The process enabled synthesization of coatings with HA as major phase onto stainless steel substrates. The coatings were deposited to reach the thickness of about 50μm with high rate ranging from 3μm to nearly 7μm by pass of torch. The X-ray diffraction (XRD) analysis of coatings enabled finding of HA accompanied by calcium phosphates, calcium oxide, and calcium carbonate. The presence of the carbonates was confirmed by Fourier Transform Infrared (FTIR) spectroscopy and by elemental mapping made with the use of Electron Dispersive X-ray Spectroscopy (EDS). The morphology of coatings, observed using scanning electron microscope (SEM), revealed fine-grained microstructure and porosity in the range of 1.3 to 5.1%. The adhesion of coatings obtained using scratch test characterized by critical force was in the range of 2.5 to 3.6N.

Double-Layer Gadolinium Zirconate/Yttria-Stabilized Zirconia Thermal Barrier Coatings Deposited by the Solution Precursor Plasma Spray Process

Advanced thermal barrier coatings (TBCs) with lower thermal conductivity, increased resistance to calcium-magnesium-aluminosilicate (CMAS), and improved high-temperature capability, compared to traditional yttria-stabilized zirconia (YSZ) TBCs, are essential to higher efficiency in next generation gas turbine engines. Double-layer rare-earth zirconate/YSZ TBCs are a promising solution. From a processing perspective, solution precursor plasma spray (SPPS) process with its unique and beneficial microstructural features can be an effective approach to obtaining the double-layer microstructure. Previously durable low-thermal-conductivity YSZ TBCs with optimized layered porosity, called the inter-pass boundaries (IPBs) were produced using the SPPS process. In this study, an SPPS gadolinium zirconate (GZO) protective surface layer was successfully added. These SPPS double-layer TBCs not only retained good cyclic durability and low thermal conductivity, but also demonstrated favorable phase stability and increased surface temperature capabilities. The CMAS resistance was evaluated with both accumulative and single applications of simulated CMAS in isothermal furnaces. The double-layer YSZ/GZO exhibited dramatic improvement in the single application, but not in the continuous one. In addition, to explore their potential application in integrated gasification combined cycle environments, double-layer TBCs were tested under high-temperature humidity and encouraging performance was recorded.

The Solution Precursor Plasma Spray (SPPS) Process: A Review with Energy Considerations

Solution precursor plasma spray (SPPS) is a coating deposition process that uses conventional plasma spray equipment, and solution precursors, rather than ceramic or metal powders, as starting materials. Because the process is exposed to oxygen at high temperatures, nearly all coatings, to date, are oxide ceramics. In this review, both the advantages and the disadvantages of the SPPS process and some comparisons made to the suspension plasma spray (SPS) process will be discussed. The advantages of the SPPS process include rapid exploration of compositions and fabrication of advanced coatings with unique microstructural features. Examples presented span densities from porous thermal barrier coatings (TBCs) to dense TiO2 coatings. Two TBCs are in an advanced development stage: (1) a low thermal conductivity YSZ TBC and (2) a high-temperature yttrium aluminum garnet TBC. As for disadvantages, there are (1) the additional development work for each new precursor and (2) a lower standoff distance and deposition rate than the APS process, related to the evaporation of the solvent. The SPS process shares the same disadvantages. In developing new coatings, a number of factors should be considered and understood, which would help to shorten future development efforts. Future directions of the SPPS process will also be discussed.

Hybrid Processing with Powders and Solutions: A Novel Approach to Deposit Composite Coatings

Thermal spraying employing either solution precursor or suspension feedstock offers an exciting opportunity to obtain coatings with microstructures and characteristics that differ vastly compared to those conventionally produced using spray-grade powders. Both solution precursor plasma spray and suspension plasma spray techniques have been explored extensively in recent years for depositing wide ranging ceramic coatings for various functional applications. Encouraged by the properties achieved using the above solution-based feedstocks, a hybrid approach involving dual injection of solutions and powders, either simultaneously or sequentially, has been proposed and demonstrated to yield novel coating architectures. Although prior work on such hybrid processing is very limited, this overview seeks to present the concept, outline associated challenges, and demonstrate its efficacy to realize coatings with exciting and unusual properties using some illustrative examples.

Hot corrosion behavior of solution precursor and atmospheric plasma sprayed thermal barrier coatings

Hot corrosion behavior of solution precursor plasma spray (SPPS) thermal barrier coating (TBC) in molten salt mixtures of 90wt.% Na2SO4+5wt.% V2O5+5wt.% NaCl and 50wt.% Na2SO4+50wt.% V2O5 at 900°C is compared vis-à-vis atmospheric plasma spray (APS) coating. APS TBCs show better hot corrosion resistance than SPPS TBCs in both the salt mixtures. The vertical cracks in SPPS coatings, meant for strain tolerance and high thermal cycling life, serve as channels for transporting salts across the coating to bond coat/top coat interface and accelerate failure.

Solution Precursor Plasma Spray (SPPS) technique of catalyst coating for hydrogen production in a single channel with cavities plate type methanol based microreformer

This paper proposes the development of a new and innovative configuration based on single channel with cavities plate type wall-coated microreformer (dimensions: 90mm×50mm×30mm). Microchannels are patterned on the SS plate and fabricated to make a vaporizer unit. The reformer is in the form of two SS plates placed one above the other. The water–methanol mixture enters from the top cover plate and gets vaporised in the channels cut on the vaporiser plate. The mixture then flows through the reformer plates on which the cavities are engraved to enhance mixing of water–methanol vapors. The catalyst is deposited on the fins of the reformer plates using a new promising technique for depositing nanostructured films namely, Solution Precursor Plasma Spray (SPPS) technique. The performance of the microreformer unit is investigated at various operating conditions of inlet feed flow rate, molar ratio of water to methanol and reforming temperature. The developed microreformer unit is able to generate enough hydrogen to produce a power output of 27W. The proposed design can also overcome the issue of shape and size of manifolds and ensure equi-flow distribution for multiple microchannel type microreformer designs and appears simple and suitable from fabrication viewpoint.

Microstructure and gas sensing properties of solution precursor plasma-sprayed zinc oxide coatings

ZnO nanostructured coatings have been prepared on Al2O3 substrates fitted with interdigitated Au electrodes on one side and a Pt heater on the other side, and explored as a gas sensor. The coatings were deposited by solution precursor plasma spray (SPPS) using zinc acetate Zn(CH3COO)2 aqueous solution as solution precursor. The SPPS process has proven its simplicity and reliability in fabricating polycrystalline ZnO coatings as verified by XRD structural analysis. The FE-SEM images confirmed that the coatings are nanostructured with grain size ranging from 50 to 100nm. The surface morphology and coating grain size is influenced by the H2 gas flow rate in plasma forming gas. The properties of the sensors based on the SPPS ZnO coatings towards NO2 as well as other hazardous gases were characterized and the sensors showed good sensitivity to NO2 gas in sub-ppm range. The influence of gas humidity on sensor responses was also studied.

La2Zr2O7 (LZ) Coatings by Liquid Feedstock Plasma Spraying: The Role of Precursors

Solution precursor plasma spraying (SPPS) is an innovative process for obtaining finely structured coatings from metallic salt solutions. Lanthanum and zirconium precursors were studied to understand their influence on lanthanum zirconate (La2Zr2O7) synthesis by SPPS. Thermal analysis revealed that the nature of the precursor and the solvent affected mixture decomposition by changing the decomposition temperature. The surface tensions of precursor solutions in various media were investigated and revealed the influence of the nature of the counter-cation. Different solutions of precursor mixtures were used to obtain La2Zr2O7 splats on metallic substrates. A decrease in solution surface tension led to an increase in splat size. Coating mechanisms by SPPS are governed by the nature of the precursors and solvents.

Understanding the Formation of Vertical Cracks in Solution Precursor Plasma Sprayed Yttria‐Stabilized Zirconia Coatings

Yttria‐stabilized zirconia (YSZ) deposition by the solution precursor plasma spraying (SPPS) route has been of interest for potential thermal barrier coating (TBC) applications. It has been surmised that realization of unique microstructural features like vertical cracks, nanosized pores and fine splats in the TBCs can significantly enhance coating durability and performance. However, satisfactory control over the YSZ coating microstructure has been elusive in the absence of an adequate understanding of the mechanism responsible for coating deposition in SPPS. This study demonstrates the ability to tailor microstructure of deposited YSZ coatings over a wide range, from nano‐porous coatings to a vertically cracked microstructure. Varying of precursor flow rate has been shown to dictate the pyrolysis events occurring in situ and, adopting this approach, YSZ coatings with widely varying microstructural features have been developed. The coatings have been characterized in detail and the observations correlated with in‐flight particle generation and splat formation. These studies also provide useful insights into the possible origin of vertical cracks in the coating for which a mechanism is proposed.

Solution precursor plasma-sprayed tungsten oxide coatings for nitrogen dioxide detection

Solution precursor plasma-sprayed (SPPS) tungsten oxide (WO3) coatings used as nitrogen dioxide (NO2) gas sensitive layers were investigated. X-ray diffraction (XRD) analysis, combined with field-emission scanning electron microscopy (FE-SEM) confirm the deposition of nanostructured porous and continuous WO3 coatings directly from WCl6 ethanol solution. The as-sprayed coatings, without any post heat-treatment, show well-crystallized monoclinic phase structure. The sensors using SPPS WO3 coatings as sensitive layers exhibit good response to NO2 in sub-ppm range.

Preparation of Lanthanum Zirconate Coatings by the Solution Precursor Plasma Spray

Solution precursor plasma spray (SPPS) can synthesize powders and deposit the coatings synchronously. The lanthanum zirconate coatings are deposited by SPPS in the present study, and the dense coating can be obtained through changing the precursor solution. The addition of urea can change the heat exchange process for some precursor mixtures. However, almost no effect can be found on the microstructure of powder and coating by the addition of urea. The extra heat energy caused by the addition of urea is so small, as compared with the heat input by the present plasma jet, so that the heating effect can be ignored. The porosity of coatings increase when the LaCl3·7H2O instead of La(NO3)3·6H2O reacts with Zr(CH3CO2)4.

Low Thermal Conductivity Yttria-Stabilized Zirconia Thermal Barrier Coatings Using the Solution Precursor Plasma Spray Process

The primary function of thermal barrier coatings (TBCs) is to insulate the underlying metal from high temperature gases in gas turbine engines. As a consequence, low thermal conductivity and high durability are the primary properties of interest. In this work, the solution precursor plasma spray (SPPS) process was used to create layered porosity, called inter-pass boundaries, in yttria-stabilized zirconia (YSZ) TBCs. IPBs have been shown to be effective in reducing thermal conductivity. Optimization of the IPB microstructure by the SPPS process produced YSZ TBCs with a thermal conductivity of 0.6 W/mK, an approximately 50% reduction compared to standard air plasma sprayed (APS) coatings. In preliminary tests, SPPS YSZ with IPBs exhibited equal or greater furnace thermal cycles and erosion resistance compared to regular SPPS and commercially made APS YSZ TBCs.