Dense Ceramic Films Research Articles

Numerical Simulation and Experimental Analysis of Aerosol Deposition: Investigating Nozzle Effects on Particle Dynamics and Deposition

Aerosol deposition (AD), also known as vacuum kinetic spray (VKS), is used to deposit dense ceramic films onto a substrate surface at room temperature. One predominant factor influencing the overall deposition process is the nozzle geometry, which significantly impacts the quality, shape, and thickness of the coating. To evaluate the effect of nozzle geometry in AD, particle trajectory and impact velocity were investigated via computational simulation. A Eulerian-Lagrangian model was used to simulate the gas flow, particle in-flight behavior, as well as particle deposition characteristics on a flat substrate. Three common nozzle geometries in AD were utilized: a converging-diverging nozzle with a slit cross-section (CD-Slit), a converging-barrel nozzle with a slit cross-section (CB-Slit), and a converging-diverging round (CD-Round) nozzle. Moreover, suitable drag coefficient and Nusselt number correlations were used to account for compressibility and rarefaction effects on particle dynamics and heat transfer. The simulation results were compared to the deposition pattern obtained experimentally. The results demonstrate that shape of the nozzle has profound effect on the particle impact velocity and deposition pattern. The CD-Round nozzle provides uniform, thinner coatings ideal for extensive surfaces at a slower deposition rate. In contrast, the CB-Slit nozzle is optimized for maximum coating thickness in narrow, thick linear patterns. The CD-Slit nozzle achieves high deposition rates with uniform coatings and a distinctive cat-ear shaped pattern.

Powder aerosol deposited calcium cobaltite as textured P-type thermoelectric material with power factors approaching single crystal values

In this work, the thermoelectric material calcium cobaltite Ca3Co4O9 (CCO), a promising p-type conducting thermoelectric oxide with anisotropic properties, was processed by the powder aerosol deposition method (PAD) to form a dense ceramic CCO film with a thickness in the µm range. The prepared films were characterized regarding their microstructure and thermoelectric properties between room temperature and 900 °C. After heat treatment at 900 °C, the CCO PAD film in-plane shows excellent properties in terms of electrical conductivity (280 S/cm at 900 °C) and Seebeck coefficient (220 µV/K at 900 °C). The calculated power factor in-plane (ab) reaches with 1125 µW/(m K2) 40 % of the single crystal value, surpassing the known-properties of CCO bulk ceramics. Examination of the microstructure shows a strong fiber texture of the film as well as a strong coarsening of the grains during the first heat treatment up to 900 °C.

Electrophoretic deposition of ceramic coatings from modified suspensions of microsized powders of doped BaCeO3 and BaCeO3–BaZrO3 proton-conducting electrolytes

This work investigates the influence of molecular iodine introduced as a charging agent into the suspensions based on the BaCe0.8Sm0.19Cu0·01O3 (BCSCuO), BaCe0·5Zr0·3Y0.1Yb0.1O3-δ (BCZYYbO) and BaCe0.89Gd0.1Cu0·01O3-δ (BCGCuO) proton-conducting electrolytes at concentrations up to 1.0 g/L on their electrokinetic properties. The peculiarities of changes in zeta potential, pH, conductivity of the suspensions, the thickness and morphology of the coatings depending on the amount of iodine added are determined. It has been established that when the iodine concentration increases to 1 g/L, the electrical charge of the particles and the sign of the zeta potential undergo a reversal. Additionally, there is a natural decrease in the pH value towards the acidic side and a corresponding increase in the suspension conductivity. The research has demonstrated that in the suspension with a high iodine content (1 g/L), cathodic and anodic deposition can occur simultaneously under electrophoretic deposition (EPD) conditions at low voltage values (below 8 V). However, as the voltage increases, only cathodic deposition occurs. Therefore, the impact of altering the type of the EPD is threshold in nature relative to the magnitude of the EPD voltage. It has been shown that in order to practically implement EPD of ceramic coatings from modified suspensions of microsized powders of doped BaCeO3 and BaCeO3–BaZrO3 proton-conducting electrolytes, it is necessary to select a small amount of added iodine (0.1–0.2 g/L) to initiate a stable deposition process and to ensure continuity and uniformity of the coatings. This article discusses possible mechanisms of zeta potential inversion, electrophoretic mobility, and the EPD nature under conditions of high concentrations of iodide ions in the suspension bulk. The experiments have demonstrated the viability of the EPD process for the formation of a uniform BCSCuO coating (∼10 μm) on a supporting NiO–BCSCuO anode substrate using an iodine-modified suspension. This coating was subsequently sintered into a dense ceramic film at 1450 °C. In addition to the fundamental significance, the study results have implications for the practical use to improve and simplify the thin-film SOFC technology.

Room temperature manufacture of dense NaSICON solid electrolyte films for all-solid-state-sodium batteries

Sodium (Na) Super-Ionic CONductor (NaSICON) solid electrolyte (SE) powders (Na3Zr2Si2PO4) were prepared by the mixed oxide technique using a planetary ball mill and synthesized via solid-state method at temperatures ranging from 950 to 1200 °C. The powders with 95% pure NaSICON phase were deposited on different substrates via Powder Aerosol Deposition (PAD) at room temperature directly from the powders and fully dense ceramic films were obtained. X-ray diffractometry including Rietveld refinement were carried out on both the calcined powders and the resulting films to determine the crystallographic properties. Subsequently, the electrical properties of the resulting films were characterized and the effect of annealing at temperatures between 100 and 600 °C on the ionic conductivity of NaSICON PAD films was evaluated. Annealed films were measured in the temperature range 50 and 250 °C to calculate the activation energy Ea of the PAD films. Our work demonstrates a successful room temperature deposition of dense NaSICON electrolyte films on different substrates, which is promising for stationary energy storage applications of solid-state-sodium batteries.

Preparation of thick dense ceramic films of dielectric BaTaO2N through electrophoretic deposition

Sintering of the ferroelectric perovskite oxynitride, BaTaO2N is still a big challenge, because nitrogen is partially released from the crystal lattice during high-temperature sintering. Post-sintering annealing under an NH3 flow is essential in order to compensate for this nitrogen loss and to recover the electrically insulating properties of the ceramic. However, fully densified bulk ceramics are nitrided only on their outer surface, while their interior remains semiconducting. In this work, thick ceramic films of the perovskite oxynitride with a high relative density close to 90% were fabricated using electrophoretic deposition and high-temperature sintering. The nitrogen loss was fully recovered during annealing under an NH3 flow, owing to the thickness of the sintered films being less than 100 μm. After annealing, the BaTaO2N ceramics consisted of 200 nm-sized particles with a dense microstructure. This is the first report of the fabrication of BaTaO2N ceramics with a relative density of 89%. The dielectric constant and dielectric loss were approximately 320 and 0.05 at 1 MHz, respectively.

Advanced electrodes for electrochemical energy storage and conversion devices fabricated by reactive spray deposition technology

While different electrochemical devices require electrodes with different microstructures, thicknesses, and catalyst compositions, the reactive spray deposition technology (RSDT) process has been able to demonstrate flexibility to provide what is needed for each application. From developing porous electrodes with platinum group metal catalysts for fuel cell and electrolysis applications, to the fabrication of dense ceramic thin films for solid oxide fuel cell electrolytes, to the fabrication of novel electrodes for rechargeable lithium-ion batteries, the RSDT can be modified to fabricate these layers in a one-step process. Using a combustion flame, the heat generated from the flame is used to provide the energy for sintering ceramic particles into a dense layer and it can be used to decompose a precursor solution into a catalyst particle that contains the desired stoichiometry. The RSDT process has been shown to be an effective method for the development of electrode thin films.

Nonclassical Crystallization of an Al2O3 Film by Positively Charged Secondary Nanoparticles during Aerosol Deposition

Thin film growth through nonclassical crystallization with charged nanoparticles as building blocks has been studied in chemical vapor deposition and physical vapor deposition. A similar mechanism might be applied to aerosol deposition (AD), with which the mechanism for the evolution of dense ceramic films at room temperature has not been clearly understood. Aerosol particles fracture into fragments of secondary nanoparticles during AD. In this work, secondary particles passing between the two parallel biased and grounded electrodes were captured by the transmission electron microscopy (TEM) grid membrane on each electrode, and it was revealed that they were mainly positively charged. Neutral secondary nanoparticles, not deflected by the electric field, produced a porous film on the silicon substrate, whereas charged secondary nanoparticles produced a dense film. The positive charge of the secondary nanoparticles appeared to enhance the plastic deformation required for the evolution of dense films during AD, which was supported by ab initio calculations.

Making powder aerosol deposition accessible for small amounts: A novel and modular approach to produce dense ceramic films

AbstractPowder aerosol deposition is a promising technique to deposit dense ceramic films directly at room temperature. While previous developments pointed towards larger and more complex deposition devices, this work follows a different approach and proposes a simplified and miniaturized coating device (denoted as Micro‐PAD, µPAD). The aim is twofold: creating a smaller and flexible device consisting of an aerosol generation unit and a deposition chamber with a combined low areal footprint of 30 cm by 20 cm (that, e.g., easily fits in a glove box) as well as lowering the hurdle for other researchers to use the powder aerosol deposition. Therefore, we introduce a device mainly based on commercially available components/connectors as well as manual operated valves/flow meters. A key point is the elimination of moving components by just using a spot deposition that was enabled by using a circular de‐Laval‐type nozzle.The operational capability of µPAD is proven for the deposition of alumina films and compared to conventional PAD in terms of mechanical, crystalline, and optical film properties. Thick films with a bell‐shape‐like profile are deposited by µPAD, featuring a plateau in the center of the film with a diameter of 5 mm and a FWHM (full width at half maximum) diameter of about 10 mm. Alumina films produced by µPAD do not only match the properties of corresponding PAD films, but oftentimes outperform them. Here, µPAD films exhibit increased hardness and optical transmittance values, surpassing reference values of the conventional sprayed counterparts by at least 10%. Also, film integrity and adhesion to the substrate are slightly higher in case of µPAD. Reasons for the improved film properties are found by X‐ray diffraction, with a significantly higher fracturing of impacting particles during µPAD combined with improved film consolidation as observed by SEM. Furthermore, µPAD featured doubled to tripled the deposition rates and, markedly almost doubled the deposition efficiency.

How to Make Ceramic Gas Sensor Films at Room Temperature - the Powder Aerosol Deposition Method

Introduction Typically, gas sensors are ceramic devices. They are manufactured in ceramic techniques like tape technology and/or conventional thick-film techniques (typically screen-printing with subsequent firing) [1]. During firing, interdiffusion processes occur between substrate and gas sensitive film. At least partly, they may deteriorate the gas sensing properties of the functional oxides. Some materials can even hardly be processed without decomposition. Therefore, room temperature deposition techniques are advantageous. The Powder Aerosol Deposition Method The Powder Aerosol Deposition Method (PAD) bases on the Room Temperature Impact Consolidation (RTIC) as the film densification mechanism. This allows producing dense ceramic films without any high-temperature processes directly from an initial ceramic powder on almost any substrate material. This contribution gives examples for PAD-applications in the field of gas sensing.Although the process is rather simple, the results are very promising. Driven by a pressure difference to a vacuum deposition chamber (evacuated only to rough vacuum), the aerosol is accelerated by a slit nozzle to several hundred m/s. This aerosol jet ejects particles into the deposition chamber. Here, the particles impact on a movable substrate and get fractured into nanometer-sized fragments that are compacted by subsequently impacting particles. Fig. 1 depicts the basic principle. Further process details can be found in the reviews [2], [3], or [4]. Results and Discussion Some examples for PAD-based sensors are surveyed here. Besides conventional conductometric gas sensors based on SnO2 and other metal oxides to detect limited components, applications for temperature independent oxygen sensors are reported, e.g. of SrTi1-x Fe x O3 [5], [6] or Alumina-doped BaFe1-x Ta x O3 (BFATx) [7]. Simultaneous powder aerosol co-deposition of inert and functional oxides to fine-tune the sensing properties may be promising [6].Figure 2 is a measurement protocol at 900 °C of the logarithm of the film conductivity of BFAT30 fabricated by PAD. The material is rapidly and reproducibly responding to stepwise changes of the oxygen partial pressure, pO2. In Figure 3, the log-log plot of the conductivity (log s vs. log pO2) of the sensor between 600 °C and 900 °C in the pO2 range from 0.01 to 1 bar is shown. Neither the sensitivity to oxygen (slope in the log-log-plot) nor the base line resistance changes with temperature. Log s depends linearly on log pO2 between 700 °C and 900 °C, showing a slope of 0.24. An improved formulation contains 1 % alumina (BFATx). Amongst the BFATx samples examined, particularly good properties were found with regard to temperature independency for BFAT25 (BaFe0.74Al0.01Ta0.25O3).Combined resistive and thermoelectric oxygen sensors with almost temperature-independent characteristics of both conductivity and Seebeck coefficient were manufactured using BFAT30 [8].Classical tin-oxide conductometric metal oxide gas sensors were deposited by PAD at room temperature on interdigital electrodes. As expected, they show a pronounced sensitivity to nitrogen oxides at around 300 °C and to hydrogen at around 450 °C [9].With PAD, solid electrolyte electrochemical gas sensors have also been successfully manufactured [10]. A nitrogen oxide sensor using the novel pulsed-polarization method, which attracted much attention recently with YSZ as solid electrolyte, can now be operated at lower temperatures due to the use of a Bismuth-based fast oxide ion conductors (Fig. 4).The powder aerosol deposition method is also suitable to produce thermistors with a negative temperature coefficient of resistance (NTCR) [11]. They may serve as sensitive detectors for pellistors. Conclusions It is possible to manufacture ceramic gas sensor films completely without any high-temperature process and directly from an initial ceramic powder on almost any substrate material. Even temperature sensors can be realized. Future research directions may focus on sensors on polymers or textiles by applying the powder aerosol deposition method.

Shock Absorption Effect on Particle Fragmentation and Microstructural Features of Vacuum-Kinetic-Sprayed Al2O3 Film on Polycarbonate Substrate

As the demand for flexible devices has increased, polymers have become very promising materials for these applications because they have excellent flexibility, lightweight, and low cost. Vacuum kinetic spraying can be a good alternative technology for film fabrication on polymers as dense ceramic films can be fabricated even at room temperature without thermal degradation of the polymer substrate. However, there is a lack of understanding of the deposition process of ceramic films on a polymer substrate. In this regard, the deposition behavior and microstructural features were investigated by comparing Al2O3 particle deposition on glass and polycarbonate (PC) substrates by using simulations and experimental methods. Simulations demonstrated that hard particles were prone to penetrate or be only embedded in the soft substrate without sufficient fragmentation. This is attributed to the shock absorption effect of the substrate. Particle kinetic energy was transferred mostly to the internal energy of the soft substrate but not to particle internal energy (plasticity and/or failure), which prevents particle fragmentation. Consequently, unusual interface microstructural feature was attributed to insufficient particle fragmentation by the shock absorption of the soft substrate.

Piezoelectric Thick Film Deposition via Powder/Granule Spray in Vacuum: A Review

Conventional thin-film processing techniques remain inadequate for obtaining superior dense ceramic thick films. The incompatibility of ceramic films prepared via other methods, such as screen printing, spin coating, and sputtering, is a major obstacle in the fabrication of thick film-based ceramic electronic components. The granule spray in vacuum (GSV) processes and aerosol deposition (AD) are important coating approaches for forming dense ceramic thick films featuring nanoscale crystallite structures at room temperature, which offer excellent material properties and facilitate cost-effective production. AD ceramic coatings require the acceleration of solid-state submicron ceramic particles via gas streams with a velocity of a few hundred meters per second, which are then wedged onto a substrate. This process is economical and particularly useful for the fabrication of piezoelectric thick film-based microactuators, energy harvesters, sensors, and optoelectronic devices. More recently, the GSV technique was improved to achieve more uniform and homogeneous film deposition after AD. This review article presents a detailed overview of the AD and GSV processes for piezoelectric thick films in terms of recent scientific and technological applications.

The Powder Aerosol Deposition Method - Making Ceramic Gas Sensor Films at Room Temperature

Introduction Most gas sensors are ceramic devices. They are manufactured in ceramic techniques like tape technology and/or conventional thick-film techniques (typically screen-printing with subsequent firing) [1]. During firing, between substrate and gas sensitive film interdiffusion processes occur. They may (at least partly) deteriorate the gas sensing properties of the functional oxides. Some materials can even hardly be processed without decomposition. Therefore, room temperature deposition techniques may be advantageous. The Powder Aerosol Deposition Method The Powder Aerosol Deposition Method (PAD) bases on a film densification mechanism called Room Temperature Impact Consolidation (RTIC). This allows producing dense ceramic films without any high-temperature processes directly from an initial ceramic powder on almost any substrate material. This contribution gives examples for PAD-applications in the field of gas sensing.The results are very promising, despite the process is rather simple. Driven by a pressure difference to a vacuum deposition chamber (evacuated only to a rough vacuum), the aerosol is accelerated by a slit nozzle to several hundred m/s. This aerosol jet ejects particles into the deposition chamber. Here, the particles impact on a movable substrate and get fractured into nanometer-sized fragments that are compacted by subsequently impacting particles. Fig. 1 depicts the basic principle. Further process details can be found in the reviews [2], [3], or [4]. Results and Discussion Some examples for PAD-based sensors are surveyed here. Besides conventional conductometric gas sensors based on SnO2 and other metal oxides to detect limited gaseous components, applications for temperature independent oxygen sensors are reported, e.g. of SrTi1-x Fe x O3 [5], [6] or BaFe1-x Ta x O3 (BFTx) [7]. Simultaneous aerosol co-deposition of inert and functional oxides to fine-tune the sensing properties may be promising [6].Figure 2 is a measurement protocol at 900 °C of the logarithm of the film conductivity of BFAT30 fabricated by PAD. The material is rapidly and reproducibly responding to stepwise changes of the oxygen partial pressure, pO2. In Figure 3, the log-log plot of the conductivity (log s vs. log pO2) of the sensor between 600 °C and 900 °C in the pO2 range from 0.01 to 1 bar is shown. Neither the sensitivity to oxygen (slope in the log-log-plot) nor the base line resistance changes with temperature. Log s depends linearly on log pO2 between 700 °C and 900 °C, showing a slope of 0.24. An improved formulation contains 1 % alumina (BFATx). Amongst the BFATx samples examined, particularly good properties were found with regard to temperature independency for BFAT25 (BaFe0.74Al0.01Ta0.25O3).Combined resistive and thermoelectric oxygen sensors with almost temperature-independent characteristics of both conductivity and Seebeck coefficient were manufactured using BFAT30 [8].Classical tin-oxide conductometric metal oxide gas sensors were deposited by PAD at room temperature on interdigital electrodes. As expected, they show a pronounced sensitivity to nitrogen oxides at around 300 °C and to hydrogen at around 450 °C [9].With PAD, solid electrolyte electrochemical gas sensors have also been successfully manufactured [10]. A nitrogen oxide sensor using the novel pulsed-polarization method, which attracted much attention recently with YSZ as solid electrolyte, can now be operated at lower temperatures due to the use of a Bismuth-based fast oxide ion conductors (Fig. 4).The powder aerosol deposition method is also suitable to produce thermistors with a negative temperature coefficient of resistance (NTCR) [11]. They may serve as sensitive detectors for pellistors. Conclusions It is possible to manufacture ceramic gas sensor films completely without any high-temperature process and directly from an initial ceramic powder on almost any substrate material. Even temperature sensors can be realized. Future research directions may focus on sensors on polymers or textiles by applying the powder aerosol deposition method.

Fabrication of high‐fracture‐strength and gas‐tightness PDC films via PIP process for pressure sensor application

AbstractHigh‐fracture‐strength and high‐gas‐tightness thin‐film gas‐pressure sensors were fabricated using a silicon oxycarbonitride polymer‐derived‐ceramic (SiCNO‐PDC) material via a multiple polymer‐infiltration‐pyrolysis (PIP) process. To obtain dense SiCNO ceramic films, two types of liquid polyvinylsilazane (PVSZ) precursors were chosen; a high‐ceramic‐yield precursor with high viscosity (PVSZ‐1) was designed to construct the skeleton of ceramic film, whereas a relatively high‐ceramic‐yield precursor with low viscosity (PVSZ‐2) was designed to infiltrate in ceramic defects. The results confirmed that the PVSZ‐2 can effectively fill both intergranular and intragranular defects of ceramic films pyrolyzed by the PVSZ‐1, and produce the sponge‐like structures with nanosized pores. Although the density of the ceramic films only increased by 2.2%‐5.2% after PIP process, the gas tightness was fundamentally improved, and all ceramic films after PIP process could keep gas‐tight condition without loss of pressure after 72 hours. Similarly, the fracture strengths of the ceramic films after PIP cycles have also been improved, and the value could reach 108 MPa after only three PIP cycles. In addition, because a linear relationship among the load, resonant frequency, and deflection was detected in our ceramic films, the wireless passive gas‐pressure sensors with high‐sensitivity and high‐temperature resistance have been fabricated. It strongly indicates that the ceramic films obtained by our PIP process have real potential to be used as thin‐film gas‐pressure sensing elements in high‐temperature and high‐pressure fields.

Effect of α-Al2O3 additive on the microstructure and properties of MAO coatings prepared on low carbon steel

Micro-arc oxidation (MAO) can produce metal surface coatings with excellent properties. By using appropriate auxiliary sealing technology, the micro-holes on the surface of the coatings can be reduced and the performance of the MAO coatings can be further improved. In this work, a dense and corrosion-resistant α-Al2O3 ceramic film was prepared by MAO on the surface of boron-containing low carbon steel (10B21). Based on the electrolyte including NaAlO2, NaH2PO4, Na2CO3 and Na2B4O7, we studied the effects of different concentrations of the α-Al2O3 additive (0, 1, 2, 3 and 4 g/L) in the electrolytes on the MAO layers of 10B21 and investigated the mechanisms for the effect of the added α-Al2O3. The results showed that the added α-Al2O3 particles diffused and were adsorbed into the pores in the MAO layer, and as the conversion rate from Al2O3 to the α phase in the layer increased, the pore in the films became smaller. In particular, for the α-Al2O3 concentration of 3 g/L, the lowest hole of 1∼2 μm was obtained. Since the surface of the MAO films prepared by adding α-Al2O3 had an increased higher α-Al2O3 content, excellent electrochemical corrosion performance in a 3.5% NaCl solution was obtained, and the electrochemical self-corrosion current density was 0.2 μA/cm2. After a neutral salt spray test carried out for 7 days, the corrosion rate was 20 g·m−2·d-1, and the corrosion resistance was greatly improved.

Dense Y-doped ion conducting perovskite films of BaZrO3, BaSnO3, and BaCeO3 for SOFC applications produced by powder aerosol deposition at room temperature

State-of-the-art solid oxide fuel cells (SOFC) are based on oxide ion conducting zirconia electrolytes, typically doped by yttria or scandia. Major drawback of these systems are their high operation temperatures of 800 °C and above. These are necessary for a sufficient ionic conductivity. Instead of oxide ions, also protonic charge carriers could be used in SOFC. The material classes of barium zirconates (BaZrO3), barium stannates (BaSnO3), and barium cerates (BaCeO3) are described as good proton conductors, especially when the B-site of the ABO3 perovskite structure is aliovalently doped by yttria. Their protonic conductivity values in the moderate temperature regime up to 600 °C are comparable to YSZ at 800 °C, making these compounds ideal candidates for a usage in future SOFC. Unfortunately, very high sintering temperatures up to 1800 °C are required to process dense and therefore gas-tight solid electrolyte membranes. However, a novel spray coating method called powder aerosol deposition (PAD, also known as AD) enables to form fully dense ceramic films directly at room temperature without any necessary sintering processes. Films are deposited from ceramic powders that are accelerated by a dry carrier gas flow under vacuum conditions.In this work, we investigated the film formation of three different barium based perovskite ceramics, namely yttria doped barium zirconate, barium stannate, and barium cerate by powder aerosol deposition. The optical and mechanical quality of films was evaluated using scanning electron microscopy and microhardness indentation and their crystallographic properties were characterized by X-ray diffraction. The electrical behavior was analyzed by electrochemical impedance spectroscopy and DC polarization methods up to temperatures of 1000 °C and 800 °C, respectively. Furthermore, a preliminary study about the film formation on porous electrodes was conducted.

In- and through-plane conductivity of 8YSZ films produced at room temperature by aerosol deposition

Aerosol deposition is a unique spray coating process to deposit dense ceramic films directly at room temperature just by spraying a dry powder, without any binder or additional sintering step needed. Therefore, it is a very promising coating method for functional materials that may be used to produce a variety of electrochemical devices, solid oxide fuel cells or gas sensors. However, functional properties like the electrical conductivity significantly depend on the microstructure of the produced film. Consequently, anisotropic film properties may occur even for isotropic functional materials. In this work, films of oxide ion-conducting yttria-stabilized zirconia (YSZ) were produced by aerosol deposition. The orientation-dependent electrical conductivity was measured using two different electrode configurations: one for the in-plane conductivity and another one for through-plane measurements. A slight anisotropy was observed, attributed to the present film morphology. In particular, the grain boundaries influenced the total conductivity. Furthermore, a thermal post-deposition treatment significantly affected the total conductivity of aerosol-deposited YSZ films.

Revealing the effects of aerosol deposition on the substrate‐film interface using NaCl coating

AbstractAerosol deposition is a feasible method of fabricating dense ceramic films at room temperature by the impact consolidation of submicron‐sized particles on ceramic, metal, glass, and polymer substrates at a rapid rate. Despite the potential usefulness of the aerosol deposition process, there are issues, such as deposition mechanisms and structure of the film‐substrate interface, that are not well understood. We have used complementary structural and microstructural analysis to capture the state of the substrate surface after the aerosol deposition process. The results reveal that modification of the substrate surface by the ejected submicron‐sized particles is essential for the formation of anchoring layer, thereby, a change in internal residual stress state and surface free energy of the substrate is required to deposit film using AD process. Our analysis also suggests that the adhesion between the metal substrate and ceramic particles is possibly contributed by both physical bonding and mechanical interlocking.

Powder Pre-Treatment for Aerosol Deposition of Tin Dioxide Coatings for Gas Sensors.

The Aerosol Deposition (AD) method has the unique property to allow for manufacturing dense ceramic films at room temperature. As found in many publications, the deposition process is very sensitive to powder properties. In particular, powders of nano-sized particles and grains, e.g., from precipitation, are usually beyond the conventional size range of AD processability, yielding chalk-like films of low mechanical stability. Thus, the conventional AD process is limited in applicability. In this study, we try to overcome this problem by adapting the standard milling treatment of powders for improved deposition by additional temperature pre-treatment. Using commercial tin dioxide and including a temperature treatment for grain growth, makes the powder accessible to deposition. In this way, we achieve optically translucent and conductive SnO2 thick films. With the application such as a gas sensitive film as one of many possible applications for SnO2 thick-films, the sensors show excellent response to various reducing gases. This study shows one exemplary way of extending the range of adequate powder and applications for the AD method.

Compressive stress in nano-crystalline titanium dioxide films by aerosol deposition

Aerosol deposition is a kinetic energy, particle impacting process to produce dense ceramic films or coatings at room temperature, and thus results in high residual compressive stress. The purpose of this work was to determine the stress and its thickness dependence in titanium dioxide, TiO2, films. Aerosol deposition was used to produce films, 1 to 22 μm thick, on glass substrates. A scanning interferometric optical profiler was used to generate surface maps and measure curvature values of the substrates before and after deposition. The Stoney equation was used to calculate average film stress from the measured thickness and radius of curvature. The effect of substrate shape was also investigated by using square and beam substrates in the deposition experiments. Surface maps of the square and beam substrates after deposition showed an increasing trend towards spherical curvature as the film thickness increased. Average (compressive) stress measured for square samples was 0.37 GPa, while the average for beams was 0.52 GPa. The beam-shaped sample data showed good linearity between curvature and film thickness, and fitting to the simple Stoney formula resulted in an intrinsic stress value of 0.50 GPa.

Roles of Particle Size Distribution in Bimodal Feedstocks on the Deposition Behavior and Film Properties in Vacuum Kinetic Spraying

Vacuum kinetic spray (VKS), also called aerosol deposition method, is a spray process that makes it possible to fabricate dense ceramic films at room temperature. Although the deposition rate of VKS is better than conventional ceramic coating processes, the deposition properties are still poor for industrial use. In this respect, this work investigates the role of particle size on the deposition behavior by blending two alumina powders having different sizes. It results in suggestions for increasing the deposition efficiency and rate. The microstructure and mechanical properties of films revealed that nanosized particles directly took part in deposition and participated in increasing the deposition rate despite the low adhesion between crystallites. In contrast, relatively large submicron-sized particles mainly contributed to the coating consolidation via severe friction, which strengthened the fragment bonding. Submicron-sized particles also were indirectly deposited as crystallites after sufficient fragmentation. Therefore, it is suggested that the deposition behavior and film properties in VKS can be controlled by adjusting the mixing ratio of two alumina powders with different particle size ranges.