Using nanoparticles filler rod feeding, fine coated layer can be formed successfully with higher deposition late. Nanometer sized alumina particles of 200 nm in average diameter were dispersed into liquid resins at 40 % in volume fraction. The obtained pastes were solidified through heat polymerization to crate composite rods of ᶲ4×200 mm in dimensions. The solid rods were introduced into an acetylene and oxygen gas flame torch for a coaxial direction at 5.0 mm/s in supplying speed by using a mechanical actuator. Fine coated layer of 500 µm in thickness could be formed at 100 µm/s in deposition rate on stainless steel substrates. Effective dielectric constants of these coated layers were measured to estimate porosities by time domain spectroscopic method of electromagnetic waves in a terahertz frequency range. The reducing porosities in the coated layers through the optimization of filler rods feeding speeds and nanoparticles deposition rates will be discussed.

A new variant of LVOF system was developed to deposit ceramics. For this study Cr 2 O 3 powder was used. To save on time and reduce mathematical iterations optimizing of parameters was carried out by using an online particle diagnosing system. The spray parameters were varied to study their influence on the particle in-flight characteristics. The parameters which gave best particle temperature and velocity was used for coating. The resulted coating was dense and hard.

Plasma spraying of ceramic nano-powders suspended in a liquid carrier medium is an emerging technology, which allows the formation of thinner coatings with microstructures more refined than conventional plasma spraying. An external injection system, where the suspension enters the plasma jet radially, is installed on a F4-Sulzer Metco dc torch for the production of nanostructured Al 2 O 3 and ZrO 2 coatings. The effect of injection parameters, such as initial droplet diameter, droplet velocity and suspension flow rate is studied. The suspension droplets are continuously generated through an exchangeable micron-sized nozzle with a superimposed pulse of variable ultrasonic frequency. The heat transfer from the plasma to the liquid feed is optimized at high droplet velocity, moderate counter-current injection angle and flow rates not exceeding a threshold value, which depends on the plasma enthalpy and the latent heat of the suspension medium. A significant effect of initial droplet size (220 – 500 µm) or solid concentration (5 – 15 %) is not observed. In-flight particle states are measured for different plasma conditions, and are related to the resulting microstructures by SEM and XRD. High particle temperatures give rise to a refinement in crystallite size, while the particle velocities govern the deposition efficiencies and porosity levels. The results show that the particles follow closely the gas flow in the free stream, as well as in the stagnation boundary layer close to the substrate by virtue of their limited inertia. The prominent difference in microstructure between highly porous alumina and very dense zirconia coatings is explained in terms of particle impact velocities, which are simulated for typical operating conditions as a function of particle size and free-stream gas velocity.

Traditional brazing alloys do not wet ceramics and are therefore unusable for metal-ceramic bonding. One way to overcome the problem is by depositing a metal layer onto the ceramic prior to brazing. The approach taken in this paper was to plasma spray copper onto different ceramics (Al2O3, AlN, SiAlON) and then assess the wettability of potential brazing alloys (AgCu, AgCuTi). Interface analysis showed that silver and titanium segregation occurs at the ceramic surface and that, conversely, sprayed copper diffuses into the brazed joint.

Within the equilibrium approach, thermophysical foundations were developed which allow one to predict the dynamics of simultaneous deformation and solidification of a metal – oxide droplet impinging on a substrate, with due allowance for conjugated heat transfer under conditions of an ideal contact between the solidifying layer and the base surface. A representative collection of the alumina and YSZ splats was obtained under full control of key physical parameters (KPPs): temperature – Tp0, velocity – up0, and size – Dp, of particle, and temperature –Tb0, of a polished substrate. Without introducing any empirical coefficient, it was obtained quite a satisfactory agreement between the predicted and measured thickness and diameter of splats. In the present paper a comparison of a new solution with known dependences of different authors is carried out. Multiparameter calculations of the YSZ splats characteristics (diameter of splats, rate of cooling and solidification of melt, density of heat flux into substrate, etc.) in a wide range of the KPPs under molten droplets impacted with substrates were carried out.

Nanostructured coatings of Al 2 O 3 and ZrO 2 (1.5% Y 2 O 5 ) are produced by suspension plasma spraying, introducing the liquid feedstock internally into the central part of three converging plasma jets of a Mettech Axial III torch (Northwest Mettech Corp.). Spraying nanosized ceramic powders in a liquid carrier can yield thinner coatings with more refined microstructures than conventional plasma spraying. In-flight particle states are measured for a number of plasma conditions of varying torch current, gas flow rates and compositions (Ar, H 2 , N 2 ), and related to the resulting microstructure and phase composition in the coatings, as determined by EDS, SEM and XRD. Results show that particle velocities up to 600 m/sec can be reached, yielding high impact velocities and cooling rates. Some comparison is made to previous work performed using external injection of a suspension droplet stream into a conventional dc plasma flame. At optimized conditions, dense γ-Al 2 O 3 deposits with an average crystallite size below 30 nm are obtained at deposition efficiency above 80%, which was not previously attainable. Eutectic alumina-zirconia composite coatings with a finely layered lamellar structure are also realized. The laminates have potential advantages as thermal barrier coatings with beneficial properties arising from nano-composite components.

Polymer ceramic composite coatings were applied by flame spraying on preheated steel substrates. Polyamide (PA 11, nylon) powder was blended with alumina (Al 2 O 3 ), aluminium nitride (AIN) or boron nitride (BN) powder with two different filler content to increase thermal conductivities of polymer coatings. Morphologies and particle sizes of polyamide and filler powders were examined by scanning electron microscope and laser scattering methods. Coating structures and thicknesses of composite coatings were studied by the polished cross sections. Thermal conductivities were measured by hot disc method. Thermal conductivities of polyamide coatings increased from 30 % up to few times by blending ceramic filler material on PA 11 powder. Structures of composite coatings were dense and filler materials were clearly observed in polyamide matrix.

Thermal plasma spray processes with their various operating parameters can be considered as flexible technique to carry out appropriate ceramics coatings. This work deals with plasma spraying of several ceramics powders (hydroxyapatite (HA), Al 2 O 3 -TiO 2 , Al 2 O 3 , ZrO 2 -Y 2 O 3 (YSZ) and Cr 2 O 3 ) with suitable parameters using a CAPS system ("Controlled Atmosphere Plasma Spraying"). The HPPS (High Pressure Plasma Spraying), APS (Air Plasma Spraying) and IPS (Inert Plasma Spraying) modes were applied in order to obtain the suitable microstructure. The microstructures and phase compositions allowed to establish that surrounding high-pressure in the CAPS chamber is leading to a good heating of the powder and a good quality for the coatings.

A method is described wherein a ceramic oxide nanocomposite coating has been produced via a co-precipitation route. The first step in the process consists of forming a solid solution by use of plasma melting, homogenization, and rapid quenching of two ceramics that are normally immiscible. In the best case, the resulting structure is a true solid solution in a new, metastable crystalline structure. The quenched particles can be deposited as a coating or sprayed into water or onto a chill block to form a powder. When the material is sintered via a pressureless process, such as that for a coating, the phase decomposition proceeds quickly, resulting in a homogeneously distributed two-phase structure of micron sized particles. However, when the powders are compacted and sintered at very high pressures (1-8 GPa) and low temperatures (T ~ 0.3 - 0.5 Tm), the increased nucleation of the precipitates results in a composite in which both phases have grain sizes less than 25nm. This paper will review the underlying phenomenon behind the method and the resulting kinetics.

Reusable space vehicles, which must withstand re-entry into the Earth's atmosphere, require external protection systems (TPS) which are usually in the forms of rigid surface in areas of high or moderate working temperature. High heat fluxes and temperatures related to high performance hypervelocity flights also require the use of TPS materials having good oxidation and thermal shock resistance, dimensional stability, and ablation resistance. Components by these materials are usually fabricated, starting from either billets or plate stocks, by uniaxial hot pressing, and complex parts, such as low radius edges, are then obtained by electrical discharge machining technique. This article investigates an alternative fabrication technology, based on plasma spraying, to produce near net shape components. Results of experimental activities, such as optimization of plasma spraying parameters based on a DOE approach, are reported and discussed.

Thermal spraying of oxide ceramic suspensions containing fine and ultrafine powder particles is a new approach for manufacturing ceramic coatings exhibiting a refined microstructure. Suspension sprayed coatings clearly differ from conventionally sprayed coatings regarding microstructure phase composition and resulting mechanical properties. Several industrial applications may take advantage in future; among these are thermal barrier structures, thermal shock protection, solid electrolytes, catalytically active surfaces and wear resistant coatings. Two methods, namely Suspension Plasma Spraying (SPS) and High Velocity Suspension Flame Spraying (HVSFS) are suitable to process suspensions but lead to rather different coating structures due to differences in the achievable particle velocities and temperature. Generally, HVSFS can lead to more dense coatings with low porosity values. With SPS on the other hand, coatings with a high volume fraction of porosity featuring a homogeneous pore structure are achievable. The presentation will compare SPS and HVSFS regarding the spray process, achieved properties of the oxide coatings and potential applications.

In this study, superhydrophobic samaria-doped ceria coatings are produced by plasma spray physical vapor deposition (PS-PVD) followed by fluorination treatment. Samples are sprayed at distances of 300, 400, and 500 mm in order to obtain surfaces with different morphology. SEM examination shows that the surfaces have a hierarchical structure with island-like features consisting of nanoparticles, the size of which is shown to influence sliding behavior. The superhydrophobic coating surfaces also exhibited good stability in repeated adhesive-tape tear tests.

Dense sintered technical ceramics demand special surface preparation in order to be coated by thermal spraying. Sandblasting results in the damage of the interface region and leads to bonding defects. On the contrary, by varying the laser conditions, different laser structured surfaces were generated, which at Rz roughness values in the range of 40 μm, allowed to achieve thick and well bonding coatings. Therefore, laser ablation is proved to be the best method for surface preparation of ceramic substrates. In the case of porous ceramics (including pre-sintered ceramics) substrate preparation can be omitted, depending on their porosity level. Ceramics with porosity content up to 60 % can be coated by APS, whereas HVOF can be used on ceramics with porosity up to 30 %. On ready-to-get-coated pre-sintered ceramic parts (without substrate preparation), followed by co-firing of the substrates and coatings, the development of new ceramic components is possible.

Solid resin rods including ceramics nanoparticles were fed successfully into a Rokide flame gun to create dense coated layers without micro cracks and pores applying for electric, magnetic and dielectric components. In this investigation, alumina particles of 170 nm in average diameter were dispersed into acrylic liquid resin at 40 % in volume fraction. The paste materials was injected into an brass mold of φ4 ~ 200 mm in inner dimension and thermally cured through heating at 120 °C for 60 min. Formed solid rods were fed coaxially into an oxyacetylene gas flame by using the Rokide spraying system. Sprayed particles were collected in a water bath for microstructure observations by a scanning electron microscope and crystal phase analyses by an X-ray diffraction spectroscopy. Fine ceramics layer formations will be discussed systematically by the feeding speed of solid rods and gas flame condition of air pressure and oxygen pressure.

It has been said that plasma-sprayed ceramics particles are often supercooled before the impact on substrate. Some numerical models of the droplet impact actually included the supercooling effects. However, there is no report that has experimentally confirmed the effects on splat morphology. Therefore, in this research, we have mainly investigated the supercooling effects on splat morphology as well as splat microstructure. To achieve this, we developed an in-situ measurement technique utilizing radiation from a melt particle to monitor the impact of single particle successively under plasma spraying. The system was able to identify each single particle, which enabled us to correlate the splat morphology with impact velocity and thermal history of each particle during the impact. Yttria-stabilized zirconia powders were sprayed onto quartz glass substrate by the argon-hydrogen dc-rf hybrid plasma under atmospheric pressure. Waveforms of emissions and thermal history obtained during the impact were precisely analyzed. Especially, we closely examined thermal history during particle spreading to find the recalescence. In addition, splat morphologies were examined statistically in relation to their thermal histories. Based on the measurement, we also evaluated the viscosity of zirconia, cooling rate, and thermal contact resistance experimentally.

Strontium aluminates activated by Eu, Dy 3+ ions has recently attracted more attention due to not only their bright luminescence and super long afterglow without radioactivity but also the extensive application. SrAl 2 O 4 :Eu, Dy coatings were prepared by low power plasma thermal spraying (2.5-4W). The optimum spraying conditions have been established with spray parameters. The effects of the plasma conditions on the porosity rate of the coatings were investigated by many techniques, respectively X-ray diffraction (XRD) and scanning electron microscopy (SEM). To better qualify the characteristics of these coatings prepared from spray-dried powders, luminescence characteristics were also studied.

In this work, a low-temperature melting composition located within the glass-forming region of the Y 2 O 3 -Al 2 O 3 -SiO 2 (YAS) system is proposed and tested as a protective coating for SiC ceramics. Glassy coatings 197 µm thick were obtained by flame spraying YAS granules on SiC substrates that had been grit blasted and coated with a Si bond layer. Bulk glasses of the same composition were also produced for use as a reference material. The hardness, elastic modulus, and thermal conductivity of the coatings and bulk specimens were evaluated and compared and the effect of heat treatment was investigated. Crystallization occurred in both the bulk glass and coating during isothermal treatments in air at 1100-1350 °C, but it did not compromise system integrity due to crack healing.

This study deals with the deposition of coating materials that can be difficult to process by plasma spraying, including lanthanum and gadolinium zirconate, two pyrochlores of interest for thermal barrier applications, and lanthanum strontium cobalt ferrite (LSCF), a perovskite of interest for gas separation membranes. In addition to conventional atmospheric plasma spraying (APS), the feedstock powders were applied by suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD). The spraying processes are described in detail along with the characteristics of the powders and coatings and the effects of various spray parameters on splat behavior and coating composition and structure.

Suspension Plasma Spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using extra small particles as compared to conventional thermal spraying. Suspension spraying involves, atomization, solvent evaporation and melts consolidation, which can cause substantial complexity in the system. Using feedstock mixtures for composite coatings, such as alumina and zirconia, intricacy of the system increases even more. There is consequently a need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/ 8 wt% yttria stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated by using Taguchi design of experiment (DOE). The microstructural features include microcracks, porosities and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e. temperature and velocity were also measured. The role of the porosity in this multi-component structure is studied as well. The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity.

High purity oxide ceramic powders of alumina (Al 2 O 3 ) and yttria (Y 2 O 3 ) for plasma spraying have been developed to apply to semiconductor and flat-panel-display (FPD) production equipments. The ceramic coatings onto inside chamber wall of the equipments are required to have highly erosion resistance against CF containing plasma, widely used in dry etching process for micro-fabrications of the devices. Yttria is increasingly used in this application due to the high resistance compared to alumina. It is found that the yttria coating formed from agglomerated-and- sintered powder consisting of large primary particle has smoother eroded surface. Considering that particle deposition onto the devices, this coating will be effective to decrease generation of large sized particle, which is easily deposit onto the devices. Electric insulating properties of the coatings are also investigated to apply to electrostatic chuck. Electric breakdown voltage of yttria coatings is almost comparable to that of alumina coatings. However, yttria is difficult to apply due to its lower mechanical strength. Using smaller powder as feedstock is effective to improve the electric properties and influence of coating purity is lower than the powder size.