Radio Frequency Plasma Spraying Research Articles

Bulk Processing of Hydroxyapatite Nanopowder Using Radio Frequency Induction Plasma

Spherical hydroxyapatite (HA) nanopowder was synthesized at a rate of 20 g/h from HA sol using a 30 kW inductively coupled radio frequency plasma spray system. The HA sol was axially fed with a water‐cooled steel probe in the lower temperature region of the supersonic plasma nozzle, which helped in HA phase stabilization. The HA powder was synthesized at plate power between 19 and 28 kW. Particle size, surface area, particle morphology, and phase composition of the synthesized powder were evaluated using transmission electron microscopy, BET specific average surface area, X‐ray diffraction (XRD), and Fourier‐transformed infrared spectroscopy. The synthesized nanopowder was spherical in nature, with the particle size ranging from 30 to 70 nm. The increase in plate power resulted in a decrease in particle size. XRD results indicated HA to be the primary phase along with phase decomposition products, such as tricalcium phosphate and calcium oxide. Cytotoxicity behavior was studied using human osteoblast cells to ensure biocompatibility.

Phase characterization of Sm–Lu mixed oxide powders prepared by sintering and radio frequency plasma spraying

Abstract Radio frequency plasma spraying is a promising technique to prepare rare earth oxide nano-particles. Applying this method after sintering of pellets at T = 1600 °C and subsequent grinding, Sm2O3—Lu2O3 mixed oxide powders of various compositions were synthesized. Analyzing the ground powders, the phase field can be divided into three regions: (1) Sm-rich monoclinic B-type solid solutions, (2) Lu-rich cubic C-type solid solutions, and (3) a diphasic region for Lu contents 0.33 ≤ x Lu ≤ 0.54. In the single phase areas, the volume for one formula unit of the rare earth sesquioxide is found to depend linearly on the cubed average cation radius. Plasma spraying of the Lu-rich powders leads to a second monoclinic B-type phase. Excluding the solubility gap, the monoclinic lattice parameters show quadratic dependencies on the Lu content and the molecular volume is a function of third order on the cation radius.

Phase transformation of ultrafine rare earth oxide powders synthesized by radio frequency plasma spraying

Inductively coupled radio frequency plasma spraying was used to prepare ultrafine powders of Sm 2O 3, Dy 2O 3, and Lu 2O 3. These three materials were studied because they are effective dopants in multi-layer ceramic capacitors (MLCC) to improve lifetime. The as-sprayed powders consist of both micron-sized mono-dispersed spherical particles and nano-sized particles in various shapes. In addition to the spheroidization effect, plasma treatment leads to an increase of the monoclinic phase fraction associated with a corresponding decrease of the amount of the cubic phase. The degree of this phase change was found to depend sensitively on the sprayed oxides, decreasing with increasing atomic number of the rare earth element, which is associated with their thermodynamic stability. Furthermore, the monoclinic high-temperature equilibrium phase induced by plasma treatment remains stable at room temperature and even during annealing at a temperature of 900 °C.

Fabrication of iron nitride coatings by reactive RF plasma spraying

Reactive plasma spraying is a promising process to fabricate thick non-oxide ceramics coatings. In this study, fabrication of iron nitride (Fe 4N) coatings by reactive RF (Radio Frequency) plasma spraying was investigated. Iron particles were injected in Ar/N 2 plasma and were deposited onto carbon steel substrates. In the case of applying conventional iron powder (particle size of 75 μm and under), it was possible to fabricate Fe/Fe 4N composite coatings by reactive RF plasma spraying with using water-cooled substrate holder. However, the microstructure of the coatings was porous and lower concentration of the nitride phase. Moreover, it was difficult to increase the concentration of the nitride phase in the coatings by controlling spraying conditions such as N 2 flow rate and RF power. On the other hand, it was possible to fabricate thick, dense microstructure and higher concentration of the nitride phase with applying fine iron powder as a feedstock powder material. And it was possible to control the concentration of the nitride phase in the coatings by changing N 2 flow rate in the plasma gas. Moreover, the coating which did not include original Fe phase was also fabricated with the spraying condition of higher N 2 flow rate. However, excessive N 2 flow rate and RF power decrease the nitride phase due to increasing both in plasma and substrate temperature above the decomposition temperature of Fe 4N (974 K). Therefore, fabrication of iron nitride coatings by reactive RF plasma spraying was possible with applying fine iron powder and substrate cooling.

反応性プラズマ溶射法におけるプラズマの分光測定

Reactive RF (Radio Frequency) plasma spray process, in which metal element reacts with surrounding active species in plasma, has been receiving great interest to form nitride ceramics thick coatings. It was possible to fabricate TiN, Si3N4 and AlN thick coatings by this process. However, nitriding process has not been elucidated yet. To control the formation degree of the nitride with reactive RF plasma spray process, it is necessary to verify the nitriding process. In this study, plasma temperature and active species in the plasma were investigated by emission spectroscopic measurement. Plasma temperature increased with N2 gas flow rate. Adding H2 in plasma gas increased plasma temperature. Plasma gas fraction of N2 and H2 affected the amount of generating NH radical significantly. However, plasma gas fraction did not affect plasma temperature. Both plasma temperature and the amount of generating NH radical increased with RF power.

Fabrication of Silicon Nitride Thick Coatings by Reactive RF Plasma Spraying

Silicon nitride (Si 3 N 4 ) is one of the attractive ceramics in respect of its excellent properties both in wear and thermal shock resistance. In this research, Si 3 N 4 thick coatings were fabricated by reactive RF (Radio Frequency) plasma spray process, and a reactive plasma spraying, in which metal element reacts with surrounding active species in plasma, has been considered to be an useful way for the formation of non-oxide ceramics coatings. Spraying with Ar/N 2 mixed gas was not effective for the fabrication of Si 3 N 4 coatings. Hydrogen addition as a reactive plasma gas improved the nitridation significantly. Si 3 N 4 content in the coatings could he controlled by changing N 2 and/or H 2 fraction in plasma gas. Hardness of the coatings obtained increased with increasing Si 3 N 4 content in the coating. Nitriding reaction of Si in reactive RF plasma spraying was promoted in the liquid phase of Si after deposited onto the substrate.

Spheroidization of glass powders for glass ionomer cements

Commercial angular glass powders were spheroidized using both the flame spraying and inductively coupled radio frequency plasma spraying techniques. Spherical powders with different particle size distributions were obtained after spheroidization. The effects of spherical glass powders on the mechanical properties of glass ionomer cements (GICs) were investigated. Results showed that the particle size distribution of the glass powders had a significant influence on the mechanical properties of GICs. Powders with a bimodal particle size distribution ensured a high packing density of glass ionomer cements, giving relatively high mechanical properties of GICs. GICs prepared by flame-spheroidized powders showed low strength values due to the loss of fine particles during flame spraying, leading to a low packing density and few metal ions reacting with polyacrylic acid to form cross-linking. GICs prepared by the nano-sized powders showed low strength because of the low bulk density of the nano-sized powders and hence low powder/liquid ratio of GICs.

成膜プロセスの新しい展開 高周波プラズマ溶射による成膜プロセス バイオセラミックスコーティングへの適用

成膜プロセスの新しい展開 高周波プラズマ溶射による成膜プロセス バイオセラミックスコーティングへの適用

Apatite/titanium composite coatings on titanium or titanium alloy by RF plasma-spraying process

To improve adhesiveness of hydroxapatite (HA) coatings to the titanium substrates, a HA/Ti composite was formed on substrates using a radio-frequency (RF) plasma spraying process. This process would reduce the residual stress caused by the large difference between the linear thermal expansion coefficient of the substrate and of HA. The HA/Ti composites were prepared by controlled feeding ratio of HA and Ti powder, with the composition of coatings becoming HA-rich toward the outer surface. Coating layers were evaluated by SEM-EDX, XRD, micro FT-IR and tensile testing. Orientation in c-axis direction of the prepared coatings was established from X-ray diffraction patterns. The adhesive (tensile) strength of HA/Ti composite coatings was approximately 50 MPa. The adhesiveness of the HA/Ti composite coatings was increased with increasing the inductive power of plasma.

Integrated fabrication process for solid oxide fuel cells using novel plasma spraying

This study was aimed at developing an integrated fabrication process for solid oxide fuel cells (SOFC) with radio-frequency plasma spraying (RFPS) and/or hybrid plasma spraying (HYPS). Fundamental studies concerning particle velocity and deformation showed that the novel plasma spraying processes were mainly characterized by their superior capability for homogeneous heating and spraying of large size powders with relatively low particle velocity, and that even the lower particle velocities in RFPS (20 m s-1) and HYPS (40-70 m s-1) compared with those in direct current plasma spraying (200 m s-1) were found to be sufficient for deformation of impinging molten particles on the substrate. However, RFPS imposed as a severe limitation on the substrate position because it led to a short flying distance for the molten particles. In this respect, HYPS was considered to be superior to RFPS.

Radio‐Frequency Plasma Spraying of Ceramics

This study was aimed at developing a novel spraying process using a radio‐frequency (rf) plasma. Experiments of Al2O3 and ZrO2–8 wt% Y2O3 spraying showed that the initial powder size was the most important parameter for depositing dense coatings. The optimum powder sizes of Al2O3 and ZrO2–8 wt% Y2O3 were considered to be around 100 and 80 μm, respectively. The use of such large‐size powders compared with those used by conventional dc plasma spraying made it possible to deposit adherent ceramics coatings of 150 to 300 μm on as‐rolled SS304 substrates. It was also shown that low particle velocity of about 10 m/s, which is peculiar to rf plasma spraying, was sufficient for particle deformation, though it imposed a severe limitation on the substrate position. These experimental results have proved that rf plasma spraying is an effective process and must be a strong candidate to open new fields of spraying applications.