Radio Frequency Thermal Plasma Treatment for Size Reduction and Spheroidization of Glass Powders Used in Ceramic Electronic Devices

Radio frequency (RF) thermal plasma treatment is studied for the size reduction and the spheroidization of coarse glass particles to change them into submicrometer-sized powders of spherical shape. Such ultra-fine spherical powders are the key ingredients of a sintering aid to achieve efficient package and high performance in ceramic electronic applications. The coarse glass powders injected into the high-temperature RF thermal plasma undergo rapid heating, melting, and evaporation, followed by quenching, and then condense to very fine spherical powders. In the thermal plasma treatment with high RF powers of 18–23 kW at a powder feeding rate of 3 g/min, the scanning electron microscopy images and the particle size distribution graphs obtained from the treated glass powders indicate that most glass powders with initial average diameters of around 2 μm are reformed into spherical ones with sizes of below 500 nm. It is also observed in a 4 MHz RF thermal plasma reactor that the maximum size of particles decreases down to 200 nm when the reactor is operated under conditions of reduced pressure, low powder feeding rate, and high RF power. The compositions of glass powders before and after the plasma treatment are compared by using the wet and the inductively coupled plasma-optical emission spectroscopy analyses. Negligible composition changes appear within a range of <2 wt% during the RF thermal plasma process, which demonstrates the successful preparation of submicrometer-sized glass powders in spherical shape applicable to the advanced ceramic electronic devices.     

Microstructural Evolution during the Sintering of TiC–Mo–Ni Cermets

TiC-Ni-Mo cermet specimens were prepared by using a mixture of fine (1.5 μm) and coarse (30 μm) TiC powders. When the fraction of fine TiC particles was 80%, a (Ti,Mo,Ni)C complex carbide phase was observed deposited on the coarse TiC particles and resulted in a typical cored structure. As the fraction of fine TiC particles decreased, the coarse TiC particles exhibited a unique microstructural evolution with the development of a concave interface. This microstructural change of the coarse TiC grains can be explained in terms of the coherency strain energy.     

Preparation of Spherical SnO2 Powders by Ultrasonic Spray Pyrolysis

Spherical SnO₂ powders were prepared from SnCl₄ aqueous solution by ultrasonic spray pyrlysis. The particle size distributions normalized by mean diameters are almost identical in spite of the variation in the concentration of the source solution. The mean diameter of SnO₂ particles increases with the concentration of the source solution and it is in the range of 0.2 to 0.8 μm. Each spherical particle is composed of many primary particles and has a solid, microporous structure.     

Hydrothermal Preparation of Calcium Hydroxyapatite Powders

Calcium hydroxyapatite powders were prepared by hydrothermal reactions of calcium pyrophosphate and calcium oxide. Primary particles of the hydroxyapatite obtained were spherical with diameters less than 0.2 μm, and small prismatic crystals were rarely observed in some fields. The effects of temperature, pressure, and soaking time on the structural features of the resultant powders were also studied by means of XRD and SEM and were smaller than expected for the ranges investigated.     

Effect of Hollow Spherical Powder Size Distribution on Porosity and Segmentation Cracks in Thermal Barrier Coatings

The effect of characteristics of hollow spherical (HOSP) powders on porosity and development of segmentation cracks in plasma-sprayed thick thermal barrier coatings (TBCs) was investigated. Three powders with particle size ranges of 20–45, 53–75, and 90–120 μm were selected from a commercial HOSP powder feedstock for spraying the TBCs. The 20–45 μm powder has a higher deposition efficiency and a greater capability of producing segmented coatings than the other larger powders. Diagnostics of in-flight particles show that the average surface temperature and velocity of the particles sprayed from the fine powder is higher by 250°C and 50 m/s compared with those sprayed from the 90 to 120 μm powder, respectively, due to its greater ratio of surface area to mass. The lower porosity of the coating sprayed from the fine powder is mainly attributed to the decreased volume of intersplat gaps and voids.     

Effect of pH on the Carbonate Incorporation into the Hydroxyapatite Prepared by an Oxidative Decomposition of Calcium–EDTA Chelate

In this study, the carbonate incorporation into the hydroxyapatite (HAp) lattice under various pH conditions was investigated. Crystalline-sodium and carbonate-containing calcium HAp (NaCO₃HAp) powders were prepared using an oxidative decomposition of calcium–EDTA chelates in a sodium phosphate solution with hydrogen peroxide. The powders obtained were characterized by X-ray diffraction, infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and elemental analysis. Depending on pH, spherical particles approximately 3.5 μm in diameter or hexagonal prismatic particles measuring 3–9 μm in length were obtained. Various characterization techniques showed that the precipitates were a single-phase NaCO₃HAp. The carbonate content and the lattice parameters of the HAp were a function of solution pH. Maximum carbonate incorporated into the HAp lattice was at pH=10, corresponding to lattice parameters of a =0.93880 nm and c =0.69070 nm. Furthermore, spectroscopic analyses indicate that the as-prepared samples are B-type carbonated HAp, in which carbonate ions occupy the phosphate sites. After heat treatment at 965°C, most of the carbonate is removed from the HAp lattice.     

Improved Strength Recovery of a Titanium Carbide/Silicon Nitride Composite from Thermal Shock Damage via Microwave Heating

Microwave processing has been used to heat treat a TiC/Si₃N₄ ceramic composite. The strength degradation from thermal shock was substantially recovered. The recovery rate was much greater with microwave heating than with conventional heat treatment at equivalent average temperature. The mechanism of strength recovery was hypothesized to be microwave radiation, which caused selective heating of TiC particles, enhanced the reaction of grain boundaries, and resulted in the sintering of microcracks around TiC particles.     

Spheroidization of borosilicate glass powder by RF induction coupled plasma

The International Simple Glass (ISG) spherical particles were prepared by Ar–H₂ radio-frequency (RF) plasma, the effect of experimental parameters on the volatilization and size distribution of spherical particles was studied. The results show that the spherical powders can be obtained by RF plasma. The spheroidized powders (112 μm) have a smaller diameter than starting particles (124 μm). The high spheroidization (98%) was achieved under low flow rate of carry gas and low feed rate. In addition, the volatilization of B₂O₃ and Na₂O are 23.48% and 56.36%, respectively. The higher feed rate and flow rate of carry gas, the lower volatilization of B₂O₃ and Na₂O and well-spheroidization rate. Meanwhile, the particle surface is not completely smooth at low flow rate of carry gas. The distribution of elements was studied by Electro-probe Microanalyzer (EPMA), which shows the distribution of element is nearly homogeneous that provides a possibility for subsequent research.     

Electrical performance of fine-grained Y-TZP/TiC composites obtained through a hydrothermal-assisted sol-gel process

Y₂O₃-stabilized tetragonal ZrO₂ polycrystal (Y-TZP) composites with various TiC contents were successfully synthesized via a modified hydrothermal-assisted sol-gel method. Fine precursor powders can be obtained with high crystallinity, nanoscale grain size and uniform morphology. SEM images of the ceramic products show that TiC particles are distributed homogeneously in the final Y-TZP matrix, and their average grain sizes are approximately 390–670 nm and 150–230 nm for the Y-TZP and TiC phases, respectively. A higher TiC volume fraction has a negative effect on the relative density and hardness but a significant positive influence on electrical conductivity. The electrical conductivity values are increased from 115 S/m to 1.23 × 10⁵ S/m with TiC contents varying, demonstrating that the percolation threshold is approximately as low as 11.6 vol% for the samples, which is much lower than those of previous Y-TZP/TiC ceramics. The high electrical performance is probably due to the high D (the diameters of the insulating particles)/d (the diameters of conductive particles) ratio and submicron-sized grains.     

Preparation of Monodisperse ZrO2 by the Microwave Heating of Zirconyl Chloride Solutions

Based on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2-PrOH-water mixture as the solvent. The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate. The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring. The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 μm.     

Low temperature synthesis of Titanium diboride by carbothermal method

Titanium diboride powders have been synthesized by means of carbothermal reduction method utilizing Titanium oxide, Boric acid and Graphite. The effect of mechanical activation of mixed raw materials and the use of additional Boric acid on the final phases have been studied. The resultant powders were characterized by X-ray diffraction (XRD) analyzer and Field Emission Scanning Electron Microscope (FESEM). XRD patterns showed that TiB₂, TiC and C phases after heat treatment at stoichiometric ratio of reactants. By increasing the milling time, the unwanted phases such as C and TiC will be reduced. Pure TiB₂ could be synthesized with mechanical activation of raw materials for 24?h at non-stoichiometric ratio (using additional Boric acid) and heat treatment at low temperature of 1380?°C. In this condition, Titanium diboride could be achieved with residual carbon of 0.92 0.09wt% and mean average particle size of 3.28µm. Thermal analysis (TGA-DTA) was used to determine the reaction progress and mechanism. Results revealed that the intermediate phase, TiBO₃, played an important role in getting to lower temperature synthesis. This phase was identified after mechanical milling of raw materials and heat treatment at temperature of 1250?°C.     

Characteristics and Formation Mechanism of BaTiO3 Powders Prepared by Twin-Fluid and Ultrasonic Spray-Pyrolysis Methods

Spherical fine (micrometer and submicrometer in size) homogeneous BaTiO₃ powders were synthesized from ethanol: water solutions of BaCl₂ and TiCl₄ using the spray-pyrolysis technique. Two different atomizers—twin-fluid and ultrasonic, with a resonant frequency of 2.5 × 10⁶ Hz—were used for mist generation. Hollow spherical particles containing a certain amount of unreacted BaCl₂ phase and having a mean particle diameter of 2.5 μm were obtained at 1173 K using a twin-fluid atomizing system. Decomposition of precursors and their transition to the cubic BaTiO₃ phase occurred, even at 973 K in the case of the ultrasonic atomizing system. For the initial droplet size of 2.2 μm and residence time of ∼60 s, spherical BaTiO₃ particles with the mean particle diameter of 0.53 μm were obtained. A BaTiO₃ formation mechanism has been proposed as a reaction between TiO₂ and BaCl₂ rather than a reaction of oxides.     

Morphological evolution of TiC particles with different stoichiometries by hydrofluoric acid etching treatment

The effects of hydrofluoric acid (HF) etching time on the morphology of the titanium carbide (TiC) particles with different stoichiometries were investigated. TiC particles with two C/Ti molar ratios of 0.5 and 1.0 were prepared by mechanical alloying. Then, the powders were immersed in the HF solution for different times of 48, 96, and 142 h. Results showed that the morphology of TiC particles greatly changed after HF etching. In general, a roughing phenomenon was observed as a function of the immersion time in the HF solution. The irregular shape of the TiC particles changed to the spherical shapes by increasing the HF etching time. However, the changing tendency of TiC particles with different stoichiometries was different. The shape of prepared powders with a C/Ti molar ratio of 1.0 was polyhedron at the initial stages of HF treatment, while the shape of prepared powders with a C/Ti molar ratio of 0.5 was near-spherical. However, with increasing the immersion time, the shape of both samples changed to a spherical one. The degree of roughing phenomenon of the prepared powders with a C/Ti molar ratio of 0.5 was lower than that of the prepared powders with a C/Ti molar ratio of 1.0.     

Dense Alumina–Zirconia Coatings Using the Solution Precursor Plasma Spray Process

For the first time, dense coatings have been made by the solution precursor plasma spray (SPPS) process. The conditions are described for the deposition of dense Al₂O₃–40 wt% 7YSZ (yttria-stabilized zirconia) coatings; the coatings are characterized and their thermal stability is evaluated. X-ray diffraction analysis shows that the as-sprayed coating is composed of α-Al₂O₃ and tetragonal ZrO₂ phases with grain sizes of 72 and 56 nm, respectively. The as-sprayed coating has a 95.6% density and consists of ultrafine splats (1–5 μm) and unmelted spherical particles (<0.5 μm). The lamellar structure, typical of conventional plasma-sprayed coatings, is absent at the same scale in the SPPS coating. The formation of a dense Al₂O₃–40 wt% 7YSZ coating is favored by the lower melting point of the eutectic composition, and resultant superheating of the molten particles. Phase and microstructural thermal stabilities were investigated by heat treatment of the as-sprayed coating at temperatures of 1000°–1500°C. No phase transformation occurs, and the grain size is still in the nanometer range after the 1500°C exposure for 2 h. The coating hardness increases from 11.8 GPa in the as-coated condition to 15.8 GPa following 1500°C exposure due to a decrease in coating porosity.     

Thermal Softening Behavior and Application to Transparent Thick Films of Poly(benzylsilsesquioxane) Particles Prepared by the Sol–Gel Process

Thick films of poly(benzylsilsesquioxane) (BnSiO_3/2) particles, prepared by the sol–gel process, were deposited onto indium-tin-oxide-coated glass substrates by electrophoresis for the application to the micropatterning of the films. BnSiO_3/2 particles were thermally softened and sintered at ∼50°C, which was above the glass transition temperature of the particles. The films prepared by the electrophoretic sol–gel deposition consisted of aggregates of particles with diameters of 0.2–1 μm and were opaque. The film shrank from 2.5 μm to 1.4 μm in thickness and became transparent upon sintering of the particles during heat treatment at temperatures >100°C.     

Carbon nanotube/titanium carbide sol-gel coated zirconium diboride composites prepared by spark plasma sintering

With combination of a powder processing technique and a sol-gel process, carbon nanotube/titanium carbide coated zirconium diboride matrix composite was fabricated. Zirconium diboride (ZrB₂) powders were coated with a functionalized carbon nanotubes (CNTs) mixed titanium carbide (TiC) sol-gel precursor. As the results suggests, the carbothermal reduction produced nanosized TiC grains at the surface of the ZrB₂ particles with a homogenous distribution of CNTs. The densification of the CNT/TiC coated ZrB₂ matrix composite was achieved via 1900?°C spark plasma sintering(SPS). The TiC grains and the CNTs were primarily concentrated in the grain boundaries of the ZrB₂ and showed the pinning effects that restrained the growth of ZrB₂ grain. The TiC grain diffusion in the sintering coarsened the grains from nanosizes to 1–2?µm, which improved the densification of the ZrB₂. Due to the difference in coefficient of thermal expansion, CNTs bridged the gaps between the TiC and the ZrB₂ matrix, which formed a weak-bonding interface. The major toughening mechanism found was crack deflection via the TiC grains on the ZrB₂ matrix.     

Synthesis of Submicrometer Titanium Carbide Powders

A novel synthesis process, based on a carbothermal reduction of titania, has been developed for producing high–purity, submicrometer, and nonagglomerated titanium carbide powders. The process utilizes a carbothermic reduction reaction of novel coated precursor powders that has potential as a high–quality (submicrometer and high–purity) powder synthesis route. The precursor is derived from a titania (TiO₂) and a hydrocarbon (C₃H₆) gas and provides high contact area between the reactants. This yields a better distribution of carbon within the titania and inhibits the agglomeration among the titania particles, resulting in a more complete reaction and a purer product at a comparatively low temperature. The TiC powders produced at 1550°C for 4 h under argon gas flow have oxygen content of 0.6 wt% and total carbon content of 22.9 wt%, a very fine particle size (,0.1μm) (surface area of about 20 m²/g), uniform shape, and loose agglomeration.     

Leaching Behavior of Sodium from Fine Particles of Soda–Lime–Silicate Glass in Acid Solution

The leaching behavior of Na from soda–lime–silicate glass was investigated by preparing glass powders with average particle diameters of 53 and 19 μm, and leaching in HNO₃ at 90°−140°C. A new theoretical equation for Na leaching from a spherical particle is proposed based on the assumption that a rate-determining process is the three-dimensional self-diffusion of Na in glass. The diffusion constant ( D ) of Na in glass was obtained by fitting the experimental data to a theoretical equation. The values of D and activation energy obtained are comparable to those obtained in other studies on larger particles.     

Facile synthesis of high-melting point spherical TiC and TiN powders at low temperature

Preparation of high melting point sphere is of great practical value and remains a great challenge. Herein, for the first time a delicate chemical vapor deposition (CVD) process was developed for fabricating spherical TiN and TiC powders, which can hardly be attainable by conventional processes. The big equilibrium constant and released heats are key parameters for obtaining spherical TiN and TiC powders by the CVD process. Sphericity and crystallinity of these spherical powders can be controlled by adjusting nucleation and growth. The optimal TiN spheres (diameter 0.46 μm, sphericity 0.89) and TiC spheres (diameter 0.52 μm, sphericity 0.87) were obtained at 850°C under N₂ and H₂ and CH₄, respectively. The design ideas explore a novel way to fabricate high melting point spheres.