GRAIN GROWTH AND DENSIFICATION IN PALLADIUM OXIDE PARTICLES DURING SPRAY PYROLYSIS

A model for aerosol-phase densification of particles during their synthesis by spray pyrolysis is presented. The model was used to describe the evolution of the specific surface area of PdO powders synthesized at temperatures between 400 to 800 °C (residence times 27.9 to 22.7 s). Surface areas and grain sizes ranged between 56 m²/g and 4 nm at 400 °C to 3.2 m²/g and 40 nm at 800 °C The characteristic coalescence lime was determined as: τ= 1.7 x 10¹³T d³ exp(1.3 x 10⁵/RT) [for lattice diffusion] and t = 2.7 x 10¹⁹Td⁴exp (1.6 x 10⁵/RT) [for grain boundary diffusion] (τ is in seconds, Tin degrees Kelvin, R is 8.314J/(mol.K)and d is in meters), but the data and model did not allow identification of the specific mechanism. The model provides a general approach for correlating changes in particle surface area with reactor operating conditions that is applicable to a wide variety of materials.     

Effect of piezo-driven injection system on the macroscopic and microscopic atomization characteristics of diesel fuel spray

This study was conducted to determine the macroscopic and fuel atomization characteristics of a piezo-driven injection system and to compare it with a solenoid-driven injection system in a common-rail diesel engine.In order to obtain the macroscopic characteristics of fuel spray, the spray development process was visualized using the spray visualization system composed of a Nd:YAG laser and an ICCD camera. The injection characteristics of the fuel spray such as injection rate and injection delay profile were investigated under the various injection conditions. The injection and atomization characteristics were investigated in terms of the droplet mean axial and radial velocities, droplet diameter, and droplet distributions obtained using a phase Doppler particle analyzer (PDPA) system.It was found that the piezo-driven injection system has a short injection delay and quickly reaches the maximum injection rate compared to the solenoid-driven injection system. Spray tip penetration makes little difference; however, the spray cone angle of the piezo-driven injector is larger than that of the solenoid-driven injector. The atomization performance of the piezo-driven injection system is superior to that of the solenoid-driven injection system due to a faster response time and higher injection rate.     

Gradually varying mechanical properties of in situ synthesized NbC–Fe-graded composite coating

NbC–Fe-graded composite coating was fabricated by in situ synthesis using a pure niobium plate and grey cast iron as the raw materials. SEM analysis demonstrates that the thickness of coating is about 400?μm. From the surface to the matrix, the volume fraction of NbC particulates continuously decreases from 95 to 0%, while the average particulate diameter gradually increases from 200?nm to 1?μm. Along the depth towards the matrix, the nano-hardness and elastic modulus of the graded coating decrease from 23.5 to 3?GPa and from 435 to 150?GPa, respectively. In addition, the fracture toughness (K_C) of 8.62?MPa?m^1/2 is obtained on the surface of the coating by the Vickers indentation technique. And the fracture mechanism is intergranular cracking.     

Design and Fabrication of Ceramic Catalytic Membrane Reactors for Green Chemical Engineering Applications

Catalytic membrane reactors (CMRs), which synergistically carry out separations and reactions, are expected to become a green and sustainable technology in chemical engineering. The use of ceramic membranes in CMRs is being widely considered because it permits reactions and separations to be carried out under harsh conditions in terms of both temperature and the chemical environment. This article presents the two most important types of CMRs: those based on dense mixed-conducting membranes for gas separation, and those based on porous ceramic membranes for heterogeneous catalytic processes. New developments in and innovative uses of both types of CMRs over the last decade are presented, along with an overview of our recent work in this field. Membrane reactor design, fabrication, and applications related to energy and environmental areas are highlighted. First, the configuration of membranes and membrane reactors are introduced for each of type of membrane reactor. Next, taking typical catalytic reactions as model systems, the design and optimization of CMRs are illustrated. Finally, challenges and difficulties in the process of industrializing the two types of CMRs are addressed, and a view of the future is outlined.     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

Effect of heating conditions on the magnetic properties of micron-sized carboxyl modified-magnetite particles synthesized by a spray pyrolysis and heating process

Superparamagnetic carboxyl (COOH) modified-magnetite (Fe₃O₄) (COOH-Fe₃O₄) micrometer-sized porous particles were synthesized by the spray pyrolysis of a 0.1 M Fe(NO₃)₃·9H₂O and 0.2 M citric acid solution and a subsequent heating process in either an Ar + 1% H₂ (P_O2 = 10^?20 Pa) or N₂ (P_O2 = 1 Pa) gas atmosphere. Fe₃O₄ formed due to carbon and hydrogen gas generation of thermal decomposition of citric acid, even under reduction conditions with a P_O2 below 10^?23 Pa. The COOH-Fe₃O₄ particles heated in an Ar + 1% H₂ or N₂ atmosphere were porous (40% porosity) and about 1.2 to 1.3 μm in diameter. The particles consist of nano-sized COOH-Fe₃O₄ crystallite about 7 nm in diameter. The specific surface area increased from 116 to 127 m²/g by increasing the heating time in an Ar + 1% H₂ atmosphere from 10 to 20 h. The saturation magnetization of the COOH-Fe₃O₄ particles (38.7 A·m²/kg) heated in Ar + 1% H₂ for 10 h was much higher than that of commercial magnetic microbeads (17 A·m²/kg) and the coercivity was 0 kA/m. These superparamagnetic COOH-Fe₃O₄ particles dispersed in distilled water were attracted to a NdFeB magnet for 7–10 s under a 400 Mt external magnetic field, compared with 10 s for commercial magnetic microbeads.     

Spray granulation of Fe and C nanoparticles and their impedance match for microwave absorption

The microwave absorbents of Fe and C nanoparticles as magnetic loss and dielectric loss material respectively were composited with the polyvinyl alcohol(PVA) as binder by spray granulation method. The electromagnetic parameters of Fe and C composite particles were analyzed by vector network. The complex permittivity and magnetic permeability of Fe and C composite particles matched well with increasing C nanoparticle content, and then the microwave loss property was improved. A minimum reflection loss(RL) of -42.7 d B at 3.68 GHz for a composite with 4.6 mm in thickness can be obtained when the content ratio of the C nanoparticles, the modified Fe nanoparticles and the PVA is 21:49:30(Sample 3).     

Preparation of aluminum nitride granules by a two-step heat treatment method

The sintered aluminum nitride granules were prepared in a continuous process through a two-step heat treatment at 1600?°C for 5?h and 1850?°C for 5?h using the spherical γ-alumina/phenol-resin precursor obtained by spray granulation as the starting material. In the first step of heat treatment, the alumina powders were nitrided to form porous aluminum nitride granules via a carbothermal reduction reaction and then were continuously heated in the second step of heat treatment to produce dense spherical aluminum nitride granules without using sintering aids. The obtained porous and sintered aluminum nitride granules were characterized by XRD, SEM and BET measurements and exhibited an average grain size of about 1 and 3?µm, respectively. Furthermore, the specific surface area of the obtained porous and sintered aluminum nitride granules dramatically decreased from 2.49 to 0.16?m²/g showing that the low-porosity, dense, polycrystalline aluminum nitride granules were successfully prepared.     

Characteristics of piroxicam granules prepared by fluidized bed hot melt granulation

The aim of this study was to investigate the granulation of piroxicam by fluidized bed hot melt method using polyethylene glycol 4000 as the hydrophilic carrier and spray dried lactose as the fluidizing substrate. The effects of the spray nozzle air flow rate, axial position of the spray nozzle and load of fluidizing substrate on granules properties were investigated using a Box Behnken factorial design. The dependent variables evaluated were the mean particle size distribution, drug content and flow properties of the granules. The granule sizes ranged from 453.5?µm to 894.7?µm and piroxicam content was above 83.2%. However, the response surface ANOVA showed that sizes and piroxicam content were not affected by the granulation conditions and microscopy evidenced the presence of piroxicam crystals on granules surface. On the other hand, ANOVA showed that the granules flow properties were affected at the significance level of 5%. Thermal and infrared analysis showed that there was no interaction of piroxicam with carriers during the process. The dissolution profile of piroxicam was remarkably improved. Therefore, the results confirm the high potential of the fluidized bed hot melt granulation technique to obtain granules with enhanced drug solubility and release rates.     

Impact of polymers on the aggregation of wet-milled itraconazole particles and their dissolution from spray-dried nanocomposites

We explore the impact of various polymers and their molecular weight on the stabilization of wet-milled suspensions of itraconazole (ITZ), a poorly soluble drug, and its dissolution from spray-dried suspensions. To this end, ITZ suspensions with SSL, SL, and L grades of hydroxypropyl cellulose (HPC) having molecular weights (MWs) of 40, 100, and 140?kg/mol, respectively, hydroxypropyl methyl cellulose (HPMC E3 with 10?kg/mol), polyvinylpyrrolidone (PVP K30 with 50?kg/mol), sodium dodecyl sulfate (SDS, surfactant), and HPC SL–SDS were wet media milled and spray-dried. Laser diffraction results show that 2.5% HPC SL–0.2% SDS led to the finest ITZ nanosuspension, whereas without SDS, only 4.5% HPC with SL/L grades ensured minimal aggregation. Rheological characterization reveals that aggregated suspensions exhibited pronounced pseudoplasticity, whereas stable suspensions exhibited near Newtonian behavior. Spray-drying yielded nanocomposites with 60–78% mean ITZ loading and acceptable content uniformity. Severe aggregation occurred during milling/drying when 4.5% polymers with MW?≤?50?kg/mol were used; their nanocomposites exhibited incomplete redispersion due to slow matrix erosion and released ITZ slowly during dissolution test. Overall, high drug-loaded, surfactant-free ITZ nanocomposites that exhibited immediate release (>80% dissolved in 20?min) were prepared via spray-drying of wet-milled ITZ with 4.5% HPC SL/L.