Effect of particle size on densification of pure magnesium during spark plasma sintering

The effect of particles size ranges (<38 μm, 75–150 μm, 270–550 μm) of atomized magnesium powders on densification mechanisms during spark plasma sintering (SPS) process was investigated. The intrinsic driving force, local pressure and current of Mg powders with different particle sizes were analyzed by theoretical calculation. The results obviously indicate that the densification of pure magnesium can be improved by the reduction of particle size, suggesting the intrinsic driving force, local pressure and current intensity are enhanced significantly by a decrease in the particle size at the same sintering conditions, which can promote shrinkage of pores, formation of the sintering neck and mass transportation in the SPS process. Not only that, rapid densification is also interpreted in term of mechanical movement of particles, Joule heating effect and plastic deformation. However, the mechanical movement of the large particles is higher than that of small particles due to high punch displacement, and plastic deformation, detected by scanning electron microscopy, plays a main role in densification for large particles in the case during the sintering. Joule heating effect is the key factor for densification of small Mg particles, and high densification degree can be obtained by sintering small particles.     

载体炭与Pt催化剂之间的相互作用及其引起的尺寸效应(英文)

通过乙二醇还原,在VulcanXC-72炭黑上负载了三种具有不同平均粒径(1.7nm,3.0nm和5.0nm)的Pt催化剂。利用透射电子显微镜,研究了载体炭黑表面的微孔与Pt催化剂之间的几何相互作用。结果表明:尺寸较小的Pt颗粒(平均粒径为1.7nm)通常被包含在载体表面的微孔中,表现为被一薄碳层所覆盖并嵌入炭黑基体。而尺寸较大的Pt颗粒(平均粒径为3.0nm和5.0nm)则不存在这种现象,往往显示出裸露的清洁表面。这种与载体表面微孔的不同相互作用引起了Pt颗粒在电化学活性比表面上的反常尺寸效应,进而影响了其催化甲醇氧化的质量比活性。     

磁粉表面改性及粒度对注射成形粘结NdFeB磁体性能的影响

注射成形粘结NdFeB磁体满足了市场时磁体小型化、轻型化及高性能化的要求,因而有着广泛的应用前景。本文研究了磁粉特性对注射成形粘结磁体性能的影响,结果表明：采用硅烷对磁粉进行表面改性,能有效提高NdFeB磁粉的抗氧化性及相应粘结磁体的磁学及力学性能;同时NdFeB磁粉粒径太粗太细均不利于磁体性能的提高 其最佳粒径范围是60～100μm。     

Effects of intrinsic properties,particle size and specific surface area on WOP and spontaneous combustion susceptibility of coal

This study examines the effects of intrinsic properties, particle size, and specific surface area (SSA) of coal on spontaneous combustion. Moreover, it analyzes the underlying mechanism of spontaneous combustion from particle size, SSA and gas adsorption perspectives. The susceptibility of coal to spontaneous combustion is studied by wet-oxidation potential (WOP) method. Coal residues left after the WOP experiment are analyzed for change in structural and compositional behaviour. The study revealed an inverse relationship between the particle size and SSA of coal. Spontaneous combustion susceptibility increased with increase in volatile matter and decreased with increase in fixed carbon content of coal. The optimum moisture content of coal resulting maximum spontaneous combustion tendency is determined 6%. Decrease in particle size and increase in SSA augmented the spontaneous combustion propensity of coal. With decrease in coal particle size from 425 to 850 to < 38 µm, the mean D₅₀ value decreased by 27 times, the mean SSA increased by 42 times and coal spontaneous combustion susceptibility increased almost by 2 times. Critical coal particle size is determined 38–74 µm (D₅₀ = 50.56 µm), below which no appreciable change in oxidation rate is observed. Moreover, two models are developed to predict the spontaneous combustion susceptibility of coal based on particle size (D₅₀) and SSA.     

The role of particle size on the performance of pumice as a supplementary cementitious material

A critical area overlooked in previous research on pumice is understanding how its physical characteristics influence its behavior as a supplementary cementitious material (SCM). This study investigated three pumices with different particle size distributions to observe whether these porous materials exhibit enhanced nucleation and growth of hydration products, in the same way as non-porous materials, and whether the rate of pozzolanic reaction can be changed through particle size. The effect of particle size on compressive strength, rheology and resistance to alkali silica reaction (ASR) was also evaluated. Results showed that reducing particle size increased the rates of cement hydration, pozzolanic reaction, and compressive strength gain, while also increasing mixture viscosity. Interestingly, particle size did not impact the yield stress of the mixture or the resistance to ASR. These new findings give insight about how the particle size of pumice can be used to overcome drawbacks reported in previous literature.     

The influence of drug solubility and particle size on the pellet formulation in a rotoprocessor

Pellets containing drugs of different properties were prepared in a Rotoprocessor in order to study changes in the formulation process and resulting pellet characteristics. Diltiazem hydrochloride, diclofenac sodium, and theophylline were chosen as model drugs. Pellet size distribution, sphericity, density, hardness, friability, and repose angle were determined using standard methods. The amount of water as a wetting agent necessary for successful pellet formulation was observed for each sample and changed depending on drug solubility, concentration, and particle size. The pelletization of freely soluble diltiazem hydrochloride required 24.8-23.1% of the wetting agent and its amount decreased as the drug concentration increased. The demand for water in the formulation of theophylline pellets was 31.0-34.4% and it increased with increasing drug concentration. The pellet samples containing both drugs were easy to prepare. However, the cohesion of micronized diclofenac sodium particles negatively influenced both the pellet size distribution and the formulation process itself. When the drug concentration exceeded 40%, it was not possible to produce pellets of an appropriate size and the process was not reproducible.     

Influence of the valve lubricant on the aerodynamic particle size of a metered dose inhaler

Presented in this work are the results of a study designed to investigate the impact of valve lubricant (i.e., silicone oil) on the aerodynamic particle size distribution (PSD) of a steroid suspension metered dose inhaler (MDI) containing propellant HFA-227. The objective of this study was to explore whether the valve lubricant, which is often used in MDI products to prevent valve sticking, can enter an MDI product and potentially impact the aerosol spray dynamics. The results of this work have shown that samples containing valves with high silicone levels produced a larger aerodynamic particle size (by cascade impaction) than samples with low-silicone or silicone-free valves. It is postulated that the presence of silicone in the product may increase the propensity for drug aggregation, thereby leading to an increase in the aerodynamic particle size of the emitted aerosol. These findings stress the importance of evaluating the effects of valve lubricant on the aerodynamic PSD in the early formulation development stage of an MDI.     

Influence of the metering chamber volume and actuator design on the aerodynamic particle size of a metered dose inhaler

Presented in this work are the results of a study designed to investigate the impact of the valve metering chamber volume and actuator design on the aerodynamic particle size distribution (PSD) of a suspension metered dose inhaler (MDI) containing propellant HFA-227. It was hypothesized that the valve metering volume and the actuator design in the MDI could influence the PSD of the emitted dose since it would affect the aerosol spray dynamics. The PSD results from this study, measured using cascade impaction, revealed that samples containing an actuator intended for oral delivery (rectangular mouthpiece and orifice diameter of ≈0.5 mm) produced a higher fine particle dose (FPD) than those containing an actuator intended for nasal delivery (circular nosetip and orifice diameter of ≈1 mm). In addition, the drug PSD profile was shown to be more sensitive to differences in the particle size of the suspended material when the oral actuator was used compared to when the nasal actuator was used. The valve metering chamber (25 vs. 63 μL volume) did not appear to have a major effect on the product aerodynamic PSD or the droplet size. These results demonstrate the importance of actuator design and orifice size in determining the aerodynamic PSD of an MDI.     

Influence of the storage orientation on the aerodynamic particle size of a suspension metered dose inhaler containing propellant HFA-227

Presented in this work are the results of a study designed to investigate the impact of the storage position on the particle size distribution (PSD) of a steroid suspension metered dose inhaler (MDI) containing propellant HFA-227. It was hypothesized that the orientation of MDI samples upon storage could influence the PSD of the emitted dose, since it determines the amount of contact the liquid formulation has with the valve and therefore the quantity of nonvolatile leachable materials from the valve components that may enter the product and potentially impact the aerosol spray dynamics. Samples stored in the valve down orientation (i.e., complete contact of the liquid formulation with the valve) showed a higher level of leachables compared to those samples stored valve up (i.e., minimal contact of the formulation with the valve). The valve down samples were found to produce larger particles in the emitted aerosol spray using both cascade impaction, the preferred method of regulatory submission, as well as laser diffraction. It was postulated that the larger particle size of the inverted samples was attributed to its higher levels of leachables. Based on our findings, it is recommended that in order to set appropriate controls on the product PSD, the storage orientation of the product will need to be considered.     

Influence of particle size of the dispersoid on compressibility and sinterability of TiO2 dispersed Al 7075 alloy composites prepared by mechanical milling

Particulate TiO₂ (with varying particle size produced by mechanical milling) dispersed AA7075 composites are synthesised by short duration milling (10 min) followed by room temperature unidirectional compaction (with varying pressure) and sintering. Apparent and relative density of the alloy powder and composites are measured. The effect of reinforcement particle size on the compressibility behaviour of the composites is demonstrated. Mechanically milled (for 25 h) alloy powder shows lower relative density than coarse alloy powder. In addition, compressibility of the alloy composites decreases with decreasing particle size of the reinforcement. In contrast, the sinterability of the composites increases with decreasing dispersoid’s size due to easy filling up of finer pores and particle induced precipitation.     

Effect of anodization time on the growth of twinned pyramid crystals of bismite from polyhedral bismuth particle by facile electrolysis-based oxidation

Nanostructured bismite films were fabricated by both thermal oxidation and electrochemical anodization of Bi film in NaOH aqueous electrolyte. Pure phase of α-bismite was obtained by the thermal oxidation technique. Pure-phase α and β bismites were successfully prepared by varying the anodization time. Truncated polyhedral aggregates of bismuth particles were converted to twinned pyramids particles having nanoscale tips with increase in anodization time. The crystallite size increased with anodization time from 43?nm to 79?nm. The band gap value lowered from 2.835(2) eV to 2.422(1) eV with anodization time and this is in agreement with the increase in crystallite size obtained from XRD. The shift in the absorption edge to higher wavelength with anodization time was attributed to the smoothening of surface and grain growth.     

Influence of prepared plasma on THz emission from the plasma induced by ultrashort lasers: a quasi-analytical investigation

The influence of prepared plasma induced by a prepulse on the THz emission generated by main two-color femtosecond lasers (fs-lasers) has been investigated numerically and analytically by using a photocurrent model. Results observed in a previous report, such as the suppression of THz emission from the main pulse due to the existence of a prepulse, were easily reproduced. Further calculation showed that such suppression originates from residual electrons of the prepared plasma affecting the main pulse. Moreover, an exact expression between the E-field of THz waves generated by the main pulse and the residual electron density of the prepared plasma has been obtained.     

Atomic-level insights into the modification mechanism of Fe (III) ion on smithsonite (1 0 1) surface from DFT calculation

Fe(III) ion can strongly inhibit the sulphidation amine flotation of smithsonite. However, its modification mechanism on smithsonite surface is still obscure. In this work, a systematic study of the modification of Fe(III) ion on smithsonite (1 0 1) surface was performed using DFT calculation. The optimal number of H₂O ligands for Fe(III) ion hydrates in aqueous conditions was probed, and [Fe(OH)₂(H₂O)₄]⁺ and [Fe(OH)₄]^? were identified as the major modification species, then their adsorption and bonding mechanisms were further revealed by analyzing the frontier orbitals, density of state, Mulliken population, and electron density. The calculated adsorption structures were consistent with the former experiment, and we found the O site that bonded to the C atom on smithsonite surface was the most favorable position for [Fe(OH)₂(H₂O)₄]⁺ and [Fe(OH)₄]^? adsorptions. Besides, their adsorption mechanisms on smithsonite surface were principally due to the combined effect of FeO bond and hydrogen bonding. Simultaneously, hydrogen bonding greatly enhanced the stability of the adsorption structures. Moreover, the dominant orbital contribution for the bonding of FeO was primarily due to the orbital hybridization between Fe 3d and O 2p orbitals. This work can help in deeper understanding of the depression of Fe(III) ion on the sulphidation amine flotation of smithsonite.     

The control of paracetamol particle size and surface morphology through crystallisation in a spray dryer

The parameters governing the crystallisation of paracetamol using various conventional techniques has been extensively studied, however the factors influencing the drug crystallisation using spray drying is not as well understood. The aim of this work was to investigate the crystallisation of an active pharmaceutical ingredient through evaporative crystallisation using a spray dryer to study the physicochemical properties of the drug and to use semi-empirical equations to gain insight into the morphology and particle size of the dried powder. Paracetamol solutions were spray dried at various inlet temperatures ranging from 60 °C to 120 °C and also from a series of inlet feed solvent compositions ranging from 50/50% v/v ethanol/water to 100% ethanol and solid-state characterisation was done. The size and morphology of the dried materials were altered with a change in spray drying parameters, with an increase in inlet temperature leading to an increase in particle Sauter mean diameter (from 3.0 to 4.4 µm) and a decrease in the particle size with an increase in ethanol concentration in the feed (from 4.6 to 4.4 µm) as a result of changes in particle density and atomised droplet size. The morphology of the dried particles consisted of agglomerates of individual crystallites bound together into larger semi-spherical agglomerates with a higher tendency for particles having crystalline ridges to form at higher ethanol concentrations of the feed.