Powder technology

... Moussa et al. [15] investigated potential benefits of sound in speeding up fluidized bed combustion. ... Z Chem. Eng, 65 (1987) 536. [4] S. Mori, A. Yamamoto, S. lwata, T. Haruta, I. Yamada and E. Mizutani, AIChE Syrup. Ser., 86 (276) (1990) 88. ...

Mechanical alloying has been widely utilized to break down the clustered CNTs for incorporation in the metal matrix composites. However, the breakage of CNTs during the ball milling process degrades their effectiveness. Due to the challenges in collecting the CNTs for measurement, quantitative study of CNT breakage has been difficult. In this study, the CNTs with Al6061 powder were mechanically alloyed with high energy milling equipment. The CNTs from the surface of mechanically alloyed particles were collected and measured. Due to the difficulty in obtaining the CNTs embedded inside the particles, a mathematical model has been developed to predict the overall CNT length distribution in the composite. Significant CNT breakage occurred during the initial phase of the mechanical alloying due to the crushing of the clusters. The model predicted that no further change occurred in the overall CNT length during time greater than 1 h of mechanical alloying because most of the CNTs had already become embedded within the particles and were thus protected from further milling media impacts. A faster dispersion of CNTs and lower particle fracturing rate may help preserve the original CNTs.

Triboelectric charge accumulation both poses problems and offers opportunities for dry particulate processing. It generates hazards in many industrial systems, but is exploited in several important applications, including electrophotographic toner charging and triboelectric separation. However, the charging of continuous particulate flows on solid surfaces is poorly understood, and design of devices to optimise triboelectric behaviour is often qualitative or based on trial and error. This study attempts to identify the main charging mechanisms for a continuous particulate flow on a flat surface. The proposed charging models incorporate contact time, velocity and mode of contact. A model incorporating contact area effects arising from sliding and rolling contact is consistent with experimental data, as long as a charge limit is imposed on bouncing particles. A mechanism for this charge limit, involving separation discharge, is proposed. The effect of delocalised image charge on the system is estimated and found to be negligible. Some general design principles are proposed for triboelectric optimisation of particle processing devices.Triboelectrification produces hazards and offers opportunities for dry particle processing. Charging mechanisms for a continuous particulate flow on a flat surface are identified and modelled, for sliding, rolling and bouncing contact. These models are then validated using existing experimental data. Some general design principles are proposed for triboelectric optimisation of particle processing devices.

The objective of this work was to investigate the mechanism of very fine grinding in a wet ball mill as a function of process parameters, i.e. rotation speed of the mill and grinding medium bead size. The ball mill used was a Dynomill and the grinding medium consisted of zirconium oxide beads. The product is a poorly water-soluble organic compound.

The effect of binder properties on torque curves, granule growth kinetics, wet mass consistency and dry granule strength has been investigated in this study. Granulation runs have been performed on a fine cohesive microcrystalline cellulose powder (Avicel 105, d50=20μm) in two types of laboratory high shear mixers: a Mi-Pro high shear mixer using a 1.9L bowl and a 6L Diosna

A consolidating product based on nanoparticles of slaked lime (Ca(OH)2) dispersed in isopropyl alcohol was exposed under different relative humidities (RH), 33%, 54%, 75% and 90% during 7, 14, 21 and 28 days. The characterization of the calcium hydroxide nanoparticles and the formed calcium carbonate polymorphs have been performed by Micro Raman spectroscopy, Transmission Electron Microscopy (TEM), Environmental Scanning Electron Microscopy (ESEM) with Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). Precipitation and transformation of calcium carbonate polymorphs strongly depend on the relative humidity (RH). Higher RH (75%–90% RH) gives rise to amorphous calcium carbonate and monohydrocalcite, calcite, aragonite and vaterite, faster carbonation and larger particles sizes with higher crystallinity compared to lower RH (33%–54% RH) that gives rise mainly to portlandite and vaterite, slower carbonation and smaller particle sizes with lower crystallinity.Ca(OH)2 nanoparticles dispersed in isopropyl alcohol exposed under different relative humidities (RH) 7, 14, 21 and 28 days. Higher RH (75%–90% RH): faster carbonation (amorphous CaCO3, CaCO3·H2O, calcite, aragonite and vaterite) and larger particles sizes with higher crystallinity. Lower RH (33%–54% RH): mainly portlandite (Ca(OH)2) and vaterite with smaller particle sizes and lower crystallinity.

Bioactive glasses have attracted considerable interest in recent years, due to their technological application, especially in biomaterials research. Differential scanning calorimetry (DSC) has been used in the study of the crystallization mechanism in the SiO2–Na2O–CaO–P2O5 glass system, as a function of particle size. The curve of the bulk glass presents a slightly asymmetric crystallization peak that could be deconvoluted into two separate peaks, their separation being followed in the form of powder glasses. Also, a shift of the crystallization peaks to lower temperatures was observed with the decrease of the particle size. FTIR studies – that are confirmed by XRD measurements – proved that the different peaks could be attributed to different crystallization mechanisms. Moreover, it is presented the bioactive behavior of the specific glass as a function of particle size. The study of bioactivity is performed through the process of its immersion in simulated human blood plasma (simulated body fluid, SBF) and the subsequent examination of the development of carbonate-containing hydroxyapatite layer on the surface of the particles. The bioactive response is improved with the increase of the particle size of powders up to 80 μm and remains almost unchanged for further increase, following the specific surface to volume ratio decrease.