•The same CCC was gained at M(CTAB)=0.1mmolL−1 for different 30R50 concentrations.•More than 95.7% of turbidity can be removed for 30R50 0.15% with CTAB 0.1mmolL−1.•The “hydrophobic effect” plays an ...important role in aggregation of 30R25.•The results show different agglomeration mechanisms.
Nanoparticles will inevitably be found in industrial and domestic wastes in the near future and as a consequence soon in water resources. Due to their ultra-small size, nanoparticles may not only have new hazards for environment and human health, but also cause low separation efficiency by classical water treatments processes. Thus, it would be an important challenge to develop a specific treatment with suitable additives for recovery of nanoparticles from waters. For this propose, this paper presents aggregation of silica nanoparticles (Klebosol 30R50 (75nm) and 30R25 (30nm)) by cationic surfactant cetyltrimethylammonium bromide (CTAB). Different mechanisms such as charge neutralization, “depletion flocculation” or “volume-restriction”, and “hydrophobic effect” between hydrocarbon tails of CTAB have been proposed to explicate aggregation results. One important finding is that for different volume concentrations between 0.05% and 0.51% of 30R50 suspensions, the same critical coagulation concentration was observed at CTAB=0.1mM, suggesting the optimized quantity of CTAB during the separation process for nanoparticles of about 75nm. Furthermore, very small quantities of CTAB (0.01mM) can make 30R25 nanosilica aggregated due to the “hydrophobic effect”. It is then possible to minimize the sludge and allow the separation process as “greener” as possible by studying this case. It has also shown that aggregation mechanisms can be different for very small particles so that a special attention has to be paid to the treatment of nanoparticles contained in water and wastewaters.
The increasing use of nanoparticles will inevitably result in their release into the aquatic environment and thereby cause the exposure of living organisms. Due to their larger surface area, high ...ratio of particle number to mass, enhanced chemical reactivity, and potential for easier penetration of cells, nanoparticles may be more toxic than larger particles of the same substance. Some researchers have been showing some relations between nanoparticles and certain diseases. However, the doses, surface shapes, material toxicity and persistence of nanoparticles may all be factors in determining harmful biological effects. In order to better evaluate their risks, potential exposure route of nanoparticles has to be taken into consideration as well. Finally, a brief summary of techniques for nanoparticle removal in waters and wastewaters is presented, but it seems that no treatment can absolutely protect the public from exposure to a large-scale dissemination of nanomaterials.
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•The increasing use of nanoparticles will inevitably lead to their release into the environment.•Due to their specific properties, nanoparticles may be more toxic than larger particles.•Hazards of nanoparticles relevant to humans and other mammals have been studied.•Nanoparticle separation techniques from waters already exist but still have to be improved.
The present work deals with a study on the physical characteristics of stoichiometric hydroxyapatite microspheres produced by spray-drying process through different operating conditions. Obtained ...hydroxyapatite microspheres are intended to be used as powder feedstock in powder bed selective laser processing additive manufacturing technologies where the flowability and the particle size distribution of the powder feedstock are of special importance. The powders produced at different spray-drying operating parameters were evaluated by analysing the particle size, shape, moisture, and agglomerates strength. Spray air pressure (0.25–2 bars) and the solid content of the slurries (10–50% wt.) were the most influent parameters to control the final particle size distribution, whereas the higher process recovery rate (79%) was obtained at specific values of inlet temperature (250 °C), spray air pressure (2 bar), and feed rate (4.9 kg.h−1). A 5 wt% of polyvinyl alcohol as an organic binder to the ceramic part was found to increase the strength of the granules. The flowability of the produced hydroxyapatite microspheres (x50 = 64 μm; span = 1.77) was found to fulfil the defined feedstock requirements (e.g., Hausner ratio < 1.25), without alteration of the physico-chemical properties of the material. These promising results confirm the use of a spray dryer as an efficient method for the production of hydroxyapatite microspheres for powder bed selective laser processing.
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•Powder bed fusion feedstock with improved flowability properties may be achieved by spray-drying process•Spray-drying process parameters can tune the hydroxyapatite microspheres particle size distribution•Polyvinyl alcohol as organic binder improves the granules breakage resistance•HA physico-chemical properties and crystallinity remain unaltered after the spray-drying process
Stoichiometric hydroxyapatite (HAP) is a prominent biomaterial, notably used as coating on metal bone prostheses. High chemical purity and a specific particle size distribution are the main ...properties for such an application. Based on industrial practice, a reference synthesis was first performed in a lab-scale stirred reactor. Improvements were then suggested by varying the physicochemical and hydrodynamic conditions. The shear rate within the reactor, characterized by the mean Kolmogorov micro-scale, has a strong impact on the final agglomerate size distribution. By maintaining a rather high mixing rate and a high temperature, the duration of the synthesis can be reduced considerably without affecting the HAP purity provided the pH is properly regulated. This consists of imposing acidic conditions during a short period just after the initial formation of large aggregates and then setting the pH at above 7.5 to ensure the production of pure stoichiometric HAP.
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•The shear rate mainly impacts the particle size distribution of synthesized HAP.•Pure HAP can be produced at 75 °C ensuring a relevant pH regulation.•Under specific physico-chemical conditions, maturation has only a small effect on HAP.
Nanobiotechnologies have lately attracted much attention, both from therapeutic and diagnosis perspectives. In this view, the development of colloidal formulations of biocompatible nanoparticles ...capable of interacting with selected cells or tissues raises a particular interest, especially in link with cell-based pathologies such as cancer. In this context, the follow-up of colloidal stability and other physico-chemical features is of foremost relevance. In this contribution, we have focused our study on hybrid colloids based on biomimetic nanocrystalline apatites (analogous to those found in bone mineral) stabilized by adsorption of 2-aminoethylphosphate (AEP) molecules; these nanoparticles being intended to interact with cancer cells either for medical imaging (by conferring luminescence features to the apatite phase) or for therapeutic purposes. We show that various physico-chemical characteristics of the suspensions vary with time, including viscosity and mean particle size, suggesting a progressive structuration of the suspensions. Similar modifications were also noticed during the purification by dialysis. Finally, we report on preliminary experiments aimed at drying the colloids while retaining their capacity to recover their initial state after re-immersion in aqueous medium; so as to enable extended storage periods for the nanoparticles in their dry state while allowing their re-suspension at the time of use. On this matter, the addition of glucose prior to freeze-drying was found to be an effective way to avoid the formation of aggregates during drying.
This contribution thus confers additional information relative to the stability of AEP-stabilized biomimetic apatite colloidal formulations, which proved in previous studies to be of particular relevance for nanomedicine.
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•The stability of colloids based on biomimetic nanocrystalline apatites is studied.•The particle size distribution and the rheological behaviour were characterized.•The suspensions were characterized during the storage and the purification process.•The ability of the particles to be redispersed after the drying process was proved.
The production of nanoparticles in concentrated suspensions requires strict control of the stability of the systems which are strongly influenced by the physico-chemical properties and the ...hydrodynamic conditions they are placed in. This study deals with the analysis of the aggregation processes of a colloidal silica suspension destabilized by addition of salt under different flows: a turbulent flow performed in a stirred tank, a pure shear flow created thanks to a Couette geometry and an extensional flow obtained in a four-roll mill (Taylor cell). During the aggregation process, the silica suspensions behave as shear-thinning fluids and the variation of their apparent viscosity can be related to the evolution of the size distribution of the aggregates in the suspension. Pure shear and turbulent flows at an equivalent strain rate exhibit almost the same behaviour. The viscosity and the aggregate size decrease with the shear rate. On the contrary, the apparent viscosity and the aggregate size distributions were not very sensitive to a change of an extensional constraint within the considered range. Indeed, although aggregates obtained in the Taylor cell were bigger than in the Couette cell, the apparent viscosity was higher in the latter case. Different aggregate structures, characterized by their fractal dimension, were finally predicted depending on the hydrodynamic nature of the main flow under which they were produced.
This study investigates granulometric and rheological measurements in destabilized colloidal silica suspensions under different type of flows. The study discusses the effects of the hydrodynamic conditions (shear and extensional flows) on the evolution of the size of the aggregates and the viscosity of the suspensions. Fig.: Volumetric particle size distributions of the suspension at the end of the destabilisation process for the various hydrodynamic conditions experimented. Display omitted
•The shear and extensional flows that compose the turbulent flow are studied.•Three experimental devices were used: a reactor, a Couette cell and a Taylor cell.•The evolution of viscosity and particle sizes during the aggregation were measured.•The nature of the flow appear to have a great influence on the aggregation process.•Different aggregate structures were suspected depending on the nature of the flow.
The aim of this study is to analyze the behaviour of dense colloidal suspensions in flow by acoustic spectroscopy. The destabilization and the aggregation of stable colloidal silica dispersions in a ...stirred tank are obtained by the addition of salt.
Experiments were made in order to observe the influence of different operating parameters, like silica concentration, temperature and stirring speed, on the behaviour of the suspended particles.
The use of on-line acoustic spectroscopy to analyze the process enables us to evaluate the evolution of the silica suspension properties during the aggregation processes. For example, the influence of physicochemical and hydrodynamics parameters on the aggregation process can be simply explained on the basis of the acoustic attenuation spectra. Thus the direct analysis of the spectra can give information on the evolution of the aggregation process and a fast comparison of the effects of the various operational parameters.
Online acoustic spectroscopy was used to evaluate the evolution of colloidal silica suspension properties during a destabilization process obtained by the addition of salt. The direct analysis of the acoustic attenuation spectra can give information on the evolution of the aggregation process and a fast comparison of the effects of the physicochemical and hydrodynamics parameters.
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Concentrated suspensions of nanoparticles subjected to transport or shear forces are commonly encountered in many processes where particles are likely to undergo processes of aggregation and ...fragmentation under physico-chemical interactions and hydrodynamic forces. This study is focused on the analysis of the behavior of colloidal silica in dense suspensions subjected to hydrodynamic forces in conditions of destabilization.
A colloidal silica suspension of particles with an initial size of about 80
nm was used. The silica suspension concentration was varied between 3% and 20% of weight. The phenomenon of aggregation was observed in the absence of any other process such as precipitation and the destabilization of the colloidal suspensions was obtained by adding sodium chloride salt.
The experiments were performed in a batch agitated vessel. The evolution of the particle size distributions versus time during the process of aggregation was particularly followed on-line by acoustic spectroscopy in dense conditions. Samples were also analyzed after an appropriate dilution by laser diffraction. The results show the different stages of the silica aggregation process whose kinetic rates depend either on physico-chemical parameters or on hydrodynamic conditions. Then, the study is completed by a numerical study based on the population balance approach. By the fixed pivot technique of Kumar and Ramkrishna 1996. On the solution of population balance equations by discretization—I. A fixed pivot technique. Chemical Engineering Science 51 (8), 1311–1332, the hypothesis on the mechanisms of the aggregation and breakage processes were justified. Finally, it allows a better understanding of the mechanisms of the aggregation process under flowing conditions.
The present work deals with the use of stirred bead milling process to tune the hydroxyapatite particles size adjusting the process conditions. Our goal is to find the optimal parameters to obtain ...particulate suspensions within a 0.2–1.5 μm particle size range. This size range is preferable to produce spherical feedstock for powder bed fusion technologies through the atomization process. A Darvan C dispersant agent dosage of 2.1 mg m−2 (active component) to the specific surface of the ceramic was found, through stability and rheological analyses, to be the most outstanding dosage for stabilizing the dispersion. Milling chamber, bead wear, and energy consumption were evaluated and minimized, finding the most efficient operating parameter setting for the process. For the studied material, the use of a fast stirrer speed, smaller grinding media size, and higher solids concentration increased the energy efficiency. This work confirmed the presented laboratory-scale milling process as a promising method to study the processing of hydroxyapatite-filled slurries, as a first-step product, on the manufacture of hydroxyapatite microspheres for the powder bed fusion industry.
This paper focuses on the tailoring of calcium phosphate powders for their use as powder bed selective laser process feedstock. Hydroxyapatite and chlorapatite were used as starting powders for the ...preparation of different blends through the addition of graphite as a laser absorptance additive. A methodical study was conducted to compare the processing windows of the blends containing different amounts of graphite through the laser patterning of circular samples. It was found that the addition of graphite increases the process window of the powder blends being the powder without additive non processable. Hydroxyapatite showed a clear phase transition (decreased when using higher volumetric energy density) into other calcium phosphate phases while chlorapatite was demonstrated to be thermally stable during the whole process (examined through X-ray diffraction and vibrational spectroscopies). In parallel, the study evaluating the powder blend composed of hydroxyapatite and graphite for the production of solid and complex parts was carried out although it required long printing times. The productivity of the process was improved by modification of printing parameters. Then, a series of solid samples were produced for the analysis of the microstructure and mechanical properties. High interconnected porosity was observed in the samples which could improve the bioactivity of the bioceramic scaffolds. A post-treatment of the parts increased their proportion in the hydroxyapatite phase and their mechanical properties. These results are expected to contribute to the application of powder bed selective laser processing of calcium phosphates powders toward bone tissue engineering.
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•Graphite as absorption additive improves the laser-material interaction enlarging the process window.•Laser parameters directly influence the hydroxyapatite phase transition into other calcium phosphate phases.•Chlorapatite did not undergo phase transition during the process due to its inherent higher thermal stability.•Solid parts containing a majority of HA phase in the structure were obtained although with low mechanical properties.
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