Dispersion Of Powders In Liquids And Stabilization Of Suspensions Pdf


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In this study, we investigated the effects of near supercritical carbon dioxide SCCO 2 parameters, including pressure, temperature, and saturation time on titanium dioxide TiO 2 nanopowder dispersion in water-containing sodium hexametaphosphate SHMP.

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Dispersion of Fumed Silica

Metrics details. This study reports useful application of the electrokinetic sonic amplitude ESA technique in combination with rheometry and electron microscopy techniques for direct probing the stability of low and high-concentrated zirconia ZrO 2 nanosuspensions in the presence of an alkali-free anionic polyelectrolyte dispersant Dolapix CE A comparative study of the electrokinetic characteristics and the rheological behavior of concentrated ZrO 2 nanosuspensions has been done.

Good agreement was obtained from relationship between the electrokinetic characteristics zeta potential, ESA signal , viscosity, and its pH dependence for each concentrated ZrO 2 nanosuspension with different dispersant concentration in the range of 0. A nanoscale colloidal hypothesis is proposed to illustrate that the addition of different amounts of dispersant influences on both the stability and the electrokinetic and rheological properties of concentrated ZrO 2 nanosuspensions.

It is found that an optimum amount of 1. Supplementary scanning electron microscopy SEM and high-resolution transmission electron microscopy HR-TEM analyses followed by colorization effect were taken to verify the visible interaction between dispersant and nanoparticles surfaces.

Ceramic colloidal processing methods require stable, well-dispersed suspensions with extremely high levels of solids loading to achieve optimal casting condition and green body properties and also to minimize drying induced shrinkage [ 9 — 11 ].

Several techniques are available to characterize the dispersion quality of micron and sub-micron -sized powder suspensions at low solids loading. One of the available techniques that can be used for characterization of the electrokinetic properties of dispersed nanoparticle suspensions is laser light scattering technique.

But, the majority of standard laser light scattering techniques are indirect. In addition, applying existing light scattering techniques has several limitations: i The light scattering techniques require dilution of the concentrated suspension.

This may lead to the shift of the equilibria involving adsorption and may be irreversible, unless particular care is taken to compensate for the dilution process [ 13 ]. Because of recent advances in purity, high-strength, high-fracture toughness and wear resistance over a wide temperature range, and other versatile applications, zirconia ZrO 2 has become an important ceramic material [ 7 , 16 ] for a variety of applications.

It is being used as an important material for Orthopedic and dental applications [ 17 ], electrolytes and electrochemical sensors [ 18 , 19 ], gas and humidity sensors [ 20 , 21 ], anode in fuel cells [ 22 ], catalysts [ 23 ], and optoelectrics [ 24 ].

Thus, due to the above important characteristics of zirconia, in this study, we used high-purity ZrO 2 nanopowder. For fabrication of ZrO 2 -based ceramic materials with final sintered properties of high tetragonal-phase t -phase content, along with dense and uniform microstructure leading to good mechanical properties, it is preferable to start with a concentrated nanopowder suspension with an appropriate dispersant stabilizer [ 25 ].

Some of the dispersants which have been used to disperse sub-micron-sized zirconia powder include Tiron, Aluminon [ 26 ], ammonium polyacrylate [ 27 ], polymethacrylic acid, polyethyleneimine and diammonium citrate [ 28 ], 2-propenoic acid and a metal-organic polymer [ 29 ], and Triton-X [ 30 ]. Greenwood and Kendall [ 31 ] have conducted a research study using 14 different reagents for dispersing sub-micron-sized zirconia powder. Lower viscosity will lead to a higher packing density in the sediment [ 32 , 33 ].

The zeta-potential can be modified by adjusting the suspension pH and by using suitable dispersants, such as polyelectrolytes. However, conventional polyelectrolytes like polyacrylic acid PAA , polymethacrylic acid PMAA , or sodium dodecyl sulfate SDS are weak dispersants based on steric or electrostatic stabilization and not suitable for dispersion of high-concentrated nanoparticle suspensions [ 34 — 36 ]. In addition, solids loading and using suitable dispersant have also important impact on dispersion quality of concentrated colloidal nanoparticle suspensions.

Several studies have been reported about the effects of volume fraction and the adsorption of different conventional polyelectrolytes onto different sub-micron-sized powders like calcium pyrophosphate [ 34 ], alumina, kaolin [ 37 — 39 ], and barium titanate BaTiO 3 at different low and moderate-concentrated suspensions [ 9 , 35 ]. The desirable combination is to apply a dispersant which can adsorb strongly onto the ceramic nanoparticles at high solids loading suspensions with optimal viscosity.

Therefore, one of the most important concerns in this study was to use the most suitable dispersant that could stabilize highly concentrated suspensions of ZrO 2 nanoparticles based on electrosteric stabilization with ultimate goal for fabrication of dense zirconia ceramic with homogenous microstructure and improved mechanical properties.

According to the results reported by manufacturer and different authors [ 4 , 12 , 26 — 32 , 40 — 45 ], this particular dispersant has several advantages over traditional dispersants. Specifically, Dolapix CE64 has the following unique properties:. Dolapix CE64 is an alkali-free anionic polyelectrolyte dispersant which does not foam.

Specially, it has minimum side effect on gypsum-based casting molds used for shaping final products. Therefore, this dispersant makes it possible to produce slips with a high solids loading, particularly, suitable for dispersion before slip casting, tape casting, and spray drying. It is a liquid and its density is just slightly above the density of water.

Comparing to other types of dispersant agents, it has lower molecular weight and higher pH of around 9 that helps better absorption coverage of nanoparticles in concentrated colloidal systems. Hence, it is possible to any time to adjust the viscosity of the suspension by rapid, homogeneous incorporation into the suspension. For this matter, dispersant Dolapix CE64 was used in this study as the most reliable candidate for this mission. Rao et al.

However, these techniques are indirect methods and time consuming processes. The results obtained from rheology were compared with those obtained using the electroacoustic ESA technique. Imaging and characterization of nanoparticles by high-resolution electron microscopy techniques are also important tools in multi-component material characterization [ 48 ].

Such techniques are used to assess nanoparticle shape, surface, size, morphology, coating, and elemental distributions [ 49 ]. Therefore, in this study, we also applied SEM and HR-TEM as supplementary tools to verify the visible interaction between polyelectrolyte dispersant and nanoparticle surfaces, qualitatively.

ZrO 2 nanopowder Nanopowder has a bulk density of 6. The manufacturer does not give further information about this dispersant. A predicted orthographic display of the 3-D molecular structure simulated by using materials studio, Accelrys of this dispersant is illustrated in Fig.

An orthographic display of predicted 3-D molecular structure of alkali-free anionic polymer, Dolapix CE One set of samples was prepared with and the others without addition of Dolapix CE64 in the range of between 0. At least ten suspensions were prepared for each different nanosuspension composition, in order to determine the optimal amount of dispersant which would give the lowest viscosity and control reproducibility of suspensions. The effect of dispersant concentration in the range of 0.

Separate samples were prepared at the required dispersant concentrations in the range of 0. Three measurements were made for each suspension, and each result was identical on the whole. Immediately, the viscosity of the suspensions was determined. The principles of electroacoustic techniques and theoretical background of ESA technique and its application in concentrated colloidal suspensions have already been reported in details by several authors [ 56 — 58 ].

According to electroacoustic theory, when an alternating electric field is applied to a suspension of charged particles, the particles will oscillate at the same frequency of the applied field [ 59 ]. Due to the density difference between the particles and the aqueous suspension, this motion will generate tiny acoustic dipoles associated with each individual particle [ 12 , 57 , 58 ].

These dipoles cancel one another throughout the body of suspension except near the electrodes where the acoustic dipoles generate an acoustic wave. This can emerge from the suspension and move down the delay rod where it is detected by the transducer. The transducer can detect the amplitude and phase angle of this acoustic wave as a function of the applied frequency.

The phase angle measures the time lag between the applied field and the subsequent particle motion [ 44 ]. Particle motion is adjusted by periodical polarization of the electrical double layer to form a dipole, as shown schematically in Fig. This phenomena is called the electrokinetic sonic amplitude or ESA effect. The first ESA device was invented by T. Oja et al. The zeta-potential value is closely related to suspension stability and particle surface morphology [ 31 , 61 ].

For the suspending medium, the density, viscosity, and dielectric constant are required. For the particles, the density, volume fraction, and average size are necessary [ 59 , 62 ]. These high viscosities can lead to poor mixing properties that result in sample heterogeneity during titrations.

Therefore, it is advisable to determine the viscosity behavior of applied suspensions prior to ESA measurements [ 32 , 35 , 52 ]. In the present work, calibration and size correction were not performed, so the zeta-potential values reported are of a relative nature. In the experimental setup using ESA technique, two different sets of concentrated ZrO 2 nanosuspensions were prepared, as follow:. This study indicates that this alignment helps to settle a very small volume of highly concentrated nanosuspensions on the ESA electrode and it minimizes challenging experimental errors during measurements.

By this alignment charged, particles in highly concentrated suspensions could be settled on the surface of the ESA electrode in the same direction of the applied electric field and gravity. This helps to obtain better ESA signals. The reported values of the electrokinetic characteristics i. Merck brand 0. For high More detailed information on this method can be found in the literature [ 63 ]. As a supplementary step, we have proposed a hypothesis that the addition of different amounts of dispersant influences both the stability and the electrokinetic and rheological properties of concentrated ZrO 2 nanosuspensions.

A schematic nanoscale model using ZrO 2 nanoparticles as host particles and dispersant Dolapix CE64 as the coating polymer is shown in Fig. HR-TEM was used for surface visualization of individual nanoparticles before and after the addition of optimum amount of 1. Two different parts of particle are distinguished by apparent color: The dark image b and blue image c parts represent the original particle. The light or transparent image b and pink image c one on the edge represent polyelectrolyte coating.

Shell polyelectrolyte indicated by arrows. Two sets of TEM samples were prepared as follows: i A very diluted drop 0. False colors based on colorization effect were used to distinguish the interface between nanoparticle and potential coating dispersant layers. To false color TEM images see Fig.

All suspensions exhibit shear-thinning behavior with a reduction in viscosity at increasing shear rate, see Fig. For suspension with 1. These characteristics indicate a poor dispersion of the suspension. This means that in spite of the insufficient amount of an electrosteric dispersant, bridging flocculation occurs. This is in agreement with our proposed model, see Fig. From Fig. More dispersant will be required to adsorb onto the surface of the particles to maintain a stable suspension.

As the dispersant addition increases, the yield value decreases and the thixotropic loop diminishes. This means that with the addition of optimum amount of an electrosteric dispersant, deflocculation occurs in a dispersed suspension. This is in agreement with our proposed hypothesis model, see Fig. The results are shown in Fig. The addition of dispersant has a strong effect on shifting of the pH at isoelectric point pH i.

The graphs in Fig.

Dispersion and Stabilization of Exfoliated Graphene in Ionic Liquids

The liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. Because ionic liquids can be easily obtained with chosen molecular structures and tuneable physicochemical properties, they can be use as media to optimize the exfoliation of graphite. The understanding of the interactions involved between graphite and various chemical functions in the solvent ions will be helpful to find liquids capable of dissociating and stabilizing important quantities of large graphene layers. After a step of sonication, as a mechanical precursor, samples of suspended exfoliated graphene in different ionic liquids have been characterized experimentally in terms of flake size, number of layers, total concentration and purity of the exfoliated material. Nine different ionic liquids based on imidazolium, pyrrolidinium and ammonium cations and on bis trifluoromethylsulfonyl imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate anions have been tested. UV-vis, Raman and X-ray photoelectron in addition to high resolution transmission electron and atomic force microscopy have been selected to characterize suspended exfoliated graphene in ionic liquids.

Dispersion of Nanomaterials in Aqueous Media: Towards Protocol Optimization

Richard C. Schrand, John J. Schlager, Saber M. The need to characterize nanoparticles in solution before assessing the in vitro toxicity is a high priority.

Metrics details. This study reports useful application of the electrokinetic sonic amplitude ESA technique in combination with rheometry and electron microscopy techniques for direct probing the stability of low and high-concentrated zirconia ZrO 2 nanosuspensions in the presence of an alkali-free anionic polyelectrolyte dispersant Dolapix CE A comparative study of the electrokinetic characteristics and the rheological behavior of concentrated ZrO 2 nanosuspensions has been done.

Particle Size Measurement pp Cite as. In many size analysis methods it is necessary to incorporate a powder into a liquid medium such that the particles are evenly dispersed. If the powder surface is lyophobic the powder is difficult to disperse, if it is lyophilic the powder disperses easily for water dispersions the terms are hydrophobic and hydrophilic respectively. Dispersing agents are, therefore, added to wet the surface of lyophobic materials to make them lyophilic. Unable to display preview.

With both hydrophobic and hydrophillic grades available, it is widely used as a rheology modifier, imparting highly thixotropic properties at relatively low percentages. For this reason it is particularly suitable for coatings, inks, adhesives, resins, sealants and greases. Using conventional mixers and agitators, a number of problems can be encountered during production:.

Background

Почему Стратмор отмел такую возможность. Хейл извивался на полу, стараясь увидеть, чем занята Сьюзан. - Что. Скажи. Сьюзан словно отключилась от Хейла и всего окружающего ее хаоса.

Кнопка на полу привела ее в движение, и дверь, издав шипящий звук, отъехала в сторону. Чатрукьян ввалился в комнату. - Коммандер… сэр, я… извините за беспокойство, но монитор… я запустил антивирус и… - Фил, Фил, - нехарактерным для него ласковым тоном сказал Стратмор.  - Потише и помедленнее. Что случилось.

Dispersion of powders

 Как ее зовут? - Женщина лукаво подмигнула. - Меган, - сказал он печально. - Я полагаю, что у вашей подруги есть и фамилия.

Но это значит… значит… что мы не можем… - Это значит, что нужен другой план действий.  - Фонтейн, как обычно, говорил спокойно и деловито.

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Jen G.
30.03.2021 at 08:40 - Reply

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