Effect of sucrose on rheological properties of aqueous zirconia suspensions with polyacrylate

The role of pH, additive concentration, aging time and solids loading in determining the rheological properties of aqueous zirconia suspensions, which contained polyelectrolyte and sucrose molecules, was investigated. It was found that at alkaline pH, the appropriate sucrose addition (4 wt.%) enhanced the stability of zirconia suspensions with polyacrylate, and the amount of polymer required to obtain the maximum fluidity decreased as sucrose was added. However, the positive effect of sucrose on stability cannot maintain at the higher solids loading (40 vol.%) because of the bridging attraction between the overlapping adlayers. On the other hand, the effectiveness of sucrose would be greatly weakened by hydrolyzation in acidic media as well as biodegradation with aging time.     

Obtaining corundum-zircon suspensions,their rheological and bonding properties

Conclusions It is shown that the combined grinding of corundum (80%) and zircon (20%) will produce suspensions with high concentrations and binding properties. A study was made of the effect of pH and slip concentration on their rheological properties, density, and the strength of the castings. With a pH of 2.5–3.5 and of 0.50–0.54 we obtained castings with an open porosity of up to 28–30% and _bend of up to 8–9 MPa.Substantial sintering of the material is accomplished even at reduced (1450°C) temperatures. The factors for _bend (on specimens measuring 7×7×70 mm) and _comp (on specimens measuring 10×10×10 mm) with an open porosity of 16–18% are up to 180 and 740 MPa respectively. At 1100 and 1200°C the value of _comp equals 300–340 and 250–300 MPa, respectively.Translated from Ogneupory, No. 6, pp. 22–25, June, 1984.     

Influence of polyacryl amide on the rheological and technological properties of corundum suspensions and castings of them

Conclusions The stability and rheological properties of suspensions prepared from alumina with the addition of MgCl₂ fired at 1550 and 1750°C, washed with polyacryl amide and without it, dried, and stored for a certain time were investigated. It was established that drying and storage promote a significant breakdown in the floccules and, as a consequence, the obtaining of suspensions with close properties.The addition to the composition of such slips of small quantities of organic additions makes it possible to obtain parts with high properties with significantly shorter expenditures of time (by approximately four times) for preparation of the slips.Translated from Ogneupory, No. 1, pp. 12–16, January, 1985.     

The rheological properties of paper coating suspensions and their application

Conclusions  The experimental results lead to the following observations:

Effect of blend ratio on rheological properties of aqueous SiC suspensions

The relationship between blend ratio and rheological properties of concentrated suspensions is of great importance since it is the key to get high solid suspensions. The rheological properties of bidisperse aqueous suspensions made of two SiC powders with different particle size [d_(0.5)=1.63 and 18.43 μm, respectively] has been studied as a function of blend ratio ξ (the volume fraction of larger particle size). The results showed that the value of critical blend ratio ξ, at which the viscosity is minimized, is in close relation to the shear rate applied. At shear rates below 10 S⁻¹, the critical ξ was greater than 70%. But at shear rates from 10 to 500 S⁻¹, ξ turned to be 50%. The change of shear region from shear-thinning behavior to shear-thickening behavior may be used to account for the variation of critical ξ. Dynamic oscillatory tests showed that the moduli and the linear viscoelastic region of suspensions with higher ξ are smaller than those with low ξ and the increment of blend ratio ξ leads to the change of suspension from nearly an elastic response to a liquid like response.     

Effect of kyanite on rheological properties of dense aqueous alumina suspensions

Abstract

The present work examines the effect of pH on aqueous suspensions of alumina and alumina–kyanite mixtures to assess the influence of kyanite additions on suspension properties. This system is of interest because on heating to temperatures above 1400°C the mineral kyanite (Al₂O₃ . SiO₂ ) reacts to form silica and mullite (3Al₂O₃ . 2SiO₂ ) and as the latter mineral has attractive elevated temperature properties, its incorporation into a common refractory material such as alumina is of importance in the field of technical ceramics. A popular method to produce such materials is to prepare a stable suspension of the components of interest and cast a green compact from the slurry; this compact is subsequently sintered at an appropriate temperature to densify the product. As the solids content of the original suspension influences the final product density, rheological properties are of critical importance. Both microelectrophoresis and rheological techniques suggested that a pH of 3–4 provided optimum stability. The flow behaviour of the binary mixture could be predicted by the Casson model and it is suggested that the surface characteristics of the kyanite were primarily responsible for the resulting stability regime.     

A new approach to prepare highly loaded aqueous alumina suspensions with temperature sensitive rheological properties

Poly(acrylic acid) (PAA)-free alumina suspensions with temperature sensitive rheological properties have been successfully produced using the combination of tri-ammonium citrate and magnesium citrate powders with slurry loading up to 60 vol.%. A new approach using the DLVO concept is proposed to design the suspension composition. Both the shear viscosity and the shear modulus of the suspensions start to increase when the suspension temperature is above a critical value. The flocculation of the suspensions is controlled by the dissolution of the magnesium citrate that increases the ionic strength in the suspensions. The dissolution is controlled by the pH of the suspensions, which decreases with increasing temperature. Compared with the same solid loading suspensions containing PAA, the suspension shear viscosity of 25 °C can be reduced, which is useful in developing new near net shape forming technologies.     

Optimization of the rheological properties of yttria suspensions

To advance the rheological quality of yttria suspensions, the effects of three dispersants were evaluated and compared. It was found that after adding each of these dispersants, zeta potential moved toward negative direction and the pH_IEP shifted from basic to acidic. An increase of the pH could increase the absolute zeta potential. The fluidity and stability of yttria suspensions were examined by viscosity measurements and sedimentation tests.     

Comb‐like polymer with sulfo groups and its dispersion and rheological properties in aqueous ceramic suspensions

Two types of new comb‐like polymers were formed as dispersants for aqueous ceramic suspensions with isoprenyloxy poly(ethylene glycol ether), acrylic acid, maleic anhydride as the main starting materials. During the synthesis, one comb‐like polymer introduced sodium methylallyl sulfonate (SMAS) into the reaction media, whereas the other did not. The chemical structure and molecular weight were characterized by Fourier transform infrared spectroscopy and gel permeation chromatography. The effects of the polymers on the dispersion, ζ potential and rheological properties of the kaolin suspensions are discussed in detail. The results indicate that SMAS facilitated chain transfer, controlled the effective charge density of the surface, and increased the electrostatic repulsion force. The kaolin suspensions displayed shear‐thinning behavior on the basis of the electrostatic and steric effects of the comb‐like polymers. The apparent viscosity decreased from 1088 to 258 mPa s with the assistance of the SMAS‐prepared comb‐like polymer as a dispersant. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44563.     

Investigation of the rheological and technological properties of corundum-zirconia suspensions

Conclusions An investigation was made of the influence of the water content of slips on their viscosity and surface tension, and also on the strength, apparent density and porosity of the casts. We established the optimum parameters for the slips in order to obtain casts with the maximum strength and apparent density, and the minimum porosity in the wall of the cast.Translated from Ogneupory, No. 4, pp. 16–18, April, 1991.     

Relationship between the colloidal and rheological properties of mineral suspensions

The electrokinetic and rheological behaviour of lateritic aqueous suspensions has been analyzed as a function of samples chemical composition, pH of suspensions, and nature and concentration of electrolyte added to the aqueous suspensions. First, it was determined that the isoelectric point (IEP) of suspensions in the presence of non‐adsorbing electrolytes is a function of the ratio serpentine/ goethite present in samples. The flow properties of the suspensions are strongly dependent on pH, reaching the highest values of apparent viscosity at values around the isoelectric point. Specific adsorption of silicate and magnesium species on particles surface was revealed by a shift in the IEP. In particular, silicate anions shifted the IEP value to acidic pH whilst magnesium cations shifted the value to basic pH. A similar trend was displayed in the rheological behaviour of suspensions where the highest viscosity values were shifted to the same direction.     

The rheological and technological properties of silicon carbide suspensions

Refractories and Industrial Ceramics - An investigation was carried out of the rheological and technological properties of silicon carbide suspensions. The optimal linear pH range of silicon...     

Dense m-Li2ZrO3 formed by aqueous slip casting technique: Colloidal and rheological characterization

An aqueous colloidal processing method was proposed to prepare m-Li₂ZrO₃ bodies, with high green density and a homogenous microstructure, employing a pressureless forming technique. For this purpose, the preparation conditions of m-Li₂ZrO₃ aqueous suspensions were optimized considering colloidal processing variables, such as milling time (0–40 min), dispersant concentration (1–10 wt% of the solids content) and maximum solid loading (41–74 wt%). Particle size distributions and steady-state flow curves of the slips were analyzed, together with phase composition and microstructure of the ceramic bodies. The results show that after planetary ball milling for 30 min, the aqueous suspension with 63.1 wt% of m-Li₂ZrO₃, and a dispersant content equal to 10 wt% of the solid loading, yielded green bodies with bulk densities close to 66% TD by slip casting. Then, after the heat treatment process at 1100 °C for 12 h, bulk densities close to 88% TD were achieved. It was found that density values and microstructure of the green and sintered products bear a direct relationship to the particle size and the consistency of the slips.     

Rheological properties of concentrated aqueous fluorapatite suspensions

The Ca₃(PO₄)₂ and CaF₂ powders were mixed in a 3:1.5 ratio, calcined at 1000 °C and then milled in an aqueous media with the pH initially adjusted at 9. The resulting powder had a Ca/P atomic ratio of 1.67, which corresponded to the theoretical composition of fluorapatite (FA), Ca₁₀(PO₄)₆F₂. Its reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH₄PA) was investigated as a function of time. The adsorption behaviour of NH₄PA and the influence of NH₄PA addition on the rheological properties of 40 vol.% FA slips were studied. In addition, the influence of the volume fraction of solids on the rheological behaviour of stabilized FA slips was determined. Finally, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of 38 vol.% FA suspensions stabilized with NH₄PA was investigated. The dissolution of FA was enhanced by decreasing the pH to an acidic value; the increase in pH above 7 markedly reduced the Ca²⁺/H⁺ exchange reaction rate. As a result, well-stabilized aqueous suspensions could be obtained at pH close to 9 in a wide range of solids loading. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH₄PA was added. An important increase in the yield stress was observed for suspensions with a volume fraction of solids higher than about 46 vol.%. The addition of 0.5–1 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity.     

Ultrasonication effects on thermal and rheological properties of carbon nanotube suspensions

The preparation of nanofluids is very important to their thermophysical properties. Nanofluids with the same nanoparticles and base fluids can behave differently due to different nanofluid preparation methods. The agglomerate sizes in nanofluids can significantly impact the thermal conductivity and viscosity of nanofluids and lead to a different heat transfer performance. Ultrasonication is a common way to break up agglomerates and promote dispersion of nanoparticles into base fluids. However, research reports of sonication effects on nanofluid properties are limited in the open literature. In this work, sonication effects on thermal conductivity and viscosity of carbon nanotubes (0.5 wt%) in an ethylene glycol-based nanofluid are investigated. The corresponding effects on the agglomerate sizes and the carbon nanotube lengths are observed. It is found that with an increased sonication time/energy, the thermal conductivity of the nanofluids increases nonlinearly, with the maximum enhancement of 23% at sonication time of 1,355 min. However, the viscosity of nanofluids increases to the maximum at sonication time of 40 min, then decreases, finally approaching the viscosity of the pure base fluid at a sonication time of 1,355 min. It is also observed that the sonication process not only reduces the agglomerate sizes but also decreases the length of carbon nanotubes. Over the current experimental range, the reduction in agglomerate size is more significant than the reduction of the carbon nanotube length. Hence, the maximum thermal conductivity enhancement and minimum viscosity increase are obtained using a lengthy sonication, which may have implications on application.     

Temperature induced gelation of concentrated ceramic suspensions: rheological properties

Concentrated, sterically stabilised ceramic suspensions have been reversibly gelled by changing the temperature. Using an amphiphilic polymer, Hypermer KD3, as dispersant for alumina and alumina-silicon carbide whisker composite mixtures in pentanol resulted in a transition from dispersed to flocculated state close to room temperature. The collapse of the adsorbed polymer layer with decreasing solvency (temperature) in the marginal solvent pentanol induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. Temperature induced gelation (TIG) of concentrated suspensions has a drastic effect on the rheological properties. At temperatures above 30°C, the suspensions have a low viscosity and negligible elasticity. When the temperature is lowered below 20°C, the viscosity increases significantly and the viscoelastic behaviour becomes predominantly elastic. The elasticity and the associated particle network strength are sufficiently high for a highly concentrated gelled suspension to support its own weight. The potential use of TIG as a novel forming method was discussed with relation to other new shaping techniques. ©