Optimization of the rheological properties of suspensions for the production of open-cell foamed ceramics

The possibility of using aqueous poly(vinyl alcohol) solutions as surface-active, rheological, and sticking additives to obtain aluminosilicate ceramic suspensions involved in the production of high-porosity cellular materials (open-cell foams) was studied. It is established that aluminosilicate ceramic suspensions containing 0.5–1.0% PVA additive exhibit a drop in viscosity. This increases the critical concentration for structure formation and allows slips with a high filling coefficient to be obtained. Slip compositions for fabrication of open-cell foamed porcelain were developed. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 3, pp. 23–27 March, 1997.     

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...     

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.     

The rheological properties of paper coating suspensions and their application

Conclusions  The experimental results lead to the following observations:

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. ©     

Structure/rheological properties relations of crosslinked potato starch suspensions

Some rheological properties of aqueous suspensions of crosslinked hydroxypropylated potato starches were investigated. The crosslinking was performed at a temperature above the gelatinization temperature and the degree of crosslinking varied between 0.05 and 0.75% wt. The samples were characterized by the swelling power Q and the average particle size D and observed by light microscopy and low‐temperature SEM. The swelling power decreases with the extent of crosslinking, whereas the average particle size increases. From these observations, the starch samples can be described as suspensions of deformable particles suspended in a continuous suspending medium constituted of polymer chains plus water. The rheological properties allow us to define different concentration regimes depending on the close packing of swollen particles at a concentration C*, which is close to 1/Q. In dilute conditions, that is, for C < C*, the viscosity is little influenced by the degree of crosslinking and, hence, by the particle size. Two domains can be defined: a “true dilute” one for C < 0.6C* and a semidilute one for C > 0.6C*, in which the viscosity rapidly increases with the concentration. Moreover, an apparent yield stress and elastic properties are observed in the concentrated regime, for C > C*. Two domains can be also defined: a first one for C < 2C*, in which the rheological characteristics sharply increase with the concentration, and a second one, a quasi‐plateau domain, for C > 2C*. The variations of these rheological properties suggest that the rigidity of the swollen particles can be considered, contrary to the viscosity in the true dilute regime. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2480–2489, 2001     

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.     

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.     

Effects of a strong polyelectrolyte on the rheological properties of concentrated cementitious suspensions

Strong polyelectrolytes, referred to as superplasticizers, are known to improve the initial fluidity of concentrated cement suspensions. To quantify how the polyelectrolytes affect the fluidity, we have studied the effect of a strong anionic polyelectrolyte, melamine formaldehyde sulfonate (MFS), on the zeta potential of cement particles and on the steady-shear and low-amplitude rheological properties of cement suspensions. Adsorption of low concentrations of MFS onto the cement particles leads to an inversion in the sign of the surface potential, causing the electrostatically flocculated particles to become electrostatically dispersed and giving rise to a corresponding decrease in the steady-shear viscosity and storage modulus. At an intermediate MFS concentration, the steady-shear viscosity and the storage modulus each display a minimum. This concentration corresponds to that at which the zeta potential becomes constant. Larger concentrations of MFS result in an increase in the viscosity and storage modulus, which is attributed to depletion flocculation. These results thus relate the interaction between particles to the suspension fluidity through the analysis on the surface potential of particles and microstructure of suspension.     

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.     

圆管中中性悬浮液流动阻力和流变性的实验测定

对高浓度的液固悬浮液在圆管中的流变特性进行了实验研究,实验体系为聚苯乙烯颗粒在NaCl水溶液中的中性悬浮液。测定了在层流状态下,固体颗粒的体积分数变化（20%～50%）、悬浮液流速变化（0.031～0.22 m&#8226;s^-1）以及颗粒粒度变化对悬浮液压降的影响规律。实验结果表明,固体颗粒的浓度会影响悬浮液的流变性质,颗粒粒径对悬浮液流变性影响微弱。悬浮液的压降随颗粒体积分数和流速的增大而增大,悬浮液的流动特性在较高颗粒浓度范围内符合幂率流体模型。     

Method of grinding as a factor in the rheological and technological properties of alumina suspensions

Conclusions Suspensions of alumina wet-ground and dry-ground in a ball mill are characterized by viscosity changes typical for firm systems with static {ie365-01} and dynamic (Bingham) {ie365-02} fluidity limits.These suspensions are thixotropic; the viscositygh _m of their fully broken up structure is higher and their zeta potential lower than for suspensions of vibro-ground alumina, the explanation being the considerably longer grinding time in a ball mill and the fact that in wet grinding a vigorous interaction proceeds between the solid and liquid phases directly in the grinding process.Alumina wet-ground in a ball mill contains more impurities after washing than alumina dry-ground in a vibro mill. The suspension of the former gives a faster rate of casting but the density and strength of the product are lower.Fired commercial alumina to be used for the production of high-quality dense-sintered refractory corundum ceramics should be dry-ground in a vibratory mill.Translated from Ogneupory, No. 6, pp. 44–51, June, 1977.