Availableonlineatwww.sciencedirectcom ScienceDirect E噩≈RS ELSEVIER Joumal of the European Ceramic Society 27(2007)2209-2215 www.elsevier.comlocate/jeurceramsoc Characterization of rheological properties of colloidal zirconia B. Jachimska, Z Adamczyk Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30-239 Cracow, Niezapominajek 8, Poland Received 25 March 2006: received in revised form 12 July 2006: accepted 21 July 2006 Available online 22 September 2006 Dynamic viscosity of aqueous suspensions of nanosized zirconia(ZrO2)have been studied for the low volume fraction range. The specific surface area of dry powder was determined from the Bet method. The zeta potential of zirconia particles as a function of ph was measured by the microelectrophoretic method. The isoelectric point found in this way was 4.7. The particle density in aqueous suspensions was found by the dilution method. The dynamic viscosity of suspensions was measured by using a capillary viscometer that eliminated the sedimentation effects. Experimental data showed that for dilute zirconia suspension, the relative viscosity increased more rapidly with the volume fraction than that the Einstein formula predicts. This allowed one to calculate the specific hydrodynamic volume of particles in the suspensions and their apparent density. It was found that particles forming zirconia suspensions were composed of aggregates having porosity of 40-50%. The size of the primary particles orming these aggregates was 0.2 -m that agrees well with the BET specific surface data. The influence of an anionic polyelectrolyte polysodium 4-styrenesulfonate(PSS)on zirconia suspension viscosity also was studied. First the PSs viscosity alone was measured as a function of its volume fraction for various ionic strength of the solutions. The data were interpreted in terms of the flexible rod model of the polyelectrolyte. Then, the viscosity of Zro, in PSS solutions of fixed concentration was measured as a function of the concentration of zirconia. It was revealed that the viscosity of the mixtures was proportional to the product of the zirconia and polyelectrolyte viscosities taken separately. 2006 Elsevier ltd. all rights reserved. Keyword: ZrO2; Dispersants; Rheology; Suspensions 1. Introduction important studies focused on layer by layer deposition, which utilized electrostatic interactions between oppositely charged Understanding the rheological behavior of colloid suspen- species. There is a growing interest in the use of composite mate- sions is important in the analysis and control of the proper- rials in humidity sensors, batteries, microelectronic devices, ties of ceramic materials. High quality and reliability of these magnetic memories, and quantum dot devices. Novel compos- products can be achieved by using homogeneous suspensions ite materials containing inorganic nanoparticles embedded in a composed of well-dispersed particles. Besides stability of sus- polyelectrolyte matrix are currently under investigation for cat pensions and lack of aggregation processes, a high fluidity is vital alytic, optical and other applications for producing ceramics of complex geometrical shape with a Ceramic particles can be stabilized in aqueous solutions by defect-free microstructure after sintering. -3In many technolog- electrostatic and steric interaction. However, it is difficult to ical processes this is achieved by mixing ceramic powders with obtained homogenous, well-dispersed suspension of high solid organic dispersants to obtained better fluidity of the mixture. content. Surface chemical properties are influenced by many Organic-inorganic composites have attracted substantial atten- factors, such as the nature of the ceramic particles, size distribu- ion because of the potential of combining advanced properties tion, surface impurities, nature of solvent, pH value. 3. 5-7In such of organic and inorganic components. Formation of compos- a high solid loading system, the particles have a tendency toward te films based on polyelectrolyte and inorganic nanoparticles agglomeration. This may increass the viscosity of mixtures and has become the subject of extensiv imental work. Many decrease their moldability. The agglomerates can in principle b studied by using the electron microscopy techniques(for exam- ple scanning electron microscopy SEM). However, it is difficult Corresponding author. Tel. +48 12 6395104: fax: +48 12 425 1923 to identify individual agglomerates in the mixture because of kr.edu. pl(Z. Adamczyk) high packing density of the powder. Moreover, the examination 0955-2219/S-see front matter o 2006 Elsevier Ltd. All rights reserved. doi: 10. 1016/j-jeurceramsoc. 2006.07.013Journal of the European Ceramic Society 27 (2007) 2209–2215 Characterization of rheological properties of colloidal zirconia B. Jachimska, Z. Adamczyk ∗ Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, 30-239 Cracow, Niezapominajek 8, Poland Received 25 March 2006; received in revised form 12 July 2006; accepted 21 July 2006 Available online 22 September 2006 Abstract Dynamic viscosity of aqueous suspensions of nanosized zirconia (ZrO2) have been studied for the low volume fraction range. The specific surface area of dry powder was determined from the BET method. The zeta potential of zirconia particles as a function of pH was measured by the microelectrophoretic method. The isoelectric point found in this way was 4.7. The particle density in aqueous suspensions was found by the dilution method. The dynamic viscosity of suspensions was measured by using a capillary viscometer that eliminated the sedimentation effects. Experimental data showed that for dilute zirconia suspension, the relative viscosity increased more rapidly with the volume fraction than that the Einstein formula predicts. This allowed one to calculate the specific hydrodynamic volume of particles in the suspensions and their apparent density. It was found that particles forming zirconia suspensions were composed of aggregates having porosity of 40–50%. The size of the primary particles forming these aggregates was 0.2m that agrees well with the BET specific surface data. The influence of an anionic polyelectrolyte:polysodium 4-styrenesulfonate (PSS) on zirconia suspension viscosity also was studied. First the PSS viscosity alone was measured as a function of its volume fraction for various ionic strength of the solutions. The data were interpreted in terms of the flexible rod model of the polyelectrolyte. Then, the viscosity of ZrO2 in PSS solutions of fixed concentration was measured as a function of the concentration of zirconia. It was revealed that the viscosity of the mixtures was proportional to the product of the zirconia and polyelectrolyte viscosities taken separately. © 2006 Elsevier Ltd. All rights reserved. Keyword: ZrO2; Dispersants; Rheology; Suspensions 1. Introduction Understanding the rheological behavior of colloid suspen￾sions is important in the analysis and control of the proper￾ties of ceramic materials. High quality and reliability of these products can be achieved by using homogeneous suspensions composed of well-dispersed particles. Besides stability of sus￾pensions and lack of aggregation processes, a high fluidity is vital for producing ceramics of complex geometrical shape with a defect-free microstructure after sintering.1–3 In many technolog￾ical processes this is achieved by mixing ceramic powders with organic dispersants to obtained better fluidity of the mixture. Organic–inorganic composites have attracted substantial atten￾tion because of the potential of combining advanced properties of organic and inorganic components. Formation of compos￾ite films based on polyelectrolyte and inorganic nanoparticles has become the subject of extensive experimental work.4 Many ∗ Corresponding author. Tel.: +48 12 639 5104; fax: +48 12 425 1923. E-mail address: ncadamcz@cyf-kr.edu.pl (Z. Adamczyk). important studies focused on layer by layer deposition, which utilized electrostatic interactions between oppositely charged species. There is a growing interest in the use of composite mate￾rials in humidity sensors, batteries, microelectronic devices, magnetic memories, and quantum dot devices. Novel compos￾ite materials containing inorganic nanopatrticles embedded in a polyelectrolyte matrix are currently under investigation for cat￾alytic, optical and other applications. Ceramic particles can be stabilized in aqueous solutions by electrostatic and steric interaction. However, it is difficult to obtained homogenous, well-dispersed suspension of high solid content. Surface chemical properties are influenced by many factors, such as the nature of the ceramic particles, size distribu￾tion, surface impurities, nature of solvent, pH value.3,5–7 In such a high solid loading system, the particles have a tendency toward agglomeration. This may increass the viscosity of mixtures and decrease their moldability. The agglomerates can in principle be studied by using the electron microscopy techniques (for exam￾ple scanning electron microscopy SEM). However, it is difficult to identify individual agglomerates in the mixture because of high packing density of the powder. Moreover, the examination 0955-2219/$ – see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2006.07.013