A surface study on adsorption of lignosulphonate on mixed Si3N4Y2O3 powder dispersions
Abstract
In the colloidal processing of high performance ceramics, knowledge of the interfacial properties is of crucial importance. Studies have accordingly been made of the surface composition and the dispersion behavior of a silicon nitride-yttrium oxide-lignosulphonate system, prior to sintering. The effect of pH on the adsorption of yttria (Y2O3) and lignosulphonate (LS) on the silicon nitride (Si3N4) powder surface is reported.
The samples were studied by particle size measurements, SEM, X-ray photoelectron spectroscopy (ESCA) and carbon analyses. The ESCA analyzing techniques used were (1) relative surface atomic concentrations (ACs) and (2) evaluation of the substrate coverage derived from the Tougaard background analysis.
It was found that the particle size distribution of the Si3N4-Y2O3 system to be strongly dependent on the pH and concentration of the lignosulphonate added in the dispersion. The ESCA results confirmed that lignosulphonate adsorbed both on the silicon nitride and yttrium oxide particles. It was also found that at pH 7 the relative amount of yttria was increased at the surface with increasing amount of lignosulphonate added in the dispersion.
Zusammenfassung
Bei der kolloidalen Herstellung von Hochleistungs-keramiken sind die Grenzflächen von besonderer Bedeutung. Die Grenzflächenchemie und das Dispersions-verhalten eines Siliziumnitrid-Yttriumoxid-Lignosulphonat-Systems wurde vor dem Sintern untersucht. Der Einfluß des pH-Werts auf die Adsorption von Yttriumoxid (Y2O3) und Lignosulphonat (LS) an der Oberfläche der Siliziumnitridpulver (Si3N4) wurde bestimmt.
Die Untersuchung der Proben erfolgte durch die Bestimmung der Teilchengröße, SEM, Röntgenphotoelektronenspektroskopie (ESCA) und Kohlenstoffanalyse. Bei den ESCA-Techniken handelte es sich um (1) die Bestimmung der relativen atomaren Konzentration an der Oberfläche (ACs) und (2) die Ermittlung der Substratbedeckung abgeleitet aus der Tougaard Hintergrundanalyse.
Es zeigte sich, daß die Teilchengrößenverteilung des Si3N4-Y2O3-Systems stark vom pH-Wert und der zur Dispersion zugegebenen Menge an Lignosulphonat abhängt. Die ESCA-Untersuchungen bestätigen, daß Lignosulphonat sowohl von Siliziumnitrid- als auch von Yttriumoxidteilchen adsorbiert wird. Weiterhin ergab sich, daß bei einem pH-Wert von 7 und bei Erhöhung des Lignosulphonatanteils an der Dispersion die relative Menge an Yttrium an der Oberfläche zunahm.
Résumé
Dans le processus colloïdal de fabrication de céramiques hautement performantes, la connaissance des propriétés interfaciales est d'une importance cruciale. C'est pourquoi des études ont été realisées, avant frittage, sur la composition de la surface et sur le comportement à la dispersion de systèmes nitrure de silicium-oxyde d'yttrium-lignosulfonates. L'effet du pH sur l'adsorption de l'oxyde d'yttrium (Y2O3) et du lignosulfonate (LS) sur la surface d'une poudre de nitrure de silicium (Si3N4) est décrite.
Les échantillons ont été étudiés par sédimentométrie, MEB, spectroscopie ESCA et analyses de carbone. Les techniques d'analyse ESCA employées ont été relatives (1) aux concentrations atomiques de la surface (ACs) et (2) a l'évaluation du recouvrement de la surface à partir de l'analyse de Tougaard.
Nous avons trouvé que la distribution de la taille des particules du systéme Si3N4-Y2O3 est fortement dépendante du pH et de la concentration en lignosulfonate ajouté lors de la dispersion. Les résultats ESCA confirment que le lignosulfonate s'est adsorbé sur les particules de nitrure de silicium et d'oxyde d'yttrium. Il a été aussi démontré qu'à pH 7 la quantité relative d'oxyde d'yttrium a été augmentée sur la surface avec des quantités croissantes de lignosulfonates ajoutées à la dispersion.
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The Influence of Lignosulphonate on the Colloidal Stability of Particulate Dispersions
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Organometallic precursors, an alternative route for the doping of silicon nitride powders?
2002, Journal of the European Ceramic SocietyTwo silicon nitride powders prepared by diimide precipitation and direct nitridation were doped with 5 vol.% yttria using (i) a commercial Y2O3 powder and (ii) a soluble Y-organometallic compound as additive. The aim of this work was a direct comparison between those two doping methods. Homogeneity of additive distribution was characterized by Fourier transform infra-red spectroscopy (FT-IR), photo electron spectroscopy (XPS) and transmission electron microscopy (TEM). Depending on the doping technique used, no major difference in sintering behavior and microstructure evolution were monitored. However, chemical doping results in (i) an enhanced densification rate in the early stage of sintering, (ii) a slight shift of the densification rate maximum (ds/dt) to higher temperatures, and (iii) in a slightly finer final microstructure. Note that doping via organometallic precursors can only be successfully applied, when the powder particle surface reveals the presence of silanol groups, as in case of diimide starting powders. Electron microscopy, Organometallic dopants, Sintering, Si3N4
The effect of anionic polyelectrolytes on the properties of aqueous silicon nitride suspensions
2000, Journal of the European Ceramic SocietyThe effect of anionic polyelectrolytes on the electrokinetic and rheological properties of concentrated Si3N4 suspensions was investigated experimentally. We found that polyelectrolyte adsorption and, thus, colloidal stability at pH>pHSi3N4iep is mainly governed by the surface charge density of the solid phase. Comparing anionic methacrylic acid comb copolymer modifications with grafted poly(ethylene oxide) chains (PMMA-PEO), with poly(acrylic acid) (PAA) showed that the grafted PEO chains have a minor influence on the colloidal stability. The common viscosity minimum for all the anionic polyelectrolytes around pH 7 suggests that the suspensions are electrosterically stabilized. The polyacrylic backbone attains an extended conformation perpendicular to the surface. The effect of excess addition of polyelectrolyte was also discussed; we attribute the significant increase in suspension viscosity to the increased ionic strength caused by the release of associated counterions of the polymer functional groups.
The influence of lignosulphonate on the properties of single and mixed Si<inf>3</inf>N<inf>4</inf> and ZrO<inf>2</inf> suspensions
1999, Journal of the European Ceramic SocietyLignosulphonate (LS), was evaluated as a dispersing agent for single and mixed powder slips, containing Si3N4 and ZrO2 powders, respectively. The surface charge was investigated by measuring the electrophoretic mobility in dilute powder dispersions. The slip stability was determined by visual observations of the settling of the powder and the fluidity of the slip was monitored by measuring the viscosity. It was evident that the different powder dispersions were most successfully stabilized by a high charge induced at high pH-values. However, in order to produce a sufficient fluidity of the slip, a dispersing agent had to be introduced. The optimal concentration range of LS at pH = 10 was found to be 0·2 wt%. The stabilizing mechanism in alkaline dispersions seems to be electrostatic depletion stabilization. The flow properties were finally tested by recording the viscosity for a mixed (composite) powder containing 68·4 wt% Si3N4 and 31·6 wt% ZrO2 at a total solids content of 29–37 vol%.
Surface charge and viscosity of mixed Si<inf>3</inf>N<inf>4</inf>-Y<inf>2</inf>O<inf>3</inf> suspensions containing lignosulphonate
1996, Journal of the European Ceramic SocietyWe have studied the surface charge and the dispersion behavior of silicon nitride-yttrium oxide-lignosulfonate powder dispersions, prior to sintering. In our previous study we reported on the effect of pH on the adsorption of yttria (Y2O3) and lignosulfonate (LS) on the surface of silicon nitride (Si3N4) powder. The adsorption was studied by particle size measurements, scanning electron microscopy, X-ray photoelectron spectroscopy (ESCA) and carbon analyses. In this study, we report the results from the electrophoretic mobility and surface charge determinations and viscosity measurements of the slip. The viscosity measurements were performed as a function of the LS concentration added in the dispersion. This was done in order to determine the optimum concentration of lignosulfonate added in the dispersion, i.e. the concentration which would result in the lowest viscosity for the highest possible dry content of the slip. The surface charge was determined via potentiometric titrations and by measuring the electrophoretic mobility.
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