COLLOIDAL SILICA

AGENDA Colloidal silica chemistry -Physical characteristics -Types Colloidal silica manufacturing -Evaporator -Grow/UF -UltraXol Colloidal silica applications -Investment Casting -Electronics -Refractories -Coatings -Catalysts

Forms of Silica Colloidal Silica nm Fumed: 1000 nm Precipitated: 2000 nm Gel: nm * - estimated 2004 US Demand by Freedonia

Colloid: An intimate mixture of two substances, one of which (dispersed phase) is uniformly distributed in a finely divided state through the second substance (dispersion medium). Definition

Precipitated Silica (2000 nm aggregate) Fumed Silica (1000 nm aggregate) Colloidal Particle (20 nm) Sand (600 mesh) Silica sizes

Brownian Motion Brownian forces overcome the force of gravity SiO 2

Si-OH Si-O - Si-OH Al-O - Si-OH Silica Surface Hydroxyl groups and incorporated aluminum give the particle a charged surface

Electrical Repulsion Stability SiO 2 Na +, NH 4 +, or K + Stability of sols by electostatically inhibiting collisions

SiO 2 Steric Hindrance Stability SiO 2 Stability of sols by sterically inhibiting collisions

Gelation Aggregation of particles into chains which fill the entire volume

Precipitation Aggregation of particles into dense clusters sufficiently large to settle

Stable (charge) unstable Metastable (steric) Stability versus pH pH Increased Stability

Particle Size Effects 20% SiO 2 20 nm 20% SiO 2 15 nm 20% SiO 2 10 nm Stability Stability increases with increasing particle size

Concentration Effects 10% 15 nm 30% 15 nm Increasing Concentration Dilution increases stability Increasing Stability

Increasing Concentration Increasing Particle Size Unstable Stable

Increased Stability 70 nm 20 nm 4 nm Stability - Effects of pH, Particle Size

pH Increased Stability Concentration pH Effects 10% concentration 30% concentration

Temperature Effects gelation stable 32 o F 210 o F precipitation High temperature Freezing Increases concentration

pH Increased Stability Ionic Strength Effects  mhos <2000  mhos >5000  mhos

Ionic Strength Effects Na + Ca 2+ Al 3+ Increasing Ionic Strength Increasing Stability

Oppositely Charged Particle Results in precipitation or flocculation

Stability Summary  Minimum stability in pH 4 to 7  Increased stability with larger particle diameters  Increased stability with lower concentrations  Decreased stability with higher ionic strengths  Stability dependent on order of addition

Colloidal Silica Specifications PARTICLE SIZE Titration -Method we use to measure particle size -Accurate for smaller particle sizes Light Scattering -Inaccurate for small particle sizes Transmission Electron Microscopy (TEM) -Most Accurate -Only used during product development

Colloidal Silica Specifications POLYDISPERSITY Measures particle size distribution Light Scattering gives inaccurate result TEM gives good results

COLLOIDAL TYPES Standard Colloidal Silica 2-125nm particle size Sodium, Potassium or ammonia stabilized % solids level Narrow/Broad particle distribution Anionic Surface Charge Deionized/Acid Sol nm Particle size (currently only 20nm) Low pH Slightly anionic surface charge

Organosols Colloidal Particles Dispersed In Organic Solvents

R O H O R O H O H O R O H O R SiO 2 core R O H O R O H O H O R O H O R SiO 2 core Polar solvent Organosol Silica in hydrophilic solvents

Colloidal Metal Oxides   Alumina   Silica/Alumina   Titania   Zirconia   Tin oxide

Metal Oxide Sols Properties  Low and high pH  Homogenous particles  Particle size less than 15 nm  Positively charged

++ SiO homogeneous metal oxide ++ SiO Coated Metal Oxide

Coated Metal Oxide Types  Alumina  Ceria  Others  Zirconi a  Titania Properties Low pH Cationic Charge Behave more like coating metal nm particle size

DOPED SOLS - - Si Alumina, Ceria, Titania, & Zirconia

DOPED SOLS PROPERTIES High pH Anionic Surface Charge More stable than standard sol nm particle size

Ion Exchange COLLOIDAL SILICA MANUFACTURING EVAPORATOR Sodium Silicate Reactor Water/Caustic Heal As particle grows, water is evaporated off

COLLOIDAL SILICA MANUFACTURING GROW/UF Sodium Silicate Ion Exchange Reactor Water/Caustic Heal Ultra Filtration Unit

COLLOIDAL SILICA MANUFACTURING ULTRAXOL Sodium Silicate Reactor DI Resin Caustic Ultra Filtration Unit

PILOT PLANT CAPABILITIES Drum size quantities UltraXol Capabilities Grow/UF Deionization

Applications BinderCatalysts, refractories, ceramics Abrasion resistanceFilms, coatings, paints AbrasionPolish, cleaning Better Image formationPrinting, photography Protein coagulantAnimal wastes, juices,wine Strength increasePaper Drainage aidsPaper Dispersing aidInks, dyes Anti-blockFilms, coatings Anti-soilTextile, coatings Anti-statPlastics,fibers ReinforceRubber, foam. Effect Application