Colloidal silica polishing suspension

Identity and related forms

Nouryon’s polishing sol SP3089 is sodium-stabilized with negative particles, 49.9–51.5 wt% SiO₂ and pH 9.1–9.9 at 20 °C. Its separate coating grade CT17 PDL is described as uncharged at pH 2.0–4.0 at 20 °C. Neither sheet gives a numerical particle diameter. SP3089 CT17 PDL Applied Material Solutions distinguishes aqueous silica sol from amorphous fumed silica powder made by a flame process. Applied Material Solutions, 2023

In a silica sol, amorphous particles are dispersed in liquid. Sodium silicate contains soluble species. Quartz is crystalline. Nouryon silica chemistry reference Nouryon functionality reference

A complete polishing slurry can contain ingredients beyond silica and water. Fujimi describes GLANZOX as colloidal silica in a liquid containing special ingredients. Its E-Series addresses wafer edges, with different named products for bare silicon and oxide-bearing wafers. An abrasive sol, a formulated polishing product and a working mixture therefore describe different levels of formulation. The last distinction is explanatory synthesis. Fujimi GLANZOX and E-Series brochure.

Sol chemistry belongs to the grade

Nouryon's chemistry reference describes alkali- or ammonia-stabilized negative particles, cationic surface modification, deionized acidic sols and silane modification. These are alternatives, not simultaneous attributes of every product. The page's early comparison gives pH 9–11 for colloidal silica, but its later discussion explicitly includes acidic grades. The exact-grade sheets below resolve that overly broad comparison. Nouryon chemistry reference.

The following values belong to Nouryon's sheets dated January 30, 2023. Both identify discrete, smooth, spherical amorphous particles in water. CT17 PDL is a coating and surface-treatment example, not evidence of a qualified polishing product. SP3089 is marketed primarily as a polishing agent. CT17 PDL; SP3089.

Neither sheet supplies a numerical particle diameter. A surface-area measurement is not a reported size distribution. The sheets distinguish warranted specification entries from other characteristics. For example, CT17 PDL's sodium entry is 300 mg/kg under characteristics. The producer's uncharged description therefore does not establish literal absence of every ion. CT17 PDL; SP3089.

Acidic does not uniquely mean uncharged. NYACOL's NexSil 20ZK-DI sheet, marked 20130619, describes negative particles at pH 2.3–3.0. It gives 20% SiO₂ and potassium-silicate origin, and identifies the material as an abrasive for metal CMP slurry formulations, including copper and tungsten. The percentage basis is not stated in that sheet. It cannot be silently recast as wt% or vol%. Its suitability statement retains application testing rather than guaranteeing results. NYACOL data sheet.

Particle size and measurement basis

A primary particle is an individual particle. An agglomerate contains multiple particles, while a hydrodynamic diameter describes motion through a fluid under the measurement model. These quantities need not coincide. NYACOL itself lists two size ranges for NexSil 20ZK-DI. NYACOL data sheet; Tuoriniemi et al., 2014, methods and discussion.

The sheet does not identify the Z-average instrument or detailed calculation procedure. Its headline description of 10 nm agrees with the surface-area-derived range, not a claim that every measurement returns 10 nm. Neither range is a maximum particle size. NYACOL data sheet.

Tuoriniemi and colleagues compared six methods on two batches of Eka Chemicals Bindzil 40/130. For sample A, table 1 gives arithmetic means of 33.9 ± 0.9 nm by electrospray scanning mobility sizing, 34.7 ± 2.4 nm by SEM and 31.6 ± 1.8 nm by TEM. Uncertainties are 95% confidence intervals. Their DLS result is a harmonic Z-average extrapolated to infinite dilution, not the same average as those arithmetic means. 2014 study, table 1 and footnotes.

The authors attributed smaller TEM results to grid-preparation bias. Hydrodynamic sizes were smaller than dry-particle sizes, with a permeable gel layer proposed as an explanation. These are sample-specific findings, not universal correction factors. Tuoriniemi et al., sections 3–4.

As explanatory synthesis, a size comparison needs the method, sample preparation and distribution weighting as well as units. 0.04 µm = 40 nm converts length only. It does not convert a primary-particle measurement into an agglomerate size, a Z-average into a median, or a nominal size into a coarse-particle limit.

Concentration, density and conditional calculations

Mass fraction is silica mass divided by total dispersion mass. Volume fraction has a different denominator and requires component-volume information. Dispersion density includes the liquid, so it cannot substitute for particle density. These definitions and the calculation below are explanatory synthesis of the distinct wt% and dispersion-density quantities in the producer sheets. SP3089; CT17 PDL.

Assume a hypothetical stock contains exactly 50 wt% SiO₂, all added water is silica-free, and no material is lost. Mixing 100 g of stock with 400 g of water gives 50 g SiO₂ in 500 g total, or 10 wt% SiO₂. It does not give 10 vol%, and the calculation does not establish a suitable polishing dilution. pH cannot be calculated by averaging the two liquids' pH values.

For ideal, nonporous, equal-sized spheres, geometry gives specific surface area = 6 / (particle density × diameter) in consistent units. This conditional derivation does not determine a real distribution or an agglomerate size. Surface roughness, porosity, size variation and the measured surface-area method limit that model. The separate NYACOL size entries illustrate why the model's diameter is not automatically the value from another sizing method. NYACOL.

Chemical-mechanical polishing evidence

Milošev and colleagues studied Grade 5 Ti-6Al-4V discs using grinding, diamond polishing and a final OP-S silica suspension with hydrogen peroxide. The methods report 0.04 µm silica and 0.25 µm agglomerated size. This was a combined treatment, not a comparison that isolated silica's contribution from peroxide or previous preparation. 2024 original study, experimental section and table I.

For their Ti64-OP-S specimen, 3D profilometry gave Sa of 0.017 µm over 1 mm × 1 mm. That measured result belongs to that surface, preparation and measurement area. XPS depth-profile fitting gave a 2.7 nm oxide layer after the combined treatment versus 5.5 nm after the compared grinding treatment. The authors interpret polishing through concurrent oxide removal and reformation. Their EDXS result without detected oxygen did not establish an oxide-free surface, because its analysis depth was much greater than the thin oxide layer. Milošev et al., results, figures 1 and 7.

The paper's unexplained 20 kN polishing-force entry remains a source uncertainty, not a recommended load or an assumed correction. Milošev et al., experimental section.

As synthesis, chemical modification, abrasive contact and the workpiece's surface layer can all contribute to the result. Quartz hardness and dense-glass properties cannot predict the behavior of a formulated suspension. The reviewed evidence establishes no universal relation between pH and removal rate, substrate compatibility, final roughness, pad pressure or speed. It also establishes no customer-qualified process. Finishing process references.

Storage and evidence limits

For SP3089 specifically, Nouryon gives 5–35 °C transport and storage and warns that freezing causes irreversible precipitation. It assigns twelve months of shelf life after production under its recommended conditions and notes possible sedimentation with longer storage. These are supplied-grade limits, not limits for every silica sol or diluted working slurry. SP3089 sheet, storage section.

Nouryon describes gel formation through links between particles. A gelled sol therefore differs from a freely dispersed slurry. Drying, gelation and crystallization are not interchangeable labels. Neither drying residue nor an agglomerate proves quartz formation. This is explanatory synthesis of particle organization versus crystalline ordering. Nouryon functionality; Nouryon chemistry reference.

The reviewed producer evidence includes both complete three-page Nouryon sheets, the complete one-page NYACOL sheet and Fujimi's two-page brochure marked H23.06 ver1.3. Fujimi's typical-property tables are not a complete formulation or an operating specification. The Nouryon and AMS webpages have no technical revision identifier beyond AMS's displayed August 21, 2023 date. Current hosting does not make these historical document dates current revisions.

Both original studies' main texts, tables and figure captions were read. Tuoriniemi et al. appeared June 19, 2014 in Science and Technology of Advanced Materials 15, 035009. Eka Chemicals is the supplier named in that historical experiment. Milošev et al. appeared November 13, 2024 in Journal of The Electrochemical Society 171, 111503. Supplementary files were not independently evaluated. The studies provide no complete commercial slurry formulations or universal process qualification. Sizing study; Ti-6Al-4V study.

No exact-grade safety data sheet or lot analysis was evaluated here. The amorphous particle identity does not certify zero crystalline contamination, and no universally safe exposure follows from it. Producer handling language and polishing-performance evidence address different questions.