Flowing

Understanding silica with PowderCraft expertise.

Replace silica as a flow aid...

Context

In many industries (food, pharmaceuticals, chemicals), the addition of amorphous silica (SiO₂) as a flow aid is common practice. Low percentages (0.1–2%) are generally sufficient to modify the microstructure of the powder bed, reduce residual capillary bridges, and limit interparticle cohesion phenomena.

However, the actual effectiveness of silica depends on subtle parameters: product particle size, relative humidity, porosity, mixing method, and particle surface condition. Conventional methods (shear cell, angle of repose, Hausner ratio, etc.) do not adequately capture subtle changes in cohesion. In particular, these methods do not allow the effect of silica addition on friction and cohesion to be extracted independently. Conventional methods only provide overall flow indicators, often incorporating these contributions in an inseparable manner.
PowderCraft offers a unique solution: direct measurement of cohesion and friction forces by column breakage, capable of detecting differences in the effectiveness of additive addition that are invisible to traditional techniques.

Objective

Evaluate the impact of different concentrations of amorphous silica on the cohesion of several food powders, and compare:

  • the effectiveness of silica observed using the PowderCraft column break method;
  • the sensitivity of conventional shear measurements, which are often insufficient to detect subtle variations.

Materials

Three food powders from one of our customers were tested without silica, then with 1% m/m hydrophobic amorphous silica:

  • Powder A – d50: 180 ± 5 µm – aw = 0.30
  • Powder B – d50: 320 ± 10 µm – aw = 0.25
  • Powder C – d50: 95 ± 3 µm – aw = 0.40

Methods

Shear Cell Test (SCT) : Tests classiques de cisaillement annulaire pour obtenir la cohésion par la méthode de Mohr-Coulomb.
→ Mesure peu sensible aux micro-modifications d’adhésion induites par la silice.

PowderCraft Column Rupture Test (PCRT) : Colonne de poudre tassée à porosité contrôlée. La rupture est imposée sous contrainte verticale décroissante.
→ Fournit une mesure directe de la cohésion (Pa) avec une résolution capable de percevoir l’effet réel de la silice.

Results

Shear Cell Test (SCT): Standard ring shear tests to obtain cohesion using the Mohr-Coulomb method.
→ Measurement not very sensitive to micro-changes in adhesion induced by silica.

PowderCraft Column Rupture Test (PCRT): Compacted powder column with controlled porosity. Rupture is imposed under decreasing vertical stress.
→ Provides a direct measurement of cohesion (Pa) with a resolution capable of detecting the actual effect of silica.

Discussion

The effect of silica is based on its ability to:

  • create a micro-layer between particles;
  • reduce capillary bridges at low humidity;
  • decrease van der Waals forces;
  • limit surface effects (roughness).

The PowderCraft method accurately captures these mechanisms because it directly measures the energy required to break the cohesive structure of the powder. Traditional techniques are not sensitive to some of the micro-surface effects induced by silica.

Conclusion

The addition of silica as a flow aid significantly improves the flowability of powders, but the true extent of this effect can only be revealed by detailed and discriminating measurements of cohesion and friction.

PowderCraft offers:

  • direct, reproducible, and sensitive measurement of cohesion and friction;
  • a unique ability to objectively compare the effectiveness of different additive levels;
  • an optimization tool for formulation and quality control.

Finally, to meet the growing challenges of reducing or eliminating silica in food powders, PowderCraft develops and offers alternative solutions based on bio-based powders (MCC, HPMC, rice starch, etc.). These natural substitutes offer comparable flow performance while complying with regulations, being sustainable, and meeting future market requirements.

At PowderCraft, we want to understand what other methods don’t see and support the industry in moving towards safer and more sustainable solutions.

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