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Why Does Ceramic Slip Hard Pan? A Technical Protocol Based on Colloidal Stability
Why Does Ceramic Slip Hard Pan? A Technical Protocol Based on Colloidal Stability
Root Cause: Colloidal Instability in Casting Slips
In a well-deflocculated slip, clay particles remain dispersed due to high negative zeta potential (typically <−30 mV), creating repulsive forces that overcome van der Waals attraction (per DLVO theory). Hard panning occurs when this balance collapses:
- Bacterial metabolism degrades organic dispersants (e.g., CMC), producing organic acids that lower pH → reduces surface charge → zeta potential rises toward zero.
- Electrolyte accumulation (e.g., Ca²⁺ from water or raw materials) compresses the electrical double layer, reducing repulsion range.
- Once repulsion drops below critical threshold, particles aggregate under gravity (Stokes’ Law), forming a dense, non-redispersible sediment — “hard pan”.
Technical Remediation Protocol
- Maintain pH ≥ 9.5
Use Na₂CO₃ or NaOH to buffer slip. Below pH 9, edge charges on kaolinite become positive, promoting face-edge flocculation. - Replace Organic Dispersants with Inorganic Polyphosphates
Switch to Goway’s high-purity Sodium Tripolyphosphate (STPP) or Sodium Hexametaphosphate (SHMP). These:- Chelate multivalent cations (Ca²⁺, Mg²⁺)
- Adsorb on particle surfaces, enhancing negative charge
- Resist microbial degradation → stable for >14 days
- Apply Industrial Biocide Proactively
Add 200–300 ppm formaldehyde-free biocide (e.g., Kathon LX) during slip preparation to inhibit microbial growth — especially critical in warm/humid climates. - Monitor Zeta Potential Weekly
Target: <−30 mV. If rising toward −15 mV, re-dose deflocculant immediately.
Why This Works: The Science Behind Stability
STPP and SHMP shift the slipping plane outward via adsorption, increasing |ζ| without altering bulk viscosity. Unlike lignosulfonates, they do not serve as carbon sources for bacteria — eliminating the primary pathway for pH drift and hard-pan formation in long-term storage.
Protocol developed by Goway R&D Team (PhD in Colloid Chemistry, 10+ years in ceramic process optimization). Validated in tile plants across Southeast Asia and Southern Europe.
📥 Download Full Protocol with Dosage Tables & Zeta Guidelines (PDF)
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