Conductive Graphite Ink with Sodium Silicate
This project demonstrates how to formulate a water-based conductive ink using high-purity flake graphite and liquid sodium silicate (water glass). The graphite provides electrical conductivity, while sodium silicate acts as an inorganic, high-temperature-resistant binder. The result is a durable conductive coating suitable for STEM education, demonstrations, and experimental electronics.
What You'll Need
Ingredients
- 20–30 g high macro-crystallinity graphite powder
- 20–25 mL liquid sodium silicate (water glass, SSN)
- 5–15 mL distilled water (for viscosity adjustment)
Equipment
- Glass beaker or mixing bowl
- Spatula or glass stirring rod
- Mortar and pestle (or fine sieve)
- Digital scale (recommended)
- Brush, spatula, or dropper
- Gloves and eye protection
The Process
- Prepare the workspace: Work in a clean, well-ventilated area. Wear gloves and eye protection because sodium silicate is alkaline.
- Disperse the graphite: Lightly grind the graphite powder using a mortar and pestle to break up agglomerates and improve particle dispersion.
- Add sodium silicate: Transfer the graphite into the mixing vessel. Slowly add liquid sodium silicate while stirring continuously.
- Adjust viscosity: Add distilled water in small increments until a smooth, paint-like consistency is achieved. The mixture should spread easily without running.
- Homogenize: Mix thoroughly for several minutes until the graphite is evenly suspended and no dry pockets remain.
- Rest briefly: Allow the mixture to sit for 5–10 minutes to release trapped air bubbles before application.
How to Use
- Apply using a brush, spatula, or dropper.
- Suitable substrates include paper, cardboard, ceramics, plaster, concrete, and glass.
- Allow to air dry for 12–24 hours.
- For increased conductivity, apply multiple thin layers, allowing drying between coats.
- Full curing improves adhesion and durability over 24–48 hours.
Popular Variations
High Conductivity Coating
- Increase graphite content to 35–40% by weight.
- Expect lower mechanical strength but improved conductivity.
Flexible Paper Circuits
- Thin the ink slightly with additional water.
- Apply multiple layers to paper or cardstock.
High-Temperature Conductive Layer
- Apply to ceramic or refractory substrates.
- Sodium silicate remains stable at temperatures where organic binders degrade.
Scientific Background
Graphite Conductivity
Graphite conducts electricity due to its delocalized π-electron system within stacked graphene layers. Electrical pathways form when graphite particles contact one another within the binder matrix.
Role of Sodium Silicate
Liquid sodium silicate (Na₂SiO₃) functions as an inorganic adhesive, film-forming binder, and high-temperature-resistant matrix. Upon drying, it forms a rigid silicate network that locks graphite particles in place while preserving conductive pathways.
Optimizing the Ratio
- Too much silicate → stronger adhesion, lower conductivity.
- Too much graphite → higher conductivity, weaker adhesion.
- Balancing these properties is a key learning objective.
Safety Notes
- Sodium silicate has a pH of approximately 11 and may cause skin or eye irritation.
- Always wear gloves and eye protection when handling alkaline solutions.
- Avoid inhaling graphite dust during grinding or mixing.
- Do not apply to skin or use for cosmetic purposes.
- Store in a sealed container to prevent premature drying.