K₃Ru₈S₈
sulfide polysulfide · sulfide low tempK3Ru8S8 is a sulfide polysulfide suitable as sulfide low temp. Color: yellow-orange. Fired at 130°C from 2 precursors (S, K2CO3). Workshop batch: 500g at €1.52. Compressive strength ~50 MPa; estimated 0.09 kg CO₂/kg (-89% vs Portland cement). Notable: forms without a kiln. Confidence: high.
- forms at
- 130 °C · hotplate · no kiln
- replaces
- portland cement
- CO₂
- 89.1% lower than Portland cement (0.09 vs 0.83 kg CO₂/kg)
- energy
- 89.1% lower than Portland cement (0.60 vs 5.50 MJ/kg)
- compressive
- 50 MPa
- density
- 4.89 g/cm³
- crystal
- triclinic
- band gap
- —
- cost
- €3.04/kg · €1.52 / 500 g batch
- confidence
- high (synthesis route)
- potential
- 0.75 · env 1.00 · novel 1.00 · struct 0.10 · lineage 1.00 · supply 0.26
- flags
- zero kiln: Forming happens without firing — the material cures through chemistry at ambient or hotplate temperature. At building scale this removes the kiln from the supply chain: on-site casting, regional workshops, cold-country fabrication all become available.
Architectural potential
A potassium-ruthenium polysulfide cast at 130 °C, carrying 50 MPa of compression and the family's eighty-nine-per-cent CO₂ cut against Portland cement. Fifty megapascals places this firmly in the non-structural register — surface, tile, inlay, signage — where the kiln-free argument and the unusual metallic-sulfide palette are doing the architectural work rather than the load. Natural placements are drop-cast wall tiles in foyer and corridor linings, cast wayfinding inlays in poured-terrazzo floors, thin decorative panels set into timber joinery, and specialty thresholds where the yellow-orange ruthenium body is wanted as a signal rather than as a ground. Because forming happens below the boiling point of water, the geometry space stays open: flexible mold work, temperature-sensitive inclusions, cast laminates over plywood substrates. At 500 g per batch the tile scale is the natural ceiling. The cement analog lets the environmental argument land with a client without overstating the structural reach. The caveat is the ruthenium supply: platinum-group-metal availability is thin, the cost per batch at €1.52 hides the scarcity upstream, and the supply-chain score at 0.29 signals that specification beyond accent-scale work would not be defensible on resource grounds.
Material character
At 4.89 g/cm³ this is one of the denser members of the low-temperature sulfide palette; an 85×85×28 mm slab already resists the single-handed lift despite its thinness. The ruthenium pushes the yellow-orange body toward a darker, slightly metallic cast — more mustard than honey, with a cool steel undertone that separates it from the titanium and calcium siblings. Surface mold-matte with the typical cast meniscus along the upper rim; edges sharp and as-cast. The sulfur bloom reads as a delicate frost against the deeper body. Compared to the Cu-Mn-Na sulfide, the face is cooler and quieter, with less of the copper-red warmth.
Recipe
500 g batch · peak 130 °C| element | precursor | formula | mass | safety |
|---|---|---|---|---|
| K | potassium carbonate / potash | K2CO3 | 100.0 g | safe |
- Pre-heatHotplate to 150 °C
- MeltSulfur liquefies at 115 °C; full liquid at 130 °C
- CastPour at 140–145 °C
- SetRoom temperature 30 min (firm) → 24 h (full strength)
Zero-kiln process — 130 °C hotplate cast only