Cr₉Cu₃S₁₆
sulfide metal composite · sulfide low tempCr9Cu3S16 is a sulfide metal composite suitable as sulfide low temp. Color: green-red-copper. Fired at 130°C from 3 precursors (Cr2O3, S, CuO). Workshop batch: 300g at €7.48. Compressive strength ~350 MPa; estimated 0.09 kg CO₂/kg (-89% vs Portland cement). Notable: forms without a kiln. Confidence: medium.
- 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
- 350 MPa
- density
- 4.03 g/cm³
- crystal
- tetragonal
- band gap
- 0.00 eV
- cost
- €24.93/kg · €7.48 / 300 g batch
- confidence
- medium (synthesis route)
- potential
- 0.80 · env 1.00 · novel 1.00 · struct 0.70 · lineage 0.50 · supply 0.46
- 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 chromium-led zero-kiln cast sulphide sitting in the same 350 MPa, eighty-nine-per-cent-CO₂-cut territory as its copper-heavy and vanadium-heavy cousins, but with distinct architectural affordances from the chromium matrix. The hotplate cast at 130 °C keeps form-work plywood-friendly and gives a surface that sits particularly well against timber and stone substrates. Natural placements are interior floor tiles in exhibition and gallery architecture, thick cast threshold-pieces in retrofit carpentry, inlay panels in joinery where the green-red mottle is wanted as a figure, and cast sill plates along timber-framed window openings. The cement-replacement argument is sharp at the small-batch scale — 300 g to 1000 g — but does not scale to wall-element dimensions, so the specification register stays at tile and threshold rather than slab and block. Against Portland cement, the building loses the kiln and keeps the compression; against conventional fired-clay tile, the project also loses the kiln and gains the cast-form freedom. The caveat is lower cost than the copper-vanadium sibling (€7.48 per 300 g) but the same workshop hygiene load: chromium dust and sulphide odour at cut require active ventilation, and the dressed edges need wet grinding rather than dry.
Material character
At 4.03 g/cm³ and 85×85×34 mm the slab sits lighter than the copper-vanadium sibling by a perceptible margin — still firmly two-handed, but the weight moves more easily in the grip. Colour reads a characteristic green-red-copper mottle, with the chromium matrix giving a cooler, greener ground than the copper-heavy Cu₁S₁₆V₉ body. Surface mould-matte, with the cast meniscus sheen playing across the upper face; edges come as-cast, crisp and slightly reflective. A fine sulphur bloom crystallises unevenly under raking light. Compared against the vanadium cousin the Cr₉ body reads more stone-like and less metallic — closer to polished serpentinite than to cast bronze.
Recipe
300 g batch · peak 130 °C| element | precursor | formula | mass | safety |
|---|---|---|---|---|
| Cr | chromium(III) oxide | Cr2O3 | 74.13 g | safe |
| Cu | copper(II) oxide (black) | CuO | 25.87 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