B₄Cr₂Fe₁₀O₂₀
iron oxide ceramic · structural ceramicB4Cr2Fe10O20 is a iron oxide ceramic suitable as structural-ceramic. Color: green. Fired at 1100°C from 3 precursors (Cr2O3, B2O3, Fe2O3). Workshop batch: 1000g at €7.38. Compressive strength ~100 MPa; estimated 0.79 kg CO₂/kg (+258% vs clay brick). Notable: visible absorber. Confidence: high.
- forms at
- 1100 °C · high-fire
- replaces
- clay brick
- CO₂
- 258% higher than clay brick (0.79 vs 0.22 kg CO₂/kg; 3.6× higher)
- energy
- 75% higher than clay brick (5.25 vs 3.00 MJ/kg; 1.8× higher)
- compressive
- 100 MPa
- density
- 4.57 g/cm³
- crystal
- orthorhombic
- band gap
- 1.37 eV
- cost
- €7.38/kg · €7.38 / 1000 g batch
- confidence
- high (synthesis route)
- potential
- 0.29 · env 0.00 · novel 0.40 · struct 0.30 · lineage 1.00 · supply 0.00
- flags
- visible absorber: A real-colour solar-gain control layer. Where the body takes visible light into itself rather than reflecting it, the material becomes a selective heat collector — useful on thermal-mass walls, absorber panels, and warm-toned cladding.
Architectural potential
An iron-oxide-chromium-boride ceramic with a visible-absorber face: the body takes in visible light as heat rather than reflecting it, turning a dense fired ceramic into a selective thermal collector. Natural placements are south-facing absorber panels in passive-solar façades, warm-toned cladding tiles over thermal-mass walls, hypocaust floor tiles that double as daytime collectors, and summer-pavilion thermal-wall infills where the deep green body colour and the heat uptake are the dual argument. At 100 megapascals of compression the body sits at block-work and thick-cladding scale — compressive vault tiles, structural tile patches — rather than primary-post territory, which separates it from the thin-section cousins in the same family. The caveats are unusually severe for a dense ceramic of this kind. Embodied CO₂ runs 258 per cent higher than fired clay brick, the supply-chain score sits at zero, and the chromium content pushes safety attention up during firing and cutting. These trades forbid bulk specification entirely. The material belongs in the signature-tile register: a field of solar-absorber tiles on one sun-facing passive-thermal wall, paid for by the colour-and-heat coupling rather than by the load capacity, which is incidental. Confidence is high and kilogram-scale batches are feasible, so production at facade-tile scale is tractable if the argument holds.
Material character
A saturated deep-forest green body at 4.57 g/cm³ in an 85×85×30 mm slab — the green is the chromium-iron-boride signature, distinct from the cobalt-blues and olive-titanium greens elsewhere in the ceramic palette. The slab firms two-handed, mid-density for a fired ceramic block, closer in hand-feel to a glazed stoneware paver than to a technical perovskite tile. Surface sits vitrified matte from the 1100 °C fire, with a slight oxidised sheen where the iron-rich phase concentrates. Edges cold-cut with kerf-whitening. Fully opaque; the visible-absorber face reads warm under direct sunlight as heat enters rather than reflects. Against a plain iron-oxide brick sibling the chromium deepens the green and the absorber behaviour is the legible difference.
Recipe
1000 g batch · peak 1100 °C| element | precursor | formula | mass | safety |
|---|---|---|---|---|
| B | boron oxide (or borax Na2B4O7) | B2O3 | 12.78 g | safe |
| Cr | chromium(III) oxide | Cr2O3 | 13.95 g | safe |
| Fe | iron(III) oxide (red) | Fe2O3 | 73.27 g | safe |
- 1Ramp
- 2Hold
- 3Ramp
- 4Hold
- 6Ramp
- 7Hold
Visible absorber — saturated color from bandgap in the visible range