Lightweight Silica Brick

Lightweight silica bricks are insulating refractories carrying at least 91% SiO₂, in which the silica is converted to tridymite and cristobalite during firing. That conversion is the whole point of the material: it gives the brick the same low and predictable thermal expansion as the dense silica working crown it backs. XZK supplies grades LS160, LS162 and LS164 at bulk densities of 0.8, 1.0 and 1.2 g/cm³, with cold crushing strength from 2.0 to 4.0 MPa and refractoriness under load from 1600 to 1640°C.

XZK Group manufactures lightweight silica bricks at our Xinmi plant in Henan. Their principal application is the insulation layer above a silica crown in a float, photovoltaic or end-fired glass furnace, where the backing course must expand and contract in step with the working arch.

What Is a Lightweight Silica Brick?

The material is built from crushed silica rock, graded and bonded with a small addition of mineraliser, then fired to a high temperature and soaked long enough to complete the conversion of quartz into tridymite and cristobalite. That conversion happens once, in the kiln, and is deliberately finished before the brick is shipped. A brick that still contained unconverted quartz would continue to expand in service, which is unacceptable in an arch. The finished brick has a very low and well-defined residual expansion, and that predictability is what makes it usable in a crown.

The reason lightweight silica, specifically, is used to insulate a silica crown comes down to expansion matching. A silica crown grows measurably as it heats from cold to operating temperature, and the expansion is not uniform through the arch. If the insulation course above it were made of fireclay or mullite, whose expansion is different, the two layers would move by different amounts at the interface. The bond between them would be sheared, a gap would open and hot gas would channel through the crack, concentrating heat loss and eventually damaging the working brick. A lightweight silica backing expands with the crown, so the two courses act as one structure.

The silica body also retains the property that makes dense silica the standard crown material in the first place. Under sustained load at temperature, silica develops a viscous liquid phase that allows the brick to accommodate local stress rather than crack, and a lightweight silica brick carries the same chemistry, at 91% SiO₂ minimum and with alumina held to 1.0% or below. Alumina is controlled because it raises the temperature at which the liquid phase forms and stiffens the body, so keeping it low protects the behaviour the crown relies on.

The trade-off is that silica insulation is not the lightest option. The three grades run from 0.8 to 1.2 g/cm³ with conductivity at the moderate end of the insulating range, and their cold crushing strength of 2.0 to 4.0 MPa is modest. The value is not maximum insulation value per kilogram; it is that the brick can be placed directly on a silica crown at all, allowing a lighter and cooler stack above it.

Key Properties

• SiO₂ ≥ 91% with Al₂O₃ ≤ 1.0%, keeping the body in the silica chemistry that a crown relies on and avoiding the stiffening effect of alumina.
• Low and predictable thermal expansion after complete conversion to tridymite and cristobalite in the kiln, so the insulation course moves with the working crown rather than shearing away from it.
• Bulk density from ≤ 0.8 to ≤ 1.2 g/cm³ — roughly half that of a dense silica crown brick — so the arch carries far less additional deadweight than a dense backing course would impose.
• Cold crushing strength from ≥ 2.0 MPa (LS160-0.8) to ≥ 4.0 MPa (LS164-1.2), sufficient for a crown backing course and for handling during bricklaying.
• Refractoriness under load from ≥ 1600°C (LS160) to ≥ 1640°C (LS164), giving good margin above the interface temperature that develops above a working crown.
• No free silica reaction with alkali vapour that would open the backing course, and the same resistance to flue-gas attack that makes dense silica the standard crown material.