Quartz sand is a widely‑used raw material for refractory products, valued for its excellent high‑temperature resistance. Its thermal performance originates from its chemical composition, crystal structure, and phase transformation behaviour under heating conditions, which define its applicable temperature range and limitations within refractory systems.
Chemical and structural basis for high‑temperature resistance
Quartz sand consists mainly of silicon dioxide (SiO₂), an oxide with extremely high chemical stability. Pure silica does not melt until it reaches approximately 1713 °C. Under oxidising high‑temperature environments, it hardly reacts with air, making it inherently resistant to thermal degradation. The strong covalent bonds inside the quartz crystal lattice deliver good structural stability at elevated temperatures, forming the foundation for refractory service.
However, quartz undergoes polymorphic phase changes during heating. α‑quartz transforms into β‑quartz, further changing into tridymite and cristobalite as temperature rises. Each crystal‑structure transition brings volume expansion. This thermal expansion effect is the most critical factor restricting quartz‑based refractory service performance, rather than melting failure.
High‑temperature performance in refractory service
- Operating temperature range
Well‑processed quartz‑based refractory materials normally work continuously between 1000 °C and 1450 °C. When the temperature approaches 1600 °C, softening and creep gradually occur, so quartz sand refractories are not suitable for long‑term service close to its melting point. Impurities such as alumina, iron oxide and alkali metal oxides inside quartz sand will form low‑melting eutectics, lowering the actual service temperature and accelerating high‑temperature deformation. High‑purity quartz sand with low impurity content obtains better refractory performance. - Thermal shock challenges
Phase‑transition‑driven volume expansion and contraction take place during heating and cooling cycles. Rapid temperature fluctuation creates internal thermal stress inside refractory bricks or castables. Without reasonable formulation control, repeated thermal cycling may trigger cracking, spalling and structural damage. For this reason, quartz‑containing refractory formulations often adopt graded particle size distribution, introduce fused silica components, or add stabilisers to buffer volume variation. - Resistance to slag and chemical corrosion
Quartz sand belongs to acidic refractory raw material. It exhibits good corrosion resistance against acidic slags and gaseous atmospheres at high temperature. Nevertheless, it reacts violently with basic substances such as calcium oxide and magnesium oxide. In contact with basic molten slag, chemical erosion will happen, generating low‑melting silicate phases and destroying the refractory structure. Therefore quartz‑based refractories are selected for acidic working conditions instead of alkaline slag environments.
Practical processing measures for refractory‑grade quartz sand
To maximise high‑temperature performance, refractory‑grade quartz sand requires strict raw‑material control and processing:
- Strictly reduce alkali metals, iron and other harmful impurities by washing, magnetic separation and flotation, avoiding low‑melting point phases.
- Adopt rational particle gradation of coarse and fine quartz grains to improve bulk density and reduce thermal stress risk.
- Part of the raw material can use fused quartz to mitigate volume change caused by crystal phase transitions.
- Match suitable binders to guarantee high‑temperature structural strength without introducing low‑melting impurities.
Quartz sand achieves high‑temperature resistance mainly from the high melting point and chemical stability of silica. Its practical service limit is constrained by crystal‑phase transition volume expansion, impurity‑induced low‑melting eutectics and chemical incompatibility with basic slags. When raw‑material purity, particle grading and working‑condition matching are well controlled, quartz sand serves as a cost‑effective acidic refractory raw material for kilns, furnaces and high‑temperature lining systems.
