Introduction
Quartz is one of the most critical raw materials in ceramic body formulations.
As a stable mineral with a high melting point and strong chemical inertness, quartz plays a pivotal role in controlling dimensional stability and thermal behavior during the firing and cooling processes of ceramic products.
Different types of quartz influence the thermal expansion characteristics of ceramic bodies through particle size, purity, and morphology. Finer quartz particles result in higher thermal expansion coefficients and generate more microcracks during cooling. Coarser particles, however, may reduce mechanical strength due to greater stress mismatch between grains and the matrix. Pure fused quartz (amorphous silica) exhibits an extremely low thermal expansion coefficient, whereas crystalline quartz undergoes phase transitions that cause significant volume changes, potentially leading to cracking if improperly handled.
The core impact of different quartz types on ceramic bodies manifests in:
| Dimensional stability during firing | Reaction with feldspar and clay | Microstructure and strength | Thermal shock resistance | |||
High-expansion quartz (natural type) is prone to warping or cracking during cooling. Fused quartz, with its near-zero expansion properties, significantly enhances thermal shock resistance. | Quartz reacts with alkali elements in feldspar to form silicate glass phases, which may accelerate vitrification but potentially exacerbate shrinkage. | Fine quartz particles promote dense packing and reduce pore formation. Coarse quartz may cause uneven stress distribution. | Low-expansion silica or partially amorphous quartz significantly enhances resistance to temperature fluctuations. |
Differences Between Crystalline and Amorphous Silicon
Crystalline Quartz: Natural crystalline quartz undergoes significant volume changes when crossing its inversion temperature during firing and cooling, leading to stress accumulation and microcrack formation. This characteristic readily causes issues like body cracking (dunting) and is the primary cause of thermal expansion in ceramic bodies.
Amorphous Silicon Dioxide: The amorphous structure found in materials like fused quartz glass lacks the crystalline framework that causes volume changes during temperature fluctuations. Consequently, its thermal expansion coefficient is significantly reduced.
Particle Size
Finer Particles: Smaller quartz particles exhibit higher thermal expansion values and generate more microcracks during the cooling phase.
Coarse particles: Larger quartz particles reduce mechanical strength and cause more severe microcracks due to increased stress between quartz grains and the surrounding matrix.
Summary:
The type, purity, and particle size of quartz are critical factors determining the thermal expansion behavior and ultimate performance of ceramic bodies. The dramatic volumetric change of crystalline quartz at phase transition points is the primary source of in-situ stress and microcracks within the body. In contrast, fused quartz, with its near-zero expansion characteristic, significantly enhances product dimensional stability and thermal shock resistance. While fine-grained quartz promotes densification, it may exacerbate thermal expansion; coarse grains, meanwhile, readily become stress concentration points, weakening mechanical strength. Therefore, in the development of high-end products like sanitaryware, scientifically selecting quartz raw materials is crucial for optimizing green body microstructure, mitigating cracking risks, and enhancing product reliability. Precise control over quartz thermal behavior serves as an indispensable bridge connecting ceramic formulation design with exceptional product performance.