How to deal with the stress generation in quartz

1. Thermal stress induced by temperature gradient

Quartz glass can experience significant thermal stress when exposed to an uneven temperature field. This stress essentially stems from the material's microstructural response to temperature changes: the atomic spacing in quartz glass changes with temperature, resulting in thermal expansion and contraction. When a portion of the material is heated, the atoms in the hot zone attempt to expand outward, but are constrained by the surrounding cold zone, thus creating compressive stress. This stress can be alleviated through structural reorganization when the material is in a plastic state. However, when the cooling rate exceeds a critical value, the material's viscosity rises sharply, impeding atomic rearrangement and resulting in dangerous tensile stress. It is worth noting that when the temperature drops below the strain point (corresponding to a viscosity of 10^4.6 poise), this stress will remain permanently in the material.

II. Inherent stress caused by structural evolution

Metastable structural stress

Quartz glass in its high-temperature molten state exhibits a highly disordered atomic arrangement. During the cooling process, atoms tend to transition towards a more stable configuration. However, due to the high viscosity characteristic of the glassy state, this structural relaxation is often incomplete, resulting in residual stress within the material. This stress will slowly release over time, manifesting as the "aging" phenomenon of the material.

Microscopic phase transition stress

When heat treatment is conducted within a specific temperature range (such as near the crystallization temperature), local crystallization may be induced. The volume difference between the newly formed crystalline phase and the glass matrix generates phase transformation stress, which tends to concentrate in the grain boundary region.

III. Stress generated by mechanical action

1. Processing-induced stress

During mechanical processes such as cutting and grinding, the interaction between the tool and the material can lead to lattice distortion on the surface layer. Especially when diamond tools are used for finishing, the combined effects of localized high temperatures and mechanical compression can form a residual stress layer on the processed surface.

2. Service load stress

When used as load-bearing components, external mechanical loads induce stress distribution within the material. A typical example is the bending stress generated in quartz glass supports under sustained load, which exhibits a distinct gradient distribution characteristic.

IV. Transient stress induced by thermal shock

1. Rapid temperature change stress

Although quartz glass has a low coefficient of thermal expansion, significant transient thermal stress can still be generated by transient temperature gradients when encountering rapid temperature changes (such as sudden cooling of high-temperature components). This stress is dynamic and its magnitude is directly related to the rate of temperature change.

2. Cyclic thermal stress

In an alternating temperature environment, materials undergo stress accumulation due to repeated thermal expansion and contraction. This cyclic stress is the primary cause of thermal fatigue failure, commonly observed in applications such as high-temperature windows.

V. Stress induced by chemical environment

1. Corrosion-related stress

Chemical corrosion (such as alkali corrosion) can lead to changes in the composition and structure of the material surface, and this uneven change can generate chemical stress. Especially in high-temperature corrosive environments, stress and corrosion often produce a synergistic effect.

2. Interfacial bonding stress

During surface modification processes (such as coating), the difference in thermophysical properties between the coating and the substrate can generate interfacial stress. This stress is particularly pronounced during temperature changes, potentially leading to coating delamination.

VI. Stress concentration effect of material defects

1. Inclusion stress

Defects such as bubbles and impurities in the material can disrupt the uniform distribution of the stress field. Due to the mismatch in physical properties between the defects and the matrix, significant stress concentration can form at the edges of the defects.

2. Microcrack stress

Microcracks generated during material preparation or processing can act as stress amplifiers, particularly in the crack tip region, where the stress concentration factor may reach several times the theoretical value.