Sapphire glass, as one of the materials in modern technology, is widely used in fields such as smartphone screens, watch mirrors, aerospace windows, and precision instruments due to its high hardness, strength, transparency, and corrosion resistance. However, a significant challenge in the manufacturing process is the generation of internal stress. If these stresses are not properly handled, they will not only affect optical performance, but may also lead to cracks or even breakage during use. Therefore, annealing treatment has become a key step in solving this problem.

1、 The basic principle of annealing treatment

Annealing is a heat treatment process that eliminates or reduces internal stress by heating and slowly cooling materials. For sapphire glass, the core of annealing treatment lies in precise control of heating temperature and cooling rate to optimize the microstructure of the material and reduce residual stress. During the heating phase, the atoms and molecules in sapphire gain sufficient energy to begin rearranging, releasing some of the stress; During the subsequent slow cooling process, these newly formed microstructures are stabilized, effectively reducing internal stresses caused by rapid cooling.

2、 Specific steps of annealing treatment

1. Preheating stage: Place the sapphire glass sample in an annealing furnace and gradually raise the temperature to the preheating temperature. The purpose of this stage is to ensure uniform heating of the entire body and prepare for subsequent heating treatments. The selection of preheating temperature should be based on the thickness to avoid excessive thermal stress during the heating process.

2. Heating to peak temperature: After preheating is complete, continue to increase the temperature to the peak temperature of annealing treatment. The selection of peak temperature is one of the key parameters in annealing treatment, which directly affects the effect of stress relief and the performance of sapphire glass.

3. Insulation treatment: After reaching the peak temperature, maintain for a period of time to allow sufficient rearrangement and stress release of atoms and molecules inside the sapphire. The length of insulation time depends on the thickness and the required degree of stress relief.

4. Slow cooling: After the insulation is completed, slowly reduce the temperature inside the furnace and perform slow cooling. This step needs to be carried out slowly as rapid cooling may result in the generation of new stresses. Slow cooling helps to form a stable microstructure internally, thereby retaining the effect of annealing treatment.

5. Discharge and subsequent processing: When the temperature inside the furnace drops to around room temperature, annealing treatment has already been carried out, and the internal stress is significantly reduced. Further cleaning, polishing, and other subsequent treatments may be required as needed to improve surface quality and appearance.

3、 The function of annealing treatment

1. Eliminating or reducing internal stress: The direct effect of annealing treatment is to eliminate the internal stress generated during the growth and processing of sapphire glass. The reduction of these stresses helps to improve strength and stability, and reduce the risk of cracking or breakage in subsequent use.

2. Optimizing microstructure: Through annealing treatment, the atoms and molecules inside sapphire are arranged more orderly, and the microstructure is optimized. This helps improve optical performance, such as increasing transmittance and reducing scattering.

3. Improving material properties: Annealing treatment can also enhance properties such as thermal shock resistance, corrosion resistance, and mechanical strength, which enable sapphire glass to exhibit higher reliability and durability in a wider range of applications.

4. Ensuring product quality: In electronic products and precision instruments, sapphire glass is a key component, and its quality directly affects the performance and reliability of the entire product. Annealing treatment is of great significance in ensuring quality and improving the overall quality of products.

Annealing treatment is an indispensable process in the manufacturing of sapphire glass. By precisely controlling parameters such as heating temperature, holding time, and cooling rate, annealing treatment can effectively eliminate internal stress in sapphire, optimize its microstructure, improve material properties, and ensure excellent performance in various application scenarios.