1. Fire resistance, fire resistance is the ability to resist melting at high temperatures. The fire resistance mainly depends on the chemical composition of the thermal storage ball and the fusible impurities in the material. The content of (FeO, NaO, etc.). The fire resistance does not represent the actual operating temperature of the thermal storage ball, as the softening and deformation temperature of the thermal storage ball will decrease under high temperature load. So its actual allowable maximum operating temperature is lower than the fire resistance, which is generally determined through experiments.

2. High temperature structural strength (load softening temperature) refers to the resistance of thermal storage balls to withstand pressure without deformation at high temperatures. It is often evaluated based on the load softening temperature. The so-called load softening temperature refers to the temperature at which the thermal storage ball is heated at a certain heating rate under 0.2 pressure, and the temperature at which the sample begins to deform and the temperature at which compression deformation reaches 4% or 40% is measured. The temperature of the former is called the beginning humidity of load softening, while the latter is called the softening point of load softening at 4% or 40%.

3. Thermal stability refers to the ability to resist rapid temperature changes without breaking or peeling, sometimes also known as resistance to sudden cold and heat. Its measurement involves heating the thermal storage ball to a certain temperature of 850 ℃, then cooling it with flowing cold water until it reaches a weight of 20% of its original weight due to partial peeling due to its rupture. The number of cold and hot alternations it undergoes is the indicator for evaluating thermal stability.

4. Volume stability refers to the percentage change in volume of heat and cooling repeatedly applied to a thermal storage ball at a certain temperature. Under multiple high temperatures, recrystallization and further sintering occur in the composition, resulting in residual expansion or contraction. The allowable residual expansion or contraction should not exceed 0.5-1.0%.