Because of the above excellent properties of silicone products, it has a very wide range of applications. It is not only used as a special material for aviation, technology and military technology departments, but also for various departments of the national economy, and its application scope has expanded to: construction, electronics and electrical, textile, automobile, machinery, leather and paper, chemical and light industry, metal and paint, medicine and medical treatment.

1. Aging of contact medium

The silica gel material used in the natural environment will be affected by the moisture in the air, or other conditions, such as the external insulation material of the power system, in salt-contaminated areas, extremely susceptible to the impact of salt spray, so aging research and analysis of the aging performance under such conditions become necessary. In addition, some silicone products in contact with oil, to test their oil resistance, improve their oil resistance performance is also the focus of practical applications.

The aging behavior of silica gel in different kinds of oil, the occurrence of wear is on the one hand due to the mechanical damage of aging, but also due to the degradation of the material crosslinking system, resulting in the production of low molecular weight substances. The presence of fluid can reduce the coefficient of friction, but it can also accelerate the chemical degradation of silica gel, thus accelerating wear.

2, silica gel hot oxygen aging

Natural silica gel (NR), ethylene-propylene silica gel (EPM, EPDM), butadiene silica gel (SBR), butyl silica gel (IIR), silica gel (NVQ), etc., all belong to this form during the use of thermal oxygen aging. NR contains a large number of unsaturated double bonds, under the joint action of heat and oxygen, vulcanized rubber will produce degradation reaction, molecular chains, crosslinked bonds cracking and breaking, resulting in aging.

Hot oxygen aging is a free radical reaction and an oxidation reaction. Under the condition of anaerobic thermal aging, free radical decomposition will occur, and the lower the bond cleavage energy, the faster the decomposition will be. The polymer is ionized by radiation and excited at the same time, when the molecule cracks and generates free radicals, and then the main chain breaks and forms crosslinking, and finally produces a variety of gases; In ultraviolet aging, molecules absorb ultraviolet rays and stimulate specific functional groups, and decompose or decompose through energy transfer in other functional groups, and react by forming active groups.

The oxidation and decomposition reaction of side chain organic groups occurred mainly in the high temperature and open environment of aerobic silica gel, resulting in the hardening of silica gel. In the oxygen-free high temperature closed environment, the main chain fracture reaction occurs, generating volatile cyclic polysiloxane, resulting in silica gel softening. The oxidation reaction of side chain methyl group and main chain degradation break reaction of silica gel occur mainly at high temperature.

3. Fatigue and aging

The fatigue aging of silica gel refers to the aging phenomenon of silica gel products under the action of a certain frequency and periodic stress, the molecular structure of silica gel material is changed, which is the result of the activation of two main factors, that is, force and heat (due to the hysteresis phenomenon of silica gel when it is deformed multiple times, so that the internal heat of silica gel is generated).

The fatigue resistance of natural silica gel is a very important performance for the vibration damping elastic elements that are repeatedly subjected to stress, which is directly related to the failure of the vibration damping function and the safe operation of the locomotive and vehicle, and is gradually attracting the attention of researchers.

4. Ozone aging

Ozone content in the atmosphere is very low, silica gel in the aging process, ozone attacks silica gel molecules, silica gel expansion, resulting in cracks on its surface. Ozone reacts with double bonds in silicone molecules to form molar ozonides and peroxides, which are then regenerated into ozonides. The ozonide is decomposed into free radicals under the action of light and heat, etc., resulting in a chain growth reaction. In addition, silica gel will produce molecular fracture under the action of stress, and do not generate ozonides, and crack aging phenomenon.

Through the study of different types of rubber under the action of ozone, including natural silica gel, oil-filled methyl butadiene silica gel and polyisoprene silica gel and butadiene silicone gel, it is shown that with the extension of ozone action time, the service life of silica gel decreases, and the decline is rapid in a short time of ozone action, proving that silica gel has obvious degradation in the early stage of ozone action. With the extension of ozone action time, the life of ozone decreases slowly. This may be due to the slowing down of the degradation process during the deepening phase of polymer decomposition.