Three Innovative Application Directions and Characteristics of Adhesives

I. New Applications of Adhesives

1. Anti-corrosion of Mechanical Equipment

At present, the steam pipes of ships mostly use aluminosilicate insulation covered with asbestos to achieve heat insulation. However, due to leakage or the generation of condensed water caused by alternating hot and cold conditions, the condensed water accumulates on the outer wall of the bottom steam pipes. Moreover, the outer walls of steam pipes are severely corroded due to long - term exposure to high temperatures and the action of soluble salts. Therefore, water glass - based adhesives can be used as coating materials at the bottom layer of aluminosilicate to form an enamel - like coating. Its coefficient of thermal expansion is similar to that of the pipe material, resulting in low thermal stress and no cracking.

In mechanical installation, components are often fixed with bolts. Devices fixed by bolts are exposed to the air for a long time, which can cause crevice corrosion. During the operation of machinery, bolts may sometimes loosen due to severe vibration. To solve this problem, in mechanical installation, the connecting components can be bonded with inorganic adhesives first, and then bolted. This can not only play a reinforcing role but also have an anti - corrosion effect.

2. Biomedical Applications

The composition of hydroxyapatite $Ca_{10}(PO_{4})_{6}(OH)_{2}$ (abbreviated as HA) bioceramics is close to the inorganic components of human bone. It has good biocompatibility and can form a strong chemical bond with bone, making it an ideal substitute material for hard tissues. However, currently, the commonly prepared HA implants generally have a high elastic modulus, low strength, and unsatisfactory activity. Phosphate glass adhesives are selected. Through the action of the adhesives, the HA raw material powder is bonded together at a temperature lower than the traditional sintering temperature, thereby reducing the elastic modulus and ensuring the material's activity.

The application of adhesives in the medical field is regarded as a new growth point in the adhesive industry. Structural glues composed of epoxy resin or unsaturated polyester are used. In contemporary defense technology, stealth submarines are one of the symbols of modernization of naval equipment. An important method for submarine stealth is to lay anechoic tiles on the outer shell of the submarine. Anechoic tiles are a type of rubber with sound - absorbing properties. To achieve a firm bond between the anechoic tiles and the steel plate of the submarine wall, adhesives are relied on.

3. Military Applications

3.1 Tank Maintenance

Cracks in the outer shell of tank engines are common defects. Defects in the internal structure of metals, stress concentration, fatigue, and the action of prominent external forces often cause cracks in different parts of the engine block shell. If welding is used to solve such problems, there are disadvantages such as material embrittlement, deformation, and strength reduction. At the same time, it also consumes electrical energy and equipment. However, using special bonding technology to deal with these cracks can achieve quick, good, and cost - effective results.

3.2 Application in Military Light Bombers

Military light bombers mainly fly at subsonic or transonic speeds. The outer skins of the fuselage and wings are made of aluminum alloy sheets with a thickness of less than 1.5mm, and some are only 0.4 - 0.8mm thick, which are strengthened by corrugated profiles below. Riveting such thin - skinned structures is very difficult. However, using a bonding structure can not only overcome the deformation easily caused by riveting thin skins, the overall strength loss caused by rivet dimpling, reduce tooling, and shorten the assembly cycle, but also improve the structural corrosion resistance, fatigue resistance, and damage tolerance. In modern high - performance military aircraft, adhesives are required for the sealing of integral fuel tanks in wings or fuselages. High - performance adhesives are needed for the bonding and sealing between the cockpit acrylic glass and the polyester tape of fighter jets.

3.3 Preparation of Camouflage Materials

For army ground weapons, the main threat comes from 8 - 14μm infrared thermal imagers. The main way to achieve infrared stealth is to develop infrared camouflage coatings with different emissivities. Through the different emissivities of the coatings, the infrared image of the target is effectively segmented, achieving the goal of integrating the target with the background. From the research content of infrared stealth coatings, high - transparency adhesives are one of the technical approaches. The resin is used to achieve the low - radiation characteristics of the adhesive itself in the infrared window by ensuring that it does not contain absorption groups in the 8 - 14μm infrared atmospheric window. Radar - absorbing coatings are functional materials that can absorb electromagnetic waves, reduce the radar signature signals of targets, and make them difficult to detect and identify. They are one of the main ways to achieve radar stealth for weapons and equipment. They are composed of absorbers and adhesives, and the adhesives determine the physical and mechanical properties and construction properties of the absorbing coatings.

II. Characteristics of Adhesives

1. Heat Resistance

Inorganic high - temperature adhesives usually have a service temperature range of 1500 - 1750°C. The temperature resistance range of copper phosphate - based adhesives is even wider, which can be used in the range of 180 - 1400°C. However, the main aggregates used in inorganic high - temperature adhesives are zircon sand and refractory clay. Zircon sand is expensive and mainly imported, and refractory clay is obtained at the cost of sacrificing land, which is a huge price. Therefore, it is urgent to find inexpensive and readily available products to replace traditional aggregates to reduce production costs. Some organic adhesives have also achieved high - temperature resistance through modification. For example, phenolic resin glue modified with $B_{4}C$ can withstand a high temperature of 1500°C. The market demand for heat - resistant adhesives is constantly increasing, so such adhesives have broad development prospects.

2. Low Pollution

With the increasing deterioration of the global environment, people have gradually started to use some environmentally friendly products. Although adhesives are not a large - scale chemical product category, their harm to the environment cannot be ignored. Non - environmentally friendly adhesives will gradually be abandoned. Polyvinyl formal adhesive (commonly known as "107 glue") contains free formaldehyde, which is harmful to human health. It has long been banned in developed countries. However, due to its low price, it still has a considerable market share in China. However, its usage has been gradually decreasing and will be completely phased out in the near future. It is imperative to modify non - environmentally friendly adhesives to make them environmentally friendly.

3. Non - Destructive Bonding

The connection of materials mainly includes bolt connection, riveting, welding, and bonding. Although technologies such as bolt connection can achieve rapid connection, they damage the material by drilling holes or locally heating the material components, and stress concentration cannot be avoided during use. In contrast, bonding technology is a non - destructive connection technology. It can improve the load - bearing capacity because the bonding interface bears the load as a whole, and it also extends the service life.

4. Lightweight

The density of adhesives is relatively small, mostly between 0.9 and 2, which is about 20% - 25% of the density of metals or inorganic materials. Therefore, it can greatly reduce the weight of the connected materials of the adhered objects. This is of great significance in aerospace, aviation, missiles, and even in automobiles and ships for reducing self - weight and saving energy.