With the continuous development of society, people have higher and higher requirements for automobiles to be lightweight, intelligent, reliable, environmentally friendly, comfortable and economical. In order to meet these requirements, with the continuous development of science and technology, automobile research and development New materials and new processes are increasingly used in production and production, and ceramics is one of them for the use of new materials. Special ceramics are different from traditional ceramics in terms of chemical composition, internal structure, performance and efficiency. They have various excellent and unique properties. Researchers engaged in automotive materials have proven after years of development, research, testing and industrial application that after many automotive parts and components are converted to ceramic materials, their mechanical properties are far superior to those made of metal materials or other materials. . It is precisely because of these excellent properties of special ceramics that they have positive significance in reducing the weight of the vehicle itself, improving engine thermal efficiency, reducing fuel consumption, reducing exhaust pollution, increasing the life of wearing parts, and improving the intelligent functions of automobiles.
1. Characteristics of special ceramics
Commonly used automotive special ceramics are as follows:
1. Alumina ceramics. The main performance characteristics of alumina ceramics are high strength, high hardness, wear resistance, corrosion resistance, high temperature resistance and good insulation properties, with a heat resistance temperature of up to 1600°C. But the disadvantages are high brittleness, poor earthquake resistance, complex process and high cost. The excellent high temperature performance and dielectric properties of alumina ceramics can be used to make engine spark plugs, and the good wear resistance can be used to make bearings and pistons.
2. Silicon carbide ceramics. The biggest features of silicon carbide ceramics are high high-temperature strength (the flexural strength remains 500-600MPa at 1400°C), strong heat transfer capacity, good thermal stability and wear resistance, and a small thermal expansion coefficient. Suitable for making gas turbine blades, bearings and other parts.Due to its high thermal conductivity, it is also suitable as a heat exchanger material under high temperature conditions and can also be used to make sealing rings for various pumps.
3. Silicon nitride ceramics. Silicon nitride ceramics can produce a variety of components with precise dimensions and complex shapes at low cost, with a higher yield than other ceramic materials. The main performance characteristics are high strength and high hardness. Its hardness is second only to diamond, boron nitride and other substances. It has good chemical stability, wear resistance, insulation and high product precision. It can be used to manufacture wear-resistant, corrosion-resistant, high-temperature-resistant and insulating parts. Reaction sintered silicon nitride can be used to manufacture pump mechanical seal rings, high-temperature bearings, valves and other parts.
4. Boron nitride ceramics. Boron nitride ceramics have good heat resistance, thermal stability, thermal conductivity, and high-temperature dielectric strength. They are ideal heat dissipation materials and high-temperature insulation materials. Boron nitride ceramics have good chemical stability and can resist the erosion of most molten metals. It also has good self-lubricating properties. Its products have low hardness and can be machined.
5. Zirconia ceramics. The melting point of zirconia ceramic is 2715℃, and the service temperature can reach 2300℃. Pure zirconia cannot be used. It can be used after adding stabilizers. Its high strength and toughness, high hardness and wear resistance, high resistance to chemical corrosion and small thermal conductivity can be used as cutting tools, heat insulation materials and sliding parts.
2. Application of ceramics in automobiles
(1) Application of ceramics in automobile engines
1. Ceramic adiabatic engine. Utilize the characteristics of ceramic materials (such as silicon nitride ceramics) such as heat resistance, wear resistance, corrosion resistance, low expansion coefficient, low density, and good heat insulation to make ceramic insulated engines. The operating temperature can reach 1300℃-1500℃, and can Reduce heat energy loss in the cylinder, enable full combustion of fuel, and reduce the impact of exhaust gas on the environmentof pollution. Moreover, ceramic engines do not require a water cooling system, and their density is only about half that of steel, which can simplify the overall structure of the engine, reduce engine weight and energy consumption, and increase the working power by more than 45% compared to steel engines.
2. Ceramic piston. The ceramic fiber piston made of silicon nitride ceramic material has good wear resistance and can prevent the "cold knocking and hot drawing" phenomenon caused by the large thermal expansion coefficient of the aluminum alloy piston.
3. Ceramic cylinder liner. Using ceramic materials to make the upper ring of the cylinder liner or using metal and ceramic materials to make a full ceramic cylinder liner instead of the traditional cylinder liner can prevent the loss of heat energy in the cylinder, simplify the engine structure, thereby improving thermal efficiency and reducing engine quality.
4. Ceramic valve mechanism parts. Utilizing the low-density, heat-resistant and wear-resistant characteristics of ceramic materials to manufacture valves, valve seats, tappets, valve springs and rocker arms can reduce valve seat deformation and bounce when seated, reduce noise and vibration, and extend service life. Mitsubishi uses ceramics to make engine rocker arms; Isuzu's ceramic valves made of silicon nitride are lighter than steel valves, have a certain fuel-saving effect, and can reduce harmful emissions; Ford uses ceramic valve lifters formed by injection Rods are used on engines and have achieved good results.
5. Ceramic valve heater. The valve heater is a heating device equipped on the suction side and is a barium titanate ceramic series thermistor. When heating the suction air, it can control the temperature and improve the reliability of the device, promote the heating of the suction air, complete the evaporation and mixing of the fuel, and complete the combustion when the engine is started, thereby improving the combustion efficiency and net gas emissions.
(2) Application of ceramics in automobile brakes
The brake disc in ceramic brakes can be made of reinforced ceramics, that is, ceramic powder and carbon fiber are used to replace metal in the existing technology. The hardness of its carbon-silicon compound surface is close to that of diamond, and its carbon fiber structure makes it strong, impact-resistant, corrosion-resistant, and extremely wear-resistant. Compared with steel brake discs, ceramic brake discs reduce the weight of the entire vehicle, reduce fuel consumption, extend the service life, and greatly improve the wear resistance, high temperature resistance, corrosion resistance, and braking performance of the brake disc.The heat dissipation effect is good.
(3) Application of ceramics in automobile shock absorbers
Automobile shock absorbers using high-sensitivity ceramic components have the function of identifying the road surface and making self-adjustments. The sensing and adjustment process while the car is driving only takes 20 seconds, so the vibration caused by the rough road surface can be reduced to At least, so as to protect the passengers from the pain of bumps.
(4) Application of ceramics in automobile spraying technology
In recent years, ceramic film spraying technology, which is widely used in aerospace technology, has begun to be applied to automobiles. This technology uses plasma spraying technology to coat ceramics such as zirconium trioxide, titanium carbide and titanium dioxide to obtain a durable coating within 1mm. Coating the high-temperature-resistant parts of the engine with a layer of high-temperature ceramics can not only maintain the inherent strength and toughness of the metal material, but also have high-temperature resistance. For example, spraying zirconia on the top of the piston, and spraying ceramic coating on the working surfaces of the cylinder liner and piston ring can improve wear resistance and service life. The use of this technology can also increase the heat resistance of the engine air intake duct surface from 1200°C to 1700°C. The engine after this treatment can reduce heat loss, reduce the weight of the engine itself, reduce the size of the engine, and reduce fuel consumption.
(5) Application of ceramics in automotive sensors
As the information source of the automotive electronic control system, automotive sensors are key components of the automotive electronic control system. The higher the degree of automotive electronics and automation, the greater the dependence on sensors. Some functional ceramic materials can long-term adapt to the harsh environments unique to automobiles (high temperature, low temperature, vibration, acceleration, moisture, noise, exhaust gas) and are used in automobile sensors.
1. Ceramic temperature sensor. The engine electronic injection system can use ceramic temperature sensors to continuously and accurately measure cooling water temperature, intake air temperature, and exhaust temperature, so as to correct or compensate the fuel injection amount according to temperature changes, change the idle speed control target value, etc., and obtain the best air-fuel ratio.
2. Ceramic exhaust gas sensor. The zirconia sensor used for automobile exhaust gas monitoring is installed in the manifold or front exhaust pipe. It uses solid electrolyte gas-sensitive ceramic materials to measure the O2 concentration in exhaust emissions, and then feeds the measured value back to the engine air intake and fuel supply systems. , detect the engine air-fuel ratio and promote the combustion of fuel to always maintain a full combustion state. In addition to saving fuel, it can also reduce emissions of harmful gases such as CO and NO2. It has high sensitivity, good reliability and long service life.
3. Ceramic knock sensor. The ceramic knock sensor enables the engine to work at the ignition moment close to knocking, with the highest thermal efficiency and the lowest fuel consumption, achieving a knock-free working state and ensuring that it operates with the maximum possible power and economic indicators.
4. Ultrasonic sensor. Ultrasonic sensors are usually composed of aluminum alloy shells, piezoelectric ceramic transducers, sound-absorbing materials, and lead electrodes. They are used as car reversing anti-collision alarm devices to guide safe driving of cars. They are especially suitable for extended-loading cars and heavy trucks. , mining trucks and other large vehicles. Ultrasonic sensors are also used in air flow meters to detect the amount of engine air intake.
5. Ceramic acceleration sensor. Ceramic acceleration sensors are used in automobile airbag systems. They can be used to detect the instantaneous low-speed or high-speed collision intensity of the car and convert it into electrical signal output to ensure that when the collision intensity is high, the airbag is opened accurately and timely, thereby improving the safety performance of the car. It has high precision and reliability, and can quickly distinguish the actual collision situation.
6. Ceramic humidity sensor. The interior of the automobile humidity sensor is equipped with a porous sintered body made of metal oxide series ceramic materials. The adsorption of water molecules on the surface of the sintered body is used to sense humidity. The humidity-sensing characteristic quantity is resistance, and the humidity is detected by the change in resistance value. changes. It is suitable for the detection of frost and condensation on car window glass and the detection of air humidity in the engine air intake.
(6) Application of ceramics on automotive catalytic converter carriers
Compared with metals, polymers and other materials, ceramic materials are more suitable for various high temperatures and corrosive environments, so they are widely used in the field of catalyst carriers. The performance of the carrier itself in the catalytic reaction will directly affect the performance of the catalyst. The commonly used cordierite honeycomb ceramic carrier is placed on the car exhaust purifier when used. Nitrogen oxides (NOX), carbon monoxide (CO) and other harmful gases in the car exhaust can be converted into Emitting non-toxic gases such as nitrogen (N2) and carbon dioxide (CO2) into the atmosphere can greatly reduce the pollution level of vehicle exhaust emissions.
(7) Application of ceramics in automobile mufflers
When the sound wave propagates to the honeycomb porous ceramic installed in the automobile exhaust pipe, it causes air vibration in the rich network pores, and then through the friction between the air and the porous ceramic matrix, the energy of the sound wave is converted into heat energy and is consumption, thereby achieving the effect of eliminating noise.
(8) Application of ceramics in car wipers
Using the piezoresistive effect of barium titanate ceramics to make smart ceramic wipers, which can automatically sense the amount of rain and automatically adjust the wiper to the optimal speed.
(9) Application of ceramics in automobile film
Compared with the metal thermal insulation films currently on the market, multi-layer nano-ceramic insulation films have better thermal effects and light transmittance, which can relieve visual fatigue, significantly reduce the heat in the car, increase driving comfort, and reduce air-conditioning load and Fuel consumption; heat insulation, durable, anti-oxidation, never fade; anti-scratch and glass burst flying, increasing driving safety. At the same time, the multi-layer nano-ceramic insulation film uses non-metallic ceramic technology, which can completely eliminate the unique shielding effect of metal films on electromagnetic waves and will not have any impact on satellite navigation systems, mobile phones, remote controls and automatic highway toll collection systems. Ceramic insulation film used in the world's top sports carsJieshang has some applications.
3. Problems in the application of special ceramics in automobiles
Special ceramics are materials that are constantly being developed. There are many issues that need to be solved in the preparation of raw materials, material evaluation and utilization technology. At present, the main reasons that hinder the application of special ceramics in automobiles are: first, the cost has remained high for a long time, much higher than the price of metal parts; second, special ceramics have strict requirements on raw materials and the process is difficult to master, making each batch of products It is difficult to maintain uniform performance; third, it has poor processability, high brittleness, and poor reliability; fourth, the manufacturing process is complex and requires high requirements.
4. Conclusion
Although there are currently some problems that need to be solved in the application of special ceramics in automobiles, due to their various excellent and unique properties, the development of special ceramics is very rapid. In modern industrial technology, especially in the fields of high technology and new technology is becoming increasingly important. In order to achieve the sustainable development strategy of human society, meet the lightweight, intelligent, energy-saving, safety and environmental protection requirements of the new generation of automobile products, and accelerate the new technological revolution, the United States, Japan, Germany and other countries have invested a lot of manpower, material and financial resources in the research and development of special Ceramics, using special ceramics with different chemical compositions and organizational structures to have different special properties and functional characteristics, have made great technological breakthroughs in developing ceramic parts and components for automobiles. Our country has also made great progress in this field, and the development and application prospects of ceramic parts for automobiles will be very attractive. I believe that in the near future, with the rapid development of science and technology, ceramic materials will have greater breakthroughs in the field of automobile manufacturing. More special ceramics and smart ceramics will be introduced and applied to improve the performance of automobiles.able.
