Ceramic pressure sensor is a new type of strain gauge pressure sensor developed by utilizing the piezoresistive effect and force-sensitive effect of thick film resistors.
1.How it works
Through laser calibration, the sensor has high temperature stability and time stability. The sensor has built-in temperature compensation of 0 to 70°C and can be in direct contact with most media.
2.Technical Parameters
● Bridge arm resistance: 11k±20%
● Measuring range: 100kPa～60Mpa
● Response time: <1mS
● Comprehensive error (including: linearity, hysteresis, repeatability): 0.2～0.4FS%
● Zero output: 0±0.2mV/V
● Full-scale output: 2.0～4.8mV/V
● Temperature characteristics (temperature compensation range: 0～70℃): ±0.015 %FS/℃
● Stability: <0.2%FSO/year
● Working temperature: -40～135℃
● Insulation resistance: >2kV
3. Basic structure
he ceramic pressure sensor is mainly composed of three parts: ceramic ring, ceramic diaphragm and ceramic cover. The ceramic diaphragm is made of 95% AL2O3 ceramic as a sensitive elastic body. It is required to be flat, uniform and dense. Its thickness and effective radius depend on the design range. The ceramic ring is formed by high-temperature sintering using a hot die-casting process. High-temperature glass slurry is used between the ceramic diaphragm and the ceramic ring, and they are fired together through thick film printing and hot sintering technology to form a peripheral fixed force cup-shaped elastic body, that is, a rigid structure without creep should be formed in the peripheral fixed part of the ceramic. The circuit of the sensor is made on the upper surface of the ceramic diaphragm, that is, the bottom of the ceramic cup, using thick film technology. The circular groove at the bottom of the ceramic cover forms a certain gap between the cover and the diaphragm. The limiter can prevent the diaphragm from breaking due to excessive bending when overloaded, forming an anti-overload protection for the sensor.
4. Basic characteristics
Ceramic is a material that is recognized as highly elastic, corrosion-resistant, wear-resistant, shock-resistant and vibration-resistant. The thermal stability of ceramics and its thick film resistor can make its operating temperature range as high as -40 to 135°C, and it has high precision and high stability in measurement. The electrical insulation level is >2kV, the output signal is strong, and the long-term stability is good. High-performance, low-priced ceramic sensors will be the development direction of pressure sensors. In Europe and the United States, there is a trend of fully replacing other types of sensors. In China, more and more users are using ceramic sensors to replace diffused silicon pressure sensors.
5.Applicable occasions
Process control, environmental control, hydraulic and pneumatic equipment, servo valves and transmissions, chemicals and chemical industry, medical instruments and many other fields.
Thermal spray high temperature resistant ceramic coatings can best reflect the characteristics of thermal spraying technology, and the application effect is the most prominent, which is the application field with the greatest impact.
5.1 Thermal barrier coatings (TBCs)
The heated parts of gas turbines, such as blades, nozzles and combustion chambers, are in harsh environments such as high temperature, oxidation and high-speed airflow erosion. For gas turbine parts that withstand temperatures as high as 1100 ℃, the limit temperature of nickel-based high-temperature alloys (1075 ℃) has been exceeded. An effective way is to apply a high melting point ceramic coating with good thermal insulation to put on a "fireproof armor" for the high-temperature alloy substrate to act as a thermal insulation shield. This is called a thermal barrier coating.
The basic requirements for thermal barrier coatings are:
(1) high temperature resistance;
(2) high temperature oxidation resistance;
(3) strong bonding with the metal substrate;
(4) low thermal conductivity and good thermal insulation;
(5) good matching of thermal expansion coefficient with the metal substrate and high number of heat resistance cycles.Practice shows that the use of MCrAlY alloy as a bonding base layer and spraying of Y2O3 partially stabilized ZrO2 thermal insulation ceramic coatings can make the coating hard and dense, with excellent resistance to high temperature gas erosion and thermal shock. Even if used for a long time at 1650℃, its thermal stability and chemical stability are very good. Adding a small amount of CeO to Y2O3ZrO2 can further improve the thermal shock resistance of the coating. When the operating temperature is lower, MgO or CaO stabilized ZrO2 can be used as a thermal barrier ceramic barrier layer.
Some of the latest developments in the field of thermal barrier coatings include pre-oxidation of the bonding base layer of thermal barrier coatings, aluminization of thermal barrier ceramic coatings, laser remelting modification of the surface ceramic coatings, and the development of multi-layer or gradient functional coatings.
Thermal barrier coatings are mainly used for heated parts of aviation, ships and land-based gas turbines, and are now being promoted for use in civil internal combustion engines, supercharged turbines, oxygen spray guns for metallurgical industries, and other fields.
5.2 Abradable sealing coating
Modern aircraft engines use compressors to pressurize and heat the air. High-temperature compressed air enters the combustion chamber to fully burn the fuel, which is one of the main measures to improve the power and thermal efficiency of the engine. Thermal spraying technology is used to spray an abradable sealing coating on the inner surface of the compressor volute, forming a pair of abradable sealing wear pairs with the hard coating on the tip of the compressor blade. During operation, an ideal radial airflow gap can be formed to obtain the maximum pressure difference, thereby significantly improving the power of the engine, reducing the consumption of aviation gasoline, and improving the first test pass rate of the engine. This is one of the major application results of thermal spraying technology in the field of aircraft engines.
As the temperature of compressed air increases step by step, the use temperature of the abradable sealing coating is raised from 300 ℃ to 1100 ℃.
The highest temperature of modern abradable sealing coatings has reached 1350 ℃. Composite powder series materials such as AlSi-polyphenylene ester, nickel/graphite, Ni/diatomaceous earth, NiCrAl/BN, Y2O3. ZrO2-BN have been successfully applied. Among them, the working conditions of high-temperature abradable sealing coatings are the most severe. They have to withstand high temperatures of 1000-1350 ℃, be eroded by high-temperature airflows of 2-3 times the speed of sound, and be scraped by the blade tip at a linear speed of more than 300 m/s without peeling off. Therefore, in addition to the high-temperature resistance, oxidation resistance, thermal shock resistance, chemical inertness, and strong bonding properties that high-temperature resistant coatings should have, their most important characteristics are softness (usually the surface Rockwell hardness of the coating is 50-80 HR15Y) and porosity (porosity is about 25%-30%).
Thermal spray abradable sealing coating technology can be used in civilian industrial fields such as clearance control of rotating compressed air components in the compressor industry.
5.3 High-temperature adhesive wear-resistant coating
High-temperature rollers such as annealing furnace rollers, heat treatment furnace rollers, continuous casting machine stretching rollers, support rollers, sintering furnace rollers, etc., mostly operate at high temperatures of 800-1,200 ℃. At such high temperatures, steel softens and forms iron oxide scales on the surface, and the high-temperature hardness of the furnace rollers is also significantly reduced. When soft high-temperature steel parts, especially steel strips, move on the furnace rollers or even slide slightly, nodules will form due to high-temperature adhesion. Such nodules fall off as abrasives under the action of shear force, causing scratches, scratches, furrows, depressions and other defects on the surface of the steel parts (strips). These defects are often difficult to eliminate on the subsequent surface smooth rolling rollers, which will ultimately affect the quality of the hot-rolled steel strips.
Using high-speed gas flame spraying (HVOF), detonation spraying (DGS) or plasma spraying technology, special ceramics or metal ceramic coatings are sprayed on the surface of high-temperature furnace rollers, which have excellent high-temperature resistance, oxidation resistance, anti-adhesion, anti-nodulation and self-cleaning purification properties, which can not only significantly improve the service life of furnace rollers, but also produce steel with smooth surface and excellent quality, such as high-quality silicon steel plates, high-quality automotive thin plates and hot-dip galvanized thin plates. The high-temperature wear resistance of the furnace rollers of hot-rolled stainless steel strip annealing furnaces can be increased by more than 4 times by spraying metal ceramic coatings containing BN.
In Japan, the main objects of thermal spraying technology applied in the steel industry are various rollers. Thermally sprayed rollers account for more than 85% of all thermally sprayed parts, which has extremely significant technical and economic effects. For example, the annealing furnace guide rollers used to be shut down for maintenance for an average of 30 minutes per month. After spraying, they can be maintained without maintenance for 3 years, which greatly improves the quality of the strip steel. The ratio of thermally sprayed annealing furnace rollers of Japan Steel Corporation increased from 20% in 1982 to 100% in 1989, while the scrap rate of strip steel caused by nodules, etc., dropped from 80% to 0.
5.4 Coatings resistant to high-temperature molten metal or melt erosion
Various furnace lining materials for metal smelting are basically ceramic refractory materials. This is because they not only have the characteristics of high melting point and stable high-temperature chemical properties, but also have the characteristics of small wetting angle with the melt or even no wetting. Using these characteristics, spraying refractory ceramics or metal ceramic coatings on the surfaces of metal parts used in the molten pool, such as sinking rollers and stabilizing rollers in hot-dip galvanizing tanks, molten pool agitators, blowpipes, thermocouple sleeves, hot die-casting molds, etc., can obtain high-performance resistant coatings resistant to high-temperature molten metal or melt erosion. For example, sinking rollers and stabilizing rollers in hot-dip aluminum galvanizing tanks.
Because aluminum liquid has extremely high chemical activity, it can react with a variety of metals to form intermetallic compounds by aluminothermic reactions, which are called "solvents" for metals. Therefore, metal alloy furnace rollers corrode very quickly in aluminum galvanizing tanks, and their service life is only 5 to 10 days.
The use of thermal spraying special ceramic coatings is considered by the Germans to be the only effective solution, and the service life can be increased to 20 to 30 days.
5.5 Anti-corrosion and wear
Many mechanical equipment used in the petroleum, chemical, pharmaceutical, papermaking, printing and dyeing, metallurgy, building materials, marine development, environmental protection and other departments are corroded by various chemical media, corrosive gases and seawater. The corrosion products become abrasive particles, which, together with foreign particles or dust, or crystals in the production process of the medium, can cause both corrosion and wear between the surfaces of relatively moving mechanical parts. Abrasives cause "wrinkles" and "scratches" on the metal surface, exposing the new surface to accelerate corrosion, and the corrosion products become abrasive particles to accelerate wear. Since corrosion and wear play a destructive role at the same time and promote each other, they accelerate the premature failure of such mechanical parts and even cause major accidents.
Under corrosive and wear conditions, stainless steel or titanium alloy has good corrosion resistance, but is not wear-resistant. Hard chrome plating is widely used in industry, but hard chrome plating has three major disadvantages:
(1) The process is long, there are many steps, it occupies a large area, the deposition rate is low, and it is difficult to deposit a thick coating. Material Protection 990119
(2) Above 260°C, the chrome plating layer will soften and its wear resistance will decrease significantly. Local oil-free critical lubrication or abrasive scratches will cause the plating layer to overheat and soften locally, forming grooves;
(3) Environmental pollution. Several toxic wastes (such as hexavalent chromium) produced during chrome plating that are harmful to the environment aggravate the pollution of water, soil and air. Most chromium compounds contain strong carcinogens, and their toxicity is 4 orders of magnitude higher than that of methylene chloride, which has been banned in most industries. Obviously, replacing hard chrome electroplating technology as much as possible has become an urgent task.
Thermal sprayed ceramic coatings and metal ceramic coatings not only have high hardness and excellent corrosion resistance, but also have low friction coefficient, low energy consumption, low wear on sealing packing, and the hardness and wear resistance of the coating will not be reduced due to local overheating.
Therefore, it is becoming the strongest competitor and replacement of electroplating hard chrome technology in the field of corrosion resistance and wear. For example, the plunger of the high-pressure reciprocating metering pump used in chemical plants is plasma-sprayed with Al2O3. TiO2 composite oxide ceramic coating, and its service life is 6 times longer than that of the original chrome-plated plunger, and the service life of the sealing packing is also increased by 3 times. The large piston rod of the hydraulic cylinder of the hydraulic hoist for large reservoirs, hydropower stations and marine development uses plasma sprayed ceramic coating instead of hard chrome plating, which can achieve high quality, long life and maintenance-free.
Super-large ceramic-coated piston rods with a length of 16 m and a weight of more than 10 t and corresponding hydraulic hoists have been manufactured. Hydraulic piston rods for large bulldozers, hydraulic piston rods for rolling mills, hydraulic press piston rods for building tile pressing, turbine impeller shafts and grinding rings, armature shaft heads, grinder shafts, fuel pump shafts, anti-seizure sleeves, piston rings, cam followers, etc. Under low stress sliding wear and corrosion conditions, almost all the original chrome-plated products can be replaced by thermal sprayed ceramic or metal ceramic coatings.
5.6 Fiber wear-resistant coating
5.6.1 Ceramic coating resistant to textile fiber wear
Modern textile machinery, especially chemical fiber machinery, is developing towards high speed, light weight and energy saving. In the spinning process, various wire guides and spinning parts are mostly made of aluminum alloy in order to reduce weight, increase rotation speed and reduce energy consumption. The surface of the wire guides and spinning parts is worn by very fine high-speed chemical fiber yarns (up to 700-1 000 m/s) to form grooves. Replacement not only causes downtime losses, but also affects the quality and grade of spinning.
On the surface of the wire guide parts of chemical fiber spinning machines, plasma spraying Al2O3-based composite ceramic coating is used to obtain an "orange peel-like" appearance after treatment, and the surface roughness Ra is about 1.5 μm. The outstanding features of this ceramic coating are:
(1) It has excellent resistance to high-speed fiber wear and its service life is five times longer than that of chrome-plated parts;
(2) It has moderate friction and can exert moderate "twist force" on the fiber to achieve the necessary strength and toughness;
(3) It has moderate surface roughness and can make the fiber obtain the necessary "velvet" to achieve good dyeing performance and certain hygroscopicity.
Due to these characteristics of ceramic coating, the service life of key basic parts of chemical fiber machinery is increased by five times compared with the original chrome-plated parts, and production has reached a new level. The Czech Republic uses this technology to make its chemical fiber machinery exports more competitive.
5.6.2 Wear-resistant coating for metal wire drawing
The metal wire drawing industry, such as the production of steel wire, wire rope and wire and cable, uses a large number of wire guide wheels and rollers. The metal wire slides at high speed on its surface and undergoes cold work hardening, which produces strong friction and wear on the contact surface of the guide wheel, resulting in defects such as "furrows" and pits, resulting in short life, frequent replacement and maintenance, and affecting the quality of wire drawing. Using supersonic flame spraying or explosion spraying technology, a Wc-containing cemented carbide coating is sprayed on the surface of the metal wire drawing guide wheel, which has high hardness and wear resistance, and the life is increased by 5 to 10 times, which has achieved great success.
5.6.3 Hydrophilic and dielectric coatings
Modern papermaking and printing machinery, despite running at high speeds, are in a low stress state due to light loads, and are particularly suitable for thermal spray coatings.
Plasma spraying ceramic coating technology has been successfully applied to papermaking and printing machine rollers in foreign countries for many years, and its application is expanding day by day. This is because ceramic coatings have many characteristics: high abrasion resistance; high selective wettability and hydrophilicity; high electrical insulation and dielectric properties; high anti-stickiness; high etchability and pattern clarity; paper bite with moderate roughness, etc.
For example, the ceramic coating sprayed on the water roller of a color offset printing machine is not only wear-resistant and ink-resistant, but also the ceramic coating part left after etching can form a thin water film on its surface due to its good hydrophilicity to prevent ink from mixing in. The etched roller surface without ceramic coating is covered with ink, so a clear color print can be obtained without color bleeding. For example, the roller of the corona treatment machine used for electro-etching of plastic films needs to operate at 1-2×104 V. Spraying a high dielectric ceramic coating on the roller surface meets this need.
The surface roughness of the plasma sprayed ceramic coating is about 2-5 μm after spraying, and can reach Ra 0.13-0.20 μm after grinding, and 0.03-0.10 μm after fine grinding, which can meet the needs of different grades of paper production.
From the above application fields, it can be seen that thermal spraying high-performance ceramic coatings have a broad market and huge economic benefits.
Application and potential prospects in high-tech fields
Thermal spraying high-performance ceramic coating technology is emerging in the high-tech field, which will drive and promote the development and rise of a series of high-tech technologies. The discovery of composite oxide superconducting ceramic materials with high critical resistance temperature for high-temperature superconductor parts was a major breakthrough in the field of materials in the 1980s. The zero resistance temperature of yttrium barium copper oxide superconducting ceramic materials tc＞90 K (higher than liquid nitrogen temperature), and the magnetic transition temperature tB＞96 K.
The unique advantages of plasma spraying superconducting ceramic coatings are: high deposition rate, easy preparation of thick coatings and large-area coatings, ability to spray superconducting parts with complex shapes, direct spraying in the atmosphere, no need for protective gas, and a promising process for realizing the practical application of superconducting materials. Plasma spraying of yttrium barium copper oxide (YBaCuO) and bismuth strontium calcium copper oxide (BiSrCaCuO) superconducting ceramic coatings have been successfully reported. It has shown good application prospects in magnetic shielding, microwave components, various sensors, quantum electronic devices, etc.
Plasma spraying technology is used to manufacture sputtering targets, such as yttrium barium copper oxide (YBa2Cu3Ox) targets used for physical vapor deposition (PVD), which can produce high-performance superconducting films with a critical current density of up to 105-106 A/cm2.
5.6.4 In the microelectronics industry
Metal-ceramic composite materials are an ideal material for substrates in the microelectronics industry. Thermally spraying insulating ceramic coatings on metal plates (such as Kovar, copper, aluminum, and steel) can dissipate the heat generated by strong currents, while ceramic coatings provide good dielectric insulation properties. For example, spraying Al2O3 ceramic coatings on copper plates has a total thermal conductivity that is 5 times higher than that of sintering an alumina layer on a copper plate of the same thickness, which is very beneficial for heat dissipation and power improvement of integrated circuit boards. The United States has been able to spray 25 mm×25 mm dielectric ceramic coating composite circuit boards and has reached a mass production scale of 5×104 pieces.
5.6.5 Biomedical functional ceramic coatings
The improvement of people's living standards and the extension of the average life expectancy of humans have increased the demand for artificial bones.
Previously, metal skeletons such as stainless steel or titanium alloys were used to implant into the human body to replace damaged bones, but they had problems such as insufficient resistance to body fluid corrosion and incompatibility with muscle cell tissues, resulting in water accumulation.
Modern research shows that the crystals that constitute the hard tissues of organisms are apatite-based inorganic ceramic materials.
Plasma spraying biomedical functional ceramic coatings on metal substrates have the following characteristics:
(1) Non-toxic to organisms and suitable for safe use in vivo;
(2) Good adaptability and affinity to organisms and cells, no side effects;
(3) Resistant to corrosion by human body fluids;
(4) Resistant to wear during long-term use;
(5) Possessing mechanical properties such as strength and toughness required for human movement;
(6) The porosity and rough surface of the sprayed layer are conducive to the growth and affinity of biological tissues to the surface of artificial bones.
Therefore, artificial bones with thermal spraying metal-based bioceramic coatings are relatively ideal artificial bone materials. They have been successfully clinically applied in human femurs, hip joints, elbow joints, pelvises, artificial teeth, etc. Americans call it "a revolution in medical biofunctional materials."
Thermal spraying high-performance ceramic coating technology is a high-tech technology that has been widely used and has outstanding benefits abroad, but it is just starting in my country. Admittedly, there is no magic cube that can turn stone into gold or mud into gold, but the use of thermal spray ceramic coating technology can achieve high added value with very little material consumption and open up a huge potential market, which will undoubtedly achieve twice the result with half the effort.
6.Performance characteristics
● Strong ceramic sensitive diaphragm
● Zero point and full scale laser calibration
● Excellent corrosion and wear resistance
● Shock and vibration resistance
● High precision and high stability
● Wide operating temperature range
● Small size and easy packaging
● Most competitive price
7. Common measuring ranges
● 0…100kPa
● 0…200kPa
● 0…500kPa
● 0…1Mpa
● 0…2Mpa
● 0…5Mpa
● 0…10Mpa
● 0…25Mpa
● 0…40Mpa
● 0…60Mpa
● 0…200kPa
