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Advanced ceramics are everywhere in people's lives

2019年12月20日 | Advanced ceramics
Advanced ceramics is a new material with wide application. When it comes to advanced ceramics, people often think of it as a stone, or only as a container like a teacup. However, modern advanced ceramics can produce electricity or mechanical processes, which have been developed many functional applications.

Under the command of the teacher's password in P.E class, the students will move quickly to the left or to the front. And advanced ceramics, such as piezoelectric ceramics, can also be arranged rapidly under the action of an electric field. When the electric field turns 90 degrees, it immediately follows the direction, and the response time is within milliseconds. In addition, the transfer of charge within the material can be observed. Under the action of the outfield, the function of the ceramic interior is the foundation of many applications.

Piezoelectric ceramics, as the name suggests, it produces electric charges under pressure; the reverse is also true, it produces deformation or vibration under the action of an electric field. Piezoelectric ceramic can be used in the piezoelectric ignition with the piezoelectric effect. When the hand presses the spring on the lighter, the force on the ceramic produces an electric charge. If there is a gap between the slit, this kind of electrostatic pressure will jump fire and form an electric spark, which can ignite the gas and can also be used for projectile detonation and rocket fire.

Piezoelectric porcelain can also be used as a microphone. Under the pressure of human speech, the corresponding telecommunication number of the human voice will be transmitted. A piezoelectric element with a circuit can be a buzzer or an electronic instrument. The piezoelectric element is actually an energy conversion device, the transducer, which enables the conversion of mechanical energy and electrical energy.



Electronic ceramic components are often used in modern life. For example, when people come back to their homes to press the doorbell, the piezoelectric doorbell can make a magpie sound. In hot weather, the fan can be turned on with a piezoelectric remote control; when the weather is cold, the PTC heater can warm the room. The household refrigerator is cooled by the compressor motor, and in which the PTC starter is also used. When watching TV in the evening, first of all, the PTC color eraser removes the image and makes the color image clear. A large number of electronic ceramic components (more than 50%) are used in color TV.

It can be seen from the above that people in modern life have a lot to do with new materials. At present, the production of advanced precision ceramics is very large, and the annual output of piezoelectric ceramics is thousands of tons.

CVD Products Made of Pyrolytic Boron Nitride for Demanding Applications

2019年09月27日 | Advanced ceramics
Pyrolytic Boron Nitride is a boron nitride ceramic product that does not react with acids, bases, organic solvents, molten metals or graphite. It can withstand temperatures of 1800 ° C in a vacuum and 2000 ° C in nitrogen, making it ideal for use as a furnace assembly and melting vessel. PBN crucible heated to 1200 ° C can be inserted into liquid nitrogen without causing significant damage. PBN coated graphite heating elements provide an extremely uniform temperature profile for compound and silicon semiconductor fabrication.
By means of the CVD process, it is possible to produce a component of pyrolytic boron nitride or graphite products with numerous properties, which can provide customers with decisive added value:
In ultra-high vacuum applications, the decarburization of pyrolytic boron nitride at the highest temperatures is minimal.
Pyrolytic boron nitride components not affect the chemical reaction or physical properties of the product being tested.
Components made of pyrolytic boron nitride have good toughness and a stable shape.

Pyrolytic boron nitride crucible
CVD is capable of producing tantalum made of pyrolytic boron nitride of different sizes and forms. Such as:
Straight
Conical shape
Special form
PBN and graphite coating
Using a chemical vapor deposition process, we can coat a suitable graphite material with pyrolytic boron nitride to combine the thermal, chemically stable, and electrically insulating properties of anisotropic PBN with the conductivity of graphite. This means it can make thicker parts such as heaters, furnaces and furnaces.

PBN-PG heater
Since pyrolytic boron nitride and pyrolytic graphite can be combined because they have comparable CTE (coefficient of thermal expansion), they can be used to construct a heating element. The light weight and associated good rapid temperature change behavior, as well as the chemical inertness associated with other substances, should be emphasized here. PBN-PG heater can be manufactured in the form of a planar heater or a 3D heater such as a tube.
For more information, please visit https://www.preciseceramic.com/.

Unexpected Catalytic Activity: Boron Radicals Make Boron Nitride Active

2019年09月18日 | Advanced ceramics
Boron nitride has long been considered a chemically inert ceramic material, but recently, this material has exhibited unexpected activity in the field of catalysis, causing widespread concern. Different morphologies of boron nitride (such as nanosheets, nanotubes) have been successfully used to catalyze some important industrial processes, such as acetylene hydrochlorination and propane dehydrogenation. According to these findings, the catalytic activity of boron nitride is derived from various defects and edge effects in its structure. However, the precise active site and catalytic mechanism of BN are still unclear.



Recently, Yang Wenrong Research Group of Deakin University in Australia cooperated with Chen Ying Research Group to detect the working mechanism of boron radicals and their catalytic reactions in boron nitride nanostructures for the first time. Through chemical experiments and theoretical calculations, they confirmed that boron radicals are active sites for boron nitride catalyzed reactions. Experimentally, the team used boron radicals to quench a stable active free radical (2,2-diphenyl-1-picrylhydrazyl, DPPH), and the density of boron radicals on the surface of boron nitride (nanosheets or nanoparticles) is determined by electron spin resonance (ESR) spectroscopy. Density functional theory (DFT) calculations show that boron radicals are generated at the defects and edges of boron nitride nanosheets. By strong ultrasonic stripping, the authors increased the number of boron-nitrogen bond cleavage and produced more defects and unsaturated boron atoms (boron radicals), which made the quenching effect on DPPH stronger. Interestingly, by comparison experiments, boron nitride was modified with different terminal groups (amino or hydroxyl) without affecting the detected free radical strength and catalytic activity. This further confirms that the active site is a boron radical centered on a boron atom, rather than other groups centered on a nitrogen atom or an oxygen atom.

Subsequently, the research team successfully used boron nitride nanosheets for the catalytic oxidation of hydrogen peroxide to 3,5,3',5'-tetramethylbenzidine (TMB). They found that boron radicals can promote the catalytic decomposition of hydrogen peroxide, and the formed hydroxyl radicals further react with colorless TMB, and are oxidized into a blue, diimine-type product by transfer of their own electrons. The hydroxyl radical generated by the decomposition of hydrogen peroxide can be captured by a 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and determined by ESR spectroscopy. It has been found through experiments that the presence of boron nitride nanosheets promotes the generation of hydroxyl radicals. This study first proposed a catalytic reaction mechanism based on boron radicals, which is a new way for the development of boron nitride in the field of catalysis.

Boron Radicals Identified as the Source of the Unexpected Catalysis by boron Nitride Nanosheets
Zhen Liu, Jingquan Liu, Srikanth Mateti, Chunmei Zhang, Yingxin Zhang, Lifen Chen, Jianmei Wang, Hongbin Wang, Egan H. Doeven, Paul S. Francis, Colin J. Barrow, Aijun Du, Ying Chen and Wenrong Yang
ACS Nano, 2019, DOI: 10.1021/acsnano.8b06978

For more information, please visit https://www.preciseceramic.com/.

六方晶窒化ホウ素および立方晶窒化ホウ素 (Hexagonal Boron Nitride and Cubic Boron Nitride)

2019年06月20日 | Advanced ceramics
In recent years, new materials based on ceramics have developed rapidly. Boron nitride ceramic is a kind of hexagonal crystal system with phosphorus structure and special physicochemical properties. It is a new industrial material developed with the development of the aerospace and electronics industry and has a wide range of applications in industry and production.

At present, research on boron nitride is mainly concentrated on the hexagonal phase (h-BN) and the cubic phase (c-BN). Hexagonal boron nitride has good lubricity, thermal conductivity and high temperature performance. Recent studies have shown that the hexagonal phase is also in thermodynamic equilibrium and steady state at room temperature and pressure. The main application of hexagonal boron nitride is to act as a raw material for the synthesis of cubic boron nitride.



Hexagonal boron nitride is called white graphite because it has a similar layered crystal structure and physical and chemical properties similar to graphite (good lubricity and thermal conductivity). Hexagonal boron nitride is commonly used as a sintered ceramic material. In addition, due to its high thermal conductivity, good electrical insulation properties, low thermal expansion coefficient and non-thermal properties, h-BN structural ceramics have been widely used in high temperature insulation components, atomic energy, metallurgy, aviation and other fields. As a raw material for synthesizing cubic boron nitride, hexagonal boron nitride is a theoretical low-temperature stable phase, and its excellent performance is more attractive. Therefore, hexagonal boron nitride is commonly used to synthesize cubic boron nitride.

Boron nitride ceramics have excellent thermal stability and dielectric properties. They are one of the few compounds that can decompose at high temperatures, and have excellent thermal and electrical stability even over a wide temperature range. However, single-phase boron nitride ceramics have not been put to practical use due to low strength, hardness, elasticity, high thermal conductivity, low corrosion resistance, and difficulty in forming a shape component.
As an advanced ceramic material, boron nitride is widely favored in the field of materials research due to its excellent mechanical properties. The new boron nitride synthesis method has become a hot topic in boron nitride research.

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