Introduction of common carbon-based superhard materials

The rapid development of modern science and technology has put more and more stringent performance requirements on materials. Among the many properties of materials, hardness is one of the most important and basic performance indicators. The synthesis of superhard materials and their properties have been It is one of the focuses of condensed matter physics and materials science research. Since the successful synthesis of diamond films by chemical vapor deposition at low temperature and low pressure, ie, metastable conditions, researchers in various countries have made great progress in the artificial synthesis of diamond films. However, due to the poor thermal stability of diamond, oxidation occurs when heated in air, and it is easy to react with iron group metals. Therefore, it is greatly restricted in the processing of steel materials, so the synthetic hardness is close to or even exceeds that of diamond. The new super-hard materials are necessary. The molecular structure, physical properties and synthesis methods of cubic boron nitride are very similar to those of diamond. Its hardness is second only to diamond, and its thermal stability and chemical stability are superior to those of diamond, which is suitable for processing iron group metals. In addition, c-BN has great application potential in the fields of electronics and optics. Recently, the development of c-BN film has been very rapid. In 1989, the elastic modulus and structural properties of β-C 3 N 4 were calculated. The results show that it has a large binding energy and is greater than the elastic modulus and hardness of diamond. As soon as the results were announced, this new material has received widespread attention from researchers in various countries. Different experimental methods have been used to synthesize β-C 3 N 4 . In addition to diamond, c-BN and β-C 3 N 4 , the diamond-like cubic boron nitride c-BCN material is also receiving increasing attention from the international material community. Because it has the hardness of diamond and the thermal stability of c-BN, c-BCN is very likely to become a new generation of super-hard materials, which has broad application prospects. At present, β-C 3 N 4 and c-BCN have been widely studied by the international material community as alternative materials for diamond. The two most common allotropes of carbon are graphite and diamond graphite crystals. The carbon atoms are bonded by sp 2 hybrid orbitals. The softer crystals of the diamond crystals form bonds with sp 3 hybrid orbitals. The crystal structure is Sphalerite structure. Another allotrope of carbon is the C 60 molecule, which has attracted the attention of many researchers in recent years because of its extraordinary hardness at high pressure. In addition, β-C 3 N 4 is also considered to be a new generation of superhard materials in the future. In addition to its unmatched hardness, diamond diamond has some other excellent physicochemical properties such as wide band gap, high breakdown field strength, maximum electron saturation speed, lowest dielectric constant, high thermal conductivity and Good light transmission and so on. Therefore, it has a very wide application prospect in the fields of mechanics, thermals, electronics and optics. There are generally two ways to synthesize diamond: high temperature and high pressure and CVD. The commercially available diamonds for cutting, grinding and polishing are mostly high temperature and high pressure synthetic diamonds. The CVD method for synthesizing diamond film was developed in the early 1980s. Generally, a carbon-containing gas or a volatile liquid and a carrier gas are introduced into a vacuum chamber, under the action of microwave, radio frequency, hot wire, etc. The gas decomposes and a diamond film is formed on the substrate. At present, low pressure vapor deposition of diamond thin films has been achieved in a variety of ways. In the process of preparing diamond thin films by CVD, the strong etching effect of atomic hydrogen on the graphite phase is considered to be a key factor in diamond formation. As a superhard material, the poor thermal stability and chemical stability of diamond seriously affect its industrial application. Diamond-like carbon (DLC) and amorphous carbon α-C:H films not only have similar performance characteristics as diamond films, but also have good biocompatibility, and have been successfully applied in the fields of machinery, electronics, optics and medicine. The preparation process of diamond-like carbon film is becoming more and more mature, and a series of plasma enhanced CVD methods such as DC glow discharge method, RF glow discharge method and microwave-RF glow discharge method have been appeared, and magnetron sputtering, RF sputtering, vacuum Physical vapor deposition (PVD) methods such as arcing and laser ablation. The deposition of diamond-like carbon films has the advantages of high deposition rate, wide selection of substrates, and large-area deposition. When α-C:H film is prepared by radio frequency self-bias method, a small amount of diamond particles are sometimes present in the sample, so it can be considered that the α-C:H film is formed during the transition of hydrocarbons into diamond in the plasma. of. The nuclear magnetic resonance and electron energy loss spectra can be used to accurately measure the percentage of each configuration of carbon atoms. The results show that the carbon atoms in the α-C:H film are mainly composed of sp 2 and sp 3 configurations, sp 1 configuration. The carbon atom content is small. The mechanical properties of the α-C:H film strongly depend on the hydrogen content of the film. As the hydrogen content in the film increases, the hardness of the film decreases and the wear resistance decreases. The microhardness of a film measured experimentally was between 30-50 GPa, which was significantly higher than the microhardness of SiC (25-30 GPa). Another type of α-C film with little or no hydrogen, the nature of which depends on the ratio of the sp 3 configuration to the sp 2 configuration. Fullerene as an allotrope of carbon, a fullerene family represented by C 60 , has a unique cage structure and excellent physicochemical properties, and is new in semiconductor, magnetic, nonlinear optics, superconductivity, and preparation. Derivatives and other aspects have shown fascinating prospects and have become the focus of attention among physicists, chemists and materials scientists. It has been found that fullerenes can not only be used as a source material for synthetic diamond, but also fullerene exhibits a high hardness under high pressure conditions. In 1992, C 60 was converted to polycrystalline diamond at a pressure of >20 GPa at room temperature, and other researchers repeated this at a pressure of 16-54 GPa using impact compression and rapid quenching techniques. It is well known in the C 60 carbon atoms in the form of 48 carbon atoms tetrahedrally coordinated registration, so the diamond into the process requires only minor structural changes in the C 60. It is calculated that the bulk modulus of a single C 60 molecule is 843 GPa, which is almost twice the modulus of diamond elasticity, so C 60 is considered to be harder than diamond. Considering that the C 60 solid is a van der Waals crystal with a face-center structure, the distance between the C 60 molecules in the crystal is about 1 nm, and thus the elastic modulus of the C60 crystal is smaller than that of the single C 60 molecule. However, when the C 60 balls are compressed to abut each other, the elastic modulus of the crystal will be very close to the elastic modulus of the C 60 molecule. Considering the 74% effective volume factor in the face-centered cubic structure, the elastic modulus of the C 60 solid is calculated to be about 624 GPa, so the hardness of the C 60 crystal may exceed the diamond from the viewpoint of bulk modulus. Although C 60 shows extraordinary hardness only under high pressure, this result is still encouraging. The high hardness of carbon nitride β-C 3 N 4 β-C 3 N 4 has caused a boom in the material science community, but since the synthesized crystal grains are too small, many important physical properties cannot be determined, and The crystals that are truly stoichiometric are still not experimentally validated. In addition, preliminary hardness tests have shown that hard metals can leave scratches on their surfaces. Smaller grains and lower nitrogen content are two important factors hindering the acquisition of higher quality films. At present, research on them still remains in the development and improvement of preparation methods. Similar to the c-BN film, it is expected that a non-equilibrium technique such as high-energy ion bombardment will make it possible to achieve a breakthrough in Zhuang preparation technology.

Grips Clips And Clamps

A wire rope clamp (sometimes called a clip) is used to secure the loose end of the loop back to the wire rope. It usually consists of a U-bolt, a forged saddle, and two nuts. Two layers of wire rope are placed on the U-bolts. Then slide the saddle over the rope and attach to the bolts (the saddle includes two holes for the U-bolts). Nuts hold the unit in place. The wire rope is usually terminated using two or more clips depending on the diameter. A 2" (50.8 mm) diameter rope may require as many as eight.
There is an old saying: "A dead horse is without a saddle". This means that when installing the clips, the saddle portion of the assembly should be placed on the load bearing or "live" side of the cable, not the non-load bearing or "live" side of the cable. The "no power" side. According to U.S. Navy Manual S9086-UU-STM-010 Chapter 613R3, Wire and Fiber Ropes and Slings, "This is to protect the live or pressure-bearing end of the rope from pinching and damage. The flat bearing housing and body (saddle-shaped ) extension claws are designed to protect the rope and remain on the live end at all times."[18]

The U.S. Navy and most regulatory agencies do not recommend using such clips as permanent terminals unless regularly inspected and retightened. Encyclopedia website: ewikizh.top

Grips Clips And Clamps

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