Diamond Instruction
Diamond, which is a mineral composed of carbon elements, has a chemical formula of C. Diamond is the hardest substance naturally occurring in nature. The absolute hardness of diamond is 4 times that of corundum and 8 times that of quartz. The detailed absolute hardness is as follows:
Diamond: 10000-2500
Corundum: 2500-2100
Quartz: 1550-1200.
Electronic structure and crystal structure of diamond structure:
Electronic structure: According to the hybrid theory, when the C atom is reacting, it excites a 2s electron to the 2pz orbital. One s orbital and three p orbitals are mixed to form four new orbitals—sp3 equivalent hybrid orbitals. Each sp3 hybrid orbital has 1/4 of the s component and 3/4 of the p component, and the shapes are all the same. The angles between the symmetry axes of the four tracks are all 109.28.
Synthetic diamond requirements for reaction vessels:
(1) Good pressure transmission performance;
(2) Good sealing performance;
(3) Good insulation performance;
(4) Good heat insulation performance;
(5) Good thermal stability;
(6) Good chemical stability;
(7) Good machining performance.
Types of diamond tools
① Natural diamond tool: Natural diamond has been used as a cutting tool for hundreds of years. Natural single crystal diamond tool has been finely ground, the cutting edge can be sharpened, and the cutting edge radius can reach 0.002μm, which can realize ultra-thin cutting. It is a recognized, ideal and irreplaceable ultra-precision machining tool to process extremely high workpiece accuracy and extremely low surface roughness.
② PCD diamond tools: Natural diamonds are expensive, and diamonds are widely used in cutting and processing are polycrystalline diamonds (PCD). Since the early 1970s, polycrystauine diamonds (PCD for short) prepared by high temperature and high pressure synthesis technology have been developed After its success, natural diamond tools have been replaced by synthetic polycrystalline diamonds on many occasions. PCD has a rich source of raw materials, and its price is only one-tenth to one-tenth of that of natural diamond.
③ CVD diamond tools: Since the late 1970s to the early 1980s, CVD diamond technology has appeared in Japan. CVD diamond refers to the use of chemical vapor deposition (CVD) to synthesize a diamond film on a heterogeneous matrix (such as cemented carbide, ceramic, etc.). CVD diamond has exactly the same structure and characteristics as natural diamond.
Compared with natural diamond, the performance of CVD diamond is very close. It has the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.
Application of diamond tools
Diamond tools are mostly used for fine cutting and boring of non-ferrous metals and non-metal materials at high speeds. Suitable for processing various wear-resistant non-metals, such as glass fiber reinforced plastic powder metallurgy blanks, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon-aluminum alloys; various non-ferrous metals finishing.
The disadvantage of diamond tools is poor thermal stability. When the cutting temperature exceeds 700℃～800℃, it will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because diamond (carbon) easily interacts with iron at high temperatures. Atomic action transforms carbon atoms into graphite structure, and the tool is easily damaged.
