Diamond abrasives is more and more widely used in the superhard abrasive industry. Today, the author gives a comprehensive introduction to diamond abrasives.
Classification and use of diamonds
Diamonds are generally divided into natural diamonds and synthetic diamonds. The crystalline shapes of natural diamonds can be divided into single crystals, conjoined crystals, polycrystals. Type.
Industrial classification of diamonds: GB/T 23536-2009 specifies the variety code and scope of application of synthetic diamond powder: RVD is used for making resins, bonded abrasives or abrasive pastes; MBD is used for making metal bonded abrasives, electroplated products, drilling tools, abrasive pastes; SCD is used for making metal bonded abrasives, geological drills and cutting tools, etc. SMD for cutting tools, geological drills and dressing tools, DMD for dressing tools and other single-grain tools.
Main characteristics of the diamond
The excellent properties of diamond
high hardness, wear resistance, applied to cut, grinding, sawing and drilling tools.
The friction coefficient is small. It is applied to wire drawing die, high-speed bearing, precision navigation, disk head protection grinding.
Has good thermal conductivity and can be used in large-scale high-power integrated circuit substrates, solid-state microwave devices, solid-state laser fins, super-thermal sensors.
The full wavelength transmittance of light is large. It is applied to all kinds of optical lens and optical window protective film.
Good chemical stability, applied to the rectifier, triode and thermometer.
Infrared transmittance is good, applied to infrared remote sensing, telemetry.
UV sensitive applied to cosmic communication system UV laser.
Sensitive to sound vibration, applied to high fidelity loudspeaker diaphragm.
The fastest speed of sound propagation.
Semiconductor prohibited broadband
Diamond synthesis
The main raw materials for diamond synthesis are graphite and catalyst.
There are three types
Single substance: usually through excessive elements and its adjacent elements, Fe, Co, Ni, Pt, Cr, Mn, Ta.
Alloys: Binary or ternary alloys consisting of elements of the first group, such as Ni-Mn, Ni-Mn-Fe, Ni-Mn-Co, Ni-Mn-Cu.
The synergistic catalysts consist of two or more elements that alone do not act as catalysts or metal compounds (or alloys) plus a single element, such as Nb-Cu, Mo-Mg, Cu-Cr, Cu-Ti and NbC-Cu. The pressure transmitting medium is Ye Shila.
Graphite
The bond between layers is weak in graphite leaching. Shear stress caused by ultra-high temperature makes the grain of graphite broken and refined, and stacking faults occur. The results can be used as the six-party diamond in the structure of Pb Zn deposit.
Before and after solvent-touch melting, graphite carbon atoms and their clusters enter the flux-catalyst through certain defects such as vacancies and their clusters, melting pores, etc. In a certain temperature range of melting, flux catalyst has short range ordered structure. Carbon atoms and their clusters enter fluxes with a near-range ordered structure – each of which forms an ideal interstitial solid solution.
At high pressure, the graphite layer spacing is compressed. The vibration of carbon atoms intensified at high temperatures. Under the action of high temperature and high pressure, the atoms corresponding to the layers are approached regularly, and a covalent bond perpendicular to the layers is established between the layers. And the regular distortion is the distortion of the graphite layer into a diamond structure. Finally, graphite is transformed into the diamond.
Purification and separation of diamond abrasives
After diamond synthesis, it needs to be soaked in mixed concentrated acid, then washed off graphite, dilute acid to remove metal: ball milling, shaking off graphite, drying, acid and alkali treatment, alkali removal of pyrophyllite wax, washing and drying to the separation process.
Diamond sorting
First is the plastic process, followed by acid treatment and screening. It is coarser than 140/170, semicolon selection, magnetic separation, detection and storage, and less than 140/170. Type selection is usually carried out on the electromagnetic vibrator. The working principle is to use the same density and different shapes of particles. Due to the different friction coefficient, the motion locus is different on the inclined vibrating table. And separate particles of different shapes.
Magnetic separation
Magnetic diamonds are nonmagnetic materials. In the process of magnetic separation, diamonds with different magnetic properties are divided into magnetic, intermediate or weak magnetic grades by means of magnetic and mechanical forces.
Diamond polycrystalline PCD
Diamond polycrystalline is a new superhard abrasive. It is generally considered that it is composed of many diamond grains or diamonds.
Since the development of diamond polycrystalline from simulating natural diamond, according to different mechanisms, different manufacturing processes have been adopted, forming a series of different forms, properties, functions. Artificial polycrystalline products mainly include sintered polycrystalline diamond, growth polycrystalline diamond and polycrystalline diamond with the substrate.