What Is Diamond Powder?
Generally speaking, diamond powder refers to artificially produced nm to μm-sized diamond crystals, mainly used as abrasives. However, once it became possible to make diamond powder artificially, the demand for diamond powder rapidly increased, especially in the fields of cutting and polishing, taking advantage of the fact that diamond is one of the hardest substances in the world. The types of diamond powder include
There are two types of diamond powder: mono-crystalline and poly-crystalline. Poly-crystalline diamond powder has higher performance than mono-crystalline diamond powder due to its later development and improvement.
Uses of Diamond Powder
Diamond powder is often used as abrasive grains, or attached to the cutting edge as diamond cutters, blades, and saw wire. Diamond cutters are for industrial use and on-site work, but since they are very inexpensive, they are now used in some DIY situations. In the beauty industry, diamond powder is used in nail care products, face powders, perfumes, moisturizers, and handmade accessories.
Principles of Diamond Powder
There are several methods for producing diamond powder, and single crystals are obtained by high-pressure static synthesis.
In principle, a hydraulic press is used to pressurize the sample (graphite, etc.), and high temperature is also required, so although it is a simple mechanism, it is a large-scale device.
On the other hand, the high-pressure/impact synthesis method is used to obtain polycrystals.
The principle of this method is to pressurize a sample (graphite, etc.) in a sealed state instantaneously (a few microseconds) with an explosive explosion (adiabatic compression also occurs at the moment of explosion). The diamond powder produced by this method is tiny (tens to thousands of nm) but was immediately put to practical use because it was excellent as an abrasive grain.
However, both methods are considered to have room for improvement as manufacturing methods and new manufacturing methods are still being researched.
In some cases, diamond powder is sold as is for actual use as abrasive grains, while in other cases, it is processed into grinding wheels. The manufacturing of abrasive stones requires the uniform mixing of diamond powder, the primary raw material (resin or metal) that serves as the body, and a diamond binder, followed by the molding, firing, and finishing (polishing) processes.
Although diamonds have high hardness, they are sensitive to heat, so measures such as cooling with water or setting an upper limit to the continuous operation time are necessary when using them.
Types of Diamond Powder
There are two main types of diamond powder.
- Mono-Crystalline Diamond Powder This is a diamond powder containing synthetic diamonds synthesized under high-temperature and high-pressure conditions. Like natural diamonds, it is characterized by its cleavage property (the tendency to break in a specific direction).
- It contains few impurities and has good hydrophilic properties.
- Polycrystalline Diamond Powder Polycrystalline diamond powder is composed of nano-sized micro-diamonds firmly bonded together to form a lumpy structure. It is used for polishing SiC, ceramics, and sapphire.
Lapping with Diamond Powder
Loose abrasive refers to a technique in which a tool (also called a lap) and a sample are rubbed together with an abrasive to obtain a smooth surface while removing a small amount of convexity from the surface of the sample. Diamond powder is often used as a loose abrasive (lapping). It is also called polishing.
Lapping is divided into two methods:
- Wet Lapping Wet lapping is a method that uses an abrasive mixed with a lapping liquid. Applying a mixture of abrasive grains and lapping liquid to a lapping surface plate, the sample is pressed onto the lapping surface, and the surface is scraped by moving the sample. The result is a pear-shaped surface, making this lapping method suitable for rough finishing.
- Dry Lapping Abrasive grains are embedded in the lapping surface plate using an abrasive. The surface is scratched by the specimen tracing the surface of the abrasive grains. The embedded abrasive grains are ground to a fine powder as they are processed, and the ground abrasive grains are further embedded, and some roll on the lapping surface plate to affect the processing. Compared to wet lapping, the amount of abrasive used can be reduced, and the finished surface is shiny.
Compared to general grinding wheel processing, lapping has a feature that makes it easier to achieve the required accuracy, i.e., higher processing accuracy. However, lapping is often performed after rough finishing in a separate process because the processing speed is slower than in other methods.