Hydration polishing of advanced ceramics

1. Polishing mechanism

Hydration polishing is an efficient and ultra precision polishing method that utilizes the phenomenon of hydration reaction at the workpiece interface to remove the hydration layer formed on the workpiece surface using the friction force of the polishing disc. Its main feature is that it does not use abrasive particles or processing fluids. The processing device is the same as a regular polishing machine. The difference is that processing is carried out in a water vapor environment. The selected polishing disc material must not produce Dry media reaction with the workpiece. The removal amount of hydration polishing is only a few nanometers to more than ten nanometers, so a clean surface without scratches, smoothness, and lattice distortion can be obtained.

In the polishing process, the workpiece and polishing disc generate relative friction, high temperature and high pressure are generated at local real contact points, so that atoms or molecules on the surface of the workpiece are activated. At the same time, Superheated water vapor molecules and water act on its surface to form a hydration layer on the interface, and the friction of polishing disc is used to remove the hydration layer on the surface of the workpiece, so as to achieve mirror processing.

2 Processing characteristics

When sapphire is hydrated and polished, the higher the pressure at the contact point, the more it can promote the reaction. The contact friction rate (sliding rate) is effective for generating high temperatures, but the contact time of real contact points decreases with increasing speed, and the reduction in reaction time sometimes leads to side effects. The water polishing example of Si3N4 mutual grinding shows that the volume removed per unit of machining distance gap is not related to the mutual grinding rate, and is basically a constant value. The interface reaction products are proportional to the reaction time, which is the accumulation of the contact time of a real contact point. If the processing distance is constant, the higher the processing rate and the shorter the processing time, the less processing amount.

3 Processing surface properties

The mutual grinding and polishing experiment of sapphire in water shows that the pre processing of hydration reaction polishing does not have high requirements for surface roughness. As long as 400 diamond grinding wheels are used for grinding, it is sufficient. The surface roughness achieved after polishing is about lOnm for single crystal materials and around 30nm for polycrystalline materials.

To study the crystallinity of polished disc surfaces of sapphire materials. Comparing the broken section of sapphire with the polished disk surface of sapphire, it can be seen from the Electron diffraction diagram that both of them have excellent single crystallinity and no processing metamorphic layer. No character distortion was found using photoelectron spectroscopy analysis (ECSA).

The hydration polishing method is processed in the form of removing interface reaction products, therefore, there is also a problem of residual reaction products on the processing surface. The results of polarization mirror analysis (IMA) using ion microscopy showed that there were only residual hydroxides on the processed surface.

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