Synthesis method of zirconia

The "cold crucible" method of zirconia invented by the Soviet Union is still the main synthesis method to this day. Firstly, wrap the copper tube into a cup shape, and inject cooling water into the copper tube. Add a small amount of zirconium metal sheet to the cup, add zirconia and stabilizer powder in the middle, and press tightly. The entire device is surrounded by a radio frequency induction coil. When the induction coil is energized, the zirconium metal generates an electric current due to induction, which is heated to high temperature and melted, and then heat is transferred to the internal zirconia to melt it. Cooling water maintains the solid state of zirconia 1-2mm near the surface in the cup. After several hours of heating, the heat gradually decreases and flawless columnar crystals begin to form. Afterwards, annealing was performed at 1400 ° C for a long time to eliminate stress in the crystal. The annealed crystal is usually 5cm long and 2.5cm wide, and can be cut into gemstones.

If different metal oxides are added to the zirconia raw material, different colored crystals can be obtained. For example:

Cerium: yellow, orange, red

Chromium: Green

Neodymium: Purple

Erbium: pink

Titanium: gold brown

Some manufacturers have also improved their products in different ways. The most common is to add a layer of Diamond-like carbon (DLC) on the surface of Cubic zirconia by vapor condensation. The resulting product is harder than ordinary zirconia and looks more like a diamond. Another method is to vacuum spray a layer of metal oxide on the surface to create a halo. But unlike coating with diamond like carbon, this process can be worn out.

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