The Manufacturing Process of synthetic Ruby Crystal growth


1(Flame Fusion) A fine powder of the aluminum and chromium oxides is placed in a hopper at the top of the Verneuil apparatus. A hammer atop the apparatus strikes the hopper repeatedly; each stroke causes a small amount of powder to fall through the fine mesh that forms the hopper's floor. This discharged powder falls into a stream of oxygen that carries it down to a nozzle where it mixes with a stream of hydrogen and is ignited. The intense heat of this flame (around 3,600° F or 2,000° C) melts the nutrient, which falls onto a ceramic pedestal below the flame. Initially, the hammer taps at a rate of 80 beats per minute; after a suitable base for the crystal is formed, the rate is decreased to about 20 beats per minute.

After the base is built up to the desired diameter (about 0.8 in or 20 mm) and formation of the high-quality crystal proceeds, the pedestal is lowered at a rate that just keeps the top of the crystal in contact with the flame. After about five and a half hours, the crystal reaches a length of approximately 2.75 in (70 mm); the gas flow is halted, extinguishing the flame. The crystal, now weighing around 150 carats, is allowed to cool in the enclosed furnace.
 
2 (Czochralski Process) The nutrient is heated well above its melting point in a crucible that is surrounded by an electric heater. A small ruby crystal is attached to a rod; the desired crystal will grow on this socalled seed crystal. The seed is lowered into the crucible until it is barely immersed in the melt (i.e., the molten nutrient). To maintain a constant contact temperature between the melt and the entire circumference of the seed crystal, the rod is constantly rotated. As nutrient material attaches itself to the seed and crystalizes (a process that is assisted by the seed's attachment to the relatively cooler rod), the rod is slowly raised, pulling the growing crystal out of the melt. The growing tip is kept in contact with the melt until all the nutrient has been used. The rate of growth can be quite rapid, up to a rate of 4 in (100 mm) per hour. Very large crystals can be pulled, with diameters exceeding 2 in (50 mm) and lengths reaching 40 in (1 m) or more.
Heart Ruby Synthetic Gemstones

3 (Flux Growth) Flux is any material that when melted will dissolve another material that has a much higher melting point. Although temperatures in excess of 3,600° F (2,000° C) are needed to melt aluminum oxide, the material will dissolve in certain fluxes at a temperature as low as 1,470° F (800° C). Process temperatures above 2,200° F (1,200° C) are generally used because they produce higher-quality crystals. While dissolved in the flux, ruby molecules can travel freely and attach themselves to a growing crystal. Some manufacturers immerse seed crystals in the solution, and others simply allow the molecules to combine randomly and form an unplanned number of crystals. The temperature is maintained for a period of three to 12 months. Some manufacturers then pour off the still-molten flux to expose the ruby crystals. Other manufacturers cool the material slowly (4° F or 2° C per hour) and then extract the ruby crystals by breaking off the solidified flux or dissolving it in acid.

4(Hydrothermal Process) Powdered or crystalline nutrient is placed at one end of a pressure-resistant tube. A seed crystal is mounted on a wire frame near the other end of the tube. An appropriate water-based solution is placed in the tube, which is sealed shut. The tube is placed vertically in a furnace chamber, with the nutrient-containing end of the tube resting on a heating element. As the floor of the furnace is heated, the bottom end of the tube becomes hotter than the top (about 835° F or 445° C, compared to 770° F or 410° C); dissolved nutrient material migrates toward the seed and crystalizes on its relatively cooler surface. Pressure within the tube can range from 83,000-380,000 kPa (12,000-55,000 lb per sq in), depending on the amount of free space left in the tube when the solvent was inserted.
The tube used for the hydrothermal process can be made in any appropriate size, with a height-to-diameter ratio ranging from 8-16. In an example described in Synthetic Gem and Allied Crystal Manufacture, five seed crystals were placed in a 12 in (300 mm) long tube; each crystal grew at a rate of 0.006 in (0.15 mm) per day during the 30-day processing period.

Surface finishing
Whether it will be used as a gem or an industrial device, the ruby must be given a smooth, glossy finish after it has been cut or faceted to the desired shape. The following methods may be used.

5 (Polishing) The surface is rubbed with increasingly fine particles of an abrasive such as diamond powder. This traditional technique leaves only microscopic scratches and pits.
6 (Glossing) After initial polishing, the surface of the stone may be heated rapidly in a gas flame to melt any tiny projections. The surface is then allowed to cool, and the thin layer of molten material solidifies as a smooth surface. Treating ruby rods in this way nearly doubles the rod's tensile strength (resistance to a pulling force).