Shaped Sapphire Crystals
Authors: V.N. Kurlov. E-mail:
Some novel sapphire shaped crystal growth techniques were developed in ISSP RAS. These techniques allow to produce sapphire products in various sizes and shapes.
Sapphire has been recognized for a long time as a material with important properties. It has a high refractive index and a broad transmission band spanning the ultraviolet, visible and infrared bands, a high hardness, melting point, very good thermal conductivity, tensile strength and thermal shock resistance. The favorable combination of excellent optical and mechanical properties, along with high chemical durability, makes sapphire an attractive structural material for high-technology applications. Sapphire crystals are used in medicine and blood chemistry as they are resistant to human blood and body fluids, are totally impervious to moisture, and are chemically inert. Frequently it is the combination of two or more of its properties that makes sapphire the only material available to solve complex engineering design problems.
The main applications of shaped sapphire crystals are scanner windows, windows for high-temperature and high-pressure applications, CVD reactors, arc envelopes for vapour lamps, thermocouple sleeves, wear-resistant nozzles, substrates, watch windows, transparent armour, optical systems for high-power laser optics, plasma sources, insulators, high-pressure reactors, thermoluminescent dosimeters, plasma tubes and components, effusion cells for MBE, high-vacuum equipment, moving pieces for friction welding, guides for textile machinery, precision bearings, heat and water impeller meters, chromatograph pistons, engines, domes for high-speed missiles, light guides, acoustic rods, reinforcing elements for composite materials, sensors, nuclear components, research and technological equipment, crucibles for pure metal melting, medicine (implants, scalpels, needles for laser therapy, medical power delivery systems), jewels, etc.
The sapphire shaped crystal growth techniques represent extremely extensive combination of technological, engineering and material science development with know-how allowing one to grow sapphire crystals with specified shape including complex one directly from the melt.
Sapphire crystals of any predetermined cross-section, constant along the crystal length (rods of various cross-sections for optics, thick ribbons, and tubes with large wall thickness), and crystals with discretely changing cross-section configuration can be grown by this technique.
Sapphire crystals can be grown in an automated way with weight control. Automated computer systems provide in situ crystal quality control as well as crystal shape control, which allow an increase in the output of high-quality crystals and the expansion of the areas of applications of sapphire crystals as constructive and optical material.
The noncapillary shaping (NCS) method was developed for the growth of high-quality shaped sapphire crystals with large cross-section. Sapphire crystals of any predetermined cross-section, constant along the crystal length (rods of various cross-sections for optics, thick ribbons, and tubes with large wall thickness), and crystals with discretely changing cross-section configuration can be grown by this technique.