HEM Sapphire
What is HEM Sapphire
The Heat Exchange Method (HEM) is a technique used to grow large, high-quality synthetic Sapphire crystals. This method is particularly known for producing crystals with excellent optical and structural properties, making them suitable for a wide range of industrial and technological applications.
Technical informations
| Growth Process | |
|---|---|
| In Heat Exchange Method (HEM) the Sapphire crystal grows in a specially designed furnace where heat is carefully controlled and distributed. The process is designed maintain a precise temperature gradient | |
| Controlled Growth | The slow cooling and precise temperature control result in a crystal with fewer defects and inclusions, leading to high optical clarity and uniformity |
| Chemical Composition | |
| Formula | Al₂O₃ (Aluminum oxide) |
| EFG Sapphire is chemically identical to natural Sapphire, consisting of pure aluminum oxide with minimal impurities | |
| Physical Properties | |
| Hardness | 9 on the Mohs scale, only second to diamond |
| Density | Approximately 3.98 g/cm³ |
| Optical Properties | |
| Clarity | HEM Sapphires have exceptional clarity due to the controlled growth process, which minimizes inclusions and defects |
| Transparency | High transparency, making these Sapphires ideal for high end optical applications |
| Birefringence | Low birefringence, which is desirable for applications requiring consistent optical properties |
| Transmission range | 0.15 to 5.5 micron (from UV to mid-IR) |
| Mechanical Properties | |
| High mechanical strength, making HEM Sapphire suitable for demanding applications where durability is critical | |
| Excellent wear resistance due to its hardness | |
| Thermal Conductivity | High thermal conductivity, which is useful in heat-dissipating components |
| Thermal Properties | |
| Melting Point | Approximately 2,050°C, similar to other forms of Sapphire |
| Thermal Shock Resistance | Excellent, allowing it to withstand rapid temperature changes withoutcracking |
| Thermal Conductivity | 25 W/mK at 300K |
| Market Value | |
| HEM Sapphires are valued primarily for their use in high-tech and industrial applications, where their superior properties are critical. The cost is often related to the size, purity, and intended application of the Sapphire | |
HEM Sapphire applications
Optical Components
HEM Sapphire is commonly used in the production of high-quality optical
windows, lenses, and other components that require superior clarity and durability.
Semiconductors
It is widely used as a substrate in LED manufacturing and other semiconductor applications due to its excellent thermal and electrical properties.
Aerospace
Employed in aerospace applications for windows and other components that require extreme durability and resistance to harsh environments.
Watch Crystals
Used for high-end watch faces due to its scratch resistance and clarity.
Medical Devices
Applied in medical lasers and other devices where high-purity, transparent materials are required.
The HEM method: how it works
The HEM method begins by melting high-purity alumina in a crucible inside a furnace with carefully controlled thermal gradients. A seed crystal is placed at the bottom, above a water-cooled heat exchanger. As the melt slowly solidifies from the bottom upward, the cooling system helps manage stress and ensures even crystal growth.
This bottom-up growth process enables the production of very large sapphire boules, sometimes over 40 cm in diameter, while maintaining exceptional clarity, mechanical strength, and low birefringence.
FAQ
HEM Sapphire (Heat Exchanger Method Sapphire) is a synthetic sapphire grown using a technique designed to minimize thermal stress during crystal formation.
Unlike Kyropoulos or EFG, the HEM process uses a special furnace equipped with multiple heating zones and a heat exchanger at the base.
The result is the growth of very large sapphire boules with excellent homogeneity, low internal stress, and outstanding optical quality.
HEM Sapphire is produced by melting high-purity alumina in a crucible and cooling it from the bottom up with a heat exchanger. A seed crystal at the base guides the growth, while the controlled thermal gradient minimizes stress.
This process allows large, high-quality sapphire boules to form with excellent clarity and low internal defects.
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