Sapphire

Sapphire is a variety of the mineral corundum. Be the sapphire attributed all colorless and colorful colored varieties with the exception of the red ruby. In a narrower sense, the term refers today to the blue variants, ranging from sky blue to a bull's-eye going dark blue and may vary depending on the light in the shade.

Etymology

The word " sapphire " derives from Latin " sapphirus " and further " sappirus " from the Greek " σάπφειρος " ( sappheiros ) from the Hebrew " סַפִּיר " ( Sappir ) from Old Iranian " Sani - prijam ", from the Sanskrit " Shanipriya " ( शनिप्रिय ), of " Shani " ( शनि ) meaning " Saturn " and " Priya " ( प्रिय ), precious or love, that is " much loved / revered to Saturn " or literally "love of Saturn" from. There are outdated or erroneous trade names: Oriental aquamarine (greenish blue sapphire ), Oriental Huazinth ( pink sapphire ), Oriental emerald (green sapphire) and Oriental Topaz ( yellow sapphire ).

Special Features

Like all Corundum crystallizes in the trigonal crystal system of sapphire with the chemical composition Al2O3 and developed predominantly double-sided tapered, barrel-shaped, six-sided pyramidal and prismatic crystals. Korundtypisch also the chemical resistance. Säureunlöslich as sapphire, among other things, and melts at a temperature of 2040 ° C.

At 25 ° C the thermal conductivity be 41.9 W / ( m · K) and the heat capacity of 754 J / (kg · K) .. The relatively high thermal conductivity of insulating materials increases at lower temperatures and drops off sharply at higher temperatures - in 1200 ° C to one-tenth of the value at room temperature.

Color and optical effects

Sapphires contain as coloring substances minor admixtures of Fe2 and Ti4 ( blue), Fe3 ( yellow and green), Cr3 ( depending on the concentration red ( by definition a ruby ​​) to pink ), Ti3 ( pink) and / or V4 ( violet, together orange with chromium and iron). In contrast, the colorless Leukosaphir contains no additives.

The classic gemstone sapphire is intense, but not too dark blue ( "Kashmir sapphires "). Sapphires that are found in the canyon Yogo Gulch in Montana, are predominantly deep blue. As a special feature under the gem sapphires applies the derived mainly from Asia known as Padparadscha, a pink to orange-colored variant whose name is attributed to the Sinhalese word for lotus blossom. Padparadschas are originally from Sri Lanka, but are now often color- treated and then can come from around the world.

Also popular are the excellent with the optical effect asterism star sapphires. Because of oriented rutile needles embedded itself shows a more or less perfect, sechsstrahlig - star-shaped reflection.

Education and Locations

The formation conditions, see # corundum formation and discovery sites.

The most important producers of sapphires were, until recently, Sri Lanka and India, today the gemstones come from the U.S., particularly Montana, where found, among others, in Yogo Gulch sapphires, Australia and Nigeria. Sapphires from Madagascar, specifically Ilakaka, are considered very high quality, however Sri Lanka declared to arise usually as, since they achieve higher prices. The promotion in Australia has fallen sharply in recent years.

Synthetic production and chemical-technical treatment

Synthetic sapphires can be produced from 1910 in perfect quality and in virtually unlimited size. Colorless, synthetic sapphires are thereby partially under the misleading trade name " Diamandit " and brought " Diamondit " in circulation and serve as a diamond imitation.

The sapphires offered as "natural " in the trade are mostly heat-treated, wherein the heat treatment is carried out both for the color change as well as to increase the clarity of a sapphire. In mild heat treatment Microscopic structures such as rutile needles ( " Silk" ) are retained; if strongly heated (approx. 1800 ° C) are resolved, these natural micro-inclusions and the sapphire clear. If the sapphire cooled very slowly, the micro-inclusions can form again. In this way it can be made ​​of a Ti-rich, synthetic sapphire a star sapphire (or ruby ). Superficial cracks or small bumps are often dubbed by melting borax and lead crystal glass or oil treatment.

Especially blue sapphires can also be achieved by a diffusion process, where the blue layer is very thin and superficial. Since about 2000 sapphires are often heated with Berylliumpulver at 1800 ° C in order to suppress blue tones. This creates intense yellow to orange sapphires. Also known providers use sapphires treated, partially including the disputed diffusion treatment, but no single declaration ( for example, Tiffany & Co.).

Synthetic colorless sapphires

Sapphire ( Sapphire synonymous flow ) denotes flat, usually colorless plates of synthetic corundum. They are used among other things in watchmaking as watch crystals. The term is misleading, since sapphire glass is not glass. Sapphire has a crystalline and no glassy ( amorphous ) structure. Sapphire is having a Mohs hardness of 9, the second hardest of all transparent materials after diamond and in this application is therefore particularly appreciated for its scratch resistance. Sapphire crystal is a highly purified, synthetic sapphire ( single crystal ), which is made ​​of fused alumina. The chemical formula is Al2O3, the sapphire crystal is one of the corundum.

Sapphire crystal is slightly less sensitive to impact than ordinary quartz glass or mineral glass and has a very high light transmission and refraction of light. Nevertheless, sapphire glass breaks under heavy pressure from sharp objects. The common opinion that sapphire crystals are absolutely unscratchable is exaggerated: If other very hard materials ( eg granite ) and high pressure (eg, shock ) act on the sapphire crystal, fine scratches can also arise here, but what very rare. More often, one can observe the falsely called " scratches " Aufriebe of aluminum that can arise when pushed on aluminum surfaces. This Aufriebe represent a durable material compound can be easily removed with a pencil eraser, however.

Physical properties of synthetic sapphire crystal:

• Hexagonal crystal structure
• Density: about 4 g / cm ³
• Melting point 2050 ° C
• Thermal conductivity at 25 ° C: 42 W / (m · K)
• Compressive strength at 24 ° C: 2 GPa
• Tensile strength at 24 ° C: 186.4 MPa
• 100 % acid resistance

Using an electronic Diamantprüfgerätes as it takes for the safe provision of natural polished diamonds in the jewelry industry application, one can reliably distinguish sapphire crystal of ordinary glass. This is based on the thermal conductivity testing principle shows a significant level of rash only diamonds and sapphires.

There are various manufacturing processes from the melt (among other, not technically important processes from the Flux (metal salt melt) or hydrothermal ):

• The crucible- Verneuil process (after the invention of the French chemist Auguste Verneuil 1902)
• The EFG method (of English. edge -defined film - fed growth ), actually the Stepanov method for the production of sapphire profiles (plates, tubes, rods, etc.) with constant cross section.
• The Czochralski method, invented by the Polish scientist, Jan Czochralski in 1916
• The neck Kyropoulos method, named after Richard neck and Spyro Kyropoulos ( Physics Institute Göttingen) in 1926.

In the Verneuil process is melted on a small piece of sapphire in a chamber at temperatures above 2050 ° C by oxyhydrogen flame alumina powder, so that it grows up to a crystal bulb 3-4 cm in diameter and 11 to 14 cm in length. This sapphire crystal is cut by diamond saw blades into slices, which are then ground and polished to a transparent sapphire crystal discs created with a gloss finish. The slices obtained, depending on customer specifications nor a polished bevel. Knowledge of the efficient production of high-quality sapphire crystals, and in particular the production of the required machinery and equipment has long been a closely guarded trade secret.

Since sapphire crystal is extremely scratch resistant due to its high hardness, it is often used in high-grade watches, but watches are also already available at 60 euros with sapphire crystals on the market. In a few very high quality watches brands of Swiss manufacture the entire watch case is made of sapphire. Furthermore, there are even mass-produced mechanical watch movements, the entire circuit boards are made ​​of sapphire crystal to give insight into the interior of mechanics. A very small number of producers and processors of synthetic sapphire glass dominate the global market, in particular by its complex processing in particularly complex forms. Producers are located in France, Switzerland, Poland and China / Hong Kong, Mauritius and Japan.

There are typically special coatings such as for anti-reflection to reduce light reflection at high Saphiruhrgläsern. Here, a bluish glow was seen earlier in some manufacturers. Manufactured before 2000, these anti -reflective coatings are usually not sufficiently scratch resistant. More recently, however, these coatings are usually not removable or abrade, the recognition of such a coating is usually added by the effect that the viewer can recognize no more glass. Especially with double-sided anti-reflective sapphire crystals, this feature is very pronounced; the observer believes to have a clock with no glass in front of him.

In high-priced mobile phones from some manufacturers, the cover glass is made of sapphire glass. Normally, the cover glass of the liquid crystal display of special cover glass for displays (eg Gorilla glass). Sapphire glass can also be mounted as scratch-resistant camera lens cover in smartphones.

Use as a gemstone

Sapphires are mainly processed into semi-precious stones. Transparent stones of high quality ( as little as possible inclusions) thereby obtained a bevelled edge, opaque and especially those with asterism other hand, are made ​​into cabochons to highlight the star effect.

The largest ever polished sapphire is the " Star of India" with a weight of 563.35 carats ( 112.67 grams). The Sri Lanka found, about two billion years old stone 1901 is by John Pierpont Morgan at the American Museum of Natural History and can be visited there.

Other Uses

Besides its use as a gemstone sapphire was used in record players in the 1950s and 1960s as the material for the pickup stylus and led to the colloquial name for this sapphire needle.

Because of its high hardness and abrasion resistance sapphire is also as a guide among others used for wire EDM and textile machinery. Compared to the more solid diamond he has, despite shorter life spans, significant cost advantages.

Synthetic single crystal sapphire wafers are the most important substrate material for the artificial growth ( heteroepitaxy ) of single-crystal gallium nitride, the material for blue, white and green LEDs and blue laser diodes.

Titanium as the active laser ion doped, synthetic sapphire is used as the host crystal for the titanium: sapphire lasers - a operating in the wavelength range of 700 to about 1000 nanometers laser.

For extreme loads exposed window of reconnaissance aircraft, anti-aircraft missiles or space missiles synthetic sapphires of up to 75 centimeters in diameter are used.

In special cases, sapphire is also used in scientific instruments for space use, for example in the Genesis mission.

Due to its compared to other insulating materials, high thermal conductivity of 40 W / (m • K ) at a temperature of 25 ° C are accessed in scientific experiments to disks made ​​from this material, when, for example, an effective cooling and accurate temperature control by means of a for the purpose must be made of the transparent medium through observation. As the temperature increases, the thermal conductivity decreases, however, and is at 400 ° C for a further 12 W / ( m • K), and at 1200 ° C, only 4 W / ( m • K). A reduction in temperature, however, provides for a large increase in thermal conductivity at a temperature of -200 ° C and a value of 10,000 W / ( m • K ) is reached, whereby the sapphire is very suitable for low temperature experiments.

In high-quality wristwatches protection glasses are used in synthetic sapphire. They are called sapphire.

In the so-called silicon-on- Sapphire technology integrated circuits are produced by heteroepitaxially produced upon sapphire silicon layers.

Esoteric

The sky-blue variant is usually associated with features such as peace, purity and peace. Scientific evidence for the alleged physical and mental effects do not exist.