Introdction

Transparent ceramic spinel (Transparent Magnesium Aluminate spinel, MgAl₂O₄ transparent spinel,  MA polycrystalline spinel) is an attractive material for uses in a wide range of optical, electronic and structural applications including windows and lenses, which require excellent transmission from the visible through to the mid IR. Theoretical transmission is very uniform and approaches 87% between 0.3 to 5 microns. Transmission characteristics rival that of ALON and sapphire in the mid-wave IR, making it especially attractive for the ever-increasing performance requirements of current and next-generation IR imaging systems.

Physical properties

Spinel Structure

The spinel structure has the form of AB^₂O₄, where A is a metal ion with a +2 valence and B is a metal ion with a +3 valence. This structure is viewed as a combination of the rock salt and zinc-blend structures (see figure VI-1). The oxygen ions are in face-centered cubic close packing. A and B ions occupy tetrahedral and octahedral interstitial sites. Spinel structure can be divided into two types: normal and inverse spinel. In normal spinels, A²⁺ ions are on tetrahedral sites and the B³⁺ ions are on octahedral sites. In inverse spinels, the A2+ ions and half the B³⁺ ions are on octahedral sites; the other half of the B³⁺ are on tetrahedral sties, B(AB)O₄.

Figure. Spinel structure.

Application fields:

pressure vessel sight glass, furnace sight glass, boiler water gauge.
Domes, optical window, lens, prism.
LED, ceramic substrate material for electronic packaging.
A valve flap, valve seat, a water-jet cutting flow-shaper, a nozzle for process fluids.
High-pressure arc lamp and lens, safety goggles.

size of product: 

Tile and camber less than Ф280×20mm(dia.× thk.)； 
Dome less than Ф255×8 mm(dia.× thk.)； 
Other spec. upon request.

We are the unique producer to supply the transparent ceramic spinel in China. It has the best ratio of performance to price.

Transmittance of transparent ceramic spinel

Samples

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THE MINERAL SPINEL

• Chemistry: MgAl₂O₄ , Magnesium Aluminum Oxide
• Class: Oxides
• Group: Spinel
• Uses: as a gemstone and as a mineral specimen
• The physical properties of spinel.

Spinel is a very attractive and historically important gemstone mineral. Its typical red color, although pinker, rivals the color of ruby. In fact, many rubies, of notable fame belonging to crown jewel collections, were found to actually be spinels. Perhaps the greatest mistake is the Black Prince's Ruby set in the British Imperial State Crown. Whether these mistakes were accidents or clever substitutions of precious rubies for the less valuable spinels by risk taking jewelers, history is unclear. The misidentification is meaningless in terms of the value of these gems for even spinel carries a considerable amount of worth and these stones are priceless based on their history, let alone their carat weight and pedigree.

Today, expensive rubies are still substituted for by spinel in much the same way a diamond is substituted by cubic zirconia. Not to commit a fraud or theft but to prevent one. Spinel may take the place of a ruby that would have been displayed in public by an owner who is insecure about the rubies safety. The spinel probably is still valuable but better to lose a $100,000 dollar spinel than a $1 million dollar ruby!

Spinel and ruby are chemically similar. Spinel is magnesium aluminum oxide and ruby is aluminum oxide. This is probably why the two are similar in a few properties. Not suprisingly, the red coloring agent in both gems is the same element, chromium. Spinel and Ruby also have similar luster (refractive index), density and hardness. Although ruby is considerably harder (9) than spinel, spinel's hardness (7.5 - 8) still makes it one of the hardest minerals in nature.

Spinel may be the poorer cousin of ruby, but its pinker color and other qualities make it attractive in its own right. Spinel typically forms in well formed octahedrons. But it is famous for a type of twinning that bears its name, the Spinel Twin Law. Spinel Law twinning is also found in other isometric minerals such as diamond, galena, cristobalite , magnetite , franklinite and other members of the Spinel group. This type of twinning produces a twin plane that is parallel to one of the octahedral faces. The plane acts as a mirror plane and produces a left and right side that are mirror images of each other. This may not sound all that spectacular for a very symmetrical mineral like spinel which is loaded with mirror planes. However this mirror plane is not parallel to any of the others and actually lowers the symmetry of the crystal (only in appearances though).

A good description of the twin is hard to explain, but here it goes. The plane falls (of course) in the center of the crystal, dividing it in half. The two octahedron faces parallel to the twin plane are equilateral triangles. Each point of the triangles is doubled across the twin plane with an indentation between them. The crystal looks like it has trigonal symmetry, but the three indentations are a clue that this crystal is a twin. Twins of spinel are rare, but their popularity makes them readily available on the market.

PHYSICAL CHARACTERISTICS:

• Color is red, green, blue, purple, brown, and black; but red is by far the more common color.
• Luster is vitreous.
• Transparency: Crystals are transparent to translucent and sometimes nearly opaque.
• Crystal System: Isometric; 4/m bar 3 2/m
• Crystal Habits include the typical octahedron, but can be found as dodecahedrons and combinations of other isometric forms. Also as rounded grains in alluvial placer deposits.
• Cleavage: None
• Fracture is conchoidal.
• Hardness is 7.5-8.0
• Specific Gravity is 3.6-4.0
• Streak is white.
• Other Characteristics: index of refraction is approximately 1.71 - 1.76 and rutile    inclusions may produce six or four rayed stars or asterisms.
• Associated Minerals include Calcite, dolomite, corundum and garnets .
• Notable Occurrences include Burma, Sri Lanka, Brazil and Afghanistan.
• Best Field Indicators are twinned crystals if present, color, hardness, density and locality.

Spinel: collector's favourite

Spinel is the great impostor of gemstone history: many famous rubies in crown jewels around the world are actually spinels. The most famous is the Black Prince's ruby, a magnificent 170-carat red spinel that now adorns the Imperial State Crown of England in the British Crown Jewels after a long history: Henry V even wore it on his battle helmet! The Timur ruby, a 361-carat red spinel now owned by Queen Elizabeth, has the names of some of the Mughal emperors who previously owned it engraved on its face: an undeniable pedigree!

In Burma (now known as Myanmar), where some of the most beautiful colours are mined, spinel was recognised as a separate gem species as early as 1587. In other countries the masquerade went on for hundreds of years. Spinels were most often referred to as 'balas rubies', which may have referred to their colour or their country of origin.

Now treasured for its own sake, spinel is a favourite of gem dealers and collectors on account of its brilliance, hardness and wide range of spectacular colours. In addition to beautiful rich reds, spinel can be found in a range of gorgeous pastel shades of pink and purple. Of particular interest is a vivid hot pink with a tinge of orange mined in Burma. It is one of the most spectacular gemstone colours seen in any species at all. Spinel also comes in beautiful blue tones called cobalt spinel, but these are very, very rare.

Because spinels made in a laboratory are often used for imitation birthstone rings, many people think 'synthetic' when they hear the name spinel. Often enough, they have never even seen the real thing.

In fact, the main factor preventing the spinel from achieving greater recognition is its rarity. Fine spinels are now rarer than the rubies they used to imitate. Strangely, they are also more affordable: in the gem world, being too rare can be a drawback because so few people even get a chance to develop a fondness for the varieties in question.

In addition to Burma, spinel is mined in Sri Lanka, Tanzania, and Tadzhikistan, part of the former Soviet Union.

Spinel is a durable gemstone that is perfect for all jewellery uses. It is most often faceted in oval, round, or cushion shapes and is not currently found in calibrated sizes due to its rarity.