What Are The Major Characteristics Of Sapphire?

[owl]

One important characteristic is that it is denser than most gravel. When we pan for them typically we take sapphire bearing gravel, and shake it in a screen under water, then flip the whole works over, that puts the sapphires on top of the gravel so that they can be picked out.

 

[Ulma Doctor]

my last employer gave us a Rolex. Have to say they're tough, the synthetic sapphire crystal seams impact proof, (I haven't cracked it), totally scratch proof and weld spatter doesn't stick. the Rolex lasted for years. Mind weld spatter sticks and craters the gold plating and stainless. Greg

 

[4GSR]

They make a woman happy...

 

[JPMacG]

Sapphire is alumina, Al2O3, with a particular crystal structure. Pure sapphire is clear like glass. The blue color in naturally occurring sapphire is from impurities. Grown (man made) sapphire has many industrial applications and can be ground to high accuracy. It is a very good electrical insulator but has a relatively high thermal conductivity. It has very low dielectric loss, which makes it attractive for use in microwave circuits. It has a weird property of having a dielectric constant that varies with direction = "anisotropic".

This website has some good information: http://www.insaco.com/

 

[Mike2Machine]

Shock propagation properties (my wife's research work) also anisotropic.

 

[RJSakowski]

Twenty years ago, I was working on a product improvement project of a product called a mammography accreditation phantom (e.g. https://www.supertechx-ray.com/BreastImagingandMammography/QCC/Gammex-156.php ). The phantom was required by federal law to be used qualify every mammography facility in the country. It consisted of a patterns of test objects which represented the types of cancerous objects that might be encountered in a breast exam. To qualify, a facility had to x-ray image the phantom and be able to see all of the test objects each day before taking patients.

One group of test objects consisted of star patterns of aluminum oxide particles in decreasing sizes, the smallest of which had and average diameter of .16mm or .006". The problem was, that we were sieving corundum grit to obtain the particles but the particles had widely varying shapes with some shapes appearing brighter. My intent was to use a sapphire ball instead of the corundum grit. The material would be the same chemical composition but the size and shape would be more uniform.

I ordered samples of appropriately sized sapphire balls from a supplier. When they came in, I thought that the plastic bag for the smallest balls was empty but on closer inspection, the were a couple of dozen balls at the bottom crease of of the bag.

The construction of the phantom consists of laying the test objects in a thin sheet of dental wax and pouring a top layer of wax to fix them in place. The test objects were placed using an alignment fixture, positioned in place with a "twee" (one jalf of a tweezers). The assembler, who had made literally thousands of these phantoms, expressed his extreme frustration with the sapphire balls. Unlike the corundum particles which stayed in place when positioned, the round balls would roll around. Furthermore, at .006" diameter, the smallest balls were nearly invisible and if one escaped, you could forget about ever finding it again.

As it turned out, the balls imaged extremely consistently but the images were easier to see because of the uniform shape. The solution would have been to change the standard to use a smaller ball but this was far easier said than done. Although our company had developed the original phantom, the accreditation program was governed by federal legislation and administered by the American College of Radiology and any changes to the phantom would need to be approved by unanimous agreement. Unfortunately, I left the company before all this happened and to the best of my knowledge, the product revision never occurred.

One thing about the sapphire balls of interest was they appeared to be perfect spheres, even under a microscope. It seems incredible that the manufacturing process was able to achieve that level of form and finish on an object .006" in diameter and as hard as sapphire.

 

[cjtoombs]

Makes a great crystal for a wrist watch. For 20 years of my life, my last employer gave us a Rolex. Have to say they're tough, the synthetic sapphire crystal seams impact proof, (I haven't cracked it), totally scratch proof and weld spatter doesn't stick. A normal watch would last maybe 6 months, after that the face was obscured with scratches and weld spatter, the Rolex lasted for years. Mind weld spatter sticks and craters the gold plating and stainless. Haven't wore a watch in years so now it sits in a drawer collecting dust.

Greg

Lol, I doubt the folks that built the watch ever imagined that it would need to fend off weld spatter. Maybe they will read this and make a welders version.