diamonds are a knifes best friend

[Inky]

I was noodling around with my kitchen knife sharpener and started wondering about how they fasten the industrial diamonds to the steel shank. Some sort of fancy molecular bonding process ala Star Trek? Elmers diamond glue?
While were at it what makes a diamond "Industrial"? Are they scraps and dust from jewelry making or something cooked up in a lab?

Gaudere: thanks for the corrective information. But -- why the hell would Russia be continuing research into gem-quality artifical diamonds? I saw a '60 Minutes' piece that showed a entire hallway of rooms the size of a large walk-in closet, lined with shelves which themselves were lined with dufflebag after dufflebag of gem diamonds that had already been mined -- I believe the number mentioned was something like 5 billion carats! In fact, that was one of the points the report made -- that diamonds really aren't all that rare in nature, it's the fact that only South Africa and Russia are the main source of them, and that they strictly control the market, that makes a diamond so 'valuable'.

[DW3]

A perforated steel plate is molded onto an engineered plastic base. Precision size micron diamonds are embedded in an electro-plated nickel matrix on the perforated steel plate.

Taken from DMT's (http://www.dmtsharp.com) website.

[Gaudere]

The market is indeed primarily controlled by DeBeers, but Russia has been sneaking some diamonds out on the side. Russia is probably holding on to the diamonds to prevent a price dump (making their store less valuable), and to avoid the ire of DeBeers if Russia single-handedly drops the price of diamonds. Diamonds are still hardly common, and it takes one ton of diamond-bearing ore to get a decent 1-carat.

An artificial gem-quality diamond would still be valuable; we have synthetic rubies, sapphires, emeralds, and alexandrites currently used in jewlery. For that matter, I hear most of the amethyst used in jewlery is probably synthetic (and from Russia). Not to mention that a clear, flawless diamond would likely be more useful in industries than a flawed yellow one.

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"Eppur, si muove!" - Galileo Galilei

[Gaudere]

Just to be clear--I had to run off to a meeting so didn't get to finish my thoughts--I have never seen synthetic stones sold as genuine. Not even at the sleaziest, cruddiest jewlery store I have been in. I jeweler must provide full disclosure if the stone is man-made or mined.

I suspect synthetic diamonds will have limited appeal in the jewelery department; most people have signicant meaning attached to their purchases and would rarely get a synthetic.

The bit about amethysts is mostly a rumor; it may be true that many are synthetic. Not many jewelers will spend $20 or whatever each for the tests required to determine if a amethyst is mined or not, when you're buying 100 of them for a dollar per. If the amethyst was unsually large or good quality (hence expensive) it would be checked out.

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"Eppur, si muove!" - Galileo Galilei

[Nickrz]

Polycrystalline diamonds have been successfully manufactured for over 20 years. Dupont hold at least one patent for a method of producing them under the controlled detonation of high explosives.

General Electric developed the first polycrystalline diamond compact (PCD in a tungsten-carbide binder) in the early 80's, and this technology is now the tool of choice for cutting highly abrasive materials such as glass, plastic, fiberglass, and graphite composites used in aircraft and other types of high-stress vehicles. Innovations in PCD tool bits for the oil drilling industry allowed saving up to 1 million bucks a hole compared to conventional drill bits.

Diamond is the hardest material known to man, has thermal conductivity four times that of copper, and a coefficient of friction less than that of Teflon. It has extremely low chemical reactivity, is transparent over a wide range of the electromagnetic spectrum, and is a higher performance semiconductor substrate than either silicon or gallium arsenide.

So yes, man does synthesize diamonds - but they're not the kind you'd put in a wedding ring.

[torq]

Industrial diamonds are diamonds that are not jewelry quality for whatever reason... generally because of color or inclusions. The first "manmade" diamonds were industrial quality; I don't know if they've improved the process to the point where they can make gem-quality stones reliably now or not.

[Keeves]

Many people misunderstand what makes diamonds special. For example, people are surprised to realize that diamonds are somewhat brittle. Touch a diamond in the right way, and it will simply split in two. I realize I'm exaggerating, but I do believe that this is the basic idea behind diamond cutting.

A diamond's strength lies in its ability to scratch other things, and its ability to resist being scratch by other things. Thus, when those diamonds rub against the knife, the edge of the knife will be scratched, worn away, thinner, and sharper, while the diamonds will just sit there, unscathed. The glue thatr holds the diamonds to the sharpener does not have to be "as strong as diamonds", only strong enough to prevent entire diamonds from getting knocked off of the sharpener.

I'll step aside now, in case someone who knows more than me wants to say something.

[pluto]

<-- Not an expert!

Don't know about fastening methods, but I believe industrial diamonds are just about any non-gem-quality diamonds, which would presumably be the majority of them. Either they are too small or they are flawed, etc. My guess is that would include dust and chips from gem-quality diamond processing.

IIRC, artificial diamonds (with the exception of those made by Superman, which come already faceted) are industrial quality.



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"non sunt multiplicanda entia praeter necessitatem"
-- William of Ockham

[pluto]

Well, I was a close second!


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"non sunt multiplicanda entia praeter necessitatem"
-- William of Ockham

[Glitch]

Supermans can no longer manufacture diamonds. It would take me awhile to find the specific issue, but in one of the recent Christmas issues Superman/Kent remarks to Lois that he gets a lot of letters asking him to make diamonds and split the profits with the person who sent the letter. Lois asks if he could do that. Superman says no, he tried.

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It's bernard, just under new management

Also not an expert, but I believe the process for fastening (really imbedding) diamond dust in the surface of the sharpener wheel is called 'sintering' and involves directing a stream of the dust at extremely high pressure (sometimes even using explosives) to clad the diamond granules in place.

And, not to pick nits, but the strength of a diamond lies in its crystalline structure, which I believe (IIRC) may be pentagonal or hexagonal, as opposed to the layered, box-like structure of graphite.

On a related topic -- I read recently where a method of applying a diamond coating only a few thousandths of an inch thick has been developed for use in internal combustion engines. Some day in the foreseeable future we may (or our kids) drive cars with engines that almost never wear out.

[Gaudere]

A diamond's crystalline structure is octahedral (like an 8-sided die). Last I heard, Russia was still making a stab at gem-quality synthetic diamonds, but haven't gotten anything besides yellow industrial diamonds.

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"Eppur, si muove!" - Galileo Galilei

[Moonshine]

I know that diamonds are harded than anything else and very useful for scratching your name on the window of a bus or something; however I understand that they can scratch each other, in which case why are they transported all together in those little velvet bags or paper envelopes, oughtn't they be carried seperately?

[Omniscient]

Guady, are you sure about that octahedral part? I was fairly certain that they were tetrahedral in shape, with 120 degree bond angles.

Second, how could you differentiate a man made diamond from a mined one? A gem quality diamond is very pure. What differentiates a man made one? They both have an identical crystaline structure. I though we were on the faith of the jeweler.

[Rodd Hill]

Nickrz said:

Diamond is the hardest material known to man, has thermal conductivity four times that of copper, and a coefficient of friction less than that of Teflon. It has extremely low chemical reactivity, is transparent over a wide range of the electromagnetic spectrum, and is a higher performance semiconductor substrate than either silicon or gallium arsenide.

...and they stay crunchy, even in milk!

[Gaudere]

Pic of octahedral diamond crystal:
http://www.ags.org/info/lovetour/tour2.html


How they're made (at least one way; I think we can do them at temps as low as 1200 degrees now):
"A mixture of graphite and a catalyst (typically nickel) is subjected to
a pressure of approximately 1,000,000 pounds per square inch and a temperature of 1,800 °C for a period of approximately 1 hour. During this time diamond crystals nucleate at many sites in the mixture. The mixture is then cooled, then the pressure reduced to atmosphere. The diamond crystals are then separated from the remaining graphite and nickel using an acid wash."

for more info:
http://www.idrmag.com/history/l50t.htm

It seems I was inaccurate about gem-quality synthetics; they have been made, it's just not economically feasible. As to telling the difference between synthetic and mined diamonds, although synthetics are made under very similar conditions as in the earth, they're not exactly the same conditions. For example, a synthetic won't be found with an inclusion of a garnet crystal as you sometimes see in mined stones. The diamonds are chemically the same, but the uniformity of heat and pressure used to create in synthetics will produce different spectrophotometer results. I don't know exactly why the results are different, but I am not a gemologist. Here is a chart of synthetics compared to a natural stone (a light fancy yellow).

http://www.gis.net/~adamas/debeers.html

BTW, I have seen cubic zirconia referred to as a "synthetic diamond". It is not. It is a simulated diamond.

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"Eppur, si muove!" - Galileo Galilei

[Gaudere]

I understand that they can scratch each other, in which case why are they transported all together in those little velvet bags or paper envelopes, oughtn't they be carried seperately?

They *are* very hard, and thus if they just bump into each other they won't scratch each other. They're usually wrapped up diamond papers separately, too; the velvet bag is no longer the carrier of choice for jewelers. :)

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"Eppur, si muove!" - Galileo Galilei

[torq]

Cubic/tetrahedral/octahedral: you're talking about different things.

Each individual carbon atom within a diamond does have a tetrahedral geometry. This packs nicely into a cubic unit cell (or, for that matter, into a hexagonal one). The diamond crystal itself is usually octahedral.

So, everybody's right.

[Omniscient]

Just to nit pick a bit, the diamond molecules, made up of 4 carbon atoms, have a tetrahedral arrangement. A carbon atom can't have a shape. The differences between a crystaline structure, and an atom arrangement are a little beyond me.

[Gaudere]

You're right, I misunderstood. Thought you were talking about the shape diamonds naturally formed into. D'oh!

[pluto]

I believe they can now also make diamonds in a process similar to computer chip manufacture where they lay down the carbon atoms one atomic layer at a time. Again, it's probably not economically competitive with mining. It may be the source, however, of the earlier comment about diamond-lined cylinders in IC engines.


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"non sunt multiplicanda entia praeter necessitatem"
-- William of Ockham

[jayron 32]

Some people have mentioned some stuff about DeBeers, diamonds, and the like. Here's some interesting facts about Girls Best Friend (ever wonder why man's best friend is a dog, and a girls is a diamond? I think we got gyped fellas).

1) Diamonds are the most abundant gem quality stone on the planet. Even if you eliminate all of the industrial grade diamonds, there are more gem quality diamonds mined than any other common stone.

2) Diamonds are, expensive as they are, somewhat less expensive than rubies. A pure, flawless, blood-red ruby will be about half again as expensive as the comparable quality diamond.

3) Already mentioned, but a diamonds strength comes from its resistance to crystal deformation. Cleaving between crystals is relatively easy (which is how diamonds get "cut") but the crystals themselves are amazingly resiliant. A sharp diamond will rarely "dull" since it will easily cut through other stuff without deforming

4) Diamonds burn, and without too much trouble either. A standard housefire will turn most diamonds into so much soot and CO2.

5) Something like 90% of all gem quality diamonds mined come from South Africa. DeBeers is a South African company, a syndicate that buys up ALL of the diamonds in South Africa as well as about 90% of what's left. Thus, only about 1% of gem quality diamonds do not, at one point, go through DeBeer's vaults. Since they have a monopoly on world diamond distribution, they get to set the price. It has been estimated that on an open market, if supply and demand were left to themselves, diamonds could wholesale for less than a quarter of what they do now.

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Jason R Remy

"What we've got here is a failure to communicate"
Warden in _Cool Hand Luke_

[Gaudere]

2) Diamonds are, expensive as they are, somewhat less expensive than rubies. A pure, flawless, blood-red ruby will be about half again as expensive as the comparable quality diamond.

And a top-quality emerald is more expensive still. A true red diamond is, I believe, the rarest and most expensive stone; but when you start getting into weird stones like that it's hard to give comparative prices.

A ruby and sapphire are both the same sort of stone, BTW; the only difference is color. If it's pink, blue, green, yellow, white--it's a sapphire. If it's red, it's a ruby (the term for the best color in a ruby is "pigeon's-blood red").


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"Eppur, si muove!" - Galileo Galilei

[torq]

the diamond molecules, made up of 4 carbon atoms

A perfect diamond is a single covalently bonded molecule, no matter how large it is. Even in real (i.e. imperfect) diamonds, you'd get single perfect crystals much larger than four atoms.

The atoms have a tetrahedral geometry, meaning that (again, in a perfect crystal) each atom's nearest neighbors are at the vertices of a tetrahedron.

I believe they can now also make diamonds in a process similar to computer chip manufacture where they lay down the carbon atoms one atomic layer at a time.

Vapor deposition of diamond films has been around for a while (I recall reading about it ten years ago, and it didn't seem to be considered a particularly new and exotic technique even then). It would take forever to build up a noticeable crystal one layer at a time, so I don't think this is practical for gems, but it might be possible to use it to put a very tough surface layer on an object.