Uncovering the Truth: The Differences Between Man-Made and Natural Diamonds

[Will]

Is it true that gem quality man made diamonds are possible? How can they tell the difference between an industrial grade and gem quality and how do they grade them? I think the clearer the better and that the defects have to do with elements/compounds other than carbon. Any more info would be cool.
Does diamond have the highest index of light refraction? Thats what gives it its bling-bling right, the fact that the light just keeps bouncing around in there? And what is cubic zirconium, like is it also made of carbon but a different crystal structure, and how does its light refracting ability and clarity compare to the real thing?

 

[Astronuc]

Here is some information on man-made (artificial) diamonds, rutile, and zirconia.

Rutile is one of the few crystals that has a higher index of refraction (n = 2.605 - 2.901) than diamond (n = 2.418) - http://mineral.galleries.com/minerals/property/

Rutile is TiO2 crystalline - http://mineral.galleries.com/minerals/oxides/rutile/rutile.htm
for crystal structure of TiO2 - http://www.webelements.com/webelements/compounds/text/Ti/O2Ti1-13463677.html

Zirconia (ZrO2) is similar - http://www.azom.com/details.asp?ArticleID=133 - "In order to manufacture zirconia components, it is necessary to 'lock' the material wholly or partially into the cubic form by the use of additives or stabilising agents".
But, index of refraction of Cubic Zirconia = 2.21, slighly less than diamond, but relatively close.

Also see - Diamonds vs. cubic zirconia

This site (http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l1d.html#index ) mentions GaP as having the highest optical density or n=3.5

For discussion of diamonds and their design, see - http://www.folds.net/diamond_design/

Here is an article on 'artifical' gem quality diamonds - http://www.wired.com/wired/archive/11.09/diamond.html - which is a relatively recent development.


Most artificial or industrial diamonds have many other uses than gems.

See - http://minerals.usgs.gov/minerals/pubs/commodity/diamond/

 

[russ_watters]

Most artificial or industrial diamonds have many other uses than gems.

See - http://minerals.usgs.gov/minerals/pubs/commodity/diamond/

I think he meant real diamonds - as in carbon. Zirconia aren't, "industrial diamonds" are. AFAIK, "industrial diamonds" cannot be made to "gem quality."

 

[Astronuc]

In the article on 'artifical' gem-quality diamonds - http://www.wired.com/wired/archive/11.09/diamond.html - the synthetic diamonds of gem-quality are made of carbon.

In the article there are two comments:

"These are cubic zirconium?" Weingarten says without much hope.

"No, they're real," I tell him. "But they were made by a machine in Florida for less than a hundred dollars."

then later on

Gemesis, the Florida-based company, and Apollo Diamond, in Boston, . . . . Both startups plan to use the diamond jewelry business to finance their attempt to reshape the semiconducting world.

But first things first. . . . , they'll have to prove they can produce large volumes of cheap diamonds.

Gemesis has made gem-quality artificial diamonds from carbon. However, the example cited is yellow diamonds. I don't know if they can make white diamonds.

 

[omagdon7]

They can make clear diamonds but colored diamonds sell for more. The technology was developed at the University of Florida by a professor in the MSE department who's name I don't recall.

 

[russ_watters]

In the article on 'artifical' gem-quality diamonds - http://www.wired.com/wired/archive/11.09/diamond.html - the synthetic diamonds of gem-quality are made of carbon.

I'm not a big fan of Wired because their stories have a tabloid pseudo-science feel. This article is a great example. While it says the dealer can't tell with his naked eye, it also says "sophisticated machines designed to help distinguish man-made from mined stones" can. What the actual quality of these diamonds is, the article doesn't say - but rest assured, if a machine can tell the difference, your wife will find out. And no amount of explanation will convince her that a $100 diamond is as good as a $1000 diamond.

Now for the industrial sector, this is a big deal...

 

[Astronuc]

Russ, I agree with you. I don't vouch for Wired or Gemesis.

I am not in the diamond business, and personally, I think crystalline chunks of carbon are over-rated, and way over-priced.

As for the industrial sector, yes, this is a big deal, and its great if Gemesis can reduce the cost and increase quality and quantity for industrial diamond. That is area I would be concerned about.

 

[omagdon7]

Well the fact that the diamonds are produced cheaply in no way suggests they are of low quality. The quality of a diamond gemstones is measured in clarity, carats, cut, and color. Artificially produced diamonds are no different than natural mined gems. And the fact that they are cheaper to produce (they are still sold at the price of natural diamonds) is not a result of anything inherent but a result of the diamond monopoly which artifically holds the price of gems up.

 

[Will]

While it says the dealer can't tell with his naked eye, it also says "sophisticated machines designed to help distinguish man-made from mined stones" can. What the actual quality of these diamonds is, the article doesn't say...

I don't know where I heard this from (I think it was a physics teacher), but I was told that the reason that a machine can tell the difference is that the man-made ones are "too perfect"

 

[Gokul43201]

I am not in the diamond business, and personally, I think crystalline chunks of carbon are over-rated, and way over-priced.

Touche'

But the market disagrees. :grumpy:

 

[thecolor11]

The market doesn't have much choice with the DeBeers cartel holding ~90% of the diamond market.

There was a story on one of the network news mags(I think it was 60 Minutes) on these manufactured diamonds. One of the techniques uses nitrogen to accelerate the crystal growth and results in yellow diamonds. There was another technology producing clear diamonds. From what I gathered (this was a while back) diamond fragments were used to start the crystal, and the surrounding carbon simply filled in the crystal lattice.

DeBeers claims they have a machine that can detect the manufactured diamonds using x-rays. Not really sure how that would work. Because they can't run every diamond through these machines, they are starting to laser engrave the DeBeers logo on their diamonds.

 

[Dayle Record]

I can vouch for PBS and the Nova I saw on these diamonds. And with a gaseous process they can make very nice, sparkly white, and blue diamonds. They had a bit of florescence at first, now that is gone, I think. De Beers was protecting its monopoly by desperately searching for a way to detect the manufactured from the natural, and was coming up with the PR that has to do with natural, eternal, real, etc to keep their market share. From what I saw, the manufactured were truly flawless, and very, very bright, having to do with their affinity for high color spectrum hues. Anyhow, I would take a double sized manufactured diamond, for the same money, oh yes.

 

[Ivan Seeking]

man made diamonds

...LifeGem - the first UK firm to offer to turn cremated human remains into diamonds - say it all comes down to personal choice. ...

http://news.bbc.co.uk/2/hi/uk_news/england/berkshire/3389493.stm

Maybe this wasn't what you meant?

 

[itsmydamnation]

i know the russians back in the 80 where able to make gem quality white diamons. quite interesting why they made them, they wanted to use diamond windows for the guidance systems for the ICBM's , a icbm get launched into space get above it target and releases 10 or so warheads. now what was limiting the weight of the warhead that could be droped was that there"eye" in the war head couldn't with stand the temps so if they made the window of diamond they could have bigger and faster falling nukes. whcih would do more dmg and be harder to hit

 

[omagdon7]

I am not aware if the Russians were actually able to make the diamonds. The professor at UF who developed the diamond making technology and helped found Gemesis said that he got the prototypes for the machines he uses from the Russians and that they never were able to make them work.

 

[Locrian]

This is what I currently do for a living.

I am currently working in microwave enhanced chemical vapor deposited diamond. The company I work for is working with a local university, looking to make the research in thin diamond films they have done profitable. We deal mostly in nitrogen doped nanocrystaline films, though it is easy enough to create microcrystalene films (nitrogen off!) and we have made boron doped films at least once by acident. We could probably make single crystal diamond (the university certainly has), but since that is not in the business plan, I'm not going to be trying anytime soon.

The above posts provide a lot of background information. Needless to say, since starting with Vista, I've learned a lot of particulars. More than I would want to try and type out.

If you want particulars, fire away.

Edited per poster request

 

[hitssquad]

Perhaps a diamond beam window for the Rubbia reactor

they wanted to use diamond windows for the guidance systems for the ICBM's ... there"eye" in the war head couldn't with stand the temps so if they made the window of diamond

That is interesting since one of the problems with Carlo Rubbia's accelerator-driven reactor is the current lack of a usable window material/design for the proton-beam to shine through into the molten-lead reactor coolant (the pressures/temps are a problem for typical beam windows in this environment). Perhaps a material such a diamond might help (in addition to possibly making the window a honeycomb lattice shape, as Richard Garwin has suggested).

 

[Locrian]

This article is a great example. While it says the dealer can't tell with his naked eye, it also says "sophisticated machines designed to help distinguish man-made from mined stones" can. What the actual quality of these diamonds is, the article doesn't say - but rest assured, if a machine can tell the difference, your wife will find out. And no amount of explanation will convince her that a $100 diamond is as good as a $1000 diamond.

Now for the industrial sector, this is a big deal...

Couple of quick comments about this. From what I understand, whan Apollo diamond first produced their diamonds, they were not distinguishible from natural ones except for extremely expensive spectrometers that the vast, vast majority of jewelers would not have. However, I also understand that there are extremely subtle visual clues that some jewlers might catch. Also, Apollo has worked out deals with GIA to help identify their diamonds. Still, Apollo could very well lead this curve if they so chose and beat these new methods, just as SiC gems (moissanite) learned to beat the double refraction problem. I think apollo has purposefully (and wisely) given up trying to stay ahead of this game; their diamonds will be clearly labled as cultured.

As for whether explanation will convince your wife, I'm not so sure you are right. I do think it is true you aren't going to get away with buying a $300 engagement ring instead of a $2500 one. However, diamonds really are beautiful. If someone were selling cheap man made diamonds that were indestinguishable to the eye from real ones, then when she saw the beauty of what $2500 would get her using that, I doubt she'd hesitate for a second.

The big problem facint Apollo is that, after all the research, after all the trouble needed to make a good quality diamond... they aren't nearly as cheap as you'd think. When I tell people I work in diamond growth, their eyes get big and they immediately begin babbling about gem diamonds. I have to politely tell them that I have no interest in that sector, and for very good reason. So in short I think people will buy man made diamonds if they are cheap... but I'm not so sure they are cheap, at least not yet. Go check out Gemesis HTHP diamonds. Definately not cheap.

In any case, as everyone here has noted, man made diamond will mean a great deal to industry. Diamond has (as I'm sure you are aware)

-Super high thermal conductivity
-Super high hardness
-Super low coefficient of friction (about like teflon)
-Almost no chemical reactivity
-Reasonably high melting point (4000 kelvin i think?)
-Excellent optical transparency (depending on the doping)

Diamonds are naturally excellent insulators, and depening on the doping can be made to be semiconductive or reasonably conductive

Some uses for diamonds and diamond films:

-High energy radiation detectors (diamond detectors are in the process of being deployed at CERN and medical labs)
-Super sensitive chemical detectors
-Chemical treatment devices (excellent electrochemical properties)
-Cutting tools
-Transistors
-Protective Coatings (can be layered onto glass)
-High energy optical windows
-Super high pressure sensors
-Biomedical coatings (or any other coating where you want to reduce wear)

and many more. Of course, they've only been succesfully employed in a few of those. Some very intruiging challenges are before scientists, and as always that's the fun.

If you guys would like, I'll post some pictures of our reactor in action.

 

[hitssquad]

If you guys would like, I'll post some pictures of our reactor in action.

Yes, please.

 

[hitssquad]

Authenticity is popular

As for whether explanation will convince your wife, I'm not so sure you are right. I do think it is true you aren't going to get away with buying a $300 engagement ring instead of a $2500 one. However, diamonds really are beautiful. If someone were selling cheap man made diamonds that were indestinguishable to the eye from real ones, then when she saw the beauty of what $2500 would get her using that, I doubt she'd hesitate for a second.

She might see it as gaudy costume jewelry. I would posit that just as authenticity is the reason people read holy bibles, authenticity is the reason females demand mined diamond, no matter how small or ugly they are compared to manufactured diamonds. As you said yourself, indistinguishable to the eye from real ones. You might be able to write a computer program that produces unlimited amounts of great Bible books, indistinguishable in every way from the real ones, but would anyone care to read your apocryphs? When a typical Bible reader saw the beauty of your infinite-book Bible - downloadable for only $29.95 - you doubt he'd hesitate for a second?

Authenticity trumps quality for some people. Junky old Ferraris are worth hundreds of thousands and even millions of dollars. Googling <authenticated auction>
http://www.google.com/search?q=authenticated+auction

returns 93,000 hits. Authenticity is popular.

 

[Locrian]

Yes, but man made diamond is authentic diamond. It just didn't require underpaid africans with sub-30 year life expectancies (partly due to the job risk) to mine. Some CVD diamond is actually superior to any known natural diamond; I know the guys at Michigan state are having troubles characterizing their diamond's hardness because there is no natural diamond hard enough to compare it to.

I don't know how much research you've done on the subject, but I've done some weak, but I believe meaningful, research by trolling messageboards devoted to diamond and diamond knock-offs (cubic Z, DLC coated cZ and SiC). There is not just interest in man-made diamond, there is a fervor.

I also speak from a certain experience; my wife has SiC gemstone in her ring and SiC gemstone in her necklace. SiC is an interesting diamond substitute because it is almost identical, but not quite as a gemstone. I've watched people's reactions closely. If you see barriers to man made gemstones, I agree, there are barriers. But if you think there is not a monstrous market for cheap, real diamonds, I believe you are wrong.

Of course, the optimal word is cheap. Gemesis' $4K diamonds don't meet that requirement for me . Time will let us know.

(Couple of pics incoming)

 

[Locrian]

The pics are mostly too big to try and insert into the post, so you'll have to click the links. They are on a little server I pay almost nothing for a month, but its bandwidth should be fine for here.

Just a very quick description of CVD diamond growth so the components make sense:

1) You need a chamber in which the sample is placed, and it must be pumped to a weak vacuum (about 10mT for us) to remove air and contaminants.

2) You then add hydrogen and methane as your primary gases. Other gases can be added to change the properties of the diamond. Examples include nitrogen, boron, argon and others. Some people use acetone instead of methane.

3) This gas is pumped out at a constant rate, so there is always new gas entering and new gas leaving.

4) Now you need an energy source. The energy source has two functions; first, it needs to decompose the methane so you have free carbon floating around. Secondly, your sample must be heated to a high temperature. Diamond (sp3) bonds only form above a certain temperature; below that, you get graphite. Of course, you can't have too high a temperature or you'll melt your sample.

The original energy source (80's) were very hot filaments. Microwave plasma came along about a decade later, but has taken some time to master. There are advantages and disadvantages to both. Ours is a microwave system; you can see the 30kW microwave in the background.

http://www.pitofbabel.org/Vista/GlobalPic.jpg

There it is; it was originally operating in the Northeast, Boston area. We had to almost completely rebuild most of the system (we picked it up ourselves, and it came in many pieces). Of course, while stored up there it was subjected to freezing and warming over several cycles. There was extensive damage to the cooling system and I got to be a plumber for about a month :tongue2:

The big silver door held down by bolts is where the sample is inserted into the system. The sample is then raised into the microwave cavity - the black metal section - where the action happens. You can see the small window there where the sample can be viewed when you have a plasma.

http://www.pitofbabel.org/Vista/Plasma007a.jpg

For this pic I had turned off the lights. You can see the plasma glowing through the window. It's a small window, so its tough to get good pics of the sample through it.

First, a picture of our sample holder with samples, below:

http://www.pitofbabel.org/Vista/BNHolder.jpg

And some pictures with samples added. These are typical square (SPG-422) tungsten carbide 6% cobalt inserts.

http://www.pitofbabel.org/Vista/30Torr-1.jpg

http://www.pitofbabel.org/Vista/40samplePlasma.jpg

Those are old pics, but frankly they look better than my new ones. The plasma is purple because it is a hydrogen plasma; when methane and nitrogen are added it becomes white. There is a secondary plasma that forms on surfaces and corners and you can see it if you look closely in that second picture.

The actual chemistry that occurs at the surface is extremely complicated (no surprise in a plasma), and there is still ongoing research to discover what actually happens there.

Your substrate is important for good diamond growth. Diamond grows well on most of your M-C carbides (Titanium, Tungsten, Si etc) because of similar lattice structures. Of course, diamond grows best on diamond. Those pictures were taken at about 30torr. Increasing the pressure to 100 or more torr would reduce the size of the plasma but increase the growth rate considerably. That is how single crystal diamond is usually grown on diamond or saphire substrates.

Anyhow, I could certainly go into more, but I'll answer questions if there are any instead of writing a novel.

 

[hitssquad]

Barry Bonds, the 1919 World Series, and real good fakes vs the real goods

Yes, but man made diamond is authentic diamond.

Then it might seem peculiar that you wrote indistinguishable to the eye from real ones. If the man-made diamonds are the real ones, then which were the real ones that you were referring to before?

Some CVD diamond is actually superior to any known natural diamond.

As I wrote, authenticity ... no matter how small or ugly they are.

It seems to me that as one of the diamond articles linked here suggested, manufactured diamonds might find much of their market in replacing the small sprinkly diamonds that surround the large centerpiece diamonds in some jewelry. But authentic doesn't have anything to do with structural quality. It often has more to do with where something comes from and when it came from there. And it has directly to do with whether or not recognized authority grants it authenticity. Lists of superior-quality, inauthentic things (Barry Bonds; high-production-value 80's hair metal that was killed by "authentic" but low-production-value indie music; superior-quality copies of decaying art masterpieces; superior-quality copies of the decaying Declaration of Independence; just about any high-quality tailored dress made today vs. Marylin Monroe's Happy-Birthday-Mr.-President dress; just about any of the current Pope's potential replacements vs. the real Pope; etc.) might run endlessly.

If quality is the mark of authenticity, why might anyone be having a problem with Barry Bonds' home-run record?
http://www.abqjournal.com/news/yes/279113yes12-28-04.htm

• But when he breaks Hank Aaron's record, I'd like to see an asterisk by his name: " * used steroids during 2003 season."

"Wow, that's a fabulous engagement ring."

"Oh. Thanks, but it's not real. My fiance cheated and bought me this phony diamond ring. I guess he figured I wouldn't know the difference, but I took it to a top-flight appraiser who managed to identify it as fake since it didn't have the authentic De Beers identifier code that is molecularly stamped on all real diamonds these days. He's such a jerk, but that's why I love him."

 

[Dayle Record]

Locrian, you are generous in your contributions to this thread. I consider Diamonds to be a miracle however they come into being, they are some special carbon. Marketing won't make that any different. We can all shop for what we like, man made are certainly "blood free" diamonds.

 

[Locrian]

Then it might seem peculiar that you wrote indistinguishable to the eye from real ones. If the man-made diamonds are the real ones

That's absolutely right, I should have said natural ones! That's why your later statement "Oh. Thanks, but it's not real. My fiance cheated and bought me this phony diamond ring" isn't correct, because it wouldn't be phony. CVD diamond is perfectly real, it just doesn't require mining first.

I wouldn't feel the need to argue with you - the market will prove one of us right and the other wrong over the next twenty years - except I appreciated you pointing out the obvious mistake, and it leads me into more material worth mentioning.

The primary difference between CVD diamond and natural ones seems to be that CVD is more pure. They've actually used this to characterise them; CVD diamonds can be so pure that they lack natural contaminations you'd expect to find in natural ones. You are right about the small gems, but that is mostly because, due to the time it takes to get these things into production, most CVD diamond growth for gemstones are still using older hot filiament machines. They'll make 1 carat or so, probably not much bigger.

To be honest, exactly how you make CVD diamond to that purity and clarity is a bit of a mystery to me - most likely because I've never had the chance to research it.

Apollo diamond have a rather odd patent, if you look it up. It includes such information as the percentages of certain isotopes of carbon in their methane. I wonder if this isn't just a ploy to get a usable patent though. I do bet they require a much more severe vacuum than we do. If you are trying to eliminate contaminants, I bet a microtorr pressure would be optimal.

 

[Locrian]

CVD diamond brings a couple of very important advantages to the table over more traditional High Temperature High Pressure (HTHP from here out) methods. The first is that you can coat it directly onto a substrate. This is primarily the studies I'm doing, testing wear rates with different diamond layers. Because of diamond's extremely high thermal conductivity, diamond would make a fantastic heat sink, and it grows on silicon. Be careful though, growth temperatures tend to range from 500-800 celsius, so there's no growing it directly on silicon chips in there directly as of yet - well, or at least not without damaging the chip.

A note on surface area: the amount of surface you can coat depends firstly on the size of your reactor. Currently, the reactors in the US mostly come in two general sizes: 2.4ghz and the larger 915mhz. We have one of the large ones; the only reactor in the US that is bigger is the sister system at michigan state, who have a slightly larger microwave cavity.

In the smaller systems you are doing good if you can coat a 2" diameter flat area. Your plasma ball is typically larger, so you can do somewhat bigger objects if they are three dimensional.

In the larger systems, you can coat a circular area of 4"-6". I think Michigan might have done even larger areas, but the exact number escapes me.

Because diamond is so difficult to scratch, I think it will be very useful as a coating on glass. There is a paper I read recently where they used a titanium coating on the glass to add a layer of microcrystalene diamond without seriously damaging optical transparency. I would think that would have a great deal of potential. Of course, they didn't talk too much about adhesion. Many times adhesion is your problem.

More importantly though, CVD diamond can be doped. I suspect this is how Apollo are making their blue diamonds they are advertising, but more than optical qualities, doping is important for affecting diamond's other physical characteristics.

Boron doping is a great way of making diamond a p-type semiconductor at low dopings, and fully conductive at high dopings. As a conductor, diamond is showing great promise in electrochemical applications. They've already shown that, due to its high overpotential and other good characteristics, it can detect many chemicals - some harmful - at much lower concentrations than detectors in use. Also, due to its lack of chemical reactivity, it does not corrode like gold and platinum (or even diamond like carbon) detectors do.

The same properties that make diamond a good electrochemical sensor make it good in electrochemistry. I've seen a number of papers on water purification via boron doped diamond electrodes that were very interesting and showed the promise of nearly complete water purification going that route.

Not that there aren't problems with conductive diamond. The two biggest problems are currently the cost to make it and the consistency of the diamond. Both of these seem to be problems with solutions in the near future.

There are currently a number of different attempts to create diamond transistors, with some limited success. One method is to use a classic p-n junction diode by doping one side with boron and the other with phosphorus. Boron doping is easy, but phosphorus is not so easy. The transistors show great promise but clearly require a great deal of refinement before industry can attempt to use them. The other method is by making use of hydrogen terminated diamond surface. I'm afraid I am not equiped to give any details in regards to that at this time.

Diamond is looking to be a useful sensor for ionizing radiation. I'm only beginning my studies on this topic. I can present a wide range of papers (please just ask and I'll post them) but I'm a bit confused about what some of them mean. In essence, it would seem diamond is a useful detector of ionizing radiation because it acts as a natural ionizing chamber and its physical properties when reacting to ionizing radiation are actually quite similar to that of the human body. This has been known for 50 years now, but needless to say natural diamond radiation detectors were very expensive before CVD came along. CERN and some medical companies have shown great interest in CVD diamond detectors and there appears to be fast progress in this area now.

 

[Locrian]

Diamond is looking to be a useful sensor for ionizing radiation. I'm only beginning my studies on this topic.

A description of the mechanism that causes this can be found in

Milazzo, Mainwood. "Computer simulation of the detection mechanism in
diamond detectors," Nuclear Inst and Meth A, 514 (2003), 87-92

When a charged particle or a photon with an energy above the bandgap passes through the diamond, it ionises it, leaving a trail of electron–
hole pairs, which are separated by the externally applied electric field. The mechanism, by which the transit of a charged particle or a photon through
the detector is sensed, is he generation of an electrical signal in an external circuit. This signal is generated merely by the movement of carriers
within the detector; each carrier moving within the diamond induces charge on the electrodes. It is worth emphasising that it does not require the
collection of the carriers at the electrodes [1,2].

A good synopsis of diamond radiation sensors can be found in

Ramkumar et al. "An assessment of radiotherapy dosimeters based on
CVD grown diamond," Nucl Inst and Meth A, 460 (2001), 401-411

Diamond has a number of properties that make it a potentially useful material for use as a radiation dosimeter. The strong binding energy of diamond leads to a physically robust, chemically inert and radiation hard material. The atomic number of diamond (Z"6) is close to that of human tissue(Z"7.42). Published work on natural diamond dosimeters [1,2] indicates that they may be suitable for both photon and electron dosimetry over a wide
range of energies without the need for selective energy compensation as is required for silicon dosimeters.

I thought it would help to refer to the papers to clarify that last point. If there is a problem finding my references please let me know.

PS: After watching these publications I honestly wonder whether polycrystaline diamond is worth the trouble. I wonder if all the effort to make pcd diamond work were instead spent making better single crystal CVD diamond might not be more efficient. Maybe they know better than I?

 

[Locrian]

Diamond Cutting Tools

Diamond what?
The diamond terminology found in the marketplace can be confusing. Obviously, due to its hardness and low coefficient of friction (as well as thermal conductivity) diamond is useful in cutting tools, and has been so employed for many years in one form or another. Although simple, the terminology used doesn't always make much sense, so I thought it might be useful to review a couple of the phrases commonly heard in the sector.

Diamond Like Carbon
This form of carbon is amorphous and, frankly, not very diamond like. Significantly harder than graphite, but not nearly as hard as diamond, DLC coatings are common in the tool industry. Unfortunately, less than reputable tool sellers often simply advertise these as "diamond" tools, when in fact there may be no physical diamond on them at all. This is not to say that DLC coatings are not good wear coatings; they combine a hardness with the lubrication of graphite and extensive research has been done on their use. Still, except for specific applications DLC coatings tend to be suboptimal tools and one should read the fine print carefully before buying just any "diamond" dental burr.

Polycrystaline diamond (PCD)
The ability to make tiny diamonds with High Temperature High Pressure (HTHP) methods has been available for decades. Since these diamonds are very small, they are typically used in cutting tools by sintering them onto the tool, or mixing them into the tool material. This is effective in improving tool performance, but may not be cost efficient. Diamond embedded tools are commonly found in labs (cutting saws and polishing discs) and they have experienced extensive use in the automotive industry to cut high silicon aluminum materials. These PCD tungsten carbide tools typically have PCD diamond sintered onto one corner, which is the only corner used to cut.

CVD Diamond
Diamond made with chemical vapor deposition is generally referred to as CVD diamond. As I described above, there are two typical mechanisms of generating the energy needed to do this: hot filament, and microwave plasma deposition. You will sometimes see the microwave plasma deposited diamond referred to as MWCVD or even MWPECVD. A bit too alphabet soup for me. Single crystal diamond can be grown with these, but it is rare. Therefore you most commonly see polycrystaline diamond grown; however, it is not generally referred to as PCD, since that would confuse it with HTHP PCD diamond coatings.

The best cutting tool?
CVD diamond coatings promised great cutting tool improvements when it was first demonstrated in the 80's, but has required a great deal more time and energy than first hoped. The prospects seemed good: diamond is exceedingly hard, has excellent thermal conductivity and a coefficient of friction almost that of teflon. A diamond coated tool should be able to operate at higher speeds, for long times, with less wear.

The problems with this topic proved difficult to solve. Firstly, it should be noted that diamond coatings are very poor choices for cutting any ferritic material, which obviously reduces the number of applications considerably. This is because, although the diamond does an amazing job of cutting, once it heats it quickly chemically combines with the iron and wears away. It therefore lacks the lifetime necessary to be a useful tool on those materials.

Secondly, diamond only grows on particular materials (m-c carbides). Some materials diamond will not grow on. Other materials are detrimental to diamond growth, causing graphite to be produced instead of diamond. (Trust me, I know this from experience! A mistake in surface prep yesterday resulted in nearly 1/8th inch thick coating of pencil lead on my sample.) Unfortunately, iron is detremental do diamond growth, and therefore diamond growth will not occur on almost any ferritic material. There could be surface preparation options that will allow good growth. I have some ideas and intend to look into this at some point. I am not aware of anyone growing diamond on iron or steel with any reasonable adhesion.

So in two swift blows, most uses for diamond coated tools and most tools you could coat with diamond were removed from application. There was - and is - still hope, however. Machining aluminum is quickly becoming big business, mostly thanks to the car industry. Car frames are already being made out of aluminum, and car engines are quickly following suit. Since PCD tipped (by sintering) W-C tools were already being used for this, and diamond has strong growth on tungsten, it seemed reasonable to hope that diamond would grow on W-C tools with good adhesion.

Unfortunately W-C tools also contain typically 11-15% cobalt, which is detrimental to diamond growth. Thus the primary area of research in recent years has been finding ways of getting diamond to grow effectively on W-C-Co tools and also producing acceptable adhesion. There has been some limited success in this area. I recently read of BMW using 4um thick diamond coatings on W-C-Co tools to machine aluminum frames. A more useful tool would be one that would machine aluminum engines (which typically contain high silicon). This is one of my primary areas of research and my group is meeting with some success. There is also one other manufacturer of diamond coatings who seem to have succeeded in this area, Semicon.

Of course, success in application does not necessarily translate into economic viability. That is the next step for diamond coated tools. PCD tipped tools have been in use for decades and their production is incredibly efficient. It will require several extremely important advances in CVD diamond to match and pass their economic usefulness.

Please note that there are very, very many details I have access too (such as % of cars with aluminum engines, for example) that I see no reason to bog down these posts with. If requested I will provide them.

 

[CNT]

Locrian: Water purification using B doped diamond

Locrian: You mentioned you've seen a number of papers on water purification with boron doped diamond electrodes. Can you share those?

 

[Locrian]

Morao et al. "Degradation of mixtures of phenols using boron doped diamond
electrodes for wastewater treatment" Electrochemica Acta (2003). That was still in print at the time I found it so I only have a received and approved dates: Recieved 19 November 2003, accepted 20 November 2003. (I think it may be Volume 50, Issue 18 pg3685)

Chen, Guohua. "Electrochemical technologies in wastewater treatment" Separation and Purification TEchnology. Volume 38, Issue 1 Pages 11-41

A great introductory article that includes a little information on water treatment (and probably some good references too) is:

Hupert et al. "Conductive diamond thin-films in electrochemistry." Diamond and Related Materials 12 (2003) 1940-1949

If you use the references those three give I think that will get you started. Let me know.

 

[CNT]

thanks for refs

Thanks for the references, I appreciate it. Now the challenge is to actually find the journals...

 

[Antiphon]

You guys are missing a major element of this story.

I talked with a woman. They of course are the world's end-users
of all non-industrial diamonds.

She says that a woman would not consider a synthetic (laboratory-made)
diamond to have the same emotional impact as a natural diamond regardless
of it's quality (or price). She would not want one for an engagement ring.

So there you go...

 

[hypatia]

Eh Gads no! I would wear a plain band befor I wore a man made diamond as a wedding ring.
Now as for other jewlery made with synt. gems, I have no problem, and have several pieces that I wear often.

 

[Hurkyl]

Eh Gads no! I would wear a plain band befor I wore a man made diamond as a wedding ring.

Why is that?

 

[hypatia]

Its the symbol/ token of love that has a emotional connection historically for woman. Tho myself and many woman do not half to have one to wed or feel loved, just if I did, I would want it to be a diamond from the earth.
It dosen't half to be a new diamond, there are so many vintage ones in the market that you can get reset. My personal favorit are the early{19th c} mine cut stones.
I in no way would support the hardships of the diamond miners today.

Real quality diamonds are a investment, and normally do not loose there value.