This attempted 'crystal gazing' will be ended by consideration of a somewhat light-hearted conjecture for which we ourselves are responsible. This is the conjecture which we have made elsewhere that there may be numerous diamonds on the surface of the Moon. This theory (which we published a few years ago) is based on the following ideas. The first point is that just as there are millions of tons of carbon on Earth in one form or another, and just as there are great quantities on the Sun, so equally carbon must abound on the Moon. Now, it has already been established that an explosive shock wave can convert carbon to diamond. Furthermore, it has been established that around the rim of the great meteoric crater in Arizona (Canon Diablo) there are numerous small black diamonds. It is very probable that the mighty impact of the meteorite which produced this crater created a shock wave of sufficient temperature and pressure to convert any local carbon present to diamond and that is the reason why there are diamonds on the rim of the Arizona meteoric crater.
Now it is well known that the Moon is simply covered with craters, indeed the American satellites have sent back photographs proving that the whole of the Moon's surface is vastly pitted with craters. The Moon has no atmosphere, so that all incident meteorites produce most violent impacts. Even if the lunar force of gravity is only one-sixth that on Earth, the absence of a resisting protective atmosphere means that every impact is very violent indeed.
Thus there is high probability that just as at Arizona, so on the rims of the innumerable lunar craters there may also be diamonds. But there are thousands upon thousands of such craters, large and small, so there have been many chances indeed of diamond formation by impact.
Indeed, since some meteors carry diamond stones the very hail of projectiles could itself have brought in much diamond from outside. (These meteorites might be break-up from a former minor planet, therefore come largely from depth in this minor planet where pressure and temperature conditions would favour diamond formation.)
Thus, all in all, the Moon's surface might be very rich in diamond.
This fantasy by the author seems to have impressed the administrators of the American Apollo project for landing men on the Moon, who have taken it quite seriously, for the American Space Administration has appointed the writer to be a special investigator to search retrieved lunar material for diamond. Some of the first lunar rock to be brought back has been allocated to the writer for the express purpose of searching it for small diamonds. Who knows, the Moon may one day be mined for diamond!
četrtek, 24. julij 2008
torek, 24. junij 2008
ARTIFICIAL COLOURING OF DIAMOND
To the purist any tampering to affect the physical properties of diamond smacks of faking and is to be deplored. Yet there is one aspect of modern diamond jewelry technology which may have future repercussions. It has been established that the colour of a diamond can be changed if it be subject to bombardment by fast atomic particles. A clear transparent diamond can have its colour changed when irradiated in an atomic pile. This change in colour comes about through what is called 'radiation damage'. A bombarding particle strikes an atom which is situated in its normal strict geometrical position in the crystal and knocks it out of position, leaving a 'vacant site' behind. The displaced carbon atom must find a home and does so 'interstitially' between other atoms which are thus distorted from their normal strict geometrical positions by the intruder.
The effect of the intruder is to influence the physical properties, and one of these results is to create an absorption of some of the colours of the spectrum. As a direct result, the crystal acquires a colour which is quite a pure colour.
An atomic pile reactor is a system which creates large numbers of uncharged atomic particles called neutrons, and these are especially efficient in penetrating right through a crystal and knocking out atoms, which in turn also knock out atoms. This is done in depth right through the crystal.
Another way of creating this situation of knocked-out particles is to accelerate electrons to a high velocity with a machine called a Van de Graaff generator. This machine builds up millions of volts, and the electrons accelerated by such fields are also capable of inducing colour in diamond, but this time the colour is on the surface only.
Diamonds exposed to the neutron irradiation available from the atomic pile at Harwell became green. The intensity of the colour depends on the irradiation dosage. A light colour results from a small dosage and a progressive deepening occurs as dosage increases. Beyond this the diamond turns irretrievably black, in fact local regions of graphite have then formed.
If a diamond coloured. green by neutrons is heated, the colour changes since the interstitial atoms can move to new positions because of their increased vibrations induced by heating. Changes to amber and then to yellow appear, depending on both the temperature of heating and the time the heat is applied. The diamond never returns back to its original white transparency, having clearly suffered some permanent damage which cannot be resolved. A yellowish brown always remains at best. Any colour induced, whether green, brown or yellow, remains permanent if the diamond is cooled, at that colour, down to room temperature. Changes only occur whilst the diamond is hot, so in this sense a colour once induced is permanent at room temperature.
Electrons, contrary to neutrons, produce a pure blue colour. Electrons, even if fast, are absorbed in a skin-thin layer of diamond so that the blue coloration from electrons is only 'skin' deep (1/50 inch). Not only is this a mere thin skin colour, but also only that particular face which was exposed to the beam takes on colour. To colour a complex-shaped brilliant by exposure to electrons would be a most complicated matt« because of its elaborate shape and the inclined angles of its many faces.
Natural blue diamonds are very rare and very remarkable, but there is at present no risk of confusing the natural blue diamond with the irradiation blue diamond. The colours are visually very different and certainly also quite different when measured with spectroscopic instruments. Once more, then, we have a situation where the artificial creation can be distinguished from the natural. The man-made color is immediately recognizable and as such will not debase the value of the natural blue diamond. But it might enhance a natural colorless white! It is thus possible that a demand for radiation colored diamonds will arise in future.
The electron-irradiated blue is not stable to heat and turns to green at moderately high temperatures. Natural blues can be heated to 1250° C without any change in color.
There remains another very important point not to be overlooked. Irradiation of pure carbon seems to be harmless, but all diamonds contain some impurities. During the bombardment some of these impurities become radioactive, and this might be long-lived and possibly dangerous to a wearer. If irradiation were to be used in future for coloring diamond stud earrings , it would become imperative to test each such diamond for radiation danger.
Finally, there may possibly be a bonus from irradiating diamond. There seems to be some evidence that irradiation reduces the intrinsic hardness through damaging the atomic groupings. Thus an irradiated diamond might become easier , to fabricate. When one takes into account, however, the high cost of neutron irradiation, it may well be quite uneconomic - | the saving in polishing time might well be insufficient to make up for the cost of irradiation.
The effect of the intruder is to influence the physical properties, and one of these results is to create an absorption of some of the colours of the spectrum. As a direct result, the crystal acquires a colour which is quite a pure colour.
An atomic pile reactor is a system which creates large numbers of uncharged atomic particles called neutrons, and these are especially efficient in penetrating right through a crystal and knocking out atoms, which in turn also knock out atoms. This is done in depth right through the crystal.
Another way of creating this situation of knocked-out particles is to accelerate electrons to a high velocity with a machine called a Van de Graaff generator. This machine builds up millions of volts, and the electrons accelerated by such fields are also capable of inducing colour in diamond, but this time the colour is on the surface only.
Diamonds exposed to the neutron irradiation available from the atomic pile at Harwell became green. The intensity of the colour depends on the irradiation dosage. A light colour results from a small dosage and a progressive deepening occurs as dosage increases. Beyond this the diamond turns irretrievably black, in fact local regions of graphite have then formed.
If a diamond coloured. green by neutrons is heated, the colour changes since the interstitial atoms can move to new positions because of their increased vibrations induced by heating. Changes to amber and then to yellow appear, depending on both the temperature of heating and the time the heat is applied. The diamond never returns back to its original white transparency, having clearly suffered some permanent damage which cannot be resolved. A yellowish brown always remains at best. Any colour induced, whether green, brown or yellow, remains permanent if the diamond is cooled, at that colour, down to room temperature. Changes only occur whilst the diamond is hot, so in this sense a colour once induced is permanent at room temperature.
Electrons, contrary to neutrons, produce a pure blue colour. Electrons, even if fast, are absorbed in a skin-thin layer of diamond so that the blue coloration from electrons is only 'skin' deep (1/50 inch). Not only is this a mere thin skin colour, but also only that particular face which was exposed to the beam takes on colour. To colour a complex-shaped brilliant by exposure to electrons would be a most complicated matt« because of its elaborate shape and the inclined angles of its many faces.
Natural blue diamonds are very rare and very remarkable, but there is at present no risk of confusing the natural blue diamond with the irradiation blue diamond. The colours are visually very different and certainly also quite different when measured with spectroscopic instruments. Once more, then, we have a situation where the artificial creation can be distinguished from the natural. The man-made color is immediately recognizable and as such will not debase the value of the natural blue diamond. But it might enhance a natural colorless white! It is thus possible that a demand for radiation colored diamonds will arise in future.
The electron-irradiated blue is not stable to heat and turns to green at moderately high temperatures. Natural blues can be heated to 1250° C without any change in color.
There remains another very important point not to be overlooked. Irradiation of pure carbon seems to be harmless, but all diamonds contain some impurities. During the bombardment some of these impurities become radioactive, and this might be long-lived and possibly dangerous to a wearer. If irradiation were to be used in future for coloring diamond stud earrings , it would become imperative to test each such diamond for radiation danger.
Finally, there may possibly be a bonus from irradiating diamond. There seems to be some evidence that irradiation reduces the intrinsic hardness through damaging the atomic groupings. Thus an irradiated diamond might become easier , to fabricate. When one takes into account, however, the high cost of neutron irradiation, it may well be quite uneconomic - | the saving in polishing time might well be insufficient to make up for the cost of irradiation.
A FUTURE REQUIREMENT OF BONDED WHEELS
There is one situation in the future where the correct type of bonded wheel, should it be invented, could make an enormous difference to the technological fabrication of diamonds wedding bands, especially the fabrication of gems. Bonded wheels are far superior in speed to the classical scaife. They are also so much more abrasive that whereas formerly the octahedron planes (111) on a crystal were practically totally resistant to a scaife, the modern bonded wheel fairly easily attacks even these (hardest) faces on diamond. Despite all this, the bonded wheels as at present developed cannot be used to polish gems or to shape those diamond cutting tools which require to have a sharp cutting edge. For these wheels, although they do rapidly abrade faces, always seem to chip edges. A gem with chipped edges is just not acceptable. Equally unacceptable is a chipped edge on a cutting tool.
If future research leads to the invention of the right kind of bonded wheel (and both nature of bond and shape of grit are involved, possibly employ of a lubricant needed also), then it may become possible to abrade very rapidly and yet still to maintain sharp unchipped edges. Such a development, if it comes, will make a great difference to the cost of shaped diamonds both as gems and as tools.
If future research leads to the invention of the right kind of bonded wheel (and both nature of bond and shape of grit are involved, possibly employ of a lubricant needed also), then it may become possible to abrade very rapidly and yet still to maintain sharp unchipped edges. Such a development, if it comes, will make a great difference to the cost of shaped diamonds both as gems and as tools.
FUTURE OF SYNTHETICS
We have come a very long way now from the diamond jewelry mentioned in the Bible. It has been shown that diamond is a fundamental strategic material playing a vital part in modern industrial processes. The value of diamonds consumed both as gems and as an industrial hard material is such that the economy of many States hinge on diamond production. Vast capital sums have been sunk into diamond production and large profits have resulted.
Despite intensive research, despite production synthetically of maybe a quarter of the total world output, we still do not know how diamonds grew in the earth and we still are unable to copy this. It may be that time is against us in the sense that it may be that the strong beautiful crystals from the earth grew slowly under very uniform conditions. If this is the case, clearly it is not going to be economic to grow ordinary-size crystals industrially. Yet it must not be overlooked that if and when the time comes that big strong crystals can indeed be grown artificially, then the situation may arise where very big crystals could become a possibility. If this were so, whole new technological vistas may open up.
Even if technology succeeds in producing large perfect gem-quality crystals, then we do not believe that this is likely to upset world values of natural diamond. For it is pretty certain that technical methods of testing will be able to distinguish synthetic from natural wholesale diamond. Certainly it is very easy to distinguish currently produced synthetic from natural diamond, even if crystals of similar size are matched. We have ourselves always done so and never yet confused the two. If, indeed, a distinction can be made (and this is almost certain), then the synthetic product will certainly never kill the market for natural diamond. For not only to people of taste and discrimination but equally to those sensitive only to financial values, the idea of a synthetic material is objectionable. The invention of synthetic ruby has not debased the value of natural ruby, basically because the two can be distinguished. In like manner, the invention of cultured pearls and their production in huge numbers (despite the fact that oysters do make them) has not debased the value of real natural pearls, again basically because the two can be distinguished. Thus even if beautiful diamond gemstones were to be synthesized, as long as scientific tests can distinguish these from the natural mined gems, we believe the latter will maintain their value. Such perfect synthetic diamonds could, of course, command good prices for manufacture of diamond cutting tools; and if such new large diamonds were made, then surely new uses would soon be found. There is, therefore, every inducement to seek to create strong gem-quality synthetics.
A much greater inducement is the strategic one. For, as things are, practically all the great industrial countries (other than the U.S.S.R. now) are non-producers and therefore are dependent on import from abroad. Stockpiling for military strategy is therefore incumbent. If good strong large synthetics become a possibility, then this grave strategic deficit would be remedied.
Despite intensive research, despite production synthetically of maybe a quarter of the total world output, we still do not know how diamonds grew in the earth and we still are unable to copy this. It may be that time is against us in the sense that it may be that the strong beautiful crystals from the earth grew slowly under very uniform conditions. If this is the case, clearly it is not going to be economic to grow ordinary-size crystals industrially. Yet it must not be overlooked that if and when the time comes that big strong crystals can indeed be grown artificially, then the situation may arise where very big crystals could become a possibility. If this were so, whole new technological vistas may open up.
Even if technology succeeds in producing large perfect gem-quality crystals, then we do not believe that this is likely to upset world values of natural diamond. For it is pretty certain that technical methods of testing will be able to distinguish synthetic from natural wholesale diamond. Certainly it is very easy to distinguish currently produced synthetic from natural diamond, even if crystals of similar size are matched. We have ourselves always done so and never yet confused the two. If, indeed, a distinction can be made (and this is almost certain), then the synthetic product will certainly never kill the market for natural diamond. For not only to people of taste and discrimination but equally to those sensitive only to financial values, the idea of a synthetic material is objectionable. The invention of synthetic ruby has not debased the value of natural ruby, basically because the two can be distinguished. In like manner, the invention of cultured pearls and their production in huge numbers (despite the fact that oysters do make them) has not debased the value of real natural pearls, again basically because the two can be distinguished. Thus even if beautiful diamond gemstones were to be synthesized, as long as scientific tests can distinguish these from the natural mined gems, we believe the latter will maintain their value. Such perfect synthetic diamonds could, of course, command good prices for manufacture of diamond cutting tools; and if such new large diamonds were made, then surely new uses would soon be found. There is, therefore, every inducement to seek to create strong gem-quality synthetics.
A much greater inducement is the strategic one. For, as things are, practically all the great industrial countries (other than the U.S.S.R. now) are non-producers and therefore are dependent on import from abroad. Stockpiling for military strategy is therefore incumbent. If good strong large synthetics become a possibility, then this grave strategic deficit would be remedied.
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