Marilyn Monroe may have insisted that "diamonds are a girl's best friend," but scientists today would like to enlarge the circle of admirers by making diamonds the servant of everyman.

Besides its traditional role as the world's finest bauble, diamond is also the world's finest abrasive, finest semiconductor, finest insulator, finest refractor of light and finest thermal conductor. A synthetic diamond wafer can slice an ice cube in half in a couple of seconds using the heat from a single human hand.

But aside from creating an $800 million-per-year abrasives industry, diamond has never fulfilled its promise. Forty-five years after scientists first synthesized it, diamond continues to confound efforts to put its unsurpassed virtues to more practical use.

"It was going to be the answer to everybody's prayer," said Donald Knight, a specialist in finding practical uses for technology developed at the Argonne National Laboratory in Argonne, Ill. "But it's expensive and hard to work with, and people can always find a solution somewhere else."

Although scientists for decades have focused on making diamond into a workaday product, recent events suggest that industry may have found more profitability by moving up-market.

General Electric Co., the inventor of synthetic diamond, recently began test-marketing natural stones that have been color-enhanced with a new high-pressure process.

"Market research has shown improved buyer interest with zero to minor discounts," said Bill Woodburn, vice president and general manager of GE's super abrasives division. "I emphasize 'minor.' A deeply discounted diamond is viewed as flawed, and these diamonds are gorgeous."

And in February, Novatek Inc., a Provo, Utah-based company founded by one of the GE researchers who developed synthetic diamond, will begin online sales of fancy green and yellow-green "NovaDiamonds" made by squeezing lower-value colored stones at a pressure of 1 million atmospheres and temperatures approaching 3,600 degrees Fahrenheit.

If the public embraces the new products, economics will do the rest. The value of an off-color diamond can in some cases be nearly doubled by altering its crystal structure slightly to whiten it with GE's high-pressure process.

And in Provo, Novatek President David Hall is buying raw natural stones for hundreds of dollars per carat and transforming them into reasonably priced green diamonds, a type of stone so rare that it is virtually unavailable to the general public today. "This is the Holy Grail" of the diamond business, Hall said.

If it sells. For, as experts are careful to point out, a diamond is, above all, unpredictable. An unmounted, flaw-free, one-carat (.007 ounce) white stone can be worth $5,000 to $10,000. A one-carat Lucida diamond ring from Tiffany can retail for as much as $18,000.

But "people want the natural stones," said Robert M. Hazen, a mineralogist at the Carnegie Institution of Washington and the author of a history of synthetic diamonds. "The idea is that if it's been around a long time, it will be around a long time. If you made it in your basement last week, people don't want to hear it."

Diamond is crystalline carbon, created deep in the Earth under tremendous heat and pressure and exploded to the surface, where it is mined in "diamond pipes" or recovered in alluvial deposits.

Diamond was revered in ancient India, but throughout this century the industry has been centered in South Africa, with significant numbers of stones coming from several other African countries, India, Russia, Australia, Brazil, Venezuela and, most recently, Canada.

World sales of gem diamonds are managed by the De Beers Central Selling Organization, the commercial arm of the Kimberly, South Africa-based company that controls 50 percent to 80 percent of the diamond trade.

In 1997, the last year for which statistics are available, about $12 billion in gem diamonds were sold around the world, the vast majority in the one- to five-carat range. "That's where the money is," said George E. Harlow, curator of minerals and gems at the American Museum of Natural History in New York. "The big stones is where the hoopla is."

The synthesis of diamond was motivated primarily by a desire to find a reliable Cold War source of abrasives for oil drilling bits, quarrying saws and other heavy-duty cutting tools. Diamond is both the world's hardest known substance and its best thermal conductor, making it ideal for jobs requiring durability without overheating.

Over the years, advances in high-temperature and high-pressure synthesis have enabled industry to create diamond grit or dust in shapes and sizes to order. Novatek makes high-quality polycrystalline inserts for drill bits by fusing synthetic diamond around metal additives. Woodburn said GE makes 6,000 kinds of diamond abrasives.

For the past 20 years, however, research has focused on low-pressure synthesis, in which hydrocarbons in a vacuum chamber are "cracked" in the presence of hydrogen in a high-temperature microwave field, causing a thin film of diamond to form.

"All hell broke loose," said Pennsylvania State University's Rustum Roy, one of the world's leading low-pressure synthesis researchers. It suddenly seemed possible to make diamond microchips, diamond sheets for heat dispersal and diamond coatings so strong that knives would never dull and eyeglasses would never scratch.

So far, however, results have been modest. Low-pressure synthesis is too slow to be economically viable except in narrow product niches. Diamond films don't adhere to steel and are too expensive for eyeglasses.

In a recent paper in the journal Nature, Belgian researcher Jean Charlier reported synthesizing 10 to 100 micrometers of diamond by vaporizing graphite in a vacuum with a 10-millisecond burst of heat, a far faster rate of growth--and potentially cheaper--than any other low-pressure method. But Charlier said he does not know how cheap the process could be, or if his method can work beyond a single event.

Microcircuitry research, meanwhile, is all but "moribund," Roy said, because scientists cannot appropriately "dope" diamond--salt the film with impurities so that electricity can be conducted.

In optics, scientists have created small diamond "windows," useful in rocketry or other applications requiring high transparency and high resistance to heat and radiation. Again, however, "it's godawful expensive," Roy said, and only the government can afford it.

And in Northborough, Mass., Norton Diamond Film produces diamond disks for heat dispersal mounts for microelectronics. As chips get smaller and are grouped closer together, the need for effective heat transfer grows, and Tom Colyer, Norton's general manager, thinks the use of diamonds is an answer. "We are just starting to make money," he said.

In all the new applications, however, money is the main drawback. "Some say diamond is a good way to make a $200 part out of a $10 part," said Argonne's Knight, and diamond will probably remain a bystander until the math improves.

Making Diamond Film

`Cracked` in a vacuum chamber from hydrocarbons under high temperature in the presence of hydrogen, carbon atoms crystallize as a diamond crust on the surface of a metal substrate. Two processes are used for the condensation of diamond film: hot filaments and microwave plasma.

SOURCE: Goddard Space Flight Center, NASA