Creator:Herbert M. Strong
Date Created:January 31, 1977
Place Created:Schenectady, New York
Keywords:growth and properties of diamond
Context:talk for APS conference
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Herbert M. Strong
1165 phoenix avenue schenectady, new york 12308
Janucuiy 31, 1^77
Dean. I nxicy,
Attacked, ane my n.emank& and AlideA i planned, pjn. the cenemonleA -in San Dleg.o on niaAch 22. Youn. comments one welcome. J hope^will me^k with youn. preceding. presentation pn.openly. Twelve ok tltuvteen inuuiteA time allowance, doesn't ylve macn Koom fton. elaboration.
Again congnatulallonA on receiving thl/> well eanned aivand. IMe one looking, fionwand to seeing, you thene. tie expect to be flying In piom. ■Honolulu aA we will be vl&LLing oun Hawaii based Aon in ulancJi. We leave hene February 25.
Sincerely,
MeAjo-s
In cade you want to reach. me in 'Hawaii, the. adcbieAA Id:
Dr. Steven R. Strong Kaiser Lahafne Clinic Lahaina-Maui-HI 96761
THE QKMTH MD PROPERTIES OF D/AWAO H 1)1 Strong
illy remarks are. directed to the shaded, portion of the temperatune-pressure phase diagram, of carbon. This is the pressure temperature region that was available for. experimentation In early. 195^- Here reproducible diamond synthesis was accomplished later. In the sane
year. Here also are the conditions for. stgnlheslging Industrial. __
abrasive diamond.
In the early experiments on diamond synthesis, the first disappointment was the finding that at the available pressures and temperatures, graphite would not transform to diamond, no matter, how hand, hot or prolonged the squeeze applied. /nitially, it didn't seem that graphite, should have been much Inconvenienced to puchen its flat hexagonal carbon nets a little and then reorder its layer stacking, a bit. The The applied pressune fa.vor.ed this readjustment since the volume of diamond Is but 2/jrds that of graphite. Evidently graphite crystals would have to be taken apart and reassembled more to our liking.
Some hints about this came from the real world of one atmosphere. For example, certain carbon compounds can, by appropriate chemistry, be persuaded to release free carbon. Also, there one solvents_which can take carbon from one place and put it down in anothen. with the help of a temperature gradient or by electrolysis, If the carbon is ionised. All of these reactions yield graphite al one atmosphere, but under a pressure IheAmodynamlcally agreeable to diamond, carbon is definitely obligated to form diamond when turned loose, or so it seemed. But carbon had not heard about this so it followed its predilection to form graphite in all cases, save two. The reaction of nickel releasing, lithium from lithium carbide produced a product that gave an elusive hint of diamond in the form of weak x-ray diamond diffraction lines, but diamond crgstals were not seen.
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I he. reaction between ynaphlte and molten Lron unden. preAAure gave, a m.omeni.oiu> and. exceptional. reAutt because. Aeeabte, feelabte cryAialA {.owned having the. capability of. Acnaicking. everyihing in Aiykt. Very convincing.. Bui ike. interval between ike firAl AynihcAiA and Ua proof of. repn.oducibLLU.ij. had Ua futl Akare of AUApenAe for ike. expenimenieAA.
Ike. ex.penim.eni id quite Aimple. AlleAnating. pieceA of gAapkile and any. ferrouA metal, on many of their alloyA, are stacked in ike preAAure cell. A current La paAAed tkrouugk ike. preAAuni^ed Aiack to heat it to about I ^00°C mkereupon ike. meiat gAapkile A/yAtem meliA toyellieA at ike interfaces forming diamond AponlaneouAly and napidly beneath a thin film of molten metal. / hxA picture of a nickel piece, uilk ike. lumpy AurfaceA aIiowa ike diamonds collected at ike inierfaceA beneath a ikin akin of nickel. A Utile add Aoon bringA ike newly bo nn cJiyAtalA out into ike light of day. ' I hey may took like Aome. of tkeAe, tkelr Ai^eA ranging. from a few mi.cA.on/> to / mm, JjxaI right fan. abraAive uac. their Ai^eA, colon, and AhapeA ana controlled by the preAAure, tempenaiure, time, and nature of ike Aotvent-calahyAtA employed to bring about ike. reaction. A mule range of cryAial ckaAacleJU-AticA La ikuA available.
Ike tenia catalyst aAAOclaled milk Aotvent La appnopnLate becauAe ike fennouA mcialA and many of ikeln alloyA are unique among AolveniA in abiliig to yield diamond fnom diAAoived gAapkile. CuriouAly, copper uAick neiikeA Aotvenl non catalyAt becomeA a calalyAt and an extnemely meak Aotvent milk ike addition of about 2/o nickel. Diamonds fonm AunpriAingly easily in ike 2/1 nickel alloy. EleclnutyAiA expenimenlA indicate that canbon may be a poAilive Lon in lix/uid feAAouA metal AoluilonA, unlike moAt other AotulionA of ca/ibon mkerein ike carbon La either neutral or negative. The formation of poAilive canbon Loru, may be a precondition for dcamond formation.
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Solid fennous metals ane not diamond catahgsts. rill canbon precipitating from solid metal becomes gna^ohitic. Likewise, the metal carbides, iron carbide, nickel carbide, etc. may be decomposed under pressure by heating., but the separating carbon Is alwaigs graphite.
Diamond forms in two component systejns, carbon and ferrous metal. I heir binwuy phase diagrams for one atmosphere are well known. Under pressures near 55 kbars, the diagrams are simitar, but melting temperatures are higher, and compositions altered slightly. Also, the melting eutectics reflect the presence of two phases of carbon. In the nickel carbon system at 54 kb, the nickel graphite eutectic lies a little below the nickel diamond eutectic and at a bit higher, carbon concentration because graphite is now the unstable phase. I he small solubility difference is where the drive to form diamond is ultimately feU.. Diamond may be formed rltghl at the graphite nickel eutectic, but the crgstals are black, of poor crystal quality
and lacking the usual nickel skin. Dlcunonds are normally formed well above the diamond eutectic. A complication develops because nickel is slightly soluble In graphite. Graphite in this system Is then slightly more stable In respect to diamond than pure gnaphite. I his lowers the diamond stable temperature at 34kb by about 12°degrees.
In the Iron-carbon sigstem at 57 kb, stable Iron carbide introduces a third eutectic, Iron-Iron carbide which lies above those of diamond and graphite. At temperatures below the carbide eutectic, Iron consumes both diainond and gnaphite forming Iron carbide. Diamonds form only at tempenalures above the carbide decomposition temperature.
So j{an. in this talk only. small diamonds have, been made, li/hy not targe, ones? I he principal factor limiting growth in the system, described Is the large volume shrinkage occurring when graphite becomes diamond, The apparatus does not closely follow this volume decrease, hence the pressure falls reducing the drive for diamond growth to gero. / his problem is solved by using diamond as a carbon source in the pressure cell. Small abrasive diamonds are used as the nutrient carbon which is dissolved in a pool of molten femous metal at a high temperature and allowed to swim do/m to a cooler gone where the solution becomes supersaturated with carbon that precipitates out on a seed diamond. I hrough careful control of the supersaturatlon rate, a nice gem quality crystal can be grown to 6 to 7 nun in about a meek.
These make nice expensive gems. Strange that suck a bit of thermodynamically unstable matteA should have become the. symbol of ever enduring love. / hese crystals afford the opportunity to study diamond properties In terms of controlled additions of impurities, particularly substitutional boron acceptor atoms and substitutional nitrogen donor atoms. Pane diamond Is colorless and, except for weak carbon bands at 4 microns, it is transparent from the band gap at 2250 A to at least J mm. l\itrogen and boron Introduce characteristic visible and infrared absorption bands which impart yellow and blue colorations respectively. Boron doped dlamorid is a p-type semiconductor, but with nitrogen the donor level Is 4 ev deep and no room temperature conduction is observed.
The extremely rigid, light atom lattice of diamond imparts some unusual properties to diamond: exceptionally high Debge temperature, low specific heat, remarkably high thermal condjjctlvity and thermal dlffusivily, and lastly great strength. Impurlties do detract from these properties some, but diamond /lemains extreme in its properties.
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Diamond'a gneal strength and tranApaAency has Led to Ua wide. use fon. anvils in miniature preASure devi.ce/> capable, of generating, nearly. / megabar preAAuneA.
/ tA transparency and high, thermal conductivity find UAe for high power laAer beam windowA. Ha higti thermal conductivity 1a much required. in electronics for keeping tiny power diodeA coot. /here are many otfien uaca far diamond.
Hob U/eniorf mill next tell you about synthesizing diamond'a next of kin, cubic boron nitride, or boragon, and how this and diamond are being uAed.