PROCESS FOR ISOTHERMAL DIAMOND ANNEALING FOR STRESS RELAXATION AND OPTICAL ENHANCEMENT BY RADIATIVE HEATING
A method anneals one or more diamonds. The method provides a furnace having a chamber with a heating element configured to radiatively heat a diamond. The diamond is positioned within the chamber, and levels of gas within the chamber are modulated to achieve a prescribed pressure. The diamond is heated to a prescribed temperature using a given heating ramp rate. The given heating ramp rate is greater than about 60° C. per minute and less than about 800° C. per minute. The prescribed temperature is greater than about 1,350° C. and less than about 2,200° C. The prescribed pressure is greater than 1×10{circumflex over ( )}−9 Torr and less than about 550 Torr.
1 . A method of annealing one or more diamonds, the method comprising:
providing a furnace having a chamber, the furnace having a heating element configured to radiatively heat a diamond;
positioning the diamond within the chamber;
modulating levels of a gas within the chamber to achieve a prescribed pressure; and
heating the diamond to a prescribed temperature using a given heating ramp rate;
the given ramp rate being greater than about 60° C. per minute and less than about 800° C. per minute,
the prescribed temperature being greater than about 1,350° C. and less than about 2,200° C., and
the prescribed pressure being greater than 1×10{circumflex over ( )}−9 Torr and less than about 550 Torr.
2 . The method as defined by claim 1 , wherein graphitization of the diamond is prevented.
3 . The method as defined by claim 1 , wherein the ramp rate accelerates as it approaches the prescribed temperature.
4 . The method as defined by claim 1 , wherein the prescribed temperature is a maximum temperature, and the maximum temperature is sustained for a time that is more than an order of magnitude less than a ramp time.
5 . The method as defined by claim 1 , wherein the prescribed temperature is maintained for less than 2 seconds.
6 . The method as defined by claim 1 , wherein the prescribed temperature is maintained for less than 30 seconds.
7 . The method as defined by claim 1 , wherein the ramp rate is between about 150° C. per minute and less than about 500° C. per minute.
8 . The method as defined by claim 1 , wherein the prescribed temperature is between about 1,750° C. and about 2,100° C.
9 . The method as defined by claim 1 , further comprising positioning a plurality of diamonds within the chamber; and
simultaneously heating the plurality of diamonds using the given ramp rate to achieve substantial thermal uniformity for each of the diamonds at the prescribed temperature.
10 . The method as defined by claim 9 , wherein the plurality of diamonds includes at least 50 diamonds.
11 . The method as defined by claim 1 , wherein the prescribed gas environment includes hydrogen.
12 . The method as defined by claim 1 , wherein the prescribed gas environment includes argon and/or nitrogen.
13 . The method as defined by claim 1 , wherein the gas environment is less than 1 ppm.
14 . The method as defined by claim 1 , wherein the partial pressure of oxygen in the chamber is less than 10 milliTorr.
15 . The method as defined by claim 1 , wherein a plurality of diamonds are maintained at substantially the same temperature.
16 . A method of annealing a plurality of diamonds, the method comprising:
providing a furnace having a chamber, the furnace having a radiative heating element configured to radiatively heat a diamond;
positioning the plurality of diamonds within the chamber;
modulating levels of a gas within the chamber to achieve a prescribed pressure;
producing a hot zone within the chamber using the radiative heating element, the hot zone reaching a prescribed temperature using a given heating ramp rate, the hot zone defining a volume configured to encompass the plurality of the diamonds, the hot zone having a thermal variance of less than 3% of a maximum temperature of the hot zone;
the given ramp rate being between about 60° C. per minute and about 800° C. per minute,
the prescribed temperature being between about 1,350° C. and about 2,200° C.;
the prescribed pressure being between 1×10{circumflex over ( )}−9 Torr and about 550 Torr.
17 . The method as defined by claim 16 , further comprising heating the diamonds in the hot zone.
18 . The method as defined by claim 16 , wherein the plurality of diamonds are grown in the chamber.
19 . The method as defined by claim 16 , wherein the prescribed temperature and/or the prescribed pressure varies during the process.
20 . The method as defined by claim 16 , wherein the uniform hot zone has a width of between about 3 inches and about 5 inches, and a height of between about 3 inches and about 7 inches.
21 . A method of reducing undesirable coloration in a diamond, the method comprising:
providing a diamond having a discoloration; and
annealing the diamond in a furnace having a chamber at a pressure of between about 40 Torr and about 550 Torr, wherein the diamond is radiatively heated to a maximum temperature of between about 1,350° C. and about 2,200° C., so as to reduce the discoloration.
22 . The method as defined by claim 21 , further comprising:
positioning the diamond having the discoloration in an annealing chamber.
23 . The method as defined by claim 21 , wherein the annealing takes place in the diamond growth chamber.
24 . The method as defined by claim 21 , wherein the maximum temperature is achieved for less than a second.
25 . The method as defined by claim 21 , wherein a heating ramp rate is between about 150° C. and about 800° C.
26 . The method as defined by claim 21 , wherein the annealing occurs in the presence of hydrogen and/or an inert gas.
27 . A furnace for heating the diamonds, the furnace comprising:
a hermetically sealed chamber;
a growth stage in the hermetically sealed chamber, the growth stage configured to hold a plurality of diamonds;
a radiative heating element, the radiative heating element configured to radiatively heat the plurality of diamonds to prescribed temperatures of between about 1,350° C. and less than about 2,200° C., the radiative heating element further configured to having a heating ramp rate of about 60° C. per minute and less than about 800° C. per minute when heating in, or to, the prescribed temperature range;
a pressure modulation system configured to adjust a pressure within the chamber, the pressure modulation system configured to adjust the pressure within the chamber from between about 1×10{circumflex over ( )}−9 Torr and less than about 550 Torr.
28 . The furnace as defined by claim 27 , further comprising a gas input and a gas output.
29 . The method as defined by claim 1 , wherein the annealing process results in less than 1% loss of diamond by weight due to graphitization.