Heater for retrograde solvothermal crystal growth, method of making, and method of use
An apparatus for solvothermal crystal growth includes a vertically oriented cylindrical pressure vessel defining a growth chamber, and a cylindrical heater having independently controllable upper and lower heating zones. At least one end heater is positioned adjacent to an end of the growth chamber. A baffle may be disposed within the chamber such that an inward-facing surface of the baffle is within 100 mm of a top or bottom end surface of the chamber. The end heater is configured to control temperature uniformity during crystal growth such that temperature variation along a radial distance of a cylindrical surface within the pressure vessel is less than about 10° C., and temperature variation along an inner diameter surface of the growth chamber is less than about 20° C. within an axial distance of at least 100 mm from the proximate chamber end.
1 . An apparatus for solvothermal crystal growth, the apparatus comprising:
a pressure vessel having a cylindrical shaped portion having a vertical orientation and extending between a top end and a bottom end, wherein the pressure vessel is configured to process a material in a fluid at a pressure above about 5 megapascal and less than about 2000 megapascal and temperatures above about 200 degrees Celsius and less than about 1500 degrees Celsius;
a cylindrical heater having an upper zone and a lower zone that are each disposed around the cylindrical shaped portion;
a growth chamber having a bottom end surface, a cylindrical shape, and positioned within the cylindrical shaped portion of the pressure vessel;
a bottom insulating member below the bottom end surface; and
at least one bottom end heater, positioned between the bottom end surface and the bottom insulating member, wherein the bottom end heater includes a center, an outer radius that extends from the center, an inner region with an inner radius that extends from the center, an outer region between the inner radius and an outer radius, a ratio of the inner radius to the outer radius is at least about 3%, and is configured to provide a varying power density within the bottom end heater whereby a power density within the inner region that is at least 25% less than a power density in the outer region, wherein
the varying power density within the bottom end heater is provided by at least one of a heating element having a larger cross section, in a direction perpendicular to electrical current flow, within the inner region than within the outer region, a heating element wherein a spacing between adjacent segments is larger within the inner region than within the outer region, or at least two independently-controllable hot zones.
2 . The apparatus of claim 1 , wherein the bottom end surface of the growth chamber includes a bottom radial distance, the growth chamber includes an inner diameter with a bottom axial distance that intersects with the bottom end surface, and the bottom end heater is configured to enable:
a variation in a temperature along the bottom radial distance of the bottom end surface to be less than about 10 degrees Celsius, during a crystal growth process; and
a variation in a temperature along the bottom axial distance of at least 100 millimeters along the inner diameter of the growth chamber to be less than about 20 degrees Celsius, during the crystal growth process.
3 . The apparatus of claim 2 , wherein the at least one bottom end heater and the cylindrical heater are further configured to provide a temperature variation along the bottom axial distance of about 10 degrees Celsius or less, during a crystal growth process.
4 . The apparatus of claim 3 , wherein the at least one end bottom heater and the cylindrical heater are further configured to provide a temperature variation along the bottom axial distance of about 5 degrees Celsius or less, during a crystal growth process.
5 . The apparatus of claim 2 , wherein the bottom axial distance comprises a cylindrical portion of the inner diameter of the growth chamber within an axial distance of at least 200 millimeters of the bottom end surface.
6 . The apparatus of claim 2 , wherein the variation in the temperature along the bottom radial distance is less than about 5 degrees Celsius.
7 . The apparatus of claim 1 , wherein the pressure vessel comprises an autoclave.
8 . The apparatus of claim 1 , wherein the pressure vessel is internally heated.
9 . The apparatus of claim 1 , wherein the at least one end heater provides a power density that is azimuthally uniform to within 20%.
10 . The apparatus of claim 1 , wherein a power density in the lower zone of the cylindrical heater has a power density variation that is less than about 20% within 100 mm of the bottom end surface of the growth chamber.
11 . The apparatus of claim 1 , further including a third radius that is positioned between the inner radius and the outer radius and the outer region has a power density that increases, as a function of radius, between the inner radius and the third radius.
12 . The apparatus of claim 1 , wherein the end heater comprises a heating element member having a configuration chosen from one or more of a spiral, a double spiral, a serpentine, or a labyrinthine structure.
13 . The apparatus of claim 1 , wherein the end heater comprises a jacket that is configured to support at least one heating element within the at least one end heater, the jacket comprising one or more of stainless steel, Inconel 718, Inconel 600, iron, nickel, molybdenum, titanium, and tantalum, and alloys thereof.
14 . The apparatus of claim 1 , wherein the end heater comprises at least two independently-controllable hot zones.
15 . The apparatus of claim 1 , wherein the growth chamber includes a top end surface with a top radial distance, an inner diameter with a top axial distance that intersects with the top end surface, and the apparatus further comprising a top insulating member, one of a top end heater or a top combination insulator and heater, wherein the top end heater or combination insulator and heater is positioned between the top end surface of the growth chamber and the top insulating member and configured to enable:
a variation in a temperature along the top radial distance of the top end surface to be less than about 10 degrees Celsius, during a crystal growth process; and
a variation in a temperature along the top axial distance of at least 100 millimeters from the top end of surface to be less than about 20 degrees Celsius, during a crystal growth process.
16 . The apparatus of claim 15 , wherein a variation in temperature along the top radial distance is less than about 5 degrees Celsius.
17 . The apparatus of claim 15 , wherein the top end heater or the top combination insulator and heater and the cylindrical heater are further configured to enable a temperature distribution along the top axial distance to be constant, to within about 10 degrees Celsius, during the crystal growth process.
18 . The apparatus of claim 15 , wherein the pressure vessel comprises an autoclave and the top combination insulator and heater includes capability to generate heat.