Solar heating for thin film evaporation and directional solidification
Configurations for solar heating and processing of a material, such as a metal or metalloid, are presented. Such processing may have an end-goal of purifying the material or depositing the material as a thin film on a substrate. The use of solar heating allows these processes to occur without electricity, which may be a scarce resource on the moon. Metals and metalloids derived from lunar regolith or other impure feedstocks may lead to materials with impurities. Generally, materials, such as silicon, need to be purified before being utilized. Techniques for solar heating may be applied to purification of these materials. Purification may be achieved by melting, via solar heating, and resolidifying slowly from one direction to another using a directional solidification process.
1 . A method for solar heating and processing a material, the method comprising:
providing, via an optical assembly, a spot of concentrated sunlight onto a bulk mass of the material to i) heat the material, ii) change the phase of at least a portion of the material to a liquid phase, and iii) enable the heated, phase-changed material to leave the bulk mass of the material in response to the phase change;
varying relative positions of optical elements of the optical assembly to vary the location of the spot of concentrated sunlight on the bulk mass of the material; and
collecting at least a portion of the heated, phase-changed material leaving the bulk mass of the material in a container configured for directional solidification.
2 . The method of claim 1 , wherein the heated, phase-changed material in the liquid phase is exposed to the vacuum of the Moon while transiting from the bulk mass of the material to the container configured for directional solidification.
3 . The method of claim 1 , further comprising moving a thermal insulator panel at a bottom portion of the container configured for directional solidification to vary the rate of heat flow from the material in the liquid phase that is in the container to a cold environment of the Moon.
4 . The method of claim 1 , wherein the heated, phase-changed material forms droplets that fall through a vacuum before being collected in the container configured for directional solidification, thereby releasing volatile impurities from the droplets.
5 . The method of claim 1 , wherein the concentrated sunlight forms a spot that is rectangular, elliptical, or elongated in shape, and wherein the method further comprises cyclically moving the spot across a surface of the bulk mass of the material to provide substantially uniform heating.
6 . The method of claim 1 , wherein the optical assembly comprises at least two optical elements moveable relative to one another to vary a size of the concentrated sunlight spot on the bulk mass of the material.
7 . The method of claim 6 , wherein varying the relative positions of the optical elements varies an intensity of the concentrated sunlight on the bulk mass of the material.
8 . A method for solar heating and processing a material, the method comprising:
providing, via an optical assembly, concentrated sunlight onto a surface of a bulk mass of the material to heat and change the phase of a first portion of the material to a liquid phase;
responsive to heating and changing the phase of the first portion of the material, enabling the heated, phase-changed material to leave the bulk mass of the material;
changing relative positions of optical elements of the optical assembly to vary location and/or intensity of the concentrated sunlight on the material; and
collecting at least a part of the first portion of the material leaving the bulk mass of the material in a container configured for directional solidification.
9 . The method of claim 8 , wherein the collecting is performed in the natural vacuum environment of the Moon.
10 . The method of claim 8 , wherein the first portion of the material is exposed to the vacuum of the Moon while transiting from the bulk mass of the material to the container configured for directional solidification.
11 . The method of claim 8 , further comprising moving a thermal insulator panel to vary the rate of heat flow from the collected material in the container to a cold environment of the Moon.
12 . The method of claim 8 , wherein the container is configured for directional solidification by enabling the material in the liquid phase to solidify from a bottom portion of the container toward a top surface of the material in the liquid phase.
13 . The method of claim 8 , wherein the material includes impurities that originated from lunar regolith.
14 . The method of claim 8 , wherein the bulk mass of the material is a solid ingot or a powder.
15 . A method for solar heating and processing a material, the method comprising:
providing, via an optical assembly, concentrated sunlight onto a surface of a bulk mass of the material to heat and change the phase of at least a portion of the material to a liquid phase;
responsive to heating and changing the phase of the material to a liquid phase, enabling the liquid phase material to leave the bulk mass of the material;
collecting the liquid phase material leaving the bulk mass of the material in a container configured for directional solidification; and
moving a thermal insulator panel to vary the rate of heat flow from the collected liquid phase material in the container to a cold environment surrounding the container.
16 . The method of claim 15 , wherein the cold environment surrounding the container is a lunar environment of the Moon.
17 . The method of claim 15 , wherein the container configured for directional solidification includes a moveable thermal-insulator panel at a bottom portion of the container, and moving the thermal-insulator panel varies a rate of heat flow from the collected liquid-phase material to a cold environment surrounding the container.
18 . The method of claim 15 , further comprising coordinating variation of an intensity or location of the concentrated sunlight with movement of the thermal-insulator panel to maintain a substantially steady solidification rate of the liquid-phase material.
19 . The method of claim 15 , wherein the optical assembly includes an optical shutter operable to intermittently block and unblock concentrated sunlight incident on the material.