Patent Application
20110154832
The magnetocaloric effect is a phenomenon whereby, for appropriately chosen materials (referred to as “magnetocaloric materials”), a change in the temperature of the material can be induced by exposing the material to a changing magnetic field. Specifically, increasing the magnitude of an externally applied magnetic field orders the magnetic moments within the material, increasing the temperature via the magnetocaloric effect. Conversely, decreasing the magnitude of the externally applied magnetic field disorders the magnetic moments within the material, reducing temperature via the magnetocaloric effect.
In one aspect, a composition is provided. The composition can include a substantially contiguous second material interspersed with a granular first material. For example, the contiguous second material can be configured so as to bind together the granular first material. The granular first material may constitutes less than or equal to about 50 volume percent of the composition.
The granular first material may have granules with diameters less than or equal to about 500 μm, may have a melting temperature greater than or equal to about 400° C., and may exhibit a strain to failure of less than 1% at room temperature. In one embodiment, the granular first material may include magnetocaloric material. The second material can have a melting temperature less than or equal to about 1500° C.
In another aspect, a method is provided, which method includes providing a granular first material (e.g., a magnetocaloric material) and a sinterable second material. In some embodiments, the granular first material may be exposed to an isotropic chemical etchant. The granular first material and the sinterable second material can be combined to form an aggregate. In one embodiment, the sinterable second material may be granular, and the granular first and second materials can be mixed to form the aggregate. In another embodiment, the sinterable second material can be provided as a second material source and coated onto the granular first material.
Once the aggregate has been formed, localized sintering of the aggregate can be performed, for example, such that, subsequent to localized sintering, the second material is substantially contiguous and binds the granular first material. The localized sintering of the aggregate can be via a heating using a source such as, for example, a laser, a microwave radiation source, a radio frequency radiation source, an infrared radiation source, and/or an ultraviolet radiation source.
The aggregate can be incorporated into a regenerator. Where the first material includes magnetocaloric material, a magnetic field generating component can be provided, the magnetic field generating component being configured to vary a magnetic field to which the magnetocaloric material is exposed. A working fluid can be directed along the regenerator so as to exchange thermal energy (“heat”) with the magnetocaloric material.
In yet another aspect, an apparatus is provided. The apparatus can include a regenerator including a contiguous second material interspersed with and binding together a granular magnetocaloric material. A magnetic field generating component can be configured to vary a magnetic field to which the magnetocaloric material is exposed. A working fluid can be directed along the regenerator so as to exchange heat with the magnetocaloric material.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Example embodiments of the present invention are described below in detail with reference to the accompanying drawings, where the same reference numerals denote the same parts throughout the drawings. Some of these embodiments may address the above and other needs.
Referring to
A substantially contiguous second material 104 may be interspersed with the granular first material 102, for example, so as to bind together the granular first material. While the second material 104 may fill much of the volume between granules of the first material 102, the second material may also define voids 106 therein. Other voids 106 may exist between granules of the first material 102 and/or between the first and second materials. The second material 104 can include a metal, and can have a melting temperature less than or equal to about 1500° C. Examples of candidate second materials include, for example, gold, silver, copper, and/or certain alloys of nickel (e.g., nickel-50 atomic percent iron, nickel-bronze).
The composition 100 can also include a third material 108, which may also be granular. The third material may have properties consistent with either of the first or second materials 102, 104.
The second material 104 may be interspersed with the granular first material 102, in a variety of ways that allow the second material to bind together the first material. For example, still referring to
Referring to
Finally, localized sintering of the aggregate 210 can be performed (
The energy source 212 can be any component capable of producing an energetic beam capable of imparting sufficient energy to the second material 204 to cause sintering thereof and capable of imparting that energy in a localized area, such that second material outside the localized area would not receive sufficient energy to induce sintering. Examples of possible energy sources include, but are not limited to, a laser, a microwave radiation source, a radio frequency (RF) radiation source, an infrared radiation source, an ultraviolet radiation source, an electron beam source, and an ion beam source. In each case, the emitted energetic radiation/particles that form the energetic beam E may be focused onto a localized area, for example, with one or more appropriately chosen lenses.
The granular first material 202 can have a melting temperature greater than or equal to about 400° C., while the sinterable second material 204 can have a melting temperature less than or equal to about 1100° C. Further, the first and second materials 202, 204 can be chosen such that the energy imparted by the energy source 212 acts to induce sintering in the latter but not in the former. For example, the first material 202 may be chosen to have a melting temperature higher than that of the second material 204. In one example, the granular first material 202 can be an intermetallic, while the second material 204 can be gold.
As mentioned above, the granules of the first material 202 can be any shape. The granules of the second material 204 may also be any shape. In some embodiments, the sintering process may be facilitated through the use of a first material 202 and/or a second material 204 having granules with generally regular surface profiles, such that the surfaces of the granules lack asperities, protrusions, sharp indentations, etc. (other than nanometer and/or atomic level roughness). For example, this may allow the granules to flow past one another more readily, thereby helping to avoid instances of unusually low density and/or voids in the final sintered composition. In order to produce granules having a sufficiently smooth surface, the granules may be subjected to an isotropic chemical etch, which will tend to preferentially etch more pronounced surface features. Alternately, such regular granule surface profile can be achieved by producing the granules by atomization process.
Referring to
Subsequent to coating of the second material 304 onto the first material 302, localized sintering of the aggregate 310 can be performed (
The methods described above may allow for the production of components having substantially complex geometries while being composed substantially of brittle materials. Brittle materials are often difficult to work with due to the difficulty associated with forming such materials into component parts. Specifically, brittle materials are often not amenable to typical machining processes utilized in metal working processes. By utilising a granular form of the brittle material interspersed with a sinterable second material, an aggregate can produced that can be locally sintered to form parts with complex, irregular, or high aspect ratio geometries. The resultant parts can be substantially composed (say, up to about 50% by volume, and in some cases 80% or more) of the brittle material. Sufficient amounts of the second material (e.g., at least 20% by volume of the total aggregate) can be mixed with the brittle first material in order to ensure that, upon sintering, the second material forms a substantially contiguous matrix that binds the granules of the brittle material.
As an example, referring to
A working fluid 432 (e.g., water) may be directed through the hollow areas 424 and circulated between the heat regenerator 420 and a refrigerated compartment 434. A magnetic field generating component 436 (e.g., a movable permanent magnet and/or an electromagnet) can be configured to vary a magnetic field B to which the regenerator 420 is exposed, thereby causing a change in temperature of the magnetocaloric material 402 of the rod-like structures 422. As the working fluid 432 is directed through the hollow areas 424, it can exchange heat with the magnetocaloric material 402, for example, cooling the working fluid. Thereafter, the cooled working fluid 432 can move into thermal contact with the refrigerated compartment 434 to receive heat therefrom.
In order to enhance the thermal performance of the magnetic refrigeration system 430, efficient thermal contact may be facilitated between the working fluid 432 in the hollow areas 424 and the magnetocaloric material 402 in the rod-like structures 422. It may therefore be desirable to increase the length L of the rod-like structures 422 and/or decrease the diameter d. However, magnetocaloric materials often tend to be somewhat brittle, and therefore may be difficult to form into complex shapes such as the rod-like structures 422 (or other similarly high surface area geometries). As a further complication, many magnetocaloric materials tend to have relatively high melting temperatures and/or may be prone to oxidation at high temperatures, thereby further reducing the options for manufacturing components of magnetocaloric materials.
The above limitations notwithstanding, the methods disclosed herein may allow for the production of the regenerator 420 with rod-like structures 422 with lengths L of about 5 mm and diameters d of about 500 μm. The rod-like structures 422 may include, for example, a granular gadolinium-based magnetocaloric material 402, the granules of which are coated with, say, nickel-50 atomic percent iron (Ni-50 Fe) 404. At the peripheries of the rod-like structures 422 (see
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. For example, while the above has described compositions including a granular first material bound together by a second material, in some embodiments, the second material may be excluded, and the granules of the granular first material may be sintered directly together. This can be accomplished, for example, by supplying a higher amount of energy to the granules than may have otherwise been required in order to induce sintering in the “sinterable” second material. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
