Connected heat conducting structures in solid ammonia storage systems
A compacted block of material constructed of one or more units consisting of matter comprising an ammonia-saturated material capable of reversibly desorbing and ad- or absorbing ammonia surrounded by a gas-permeable, flexible material having a thermal conductivity of at least five times the thermal conductivity of said ammonia-saturated material at −70° C. to 250° C. and methods for producing the same are described.
1. A compacted block of material constructed of at least one unit comprising matter that comprises an ammonia-saturated material capable of reversibly desorbing and ad- or absorbing ammonia, each of which at least one unit is surrounded by a gas-permeable enclosure made of a flexible material in the form of a film or foil, which forms a completely interconnected set of closed surfaces acting as heat transfer structures and has a thermal conductivity of at least five times the thermal conductivity of said ammonia-saturated material at −70° C. to 250° C.
2. The compacted block of material of claim 1 , wherein said one or more units, in addition to said ammonia-saturated material, contain one or more secondary units identical to the units of claim 1 except for being smaller.
3. The compacted block of material of claim 1 , which has been compacted by means of a pressure of at least 5 MPa.
4. The compacted block of material of claim 3 , wherein said compacted block of material is self-supporting.
5. The compacted block of material of claim 4 , wherein said compacted block of material is contained in a container which optionally may be heated.
6. The compacted block of material of claim 5 , wherein said gas-permeable enclosure made of a flexible material in the form of a film or foil comprises 0.1 to 20 mass % of the mass of the compacted block.
7. The compacted block of material of claim 1 , wherein said compacted block of material is contained in a container which optionally may be heated.
8. The compacted block of material of claim 1 , wherein said ammonia-saturated material is selected from a metal ammine complex salt of the formula M a (NH 3 ) n X z , wherein M is one or more cations selected from the group consisting of alkali metals, alkaline earth metals, and transition metals and combinations thereof; X is one or more anions selected from the group consisting of fluoride, chloride, bromide, iodide, nitrate, thiocyanate, sulphate, molybdate, and phosphate ions; a is the number of cations per salt molecule; z is the number of anions per salt molecule; and n is the coordination number of 2 to 12.
9. The compacted block of material of claim 8 , wherein the ammonia-saturated material is chosen from Mg(NH 3 ) 6 Cl 2 , Ca(NH 3 ) 8 Cl 2 , Mn(NH 3 ) 6 Cl 2 and Sr(NH 3 ) 8 Cl 2 or any mixture thereof.
10. The compacted block of material of claim 8 , which has been compacted to such a degree that the density of the ammonia-saturated material is at least 70% of its maximum density at normal temperature and pressure.
11. The compacted block of material of claim 1 , wherein the thermal conductivity of said gas-permeable enclosure made of a flexible material in the form of a film or foil is at least ten times the thermal conductivity of said ammonia-saturated material.
12. The compacted block of material of claim 1 , wherein said gas-permeable enclosure made of a flexible material in the form of a film or foil is selected from metal, metal alloys, graphite, composite materials, modified plastics, modified rubber and any mixture thereof.
13. The compacted block of material of claim 12 , wherein said gas-permeable enclosure made of a flexible material in the form of a film or foil is selected from aluminum or an aluminium alloy.
14. The compacted block of material of claim 1 , wherein the units of the compacted block of material have a shape so that at least 60% of the total surface area of said gas-permeable enclosure made of a flexible material in the form of a film or foil is parallel within ±20° to the desired direction of heat transport.
15. A method of producing the compacted block of material of claim 1 comprising:
wrapping said matter comprising an ammonia-saturated material capable of reversibly ad- or absorbing and desorbing ammonia into a gas-permeable, flexible material having a thermal conductivity of at least five times the thermal conductivity of said ammonia-saturated material at −70° C. to 250° C. so that one or more units of wrapped matter are provided, and compressing said one or more units are placed in a container or mold having one or two opposite open end(s) and optionally one or more removable walls and said external pressure is exerted uni-axial through the open end(s), optionally via a plate.
16. A method of producing the compacted block of material of claim 1 comprising:
wrapping matter comprising an ammonia-depleted material capable of reversibly ad- or absorbing and desorbing ammonia into a gas-permeable, flexible material having a thermal conductivity of at least five times the thermal conductivity of said ammonia-saturated material at −70° C. to 250° C. so that one or more units of wrapped matter are provided,
filling the one or more units into a container, such that the unit(s) are immobilized in the container, and
treating the ammonia-depleted material capable of reversibly ad- or absorbing and desorbing ammonia with ammonia, thereby saturating and compacting the material capable of reversibly ad- or absorbing and desorbing ammonia.
17. The compacted block of material of claim 1 , wherein the units of the compacted block of material have a shape so that at least 80% of the total surface area of said gas-permeable enclosure made of a flexible material is parallel within ±10° to the desired direction of heat transport.