Latent heat storage material and process for manufacture of the latent heat storage material

#1. Field

#A latent heat storage material and a process for the preparation of the latent heat storage material. More specifically, treating a mixture of expanded graphite material and a first phase change material with at least one second phase change material wherein the first and second phase change materials are immiscible to form a latent heat storage material.

#2. Background

#FIG. 1 shows a storage system including a latent heat storage material in accordance with one embodiment.

#FIG. 2 is a flow chart illustrating a method of forming a latent heat storage material in accordance with one embodiment.

#FIG. 3 is a differential scanning calorimetry graph (DSC-graph) of a latent heat storage material prepared according to an embodiment.

#Processes for the production of expanded graphite are known from, for example, sources such as U.S. Pat. No. 3,404,061. A starting material may be flaky natural graphite or synthetic graphite. The graphite flakes of the starting material are treated with a solution of an intercalating agent, for example, with a mixture of concentrated sulfuric acid and nitric acid, with fuming nitric acid or with a mixture of hydrogen peroxide and concentrated sulfuric acid, resulting in the formation of a graphite salt or a similar graphite intercalation compound. Further intercalation agents are contemplated and known in the art.

#U.S. Pat. No. 6,645,456 discloses an intercalation mixture formed of at least one strong concentrated acid selected from the group including sulfuric acid and nitric acid, an oxidizing agent selected from the group including concentrated nitric acid, hydrogen peroxide and peroxo sulfuric acid for oxidizing the graphite, and a thermal polyphosphoric acid. The graphite-intercalation compounds or graphite salts, for example, graphite hydrogen sulfate or graphite nitrate, are heated in a shock-like manner. Upon heating, the volume of the graphite significantly increases. The obtained expanded graphite comprises concertina-shaped bulky aggregates.

#It is appreciated that the components described above may be combined by adding both particles of expanded graphite material and particles obtained by shredding a planar web formed by compression of expanded graphite material into fragments, to the phase change material. The bulky concertina-shaped particles of the expanded graphite are generally difficult to handle and tend to be difficult to mix with a phase change material. To overcome this problem, the expanded graphite particles prepared by the expansion process described above may be compressed into a planar foil-like web that is cut (shredded) into fragments resulting in pieces having an average diameter between about 5 microns (μm) and about 20 millimeters (mm), and in some embodiments between about 50 μm and about 5 mm. Particles prepared in this manner can be readily mixed with a phase change material. Shredding of the graphite foil can be done in a cutting mill, a jet mill or other suitable mill. The term “expanded graphite material” as used herein includes various forms of graphite, including expanded graphite and graphite particles obtained by shredding compressed structures of expanded graphite.