Field of Invention

[0001] The present invention relates to a process for preparing aluminum- graphene composite material for an enhancement of thermal conductivity property. The invention further relates to the process for preparation of higher thermally conducting aluminium-graphene composite material, by melting- casting process using aluminium and nano size graphene or reduced graphene oxide (rGO).

Background of Invention

[0002] US20130000952A1 relates to a film of a conductive ceramic. Additives are at least partially incorporated into the film. The additives are at least one of electrically conductive and semiconducting and at least one of the additives has an aspect ratio of at least 3.

[0003] Whereas the present invention is not related to a transparent electrical conductor, its opaque material gives very high thermal conductivity. Further, the present invention is different as it is focusing on the process of amalgamation of aluminium either in the form of a powder or in a form of a metal and reduced graphene oxide (or graphene) composite material prepared by melting followed by the casting process, for significant increase in thermal conductivity (plus 80% more than pure aluminium). The extent of enhancement of thermal conductivity is dependent on the art of the synthesis process as well as composition.

[0004] Similarly, www.elsevier.comllocatelmsea relates to aluminium graphene composites with regard to strength and hardness. The paper concludes decrease in strength and hardness by incorporating graphene in aluminium due to formation of the carbides. Whereas the present invention is contrary to the conclusion of the published paper . The referred paper published in the journal mentions formation of carbide which makes the difference as of. The present invention is a process with superior control which blocks the formation of such carbides after a similar experience during the development of such process. Furthermore, the claims relate to the enhancement of the thermal conductivity property.

[0005] The journal of Structural and Mechanical Properties of Graphene reinforced Aluminium (Al) Matrix Composites, mentions about Aluminium and graphene oxide composite and enhancement of mechanical properties. Whereas the subject invention is having a composite material of Aluminium either with reduced Graphene Oxide or with Graphene and enhancement of thermal properties. Hence, such published journal is different from that of the subject application which is focusing on Thermal conductivity property. Moreover, the published research article relating to the effect of sintering time, temperature, and graphene addition on the hardness and microstructure of aluminium composites, which is also focusing on microstructure and hardness and not on the Thermal conductivity property.

[0006] Another article, the City University of London institutional repository mentioned the process which is entirely different from the present invention. It discusses the coating of graphene over the surface of aluminium metal following ultrasonic medium and focuses on the hardness of the produced material which is not the composite material. The pre sent invention focuses on thermal conductivity prope rty as we 11 as distinct proce sses to produce composite mate rials of aluminium and graphene or reduced graphene oxide through melting and casting which is unique .

[0007] Thus, the present invention relates to the aluminium and graphene or reduced graphene oxide composite material to be produced using present novel melting and casting process to accrue the energy savings on account of the sharp rise in the thermal conductivity property by their applications.

[0008] Indian application 201831047022 relates to the process for enhancement of thermal conductivity of aluminium up to 75% by incorporating graphene of two to five layers at room temperature. Graphene with purity 99% plus was incorporated into nano size aluminium through powder sintering process at a temperature of 600-640 deg C for 30-120 minutes under inert atmosphere. Graphene powder of 0.1 to 5% weight of aluminium has been used in the process. The sintered aluminium prepared was evaluated for its thermal conductivity and compared with pristine aluminium standard. Under optimum conditions enhancement of thermal conductivity up to 75% has been observed in this process. Similarly, the Vickers hardness number (micro hardness) for Al with G sintered product has been found to be enhanced by 25-35% by using 0.1 to 0.5% graphene with aluminium.

[0009] This application is different as it is following distinct powder sintering process. The present invention relates to a process for preparing aluminum- graphene composite material, by melting-casting process using aluminium and nano size graphene or reduced graphene oxide (rGO).

Objects of the Invention

[0010] The principal object of the present invention is to prepare the aluminium graphene composite material by melting and casting process using aluminium and graphene or reduced graphene oxide.

[0011] Another object of the pre sent invention is to provide a process for preparation of aluminium graphene composite material using nano to micro size aluminium powder and graphene or reduced graphene oxide and melting them together. [0012] Another object of the pre sent invention is to provide a process for preparation of aluminium graphene composite material using molten aluminium and doping the graphene or reduced graphene oxide under special conditions.

[0013] Yet another object of the present invention is to propose a process for preparation of aluminium graphene composite material which possess a higher thermal conductivity property along with the improved micro hardness.

[0001] Yet, another object of the present invention is to provide a process for preparation of aluminium graphene composite by melting aluminium and graphene or reduced graphene oxide in the range of 700 to 950 deg C either under vacuum or inert atmosphere with the aid of dedicated salts blanketing and fluxes addition followed by casting.

SUMMARY OF THE INVENTION:

[0014] Accordingly, the present invention is a process for preparation of high thermal conducting aluminium graphene or reduced graphene oxide composite materials, through melting and casting process by doping of graphene or reduced graphene oxide into aluminium metal or powder, the process comprises the steps of: i) Doping of graphene or reduced graphene oxide nano to micro size powder around aluminium metal or its powder and charging to a controlled furnace under argon surrounding atmosphere of the charge inside the furnace at 750 to 900 deg C with or without salt and flux NaF, ii) casting the molten mass into any prefabricated shaped and sized die or mould cavity either in inert or in vacuumed or atmospheric pressured condition of the environment surrounding of it iii) cooling the temperature back to room temperature and preparing the cast composite materials to prepare the product.

[0015] The process uses the blanketing salts such as NaCl and KC1. The weight of salts used is 25% to 35% of total weight of the aluminium and graphene or reduced graphene oxide charge , and the ratio of the salts NaCl and KC1 are 70: 30. The fluxing material used is NaF of 5 % to 15% of the total weight of the aluminium and graphene or optional reduced graphene oxide charge. In this process, the time of melting varied between 60 to 120 minutes under vacuum or argon atmosphere surrounding the charge inside the furnace with the heating rate of 5 to 10° C per minute .

[0016] Further, the varying of weight percentage of graphene or reduced graphene oxide in the aluminium is from 0. 1 to 3% of the total weight of aluminium. The graphene or reduced graphene oxide powder of average size is 2 to 50 nano meter with 2 to 5 layers of higher purity. The graphene used is of 2 to 5 layers with higher purity of 70 to 99%. Further, the thermal conductivity of aluminium graphene composites is 300 to 410 Wm/K and even more with higher % of graphene.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0017] The detailed description of various exemplary embodiments of the disclosure is described herein. It should be noted that the embodiments are described herein in such details as to communicate the disclosure. However, the details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the present disclosure .

[0018] It is also to be understood that various substitutions /arrangements /permutations or combinations may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.

[0019] The terminology used herein is to describe particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including” when used herein, specify the presence of stated features, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components and/or groups thereof.

[0020] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e .g. , those defined in commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. [0021] The pre sent invention relates to the methods where aluminium graphene or reduced graphene oxide composites are prepared by: Doping of graphene or reduced graphene oxide of nano to micro size powder over and around the body of aluminium metal or aluminium powder with varied weight ratios to be kept within a ceramic container and charging them into a controlled furnace where increasing the temperature of such charge is to be carried out at a regulated manner of 5 to 10 deg C per minute and maintaining at 700 to 950 deg C for 60 to 120 minutes under vacuum or argon atmosphere with or without salt and fluxing material. Fluxing materialNaF is use d in the range of 5 % to 15% of the total weight of the aluminium and graphene or reduced graphene oxide charge and the blanketing salts used are NaCl and KC1, with the combination of 70% and 30% by their weight respectively to have total weight of such combination in the range of 25% to 35% of the total weight of the aluminium and graphene or reduced graphene oxide charge.

[0022] Then, casting the molten charge in a prefabricated die or mould cavity either in inert or in vacuumed or atmospheric pressured condition of the environment surrounding it followed by cooling the temperature back to room temperature and preparing the cast composite materials for further characterization. Casting of molten charge is carried out with or without the addition of the salt and flux.

[0023] Graphene or reduced graphene oxide doped Aluminium composites as above exhibit up to 50 to 90% higher thermal conductivity compared to the original thermal conductivity of aluminium or sintered aluminium powder. The thermal conductivity is further increased with higher % of graphene and could be controlled by controlling the layer of graphene and its weight percentage. [0024] The following process parameters were studied to synthesize the aluminium incorporated graphene composites a) Aluminium powder of different particle size studied b) Graphene of 99% purity or reduced graphene oxide of higher purity of 2 to 5 layers having average thickness of 2 to 10 nano meter c) Melting method temperature varied from the range of 750 to 950 deg C for 30 to 120 minutes with rate of heating 5 to 10 deg C per minute d) Graphene percentage varied from 0. 1 to 5 % weight range of the total weight of aluminium e) Effect of fluxing and salt percentage and inert vs atmospheric conditions during casting studied

[0025] The typical characteristics of aluminium powder and graphene used in the process are given in Table - 1 and Table - 2 respectively.

[0026] The purpose of development of an innovative material using commercial grade aluminium or aluminium powder and graphene or reduced graphene oxide and its synthesis following melting process under a set of process conditions to validate its application as highly thermally conducting material in solar thermal collector system, cooking system, conductors, heat exchangers etc. to replace the copper and other conventional materials. This will re suit the higher efficiency of the devices with cost improvement. EXAMPLES

[0027] The following examples illustrate the exact process for preparation of graphene or reduced graphene oxide doped aluminium composites:

Example- 1

[0028] Aluminium pieces with 3 weight % of graphene nano powder along with 25% salt (NaCl and KC1 in the ratio of 70:30) of the total weight of the aluminium and graphene or reduced graphene oxide charge taken in a high alumina ceramic container or alumina boat. The container with the material was charged to a furnace at 800 deg C temperature for 120 minutes with heating rate of 10 deg C per minute under argon surrounding atmosphere inside the furnace. The molten composite material was cast in the prefabricated die or mould cavity and cooled to room temperature. The cast product was analysed to have a thermal conductivity of 390 Wm/K at room temperature with micro vicker’s hardness of 55.

Example -2

[0029] Aluminium powder with 1.5 % weight of graphene nano powder of the total weight of aluminium powder was taken in an alumina container. The container with the material was charged to a furnace at 700 deg C temperature for 90 minutes with heating rate of 10 deg C per minute under argon surrounding atmosphere inside the furnace. The molten composite material was cast in the prefabricated die or mould cavity in inert atmosphere and cooled to room temperature. The product was analysed to have a thermal conductivity of 305 Wm/K at room temperature with micro vicker’s hardness of 45. Table -1

Typical Characteristics of Aluminium used

Table -2

Typical Characteristics of Graphene used Table -3

Typical Characteristics of Aluminium Graphene Composites Obtained

[0030] It will be appreciated by those skilled in the art that the pre sent invention can be embodied in other specific forms without departing from the essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.