ENHANCEMENT OF THERMAL CONDUCTIVITY OF ALUMINIUM BY DOPING GRAPHENE FOLLOWED BY MELTING AND CASTING PROCESS

Abstract

The present invention relates to the process for enhancement of thermal conductivity property of aluminium up to 50 to 90% or more by doping graphene or reduced graphene of two to five layers into aluminium by melting and casting process under inert or vacuum or atmospheric condition using salt and flux. Graphene with purity of 70 to 90% was incorporated into aluminium of any form for 30 to 120 minutes under inert atmosphere or vacuum at 700-900 deg C. Graphene of 0.1 to 5% weight of the total weight of aluminium has been used in the process. Under optimum conditions enhancement of thermal conductivity up to 80 to 90% has been observed using this process.

Claims

1. 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 of any form, the process comprises the steps of: i) doping of graphene or reduced graphene oxide nano to micro size around aluminium metal and charging to a controlled furnace under argon surrounding atmosphere of the charge inside the furnace at 700 to 900 deg C. to melt the mass 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 using salt and flux. iii) cooling the temperature back to room temperature and preparing the cast composite materials to prepare the product; wherein the weight of salts is 25% to 35% of total weight of the aluminium and graphene or reduced graphene oxide charge.

2. The process as claimed in claim 1 where in the blanketing salts used are NaCl and KCl and flux used was NaF under atmospheric condition.

3. The process as claimed in claim 1 wherein the ratio of the salts NaCl and KCl are 70:30.

4. The process as claimed in claim 1 where in the fluxing material used is NaF of 5% to 15% of the total weight of the aluminium and graphene or reduced graphene oxide charge.

5. The process as claimed in claim 1 wherein 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.

6. The process as claimed in claim 1 wherein the varying of weight percentage of graphene or reduced graphene oxide in the aluminium is from 0.1 to 5% of the total weight of aluminium.

7. The process as claimed in claim 1 wherein the graphene or reduced graphene oxide of average size is 2 to 50 nano meters with 2 to 5 layers of higher purity.

8. The process as claimed in claim 1, wherein the graphene is of 2 to 5 layers with higher purity of 70 to 99%.

9. The process as claimed in claim 1, wherein the thermal conductivity of aluminium graphene composites is enhanced to 300 to 410 W/mK and it increases with higher weight % of graphene.

Description

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0022] 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.

[0023] 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.

[0024] 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 comprise, 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.

[0025] 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 meaning that 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.

[0026] The present 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 over and around the body of aluminium metal of any form 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 900 deg C. for 60 to 120 minutes under vacuum or argon atmosphere with or without salt and fluxing material. Fluxing material NaF is used 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 KCl, 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. Salt and Flux are used to avoid inert or vacuum medium.

[0027] Then, casting the molten charge in a prefabricated die or mould cavity either in inert or in vacuumed or atmospheric pressured condition (using salt) followed by cooling the temperature back to room temperature and preparing the cast composite materials for further characterization. Casting of molten charge can be carried out with or without the addition of the salt and flux.

[0028] 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. The thermal conductivity is further increased with higher percentage of graphene and could be controlled by controlling the layer of graphene and its weight percentage.

[0029] The following process parameters were studied to synthesize the aluminium incorporated graphene composites [0030] a) studied about primary available aluminium metal and commercially available aluminium [0031] b) Graphene of 99% purity or reduced graphene oxide of higher purity of 2 to 5 layers having average thickness of 2 to10 nano meter [0032] c) Melting method temperature varied from the range of 700 to 900 deg C. for 30 to 120 minutes with rate of heating 5 to 10 deg C. per minute. [0033] d) Graphene percentage varied from 0.1 to 5% weight range of the total weight of aluminium [0034] e) studied the effect of fluxing and salt percentage and inert/atmospheric

[0035] The typical characteristics of aluminium and graphene used in the process are given in Table-1 and Table-2 respectively.

[0036] The purpose of development of an innovative material using commercial grade aluminium or aluminium of different grain sizes and graphene or reduced graphene oxide and its synthesis following melting process and innovative casting 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 result the higher efficiency of the devices with cost improvement.

EXAMPLES

[0037] The following examples illustrate the exact process for preparation of graphene or reduced graphene oxide doped aluminium composites:

Example-1

[0038] Aluminium pieces with 3 weight % of graphene nano sizes along with 25% salt (NaCl and KCl 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 analyzed to have a thermal conductivity of 390 W/mK at room temperature with micro vicker's hardness of 55.

Example-2

[0039] Aluminium with 1.5% weight of graphene of 3-layer size of the total weight of aluminium 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 to the mould in inert atmosphere and cooled to room temperature. The product was analysed to have a thermal conductivity of 305 W/mK at room temperature with micro vicker's hardness of 45.

TABLE-US-00001 TABLE 1 Typical Characteristics of Aluminium used Parameters Value Purity 99.5% Si <0.15% Fe <0.35% Melting Point 660 deg C.

TABLE-US-00002 TABLE 2 Typical Characteristics of Graphene used Parameters Value Bulk density 0.08 g/cc Diameter Average X &Y Dimensions <5 micron Thickness Average Z Dimension 2-5 nm Carbon Purity >99% Number of Layers Average, 2-5 Pore size 0.34 nm-2 nm Carbon ash <0.001% pH 7 Surface Area 330 m.sup.2/g

TABLE-US-00003 TABLE 3 Typical Characteristics of Aluminium Graphene Composites Obtained Properties Value Quantitative distribution Well distribution over the scan of Al and Graphene in the areas as evidenced from EDAX, composite materials EPMA and Raman mapping Electrical conductivity of Al- In the order of 10.sup.7 S/m Graphene composite devices Thermal conductivity of Al- Graphene doped into the Graphene composite products aluminium resulted into the enhanced thermal conductivity of the range from 200 to 400 W/mK with 0.25 to 3% by weight of the total weight of aluminium. The thermal conductivity depends on the quality of graphene or reduced graphene oxide, its weight % and purity of aluminium as thermal conductivity increases with higher % of graphene beyond 3%. Micro-Hardness 45 to 56 VHN (Vickers Hardness Number)

[0040] It will be appreciated by those skilled in the art that the present 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.