Development of a copper matrix composite reinforced with graphene

and analysis of its thermal conductivity

Università degli studi di Roma Tor VergataTecnun Universidad de Navarra

Laurea Magistrale in Ingegneria Meccanica

Under the supervision of

Prof. Maria Elisa Tata

Dr. Nerea Ordas

Ing. Girolamo Costanza

Presented by

Stefano Mascellino

Objective

Background knowledge

Experimental procedure

Results

Conclusions

Future work

TABLE OF CONTENTS

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

OBJECTIVEDevelopment of a copper matrix composite reinforced with

graphene oxides and analysis of its thermal conductivity

STEPS

1. Dispersion of graphene oxides in copper matrix

2. Reduction of interface resistance by introducing a third phase element

3. Microstructural analysis of the composite

4. Analysis of thermal conductivity

5. Comparison of results

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

BACKGROUNDHighly conductive materials

• Many engineering applications require high thermal conductivity

• Increasing calculation capacities of electronic devices induce heat dissipation issues

• Most common material used when high thermal performances are required is copper

• New materials are under investigation to ensure high thermal conductivity and low CTE

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Graphene oxidesGraphene oxides are produced from graphite. Oxides are generally reduced to obtain reduced graphene oxide. The process is as follows:

• strong oxidation of graphite with H2SO4 and KMn04 solutions in water

• exfoliation of oxidized graphite and separation of exfoliated fraction• reduction with hydrazine or green agents• desiccation

rGO, reduced graphene oxide: in the form of powder between 40 and 70µm in size.

dGO, dried graphene oxide: in the form of flakes 2÷5mm x 5÷10mm, tens of µm thick , being desiccated on a support, cut and carbonized at 1100ºC.

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

EXPERIMENTAL PROCEDUREPowder selection

Mixing and mechanical alloying

Hot press

Grinding and polishing

Microstructural and thermal analysis

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Laser flash analysisIn laser flash technique a laser pulse hits one face of the sample and a detector on the front reveals the increase in temperature. The variation of temperature is described by the equation:

where and with Parker’s approximation: .

• Radial distance between the section of incident laser pulse and the section of detection allows the measurement of in plane thermal conductivity

• Thickness of the sample should be thin to reduce the error

RESULTSSummary of samples1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Pure copper samples

Copper – chromium samples

Cu – Cr – rGO samples

Cu – Cr – dGO samples

Graphitized graphite samples

Pure copper samples1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

• The grade of compaction achieved is above 95%.

• Reduced powder has an oxygen content of 250ppm, while unreduced reaches 900 ppm.

• Thermal conductivity of reduced Cu sample is 20% higher compared to unreduced Cu: oxygen is detrimental to thermal properties.

• Maximum values are 9% lower than those of bulk copper.

• Reduced copper• Unreduced copper

Copper – chromium samples1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

• Chromium is needed to create an

interphase between copper and carbon.

• Samples produced to verify the solubility

of chromium in copper lattice.

• Solubility of chromium: 0.7% wt. at HP

temperature, 0.2% at room temperature

3 percentages chosen: 1% wt., 0.15%

and 0.5%.

• Reduced Cr powder used to decrease

the oxygen content.

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

MicrostructureCu 1% Cr

Cu 0.15% Cr Cu 0.5% Cr

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Thermal conductivity Cu-Cr samples

Cr adding is detrimental to thermal conductivity of copper due to lattice distortion

Differences between 0.15% wt. Cr and 0.5% are limited

• reduced Cu• 0.15% Cr• 0.5% Cr• 1% Cr 20’ MA• 1% Cr 10’ MA• 1% Cr annealed

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Cu – Cr – rGO samples• Chromium is needed to create an interphase between copper and

carbon, 0.15% and 0.5% wt..• rGO in the shape of a powder distribution between 40 and 70µm.

• 2% wt. rGO alloyed in SPEX with Cu and Cr for 20’.

• Production of annealed samples.

MicrostructureCu 0.15% Cr 2%rGO

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work0.5% Cr Ann.980°C, 30’ Structure of rGO

Cu 0.5% Cr 2%rGO

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Thermal conductivity Cu – Cr - rGO samples• 0.5 Cr 2rGO ann.• 0.15 Cr 2rGO ann.• 0.15 Cr 2rGO• 0.5 Cr 2rGO

• rGO addition is lowering thermal conductivity: this is due to impurities and disordered structure

• Annealing changes the trend of the curves

• Cr is effective on reducing the interface resistance

best specimen: annealed 0.5%Cr

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Cu – Cr – dGO samples

MicrostructureCu0.5%Cr, 2% dGO. Turbula 60’

• Chromium is needed to create an interphase between copper and carbon, 0.5% wt..

• dGO in the shape of flakes: 2÷5mm x 5÷10mm, tens of µm thick .

• 2% wt. dGO alloyed in turbula with balls. Different milling times: 60’, 30’, 5’.

• Production of annealed samples.

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Turbula 30’ Turbula 5’

Effects of annealing: 980°C, 60’

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Thermal conductivity Cu – Cr - dGO samples• reduced Cu• Turbula 30’• Turbula 5’• Turbula 60’

• Annealed samples not analyzed due to voids caused by gas formation

• Results are worse than using rGO: more difficult dispersion in the matrix

• Better performances for sample treated 30’ in Turbula

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Graphitized graphite samples• Graphene oxides substituted with graphitized

graphite

• Graphitization removes impurity in graphite structure

• Graphite particles are big, it is difficult to obtain a homogeneous distribution in the matrix

• Samples produced with graphitized graphite and Ni

• Ni substitutes Cr since it has a lower affinity with oxigen

• Ni has a complete solubility in copper lattice; 0.5% and 1% chosen

Samples with nickel

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

Thermal conductivity of graphitized graphite samples

• reduced Cu• 0.5% Cr 2% G1 graph.• 0.5% Ni 2% G1 graph.• 1% Ni 2% G1 graph.

• Annealed samples not analyzed due to voids caused by gas formation

• Results are worse than using rGO: more difficult dispersion in the matrix

• Ni is not effective in covering graphite particles

1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

CONCLUSIONS1. A very limited addition of chromium is responsible for a

sensible decrease in conductivity figures

2. rGO gives always worse results compared to pure copper

• structure is not ordered

• impurities are present

3. dGO has similar problems to rGO

• absence of microstructural long-range order

• presence of impurities: among them traces of volatiles

4. Graphitized graphite leads to higher thermal conductivities compared to graphene oxides

5. Ni is not effective in covering graphite particles

FUTURE WORK1. Objective

2. Background

3. Experimental procedures

4. Results

5. Conclusions

6. Future work

High heat conductive materials are of increasing interest: future work could be dedicated to investigate reinforcement to improve the very good thermal conductivity of copper.

Some of the routes that could be analyzed are:

1. use nano-crystalline diamond dispersed in a copper matrix through a powder metallurgy route

2. reengineer the process of reinforcing copper with GOs

• electroless coat graphene oxide particles with Cr

• substituting Cr with other elements (Ti, Mo, W)