Development, microstructural and thermal conductivity analysis of a copper matrix composite reinforced with commercial graphene oxides

1. Development of a copper matrix composite
reinforced with graphene and analysis of its
thermal conductivity
Università degli studi di Roma Tor Vergata
Tecnun 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

2. Objective
Background knowledge
Experimental procedure
Results
Conclusions
Future work
TABLE OF CONTENTS

3. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
OBJECTIVE
Development 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

4. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
BACKGROUND
Highly 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

5. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
Graphene oxides
Graphene 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.

6. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
EXPERIMENTAL PROCEDURE
Powder selection
Mixing and mechanical alloying
Hot press
Grinding and polishing
Microstructural and thermal analysis

7. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
Laser flash analysis
In 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:
𝑉 𝑡 =
𝑇(𝐿, 𝑡)
𝑇∞
= 1 + 2
𝑛=1
∞
(−1) 𝑛
𝑒𝑥𝑝 −𝑛2
𝜋2
𝑡
𝑡 𝑐
where 𝑇∞ =
𝑄
𝜌𝐶𝐿
and 𝑡 𝑐 =
𝐿2
𝛼
, with Parker’s approximation:
𝛼 = 0.1388
𝐿2
𝑡1/2
.
• 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

8. RESULTS
Summary 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

9. Pure copper samples
1. 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

10. Copper – chromium samples
1. 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.

11. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
Microstructure
Cu 1% Cr
Cu 0.15% Cr Cu 0.5% Cr

12. 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

13. 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.
Microstructure
Cu 0.15% Cr 2%rGO

14. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
0.5% Cr Ann.980°C, 30’ Structure of rGO
Cu 0.5% Cr 2%rGO

15. 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

16. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
Cu – Cr – dGO samples
Microstructure
Cu0.5%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.

17. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
Turbula 30’ Turbula 5’
Effects of annealing: 980°C, 60’

18. 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

19. 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

20. 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

21. 1. Objective
2. Background
3. Experimental
procedures
4. Results
5. Conclusions
6. Future work
CONCLUSIONS
1. 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

22. FUTURE WORK
1. 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)