The document discusses anodization of copper samples to create nano-CuO coatings. It describes how coatings with different grain sizes were produced by anodizing in oxalate solutions under varying conditions. The coatings were characterized for grain size, thickness, hardness, hydrophobicity, electrical resistivity, and heat transfer performance. The results showed that a coating with a critical grain size of 45nm demonstrated maximum hardness of 188Hv and super hydrophobicity, with a contact angle of 167.5°. This coating improved the heat transfer efficiency by 95% compared to uncoated samples, by increasing the specific surface area and thermal conductivity while decreasing thermal resistance.

1. M. H. Mahmood

2. 1.1 What is Anodization
Anodization is an electrochemical coating technique that
converts the metal surface into a durable, corrosion-resistant,
oxide finishing. Despite being a kind of metal corrosion, it is one
of the corrosion protection methods. The nonferrous metals as
aluminum, copper, magnesium, zinc, and titanium are ideally
suited for anodizing (Joseph, 2014). In industry, it is often known
as, the beauty of corrosion.

3. 1.3 Research Philosophy
The effect of the nano-CuO coating grain size on its characteristics of hardness,
hydrophobicity, in parallel with its heat transfer performance hasn't been studied
carefully. this research focused on the effects of coating parameters on the fabrication
of hard nano-CuO coating with hydrophobic properties, in addition, to study the
effect of coating grain size on the coating characteristics and heat transfer
performance.
This research was conducted by using the electrochemical anodizing technique in
oxalate solution.

4. 1.4 1.4 Hypothesis
The history of Aluminum Anodizing researches, produced a clear and detailed
information about the anodizing parameters of hard organized oxide coating. It was
observed that the anodizing temperature effect on the hardness of the anodized
coating according to the proportional relation between the anodizing temperature
and the resulted anodized coating grain size. A research study in the aluminum
anodization (Aerts 2007). Harder and more effective corrosion protective film of metal
oxides can be developed by careful controlling of the coating parameters. Therefore,
this research assumed that copper has the same ability of aluminum to form a hard
and organized oxide film to increase copper corrosion resistance.

5. The novelty of the research is by performing an
optimization analyzing study on the effects of the
anodization process parameters on the coating
characteristics reaching obvious practical steps for the
tuning of the CuO nano-coating characteristics by
adjusting the parameters of the anodization process.
Expected from this study to contribute to the
knowledge developments of hydrophobic surfaces, gas
detectors, solar cells, corrosion protection,
supercapacitors, fuel cell, batteries, and memory storage
devices. Moreover, it is also expected from this study to
contribute to developing different applications such as
EMI shielding, radar absorbing properties for stealth
technology, through enhancing the fillers based
reinforced composites materials properties.
1.5 Research Novelty

6. 1.6 Application of CuO coating

7. 1.7 Previous Work
Many researchers investigated the formation of nano CuO coating by various method (Farshad 2017), (Song 2017),
(Fredj 2011). It was found that the coating temperature is an effective parameter on the formation of the CuO protective film.
The other effective parameter on the formation of CuO coating is the solution acidity.
In 2006, the improvement of copper’s mechanical properties using anodization in oxalate solution was studied for
developing the Electrochemical Mechanical Planarization (ECMP) (Lowalekar 2006). Cyclic voltammetry was used for
characterizing the oxidation potentials. The testing scans were initiated at various open circuits’ potentials and scan rates. In this
study (Lowalekar 2006) effects of oxalate concentration of anodizing solution on anodized copper coating, characteristics were
investigated. According to the kinetic mechanism of copper passivation in oxalic acid solution, it was found that the stability of
the anodized coating increases with the increase in the oxalate concentration. Stability of cupric oxide CuO in oxalic acid
solution was studied at a wide range of solution’s acidities. It was found that cupric oxide CuO was stable at high alkalinity
solution. In this study, the behaviour of copper in oxalic acid was also investigated (Lowalekar 2006).
Many other researchers (Caballero 2010), (Chen 2016) and (Zerbino 2009) studied the synthesis of anodized copper
coating on metals. In these studies, various nanometals oxides, including copper oxide, were synthesized using the
electrochemical method.
from the literature review on copper anodizing technique, appendix A, the following table have been summarized to proceed
with the latest knowledge published in this field. More in Apendex-1 last slides

8.  The influence of grain size for nano CuO coating in heat transfer performance was investigated by
performing coating of various grain sizes using the electrochemical oxidation method for copper samples
in oxalate solutions at range of operating conditions; temperature ~24 ºC, oxalate concentrations 0.1 - 0.5
molarity M, and voltage 7.5-9 V. The morphology phases of the crystal structure for the nano-coating and
its chemical composition were investigated using X-ray diffraction XRD, energy dispersive X-ray
Spectroscopy EDX. Moreover, the microstructure and grain size were investigated using field emission
scanning electron microscopy FESEM. Electrical resistivity (ER) of the nano-coating was measured using a
four-point probe Mitsubishi electrical resistivity meter model MCP T400. To evaluate the impact of the
coating’s grain size on the heat transfer performance, hydrophobicity, and hardness of the coating the
anodic coating experiments were conducted based on Taguchi L16 orthogonal array using the design
expert DOE software for planning the design of experimental work with three factors of temperature,
oxalate concentration and voltage and four levels, as shown in Table 1.
2.1 Experimental Optimization
Parameters
Levels and values
Responses
Level
1
Level
2
Level
3
Level
4
Oxalate Concentration(M) 0.1 0.23 0.36 0.5
Grain Size
Thickness
Temperature (°C) 0 8 16 24
Voltage (V) 7.5 8.0 8.5 9.0
Table 1 Experimental design plan

9. 2.2 Experimental Work
Anodization is an electrochemical
treatment of which a stable corrosion
protection layer on metal achieved, it involves
immersing metal in a bath of diluted acid
figure 3.1, called electrolyte, and apply a low-
voltage between the electrochemical cell
poles to form a thin surface layer of metal
oxide.
18:07
Electrochemical Anodization cell

10. SEM images (×6,000) results for copper sample before
coating
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FESEM image of the nano-CuO coating with magnification of ×30,000

11. The coating's thermal property was characterized using a
thermal testing system to evaluate the effect of nano-CuO
coating on the heat transfer performance of copper material.
Figure: 3 shows the thermal experimental system consists of a
99.95% high purity copper pipe with a dimension of 3.18 mm
outside diameter OD, 1.55 mm inside diameter ID, and 0.81 mm
thickness T. The pipe was passed through the evaporation,
adiabatic, and condensation section. The evaporator was
heated by an electrical heater mantel, while the condenser
cooled by immersed in a cooling bath of constant temperature.
The testing sample was bent to six paths supported with
eighteen temperature indicators to measure the sample's
surface temperature, as illustrated in Figure 3. Distilled water
was used at an operating temperature between 20 - 100 °C. The
sample was heated up in the evaporator section by the heater
mantel, which was controlled using an electrical power supply.
The warming up of the evaporator was initiated when the
condenser temperature settled at 20 οC. The delay time of the
condenser to reach the settlement state was 15 min.
2.3 coating's thermal characterization

12. Loresta-GP MCP-T610
Electrical resistivity (ER) of the nano-coating was measured using a four-point
probe Mitsubishi electrical resistivity meter model MCP T400. The coated
surface's electrical sheet resistance was determined by measuring the ratio of
the voltage drop between the two inner probes to the passed current between
the two outer probes. The results were multiplied by a geometric correction
factor that depends on the probe geometry.
Sheet resistance Rsh was considered as the ratio of the resistivity (r) of the
coating divided by its coating thickness (t) as in equation;
Rsh=r/t
Coating thickness were calculated by dividing resistivity to sheet resistance as
in the equation 3.9 (Valladares, 2012).
t=r/Rsh
2.4 Electrical resistivity measurements

13. The coatings thickness measured from the
cross-sections FESEM micrographic results,
according to ASTM B-487.
18:07
2.5 coating thickness measurements

14. Fig. 1. Classification of surface wettability according to the contact angle
The hydrophobic property of any solid surface is related to the free energy of that surface. It must be
reduced to be less than the solid-liquid interfacial energy to increases the contact angle to greater than
90°. This is achieved by modifying surface characteristics that must allow trapped air pockets beneath
the water droplets.
2.6 Characterization of coating wettability

15. The results demonstrated that the nano-CuO coating promoted the coated surface with a super-
hydrophobic characteristics feature. The average contact angle for the coated samples was ~167.5°.
Fig. 9 Hydrophobic characteristic of nano-CuO coating

16. a
Fig. 8 Measurement of the contact angles for the coated sample by analyzing the image
results of water droplet resting on the coated surface
b

17. 2.7 Characterization of
Coating Hardness
18:07
The nano CuO samples' micro hardness tested on Automatic Micro-
hardness tester MHT- Smart by Omnitech. The tests were carried out by
pyramid indenter with100 of the applied load.
Figure4: Automatic Micro- hardness tester

18. Hall–Petch (HP) relation explained why the increase in the hardness strength in the critical grain size range. This
increase resulted in the rise in the area fraction of the grain boundaries, which considered the most affecting
resistance against dislocation motions .
∆σg = KHP/√dg
Where;
KHP is the strengthening coefficient (for each metal)
Figure: 2. Schematic of materials hardness versus grain size
At the Nano scale grain size, higher grain boundaries
fraction, which is the main affecting resistance on
dislocation motion of grains, therefore, higher applied
stress is required to make a dislocation through this
material
At Nano scale grain size, Fewer dislocation's stresses
accumulated at the grain boundaries

19. A uniform nano-CuO coating was successfully developed on a copper
surface using the oxalate solution's electrochemical oxidation method.
The average grain size of the nano-coated samples was 47 nm with an
average coating thickness of 13μm.
The thermal resistance of the nano-CuO-coated sample was lower than
the uncoated model. The nano-CuO coating increases the specific
surface area by 272 times, which increases heat transfer performance
across the nano-coated surface about 22 times compared to the
uncoated surface.
The nano-CuO coating demonstrated a hard-hydrophobic characteristic
feature on the surface with the maximum hardness attainment of 178
H.V at the critical grain size of 45 nm.
The nano-coating increases the thermal conductivity and decreases the
thermal resistance due to the specific surface area's increases.
Therefore, the heat transfer efficiency (Eff %) was enhanced by ~95%
after coating.
The morphological structure of nano-coating was investigated using a
high-resolution surface imaging field emission scanning electron
microscopy (FESEM), as shown in Fig. 6.
(a) (b)
(c) (d)
Fig. 6. FESEM image of the nano-CuO coating prepared in oxalate concentrations; 0.3 M (a), (b) and 0.5
M (c), (d), with magnification of ×30,000 (a), (c) and ×60,000 (b), (d).
2.7 coating Grain size measurements

20. A comparison among the experimental result data was
made for coated samples in 0.36 M oxalate concentration
to investigate the relation among coating’s grain size,
hardness, and specific surface area, as shown in Fig. 10.
From Figure 10, it can observe that the critical grain size of
the coating at these operating condition was ~45 nm,
where the maximum coating surface hardness was 188
H.V. this result confirms the formation of hard nano-CuO
coating development in addition to its super hydrophobic
characteristic.
3.Results
Fig. 10 Relation between hardness and specific surface area with its grain size for
samples coated in 0.36 M oxalate concentration

21. Fig. 11 Comparison between the thermal resistance (K/W) of coated and uncoated samples
as a function of the Input power in Watt
It was also noticed that the thermal resistance
for both nano-coated and uncoated samples
decreased with the increase of the heating
load from 25 to 250 Watt. This finding is in
line with the reversible relationship between
the applied heating load and the thermal
resistance.

22. Figure: 12 illustrates the effect of surface
area on the effective thermal
conductivity and thermal resistance of
nano-coated material. This figure
observed that the effective thermal
conductivity increased dramatically,
whereas the thermal resistance was
reducing sharply with the increase in the
total surface area.
Fig. 12 Effective thermal conductivity (W/M.K) and thermal resistance (R= K/W) as a function
of surface area (cm2) of the coated samples

23. The decrease of the coating grain size increases the surface area by distributing the surface particles to a tiny small size.
This increment in the surface area has a significant contribution to enhancing the heat transfer performance across the
material’s surface. the effect of reducing grain size in the heat transfer performance is the same principle as the effect of
the fins heats sinks in the cooling by heat convection.

24. From the current study, the following conclusion can be drawn:
From the current study, the following conclusion can be drawn:
1. A uniform nano-CuO coating was successful developed on a cop-per surface using the electrochemical oxidation
method in oxalate solution. The nano-coated samples' average grain size was 45 nm, with an average coating
thickness of 15μm.
2. The thermal resistance of the nano-CuO coated sample was lower than the uncoated sample. The nano-CuO coating
increases the specific surface area by 272 times, which increases heat transfer performance across the nano-coated
surface about 22 times compared to the uncoated surface.
3. The nano-CuO coating in 0.36 M oxalate concentration and °C demonstrated a hard-hydrophobic characteristic on the
surface with the maximum hardness attainment of 188 H.V. at the critical grain size of 45 nm.
4. The nano-coating increases the thermal conductivity and decreases the thermal resistance due to the specific surface
area's increase. Therefore, the heat transfer efficiency (∆Q %) was enhanced by ~95% after coating.
5. We recommend for further research has to be carried out in the future to evaluate the relation between the surface
roughness and contact angle of the hydrophobic coated surface. With investigating the effect of the coating
roughness on heat transfer performance for the coated sample compared with the uncoated samples.
Conclusions

25. Thank you very much