This study examines the corrosion rate of aluminum, copper, and stainless steel metals when immersed in the phase change materials (PCMs) palmitic acid and myristic acid. Samples of each metal were immersed in the liquid PCMs at 70°C and observed over 20 days. Mass loss and physical appearance changes were measured. Copper exhibited the greatest mass loss of 36.5mg and 41.9mg in myristic and palmitic acid respectively. Aluminum showed more corrosion in myristic acid than palmitic acid. Stainless steel displayed minimal mass loss and corrosion in both PCMs. The study aims to evaluate which metals exhibit less corrosion for use as containers for

1. Study of corrosion rate for metals with Palmitic acid and Myristic acid above
melting point temperatures
Sharabh kochar*, D. Jaya Krishna$
Department of Mechanical Engineering
BITS PILANI Hyderabad campus, Hyderabad (INDIA)
$
corresponding author and Assistant Professor, *Student, M.E (Hons)
Tel.: +91 40 66303 577, Fax: +91 40 66303 998
Email address: djayakrishna.iitm@gmail.com,
ABSTRACT
In this study three most commonly found metals in heat transfer equipments such as aluminium, copper and
stainless steel are used to test the corrosion resistance when kept in contact with PCMs (Palmiticacid and Myristic
acid). The method used was the immersion corrosion test. We have performed and evaluated the immersion
corrosion test on these three commonly used metals in the PCM’s on short term basis. Since in most cases, in
thermal energy storage the PCM is in direct contact with the metal, with no circulation of the salt, this kind of
immersion corrosion test seems to be very suitable. During the performance of these tests the PCM was isolated
from contact with the oxygen of the air there by creating a mostly practical and realistic situation of thermal energy
storage.
KEY WORDS: thermal energy, storage energy, corrosion of metal.
INTRODUCTION
The storage of thermal energy has got wide applications in the industrial as well as domestic field. The thermal
energy can be contained in different type of metallic containers commonly made up of aluminum, stainless steel,
copper, brass etc. which are very vulnerable to corrosion attack. They temporarily hold thermal energy for later
utilization. Energy demands vary on daily, weekly and seasonal bases. These demands can be matched with the
help of TES systems that operate synergistically, and deals with the storage of energy by cooling, heating,
melting, solidifying or vaporizing a material and the thermal energy becomes available when the process is
reversed. TES is a significant technology in systems involving renewable energies as well as other energy
resources as it can make their operation more efficient, particularly by bridging the period between periods
when energy is harvested and periods when it is needed. That is, TES is helpful for balancing between the
supply and demand of energy. TES systems have the potential for increasing the effective use of thermal energy
equipment and for facilitating large-scale fuel commutating. The main types of TES are sensible and latent.
Sensible TES systems store energy by changing the temperature of the storage medium, which can be water,
brine, rock, soil, etc. Latent TES systems store energy through phase change, e.g., cold storage water/ice and
heat storage by melting paraffin waxes. Latent TES units are generally smaller than sensible storage units. More
compact TES can be achieved based on storages that utilize chemical reactions. In this study we have chosen
two phase change materials such as palmitic acid, myristic acid and three metals such as aluminium, stainless
steel, copper Farrell et al. (Farrell, Norton, & Kennedy, 2006)[ 1 ] investigated the corrosion rate of aluminium
and copper samples over a 17 hours period by using the ASTM G1 standard testing method.. Samples were
visually observed with a microscope and images were highlighted in the areas of corrosion. Oro et al [ 2] studied
that the corrosion effect of different metals and polymeric material in contact with some PCM used in low
temperature applications. In this study 9 commercial phase change materials were used. The metals for PCM
containers were selected as Cu, Al , Stainless Steel 316 and carbon Steel The study concluded and
recommended that copper, carbon steel must be avoided as PCM container due to their high corrosion rate,
similarly Al is also not recommended because of pitting and bubble phenomena leading to development of holes
in the containers. The stain less steel 316 exhibit low corrosion rate with all PCM combination hence it may be
useful for long term uses. Cabeza et al. [3] Studied corrosion resistance of different common metals VIZ ,
Aluminium ,Brass ,Copper ,Steel and Stainless Steel by applying short term (2 weeks) immersion corrosion test
with salt hydrates as PCMs (zinc nitrate hex hydrate, sodium hydrogen phosphate, dodecahydrate, calcium
chloride hexahydrate. They have concluded that Al and steel are highly corroded by zinc nitrate hexahydrate , it
gives a very corroding material so this combination should be avoided . It was reported that brass and copper are
also corroded at slower rate with zinc nitrate hexahydrate. But steel gets easily corroded with sodium hydrogen
phosphate dodecahydrate and the aluminium gets easily corroded with this PCM where as brass copper and stain
less steel found to be corrosion resistance. Al gets surely pitted corrosion by calcium chloride hexahydrate .
Steel and Stainless Steel both gets corroded with longer period of contact. Brass and copper found to be
corrosion resistant to this salt hydrate.Sakamoto et al. [ 4] They studied the damaged mechanism and the
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2. development of testing methodology for selecting the durable material for the domestic water taps which are
usually made up of copper alloys and their valve seats get damaged as a result of corrosion process(cavitations)
related to water quality . They selected various copper alloys (5 brasses, 5 bronzes) and subjected to 3 test
methods. The ISO 6509 dezincification test for pure corrosion.
EXPERIMENTAL METHODOLOGY
The setup consists of thermostatic water bath, boiling tubes contained phase change materials and metals. In the
present study experimental methodology is followed into three stages: first stage is preparation of the sample.
Second stage is corrosion and degradation test for metal. Third stage is sample cleaning-up and measured
surface characteristics of metal through microscope. It is studied that the surface characteristics of material
under metallurgical microscope. Metal samples are obtained from cutting big plates, and then it is cleaned with
acetone in order to remove the oil coming from the cutting process. Before starting the experiment all specimens
are kept under metallurgical microscope to find the surface characteristics of material. Then the samples are
weighed, Then it is immersed inside glass test tubes containing the phase change material in order to combine
each metal sample with the six different phase change material which are placed in a thermostatic water bath.
Then, the glass tubes are covered with rubber lids to avoid contact with environmental agents. The phase change
temperature of all the PCM tested in a digital water bath at a temperature of 70oC, it is ensured that during all
the process of the PCMs are at liquid phase, in order to see the evolution of corrosion rate in time. Visual
evaluations are done by seeking the bubbles, precipitates, surface changes and pitting process. The metal
samples are removed from the test tubes after 5,10,15,20 days and are evaluated with the following procedure:
Change in the solution appearance and characteristics are evaluated to identify qualitatively the precipitate
formed. The metal pieces are cleaned thoroughly with tap water and their change in appearance is evaluated
visually. Before re-weighted, samples are cleaned and dried. The metal samples are polished with abrasive paper
and dried with compressed air at the end of all specimens are kept under metallurgical microscope to find the
surface characteristics of material. Compared before and after surface characteristics of the metal samples and
required observations are noted down.
Standard expression for corrosion rate : [5]
In most cases , aside from contamination problem , the primary concern is the life (usually the life in years) of
the equipment involved . A good rate corrosion expression should involve:
familiar units , easy calculation with minimum oppurnity in error , ready conversion to life in years ,
penetration, whole numbers without cumbersome decimals.
mils per year = (534W) / (DAT)
where w= weight loss (mg) d=density fo specimen (g/cm3
) a=area of specimen (sq. in.) t=time of
exposure(hr.)
RESULTS AND DISCUSSION:
The three most commonly used thermal energy containment metals VIZ. copper , aluminium , stainless steel having
density 8.94 (g/cm3) , 2.7 (g/cm3) , 8.03 (g/cm3) respectively and Area 0.465 (inch2) was subjected to corrosion
immersion test in PCM VIZ palmitic acid, myrstic acid at fix temperature of 70o
C in lab environment and the changes in
the weight, physical and microscopic appearance are critically observed .
At interval of 5,10,15 and 20 days respectively. Table 1 shows the mass loss of the metal with pcm after 20 days.Table 2
shows the change in physical appearances after 20 days of immersion test.
Table 1: Mass loss of the metals with phase change material after 20 days
Phase change materials Mass loss after 20 days
Copper Aluminium Stainless steel
Myristic acid 36.5 mg. 26.6 mg. 2.2 mg.
Palmistic acid 41.9 mg. 13.7 mg. 2.6mg.
Table 2: The physical changes in different metals after 20 days immersion in test medias
s.no Physical Copper Aluminium Stainless steel
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3. appereance
Metallurgical
macroscopic
appearance
prior to test
1. In myristic
acid
2. In palmistic
acid
Appearance
prior
to test
reddish orange colour
with metallic lustre and
even surface.
silvery white with soft
metallic lustre and even
surface.
bright shiny star like
metallic lustre with even
surface.
1 In myristic
acid
Colour changes to
light Orange.
With significant loss in
metallic lustre and
even surface.
Myristic acid sticks to
the metal chip.
Bright shiny star like
metallic Lustre with even surface is
completely vanished.
2 In palmitic
acid
palmitic acid sticks to
metal chip.
Metallic lustre is lost .
completely.
palmistic acid sticks to
metal chip.
palmitic acid sticks
to metal chip.
Fig 1 and Fig 2 shows the comparison of corrosion behaviour of different metals in myristic acid and Palmitic
acid at variable time
From this study it is observed that aluminium has more amount of mass loss with both phase change materials.
It is also observed that appearance of colour changes of phase change solution with copper for both the phase
change materials as shown below. PCM getting sticks on the copper metal with palmitic and myristic acid. PCM
getting sticks on the aluminium metal with myristic acid. It is observed that there is less amount of metal loss in
stainless steel with all the phase change materials.
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4. CONCLUSION:
In the above experiment performed , the three most commonly found metals in heat transfer equipments such as
aluminium, copper and stainless steel are used in immersion corrosion test when kept in contact with PCMs
i.e.Palmiticacid and Myristic acid.At the end of the experiment it is found that copper solution changed its colour
with both pcm’s as shown in above figure and also pcm are getting stick to the copper surface whereas myristic
acid is getting stick to aluminium surface. The good amount of metal loss can be seen on both copper and
aluminium.Stainless steel was found best out of three metals (almost immune to corrosion) and can be used as a
container material.
References :
1. Anthony J. Farrell, Brian Norton, David M. Kennedy. : Corrosive effects of salt hydrate phase change
materials used with aluminium and copper Journal of Materials Processing Technology 175 (2006)
198–205.
2. Eduard Oró, LaiaMiró, CamilaBarreneche, Ingrid Martorell, Mohammed M. Farid,Luisa F. Cabeza. : Corrosion
of metal and polymer containers for use in PCM cold storage. Applied energy xxx2012xxx-xxx (article in
press).
3. Cabeza, Illa, Roca, Badia, Mehling, Hiebler and Ziegler. : Immersion corrosion tests on metal-salt hydrate pairs
used for latent heat storage in the 32 to 36 8oC, Materials and Corrosion 52, 140±146 (2001).
4. Sakamoto, A., Yamasaki, T., & Matsumura, M. (1995). Erosion-corrosion tests on copper alloys for
water tap use, 186187, 548–554.
5. corrosion engineering (third edition) Mars G. Fontana chapter 2 page 13.
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