Identification of sample
Identification of the material weathering iron relics underwater observation is made by visually. The result of the identification of the sample shown in Fig.4. Fig.4. shows identify the weathering and corrosion that occurs on an iron cannonball material that raises concretion (buildup of crust), and the damages cause breaking and destruction of objects. Fig. 4a. shows the metal iron that undergoes weathering and corrosion of a low level. Fig. 4b. shows the metal iron that undergoes weathering and corrosion rates are and start the presence of cracks on ferrous objects. Fig. 4c. shows the metal iron that undergoes weathering and corrosion of metal objects where high levels of iron suffered a split. Fig.3d. shows metal iron that undergoes weathering and corrosion already advanced damage giving rise to a rupture of the destruction of the iron objects.
When iron exposed to the atmosphere, the environment forms different iron-oxides, such as Magnetite (Fe3O4), Hematite (α-Fe2O3), and maghemite (γ-Fe2O3) [3]. At temperatures higher than 560 oC, the general sequence of the iron-oxide layer (from internal to each surface) is Fe/FeO/Fe3O4/Fe2O3/O2 [4]. The redness of the rust powder and the presence of many cracks and cavities on the surface of the object are indicative of an active corrosion process in progress, causing continuous loss of metals, as well as degradation of mechanical properties [5]. Corrosion of archeological artifacts of iron buried under seawater is an electrochemical process, which involves anodic and cathodic reactions in an aqueous electrolyte environment and biological processes also involve anaerobic bacteria [2]. When iron put into solution, the oxide layer grows slowly so that oxide compounds such as goethite (α-FeOOH), akaganeit (β-FeOOH), and lepidocrocite (γ-FeOOH) [3, 6, 7, 8, 9, 10, 11, 12].
Characterization of surface corrosion of iron cannonball material underwater heritage using the handy microscope
The results of the analysis and characterization of objects using the handy microscope shown in Fig.5. Fig.5. can show the presence of corrosion on materials of iron cannonball underwater cultural remnants can distinguish into two, namely dry active corrosion like in Fig.5a. Fig.5b. shown the wet active corrosion.
The ongoing problem with iron archeology is the continued corrosion after excavation caused by salt accumulation during burial. One way to repair iron material cultural heritage is by immersing objects in solution and waiting for chloride ions to spread out [5]. Weathering of underwater relics generally takes place faster than land-based relics. The rate of weathering of cultural objects underwater can reach 5-10 times faster than objects of cultural heritage on land [1]. The speed of weathering is a result of the interaction of the material with water containing salt and biological activity. Weathering chemical reactions occur more quickly in an aqueous medium because the reaction takes place effectively.
Characterization of surface corrosion of iron cannonball material underwater heritage using XRD
The result of the characterization of surface corrosion using XRD has shown in Fig.6a and Fig.6b. X-ray spectrometry such as XRD, XRF, SEM-EDX/EDS is very suitable for the analysis of inorganic material in the field of conservation and heritage restoration [13, 14, 15, 16, 17]. Before carrying out conservation must make a diagnosis of the material to be conserved, so it is more appropriate in determining conservation techniques, including consideration of costs and resources [18].
Fig.6. X-ray diffraction clearly show the distinction of compounds contained in corrosion. Fig.6a. generated a peak 2θ in 26.67o and 35.11o, while in Fig.6b. is generated peak 2θ in 26.67o and 35.17o. The peaks are the peak of akaganeite, supported by research Gil et al. [19] found the presence of akaganeite at the height of 2θ = 26.68o and 2θ = 35.18o. The x-ray diffraction results on a sample of corrosion of iron in the shape of a dried form two types of iron oxide, akaganeite, and lepidocrocite.
The dominant phases of iron artifacts are goethite (α-FeOOH) and magnetite (Fe3O4). The presence of these types in corrosion products explains the centuries-old good preservation of base metal (iron) and stability after excavation. Corrosion of iron-containing chloride ions, for example, is akaganeite [20]. In addition to artifact material, the corrosion process influenced by environmental pollutants, other archeological materials, geography, microorganisms in the soil, vegetation, land use, soil chemistry, soil physical properties, and the presence or absence of water and air [5].
Fig.6 shows the x-ray diffraction results on corrosion of iron cannonball sample in the way of wet that form four types of iron oxide, i.e. halite (NaCl), akaganeite, briartite iron mineral gray metallic opaque sulfide, Cu2 (Zn, Fe) GeS4, famatinite (copper, antimony, sulfide), namely pink-brown mineral containing copper, antimony, and sulfur.
Various artifacts found on the shipwreck, including small arms and ammunition, show their involvement in naval battles [21]. The results showed that the cannonball was made of iron and produced with sand casting molds. Sand found in cavities in cannonballs also studied by petrography [22]. The mineral composition of the results of the characterization using XRD. The result of the investigation of the mineral composition shown in Table 1.
Table 1 Characterization of surface corrosion using XRD
No.
|
Dried active corrosion
|
Wet active corrosion
|
Mineral
|
Amounts (%)
|
Mineral
|
Amounts (%)
|
1
|
Halite
|
9.12
|
Akaganeite
|
96.68
|
2
|
Akaganeite
|
89.63
|
Lepidocrocite
|
3.32
|
3
|
Famatinite
|
0.72
|
-
|
-
|
4
|
Briartite
|
0.53
|
-
|
-
|
The iron mineral is akaganeite (III) oxide hydroxide/chloride with the formula: Fe3+O (OH, Cl). Whereas lepidocrocite, also called esmeraldite or hydrohematite is an iron oxide-hydroxide mineral with formula natural occurring γ-FeO(OH). Table 1 shows the visible presence of significant minerals in the form of akaganiete, which is the most abundant mineral results from corrosion of ferrous metals under seawater. It indicates that the leading causes of corrosion of the metal bottom of the saltwater are chloride ion.
The degradation process of artifacts containing ferrous and non-ferrous, which is induced by contact with aggressive environments such as seawater, will occur more quickly [23]. Analysis by XRD can determine the types of minerals from artifacts to conserved and inhibitors used based on the type of metal: copper and its alloys, iron, and alloys, and other metals (including silver, lead, and zinc) [24]. Information about the morphology, elemental composition, and structure of the crystal makes it possible to determine the constituents of the corrosion layer [25].
The reaction mechanism that occurs in underwater metal corrosion is as follows Hamilton [1]:
Reactions that occur on a more inert metal surface (cathode)
2H2O + 2e- → H2 + 2(OH)-
Hydroxide ions react with sodium ions in water
Na+ + OH- → NaOH
At the anode the reaction produces iron ions
Fe2+ + 2e- → Fe
Fe3+ + 3e- → Fe
Fe reacts with chloride ions in salt-containing water (the sea)
Fe2+ + 2CI- → FeCl2
Under water conditions containing oxygen the reaction will continue to form hydroxide:
FeCl2 + 2NaOH → Fe(OH)2 + 2NaCl
The hydroxide compound formed in the oxygen-containing solution will experience a secondary reaction with the formation of corrosion deposits around the metal surface of the anode:
Fe + 2e- → Fe2+ (Ferrous ion)
Fe2++ 2OH- → Fe(OH)2 (Ferrous hydroxide)
4Fe(OH)2 + O2 → 2H2O + 2Fe2O3 • H2O (Hydrated ferric hydroxide)
Secondary reactions involving ferry ions produce other products from corrosion:
6Fe(OH)2 + O2 → 4H2O + 2Fe3O4 • H2O (Green hydrated magnetite)
Fe3O4 • H2O → H2O + Fe3O4 (Black magnetite)
The analysis of surface corrosion of iron cannonball material underwater heritage using XRF
The results of the analysis of surface corrosion of iron cannonball material underwater heritage using XRF shown in Table 2.

Table 2. shows the results of the characterization of the corrosion of cannonball iron culture underwater using XRF. Table 2 it can be seen the presence of corrosion contain the most abundant elements are chloride. Table 2 shows indicate that the leading causes of corrosion of cannonball culture underwater remnants (submerged seawater) are chloride ion.
Characterization of surface corrosion of iron cannonball material culture underwater using SEM
The results of the characterization of surface corrosion of cannonball heritage using SEM (Scanning Electron Microscope) shown in Fig. 7. The existence of corrosion that occurs in cannonball in the form of hollow-cavity and damages the iron material shown in Fig.8.
Passivation/deactivation of material corrosion of cannonball heritage
Passivation corrosion is the dismissal of corrosion on the object with a particular method. At the passivation in this study, the sample is soaked in a solution of sodium carbonate 5%. The pH maintained between 11-13 using sodium hydroxide. If the pH goes down, then it should be raised on the range with a solution of sodium hydroxide, then rinsed with water objects continued wash using distillate water. The purpose of dried and seen its development, if it still happens, then the corrosion process is repeated until corrosion stops. Soaking in this research was conducted for five months, and a mixed solution replaced about four days to a week. Before the process, the passivate not to do cleanup crust or rust. Layers of the coating would be a natural protector in the meantime. Next, do a manual cleanup using tools such as brushes, skavel, needles, chisel, hammer and other devices. The cleaning level is adjusted to the level of corrosion of the object if the object is still obviously in shape then be organized as clean as possible. If the form object is already less precise, then the cleanup should be careful so that the part of the purpose did not enter apart at the time of releasing the crust. Not all of the coat should be clean, preferred to maintain/find the form objects. If corrosion is already very advanced, shapes are not visible at all, and then the mechanical cleaning is only on the surface.
Alkali solutions such as sodium hydroxide and potassium hydroxide will remove rust from iron and steel, and when combined with sequestering agents to hold the dissolved iron in solution, they can be very effective, particularly at near-boiling temperatures. Under the Fe3O4 deposit, the following reactions can occur on the substrate:
Fe3O4 + 5H2O → 3Fe(OH)3(s) + H+ + e−
Fe3O4 + 4H2O + OH− + 2e− → 3Fe(OH)3−
Next, do the cleaning, the cleaning phase this is the core of the activities of conservation, so should be able to complete the conservation problems of the object until they can last for the long term. Materials were processed cleaning with soapy water, using washing fruit and extract kaffir lime water, rinsed with distilled water. At flushing and drying, at the end of all this stage done flushing to completely clean from chloride solution and used. After completion of the drying, proceed with rinsing. The drying process is carried out by warming in the blazing sun and using a blow dryer.
Stabilization/coating material of iron cannonball underwater heritage
The coating material used is a microcrystalline wax with variations in concentrations of 5, 10, 20, and 50% with turpentine oil solvents. The use of inhibition of the corrosion process of heritage objects made of iron done by several researchers, namely carboxylic monoacids and ethanol solution [26], acidic solutions from plants [27], coating with carboxylates after the conservation process is completed [28]. Microcrystalline wax used to coat or coating iron metal that has finished passivated so that it is not prone to corrosion again. The results of coating using microcrystalline wax can show in Fig.9. Fig.10. shown the iron cannonball has been conserved and ready to be sent to the museum.
Fig.11. shows some color differences in iron cannonball material coated with the microcrystalline solution. From the results of the image stabilization or coating of iron cannonball material using a 5, 10, 20, and 50% microcrystalline wax solution. The results showed that the most suitable solution was because it did not change the color of the sample, namely a microcrystalline wax solution with a concentration of 5%. Iron cannonball material after passive is still prone to further corrosion. Therefore it must be done the stabilization/coating as soon as possible. This stabilization stage is the last stage of the passivated process was complete after all. In this study, the author uses wax microcrystalline 5% with solvent turpentine oil to coating metal iron that has finished passivated, so it is not prone to corrosion returns.
Fig.11. shows a significant difference between the tangible cultural heritage of cultural iron cannonball underwater before conservation (a) and after conservation (b). Fig.11. shown it can conclude that the method of conservation on this research is very suitable to be used in the conservation of iron material underwater. However, this conservation research is research that is not ideal because the iron cannonball material used in the study was far too long in the Mainland has publicly after the adoption of the ocean floor that should iron this cultural heritage material directly conservation after the rapture of the deep sea. The results of the analysis and characterization of iron cannonball material objects linger underwater culture using XRF before and after conservation can be seen in Table 3.
Table 3. shows the after conservation element Cl and some metals have reacted with NaOH. Element Cl is the main element causing wet and dry corrosion. After immersion with 5% NaOH, the Cl element reacts with NaOH.
Cl- + NaOH → NaCl(aq) + OH-
The artifact is soaked for one week with 5% NaOH, rinsed and distilled water, then cleaned physically with a brush, if the corrosion has not stopped the process of soaking repeated until the corrosion stops. After the corrosion stops, the iron cannonball refined in shape. The reaction between NaOH and metal in the following example:
Zn + 2NaOH → Na2ZnO2 + H2
Al3+ + 3NaOH → Al(OH)3 + 3Na+
Al(OH)3 + NaOH → 2Na+[Al(OH)4]- or
Al + NaOH + H2O → NaAlO2 + H2
Table 3 Characterization of surface corrosion of iron cannonball material using XRF before and after conservation
No
|
Before conservation
|
After conservation
|
Dried active corrosion
|
Wet active corrosion
|
Test 1
|
Test 2
|
Test 3
|
Ele-ment
|
Amount (%)
|
Ele-ment
|
Amount (%)
|
Ele-ment
|
Amount (%)
|
Ele-ment
|
Amount (%)
|
Ele-ment
|
Amount (%)
|
1
|
Cl
|
66.603
|
Cl
|
64.963
|
Fe
|
98.90
|
Fe
|
98.72
|
Fe
|
99.35
|
2
|
Fe
|
32.105
|
Fe
|
24.730
|
Co
|
0.40
|
Cu
|
0.45
|
Mn
|
0.44
|
3
|
Ca
|
0.320
|
Mn
|
0.265
|
Mn
|
0.31
|
Zn
|
0.37
|
Cu
|
0.12
|
4
|
Mn
|
0.259
|
Al
|
0.095
|
Cu
|
0.20
|
Mn
|
0.29
|
V
|
0.06
|
5
|
Al
|
0.147
|
SiO2
|
0.195
|
Zn
|
0.17
|
Ti
|
0.17
|
Ni
|
0.04
|
6
|
SiO2
|
0.193
|
S
|
0.085
|
-
|
-
|
-
|
-
|
-
|
-
|
7
|
S
|
0.064
|
P
|
0.051
|
-
|
-
|
-
|
-
|
-
|
-
|
8
|
P
|
0.039
|
Cd
|
0.0092
|
-
|
-
|
-
|
-
|
-
|
-
|
9
|
Cd
|
0.011
|
Sb
|
0.0047
|
-
|
-
|
-
|
-
|
-
|
-
|
10
|
Sb
|
0.0066
|
Sn
|
0.0047
|
-
|
-
|
-
|
-
|
-
|
-
|
11
|
Sn
|
0.0041
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
-
|
The next step is cleaning with soapy water to remove any residual corrosion. Soap is an alkaline salt of fatty acids so that it will partially to be hydrolyzed by water. Therefore the soap solution in water alkaline.
CH3(CH2)16COONa + H2O → CH3(CH2)16COOH + OH- + Na+
The weak base solution from soapy water can help clean surface corrosion. Iron material cannonball washing with soapy water, and then washed with extract water kaffir lime (weak acid solution). Citric acid is a type of acid that is non-toxic, non-irritating, and environmentally friendly [29]. Citric acid is also easy to find in citrus-like organic substances including citrus (kaffir lime) and lemon (Citrus lemon). The citric acid content contained in kaffir lime is 45.8 g/L, while the citric acid content contained in lemon is 48.0 g/L [30]. Extract water kaffir lime citric acid and ascorbic acid which are weak acids so that it removes impurities on the surface of the ball cannon.
Characterization of iron material ball cannon using XRF before and after conservation (Table 3) showed a significant difference in the data. On the object of active corrosion wet and dry before conservation showed the presence of chloride that is the result of corrosion of the iron material, whereas on the object test results after conservation showed very significant differences, in which chloride is no longer detected. From this, it can conclude the process of corrosion on the object was lost and stopped.