Spontaneous Symmetry-Breaking in the Corrosion Transformation of Ancient Bronzes
Round 1
Reviewer 1 Report
The manuscript “Spontaneous Symmetry-Breaking in the Corrosion Transformation of Ancient Bronzes” (manuscript n° 870903 by Yanpeng Yang, Xiaojuan Cao, Yang Li, Zhongchi Wang, Bingjie Li, Xudong Jiang, Junji Jia and Chunxu Pan), submitted for publication on Minerals contains some contributions concerning the chemical and structural modification of corrosion products grown on bronze archaeological artefacts after the excavation.
In the present form it could be considered interesting and useful for the readership of Minerals.
The English style in some parts is poorly appropriate, the writing quality of the manuscript could be improved by rephrasing some sentences and avoiding the improper use of some terms as the term symbiosis.
Hereafter, some comments and questions are reported to be used by the Authors to improve the quality of the manuscript.
The experimental paragraph is too lacking in details, as example, did the authors coat the sample with a conductive coating before SEM observation ? Which is the “standard process” used “to prepare the metallographic” sections ? Major details or explanations should be reported as the meaning of the sentence “The area-scanning was used to measure the average chemical compositions”, what is the meaning of this sentence ? Which analytical technique was used to determine the chemical composition ? Furthermore, the Authors should describe the sampling methods.
Concerning the formation of the secondary corrosion products, the Authors claim at page 5 that “malachite (CuCO3·Cu(OH)2) belonged to the secondary corrosion formed during museum conservation” without considering that it is well known that malachite, sometimes with also azurite, can be commonly and largely formed during the long-term burial in the soil before the finding of the archaeological bronzes. The formation of malachite on the bronze surface needs of a large amount of carbonate anions in addition to certain well precise chemical-physical conditions, the authors should explain in details the reasons of the above cited sentence and in particular, how it is possible to distinguish the “primary corrosion” and the “secondary corrosion” products as the malachite or azurite mineral species.
At the lines 198-208, some conclusions should be better justified as the sentence “That was to say, the co-existence of carbon and the poor crystallized malachite (CuCO3·Cu(OH)2) demonstrated its early usage and soil corrosion”, what does “early usage” mean ? This conclusion is wrong. The presence of azurite does not reveal “the improper museum conservation conditions, such as unstable humidity and high CO2 concentration, which could made a corrosion transformation from malachite (CuCO3·Cu(OH)2) into azurite (2(CuCO3)·Cu(OH)2”. The authors should also quantify the high concentration of CO2 and explain its role in the transformation of malachite in azurite.
Furthermore, many of the described transformations from a high symmetry of the “primary corrosion” to a low symmetry of the “secondary corrosion” are simply chemical reactions caused by the presence of aggressive environmental species that chemically react with the archaeological corrosion products as humidity and oxygen.
It is interesting the concept reported by the Authors at lines 330-334 “In case of the harmful "primary corrosion", make the "secondary corrosion" be a harmless one by reasonable control the atmospheric gas and ion concentration of the protection environment. For example, when the "primary corrosion" was orthohombic crystal system of atacamite (CuCl2·3Cu(OH)2) or monoclinic crystal system of clinoatacamite (Cu2(OH)3Cl), it could be converted into monoclinic crystal system of malachite (CuCO3·Cu(OH)2)”. The authors should explain better this concept also on a practical point of view to give a new chance to the conservators to save from the destruction the bronze archaeological artefacts caused by the “bronze disease”. Furthermore, the authors should consider the consequences of an irreversible chemical and structural treatment that could influence the chemical-physical stability of the whole artefact, the authors should also consider that the proposed method could not be a real solution reminding the genesis of the “bronze disease” caused by the presence of nantokite inside the patina.
Author Response
Reply to the Comments
Comments and Suggestions for Authors
- The manuscript “Spontaneous Symmetry-Breaking in the Corrosion Transformation of Ancient Bronzes” (manuscript n° 870903 by Yanpeng Yang, Xiaojuan Cao, Yang Li, Zhongchi Wang, Bingjie Li, Xudong Jiang, Junji Jia and Chunxu Pan), submitted for publication on Minerals contains some contributions concerning the chemical and structural modification of corrosion products grown on bronze archaeological artefacts after the excavation.
In the present form it could be considered interesting and useful for the readership of Minerals.
The English style in some parts is poorly appropriate, the writing quality of the manuscript could be improved by rephrasing some sentences and avoiding the improper use of some terms as the term symbiosis.
Hereafter, some comments and questions are reported to be used by the Authors to improve the quality of the manuscript.
Reply: Regarding the comments, the manuscript writing has been checked and polished again. We hope it will meet the publishing level.
- The experimental paragraph is too lacking in details, as example, did the authors coat the sample with a conductive coating before SEM observation? Which is the “standard process” used “to prepare the metallographic” sections? Major details or explanations should be reported as the meaning of the sentence “The area-scanning was used to measure the average chemical compositions”, what is the meaning of this sentence? Which analytical technique was used to determine the chemical composition ? Furthermore, the Authors should describe the sampling methods.
Reply: Thanks for the comments. The more detailed about the sample preparation has been added in the revised manuscript.
1) did the authors coat the sample with a conductive coating before SEM observation?
No. The samples were put on the SEM sample stage and adhere with conductive silver glue. The samples were not coated with carbon or gold, because it would influence the chemical compositions, and in addition, the samples’ conductivity was acceptable for the SEM observation.
2) Which is the “standard process” used “to prepare the metallographic” sections?
Thanks for the comment! The detailed preparation process has been added in the revised manuscript. “Before examination, firstly, the bronze relics were ultrasonically cleaned in ethanol solution for 5-10 minutes for removing surface impurities, blemishes, muddiness and foreign substances; And then, the samples were used for stereomicroscope observation, X-ray diffraction (XRD) and Raman analysis; At last, the samples were mounted on the specimen stage by using conductive silver for high-magnification observation and chemical composition measurement by using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). Due to the better conductivity of bronze, the sample's surface was not carried on the gold or carbon coating, because it would make additional influence on the corrosion compositions. a standard process was use to prepare the metallographic samples, including cutting, mosaic, grinding, polishing, and etching by using FeCl3 acid solution.”
3) Major details or explanations should be reported as the meaning of the sentence “The area-scanning was used to measure the average chemical compositions”, what is the meaning of this sentence? Which analytical technique was used to determine the chemical composition?
The chemical compositions of the samples were measured by using an energy-dispersive X-ray spectroscopy (EDS), which is attached to SEM. In general, there are three modes to measure the chemical compositions in EDS, i.e., point-scanning, line-scanning and area-scanning. The point-scanning is the most used mode for getting the chemical composition at a point or a very small area. The line-scanning mode can provide a composition variation along a preset line. When using the area-scanning mode, firstly, to preset a square frame (large or small), and then the electron beam scans within the frame and give the chemical compositions of this area, which can avoid the composition segregation and inhomogeneity, and generally is considered as the average chemical compositions of the substance.
- Concerning the formation of the secondary corrosion products, the Authors claim at page 5 that “malachite (CuCO3·Cu(OH)2) belonged to the secondary corrosion formed during museum conservation” without considering that it is well known that malachite, sometimes with also azurite, can be commonly and largely formed during the long-term burial in the soil before the finding of the archaeological bronzes. The formation of malachite on the bronze surface needs of a large amount of carbonate anions in addition to certain well precise chemical-physical conditions, the authors should explain in details the reasons of the above cited sentence and in particular, how it is possible to distinguish the “primary corrosion” and the “secondary corrosion” products as the malachite or azurite mineral species.
Reply: Practically, it is difficult to distinguish a corrosion product belongs to the “primary corrosion” and the “secondary corrosion”. In our previous work [1], we proposed the criteria to judge the types, i.e., 1) whether having the soil contained elements; 2) whether having the free water H-O-H vibrational Raman peak at 1602 cm-1; 3) stacking relation in-between corrosions. In addition, we also reference the museum records.
Yes. Malachite (CuCO3·Cu(OH)2) commonly forms during the long-term burial in the soil due to chloride ion in the soil. However, in our previous work [2], it was found that malachite can also be generated in the environment with the excess of H2O and CO2 gas concentrations during museum conservation. The reactions include, firstly, cuprite (Cu2O) formed by oxidation of the bronze surface in the air, and then, it further reacted with O2, H2O, and CO2, which at last resulted in the formation of malachite. That is, in the proper temperature and redox conditions, the Cu2O could form upon bronze surface. If there were certain amount of free CO2 and steam in the air, Cu2O could transform into malachite. In the reference [2]'s case, it was a very special condition, and the malachite grew into a large size up to several millimeters. In general museum condition, it is possible to has small amount of malachite.
[1] Yang Li: “Fabrication Processes and Corrosion Products of Ancient Bronzes”, Doctoral Dissertation, Wuhan University, 2012.
[2] Yang Li, Zhirong Bao, Taotao Wu, Junchun Jiang, Guantao Chen, Chunxu Pan: “Specific Corrosion Products on Interior Surface of a Bronze Wine Vessel with Loop-handled (You) and Its Growth Mechanism, Shang Dynasty, China”, Materials Characterization, 2012, 68: 88-93.
- At the lines 198-208, some conclusions should be better justified as the sentence “That was to say, the co-existence of carbon and the poor crystallized malachite (CuCO3·Cu(OH)2) demonstrated its early usage and soil corrosion”, what does “early usage” mean? This conclusion is wrong. The presence of azurite does not reveal “the improper museum conservation conditions, such as unstable humidity and high CO2 concentration, which could made a corrosion transformation from malachite (CuCO3·Cu(OH)2) into azurite (2(CuCO3)·Cu(OH)2”. The authors should also quantify the high concentration of CO2 and explain its role in the transformation of malachite in azurite.
Reply: Thanks for the comment!
“early usage” may be a wrong sentence! We want to say that, probably, the bronze vessel (Ding) was practically used during the Western Han Dynasty, because the element carbon was detected. Therefore, we change the sentence into a new one: "That was to say, the co-existence of carbon and the poor crystallized malachite (CuCO3·Cu(OH)2) demonstrated that the bronze vessel (Ding) might be practically used during the Western Han Dynasty its early usage and corroded during the long-term burial in the soil corrosion”
About the mutual transformation in-between malachite and azurite. As for our knowledge, in case of high CO2 concentration, malachite tends to transform into azurite, while in case of low CO2 concentration, azurite tends to malachite. This phenomenon was also confirmed in our previous work from the experimental simulations [1]. This reference has been added in the revised manuscript.
In this study, the conclusion of azurite as the "secondary corrosion" product was based upon the results, i.e., "Raman peak of bound water was missing, and the peak of free water H-O-H bending modes at 1612 cm-1 was very strong". Conversely, we speculated a high CO2 concentration during museum conservation. This measurement was carried out several years ago, and the sample has been returned to the museum. Actually, it will be better to have corrosion's co-existing relation for conforming this transformation. We will accept reviewer's good comments and pay more attentions in the further work.
[1] Wu Taotao, Meng Weiwei, Bao Zhirong, Li Yang, Pan Chunxu：“Study of synthesizing malachite corrosion product on the bronze surface in excessive CO2 atmosphere environment”，Journal of Chinese Society for Corrosion and Protection，2014, 34(1): 82-88。(In Chinese)
- Furthermore, many of the described transformations from a high symmetry of the “primary corrosion” to a low symmetry of the “secondary corrosion” are simply chemical reactions caused by the presence of aggressive environmental species that chemically react with the archaeological corrosion products as humidity and oxygen.
Reply: This transformation rule is occasionally summarized from the experimental results, and found it just meet the physical law of spontaneous symmetry-breaking. Actually, in our current work, it is also found that all metallic elements in the periodic table of elements and their corrosions meet this law, i.e., transformations from a high symmetry of pure metal to a low symmetry of the corrosion stage. This paper’s content regarding bronze corrosion is only a special case.
Actually, since the law of “spontaneous symmetry-breaking” won the Nobel Prize in Physics in 2008, many researches have demonstrated that the law of spontaneous symmetry-breaking can happen in a broad areas, not only in physics, but also in chemistry, biology, geography, astronomy and even sociology. The metal corrosion may also meet this general law of nature, and this is the significance of this paper. We are still working on this new area currently. In addition to the simple chemical reactions, possibly, there is an another crystalline factor controls the phase transforming direction.
- It is interesting the concept reported by the Authors at lines 330-334 “In case of the harmful "primary corrosion", make the "secondary corrosion" be a harmless one by reasonable control the atmospheric gas and ion concentration of the protection environment. For example, when the "primary corrosion" was orthohombic crystal system of atacamite (CuCl2·3Cu(OH)2) or monoclinic crystal system of clinoatacamite (Cu2(OH)3Cl), it could be converted into monoclinic crystal system of malachite (CuCO3·Cu(OH)2)”.
The authors should explain better this concept also on a practical point of view to give a new chance to the conservators to save from the destruction the bronze archaeological artifacts caused by the “bronze disease”.
Furthermore, the authors should consider the consequences of an irreversible chemical and structural treatment that could influence the chemical-physical stability of the whole artifact, the authors should also consider that the proposed method could not be a real solution reminding the genesis of the “bronze disease” caused by the presence of nantokite inside the patina.
Reply: The reviewer gives very good questions! This concept is just a prospect and possible further applications. We understand that the reviewer has many queries on this paper. We also want to know the answers. In our next work, we are planning to do the works, such as spontaneous symmetry-breaking in other metals’ corrosion transformation, do some experiments to confirm the controllability of the corrosion direction via adjusting the chemical reaction conditions. This is the first paper about this new discovery, and we expect to have more important results in the future.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper aims to discuss the Spontaneous Symmetry-Breaking in the study of the corrosion products of Ancient Bronzes.
The experimentation is appropriate and the results show different corrosion products found in different ancient artifacts under different burial conditions. Corrosion products are well analysed using different techniques. However, authors should explain better the conditions that could lead to the formation of those corrosion products, i.e. bronze composition, microstructures, environmental conditions and local chemistry while buried and also the conditions during preservation at the museum.
There are few misprints along the manuscript that should be checked.
As a suggestion I would change the word corrosions by something like corrosion stage or corrosion type.
Finally, while the paper is well structured and there is a good amount of experimental analysis, it is not properly explained how the spontaneous symmetry-breaking can predict the exact evolution of the corrosion product and how there is a real advantage in using that instead of controlling the conservation conditions based on thermodynamics and the Gibbs free energy. Could the authors explain a bit more how they would use the spontaneous symmetry breaking to predict the corrosion products evolution?
Author Response
Reply to the Comments
Comments and Suggestions for Authors
- The paper aims to discuss the Spontaneous Symmetry-Breaking in the study of the corrosion products of Ancient Bronzes.
The experimentation is appropriate and the results show different corrosion products found in different ancient artifacts under different burial conditions. Corrosion products are well analysed using different techniques.
However, authors should explain better the conditions that could lead to the formation of those corrosion products, i.e. bronze composition, microstructures, environmental conditions and local chemistry while buried and also the conditions during preservation at the museum.
Reply: Thanks for the comment! In general, the environmental conditions and local chemistry for growing ancient bronze corrosion are very complicated, and the corrosions were grew slowly within a long time. Sometimes, it is difficult, even impossible, to precisely detect the conditions, and the museum also does not have this data. Therefore, we can only infer the possible environmental conditions, such as the excess of H2O and CO2 gas concentrations, etc. from the detected corrosion products.
In the case of this paper, the experiments were carried out several years ago, and the samples have been returned to the museums. Currently, When we occasionally re-read the results, an interesting phenomenon is found that the corrosion transformation just meet the physical law of spontaneous symmetry-breaking. We think the present data in the manuscript is enough to support the conclusions.
There are few misprints along the manuscript that should be checked. As a suggestion I would change the word corrosions by something like corrosion stage or corrosion type.
Reply: Thanks for the comment! "corrosion stage" seems better. It has been added in the revised manuscript.
- Finally, while the paper is well structured and there is a good amount of experimental analysis, it is not properly explained how the spontaneous symmetry-breaking can predict the exact evolution of the corrosion product and how there is a real advantage in using that instead of controlling the conservation conditions based on thermodynamics and the Gibbs free energy. Could the authors explain a bit more how they would use the spontaneous symmetry breaking to predict the corrosion products evolution?
Reply: Thanks for the comment! These queries are also what we concern and are looking forward to having an answer.
Actually, since the law of “spontaneous symmetry-breaking” won the Nobel Prize in Physics in 2008, many researches have demonstrated that the law of spontaneous symmetry-breaking can happen in a broad areas, not only in physics, but also in chemistry, biology, geography, astronomy and even sociology. This corrosion transformation may be a new area.
Currently, we are working on this area, and new research reveals found that all metallic elements in the periodic table of elements and their corrosion transformations also meet this rule, i.e., transformations from a high symmetry of pure metal to a low symmetry of the corrosion stage. In addition, We are going to carry out experiments to intensively control the condition and get the desired corrosions based on the prediction from the law of spontaneous symmetry breaking. This paper is only the first work on this new discovery, and we expect to have more important results in the future.
Regarding the mechanism of corrosion transformation, in addition to the thermodynamics and the Gibbs free energy, the “spontaneous symmetry-breaking” seems a new criterion. However, what is the internal relation and why does the crystalline symmetry tend to reduce? It still a question! In general, a crystal structure with high symmetry is of a high internal energy and tend to transform into a state of low internal energy, such as γ-Fe to α-Fe, during cooling. This transformation can be comparable due to the isomeric. However, the metal corrosion occurs in regard to chemical reaction and seems that the internal energy of the substances before and after corrosion has no compatibility. Therefore, more deep study needs to be done in the future.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The quality of the manuscript has been improved and I suggest to publish it in the present form.
Reviewer 2 Report
changes have been addressed
