Tribological Properties of Attapulgite Nanofiber as Lubricant Additive for Electric-Brush Plated Ni Coating
Round 1
Reviewer 1 Report
-In the line of 15, not ball-disk, ball-disc. Moreover, please dont use abbreviation before given its meaning, for example, SRI-IV.
-In the line of 17, what is 150SN? provide describing.
-I couldnt understand the novelty of this work. The novelty of the work must be given in the last paragraph of introduction in detail. At what point is there a deficiency in this field in the literature, and what deficiency does this study address? Specify.
-How did the authors determine the hardness of the coating?
-Coating layer characterization, such as coating thickness, nanofiber distribution within the nanofiber doped coating layer, is a major shortcoming for this publication. These characterization processes can be done by presenting SEM and EDs-mapping, EDS-spectrum images.
-I suggest analyzing SEM images of the debris to better understand the wear mechanisms. In addition to SEM images, EDS mapping images can also provide evidence.
Author Response
-In the line of 15, not ball-disk, ball-disc. Moreover, please dont use abbreviation before given its meaning, for example, SRI-IV.
Reply: All ball-disk in the paper has been corrected to ball-disc. SRV- IV is the model of the friction and wear tester.
-In the line of 17, what is 150SN? provide describing.
Reply: 150SN is the brand of the lubricating oil, we have corrected it.
-I couldnt understand the novelty of this work. The novelty of the work must be given in the last paragraph of introduction in detail. At what point is there a deficiency in this field in the literature, and what deficiency does this study address? Specify.
Reply: We have specified in the introduction of revised manuscript.
-How did the authors determine the hardness of the coating?
Reply: The hardness of the coating was determined by HVS-1000 microhardness tester.
-Coating layer characterization, such as coating thickness, nanofiber distribution within the nanofiber doped coating layer, is a major shortcoming for this publication. These characterization processes can be done by presenting SEM and EDs-mapping, EDS-spectrum images.
Reply: We have added the cross-sectional morphology of the coating, so the coating thickness can be seen. We are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide the nanofiber distribution in the coating. We will analysis the SEM and EDs-mapping, EDS-spectrum images of the nanofiber distribution in the coating after the repairing of the friction and wear tester.
-I suggest analyzing SEM images of the debris to better understand the wear mechanisms. In addition to SEM images, EDS mapping images can also provide evidence.
Reply: The suggestion is very good. But, we are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide the SEM images and EDS mapping images of the debris. We will analysis the SEM images of the debris after the repairing of the friction and wear tester.
Reviewer 2 Report
The authors have presented quite an interesting topic concerning the tribological properties of attapulgite – a natural mineral as an additive to lubricating oil. The article summarized the results of experiments on friction and wear behaviour of the additive applied for specific tribological pair. Tribological tests were performed on a ball-on-flat tribometer to assess the effectiveness of the additive’s antifriction and antiwear properties. After the tests, the coefficient of friction and wear were measured/calculated; the surface of the samples have been examined using SEM+EDS and XPS spectroscopy. The results of the experiments confirmed the improvement in friction and wear reduction of the attapulgite additive.
The manuscript as a whole is clear and provides quite new knowledge about understanding the mechanism of the action of the additive, the influence of its concentration in the lubricant and the influence of load on friction and wear behaviour. The results of the experiments seem to have a practical meaning for future technological development. The layout of the article and its structure are appropriate for this type of work. Unfortunately, not all methodological details are presented comprehensively and systematically.
In my opinion, some issues will need to be addressed before becoming suitable for publication, i.e., it can be reconsidered for publication after a minor revision. Spell-check and stylistic revision of the English of the paper are still necessary. Some misspellings, wrong word order, etc. are noticeable throughout the whole text. The main substantive issues are as follows:
1. It is not clearly explained why the authors chose: Ni coatings, AISI 1045 substrate, 150SN lubricating oil.
2. Keywords – the word “keyword” should be removed.
3. Line 35 – the references [8-] should be specified ([8-9]?
4. Line 42 – “Substrate” should rather be replaced by “substrate”
5. Line 81 – There is no such information about the grain size (grain size distribution) of the ATP powders. One type or more? This information seems to be important for the results of the experiment.
6. Lines 100-103 – There is no information concerning the thickness of the coating. Has it been assessed?
7. Line 116 – agglomeration of the particles can be crucial when it comes to their effectiveness – was the dispersion assessed? Are you sure that particles do not agglomerate or condense? Any confirmation with test results (photographs)?
8. Line 127-128 – what about the wear of the AISI 52100 steel balls? Was it measured? What about SEM+EDS and XPS analysis of steel balls?
9. Line 148 – the word “nanoparticles” is repeated.
10. Line 154 – was the roughness of the coatings measured? The authors only informed that the coating was smooth – that information requires more precise data. How about the adhesion of the coating to the substrate? Was it assessed?
11. Line 162 and Figure 3 – it is not clearly indicated if the value of friction coefficient and wear volume (0%) is for pure 150SN or with oleic acid. Was the oleic acid added to the pure (0% ATP) oil?
12. Line 175 – actually, the friction pair (ball and disk) are running-in - not the lubricant.
13. Line 312 – only for the Ni coatings? Any conclusions/predictions when it comes to other materials?
Author Response
The authors have presented quite an interesting topic concerning the tribological properties of attapulgite – a natural mineral as an additive to lubricating oil. The article summarized the results of experiments on friction and wear behaviour of the additive applied for specific tribological pair. Tribological tests were performed on a ball-on-flat tribometer to assess the effectiveness of the additive’s antifriction and antiwear properties. After the tests, the coefficient of friction and wear were measured/calculated; the surface of the samples have been examined using SEM+EDS and XPS spectroscopy. The results of the experiments confirmed the improvement in friction and wear reduction of the attapulgite additive.
The manuscript as a whole is clear and provides quite new knowledge about understanding the mechanism of the action of the additive, the influence of its concentration in the lubricant and the influence of load on friction and wear behaviour. The results of the experiments seem to have a practical meaning for future technological development. The layout of the article and its structure are appropriate for this type of work. Unfortunately, not all methodological details are presented comprehensively and systematically.
In my opinion, some issues will need to be addressed before becoming suitable for publication, i.e., it can be reconsidered for publication after a minor revision. Spell-check and stylistic revision of the English of the paper are still necessary. Some misspellings, wrong word order, etc. are noticeable throughout the whole text. The main substantive issues are as follows:
- It is not clearly explained why the authors chose: Ni coatings, AISI 1045 substrate, 150SN lubricating oil.
Reply: Electroplated Ni coatings has excellent physical and chemical properties and good atmospheric corrosion resistance, and is widely used in automobiles, machinery, instruments, and daily industrial products.
AISI 1045 substrate is a commonly used substrate material for electric-brush plated Ni coating.
150SN lubricating oil is a common type lubricating oil.
- Keywords – the word “keyword” should be removed.
Reply: We have removed the word “keyword”.
- Line 35 – the references [8-] should be specified ([8-9]?
Reply: We have corrected it.
- Line 42 – “Substrate” should rather be replaced by “substrate”
Reply: We have corrected it.
- Line 81 – There is no such information about the grain size (grain size distribution) of the ATP powders. One type or more? This information seems to be important for the results of the experiment.
Reply: We have added the grain size distribution of the ATP powders in the revised manuscript.
- Lines 100-103 – There is no information concerning the thickness of the coating. Has it been assessed?
Reply: We have added the cross-sectional morphology of the coating, so the thickness of the coating can be seen.
- Line 116 – agglomeration of the particles can be crucial when it comes to their effectiveness – was the dispersion assessed? Are you sure that particles do not agglomerate or condense? Any confirmation with test results (photographs)?
Reply: We had assessed the particles dispersion in oil. We found that the ATP powders has good dispersion stability in oil more than one month. We are so sorry that the oil was poured out. So we cannot provide relevant photographs.
- Line 127-128 – what about the wear of the AISI 52100 steel balls? Was it measured? What about SEM+EDS and XPS analysis of steel balls?
Reply: The suggestion is very good. But, we are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide the wear, SEM+EDS and XPS analysis of the AISI 52100 steel balls. We will analysis the steel balls after the repairing of the friction and wear tester.
- Line 148 – the word “nanoparticles” is repeated.
Reply: We have corrected it.
- Line 154 – was the roughness of the coatings measured? The authors only informed that the coating was smooth – that information requires more precise data. How about the adhesion of the coating to the substrate? Was it assessed?
Reply: We have added the surface roughness and the cross-sectional morphology of the coating in the revised manuscript.
- Line 162 and Figure 3 – it is not clearly indicated if the value of friction coefficient and wear volume (0%) is for pure 150SN or with oleic acid. Was the oleic acid added to the pure (0% ATP) oil?
Reply: The oleic acid was added to the pure oil.
- Line 175 – actually, the friction pair (ball and disk) are running-in - not the lubricant.
Reply: We have corrected it.
- Line 312 – only for the Ni coatings? Any conclusions/predictions when it comes to other materials?
Reply: We have only studied the Ni coatings. We will continue to study other materials In the future.
Reviewer 3 Report
Response of the reviewer
Manuscript Number: 2273176
Title: Tribological properties of attapulgite nanofiber as lubricant ad-2 ditive for electric-brush plated Ni coating
This work deals with the capability of Attapulgite fibers to improve the tribological properties of 150SN oil when lubricating a steel-Ni pair. In the work the friction coefficient and the surface wear rate were estimated by means of reciprocating ball-on-disc tests for different additivation percents and different loads, in the range of 0-0.8 wt% and 10-100 N, respectively. At 50 N load the tests show that in the exploited concentration range all the solutions enable a decrease of the CoF and wear rate with respect to the non-additivated oil, but an optimal percent of 0.4wt% was found. Fixing 0.4wt% concentration, in the load range 10-100 L the CoF of the additivated oil results always lower with respect to the corresponding non-additivated, but no trend were found varying the load. Similar results were found for the wear rate, but in this case the wear appears increasing with increasing load. For the chemical analysis it follows that a tribofilm forms on the wear track, based on the species which composes Attapulgite.
Response
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Comments and remarks
- Page 1, line 24-26, the Authors mention that 1/3-1/2 of the energy produced in the world is lost by friction. They should add at least one reference to support this statement.
- Page 2, line 64, the Authors write:" (2) Attapulgite possess high storage capacity in nature;". What do they mean with "storage capacity"?
- Page 4, line 142-150, check English.
- Page 4, line 154, the Authors commenting Fig. 2a describe the surface as "smooth". Could they add a value of the roughness?
- Page 5, line 164, check English.
- Page 5, Fig. 3, the Authors plot the CoF vs Additive amount.
How are calculated the reported value?
Are they the average CoF all over the tribo test?
Are the error bars related to the CoF oscillation in one single test, or are they related to the CoF dispersion in the 3 tests?
- Page 6, line 184-186, the Authors report on the decrease of friction increasing the load. This behavior was already observed for C-based materials [Tribol. Lett. 52 (2019) 469-475. https://doi.org/10.1007/s11249-013-0230-y.; Surf. Coat. Technol. 86-87 (1996) 564-568. https://doi.org/10.1016/S0257-8972(96)03057-5].
Can the Authors give an interpretation about this behavior for Attapulgine?
- Page 6, Fig. 4, all the friction curves show an initial peak in the CoF. Have the Authors an interpretation of this phenomenon?
- Page 6, Fig. 5, the error bars associated to the average CoF appear very small, but observing the friction curve of Fig. 4, the CoFs undergo much higher variation. For example, the CoF in Fig. 4 for 20N load varies from about 0.17 to 0.3; however, in Fig. 5 the corresponding CoF varies between about 0.23 and 0.24 (or even less), considering the error bar.
How the Authors calculated the error average value and the error bars in Fig. 5?
- page 6, line 206-212, the Authors describe the SEM image of Fig. 6, identifying some surface features. It should be useful to mark some of these features in the image.
- Page 7, line 234-238, the Authors analyzed the XPS spectra in the wear tracks, finding "Ni, NiO, Al2O3, SiO2, graphite and organic compound" on the basis of the fitting procedure with Gaussian peaks. However, the XPS peaks appear very noisy and the corresponding fitting operation becomes very inaccurate. In particular, the deconvolution of C1s and O1s peak are really overly ambitious.
The Authors should present less noisy data in order to state about the chemical composition of the tribofilm.
- Page 8, line 253-259, this paragraph is very general and it would be much more useful in the Introduction, where discussing on Attapulgite. Same thing for Fig. 10.
- Page 9, Fig. 9, this figure is overabundant and it should be removed.
- Page 10, line 283-287, the Authors state that the reason why the tribological performances of Attapulgite decreases for more than 0.4% is related to the formation of abrasive particles. This explanation shouldn't be the unique explanation. It is possible that for concentration higher than 0.4% the tribofilm has different chemical characteristics, for example.
Did the Authors check with XPS the worn surface for different amount of Attapulgite?
Did they check with SEM the presence of nanoparticles that can induce abrasive wear?
- Page 10, line 289-294, the Authors attribute the fluctuation of the CoF to the roughness of the surface. However, the roughness can increase the average CoF value and/or the noise, but not the trend during the test. The variation of the average CoF along the test must be related to other processes.
- Page 10, line 307-309, the Authors state that changing the contact configuration should influence the formation of the tribofilm. This statement must be supported by some tests.
Author Response
- Page 1, line 24-26, the Authors mention that 1/3-1/2 of the energy produced in the world is lost by friction. They should add at least one reference to support this statement.
Reply: We have added a reference.
- Page 2, line 64, the Authors write:" (2) Attapulgite possess high storage capacity in nature;". What do they mean with "storage capacity"?
Reply: We have corrected "storage capacity" into "reserves".
- Page 4, line 142-150, check English.
Reply: We have checked and modified it.
- Page 4, line 154, the Authors commenting Fig. 2a describe the surface as "smooth". Could they add a value of the roughness?
Reply: We have added the surface roughness of the coating.
- Page 5, line 164, check English.
Reply: We have checked and modified it.
- Page 5, Fig. 3, the Authors plot the CoF vs Additive amount.
How are calculated the reported value?
Are they the average CoF all over the tribo test?
Are the error bars related to the CoF oscillation in one single test, or are they related to the CoF dispersion in the 3 tests?
Reply: The average CoF is the average value after running-in. The error bars are related to the CoF dispersion in the 3 tests.
- Page 6, line 184-186, the Authors report on the decrease of friction increasing the load. This behavior was already observed for C-based materials [Tribol. Lett. 52 (2019) 469-475. https://doi.org/10.1007/s11249-013-0230-y.; Surf. Coat. Technol. 86-87 (1996) 564-568. https://doi.org/10.1016/S0257-8972(96)03057-5].
Can the Authors give an interpretation about this behavior for Attapulgine?
Reply: The two articles are about DLC films. Its composition is more simple than the tribofilm formed through attapulgite. In addition, we have preliminary explore the behavior in the discussion section. We will conduct in-depth research in the future.
- Page 6, Fig. 4, all the friction curves show an initial peak in the CoF. Have the Authors an interpretation of this phenomenon?
Reply: This phenomenon is attributed to the running-in of the friction pair.
- Page 6, Fig. 5, the error bars associated to the average CoF appear very small, but observing the friction curve of Fig. 4, the CoFs undergo much higher variation. For example, the CoF in Fig. 4 for 20N load varies from about 0.17 to 0.3; however, in Fig. 5 the corresponding CoF varies between about 0.23 and 0.24 (or even less), considering the error bar.
How the Authors calculated the error average value and the error bars in Fig. 5?
Reply: The error average value and the error bars are calculated through at least 3 tests.
- page 6, line 206-212, the Authors describe the SEM image of Fig. 6, identifying some surface features. It should be useful to mark some of these features in the image.
Reply: We have marked some of these features in the image.
- Page 7, line 234-238, the Authors analyzed the XPS spectra in the wear tracks, finding "Ni, NiO, Al2O3, SiO2, graphite and organic compound" on the basis of the fitting procedure with Gaussian peaks. However, the XPS peaks appear very noisy and the corresponding fitting operation becomes very inaccurate. In particular, the deconvolution of C1s and O1s peak are really overly ambitious.
The Authors should present less noisy data in order to state about the chemical composition of the tribofilm.
Reply: We are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide less noisy data.
- Page 8, line 253-259, this paragraph is very general and it would be much more useful in the Introduction, where discussing on Attapulgite. Same thing for Fig. 10.
Reply: Figure 8 is the experimental results. I think it is not suitable to be put it in the Introduction.
Figure 10 is used to discuss the friction-reduction and antiwear mechanism. So we put it in the discussion section.
- Page 9, Fig. 9, this figure is overabundant and it should be removed.
Reply: We have removed this figure.
- Page 10, line 283-287, the Authors state that the reason why the tribological performances of Attapulgite decreases for more than 0.4% is related to the formation of abrasive particles. This explanation shouldn't be the unique explanation. It is possible that for concentration higher than 0.4% the tribofilm has different chemical characteristics, for example.
Did the Authors check with XPS the worn surface for different amount of Attapulgite?
Did they check with SEM the presence of nanoparticles that can induce abrasive wear?
Reply: We are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide the XPS and SEM. We will do the work after the repairing of the friction and wear tester.
- Page 10, line 289-294, the Authors attribute the fluctuation of the CoF to the roughness of the surface. However, the roughness can increase the average CoF value and/or the noise, but not the trend during the test. The variation of the average CoF along the test must be related to other processes.
Reply: We are so sorry that we don't know how to answer this question.
- Page 10, line 307-309, the Authors state that changing the contact configuration should influence the formation of the tribofilm. This statement must be supported by some tests.
Reply: We are so sorry that the SRV- IV friction and wear tester is out of condition now. Therefore, we cannot provide related test datas. We will do the work after the repairing of the friction and wear tester.
Round 2
Reviewer 1 Report
Thanks the authors for their laborious revisions.
