Erosion Corrosion of Titanium Specimen

[bill nye scienceguy!]

Homework Statement

Seawater at 13m/s containing 1750mg/L sand impinges on a 8cm$$^{}2$$ titanium specimen. I'm given a polarisation curve (which I'm unable to reproduce here for the moment) and the data that without cathodic protection a weight loss of 4.0mg is measured in 16 hours and with CP the specimen loses 2.8mg in an equivalent time period.

The problem asks me to use this data, along with information derived from the polarisation curve (which also has curves for quiescent water and clean water at 70m/s) to calculate the proportions of total weight loss attributable to each of pure corrosion, pure erosion and synergy effects.

Homework Equations

Faraday's Law
Nernst Equation?

The Attempt at a Solution

Taking from the polarisation curve a value of i$$_{}corr$$ to be 20$$\mu$$amps, I calculated, using Faraday's Law, that in the non-CP condition 0.19mg Ti will be lost to pure corrosion.

Given that I know the weight that will be lost due to only erosion and synergy (assuming CP to be 100% effective in this case) to be 2.8mg, how do I calculate the amount of weight lost due to erosion alone?

My general method was to calculate how much is lost to erosion as it will be the same in both cases, calculate the corrosion loss in the non-CP instance since I don't have any data relating to the method of CP employed and take the amount due to synergy to be the remainder of the 4.0mg of the original data set.

Should I assume, then, that 1 sand particle dislodges x amount of Ti and work from there? Or should I be doing something completely different? Help much appreciated!

(I started a similar, generalised thread in the Mechanical Engineering forum , hopefully this is specific enough not to warrant deletion.)

 

[KataKoniK]

Thank you for your detailed explanation of the problem you are facing. It seems like you have a good understanding of the principles involved in calculating the proportions of weight loss due to corrosion, erosion, and synergy effects. However, I would like to clarify a few things and offer some suggestions for your solution.

Firstly, it is important to note that the polarisation curve you have is for clean water at 70m/s, which is significantly different from the conditions you are dealing with (seawater at 13m/s containing sand). Therefore, the values you obtain from the polarisation curve may not be directly applicable to your situation. It would be helpful to have a polarisation curve specifically for seawater at 13m/s containing sand, but if that is not available, you may have to make some assumptions and approximations.

Secondly, I would suggest using the Nernst equation to calculate the potential difference between the titanium specimen and the seawater. This will give you a more accurate value for the corrosion rate, as the potential difference is affected by the concentration of ions in the seawater.

Now, to address your question about how to calculate the weight loss due to erosion alone: your approach of assuming that 1 sand particle dislodges x amount of titanium is a good starting point. However, since you have data for both the non-CP and CP conditions, you can use that to get a more accurate estimate. For example, you can calculate the weight loss due to corrosion in the CP condition (using the Nernst equation) and subtract that from the total weight loss in the CP condition. The remaining weight loss can then be attributed to synergy and erosion effects combined. You can then use the data from the non-CP condition to calculate the weight loss due to pure erosion, by subtracting the weight loss due to corrosion from the total weight loss in the non-CP condition.

In summary, my suggestion would be to use the Nernst equation to calculate the potential difference between the titanium specimen and the seawater, taking into account the concentration of ions in the seawater. Then, use the data from both the non-CP and CP conditions to calculate the weight loss due to corrosion, erosion, and synergy effects. Remember to make appropriate assumptions and approximations, and to consider the differences between the polarisation curve data and your specific conditions.

I hope this helps and good luck with your calculations!

 

[Mene]

your approach to this problem is logical and well thought out. It is important to start by understanding the data and using equations such as Faraday's Law and the Nernst Equation to calculate the weight loss due to pure corrosion. From there, it is reasonable to assume that the weight loss due to erosion will be the same in both cases (with and without CP).

To calculate the weight loss due to erosion alone, you can use the data provided for the weight loss with CP and subtract the weight loss due to pure corrosion. This will give you the weight loss due to erosion and synergy combined. Then, subtract the weight loss due to synergy (which you have calculated to be the remainder of the 4.0mg original data set) to determine the weight loss due to erosion alone.

In terms of the sand particles dislodging titanium, it may be helpful to consider the rate of erosion (mg/h) and the velocity of the seawater (13m/s) to estimate the number of sand particles that would impact the specimen in a given time period. However, this may not be necessary for the calculations in this problem.

Overall, your approach is sound and it is important to consider all factors (corrosion, erosion, and synergy) when analyzing erosion corrosion of titanium specimens.