ISIJ

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ELECTROLYTE CHARACTERIZATION

ANALYSIS AND PROPERTIES FOR PROCESS OPTIMIZATION

Index

Introduction

Lifespan

Performance

ATest

BTest

Baumer sensor

Results

Conclusions

Final coments

What is it?

The lifetime of the media will be defined as the amount of material able to remove by a specific volume of electrolyte (g/L), capable of performing a proper polishing result.

LIFESPAN

Intro

The electrolyte contains ion-exchange resins with reactive sites that trap metal ions during polishing. As these sites become saturated, the electrolyte loses its ability to continue reacting efficiently with the metal

*1 (weighted according to the elements present in the titanium alloys)

Using the following values the theoretical charge per liter is determined:

• Faraday constant
• Number of exchanged electrons*1
• Molar mass*1
• Mass per liter

A theoretical value is calculated based on the maximum capacity of the electrolyte to capture mass. For example, in the case of titanium, it is established that 260 liters of electrolyte can capture up to 2 kg, equivalent to 0.00769 kg/L.

THEORETICAL CHARGE PER MASS

STEP

1st

How is it calculated?

LIFESPAN

Intro

b)

a)

The ratio between these two values is applied to the initial theoretical value in coulombs per liter. This adjusts the charge to reflect real operating conditions.

Experimental tests are conducted under varying parameters, measuring: a) The charge per current passing through the system. b) The charge per mass, obtained from the weight variation of the sample.

CALCULATION OF EXPERIMENTAL RATIO

STEP

2nd

How is it calculated?

LIFESPAN

Intro

From the maximum charge adjusted per liter, it is multiplied by the total volume of electrolyte in the system. This yields the maximum charge configured for the electrolyte in the machine.

MAXIMUM TOTAL CHARGE

STEP

3rd

How is it calculated?

LIFESPAN

Intro

The time pulse in which the metal oxidizes, i.e. transforms into an ion, corresponds to the positive one. In addition, experimentally the positive current charge is the most similar to that calculated through the mass.

How is it calculated?

LIFESPAN

Intro

Component degradation: Secondary reactions can degrade electrolyte components, affecting its performance. Temperature: Fluctuations in temperature can alter reactivity and polishing efficiency.

TO CONSIDER DURING POLISHING

Important factors

Water evaporation: Water loss can change the concentration of solutes and thus affect the polishing process. Solid-liquid ratio: Changes in this ratio can alter polishing effectiveness as, for example, a more compact medium can be reflected on a conductivity increase.

PERFORMANCE

Intro

The performance of an electrolyte refers to the effectiveness and quality of the polishing performed during the use of the electrolyte. This performance can be affected by several factors not necessarily related to the electrolyte's lifespan.

1. Water 23.8 mm Hg
2. MSA 0.000428 mmHg
3. Sulfuric acid 5.93 × 10⁻⁵ mmHg

Stabilization time: There is typically a stabilization period where the system reaches equilibrium.

Absortion capacity: Resins have a certain capacity to absorb water and other ionic solutions. This limit is crucial for controlling the overall water content in the system.

CHALLENGES AND KEY FACTORS

What are the challenges involved?

Water absortion: Water enters the resin particles with other components such as acid. Then, only water content is reduced by evaporation. At 25ºC the vapor pressure of the following substances is:

PERFORMANCE

Intro

How much variation in water content is necessary for the parts to still yield good results?

Initially, it seemed like a potential control variable, but

To determine if it could be used as an indicator initially, the % of water in an electrolyte was measured in its initial state. Several polishing steps were performed without controlling the temperature, in order to heat it and induce a decrease in water content.

VARIANCE OF MEASUREMENTS

Is IR useful for electrolyte characterization?

ATest

Machine: Pro100 & chiller (16L)

SAMPLES PER HOLDER

POLISHED SAMPLES

300

HOURS

150

POLISHING PROCESSES

50

PROCESS

BTest

SAMPLE'S CHARACTERIZATION

ELECTROLYTE'S CHARACTERIZATION

CHARGE

IMPEDANCE

CONFOCAL ANALYSIS (SA)

COLLOCATION

EYE CONTROL

LIFESPAN

IMAGE CONTROL

INTENSITY

IR - WATER CONTENT

WEIGHT

TEMPERATURE

BTest

VARIABLES

IMPEDANCE

Baumer sensor

IMPEDANCE

Baumer sensor

Water content

Acid concentration

Surfactants

Vibration

Solid-liquid proportion

Temperature

FOUNDRY+VIBRATORY GRINDING

DOWN

Preprocess

Visual Aspect Scores

MILLING +VIBRATORY GRINDING

RESULTS

VISUAL REFERENCE EXAMPLE

UP

Before

DOWN

UP

RESULTS

VISUAL REFERENCE EXAMPLE

RESULTS

VISUAL PUNCTUATION RESUME

This chart presents a summary of the visual valuation established for each piece, from the top - in the chart above - and from the bottom - in the chart below. Those numbered 4 were passivated pieces due to external technical errors.

RESULTS

STABILIZATION TIME

It took 4 polishing process to completely stabilize the electrolyte from the beggining mix performed.

RESULTS

STABILIZATION TIME

Part 2 was added because of a pump change. This implied a liquid refill in order to compensate the liquid lost during the change. In the part two there is water, so the intensity incresed, the impedance decreased and oxide was formed in some samples. It can be seen as the electrolyte liquid part turns white when there is exces of water.

RESULTS

MASS AND LIFETIME

This graph shows the variation of mass with respect to intensity. In this one there is a clearly visible relation: the more intensity the more mass extracted. This relationship is described by Faraday's law of electrolysis already presented.

RESULTS

MASS AND LIFETIME

This graph compares the load calculated from the amperes flowing through the system with the load corresponding to the extracted mass of titanium. It is observed a straight line with a slope, quite located at 45 degrees. Therefore, there is a direct correlation between these two.

RESULTS

MASS AND LIFETIME

This graph shows how the percentage of useful life decreases according to the average intensity applied to the system. With this and the previous graph, the concept of electrolyte life can be better understood.

RESULTS

BAUMER - IMPEDANCE

This graph shows that lower values of the baumer sensor pass more current in the circuit. This is because it decreases the impedance of the electrolyte, adding water. The main effect of adding water to the electrolyte is to increase the ion transfer surface area, which improves conductivity and reduces impedance.

This is the same graph as the previous one, but the different points are differentiated by the visual evaluation of the lower part of the piece, where green points are good results, yellow points are intermediate and red points are bad results. It is observed that from baumers higher than 12.5 good results are obtained. This is a reference value to be taken into account.

RESULTS

BAUMER - IMPEDANCE

Remember: Impedance Intensity

In order to not only make a visual assessment, the baumer was also compared with the roughness variation experienced on both sides of the part. In this graph the lower part is compared. Negative variations - due to the creation of oxides - are observed in the parts made at lower baumer responses.

RESULTS

BAUMER - IMPEDANCE

Remember: Impedance Intensity

The upper part of the part always presents similar variations of Sa without depending on the impedance of the electrolyte, therefore, as it is observed, it does not allow to draw conclusions. Neither through visual assessment, since the results are similar.

RESULTS

BAUMER - IMPEDANCE

In this graph, instead of comparing the variation of Sa with the baumer, it is compared with the intensity to see if there is any limiting value. It is possible to estimate a limiting value of 4 amperes, since above this value there are no results marked as really good.

RESULTS

INTENSITY - SURFACE

The IR technique does not allow for definitive conclusions, as the detected water percentage shows considerable variation across the range of results. For example, with a reading of 38% water content, both good and poor results are observed. Similarly, with a reading of 48% water content, there is a wide range of different results. This variability makes it difficult to draw conclusive findings using the IR method.

RESULTS

IR - VARIATION DOWN

*1 (only in this set up)

consumed

29%

Coulombs

322.865

CHARGE THROUGH INTENSITY

consumed

24%

Coulombs

260.143

CHARGE THROUGH MASS

CONCLUSIONS

*1 (only in this set up)

CONCLUSIONS

SAMPLE ORIENTATION

OTHER PARAMETERS

to stabilize

12 h

max

4 A

BAUMER

12,5 %

total

35,84 g

stainless steel

33,15 g

titanium

2,7 g

METAL EXTRACTION

Surfactants

In this case, the p-value exceeds 0.025, presenting a close value that is 0.06. As it presents a value close to the limit, it may be that surfactants have small influence on the reactance, even so, since its value is of a much higher order than other values, it will not be taken into consideration.

Solid-liquid proportion

As we have just discussed, the proportion of solid liquid influences the response due to the pressure exerted on the sensor.

Vibration

Vibration influences the results, since the lower the pressure on the sensor, the higher the measured reactance value. This effect can also be observed in the response according to the solid-liquid ratio for the same reason.

Water content

In this case, the p-value is lower than 0.025, indicating that the result presents a statistical significance. The amount of water influences the reactance response displayed by the sensor. In the previous study, it is the second most important variable.

Acid concentration

In this case, the p-value exceeds 0.025, indicating that the result lacks statistical significance. The detection of the impedance presents high variability depending on the amount of acid, therefore it cannot be said that it influences the response.

Temperature

Finally, temperature exceeds the p-value of 0.025, therefore it has no statistical significance. Thus it does not matter at what time the electrolyte reactance measurement is taken, before or after use.