Increasing Viscosity of low concentration acid

[Pashtet]

Hi everyone,

I am looking for a bit of help with a chemistry question. I am doing a lot of metallographic etching (weld cross sections) and are currently using two different diluted acids:

1. For steel metallographic samples - 10% ammonium persulfate in water

2. For aluminum metallographic samples - 10% NaOH in water

Both liquids are very thin (low viscosity) and run off the samples so I have to constantly reapply the acid. I would like to make them thicker (e.g. paint or gel viscosity level). I was thinking of using some off the shelf water thickeners like gelatin. However, I do not know if this will create any unexpected reactions. I do not remember much from the high school/university chemistry courses (I am a mechanical engineer by training). Can somebody help me to predict what reactions I am going to see or suggest some other thickeners? 

I would really appreciate any suggestions,

Thanks!

[studiot]

Can I start with a small correction ?

Neither of the compounds you mention are acids!

Ammonium persulphate is a moderately strong oxidising agent

Sodium hydroxide is moderately strong alkali.

 

Not that I am concerned for your etching processes but it could make a significant difference to your thickener.

I'm not sure about gelatin, so I would suggest thegood old fashioned method of try a small amount and see.

But I would also suggest perhaps some alternatives,

Gloy  that old fashioned gloopy paper glue/paste.

Perhaps a starch based thickener (mashed potato, cornflour etc ) rather than a protein based one (proteins are pH sensitive)

 

 

[exchemist]

18 minutes ago, studiot said:

Can I start with a small correction ?

Neither of the compounds you mention are acids!

Ammonium persulphate is a moderately strong oxidising agent

Sodium hydroxide is moderately strong alkali.

 

Not that I am concerned for your etching processes but it could make a significant difference to your thickener.

I'm not sure about gelatin, so I would suggest thegood old fashioned method of try a small amount and see.

But I would also suggest perhaps some alternatives,

Gloy  that old fashioned gloopy paper glue/paste.

Perhaps a starch based thickener (mashed potato, cornflour etc ) rather than a protein based one (proteins are pH sensitive)

 

 

I think the persulphate may oxidise starch. But it could be tried, at least.

Alkali I think can make starch more gelatinous - which could be what is wanted.  

[chenbeier]

2 hours ago, Pashtet said:

Hi everyone,

I am looking for a bit of help with a chemistry question. I am doing a lot of metallographic etching (weld cross sections) and are currently using two different diluted acids:

1. For steel metallographic samples - 10% ammonium persulfate in water

2. For aluminum metallographic samples - 10% NaOH in water

Both liquids are very thin (low viscosity) and run off the samples so I have to constantly reapply the acid. I would like to make them thicker (e.g. paint or gel viscosity level). I was thinking of using some off the shelf water thickeners like gelatin. However, I do not know if this will create any unexpected reactions. I do not remember much from the high school/university chemistry courses (I am a mechanical engineer by training). Can somebody help me to predict what reactions I am going to see or suggest some other thickeners? 

I would really appreciate any suggestions,

Thanks!

I worked also in a metallographic lab. I know this problem, we used the etchchemical in this way that either the whole microsection of the sample was immersed into the etching solution in a small bowl or a Q tip was used and wiped over the sample followed by good rinsing. Changing of the receipe guide to different etching results. Also the etching glue sticks to strong and cannot removed quick enough to avoid over etching.

Edited July 15, 2022 by chenbeier

[sethoflagos]

On 7/15/2022 at 3:27 PM, Pashtet said:

Hi everyone,

I am looking for a bit of help with a chemistry question. I am doing a lot of metallographic etching (weld cross sections) and are currently using two different diluted acids:

1. For steel metallographic samples - 10% ammonium persulfate in water

2. For aluminum metallographic samples - 10% NaOH in water

Both liquids are very thin (low viscosity) and run off the samples so I have to constantly reapply the acid. I would like to make them thicker (e.g. paint or gel viscosity level). I was thinking of using some off the shelf water thickeners like gelatin. However, I do not know if this will create any unexpected reactions. I do not remember much from the high school/university chemistry courses (I am a mechanical engineer by training). Can somebody help me to predict what reactions I am going to see or suggest some other thickeners? 

I would really appreciate any suggestions,

Thanks!

Perhaps you could thicken your reagents by adding - 15% by weight plain tissue paper and grinding it into a thick slurry. This should adhere pretty well to your surface and keep the surface evenly wetted via capilliary action. When you're done, a quick rinse under the tap will remove it immediately.

There shouldn't be any adverse reactions since the cellulose fibres will almost certainly have seen both high alkalinities and aggressive bleaching during manufacture. 

Edited July 20, 2022 by sethoflagos
sp

[studiot]

55 minutes ago, sethoflagos said:

Perhaps you could thicken your reagents by adding - 15% by weight plain tissue paper and grinding it into a thick slurry. This should adhere pretty well to your surface and keep the surface evenly wetted via capilliary action. When you're done, a quick rinse under the tap will remove it immediately.

There shouldn't be any adverse reactions since the cellulose fibres will almost certainly have seen both high alkalinities and aggressive bleaching during manufacture. 

What a good idea and example of lateral thinking.  +1

 

Take an immediate lateral flow test!

[sethoflagos]

6 hours ago, studiot said:

What a good idea and example of lateral thinking.  +1

 

Take an immediate lateral flow test!

A non sequitur fit for yesterday's Westminster PMQs!

[studiot]

4 hours ago, sethoflagos said:

A non sequitur fit for yesterday's Westminster PMQs!

Do you never blow jokes out of that trumpet (cornet I think, but I am no expert) of yours ?

Edited July 21, 2022 by studiot