Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: MoS2 in phosphating bath  (Read 1588 times)

0 Members and 1 Guest are viewing this topic.

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
MoS2 in phosphating bath
« on: July 11, 2018, 03:46:11 PM »

I ran a quick test by mixing 1g/l on MoS2 powder in my phosphating bath.

My question for the world is about the MoS2 activity is dilute phosphoric acid. Wiki states that MoS2 is not soluable in weak or dilute acids. Am I correct to expect a colloidal suspension (given that by MoS2 partickes are small enough) in my phosphating bath, or are there some side reactions which may be occurring, which I do not know about.

The composition of the bath is phosphoric acid 8.5 g/L
Mn - 1g/L
iron 0.2% by mass
MoS2 - 1g/L (1.5 micron powder)

I did a test today in this solution. Visually the coated part is dark grey, very similar to other specimens. But when i try to rub this part against earlier coated items i see less wear on the part coated in the bath with MoS2 suspension. I am hoping that Mo2 is getting embedded into phosphate layer, but i do not know how to test for it at home. I do not have an electron scanning microscope...
Logged

Enthalpy

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +227/-51
  • Offline Offline
  • Posts: 2679
Re: MoS2 in phosphating bath
« Reply #1 on: July 13, 2018, 02:01:53 AM »

I made and used a 50nm MoS2 suspension in a synthetic hydraulic fluid, and after one day I could see the powder begin to sediment. 1.5µm is coarse and will sediment much faster. If you observe that, at least a part of the powder is as a suspension, not as a solution. If you see nothing, it's undecidable that way.

Phosphatation often serves as a corrosion lingerer, but MoS2 is known to promote corrosion as it forms an acid by reaction with humidity or air. What do you want to achieve?
Logged

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
Re: MoS2 in phosphating bath
« Reply #2 on: July 13, 2018, 09:18:27 AM »

I made and used a 50nm MoS2 suspension in a synthetic hydraulic fluid, and after one day I could see the powder begin to sediment. 1.5µm is coarse and will sediment much faster. If you observe that, at least a part of the powder is as a suspension, not as a solution. If you see nothing, it's undecidable that way.

Phosphatation often serves as a corrosion lingerer, but MoS2 is known to promote corrosion as it forms an acid by reaction with humidity or air. What do you want to achieve?
From what I understood from online research is that Mn phosphate just as black oxide are not corrosion preventers by themselves. An immersion into oil allows the porous layer of oxide or phosphate to be impregnated with oil, which in turn seals the surface from air and prevents corrosion. My goal with using MoS2 embedded into Mn phosphating layer is to add a bit of abrasion resistance to the Mn phosphate layer by having slick MoS2 particles embedded into phosphate, hence reducing damage done to phosphate in case of mechanical wear. I do see the particles precipitate out of solution, so, by no means is this a colloidal suspension or a solution. I am hoping the MoS2 are basically getting trapped into phosphate layer as it forms. What i am not sure about is if there are any sideways chemical reactions happening at the same time.

Interesting to note is that when i used the MoS containing bath there was no sludge formed at the bottom of the pot. Usually phosphate baths form a bunch of yellow/grey sludge which i have to filter after the baths use, but in this case there was ZERO sludge.
« Last Edit: July 13, 2018, 10:07:32 AM by pcm81 »
Logged

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
Re: MoS2 in phosphating bath
« Reply #3 on: July 13, 2018, 02:58:43 PM »

All this does get me thinking: I have some 0.03 micron alumina and 0.5 microm aluminum oxide grit. I wonder if those can be used as part of phoshating bath to strengthen the deposited layer.
Logged

Enthalpy

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +227/-51
  • Offline Offline
  • Posts: 2679
Re: MoS2 in phosphating bath
« Reply #4 on: July 15, 2018, 09:02:38 AM »

To linger abrasion, alumina is a bad idea.

And whatever the way phosphatation improves the corrosion resistance, MoS2 will worsen corrosion.

Graphite nanopowder is a better start, PTFE powder too.
Logged

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
Re: MoS2 in phosphating bath
« Reply #5 on: July 15, 2018, 04:07:57 PM »

To linger abrasion, alumina is a bad idea.

And whatever the way phosphatation improves the corrosion resistance, MoS2 will worsen corrosion.

Graphite nanopowder is a better start, PTFE powder too.
I intended to do more tests with other substances later. I have 1lb of ptfe powder, but i think it may be too coarse for the application. I was "hoping" that MoS2 would dissolve into solution after having read about it here: http://jcpr.kbs-lab.co.kr/file/JCPR_vol.18_2017/JCPR18-10/04.2017-138_716-721.pdf
Although i see little if any at all solubility and mostly just precipitation.

I am shooting for surface protection, and reduction of coefficient of friction was an attempt at making the surface slicker and less grabby; although protection with hard grit embedded in the phosphate deposit may be another option.
Logged

Enthalpy

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +227/-51
  • Offline Offline
  • Posts: 2679
Re: MoS2 in phosphating bath
« Reply #6 on: July 16, 2018, 08:06:45 AM »

Why not embed the lubricating particles later, when you oil the phosphated steel parts?

First make a completely standard phosphatation of you steel. Then, use a graphite-loaded oil or grease. They do a fabulous job at reducing friction, when parts move very slowly with high contact pressure, for instance screws.

Even with oil or grease, don't use MoS2 on phosphated steel. The protection doesn't suffice, steel would corrode.
Logged

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
Re: MoS2 in phosphating bath
« Reply #7 on: July 19, 2018, 05:07:45 PM »

Why not embed the lubricating particles later, when you oil the phosphated steel parts?

First make a completely standard phosphatation of you steel. Then, use a graphite-loaded oil or grease. They do a fabulous job at reducing friction, when parts move very slowly with high contact pressure, for instance screws.

Even with oil or grease, don't use MoS2 on phosphated steel. The protection doesn't suffice, steel would corrode.

From what i read the MoS2 is preferred to graphite in some applications. For instance, graphite does not work well in vacuum although it does work at slightly higher temperatures than MoS2.
I am not sold on idea of graphite in oil or grease. Graphite, just as MoS2 is a dry lubricant. Specifically in case of graphite, it can lump up when mixed with oil and cake up into semi solid aggregates. Locksmiths done tests and posted videos on youtube about lock lubes, which included graphite. Graphite beat all other lubes on the temperature performance, but graphite + oil was a mess.
https://www.youtube.com/watch?v=zZaPWGo8TbE
This is not a scientific study, but it gets the point across.

As far as additives in the bath are concerned, I'll try the teflon next. But next might not be any time soon.

I usually use vacuum chamber to suck oil into phosphate or black oxide layers. I like vacuum chamber results better than regular soaking. The phosphate bath additives i am playing with to see if i can actually embed protective particles into phosphate layer and either strengthen it or smooth it to reduce wear effects.
Logged

Enthalpy

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +227/-51
  • Offline Offline
  • Posts: 2679
Re: MoS2 in phosphating bath
« Reply #8 on: July 20, 2018, 12:01:52 AM »

I too read that graphite doesn't lubricate in vacuum. I didn't try by myself. Only limit I know to graphite.

Solids are the only good lubricants for high contact pressure and very low speed, that is, when contact between the moving surfaces can't be avoided.

Lumps: why care if you embed the solids in a phosphate coating? This is a worry for hydraulic fluids and for circulating oils.

Logically enough, solids tend to be used with greases rather than oils, as greases fit high pressure and low speed.

If your application is at high speed, then a phosphate layer is a bad choice anyway, as it will wear too quickly.
Logged

pcm81

  • Full Member
  • ****
  • Mole Snacks: +3/-2
  • Offline Offline
  • Posts: 130
Re: MoS2 in phosphating bath
« Reply #9 on: July 20, 2018, 04:26:03 PM »

I too read that graphite doesn't lubricate in vacuum. I didn't try by myself. Only limit I know to graphite.

Solids are the only good lubricants for high contact pressure and very low speed, that is, when contact between the moving surfaces can't be avoided.

Lumps: why care if you embed the solids in a phosphate coating? This is a worry for hydraulic fluids and for circulating oils.

Logically enough, solids tend to be used with greases rather than oils, as greases fit high pressure and low speed.

If your application is at high speed, then a phosphate layer is a bad choice anyway, as it will wear too quickly.

My application is being able to protect items from rusting in Florida humidity while also having surface coating tough enough to take some punches and wear and tear. EN used to be my go to choice, but it can be a hassle sometimes, so i am researching other options. Started with hot caustic bluing and now worked my way to phosphating. 80% of the value of this project to me is learning.
Logged
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.126 seconds with 24 queries.