Adsorbtion or Absorbtion - How Iron processes work?

Discussion in 'Alternative Processes' started by DPVisions, Aug 2, 2011.

  1. DPVisions

    DPVisions Member

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    I am looking for details on the chemistry details of how iron processes work at the time the sensitized emulsion is mixed, is this a process of adsorbtion or absorbtion with water? What is happening when the coated emulsion drys on the paper, and of course finally what happens after exposure, for example specific type of reaction is taking place in a clearing bath of EDTA for Pt./Pd. print.

    Cheers,
    David
     
  2. Loris Medici

    Loris Medici Member

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    Not an answer to all of your questions (couldn't get some...) but:

    1.a. See this article for the chemistry of iron processes - specifically pt/pd process. ("Chemistry of the Iron-based Processes" by Mike Ware.)
    1.b. Also this one. ("An Investigation of Platinum and Palladium Printing" by Mike Ware. It's a ".doc" file...)
    2. Search for the words "chelating", "chelation", "chelating agent" for the effect of clearing baths. (Clearing baths dissolve/chelate excess iron impurities which are detrimental to the integrity of the paper in the long term - I mean if they stay in it!)

    Hope this helps,
    Loris.
     
  3. snallan

    snallan Member

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    Just a couple of quick definitions. Adsorption is the binding of atoms or molecules to a surface, whereas absorption is the filling of pores in a solid.

    In the case of the iron processes, the sensitiser solution is absorbed into the fibres of the paper substrate, such that the image metal formed in the process is contained within the paper fibres and not easily washed away during the processing.
     
  4. Mike Ware

    Mike Ware Member

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    Hello again David - greetings Loris - Steve's definitions are spot on. To elaborate a little at the molecular level, a special case of absorption is chemisorption, where the absorbed substance is bound chemically to the substrate. There is a possibility of this occurring with the iron-based processes on cellulose paper - perhaps only via weak hydrogen-bonding, but my chemical instincts suggest that residual iron(III) may well bind to the glucosidic hydroxyl functions - hence the persistence of the dreaded yellow stain in platinum-palladium prints. This is currently being researched.

    To save you downloading a .doc from my website (will put that right one day) I'm attaching a .pdf of the original MS of that JPhotSci paper. There will be more to add to it soon.

    Best wishes to all

    Mike
     

    Attached Files:

  5. Loris Medici

    Loris Medici Member

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    Exciting!

    Regards,
    Loris.
     
  6. DPVisions

    DPVisions Member

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    All this is great information and really helps getting me pointed in the right direction. My only wish now is that I paid more attention in chemistry class instead of trying to figure out how to sneak more potassium to dump into water.

    Cheers,
    David
     
  7. Mike Ware

    Mike Ware Member

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    All the best chemists started off as pyromaniacs...

    Mike
     
  8. michaelbsc

    michaelbsc Member

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    Ok, were you spying the kids from my neighborhood?

    Honestly, the stuff we did as kids "for fun" would probably get us committed as ADHD patients today.
     
  9. alchemyadrian

    alchemyadrian Member

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    Here are some useful definitions for any budding chemists out there (from Quantachrome UK's Particle Characterisation Dictionary at www . quantachrome . co . uk)

    adsorption (noun) - the adhesion of atoms, gases, solutes or liquids (the adsorbate) to the surface of a solid or liquid (the adsorbent). Note the difference with absorption where one fluid permeates into the other material.

    chemisorption (noun) - Type of adsorption where the monolayer adhesion results from a chemical bond formation between the adsorbent and the adsorbate. Abbreviated from "chemical adsorption."

    physisorption (noun) - Type of adsorption where the monolayer adhesion results from intermolecular forces (van der Waals forces) between the adsorbent and the adsorbate. Abbreviated from "physical adsorption."