• Chemistry 17.05.2013 No Comments

    Another little chemistry project: Photographic prints using the cyanotype and salted paper process.

    Cyanotype

    Cyanotype Print

    Cyanotype Print

    The cyanotype process (or blueprint) is used to produce blue contact prints from transparent negatives. The blue color is the water insoluble pigment Iron(II,III) hexacyanoferrate(II,III) which is normally produced by reacting an Iron(II) salt with a ferricyanide salt or a Iron(III) salt with a ferrocyanide.

    To make photographic prints, the reaction has to be catalyzed by light. This is done by utilizing a light sensitive compound which releases Iron(III)-Ions upon exposure. The original cyanotype process uses an Ammonium iron(III) citrate solution, which has several disadvantages. An improved process[1] replaces the citrate with Ammonium Iron(III) Oxalate, which can be produced from simple chemicals in a two step synthesis.

    Synthesis of Ammonium Iron(III) Oxalate

    In the first step oxalic acid reacts with ammonia to form ammonium oxalate:

    Ammoniumoxalatsynthese

    Oxalic acid has a molar weight of 90.04 g/mol but is a dihydrate (two water molecules attached to each acid molecule) which results in a molar weight of 126,10 g/mol. Ammonia has a molar mass of 17,03 g/mol and was available as a 25% (13.4 Mol/L) solution which has a density of 0.91 g/mL. Those numbers allow to convert the molar ration of 1:2 to a weight ratio of 1 g : 1.35 g. I used 1.77 g of oxalic acid and 2.3 g ammonia solution. To react, the oxalic acid is added to the ammonia solution. The resulting solution is evaporated and the remaining solid ammonia oxalate monohydrate is collected. Ideally, it should weigh 2.00 g (14.04 mmol).

    The next step converts the Ammonium Oxalate to Ammonium Iron(III) Oxalate with the help of Iron(III) Chloride. As both reactants are solids, solutions have to be prepared.

    Ammoniumoxalatoferratsynthese

    Ferric chloride has a solubility of 920 g/L, while of the oxalate only 45 g will dissolve in 1 L of water. Having produced 14.04 mmol of the oxalate, we need to add 4.68 mmol of the chloride. When weighing the substances, the fact that Fe3Cl is a hexahydrate, has to be kept in mind. The molar mass of 162.21 g/mol has to be corrected to incorporate the mass of six water molecules, resulting in mass of 1.26 g. The 2.00 g of oxalate and 1.26 g of chloride are dissolved in 44.34 mL H2O and 1.37 mL H2O respectively.

    Vial of Ammonium Iron(III) Oxalate

    Vial of Ammonium Iron(III) Oxalate

    The solution, which should be of a light green color, now contains 2.00g or 4.68 mmol of Ammonium Iron(III) Oxalate and 14.04 mmol of Ammonium Chloride. Unfortunately, I could not come up or find a reaction to separate the two components. But I later verified, that the Ammonium Chloride has no negative effect on the print process.

    Preparing the Sensitizing Solution

    The sensitizing solution is later applied to a piece of paper to make it sensitive to light. It contains three parts Ammonium Iron(III) Oxalate and one part Potassium hexacyanidoferrate(II) by mass.

    The previously prepared 2.00 g of oxalate are added to 2 mL of water, heated to approx. 50°C and stirred until dissolved. In a second container, 0.67 g of Potassium hexacyanidoferrate(II) are added to 1.2 mL of water, heated to 70°C and stirred until dissolved.

    Subsequently, the two solutions are mixed together while continuously stirred. The solution is then filtered, filled up with water to a volume of 12 mL and, after it has cooled, stored in a dark place.

    Preparing the Paper and Making the Print

    The sensitizing solution should be stored in a dark place until needed. It can be applied to paper by placing a few drops on the sheet and dragging them over the surface with a glass rod. This is best done with minimal lighting. When the paper has soaked up the solution evenly, it is hung up to dry.

    The negative can be printed on sheets of overhead transparency. For best results, the image should be black and white and printed with high toner density.

    The dry sensitized paper is attached to the negative and then exposed either by sunlight or by ultraviolet light. I produced good results with UV tubes from a tanning lamp (which I also use to expose circuit boards). The exposure time is about 10s-20s with UV light. With sunlight, you can see that the exposure is finished, when the transparent areas of the negative have sufficiently darkened.

    To finish the print, the paper is rinsed with tap water until all green/yellow color is washed out and a blue and white image remains. After drying the paper, the print can be framed.

    Salt Print

    The salted paper process uses different chemicals and a different method to sensitize the paper. While the cyanotype is based on iron, the salted paper uses silver in the form of silver chloride. This salt is sensitive to light and decomposes to black elemental silver upon exposure. This results in a brown and white image.

    Preparing the Paper

    As the name implies, the paper is treated with a Sodium Chloride solution (2 g NaCl per 100mL water). After the paper has been soaked in the solution, it is dried. Meanwhile, a solution of silver nitrate is prepared (1 g AgNO3 per 10mL water). All steps involving the silver have to be carried out in a dark room to not expose it prematurely.

    The silver nitrate solution is then spread over the salted paper using the same method as with the cyanotype sensitizing solution. When the silver nitrate comes in contact with the sodium chloride in the paper, it reacts to sodium nitrate and the light sensitive silver chloride:

    Silberchloridsynthese

    The exposure follows the same procedure as with the cyanotype. Afterwards, the print has to be fixed to inhibit the further exposure of silver chloride. Due to the very low solubility of silver chloride in water rinsing is not enough.

    Instead, the print has to be soaked in a mixture of sodium thiosulfate, ammonia and water (10:2:100 ratio by weight). The print is soaked in this solution for about 15 min until all the unexposed silver is removed.

    The finished print can then be rinsed, dried and framed.

    Salt Print and Cyanotype

    Salt Print and Cyanotype

    Choosing the Paper

    The right paper plays an important role in making a good looking print. Standard printer paper does not take up the solution very well and wrinkles when drying. I had good results with index cards and water colour paper.


    [1] : The New Cyanotype Process (http://www.mikeware.co.uk/mikeware/New_Cyanotype_Process.html)

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  • Chemistry 15.05.2013 No Comments

    A few years ago I saw a video about ferrofluid on YouTube. A ferrofluid or magnetic fluid is a stable suspension of magnetite nanoparticles which reacts to magnetic fields in interesting ways. Naturally, I wanted to make some ferrofluid myself.

    There are three easy ways to produce Magnetite (Iron(II,III)-oxide, Fe3O4), at least that I know of. Both are based on the precipitation of an iron salt in an ammonia solution. The first [1] uses Iron(II)-chloride and Iron(III)-chloride as precursors whereas the second[2] uses Iron(II)-sulfate. The third, the one I tried, is explained in this YouTube Video.

    Synthesizing the Precursors

    All three iron precursors are easy to manufacture by dissolving iron wool in hydrochlorid acid and sulfuric acid, respectively.

    Fe+HCl

    Solutions of Iron(III)chloride and Iron(II)chloride

    Solutions of Iron(III)chloride and Iron(II)chloride

    Iron(II)chloride turns to Iron(III)chloride when left in contact with air for some time. The conversion from Iron(II)- to Iron(III)-chloride can be greatly accelerated by adding the oxygen in the form of hydrogenperoxide. The iron wool and the acid is weighed to produce an approximately known concentration of the products.

    Producing the Magnetite

    After the iron has completely dissolved, the solutions are filtered and then then mixed together in a 2:1 ratio of Iron(III)chloride to Iron(II)chloride. This mixtured is then added to a 25% solution of ammonia. The magnetice particles will start to fall out immediately and colour the solution a dark brown or black.

    Preparing the Suspension

    The video instructions said to boil the excess ammonia off and then add oleic acid which should act as a surfactant for the magnetite particles. Unfortunately, this step did not work for me. The particles did not bind to the oleic acid and repeatedly settled on the bottom of the flask when trying to dissolve the resulting black goo in kerosene.

    Perhaps one of the other to methods or using a different surfactant will produce better results in the future.


    [1] : Synthesis and Some Physical Properties of Magnetite(Fe3O4) Nanoparticles (Int. J. Electrochem. Sci.,7 (2012)5734 – 5745)

     

    [2]: Room Temperature Synthesis of Magnetite (Fe3-δO4) Nanoparticles by a Simple Reverse Co-Precipitation Method (IOP Conf. Series: Materials Science and Engineering18(2011) 032020)

     

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  • Chemistry 30.04.2011 No Comments
    Molecular Structure of Umbelliferone

    Molecular Structure of Umbelliferone

    And once again the quest for easily synthesizable fluorescent dyes was successful: Umbelliferone. (Notice the similarity of the molecule to Aesculine. It is just missing the glycosidically bound glucose.)This substance is a naturally occurring dye of the courmarin family, but it can also be manufactured by a simple reaction. Only two reactants are needed, Resorcinol and Malic Acid. Sulfuric Acid is added as a hygroscopic catalyst to produce Formylacetic Acid from the Malic Acid in situ.

    The empirical reaction equation is as follows:

    C4H6O5 + C6H6O2 ————> CO + 3 H2O + C9H6O3

    Resorcinol has a molar mass of  110.10 g/mol, Malic Acid 134.09 g/mol.
    This equates to a 1:0.82 weight ratio.
    I used 1 gram of Malic Acid and 0.82 gram of Resorcinol and added a few drops of Sulfuric Acid. The whole mixture was heated with hot air until both educts were solved in the acid and bubbling started.
    After a short while, the solution began to change color to a dark orange. Upon further heating, the color got darker until it was deep red and had the viscosity of honey.

    Umbelliferon in Water

    Umbelliferon in Water

    A drop of the cooled product was added to a 600ml beaker of cold water and observed under ultraviolet light. Instantly, a bright green plume descending from the surface was visible, changing color to a bright blue while getting more diluted.

    Umbelliferon in Water

    Umbelliferon in Water

    A small concentration in water fluoresces blue under UV light and green in sunlight. In ethanol the concentration shows no influence on the color, as it is always a bright yellowish green.

    Umbelliferon in Ethanol

    Umbelliferon in Ethanol

    EDIT: On a second thought, the green color might come from fluorescein that was formed by a side reaction during synthesis of the umbelliferone. I will try to record absorption and emission spectra to figure out which substances are present.

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  • Chemistry 25.04.2011 No Comments
    Molecular Structure of Parietin

    Molecular Structure of Parietin

    While preparing the treebark for the extraction of the Aesculin (see previous entry), I noticed that some lichen, growing on the bark, glowed yellow in ultraviolet light. Under normal light it has an orange color. Some research on Wikipedia revealed the lichen as Xanthoria parietina (Xanthus meaning “yellow” in greek, parietina “on walls”). The fluorescent dye contained in the upper layers of the lichen is Parietin.

    I collected some of the lichen and tried several solvents (Isopropanol, Acetone and Ethanol)  to extract the parietin. All solvents were heated to their respective boiling point to accelerate the process.

    The color of the solution differs between the solvents under visible light as well as under ultraviolet light. The Isopropanol-solution is dark green and fluoresces orange while the Acetone- and Ethanol-solutions have a brighter green and glow yellow.

    Due to this result I tested the influence of different solvents on the color of Aesculin. Here, the effect was not as distinct as with the parietin solutions, but the brightness of the fluorescence differed.

    Aesculine & Parietin Solutions in visible Light

    Aesculine & Parietin Solutions in visible Light

    Aesculin & Parietin Solutions in ultraviolet Light

    Aesculin & Parietin Solutions in ultraviolet Light

    Solutions in the images from left to right:

    1. Aesculin in distilled Water
    2. Aesculin in 75% Isopropanol
    3. Aesculin in Acetone
    4. Aesculin in 96% Ethanol
    5. Parietin in Acetone with 33% Sodium Hydroxide
    6. Parietin in 75% Isopropanol
    7. Parietin in Acetone
    8. Parietin in 96% Ethanol
    Parietin in Isopropanol with NaOH

    Parietin in Isopropanol + NaOH (405nm)

    Interestingly, the effect of the NaOH also depends on the solvent. On the one hand, the color in visible light is either violet/pink (in case of Aceton) or it stays green (in case of Isopropanol). On the other hand, the response to ultraviolet light changes. The Isopropanol solution emits a bright magenta fluorescence when irradiated with  405nm light and a dim orange fluorescence with 350nm – 370nm.
    The Acetone solution shows no fluorescence with 350nm – 370nm and almost none with 405nm.

    Aesculin & Parietin Solution

    Aesculin & Parietin Solution

    To further concentrate and purify the Aesculin and the Parietin, the Isopropanol solutions are slowly evaporated to crystallize the dyes.
    The previous attempt with water solutions failed, due to the many other substances that solved in the water and caused mold to grow.

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  • Chemistry 29.03.2011 No Comments
    Molecular Structure of Aesculin

    Molecular Structure of Aesculin

    While searching for easily obtainable fluorescent dyes I stumbled upon the Wikipedia entry for Aesculin. This is a naturally occurring substance which exhibits a blue fluorescence under ultraviolet light (360 nm). Its main source are the bark and leaves of horse chestnut trees (Aesculus hippocastanum).

    To extract the Aesculin from the tree bark a larger piece of it was broken down into small chips and put in warm/hot water.
    Under normal light no change will be visible, but under ultraviolet light, the water will get blue almost instantaneously.

    Afterwards, the solution needs to be filtered several times.

    Filtered Aesculin Solution

    Filtered Aesculin Solution under UV Light

    The next step is to dry the solution until the Aesculin remains as a powder.
    Actually crystallisation from a boiling solution might produce a much higher yield, because the solubility in boiling water is 74g/l, as opposed to only 1.7g/l in cold water. The resulting sesquihydrate forms white needle crystals.

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  • Manufacturing circuitboards containing SMD-parts with toner-transfer is nearly impossible. The thin traces almost never get transferred completely to the copper.

    One solution to this problem is to use photoresist boards and expose them with UV light.

    The layout is printed onto a transparency, which is then used as a mask for the photoresist.
    I got the best results with inkjet-printed layouts. They seem to be more opaque than laserprinted ones.

    The cheapest UV exposure unit from Reichelt costs 200€. That’s far too much for what is essentially some UV-light source and a glassplate.

    UV Exposure Unit

    UV Exposure Unit

    A much cheaper way to get one, is to build it yourself.
    So i got a broken scanner (the older, the better (bigger housing)) and a face tanner (not broken, but old) from eBay.

    The tanner contained 4 UV tubes, 2 trafos and 4 starters.

    All this was glued into the gutted scanner with hot glue.

    About 90 seconds per layout seem to sufice for good exposure.

    The boards are then developed in a 10% sodiumhydroxide solution and etched in a mixture of hydrochloric acid and hydrogen peroxide. (More information on this etching solution in this great tutorial).

    The remaining photoresist can be removed with isopropanol.

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  • Chemistry 11.09.2008 1 Comment

    I don’t know what my motivation for this experiment was, but the outcome was surprisingly successful.

    Normally sodium is produced by electrolysis of an eutectic mixture of sodium chloride and calcium chloride, but this requires high temperatures of about 700°C.

    Sodium production 1. try

    Sodium production 1. try

    So I went for the so-called Castner process, which is based on electrolysis of molten sodium hydroxide. This requires only a temperature of about 330°C, which is easily achievable by an alcohol burner.

    To protect my table from spills of molten sodium hydroxide, I placed the bowl that contained the melt inside a metal can. To guarantee heat conduction and electrical contact i placed the bowl on top of some tin, which would then melt and provide good connection between the two cans.

    The cathode was a thick steel wire which was placed above the can.

    The first try was moderately successful. As you can see in the photos, a lot of blue crystals formed. I don’t know where they came from and they did not occur in the second try.

    Sodium production 2. try

    Sodium production 2. try

    A small droplet of molten sodium quickly formed at the cathode but it proved to be nearly impossible to get it out of the melt. I finally manged to get some out with a loop of wire. The sodium was immedatly put in molten wax to protect it from humidity.

    Next time i will try to build something resembling the draft from the wikipedia article to get better results.

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  • Solving stuff in other stuff can be exhausting. I first discovered this problem when making the PVA slime. The pva-flakes did not dissolve completely when stirred by hand. So i looked up magnetic stirrers on eBay and immediately decided to go for plan B: build one myself.

    Magnetic stirrer

    Magnetic stirrer

    I previously had bought some strong neodymium magnets and just needed something rotating to attach them to. The first thing i found was an old 8cm fan. I had concerns on wether the magnets would interfere with normal motor operation, but they proved to be needless.

    To magnets were glued on top of the rotor with opposite poles facing upwards. I used double-sided adhesive tape and superglue and another layer of tape on top.

    For the stirrer itself i used a small cylindrical magnet. To protect it from aggressive solutions i stuck it in PVC tube and sealed the ends by melting the pvc.

    Then i tested wich distance from the rotor was best to achieve good rotation of the stirrer and place a piece of plexiglass over the rotor in that height. (Fortunately i had screws that fit perfectly).

    As you can see in the picture, it worked quite well.

    If you want heating too, you can just place a peltier-element between the stirrer and jar.

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  • Chemistry 09.09.2008 No Comments

    In my entry about the slime I mentioned fluorescein as dye. Today I am going to explain how I made it.

    I had some phthalic anhydride and resocinol in an old chemistry set but the resorcinol was quite dirty so I got some new at the pharmacy.

    Most synthesis instructions recommend zincchloride as catalyst but some drops of sulfuric acid work as well. (Sulfuric acid and zincchloride are both hydrophile, which is the needed effect).

    Fluorescein drop in water

    Fluorescein drop in water

    15g phtalic anhydride an 22g resorcinol are ground to a fine powder and placed in a test-tube and heated. I used an alcohol burner but i recommend a hot air gun.

    When the powder melts and turns into a thick, red, honeylike substance stop heating and let it cool down.

    The fluorescein can then be dissolved in a small amount of water resulting in a dark red/brown solution.

    One-two drops of this solution are enough to colour 500ml of water to a bright green.

    The best results are achieved when the coloured water is viewed in sunlight.

    A more detailed synthesis manual can be found at LambdaSyn.

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  • Chemistry 08.09.2008 No Comments

    Polymers are always fun. Especially when they are slimy.

    A great polymer gel can be made from Polyvinylalcohol and Borax (Disodium tetraborate).

    Just prepare a 4% solution of Polyvinylalcohol (i used the one with a molecular weight of 72000) and a 4% solution of disodium tetraborate.

    The PVA best dissolves under constant agitation and slight heating. Let it stir until the solution is clear and has no chunks left in it.

    Then add 2 parts of the boraxsolution to 10 parts PVA-solution and stir until the consistency gets slimy.

    PVA Slime coloured with fluorescein

    PVA Slime coloured with fluorescein

    If you want to color the slime, add the color to the PVA prior to adding the borax. A few drops of fluoresceinsolution give it a nice, shining green and quite some resemblance to Flubber.

    The slime quickly dries out when stored open, so it is best keept in a glas jar or in a plastic bag. This also delays the growth of mould in/on the slime.

    I have not yet tested the effect of preservative agents on the moldering.

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