Wikipedia:Reference desk/Archives/Science/2018 February 18

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February 18

Chemical purification

In industry and in the lab, how do they remove iron phosphate contamination from phosphoric acid if the product needs to be free from iron? How effective is it in terms of iron removal? Can the same objective (iron removal to a very low residual iron content) be achieved with solid chemicals (such as copper oxide or aluminum oxide)? 2601:646:8E01:7E0B:0:0:0:64DA (talk) 07:38, 18 February 2018 (UTC)

Hmmm... I was thinking of an electrochemical reaction (Feⁿ⁺ + n e- -> Fe(s), here electrodialysis) but this paper illustrates that as the concentration of iron decreases, so does the efficiency of the process. Hydronium ions directly compete for the current so the amount of iron deposited tends to zero. Back to the drawing board... Wnt (talk) 12:09, 18 February 2018 (UTC)

Googling for phosphoric acid iron content gave a bunch of useful-looking refs. DMacks (talk) 12:17, 18 February 2018 (UTC)

Thanks, DMacks! Your link gives a whole bunch of methods, a few of which are actually suitable for my own use. 2601:646:8E01:7E0B:0:0:0:64DA (talk) 05:25, 21 February 2018 (UTC)

Is ordinary canned spray paint flexible enough to be applied on fabrics?

Is ordinary canned spray paint flexible enough to be applied on fabrics? More particularly, is ordinary canned spray paint flexible enough to not crack or flake off when used on umbrellas? If not, are there specialized paint products for this type of applications? --98.115.54.114 (talk) 20:47, 18 February 2018 (UTC)

The category "canned spray paint" is not a homogeneous group; there are several manufacturers and they make many different kinds of paint; you're going to have to look at a particular brand and see what it's rated for. Popping spray paint umbrella into Google got me this, so it's certainly available. Matt Deres (talk) 22:31, 18 February 2018 (UTC)

Paints sold as fabric paints are designed to be absorbed onto the fibres of the material, rather than to form a solid surface coating. Whether they will work on an umbrella will depend on the type of material used, and the degree of water-proofing (plastic umbrellas will need something totally different). You can buy plain fabric umbrellas specifically for painting on (try craft shops). This will also depend on whether you are talking about a small, handheld umbrella which needs to be folded and rolled regularly, or a large patio umbrella which will not be tightly rolled or folded. Check also whether the paint you are using needs to be ironed to fix it: ironing an umbrella is going to be fiddly, to say the least. Wymspen (talk) 15:29, 19 February 2018 (UTC)

Applied on is also vague. If you spray a little black paint on a white cotton shirt, you'll get a black stain. But if you apply a thick coat that forms a plaque, it is likely that that plaque will crack up and fall off over time and especially with agitation from a washing machine, but you'll still have a black stain underneath. Since an umbrella is regularly flexed and pelted, a permanent hard surface of paint is unlikely. Rit brand dye is used for various types of cloth, although the usual way to do so is in a washing machine--getting it on an umbrella per the normal instructions might be difficult. I dye my fading reds and blacks with excellent results using Rit Dye. μηδείς (talk) 15:55, 19 February 2018 (UTC)

• Oh, and see fabric sealant if it is waterproofing, and not coloring you are concerned with. μηδείς (talk) 16:41, 19 February 2018 (UTC)
  • Another distinction might be made between application of paint to a fully assembled umbrella versus application of paint to fabric out of which eventually will be made an umbrella. The optimum results are likely to result from application of spray-painted imagery to fabric that can be laid flat on a table or suspended vertically on a wall before being eventually assembled into a traditional umbrella configuration. Spray painting onto a fully assembled umbrella might be cumbersome—but doing so may serve purposes of expediency and immediacy. Bus stop (talk) 17:23, 19 February 2018 (UTC)

No; in my personal experience on both leather and cloth it flakes off in days to weeks. Abductive (reasoning) 09:18, 20 February 2018 (UTC)

We found https://www.spraypaint4fabric.com/ which says it can be used on umbrellas of the patio sort. As for durability of fabric paint, I have a shirt with a lot of applied decor with the college logo which is in good shape though several decades old and washed numerous times. The film of somewhat rubbery paint has cracked a little in places. The use special paint for silkscreening fabric. See Googling silk screen paint for fabric Edison (talk) 16:30, 21 February 2018 (UTC)

Rubbing alcohol

Is it true that rubbing alcohol only kills germs when it completely dries on a surface?--User777123 (talk) 20:48, 18 February 2018 (UTC)

Rubbing alcohol is a desiccant and it also is fat soluble, so it penetrates cell walls, if not other membranes. Its germ-killing properties have nothing to do with its eventual evaporation per se. μηδείς (talk) 22:50, 18 February 2018 (UTC)

Then why is 70% alcohol more effective at killing bacteria than 91% alcohol? Some microbiology professor says you need the water to evaporate. Well, I read an article that alcohol is best at killing bacteria 60-90% and so perhaps 90% is better than 99%. 12.130.157.65 (talk) 16:02, 20 February 2018 (UTC).

This article[1] would suggest the opposite. As noted by Medeis, the alcohol basically disintegrates bacteria. If you listen closely, you can hear them screaming, "We're melting!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:54, 18 February 2018 (UTC)