blogfast25
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The sealing and bonding agents thread
Most of us here cannot afford to have wonderful ground glass apparati custom built for them and often rely on ad hoc 'let's throw something together'
solutions for home experimentation. Sealing (between substrates) and bonding (substrates to each other) can be a real head ache.
I think it could be interesting to build something of a compendium of members' experience with sealing materials and bonding agents that are
preferably relatively OTC.
Data on application, substrates, temperature resistance (melting, softening or hardening), ageing (property changes over time), chemical resistance,
cold resistance, brand names etc could be interesting to exchange, in my honest opinion.
What say the plenum?
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Dan Vizine
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This is an excellent topic. But, it's just too late at night to do justice to this intricate discussion, see you tomorrow.
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thesmug
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If you mean bonding as in the joining of glassware I've connected pieces of glassware by melting NaOH and applying that to the joint, waiting about
30-60 seconds, and then washing the NaOH away. It works pretty well and can be repeated until the desired bond strength is achieved.
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blogfast25
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Thanks Dan.
Smug: that's interesting. Will definitely look into that. I mean bonding as in bonding two substrates, whatever they may be: glass/glass, glass/metal,
glass/rubber etc.
There's a wealth of these 'glues' about, many OTC for auto repairs etc.
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Dan Vizine
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For general purpose applications where I need an adhesive with high-strength which is relatively heat resistant, I use a steel-filled epoxy (the side
arm on the potassium filtering apparatus I mentioned in another thread was reinforced on the outside with it). My favorite brand is JB Weld. I avoid
the quick set variety because the physical properties are just not as good. I've fixed vacuum leaks in SS bellows hose with this and it was permanent.
I've also held broken ground glass joints together with a "belly band" all the way around the joint, usually applied over a few turns of light gauge
SS wire.
Is that glass fusing method applied to soft glass or borosilicate, Smug?
When a more moldable putty type adhesive is needed, I use Alvin Lab Metal. It's another metal filled putty, one part. The aluminum based variety is
good to 350 F and the SS filled to 1000 F. I buy it at a welding store, because I've never seen it anywhere else. Thin with MEK.
Furnace cement is the only "adhesive" that you can use at real temperatures, say 1000 C. I don't believe any non-mineral (read: organic) adhesive
exists for this temperature range. Three main varieties seem to be the gray, the black and the tan. The black and tan are both creamy pastes which dry
to smooth solids which have moderate strength at best. If you get them up to 1000 - 1100 C for a while they begin to sinter and in some areas actually
start to glaze. The gray material has coarser grain sizes and dries to a harder solid. These all have zero flex. They tend to crack over time if not
fired. Also, if fired. All in all, not perfect, but it is 1000 C after all. You might think this would be good for holes and imperfections in heating
mantles, but it isn't. It applies wonderfully, but the mantle never approaches a temperature which causes the cement to consolidate. It just dries it
up and it flakes/cracks off. Mantles are best fixed by sewing with mineral based threads. Furnace cement is solvent resistant. It can be reinforced by
adding short pieces of mineral fibers and mixing well.
Stretchable wax films, sold as "Parafilm" are a super quick and easy way to seal flasks, beakers etc. It will disintegrate if left exposed to most
solvent vapors for too long, it isn't meant for long term storage.
I have a reference to a material called "piscein" which was used in some very demanding structural/sealing applications by chemists of a bygone era.
I'll look for it, I was meaning to anyway.
Cyanoacrylates have their place, I find them useful when I need to immobilize things for a more permanent fix. They are extremely good for
rubber-to-metal bonds.
RTV Silicones have unique flexibility and some degree of resistance to certain chemicals. They are among the most gas permeable of all adhesives,
which is a blessing or a curse depending on your application. They resist gas permeation only about 5% as well as butyl rubber. I've seen a lot of
varieties and some are much tougher than others. Avoid cheap aquarium cements, you get what you pay for. RTV Silicones are subject to a weird curing
phenomena. A small percentage develope a gritty texture throughout the bulk, like some partial curing has happened. If you find a tube like this,
don't use it, it will never cure fully for a reason I haven't figured out yet.
Butyl rubber adhesives excel at resisting water leaks. Sold in cartridges for gutter repair, they are extremely sticky, persistent adhesives that
remain "gooey" for days and weeks depending on thickness.
Aluminum duct tape is unbeatable for sealing containers that it can adhere to without wrinkles. It stops oxygen. No other tape, unless it's metal, can
really say this. Naturally, diffusion driven leaks still occur through the adhesive, but you can't stop that.
Two part polyester body putties can be used to fashion any number of improvised solid bodies without cracking from solvent loss. Very convenient
material. Watch out for the runny-firm transition, it sneaks up on you.
BTW, Is everybody on extended spring break or something? I was sure I was going to be comment 20 or 30 this long after the thread appeared. It's one
of the most practical possible, because everybody faces this issue all the time.
[Edited on 8-4-2014 by Dan Vizine]
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Zyklon-A
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I turn test tubes into glass tubes (hollow on both ends) whenever I brake the closed end. (With sadly is more often than I wish.) I would like to
attach the tubes to metal tubes, which would be very useful.
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Dan Vizine
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Quote: Originally posted by Zyklonb  | | I turn test tubes into glass tubes (hollow on both ends) whenever I brake the closed end. (With sadly is more often than I wish.) I would like to
attach the tubes to metal tubes, which would be very useful. |
Well, there is a kind of seal you can make with a little effort and a little luck. You clean the glass area completely free of greases and oil. A base
bath does this well. Then, you roll the end of the tube in molten gallium. Keep rubbing it against the side of the gallium container until you have
made the gallium wet the glass all the way around. The glass will now accept solder. Work quickly, heat the metal and not the glass, flow in the
solder and allow to cool. Sometimes the glass cracks and sometimes not.
Of course, for joints not exposed to solvents and chemicals, steel-filled epoxy is excellent.
This technique was adapted from the electronics industry, where it is used to solder wires to glass substrates.
[Edited on 9-4-2014 by Dan Vizine]
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thesmug
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Wouldn't that not be a good idea to heat since their thermal expansion rates are different?
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Dan Vizine
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That's exactly the problem, that's why some crack. There isn't a perfect diy way to duplicate commercial graded glass to metal seals (that I know of).
It is, at minimum, solvent impervious and gas-tight. That's no small accomplishment
[Edited on 9-4-2014 by Dan Vizine]
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blogfast25
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Another one I've used is contact glue. The 'real Macoy' is made from low MW polychloroprene (CR) dissolved in a chlorinated solvent system. It has
some interesting properties like good and versatile bonding, flexibility, good chemical and cold resistance, ozone resistance. Generously applied it
can provide quite flexible seals/bonds.
'RTV': you mean room temp. vulcanisation, right?
Anyone tried hot melt adhesives, SBS block copolymer based? Or even SEBS based?
[Edited on 9-4-2014 by blogfast25]
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Dan Vizine
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Hi Blogfast,
You're absolutely correct about the acronym RTV.
I've used hot-melt adhesives in a few cases. For a side chain chlorination of boiling xylenes with chlorine gas, I needed to run several glass tubes
through one 24/40 joint (Cl2 in, HCl out & thermocouple). I had a block of Teflon which I machined into a 24/40 plug and fitted with a
fluoropolymer O-ring for the seal to the joint.
The glass tubes were pressure fitted into holes drilled through the plug, and not surprisingly, the holes leaked in service. I wrapped aluminum tape
around the upper 1/8 of the adapter so that tape was 1/4" higher than the face it surrounded. I flowed in melted adhesive and this was able to
maintain a seal for the 8 - 10 hour chlorination. I re-used this several times and it was more durable than I had hoped or expected.
They've really screwed contact adhesives up on this side of the ocean.
Like so many other substitutes, water-based formulation are lame. I will never purchase stabilized emulsions in water if the original (anything) is
still around with all my dear friends, the VOC's, right where they belong.
[Edited on 9-4-2014 by Dan Vizine]
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macckone
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Let us not forget lead. It is somewhat flexible. It is resistant to chlorides and sulfates including the acids. It seals well with metals and
modedately well with glass.
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macckone
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Let us not forget lead. It is somewhat flexible. It is resistant to chlorides and sulfates including the acids. It seals well with metals and
modedately well with glass.
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blogfast25
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| Quote: Originally posted by macckone | | Let us not forget lead. It is somewhat flexible. It is resistant to chlorides and sulfates including the acids. It seals well with metals and
modedately well with glass. |
How do you apply that?
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Praxichys
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The best way to do distillation chemistry on the cheap is to use stoppers and glass tubing. Learn to use a torch to flame-polish and bend the glass to
your needs. Thermometers fit into stoppers with a little grease, and cheap PVC pipe makes a great condenser jacket.
Stoppers can be bought by the pound, a cork borer is a few dollars, and glass tubing is also dirt cheap even on Amazon. Though I would recommend
borosilicate glass tubing, soda-lime glass tube works just fine, is cheap, and is easy to work with. Glass-glass tube connections can be made with
clear vinyl tube from the hardware store, though they should be minimized because of its lack of general chemical resistance.
I used to get mine from Cynmar:
$6.50 for a pound of tubing (Probably 5 or 6m)
$9 for a cork borer
$6.60 for a pound of assorted stoppers
$2 for a boiling flask
Then go to your local hardware store for the torch, the propane, the condenser jacket, and some vinyl tube for joints and condenser supply lines. I
will assume you already have a suitable thermometer.
A savvy person can make a decent 1000mL distillation setup for less than $50.
However, keep in mind that rubber stoppers and vinyl tube are fairly succeptible to chemical attack. Don't be surprised if you have to replace these
items often if you plan on working with certain organic solvents (which cause them to swell and fall apart), halogens (makes them hard and brittle
after a few exposures), or oxidizing acids (don't even try HNO3 with such a shoddy setup). (See attachment for a sketch of how this goes together)
But, if your goal is to distill some acetic acid or run a fischer esterification at reflux, or make some distilled water, or remove dissolved
impurities from solvents, or make a basic generator of oxygen or chlorine, this will work.
Just keep in mind that you can get a 14/20 all-glass kit for $120. Save your pennies. It's worth it.
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macckone
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Metal would be soldering.
Glass is a wrapping with thin sheeting like the wax sheeting only more
resistant and less malleable. You can also make lead fittings for glass
that will bond with application of some heat and pressure. The bond is
not strong but it is a good seal. These techniques are useful with DRY
Sulfur trioxide, weak sulfuric (<60%), and aqueous hydrochloric. Lead is
unaffected by most organics but may be a contaminant in some
reactions. Lead bonds well to leaded glasses. Leaded glasses are not
commonly found in professional labs but are in abundance in antique
stores. Which is useful for people building makeshift labs. Lead also
makes a good gasket material for compatible reactions
Of course don't use lead if the end product is for human or animal
consumption.
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aga
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Has anyone tested whatever Hot Melt Glue is made of ?
So far (which is not very far) i have used it to make gas-tight seals for some acids & bases, and it seems un-bothered by anything so far.
Clearly, to get it to separate, you just heat it, and pull.
Heating and Not pulling weakens it, but it remains in-place as a seal, depending on the pressure i guess.
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Dan Vizine
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Paraphrased a little from Brauer, extracted by OCR:
REMOVABLE CEMENTS
Suitable cements should have low vapor pressures and should not be too brittle. Picein, vapor pressure approximately10-4 mm. (20°C), is useful.
It may be used up to approximately 60°C, and is readily soluble in benzene and toluene. Other waxes with low vapor pressures and variable
hardnesses and usable up to 80°C are available from the J. G. Biddle Co., Philadelphia.
In place of the opaque, black picein, clear and transparent polyvinyl acetate may also be employed. Those polyvinyl acetates which soften at a low
temperature are used in a manner similar to picein. It should be noted, however, that polyvinyl acetate chars rather easily when in contact with a
free flame. Polyvinyl acetate is insoluble in water and aliphatic hydrocarbons but is soluble in esters, ketones, chlorinated hydrocarbons and
benzene.
Polyethylene, in the form of a film placed between the previously heated surfaces of a ground joint, is especially suited as a sealing material for
joints used at higher temperatures.
CEMENTS FOR HIGHER TEMPERATURES
Silver chloride, melting point 455°C, adheres excellently to glass, quartz and metals, but only if a few small granules of Ag20 have been dissolved
in the previously fused AgCl; the Ag2O is dissolved essentially without decomposition. Monch recommends lowering the melting point by addition of
TlCl. A mixture of 27.2 g. of TlCl and 18.2 g. of AgCl melts at 210°C. A mixture of 3 g. of TlCl, 4 g. of AgCl and 6 g. of Agl melts still lower
(131°C).
Alloys. Wood's metal, Rose's metal. Alloys of 40 parts Bi, 15 parts Hg, 25 parts Pb, 10 parts Sn and 10 parts Cd adhere especially well to
glass. Pure indium metal (m.p. 155°C) and various indium alloys (for example, 50% In +50%Sn, m.p. ll7°C) are suitable for joining metal to
glass, quartz or ceramics. The surfaces of the parts must be very clean. Precautions should be taken with regard to the temperature ranges suitable
for the various alloy cements and for the materials to be cemented.
PERMANENT CEMENTS
Glycerol-litharge cement. Glycerol is dehydrated as completely as possible by heating at a high temperature; litharge is likewise heated at 200 to
400°C. After cooling, 20 g. of litharge is stirred with 5 ml. of the anhydrous glycerol. The surfaces to be cemented are rubbed beforehand with
glycerol. Setting time, approximately 1/2 hour. The cement withstands temperatures up to approximately 300°C. The cemented spots can be loosened with
a strong sodium hydroxide solution.
Waterglass cements. Mixtures of feldspar and waterglass or of talc and waterglass are serviceable up to quite high temperatures. The two components
are stirred together to form a thick paste and the cemented parts are then first allowed to dry in the air and later, slowly in the drying oven. The
cement withstands quite high temperatures.
Zinc oxide cements. Zinc oxide, stirred with zinc chloride solution, hardens in a few minutes to a stonelike mass. Dental cement (obtainable from
dental supply houses) also belongs to the class of zinc oxide cements; it consists of a solid and a liquid component and after trituration hardens in
a few minutes. The fact that the volume remains constant on hardening is especially advantageous.
Crazy old bastards, weren't they? But very ingenious.
[Edited on 9-4-2014 by Dan Vizine]
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macckone
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| Quote: Originally posted by aga | Has anyone tested whatever Hot Melt Glue is made of ?
So far (which is not very far) i have used it to make gas-tight seals for some acids & bases, and it seems un-bothered by anything so far.
Clearly, to get it to separate, you just heat it, and pull.
Heating and Not pulling weakens it, but it remains in-place as a seal, depending on the pressure i guess. |
http://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSuUn_z...
ethylene vinyl-acetate polymer plus some type of hydrocarbon for
the 3M brand. brands are going to vary in formulation.
As will the softening point for each brand.
http://www.surebonder.com/upload/msds/mixmds.pdf
Surebonder has a softening point of 80C.
**edit fixed 3m link **
[Edited on 9-4-2014 by macckone]
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blogfast25
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| Quote: Originally posted by aga | So far (which is not very far) i have used it to make gas-tight seals for some acids & bases, and it seems un-bothered by anything so far.
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I worked for a company that produced them and going by composition, chemical resistance of these products should be quite high, 'within reason'...
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