Quote:
Originally Posted by DanielDudley
So...
Cement is a powder that when mixed with water forms a supersaturated solution that turns into limestone crystals. Limestone is not super strong. Concrete is cement mixed with small rocks known as aggregate. The cement forms limestone crystals around the hard stone aggregate. concrete is very strong, for a variety of reasons, mostly having to do with the aggregate.
Epoxy is a catalyzed plastic. JB Weld is epoxy with steel filings as aggregate. Fiberglass is epoxy with glass fibers. Epoxy isn't inherently strong, but it is a good binder. Carbon fiber, glass fiber, and steel filings are all inherently strong. Epoxy binds them, and gives them form. JB Weld isn't epoxy. It is steel, with epoxy as a binding agent.
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I'd like to see the ratio of ingredients by volume for the resins, steel particles and
other fillers. I think you are correct about the binding aspect but I'd fall short of calling JB "steel."
This may be of interest as no "steel" or even AL particles are mentioned:
What is in JB Weld?
Bisphenol-A-(epichlorohydrin)
The resin in J-B Weld epoxy is bisphenol-A (yep, that BPA) combined with garlicky-smelling epichlorohydrin. Chemically, the molecule is a chain with little carbon-and-oxygen triangles, called epoxide rings, on the ends. That’s where the sticky action happens.
Crystalline Silica
Basically
quartz. It’s added to the resin for body and viscosity, without which the goop would be too fluid to adhere and set properly—more like J-B Melt.
Carbon Black
The name says it all. Made up of sooty bits often produced by burning hydrocarbons, it gives the resin its inky color.
Calcium CarbonateA
cheap filler, found in both the resin and the hardener. Like the silica, it gives the product more volume while decreasing the cost per ounce.
Tetraethylene*pentamine
This is the curing agent. It contains amine groups that break open the epoxide rings so their carbons can hook up with the amine’s nitrogen. One TEPA molecule can lock onto four epoxy resin chains, and the other ends of those chains can bond to other TEPA molecules. All that cross-linking forms a super-strong network structure—a thermoset polymer. When it hardens, J-B Weld can withstand forces of nearly 2 tons per square inch and temperatures up to 550 degrees Fahrenheit.
DMP-30
The curing agent on its own is kind of lackadaisical at opening the rings, so epoxies often use accelerators like this one. DMP-30 is short for 2,4,6-tris(dimethylaminomethyl)phenol. It has a reactive hydroxyl group (–OH) hanging off the side that helps rip those epoxide rings open like Christmas presents.
Benzyl Alcohol
This colorless liquid modifies viscosity and acts as a solvent to help the curing agent disperse during mixing. Like DMP-30, benzyl alcohol also has a hydroxyl group that can trigger curing, so it’s put in the hardener tube.
Titanium Dioxide
This stuff adds more body to the mix, and it turns the curing agent a color-coded white. Mix with the black resin and you get that famous gray.
Barium Sulfate
More filler. BaSO4 is radiopaque, which is why they make you swallow it to x-ray your innards. Pro tip: Do not attempt this with J-B Weld.
Source:
https://www.wired.com/2016/08/whats-inside-industrial-epoxy-bpa-somethin-garlicky/