strongest material with low thermal conductivity? - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 08:25:09 am
content: Fiberglass/epoxy (PCB style material) has a temperature conductivity of ~0.2W/mk to 0.3W/mkDoes anything with a similar strength exist which has a lower thermal conductivity?The idea is mounting hardware for cold things.

author: brucehoult
author_rank: Super Contributor
timestamp: September 25, 2024, 09:08:45 am
content: Plywood.Or sandwiches of things that are mostly air e.g. expanded polystyrene, ceramic foams (aerogel etc), with fiberglass, carbon fibre, or wood skins.Corflute is probably the cheapest thing that is very insulating and relatively strong. It depends what you mean by "strong", how thin you want the thing to be etc. Otherwise, yeah, fiberglass or carbon fibre, if the fibre orientation is the "right" way.

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 09:11:31 am
content: PCB material is pretty damn strong. Something at least 1/3 as strong for the same size I reconcanadian poplar might be the best thing?

author: Phil1977
author_rank: Frequent Contributor
timestamp: September 25, 2024, 09:16:05 am
content: You will probably need some composite material if it needs to be strong *and* thermally isolating.Quite ideal would be a sandwich of thin steel plates with aerogel in between. If aerogel is to expensive/exotic then replace it with some other foam material like neoprene or styrofoam.

author: brucehoult
author_rank: Super Contributor
timestamp: September 25, 2024, 10:03:26 am
content: Quote from: coppercone2 on September 25, 2024, 09:11:31 amYou haven't said what you mean by "strong". In tension? Compression? Stiffness? Deforming at the limit or shattering? Is price a factor?What do you want to improve on compared to PCB material? Which properties can be worse than PCBs?If it's "just like PCBs, but better" then the chances are that PCB manufacturers already made a very near optimum choice, unless you want to go significantly cheaper, or can spend much more.Another material not mentioned: bakelite. Great stuff if you don't need to go near 300+ C. And of course it's brittle.

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 08:30:07 pm
content: yeah im using bakelite right now for a pressure plate but canadian popler has 2.1x lower thermal conductivityI don't know how to describe it, its similar. If you can make it out of bakelite you can make a similar thing from wood. Foam is dissimilar.Aerogel steel sounds interesting but that sounds crazy expensive.Can anything beat canadian popler?

author: TimFox
author_rank: Super Contributor
timestamp: September 25, 2024, 10:42:56 pm
content: You are loading the material in compression?If you have a large number of thin laminae, the conductivity will be much less than the same thickness of solid material.

author: coppercone2
author_rank: Super Contributor
timestamp: September 25, 2024, 10:56:42 pm
content: I wonder what it would look like if I used a stack of thin PCB instead of a thick bakelite in that casethat might be a reasonable improvement actually

author: brucehoult
author_rank: Super Contributor
timestamp: September 26, 2024, 12:41:32 am
content: Oh! Just did a little research.I hadn't realised that things said to be made from "Bakelite" are actually not solid resin but usually composites of things such as paper, wood, canvas, linen, asbestos (in the old days), glass fibres, wood "flour" with the Bakelite resin. This includes phenolic PCBs. And plywood used in construction, especially that used in exteriors.Bakelite is also very common in kitchen countertops, if you don't have the more expensive marble, quartz, or granite.And here I was thinking it was from a bygone day.

author: coppercone2
author_rank: Super Contributor
timestamp: September 26, 2024, 12:48:24 am
content: its really good for prototyping because it cuts nicely

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 26, 2024, 02:37:53 pm
content: Yeah, bakelite is just a resin, and not a great one as pure material, strong yes but I mean in terms of engineering properties... probably it's too brittle, too much shrinkage on casting, stuff like that? AFAIK it's never used that way so you'd have a hard time looking up the raw properties (but maybe it's out there and I'm just being a silly not looking for it right here and now), but with fillers, much as with many other resins, it improves in strength, flexibility, appearance, etc.Being an aromatic/carbohydrate condensation polymer, it bonds well (even if not directly crosslinked) with natural materials like lignin and cellulose, hence basically sawdust, chopped fiber, linen, paper, etc. being common ingredients. I suppose in a sense, it acts like a super-lignin (lignin is also an aromatic polymer). It also holds mineral components well, so powdered and flaked fillers (silica, mica, whatever), fiberglass (chopped or sheet) are also handy.As for conductivity -- as with metals' correlation between electrical and thermal conductivity, so too thermal conductivity and strength correlate. At least, to a gross level; and for similar reasons. Namely, strong chemical (or ionic) bonds -- high binding energy -- necessitate strongly coupled phonon waves (i.e., thermal motion). At the peak, you have extremely densely connected materials, like diamond; in the middle, you have the majority of crystalline elements and simple compounds: metals, oxide ceramics, etc.; and at the low end, loosely connected materials, like linear chain polymers (with weak e.g. Van der Waals forces between chains), thru-plane graphite or mica, and composites.(And yes, mica is a poor (thru-plane) conductor; it's a better electrical insulator than thermal, hence its use for isolation (at least historically, but I mean it's certainly still available, and a must-have for high temperature insulation). Same goes for polyimide: it's a terrible conductor, but its high dielectric strength makes a thin layer usable. Indeed, comparing an organic polymer to an inorganic crystal should seem peculiar, but they are actually pretty comparable in these properties.)You can always reduce the conductivity of a given material, by using less cross-section, or more length; but reducing cross-section reduces strength proportionally, and increasing length obviously has mechanical restrictions (you can't fit an arbitrary length into any application). This is true whether it's a of a solid plate vs. bar geometry, or a fibrous or composite bar, rope, foam, etc. Asbestos is basically fiberglass in crystalline form, not an especially poor conductor in bulk, but once fried apart into fibers, the trapped air and weak contact between fibers makes it a particularly effective insulator.So, you might consider something like wood, which is really quite a capable material in terms of strength as an engineering material, and pretty low conductivity. But keep in mind, ballpark 5ksi isn't terribly strong as things go -- even your basic mild steel starts around 30ksi and they go up from there; even compared to solder, there are stronger tin alloys (at least give or take creep strength, which wood does better at), despite having a melting point lower than cellulose's, and there are heavier (but also more thermally conductive) materials, of comparable strength, like concrete (though that only in compression).But most importantly, wood is an organic foam. Basically, if you compacted the cellulose-lignin composite to remove its porosity, obtaining a fully densified product (or give or take removing the lignin, or perhaps even crosslinking it further?), you'd end up with something -- oh, about as strong as low-alloy aluminum, I suppose, and much more conductive than plain wood (perhaps even more conductive than concrete? Or maybe just on par, I'm not sure offhand -- is there a figure for pure solid cellulose conductivity..? Which is kind of an imaginary material, but, there are ways to process wood to delignify and consolidate it, and such products might be the place to check for these properties?). In any case, clearly it will be more conductive, a testament to the strong ether chain bonds and hydrogen inter-chain bonds holding cellulose together. Maybe one or the other extreme (fully densified, or natural foam) is a suitable compromise for a given application, but never forget, it's weaker in both (strength and conductivity) because of structure, not an intrinsic material property.An atomic/molecular bonding theory, like this, still leaves some room for certain materials to have more strength at less conductivity, or vice versa; but only within some bounds, I think.Another figure to keep in mind: the stiffness, elastic modulus. Even on a nanoscopic scale, we might have simple crystals -- FCC, BCC, hexagonal, etc. -- which are highly connected and thus high strength, high modulus, and high (thermal) conductivity; or we might have complex crystals with poorly-connected chains, or spirals winding through them, or completely amorphous; more generally, materials having lower symmetry, and thus a lower upper-limit on connectivity. As a result, they will be softer -- lower modulus. A complex crystal, with lots of "free space" (relatively large and numerous vacancies, I suppose), could have more Van der Waals than covalent or ionic character bonding it together, and thus the strength or modulus is lower than would otherwise be suggested by the raw bonding energy of the material.You can also have an apparent solid, but it's very stretchy indeed. Consider rubber, a network of side chains cross-linked together into a macromolecule. The side chains slide easily over one another, mostly filling space between the strongly-connected backbone, which has a chaotic path through the material. When stretched out, the backbone also straightens out -- perhaps in the fully-stretched state, the thermal conductivity goes up? But since it's also much longer (elongation >100% is common among rubber materials), it's not like the end-to-end conductivity will be higher (it'll be lower anyway due to the reduction in cross-section, and dominance of the side-chains acting like a liquid filler to a nanoscopic mesh).And, note that I said "strongly coupled phonon waves" very carefully; we're not after the "number" of waves, or their energy per se; the energy band structure does matter, but the energy and density of states jointly dictate heat capacity (i.e., how many states are available to soak up that heat energy). Conductivity is about how easily those waves propagate across the material, which does depend on density of states, but also on boundary conditions, anisotropy and so on. Refraction and reflection at the boundary matters; these are (very small) sound waves, after all. A heterogeneous, granular material has lower conductivity because there's more boundaries, scattering waves around rather than letting them propagate freely. A granular substance like thermal grease, I mean, it's better than the liquid (oil) base itself, sure; again, Van der Waals forces are in play there, so it's not hard to improve -- but it's a far fraction of the conductivity of the filler it's based on. Put another way: as we go from 0% oil and 100% filler, to 100% oil and 0% filler, the curve rises gradually from the 100% oil side (as the path length through the poor conductor decreases; or if we're allowing convection in the fluid, it'll even drop as the material gels, blocking convection); but as we go from say 100% to 99% filler, the fact that at 100% the filler is a pure solid and at 99% it's completely fractured up, makes a much steeper difference. At practical mixtures (say 20/80%?), the performance is pretty middling, even for high-K fillers (ZnO is a common choice, ballpark 50 W/(m K) in bulk, but a typical thermal paste is just a few W/(m K)). But it's still wildly better than an air-filled space (air and solid material have a wide mismatch in acoustic properties, besides the air itself having low density and thus particularly poor propagation), let alone an effective vacuum (~10nm gaps are shorter than the MFP in air, but still not close enough for phonons to tunnel across the gap).(Also, nonpolar liquids are really the extreme case, aren't they? Zero static tensile or compressive strength (unless confined hydraulically), but still some finite conductivity, even when convection is constrained, e.g. a liquid soaked into a foam or fiber product. The lower limit on strength is therefore zero. Though there is still a compressive modulus, which with the density, gives a speed of sound, so we might consider modulus the more fundamental or interesting property to compare.)It's no accident that diamond has such high strength, modulus, thermal conductivity, and anomalously low heat capacity: the high-energy bonds restricts thermal motion into modes of comparably high energy, thus the number of states accessible at room temperature is small, and the heat capacity is small. (Compare bonds of some eV strength, to average 10s meV energy at room temperature.)Tim

author: Ice-Tea
author_rank: Super Contributor
timestamp: September 26, 2024, 03:39:15 pm
content: Delrin?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 27, 2024, 02:46:38 am
content: Depending on your proposed application wood may give issues with moisture absorption. Since you have ill defined requirements on strength, it is hard to say if you can make geometry work for you. In most configurations I can thing of compressibility (or spring rate) is probably the aspect of strength you are concerned with. That is consistent with your observation that foam is not suitable. If that is true look to the heat flow equation for other solutions than reducing conductivity. Heat flow is delta temperature times conductivity times area divided by thickness. You seem constrained on thickness, but the area term may have much potential. Consider instead of a sheet of PWB material just a lattice. Can reduce area by a huge amount while still retaining compression stiffness and also preventing lateral air flow. If the conductivity of the air in the cavities (and potential convection) is a concern they can be filled foam or as many layers of "space blanket" as convenient. The stuff NASA uses is expensive and difficult to source, but the common survival blankets are cheap, widely available and nearly as good. Another option might be a hand full of ceramic standoffs with RTV or other material sealing the edge gaps. Or a foam pad with ceramic standoffs to provide the incompressible aspect.

author: bairdbankovic
author_rank: Newbie
timestamp: December 25, 2024, 11:51:41 pm
content: If this is going in a vacuum chamber, Macor or alumina is a (very carefully) machinable ceramic. Quite strong, but brittle. Mainly used for electrical and thermal isolation in ultra-high vacuum chambers due to its low outgasing.

author: antenna
author_rank: Frequent Contributor
timestamp: December 26, 2024, 01:32:26 am
content: What about a tensegrity table? I guess I don't know the application, so maybe thats not stable enough

author: coppercone2
author_rank: Super Contributor
timestamp: December 26, 2024, 01:49:33 am
content: Its been sitting idle for a while, cold is not interesting when its coldI think I am happy with just using FR4. While interesting I am not gonna be buying popler.

author: jfiresto
author_rank: Frequent Contributor
timestamp: December 26, 2024, 12:56:14 pm
content: Quote from: bairdbankovic on December 25, 2024, 11:51:41 pmI was also going to suggest a ceramic. Ceramics would the rule the world if it were not for cracks.Come to think of it, the makers of Roman concrete solved that problem – and Rome did rule the ancient world, or a tolerable bit of it, for a while.If you get stuck, I can ask my father who is a materials scientist specializing in ceramics.

author: lokin4areason
author_rank: Contributor
timestamp: December 26, 2024, 01:33:24 pm
content: if we are considering ceramic s , what are your thought(s) on alumina and aluminum nitride ?

author: coppercone2
author_rank: Super Contributor
timestamp: December 26, 2024, 03:00:38 pm
content: they have fairly high thermal conductivity compared to fiberglass, you would need some special reason to choose them.That might be important for mounting stiff things or things that don't tolerate motion at all because it would ruin alignment or stress something like pipe or what evermacor is 7x worse then fiberglass on face value, buut you should look at a graph over temperature range of materials because its probobly different

author: antenna
author_rank: Frequent Contributor
timestamp: December 26, 2024, 11:14:09 pm
content: CRC handbook of chemistry and physics has, IIRC, charts on the thermal conductivity and strengths of many different materials. That may be a good place to look.

author: Langdon
author_rank: Frequent Contributor
timestamp: February 26, 2025, 05:50:37 pm
content: High-carbon steel?Fiberglass?Glass?Polycarbonate?Remember: Thermal conductivity does not mean thermal impunity, glass shatters when exposed to heat.Insulated concete forms?

author: Milmat1
author_rank: Contributor
timestamp: July 23, 2025, 01:22:42 pm
content: Phenolic materials typically have a thermal conductivity ranging from 0.1 to 0.3 W/m·K. and very strong

author: DTJ
author_rank: Super Contributor
timestamp: July 31, 2025, 08:42:33 am
content: Would machinable "Macor" ceramic do the job?

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2025, 11:16:28 am
content: We used Garolite composite where we needed a strong thermal insulator, but it is essentially printed circuit board material.Model makers use thin beech plywood which is very strong.Foam core board is an excellent thermal insulator.I might try an adhesive film pressed onto both sides of balsa wood.

author: EC8010
author_rank: Frequent Contributor
timestamp: August 25, 2025, 11:28:10 am
content: Stainless steel. Stainless steel fasteners are great when you want to avoid something hot heating everything else.