Possible webpage title: Coal Dust for Snow Removal: Effective or Hazardous?

[itzkovitch]

Hi

I have a project where I am trying to make a coating or paint that will give off heat when an electrical current is passed through it. I got graphite powder and made it into a paste and allowed it to dry on a substrate. The problem is that it is highly resistive (a small section has a resistance of thousands of ohms) so little or no current is flowing though it unless I pass thousands of volts through it (not practical). The other problem is that this graphite coating does not seem to be stable under heat.

Does anyone have any suggestions as to what material/s I can use to form a coating that will have low electrical resistivity, will not degrade at higher temperatures (~60 degrees Celsius) and preferably non-toxic?

Thank you

 

[billy_joule]

There's a pretty big range of conductive paints and pastes out there already, why didn't any of those meet the spec?

 

[itzkovitch]

There's a pretty big range of conductive paints and pastes out there already, why didn't any of those meet the spec?

Thanks for replying Billy. I need large quantities of this and commercial conductive paints out there are very expansive. I figure I could make it myself for a fraction of the cost.

 

[Team]

[mentor note: content deleted, off-topic]

 

[itzkovitch]

[mentor note: content deleted, replying to off-topic content]

 

[Matcon]

Your graphite paste ought to work but you need to get the structure right in order to get optimum conduction. I have a resource somewhere that describes a graphite heating paste that can be applied to glass and cured by passing a current, so I know it can be done. If I can't find it, I'm afraid you'll have to wing it on the info below.

First, you have to align the flakes with the direction of required current flow. Then, you have to make sure the flakes are wetted by the binder. I find that treatment of the flakes with fatty acids is useful but such reagents may not be compatible with your binder. It is useful if your binder is conductive when dry and shrinks sufficiently on drying or curing to pull the flakes into contact with each other.

I also find it useful to apply a layer of (relatively) large natural graphite flakes to the coating surface while still wet and mechanically flatten them. Where possible, I use a domestic flatiron.

You will probably find that you get better conductivity the more heat you can apply.

 

[NascentOxygen]

Thanks for replying Billy. I need large quantities of this and commercial conductive paints out there are very expansive. I figure I could make it myself for a fraction of the cost.

What sort of object are you wanting to coat? 2D or 3D? How mechanically robust does the final coating need to be? Graphite won't take a lot of knocks, and I expect it will leave black marks on surfaces it is dragged against. You want the coating to be 40C above ambient? Cyclic expansions and contractions are going to be a problem long-term. Will you need a resin coat over the conductive layer to prevent shorts to metal objects it contacts?

Could you electroplate the object with copper?

Probably well worth doing a google search before investing heavily.

I'm picturing a hen's egg coated with copper or nickel, and what current would be needed to warm it to 60C as you suggest. With electrical contacts at either end, I'm guessing a ballpark figure of 10-20W. Consider at least 1A at 12V. You'll have that power available?

 

[Matcon]

What sort of object are you wanting to coat? 2D or 3D? How mechanically robust does the final coating need to be? Graphite won't take a lot of knocks, and I expect it will leave black marks on surfaces it is dragged against. You want the coating to be 40C above ambient? Cyclic expansions and contractions are going to be a problem long-term. Will you need a resin coat over the conductive layer to prevent shorts to metal objects it contacts?

Could you electroplate the object with copper?

Probably well worth doing a google search before investing heavily.

I'm picturing a hen's egg coated with copper or nickel, and what current would be needed to warm it to 60C as you suggest. With an electrode at either end, I'm guessing a ballpark figure of 10-20W. Consider at least 1A at 12V. You'll have that power available?

Surely the OP isn't making a trivial request for an inexpensive conductor to generate enough heat to get to 60°C? If it were that simple, why not simply glue a copper, steel or even nichrome resistance wire to whatever it is that you want to heat?

I agree that we can give better answers if the OP were to give us a better idea of what the aim of the heater is, even in generic terms, eg conductor/nonconductor to be heated, duty cycle, desired lifetime as well as the questions that you have posed. Perhaps graphite is required for a hostile chemical environment.

For myself, I am working on a heating element material that will reach 1500°C and last 30 minutes, tops. My formulation may be completely inappropriate for the OP

 

[itzkovitch]

Hey thanks for your reply guys.

Well I really thought of coating my driveway with this substance and use it for defrosting purposes. Then I realized that since the driveway is soft and porous any cracks that might occour on the driveway overtime will stop the current flow and render my coating useless. So I guess going that route is probably not a good idea since it will not be durable. Maybe a flexible heating polymer should do it?

 

[Matcon]

Always up for a challenge, itzkovitch. Sometimes you can apply first principles to a problem and come up with a different solution. The strength of your idea to apply a coating is that you want intimate thermal contact with the surface that you are trying to heat and minimal extraneous heat load. Durability in an outside environment makes a difference to what you can use.

You can buy flexible heating elements encased in silicone rubber. You may want to overlay it with expanded metal and/or thin metal sheet, the latter being to protect against UV degradation (if it does not already contain UV-resistant additives)

It's worth another look at this problem, taking onboard a few assumptions.
The first assumption is that there is a good reason for not wanting to simply buy an existing driveway defrosting system; just wondering whether there is a better way is good enough reason.
The second assumption is that there is insufficient daytime sunlight to consider a solar heat storage system containing a high heat capacity liquid.
The third assumption is that, if you're looking at a home-made system, materials need to be restricted as far as possible to those that are readily available
The final assumption is the size of the area to be heated. I'm going to assume 2 parallel strips 20 yards long, 8 inches wide

 

[itzkovitch]

Always up for a challenge, itzkovitch. Sometimes you can apply first principles to a problem and come up with a different solution. The strength of your idea to apply a coating is that you want intimate thermal contact with the surface that you are trying to heat and minimal extraneous heat load. Durability in an outside environment makes a difference to what you can use.

You can buy flexible heating elements encased in silicone rubber. You may want to overlay it with expanded metal and/or thin metal sheet, the latter being to protect against UV degradation (if it does not already contain UV-resistant additives)

It's worth another look at this problem, taking onboard a few assumptions.
The first assumption is that there is a good reason for not wanting to simply buy an existing driveway defrosting system; just wondering whether there is a better way is good enough reason.
The second assumption is that there is insufficient daytime sunlight to consider a solar heat storage system containing a high heat capacity liquid.
The third assumption is that, if you're looking at a home-made system, materials need to be restricted as far as possible to those that are readily available
The final assumption is the size of the area to be heated. I'm going to assume 2 parallel strips 20 yards long, 8 inches wide

Macon, you are right about me being up for a challenge and you summarized my problem quite well. :)

Ideally, I would have like to have a passive system were no energy input is required. I looked at the super hydrophobic sprays that are newly available today which show some de-frosting capabilities. After reading up on it I discovered that they are not abrasive resistant and easy smudge off. So that's not going to work for my purposes. Do you know of any other substances that show de-icing capabilities without requiring constant re-application and that are durable enough?

I guess flexible heating elements would be the most practical solution that is readily available today. I would need to cover a large area since my driveway is 800 square feet.

 

[lvj611]

paint the driveway black.
one common simple snow removal technique is to sprinkle coal dust on the snow. one sunny day and snow is gone.

 

[NascentOxygen]

paint the driveway black.
one common simple snow removal technique is to sprinkle coal dust on the snow. one sunny day and snow is gone.

Hi lvj611.

But won't a black driveway be more likely to ice over in borderline conditions where an unblackened one would not?