Has anybody in this group considered using fluffy nanotubes (like
fiberglass insulation material) for a sound absorption material. It
seems to me that the delocalized sp3 orbital electrons of the nanotube
would be capable of absorbing acoustic energy via an inelastic collision
with air molecules. These inelastic collisions would result in a phonon
traveling down the nanotube delocalized sp3 electrons where it could be
absorbed (turned into heat) by coupling the phonon energy into the
carbon nanotube matrix when the phonon hits the impedance mismatch at
the end of the tube. I have done a number of google searches for the
acoustic properties of nanotubes, but most of the hits I find are
related to optical or ultrasonic absorption of nanotubes. My particular
interest is looking at a better sound insulation material for business
aircraft.

Has anybody in this group considered using fluffy nanotubes (like
fiberglass insulation material) for a sound absorption material.

It seems to me that the delocalized sp3 orbital electrons of the
nanotube would be capable of absorbing acoustic energy via an
inelastic collision with air molecules.

My particular interest is looking at a better sound insulation
material for business aircraft.

Any thoughts about this?

CNTs are currently dramatically more expensive than virtually any
other material one could consider using as sound insulation --
something like $20/gram I believe.

Steve Werner <steve.werner@cox.net> writes:
Has anybody in this group considered using fluffy nanotubes (like
fiberglass insulation material) for a sound absorption material.

Presumably you mean carbon nanotubes, based on the rest of your
post.

It seems to me that the delocalized sp3 orbital electrons of the
nanotube would be capable of absorbing acoustic energy via an
inelastic collision with air molecules.

The carbon atoms in graphene or carbon nanotubes have sp2
hybridization, not sp3. I would have imagined that sp3 was a typo, but
you repeat it. On the other hand, neither electrons in sp2 nor sp3
orbitals are widely delocalized -- it would be the electrons in the pi
system (based on the p orbitals -- the sp2 hybrids form the sigma
orbital framework) that would be widely delocalized.

Presumably when you say "air molecules" you mean gas molecules in air
(air is not itself a pure substance).

Generally speaking, it is not a reasonable description of the
collision between an O2 or N2 molecule and a carbon nanotube as an
"inelastic collision" with "sp3 orbital electrons". I'm not even sure
what you would mean by this.

Much of the rest of your posting similarly isn't terribly clear and
contains malapropisms.

My particular interest is looking at a better sound insulation
material for business aircraft.

CNTs are currently dramatically more expensive than virtually any
other material one could consider using as sound insulation --
something like $20/gram I believe.

I would guess offhand that a quarter inch layer of the things outside
of the passenger compartment of an airplane would probably cost more
than the rest of the airplane. (That is only a guess -- I haven't done
the back of the envelope.)

Any thoughts about this?

I'd say that the sound absorption idea doesn't make much sense a priori.
I am not an expert on the sort of QM calculations one would need to do
to evaluate the idea, but I haven't seen anything in the literature
about this, and I suspect (based on the context of your message) that
you have done no new theoretical calculations or experiments to lead
you to this novel conclusion.


Perry

Steve Werner <steve.werner@cox.net> writes:
Has anybody in this group considered using fluffy nanotubes (like
fiberglass insulation material) for a sound absorption material.



Any thoughts about this?

I'd say that the sound absorption idea doesn't make much sense a priori.
I am not an expert on the sort of QM calculations one would need to do
to evaluate the idea, but I haven't seen anything in the literature
about this, and I suspect (based on the context of your message) that
you have done no new theoretical calculations or experiments to lead
you to this novel conclusion.

This was a simple question from a mechanical engineer working for an
aircraft manufacturer. I felt your answer was way too condescending
for my taste. Is it any wonder that the number of posts have fallen to
nearly zero on the sci.nanotech news group.

On Thu, 20 Sep 2007 00:01:46 -0000, "Perry E. Metzger"
perry@piermont.com> wrote:


Steve Werner <steve.werner@cox.net> writes:
Has anybody in this group considered using fluffy nanotubes (like
fiberglass insulation material) for a sound absorption material.

Any thoughts about this?
I'd say that the sound absorption idea doesn't make much sense a priori.
I am not an expert on the sort of QM calculations one would need to do
to evaluate the idea, but I haven't seen anything in the literature
about this, and I suspect (based on the context of your message) that
you have done no new theoretical calculations or experiments to lead
you to this novel conclusion.

generally agree with all that.

Wouldn't the "theory" -- such as it is -- be equally applicable to
graphite, say a powder or foam?

An experiment would help? Easy enough with graphite. Maybe even with
CNT if you insist; after all, it would be a non-destructive test.

bob


Bob,

I had always assumed the electrical conduction of graphite (and hence
carbon nanotubes) was the delocalize sp2 electrons

This was a simple question from a mechanical engineer working for an
aircraft manufacturer. I felt your answer was way too condescending for
my taste.

The cheapest aircraft we sell goes for 38 million, and a considerable
amount of that money goes for active and passive noise suppression.

I have read a number of places that multi-walled carbon nanotubes are
excellent conductors of heat and electricity.

We currently use a fiber-based material to provide some cabin sound
attenuation for the aircraft, but the sound insulation material really
just disperses the sound without really absorbing much of the energy
from the sound wave. The molecular collision between the gaseous
molecules and a solid material are going to be elastic collisions with
very little net exchange of energy if both are at the same temperature.

My "Thought" experiment was to look for a solid material where the
molecular collisions between the gas and the solid would transfer a
substantial amount of the kinetic energy from the gas molecule collision
to a ballistic conduction wave in the solid sound absorption material.