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Q: Copper Oxidation ( Answered,   0 Comments )
Subject: Copper Oxidation
Category: Science > Chemistry
Asked by: skippyaust-ga
List Price: $100.00
Posted: 06 Sep 2004 15:50 PDT
Expires: 06 Oct 2004 15:50 PDT
Question ID: 397640
Complex oxidation reactions occur with copper heated between room
temperature and 1000 deg. C.  What are the oxides formed over this
temperature range and what are their resistivities and effect on
electrical contact resistence
Subject: Re: Copper Oxidation
Answered By: adiloren-ga on 16 Sep 2004 15:47 PDT
Hello and thank you for the question. Below I have provided you with
some general background information on the copper oxidation process
and information specific to the topic areas outlined in your question.
Please request clarification if you need further assistance with your



Fact Index Entry on Copper Oxide

"Copper oxide is a substance formed when copper oxidizes. There are
two forms, copper (I) oxide (cuprous oxide Cu2O) a red powder and
copper (II) oxide (cupric oxide CuO) a black powder. It has some
scientific uses, including use as a superconductor. The mineral
cuprite, a red colored crystal, is copper I oxide."

Copper (I) oxide or cuprous oxide (Cu2O) Encyclopedia Entry (explains
some of the conduction properties)


"Cuprous oxide was used in one kind of metallic rectifier, a
predecessor of the semiconductor diodes of today. A plate of copper
was strongly oxidized on one side to produce a thick layer of CuO.
This was heat-treated so that a thin layer of Cu2O would grow between
the Cu and the CuO. Then the CuO was stripped off with acid, and a
contact of lead or similar material applied. The copper base plate
acted as an n-type material, while the Cu2O was p-type, and a
pn-junction was formed. This junction had a forward bias voltage of a
few tenths of a volt, a reverse breakdown voltage of 5V or 6V, and a
rather low maximum operating temperature. A stack of such elements
could be assembled for higher voltages. The reverse current was larger
than would be tolerated now, but was satisfactory for battery chargers
and other similar devices. Similar rectifiers were made from Cu2S on
magnesium, and selenium on iron or aluminium. These were quite
satisfactory for low voltages and moderate currents, but have been
completely replaced by the cheaper silicon diodes with far superior

Heating the copper produces Cuprous oxide- which acts as a semi-conducter:

"As the copper starts to heat up, you will see beautiful oxidation
patterns begin to form. Oranges, purples, and reds will cover the

"As the copper gets hotter, the colors are replaced with a black
coating of cupric oxide. This is not the oxide we want, but it will
flake off later, showing the reds, oranges, pinks, and purples of the
cuprous oxide layer underneath."

"Cuprous oxide is a type of material called a semiconductor. A
semiconductor is in between a conductor, where electricity can flow
freely, and an insulator, where electrons are bound tightly to their
atoms and do not flow freely.
  In a semiconductor, there is a gap, called a bandgap between the
electrons that are bound tightly to the atom, and the electrons that
are farther from the atom, which can move freely and conduct
  Electrons cannot stay inside the bandgap. An electron cannot gain
just a little bit of energy and move away from the atom's nucleus into
the bandgap. An electron must gain enough energy to move farther away
from the nucleus, outside of the bandgap.
  Similarly, an electron outside the bandgap cannot lose a little bit
of energy and fall just a little bit closer to the nucleus. It must
lose enough energy to fall past the bandgap into the area where
electrons are allowed."

Conduction of Copper Oxides:

"At temperatures your workers will encounter, copper metal is a MUCH better
conductor than copper oxide.  The new "high temperature" superconductors
(which actually are superconducting only at temperatures far below that of
dry ice) contain copper and oxygen, but they also must contain other
elements, such as yttrium and barium, as well.  Copper oxide alone doesn't
do the trick."

"Metal oxides are generally not very good conductors, in fact, most are
dielectrics and hence non-conductors. Some metal oxides are semi-conductors
(and also super conductors at low temperature in some cases). Certainly,
copper and aluminum are much better conductors than their corresponding
oxides at any temperature linemen will encounter.

Copper, lead, and aluminum oxides formed by corrosion are decidedly poor
conductors. I am not an electrical engineer but I know if I let the terminals
of a battery become corroded, the battery no longer delivers electricity
(i.e. the corrosion products are insulators).

Superconductivity -- the disappearance of electrical resistance -- only
operates at very low temperatures obtainable only in labs at the present
time -- although there is a lot of research seeking higher temperature

Most metals, including copper and aluminum, form thin metal oxide film
layers when exposed to air for even a brief time -- this is what makes a new
penny turn dull after a few days or weeks. These oxide layers are so thin
however that for all practical purposes they do not interfere with the
conductivity across such layers."



"The common building blocks for most high temperature (high
tex2html_wrap_inline5335 ) superconductors   are copper oxide layers,
as depicted in Figure 1.6. Assume the distance between copper atoms
(filled circles) is a. For simplicity let us also assume that in the
third dimension these CuO tex2html_wrap_inline5079 layers are simply
stacked with spacing c, and there are no other atoms in the crystal.
In first approximation the layers have a four-fold symmetry; the
crystal is tetragonal."



    * Chemical Formula: Cu2O, Copper Oxide
    * Class: Oxides and Hydroxides
    * Uses: Ore of copper, rarely as a gemstone.
* Specimens

Cuprite has been a major ore of copper and is still mined in many
places around the world. Of all the copper ores except for native
copper, cuprite gives the greatest yield of copper per molecule since
there is only one oxygen atom to every two copper atoms. As a mineral
specimen, cuprite shows fine examples of well-developed cubic crystal
forms. Cuprite's dark crystals show internal reflections of the true
deep red inside the almost black crystal. Other varieties, such as
chalcotrichite, show tufts of needle-like crystals that have a
beautiful red color and a special sparkle that make them popular
display cabinet specimens."


"Molecular Weight (g/mol.) CuO=79.55:Cu2O=143.08
Merck 11, 2650/ 11,2671
Theoretical Density (g/cm3) 6.3- 6.49
Melting Point (C) 1235- 1326
Boiling Point (C) ~ 1800"



Surface Chemistry of Copper Nanoparticles and Direct Spray Printing of
Hybrid Particle/Metallorganic Inks
Douglas L. Schulz, Calvin J. Curtis, and David S. Ginley National
Renewable Energy Laboratory, Golden, Colorado 80401-3393, USA
"Copper films have been direct written on heated substrates using both
neat metallorganic and two-component, copper nanoparticle/copper
metallorganic inks. Commercial nanoparticle copper (nano-Cu) was
characterized by transmission electron microscopy and powder X-ray
diffraction (PXRD) and found to consist of Cu/Cu2O spherical particles
measuring 100-500 nm in diam. The Cu2O was etched away using an excess
of hexafluoroacetylacetone (Hhfa) and vinyltrimethylsilane (VTMS)
yielding pure Cu by PXRD. Hhfa etching in the absence of VTMS led to
the formation of millimeter-sized Cu particles at room temperature.
Neat (hexafluoroacetylacetonato)Cu(I)-(VTMS) (Cu(hfa)VTMS) was spray
printed in a nitrogen ambient on glass microscope slides and Kapton at
210-230C to give dense, adherent films. Hhfa/VTMS-etched nano-Cu was
mixed with (Cu(hfa)VTMS) and spray printed in a nitrogen ambient on
glass microscope slides and Kapton at 210-220C. Copper films produced
by both approaches were characterized by scanning electron microscopy
and standard four-probe resistivity techniques."

[PDF] Superconducting Bi Sr Ca Cu O phase formed by penetration

[PDF] Anisotropic Resistivities

"A specimen of the copper oxide-filled carbonate material was
subjected to a parallel-bar-contact surface-resistivity test and a
static-discharge test at a temperature of 22 C and relative humidity
of 50 percent. The specimen was found to have a surface resistivity of
109 ohms per square on its rough side and 1010 ohms per square on its
smooth side. The time for discharging from a potential of 5,000 V to
500 V was measured to be about 0.1 s, and there was no measurable
charge left after 5 s. These measured characteristics are well within
the acceptable ranges for an antistatic material according to
applicable NASA and military standards."


"*  Copper Oxide 

Cu2O is used in red ceramic porcelain glazes and red glasses. Also a
pigment for anti-fouling paints. CuO is used as a flux for CA
metallurgy, as an optical glass polishing agent, as a pigment, in
sweeting petroleum gases and in galvanic electrodes"

Oxygen Free Copper:

"C103 or Cu-OF and CU110 or Cu-OFE are produced by melting and casting
the copper under a near vacuum atmosphere to give very low residual
oxygen content. Such grades should be specified for applications where
resistance to hydrogen embrittlement is required with no loss in
conductivity. The grade C110 is designated for electronic purposes and
is relatively expensive. The oxide film formed on its surface at high
temperature is tightly adherent, making it suitable for vacuum tight
glass to metal seals. It also has a very low content of volatiles,
making it ideal for use in conditions requiring consistently high



"copper oxide"

Thanks for the question and please don't hesitate to request
clarification if necessary.

Anthony (adiloren)

Request for Answer Clarification by skippyaust-ga on 06 Oct 2004 20:54 PDT
Anthony the answer so far is usefull.  However I am trying to get an
actural temperature at which cupric oxide CuO starts to form in the
normal atmospheric air.  This is to enable thermographic images of
copper busbars and contacts to be rated against when CuO forms.  We
had a recent switchboard fire caused by the formation of Cuo
There are no comments at this time.

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