Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 13

10 μm 5 μm

(A) (B)

FIGURE 2.1 Microstructure.of.two.typical.spectroscopic.graphite.powders..(A).“RW-B” 1 .and.(B).“CR-5”. 2 .
Other. speciication:. (1). spectral. coal. (series. “X-69-257”;. Ringsdorff. Werke,. Bonn,. Germany). and. (2) gear.
lubricant. (Maziva. Tyn,. Týn. nad. Vltavou,. Czech. Republic).. Scanning. electron. microscope. (SEM,. model.
“JSM-5500LV”;.JEOL,.Tokyo,.Japan),..magniication.used:.1:3000..(From.authors'.archives.)

Note: . Some. authors. had. tried. to. solve. the. problems. associated. with. the. presence. of. oxygen. in.
graphite.powder.by.its.pretreatment.with.the.aid.of.special.procedures..One.of.such.purifying.opera-
tions.utilized.the.effect.of.thermal.desorption.of.oxygen.at.approximately.400°C.in.the.atmosphere.
of. inert. gas. passed. over. a. small. portion. of. graphite.. Reportedly,. the. whole. process. taking. 3-5.h.
allowed.them.to.remove.irreversibly.a.signiicant.part.of.adsorbed.oxygen.[177]..A.similar.opera-
tion,.yet.improved.by.thoroughly.impregnating.the.reined.graphite.with.ceresin.wax,.was.found.
to.be.effective.as.well.[39]..Otherwise,.however,.further.attempts.to.purify.graphite.powders.from.
oxygen.appeared.only.rarely.(see,.e.g.,.[178-181]),.when.some.of.these.operations.had.even.had.dif-
ferent.motivation.(e.g.,.improvement.of.kinetic.characteristics.[179])..The.unwillingness.to.follow.
similar.procedures.can.be.explained.by.their.unease.and.sophistication..Finally,.from.the.present.
day's.point.of.view,.it.seems.that.such.additional.deoxygenation.and.impregnation.is.not.so.inevi-
table.since.spectroscopic.graphites.produced.by.modern.technologies.usually.exhibit.satisfactory.
low.adsorption.capabilities.[175]..Also,.carbon.pastes.are.still.being.prepared.by.manual.hand.mix-
ing.and,.during.this.operation,.the.powder.may.get.back.a.part.of.previously.removed.oxygen.by.
absorbing.ambient.air.

. iii.. . High purity ..It.is.obvious.that.carbon.powder.should.not.contain.any.impurities.interfering.

with.measurements..This.is.the.particular.case.of.experiments.connected.with.detection.of.
very.low.currents.(at.the.low.nA.level.[152,182]),.where.even.negligible.traces.of.electroac-
tive.impurities.may.release.unwanted.and.overlapping.signal(s)..Again,.the.manufacturers.
usually.offer.the.purity.proile.of.their.goods.[171,183,184],.including.speciication.of.the.
remaining.traces.from.the.production.process.

Note: . The.latter.is.also.the.case.of.the.aforementioned.“RW”.spectral.coal.powder,.where.the.
corresponding.certiicate.declares.the.following.content.of.trace.impurities.(in.μg.·.g):.B.<.0.01,.
Ca <.0.20,.Cu.<.0.08,.Fe.=.0.20,.Mg.=.0.05,.Si.=.0.6,.Ti.<.0.50,.and.V.<.0.20.[171].

2.1.2.2 Other Carbonaceous Materials
Occasionally,.carbon.pastes.are.also.made.from.less.common.carbon.powders..The.irst.example.
is.(i).acetylene.black.(AB).[115,185,186]),.obtainable.by.controlled.combustion.of.acetylene.in.inert.
atmosphere.or,.better,.by.chemical.decomposition..Reportedly,.the.AB.has.a.crystalline-like.con-
solidated.structure,.which.contributes.to.a.more.reproducible.behavior.of.the.corresponding.carbon.
paste.that.also.exhibits.markedly.enhanced.adsorption.capabilities.[185].
Atypical. forms. of. carbon. used. by. Kauffmann. et. al.. [187]. were. also. (ii). carbon. black. (an.
amorphous. material. obtainable. by. the. incomplete. combustion. of. heavy. petroleum. fractions). and.