Brochure: A Synopsis of Analytical Procedures - Timcal

Analytical procedures forTIMREX ® Graphite and CokeAsh contentA low-walled ceramic crucible is ignited at800° C in a muffle furnace and dried in adessicator.A sample of 10 g of dry powder (accuracy0.1 mg) is weighed in a low-walled ceramiccrucible. The powder is combusted at atemperature of 815° C (1472° F) to constantweight (at least 8 h). The residue correspondsto the ash content. It is expressedas a percentage of the initial weight of thesample.References:- DIN 51903 and DIN 51701 (dividing process)- ASTM C 561-91Water contentThe method is based on the chemicalreaction of water with sulphur dioxide andiodine (Karl Fischer Titration). We alsoemploy an alternative method where a sampleof 30-70 g of carbon powder (accuracy0.1 mg) is weighed in a glass beaker anddried at 110° C (210° F) until constantweight is reached (approx. 8-10 h). T h eweight loss corresponds to the water content.It is expressed as a percentage of theoriginal weight of the sample.References:- DIN 51777 and DIN 51701- DIN 51904 - ASTM C 562-91- Eberius, Wasserbestimmung mit KF-Lösung,Verlag Chemie, Weinheim (1958)- Mitchell/SmithAquametryInterscience Publisher NY/London (1948)2003004005006007008009001000Trace elementsThis analysis is performed by an SDAROES Simultaneous emission spectrometer.Graphite powder, ground to a maximumparticle size of 80 µm by means of a vibratedmill is compacted to a tablet. The sampleis placed onto the excitation standunder argon atmosphere of the spectrometer.Subsequently the fully automatic analysiscan be initiated.References:- K. SlickersAutomatic Emission SpectroscopyBrühl Druck und Presshaus Giessen (D) (1992)- M. Wissler und P. GebhardtProtokoll der 29. Sitzung des Unterausschusses Feststoffeim Arbeitkreis Kohlenstoff der Deutschen KeramischenGesellschaft (12./13. Dez 1984)Trace Elements -2 (XRF)Another possibility to determine traceelements concentration is using X-rayFluorescence Spectroscopy (XRF).The sample to be analyzed is compactedinto a 40 mm tablet at a pressure of 12tons. Multiple tablets are placed in a sampleloader which is placed inside the vacuumchamber of the XRF. Once the vacuumis established, each tablet is in turn exposedto an X-ray beam. To maximize the surfaceanalyzed, the tablets are slowly rotated duringexposure. The energy of the beamexcites the different atoms constituting thesample; when returning to their normalstate, these atoms emit characteristic X-rayfluorescence. Their specific energy levelsare analyzed by a Si-Li detector.For each element, the energy of the characteristicX-ray determines the nature ofthe elements while the number of counts ofeach characteristic X-ray allows for the calculationof the relative proportion of eachelement in the sample. The XRF analysisprocess is fully automated.Reference:- TIMCAL methodInterlayer spacing c/2The interlayer space c/2 is determined byX-ray diffractometry. The angular positionof the peak maximum of the (002) and(004) reflection profiles are determinedand, by applying the Bragg equation, theinterlayer spacing is calculated.The graphite sample is mixed with a siliconstandard. A mixture of polyglycol andethanol is added in order to obtain a highlyviscous slurry. Subsequently, a thin layer ofapprox. 150 µm is applied to a glass plateand dried. A Cu Kα X-ray beam is used.References:- Klug and Alexander, X-Ray diffraction ProceduresJohn Wiley and Sons Inc., New York London (1967)Crystallite size LcCrystallite size is determined by interpretationof the (002) and (004) diffractionprofiles. However, the analysis is somewhatproblematic in view of the fact that texture(e.g. porosity) tends to superimpose theangular profile. Several methods have beenoffered to calculate the line broadeningwhich should be affected by crystallite sizealone.TIMCAL has chosen the approach suggestedby Iwashita. The algorithm proposedby Iwashita has been specifically developedfor carbon materials.The widths of the line profiles at the halfmaximum of sample and reference aremeasured. By means of a correction function,the width of pure diffraction profilecan be determined. The crystallite size issubsequently calculated by applyingScherrer's equation.References:- P. Scherrer, Göttinger-Nachrichten 2 (1918) S.98- N. Iwashita, C. Rae Park, H. Fujimoto, M. Shiraishiand M. Inagaki, Carbon 42, 701-714 (2004).13012011010090807060504030