Cathodoluminescence Microscopy: A Valuable Technique for Studying Ceramic Materials
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molybdenite mine, and ore guides in other metallic deposits by CL was discussed by Hagni.10"11 CLM also has found use in such areas of geology as the identification of minerais of météorites 12 ' 13 and soils:14 An extensive bibliography of about 465 références on CL applications to geological materials was published by Barker and Wood.15 A volume devoted to the cathodoluminescence of geological materials recently was authored by Marshall.16 Applications of CL to metallurgical problems hâve been limited. CLM has been used to detect and characterize the mineralogy, grain size, and distribution of the phosphate minerais in the Birmingham iron ores as an aid to beneficiation expérimentation to produce concentrâtes with higher grades and lower phosphbrus contents by Hagni and Côoper.10"11 A récent study by Karakus and Hagrii19 of the Alsace-Lorraine iron ores of France has dramatically revealed the character of the phosphate grains in those sedimentary ores. Other applications to metallurgical products hâve been discussed by Hagni.1011 The application of CLM to ceramic materials has been limited largely to the study of semiconductors20 and phosphore. Harmer et al.21 noted the CL of ceramic and glass microstructures. Czernuszka and Page22 and Rincon et al.23 used CLM to study phase distributions and déformation structures in zirconia ceramics. Hagni11 discussed the
application of CLM to a variety of refractory problems. Karakus et al,24"25 recently showed that CLM can be spectacularly effective in distinguishing and studying deleterious ceramic build-ups that form in electric induction furnaces used as melting and holding ladles in the steel industry. This article will briefly discuss the technique of CLM and illustrate the value of its application tb refractory materials with CLM photomicrographs. Principles The cathodoluminescence microscope utilizes a beam of électrons, produced by a cathode électron gun, that are trained on the surface of a spécimen. The energy input of the électron beam causes mahy minerais or synthëtic phases to produce colored light or "càthodoluminesce." The phenomena of cathodoluminescence is similar to that of the better known fluorescence, but the energy input or excitation source is that of an électron beam rather than an ultraviolet radiation source, and the intensity of CL is stronger than fluorescence for a given minerai. Energy input from the électron beam causes électrons within transition and lanthanide éléments to be elevated to brbits of higher energy. Emission of radiation occurs when the électrons return from the excited states to orbits of lower energy. It is that radiation in the visible portion of the spectrum that is viewed with the CLM. In contrast to the scanning électron microscope and the électron microprobe, which in their normal modes of opération utilize a beam focused on a spot one micrometer or less in diamëter, the beam for the CLM is defocused to cover a relatively large portion of the spécimen. A coverage of about two millimetérs is common, and this provides a fiel
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