Ceramography
The microstructure is the structure level of approximately 0.1 to 100 μm, between the minimum wavelength of visible light and the resolution limit of the naked eye.
Ceramography is part of the broader field of materialography, which includes all the microscopic techniques of material analysis, such as metallography, petrography and plastography.
Alois de Widmanstätten of Austria etched a meteorite in 1808 to reveal proeutectoid ferrite bands that grew on prior austenite grain boundaries.
Geologist Henry Clifton Sorby, the "father of metallography", applied petrographic techniques to the steel industry in the 1860s in Sheffield, England.
[2] French geologist Auguste Michel-Lévy devised a chart that correlated the optical properties of minerals to their transmitted color and thickness in the 1880s.
The preparation of ceramic specimens for microstructural analysis consists of five broad steps: sawing, embedding, grinding, polishing and etching.
The tools and consumables for ceramographic preparation are available worldwide from metallography equipment vendors and laboratory supply companies.
[8] To facilitate further preparation, the sawed specimen is usually embedded (or mounted or encapsulated) in a plastic disc, 25, 32 or 38 mm in diameter.
[9][citation needed] A thermosetting solid resin, activated by heat and compression, e.g. mineral-filled epoxy, is best for most applications.
A castable (liquid) resin such as unfilled epoxy, acrylic or polyester may be used for porous refractory ceramics or microelectronic devices.
Grinding erases saw marks, coarsely smooths the surface, and removes stock to a desired depth.
A typical polishing sequence for ceramics is 5–10 minutes each on 15-, 6- and 1-μm diamond paste or slurry on napless paper rotating at 240 rpm.
Alternatively, non-cubic ceramics can be prepared as thin sections, also known as petrography, for examination by polarized transmitted light microscopy.
Cubic ceramics, e.g. yttria-stabilized zirconia and spinel, have the same refractive index in all crystallographic directions and appear, therefore, black when the microscope's polarizer is 90° out of phase with its analyzer.
Ceramographic specimens are electrical insulators in most cases, and must be coated with a conductive ~10-nm layer of metal or carbon for electron microscopy, after polishing and etching.
Bare alumina (η ≈ 1.77, k ≈ 10 −6) has a negligible extinction coefficient and reflects only 8% of the incident light from the microscope, as in Fig.
Ceramography is often done qualitatively, for comparison of the microstructure of a component to a standard for quality control or failure analysis purposes.
The occurrence of AGG has consequences, positive or negative, on mechanical and chemical properties of ceramics and its identification is often the goal of ceramographic analysis.
In each case, the measurement is affected by secondary phases, porosity, preferred orientation, exponential distribution of sizes, and non-equiaxed grains.
Image analysis can measure porosity, pore-size distribution and volume fractions of secondary phases by ASTM E1245.
Grain size, porosity and second-phase content have all been correlated with ceramic properties such as mechanical strength σ by the Hall–Petch equation.
The hardness of very small particles and thin films of ceramics, on the order of 100 nm, can be measured by nanoindentation methods that use a Berkovich indenter.
