| Uses |
|
|---|---|
| Manufacturer | Tescan |
| Components |
|
TIMA (Tescan Integrated Mineral Analyzer) is an automated mineral analysis system manufactured by the Czech company Tescan. It combines scanning electron microscopy, backscattered-electron imaging and energy-dispersive X-ray spectroscopy with software to identify and quantify minerals in solid samples. The system produces mineral maps and data on mineral abundance, grain size, mineral associations (contacts between neighboring minerals) and liberation (the extent to which a mineral occurs separately from other minerals within particles).
TIMA was introduced in 2011. It is used in mineral processing and geological research, including the characterization of ores and petroleum reservoir rocks. The system has also been applied to extraterrestrial materials such as lunar soil returned by the Chang'e-5 mission.
TIMA's mineral analysis software was introduced in 2011. The TIMA system used Tescan's MIRA and VEGA scanning electron microscope platforms. In 2021, Tescan released a new generation of TIMA, which shared its hardware platform with the MIRA G4 field-emission scanning electron microscope.
TIMA combines a scanning electron microscope with backscattered-electron (BSE) and secondary-electron detectors, energy-dispersive X-ray (EDS) silicon drift detectors and software for automated data acquisition. TIMA instruments have used either field-emission or tungsten-filament electron sources, with one to four EDS detectors. Multiple EDS detectors increase the rate of X-ray collection and reduce shadowing from uneven sample surfaces. TIMA sample holders accommodate batches of thin sections or polished blocks.
Rock sections and grain mounts are typically polished to expose a flat surface and given a conductive coating to reduce charging. Surface preparation affects focusing and the quality of BSE and EDS data.
TIMA identifies mineral phases using BSE image contrast and EDS spectra. BSE contrast reflects differences in average atomic number, while EDS spectra provide information on elemental composition. The software uses these measurements and a mineral classification scheme to assign phase identities and generate a two-dimensional mineral map. Stored measurements can be reprocessed after the classification scheme is revised.
The software reports mineral abundances as volume percentages and converts them to mass percentages using assigned phase densities. These abundances and assigned phase compositions are used to calculate bulk chemical composition and elemental deportment, or the distribution of individual elements among mineral phases. Spatial data provide grain and particle size distributions, mineral associations and liberation. The software can export grain coordinates for subsequent electron probe microanalysis or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).
These surface measurements do not directly describe the complete three-dimensional structure of the sample; two-dimensional sections can lead to errors in estimates of mineral size and spatial relationships. Quantification also depends on whether the analyzed surface represents the sample.
Identification accuracy depends on how well the classification library represents the minerals and compositional variations present in the sample. Generic libraries can leave phases unclassified or misidentify them; refinement can also be checked using complementary techniques such as electron probe microanalysis. Phases with similar chemical compositions can be difficult to distinguish. Small intergrown mineral grains and mineral boundaries can produce mixed EDS signals, which the software attempts to classify by matching the resulting spectra against adjacent phases. Although EDS cannot directly detect elements such as hydrogen and lithium, phases containing these elements can still be identified based on the proportions of other detectable elements. Low elemental concentrations and overlapping X-ray peaks can also limit chemical quantification.
TIMA uses four acquisition modes:
These acquisition modes are used within separate analysis types. Modal analysis measures mineral abundances, while liberation analysis collects mineralogical and textural information. Bright phase search targets phases selected by BSE intensity, chemical composition or both, with an option to analyze surrounding material. Section analysis maps phases in thin sections or polished rock surfaces without detecting individual particles.
TIMA has been used in: