Computer-controlled Scanning Electron Microscopy Research Articles

Heterogeneous ice nucleation and water uptake by field‐collected atmospheric particles below 273 K

Ice formation induced by atmospheric particles through heterogeneous nucleation is not well understood. Onset conditions for heterogeneous ice nucleation and water uptake by particles collected in Los Angeles and Mexico City were determined as a function of temperature (200–273 K) and relative humidity with respect to ice (RHice). Four dominant particle types were identified including soot associated with organics, soot with organic and inorganics, inorganic particles of marine origin coated with organic material, and Pb/Zn‐containing particles apportioned to emissions relevant to waste incineration. Single particle characterization was provided by micro‐spectroscopic analyses using computer controlled scanning electron microscopy with energy dispersive analysis of X‐rays (CCSEM/EDX) and scanning transmission X‐ray microscopy with near edge X‐ray absorption fine structure spectroscopy (STXM/NEXAFS). Above 230 K, significant differences in onsets of water uptake and immersion freezing of different particle types were observed. Below 230 K, particles exhibited high deposition ice nucleation efficiencies and formed ice atRHicewell below homogeneous ice nucleation limits. The data suggest that water uptake and immersion freezing are more sensitive to changes in particle chemical composition compared to deposition ice nucleation. The data demonstrate that anthropogenic and marine influenced particles, exhibiting various chemical and physical properties, possess distinctly different ice nucleation efficiencies and can serve as efficient IN at atmospheric conditions typical for cirrus and mixed‐phase clouds.

Quantitative Analysis of Unique Deposition Pattern of Submicron Fe3O4Particles Using Computer-Controlled Scanning Electron Microscopy

This study was designed to optimize particle counting of a unique deposition pattern of iron oxide (Fe3O4) particles that were collected by a multidomain magnetic passive aerosol sampler (MPAS). Fe3O4 is paramagnetic with a high magnetic susceptibility, rendering high collection efficiencies. The MPAS was designed exclusively for measuring particle penetration through protective clothing. To quantify particle deposition by size, two counting methods were employed with a computer-controlled scanning electron microscope (CCSEM). Based on a sequential set of measurements at known coordinates, particles were quantified across particle clusters collected by individual magnets. Because all magnets were of equal dimensions and strength, the particle concentration per cluster across the entire MPAS substrate was expected to be relatively uniform. However, since individual CCSEM fields are extremely small compared with the full sample, a randomized counting approach was used to determine how many fields were needed to obtain a representative subsample. Results by the sequential method show that particle numbers were higher toward the edge of the cluster, dominated by smaller particles; moderate at the center, dominated by larger particles; and null at the corners. The results additionally show that counting by the random method was comparable with the sequential method and repeatable for particle counts ranging from 3 to 383 particles per field, or 409,565–52,287,826 particles per substrate, taking between 25 and 53 min, respectively. The results suggest that with the random method, the CCSEM provided a powerful tool for quantitative analyses of particle numbers with unique deposition patterns. Copyright 2012 American Association for Aerosol Research

Single-Particle SEM-EDX Analysis of Iron-Containing Coarse Particulate Matter in an Urban Environment: Sources and Distribution of Iron within Cleveland, Ohio

The physicochemical properties of coarse-mode, iron-containing particles and their temporal and spatial distributions are poorly understood. Single-particle analysis combining X-ray elemental mapping and computer-controlled scanning electron microscopy (CCSEM-EDX) of passively collected particles was used to investigate the physicochemical properties of iron-containing particles in Cleveland, OH, in summer 2008 (Aug-Sept), summer 2009 (July-Aug), and winter 2010 (Feb-March). The most abundant classes of iron-containing particles were iron oxide fly ash, mineral dust, NaCl-containing agglomerates (likely from road salt), and Ca-S containing agglomerates (likely from slag, a byproduct of steel production, or gypsum in road salt). The mass concentrations of anthropogenic fly ash particles were highest in the Flats region (downtown) and decreased with distance away from this region. The concentrations of fly ash in the Flats region were consistent with interannual changes in steel production. These particles were observed to be highly spherical in the Flats region, but less so after transport away from downtown. This change in morphology may be attributed to atmospheric processing. Overall, this work demonstrates that the method of passive collection with single-particle analysis by electron microscopy is a powerful tool to study spatial and temporal gradients in components of coarse particles. These gradients may correlate with human health effects associated with exposure to coarse-mode particulate matter.

Measurement of ambient particulate matter concentrations and particle types near agricultural burns using electron microscopy and passive samplers

Abstract Computer-controlled scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to obtain ambient PM mass concentrations, elemental size distributions, morphologies, and particle types during four Bermuda grass burn events in Imperial Valley, California. Passive PM samplers were deployed to three to six locations surrounding each burn for durations of 24–120 h. Average PM 2.5 and PM 10 levels were modestly but significantly higher at locations less than 3.2 km (two miles) from the nearest burn ( n = 37). During one monitored burn, higher winds caused an intense ground-level plume to envelop two samplers mounted on telephone poles very close to the field. For this event, 24-h PM 2.5 exposures downwind were up to 17 times higher than that measured upwind. Particles were classified into five distinct chemical types consistent with local area sources. Burn-related particle types, primarily submicron carbonaceous particles, contributed 95% of the PM 2.5 in the location directly impacted by the ground-level plume, compared to only 12% in the upwind location. Downwind PM 10–2.5 particles were enriched in potassium, phosphorus, chlorine, calcium, silicon, and sulfur, consistent with analyses of bulk and partially-burned Bermuda grass. The accuracy and precision of passive sampler PM measurements were all within 4 μg m −3 , though low median values caused high percent differences for PM 2.5 . The use of electron microscopy and passive sampling in this study enabled detailed PM characterizations, spatial comparisons, and rapid deployment in often dynamic sampling scenarios.

Physical and Chemical Characterization of Coal Particles Used as Entrained Flow Gasifier Feedstock: Heterogeneity in Mineral Matter Distribution

Several challenges still exist in successful and reliable operation of entrained flow slagging gasifiers (EFG) using coal as a fuel. The formation of flyash and its carryover with the gas stream causes fouling and plugging of syngas coolers, leading to reduction in heat rate and overwhelming of the solids handling systems. In order to predict flyash formation as well as carbon loss in an EFG, a thorough understanding of the effect of feedstock properties on fuel conversion rates during gasification is required. Current state of the art in gasification modeling treats coal as a homogenous material although it well known that coal is heterogeneous. Different classes of particles, when fed into an EFG, behave differently in terms of carbon conversion and mineral transformations. Therefore, it is critical to develop modeling tools that can incorporate physical and chemical characteristics of the feedstock and the effect of the operating conditions on particle transformations, in order to predict fate of the char/ash particles generated in the gasifier. During the grinding of coal, macerals and minerals separate due to mineral liberation. When subjected to gravity fractionation, the liberated minerals tend to accumulate in heavier density particles. Various physical and chemical characterizations are performed on size separated particle classes of the four gravity fractions with an aim to bring out the heterogeneity in the coal and its impact on conversion. Characterization indicated that almost all of the gasifiable matter is present in the two lighter gravity fractions and bulks of the minerals are present in the two heavier gravity fractions. The mineral matter was characterized and quantified using ash yield measurements, X-ray fluorescence, X-ray diffraction, Computer Controlled Scanning Electron Microscopy (CCSEM) and the iron minerals were measured using Mossbauer spectroscopy. Characterization results show the heterogeneity across the coal in multiple chemical components and prompt the need to account for heterogeneity in models.

CCSEM investigation of respirable quartz in air samples collected during power plant maintenance activities

In an earlier investigation, computer-controlled scanning electron microscopy (CCSEM) and X-ray diffraction (XRD) were used to investigate respirable quartz in several bulk coal fly-ash samples. It was shown that the XRD result for quartz in bulk fly-ash was much larger than the amount of respirable quartz determined by CCSEM because the XRD signal was derived primarily from quartz particles too large to be classified as respirable. In the current paper, CCSEM and XRD were used to investigate coal fly-ash collected using cyclone-filtered personal and area samplers at two different power plants during maintenance activities. The amounts of respirable quartz determined by the two methods were found to be in good agreement, confirming the need for cyclone-filtered samples. The amounts of respirable quartz determined by CCSEM ranged from 1.5 to 3.5vol.% for the plant burning a Southwest sub-bituminous coal and from 0.6 to 1.9vol.% for the plant burning a Mid-West bituminous coal. Very small amounts (average∼0.2vol.% for both plants) of Si-rich glass or amorphous silica were also detected by CCSEM. This paper is important because of the health implications associated with inhaling quartz particles. It demonstrates that the amounts of respirable quartz to which power plant workers are exposed can be accurately measured by two very different measurements on samples collected in cyclone-filtered samplers designed to emulate the inhalation process of human airways.

Effects of Mineral Transformations on the Reduction of PM<sub>2.5</sub> during the Combustion of Coal Blends

Two chinese bituminous coals used in coal-fired power plants are combusted under air conditions in a lab-scale drop tube furnace. The effects of minerals transformation on the formation of PM 2.5 are investigated during the combustion of coal blends. The collected PM were subjected to Computer controlled scanning electron microscopy (CCSEM) and High-resolution transmission electron microscopy(HRTEM) coupled with energy dispersive X-ray spectroscopy (EDX) analysis for determination of chemical species within them. The results show that PM 2.5 emissions are not linearly related to the wt.% of the parent coal or coal blends. Transformations of fine Si-Al mineral grains provided by the minerals in coal XQ into coarse particles (>2.5 μm in diameter) are responsible for the reduction of PM1-2.5 during the combustion of coal blending. The transformed fine Si-Al particles are captured by the coarse Ca-Mg-Al-Si provided by the minerals in coal HT to form larger Ca-Mg-Al-Si particles (>2.5 μm in diameter). Increasing Ca and Mg concentration in coal blends enhances the liquid concentration produced during combustion and hence affects the emissions of PM1 and PM1-2.5.Through adjusting the mineral compositions in coal blends, the reduction of PM1 and PM1-2.5 emissions can be achieved during combustion.

Characterization and heterogeneity of coarse particles across an urban area

Abstract Coarse particles exposures are expected to be highly heterogeneous in an urban area. However, little data are available to explore the extent of heterogeneity of coarse particles, especially on a local scale. An extensive sampling program for the coarse particles was conducted using University of North Carolina (UNC) passive aerosol samplers. The samplers were deployed for 4–5 week periods during four seasons, fall, winter, spring, and summer at 25 different sites across Syracuse, a small city located in central New York. The substrates from the UNC passive samplers were analyzed with computer-controlled scanning electron microscopy (CCSEM) providing size, shape, and elemental composition in the form of fluoresced X-ray spectra. Adaptive resonance theory (ART-2a) based neural network algorithm was applied with processed X-ray data to identify homogenous particles classes of 25,437 coarse particles from all four seasons. Thirty-four particle classes were identified with similar chemical characteristics. The mass fractions of particles in each identified class were then used to assess the homogeneity of composition and concentration across the measurement domain for each season. Road/soil dust, carbonaceous dust, biological materials, and deicing road salt were identified as the major sources of the urban coarse particles. Spatial and seasonal variations in both composition and concentration were observed and a noticeable heterogeneity between adjacent sites is indicated by the coefficient of divergence and correlation coefficient analysis.

Differential Individual Particle Analysis (DIPA): Applications in Particulate Matter Characterization

Operator-controlled and computer-controlled scanning electron microscopy (CCSEM) are used extensively to characterize particulate matter in environmental media. Analysis in a scanning electron microscope (SEM) coupled with chemical extraction is a potentially powerful tool that is capable of determining how various sample components are associated at the individual particle level. This involves initial characterization in a SEM, after which the material is exposed to a liquid or gas phase reaction for a specified time, and once exposure is concluded, the particles are reanalyzed in the SEM. This particle analysis by difference, or differential individual particle analysis (DIPA), possesses considerable potential for describing the behavior of environmental particles under changing chemical conditions. Here we describe DIPA applications with illustrative examples drawn from the analysis of particulate matter modified by reactions in a fluid environment. In situ DIPA permits the same particles to be analyzed in the SEM before and after modification. Repeated exposure to the same, or different modifying conditions, provides information on the time dependence of specific reactions. Significant numbers of particles can be analyzed using CCSEM, and the same particles can be analyzed after the reaction by accurate sample relocation in the SEM. Ex situ DIPA, which involves a bulk sample modification, uses CCSEM to characterize significant numbers of particles pre- and postreaction. The CCSEM approach is extremely efficient; recent developments in silicon drift detectors have increased the speed of characteristic X-rays detection, and very large numbers of particles can be analyzed in a short period of time.

Study on Fly Ash Adhesion Characteristics and Deposition Mechanism in Shell Coal Gasification Process

This paper describes the characteristics and mechanism of fly ash deposited in Shell coal gasification process. The chemical composition, particle size distribution, surface topography and elemental composition of fly ash samples derived from coal A and coal B are studied by X-ray fluorescence spectrometer, JX-2000 microscopic image analyzer and computer controlled scanning electron microscopy (SEM/EDX) respectively. The results show that the differences in ash deposition characteristics result from the differences in surface properties and element composition of fly ash particles generated from different coal feed. The fly ash formation and deposition mechanism are discussed based on physicochemical changes in gasification, particle size distribution and surface composition enriched in Ca, Fe in fly ash particles. The results can serve as reference data for a variety of deposition studies.

Heterogeneity of Coarse Particles in an Urban Area

The variation in composition and concentration of coarse particles in Rochester, a medium-sized city in western New York, was studied using UNC passive samplers and computer-controlled scanning electron microscopy (CCSEM). The samplers were deployed in a 5 × 5 grid (2 km × 2 km per grid cell) for 2-3 week periods in two seasons (September 2008 and May 2009) at 25 different sites across Rochester. CCSEM analysis yielded size and elemental composition for individual particles and analyzed more than 800 coarse particles per sample. Based on the composition as reflected in the fluoresced X-ray spectrum, the particles were grouped into classes with similar chemical compositions using an adaptive resonance theory (ART) network. The mass fractions of particles in the identified classes were then used to assess the homogeneity of composition and concentration across the measurement domain. These results illustrate how particle sampling using the UNC passive sampler coupled with CCSEM/ART can be used to determine the concentration and source of the coarse particulate matter at multiple sites. The particle compositions were dominated by elements suggesting that the major particle sources are road dust and biological particles. Considerable heterogeneity in both composition and concentration were observed between adjacent sites as indicated by cofficient of divergence analyses.

Application of X-ray Photoelectron Spectroscopy (XPS) for the Surface Characterization of Gunshot Residue (GSR)

Gunshot residue (GSR) is typically found on the hands or clothing of persons who have been in the environment of a discharging firearm, but it may also be found on objects in the vicinity of the discharge. Computer-controlled scanning electron microscopy (CCSEM) is the method preferred by the forensic community for the automated analysis of GSR. GSR samples are therefore typically collected from a crime suspect's hands and/or clothing using SEM sample stubs coated with a conductive adhesive. The three major components in modern firearm cartridge primers are lead styphanate (initiator), antimony sulfide (fuel), and barium nitrate (oxidizer). GSR consists of the products of combustion of these primer materials. Large populations of particles in the size range of ~1–10 μm are rapidly screened by energy-dispersive X-ray spectroscopy (EDS) for the presence of combinations of Pb, Sb, and Ba. When combinations of these three elements are detected, the particles are flagged as potential GSR particulate. Flagged particles with significant Pb/Sb/Ba compositions are subsequently relocated for a live identification and a positive confirmation of GSR. Positive particles are classified as being either “characteristic of GSR” (that is, all three key elements are present) or “consistent with GSR” (that is, any two of the key elements are present) based on the particle composition and morphology. Classification is based on the presence of the constituent elements and is not dependant on the element amounts. If a particle does not meet the proper compositional or morphological criteria, it is rejected as GSR. However, CCSEM generally does not provide information regarding the population of particles much less than 1 μm or the surface chemistry of the GSR particles. This article examines the fine fraction of GSR particles with high-resolution electron microscopy and complements the microscopy data with surface chemistry information from X-ray photoelectron spectroscopy (XPS).

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe–Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.

Experimental investigation of the combustion of bituminous coal in air and O2/CO2 mixtures: 2. Variation of the transformation behaviour of mineral matter with bulk gas composition

Combustion of a Chinese bituminous coal was carried out in a laboratory-scale drop tube furnace (DTF) to clarify the variation of ash properties with bulk gas composition. The combustion conditions tested include three bulk gases, air, 21% O2/79% CO2 and 27% O2/73% CO2, two furnace/gas temperatures close to the fluidized bed reactor temperature range, 1073K and 1273K, and three particle residence times. Apart from bulk properties analysis, individual ash particles and the original mineral species in coal were characterized using Computer – Controlled Scanning Electron Microscopy (CCSEM). The results indicate that, under the given experimental conditions, shifting bulk gas from air to O2/CO2 mixtures is insignificant in terms of the elemental composition of bulk ash, in agreement with the literature. However, changes in the properties of individual species/metals are noticeable, including the extent of the vaporization of volatile elements, ash particle-size distribution (PSD), crystallization extent of K alumino-silicate associate, pyrite decomposition and oxidation rate and formation propensity of liquidus in ash. These changes were mostly considered to be caused by the evolution of included mineral grains in the distinct char particles in the O2/CO2 environment. Reduction in char particle temperature with bulk gas shifting from air to O2/CO2 mixtures was primarily crucial, which, however, could be overweighed by the existence of a fairly strong local reducing condition on the char surface in O2/CO2. Consequently, vaporization of the volatile elements such as Na and P was promoted; formation of the crystalline leucite in air was in contrast inhibited. Furthermore, the extent of coalescence of included minerals and oxidation rate of pyrite (or its derivative, pyrrhotite) were also influenced by char consumption rate, i.e. the receding extent of char surface. These parameters exerted a combined effect on ash formation, requiring detailed mathematical modeling to describe the dynamics of the formation of oxy-fuel ash. This study also indicated that the differences of ash properties formed between air and O2/CO2 mixtures can be greatly reduced and eventually eliminated by increasing furnace temperature. Increase in the turbulence of gas flow should also benefit the elimination of the side effects of local reducing gases on char surface.

Interactive web analysis and presentation of computer-controlled scanning electron microscopy data

In the following we describe the result of the Titan Project, an interactive web application (Titan) developed at the Geological Survey of Denmark and Greenland (GEUS) together with DuPont Titanium Technologies. The main aim of Titan is to make computer-controlled scanning electron microscopy (CCSEM) data, generated at GEUS, available via the internet. In brief, CCSEM is a method automatically to detect particles with a scanning electron microscope (SEM), and based on computer-controlled imagery to measure the chemistry and grain morphology of each particle in a given sample (Knudsen et al. 2005; Bernstein et al. 2008); Keulen et al. 2008. Titan makes data available on-line so that the user can interact with the data sets and analyse them using a web browser. In addition to CCSEM data, Titan contains a global database of titanium deposits and various reports. The web application is customised, such that the functionality and amount of data available for a given user depend on the privileges of that user.

Heterogeneous nucleation of ice on anthropogenic organic particles collected in Mexico City

This study reports on heterogeneous ice nucleation activity of predominantly organic (or coated with organic material) anthropogenic particles sampled within and around the polluted environment of Mexico City. The onset of heterogeneous ice nucleation was observed as a function of particle temperature (Tp), relative humidity (RH), nucleation mode, and particle chemical composition which is influenced by photochemical atmospheric aging. Particle analyses included computer controlled scanning electron microscopy with energy dispersive analysis of X‐rays (CCSEM/EDX) and scanning transmission X‐ray microscopy with near edge X‐ray absorption fine structure spectroscopy (STXM/NEXAFS). In contrast to most laboratory studies employing proxies of organic aerosol, we show that anthropogenic organic particles collected in Mexico City can potentially induce ice nucleation at experimental conditions relevant to cirrus formation. The results suggest a new precedent for the potential impact of organic particles on ice cloud formation and climate.

Microscopic characterization of carbonaceous aerosol particle aging in the outflow from Mexico City

Abstract. This study was part of the Megacities Initiative: Local and Global Research Observations (MILAGRO) field campaign conducted in Mexico City metropolitan area during spring 2006. The physical and chemical transformations of particles aged in the outflow from Mexico City were investigated for the transport event of 22 March 2006. A detailed chemical analysis of individual particles was performed using a combination of complementary microscopy and micro-spectroscopy techniques. The applied techniques included scanning transmission X-ray microscopy (STXM) coupled with near edge X-ray absorption fine structure spectroscopy (NEXAFS) and computer controlled scanning electron microscopy with an energy dispersive X-ray analyzer (CCSEM/EDX). As the aerosol plume evolves from the city center, the organic mass per particle increases and the fraction of carbon-carbon double bonds (associated with elemental carbon) decreases. Organic functional groups enhanced with particle age include: carboxylic acids, alkyl groups, and oxygen bonded alkyl groups. At the city center (T0) the most prevalent aerosol type contained inorganic species (composed of sulfur, nitrogen, oxygen, and potassium) coated with organic material. At the T1 and T2 sites, located northeast of T0 (~29 km and ~65 km, respectively), the fraction of homogenously mixed organic particles increased in both size and number. These observations illustrate the evolution of the physical mixing state and organic bonding in individual particles in a photochemically active environment.

Radiological dispersal device outdoor simulation test: Cesium chloride particle characteristics

Particles were generated from the detonation of simulated radiological dispersal devices (RDDs) using non-radioactive CsCl powder and explosive C4. The physical and chemical properties of the resulting particles were characterized. Two RDD simulation tests were conducted at Lawrence Livermore National Laboratory: one of the simulated RDDs was positioned 1 m above a steel plate and the other was partially buried in soil. Particles were collected with filters at a distance of 150 m from the origin of the RDD device, and particle mass concentrations were monitored to identify the particle plume intensity using real time particle samplers. Particles collected on filters were analyzed via computer-controlled scanning electron microscopy coupled with energy dispersive X-ray spectrometry (CCSEM/EDX) to determine their size distribution, morphology, and chemical constituents. This analysis showed that particles generated by the detonation of explosives can be associated with other materials (e.g., soil) that are in close proximity to the RDD device and that the morphology and chemical makeup of the particles change depending on the interactions of the RDD device with the surrounding materials.

Characterization of Ash Deposition and Heat Transfer Behavior of Coals during Combustion in a Pilot-Scale Facility and Full-Scale Utility

Experimental measurements as well as theoretical models were used to investigate the impact of mineral matter of three coals on ash deposition and heat transfer for pulverized coal fired boilers. The ash deposition experiments were conducted in a pulverized fuel combustion pilot-scale facility and a full-scale unit. A mathematical model with input from computer-controlled scanning electron microscopy analysis of coal minerals was used to predict the effect of ash deposition on heat transfer. The predicted deposit thickness and heat flux from the model are shown to be consistent with the measurements in the test facility. The model differentiates the coals according to the deposits they form and their effect on heat transfer. The heat transfer predictions in the full-scale unit were found to be most suitable for the water wall under the furnace nose. The study demonstrates that the measurements in a full-scale unit can differ significantly from those in pilot-scale furnaces due to soot-blowing operations.

Computer-controlled scanning electron microscopy: A fast and reliable tool for diamond prospecting

Computer-controlled scanning electron microscopy is introduced as a faster, reliably and cost-reducing alternative to conventional electron microprobe analyses on kimberlite indicator minerals. The method is based on conventional scanning electron microscopy and energy dispersive X-ray spectrometry, but due to extended counting times, optimised settings and computer-controlled particle recognition valid data can be obtained on a low amount of operator and machine time. A comparison of the results between both methods yields that computer-controlled scanning electron microscopy is able to investigate major and minor element concentrations in indicator minerals with almost the same precision as the electron microprobe.