SummaryA recently developed technique based on the transmission electron microscope, which makes use of electron beam precession together with spot diffraction pattern recognition now offers the possibility to acquire reliable orientation/phase maps with a spatial resolution down to 2 nm on a field emission gun transmission electron microscope. The technique may be described as precession-assisted crystal orientation mapping in the transmission electron microscope, precession-assisted crystal orientation mapping technique-transmission electron microscope, also known by its product name, ASTAR, and consists in scanning the precessed electron beam in nanoprobe mode over the specimen area, thus producing a collection of precession electron diffraction spot patterns, to be thereafter indexed automatically through template matching. We present a review on several application examples relative to the characterization of microstructure/microtexture of nanocrystalline metals, ceramics, nanoparticles, minerals and organics. The strengths and limitations of the technique are also discussed using several application examples.

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Exposure to ceramic powders, which is frequent during handling operations, is known to cause adverse health effects. Finding proxy parameters to quantify exposure is useful for efficient and timely exposure assessments. Worker exposure during handling of five materials (a silica sand (S1), three quartzes (Q1, Q2 and Q3) and a kaolin (K1)) with different particle shape (prismatic and platy) and sizes (3.4 -120 µm) was assessed. Materials handling was simulated using a dry pendular mill under two different energy settings (low and high). Three repetitions of two kilos of material were carried out per material and energy conditions with a flow rate of 8 -11 kg/h. The performance of the dustiness index as a predictor of worker exposure was evaluated correlating material's dustiness indexes (with rotating drum and continuous drop) with exposure concentrations. Significant impacts on worker exposure in terms of inhalable and respirable mass fractions were detected for all materials. Mean inhalable mass concentrations during background were always lower than 40 µg/m 3 whereas during material handling under high energy settings mean concentrations were 187, 373, 243, 156 and 430 µg/m 3 for S1, Q1, Q2, Q3 and K1 respectively. Impacts were not significant with regard to particle number concentration: background particle number concentrations ranged between 10620 -46421 /cm 3 while during handling under high energy settings they were 20880 -40498 /cm 3 . Mean lung deposited surface area during background ranged between 27 -101 μm 2 /cm 3 whereas it ranged between 22 -42 μm 2 /cm 3 during materials handling. TEM images evidenced the presence of nanoparticles (≤ 100 nm) in the form of aggregates (300 nm -1 µm) in the worker area, and a slight reduction on mean particle size during handling was detected. Dustiness and exposure concentrations showed a high degree of correlation (R 2 = 0.77 -0.97) for the materials and operating conditions assessed, suggesting that dustiness could be considered a relevant predictor for workplace exposure. Nevertheless, the relationship between dustiness and exposure is complex and should be assessed for each process, taking into account not only material behaviour but also energy settings and workplace characteristics.

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