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Grain size

About: Grain size is a research topic. Over the lifetime, 40166 publications have been published within this topic receiving 855016 citations. The topic is also known as: particle size.

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Journal ArticleDOI
09 Mar 2000-Nature
TL;DR: It is shown that fully dense cubic Y2O3 with a grain size of 60 nm can be prepared by a simple two-step sintering method, at temperatures of about 1,000 °C without applied pressure, and the suppression of the final-stage grain growth is achieved by exploiting the difference in kinetics between grain- boundary diffusion and grain-boundary migration.
Abstract: Sintering is the process whereby interparticle pores in a granular material are eliminated by atomic diffusion driven by capillary forces. It is the preferred manufacturing method for industrial ceramics. The observation of Burke and Coble that certain crystalline granular solids could gain full density and translucency by solid-state sintering was an important milestone for modern technical ceramics. But these final-stage sintering processes are always accompanied by rapid grain growth, because the capillary driving forces for sintering (involving surfaces) and grain growth (involving grain boundaries) are comparable in magnitude, both being proportional to the reciprocal grain size. This has greatly hampered efforts to produce dense materials with nanometre-scale structure (grain size less than 100 nm), leading many researchers to resort to the 'brute force' approach of high-pressure consolidation at elevated temperatures. Here we show that fully dense cubic Y2O3 (melting point, 2,439 degrees C) with a grain size of 60 nm can be prepared by a simple two-step sintering method, at temperatures of about 1,000 degrees C without applied pressure. The suppression of the final-stage grain growth is achieved by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. Such a process should facilitate the cost-effective preparation of other nanocrystalline materials for practical applications.

1,328 citations

Journal ArticleDOI
TL;DR: The Gazzi-Dickinson point counting method as mentioned in this paper assigns sand-sized crystals and grains within larger fragments to the category of the crystal or grain, rather than to the larger fragment.
Abstract: Differing methods of determining detrital modes of sand/sandstone have been developed by different "schools" due to different goals and different geologic settings. The Gazzi-Dickinson method of point counting was developed to maximize source-rock data, while minimizing the time, effort, and expense of gathering such data. Use of the method minimizes variation of composition with grain size, thus eliminating the need for sieving and multiple counts of different size fractions. Unsorted samples of any sand size may be used, thus allowing direct comparison between modern sands and poorly sorted ancient sandstones. The application of actualistic petrologic models relating composition to tectonic setting thus is facilitated. The unique aspect of the Gazzi-Dickinson method of point counting is the assignment of sand-sized crystals and grains within larger fragments to the category of the crystal or grain, rather than to the category of the larger fragment. In addition, every attempt is made to reconstruct original detrital compositions in spite of subsequent alterations. Six unconsolidated Holocene sand samples derived from a variety of source rocks in north-central New Mexico were collected, sieved, impregnated, sectioned, stained and point-counted, using both traditional and Gazzi-Dickinson methods. Results of these counts provide a comparative test of traditional and Gazzi-Dickinson methods. There are two reasons for variation of modal composition with grain size: 1) the breakage of fragments into constituent grains, and 2) actual mineralogic variation with grain size. The Gazzi-Dickinson method successfully eliminates the first source of compositional grain-size dependency. No point-counting method eliminates the second source. Use of the Gazzi-Dickinson method on unsorted samples produces results that are consistent with those from different size fractions of the same samples. Lithic-fragment compositions (for example, LmLvLs, QpLvmLsm) are especially consistent and provide the most useful parameters for relating composition to source rock and, ultimately, to tectonic setting.

1,324 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of grain size on gas sensitivity were investigated by using porous sintered SnO2 elements fabricated with pure and impurity-doped SnO 2 elements.
Abstract: Effects of grain size on gas sensitivity (S) are investigated by using porous sintered SnO2 elements fabricated with pure SnO2, foreign oxide-stabilized SnO2, or impurity-doped SnO2. When the SnO2 crystallite size (D) is controlled to a size in the range 5–32 nm, S for H2, CO and i-C4H10 is found to increase steeply as D decreases to be comparable with or less than 2L (≈ 6 nm) is both pure and stabilized elements, where L is the depth of the space-charge layer. However, S for ethyl alcohol gas is found to be also affected by surface acid-base properties, being greatly promoted by basic oxides. It is found that the control of L by doping impurities (Al3+ or Sb5+) into the SnO2 lattice results in great changes in S even when D is the same. Thus Al-doped SnO2 shows high sensitivity with increasing L even at D above 20 nm, while Sb-doped SnO2 is insensitive in the whole D region. A model for the grain-size effects is proposed, in which the transducer function is operated by a mechanism of grain control, neck control or grain-boundary control, depending on D.

1,275 citations

Journal ArticleDOI
TL;DR: The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to the level in OTB single crystals.
Abstract: Large-aspect-ratio grains are needed in polycrystalline thin-film solar cells for reduced charge recombination at grain boundaries; however, the grain size in organolead trihalide perovskite (OTP) films is generally limited by the film thickness. Here we report the growth of OTP grains with high average aspect ratio of 2.3-7.9 on a wide range of non-wetting hole transport layers (HTLs), which increase nucleus spacing by suppressing heterogeneous nucleation and facilitate grain boundary migration in grain growth by imposing less drag force. The reduced grain boundary area and improved crystallinity dramatically reduce the charge recombination in OTP thin films to the level in OTP single crystals. Combining the high work function of several HTLs, a high stabilized device efficiency of 18.3% in low-temperature-processed planar-heterojunction OTP devices under 1 sun illumination is achieved. This simple method in enhancing OTP morphology paves the way for its application in other optoelectronic devices for enhanced performance.

1,240 citations

Journal ArticleDOI
TL;DR: The influence of the grain size on the flow stress of extruded Mg-3Al-1Zn tested in compression is examined in this paper, where samples with grain sizes varying between 3 and 23 μm were prepared by altering the extrusion conditions.

1,160 citations


Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
20231,176
20222,293
20211,252
20201,194
20191,223