The hydration of the two most reactive phases of ordinary Portland cement (OPC), tricalcium silicate (C3S), and tricalcium aluminate (C3A) is successfully halted when the activity of water (
We report the pulsed‐laser deposition of epitaxial double‐perovskite Bi2FeCrO6(BFCO) films on the (001)‐, (110), and (111)‐oriented single‐crystal SrTiO3substrates. All of the BFCO films with various orientations show the
- Award ID(s):
- 1708615
- NSF-PAR ID:
- 10371474
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 102
- Issue:
- 9
- ISSN:
- 0002-7820
- Page Range / eLocation ID:
- p. 5234-5242
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract ) falls below critical thresholds of 0.70 and 0.45, respectively. It has been established that the reduction in relative humidity (RH) and suppresses the hydration of all anhydrous phases in OPC, including less explored phases like dicalcium silicate, that is, belite (β‐C2S). However, the degree of suppression, that is, the critical threshold, for β‐C2S, standalone has yet to be established. This study utilizes isothermal microcalorimetry and X‐ray diffraction techniques to elucidate the influence of on the hydration of ‐C2S suspensions via incremental replacements of water with isopropanol (IPA). Experimentally, this study shows that with increasing IPA replacements, hydration is increasingly suppressed until eventually brought to a halt at a critical threshold of approximately 27.7% IPA on a weight basis (wt.%IPA). From thermodynamic estimations, the exact critical threshold and solubility product constant of ‐C2S ( ) are established as 0.913 and 10−12.68, respectively. This study enables enhanced understanding of β‐C2S reactivity and provides thermodynamic parameters during the hydration of β‐C2S‐containing cementitious systems such as OPC‐based and calcium aluminate‐based systems. -
Abstract While monazite (LaPO4) does not flash sinter even at high fields of 1130 V/cm and temperatures of 1450°C, composite systems of 8YSZ–LaPO4and Al2O3–LaPO4have been found to more readily flash sinter. 8YSZ added to LaPO4greatly lowered the furnace temperature for flash to 1100°C using a field of only 250 V/cm. In these experiments,
‐Al2O3alone also did not flash sinter at 1450°C even with high fields of 1130 V/cm, but composites of Al2O3–LaPO4powders flash sintered at 900‐1080 V/cm at 1450°C. Alumina–monazite (Al2O3–LaPO4) composites with compositions ranging from 25 vol% to 75 vol% Al2O3were flash sintered with current limits from 2 to 25 mA/mm2. Microstructures were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A eutectic microstructure was observed to form in all flash sintered Al2O3–LaPO4composites. With higher power (higher current limits), eutectic structures with regular lamellar regions were found to coexist in the channeled region (where both the current and the temperature were the highest) with large hexagonal‐shaped ‐Al2O3grains (up to 75 m) and large irregular LaPO4grains. With lower power (lower current limits), an irregular eutectic microstructure was dominant, and there was minimal abnormal grain growth. These results indicate that Al2O3–LaPO4is a eutectic‐forming system and the eutectic temperature was reached locally during flash sintering in regions. These eutectic microstructures with lamellar dimensions on the scale of 100 nm offer potential for improved mechanical properties. -
Abstract The mineral apatite, Ca5(PO4)3(F,Cl,OH), is a ubiquitous accessory mineral, with its volatile content and isotopic compositions used to interpret the evolution of H2O on planetary bodies. During hypervelocity impact, extreme pressures shock target rocks resulting in deformation of minerals; however, relatively few microstructural studies of apatite have been undertaken. Given its widespread distribution in the solar system, it is important to understand how apatite responds to progressive shock metamorphism. Here, we present detailed microstructural analyses of shock deformation in ~560 apatite grains throughout ~550 m of shocked granitoid rock from the peak ring of the Chicxulub impact structure, Mexico. A combination of high‐resolution backscattered electron (BSE) imaging, electron backscatter diffraction mapping, transmission Kikuchi diffraction mapping, and transmission electron microscopy is used to characterize deformation within apatite grains. Systematic, crystallographically controlled deformation bands are present within apatite, consistent with tilt boundaries that contain the <
c > (axis) and result from slip in <> (direction) on (plane) during shock deformation. Deformation bands contain complex subgrain domains, isolated dislocations, and low‐angle boundaries of ~1° to 2°. Planar fractures within apatite form conjugate sets that are oriented within either { , { , { , or . Complementary electron microprobe analyses (EPMA) of a subset of recrystallized and partially recrystallized apatite grains show that there is an apparent change in MgO content in shock‐recrystallized apatite compositions. This study shows that the response of apatite to shock deformation can be highly variable, and that application of a combined microstructural and chemical analysis workflow can reveal complex deformation histories in apatite grains, some of which result in changes to crystal structure and composition, which are important for understanding the genesis of apatite in both terrestrial and extraterrestrial environments. -
Abstract Microbial sulfur cycling in marine sediments often occurs in environments characterized by transient chemical gradients that affect both the availability of nutrients and the activity of microbes. High turnover rates of intermediate valence sulfur compounds and the intermittent availability of oxygen in these systems greatly impact the activity of sulfur‐oxidizing micro‐organisms in particular. In this study, the thiosulfate‐oxidizing hydrothermal vent bacterium
Thiomicrospira thermophila strain EPR85 was grown in continuous culture at a range of dissolved oxygen concentrations (0.04–1.9 mM) and high pressure (5–10 MPa) in medium buffered at pH 8. Thiosulfate oxidation under these conditions produced tetrathionate, sulfate, and elemental sulfur, in contrast to previous closed‐system experiments at ambient pressure during which thiosulfate was quantitatively oxidized to sulfate. The maximum observed specific growth rate at 5 MPa pressure under unlimited O2was 0.25 hr−1. This is comparable to theμ max(0.28 hr−1) observed at low pH (<6) at ambient pressure whenT. thermophila produces the same mix of sulfur species. The half‐saturation constant for O2() estimated from this study was 0.2 mM (at a cell density of 105cells/ml) and was robust at all pressures tested (0.4–10 MPa), consistent with piezotolerant behavior of this strain. The cell‐specific was determined to be 1.5 pmol O2/cell. The concentrations of products formed were correlated with oxygen availability, with tetrathionate production in excess of sulfate production at all pressure conditions tested. This study provides evidence for transient sulfur storage during times when substrate concentration exceeds cell‐specific and subsequent consumption when oxygen dropped below that threshold. These results may be common among sulfur oxidizers in a variety of environments (e.g., deep marine sediments to photosynthetic microbial mats). -
Purpose Recent observations of several preferred orientations of diffusion in deep white matter may indicate either (a) that axons in different directions are independently bundled in thick sheets and function noninteractively, or more interestingly, (b) that the axons are closely interwoven and would exhibit branching and sharp turns. This study aims to investigate whether the dependence of dMRI Q‐ball signal on the interpulse time
can decode the smaller‐than‐voxel‐size brain structure, in particular, to distinguish scenarios (a) and (b). Methods High‐resolution Q‐ball images of a healthy brain taken with
s/mm2for 3 different values of were analyzed. The exchange of water molecules between crossing fibers was characterized by the fourth Fourier coefficient of the signal profile in the plane of crossing. To interpret the empirical results, a model consisting of differently oriented parallel sheets of cylinders was developed. Diffusion of water molecules inside and outside cylinders was simulated by the Monte Carlo method. Results Simulations predict that
, agreeing with the empirical results, must increase with for large b ‐values, but may peak at a typicalthat depends on the thickness of the cylinder sheets for intermediate b ‐values. Thus, the thickness of axon layers in voxels with 2 predominant orientations can be detected from empiricaltaken at smaller b ‐values.Conclusion Based on the simulation results, recommendations are made on how to design a dMRI experiment with optimal
b ‐value and range ofin order to measure the thickness of axon sheets in the white matter, hence to distinguish (a) and (b).