scholarly journals Intense aqueous alteration on C-type asteroids: Perspectives from giant fine-grained micrometeorites

2019 ◽  
Vol 245 ◽  
pp. 352-373 ◽  
Author(s):  
M.D. Suttle ◽  
L. Folco ◽  
M.J. Genge ◽  
S.S. Russell ◽  
J. Najorka ◽  
...  
Keyword(s):  
Aqueous Alteration ◽  
Fine Grained

Phyllosilicates and other layer-structured materials in stony meteorites

Clay Minerals ◽  
1985 ◽  
Vol 20 (4) ◽  
pp. 415-454 ◽  
Author(s):  
D. J. Barber
Keyword(s):  
Major Part ◽  
Solar Nebula ◽  
Layered Compounds ◽  
Carbonaceous Chondrites ◽  
Aqueous Alteration ◽  
Structured Materials ◽  
Fine Grained ◽  
Current Thinking ◽  
The Matrix ◽  
Detailed Chemical

AbstractCurrent thinking regarding the possible origins and probable evolutionary histories of meteorites is summarized. Selected data concerning the composition, petrology and other characteristics of the CI and CM groups of stony meteorites in which layered minerals principally occur are then presented. Layered compounds, mainly phyllosilicates, are shown to form a major part of the fine-grained matrix of the CI and CM meteorites, which are classified as carbonaceous chondrites. The results of recent investigations of matrix mineralogy are reviewed, with particular emphasis on the findings of electron microscopy. Several forms of Fe-Mg-serpentine have been identified as the principal phyllosilicates. ‘Poorly-characterized phases’ in CM meteorites have proved to be tochilinite and intergrowths of tochilinite with serpentines. The results generally indicate that the phyllosilicates and most other matrix minerals formed by aqueous alteration in the regoliths of the CI and CM parent bodies; but there is isotopic evidence for the incorporation of components and possibly mineral grains which predate the solar nebula. It is concluded that more detailed chemical and mineralogical information about the phyllosilicates and associated minerals will enable useful constraints to be placed on the possible identities of their precursors and the environments in which both they and the matrix minerals formed.

scholarly journals Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites

Science ◽  
2019 ◽  
Vol 365 (6455) ◽  
pp. 817-820 ◽  
Author(s):  
R. Jaumann ◽  
N. Schmitz ◽  
T.-M. Ho ◽  
S. E. Schröder ◽  
K. A. Otto ◽  
...  
Keyword(s):  
Solar Nebula ◽  
Carbonaceous Chondrite ◽  
Aqueous Alteration ◽  
Earth Asteroid ◽  
Fine Grained ◽  
Dark Object ◽  
Sharp Edges ◽  
Fine Grained Material ◽  
Asteroid Surface

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu’s surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

Meteorite Mineralogy

2020 ◽  
Author(s):  
Alan E. Rubin ◽  
Chi Ma
Keyword(s):  
Outer Space ◽  
Matrix Material ◽  
Parent Body ◽  
Primary Phase ◽  
Shock Metamorphism ◽  
Aqueous Alteration ◽  
Fine Grained ◽  
Thermal Metamorphism ◽  
Geochemical Properties ◽  
Gaseous Envelopes

Meteorites are rocks from outer space that reach the Earth; more than 60,000 have been collected. They are derived mainly from asteroids; a few hundred each are from the Moon and Mars; some micrometeorites derive from comets. By mid 2020, about 470 minerals had been identified in meteorites. In addition to having characteristic petrologic and geochemical properties, each meteorite group has a distinctive set of pre-terrestrial minerals that reflect the myriad processes that the meteorites and their components experienced. These processes include condensation in gaseous envelopes around evolved stars, crystallization in chondrule melts, crystallization in metallic cores, parent-body aqueous alteration, and shock metamorphism. Chondrites are the most abundant meteorites; the major components within them include chondrules, refractory inclusions, opaque assemblages, and fine-grained silicate-rich matrix material. The least-metamorphosed chondrites preserve minerals inherited from the solar nebula such as olivine, enstatite, metallic Fe-Ni, and refractory phases. Other minerals in chondrites formed on their parent asteroids during thermal metamorphism (such as chromite, plagioclase and phosphate), aqueous alteration (such as magnetite and phyllosilicates) and shock metamorphism (such as ringwoodite and majorite). Differentiated meteorites contain minerals formed by crystallization from magmas; these phases include olivine, orthopyroxene, Ca-plagioclase, Ca-pyroxene, metallic Fe-Ni and sulfide. Meteorites also contain minerals formed during passage through the Earth’s atmosphere and via terrestrial weathering after reaching the surface. Whereas some minerals form only by a single process (e.g., by high-pressure shock metamorphism or terrestrial weathering of a primary phase), other meteoritic minerals can form by several different processes, including condensation, crystallization from melts, thermal metamorphism, and aqueous alteration.

Application of an image management system in microscopy

1992 ◽  
Vol 50 (2) ◽  
pp. 1052-1053
Author(s):  
Richard S. Chemock
Keyword(s):  
Data Storage ◽  
Cost Savings ◽  
Image Data ◽  
Analytical Techniques ◽  
Operational Mode ◽  
Fine Grained ◽  
Image Recording ◽  
Primary Output ◽  
Capacity Data ◽  
Image Management System

One of the most common tasks in a typical analysis lab is the recording of images. Many analytical techniques (TEM, SEM, and metallography for example) produce images as their primary output. Until recently, the most common method of recording images was by using film. Current PS/2R systems offer very large capacity data storage devices and high resolution displays, making it practical to work with analytical images on PS/2s, thereby sidestepping the traditional film and darkroom steps. This change in operational mode offers many benefits: cost savings, throughput, archiving and searching capabilities as well as direct incorporation of the image data into reports.The conventional way to record images involves film, either sheet film (with its associated wet chemistry) for TEM or PolaroidR film for SEM and light microscopy. Although film is inconvenient, it does have the highest quality of all available image recording techniques. The fine grained film used for TEM has a resolution that would exceed a 4096x4096x16 bit digital image.

Use of fractals to describe microstructures of porous thick-film platinum electrodes

1992 ◽  
Vol 50 (1) ◽  
pp. 314-315
Author(s):  
Steven D. Toteda
Keyword(s):  
Fractal Dimension ◽  
Power Plants ◽  
Electrical Response ◽  
Cubic Phase ◽  
Platinum Electrodes ◽  
Fine Grained ◽  
Impedance Response ◽  
Platinum Particles ◽  
Energy Surfaces ◽  
Highly Porous

Zirconia oxygen sensors, in such applications as power plants and automobiles, generally utilize platinum electrodes for the catalytic reaction of dissociating O2 at the surface. The microstructure of the platinum electrode defines the resulting electrical response. The electrode must be porous enough to allow the oxygen to reach the zirconia surface while still remaining electrically continuous. At low sintering temperatures, the platinum is highly porous and fine grained. The platinum particles sinter together as the firing temperatures are increased. As the sintering temperatures are raised even further, the surface of the platinum begins to facet with lower energy surfaces. These microstructural changes can be seen in Figures 1 and 2, but the goal of the work is to characterize the microstructure by its fractal dimension and then relate the fractal dimension to the electrical response. The sensors were fabricated from zirconia powder stabilized in the cubic phase with 8 mol% percent yttria. Each substrate was sintered for 14 hours at 1200°C. The resulting zirconia pellets, 13mm in diameter and 2mm in thickness, were roughly 97 to 98 percent of theoretical density. The Engelhard #6082 platinum paste was applied to the zirconia disks after they were mechanically polished ( diamond). The electrodes were then sintered at temperatures ranging from 600°C to 1000°C. Each sensor was tested to determine the impedance response from 1Hz to 5,000Hz. These frequencies correspond to the electrode at the test temperature of 600°C.

Amorphous silica coating on α-alumina particles

1995 ◽  
Vol 53 ◽  
pp. 210-211
Author(s):  
J. W. Mellowes ◽  
C. M. Chun ◽  
I. A. Aksay
Keyword(s):  
Amorphous Silica ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Silica Coating ◽  
Full Density ◽  
Optimal Conditions ◽  
Fine Grained ◽  
Alumina Particles ◽  
Complete Mullitization ◽  
Powder Compacts

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

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