Sample records for microconcrete
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Preliminary tests of silicon carbide based concretes for hybrid rocket nozzles in a solar furnace
NASA Astrophysics Data System (ADS)
D'Elia, Raffaele; Bernhart, Gérard; Cutard, Thierry; Peraudeau, Gilles; Balat-Pichelin, Marianne
2014-06-01
This research is part of the PERSEUS project, a space program concerning hybrid propulsion and supported by CNES. The main goal of this study is to characterise silicon carbide based micro-concrete with a maximum aggregates size of 800 μm, in a hybrid propulsion environment. The nozzle throat has to resist to a highly oxidising polyethylene (PE)/N2O hybrid environment, under temperatures ranging up to 2980 K. The study is divided into two main parts: the first one deals with the thermo-mechanical characterisation of the material up to 1500 K and the second one with an investigation on the oxidation behaviour in a standard atmosphere, under a solar flux up to 13.5 MW/m2. Young's modulus was determined by resonant frequency method: results show an increase with the stabilisation temperature. Four point bending tests have shown a rupture tensile strength increasing with stabilisation temperature, up to 1473 K. Sintering and densification processes are primary causes of this phenomenon. Visco-plastic behaviour appears at 1373 K, due to the formation of liquid phases in cement ternary system. High-temperature oxidation in ambient air was carried out at PROMES-CNRS laboratory, on a 2 kW solar furnace, with a concentration factor of 15,000. A maximum 13.5 MW/m2 incident solar flux and a 7-90 s exposure times have been chosen. Optical microscopy, SEM, EDS analyses were used to determine the microstructure evolution and the mass loss kinetics. During these tests, silicon carbide undergoes active oxidation with production of SiO and CO smokes and ablation. A linear relation between mass loss and time is found. Oxidation tests performed at 13.5 MW/m2 solar flux have shown a mass loss of 10 mg/cm2 after 15 s. After 90 s, the mass loss reaches 60 mg/cm2. Surface temperature measurement is a main point in this study, because of necessity of a thermo-mechanical-ablative model for the material. Smokes appear at around 5.9 MW/m2, leading to the impossibility of useful temperature measurements by optical pyrometry. Micro-concrete is really interesting for the nozzle realisation, thanks to its workability, and its thermo-mechanical properties. After 30 s, mass loss in micro-concrete is one half of pure α-SiC. This result is really interesting to study SiC-based concretes in oxidising environments, instead of sintered α-SiC.
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NASA Astrophysics Data System (ADS)
Potter, Sally L.; Chan, Marjorie A.; Petersen, Erich U.; Dyar, M. Darby; Sklute, Elizabeth
2011-01-01
The eolian Jurassic Navajo Sandstone spheroidal hydrous ferric oxide (HFO) concretions are divided into two size classes: macro-concretions of > 5 mm diameter and micro-concretions of < 5 mm diameter. Three internal structural end-members of macro-concretions are described as rind, layered, and solid. Two end-members of micro-concretions are rind and solid. Chemical and mineralogical gradients (μm- to mm-scale) are identified with QEMSCAN (Quantitative Elemental Mineralogy using a SCANning electron microscope) and visible to near infrared (VNIR) reflectance spectroscopy. Three HFO phases are identified using VNIR reflectance spectroscopy. An amorphous HFO phase is typically located in the rinds. Goethite is present along interior edges of rinds and throughout the interiors of layered and solid concretions. Hematite is present in the centers of rind concretions. A synthesis of petrographic, mineralogical and chemical analyses suggests that concretions grow pervasively (as opposed to radially expanding). Our model proposes that concretions precipitate initially as an amorphous HFO that sets the radius and retains some original porosity. Subsequent precipitation fills remaining pore space with younger mineral phases. Inward digitate cement crystal growth corroborates concretion growth from a set radius toward the centers. Internal structure is modified during late stage precipitation that diffuses reactants through semi-permeable rinds and overprints the interiors with younger cements. Physical characterization of textures and minerals provides diagnostic criteria for understanding how similar concretions ("blueberries") form in Meridiani Planum, Mars. The analogous Navajo Sandstone concretions show similar characteristics of in situ self-organized spacing, spheroidal geometries, internal structures, conjoined forms, and precursor HFO phases that dehydrate to goethite or hematite. These characteristics indicate a common origin via groundwater diagenesis.
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The formation of cobalt-bearing ferromanganese crusts under fluid destruction of silicate matter
NASA Astrophysics Data System (ADS)
Maksimov, S. O.; Safronov, P. P.
2016-02-01
The processes of fluid destruction of various silicate rocks under diffusion of flows of compressed gases (mainly carbonaceous) were studied. The gas condensate nature was ascertained for the forming alumoslilicate and ore (cobalt-iron-manganese hydroxide) substances produced under this fluid destruction in the forms of microcrusts and microconcretions. The ore condensates contained in high concentrations the typomorphic elements of oceanic ferromanganese formations (Mn, Co, Ni, Cu, Pb, Ce, and Pt). The elemental composition of the ore oxide substance formed under the destruction of various silicate matrices exhibits a definite degree of endemism with prevalence of the Co-Mn association. The pronounced concentration of barium is related to the substantially carbonaceous composition of the fluid systems. A cerium paradox is revealed: Ce3+ is oxidized into Ce4+ and absorbed by ferromanganese hydrogel and the minimum of cerium appears in rare-earth phosphates.
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Experimental analysis of SiC-based refractory concrete in hybrid rocket nozzles
NASA Astrophysics Data System (ADS)
D'Elia, Raffaele; Bernhart, Gérard; Hijlkema, Jouke; Cutard, Thierry
2016-09-01
Hybrid propulsion represents a good alternative to the more widely used liquid and solid systems. This technology combines some important specifications of the latters, as the possibility of re-ignition, thrust modulation, a higher specific impulse than solid systems, a greater simplicity and a lower cost than liquid systems. Nevertheless the highly oxidizing environment represents a major problem as regards the thermo-oxidation and ablative behavior of nozzle materials. The main goal of this research is to characterize a silicon carbide based micro-concrete with a maximum aggregates size of 800 μm, in a hybrid propulsion environment. The nozzle throat has to resist to a highly oxidizing polyethylene/nitrous oxide hybrid environment, under temperatures up to 2900 K. Three tests were performed on concrete-based nozzles in HERA Hybrid Rocket Motor (HRM) test bench at ONERA. Pressure chamber evolution and observations before and after tests are used to investigate the ablated surface at nozzle throat. Ablation behavior and crack generation are discussed and some improvements are proposed.
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Fungal Ferromanganese Mineralisation in Cretaceous Dinosaur Bones from the Gobi Desert, Mongolia.
Owocki, Krzysztof; Kremer, Barbara; Wrzosek, Beata; Królikowska, Agata; Kaźmierczak, Józef
2016-01-01
Well-preserved mycelia of fungal- or saprolegnia-like biota mineralised by ferromanganese oxides were found for the first time in long bones of Late Cretaceous dinosaurs from the Gobi Desert (Nemegt Valley, Mongolia). The mycelia formed a biofilm on the wall of the bone marrow cavity and penetrated the osteon channels of the nearby bone tissue. Optical microscopy, Raman, SEM/EDS, SEM/BSE, electron microprobe and cathodoluminescence analyses revealed that the mineralisation of the mycelia proceeded in two stages. The first stage was early post-mortem mineralisation of the hyphae by Fe/Mn-oxide coatings and microconcretions. Probably this proceeded in a mildly acidic to circumneutral environment, predominantly due to heterotrophic bacteria degrading the mycelial necromass and liberating Fe and Mn sorbed by the mycelia during its lifetime. The second stage of mineralisation, which proceeded much later following the final burial of the bones in an alkaline environment, resulted from the massive precipitation of calcite and occasionally barite on the iron/manganese-oxide-coated mycelia. The mineral phases produced by fungal biofilms colonising the interiors of decaying dinosaur bones not only enhance the preservation (fossilisation) of fungal remains but can also be used as indicators of the geochemistry of the dinosaur burial sites.
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Fungal Ferromanganese Mineralisation in Cretaceous Dinosaur Bones from the Gobi Desert, Mongolia
Wrzosek, Beata; Królikowska, Agata
2016-01-01
Well-preserved mycelia of fungal- or saprolegnia-like biota mineralised by ferromanganese oxides were found for the first time in long bones of Late Cretaceous dinosaurs from the Gobi Desert (Nemegt Valley, Mongolia). The mycelia formed a biofilm on the wall of the bone marrow cavity and penetrated the osteon channels of the nearby bone tissue. Optical microscopy, Raman, SEM/EDS, SEM/BSE, electron microprobe and cathodoluminescence analyses revealed that the mineralisation of the mycelia proceeded in two stages. The first stage was early post-mortem mineralisation of the hyphae by Fe/Mn-oxide coatings and microconcretions. Probably this proceeded in a mildly acidic to circumneutral environment, predominantly due to heterotrophic bacteria degrading the mycelial necromass and liberating Fe and Mn sorbed by the mycelia during its lifetime. The second stage of mineralisation, which proceeded much later following the final burial of the bones in an alkaline environment, resulted from the massive precipitation of calcite and occasionally barite on the iron/manganese-oxide-coated mycelia. The mineral phases produced by fungal biofilms colonising the interiors of decaying dinosaur bones not only enhance the preservation (fossilisation) of fungal remains but can also be used as indicators of the geochemistry of the dinosaur burial sites. PMID:26863014
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Small-scale solutions. Millennium trailblazers 1: Ashok Khosia.
Bhatia, R
1999-01-01
Development Alternatives (DA) is a nongovernmental organization founded by Ashok Khosla in 1982 that seeks to improve the quality of life for those denied the basics and promote the sustainable use of natural resources in India through the intelligent application of technology. DA focuses on sustainable livelihoods that create several jobs in a village and has by far helped a quarter of a million people. One of its most successful projects can be found in Tikamgarh District where it has trained local villagers to run off-farm enterprises such as paper production. DA is now one of the biggest producers of hand-made paper, producing about 5 tons of paper every month at its plant in Delhi, and 15 tons from its Jhansi plant. DA has also created the most advanced handloom weaving machine called the Flying Shuttle Loom, and a new roofing tile made of microconcrete known as the TARAcrete tile. Aside from creating low cost building materials which has generated immense employment in the housing sector, DA also caters to the larger population through its welfare programs such as the water for life project which ensures water supply in a number of villages. In addition, DA also launched the Delhi Environment Action Network (DEAN) program that is designed to motivate children and others to improve the quality of their neighborhood.
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NASA Astrophysics Data System (ADS)
Glikson, M.; Rutherford, S.; Simpson, R. W.; Mitchell, C. A.; Yago, A.
The study identifies the various components contributing to atmospheric particulate matter in Brisbane, Queensland, Australia, during the period from the end of April and the months of July-August in 1992, covering the autumn period which is typically the period of high asthma incidence in Brisbane. Most particulate matter is < 2 μm and submicronic. Electron microscopy revealed that the submicron material is composed mainly of combusted ("soot") and incompletely burned hydrocarbons arising from motor vehicle exhaust emissions, crustal matter in the form of quartz microconcretions and other silicates, quiescent spores of Mucorales, and soil bacteria. The contribution from pollen and fungal spores has been evaluated and quantified. Fungal spores counts dominate the bioaerosol counts in the 2-10 μm range and are very high in Brisbane from the end of April through May to mid-June. However even at peak periods the total bioaerosol count only contributes of the order of 5-10% of the total particulate mass. The results show that Pm 10 (particulate matter less than 10 μm in diameter) and nephelometer readings do not indicate peak periods of allergenic bioaerosol readings (in fact there is a negative correlation) due to the low contribution of the bioaerosol count to the total and the different influences of wind speed. However the electron microscopy results show that this does not mean there are no synergies between aerosols from anthropogenic sources and bioaerosols. The cytoplasmic content of spores and pollen was often found to be adhered to motor vehicle emission material and crustal matter. The latter may therefore act as carriers for dispersed cytoplasmic allergenic material released from pollen and fungal spores.
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NASA Astrophysics Data System (ADS)
Barge, L. M.; Petruska, J.
2009-04-01
We present the results of diffusion experiments in combined glass bead and gel media that produced silver chromate precipitates under a variety of conditions. Precipitates took various forms including finger fluid fronts, rhythmic (Liesegang) bands, and mm-size spheroidal "concretions". The silver chromate spherules produced in our experiments are morphologically similar to spheroidal HFO "mini-concretions" that are commonly found in the Jurassic Navajo Sandstone, Utah (USA), which are considered a terrestrial analog for the hematite concretions ("blueberries") discovered at Meridiani Planum, Mars (Chan et al. 2004, Nature). Like the Utah and Martian concretions, the spherules formed in our experiments exhibit a self-organized distribution, lack of an obvious macro nucleus, and ability to form "twin" morphologies. In all cases, the spheroidal precipitates nucleated under diffusion-controlled conditions, and some growth occurred although advection was not present. Other forms of precipitate such as periodic banding and fluid fronts were produced in our experiments as well, which also resemble types of iron mineral precipitation that are observed in the Navajo Sandstone, although thus far only spheroidal self-organized precipitates are seen on Mars. The presence of self-organized precipitates in the Utah and Martian environments most likely resulted from nucleation in a diffusion-controlled environment, and the specific morphology of iron oxide precipitates in porous and permeable systems is likely determined by chemical and physical parameters of the fluid environment in which they precipitated. Although the chemical conditions in our precipitation experiments are obviously very different from what would be expected in the Navajo Sandstone or on Mars, we show in this work how the morphology of self-organized mineral precipitates in a porous/permeable medium is affected by specific physical and chemical parameters.