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The various stages describing the mechanism for the phase transformation and the migration of the various oxides from olivine particles toward the surface at high temperature.
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A framework is presented to define the formation and migration mechanisms of oxides in olivine during
their phase transformations at high temperature. The behaviour of olivine particles has been investigated
at 1400°C at two different residence times: 4 h and 115 h. The structural and vibrational properties of
the resulting materials were analysed...
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Recibido 22 de Oct. 2007; Aceptado 3 de Mar. 2008; Publicado en línea 15 de Abr. 2008 Resumen Se investigó la influencia del tipo de acero y el tiempo de inmersión sobre la formación de magnetita en procesos de corro-sión. Con este propósito, se sometieron aceros autoprotectores (WS) y al carbono (CS) a pruebas de inmersión total en una solución 0....
Citations
... Consequently, the XRD analysis did not record silica, but it showed an increase in enstatite. This is in agreement with the mechanism of phase transformations and migration in olivine at 1400 • C developed by Michel et al. [47]. Finally, hematite could be reduced to magnetite or produce magnesioferrite because of olivine oxidation. ...
The biodiesel industry currently generates large amounts of crude glycerol that are not marketed, thus accumulating, and causing environmental problems. This study evaluates the catalytic potential of Colombian olivine, using glycerol steam reforming to assess valorization alternatives for this by-product. The analyzed olivine was thermally treated at 1200 °C and reduced at 900 °C, then producing nanometer-sized Fe compounds. The catalyst was characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), temperature-programmed reduction (TPR), and transmission electron microscopy (TEM). Calcined olivine increased glycerol conversion at 600 °C from 43% (without catalyst) to 96% with the formation of liquid-phase products such as aldehydes and carboxylic acids. In addition, syngas with H2/CO ratios of 1.1 and 1.5 was generated at reaction temperatures of 700 °C and 800 °C, respectively, with low CH4 content. Finally, it was established that olivine from Medellín, under the conditions used for glycerol steam reforming, is a viable and interesting alternative to valorize glycerol into gas- or liquid-phase products.
... Thermal treatment (calcination) at high temperatures (greater than 900 • C) is known to produce phase transformation and migration of iron from the inner part of olivine grains towards the surface [18][19][20][21], impacting positively the attrition resistance, as well as improving the tar abatement activity of olivine grains [17,22]. ...
Gasification experiments were carried out in a pilot scale fluid bed reactor operated under allothermal mode and low fluidisation regime with iron-doped olivine and char as catalyst for in-situ tar abatement.
The catalyst combination resulted in a reduction of 50% in the overall tar yield with respect to the reference values. Furthermore, the integration of an oxidative Hot Gas Filtration unit downstream the gasification reactor led to a further reduction in overall tar yield and relatively clean gas was obtained (approx. 1 g/Nm³, benzene-free). The tar dew point of the resulting producer gas was estimated to 80 °C, only 40 °C above the threshold value recommended for its valorisation in standard internal combustion engines. Moreover, catalyst elutriation and char hold-up took place to a large extent inside the reactor. The analysis of catalyst samples at different Time-On-Stream (TOS) revealed: (i) a considerable loss of iron oxides during the first hour of test because of the interparticle mechanical attrition (mostly surface abrasion) and partial reduction of hematite to magnetite and wustite but, stable composition at higher TOS, (ii) the loss of the iron oxide coverage of Fe/olivine particles and the formation of agglomerates with increasing TOS and, (iii) the amount of carbon deposited in the surface of the Fe/olivine particles increased with TOS, but in any case, these carbon deposits can be completely oxidized above 650 °C.
... Additional peaks corresponding to secondary crystalline phases may also be observed, such as enstatite (MgSiO 3 ) and quartz (SiO 2 ). According to Michel et al. [67,68] and Swierczy nski et al. [69], numerous phases of iron oxide may appear subsequent to olivine calcination, as are g-Fe 2 O 3 , α-Fe 2 O 3 , Fe 3 O 4 and MgFe 2 O 4 . The presence of these iron oxides is explained by the migration of the iron Fe 2+ located within the Table 2 Physical properties of the calcined olivine and Fe/olivine catalyst. ...
The performance of Fe/olivine catalysts was tested in the continuous steam gasification of sawdust in a bench scale plant provided with a fountain confined conical spouted bed reactor at 850 °C. Olivine was used as catalyst support and loaded with 5 wt% Fe. The activity and stability of the catalyst was monitored by nitrogen adsorption-desorption, X-ray fluorescence spectroscopy (XRF), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, which were conducted before and after the runs. The fountain confined conical spouted bed performs well in the biomass steam gasification with primary catalysts. In fact, this reactor allows enhancing the gas-solid contact, and therefore the catalytic activity by avoiding the elutriation of fine catalyst particles. The uncatalysed efficiency of the gasification process, assessed based on the gas production and composition, H2 production, tar concentration and composition, and carbon conversion efficiency, was consideraby improved on the Fe/olivine catalyst, with tar reduction being especially remarkable (to 10.4 g Nm⁻³). After 140 min on stream, catalyst deactivation was particularly evident, as tar concentration increased to 19.84 g Nm⁻³ (90% of that without catalyst). However, Fe/olivine catalyst was still active for WGS and CH4 steam reforming reactions, with gas and H2 productions being 1.35 Nm³ kg⁻¹ and 5.44 wt%, respectively. Metal iron oxidation to Fe3O4 caused catalyst deactivation, as the reaction environment shifted from oxidizing to reducing conditions due to operational limitations.
... Additionally, thermal reactions of minerals may cause rock structural damage upon heating. Some rockforming minerals, such as biotite (Pavese et al. 2007), phlogopite (Tutti et al. 2000), chlorite (Nelson and Guggenheim 1993) and olivine (Michel et al. 2014), can react with oxygen and alter the micro-structure of rocks at elevated temperatures. Clay and carbonate minerals decompose after different thermal treatments and induce the development and propagation of microcracks (Barshad 1952, Zhang et al. 2015. ...
... Clay and carbonate minerals decompose after different thermal treatments and induce the development and propagation of microcracks (Barshad 1952, Zhang et al. 2015. Some minerals, such as quartz (Mainprice et al. 1986, Somerton 1992, pyroxene (Yamanaka et al. 1985) and olivine (Michel et al. 2014), undergo a phase transition or dominant c-slip and experience structural damage upon heating. Losses of bound water and constitution water can also destroy mineral crystal structures and increase micro-defects inside rock bodies (Zhang et al. 2016). ...
A deep understanding of the physico-mechanical characteristics of rocks undergoing thermal treatments has gained a great interest in deep rock projects. In this research, the size and mass of cylindrical granite samples were measured before, under and after a temperature up to 1000°C, and their bulk densities at different temperature levels were calculated. Under and after high temperature, the granite density decreased with temperature due to the increase of the granite volume and decrease of the granite mass, with the rock volume increase being the prominent factor driving this behaviour. Additionally, the rate at which density increased under high temperature was always larger than the rate after high temperature. The rock mass loss after thermal treatment was attributed to the evaporation of different types of water, thermal reactions of rock-forming minerals and generation of rock fragments, while the rock volume expansion was mainly caused by thermal expansion and reactions of the rock-forming minerals, which was in accordance with the optical microscope observation results. 400°C is considered as the threshold temperature for the relationship between the decrease rate of rock density and temperature. Two fitting equations were proposed as the two boundaries of the rock density decrease rates.
... This initial calcination is used to improve the mechanical properties of olivine for fluidized bed. --Prior works [47,48] have documented the characterization of olivine used for different physical and chemical applications and the mechanism of olivine evolution at high temperature was described. The in situ XRD and Raman spectroscopy have allowed to identify and to determine the phase transformations that occur when olivine is subjected to high temperatures. ...
This paper presents an experimental and thermodynamic contribution about the role of inorganics in ash-bed material interactions during thermal conversion of miscanthus in fluidized bed. The objectives are (1) to describe the transformation of inorganics at high temperature, (2) to reveal their role in the agglomeration and (3) to provide recommendations for miscanthus gasification in fluidized bed. The main ash forming elements in miscanthus are K, Si, Ca, Mg, P, S and Cl. The ashes are composed of silica, carbonates and salts. The carbonates and salts decompose and volatilise at 700 °C. At elevated temperature, the dominant solid phases are Ca and Mg silicates. The liquid phase is composed of SiO2, K2O, CaO, MgO regardless of the atmosphere. The accuracy of thermodynamic prediction tool is evaluated with the experimental results. The ash-bed interactions show that the wetting of bed material by molten ashes is one of the key parameters of the agglomeration. The adhesion of particles increases in the order of silica sand, olivine, calcined olivine. There is no significant difference in the agglomeration mechanism in oxidizing or reductive atmosphere. However, in reductive atmosphere, two immiscible liquid phases can occur. The parametric investigation shows that the operating temperature has a significant effect on the agglomeration ratio and the addition of kaolin or dolomite is the most effective tool to reduce agglomeration risks.
... As shown in the diagram, the hematite phase is still detected at room temperature after cooling. The formation of iron oxide about 700°C was also confirmed by Michel et al. [186]. ...
Compare to fossil fuel energy resources, solar energy is known for its intermittent nature. This observation highlights the need for the use of a thermal energy storage system. The thermocline storage system is considered as a cost-effective storage system. This thesis aims to study the potential of basalt and silex rocks as candidate storage materials for concentrated solar power plants. Experimental studies of the thermo-physical and thermo-mechanical properties of these rocks at temperatures up to 1000°C show that these rocks offer good thermal properties compared with conventional storage materials. The analysis of the thermocline storage system of air rock-packed bed is carried out using a numerical approach. This research also aims to assess the environmental impact of this type of storage system by conducting a comparative analysis of its life cycle. Finally, a complementary study carried out with the aim of producing a relevance index map made it possible to identify the most suitable areas for the construction of solar power plants in Egypt. The originality of this alternative approach for thermal energy storage is that it combines the performance and availability of storage materials while reducing their environmental and financial impacts.
... The second bed material was calcined olivine. When used as a catalyst, olivine is calcined at 1400 1C in air for 4 h, which improves its mechanical properties for use in a fluidized bed [20,21]. ...
... Our previous papers have shown that natural olivine is not an inert silicate; it is transformed by thermal decomposition (dehydration and oxidation of the fayalite) at a high temperature [20,21]. The structural transformations consist of the dehydration of serpentine below 600 1C, the disappearance of the quartz phase at 1030 1C, and the formation of iron oxide phases. ...
... It was shown that the material forms magnetite spinel and enstatite at high temperatures which spread from the inner part of the particles toward the surface [20,21]. ...
Olivine is one of the refractory materials well-suited for fluidized-bed reactor technology. However, this material agglomerates at high temperatures due to the presence of sticky molten ash. The aim of this work is to investigate the mechanism of olivine agglomeration in fluidized-bed reactors and to determine the risk factors for agglomeration. A laboratory fluidized-bed reactor was designed to study the agglomeration effect between the ash and the refractory bed material. A systematic experiment was performed to determine the agglomeration ratio as a function of different parameters (operating time, bed materials, ash content, temperature, gas flow and additives). The mechanism of adhesion between the molten ash and the bed material is described, and the optimization of parameters to prevent this agglomeration is determined. © 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
... Olivine is often calcined to increase its mechanical stability and catalytic effect in tar decomposition. During the calcination at high temperature (N 1000°C), the fayalite decomposes and forms Fe 2 O 3 and Fe 3 O 4 on the surface of the olivine grains [14]. The accumulation of iron oxides at the surface can influence the interaction with the biomass ash. ...
KLS-1 Lunar regolith simulant was microwave sintered to explore its potential applicability in future lunar construction. The effects of sintering temperature on linear shrinkage, density, porosity, and microstructural, mechanical, and thermal properties were investigated. As the sintering temperature increased, linear shrinkage and density increased and porosity decreased. Structural evolution in the sintered samples was characterized by scanning electron microscopy and X-ray diffraction. Unconfined compressive strength testing showed that mechanical strength increased significantly with increasing sintering temperature, with 1120 °C giving the highest strength of 37.0 ± 4.8 MPa. The sintered samples exhibited a coefficient of thermal expansion of approximately 5 × 10⁻⁶ °C⁻¹, which was well-maintained even after cyclic temperature stress between −100 and 200 °C. Therefore, this microwave processing appears promising for the fabrication of building material with sufficient mechanical strength and thermal durability for lunar construction.
Raman spectroscopy is experimentally widely available and relatively simple to perform at room temperature. Some difficulties nevertheless remain, as for instance separating some various contributions from the Raman spectrum, such as thermal emission for high temperature measurements or luminescence. Here, an optimized time-resolved Raman spectroscopy system based on a gated detection and a nanosecond pulsed laser excitation (30 ns width, 532 nm wavelength) is described. The system allows contactless Raman measurements, at high temperatures, of some materials such as zirconia and yttria. An example of Raman spectra collected on yttria at very high temperature up to 2100 °C is provided. This optimized system may also be used to discriminate between Raman scattering and luminescence as demonstrated in zirconia material.
