Forsterite Formation Research Articles

Kinetics of antigorite dehydroxylation for CO2 sequestration

Heat-treatment of serpentine minerals generates structural amorphicity and increases reactivity during subsequent mineral carbonation, a strategy for large-scale sequestration of CO2. This study employs thermal analyses (TGA-DSC) in conjunction with in-situ synchrotron powder X-ray diffraction (PXRD) to record concurrent mass loss, heat flow, and mineralogical changes during thermal treatment of antigorite. Isoconversional kinetic modelling demonstrates that thermal decomposition of antigorite is a complex multi-step reaction, with activation energies (Eα) varying between 290 and 515 kJ mol−1. We identify three intermediate phases forming during antigorite dehydroxylation, a semi-crystalline chlorite-like phase (γ-metaserpentine) showing an additional reaction pathway for the decomposition of Al2O3-rich antigorite into pyrope, and two distinct amorphous components (α and β-metaserpentine) which convert into forsterite and enstatite at higher temperature, respectively. The combination of isoconversional kinetics with in-situ synchrotron PXRD illustrates, for the first time, that local crystal structure changes, related to intermediate phase and forsterite formation, are responsible for the steep increase in activation energy above 650 °C and only 49% dehydroxylation can be achieved prior to this increase. This suggests that the high thermal stability of Al2O3-rich antigorite would severely limit Mg extraction during application of mineral carbonation under flue gas conditions.

Formation mechanism and microstructure of a forsterite film in grain-oriented electrical steel

Grain-oriented (GO) electrical steel is widely used as electrical and magnetic engineering materials and its core loss is required to be as low as possible. An effective way to reduce the core loss of iron is to apply tensile stress to GO electrical steel. A method to form an Mg2SiO4 (forsterite) film with a lower thermal expansion coefficient on the surface of GO electrical steel has been commonly used for the application of tension to the steel. In this article, the formation mechanism of a forsterite film changed from a decarburized oxide layer on GO electrical steel surface through the process of the secondary recrystallization annealing is studied. Additionally, it is reported that intermediate compositions have been generated in the reaction process at each temperature range during annealing. For the investigation of the forsterite formation mechanism, such several characterization methods as X-Ray Diffraction, Scanning Electron Microscopy, and transmission electron microscopy with energy dispersive X-ray spectroscopy were employed.

In situ reinvestigation of reaction phase A plus high-pressure clinoenstatite to forsterite plus water in the system MgO-SiO<sub>2</sub>-H<sub>2</sub>O (MSH)

Abstract. The dehydration reaction of phase A + high P clinoenstatite to forsterite + water was experimentally investigated at water-saturated conditions in the pressure range between 7.0 and 10.0 GPa by in situ reversal runs in a multi-anvil press at the synchrotron source of PETRA III in Hamburg. By using closed watertight X-ray transparent Ti capsules, its position is determined by reversal brackets at 8.3 GPa (700–760 ∘C), 8.6 GPa (700–740 ∘C), and 9.8 GPa (750–800 ∘C); thus, the equilibrium of the reaction corresponds ideally to the data reported by Wunder (1998). Optical investigations of the quenched product phases show strong grain coarsening of phase A and clinoenstatite, whereas nucleated forsterite from the breakdown of the aforementioned phases is very fine grained. This corresponds to recent experimental observations that the grain size of phases formed in hydration reactions are significantly larger than those from dehydration reactions. In addition, we performed three time-dependent in situ experiments at 9–10 GPa and 800–870 ∘C and monitored the reaction progress every 10 min to determine the kinetics of the forsterite formation from phase A + high P clinoenstatite. The growth of forsterite at these P–T conditions, already visible after 10 min, confirms the results of the bracketing experiments. However, the reaction is extremely slow, and even after more than 3 h, significant amounts of phase A and high P clinoenstatite are still present. This is in contradiction to other dehydration reactions of former experimental studies, e.g. the fast dehydration of serpentine, which completely dehydrates within 3 h, even at much lower temperatures, closely overstepping serpentine stability. Despite its reaction sluggishness, which would contradict the concept of earthquake initiation, the observed formation of nano-sized forsterite as a dehydration product may still indicate the potential of this reaction to cause mechanical instabilities and, thus, seismicity within cold subduction zones at depths of the Earth's mantle. Additionally, at depths exceeding serpentine dehydration, the phase A + high P/low P clinoenstatite breakdown to forsterite + water might induce geochemical and geophysical processes, including the formation of low-velocity zones within the overlying mantle wedge from the large amounts of fluid liberated by this water line reaction. After the breakdown of antigorite, the assemblage phase A + clinoenstatite might act as a bridge to transport water to larger depths during cold subduction, followed by the formation of other hydrous high P phases.

Effect of sintering temperature on the structural and physical properties of forsterite using amorphous rice husk silica as refractory precursors

This study aims to investigate the effect of sintering temperatures on both the phase formation and physical characteristics of forsterite prepared from rice husk silica and magnesium nitrate hydrate. The samples were subjected to sintering temperatures of 1000–1300 °C, and the development of structures was characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Some physical properties include density, porosity, hardness, bending strength, and thermal expansion coefficient of the samples were measured. It is concluded that forsterite formation started at 1000 °C, and its abundance increased slowly from an increased temperature up to 1300 °C, resulting in increased phase contents from 87.7 to 90.0 wt%. Thermal expansion coefficient of the samples with increasing temperature of sintering from 1100 to 1300 °C reaches the relatively constant value of 9.1 × 10−6/°C, with the main crystalline phase being forsterite.

ACEME: Direct Aqueous Mineral Carbonation of Dunite Rock

This research explores the use of serpentinized dunite (which is comprised of 61% lizardite) as a feedstock for aqueous mineral carbonation. In initial experiments, dunite was heat‐activated (630°C, 4 h), adopting a procedure which is similar to that used for serpentinite to enhance their carbonation reactivity. Heat‐activation converts crystalline lizardite mineral into an amorphous, reactive phase, and the carbonation of this heat‐activated material resulted in a magnesite yield of 55% compared to 27% obtained with raw dunite under the same reaction conditions. The formation of silanol nests occurred during carbonation of heat‐activated dunite as deduced through FTIR and TGA‐MS analyses. Samples of dunite were also heat‐transformed at high temperatures (800°C, 3 h) to convert lizardite into forsterite, and these samples were also studied as potential feedstocks for mineral carbonation. Heat‐activated dunite was found to engender much higher magnesite yields compared to heat‐transformed dunite (forsterite rich) and raw dunite. This study suggests that during heat‐activation of dunite, as it is for lizardite, conditions should be maintained to avoid forsterite formation. © 2018 American Institute of Chemical Engineers Environ Prog, 38:e13075, 2019

A novel and green preparation of porous forsterite ceramics with excellent thermal isolation properties

This work provides a novel and green approach to preparing porous forsterite ceramics by a transient liquid phase diffusion process based on fused magnesia and quartz powders without detrimental additives. The size of quartz particles markedly affected the sintering behaviors, phase composition, microstructure and properties of the porous forsterite ceramics. Fine quartz particles (D50, 3.87 µm) accelerated the rate of the forsterite formation at elevated temperatures and promoted solid-state sintering behavior of the porous ceramics. Conversely, coarse quartz particles (D50, 25.38 µm) reduced the rate of the solid state reaction and a large amount of unreacted SiO2 and enstatite (MgSiO3) phases transformed into a transient liquid-phase during the firing process. This effect resulted in a high porosity (approximately 58.89%) and formation of many large pores (mean pore size of 42.36 µm). These features contributed to the excellent thermal isolation properties of the prepared porous forsterite ceramics. The strength of the obtained porous ceramics (about 23.6 MPa) is relatively high compared with those of conventional ceramics.

Mg-O-Si Chemical Bond Formation in Light Burned Magnesia and Fumed Silica Mixture During Mechanical Activation

Mg-O-Si chemical bond formation in a light burned magnesia (MgO) and fumed silica (SiO2) mixture during mechanical activation was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), magic angle spinning nuclear magnetic resonance (MAS-NMR), and X-ray photoelectron spectroscopy (XPS). Crystallinity and intrinsic structure changes of the starting mixture during high-energy milling were examined by XRD. The formation of new Mg-O-Si chemical bonds of the ground mixture was illustrated by the incorporation of Mg2+ in Si-O-Si linkages, the appearance of new resonance in the 29Si NMR spectrum and the decrease of the Si 2p binding energy. The formation of Mg-O-Si chemical bonds created during grinding partly contributed to the lowered temperature of complete forsterite formation from 1400 to 1100°C.

Low temperature synthesis of forsterite from hydromagnesite and fumed silica mixture

Forsterite was prepared via solid-state reaction by using hydromagnesite (basic magnesia carbonate) and fumed silica, aiming at completing the reaction 2MgO+SiO2→Mg2SiO4 at low calcination temperature. The phase development and morphology evolution of the hydromagnesite and hydromagnesite–fumed silica mixture during heat treatment were characterized by means of scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) nitrogen-gas adsorption method, and X-ray powder diffraction (XRD). A diffusion distance of less than 300nm for Mg2+ and Si4+ for forsterite formation was obtained because the formed high reactivity MgO with the nanosheet structure of its parental hydromagnesite and the fumed silica with particle size of less than 100nm were homogeneously mixed. Monolithic forsterite was synthesized after calcination of the hydromagnesite–fumed silica mixture at 1100°C.

Magnesia-zircon brick: Evolution of microstructure, properties and performance with increasing sintering temperature

Depending on phase components and densification, Magnesia-Zircon brick varies in appearance from white to veined and then brown with increasing sintering temperature. Properties including bulk density, apparent porosity and hot modulus of rupture as well as performance embodied with creep resistance and refractoriness continue to improve with sustaining enhancement of sintering temperature. Exceptionally, cold crushing strength first increases then decreases with rising sintering temperature and a peak exists at 1550oC. Microstructural evolution suffers zircon decomposition companying by silica escape, forsterite formation, matrix solidification and zirconia coagulation, until a zirconia/forsterite composites belt tightly coating on magnesia aggregates. Excessive coagulation of zirconia caused by oversintering probably results in microcracks formation and defects enlargement thereby degrades cold crushing strength.<br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/SOS1303387E">10.2298/SOS1303387E</a><u></b></font>

Mechanism and kinetics of forsterite formation in metamorphic siliceous dolomites: findings from a rock-sample experiment

Mechanism and kinetics of forsterite formation in metamorphic siliceous dolomites: findings from a rock-sample experiment

Mechanism and kinetics of forsterite formation in metamorphic siliceous dolomites: Findings from a rock-sample experiment

A cylindrical sample of a tremolite-dolomite marble was used as starting material for a long-term experiment of 184 days at 581 °C and a CO2–H2O-fluid pressure of 100 MPa. The fluid, which was always present in excess, had a composition in the range of XCO2 = 0.21−0.37. During the run forsterite and magnesian calcite formed both within the rock sample as well as on its cylindrical surface. In areas where a tremolite crystal was exposed on the sample surface a 400–500 μm thick forsterite – magnesian calcite reaction rim evolved with a composition of 58 ± 2 mol% forsterite and 42 ± 2 mol% calcite. The dolomite areas of the surface of the rock cylinder are similarly covered by a reaction rim of forsterite plus magnesian calcite. This ca . 300 μm thick rim, however, is composed of 28 ± 5 mol% of forsterite and 72 ± 5 mol% of calcite. From the different compositions of the reaction rims we conclude that the well-known overall reaction: 1 tremolite + 11 dolomite ⇔ 8 forsterite + 13 calcite + 9 CO2 + 1 H2O occurs via the following two partial reactions: (1) 1 tremolite + 2 CO2 + 21 H2O ⇔ 2.5 forsterite + 2 calcite + 5.5 Si(OH)4 · 2 H2O and (2) 11 dolomite + 5.5 Si(OH)4 · 2 H2O ⇔ 5.5 forsterite +11 calcite + 11 CO2 + 22 H2O. All three equations are slightly simplified, because they assume the formation of pure instead of magnesian calcite. The derived partial reactions, which occur as expected via dissolution-transport-precipitation mechanisms, are sequential reactions; they are linked by the production, diffusion, and consumption of the component Si(OH)4 · 2 H2O. In contrast to the two kinds of rims on the rock cylinder’s surface, only one combined forsterite – magnesian calcite reaction rim was formed between tremolite and dolomite in the interior of the sample. The formation of this reaction rim can be explained by a combination of the two partial reactions given above. For the formation of forsterite plus magnesian calcite on the surface of the rock cylinder we come from an interpretation of the experimental results to the conclusion that the diffusion of the component Si(OH)4 · 2 H2O through the forsterite – calcite reaction rim that developed on dolomite is the rate-controlling step in the sequence of the two partial reactions given above. For the formation of forsterite plus calcite within the rock sample it is not possible to derive a rate-controlling step for the overall reaction, because of different diffusion paths of the reaction fluid and the components dissolved in it. The observed partial reactions are crucial for deciphering the formation of the various textures of forsterite – calcite –dolomite (−tremolite) assemblages developed in metamorphic siliceous dolomites. The magnesian calcites of the reaction rims have different compositions, which all deviate considerably from the equilibrium composition according to the calcite-dolomite solid solution. This result sheds light on the difficulty to attain equilibrium between the reactant dolomite and the product magnesian calcite. The consequences of the observed disequilibrium for the calcite–dolomite geothermometry are discussed.

The comparison of mechanical behavior of MgO–MgAl 2O 4 with MgO–ZrO 2 and MgO–MgAl 2O 4–ZrSiO 4 composite refractories

Mechanical properties of different compositions obtained from the additions of 5, 10, 20 and 30 wt.% zircon (ZrSiO 4) into the MgO–spinel composite refractories and ZrO 2 into MgO have been examined, the variations that occurred have been determined, and the parameters affecting those factors have been investigated with the reasons. The density, strength, Young's modulus, fracture toughness, fracture surface energy and work of fracture were measured and evaluated. Microstructural variations and fracture surfaces have been examined and the formation of new phases has been identified depending on the additive type and quantity. The relationships between mechanical properties and structural variations for different compositions have been examined. In MgO–spinel materials, strength, Young's modulus and fracture toughness values decrease up to 20% spinel addition and stay almost constant for further loads. ZrO 2 addition displays same trend but not as effective as spinel. Besides, since ZrO 2 is stable in cubic form, it does not show any toughening mechanism. Forsterite formation is the most important factor for 2-fold improvement in the mechanical properties of MgO–spinel–zircon refractories. The more the zircon addition, the more the mechanical properties improve. The generation of natural bonding between matrix particles with forsterite formation, on the other hand, causes the fracture path to turn to transgranular fracture with an increase in fracture surface energy and a decrease in work of fracture, among which the latter is considered as an indicator of thermal shock resistance of the materials being high.

ENHANCEMENT MECHANISM OF NANOSTRUCTURE FORSTERITE FORMATION RATE BY MECHANICAL ACTIVATION AND AMMONIUM CHLORIDE

The single-phase nanostructure forsterite powder was successfully synthesized by mechanical activation of talc and magnesium carbonate powder mixture followed by annealing in the presence and absence of ammonium chloride. Mechanical activation was used as an efficient method for the optimization of powder properties by means of combination and uttermost homogenization of the powder mass. Besides, the presence of chlorine ion affected the forsterite formation rate via producing smaller particle size during subsequent annealing which is very important in the case of diffusion-controlled reactions. The single-phase nanostructure forsterite powder with crystallite size of about 36 nm was successfully synthesized by 10 h mechanical activation with subsequent annealing at 1000°C for 1 h. While in the presence of chlorine ion, the single-phase nanostructure forsterite powder with crystallite size of about 20 nm could be obtained by 5 h of mechanical activation with subsequent annealing at 1000°C for 2 min.

Effects of mechanical activation and chlorine ion on nanoparticle forsterite formation

This paper reports the positive effects of chlorine ion on the forsterite formation rate. The influence of mechanical activation of talc and magnesium carbonate mixture on the formation of forsterite structure was studied in the presence of chlorine ion. Mechanical activation increased the contact surface area of the reacting phases as a consequence of intensively reduced particle size, which is very important in the case of diffusion-controlled reactions. Besides, the presence of chlorine ion affected the forsterite formation rate following annealing. The single-phase nanostructure forsterite powder with a crystallite size of about 20 nm was obtained by 5 h of mechanical activation and subsequent annealing at 1000 °C for 2 min in the presence of the chlorine ion.

Effects of fluorine ion and mechanical activation on nanostructure forsterite formation mechanism

The single-phase nanocrystalline forsterite powder was successfully synthesized by mechanical activation of talc and magnesium carbonate powder mixture followed by annealing in the presence and absence of fluorine ion. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectrometry (AAS), and transmission electron microscopy (TEM) techniques were utilized to characterize the synthesized powders. The results showed that fluorine ion affected the mechanism of forsterite formation through producing some intermediate compounds. Chondrodite, humite, and clinohumite formed in the presence of fluorine ion during subsequent annealing as a transition compound and enhanced the forsterite formation rate. Fluorine ion was released from the system by hydrolysis in the form of HF. The single-phase nanocrystalline forsterite powder was successfully synthesized by 5 and 10 h of mechanical activation with subsequent annealing at 1000 °C for 1 h in the presence of fluorine ion. The obtained forsterite powder had crystallite sizes of about 53 and 47 nm, respectively, under each treatment. Their particle size was less than 150 nm. In the absence of fluorine ion, forsterite was fabricated with a crystallite size of about 36 nm by 10 h of mechanical activation with subsequent annealing at 1000 °C for 1 h.

Influence of mechanical activation and thermal treatment time on nanoparticle forsterite formation mechanism

This paper reports the successful synthesis and formation of nanoparticle forsterite powder by mechanical activation and its subsequent annealing. Talc and magnesium carbonate were used as basic starting reactants. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), atomic absorption spectrometry (AAS) and Fourier transform infrared spectroscopy (FT-IR) techniques were utilized to characterize the as-milled and annealed samples. The results showed that forsterite was not produced directly and that the formation of enstatite was unavoidable during the synthesis of forsterite. The nanoparticle forsterite powder obtained had a crystallite size of 30 nm and mean particle size of 135 nm after 10 h milling and subsequent annealing at 1000 °C for 10 min.

MECHANOCHEMICAL SYNTHESIS AND CHARACTERIZATION OF NANOSTRUCTURE FORSTERITE BIOCERAMICS

Recent investigations suggest that forsterite ceramics possess good biocompatibility and mechanical properties and might be suitable for potential application like bone implant material. In this study, nanocrystalline forsterite ( Mg 2 SiO 4) powder was prepared by mechanochemical method and subsequent heat treatment and the effect of fluorine ion as catalyst was studied. Mechanochemical process and heat treatment were done on the MgCO 3, SiO 2 and ( NH 4)2 SiF 6 powders. The synthesized powders were characterized by X-ray diffraction (XRD), thermogravimetric (TG) analyses and scanning electron microscopy (SEM). The synthesized nano-powder had particle size smaller than 100 nm. The crystallite size of powders after 5 hours mechanical activation was 18 nm. Mechanical activation in the presence of fluorine ion affects the mechanism of forsterite formation and increase the rate of decomposition of MgO and fabrication of forsterite.

Mechanically activated crystallization of phase pure nanocrystalline forsterite powders

Pure nanocrystalline forsterite was successfully synthesized via a mechanical activation route assisted with heat treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM) and simultaneous thermal analysis (STA) techniques were utilized to characterize the prepared powders. Results showed that pure nanocrystalline forsterite could be fabricated completely by 10 h of mechanical activation and post-heat treatment at 1000–1200 °C for 1 h. By 10 h mechanical activation, the initial temperature of forsterite crystallization was reduced to about 820 °C. The obtained nanocrystalline forsterite powder had crystallite size about 57 nm according to Williamson-hall approach and particle sizes smaller than 1000 nm. XRD patterns showed that pure forsterite could not be obtained by mechanical activation process alone and that enstatite could be fabricated by increasing the time of milling. Liberation of CO 2 gas increased the rate of forsterite formation by increasing contact surface between grains.

The effect of fluorine ion on fabrication of nanostructure forsterite during mechanochemical synthesis

Pure nanocrystalline forsterite could be fabricated by mechanochemical synthesis in the presence of fluorine ion. Mechanochemical process and post-heat treatment were performed using MgCO 3, SiO 2 and (NH 4) 2SiF 6 powders as starting materials. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to characterize the synthesized powders. Pure forsterite could be obtained after 5 h of mechanical activation and post-heat treatment for 1 h at 900 °C. Nanocrystalline forsterite was fabricated with the grain size of about 30 nm. The synthesized forsterite nanopowder had particle size smaller than 100 nm. The results showed that in the presence of fluorine ion, the rate of forsterite formation was increased by combustion reaction.

Laboratory study of annealed amorphous MgSiO$_{\sf 3}$ silicate using IR spectroscopy and synchrotron X-ray diffraction

We present the results of combining in situ high resolution synchrotron X-ray powder diffraction and infrared spectroscopic measurements on an amorphous pyroxene powder sample annealed in the region of 1000 K. We find using both techniques that the crystalline structure formed during annealing is Mg2SiO4 (forsterite), but that the presence of certain features in the 10 μm band normally attributed to crystalline enstatite (MgSiO3) is contradicted by spectroscopy in the 20 μm region (along with certain other 10 μm band features) and X-ray diffraction. Both indicate crystalline forsterite as the only crystalline phase formed at this temperature. We discuss the possible mechanism of forsterite formation from amorphous pyroxene and identify the presence of proto-forsteritic structures in the amorphous starting material. We suggest the likely origin of the 10 μm band “crystalline enstatite” features as being due to short-range improvements in the amorphous MgSiO3 network ordering which are not necessarily accompanied by the formation of crystalline enstatite structure. These results not only suggest that the formation of crystalline enstatite dust grains via annealing may be difficult to realise at this temperature, but also highlight the possibility, in the absence of additional corroborating evidence, of misidentifying the nature of the carrier of the 10 μm “enstatite” features when observed in the spectra of objects such as comets. We also discuss the evolution of fine structure in the region of 15 to 16 μm, which may serve as an observational indicator of grain processing in stellar sources.