Nanocrystalline Forsterite Powder Research Articles

Shear deformation of nano- and micro-crystalline olivine at seismic slip rates

Several thermally activated mechanisms have been proposed to explain the dynamic weakening of faults at fast, seismic slip rates v > 0.1 m s−1. Nevertheless, direct constraints from microstructural observations on the operation of such weakening mechanisms are still lacking for most rock forming minerals. This includes olivine, a very refractory mineral relevant for seismic activity occurring in peridotite massifs. Here, we report mechanical data and microstructures of olivine aggregates deformed in a rotary shear apparatus at slip rates from 10−2 m s−1 to 1 m s−1. A number of 34 shear deformation experiments were performed under axial stresses of 20 MPa and at room temperature. Samples are composed of either synthetic iron-free nanocrystalline forsterite powder (initial grain size = 0.07 μm) or natural iron-bearing olivine powder from San Carlos or San Bernardino (Fo91, Arizona, USA; initial grain size = 70 ± 2 μm). Shear deformation lasts from a few seconds up to 5 min and ends after 0.03 to 3 m of slip. Independently of the initial grain size or composition, friction coefficients decrease from peak values of 0.8 to values below 0.4, after only 0.1 m of slip. The recovered samples were characterized by scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. For all samples, before the onset of dynamic weakening, the deformation localizes in a principal shear zone, well-marked in the natural olivine aggregates by a rapid decrease of grain size down to <1.7 μm. Variations in texture, fractured grains and the formation of a fine-grained matrix support cataclastic flow at an early stage of deformation, responsible for the foremost grain size reduction. The samples display well-defined zones with partially sintered microstructure, and shape preferred orientation. The initial texture of the cold-pressed starting material is rapidly reduced to a near random distribution after only 0.03 m of slip. All crystal preferred orientations (CPO) remain weak, with a J-index ≲2. Based on the microstructures, the dominant deformation mechanism may be enhanced effective diffusion (by surface and grain boundary diffusion) causing mechanical weakening and a viscous behavior, which is then temperature-dependent under sub-solidus conditions. We find no microstructural evidence for frictional melting, flash heating or thermal decomposition. Our results advocate that dynamic weakening of faults is independent of initial grain size, and can be achieved after displacements as low as 0.1 m without production of frictionally induced-melt.

The physicochemical and biomechanical profile of forsterite and its osteogenic potential of mesenchymal stromal cells.

It has been demonstrated that nanocrystalline forsterite powder synthesised using urea as a fuel in sol-gel combustion method had produced a pure forsterite (FU) and possessed superior bioactive characteristics such as bone apatite formation and antibacterial properties. In the present study, 3D-scaffold was fabricated using nanocrystalline forsterite powder in polymer sponge method. The FU scaffold was used in investigating the physicochemical, biomechanics, cell attachment, in vitro biocompatibility and osteogenic differentiation properties. For physicochemical characterisation, Fourier-transform infrared spectroscopy (FTIR), Energy dispersive X-ray (EDX), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoemission spectrometer (XPS) and Brunauer-Emmett-Teller (BET) were used. FTIR, EDX, XRD peaks and Raman spectroscopy demonstrated correlating to FU. The XPS confirmed the surface chemistry associating to FU. The BET revealed FU scaffold surface area of 12.67 m2/g and total pore size of 0.03 cm3/g. Compressive strength of the FU scaffold was found to be 27.18 ± 13.4 MPa. The human bone marrow derived mesenchymal stromal cells (hBMSCs) characterisation prior to perform seeding on FU scaffold verified the stromal cell phenotypic and lineage commitments. SEM, confocal images and presto blue viability assay suggested good cell attachment and proliferation of hBMSCs on FU scaffold and comparable to a commercial bone substitutes (cBS). Osteogenic proteins and gene expression from day 7 onward indicated FU scaffold had a significant osteogenic potential (p<0.05), when compared with day 1 as well as between FU and cBS. These findings suggest that FU scaffold has a greater potential for use in orthopaedic and/or orthodontic applications.

Mixed-mode fracture of synthesized nanocrystalline forsterite for biomedical applications

Nanocrystalline forsterite is an important biocompatible, nanostructured bioceramic. Various studies have examined essential properties of this biomaterial, including bioactivity, biocompatibility, typical mechanical features, etc. In this research nanocrystalline forsterite powder was produced by the sol–gel method and was characterized via XRD and SEM analysis. By pressurizing the nanopowder under 200 MPa and sintering at 1500 °C, semi-circular bending (SCB) samples were prepared with cracks of different angles. Fracture tests were then performed under mode-I, mode-II and mixed-mode loading in order to investigate the fracture resistance of forsterite. The specimens were all failed in a brittle manner. The results, then, were compared with two common mixed-mode fracture models called maximum tangential stress (MTS) and generalized maximum tangential stress (GMTS). The generalized MTS criterion provided very good estimations for the experimental results.

A modified method to synthesize single-phase forsterite nanoparticles at low temperature

In this paper forsterite (Mg2SiO4) nanopowder with particle size in the range of 33 and 112nm was synthesized by a combination of sol–gel and ball milling methods. Magnesium nitrate and silica were used as the sources of magnesium and silicon in the forsterite nanopowder. Thermogravimetry (TG) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and dynamic light scattering (DLS) techniques were utilized to characterize the synthesized powders. Single-phase nanocrystalline forsterite powder with mean crystallite size of about 16nm was obtained from sol–gel method with subsequent ball milling for 5h and heat treatment at 750°C for 1h. A combination of sol–gel and mechanical activation led to the formation of more homogeneous powder and subsequently lower sintering temperature to produce forsterite powder. In vitro biological studies were performed by immersing the forsterite samples in simulated body fluid (SBF). The results showed that nanostructure forsterite is bioactive and possessed apatite formation ability.

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.

MECHANOCHEMICAL SYNTHESIS OF SINGLE PHASE NANOCRYSTALLINE FORSTERITE POWDER

Pure nanocrystalline forsterite ( Mg 2 SiO 4) powder was successfully synthesized by mechanochemical route and subsequent annealing. The starting materials were talc ( Mg 3 Si 4 O 10( OH )2) and magnesium carbonate ( MgCO 3) powders. To produce forsterite powder, first talc and magnesium carbonate powders were calcined at 1200°C for 1 h and 700°C for 2 h, respectively. After that the mixture of obtained powders was milled by a planetary ball mill, and then annealed at 1000°C and 1200°C for 1 h. Thermogravimetric (TG) analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques were utilized to characterize the initial and prepared powders. The results showed that a single phase nanocrystalline forsterite powder with a crystallite size of 49 nm was obtained after 40 h milling and subsequent annealing at 1000°C for 1 h.

Synthesis of nanocrystalline forsterite (Mg 2SiO 4) powder by combined mechanical activation and thermal treatment

This study investigates the synthesis of single-phase nanocrystalline forsterite powder by mechanical activation with subsequent annealing. To produce forsterite powder, a mixture of talc and magnesium oxide powders was first milled by a planetary ball mill, and then annealed at 1000 and 1200 °C for 1 h. The synthesized powder was characterized by X-ray diffraction (XRD), simultaneous thermal analysis (STA), scanning electron microscopy (SEM), and atomic absorption spectrometry (AAS). The initial temperature of forsterite crystallization was reduced to about 825 °C after 20 h of mechanical activation. The forsterite powder synthesized by 5 h of mechanical activation with subsequent annealing at 1000 °C for 1 h had crystallites 40 nm in size. The particle size of this sample was less than 500 nm.

Mechanical activation assisted synthesis of pure nanocrystalline forsterite powder

Single phase nanocrystalline forsterite powder was successfully synthesized by mechanical activation of talc and magnesium carbonate powder mixture followed by annealing. Simultaneous thermal analysis (STA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilized to characterize the as-milled and annealed samples. The results showed that a single phase nanocrystalline forsterite with a crystallite size of 35 nm was obtained by annealing of 10 h ball milled sample at 1000 °C for 1 h. Further milling had no significant effect on structure and crystallite size of forsterite phase. Atomic absorption spectrometry (AAS) analysis showed that the amount of Fe and Cr in 100 h ball milled sample were 0.2838% and 0.00175%, respectively.

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.