Nanocrystalline forsterite for biomedical applications: Synthesis, microstructure and mechanical properties

Preceramic Polymers for Additive Manufacturing of Silicate Ceramics

The utilization of preceramic polymers (PCPs) to produce both oxide and non-oxide ceramics has caught significant interest, owing to their exceptional characteristics. Diverse types of polymer-derived ceramics (PDCs) synthesized by using various PCPs have demonstrated remarkable characteristics such as exceptional thermal stability, resistance to corrosion and oxidation at elevated temperatures, biocompatibility, and notable dielectric properties, among others. The application of additive manufacturing techniques to produce PDCs opens up new opportunities for manufacturing complex and unconventional ceramic structures with complex designs that might be challenging or impossible to achieve using traditional manufacturing methods. This is particularly advantageous in industries like aerospace, automotive, and electronics. In this review, various categories of preceramic polymers employed in the synthesis of polymer-derived ceramics are discussed, with a particular focus on the utilization of polysiloxane and polysilsesquioxanes to generate silicate ceramics. Further, diverse additive manufacturing techniques adopted for the fabrication of polymer-derived silicate ceramics are described.

Corrosion Resistance of Novel Fly Ash–Based Forsterite–Spinel Refractory Ceramics

This article aims to investigate the corrosion resistance of novel fly ash–based forsterite–spinel (Mg₂SiO₄-MgAl₂O₄) refractory ceramics to various corrosive media in comparison with reactive alumina–based ceramics. Because fly ash is produced in enormous quantities as a byproduct of coal-burning power stations, it could be utilized as an affordable source of aluminum oxide and silicon oxide. Corrosion resistance to iron, clinker, alumina, and copper was observed by scanning electron microscope with an elemental probe. The influence on the properties after firing was also investigated. Fly ash–based and reactive alumina–based mixtures were designed to contain 10%, 15% and 20% of spinel after firing. Raw material mixtures were sintered at 1550 °C for two hours. X-ray diffraction analysis and scanning electron microscopy were used to analyze sintered samples. The apparent porosity, bulk density, modulus of rupture, and refractory and thermo–mechanical properties were also investigated. The experimental results disclosed that the modulus of rupture, thermal shock resistance and microstructure were improved with increasing amounts of spinel in the fired samples. An analysis of the transition zones between corrosive media and ceramics revealed that all mixtures have good resistance against corrosion to iron, clinker, aluminum and copper.

Review on calcium- and magnesium-based silicates for bone tissue engineering applications

Bone is a self-engineered structural component of the human body with multifaceted mechanical strength, which provides indomitable support to the effective functioning of the human body. It is indispensable to find a suitable biomaterial for substituting the bone as the bone substitute material requirement is very high due to the rate of bone fracture and infection lead to osteoporosis in human beings increases rapidly. It is not an easy task to design a material with good apatite deposition ability, a faster rate of dissolution, superior resorbability, high mechanical strength, and significant bactericidal activity. Since the synthetic hydroxyapatite was not able to achieve the dahlite phase of hydroxyapatite (natural bone mineral phase), silicates emerged as an alternate biomaterial to meet the need for bone graft substitutes. All silicates do not exhibit the properties required for bone graft substitutes, as their composition and methodology adopted for the synthesis are different. Calcium, magnesium, and silicon play a major role in the formation of bone mineral and their metabolism during bone formation. In this review, the relationship between composition and activity of calcium, magnesium-based silicates have been discussed along with the future scope of these materials for hard tissue engineering applications.

Multiscale Computational Simulation of Amorphous Silicates’ Structural, Dielectric, and Vibrational Spectroscopic Properties

Silicates are among the most abundant and important inorganic materials, not only in the Earth’s crust, but also in the interstellar medium in the form of micro/nanoparticles or embedded in the matrices of comets, meteorites, and other asteroidal bodies. Although the crystalline phases of silicates are indeed present in nature, amorphous forms are also highly abundant. Here, we report a theoretical investigation of the structural, dielectric, and vibrational properties of the amorphous bulk for forsterite (Mg2SiO4) as a silicate test case by a combined approach of classical molecular dynamics (MD) simulations for structure evolution and periodic quantum mechanical Density Functional Theory (DFT) calculations for electronic structure analysis. Using classical MD based on an empirical partial charge rigid ionic model within a melt-quenching scheme at different temperatures performed with the GULP 4.0 code, amorphous bulk structures for Mg2SiO4 were generated using the crystalline phase as the initial guess. This has been done for bulk structures with three different unit cell sizes, adopting a super-cell approach; that is, 1 × 1 × 2, 2 × 1 × 2, and 2 × 2 × 2. The radial distribution functions indicated a good degree of amorphization of the structures. Periodic B3LYP-geometry optimizations performed with the CRYSTAL14 code on the generated amorphous systems were used to analyze their structure; to calculate their high-frequency dielectric constants (ε∞); and to simulate their IR, Raman, and reflectance spectra, which were compared with the experimental and theoretical crystalline Mg2SiO4. The most significant changes of the physicochemical properties of the amorphous systems compared to the crystalline ones are presented and discussed (e.g., larger deviations in the bond distances and angles, broadening of the IR bands, etc.), which are consistent with their disordered nature. It is also shown that by increasing the unit cell size, the bulk structures present a larger degree of amorphization.

Antibacterial forsterite (Mg2SiO4) scaffold: A promising bioceramic for load bearing applications

In the current work, forsterite samples with different surface area were investigated for its antibacterial activity. Dissolution studies show that the lower degradation of forsterite compared to other silicate bioceramics, which is a desirable property for repairing bone defects. Forsterite scaffold shows superior compressive strength than the cortical bone after immersion in simulated body fluid. Bactericidal tests indicate that the forsterite had inhibition effect on the growth of clinical bacterial isolates. Forsterite may be a suitable candidate material for load bearing applications with enhanced mechanical properties and lower degradation rate.

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Forsterite with higher surface area shows better degradation, mechanical stability and antibacterial activity.

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The compressive strength of forsterite is similar to that of cortical bone.

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The dissolution of Mg²⁺ ion and change in pH are responsible for antibacterial activity of forsterite.

Preparation of magnesium oxide and magnesium silicate replicas retaining the hierarchical structure of pine wood

Replicas retaining the structural characteristics of softwood (Pinus sylvestris) were obtained by infiltrating pretreated templates with a methanolic methoxymagnesium methyl carbonate (MeOMgOCO2Me) solution as a precursor which then hydrolyzed into MgCO3 nanoparticles. Subsequent calcination at temperatures ranging from 500 to 1450°C yielded annealed MgO replicas on levels of hierarchy from the macroscopic to the submicron scale. The mechanical stability of the replicas could be improved through calcination at 1450°C. However, this treatment leads to considerable shrinkage (Δax=56%). Even more stable MgO replicas were obtained by infiltrating the pine template first with MeOMgOCO2Me, followed by a second infiltration step with an ethanolic tetraethyl orthosilicate (TEOS) solution and subsequent calcination at 1350°C. The resulting replicas constitute an MgO framework overgrown with Mg2SiO4 (forsterite) and exhibit compression strengths of 31±8 MPa, as well as hierarchical structures combined with an anisotropic porosity.

Glass Ceramization as an Alternative Production Route of Forsterite Glass-Ceramics for Possible Multipurpose Uses

Homogenous, transparent and bubble-free glass was produced through the addition of an extra silica as a replacement for its structurally analogous AlPO4in an aluminophosphosilicate base glass. FT-IR, DSC, XRD and SEM coupled with EDX, were all used to characterize the obtained glass, and to establish the effect of silica as a substitution for AlPO4on the vibrational spectra and crystallization behavior of the obtained glass.Silica was found to lower the wavenumber of the main stretching vibrational band of aluminophosphosilicate glass, thus counterbalancing the increment in the wavenumber of the main stretching band caused by P2O5in the former base glass. The obtained glass crystallized in bulk at relatively low temperatures, and the first phase to crystallize was enstatite. As temperature was increased, both enstatite and forsterite coexisted. At yet higher temperatures, forsterite was the predominantly crystallizing phase with just traces of enstatite.Thus, it is believed that glass ceramization represents a challenging and yet a promising fabrication route with many technological advantages, over other making techniques, such as sol-gel and solid-state or solid solution routes, for production of forsterite-enstatite and forsterite ceramics. The obtained glass-ceramics are possible candidates for advanced applications, utilizing properties of forsterite, such as bioactivity, dielectricity and birefringence, among many others.