Search Results (5)

This study investigates the additive manufacturing of 3D porous scaffolds based on walstromite-type silicate ceramics for bone tissue engineering applications. Walstromite powders were synthesized using the sol-gel method and printed using extrusion-based 3D printing. Both sintered and unsintered scaffolds were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analyses to evaluate the effects of sintering on microstructure, porosity, and mechanical properties. Results indicate that the unsintered scaffolds exhibited significantly higher compressive strength due to the presence of organic binders, whereas the sintered scaffolds demonstrated enhanced porosity, facilitating cell infiltration and nutrient flow. Therefore, the sintering process reduced compressive strength, probably due to the loss of organic compounds and increased porosity. These findings underline the need for optimizing sintering parameters to balance mechanical integrity and porosity, ensuring that the scaffolds meet the mechanical and biological requirements for bone regeneration. Alternative sintering methods, such as microwave sintering, are also suggested for future research to minimize the mechanical degradation observed post-sintering. Full article

This study explores the potential utilization of walstromite (BaCa₂Si₃O₉) as a foundational material for creating new bioceramics in the form of scaffolds through 3D printing technology. To achieve this objective, this study investigates the chemical–mineralogical, morphological, and structural characteristics, as well as the biological properties, of walstromite-based bioceramics. The precursor mixture for walstromite synthesis is prepared through the sol–gel method, utilizing pure reagents. The resulting dried gelatinous precipitate is analyzed through complex thermal analysis, leading to the determination of the optimal calcination temperature. Subsequently, the calcined powder is characterized via X-ray diffraction and scanning electron microscopy, indicating the presence of calcium and barium silicates, as well as monocalcium silicate. This powder is then employed in additive 3D printing, resulting in ceramic scaffolds. The specific ceramic properties of the scaffold, such as apparent density, absorption, open porosity, and compressive strength, are assessed and fall within practical use limits. X-ray diffraction analysis confirms the formation of walstromite as a single phase in the ceramic scaffold. In vitro studies involving immersion in simulated body fluid (SBF) for 7 and 14 days, as well as contact with osteoblast-like cells, reveal the scaffold’s ability to form a phosphate layer on its surface and its biocompatibility. This study concludes that the walstromite-based ceramic scaffold exhibits promising characteristics for potential applications in bone regeneration and tissue engineering. Full article

CaSiO₃ polymorphs are abundant in only unique geological settings on the Earth’s surface and are the major Ca-bearing phases at deep mantle condition. An accurate and comprehensive study of their density and structural evolution with pressure and temperature is still lacking. Therefore, in this study we report the elastic behavior and structural evolution of wollastonite and CaSiO₃-walstromite with pressure. Both minerals are characterized by first order phase transitions to denser structures. The deformations that lead to these transformations allow a volume increase ofthe bigger polyhedra, which might ease cation substitution in the structural sites of these phases. Furthermore, their geometrical features are clear analogies with those predicted and observed for tetrahedrally-structured ultra-high-pressure carbonates, which are unfortunately unquenchable. Indeed, wollastonite and CaSiO₃-walstromite have a close resemblance to ultra-high-pressure chain- and ring-carbonates. This suggests a rich polymorphism also for tetrahedral carbonates, which might increase the compositional range of these phases, including continuous solid solutions involving cations with different size (Ca vs. Mg in particular) and important minor or trace elements incorporation. Full article

The equations of state of different phases in the CaSiO₃ system (wollastonite, pseudowollastonite, breyite (walstromite), larnite (Ca₂SiO₄), titanite-structured CaSi₂O₅ and CaSiO₃-perovskite) are constructed using a thermodynamic model based on the Helmholtz free energy. We used known experimental measurements of heat capacity, enthalpy, and thermal expansion at zero pressure and high temperatures, and volume measurements at different pressures and temperatures for calculation of parameters of equations of state of studied Ca-silicates. The used thermodynamic model has allowed us to calculate a full set of thermodynamic properties (entropy, heat capacity, bulk moduli, thermal expansion, Gibbs energy, etc.) of Ca-silicates in a wide range of pressures and temperatures. The phase diagram of the CaSiO₃ system is constructed at pressures up to 20 GPa and temperatures up to 2000 K and clarifies the phase boundaries of Ca-silicates under upper mantle conditions. The calculated wollastonite–breyite equilibrium line corresponds to equation P(GPa) = −4.7 × T(K) + 3.14. The calculated density and adiabatic bulk modulus of CaSiO₃-perovskite is compared with the PREM model. The calcium content in the perovskite composition will increase the density of mineral and it good agree with the density according to the PREM model at the lower mantle region. Full article

Walstromite, BaCa₂Si₃O₉, known only from metamorphic rocks of North America, was found in small veins of unusual rankinite paralava within gehlenite hornfelses of the Hatrurim Complex, Israel. It was detected at two localities—Gurim Anticline and Zuk Tamrur, Hatrurim Basin, Negev Desert. The structure of Israeli walstromite [with P $\overline{1}$ space group and cell parameters a = 6.74874(10) Å, b = 9.62922(11) Å, c = 6.69994(12) Å, α = 69.6585(13)°, β = 102.3446(14)°, γ = 96.8782(11)°, Z = 2, V = 398.314(11) ų] is analogous to the structure of walstromite from type locality—Rush Creek, eastern Fresno County, California, USA. The Raman spectra of all tree minerals exhibit bands related to stretching symmetric vibrations of Si-O-Si at 650–660 cm⁻¹ and Si-O at 960–990 cm⁻¹ in three-membered rings (Si₃O₉)⁶⁻. This new genetic pyrometamorphic type of walstromite forms out of the differentiated melt portions enriched in Ba, V, S, P, U, K, Na, Ti and F, a residuum after crystallization of rock-forming minerals of the paralava (rankinite, gehlenite-åkermanite-alumoåkermanite, schorlomite-andradite series and wollastonite). Walstromite associates with other Ba-minerals, also products of the residual melt crystallization as zadovite, BaCa₆[(SiO₄)(PO₄)](PO₄)₂F and gurimite, Ba₃(VO₄)₂. The genesis of unusual barium mineralization in rankinite paralava is discussed. Walstromite is isostructural with minerals—margarosanite, BaCa₂Si₃O₉ and breyite, CaCa₂(Si₃O₉), discovered in 2018. Full article