Evaluation of direct light processing for the fabrication of bioactive ceramic scaffolds: Effect of pore/strut size on manufacturability and mechanical performance

Bioactive ceramic scaffolds for bone regeneration consisting of a three-dimensional mesh of interpenetrating struts with square section were fabricated via Digital Light Processing (DLP). The ability of the technique to manufacture 3D porous structures from β-tricalcium phosphate (β-TCP) powders with different dimensions of struts and pores was evaluated, identifying the possibilities and limitations of the manufacturing process. Small pore sizes were found to seriously complicate the elimination of excess slurry from the scaffold’s innermost pores. The effect of the strut/pore size on the mechanical performance of the scaffolds under compressive stresses was also evaluated, but no significant influence was found. Under compressive stresses, the structures resulted weaker when tested perpendicularly to the printing plane due to interlayer shear failure. Interlayer superficial grooves are proposed as potential failure-controlling defects, which could also explain the lack of a Weibull size effect on the mechanical strength of the fabricated DLP scaffolds.     

Fabrication and properties of 3D printed zirconia scaffold coated with calcium silicate/hydroxyapatite

The scaffold of bone repair needs a variety of material combinations to meet its intended performance; a typical single material such as zirconia has excellent mechanical properties, while hydroxyapatite and calcium silicate are bioactive materials with different degradation rates. In this paper, porous zirconia scaffolds were fabricated using 3D printing technology. The surface of the scaffold was coated by dipping with different contents of calcium silicate and hydroxyapatite to improve the biological activity and mechanical properties. Mechanical tests show that the coating material can effectively fill the pores of the porous scaffold, increasing its compressive strength by an average of 55%. The simulated body fluid (SBF) test showed that the higher calcium silicate in the coating increased the degradation rate. Cell experiments showed that the coated scaffolds exhibited good cytocompatibility and were beneficial to the proliferation and differentiation of cells. In conclusion, coated scaffolds have potential applications in the field of bone repair.     

Predictive process mapping for laser powder bed fusion: A review of existing analytical solutions

One of the main challenges in the laser powder bed fusion (LPBF) process is making dense and defect-free components. These porosity defects are dependent upon the melt pool geometry and the processing conditions. Power-velocity (PV) processing maps can aid in visualizing the effects of LPBF processing variables and mapping different defect regimes such as lack-of-fusion, under-melting, balling, and keyholing. This work presents an assessment of existing analytical equations and models that provide an estimate of the melt pool geometry as a function of material properties. The melt pool equations are then combined with defect criteria to provide a quick approximation of the PV processing maps for a variety of materials. Finally, the predictions of these processing maps are compared with experimental data from the literature. The predictive processing maps can be computed quickly and can be coupled with dimensionless numbers and high-throughput (HT) experiments for validation. The present work provides a boundary framework for designing the optimal processing parameters for new metals and alloys based on existing analytical solutions.     

Triggering the aqueous interparticle association of γ‒Al2O3 hierarchical assemblies using divalent cations and cellulose nanofibers

Understanding aqueous dispersion, rheological properties and colloidal stabilisation mechanisms of hierarchically assembled ceramic powders is important for progress in the fields of catalysis, separation and/or adsorption. The present study was designed to evaluate the rheological and sedimentation behaviour of highly loaded aqueous suspensions (up to φ_A = 0.126) containing AlN-powder-hydrolysis-derived, micron-sized, mesoporous, gamma alumina (MA) particulates with a high surface area (～180 m²/g) dispersed with sodium polyacrylate (NaPAA). The as-prepared suspensions were prone to sedimentation and segregation. However, when divalent cations (Mg²⁺, Ca²⁺) or cellulose nanofibers were added, the formation of interparticle association networks in the aqueous suspensions containing MA particles was triggered, facilitating their long-term resistance to sedimentation lasting more than 12 weeks.     

Review on development of metal/ceramic interpenetrating phase composites and critical analysis of their properties

Metal/ceramic composites are in high demand in several industries because of their superior thermo-mechanical properties. Among various composite types, the interpenetrating phase composites (IPCs) with percolating metallic and ceramic phases offer manifold benefits, such as a good combination of strength, toughness, and stiffness, very good thermal properties, excellent wear resistance, as well as the flexibility of microstructure and processing route selection, etc. The fabrication of metal/ceramic IPCs typically involves two steps - i) processing of an open porous ceramic body, and ii) infiltration of metallic melt in the pores to fabricate the IPC. Although significant progress has been made in recent years for developing both porous ceramics and melt infiltration methods, to the best of the knowledge of the authors, no review article summarizing all the aspects of processing and properties of IPCs has been published till date. This review article is aimed at filling this gap. Starting with a brief introduction about the current status and applications of IPCs, the various processing routes for fabricating open porous ceramic preforms and melt infiltration techniques have been discussed. Subsequently, the data available for various important physical, mechanical, and thermal properties for IPCs have been critically analyzed to thoroughly understand their dependence on various structural and processing parameters. To compare the properties of IPCs with other relevant materials, seven different Ashby material property maps have been used, and the domains for IPCs have been created in them. For each map, the concept of material indices has been employed to critically discuss how IPCs perform in relation to other material classes for various optimum design conditions. Finally, a detailed future outlook for further research on IPCs has been provided.     

Processing capabilities of micro ultrasonic machining for hard and brittle materials: SPH analysis and experimental verification

Micro ultrasonic machining (micro-USM) is an unconventional micromachining technology that has capability to fabricate high aspect ratio micro-holes, intricate shapes and features on various hard and brittle materials. The material removal in USM is based on brittle fracture of work materials. The mechanical properties and fracture behaviour are different for varied hard and brittle materials, which would make a big difference in the processing capability of micro-USM. To study the processing capability of USM and exploit its potential, the material removal of work materials, wear of abrasive particles and wear of machining tools in USM of three typical hard and brittle materials including float glass, alumina, and silicon carbide were investigated in this work. Both smoothed particle hydrodynamics (SPH) simulations and verification experiments were conducted. The material removal rate is found to decrease in the order of glass, alumina, and silicon carbide, which can be well explained by the simulation results that cracking of glass is faster and larger compared to the other materials. Correspondingly, the tool wear rate also dropped significantly thanks to the faster material removal, and a formation of concavity on the tool tip center due to intensive wear was prevented. The SPH model is proved useful for studying USM of different hard and brittle materials, and capable of predicting the machining performance.     

招远市金矿资源开发利用调查评价研究

为深入贯彻生态文明思想，促进矿产资源全面节约和高效利用，对招远市展开了金矿矿产资源开发利用水平调查评价，对2018年度数据进行整理和实地核查后，进行了单个矿山评价和多矿山评价，包括矿种评价、地区评价、行业评价。招远市16个矿山实际数据和基准值指标对比显示，单个矿山评价和多矿山评价的达标率均为100%。在此基础上，分析了金矿矿产资源资源开发利用水平调查评价的意义和存在问题。     

Synthesis and characterization of calcium aluminate compounds from gehlenite by high-temperature solid-state reaction

The mineral transition mechanism and self-pulverization property of the sintered products in the Ca₂Al₂SiO₇-CaO system were systematically studied using pre-synthesized gehlenite determined by XRD, SEM, FTIR and particle size analyses. The minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄, Ca₃SiO₅ and Ca₂SiO₄ are formed by the direct reactions of Ca₂Al₂SiO₇ with CaO. CaAl₂O₄ reacts with CaO to form Ca₁₂Al₁₄O₃₃ or Ca₃Al₂O₆, while Ca₃SiO₅ reacts with Ca₂Al₂SiO₇ to form Ca₂SiO₄ and calcium aluminate compounds. The sintered products mainly contain CaAl₂O₄, Ca₁₂Al₁₄O₃₃ and Ca₂SiO₄ at 1350?°C or above 1500?°C when the molar ratio of CaO to Al₂O₃ is 1.0. Increasing the sintering duration or the CaO consumption promotes the transition of Ca₂Al₂SiO₇ to Ca₂SiO₄ and calcium aluminate compounds when sintered at 1350?°C, which accordingly improves the self-pulverization property of the sintered products. The formed minerals of Ca₁₂Al₁₄O₃₃, CaAl₂O₄ and Ca₂SiO₄ transform into Ca₂Al₂SiO₇ again when the sintering temperature is between 1400?°C and 1450?°C, and the corresponding self-pulverization property of the sintered products deteriorates sharply.     

Influence of Alkaline Additives and Buffers on Mineral Trapping of CO2 under Mild Conditions

Carbon dioxide (CO₂) gas is the main contributor to climate change. CO₂ storage in underground brines and oil‐field brines by mineral trapping has been considered as a promising alternative in order to reduce CO₂ emissions. However, permanent storage of CO₂ in stable carbonate minerals is greatly dependent on brine pH, being favored over an alkaline pH. The effect of alkaline additives (NaOH, KOH, CaO) and buffer solutions (NaHCO₃/NaOH, Na₂HPO₄/NaOH, NH₄Cl/NH₄OH) on the mineral trapping of CO₂ under mild conditions using a synthetic brine is investigated. The results indicate that both NaOH+NH₄Cl/NH₄OH and KOH+NH₄Cl/NH₄OH mixtures promote precipitation mainly of calcium carbonate (CaCO₃).