Three-Dimensional Finite Element Analysis of Different Connector Designs for All-Ceramic Implant-Supported Fixed Dental Prostheses

All-ceramic fixed dental prostheses (FDPs) tend to fracture at the connector regions due to high stress concentration at these areas influenced by their design. This study was performed as an adjunct to an existing clinical study to evaluate the influence of the different radii of curvature of gingival embrasure on the stress distribution of a three-unit all-ceramic implanted supported FDP. Three three-dimensional (3D) models were created by scanning two titanium dental implants, their suitable zirconia abutments, and a patient-retrieved dental prosthesis using a micro-CT scanner. The radius of curvature of the gingival embrasure for the distal connector of the FDP was altered to measure 0.25 mm, 0.50 mm, and 0.75 mm. A finite element analysis (FEA) software (ABAQUS) was used to evaluate the impact of different connector designs on the distribution of stresses. Maximum Principal Stress data was collected from the individual components (veneer, framework, and abutments). The radius of curvature of gingival embrasure had a significant influence on the stress distribution at the assessed components. The tensile peak stresses at all structures were highest in the 0.25 mm model, while the 0.50 mm and 0.75 mm models presented similar values and more uniform stress distribution.

Structure and Properties of Highly Porous Alumina-Based Ceramic Materials after Heating by Concentrated Solar Radiation

Three ceramic fibrous materials of the Al2O3-SiO2 system with different densities have been treated using concentrated solar radiation. The experiment was performed using technological capabilities of the Big Solar Furnace in the 2 modes: the first mode includes heating up to 1400–1600 °C, holding for 1.5–2 h; the second mode (the fusion mode) includes heating up to 1750–1900 °C until the sample destruction, which is accompanied by fusion. Upon completion of the experiment, the phase composition, microstructure, and compressive strength of the materials were studied. It was shown that the investigated materials retained their fibrous structure under prolonged treatment in the first mode up to temperatures of 1600 °C. The phase composition of the ceramic materials changes during the experiment, and with a decrease in the density, the modification is more pronounced. Treatment of all three materials under study in the fusion mode resulted in the formation of the eutectic component in the form of spherulites. The compressive strength of the materials was found to be slightly reduced after exposure to concentrated solar radiation.

Study of Radiation Embitterment and Degradation Processes of Li2ZrO3 Ceramic under Irradiation with Swift Heavy Ions

The work is devoted to the study of radiation damage and subsequent swelling processes of the surface layer of Li2ZrO3 ceramics under irradiation with heavy Xe22+ ions, depending on the accumulation of the radiation dose. The samples under study were obtained using a mechanochemical synthesis method. The samples were irradiated with heavy Xe22+ ions with an energy of 230 MeV at irradiation fluences of 1011–1016 ion/cm2. The choice of ion types is due to the possibility of simulating the radiation damage accumulation processes as a result of the implantation of Xe22+ ions and subsequent atomic displacements. It was found that, at irradiation doses above 5 × 1014 ion/cm2, point defects accumulate, which leads to a disordering of the surface layer and a subsequent decrease in the strength and hardness of ceramics. At the same time, the main process influencing the decrease in resistance to radiation damage is the crystal structure swelling as a result of the accumulation of defects and disordering of the crystal lattice.

Reactive Sintering of Al2O3–Y3Al5O12 Ceramic Composites Obtained by Direct Ink Writing

The main goal of this work was to obtain dense Al2O3–Y3Al5O12 ceramic composites by reactive sintering of three-dimensional samples, built by direct ink writing from a paste containing a mixture of Al2O3 and Y2O3 powders. To obtain a ceramic ink with proper rheological properties for extrusion-based printing, highly pure Al2O3 and Y2O3 powders in a percentage–weight ratio of 64:36 was mixed with 0.2 wt% MgO in a total solid loading of 42 vol% in aqueous media, adding carboxymethyl cellulose and polyethyleneimine solution as additives. The dried printed samples were sintered at final temperatures in the range of 1550 °C and 1650 °C; thus, relative densities of 83.7 ± 0.8%, 95.4 ± 0.4%, and 96.5 ± 0.5% were obtained for 1550 °C, 1600 °C, and 1650 °C, respectively. Rietveld refinement performed on the X-ray diffraction patterns indicated the presence of Al2O3 (42 to 47%) and Y3Al15O12 (58 to 61%) as crystalline phases, while micrographs showed the presence of equiaxial micrometric grains with average sizes of 1.8 ± 0.6 μm, for both phases and all sintering conditions. Samples sintered at 1600 °C and 1650 °C presented similar average Vickers hardness values of 14.2 ± 0.27 GPa and 14.5 ± 0.25 GPa, respectively. A slight increase in fracture toughness as sintering temperature increases was also stated, consistent with the densification.

Porous Functional Graded Bioceramics with Integrated Interface Textures

Porous functional graded ceramics (porous FGCs) offer immense potential to overcome the low mechanical strengths of homogeneously porous bioceramics used as bone grafts. The tailored manipulation of the graded pore structure including the interfaces in these materials is of particular interest to locally control the microstructural and mechanical properties, as well as the biological response of the potential implant. In this work, porous FGCs with integrated interface textures were fabricated by a novel two-step transfer micro-molding technique using alumina and hydroxyapatite feedstocks with varied amounts of spherical pore formers (0–40 Vol%) to generate well-defined porosities. Defect-free interfaces could be realized for various porosity pairings, leading to porous FGCs with continuous and discontinuous transition of porosity. The microstructure of three different periodic interface patterns (planar, 2D-linear waves and 3D-Gaussian hills) was investigated by SEM and µCT and showed a shape accurate replication of the CAD-designed model in the ceramic sample. The Young’s modulus and flexural strength of bi-layered bending bars with 0 and 30 Vol% of pore formers were determined and compared to homogeneous porous alumina and hydroxyapaite containing 0–40 Vol% of pore formers. A significant reduction of the Young’s modulus was observed for the porous FGCs, attributed to damping effects at the interface. Flexural 4-point-testing revealed that the failure did not occur at the interface, but rather in the porous 30 Vol% layer, proving that the interface does not represent a source of weakness in the microstructure.

Sol–Gel Approach for Design of Pt/Al2O3-TiO2 System—Synthesis and Catalytic Tests

Al2O3-TiO2 systems with Ti:Al 0.1, 0.5 and 1.0 molar ratio obtained by the sol–gel method have been used as a platinum support. As a precursor of alumina gel, aluminum isopropoxide has been chosen. Titanium tert-butoxylate was applied to obtain titania gel and hexachloroplatinic acid was applied as a source of platinum. The systems have been characterized by the following methods: thermogravimetric analysis (TGA), Fourier transformation infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), low-temperature nitrogen adsorption–desorption isotherms (BET, BJH), temperature-programmed reduction with hydrogen (TPR-H2) and hydrogen chemisorption. Reactions of toluene to methylcyclohexane and selective o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) hydrogenation were used as the tests of systems’ catalytic activity. The application of Al2O3-TiO2 as a support has enabled the obtaining of platinum catalysts showing high activities for hydrogenation of toluene and selective hydrogenation of o-chloronitrobenzene to o-chloroaniline in the liquid phase. The highest activity in both reactions has been found for Pt/Al2O3-0.5TiO2 catalyst and the highest selectivity for Pt/Al2O3-. The activity of Pt/Al2O3-TiO2 catalysts was higher than that of alumina-supported ones.

Design of Magnesia–Spinel Bricks for Improved Coating Adherence in Cement Rotary Kilns

It is well known that doloma bricks present better coating adherence than magnesia–spinel bricks when applied in cement rotary kilns, which is related to the different coating formation mechanism. The coating has an essential role in prolonged operation by protecting the refractory lining; thus, it is important to improve its adherence on magnesia–spinel refractories. The objective of this investigation is to study different compositions of magnesia–spinel bricks, achieved by varying additives used (calcined alumina, limestone, hematite and zirconia) and firing temperature (1500 °C and 1700 °C), to enhance the coating adherence measured by the sandwich test. The results have pointed out that the use of higher firing temperature contributes positively to physical adherence due to well-sintered refractory structure and elevated permeability, attaining coating strength superior to 2 MPa. For the chemical adherence, the addition of 2 wt.% of limestone increased the coating strength to 3 MPa, but resulted in a drop in hot properties. In this context, the most suitable approach to improve adherence of clinker coating and maintain hot properties in suitable levels is to increase the firing temperature.

Synthesis and Characterization of Novel Calcium-Silicate Nanobioceramics with Magnesium: Effect of Heat Treatment on Biological, Physical and Chemical Properties

Glass-ceramic nanopowder with a composition of 55SiO2-35CaO-10MgO (mol %) was synthesized by the sol–gel method and was heat treated at three temperatures (T1 = 835 °C, T2 = 1000 °C, T3 = 1100 °C) in order to obtain different materials (C1, C2, C3, respectively) varying in crystal structure. Bioactivity and oxidative stress were evaluated in simulated body fluid (SBF) for various time periods (up to 10 days). The structure of the synthesized materials and their apatite-forming ability were investigated by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM/EDS). The antibacterial properties of the synthesized materials were evaluated against three Gram-positive and four Gram-negative bacterial strains and their biocompatibility was verified on a primary cell line of human gingival fibroblasts (HGFs) by the MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5 diphenyl tetrazolium bromide) assay. The crystallization of the materials was increased by sintering temperature. Heat treatment did not inhibit the bioactive behavior of the materials as apatite formation started after 3 days in SBF. C2, C3 showed some indications of apatite forming even from the first day. Regarding cell viability, a variety of biological behaviors, concerning both dose and time points, was observed between the positive control and the tested materials by both the MTT assay and oxidative stress analysis. In conclusion, the nanobioceramic materials of this study possess a multitude of attractive physicochemical and biological properties that make them suitable candidates for bone regeneration applications, fillers in nanocomposite scaffolds, or as grafts in bone cavities and periodontal lesions.

Effect of Machining Limiting Factors on Drilling Progress during Spark Assisted Chemical Engraving (SACE): General Trends

Spark Assisted Chemical Engraving (SACE) is a micro-machining technology for non-conductive materials, mainly glass, based on thermal assisted etching. Generally, during SACE, drilling proceeds at a fast rate reaching 100 µm/s for the first 100 µm and then it slows down for depths higher than 300 µm. While several techniques have been proposed to establish faster drilling, they mainly rely on tuning the machining parameters to enhance the machining performance. However, with this approach machining parameters need to be constantly tuned to achieve certain machining performance depending on the size of the tool and the features needed. Therefore, this necessitates further work to enhance understanding regarding the SACE machining process fundamentals in order to enhance machining speed and quality. Since SACE is a thermal assisted etching process, both local heating and flushing of electrolyte in the machining zone are required. However, to the authors’ knowledge there is not any study that attempts to analyze the effect of each of these machining limiting factors on the machining performance. This work attempts to clarify the effect of each flushing and heating on the drilling progress for hole depths higher than 100 microns. It therefore provides a deeper understanding of the fundamentals of the SACE machining process.

An Experimental Study of the Effects of Low-Calcium Fly Ash on Type II Concrete

In this study, the compressive strength and the permeation properties of fly ash-based Geopolymer were experimentally investigated. Type 2 Portland cement (T2PC) was partially or entirely replaced with 0, 10, 20, 30, 50, 70, and 100% of fly ash (FA). The laboratory tests were conducted for compressive strength at 7, 28, and 90 days, and permeation properties such as water absorption at 7 and 28 days. The main goal was to produce eco-friendly concrete with high strength and low permeability through blending cementitious materials including low Calcium (Ca) (T2PC and FA) for protecting concrete against sulphate attacks and other chemically destructive compounds in the environment. This study focused on the effectiveness of the curing period, combinations of chemical activators by varying the molarity of alkaline solutions between 4.16 and 12.96 M and keeping the sodium silicate (SS) to sodium hydroxide (SH) by the weight ratio of 2.5. Lab observations from this study demonstrated that the compressive strength was enhanced with the increment in fly ash content at all ages, with optimum being at 20% as the replacement of T2PC.