Sintering Protocol Research Articles

Structural Alterations of Zirconia Depending on Sintering Parameters and Effects on Bond Strength After Different Surface Treatments

Objectives: Zirconia having different physical and optical properties is obtained after the application of different sintering parameters. This study aims to investigate structural variations after administering different sintering protocols and to evaluate the effect of different surface treatments on shear bond strength.Materials and Methods: Eighty translucent zirconia specimens (7x3 mm) were divided into two different sintering groups (1480 0C for 180 min; 1510 0C for 30 min), then divided into four subgroups according to surface treatments: control, sandblasted, Er-YAG, and Nd-YAG (n:10). One specimen from each group was analyzed with XRD and one from each subgroup was analyzed with SEM. Ceramics (5x3 mm) were fired onto the zirconia for shear bond strength test using universal testing machine and the failure mode was determined by using stereomicroscope. Translucency and contrast ratio were measured by using spectrophotometer, and biaxial flexural strength test performed by employing universal testing machine on specimens with a diameter (15x1,3 mm) from each sintering group (n:10). Data was analyzed by using two-way ANOVA and Bonferroni Post hoc tests (P<.05).Results: The short sintering group showed higher biaxial flexural strength (943.87±48.69 MPa). The highest surface roughness values were obtained in short sintering groups and within the groups Nd-YAG application was found the most effective method (4.11±0.28 Ra). The highest bond strength value was obtained in sandblasted short time sintered group (29.71±2.52 MPa). The translucency and contrast ratio showed no significant difference. Conclusion: Although a physically stronger zirconia is obtained by short sintering process, long-term sintered zirconia forms a more durable bond strength with ceramics. Sandblasting improve the ceramic-zirconia bond strength may have more benefits than the use of Er-YAG, and Nd-YAG lasers.

Processing and properties of Bi0.98R0.02FeO3 (R = La, Sm, Y) ceramics flash sintered at ~650°C in <5 s

AbstractWe show that flash sintering produces single‐phase, nanograin‐sized polycrystals of isovalent‐substituted multiferroic ceramics of complex compositions. Single‐phase polycrystals of Bi0.98R0.02FeO3 (R = La, Sm, Y) were produced at a furnace temperature of ~650°C in a few seconds by the application of an electric field of 50 V cm−1, with the current limit set to 40 mA mm−2. The dielectric and insulating properties compared favorably with expected values. Impedance spectroscopy suggests electrically homogenous microstructure, except for the sample Bi0.98La0.02FeO3 that shows a small grain boundary contribution to the impedance. These results reinforce the enabling nature of flash sintering for ceramics which pose difficulties in conventional sintering because they contain low melting constituents or develop secondary phases during the sintering protocol.

The influence of altering sintering protocols on the optical and mechanical properties of zirconia: A review.

As a result of advancements in chairside technology and speed sintering techniques and increased esthetic demands of patients, efforts have been made to produce monolithic zirconia restorations that are highly translucent, strong, and dense. While methods for processing zirconia are well known, there is a tendency to modify the process parameters with the aim of decreasing the overall processing time and, in particular, the sintering time. This review provides clinicians with scientific evidence of the effects of altering sintering parameters used for dental zirconia on its microstructure, phase transformation, and mechanical and optical properties. A systematic search of Embase and Medline using Boolean operators was performed to locate relevant articles. Eleven articles were selected for this review. The following characteristics of monolithic zirconia have been confirmed to be affected by alterations in sintering: the microstructure, mechanical properties, optical properties, wear behavior, and low thermal degradation. The alteration of sintering parameters has been found to alter the grain size, wear behavior, and translucency of zirconia. There is a lack of clinical studies that investigate the influence of altering sintering parameters or methods on the clinical performance of monolithic zirconia restorations. Alteration of sintering parameters alters the microstructural, mechanical, and optical properties of zirconia. This will consequently impact the clinical performance of zirconia prostheses. Future clinical investigations are encouraged to support these in vitro findings.

Impact of high-speed sintering on translucency, phase content, grain sizes, and flexural strength of 3Y-TZP and 4Y-TZP zirconia materials

Statement of problemThe lengthy sintering time of zirconia is costly and limits applications. The consequences of shortening the sintering time are mainly unknown. PurposeThe purpose of this in vitro study was to test and compare 2 high-speed sintering protocols and 1 conventional sintering protocol on the translucency, phase content, grain sizes, and flexural strength of 3 zirconia materials. Material and methodsIn total, 450 specimens of 3 zirconia materials—two were 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZPs), Ceramill ZI and Zolid (ZD), and a 4 mol% yttria-stabilized tetragonal zirconia polycrystal (4Y-TZP), Zolid HT+ (n=150)—and 5 thicknesses (1.0, 1.5, 2.0, 2.5, and 3.0 mm; n=30) were sintered according to 2 high-speed sintering protocols (final temperature 1570 °C and 1590 °C; n=10) and a reference sintering protocol (1450 °C; n=10). After measuring the monoclinic phase content with Raman spectrometry (n=3), the specimens were polished, and translucency was determined. The biaxial flexural strength of specimens with a thickness of 1.0 mm and 1.5 mm was tested (n=20). Statistical evaluation included 1-way ANOVA, the Kolmogorov-Smirnov, Kruskal-Wallis, Mann-Whitney-U, and Spearman-Rho tests and the Bonferroni correction (α=.0011). ResultsFor ZI, the sintering protocols did not affect the translucency or biaxial flexural strength. ZD and HT+ showed significantly lower translucency for high-speed sintering protocols (P≤.001), but the biaxial flexural strength remained the same after the high-speed sintering protocol at 1590 °C. Grain sizes increased with increasing final sintering temperature for ZI and HT+, whereas translucency generally decreased with increasing material thickness. No monoclinic phase was detected in any group. ConclusionsThe flexural strength was maintained with high-speed sintering but led to a decrease in translucency for ZD and HT+.

Impact of speed sintering on marginal discrepancy, internal fit and microleakage of monolithic zirconia crowns with different chamfer width

Purpose: The current in-vitro investigation analyzed the impact of speed sintering and different finish line width on marginal adaptation, internal fit and microleakage of translucent monolithic zirconia crowns.Materials and Methods: Sixty maxillary premolars were reduced based on basic guidelines of tooth preparation for a zirconia crown with either 0.5, 0.8 and 1.2 mm chamfer width (n=20each finish line width). After digital scanning and milling of zirconia crowns, the sintering procedure was performed in special furnace for two different sintering programs (n =10 per group) following either standard or speed sintering procedure. Each crown was cemented to its corresponding prepared tooth utilizing self-adhesive-resin cement. After 15000 thermal cycles between 5°C and 55°C, specimens were submersed in methylene blue for 12 hours. After sectioning bucco-lingually, marginal gap and cement film thickness values were recorded at nine sites using a digital microscope followed by microleakage scores examination.Results: Tested groups with 0.5 mm chamfer widths had the greatest mean marginal gap values of 47.9±5.4 and 50.1±5.6 µm for both conventional and speed sintering respectively, while groups with 1.2 chamfer widths had the lowest mean gap values of 42.3±5.6 and 44.5±5 µm for both standard and speed sintering, respectively. Two-way ANOVA revealed statically insignificant impact of sintering procedure on crown adaptation (p=.08). The greatest mean microleakage score (3±088 µm) was obtained from the 0.5 mm chamfer width group, while the smallest (2±0.78 µm) score was obtained from the 1.2 mm chamfer width group. Conclusions: Marginal adaptation and internal fit of translucent monolithic zirconia crowns are affected by width of the preparation margin while sintering protocol has little impact on adaptation.

Effects of Speed Sintering on Multilayered Monolithic Zirconia

Objective:In dentistry, different products are being developed in order to shorten the chairside but the interactions between these materials needs further investigations. This study aims to investigate the two different short time sintering protocols on monolithic multilayered zirconia’s surface roughness (SR), translucency parameter (TP), and contrast ratio (CR). Material and Methods:Twenty monolithic multilayer zirconia specimens were prepared with the dimension 10x10x1 mm and divided into two sintering groups (speed sintering group 30 min at 1510 0C, high speed sintering group 10 min 1580 0C) and SEM analyzed were performed. Surface roughness tests were performed by using profilometer and optical measurements were performed by using spectrophotometer. The data was statistically analyzed by using Wilcoxen test at the 0.05 probability level.Results:SR values and CR did not show any significant difference at any layer of any group. In all parts of monolithic multilayered zirconia, the difference of TP between sintering groups were statistically significant (P<.05). Conclusion: High speed sintering parameters has promising effects on monolithic multilayered zirconia with combined acceptable optical properties. Because of their different content, different layers show different reactions in terms of contrast ratio and translucency parameters and these changes should be taken into account in treatment planning.

Marginal Discrepancies of Monolithic Zirconia Crowns: The Influence of Preparation Designs and Sintering Techniques.

The marginal fit is an essential component for the clinical success of prosthodontic restorations. The aim of this study was to investigate the influence of different abutment finish line widths and crown thicknesses on the marginal fit of zirconia crowns fabricated using either standard or fast sintering protocols. Six titanium abutments were fabricated for receiving zirconia molar crowns. Crowns were designed virtually and milled from partially sintered zirconia blanks and divided into 12 groups (n = 10/group). Crowns in groups 1 to 6 were sintered by standard sintering, while those in groups 7 to 12 were sintered by fast sintering. Groups were further categorized according to abutment finish line and crown thickness: G1/G7 (0.5 mm chamfer, 0.8 mm thick); G2/G8 (0.5 mm chamfer, 1.5 mm thick); G3/G9 (1.0 mm chamfer, 0.8 mm thick); G4/10 (1.0 mm chamfer, 1.5 mm thick); G5/G11 (1.2 mm chamfer, 0.8 mm thick); G6/G12 (1.2 mm chamfer, 1.5 mm thick). The marginal gaps were assessed at 8 locations using digital microscopy. The linear mixed effect model analysis was performed at a significance level of 0.05. All vertical marginal gaps were within the clinically acceptable range (∼11-52 μm). G8 (FS, 0.5 mm chamfer, 1.5 mm thick) demonstrated the largest gaps (47.95 μm, 95% CI: 44.57-51.23), whereas G3 (SS, 1.0 mm chamfer, 0.8 thick) had the smallest marginal gap (14.43 μm, 95% CI: 11.15-17.71). A linear mixed effect models showed significant differences for the interaction between finish line × crown thickness × sintering (F = 18.96, p < 0.001). The lingual surfaces showed the largest gaps in both sintering protocols, while the mesial and mesiobuccal surfaces demonstrated the smallest gaps. There was a significant interaction between finish line widths, crown thickness, and sintering protocol on the marginal gaps in both sintering protocols; 1.0 mm finish line preparations with either 0.8 mm or 1.5 mm occlusal reduction had better marginal fit in both sintering protocols compared to 0.5 mm or 1.2 mm finish lines. Smaller marginal discrepancies were observed for standard sintering crowns with a 0.5 mm finish line and 1.5 mm occlusal reduction. Conservative occlusal reduction should be accompanied with a 1.2 mm finish line to obtain better marginal fit for full-contoured zirconia crowns.

İki Farklı Hızlı Sinterleme Protokolünün ve İki Farklı Yüzey İşleminin Çok-Katmanlı Monolitik Zirkonyanın Işık Geçirgenliği Üzerine Etkisi

İki Farklı Hızlı Sinterleme Protokolünün ve İki Farklı Yüzey İşleminin Çok-Katmanlı Monolitik Zirkonyanın Işık Geçirgenliği Üzerine Etkisi

Chemical sintering reduced grain boundary defects for stable planar perovskite solar cells

Organic–inorganic hybrid perovskite solar cells have attracted tremendous attention in photovoltaic research, but the presence of massive parasitic traps at the grain boundaries in perovskite films discourages efficient bimolecular recombination and carrier dynamics, which limits device performance and stability. Here we report a simple and fast chemical sintering protocol to substantially reduce grain boundary defects for as-formed films for different PbI2-templated perovskite materials. With this method parasitic traps on grain boundaries are intrinsically reduced, featuring the Urbach energy reduced by 1.5 meV. For optimal photovoltaic devices, we demonstrate a planar solar cell with power conversion efficiency (PCE) of 19.68% which retains 80% of this efficiency over 720 h in ambient air without any encapsulation. These findings offer a widely applicable, versatile process to efficiently reduce grain boundary defects and will be of interest to many other film material systems afflicted by polydispersity and grain boundary disturbances.

Rapid sintering protocol produces dense ceria‐based ceramics

AbstractWe report on a rapid sintering protocol, which optimizes the preparation of 0‐29 mol% Gd‐doped ceria ceramics with density ≥98% of the theoretical crystal lattice value. The starting material is a nanometer grain‐sized powder prepared by carbonate co‐precipitation and calcined with minimal agglomeration and loss of surface area. Slow (5°C/min) heating of the green‐body from 500°C to the optimum temperature of rapid sintering (, dwell time &lt;1 minute) followed by 20°C/min cooling to 1150°C with 6 minutes dwell time, produces maximum pellet density. increases from 1300 to ~1500°C with increase in Gd‐content, while the average grain size in the maximally dense pellets, as determined by scanning electron microscopy, ranges between 600 nm and ~1 μm. For each doping level, the logarithm of the average grain size decreases linearly with 1/T1. By avoiding extended exposure to sintering temperatures, this protocol is expected to minimize undesirable Gd segregation.

Surface roughness and volumetric contraction of a Y-TZP ceramic sintered by microwave energy and by resistive heating

Objective: The aim of this study was to evaluate a Y-TZP ceramic sintered by a microwave protocol on volume shrinkage and surface roughness. Material and Methods: Twenty four (N=24) Y-TZP discs were fabricated by milling in CAD/CAM for size standardization. The mean final dimensions of the specimens were 15 mm X 1.6 mm. Samples were divided into 2 groups (n=12): conventional resistive heating sintering protocol (C - Control) and microwave sintering protocol (MO - experimental). For the characterization of the specimens, surface roughness (Ra and Rz parameters) was evaluated with a roughness tester, and volume shrinkage was measured with a hand micrometer. Data were statistically evaluated by Student’s t and Mann-Whitney U tests (?=0.05). Results: The roughness results were: 0.25 ?m ± 0.02 (Ra) and 2.68 ?m ± 0.666 (Rz) for the MO samples; 0.26 ?m ± 0.04 (Ra) and 2.73 ?m ± 0.461 (Rz) for the C group (Ra: p = 0.19; Rz: p = 0.81). The shrinkage results was: MO (21.02% ± 2.70) and C (20.10% ± 0.52) (p = 0.274). Conclusion: The conventional and microwave sintering methods were similar regarding surface roughness and volume shrinkage of Y-TZP dental ceramic.KeywordsBioceramics; Microwave sintering; Roughness surface; Zirconia.

A new approach for fabrication of titanium-titanium boride periodic composite via additive manufacturing and pressure-less sintering

Abstract This study proposes a new additive manufacturing (AM) based methodology to fabricate periodic metal matrix composite architectures, with a focus on titanium (Ti)-titanium boride whisker (TiBw) composites. The manufacturing method includes binder jetting AM of the titanium matrix reinforced periodically by the extrusion of a custom-developed highly loaded resin, containing titanium di-boride (TiB2) particles. A low-temperature pressure-less sintering method was then applied to increase the mechanical strength of green samples produced from the additive manufacturing step. The sintering process also fosters the chemical reaction between the matrix and ceramic, resulting in the growth of titanium boride whisker (TiBw). The ceramic volume fraction and sintering protocol were studied as two main input variables in the design and fabrication steps. Investigating the influence of input parameters on the volume fraction and morphology (whisker formation) of TiB determined that the physical properties of the specimens, such as stiffness, were affected. The data analysis suggested a higher possibility for the formation and growth of TiBw as the temperature elevated in the sintering step (1400 °C). The ranges of 1.6 ± 0.2 GPa–3.7 ± 0.4 GPa and 83.9 ± 18.7 MPa–165 ± 13.2 MPa for the Young's modulus and Yield stress of the specimens were obtained, respectively. The stiffness of the samples was enhanced significantly by increasing the temperature and volume fraction. In particular, those samples sintered up to 1400 °C displayed 6.4%–15.2% improvement in the stiffness, although only a small fraction of the ceramic material was incorporated into the design: 2% and 4%, respectively. The similar trend of the improvement in density of the porous matrix was observed (i.e., 4.5%–19%). The range of mechanical and structural properties of the periodic composite developed in this study demonstrated the relevance of applying this method to the fabrication of biomedical and other lightweight titanium composite structures.

Novel Zirconia Materials in Dentistry

Zirconias, the strongest of the dental ceramics, are increasingly being fabricated in monolithic form for a range of clinical applications. Y-TZP (yttria-stabilized tetragonal zirconia polycrystal) is the most widely used variant. However, current Y-TZP ceramics on the market lack the aesthetics of competitive glass-ceramics and are therefore somewhat restricted in the anterior region. This article reviews the progressive development of currently available and next-generation zirconias, representing a concerted drive toward greater translucency while preserving adequate strength and toughness. Limitations of efforts directed toward this end are examined, such as reducing the content of light-scattering alumina sintering aid or incorporating a component of optically isotropic cubic phase into the tetragonal structure. The latest fabrication routes based on refined starting powders and dopants, with innovative sintering protocols and associated surface treatments, are described. The need to understand the several, often complex, mechanisms of long-term failure in relation to routine laboratory test data is presented as a vital step in bridging the gaps among material scientist, dental manufacturer, and clinical provider.

Development and Testing of Impregnated La0.20Sr0.25Ca0.45TiO3 Anode Microstructures for Solid Oxide Fuel Cells

The Ni-based cermet SOFC anode material exhibits a number of undesirable properties. It is often redox unstable 1, Ni-particles agglomerate over time 1, ultimately reducing the catalytic activity of the anode and, in unprocessed natural gas feeds, this material exhibits severe coking intolerance 1 as well as sulphur poisoning 1. Therefore, there is a requirement to produce a novel anode material which can offer better durability under the aforementioned conditions. An ideal replacement material comprises a ‘backbone’ microstructure of the A-site deficient perovskite: La0.20Sr0.25Ca0.45TiO3 (LSCTA-), impregnated with an oxide ion conducting material and a metallic electrocatalyst. This ‘backbone’ material, impregnated with Ce0.8Gd0.2O1.9 (CGO) and Ni, has previously been employed as a SOFC anode material on an industrially relevant scale at HEXIS AG, with promising results 2. Current research focusses on optimisation of the LSCTA- ‘backbone’, to improve current distribution through the anode, and development of impregnated catalyst systems that provide enhanced durability and tolerance to natural gas feeds containing sulphur. Thick-film ceramic processing techniques, such as ink formulation, screen printing and control of sintering protocol, have been used as the primary method in controlling the anode microstructure. Rheological analysis of a variety of LSCTA- inks showed that a formulation with 75 wt. % solids loading possessed ideal (pseudoplastic) properties for screen printing. Extensive investigation of screen printing parameters and screen mesh counts, as well as sintering temperatures and dwell times, allowed determination of the optimal conditions required to produce a LSCTA- anode ‘backbone’ microstructure with an advantageous combination of porosity and grain connectivity. Screen printing of the 75 wt. % solids loading ink with a 230 mesh count (per inch) screen and sintering at 1350 °C for 2 hours facilitated production of the required anode microstructure, ensuring sufficient lateral electronic conductivity through the anode to prevent generation of localised temperature ‘hotspots’. Four-point DC conductivity analysis of several LSCTA- ‘backbone’ microstructures showed that ‘effective’ conductivities of up to 21 S cm-1 could be achieved (in 5% H2/Ar), with the highest values pertaining to the most advantageous microstructure. Electrolyte-supported fuel cells employing this ‘backbone’ microstructure, impregnated with 12-16 wt. % (of the ‘backbone’) of CGO and 2-5 wt. % of either Ni, Ru, Rh, Pt or Pd, showed very promising performances during short-term electrochemical testing in humidified hydrogen. Fuel cells with anodes containing Rh/CGO and Pd/CGO catalyst systems were particularly promising, achieving Area Specific Resistances (ASR) of 0.41 Ω cm2 and 0.39 Ω cm2 (figure 1), respectively.

Development and Testing of Impregnated La0.20Sr0.25Ca0.45TiO3 Anode Microstructures for Solid Oxide Fuel Cells

The A-site deficient perovskite: La0.20Sr0.25Ca0.45TiO3 (LSCTA-) is a mixed ionic and electronic conductor (MIEC) which shows promising performance as a Solid Oxide Fuel Cell (SOFC) anode ‘backbone’ material, when impregnated with metallic and oxide-ion conducting electrocatalysts. Here, we present data on the complete ceramic processing and optimisation of the LSCTA- ‘backbone’ microstructure, in order to improve current distribution throughout the anode. Through control of ink rheology, screen printing parameters and sintering protocol an advantageous LSCTA- microstructural architecture was developed, exhibiting an ‘effective’ conductivity of 21 S cm-1. Incorporation of this LSCTA- anode microstructure into SOFC and impregnation with Ce0.80Gd0.20O1.9 and either Ni, Ru, Rh, Pt or Pd resulted in promising initial performances during fuel cell testing in a fuel stream of 97% H2:3% H2O. Area Specific Resistances of 0.41 Ω cm2 and 0.39 Ω cm2 were achieved with anodes containing Rh/CGO and Pd/CGO, respectively.

Speed sintering translucent zirconia for chairside one-visit dental restorations: Optical, mechanical, and wear characteristics

The fabrication of zirconia dental restorations is a time-consuming process due to traditional slow sintering schemes; zirconia (Y-TZP) produced by these conventional routes are predominantly opaque. Novel speed sintering protocols have been developed to meet the demand for time and cost effective chairside CAD/CAM-produced restorations, as well as to control ceramic microstructures for better translucency. Although the speed sintering protocols have already been used to densify dental Y-TZP, the wear properties of these restorations remain elusive. Fast heating and cooling rates, as well as shorter sintering dwell times are known to affect the microstructure and properties of zirconia. Thus, we hypothesize that speed sintered zirconia dental restorations possess distinct wear and physical characteristics relative to their conventionally sintered counterparts. Glazed monolithic molar crowns of translucent Y-TZP (inCoris TZI, Sirona) were fabricated using three distinct sintering profiles: Super-speed (SS, 1580 °C, dwell time 10 min), Speed (S, 1510 °C, dwell time 25 min), and Long-term (LT, 1510 °C, dwell time 120 min). Microstructural, optical and wear properties were investigated. Crowns that were super-speed sintered possessed higher translucency. Areas of mild and severe wear were observed on the zirconia surface in all groups. Micropits in the wear crater were less frequent for the LT group. Groups S and SS exhibited more surface pits, which caused a scratched steatite surface that is associated with a greater volume loss. Tetragonal to monoclinic phase transformation, resulting from the sliding wear process, was present in all three groups. Although all test groups had withstood thermo-mechanical challenges, the presence of hairline cracks emanating from the occlusal wear facets and extending deep into the restoration indicates their susceptibility to fatigue sliding contact fracture.

구강스캐너와 급속 지르코니아 소결을 이용한 당일 풀지르코니아 보철수복

당일수복 보철물 제작을 위해 디지털 프로세스 사용은 필수적이다. 이러한 디지털 프로세스는 구강스캔, 컴퓨터를 이용한 보철물을 디자인 과정(CAD)과 보철물을 가공하는 과정(CAM)을 포함한다. 지르코니아의 굴곡강도는 900Mpa로 리튬디실리케이트의 400MPa보다 더 단단하지만, 리튬디실리케이트를 이용한 보철물 기공시간이 지르코니아와 비교하여 더 짧기에 당일수복 보철물 제작시 리튬디실리케이트 사용이 선호되었다. 하지만, TZI C 와 LUXEN Enamel 와 같은 새로운 소재의 지르코니아가 출시되고, 새로운 소결방식이 개발되어 지르코니아 기공시간을 단축시킬수 있게 되었고, 높은 투명도의 풀지르코니아 크라운을 짧은 시간 안에 제작할 수 있게 되었다. 이러한 발전은 당일 풀지르코니아 보철수복을 현실로 이끌고 있다. Single visit monolithic restoration can be proceed with digital workflow which consist of intraoral scanning, dental CAD(computer aided design) and restoration milling with CAM(Computer aided manufacturing). While zirconia has more than 900MPa of flexural strength compared with 400MPa for lithium disilicate, shortened fabricating time of lithium disilicate is considered to be a better choice for fabricating single visit full contour monolithic restoration. However, new zirconia materials which are TZI C(Dentsply Sirona) and LUXEN Enamel(Dental Max), new induction heating method of sintering furnace, and new sintering protocols for MoSi2 heating elements sintering furnace offer significantly reduction of full contour monolithic zirconia restoration fabrication time with greater translucency. These new developments lead single visit zirconia restoration in reality.

On the influence of sintering protocols and layer thickness on the physical and mechanical properties of additive manufactured titanium porous bio-structures

This article aims at a thorough study about the effects of sintering protocols and layer thickness on mechanical and physical properties of additive manufactured porous structures used in orthopedic applications. Stress shielding effects induced on the bone interfacial surfaces due to the fixation of the metallic implant must be minimized to prevent implant loosening resulting in inflammation and pain. To this end, controlling the mechanical and physical properties of the implant is crucial to address the abovementioned issue. This control can be enhanced by understanding the role of additive manufacturing parameters in anisotropic properties of titanium structures. In addition to the experimental tasks, a model was developed according to the microstructural arrangement of particles to predict the porosity of the produced structures. The results showed a good agreement between the developed model and the experimental results. Furthermore, with the variation of process parameters, titanium parts with a wide range of porosity (17–44%), Young’s modulus (0.77–11.46GPa), yield strength (27–383MPa), and shrinkage (∼2–11%) were produced. Finally, the achieved porosity, young’s modulus property and yield strength were comparable with the cortical bone properties.

Thermoelectric properties of Ca3Co4O9 ceramics prepared by an alternative pressure-less sintering/annealing method

Nearly dense polycrystalline samples of Ca3Co4O9 (CCO) thermoelectric misfit layer cobaltite were prepared by the mixed-oxide route and pressure-less sintering along a two-step sintering protocol. Samples were first sintered at high temperature (e.g. 1200 °C) to reach a high degree of densification coupled with complete CCO decomposition into CaO and CoO phases. Subsequent annealing at 900 °C within the stability range of Ca cobaltite leads to complete re-formation of CCO after 72 h. The samples prepared using this sintering/annealing route exhibit an increased conductivity compared to samples sintered conventionally at 920 °C. This leads to an enhanced power factor of 170 μW/(K2m) at 600 °C. The thermal conductivity of these samples is κ = 2.8 W/mK at 100 °C which is larger as compared to porous and anisotropic conventionally sintered samples. The figure of merit of samples sintered with the proposed sintering/annealing process is ZT = 0.06 at 600 °C. This process enables simple preparation of dense CCO ceramics as p-type component in thermoelectric generators.

Shape Forming of Ceramic Tubes for Electrochemical Reactors by Gel-Casting Method

Three-dimensional structures are required as electrodes to increase the space time yield of electrochemical reactors when the reactions take place at low current densities. However, a tubular arrangement is necessary in some cases even in the industrial practice. Tubular Electrochemical Reactors (TERs) consist of a dense co-ionic ceramic membrane and two porous electrodes [1,2]. Gel-casting is a promising method of producing tailor-made dimensions of electrolyte and/or electrode tubes for the needs of the above reactors. The basic principle of gel-casting concerns a combination of a solvent, a dispersant, organic monomers and low particle sized ceramic powders to form a high-solids-content, fluid slurry. The slurry is poured under conditions into a casting mold where by an initiator and a catalyst the organic monomers polymerize to form a 3-D polymer network of a solid gel in the shape of the mold. In particular, an aqueous solution of water soluble monomer acrylamide (AM) and cross-linker methylene–bis-acrylamide (MBAM) in appropriate ratio was prepared. Darvan C was used as dispersant and added to the AM and MBAM solution. Subsequently, the ceramic powder was added (i.e 50-80 wt%) and the system was mixed thoroughly to a stable slurry. Finally initiator and catalyst were added to the slurry, respectively ammonium persulfate (APS) and tetra methyl ethylene diamine (TEMED)/g of slurry. The casting slurry is poured into molds of various shapes to form within minutes a gelled green tubular body. Prior any further heating treatment the green bodies may subject to machining i.e cutting and drilling. All volatiles are removed by a heating treatment up to 6000C. Calcination at higher temperatures was applied in order to introduce mechanical strength to the shaped structures through controlled sintering [3]. The sintering temperature is totally depended on the composition of the ceramic powder. Major crucial factors in the overall success of the process are particle size distribution of the ceramic powder, drying conditions, slurry rheology, mold features and sintering parameters. In this study, ceramic powders of an oxygen ion conductor such as apatite-type lanthanum silicates (ATLS) and a proton conductor such as yttrium-doped barium zirconate (BZY) where prepared, optimized and used in gel-gasting methods. They are considered promising electrolytes for intermediate temperature (IT-SOFCs) solid oxide fuel cells. ATLS have attracted interest as promising electrolytes due to their thermodynamic stability, robustness (as ceramics) and their ability to maintain distorted crystal structure by doping but more important due to their high oxide ion conductivity at intermediate temperatures. Additionally they exhibit satisfactory refractoriness with high ionic but low electronic conductivity, low cost and good availability of raw materials [4,5]. On the other hand BZY proton conducting ceramics are regarded as promising electrolyte materials for low temperature proton conducting solid oxide fuel cells due to their higher ionic conductivities and lower activation energy as compared to conventional oxygen-ion conducting electrolytes [6-8]. The above materials were synthesized from various routes, providing thus singled-phased structures and a suitable particle sized distribution for their use in the shape-forming with gel-casting. Powders are verified by XRD, SEM and particle size laser distribution analysis. In addition, rheological measurements were performed at the slurries in order to evaluate the suitable viscosity for a successful shape-forming casting. Different sintering protocols were applied. The porosity of the produced tubes was evaluated by Archimedes method while the microstructure was studied by SEM.