Optimization of the spark plasma sintering conditions for the consolidation of hydroxyapatite powders and characterization of the obtained products

A comparative investigation regarding the consolidation behavior displayed by three commercially available hydroxyapatite powders during Spark Plasma Sintering (SPS) is performed in this work. Starting powders are different in terms of purity, particle size, morphology and thermochemical stability. A completely dense product without secondary species is produced by SPS at 900 °C, when starting from highly pure powders with relatively small sized particles and grains. The resulting consolidated material, consisting of sub-micrometer sized hydroxyapatite grains, exhibits optical transparency and good mechanical properties. On the other hand, temperature levels up to 1,200 °C are needed to sinter powders with larger particles. This holds also true when relatively finer powders are used, also containing CaHPO4, are used. In both the latter cases products with coarser microstructures and/or significant amount of β-TCP, as a result of hydroxyapatite decomposition, are obtained. Optical, chemical resistance and mechanical properties of the resulting dense materials are correspondingly deteriorated

Rheology of Conductive High Reactivity Carbonaceous Material (HRCM)-Based Ink Suspensions: Dependence on Concentration and Temperature

The present case study reports a shear rheological characterization in the temperature domain of inks and pastes loaded with conductive High Reactivity Carbonaceous Material (HRCM) consisting mainly of few-layers graphene sheets. The combined effect of filler concentration and applied shear rate is investigated in terms of the shear viscosity response as a function of testing temperature. The non-Newtonian features of shear flow ramps at constant temperature are reported to depend on both the HRCM load and the testing temperature. Moreover, temperature ramps at a constant shear rate reveal a different viscosity-temperature dependence from what is observed in shear flow ramps while maintaining the same filler concentration. An apparent departure from the well-known Vogel-Fulcher-Tamman relationship as a function of the applied shear rate is also reported

Validation of a tool for estimating the effects of Soft- Errors on modern SRAM-based FPGAs

Predicting soft errors on SRAM-based FPGAs without a wasteful time-consuming or a high-cost has always been a very difficult goal. Among the available methods, we proposed an updated version of analytical approach to predict Single Event Effects (SEEs) based on the analysis of the circuit the FPGA implements. In this paper, we provide an experimental validation of this approach, by comparing the results it provides with a fault injection campaign. We adopted our analytical method for computing the error-rate of a design implemented on SRAM-based FPGA. Furthermore, we compared the obtained soft-error figure with the one measured by fault injection. Experimental analysis demonstrated the analytical method closely match the effective soft-error rates becoming a viable solution for the soft-error estimation at early design phase

Validation of a tool for estimating the effects of Soft- Errors on modern SRAM-based FPGAs

Predicting soft errors on SRAM-based FPGAs without a wasteful time-consuming or a high-cost has always been a very difficult goal. Among the available methods, we proposed an updated version of analytical approach to predict Single Event Effects (SEEs) based on the analysis of the circuit the FPGA implements. In this paper, we provide an experimental validation of this approach, by comparing the results it provides with a fault injection campaign. We adopted our analytical method for computing the error-rate of a design implemented on SRAM-based FPGA. Furthermore, we compared the obtained soft-error figure with the one measured by fault injection. Experimental analysis demonstrated the analytical method closely match the effective soft-error rates becoming a viable solution for the soft-error estimation at early design phases

Hardening Dynamically Reconfigurable Processing Modules Architectures: A Neutron Test Experience

Desogus M, Sterpone L, Porrmann M, Hagemeyer J, Illstad J. Hardening Dynamically Reconfigurable Processing Modules Architectures: A Neutron Test Experience. In: RADECS proceedings. Vol 2. IEEE / Institute of Electrical and Electronics Engineers; 2013: 13-16.In this paper we describe the hardening of a Dynamically Reconfigurable Processing Module (DRPM) Systems implemented on modern SRAM-based FPGAs. We also report the neutron radiation testing campaigns when the system is implemented on Xilinx Virtex-4 and Virtex-5 SRAM-based FPGAs. Experimental results demonstrate the effectives of the proposed metho

In-vitro behavior of different fully dense calcium phosphate materials fabricated by Spark Plasma Sintering

Results obtained during in-vitro experiments concerning human osteoblasts cultivated on the surface of dense samples produced by Spark Plasma Sintering from three types of hydroxyapatite powders are described and discussed. The sintered products display diverse composition and microstructures which are found to significantly influence the biological response of the cells. Osteoblasts adhesion, viability and proliferation are quantitatively comparable for the three classes of bioceramics, whereas matrix mineralization occurs only in products exclusively consisting of hydroxyapatite. Correspondingly, a calcium-phosphate layer exhibiting a trabecular-like microstructure is deposited on the materials surface. Matrix mineralization is favored when the substrate is composed of submicrometer-sized apatite grains. On the other hand, the latter phenomena is markedly suppressed, and so does the formation of the new apatite phase, when cells are seeded on sintered disks composed of β-Tri-Calcium Phosphate, which was formed during the sintering process from the decomposition of initial apatite

On the fabrication of functional graded 3Y-PSZ/316L materials by SPS: Process optimization and characterization of the obtained products

Dense and crack free six-layered functional graded materials were successfully produced by Spark Plasma Sintering by combining 3 mol% Y2O3-partially stabilized ZrO2 (3Y-PSZ) and 316L stainless steel. All the sintered products consisted of a steel free layer on one side and a cermet composite containing 50 vol% of both constituents on the opposite side. Conversely, the stainless steel concentration in the interlayers was progressively changed following diverse spatial profiles. It was found that the temperature interval from 1080 to 1180 °C required for the full consolidation from the 50 vol% composite layer to the 3Y-PSZ one, respectively, can be reached when adopting a specific die configuration where the cross section was varied from 30 to 28 mm, respectively. Correspondingly, the densification level of each layer, as well as the related hardness and fracture toughness properties, were highly enhanced with respect to the standard cylindrical die. In addition, a significant improvement of the material toughness was obtained when the material concentration exponent was decreased from 2 to 1, whereas this effect tends to vanish when such parameter was further reduced to 0.5

Innovative hydroxyapatite/bioactive glass composites processed by spark plasma sintering for bone tissue repair

Hydroxyapatite-based composites (HA-C) with bioglass as second phase are usually produced by hot-pressing or pressureless sintering. However, such methods require thermal levels which exceed the crystallization temperature of the glass, with possible negative effects on the bioactivity of the final system. Spark plasma sintering (SPS) is a powerful consolidation technique in terms of both processing time and temperature. In this work SPS has been employed, for the first time, to obtain HA-C with an innovative bioglass as second phase. Such glass was designed to be used whenever a thermal treatment is required, thanks to its low tendency to crystallize. A systematic study is conducted to identify the optimal sintering conditions for preparing highly dense composites and, at the same time, to minimize the crystallization of the glassy phase. The obtained samples are highly bioactive and display higher compactness and hardness with respect to the counterparts produced by conventional sintering methods

Classical Bioglass®and innovative CaO-rich bioglass powders processed by Spark Plasma Sintering: a comparative study

Densification and crystallization phenomena taking place when a recently developed CaO-rich bioactive glass and conventional 45S5 Bioglass® are processed by Spark Plasma Sintering (SPS) are examined. Fully dense and wholly amorphous products can be obtained from the new glass composition at 730°C after 2min dwell time. Moreover, temperatures equal or higher than 830°C are needed to induce crystallization (α- and β-CaSiO3) in the parent glass. Conversely, Na6Ca3Si6O18 crystals are formed in sintered 45S5 samples produced under optimal conditions (550°C, 2min), although the glassy character is still preserved.Products resulting from the innovative glass powders generally display higher hardness and local elastic modulus. Devitrification also provides improvements in this system. In contrast, mechanical properties become slightly worsen when classical bioglass is processed at 600. °C. This can be probably associated to the corresponding decrease in compactness which, apparently, overcomes the benefits arising from the crystallization progress