Powder/die friction in the spark plasma sintering process: Modelling and experimental identification

The powder/die friction phenomenon is known to generate densification inhomogeneities in the spark plasma sintered sample. The measurement of a powder/solid friction coefficient at high temperature is very difficult if not impossible by classical means. Then, an experimental/simulation method of identification of the friction coefficient based on the sample displacement field is introduced. This reveals that the friction of contact type powder/wall is low and about 0.1 and the friction type powder/graphite-foil/wall is close to zero. The relative density inhomogeneities are limited to a maximum difference of 3%

Electro-thermal measurements and finite element method simulations of a spark plasma sintering device

Current, voltage and temperature measurements were performed at different points of the system to identify the controlling parameters of the spark plasma sintering (SPS) process. The very low inductance effects despite the high intensity current circulating through the SPS column justifies the use of Joule heating to characterize the phenomenon. The measurements also enabled the improvement and validation of an earlier electro-thermal numerical model developed using the finite element method (FEM). It has been shown that the electrical resistivity and the thermal conductivity of each of the elements are crucial parameters for the simulations. These parameters strongly modify the current modeled, thereby affecting the temperature distribution throughout the SPS column

Contact resistances in spark plasma sintering: From in-situ and ex-situ determinations to an extended model for the scale up of the process

tHeating in spark plasma sintering is a key point of this manufacturing process that requires advancedsimulation to predict the thermal gradients present during the process and adjust them. Electric andthermal contact resistances have a prominent role in these gradients. Their determination is difficult asthey vary with pressure and temperature. A calibration method is used to determine all of the contactresistances present within tools of different sizes. Ex situ measurements were also performed to validatethe results of the in-situ calibrations. An extended predictive and scalable contacts model was developedand reveals the great importance and diversity of the contact resistances responsible for the generalheating of the column and high thermal gradients between the parts. The ex/in situ comparison highlightsa high lateral thermal contact resistance and the presence of a possible phenomenon of electric currentfacilitation across the lateral interface for the high temperatures

Pulse analysis and electric contact measurements in spark plasma sintering

In order to model the current density distribution and the temperature changes of the tools used during a spark-plasma-sintering (SPS) cycle, the variation of the power delivered by an SPS machine and the graphite-Papyex®-graphite electrical contacts were studied experimentally. The electric device was also characterized; in particular current pulse characteristics and their behavior with time were studied in various conditions of temperature, pulses sequences, materials and total electric power dissipated. It is well known that the performance of an electric contact is dependent on the applied pressure and the temperature. First, by varying the pressure during the SPS cycle the effect of the electric contacts is clearly seen. Secondly, in order to determine the behavior of such contacts experimentally over a pressure range of 10–50 MPa and temperatures of 50–800 °C, a Dœhlert experimental design was used

Spark-plasma-sintering and finite element method: From the identification of the sintering parameters of a submicronic α-alumina powder to the development of complex shapes

In the present paper, we studied the sintering of a submicronic a-alumina powder and modeled its behavior using Olevsky's model. We further introduced a method for the identification of the creep parameters based on SPS experiments that greatly simplify parameter determination. Subsequently, we used the set of parameters obtained to study the densification of a part with a complex shape.We clearly showed that the thickness shrinkage with different heights engender densification inhomogeneities

Finite-element modeling of the electro-thermal contacts in the spark plasma sintering process

Spark plasma sintering (SPS) is a breakthrough process for powder consolidation assisted by pulsed cur-rent and uniaxial pressure. In order to model the temperature variations of the tools during a SPS cycle,the Graphite-Papyex-Graphite contact phenomena are studied experimentally and modeled by finite ele-ment calculations. Compared to conducting materials, the thermo graphic image of an insulating sample(alumina) shows strongly localized heating along the Papyex implying contact effects are predominant.The aim of this modeling study is to determine the main contact phenomena due to Papyex. It is basedon numerous experimental data and studies the case of alumina sintering. Finally the contact model isconfronted to experimental thermal images

Dog-bone copper specimens prepared by one-step spark plasma sintering

Copper dog-bone specimens are prepared by one-step spark plasma sintering (SPS). For the same SPS cycle, the influence of the nature of the die (graphite or WC–Co) on the microstructure, microhardness, and tensile strength is investigated. All samples exhibit a high Vickers microhardness and high ultimate tensile strength. A numerical electro-thermal model is developed, based on experimental data inputs such as simultaneous temperature and electrical measurements at several key locations in the SPS stack, to evaluate the temperature and current distributions for both dies. Microstructural characterizations show that samples prepared using the WC–Co die exhibit a larger grain size, pointing out that it reached a higher temperature during the SPS cycle. This is confirmed by numerical simulations demonstrating that with the WC–Co die, the experimental sample temperature at the beginning of the dwell is higher than the experimental control temperature measured at the outer surface of the die. This difference is mostly ascribed to a high vertical thermal contact resistance and a higher current density flowing through the WC–Co punch/die interface. Indeed, simulations show that current density is maximal just outside the copper sample when using the WC–Co die, whereas by contrast, with the graphite die, current density tends to flow through the copper sample. These results are guidelines for the direct, one-step, preparation of complex-shaped samples by SPS which avoids waste and minimizes machinin

EFSA Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF); Scientific Opinion on Flavouring Group Evaluation 96 (FGE.96): Consideration of 88 flavouring substances considered by EFSA for which EU production volumes / anticipated production volumes have been submitted on request by DG SANCO. Addendum to FGE. 51, 52, 53, 54, 56, 58, 61, 62, 63, 64, 68, 69, 70, 71, 73, 76, 77, 79, 80, 83, 84, 85 and 87

Overgrowth disorders are a heterogeneous group of conditions characterized by increased growth parameters and other variable clinical features such as intellectual disability and facial dysmorphism1. To identify new causes of human overgrowth, we performed exome sequencing in ten proband-parent trios and detected two de novo DNMT3A mutations. We identified 11 additional de novo mutations by sequencing DNMT3A in a further 142 individuals with overgrowth. The mutations alter residues in functional DNMT3A domains, and protein modeling suggests that they interfere with domain-domain interactions and histone binding. Similar mutations were not present in 1,000 UK population controls (13/152 cases versus 0/1,000 controls; P < 0.0001). Mutation carriers had a distinctive facial appearance, intellectual disability and greater height. DNMT3A encodes a DNA methyltransferase essential for establishing methylation during embryogenesis and is commonly somatically mutated in acute myeloid leukemia2, 3, 4. Thus, DNMT3A joins an emerging group of epigenetic DNA- and histone-modifying genes associated with both developmental growth disorders and hematological malignancie