SPS Experiments Research Articles

Toughening, reinforcement and repair mechanisms of TiSi2 in Al2O3/TiN/TiSi2 ceramics

The short sintering time of discharge plasma sintering (SPS) can effectively improve the research efficiency. Through the self-repair phenomenon, ceramic materials can repair surface cracks and improve their reliability. In this study, self-repairing ceramic materials—Al2O3/TiN and Al2O3/TiN/TiSi2—are prepared through SPS and surface crack-repair experiments are performed under different heat-treatment conditions to determine the optimum sintering parameters and analyse the surface crack repair effects. The effects of TiSi2 on the toughening, strengthening, and repair mechanisms of Al2O3/TiN ceramics are analysed. The results show that the bending strength and fracture toughness increase by 25.20 and 4.42 %, respectively, with the addition of TiSi2. The increase in the bending strength is due to the decrease in the sintering temperature and grain refinement. The fracture toughness increases because the addition of TiSi2 increases the crack deflection and bridging. TiSi2 forms an oxide layer on the ceramic surface, which prevents the contact between oxygen and cracks, thereby reducing the porosity of the repaired surface of the Al2O3/TiN ceramic material.

Role of microstructure reactivity and surface diffusion in explaining flash (ultra-rapid) sintering kinetics

The competition between sintering and coarsening is cited by numerous authors as one of the potential factors for explaining the ultra-rapid sintering kinetics of flash sintering. In particular, surface diffusion is a mechanism decreasing the driving force of sintering by changing the initial highly reactive microstructures (particle contact) into poorly reactive porous skeleton structures (spherical porosity). We show by finite element simulations that flash SPS experiments high specimen temperatures close to 2000 °C. These high temperatures are not sufficient to explain the ultra-rapid sintering kinetics if typical spherical pore theoretical moduli are employed. On the contrary, reactive experimentally determined moduli succeed in explaining the ultra-rapid sintering kinetics. Mesoscale simulations evidenced that the origin of such reactive experimental moduli is a porous skeleton geometry with a significant delay in surface diffusion and particle rearrangement. This highlights the important role of the surface diffusion negation (favoring higher stress intensification factor) in flash sintering.

Ta-LLZO Garnet Processed By Spark Plasma Sintering for All Solid State Batteries

All Solid State Lithium based Batteries (ASSLB) using a stable inorganic solid state electrolyte are envisaged as the most promising answer to solve the safety issues of Li-ion batteries using inflammable organic liquid electrolyte. Garnet Li7La3Zr2O7 showing high ionic conductivity and high stability versus metallic lithium is currently the most appealing solid electrolyte to be used in oxide based ASSLB. However, its high reactivity with moisture and sensitivity to all energetic process lead to strong difficulties in obtaining stable fully dense pellets while mandatory to ensure its role as mechanical barrier to avoid the short-circuit caused by Li-dendrites [1-2]. In this work, Spark Plasma Sintering is used as both a characterization and a fast sintering techniques to determine the influence of side products and efficiency of applied processes to remove them in reaching dense pellets with high ionic conductivity.Commercial Ta-doped LLZO powder is fully characterized using conventional techniques to identify chemical and thermal stability. SPS experiments are conducted to determine the influence of the side products on the sintering. The efficiency of powder pretreatment designed to remove side products is determined based on data collected during SPS experiments. SPS parameters (applied pressure, temperature ramping, densification dwell ...) are then optimized allowing reaching in a reproducible way pellets with high density (>97 %) and high mechanical strength. Analysis using XPS, SEM and XRD of obtained pellets shows that decomposition occurs only at the surface while the core of the pellet is made of pure cubic phase Ta-doped LLZO. Impedance spectroscopy is used to evidence the influence of side products on the electrical properties and confirms high ionic conductivity (0.5 mS/cm) and very low electronic conductivity of optimized electrolyte. The sintering temperature and dwell time are then optimized by advanced sintering techniques (high pressure, Flash SPS) allowing to prevent the chemical instability usually observed between LLZO and active materials (LiCoO2 or Li[Ni1-x-yCoxMny]O2 (NCM)) and to obtain a cathodic half-cell (LLZO/positive electrode) in one step. References : [1] H. Yamada, T. Ito, R. Basappa, Electrochimica Acta 222 (2016) 648–656.[2] M. Kotobuki, M.Koishi, Journal of Alloys and Compounds 826 (2020) 15421.

Rapidity distribution within Landau hydrodynamical model and EPOS event-generator at AGS, SPS, and RHIC energies

The rapidity distribution of well-identified particles such as pions, kaons, protons and their antiparticles measured in AGS, SPS, and BRAHMS experiments (Au+Au collisions), at various energies spanning from higher energies = 200 down to lower energies 2 GeV, are compared with that obtained from huge statistical ensembles of 100, 000 events generated from the Cosmic Ray Monte Carlo (CRMC) EPOS event-generator. All these data are then compared to the results calculated in the frame work of Landau hydrodynamical model. The EPOS event-generator can describe the experimental data of the rapidity distribution for all mentioned particles at all considered energies. This leads to use the EPOS event-generator to produce the rapidity distribution for various particles at energies where there are no experimental data yet to compare with. Such a prediction might serve as an input for future experiments such as FAIR and NICA for instance. A successful comparison between the Landau hydrodynamical approach and the computational CRMC EPOS 1.99 model in describing the rapidity distribution for the mentioned particles is shown in the presence of the experimental data. We conclude that the Landau hydrodynamical model is capable of describing both experimental data and EPOS 1.99 event-generator results, and they are in a good agreement.

Strange hadron correlations in heavy-ion collisions at RHIC energies and below

Geometry and dynamics of the particle-emitting source in heavy-ion collisions can be inferred via the femtoscopy method. Two-particle correlations at small relative momentum exploit Quantum Statistics and the Final State Interactions (Coulomb and strong), which allow one to study the space-time characteristics of the source of the order of 10−15 m and 10−23 s. Femtoscopic measurements allow one also to study FSI, especially the strong one, which is unknown for many two-particle systems. The RHIC program covers a significant part of the QCD phase diagram using collisions of Au nuclei for several beam energies from 7.7 to 200 GeV for which baryon-rich region is studied via femtoscopy. These measurements complement those obtained from AGS, SPS, and SIS experiments. Strange hadron measurements together with nonstrange ones provide complementary information about source characteristics. Strangeness is a significant observable for many regimes of collision energies providing a complete view of strangeness production in heavy-ion collisions. These proceedings shows the femtoscopic measurements of various strange particle combinations at different collision energies and centralities of the collision.

Nuclear Modification of Excited Quarkonia States from SPS to LHC Energies

The study of quarkonia spectroscopy in the presence of hadronic or deconfined medium is a powerful procedure to study density and temperature of different kinds of nuclear matter. Most of the efforts are made with the ground states \(J/\psi \) and \(\Upsilon \)(1S), but excited state quarkonia offers a rich spectrum of binding energies and particle sizes for nuclear medium studies. This report summarizes measurements of several quarkonium excited states in the last three decades by Fermilab, SPS, HERA, RHIC and LHC experiments along with the current understanding on how nuclear medium affects their yields.

Thermal-electrical-mechanical simulation of the nickel densification by Spark Plasma Sintering. Comparison with experiments

Spark Plasma Sintering is a non-conventional process of the powder metallurgy field which uses a high electrical current to rapidly produce fully dense materials. In the present paper, a thermal-electrical-mechanical model developed on ABAQUS Software is proposed to simulate the densification of a nickel disk. A compaction model, studied in [Wolff, C., Mercier, S., Couque, H., Molinari, A., 2012. Modeling of conventional hot compaction and spark plasma sintering based on modified micromechanical models of porous materials. Mechanics of Materials 49 (0), 72–91. URL http://www.sciencedirect.com/science/article/pii/S0167663611002195], has been used to reproduce the densification of the sample. Two SPS experiments have been necessary to identify the parameters of the densification law. In order to evaluate the robustness of the present model, two other SPS experiments have been performed. The whole results of the simulation show a good agreement with the experimental data confirming the validity of the compaction model developed in [Wolff, C., Mercier, S., Couque, H., Molinari, A., 2012. Modeling of conventional hot compaction and spark plasma sintering based on modified micromechanical models of porous materials. Mechanics of Materials 49 (0), 72–91. URL http://www.sciencedirect.com/science/article/pii/S0167663611002195].

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 α-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.

Centrality and system-size dependencies of temperatures of soft and hard components ofptdistributions of negative pions inHe4+C12,C12+C12, andC12+Ta181collisions atsNN=3.14GeV

Collision centrality as well as the system-size dependencies of the temperatures of the soft (${p}_{t}=0.1\ensuremath{-}0.5\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$) and hard (${p}_{t}=0.5\ensuremath{-}1.2\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$) components of the experimental transverse momentum distributions of the negative pions produced in $^{4}\mathrm{He}{+}^{12}\mathrm{C}, ^{12}\mathrm{C}{+}^{12}\mathrm{C}$, and $^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ collisions at $4.2A\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$ ($\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$) are analyzed. For the studied collision systems and selected collision centralities, the temperatures are extracted from fitting separately the soft and hard ${p}_{t}$ components of the negative pions by one-temperature Hagedorn and one-temperature Boltzmann functions. The extracted temperatures of both the soft and hard components of the ${p}_{t}$ distributions of ${\ensuremath{\pi}}^{\ensuremath{-}}$ depend on the geometry (size) and degree of overlap of the colliding nuclei in peripheral, semicentral, and central nucleus--nucleus collisions at $\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. The gap (differences) between the extracted temperatures in the studied collision systems increases with increasing the degree of overlap of the colliding nuclei, i.e., with an increase in the collision centrality and the corresponding increase in the numbers of participant nucleons and binary collisions. The temperature of the soft ${p}_{t}$ component of the negative pions in $^{12}\mathrm{C}{+}^{12}\mathrm{C}$ ($^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$) collisions increases (decreases) with increasing of the collision centrality. The temperature of the hard ${p}_{t}$ component of ${\ensuremath{\pi}}^{\ensuremath{-}}$ in $^{12}\mathrm{C}{+}^{181}\mathrm{Ta}$ ($^{4}\mathrm{He}{+}^{12}\mathrm{C}$) collisions increases (decreases) consistently with an increase in the collision centrality. The temperature of the soft ${p}_{t}$ component of ${\ensuremath{\pi}}^{\ensuremath{-}}$ decreases with an increase in the system size in semicentral and central nucleus--nucleus collisions at $\sqrt{{s}_{NN}}=3.14\phantom{\rule{0.16em}{0ex}}\mathrm{GeV}$. In central collisions, the temperature of the hard ${p}_{t}$ component increases consistently with an increase in system size. The physical interpretations of the results obtained are given. The quantitative results on temperatures extracted from the ${p}_{t}$ spectra of negative pions in nucleus--nucleus collisions at $4.2A\phantom{\rule{4.pt}{0ex}}\text{GeV}/c$ are compared to those obtained in lower, intermediate, and higher energies in other Joint Institute for Nuclear Research (JINR), Gesellschaft f\"ur Schwerionenforschung (GSI), and SPS experiments.

On influences of the jet production to charged particles multiplicity distribution in pp-collisions at Tevatron energies

Effect of the jet production on the multiplicity distribution (MD) of secondary charged particles produced in pp-collisions at 1.8 TeV is studied using the HIJING code. The charged particles MDs for a whole polar angle range and for six polar angular regions as a function of different number of jets were analyzed. The obtained simulation results were compared with experimental MDs coming from the Tevatron and SPS experiments. The increasing behavior of multiplicity of the secondary charged particles influenced by multi-jet events is discussed.

Color screening scenario for quarkonia suppression in a quasiparticle model compared with data obtained from experiments at the CERN SPS, BNL RHIC, and CERN LHC

We present a modified colour screening model for $J/\psi$ suppression in the Quark-Gluon Plasma (QGP) using quasi-particle model (QPM) as equation of state (EOS). Other theoretical ingredients incorporated in the model are feed-down from higher resonances namely, $\chi_c$, and $\psi^{'}$, dilated formation time for quarkonia and viscous effects of the QGP medium. Assuming further that the QGP is expanding with Bjorken's hydrodynamical expansion, the present model is used to analyze the centrality dependence of the $J/\psi$ suppression in mid-rapidity region and compare it with the data obtained from SPS, RHIC and LHC experiments. We find that the centrality dependence of the data for the survival probability at all energies is well reproduced by our model. We further compare our model predictions with the results obtained from the bag model EOS for QGP which has usually been used earlier in all such calculations.

Control of FeAl Composition Produced by SPS Reactive Sintering from Mechanically Activated Powder Mixture

The effects of mechanically activated powder mixture (Fe + Al) on the microstructure and the chemical composition of FeAl compound produced by reactive sintering implying an exothermic reaction were studied. Firstly, the characteristics of Fe/Al mechanically activated powder mixtures were investigated in terms of their phase composition and microstructure. The high‐energy milling allowed the formation of micrometric agglomerates composed of nanometric crystallites of iron and aluminum. Three aggregate sizes class A: ϕ < 125 µm, class B: 125 µm≤ϕ < 250 µm, and class C: ϕ ≥ 250 µm were considered. The latter class enhanced the reactivity of powder mixtures due to an increase of interfaces in contact as an analogy to nanostructured multilayer systems. Interrupted SPS experiments were performed on these mixtures to understand the origin of chemical heterogeneities observed after the reactive sintering. Formation of the intermediate phase Fe2Al5 at ~510°C was accompanied by an exothermic reaction and a linear expansion and followed by the formation of small amount of FeAl. The conversion to FeAl was complete at temperatures higher than the melting point of Fe2Al5 (1170°C). Finally, a phase evolution between Fe and Al versus the temperature during the reactive sintering is suggested.

Highlights of the beam energy scan from STAR

Abstract The first part of the beam energy scan (BES) program at RHIC was successfully completed in the years 2010 and 2011. First STAR results from particle yield measurements are in good agreement with previously published data from SPS and AGS experiments whereas other results like azimuthal HBT and K/π event-by-event fluctuations differ at some energies. In addition, new observations like the centrality dependence of chemical freeze-out parameters (T ch and µB) or the smoothly increasing difference with decreasing energy in the elliptic flow v 2 between particles and corresponding anti-particles, are discussed.

Quarkonia and QGP studies

We summarize results of recent studies of heavy quarkonia correlators and spectral functions at finite temperatures from lattice QCD and systematic T-matrix studies using QCD motivated finite-temperature potentials. We argue that heavy quarkonia dissociation shall occur in the temperature range $1.2 \le T_d/T_c \le 1.5$ by the interplay of both screening and absorption in the strongly correlated plasma medium. We discuss these effects on the quantum mechanical evolution of quarkonia states within a time-dependent harmonic oscillator model with complex oscillator strength and compare the results with data for $R_{\rm AA}/R_{\rm AA}^{\rm CNM}$ from RHIC and SPS experiments. We speculate whether the suppression pattern of the rather precise NA60 data from In-In collisions may be related to the recently discovered X(3872) state. Theoretical support for this hypothesis comes from the cluster expansion of the plasma Hamiltonian for heavy quarkonia in a strongly correlated medium.

Charmonium in strongly coupled quark-gluon plasma

The growing consensus that a strongly coupled quark-gluon plasma (sQGP) has been observed at the SPS and RHIC experiments suggests a different framework for examining heavy-quark dynamics. We present both a semianalytical treatment of Fokker-Planck (FP) evolution in pedagogical examples and numerical Langevin simulations of evolving cc pairs on top of a hydrodynamically expanding fireball. In this way, we may conclude that the survival probability of bound charmonia states is greater than previously estimated, as the spatial equilibration of pairs proceeds through a 'slowly dissolving lump' stage related to the pair interaction.

Effects of Initial Punch-Die Clearance in Spark Plasma Sintering Process

In recent years the number of publication on SPS has grown exponentially although the process itself is still not completely understood. The SPS process is governed by a complex bulk and contact multiphysics. The contact resistance between SPS system elements is crucial to understand the overall current and temperature distribution. This work is undertaken in order to improve our fundamental understanding on the contact resistance behaviour in the SPS system. The effect of the initial punch-die clearance is experimentally investigated for the first time during SPS heating. The results are given in terms of temperature-time and voltage-time profiles for various clearance values. It is shown that the initial punch-die clearance is a key SPS parameter to be specified when different SPS experiments or apparatus features have to be compared and offers another means to control the temperature gradient along the radius.

New results from NA60 and other SPS experiments

NA60 has been the last heavy ion experiment running at the SPS. It has performed measurements on dimuon production with an indium beam at 158 AGeV/c and with a proton beam at 158 and 400 GeV/c, focusing on (i) the study of the ρ spectral function in nuclear collisions, (ii) the unambiguous determination of the open charm yield and the quantitative assessment of the production of thermal radiation in the intermediate mass region, and (iii) the study of the J/ψ suppression in a collision system other than Pb–Pb. This paper provides an overview of the latest results. In addition, several other SPS experiments are still producing physics results. Interesting highlights from WA98, NA45 and NA49 on (i) nuclear modification factors of neutral and charged pions, (ii) three particle correlations at high transverse momentum and (iii) net baryon distributions will be addressed at the end of the paper.

Recent results on heavy-ion physics from the SPS

The CERN SPS heavy-ion physics program was recently given an important and fresh impetus with the running of the NA60 dimuon experiment, which probed indium-indium collisions at 158 GeV per incident nucleon (in 2003), as well as proton-nucleus collisions at 158 and 400 GeV (essentially in 2004). Several interesting physics results have been obtained and were recently presented by NA60. They address such varied physics topics as the search for in-medium modifications on the ρ short-lived vector meson (which could be related to the restoration of chiral symmetry, spontaneously broken in the hadronic world), the understanding of the “anomalous” J/ψ suppression (expected to be a signature of quark-gluon deconfinement), the search for thermal dimuons (presumably radiated from a thermal system, maybe composed of deconfined quarks and gluons — the “quark-gluon plasma”), the understanding of the enhancement of θ production in heavy-ion collisions, etc. These topics were previously studied by other SPS experiments, and very interesting observations were made, but serious doubts remained concerning the interpretation of those earlier results. It is remarkable that one single experiment, NA60, is able to provide high-quality information on each of these many topics, potentially triggering a very significant step forward in our understanding of “quark-matter physics”.

Strange and charged particle elliptic flow in Pb+Au collisions at 158 AGeV/c

We present Λ and π elliptic flow measurements from Pb+Au collisions at the highest SPS energy. The data, collected by the CERES experiment which covers η = 2.05 , 2.70 with full azimuthal coverage and wide p T sensitivity up to 3.5 GeV/c, can be used to test hydrodynamical models and show sensitivity to the EoS. The value of v 2 as a function of centrality and p T is presented. Values of v 2 observed by STAR at RHIC are larger by about 1/3. Our measurements are compared to results from other SPS experiments and to hydrodynamical calculations. Huge statistics allows for a precise measurement of the differential pion elliptic flow.

Dimuon and charm production in In+In collisions at the CERN SPS

The NA60 experiment studies muon pair production with proton and Indium beams. It is a second generation experiment, designed to answer specific questions left open, in the leptonic sector, by the previous round of SPS experiments, finished in 2000. The results presented in this paper cover the dimuon invariant mass range from the threshold to the J/ ψ . The main physics topics that we address include the in-medium modifications of the ρ meson, the origin of the dimuon excess observed between the ϕ and the J/ ψ , and the study of the anomalous J/ ψ suppression. For each of these subjects, the NA60 results represent a significant step forward towards a deeper understanding of the physics of heavy ion collisions at SPS energies.