Engineering Commons^™

Role Of Defects In Electric–Field–Assisted Sintering, Stephen Hellberg

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

We examine the roles that charged defects play in electric-field-assisted sintering using first principles density functional theory. We consider individual point defects and defect complexes, such as Frenkel pairs and Schottky defects. For each defect, the formation energy is calculated as a function of the temperature and applied electric field to estimate its density under experimental conditions. The effects of the defects on the observed densification are then modeled. Optical transitions of the defects are computed to allow for spectroscopic identification. The modification of the lattice constants due to the defects is presented for comparison with diffraction measurements

Field And Thermal Factors In Field–Assisted Consolidation Of Powder Materials, Eugene Olevsky

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Possible thermal and field factors, which may influence densification during spark-plasma sintering (SPS), are considered. Two experimental setups revealing the role of both groups of factors for SPS processing of conductive and semi-conductive materials are described.

To de-convolute the influence of the electrical current, spark plasma sinter-forging experiments are conducted to compare the constitutive behavior of a copper powder under current-insulated and current-assisted SPS process conditions. The processing mode with specimen’s free lateral surface enables the direct in-situ measurement of the powder material temperature. The experimental results are interpreted in the framework of the developed constitutive model of the spark-plasma …

Flash Sintering Of Complex Oxides, Luis Perez-Maqueda

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

BiFeO₃ is one of the most promising multiferroic (materials combining two or more ferroic properties in the same phase) materials. Preparation of high quality BiFeO₃ ceramics is quite challenging. The temperature required for processing is relatively high and partial decomposition takes place damaging the properties of the material. Moreover, the Curie temperature of BiFeO₃ is within the same temperature range required for conventional sintering. The volume change during Curie transition produces damage in the obtained pellets.

In this work high density ceramics of BiFeO3 have been obtained from nanostructured powders, prepared by direct mechanochemistry, followed by FLASH …

Estimating Ionic Conductivity During Flash Sintering Of 8ysz, Daniel Marinha

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

We provide evidence for temperature-driven flash sintering process, accounting for otherwise interpreted as abnormal behavior. Using 8%-Yttria-doped Zirconia as reference material, we selected moderate flash conditions to avoid external current-limiting control. Samples were dry-pressed and pre-sintered to relative densities between 50 and 85 %TD by interrupting sintering at pre-determined shrinkage values, in conventional and flash sintering processes. SEM characterization shows similar trends for average grain size, porosity levels and distribution between flash and conventional samples. Bulk and grain boundary conductivity and characteristic frequencies, measured by impedance spectroscopy, show similar behavior regardless of the processing route.

A third series of samples …

Final Program, Kathy Chan

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

No abstract provided.

Effect Of Electric Field/Current On Liquid Phase Sintering, Jesus Gonzalez-Julian, Olivier Guillon

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Sintering behavior of ionic and electric conductor ceramics is enhanced when an external electric field is applied during the sintering process by Joule heating, generation of Frenkel defects, mobility of point defects, electrochemical reactions and electromigration mechanisms. The applied electric field modifies the sintering behavior in two ways, depending mainly on the strength of the field (V/cm) and the electrical properties of the sample. Intermediate fields enhance the sintering kinetics apparently due to the retardation of grain growth, which is called field assisted sintering. In contrast, high fields generate massive densification just in few seconds, which is recently referenced as …

First Stage In Flash Sintering Of Zirconia Based Ceramics, Marlu Cesar Steil, Emmanuelle Bichaud, Claude Carry, Jean Marc Chaix

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Flash sintering ability to densify ceramic material in less than 5 seconds, at much lower furnace temperatures than conventional sintering has been reported and studied for a large set of conductive ceramics and recently of composite ceramic materials. Since no die is used, the current mandatorily flows through the sample and the flash process is characterized by an abrupt increase in the sample conductivity accompanied by shrinkage and densification. In the literature two types of experiments are reported, referring to the furnace temperature: Constant heating rate (CHR) and isothermal experiments. The flash sintering elementary mechanisms are not yet fully understood. …

Effect Of (External) Electric Fields On Heterogeneous Solid State Reactions – Special Role Of Grain Boundary Diffusion, Carsten Korte

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

During ope­ra­tion ceramic materials are of­ten ex­posed to high elec­tri­cal fields, which create a se­cond dri­ving force for mobile com­po­nents in ad­di­tion to the chemical po­ten­tial gra­dient. Due to the ongoing miniaturisation in modern appli­ca­tions, interfaces gain in importance for the materials pro­per­ties. So­lid state reac­tions, neg­li­gi­ble on ma­cro­scopic length sca­les, be­come more im­portant on the nanoscale and thus be­come a frequent source of materials degra­da­tion

In this contribution the influence of an electric field on the kinetics and the morphological evo­lution of (hetero­ge­ne­ous) solid state model reactions will be highlighted [1-4]. Experiments on the reac­tion couples MgO + In …

Electric Field–Induced Electronic Conduction In Bulk Oxide Ceramics, Anthony West

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Field-induced electronic conduction is widely recognised in (a) materials whose resistance is dominated by interfacial Schottky barriers and (b) thin films that exhibit high field-induced filamentary conduction. A third category of (low) field-sensitive conduction occurs in bulk oxide ceramics that show enhanced hole conduction if they are acceptor-doped, but reduced n-type conduction if they are donor-doped. Examples in these two categories are acceptor-doped titanate perovskites [1] and rutile that is slightly oxygen-deficient [2]. More recently, reversible, field-induced electronic conduction has been demonstrated in yttria-doped zirconia ceramics [3] and a reversible, insulator-metal transition in Ca-doped BiFeO3 ceramics [4].

A survey of …

Oxygen Vacancy Formation Due To Dc Electric Fields During Flash Sintering In Batio3, Takashida Yamamoto

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

A unique sintering technique called FLASH sintering has been developed by Raj’s research group¹⁾. When green compacts are heated under DC electric fields beyond threshold strength, specimen current abruptly increases at a critical temperature, and then densification is immediately completed at very short time. The sintering temperature and time largely decrease with the increasing DC electric fields. Cologna et al. successfully obtained fully densified YSZ at 850°C for 5s at 120V/cm without any outer pressure. After their reports, flash sintering has been applied for various kinds of ceramic materials such as Y₂O₃, Al …

The Modification Of The Temperature Gradient In A Large Sample Sintered By Sps, Mirva Eriksson

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The SPS is a sintering unit where heating and the uniaxial pressure is applied to a powder placed in a die. The best pressure and temperature distribution in the sample is achieved when the sample has the shape of a round pellet. In some cases it would be beneficial to be able to sinter square or rectangular plates. The processing of a large square/rectangular plate is a challenging task because the shape will increase the temperature gradient in the horizontal direction in the plate resulting to uneven properties in corners compared to the middle. In this study we present results …

Spark And Plasma Aided Densification Mechanisms During Spark Plasma Sintering Of Ceramic Powders, Rachman Chaim

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Spark plasma sintering (SPS) currently used for rapid and full densification of ceramic particles assisted by a pulsed dc current passed through the powder compact. Our investigations with different ceramic powders (LiF, NiO, and YAG) as model systems discovered local melting of the particle and nano-particle surfaces, confirming the formation of spark and plasma during the SPS. However, spark and plasma form at certain material and process conditions. The ceramic yield stress and its electrical conductivity, and their temperature dependence mainly determine the conditions at which spark and plasma will take place in a given non-conducting granular compact. We introduce …

Electrical Conduction Mechanism At High Voltages And Dielectric Breakdown Strength In Bulk Ceramic Insulators, Gerold Schneider, Claudia Neusel

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Electrical conductivity at high electric fields and dielectric breakdown of bulk ceramic insulators is not well understood. In order to gain more insight we performed current-voltage measurements on different ceramics to identify whether ohmic, space charge limited, Schottky, or Poole-Frenkel conduction, is the dominating conduction mechanism. Voltages up to 70 kV were applied and revealed that space charge limited conduction (SCLC) prevails at high electric fields in all investigated ceramics. As SCLC is a size dependent phenomenon the transition from ohmic to SCLC was determined as a function of the thickness of the disc-shaped samples. As a consequence electric field …

Flash Sintering Of Covalent Non–Oxide Ceramics At Low Temperatures With Low Dc Electric Fields: An In Situ Edxrd Study By Synchrotron Probe, Thomas Tsakalajos

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

The fundamental purpose in Functional Ceramics Technology is to obtain 100% dense polycrystalline covalent nonoxide ceramics with grain size / micro B₄C powder at low temperature <1000 >^oC so as to obtain a properly sintered ceramics. Also as to obtain a fully with small grain size. The applied electric field helps to reduce the sintering temperature by at least a factor 0.33. The time frames involved are measured in minutes/seconds and not in tens of hours/days. We will focus on the B4C system. However, other nonoxide ceramics nanocomposites such as ZrB₂, TiB₂, Si_{3 …}

Highly Transparent Spinel Windows By Microwave Sintering, Jasbinder Sanghera

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Transparent magnesium aluminate spinel (MgAl₂O₄) ceramic possesses excellent mechanical and optical properties enabling its potential use in many applications, especially those in harsh environments. We have previously demonstrated fabrication of transparent spinel ceramic with very low absorption loss (6ppm/cm) at 1 mm using the hot pressing method. However, microwave sintering offers several potential advantages over conventional densification methods such as uniform heating, shorter sintering time, finer microstructure of the ceramics, and scalability to large sizes. Previous attempts to microwave sinter spinel powder resulted in only opaque or translucent ceramics. In this talk, we report the fabrication …

Spark Plasma Sintering Of A Functionally Graded Material Consisting Of A High– Alloyed Crmnni–Steel And Varying Mg–Psz Content, Sabine Decker, Lutz Kruger

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

A functionally graded material (FGM) consisting of a TRIP steel matrix (TRansformation Induced Plasticity) and a varying Mg-PSZ particle reinforcement (MgO Partially Stabilized Zirconia) was sintered by Spark Plasma Sintering (SPS). The used steel is high-alloyed (16 wt.% Cr, 7 wt.% Mn, 3 wt.% Ni) and the Mg-PSZ content decreases along the sample height from 100 vol.% to 0 vol.%. Hence, the bottom of the sample consists of a pure ceramic layer. Due to the different melting temperatures and therefore different optimal sintering temperatures of steel and Mg-PSZ, it is challenging …

Influence Of An Electric Field On Grain Growth And Sintering In Strontium Titanate, Wolfgang Rheinheimer, Fabian Lemke, Michael Hoffman

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Within the last five years considerable efforts were done in investigating electric field assisted sintering (flash sintering). However the experiments are hard to control: shrinkage occurs within seconds and the local temperature is undefined due to joule heating. Therefore the present study removes these two parameters by investigating grain growth under electric field in the no-current-case for strontium titanate.

The impact of an electric field on grain growth in strontium titanate is investigated between 1350°C and 1550°C for fields of up to 50V/mm. To prevent joule heating by a current flowing through the material insulating Al2O3 plates separate the electrodes …

The Influence Of Fields And Dopants On Grain Boundary Mobility, Wayne Kaplan, Amir Gabay

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

During field assisted sintering, exposure to an electric field often results in faster sintering rates compared to conventional sintering methods. This research focuses on the influence of electromagnetic fields on grain growth. As a model system, SiC was sintered using conventional pressureless sintering at 2100°C. Samples then underwent conventional annealing, and annealing using spark plasma sintering (SPS) without pressure, at identical and at lower temperatures, and the grain size as a function of annealing time was characterized.

From these experiments, the grain boundary mobility of SiC at 2100°C under conventional heating versus SPS was determined. SPS annealing resulted in a …

Field–Assisted And Flash Sintering Of Nanocrystalline Yttria: Densification And Microstructural Evolution, Hidehiro Yoshida

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Y₂O₃ ceramics have special chemical and physical properties such as high resistance to halogen-plasma corrosion and thermal stability. At the same time they are difficult to sinter. Conventional sintering requires very high temperatures typically >1400°C, and a vacuum or hydrogen atmosphere. We show that high-purity, undoped Y₂O₃ can be sintered nearly instantaneously to almost full density by flash-sintering, where densification occurs in a few seconds under a threshold condition of temperature and applied field [1]. The Y₂O₃ shows flash-sintering at the fields above 300 V/cm. For instance, full densification is achieved …

Flash Sintering Of Zno, Tio2 And Other Oxides: The Origin Of Onset Flash And Effects Of Atmosphere, Doping And Particle Size, Jian Luo

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

Flash sintering of ZnO, TiO₂ and a few other oxide systems has been investigated. A quantitative model has been developed to forecast the thermal runaway conditions (Fig. 1) [1]. The predicted thermal runaway temperatures from the measured conductivities are in excellent agreements with the observed onset flash temperatures for at least 15 cases with different base materials, doping and surface treatments, particle sizes, and sintering atmospheres, attesting that the “flash” starts as a thermal runaway.

Furthermore, a range of new phenomena of electric field/current effects on sintering and microstructural evolution have been observed and explained, which include: …

Flash Microwave Sintering Of Oxide Ceramics, Kirill Rybakov

Electric Field Assisted Sintering and Related Phenomena Far From Equilibrium

We report the results of flash microwave sintering of various oxide ceramics to full density in a time less than several minutes. Ultra-rapid microwave sintering has been observed on Al₂O₃, Y₂O₃, MgAl₂O₄, and (Yb_0.05La_0.1Y_0.85)₂O₃ samples compacted from nanosized and submicron powders.

The samples were heated in the applicator of a gyrotron system for microwave processing of materials with a maximum microwave power of up to 6 kW at a frequency of 24 GHz with a feedback computer control over …

Conference Program (Gpe 2016), Franco Berruti, Cedric Briens

5th International Congress on Green Process Engineering (GPE 2016)

No abstract provided.

Augmented Finite Element Method For Virtual Testing Of High Temperature Cmcs, Qingda Yang, Jaedal Jung, Bao-Chan Do

Composites at Lake Louise (CALL 2015)

Ceramic matrix composites (CMCs) have been increasingly used in high heat flux applications due to their ultra-high temperature resisting capabilities. However, CMCs are prone to processing-induced or in-serve cracking due to the large thermal stresses. Thermally-induced cracking are dangerous because they provide pathways for further damaging processes such as oxidation and vapor-assisted corrosion, which may lead to catastrophic failure [1]. High-fidelity thermal-mechanical analyses to CMCs with consideration of arbitrary cracking are very challenging because the heterogeneous nature makes it impossible to know the cracking locations a priori. Yet correct and efficient treatment of crack coalescence and bifurcation is critical …

Novel Anti-Decay Self-Setting Paste Of Hydroxyapatite/Collagen Nanocomposite Utilizing Gptms, Masanori Kikuchi, Taira Sato, Mamoru Aizawa, Yuki Shirosaki

Composites at Lake Louise (CALL 2015)

Bone is a typical inorganic/ortganic nanocomposite mainly composed of hydroxyapatite (HAp) nanocrystals and collagen molecules. The composition and nanostructure is closely related to bone’s biomechanical and biochemical properties. One of the most important things for bone is a bone remodeling process that maintains mechanical strength of bone to allow walking and running as well as homeostasis of calcium in our body. In fact, sintered HAp composed of HAp crystals approximately 1 µm in particle size is considered as non-bioresorbable; however HAp nanocrystals easily resorbed by osteoclasts. A hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) was successfully synthesized by the authors via self-organizing process. …

Physical Aging And Glass Transition Of Single Component Nanocomposites, Hilmar Koerner

Composites at Lake Louise (CALL 2015)

Matrix free assemblies of polymer-grafted, “hairy” nanoparticles (HNP) exhibit novel morphology, dielectric and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer-inorganic blended nanocomposites. Physical aging of the amorphous polymer glass between the close-packed nanoparticles (NPs) will dominate long-term stability. However, the energetics of cooperative relaxation of tethered chains confined within the interstitial spaces in single component nanocomposites is unknown. Herein, we compare glass transition temperature (Tg) and physical aging behavior of matrix free assemblies of HNPs (aHNPs) to conventional NP-polymer blends, across different nano-silica loadings (0-50 v/v%) and brush architecture of grafted polystyrene …

Printed And Structurally Integrated Electronics For Air Force Applications, Daniel Berrigan, Benjamin Leever, Michael Durstock

Composites at Lake Louise (CALL 2015)

Both printed and flexible electronic systems promise to integrate functional devices into new form factors (e.g., structures or clothing) and environments. Of particular interest are the mechanically harsh environmental conditions to which military systems are sometimes exposed, which can be quite severe (i.e., upward of 100,000 G peak acceleration within 0.1 ms), and commercial off-the-shelf components are not designed to maintain functionality under such rugged conditions. The overarching aim of this project is to leverage the unique ability of additive manufacturing to digitally control materials properties in three dimensions to create multifunctional systems whose structure is ruggedized for mechanically these …

Ice Formation In Iron Containing Hydrogel Films, Hyun-Joong Chung

Composites at Lake Louise (CALL 2015)

The states of water in polymers, including ice formation, is of increasing interest for a broad range of science and engineering, including the application and the longevity of water-bourne polymeric coatings, cryogenic preservation of cells and organs, ice mediated porous structure formation, freeze-drying process in food preservation, low temperature operation of batteries and supercapacitors, and the tailing pond sedimentation in oil sands production. The freezing point of water is heavily influenced by the polymer-water interaction and the concentration of ionic species in the water and in the polymer backbones. Various species of salt ions are abundant in the operating conditions …

Simultaneously Strong And Tough Continuous Nanofibers For Next Generation Structural Supernanocomposites, Yuris Dzenis

Composites at Lake Louise (CALL 2015)

Modern advanced composites and fibers are strong but brittle. Optimization of damage progression in composites has led only to moderate toughening. The advent of novel nanomaterials such as CNT and graphene has raised hopes for the development of strong and tough structural materials. However, problems with dispersion, alignment, achieving high volume fraction of discontinuous nanoreinforcement, and interfacial stress transfer proved to be more difficult than was initially thought. Recently, a different class of nanomaterials, i.e. continuous nanofibers, has been shown to possess unusual mechanical properties. This presentation will review recent breakthroughs on ultra-high-performance continuous nanofibers and their composites. Controlled nanofiber …

Biopolymer Composites From High-Cellulose Pulps And/Or Nanocellulose, Fabiola Vilaseca

Composites at Lake Louise (CALL 2015)

Increasingly our society seeks an economy based on renewable resources (bio-based economy) with the goal of providing materials of high value and from renewable resources. One popular renewable resource is cellulose, or forest products in general. In this study, cellulose derivatives will be combined together with bio-plastics to produce granules of thermoplastic nano-biocomposites by melt processing. The intention is to get bio-based materials with highly advanced properties that can be shaped into complex geometries using widely used industrial melt-processes such as extrusion or injection molding.

The challenges in this study deal with production technologies for the realization of nanocomposites for …

Chemical Heterogeneity In Electroceramics: The Good, The Bad, And The Difficult To Characterize, Michaela Kuzara, Narit Triamnak, Harlan Brown-Shaklee, David Cann, Geoff Brennecka

Composites at Lake Louise (CALL 2015)

As characterization techniques continue to advance, the materials community is reminded again and again that our samples are not as perfect as we generally describe them to be. This presentation will focus on Bi(Zn_0.5Ti_0.5)O₃–BaTiO₃-based ceramics in which subtle mesoscale cation gradients have been identified as a key factor in the phenomenal temperature- and field-stable permittivity of these unusual dielectrics as well as their remarkably high resistivity values and associated activation energies.[1,2] Earlier work has shown that the single perovskite phase that results after calcination of mixed oxides and carbonates is formed through …