Shrinkage Rate Curves Research Articles

Shrinkage Behavior, Thermal Expansion Behavior, and Electrical Conductivity Study of Samarium Doped Ceria Electrolytes

Ceria-based electrolytes generally have high sintering temperatures (~1500 °C)1,2, which increases the cell fabrication cost and decreases the mechanical stability of the cell due to rapid grain growth. In this work, the Ce0.9Sm0.1O2 (SDC) electrolyte is synthesized by microwave-assisted co-precipitation method using ethanol as a solvent. The sintering behavior of the green compact is studied using a dilatometer. Linear shrinkage and shrinkage rate behavior study shows a low sintering end temperature (1200 °C) and a final relative density of ~92%. A maximum linear shrinkage of -15.70% is observed at 1200 °C. A uni-modal shrinkage rate curve is seen, which confirms uni-modal pore size distribution in the powder. After 1388 °C, a dedensification is observed (+ 0.29% linear shrinkage), which might be associated with the reduction of Ce4+ to Ce3+ (please see Figure 1). Initial sintering results suggest that the synthesis method used has significantly lowered the SDC electrolyte's sintering temperature. Although the densification is completed at 1200 °C, the microstructure may change with further increase in the sintering temperature, affecting electrical conductivity. Inspired by the initial results, a detailed study on the effect of sintering temperature (1200 °C to 1500 °C) on the microstructure and electrical conductivity of SDC will be carried out and presented in the paper. S. Medisetti et al., Nano-Structures & Nano-Objects, 11, 7–12 (2017) https://www.sciencedirect.com/science/article/pii/S2352507X16301275.G. Accardo et al., J. Appl. Biomater. Funct. Mater., 14, 35–41 (2016) https://journals.sagepub.com/doi/abs/10.5301/jabfm.5000265. Figure 1

Dynamic tensile process of blended fabric using finite element method

PurposeTensile property is one basic mechanics performance of the fabric. In general, not only the tensile values of the fabric are needed, but also the dynamic changing process under the tension is also needed. However, the dynamic tensile process cannot be included in the common testing methods by using the instruments after fabric weaving.Design/methodology/approachBy choosing the weft yarn and warp yarn in the fabric as the minimum modeling unit, 1:1 finite element model of the whole woven fabrics was built by using AutoCAD software according to the measured geometric parameters of the fabrics and mechanical parameters of yarns. Then, the fabric dynamic tensile process was simulated by using the ANSYS software. The stress–strain curve along the warp direction and shrinkage rate curve along the weft direction of the fabrics were simulated. Meanwhile, simulation results were verified by comparing to the testing results.FindingsIt is shown that there are four stages during the fabric tensile fracture process along the warp direction under the tension. The first stage is fabric elastic deformation. The second stage is fabric yield deformation, and the change rate of stress begins to slow down. The third stage is fiber breaking, and the change of stress fluctuates since the breaking time of the fibers is different. The fourth stage is fabric breaking.Originality/valueIn this paper, the dynamic tensile process of blended woven fabrics was studied by using finite element method. Although there are differences between the simulation results and experimental testing results, the overall tendency of simulation results is the same as the experimental testing results.

Effect of MnO addition on microstructures and properties of BaO-Al2O3-B2O3-SiO2 glass-ceramics for LTCC application

MnO addition had a remarkable effect on the microstructure, mechanical and electrical properties of BaO-Al2O3-B2O3-SiO2 glass-ceramics. The crystallizing behavior was investigated by the whole pattern fitting method. The sintering kinetics was also studied based on the shrinkage rate curves. The result showed that 1 wt% MnO addition effectively promoted crystallization and densification. It was found that the high crystallinity as well as the large grain size contributed to the strong bending strength and Young’s modulus. For the sample doped with 1 wt% MnO, bending strength and Young’s modulus increased significantly from 136.3 MPa to 201.2 MPa and 59.7 GPa to 79.7 GPa, respectively.

Sintering behavior of UO2[sbnd]Er2O3 mixed fuel

The incorporation of burnable neutron absorbers into nuclear fuel pellets is important regarding reactivity compensation, which enables longer fuel cycles. The dry mechanical blending route is the most attractive process to accomplish absorbers incorporation because of its simplicity. By using this route, the present work has investigated the sintering behavior of UO2Er2O3 mixed fuel. A comparison with UO2Gd2O3 sintering behavior was presented. The behavior of UO2Er2O3 fuel sintering was similar to that reported for UO2Gd2O3 fuel, e.g. two-stage sintering with two peaks in the shrinkage rate curves. The effect showed to be less pronounced for Er2O3. This was attributed to the characteristics of the Er2O3 powder particles used as raw-material, whose agglomerates can be more easily broken and thus better homogenized during the blending with UO2 powder. These results confirmed that sinterability depends directly on the quality of the homogenization of the powders, as seen previously. A second phase was experimentally detected in the UO2Er2O3 system, but its impact on the sintering behavior of this mixed fuel has not yet been clarified.

Morphological Evolution of a Single Char Particle with a Low Ash Fusion Temperature during the Whole Gasification Process

Morphological evolution of single char particle with low ash fusion temperature (Tf ) was investigated during the whole gasification process using high temperature stage microscope. The experimental results showed that the shrinkage ratio of char particles above the Tf (1300 °C) was higher than that below the deformation temperature (1000 °C) finally. The TEM and SEM analysis results showed that the ash was a dispersed distribution in coal char. Dispersed molten slag aggregated to molten slag layer during the gasification process at the temperature above Tf, which evidently hindered the diffusion of gasifying agent. Therefore, there was a critical shrinkage ratio during the gasification process when the temperature above the Tf, and the critical shrinkage ratio of XLT char particles was 0.7-0.8. The SEM-EDS analysis results indicated that the critical points in the shrinkage rate curve were related to the molten slag on char surface. And the reaction mechanism was analyzed, the calculating critical thickn...

Investigation of the sintering mechanisms of GDC pellets obtained by the compaction of nanostructured oxide microspheres

AbstractThe sintering behavior of green pellets obtained from nanostructured Ce0.8Gd0.2O1.9 submillimetric microspheres is studied in the present paper. Corresponding shrinkage rate curve shows a two‐step densification in dynamic conditions, with the presence of two successive extrema, at 1200 K and 1500 K. To fully understand this non‐common densification behavior, an iterative study was performed. Multiple characterizations point out multiscale organization of the matter with temperature giving rise to differential sintering stages of two different particle size classes. Concerning 1200 K‐first shrinkage rate maximum, it corresponds to the densification of nanometric aggregates of crystallites into submicrometric pre‐sintered aggregates, resulting in a specific porous microstructure with residual open porosity. As‐generated porosity combined with submicron size of pre‐sintered aggregates thus prevent from a homogeneous sintering illustrated by a single maximum shrinkage rate. Finally, the second maximum shrinkage rate at 1500 K can then be associated to optimal temperature for submicrometric particles sintering.

Effect of Li3BO3 Additive on Densification and Ion Conductivity of Garnet-Type Li7La3Zr2O12 Solid Electrolytes of All-Solid-State Lithium-Ion Batteries

In this study, we investigate the effect of the Li₃BO₃ additive on the densification and ionic conductivity of garnet-type Li 7 -La₃Zr₂O 12 solid electrolytes for all-solid-state lithium batteries. We analyze their densification behavior with the addition of Li₃-BO₃ in the range of 2-10 wt.% by dilatometer measurements and isothermal sintering. Dilatometry analysis reveals that the sintering of Li 7 La₃Zr₂O 12 -Li₃BO₃ composites is characterized by two stages, resulting in two peaks, which show a significant dependence on the Li₃BO₃ additive content, in the shrinkage rate curves. Sintered density and total ion conductivity of the system increases with increasing Li₃BO₃ content. After sintering at 1100℃ for 8 h, the Li 7 La₃Zr₂O 12 -8 wt.% Li₃BO₃ composite shows a total ionic conductivity of 1.61 × 10 −5 Scm −1 , while that of the pure Li 7 La₃Zr₂O 12 is only 5.98 × 10 −6 Scm −1 .

Shrinkage kinetics of large-sized briquettes during pyrolysis and its application in tamped coal cakes from large-scale chambers

Aiming at the general problem that both for the production of foundry coke made by anthracite pulverized coal and furnace coke made by tamped coke in the coke oven, namely the shrinkage problem for large-size briquette and tamped coke in the pyrolysis process, a mass and volume integrated measuring device was used to study the shrinkage process of large-sized briquettes (volume equals 103cm3) under constant temperature (450°C, 550°C, 650°C and 850°C). The briquette shrinkage kinetic model was also established according to the regulation of mass loss and volume shrinkage, where the volume shrink calculation method of tamped coal cakes (13,280mm×500mm×4300mm) was also obtained. Three conclusions were drawn in this study: 1. In the process of the carbonization, the dehydration and degassing reaction before 450°C as well as polycondensation reaction at 650°C were the main reason causing the briquette shrinkage, the decomposition reaction at 550°C came second, while the hydrogen evolution reaction after 850°C has the least effect on briquette volume shrinkage. There were three main reasons causing the shrinkage of large-size briquette: the decrease of coal volume caused by the volatilization of moisture and volatiles, the decrease of coal volume caused by the pyrolysis reaction and the density increase of briquette caused by the decrease of coal volume. 2. The briquette shrinkage kinetic model was represented as follows: dVt/dt=V0[(1−x)dβ/dt−A0e−E/RT(1−x)nβ]; There was a positive correlation between the volume changing parameter β and the density of briquette, and the volume changing parameter increased with the reaction; the shrinkage reaction was divided into three stages; with the reaction went on, the reaction order and reaction rate constant decreased, the pre-exponential factor increased and the activation energy decreased firstly and increased then. 3. The shrinkage of the tamped coal cakes from the large-scale chamber was counted in the calculated unit whose thickness was 100mm. The shrinkage velocity of the tamped coal cakes in carbonization chamber was obtained by weighted calculating the shrinkage parameters of each volume unit at different temperatures. The shrink regulations of the tamped coal cakes in the carbonization chambers, which were in agreement with industrial production, were approximately the same as those of the large-sized briquettes. However, the shrinkage rate curve of the tamped coal cake in the carbonization chamber was gentler than that of the large-sized briquette, as a result of the large temperature gradient of different coal in carbonization chamber.

Al-doped ZnO nanostructured powders by emulsion detonation synthesis – Improving materials for high quality sputtering targets manufacturing

Abstract Emulsion detonation synthesis method was used to produce undoped and Al-doped ZnO nanostructured powders (0.5–2.0 wt.% Al2O3). The synthesized powders present a controlled composition and a morphology which is independent on the doping level. The XRD results indicate wurtzite as the single phase for undoped ZnO and the presence of gahnite as secondary phase for Al-doped ZnO powders. The sintering behavior of each powder was studied based on their linear shrinkage and shrinkage rate curves, showing the high sinterability of the powders. Activation energies for densification in the earlier stage were calculated for all compositions and possible sintering mechanisms are suggested depending on the doping level. The high chemical homogeneity and sinterability and the lower electrical resistivity of the bulk Al-doped sintered samples demonstrates the feasibility of emulsion detonation synthesis for the production of high quality Al-doped ZnO powders to be used in ceramic sputtering targets manufacture.

Elucidation of densification behavior of fine silicon powder particles covered with a native silica layer

Sintering of fine silicon powder covered with a native oxide, SiO 2(s) , has been studied under controlled atmosphere in a dilatometric apparatus. The densification kinetics is marked by the presence of two peaks on the shrinkage rate curve which are respectively attributed to the first and second stages of sintering. A complete description of sintering kinetics involving lattice diffusion and vapor transport is proposed to explain this unusual behavior.

Shrinkage and shrinkage rate behavior in Cdiamond-Fe-Cu-Ni-Sn-CrB2 system during hot pressing of pressureless-sintered compacts

The paper addresses the effect of pressure and a chromium diboride additive on shrinkage and shrinkage rate in hot pressing and on mechanical properties of the resulting diamond-containing composites based on Fe, Cu, Ni, and Sn powders. The shrinkage rate curves are found to have a stepwise trend. The shrinkage rate variations are shown to be associated with the phase and structural changes that occur in this system. The authors have determined the initial composition and p,T-conditions that ensure process activation and simultaneous improvement in mechanical properties of the composite.

Effect of forming pressure on densification behavior of nanocrystalline ITO powder

Since ultrafine nano-particles easily produce agglomerates, they result in an inhomogeneous particle packing structure within a green body. Nanocrystalline indium tin oxide (ITO) powder was prepared, and the compaction behavior of the powder was investigated by using an Hg porosimetry and a scanning electron microscope (SEM) as a function of the applied cold isostatic pressing (CIP) pressure. In addition, the sintering behavior of the compact was monitored with a thermo-mechanical analyzer (TMA), and the relationship between the inhomogeneity in the green body and the sintering behavior was examined. An increase in the forming pressure enhanced the homogeneity of the powder compact by crushing the larger agglomerates. The first generation agglomerate compact showed a two-step densification process in the shrinkage rate curve of TMA. The two-step densification behavior is explained by the elimination of two kinds of pores, which are small inter-crystallite pores and large inter-first generation agglomerate pores.

Dilatometric analysis on the sintering behavior of nanocrystalline W–Cu prepared by mechanical alloying

Unlike conventional W–Cu powder, the sintering of nanocrystalline W–Cu powder was significantly enhanced at solid phase sintering temperature. In the present study, in order to clarify this enhanced sintering behavior of nanocrystalline W–Cu powder prepared by mechanical alloying, the sintering behavior during heating stage was analyzed by dilatometry with various heating rates. The sintering of the nanocrystalline W–Cu powder was characterized by the densification of two stages, having two peaks in shrinkage rate curves. The temperature at which the first peak appeared was well below the Cu melting point and significantly dependent on the heating rate. On the basis of dilatometric data and microstructural observation, the possible mechanism for the enhanced sintering of the nanocrystalline W–Cu powder in the solid phase was attributable to the coupling effect of the sintering occurring inside as-milled powder and the sintering between powder particles.

Sintering of 6H(α)-SiC and 3C(β)-SiC powders with B4C and C additives

The sintering behavior of three fine industrial SiC powders (two 6H(α)-type and one 3C(β)-type) has been comparatively investigated. The powders were pressureless sintered with B4C and C additives between 1950°C and 2250°C in a high temperature dilatometer with flowing Ar atmosphere. The densification and shrinkage rate curves, polytype content, and grain growth were correlated with physical and chemical characteristics of starting powders. One of 6H(α)-type powders presented good sinterability only after extensive milling, even though it presented small average particle size, narrow particle size distribution and high specific surface area. The main difference in densification behavior among powders was the narrower shrinkage rate curve of β-SiC powder, with its maximum shifted to higher temperature. Grain growth and phase transformation simultaneously occurred. In α-SiC, 6H polytype partially transformed to 4H. This transformation was favored by aluminum impurity and resulted in a microstructure with more elongated grains. In β-SiC, 3C transformed mainly to 6H, 15R and 4H, introducing many stacking faults which resulted in elongated SiC grains.

Sintering Densification and Microstructure Formation Kinetics in Silicon Nitride Ceramics.

Research has been done on how the shrinkage rate and microstructure in the Si3N4 ― Al2O3 ― Y2O3 are dependent on temperature and nitrogen pressure during sintering. The shrinkage rate curves alter as the activator content varies. Additional densification may occur above 1800°C because of diffusion through the increased amount of liquid.

Sintering studies on UO 2–PuO 2 pellets with varying PuO 2 content using dilatometry

The sintering behaviour of UO 2, PuO 2, UO 2–20%PuO 2, UO 2–50%PuO 2 and UO 2–76%PuO 2 pellets have been studied using a dilatometer in inert, reducing and oxidizing atmospheres. The onset of shrinkage occurs by about 400°C lower in oxidizing atmosphere such as CO 2 and commercial N 2 than that occurs in reducing atmosphere. PuO 2 and UO 2–76%PuO 2 showed an expansion on heating in Ar at ∼1000°C. UO 2–20%PuO 2 pellet sinters slightly better in Ar than in Ar–8%H 2. From the shrinkage rate curves, it was found that the maximum shrinkage rate occurs in commercial nitrogen atmosphere for UO 2–50%PuO 2. For the other compositions, the maximum shrinkage rate was observed for Ar atmosphere. The sintering behaviour of above mentioned pellets was discussed with the help of point defect model and the possible mechanisms were suggested.

Sintering characteristics of microfine zirconia powder

In this paper the sintering characteristics of yttria-doped zirconia microfine powder are investigated by measuring shrinkage and shrinkage rate curves of powder compacts. The experimental results show that there is a transition point in the shrinkage-temperature curves and two peaks appear in the shrinkage rate-temperature curves. These results provide further support for the idea that the sintering of microfine zirconia powders is a two-stage process. In the first stage, sintering of the powder compact is mainly dominated by inner-sintering in agglomerates and in the second stage, sintering will occur among densified agglomerates. The microstructure of agglomerates during sintering is also studied by TEM and provides evidence that the transition point in the shrinkage-temperature curve is the end of the first sintering stage. Furthermore, the relationships between sintering characteristics and powder parameters are investigated. It is found that the shrinkage rate in the first stage is related to the primary grain size of the powder, and in the second stage it is related to agglomerate size. The effect of agglomerates on the sinterability of microfine Zr02 powder can be directly evaluated by the difference of shrinkage rate between the two sintering stages. Experiments also show that the shrinkage rate can be influenced by heating rate. A rapid heating rate would result in difficulties in the second sintering stage.

Some studies on the action of some ketones on Quiana-polyamide fibres.

Pretreatment of Quiana polyamide fabric (Q-PA) with some ketones was performed to induce some structural changes in order to improve fibre dyeability. Isothermal shrinkage rate curves of modified Q-PA were characterized by an induction period. The molecular volume of the interacting ketones/solvents influenced the corresponding energy of diffusion (ΔE) into the polymer. The difference in ΔE among the ketones/solvent may be associated with some difference in their binding capacity with the substrate. The dynamic shrinkage increased sharply with increasing temperature of pretreatment. Measurement of iodine sorption by modified polyamide allowed detection of induced structural differences.Changes in capability of modified polyamide to uptake cationic dyes were noticed. Evaluation of time of half dyeing and specific dyeing rate constant indicated that the pretreatment had more powerful influence in disordering polyamide fibre structure. The rate of dye diffusion in the modified polymer increased with rise of dyeing temperature. The apparent activation energy of diffusion showed the ability of the dye molecules to move within the fibre matrix. Calculation of the dye affinity and heat of dyeing anticipated that more disorder in fine structure due to pretreatment was imparted.