Compacted Bodies Research Articles

Effect of Indenter Angle on Bearing Performance of Coal and Accompanying Rocks Under Point Load and Characterization of Mechanical Parameters

ABSTRACTCoal, mudstone, sandstone, and limestone, which are common in coal mines, were selected as research objects, and 60°, 90°, and 120° indenters were used to conduct point load tests to study the deformation and failure laws of rocks under point loads. This study identified a process for generating and crushing compacted bodies. As the indenter angle increased, the number of compacted bodies formed decreased significantly, and the stress drop decreased. The ultimate invasion depth upon reaching the failure load decreased as a quadratic function as the indenter angle increased. Under the load of indenter points at different angles, all samples underwent splitting failure along the loading axis. As the indenter angle increased, the indentation diameter increased quadratically. The angle of the indenter had a greater influence on the indentation diameter of low‐strength rocks, and the failure of coal and accompanying rocks was more stable under the action of large‐angle indenters. The point load test data were statistically analyzed. The load intensity of the indenter point at different angles exhibited a linear relationship with the uniaxial compressive strength, tensile strength, and elastic modulus, and the fitting degree was the best when the indenter angle was 120°

The dissolution of planetesimals in electrostatic fields

ABSTRACT Planetesimals or smaller bodies in protoplanetary discs are often considered to form as pebble piles in current planet formation models. They are supposed to be large but loose, weakly bound clusters of more robust dust aggregates. This makes them easy prey for destructive processes. In microgravity experiments, we apply strong electric fields on clusters of slightly conductive dust aggregates. We find that this generates enough tensile stress on the fragile clusters to sequentially rip off the aggregates from the cluster. These experiments imply that electric fields in protoplanetary discs can dissolve pebble pile planetesimals. This process might induce a bias for the local planetesimal reservoir in regions with strong fields. Planetesimals prevail with certain kinds of compositions where they are either good isolators or compacted bodies. The less lucky ones generate pebble clouds that might be observable as signposts of electrostatic activity in protoplanetary discs.

Evaluation of Feasibility on Dental Zirconia-Accelerated Aging Test by Chemical Immersion Method.

The aim of this study was to investigate the low-temperature degradation (LTD) kinetics of tetragonal zirconia with 3 mol% yttria (3Y-TZP) dental ceramic using two degradation methods: hydrothermal degradation and immersed degradation. To study transformation kinetics, we prepared 3Y-TZP powders. We pressed these powders uniaxially into a stainless mold at 100 MPa. We then sintered the compacted bodies at intervals of 50 °C between 1300 °C and 1550 °C and immersed the specimens at various temperatures from 60 °C to 80 °C in 4% acetic acid or from 110 °C to 140 °C for the hydrothermal method. We used a scanning electron microscope (SEM) to confirm crystalline grain size and used X-ray diffraction to analyze the zirconia phase. As the sintering temperature increased, the calculated crystalline grain size also increased. We confirmed this change with the SEM image. The higher sintering temperatures were associated with more phase transformation. According to the Mehl-Avrami-Johnson equation, the activation energies achieved using the hydrothermal method were 101 kJ/mol, 95 kJ/mol, and 86 kJ/mol at sintering temperatures of 1450 °C, 1500 °C, and 1550 °C, respectively. In addition, the activation energies of the specimens immersed in 4% acetic acid were 60 kJ/mol, 55 kJ/mol, 48 kJ/mol, and 35 kJ/mol, with sintered temperatures of 1400 °C, 1450 °C, 1500 °C, and 1550 °C, respectively. The results showed that a lower sintering temperature would restrain the phase transformation of zirconia because of the smaller crystalline grain size. As a result, the rate of LTD decreased.

Morphology and Thermoelectric Properties of Mg<sub>3+δ</sub>Sb<sub>2</sub> Foams Manufactured Using Combustion Synthesis

Magnesium antimonide (Mg3Sb2) is a promising thermoelectric compound utilized for thermoelectric power generation. We have found out that the Mg3Sb2 compound can be made from Mg and Sb powder mixture via the combustion synthesizing reaction. In this study, we manufactured the compounds from the compacted bodies with different Mg fractions between 60.0 and 75.0 at% in an argon gas flow at 650°C for 1 hour via the combustion synthesis process. Morphology, porosity, phases and thermoelectric properties (electrical resistivity and Seebeck coefficient at room temperature to 500°C) were investigated for the manufactured samples. All samples manufactured with different Mg fractions mainly consisted of Mg3Sb2 and became foamed bodies with a porosity between 50 and 70%. The thermoelectric properties changed with the Mg fraction. The maximum power factor of 42.1 µW/mK2 at 488°C was obtained in the foamed body with the Mg fraction of 64 at%. The dimensionless figure of merit (ZT) of the sample was also estimated using the thermal conductivity, which was calculated considering its large porosity. The maximum dimensionless figure of merit (ZTmax) would be 0.13 at 488°C.

Fabrication of Highly Compacted Green Body Using Multi-Sized Al Powder under a Centrifugal Force

This study investigates the application of centrifugal force for the compaction of metal powder. Previous studies using the centrifugal force for manufacturing the green bodies were focused on fine powders with narrow particle size distribution or binary mixtures. This study explores the particle packing of multi-sized powder. Aluminum alloy powder with a particle size less than 100 µm and polymer binder were admixed and compacted in the centrifugal casting with ranging magnitudes of centripetal acceleration. Three different centrifugal forces were tested: 700, 1800, and 3700 G. The microstructure of the green bodies was then observed on the SEM micrographs. The obtained green bodies had high packing densities ranging from 62 to 69%. The packing density and median particle size increase at the positions further away from the center of rotation of the centrifuge with an increase of centrifugal force. The effect of centrifugal force on the segregation of particles was investigated through the quasi-binary segregation index. The segregation phenomena was not observed at 700 G, but clear particle segregation was found at higher centrifugal forces. The increase of the centrifugal force resulted in higher segregation with finer particles moving to the inner part of the spinning mold, with a significant change in the size of particles located closer to the center of rotation. Overall, the centrifugal process was found to produce highly compacted green bodies while yielding a segregation effect due to wide particle size distribution.

Experimental Method for Evaluating the Reactivity of Alkali-Carbonate Reaction Activity.

The main aim of this study was focused on the Method of testing alkali-carbonate reaction activity to avoid alkali-carbonate reaction damage. In this paper, the alkali-carbonate reaction activity and alkali-silica reaction activity of ten kinds of aggregates were determined and analysed by existing standards and methods, by making specimens with aggregates of 2.5–5 mm and 5–10 mm particle size, cured in 1 mol/L tetramethyl ammonium hydroxide solution at 60 °C and 80 °C. Tetramethyl ammonium hydroxide solution was used to exclude the expansion caused by alkali-silica reaction. Effects of aggregate particle size and curing temperature on the expansion of samples were systematically investigated to determine alkali-carbonate reactivity of aggregates. In order to explore the relationship between stress and strain of aggregates, these aggregates were prepared into compacted bodies to test their stress and try to discover the pattern. The results showed that the expansion of the mould specimen prepared by the aggregate of 5–10 mm particle size, cured in 1 mol/L tetramethyl ammonium hydroxide solution at 80 °C was greater than 0.1% after 42 days, which could be used as a reference criterion to determine the alkali-carbonate reaction activity of the aggregate. In addition, the expansion stress test suggest that the alkali-carbonate reaction can generate expansion stress. The expansion stress of aggregates with alkali-carbonate reaction activity were much larger than that of aggregates without alkali-carbonate reaction activity. Through SEM and EDX analysis of the products of the alkali-carbonate reaction, it was shown that the dolomite crystals in the dolomitic aggregates reacted with the TMAH solution and resulted in alkali-carbonate reaction, forming calcite and brucite.

Silicon dioxide dispersed effects on some physical and mechanical properties of Al2Si2O5(OH)4

Kaolin and silica of 50 μm grain size were used in different weight percentage. Four combinations have been selected as green compacted bodies. Different sintering temperatures ranging from (1000 – 1400) °C were used to sintered all the combinations under static air. The sintered density, thermal conductivity compression strength and linear shrinkage were tested after sintering. The common behavior indicated that the improvement with its optimum results was found at the combination (Kaolin 20-SiO2 80) Wt. %, sintered at 1400 °C, for 3 hours under static air.

Crystal growth behavior and sintering-resistance property of nano-sized β-Yb2Si2O7 for environmental barrier coatings

In this article, as an attractive candidate of EBCs for SiC-based ceramic matrix composites, nano-sized β-Yb2Si2O7 was synthesized by hydrothermal method. The sintering-resistance property and crystal growth behavior of β-Yb2Si2O7 powders and compacted bodies were evaluated via various techniques. Quantity analyses demonstrate that β-Yb2Si2O7 was formed at about 1100 °C, and possessed well thermal stability at even higher temperatures. The determined coefficient of thermal expansion and thermal conductivity are 4.63 × 10-6 K-1 and 1.72 W m-1 K-1, respectively. The microstructures of compacted bodies under different temperatures reveal the critical temperature of anti-sintering is about 1400 °C. Based on different growth mechanisms, the activation energy of crystal growth (Q) can be segmented into two sections with a turning point of 1076 °C. Furthermore, the relative relationship between activation energy and sintering was bridged.

A study of phase evolution and crystal growth for nano-sized monoclinic Y4Al2O9 as a novel thermal barrier coatings

Nano-sized monoclinic Y4Al2O9 was produced by sol-gel process as a novel potential candidate material for thermal barrier coatings. The thermal behavior, structural evolution of the products and the morphological characteristics of the compacted bodies were investigated by Thermogravimetric analysis and differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Field emission scanning electron microscopy (FESEM). Qualitative analyses indicate that monoclinic Y4Al2O9 was formed at about 1000 °C, and exhibited good phase stability throughout the annealing temperature ranging from 1000 °C to 1400 °C. The thermophysical properties of Y4Al2O9 ceramics were also evaluated compared with 8YSZ and La2Zr2O7. The determined activation energy of crystal growth is about 72.71 ± 0.31 kJ mol−1. Meanwhile, Y4Al2O9 represents low thermal conductivity (1.71 W m−1 K−1), moderate thermal expansion coefficient (8.73 × 10−6 K−1), and high sintering-resistance ability. Such results reveal that nano-sized Y4Al2O9 is favorable for the application of TBCs.

The effects of sintered sample thickness on the dielectric properties of CaCu3Ti4O12 ceramics prepared at 1000–1100 °C in air

Abstract In this study, the relationship between dielectric properties and sintered sample thickness (d) (0.41–2.74 mm) of CaCu3Ti4O12 (CCTO) ceramics prepared at 1000–1100 °C in air was investigated. Compacted green ceramic bodies in varying weights and sintered at different temperatures were prepared to obtain ceramics with varying thicknesses. The samples were evenly polished on either surface, electroded and measured by a precision LCR meter at 20 Hz–1 MHz. The results showed that the e′ increased monotonically with increasing sintering temperature and indicated a linear relationship with d for samples sintered at ≥1040 °C, while the e′ for samples sintered at ≤1030 °C was barely affected. Complex impedance analysis showed that the ρgb was nearly constant with the change of d. The inverse effect of e′ and ρgb with d can also be observed for the gradual thickness reduction sample sintered at 1040 °C, confirming that the grain boundary plays a key role in the variation of dielectric properties for CCTO ceramics.

Effects of wear load on mechanical and morphological properties of A356 matrix carbon nano tube composites

In this study, CNT-A356 composites were prepared by reinforcing an aluminum alloy A356 matrix material with carbon nanotubes (CNT) in 4 different ratio (0.5, 1, 1.5 and 2) and the hardness, abrasion and microstructure properties of these composites were investigated. The powder metallurgy method was used in the production of composite samples. A356 powder and CNTs’ were mixed by ball milling for 1 hour and cold pressed in the powder compression mold. The mold was then taken into a functional oven and hot pressing was performed. The compacted powder bodies were sintered at 550° C for 1 hour in a 10−6 millibars vacuum environment. Hardness measurements, wear tests and microstructure analyzes of the produced samples were carried out. As a result of experimental studies; it has been observed that the CNTs’ are placed in bulk and between the matrix grains and a more hollow structure is formed by increasing the CNT ratio. Moreover, while the CNT ratio exceeded 1%, the hardness values decreased and weight loss increased. The highest hardness value was obtained in the composites containing 1% CNT.

Grain size dependence of the microstructures and functional properties of (Ba0.85 Ca0.15–x Cex) (Zr0.1 Ti0.9) O3 lead-free piezoelectric ceramics

ABSTRACTBy the solid-state reaction route, (Ba0.85Ca0.15-x Cex) (Zr0.1Ti0.9) O3 (BCCeZT) lead-free piezoelectric ceramics were prepared. The powder was processed at 1250 ºC for 2 h, and compacted green bodies were then sintered at various sintering temperatures. X-ray diffraction analysis and Raman spectra confirmed the rhombohedral-tetragonal phase coexistence of x = 0–0.00131. Addition of CeO2 facilitated development of grain sizes greater than 10 μm at low sintering temperatures. The effects of grain size on the ferroelectric and piezoelectric properties were studied systematically and it was found that a ~ (10–12) μm grain size is critical for the processing of high-performance lead-free BCCeZT ceramics. CeO2 substitution at the A site may bring down the sintering temperature by about 200 °C without significant loss of properties. The best properties were obtained for x = 0.00131 at a low sintering temperature of 1350°C for 4 h exhibiting d33 = 501 ± 10 pC/N, kp = 38.5 ± 1.92 %, Pr = 12.19 μC/cm2, TC = 108.1°C, and a large strain of 0.14%. These results show that BCCeZT ceramics could be promising candidates for the fabrication of lead-free devices.

Microstructural evolution during sintering of copper particles studied by laboratory diffraction contrast tomography (LabDCT)

Pressureless sintering of loose or compacted granular bodies at elevated temperature occurs by a combination of particle rearrangement, rotation, local deformation and diffusion, and grain growth. Understanding of how each of these processes contributes to the densification of a powder body is still immature. Here we report a fundamental study coupling the crystallographic imaging capability of laboratory diffraction contrast tomography (LabDCT) with conventional computed tomography (CT) in a time-lapse study. We are able to follow and differentiate these processes non-destructively and in three-dimensions during the sintering of a simple copper powder sample at 1050 °C. LabDCT quantifies particle rotation (to <0.05° accuracy) and grain growth while absorption CT simultaneously records the diffusion and deformation-related morphological changes of the sintering particles. We find that the rate of particle rotation is lowest for the more highly coordinated particles and decreases during sintering. Consequently, rotations are greater for surface breaking particles than for more highly coordinated interior ones. Both rolling (cooperative) and sliding particle rotations are observed. By tracking individual grains the grain growth/shrinkage kinetics during sintering are quantified grain by grain for the first time. Rapid, abnormal grain growth is observed for one grain while others either grow or are consumed more gradually.

Effects of Steel Fibers and Surface Roughness on Squealing Behavior of Friction Materials

Noise in vehicle is induced by compounds and surface characteristics particularly in the friction contact. The purpose of the present work is to study the influence of brake pads containing steel fibers as well as to relate surface roughness on the generation of brake squeal. Two brake pads, steel fiber-free and with steel fiber materials, were studied. It was shown that both the materials generated squeal noise at frequency between 7 and 10 kHz but with a slight difference in humidity and friction coefficient. This difference was attributed to the tribological aspects of the friction material. It was also found that the pad surface roughness played a significant role towards the generation of brake squeal. For the sample without steel fibers, it was evident that the surface was neither covered by compacted third bodies nor contact plateaus were evident. However, for the other sample, the internal structure and the topography showed several cracks.

Correlation between dynamic mechanical thermo-analysis and composition-based models for C-S-H in hydrated portland cement paste

A dynamic mechanical analysis (DMTA) technique was used to assess the mechanical performance of 1.4 nm tobermorite (T), jennite (J) and mixtures of tobermorite and jennite and tobermorite and calcium hydroxide (CH). A comparison of E′ (storage modulus) and tan∂ (internal friction) versus temperature curves for compacted solid bodies of these mineral systems with corresponding curves for cement paste hydrated for 2 month and 3 years (both referred to as ‘young’) and 45-year-old paste (referred to as ‘old’) was made. Original data was provided to assess the practical validity of the Richardson–Groves composition-based models for the C-S-H in cement paste. Differences in mechanical performance between the ‘young’ paste and the ‘old’ paste could be accounted for by application of a T/J dominant model (‘young’ paste) and a J–T/CH structural model with a minor amount of T (‘old paste’).

Dps Is a Stationary Phase-Specific Protein of &amp;lt;i&amp;gt;Escherichia coli&amp;lt;/i&amp;gt; Nucleoid

Bacterial genomic DNA is highly organized into one or few compacted bodies known as nucleoid, which is composed of DNA, RNA and several DNA-binding proteins. These DNA-binding proteins require essential alterations in their expression during stationary phase of growth in order to re-spond to stressful environmental conditions. Dps (DNA-binding protein from starved cells) is one of such DNA-binding proteins, which accumulates most when E. coli cells reach to the stationary phase. Here, we have characterized Dps protein under various growth phases. Immunofluorescent microscopic observation reveals that Dps plays a key role in final round of genome compaction during the stationary phase. Similar results are also obtained by Western immunoblot analysis, after quantification of Dps protein from the exponential phase and early stationary phase nucleoid bound fractions, separated by sucrose density gradient centrifugation. Our results support the conclusion that Dps occupies more than half of the stationary phase nucleoid in E. coli.

Reaction-bond sintering of C/SiC functionally graded nanostructured materials (FGNMs)

In this study, bulk C/SiC functionally graded nanostructured materials (FGNMs) having a compositional gradient from carbon (C) to silicon carbide (SiC) were obtained by applying the powder-stacking method under pressureless sintering condition. During the sintering process, the reaction-bonded SiC was formed in the presence of pure silicon (Si) which led to increase in the density and strength of the FGNMs. At the sintering stage, the compacted bodies were heated at 1525°C for 2h in an argon atmosphere. Results showed that the number of graded layers had a marked effect on the microstructure and properties of the sintered C/SiC FGNMs. With increasing number of graded layers, the bend strength of the samples improved significantly. Moreover, SEM micrographs illustrated that the formation of SiC nanorods between adjacent particles improved the bending strength of the samples.

Thermoelectric properties of Ca1−xSrxRuO3 compounds prepared by spark plasma sintering

Single phase Ca1−xSrxRuO3 (x=0–1.0) powders were synthesized by a solid-state reaction and compacted by spark plasma sintering. The a-length of the lattice parameter showed a slight minimum around x=0.6, whereas the b-length, c-length and the unit cell volume increased continuously with increasing x from 0 to 1.0, indicating a solid solution in the whole range. The relative density of Ca1−xSrxRuO3 compacted bodies increased from 75 to 95% with increasing x from 0 to 1.0. The electrical conductivity (σ) at x=0.1–0.9 was higher than those of the end members (CaRuO3 and SrRuO3) except for that at x=0.5, and showed metallic conduction at all compositions. The Seebeck coefficient (S) was 30–40μVK−1, almost independent of composition and temperature. The thermal conductivity (κ) was 2–3Wm−1K−1 at room temperature and increased with increasing temperature. The κ showed the lowest values at x=0.2 in the whole temperature range. The dimensionless figure-of-merit (ZT) at x=0.1–0.9 was higher than those of the end members. The highest ZT was 0.07 at x=0.2 and 600K.

Si-SiC-ZrB2 ceramics by silicon reactive infiltration

Silicon carbide ceramics obtained by silicon reactive infiltration are nowadays employed within industry in several high temperature applications. Although these ceramics show good thermo-mechanical properties and oxidation resistance, they suffer temperature limitations (1400°C). At higher temperatures another type of ceramics, commonly known as ultra high temperature ceramics (UHTCs), is under study. These include the transition metal diborides of group IV; one in particular, zirconium diboride, is interesting in certain applications (e.g. aerospace) because of its low relative density. ZrB2-SiC ceramics show good thermo-mechanical properties and maintain the “protective” passive oxidation regime of their scales over a wide range of temperatures.This paper presents a feasibility study on a manufacturing methodology to produce Si-SiC-ZrB2 bulk ceramics taking advantage of the reactive infiltration technique. This technique allows lower processing temperatures and near to net shape capability due to low shrinking of the green compacted bodies. C-SiC-ZrB2 preforms were successfully infiltrated with molten silicon. The resulting Si-SiC-ZrB2 composites showed promising oxidation behavior, similarly to that reported in other works. Bulk material optimization was performed with a view to manufacturing Si-SiC-ZrB2 ceramic matrix composites by silicon reactive infiltration in future.

Sintering kinetics of a 18.8Li 2O 8.3ZrO 2 64.2SiO 2 8.7Al 2O 3 glass ceramic

The LZSA (Li 2O-ZrO 2-SiO 2-Al 2O 3) glass ceramic system has shown high potential as low temperature co-fired ceramics, the so called LTCC, for several applications, such as screen-printed electronic components, due to its low sintering temperature (< 1000 °C). However, a good microstructural control must be achieved in order to obtain a low porosity material. The 18.8Li 2O 8.3ZrO 2 64.2SiO 2 8.7Al 2O 3 LZSA glass ceramic composition was prepared by melting, quenching in water, and grinding in order to obtain a very fine powder (3.78 μm mean particle size). Subsequently, compacted bodies were obtained by uniaxial pressing (40 MPa) and drying. Sintering kinetics was investigated by optical dilatometry measurements and scanning electron microscopy (SEM) observations. The activation energy for sintering was found to be 314 kJ.mol −1, whilst a maximum linear shrinkage of 22% and porosity of 3.5% were obtained with 10 min swelling time at 800 °C.