Optimal Densification Research Articles

Effects of (Cd1/3Sb2/3)4+ co-substitution on the crystal structure, chemical bond characteristics, and microwave dielectric properties of CeO2-ZrO2-MoO3 ceramics

In this paper, Ce2[Zr1−x(Cd1/3Sb2/3)x]3(MoO4)9 (CZ1−x(CS)xM, x = 0.01–0.1) were prepared via the conventional solid-state method. XRD and Rietveld refinement analyses confirmed the formation of a single-phase CZ1−x(CS)xM solid solution with a space group of R-3c(167). The sintering behavior of the samples were investigated using SEM and relative density, which showed that optimal densification for CZ0.98(CS)0.02M ceramics were achieved at 675 °C with an average grain size of 1.70 μm. The P-V-L theory revealed the significant influence of the Zr(Cd/Sb)-O bond on the dielectric properties of CZ1−x(CS)xM ceramics. Furthermore, far-IR reflectance spectra indicated that the measured dielectric loss value (1.04 × 10−4) is in line with the calculated value (1.60 × 10−4), suggesting a substantial impact of phonon oscillation absorption on the dielectric properties. Notably, CZ0.98(CS)0.02M ceramics demonstrated superior performance at 675 °C, with εr = 10.44, Q × f = 93,152 GHz (at 12.96 GHz), and τf = −17.73 ppm/°C.

Effect of densification technology on the microstructure and mechanical properties of high-entropy (Ti, Zr, Hf, Nb, Ta)C ceramic-based cermets

High-entropy ceramic-based cermets represent a new and promising direction in improving the mechanical properties of conventional hardmetals through the formation of complex microstructures during synthesis. This has been systematically studied in two Co-free, high-entropy (Ti,Zr,Hf,Nb,Ta)C ceramic-based cermets using 10 wt% Ni and 10 wt% FeCrAl metallic binders during hot-press and spark plasma sintering. Fully densified microstructures were achieved in the temperature range of 1400–1500 °C, which is below the melting points of the pure Ni and FeCrAl alloy, owing to the liquid-phase assisted sintering. The optimal densification routes resulted in Vickers hardness (HV30) of 16.77 ± 0.72 and 18.32 ± 0.99 GPa, and fracture toughness (KIc_SENB) of 5.31 ± 0.41 and 4.83 ± 0.50 MPa m0.5, respectively for the Ni and FeCrAl bonded cermets. The improved damage tolerance of these cermets compared to the base (Ti,Zr,Hf,Nb,Ta)C high-entropy carbide is related to the reduced grain size and microstructural toughening mechanisms (e.g. crack deflection and bridging).

Microstructural Evolution and Densification of Co-Based Alloy Powder by Spark Plasma Sintering for High-Hardness Applications

This work presents the densification of Co-based alloy powders by a spark plasma sintering process. The densification process was carried out at a temperature range of 800 °C to 1100 °C in order to obtain sintered coupons and study their microstructure and mechanical properties. The shrinkage behaviour of the sintered coupons was studied, and an optimal densification temperature was defined. The microstructural analysis showed a reduction in porosity with temperature increment along with the development of a fine microstructure comprised of cobalt-molybdenum-chromium-silicon-based intermetallic laves phases, which are dispersed in a softer cobalt-based alloy matrix. X-diffraction analysis showed that these crystalline phases were well-dispersed, with a lattice parameter corresponding to a hexagonal system. The obtained high Vickers hardness values were attributed to the preservation of a fine microstructure and to the precipitation of Co-Mo phases. Three-point bending tests were performed in order to identify the strain path concerning the densification of the sintered coupons.

Spinel-trirutile microwave dielectric ceramics with high Q and excellent temperature stability based on MgO-Al2O3-Ta2O5 ternary systems

(1-x)MgAl2O4-xMgTa2O6 composite ceramics based on the MgO-Al2O3-Ta2O5 pseudoternary phase diagram were prepared by the solid-state reaction. MgAl2O4 and MgTa2O6 could coexist due to their different crystal structures. MgAl2O4 inhibited the rapid growth of MgTa2O6 grains, and dense microstructures (ρ > 95%) with a uniform grain size distribution was obtained, with an optimal densification temperature of 1550 - 1575 °C. The temperature coefficient of resonant frequency (τf) and quality factor (Q×f) were optimized by introducing MgTa2O6 phases with low dielectric loss and positive τf. In addition, the partial solid solutions of Al3+ into Ta5+ sites resulted in loosening bonds within [Al/TaO6] octahedra and abnormally large polarizabilities, which was confirmed by the decrease in VTa-O and the redshift of A1 g(Ta-O) mode. Consequently, the relative permittivity (εr) and τf values of MgAl2O4-MgTa2O6 composite ceramics were further enhanced, exceeding the predicted ones. The 0.6MgAl2O4-0.4MgTa2O6 composition sintered at 1550 °C achieved excellent performance, with a near-zero τf value of 3.3 ± 1.7 ppm/°C, a low εr of 16.4 ± 0.3 and an ultra-high Q×f of 179,000 ± 6700 GHz @ 8.94 ± 0.04 GHz. These findings hold promising applications in the field of 5 G/6 G high-frequency communication.

High-flowable and high-performance steel fiber reinforced concrete adapted by fly ash and silica fume

The incorporation of steel fibers in concrete imparts strain-hardening characteristics, significantly elevating the tensile toughness of the concrete mixture. However, this enhancement often comes at the expense of reduced workability and strength, posing challenges in achieving optimal densification in practical engineering applications. Moreover, the improvement of the performance of steel fiber-reinforced concrete (SFRC) hinges on the establishment of interfacial transition zone (ITZ) between steel fibers and the concrete paste. It has been established that the introduction of fly ash and silica fume to concrete mixtures can increase fluidity and strength. Consequently, this study investigates the impact of fly ash and silica fume on the performance enhancement and workability of SFRC mixtures, scrutinizing both macroscopic and microscopic aspects. Two sets of high-flowable steel fiber-reinforced concretes (HF-SFRC) incorporating silica fume or fly ash were prepared and subjected to testing. The assessment covered mechanical properties, including compressive strength, compressive toughness, and flexural toughness, along with the microstructure. The microstructure provides evidence that fly ash and silica fume reduced the voids in the concrete matrix to different degrees and that the fully hydrated dense matrix contributed to reinforcing the bond between steel fibers and the cement matrix. The synergistic effect among fly ash or silica fume, steel fibers, and cement in the mixture resulted in enhanced flowability and improved mechanical properties in HF-SFRC.

The reinforcing mechanism of ionic interdiffusion on MgO–MgAl2O4 composites between structural densification and mechanical property

MgO–MgAl2O4 composites are arising as promising candidates for high-temperature industrial applications. For this reason, the in-situ synthesis of such types of composites with spinel structure has attracted the attention of the scientific community. Along these lines, in this work, magnesia and bauxite were used as raw materials to fabricate MgAl2O4 composites. The mass proportion in the composites was also adjusted by using the solid-phase sintering method at 1400–1650 °C to enhance its mechanical properties and densification. XPS and SEM measurements were conducted, indicating that the MA50 sample with the mass ratio of 50:100 (MgAl2O4:MgO + MgAl2O4) exhibited the best properties at 1550 °C, in terms of uniformity of the grains’ growth morphology, optimal densification of the matrix structure, and achieving a maximum flexural strength of 113.23 MPa. From our analysis, it was demonstrated that the non-equivalent displacement of Al3+ and Mg2+ could easily lead to the formation of the (Mg1-xAlx/2)Mgx/4O solid-solution during the similar crystal structure, which enhanced mechanical strengthening between the micro-grain and framework. Meanwhile, the existence of a certain liquid phase not only effectively increased the mass transfer during the processing of interdiffusion between Al3+ and Mg2+, but also promoted the distribution of crystallite and microstructure.

Performance Analysis of Sketching Methods

One of the problems in data mining or machine learning is the high-dimensional dataset. MinHash can generate sketches of sparse datasets efficiently reducing the dimension to a few thousand. These sketches, then, can be used for different machine-learning applications. It takes O(kd) computations to generate k hash values for a data point with d non-zeros. The Sketch of a data point is the vector of k hash values. Weighted Minwise Hashing is another method to generate a sketch of size k in O(kp/d) computations. Here, p is the size of the universal set. Optimal Densification is the most efficient and accurate method as it can generate k hash values in mere O(d + k) computations. In this paper, we investigate the performance of Optimal Densification, Weighted Minwise Hashing, and Vanilla MinHash by performing two experiments. Firstly, we investigate Jaccard similarity estimation accuracy on six different synthetic datasets. Then, we perform one nearest neighbor classification (1NN) of four real datasets. Optimal Densification outperforms both Weighted Minwise Hashing and Vanilla MinHash in terms of accuracy and time taken to generate the sketches.

Densification-crystallization behavior of biodegradable copper-doped modified 45S5 glasses

In the current work, modified 45S5 glasses containing different amounts of copper oxide (1, 3, and 5 weight ratios) were prepared using melting procedure and characterized for their physical properties after sintering at various temperatures. Characterization of the copper doped glasses was performed using various analytical techniques, including X-ray diffractometry, differential thermal analysis, and scanning electron microscopy. To this purpose, a systematic study was conducted on densification-crystallization of the copper doped glasses and optimizing sintering temperature. Differential thermal analysis revealed weak exothermic peaks located above 800 °C, corresponding to the crystallization temperature (Tc) of the studied glasses. This analysis suggests that copper oxide has a limited effect on the thermal properties of the modified 45S5 glasses. Densification behavior of glass specimens was studied at temperatures ranging from 600 to 850 °C. The optimal densification temperature was found to be 650 °C, respectively. The results indicated that the presence of copper ions in the structure of studied glasses results in the formation of porous structures after sintering. It seems that copper ions generate oxygen gas during sintering and promote the formation of a cellular foam structures.

Effect of MgO and Nb2O5 co-doping on the microwave dielectric properties of Y2Ti2O7 ceramics

This study investigated the effects of MgO and Nb2O5 co-doping on the microwave dielectric properties of Y2Ti2O7 ceramics with a medium dielectric constant. Substituting (Mg1/3Nb2/3)4+ for Ti4+ in Y2Ti2O7 ceramics effectively enhanced the quality factor Qf. The interrelationship among the crystalline structure, microstructure, and microwave properties of Y2(Ti1-x(Nb2/3Mg1/3)x)2O7 (0 ≤ x ≤ 0.15) sintered at 1500 °C with different holding times were examined using XRD, SEM, TEM, XPS, Raman, and network analyzer. The research findings indicate that all samples exhibited a single cubic pyrochlore phase without a second phase. Moreover, the densification temperature increased with an increase in (Mg1/3Nb2/3)4+ content, and the relative density could be increased by increasing the sintering dwell time. The sample with x = 0.025 demonstrated an optimal densification temperature of 1500 °C. TEM/SAED pattern analysis revealed the existence of a "superlattice" due to the occurrence of a 1:2 cation ordering structure at high temperatures. As the dwell time was extended from 4 h to 12 h, the quality factor Qf increased from 10,830 GHz to 46,068 GHz. The sample with x = 0.025 sintered at 1500 °C for 12 h exhibited the best microwave dielectric properties (permittivity(εr) = 62.5, Qf = 46,068 GHz, and the temperature coefficient of frequency (TCF) = 290.8 ppm/°C).

High-density and broad band optical frequency combs generated by pseudo-random phase modulation of optically injected gain-switched semiconductor lasers

We have demonstrated optical frequency combs (OFCs) featuring low and continuously tunable line spacing in the kilohertz range. The OFCs are generated by pulsed gain-switching of optically injected commercial semiconductor lasers emitting at around 1.55 μm. After generation, the OFCs are efficiently densified by pseudo-random-binary-sequence phase modulation. The case of an OFC generated by gain-switching at a repetition rate of 1 GHz has been numerically and experimentally analyzed and the conditions for optimal densification have been found. In this case, the comb has been densified by a factor of 2047 and exhibits a 90 GHz flat and broad spectrum consisting of more than 184,000 spectral lines, separated 488 kHz. Although this densification factor is not the largest that can be achieved with the method, it is more than 100 times larger than previously reported factors for gain-switching OFCs. These results open prospects for the use of potentially integrable gain-switching OFCs in applications requiring sub-megahertz line spacing.

Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)

This work aims to investigate the processability of René 80 via laser powder–bed fusion (L-PBF). René 80 is a poorly weldable Ni-superalloy, currently processed via investment casting to fabricate turbine blades working at an operating temperature of about 850 °C. The L-PBF parameters optimization aims to increase part integrity and enhance processing repeatability. This part was tackled by creating a complete design of experiments (DOE) in which laser power, scan speed and hatching distance were varied accordingly. Optimizing the abovementioned parameters minimized the crack density and pore area fraction. Hence, five parameter sets leading to a crack density lower than 100 µm/mm2 and a pore fraction between 0.045% and 0.085% were selected. Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build. The porosity value obtained was constant among repetitions, and the crack density (around 75 µm/mm2) had a slight standard deviation. The third step of the research assessed the inter-prints repeatability by producing a replica of the five selected parameter sets in a different build and by comparing the results with those studied previously. According to this latter study, the porosity fraction (ca. 0.06%) was constant in intra- and inter-print conditions. Conversely, crack density was lower than 100 µm/mm2 only in three sets of parameters, regardless of the intra- or inter-build cross-check. Finally, the best parameter set was chosen, emphasizing the average flaw fraction (least possible value) and repeatability. Once the optimal densification of the samples was achieved, the alloy’s microstructural features were also investigated.

Cold sintering of colloidal silica particles using different alkali solutions

The present work is focused on the cold sintering of colloidal silica particles with the aid of different alkaline solutions as the transient phase. The studies were carried out with 2 M NaOH, KOH and LiOH water solutions. The densification was optimized, varying the uniaxial applied pressure between 200 and 600 MPa at 200 °C with a dwell time of 15 min. An optimal densification was achieved under 500 MPa pressure. The sintered materials also have relatively low corrosion in water. Delayed densification was observed in the LiOH system compared to KOH and NaOH which exhibited a similar behaviour.

Valorización de cascarilla de arroz y paja de frijol mediante la producción de pellets combustibles: un enfoque experimental y de modelado

Worldwide, agricultural wastes represent an environmental problem due to their high volumes and inadequate disposal. Due to this, valorization of these wastes has been studied, being the production of biofuels a promising option. In particular, rice husks were proposed to produce fuel pellets, buy they do not fulfill the ISO 17225-6 standard due to its elevated ash content; thus, it is required to mix them with other wastes available in the same region. In Mexican states where rice is produced also bean is cultivated, whose residues are not used and have an elevated content of volatile solids. Therefore, the objective of this research is to produce fuel pellets from rice husk and bean straws that meet ISO 17225-6 standard. For this, the densification was carried out using three levels of moisture content and mixing ratios of the biomasses. Based on the experimental data, optimal densification conditions were found through a response surface analysis. Results show that fuel pellets produced from bean straw (90%) and rice husk (10%) with 15.0% of moisture content fulfill ISO 17225-6 standard.  At these conditions, fuel pellets have calorific power of 3,645.78 kcal/kg, 6.98 ash, 9.76% final moisture, 610.78 kg/m3 bulk density, and 99.51% durability.

The Effect of Incorporating Ultra-Fine Spherical Particles on Rheology and Engineering Properties of Commercial Ultra-High-Performance Grout

In this study, ultra-fine spherical particles of silica fume and reactive ultra-fine fly ash were added to a mixture of commercial ultra-high-performance grout (UHPG) with the aim of enhancing the rheological properties, compressive strength, compactness, and permeability. This commercial UHPG study was conducted in collaboration with Triaxis Corporation (Changsha city, Hunan province, China). A water-to-binder ratio of 0.21 and a binder-to-fine aggregates ratio of 1.17 were used as fixed parameters, and the binders were a combination of type-II Portland cement, sulphoaluminate cement, silica fume, and reactive ultra-fine fly ash (RUFA). Polycarboxylate superplasticizer powder was used to control the rheology. The results revealed excellent compressive strength, volume stability, and resistance to chloride penetration. Mercury intrusion porosimetry and scanning electron microscopy tests revealed that the medium-sized RUFA particles with small silica fume particles completely filled the spaces between large cement particles to achieve optimal densification. This mixture also produced dense hydration and calcium-silicate-hydrates colloids, which filled the microstructures of the UHPG resulting in excellent engineering properties and durability. This commercially available UHPG mix responded to excellent compressive strengths approaching 120 MPa and exhibited good workability with a loss of slump-flow rate up to 33% after 60 min. It also exhibited very low abrasion resistance (0.5%), stable shrinkage and expansion rates (stabilization over 10 days), very low chloride diffusion coefficient (less than 0.1 × 10−14 m2/s) with a denser microstructure. This commercial UHPG (UHPG-120) has been developed to meet the needs of the market.

Binary reaction behaviors of red mud based cementitious material：Hydration characteristics and Na+ utilization

Bayer red mud (RM) occupies a large amount of land, which excessive Na+ seriously damages groundwater resources. In this research, a RM based cementitious material (RMC) composed of RM and ordinary Portland cement (OPC) was developed. It is interesting to find that a binary reaction consisting of cement hydration and geopolymer reaction in RMC. The mechanical and Na+ consolidation rate of RMC were improved by the synergistic effect of binary reaction. The results indicated that the compressive strength of RMC is the highest and reaches 32.5R OPC when the mass ratio of CaO/(SiO2+Al2O3) is 1.37, and the Na+ leaching concentration is environmentally acceptable. The 7 days compressive strength of RM-based cementitious material No.2 (RMC2) can reach 93.80% of that of 28 days. As the predominant hydration products, cement hydration product (Ca5(SiO4)2(OH)2) and geopolymer (CaAl2Si2O8·2H2O and Na3Al3Si3O12·2H2O) were principally responsible for the strength development of RMC2 at 7 days. The optimal densification microstructure and [SiO4] polymerization structure was presented in RMC2. The supreme Na+ consolidation rate was 99.23% in RMC2 due to the cooperation of physical fixation and [Si(Al)O4] charge balance principle. This paper provides a fresh theoretical guidance for the utilization of RM and its Na+ in building materials.

Effect of high-energy ball-milling on the spark plasma sinterability of ZrB2 with transition metal disilicides

A wide suite of powder mixtures of ZrB2 with five different additions of transition metal disilicides (MeSi2; 5, 17.5, or 30 vol% MoSi2; 17.5 vol% TaSi2; or 17.5 vol% ZrSi2) were prepared by high-energy ball-milling (HEBM) for different times, and their optimal densification temperatures were evaluated by dilatometric spark-plasma-sintering (SPS) tests to compare their sinterability. SPS densification tests at the so-determined optimal densification temperatures were also performed in selected cases. It was found that HEBM progressively enhanced the sinterability, especially once the ZrB2 particle sizes were refined to the ultrafine range or below (<250 nm). It was also observed that the sinterability was enhanced (i) with the greater addition of MeSi2, and (ii) with the lower refractoriness of the MeSi2. Nonetheless, under long-time HEBM, the addition of harder, more refractory MeSi2 or of softer, less refractory MeSi2 is equally effective in terms of sinterability, both enabling low-temperature densification (SPS at ∼1200 °C).

Effects of Brown Sugar Water Binder Added by Spraying Method as Solid Bridge on the Physical Characteristics of Biomass Pellets.

The binder can improve the physical characteristics of biomass pellets by forming solid bridges and increasing the adhesion of biomass materials. Taking pine sawdust as raw material and brown sugar water with different concentration as a binder, this study adopted spraying and stirring methods, respectively, and mixed brown sugar water with biomass in diverse proportions. The characteristic of pellets such as durability, relaxation ratio and compressive strength were studied by orthogonal design. Through range analysis, BP (Back Propagation) neural network factor significance analysis and mapping the relationship between physical properties and factors according to the importance of each factor, the effect of densification variables on the physical characteristics of biomass pellets was studied, and the outcome of adding brown sugar water binder to raw material by spraying method in improving the densification quality of biomass was explored. Results showed the brown sugar water binder added to pine sawdust by spraying method could mix the binder and biomass raw material more evenly compared with the stirring method. The relaxation ratio of pellets obtained by spraying method was reduced by 13.47%. The optimal densification conditions of pine sawdust were when the compaction pressure was 100 MPa, the mass ratio of brown sugar to water was 2:1, the proportion of brown sugar water to biomass material was 3%, and the adding method was spraying.

Controlling sintering and grain growth of nanoceramics

Abstract Sintering and grain growth are fundamental processes affecting microstructural evolution of ceramics. The phenomenological models describing these processes as found in textbooks are simplifications of the very dynamic set of system’s parameters, which lead to limited predictability and the need for extensive empirical analyses for process optimization. One such simplification is the underestimation of interfacial energies and their relationships with diffusion paths and growth control. The goal of this paper is to clarify how thermodynamics of interfaces can provide opportunities for a more refined control of ceramic processing. On the first part of this paper we discuss the relevance of grain boundary energies in grain growth, showing that although grain boundary mobility is the preferred parameter choice for designing of grain growth inhibition, recent studies demonstrate dopants can be selected to annihilate the process driving force and enable thermally (meta)stable nanoceramics. In the second part of the paper, we point out shortcomings from the current sintering theory and discuss that both surface and grain boundary energies with their associated rates of interfacial area evolution represent a more comprehensive sintering description. This perspective offers tunable parameters that may set a new foundation for the design of sintering aids for optimal densification.

BinDash, software for fast genome distance estimation on a typical personal laptop.

The number of genomes (including meta-genomes) is increasing at an accelerating pace. In the near future, we may need to estimate pairwise distances between millions of genomes. Even with the use of cloud computing, very few softwares can perform such estimation. The multi-threaded software BinDash can perform such estimation using only a typical personal laptop. BinDash implemented b-bit one-permutation rolling MinHash with optimal densification, an existing data-mining technique. BinDash empirically outperforms the state-of-the-art software in terms of precision, compression ratio, memory usage and runtime according to our evaluation. Our evaluation is performed with a Dell Inspiron 157559 Notebook on all bacterial genomes in RefSeq. BinDash is released under the Apache 2.0 license at https://github.com/zhaoxiaofei/BinDash. Supplementary data are available at Bioinformatics online.

Study of the Influence of TiB Content and Temperature in the Properties of In Situ Titanium Matrix Composites

This work focuses on the study of the microstructure, hardening, and stiffening effect caused by the secondary phases formed in titanium matrices. These secondary phases originated from reactions between the matrix and boron particles added in the starting mixtures of the composites. Not only was the composite composition studied as an influencing factor in the behaviour of the composites, but also different operational temperatures. Three volume percentages of boron content were tested (0.9 vol %, 2.5 vol %, and 5 vol % of amorphous boron). The manufacturing process used to produce the composites was inductive hot pressing, which operational temperatures were between 1000 and 1300 °C. Specimens showed optimal densification. Moreover, microstructural studies revealed the formation of TiB in various shapes and proportions. Mechanical testing confirmed that the secondary phases had a positive influence on properties of the composites. In general, adding boron particles increased the hardness and stiffness of the composites; however rising temperatures resulted in greater increases in stiffness than in hardness.