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The preparation of SiC w /SiC materials was realized by SLS technology. The effect of SiC powder size on the number and size of SiC whisker formation was investigated. The tortuosity and diameter of open pores are introduced to modify the classical molecular collision model, and the relationship model between the growth rate of SiC whisker and porosity was established. The influence mechanism of powder size on the number of whisker growth was revealed. According to the model, the number of in-situ whisker growth in powder can be calculated, and the calculated results by using this model agreed with the test results. So it is suitable for in-situ whisker microstructure control under SLS technology, and also suitable for other 3D printed whisker in-situ reinforced ceramic material systems. This is of great significance to expand the application of 3D printing ceramic matrix composites. [ABSTRACT FROM AUTHOR]

Intermetallic Ti–46Al–5Nb (at.%) alloys were directionally solidified by single directional solidification (SDS) process and double directional solidification (DDS) process using a Bridgman directional solidification furnace. Microstructure and crystal orientation neighboring the initial growth interface as well as the quenched mushy zone before starting directional solidification were investigated in the SDS and DDS processes, respectively. The results show that the dendrite morphology changes from equiaxial to columnar, but the directional dendrite segregation is almost keep the continuity across the initial growth interface after SDS and DDS processes, respectively. Crystal orientations in the regions neighboring the initial growth interface have preferential modifications along the growth direction. Compared with that in the first DS of DDS, the length of the initial mushy zone significantly decreases, but the β dendrite is well-orientated in the mushy zone in the second DS. Crystal orientation can be well-controlled in DDS by modifying the β growth morphology as well as the orientation in initial mushy zone of the two DS processes. The directional dendrite parallel to the growth direction and the preferred β orientation are considered as the main reasons to β seed crystallization. The process of the β seed crystallization is also discussed. Based on the β seeding, the DDS process can align the β dendrite orientation and promote the peritectic transformation undergoing completely, thus control the lamellar colony boundaries as well as the lamellar microstructures inside of the colonies. [ABSTRACT FROM AUTHOR]

Directional solidification (DS) experiments with thermal stabilization (TS) treatments were performed on Ti–46Al–5Nb (at.%) alloys in a Bridgman-type furnace using a quenching technology. Influence of the TS treatment on mushy zone and directional growth afterwards were investigated. The results show that the length of the mushy zone decreases but the β dendrite spacing in directional growth significantly increases with increasing TS time. During the DS process, β dendrite spacing is more homogeneous and its growth direction is more inclined to parallel to the axial direction with increase of the TS time. Al solute concentration in the mushy zone in a steady-state is always lower than that in original as-cast alloys. The mushy zone with the columnar β and α grains is easily produced after TS treatment on the alloys with microstructures of the directional dendrite segregation morphology before DS starting. TS treatment results in the redistribute of solute Al thus changes the phase constituent in the mushy zone. An appropriate TS is necessary to produce the L + β + α region in the mushy zone, which is of great benefit to control DS microstructures of TiAl peritectic alloys. [ABSTRACT FROM AUTHOR]

An aqueous CO 2 –cement interaction experiment along with X-ray computed micro-tomography characterisation of pre- and post-exposure cement samples was carried out to investigate the cement structure evolution under geologic carbon storage conditions. An image processing framework was proposed for mapping mineral dissolution and precipitation and characterisation of carbonate shell morphology. The main workflow covered in this framework is to, 1) register cement CT images before and after reaction; 2) generate the difference image showing chemical alteration and map the difference image to demonstrate local content changes of pore space, calcite and portlandite; 3) segment carbonate shell from the difference image; 4) generate auxiliary images including skeleton, 3D local thickness and surface boundaries of the carbonate region, and 5) spatial quantification of the area, thickness, penetration depth and pore/calcite/portlandite content changes of the carbonate shell. The effectiveness of the framework was validated through step-by-step demonstration of results when deploying the framework to process the CT images of six cement samples acquired before and after reaction with CO 2. The 3D mineral precipitation and dissolution (or local mineral content change) map and the internal and external carbonate shells were visualised. The spatial distribution of the shell area, thickness, penetration depth and pore/calcite/portlandite content changes along the height of the sample was revealed. Overall, the dissolution and precipitation map gives more intuitive and interpretable results of CO 2 -induced chemical alteration than direct visual comparison from the original CT images, and the morphological quantification of the carbonate shell gives reasonable interpretation of the spatial distribution of the carbonate reaction. [ABSTRACT FROM AUTHOR]

In this work, as-cast microstructure characteristics are identified for the TiAl–Nb alloys with four typical solidification modes, namely, single β (B mode), hypo-peritectic (BA mode), hyper-peritectic (BAA mode) and single α (A mode) solidification. B mode alloys are chemically more homogeneous, and they show netty white ridge β-segregation and fine equiaxed lamellar grains compared to the other three mode alloys due to the β→α solid-phase transformation. Increasing Nb addition decreases the size of primary β dendrite and thus decreases the lamellar colony size of the B mode alloy. In BA and BAA mode alloys, much higher Al-segregation and worm-like β-segregation are formed in the interdendritic and dendritic regions, respectively. The low fraction and rapid growth of primary β dendrite in liquid and the subsequent peritectic α growth are responsible for the sharp casting texture and coarse lamellar colonies. A mode alloy is characterized by the columnar colony and weak casting texture due to the rapid growth of primary α dendrite accompanied by the lack of solid-state transformation refinement. As-cast microstructure evolution during cooling that depends on the phase transition sequence in the TiAl–Nb alloys with different solidification modes will also be proposed. • As-cast microstructure characteristic is specified for four solidification mode alloys. • Increase of Nb addition decreases the size of primary β dendrite. • Microstructure evolution dependent on phase transition sequence is proposed. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs), promising green solvents, and ultrahigh pressure extraction (UPE) as an effective auxiliary extraction method, have attracted wide attention. In this study, DES was coupled with UPE to efficiently extract baicalin from Scutellaria baicalensis Georgi. First, choline chloride: lactic acid (ChCl-LA, molar ratio 1:1) was selected as the most appropriate DES by comparing the extraction yield of different DESs. Second, the extraction protocol was optimized by response surface methodology (RSM) considering the impacts of ChCl-LA concentration, extraction pressure, extraction time and liquid-solid ratio on the extraction yield. Under the optimal condition (40 vol% water content, extraction pressure of 400 MPa, extraction time of 4 min and a liquid-solid ratio of 110 mL/g), a maximum yield of 116.8 mg/g was achieved, higher than that obtained by the traditional extraction method. The microstructure of the raw and extracted Scutellaria baicalensis Georgi samples according to scanning electron microscope (SEM) images revealed that the dissolution of chemical components was enhanced from the disrupted root tissues after DESs-UPE. DESs coupled with UPE could effectively extract the baicalin from Scutellaria baicalensis Georgi as a rapid and efficient extraction method. [ABSTRACT FROM AUTHOR]

In this study, a HfSi 2 -HfO 2 -SiO 2 nanocomposite coating is prepared on a TiAl alloy via a one-step liquid plasma-assisted particle deposition and sintering (LPDS) method to enhance its ablation resistance. For comparison, a conventional plasma electrolytic oxidation (PEO) coating is fabricated on the substrate. The phase composition, microstructure, and elemental distribution of the coatings are investigated via scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Moreover, the ablative resistance of the coated samples under flame (> 1500 °C) ablation is evaluated using a methyl acetylene polypropylene gas spray gun. The results show that numerous HfSi 2 particles are incorporated into the coating with partial oxidation to HfO 2 during the LPDS, thus resulting in a larger thickness by approximately eight folds compared with the thickness of the PEO coating. After ablation for 360 s, 15.4 % of the PEO coating peeled off, whereas no exfoliation occurred on the HfSi 2 -HfO 2 -SiO 2 nanocomposite coating. The nanocomposite coating exhibits the smallest thickness after ablation. The superior high-temperature ablation resistance of the nanocomposite coating is primarily attributed to the presence of an oxygen-consuming HfSi 2 phase. Furthermore, the formation of HfO 2 during high-temperature ablation effectively anchors the ceramic coating, thereby impeding crack propagation and hindering oxygen diffusion. Hence, LPDS is a prominent strategy for the design and fabrication of multifunctional ceramic coatings that incorporate various functional particles, which can enhance the thermal protection of alloy substrates. • A novel HfSi 2 -HfO 2 -SiO 2 nanocomposite ceramic coating by the LPDS technique is prepared on the TiAl alloy. • No peeling occurred in the nanocomposite coating under flame ablation of MAPP gas (>1500 °C) for 360 s. • The nanocomposite coating containing HfSi 2 and HfO 2 provides more conducive to the ablation resistance. • The HfO 2 -SiO 2 oxide layer formed during the ablation process, hindering crack propagation and oxygen diffusion. [ABSTRACT FROM AUTHOR]

Highlights • An novel model for permeability of damaged fractal tree-like network was derived based on fractal geometry. • An analytical expression for permeability of damaged fractal tree-like network is found to be a function of the micro-structural parameters. • The fluid flow mechanisms in damaged fractal tree-like network was explored. Abstract Damage of the tree-like branching networks in nature is a very prevalent phenomenon, which has attracted a great deal of attention in various fields ranging from animate to inanimate flow systems for several decades. In this study, a novel model for permeability is proposed for damaged tree-like branching networks based on the fractal characteristics of tree-like branching networks. It is found that the proposed model is a function of structure parameters of damaged tree-like branching networks, such as the numbers (p) of damaged channels, the diameter ratio (β), length ratio (α), branching number (n), branching level (k), and the total number of branching levels (m) in the network. The influence of the micro-structural parameters on the effective permeability of the networks is systematically studied. It is found that the numbers of damaged channels and branching levels have significant effect on its permeability and pressure drop. The present results are much different from the heat transfer in damaged tree-like branching networks. The model may have the potential in analysis and design of fluid flow systems. [ABSTRACT FROM AUTHOR]

Sintering densification processes of the composite ceramics (Bi 3.15 Nd 0.85 Ti 3 O 12 (BNdT)/CoFe 2 O 4 (CFO)) have been investigated using dilatometric experiments combining with the TG-DTA, density measurements and microstructure studies. Microstructures analyses and quantitative calculations show that the composite ceramics achieve densification at low temperatures (<1150 °C). The formation of coherent-lattice interfaces between (200)/(020) BNdT and (310) CFO are considered to play an important role on such densification. The intrinsic preferred orientation of BNdT grains is suppressed by CFO phase because of this coherent relationship. Although the sintering activation energies of 0.8BNdT-0.2CFO are about 2.7 times larger than those of pure BNdT due to the pinning effect, the composite ceramic could still be densified, indicating the formation energy of coherent-lattices provided the extra sintering force. The even coercive electric fields of the resulting pure BNdT and 0.8BNdT-0.2CFO ceramic are approximately 89 and 97 kV/cm, respectively, at 250 kV/cm. The polarization of 0.8BNdT-0.2CFO reaches saturation around 430 kV/cm. [ABSTRACT FROM AUTHOR]

In this work, we presented investigations on the microstructural, magnetic, dielectric and conductive properties of (1- x)Na 0.5 Bi 0.5 TiO 3 - x CoFe 2 O 4 (NBT-CFO) composite ceramics (x = 0.1, 0.2, 0.3 and 0.5). The composites were synthesized using the in-situ sol-gel method, and the resulting CFO/NBT embedded structure was observed in the 0.9NBT–0.1CFO sample. Rietveld refinement confirmed that the embedded structure had remarkable effects on the c / a ratios of NBT-CFO composites. Increasing normalization saturation magnetizations were observed with increasing of CFO contents, thus revealing the influence of phase interfaces on magnetism. Dielectric relaxation anomalies were observed on both temperature dependent permittivity and loss spectra. Two sets of anomalies in these spectra were caused by space charges on the phase interfaces of embedded CFO grains and the NBT matrix. The conduction behavior of ceramics with and without the embedded structure obeyed the double power law and Jonscher's fraction power law, respectively, which inferred a transformation from the AC to the DC conduction mechanism with the disappearance of the embedded structure. [ABSTRACT FROM AUTHOR]

Abstract Lead-free 0.9Na 0.5 Bi 0.5 TiO 3 − 0.1CoFe 2 O 4 (0.9NBT-0.1CFO) composite ceramics with novel embedded microstructures were synthesized by an in-situ sol-gel method. The structural evolution, ferroelectricities and dielectricities were studied. The embedded structures were formed around 1000 °C − 1100 °C with contributions of the strong grain boundary mobility and small size of CFO grains, and then were destroyed at 1150 °C. The 0.9NBT-0.1CFO ceramic sintered at 1100 °C showed the optimal ferroelectric hysteresis loop with a remanent polarization of ~ 52 μC/cm2. Anomaly peaks in the temperature dependent permittivity curves were observed in all ceramics with embedded structures. These Debye-like type peaks generated by the interface effects of NBT and CFO appeared around ~620 °C, and could reach relatively large values of ~15000 at 100 kHz. The change rate of permittivity between zero magnetic field and 500 Oe reached 2.4%, indicating a noteworthy magnetoelectric effect. [ABSTRACT FROM AUTHOR]

• With increasing silica powder dosage, high calcium-silicon ratio phases decreased. • Dense structure composed of xonotlite was beneficial to mechanical properties. • Hillebrandite, jaffeite, reinhardbraunsite and xonotlite were all single crystals. • Xonotlite was formed by decalcification reaction and Si-OH polymerization. The effect of silica powder dosage on the mechanical properties and microstructure of C 3 S, especially on the crystallization transformation of hydration products, was studied by VHT, XRD, TGA, SEM-EDS and TEM. The results showed that at 230 °C, the optimal amount of silica powder added was 40%, and the Vickers hardness increased by 39.21%. With increasing silica powder dosage, the contents of hillebrandite, jaffeite, and reinhardbraunsite continued to decrease, and the content of xonotlite continued to increase. Coarseness of the microstructure at high temperature was the main reason for the deterioration of mechanical properties, and the dense structure composed of xonotlite was beneficial to improve the mechanical properties. The microscopic morphology and crystal structure of hillebrandite, jaffeite, reinhardbraunsite and xonotlite were confirmed. These hydration products were all single crystals. C-S-H in the C 3 S-silica powder system decalcified and produced large amounts of Si–OH, and silica powder obtained calcium from C-S-H. Si–OH on the surface of silica powder polymerized with Si–OH in decalcified C-S-H or interacted with silicate ions in the hydration system, which formed xonotlite. [ABSTRACT FROM AUTHOR]

• According to the investigation, accelerated carbonation conditions fully destroy the AAMs within 7 days. • The microstructure changes in the AAMs were mainly caused by crack and pore propagation during accelerated carbonation. • A liquid environment results in formation of carbonation products like calcite and vaterite in the AAMs samples. Alkali-activated materials (AAMs) have two major environmental benefits compared to traditional cement-based materials: reducing greenhouse gas emissions and recycling industrial by-products. To evaluate the possibility of using AAMs for well construction in carbon capture, utilization and storage (CCUS) projects, the carbonation resistance performance of AAMs was investigated under accelerated carbonation conditions. The results showed that the loss ratios of the AAMs compressive strength were 89.75% and 88.20% in the gas and liquid phase carbonation environments during the first 3 days, respectively. The structural damage in the AAMs was mainly caused by the leakage of Ca2+ from the calcium silicate hydrate (C-S-H) phase of the matrix, converting it into crystalline calcium carbonate after CO 2 attack. From 7 days of the start of carbonation, the cumulative pore volumes of the AAMs samples increased from 0.97 to 5.02 ml/g and from 0.97 to 4.37 ml/g in the gas and liquid phase carbonation environments, respectively. The presented work indicates that under accelerated carbonation conditions, the rate of destruction of AAMs is too rapid for such material to be used for the construction of CCUS wells. [ABSTRACT FROM AUTHOR]