Nucleation Effect Research Articles

Carbon nanofibers and polyvinyl-alcohol fiber hybrid-reinforced high-performance concrete: Mechanical property, chloride penetration resistance, and material characterization

The hybridization of nanomaterials and macroscopic fibers is currently a popular topic. The aim of this study was to explore the application potential of incorporating carbon nanofibers (CNFs) into concrete and to analyze the effect of CNFs dispersant on concrete slump and early strength. Polyvinyl alcohol (PVA) fibers and CNFs were used to prepare composite fiber-reinforced (CNFs-PVA) concrete to improve the continuity of concrete properties at the micron/nanometer scale. The engineering properties such as compressive strength, flexural strength and resistance to chloride ion erosion performance of the concrete were investigated, and the microstructure of concrete was characterized using X-ray diffraction (XRD), scanning-electron microscopy (SEM), and X-ray computed tomography (X-CT). The results showed that CNFs could improve the early strength. The combined use of CNFs and PVA increased the 28-day compressive and flexural strength by 23.38% and 28.73%, respectively, compared to the control group. Correspondingly, the electric flux and Migration rate of chloride ions (DRCM) were minimized. From the SEM and XRD test results, it is clear that CNFs and PVA fibers can: (i) bridge low-density C-S-H to form higher-density C-S-H gels, (ii) form longer chain-like fibers with enhanced load transfer and chloride binding capacity, (iii) act as internal curing agents to enhance hydration at the interface, (iv) promote the formation of the aluminum phase hydration products and calcium carbonate phase, and (v) CNFs and PVA refine the pore size by increasing the gel pores and reducing the percentage of microcracks. The combined results indicate that the improved performance of CNFs-PVA is due to the combined effect of bridging and nucleation of hydration products by CNFs, adsorption of hydration products by CNFs-PVA, and promotion of pore filling by the generated hydrides such as calcium carbonate and ettringite. These findings provide new insights for the design of high-performance concrete materials.

An SLM-processed Er- and Zr- modified Al–Mg alloy: Microstructure and mechanical properties at room and elevated temperatures

The elements of Sc and Zr have been used to modify the Al–Mg alloys to improve the Selective Laser Melting (SLM) processability and enhance the mechanical properties. However, these alloys are very expensive due to the addition of Sc. In this study, Er is used as a cost effective substitute for Sc in an Al–Mg alloy processed by SLM and the effects of Er in combination with Zr on microstructure and mechanical properties are investigated. It is found that with optimized laser parameters, Er and Zr result in excellent grain refining, forming a bimodal grain structure with fine equiaxed grains (∼0.8 μm) and columnar grains (2–10 μm). The grain refinement is mainly attributed to the heterogeneous nucleation effect and the grain boundary pinning effect of the Al3Er and Al3(Er, Zr) particles. The as processed condition shows a large amount of Al3Er and Al3(Er, Zr) precipitates 5–50 nm in size with L12 structure, and additional post-SLM aging treatment is not required as it does not provide further benefit in hardness. The Al–Mg–Er–Zr alloy exhibits a room temperature tensile strength of 340 MPa and 329 MPa in x and z directions respectively, as well as a 300 °C tensile strength of 107 MPa and 102 MPa in x and z directions, making this alloy an attractive and economical candidate for applications at elevated temperatures.

Development of low-carbon and cost-effective ultra-high performance concrete using carbonated recycled fine aggregate

This paper studied the influence of carbonated recycled fine aggregate (RFA) on mechanical and microstructural performance of ultra-high performance concrete (UHPC), aiming to develop a low-carbon and cost-effective UHPC. This includes the changes in strength, hydration kinetics, RFA-to-paste interfacial microstructure, and pore structure with the use of carbonated RFA. The environmental and economic effect of using carbonated RFA in UHPC is evaluated. The RFA content was investigated at 0–30%, by mass of total sand. Experimental results showed that a reduction greater than 10% in crushing index and water absorption of RFA was achieved by carbonation. The increase of carbonated RFA content from 0 to 30% led to 45% reduction in autogenous shrinkage of UHPC. The use of 20% uncarbonated RFA resulted in 12% and 10% reduction in 28-d compressive and flexural strengths, respectively, while such use of carbonated RFA can secure similar 28-d compressive and flexural strengths compared to those without RFA. Despite the reduced cement hydration, the use of carbonated RFA can secure a denser RFA-to-paste interfacial microstructure and refine the pore structure of UHPC compared to those made with uncarbonated RFA, given the chemical bonding and nucleation effect of carbonated RFA. Moreover, the use of 20% carbonated RFA can enable 5% decrease in the Global Warming Potential value evaluated by life cycle assessment compared to that without RFA. Such use of RFA led to a decrease greater than 15% in UHPC cost. This indicated the low-carbon and cost-effective characteristics of the developed UHPC made with carbonated RFA.

Hybrid reinforced effect of long carbon fiber and short glass fiber on polycarbonate foams

AbstractBecause of advantages such as remarkable mechanical properties and the ease of recycling, fiber‐reinforced thermoplastic polymer composites have been increasing in importance in industrial, transport, and sporting potential extraordinary applications. To fabricate polycarbonate (PC) components with lightweight and high mechanical properties, short glass fiber (SGF), long carbon fiber (LCF) reinforcement, and foaming technology were used in this study. The effects of SGF, LCF, and SGF/LCF on the mechanical properties and foaming quality of PC samples were carefully investigated and compared. The results show that SGF has a better foaming nucleation effect than LCF, and the mechanical enhancement effect of LCF is more significant than that of SGF. The combination of SGF and LCF can effectively improve the cell quality of foam samples and significantly enhance their mechanical properties. Therefore, a comprehensive application of the fiber‐reinforcement effect of PC resin is proposed.Highlights LCF and SGF reinforced PC foams have been successfully fabricated. Hybrid reinforced effect of LCF and SGF on PC foams was verified.

Evaporation of Saline Droplets on a Superhydrophobic Substrate: Formation of Crystal Shell and "Legs".

We studied the evaporation-driven crystallization in the droplets of sodium acetate anhydrous (CH3COONa) aqueous solution, which were deposited on superhydrophobic substrates. The results reveal distinct crystallization behaviors between saturated and unsaturated droplets under identical experimental conditions. Specifically, unsaturated droplets could form a quasi-spherical crystal shell on the superhydrophobic substrate, while saturated droplets could develop crystal legs between the droplet and substrate when the crystal shell formed. Subsequently, the saturated droplet was lifted off the substrate by the growing crystal legs. The formation of crystal shell was closely associated with the evaporation from the droplet surface and the internal convection inside the droplet. The formation of crystal legs was induced by the heterogeneous nucleation effect caused by the substrate of SiO2 nanoparticles. These findings provide valuable insights into regulating the morphology of salt crystallization through adjustments in salt solution concentration and substrate surface structure.

A molecularly engineered bioderived polyphosphonate containing Schiff base towards fire-retardant PLA with enhanced crystallinity and mechanical properties

To expand the practical application and realize sustainable development, it is urgent to develop advanced polylactide composites with fire retardancy and mechanically strong properties by utilizing bio-derived additives. Unfortunately, such desired performance portfolio is still unsatisfactory due to unclear mechanism and improper design strategy. In this paper, a novel bio-derived polyphosphonate containing Schiff base (PVP) was prepared by a two-step method of condensation and addition reactions. By incorporating only 0.5 wt% PVP, the LOI value of PLA is increased to 32.5 vol% as well as achieving a UL-94 V-0 rating. Such superior fire retardancy is ascribed to the physical barrier effect of char residue, which arising from the cyclization of Schiff base and catalytic carbonization of polyphosphonate. Due to the crosslinking reaction between PLA and PVP and nucleating effect of PVP in the PLA matrix, the mechanical strength of PLA is increased by 10.2% with addition of 1.0 wt% PVP. This study provides a feasible way for designing bio-derived fire retardants to simultaneously improving the fire retardancy and mechanical strength of PLA, thus is expected to expand the practical application of PLA materials.

Influence of the Graphene Oxide on the Pore-Throat Connection of Cement Waste Rock Backfill.

The pore-throat characteristics significantly affect the consolidated properties, such as the mechanical and permeability-related performance of the cementitious composites. By virtue of the nucleation and pore-infilling effects, graphene oxide (GO) has been proven as a great additive in reinforcing cement-based materials. However, the quantitative characterization reports of GO on the pore-throat connection are limited. This study applied advanced metal intrusion and backscattered electron (BSE) microscopy scanning technology to investigate the pore-throat connection characteristics of the cement waste rock backfill (CWRB) specimens before and after GO modification. The results show that the microscopic pore structure of CWRB is significantly improved by the GO nanosheets, manifested by a decrease in the total porosity up to 31.2%. With the assistance of the GO, the transfer among internal pores is from large equivalent pore size distribution to small equivalent pore size distribution. The fitting relationship between strength enhancement and pore reinforcement efficiency under different pore-throat characteristics reveals that the 1.70 μm pore-throat owns the highest correlation in the CWRB specimens, implying apply GO nanosheets to optimizing the pore-throat under this interval is most efficient. Overall, this research broadens our understanding of the pore-throat connection characteristics of CWRB and stimulates the potential application of GO in enhancing the mechanical properties and microstructure of CWRB.

Dispersant and Protective Roles of Amphiphilic Poly(ethylene phosphate) Block Copolymers in Polyester/Bone Mineral Composites.

Composites of synthetic bone mineral substitutes (BMS) and biodegradable polyesters are of particular interest for bone surgery and orthopedics. Manufacturing of composite scaffolds commonly uses mixing of the BMS with polymer melts. Melt processing requires a high homogeneity of the mixing, and is complicated by BMS-promoted thermal degradation of polymers. In our work, poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) composites reinforced by commercial β-tricalcium phosphate (βTCP) or synthesized carbonated hydroxyapatite with hexagonal and plate-like crystallite shapes (hCAp and pCAp, respectively) were fabricated using injection molding. pCAp-based composites showed advanced mechanical and thermal characteristics, and the best set of mechanical characteristics was observed for the PLLA-based composite containing 25 wt% of pCAp. To achieve compatibility of polyesters and pCAp, reactive block copolymers of PLLA or PCL with poly(tert-butyl ethylene phosphate) (C1 and C2, respectively) were introduced to the composite. The formation of a polyester-b-poly(ethylene phosphoric acid) (PEPA) compatibilizer during composite preparation, followed by chemical binding of PEPA with pCAp, have been proved experimentally. The presence of 5 wt% of the compatibilizer provided deeper homogenization of the composite, resulting in a marked increase in strength and moduli as well as a more pronounced nucleation effect during isothermal crystallization. The use of C1 increased the thermal stability of the PLLA-based composite, containing 25 wt% of pCAp. In view of positive impacts of polyester-b-PEPA on composite homogeneity, mechanical characteristics, and thermal stability, polyester-b-PEPA will find application in the further development of composite materials for bone surgery and orthopedics.

Increase in volume stability of RO phases in steel slag by combined treatment of alkali and dry carbonation

RO phases account for 8.5–16.9 wt% of steel slags and exhibit delayed hydration activity, which may result in poor volume stability of steel slags (SS). Treatment of alkali activator (sodium silicate) followed by dry carbonation technology (ADC) was conducted on synthetic RO phases with various molar ratios of FeO, MgO, and MnO to promote its early hydration activity. Results show that 28 d compressive strength of mortar added by ADC_SS is 19.67% higher than that of added untreated SS and 26% decrease in expansion rate. Hydration degree of RO phases increases obviously during alkali treatment from 10.6% to 21.7% (RO-6), and is further stimulated by subsequently carbonation (reaching 44.1%), both resulting in much consumption of expansive component (i.e., MgO) in RO phases. The early hydration activity of cement promoted by adding ADC_RO phase/SS, which mainly attributes to the nucleation effect of hydration and carbonation products (i.e., Mg(OH)2, pyoaurite, and MgCO3·3H2O). The alkali excitation reaction of silica gels produced during carbonation as well as the formation of monocarboaluminate further contribute to the strength gain. ADC_SS used as admixture for cement makes pastes have advantage of higher strength, higher hydration rate, lower heat release, and less expansion rate compared to the system contained untreated SS. ADC may be a potential method to treat SS and makes SS to be used as admixture for Portland cement.

Effect of bias-enhanced nucleation on the microstructure and thermal boundary resistance of GaN/SiNx/diamond multilayer composites

The low effective thermal boundary resistance (TBReff) at the GaN/diamond interface is very important for the development of high-power, high-frequency and high-temperature GaN-on-diamond devices. The nucleation and growth of diamond are key processes for modulating the TBReff. This work proposed the bias enhanced nucleation technique to adjust the nucleation of GaN/SiNx/diamond multilayer composites in the MPCVD process at different bias voltages (400–700 V), thereby adjusting TBReff. Pulse bias is beneficial to a stable plasma environment and to obtain a complete GaN/diamond interface structure. The transient thermoreflectance characterization indicated that the GaN/SiNx/diamond multilayer composite prepared under 700 V bias nucleation condition had the lowest TBReff (26 ± 10 m2K/GW), whereas the GaN/SiNx/diamond multilayer composite at 600 V bias had the highest TBReff (83 ± 18 m2K/GW). The role of bias enhanced nucleation process in the TBReff was systematically analyzed by electron microscopies (TEM and SEM) and Raman spectroscopy. The GaN/SiNx/diamond multilayer composite prepared at 600 V showed a thick mixed transition layer containing multiphase structures and rough interfaces due to efficient subsurface ion implantation, resulting in high TBReff. In contrast, at 700 V, a thinner nucleation zone and smoother interface result in the lowest TBReff. This work demonstrated the potential of adjusting TBReff at the GaN/diamond interface by using bias enhanced nucleation technique to modulate the diamond nucleation and growth processes.

Microstructure Characterization of Cement Pastes with Recycled Aluminum Spent Pot Lining

The use of locally available industrial by-products as supplementary cementitious materials and mineral fillers is vital for reducing the embodied carbon of modern concretes. Spent pot lining (SPL), a by-product of the aluminum industry, is massively produced worldwide. SPL treated with the low caustic leaching and liming process (LCLL-ash) is no more hazardous and can be used as cementitious material. This study aims to better understand the microstructure changes of cement paste incorporating aluminum smelter wastes, such as LCLL-ash and synthetic anhydrite. Ground LCLL-ash was used to partially replace cement in cement pastes with a constant water-to-binder ratio of 0.35. A small amount of anhydrite was added to some mixes. This study investigated chemo-micromechanical properties of cement paste systems through multiple techniques, including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, wavelength-dispersive spectroscopy, and microindentation test. The results showed that the reactive alumina from LCLL-ash modified the hydrated phases with the presence of the carbo-aluminate phases. The pastes containing LCLL-ash exhibited a higher CH, and C-S-H contents refer to the reference, suggesting that LCLL-ash has a slight nucleation effect. Moreover, LCLL cement paste showed an increase in the Ca/Si ratio of the C-S-H phase intermix. Finally, microindentation results revealed that adding anhydrite with 10% LCLL-ash enhanced the mechanical property of the cement paste at 28 days.

Graphene oxide-coated fly ash for high performance and low-carbon cementitious composites

Graphene oxide (GO) opens a new pathway for reducing carbon footprint in the construction industry and fabricating high-strength cementitious composites. However, due to the dispersion limitation, the application of GO in practical engineering has not been widely accepted. Hence, we evaluated the potential of the GO-fly ash hybrid as additives in cement under a coating method to assist the dispersion of the GO nanosheets. The results demonstrated that the GO could be successfully coated on the surface of the fly ash particles with good dispersion and strong connection via the proposed coating method. Besides, the coating method allowed more GO nanosheets to concentrate in the interfacial transition zone (ITZ) between fly ash and cement particles, making GO application more economical. The coated GO could then generate nucleation effects to promote the hydration process and provide pore-infilling effects to decrease the ITZ width (about 12.5%) and the crack ratio in ITZ (over 10%). Compared with the plain cement pastes, the workability, mechanical strength, and impermeability of the GO-coated fly ash modified cementitious slurry can be significantly reinforced up to 21.6%, 38.4% and 106.4%, respectively. The enhancement rate is further improved by about 7.1–58.5% compared with the traditional ultrasonic dispersion method. We expect the proposed innovative coating method would provide a good perspective of the future application of high-performance, cost-effective and environmentally friendly cementitious composites.

Investigation of the optimum preheating treatment parameters for extruded Mg–Gd–Y–Zn–Zr alloy using high-throughput experiments

The effects of different preheating treatments on the microstructure and mechanical properties of extruded Mg–13Gd–4Y–2Zn–0.5Zr (wt.%) alloys were investigated by using high-throughput experiments in this paper. The results showed that the solid solution and aging prior to extrusion (SAE) samples with heterogeneous microstructure had the best strength-plasticity synergy with ultimate tensile strength (UTS), yield strength (TYS) and elongation (EL) reaching 446.35 ± 3.1 MPa, 382.5 ± 2.5 MPa and 6.5 ± 0.8%, respectively. The formation of heterogeneous microstructures was mainly attributed to the weakening of the particle stimulation nucleation (PSN) effect by the dissolution of the primary Mg5RE phase during the solid solution process and the strong Zener pinning effect of the dynamic Mg5RE phase precipitation during the extrusion process, which inhibited grain boundary migration and grain growth. Optimum strength-plasticity synergy was due to fine grain strengthening, second phase strengthening, texture strengthening and heterogeneous deformation induced (HDI) strengthening. Strain gradients between deformed grains and dynamic recrystallized (DRXed) grains were generated during deformation process, in order to coordinate the deformation and generate more geometrically necessary dislocations (GNDs) within the deformed grains, resulting in a strong HDI effect. The increase in plasticity was mainly attributed to the change in texture type due to the rotation of the lattice, which promoted the activation of non-basal slip systems. This study provided an efficient and rapid method for probing optimal heat treatment parameters, aiming to reduce the influence of uncontrollable factors on experimental results and increase the rigor of the experiment.

Understanding the Effect of Nucleation in Amorphous Solid Dispersions through Time-Temperature Transformation.

In an earlier investigation, the critical cooling rate to prevent drug crystallization (CRcrit) during the preparation of nifedipine (NIF) amorphous solid dispersions (ASDs) was determined through a time-temperature transformation (TTT) diagram (Lalge et al. Mol. Pharmaceutics 2023, 20 (3), 1806-1817). The current study aims to use the TTT diagram to determine the critical cooling rate to prevent drug nucleation (CRcritN) during the preparation of ASDs. ASDs were prepared with each polyvinylpyrrolidone (PVP) and hydroxypropyl methylcellulose acetate succinate (HPMCAS). The dispersions were first stored under conditions promoting nucleation and then heated to the temperature that favors crystallization. The crystallization onset time (tC) was determined by differential scanning calorimetry and synchrotron X-ray diffractometry. TTT diagrams for nucleation were generated, which provided the critical nucleation temperature (50 °C) and the critical cooling rate to avoid nucleation (CRcritN). The strength of the drug-polymer interactions as well as the polymer concentration affected the CRcritN, with PVP having a stronger interaction than HPMCAS. The CRcrit of amorphous NIF was ∼17.5 °C/min. The addition of a 20% w/w polymer resulted in CRcrit of ∼0.05 and 0.2 °C/min and CRcritN of ∼4.1 and 8.1 °C/min for the dispersions prepared with PVP and HPMCAS, respectively.

Scalar transport and nucleation in quasi-two-dimensional starting jets and puffs

We experimentally investigate the early-stage scalar mixing and transport with solvent exchange in a quasi-two-dimensional (quasi-2D) jet. We inject an ethanol/oil mixture upward into quiescent water, forming quasi-2D turbulent buoyant jets and triggering the ouzo effect with initial Reynolds numbers, Re0=420,840, and 1680. We study two different modes of fluid supply: continuous injection to study a starting jet and finite volume injection to study a puff. While both modes start with the jet stage, the puff exhibits different characteristics in transport, entrainment, mixing, and nucleation, due to the lack of continuous fluid supply. We also inject a dyed ethanol solution as a passive scalar reference case, such that the effect of nucleation for the ethanol/oil mixture can be disentangled.For the starting jets, the total nucleated mass from the ouzo mixture seems very similar to that of the passive scalar total mass, indicating a primary nucleation site slightly above the virtual origin above the injection needle, supplying the mass flux like the passive scalar injection. With continuous mixing above the primary nucleation site, the mildly increasing nucleation rate suggests the occurrence of secondary nucleation throughout the entire ouzo jet.For the puffs, we show that the puff with the smallest Re0 propagates the fastest and its entrainment lasts the longest. We attribute the superior performance to the buoyancy effect, which transforms a turbulent puff into a turbulent thermal, and has been proven to have stronger entrainment. Although the entrainment and nucleation reduce drastically when the injection stops, the mild mixing still leads to non-zero nucleation rates and the reduced decay of the mean puff concentrations for the ouzo mixture.Adapting the theoretical framework established in Landel et al. (2012b) for quasi-2D turbulent jets and puffs, we successfully model the transport of the horizontally-integrated concentrations for the passive scalar. The fitted advection and dispersion coefficients are then used to model the transport of the ouzo mixture, from which the spatial–temporal evolution of the nucleation rate can be extracted. The spatial distribution of the nucleation rate sheds new light on the solvent exchange process in transient turbulent jet flows.

Computational Modeling of Magnesium Hydroxide Precipitation and Kinetics Parameters Identification.

Magnesium is a critical raw material and its recovery as Mg(OH)2 from saltwork brines can be realized via precipitation. The effective design, optimization, and scale-up of such a process require the development of a computational model accounting for the effect of fluid dynamics, homogeneous and heterogeneous nucleation, molecular growth, and aggregation. The unknown kinetics parameters are inferred and validated in this work by using experimental data produced with a T2mm-mixer and a T3mm-mixer, guaranteeing fast and efficient mixing. The flow field in the T-mixers is fully characterized by using the k-ε turbulence model implemented in the computational fluid dynamics (CFD) code OpenFOAM. The model is based on a simplified plug flow reactor model, instructed by detailed CFD simulations. It incorporates Bromley's activity coefficient correction and a micro-mixing model for the calculation of the supersaturation ratio. The population balance equation is solved by exploiting the quadrature method of moments, and mass balances are used for updating the reactive ions concentrations, accounting for the precipitated solid. To avoid unphysical results, global constrained optimization is used for kinetics parameters identification, exploiting experimentally measured particle size distribution (PSD). The inferred kinetics set is validated by comparing PSDs at different operative conditions both in the T2mm-mixer and the T3mm-mixer. The developed computational model, including the kinetics parameters estimated for the first time in this work, will be used for the design of a prototype for the industrial precipitation of Mg(OH)2 from saltwork brines in an industrial environment.

New strategy for reinforcing polylactic acid composites: Towards the insight into the effect of biochar microspheres

Having even particle size and regular morphology of biochar microspheres (BM) provides the possibility for preparing polylactic acid (PLA) films. Hence, the novelty is proposing a strategy for reinforcing PLA by BM. It was found that BM exhibited regular morphology, higher thermal stability, even particle size, and better pore characteristics. Although adding BM decreased the toughness of PLA due to the poor compatibility between BM and PLA, the nucleation effect of BM facilitated the crystallization in the PLA system. The tensile strength and modulus of BM/PLA composite films increased first and then decreased with increasing BM content. The stress concentration formed by BM particle agglomeration was responsible for the tensile strength and modulus decreases of BM/PLA composite films under higher BM addition. 2% BM added and 3% added composite films exhibited the best tensile strength and modulus with 64.99 MPa and 1.59 GPa, which was mainly attributed to the proper proportion of BM to PLA and the uniform distribution of BM in PLA. The results of this study confirmed the positive reinforcing effect of BM in PLA and are expected to be available in the composite film field.

A comprehensive assessment for the structural change of waxy crude oils induced by pour point depressant beneficiation

In the petroleum industry, the solid paraffins that precipitate out from a waxy crude oil complicate the low-temperature flow characteristics, causing major difficulties in pipeline transportation. Pour point depressants (PPDs) are often utilized to improve the flow characteristics of crude oils by modifying the morphology and structure of wax crystals, becoming a great technical and economic interest. The improving mechanism of PPDs on the structure of gelled waxy crude oil can be attributed to the nucleation, co-crystallization, and adsorption effect to the precipitated wax crystals, preventing the waxy structure from growing further and forming a volume spanning network. Many previous works about the PPDs’ effect have merely focused on the pour point, apparent viscosity, and yield strength depressing ability, while other structural properties have rarely been comprehensively evaluated. The objective of this study is to comprehensively reveal the change of the wax particle structure in oils benefitted with PPDs. The structure of gelled oils doped with PPDs was found to become less elastic and more susceptible to shear perturbation with a lower linear deformation range of 0.42% and a longer relaxed time scale of 3000 s. Large amplitude oscillatory shear (LAOS) tests show that the nonlinear viscoelastic behaviors can be weakened by PPDs, whereas the third harmonic value obtained by Fourier-transform analysis increases after adding PPDs, indicating that the sensitivity to applied load are strengthened. Meanwhile, the value of yield strain increases to about 8.7%, and the irreversible plastic deformation zone becomes relatively broader (brittleness index I increases to 70.9), which mean a more ductile fracture induced by PPDs would occur when yielding. Although the additive PPDs weaken the structural strength and the non-Newtonian characteristics (kinetic index of n1 increases to 0.8), the characteristic of thixotropy is obviously strengthened, and the doped crude oils exhibit a faster structural breakdown process after yielding. All these novel changes for structural features explored in this paper provide theoretical guidance into understanding the practical engineering problems of accelerated process for the pipeline restart flow benefitted with PPDs.

Effects of In-Situ Reaction, Extrusion Ratio and CeO2 on the Performance of Al-Ti-C-(Ce) Grain Refiners for Refining Pure Aluminum Grains.

Al-Ti-C-(Ce) grain refiners were prepared by combining in-situ reaction, hot extrusion, and adding CeO2. The effects of second phase TiC particle size and distribution, extrusion ratio, and Ce addition on the grain-refining performance of grain refiners were investigated. The results show that about 10 nm TiC particles are dispersed on the surface and inside of 100-200 nm Ti particles by in-situ reaction. The Al-Ti-C grain refiners, which are made, by hot extrusion, of a mixture of in-situ reaction Ti/TiC composite powder and Al powder, increase the effective nucleation phase of α-Al and hinder grain growth due to the fine and dispersed TiC; this results in the average size of pure aluminum grains to decrease from 1912.4 μm to 504.8 μm (adding 1 wt.% Al-Ti-C grain refiner). Additionally, with the increase of the extrusion ratio from 13 to 30, the average size of pure aluminum grains decreases further to 470.8 μm. This is because the micropores in the matrix of grain refiners are reduced, and the nano-TiC aggregates are dispersed with the fragmentation of Ti particles, resulting in a sufficient Al-Ti reaction and an enhanced nucleation effect of nano-TiC. Furthermore, Al-Ti-C-Ce grain refiners were prepared by adding CeO2. Under the conditions of holding for 3-5 min and adding a 5.5 wt.% Al-Ti-C-Ce grain refiner, the average size of pure aluminum grains is reduced to 48.4-48.8 μm. The reason for the excellent grain-refining and good anti-fading performance of the Al-Ti-C-Ce grain refiner is presumedly related to the Ti2Al20Ce rare earth phases and [Ce] atoms, which hinder agglomeration, precipitation, and dissolution of the TiC and TiAl3 particles.

CeO2 Protective Material against CMAS Attack for Thermal–Environmental Barrier Coating Applications

Calcium–magnesium–alumina–silicate (CMAS) attack is a crucial issue for thermal–environmental barrier coatings (T/EBCs) with the ever-increasing operating temperature of turbine engines. In this study, CeO2 has been demonstrated as a promising protective material for T/EBCs against CMAS attack. At 1300 °C, CeO2 powder kept excellent phase and structural stability in molten CMAS; there were some CMAS constituents dissolved into the CeO2 lattice to form a solid solution. With higher CeO2 contents and longer duration time, more CeO2 solid solution particles were formed, which acted as the nucleating agent for CMAS crystallization. As a result, apatite, anorthite and wollastonite crystalline products were easily generated. At 1300 °C for 10 h, CeO2 pellets covered with CMAS powder had limited degradation, which was attributed to the rapid crystallization of molten CMAS due to the excellent nucleating agent effect of the precipitated CeO2 solid solution.