Fine Crystals Research Articles

Sucrose Esters and Beeswax Synergize to Improve the Stability and Viscoelasticity of Water-in-Oil Emulsions.

W/O emulsions are commonly used to prepare stable low-fat products, but their poor stability limits widespread applications. In this study, sucrose ester (SE) and beeswax were utilized to prepare an oil dispersion system in rapeseed oil, which was used as the external oil phase to further synergistically construct the W/O emulsion systems. The results show that spherical and fine crystals are formed under the synergistic effect of SE and BW (1.5 SE:0.5 BW). In this state, a dense interfacial crystal layer was easily formed, preventing droplet aggregation, leading to droplet size reduction (1-2 μm) and tight packing, improving viscoelasticity and resistance to deformation, and increasing the recovery rate (52.26%). The long-term stability of W/O emulsions containing up to 60 wt% water was found to be more than 30 days. The increase in the aqueous phase led to droplet aggregation, which increased the viscosity (from 400 Pa·s to 2500 Pa·s), improved the structural strength of the emulsion, and increased the width of the linear viscoelastic region (from 1% strain to 5% strain). These findings provide some technical support for the further development of stable low-fat products.

Microstructure, mechanical and tribological properties of multilayer graphene reinforced WC-10Ni3Al prepared by microwave sintering

The multilayer graphene (MLG) reinforced WC-10Ni3Al cemented carbide was prepared by microwave sintering. The effects of the sintering temperature and MLG content on the microstructure and mechanical properties of the WC-10Ni3Al cemented carbide were investigated. The promotion effect and strengthening mechanism of MLG on WC-10Ni3Al by microwave sintering were explored. The tribological properties of WC-10Ni3Al and Ti6Al4V(TC4) were studied, and the wear mechanism of WC-10Ni3Al was revealed. The experiment result show that the WC-10Ni3Al-0.5 wt.% MLG sample sintered at 1450 °C had its greatest mechanical properties with a relative density of 96.9%, hardness of 1430 HV, flexural strength of 1410 MPa and fracture toughness of 15.7 MPa mm1/2, which were 4.2%, 12.2%, 24.4%, and 29.6% greater than those of the sample without MLG added, respectively. The reinforcing and toughening mechanisms of adding MLG in WC-10Ni3Al samples consist of fine crystal strengthening, crack bridging and deflection, MLG pulling out and bridging. The results of friction experiment show that the friction coefficient and wear rate of the WC-10Ni3Al samples were lower than those of YG8 (WC-8 wt. % Co cemented carbide). The WC-10 Ni3Al-0.5 wt.% MLG sample obtained the lowest friction coefficient of 0.35 and the lowest wear rate of 1.69 × 10−5 mm3N−1m−1. A stable solid lubrication film was produced on the friction surface of the WC-10Ni3Al samples, which was conducive to reducing the breakage and wear of WC grains. MLG can enhance the stability of solid lubrication film and reduce its friction coefficient.

A Study on Microstructure and Properties of Aluminum Alloy Bracket Produced by a New Semi-Solid Rheo-Diecasting Process

The performance of bracket component is low with uneven micro-structure, internal porosity and shrinkage defects produced by traditional liquid die casting process which cannot be strengthened by T6 heat treatment. In this paper, the aluminum alloy bracket with high-performance and light weight was prepared by a novel semi-solid slurry preparation technique that included chilling rod stirring and funnel-shaped cylinder device, which rapidly reducing the liquid temperature to near liquidus and realizing explosive nucleation. The effects of pouring temperature and CRS process on the microstructure and mechanical property of bracket were studied by optical microscopy (OM) equipped with polarizing mode and bench failure test. The results show that the as-cast microstructure mainly consists of near-spherical α-Al. And the semi-solid micro-structure was affected by these two critical parameters, the pouring temperature and CRS process. Without the condition of stirring, the micro-structure is typical dendritic with a certain proportion of fine spherical crystals, which was mainly generated during the filling of die casting process. And with the addition of the chilling rod, the finer and more uniform spherical semi-solid micro-structure was obtained with the lower pouring temperature. Based on the above semi-solid process and flow controlling through the mould design and vertical die casting process optimization, the high-performance bracket component without shrinkage can be prepared. Additionally, compared with the liquid die casting process, the internal quality and bench testing force of bracket prepared by CRS vertical die casting process are significantly improved.

Effect of boron element on microstructure and mechanical properties of 316L stainless steel manufactured by selective laser melting

Boron(B)element is often utilized to enhance mechanical properties of stainless steel due to its excellent performance. In this study, selective laser melting (SLM) was used to print 316L/B stainless steel with varying boron weight content. The effects of boron content on microstructure, nanoindentation, and mechanical properties of the printed 316L stainless steel were discussed. Fine cell dendrites and columnar crystals were found in the SLM printed stainless steel due to the rapid solidification in SLM. It was found that boron has a higher growth limiting factor in the iron system and the boron solute can provide a high component supercooling. By adding boron element to stainless steel during printing, the honeycomb and grain size after solidification are significantly reduced due to interactions between the boron element and the 316L. Tensile testing results show that the ultimate tensile strength of the SLM fabricated parts with 0.5 wt% and 1 wt% boron element addition can be increased significantly to 1071 MPa and 1174 MPa, respectively.

Phylogeny, morphology and chemistry reveal two new multispored species in the Lecanorasubfusca group (Lecanoraceae, Ascomycota).

Two new multispored species from China, Lecanoraanhuiensis Li J. Li & Printzen, sp. nov. and Lecanorapseudojaponica Li J. Li & Printzen, sp. nov. are described and illustrated here, based on morphological, chemical and molecular evidence. Lecanoraanhuiensis is characterised by an epruinose, yellowish-brown to deep brown apothecial disc, an epihymenium with fine crystals, an amphithecium with small crystals, 16-spored asci and the presence of zeorin, in addition to atranorin. Lecanorapseudojaponica is characterised by an epruinose, red-brown apothecial disc, an epihymenium without crystals, an amphithecium with small crystals, 8 or 16- spored asci and the presence of zeorin and the stictic acid complex, in addition to atranorin. Phylogenetic reconstructions, based on mtSSU, nrITS and nrLSU suggest that these two species are members of the Lecanorasubfusca group. They are compared with morphologically similar and phylogenetically related species, based on a nrITS dataset. Phylogenetic results show that the multispored taxa of Lecanora are polyphyletic. The number of ascospores per ascus appears to be a taxonomic character of minor importance. Detailed descriptions, discussions and figures for the two new species from China and a key for the multispored species of Lecanora worldwide are provided.

Preparation of Molybdenum Coatings by Molten Salt Electrodeposition in Na3AlF6-NaF-Al2O3-MoO3 System

In this paper, electrodeposition of a molybdenum coating was conducted in Na3AlF6-NaF-Al2O3-MoO3 molten salts at 930 °C to investigate the availability of preparation of thick molybdenum coatings. The effects of current density and electrodeposition time on the morphology of the produced molybdenum coating were studied. With the increase of current density (10~70 mA·cm−2), the coating thickness was increased from 10 μm to 30 μm, with all the current efficiency above 97%. Under a current density of 30 mA/cm2, with the rise of electrodeposition time (10~60 min), three stages of the deposit growth were observed, including the formation of a large number of fine crystals, transformation into fibrous morphology and well-developed faceted grains. The formation of a large number of fine crystals at the initial stage of the electrodeposition could facilitate electroplating molybdenum coatings with good quality at higher current density and longer duration. Thus electrodeposition at a current density of 100 mA·cm−2 for 3 h has been performed, resulting in the preparation of relatively flat, dense, and coherent molybdenum coatings with a thickness of 140 μm on a nickel substrate, with a current efficiency above 85%. It is anticipated that the electrodeposition of molybdenum coatings in the present molten system is suitable for electroplating thick molybdenum coatings.

Intensification design of green crystallization separation: Process optimization and technology coupling

This work designs different process intensification trajectories in the layer melt crystallization (LMC) to improve the separation efficiency. Parameters of distribution coefficient, interfacial solute distribution factor, and mass transfer coefficient are proposed to figure out the intrinsic correlations of technical variables and target parameters. The first proposal strategy is the optimization of the operating curve, divided into cooling process regulation and temperature cycling strategy. Both techniques can eliminate the fine crystals, thus favoring the crystal growth and reducing the impurities' adsorption. Next is the incorporation of the stirring intensification technique into the LMC. The problem of burst nucleation is restricted significantly through the suitable design of the stirring parameters. At last, a coupling technique that combines suspension and LMC is designed. The crystal seeds generated from the suspension melt can flow into the tubular crystallizer and act as the sites for crystal growth. This coupling technique exhibits excellent separation efficiency and huge potential in industrial production. The proposals for the further development of the LMC technique are given.

Effect of multi-frequency ultrasound-assisted immersion freezing on quality changes in large yellow croaker (Larimichthys crocea) during frozen storage

The effects of multi-frequency ultrasound-assisted immersion freezing (MUIF) at different ultrasound power levels (160, 175, and 190 W, respectively) on the quality of large yellow croaker (Larimichthys crocea) during frozen storage were studied. The study found that water loss and texture deterioration of MUIF were lower and MUIF was fresher than immersed freezing (IF) by affecting the morphology of ice crystals. Although the total volatile basic nitrogen (TVB-N) and K values of each treatment increased continuously during frozen storage, MUIF was consistently lower than IF. Among them, MUIF at 175 W (MUIF-175) maintained good quality in frozen storage because of the fine and uniform ice crystals, indicating that MUIF at a specific power level can reduce the quality degradation of the samples during frozen storage.

Effects of different seed forms on crystal size distribution for seeded batch crystallization process

The effects of different seed forms on crystal product distribution are presented for optimizing crystal size distribution (CSD) in the case of seeded batch cooling crystallization process. Three different seed distributions and quality are introduced as variable parameter for CSD control of seeded batch crystallization process via simulation in Matlab software. Similar implementation is conducted in the experimental study using the same operating conditions and parameters. Cubic cooling profile is adapted as the temperature profile for potash alum crystallization system due to its ability to control secondary nucleation. The experimental data obtained from laboratory works are validated the simulation results from Matlab where good agreement has been achieved. In terms of mean crystal size of the final CSD, the seed profile with 0.29 standard deviation labelled Sieved Seed 2, produces the best seed profile for seeded batch potash alum crystallization process because it has the largest size of crystals at mean crystal size of 500 μm grown from 90 μm of seed crystals. However, considerable fine crystals at mean crystal size of 30 μm are also obtained indicating trade-off between large size of crystals and fine crystals are needed. In conclusion, this work highlights the effects of different seed quality in terms of distribution and shape on crystal size distribution as one of the important quality specifications in crystallization process and demonstrates narrow distribution of seed crystals as recommendation on the best seed quality for producing desired CSD.

Influence of process parameters on surface properties and corrosion resistasnce of Inconel 625 coating prepared by laser cladding

To obtain good corrosion resistance and save cost, Inconel 625 coating was prepared by laser cladding with different process parameters, and the Inconel 625 powder play as feed material. The influence of powder feed rate (Vp), scan rate (Vs) and laser power (P) on the surface waviness (Wa) and effective height (he) of the cladding was analyzed. The results indicate that the Wa and he increase with the increase of Vp, while decrease with the increase of Vs. In addition, the P has positive influence on the he. When the P is lager than 1.0 kW, P boost the increase of Wa. Otherwise the influence is opposite. The microstructure of the cladding exhibiting relative good formation quality was studied using X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS). It demonstrates that the cladding is mainly composed of γ-Ni matrix and laves phase. Many coarse columnar and cellular crystals are distributed at the previous clad near the fusion line, while the other side is mainly composed of fine and dense columnar crystal. The process parameters have influence on size of grains and laves phase. For the relative good formation quality, the most positive Ecorr, the smallest Icorr, and largest Epit, the cladding marked No.3 possesses more outstanding comprehensive corrosion resistance than others. It is concluded that big grains size and less number of laves phase is benefit to the corrosion resistance.

Effects of ultrasonic vibration on microstructure and mechanical properties of 1Cr12Ni3MoVN alloy fabricated by directed energy deposition

Due to the rapid melting and solidification during directed energy deposition (DED) process, the defects and columnar crystals are likely to generate in the deposition layers, which reduce the quality and performance of the whole parts. Therefore, in order to improve the microstructure and mechanical properties of 1Cr12Ni3MoVN alloy manufactured by DED method, ultrasonic vibration (UV) has been employed to assist directed energy deposition process in this work. The results indicate that the high-intensity ultrasonic vibration can weaken the epitaxy growth tendency of crystal grains, and significantly improve plasticity while keeping an approximate strength. In addition, a two-dimensional numerical model is established to simulate the effect of ultrasonic vibration in the molten pool. The simulation results show that ultrasonic vibration remarkably improves the flow velocity and pressure in the molten pool, inducing the cavitation effect that breaks dendritic crystal and affects crystal characteristics. Meanwhile, the acoustic streaming effect changes the thermodynamic conditions and promotes high-temperature diffusion, which uniforms temperature distribution and reduces the temperature gradient in the molten pool. Thus the reduced temperature gradient G and raised solidification growth rate R promote the formation of fine equiaxed crystal characteristics after UV treatment. The product G × R increases and the ratio G/R decreases after UV treatment, resulting in the formation of fine equiaxed crystals.

Microstructure and properties of carbon fiber-H62 brass matrix composites prepared by friction stir processing

Carbon fibre (CF) reinforced H62 brass matrix composites were fabricated by friction stir process (FSP). The influence of CF compound amount and welding speed on the microstructure and properties of CF-H62 brass matrix composites was investigated by variable orthogonal experiments by drilling CF filled holes in H62 brass plates. Under the set experimental process parameters, the stirred friction processed composites with good surface formation, all without macroscopic defects, no loosening or holes. Optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microstructure of the joints. The microstructure is a fine isometric crystal that is the result of dynamic recrystallisation. As the welding speed increased from 20 mm/min to 60 mm/min, the average grain size at the weld in the weld zone decreased from 5 μm to 2 μm. When the hole depth of the filled CF was 1.5 mm and the welding speed was 40 mm/min, the CF was most uniformly distributed in the composite area. This paper uses the orthogonal test method to optimise the formulation design of a variety of reinforcement fibre contents. The friction and wear properties as well as the physical properties of the two friction material samples were tested using a constant speed friction tester, a shear strength tester and a Rockwell hardness tester. The influence of each fibre and content on the friction material properties was investigated by extreme difference analysis; The best fibre ratio formulation was selected by combining a fuzzy comprehensive evaluation method. ANOVA was used to investigate the changes in friction material properties after the addition of graphene.

Synergistic effect of recovering hardened cement powder and aluminum sulfate alkali-free liquid accelerator for enhancing the hydration and hardening of cement paste

The hardened cement powder (HCP) produced by the concrete waste disposal process can have a significant impact on the environment. How to effectively use HCP is the focus of current researchers. In this work, the synergistic effect of the treated hardened cement powder (T-HCP) and accelerator (ASS) was studied. The synergistic mechanism was studied by apparent porosity, hydration heat, XRD and SEM. Results demonstrated that the T-HCP can be used together with aluminum sulfate alkali-free liquid accelerator to improve the strength of cement. The main reason is T-HCP contains cement clinker mineral phase and fine CaCO3 crystals, in which the clinker mineral phase can be rehydrated, and the fine CaCO3 crystals can be used as nucleation sites to accelerate the generation of hydration products. Besides, adding T-HCP can improve the performance of cement mortar and save cost considering the economic aspects.

Reconstructed Hierarchical Pore Structure of Porous SiC Ceramics Using Micro‐X‐Ray Computed Tomography

Porous ceramics prepared by freeze casting are strongly appealing for filtration, separation, heat insulation, energy storage, and bioengineering. Herein, a unidirectionally freeze‐casting process is effectively adopted to fabricate porous silicon carbide (SiC) ceramics. The freezing rates of 0.29, 1.59, and 22.80 °C min−1 are presented at the bottom, which are simulated by finite‐element analysis. The pore structure characterize is systematically investigated through the 3D‐reconstructed micro‐X‐Ray computed tomography. Porous SiC ceramics with reasonable densification present the layer‐stacked texture and the hierarchical interconnected porous structure. The pore sizes are in the range of 30–40 μm. With the decreasing of freezing temperatures, the pore sizes reduce, while the number of channels increases. After sublimation of the fine ice crystals, there are a large number of channels (5–10 μm). The open porosities decrease from 82.3% to 78.2%, and a maximum compressive strength of 1.97 MPa is obtained. The pore size distribution is bimodal at the top and bottom of porous ceramics. The surface of porous SiC ceramics with obviously lamellar structure is connected.

The interface microstructure and phase constitution of Nb/316L composite plates fabricated by explosive welding

ABSTRACT Niobium has a reputation for its superior superconducting, high strength and corrosion resistance at elevated temperatures. In this work, the explosive welding technique was successfully performed to join Nb/316L dissimilar metals. To reveal the phase constitution and texture distribution at the joining interface, the EBSD test was carried out. It was concluded that an irregular large wavy structure of fine crystal, sub-grains and twin structures was formed. In addition, the recrystallised structures, substructures, deformed structures and local internal stress at the joining interface were attributed to severe plastic deformation and rapid solidification of liquid metal. Furthermore, six different deformation textures and recrystallisation textures were confirmed at the joining interface due to severe plastic deformation and dynamic recrystallisation.

Synthesis of an IMF zeolite membrane for the separation of xylene isomer

The synthesis of a continuous IMF zeolite membrane was fabricated on tubular substrates by seeded growth for the first time. The straight channels of IMF zeolite with diameters of 0.53–0.59 nm are distinguishable for p-xylene from o-xylene molecules. Pure IMF-phase high-silica IM-5 zeolite seeds with uniform and fine crystal size were fabricated by a new sonication-assisted aging process. The seeds were coated on the support by dipcoating and induced the formation of continuous membrane. Separation performance in p-/o-xylene mixture was investigated at various temperature and pressure. The typical IM-5 zeolite membrane had p-/o-xylene separation factor of 3.7. Our results suggest that IM-5 zeolite is a potentially good membrane material for the separation of xylene mixtures.

Microstructure and Tribo-Behavior of WC–Cr3C2–Ni Coatings by Laser Cladding and HVAF Sprayed: A Comparative Assessment

SK5 steel is the base material used for the preparation of the wrinkle scraper, whose service life strongly affects the working efficiency and economic benefits. In this work, WC-Cr3C2-Ni coating was deposited on the SK5 steel substrate by using High-velocity air fuel spray (HVAF) and Laser cladding (LC) processes respectively, named HVAF-WC coating and LC-WC coating. The microstructure and wear resistance of both coatings were analyzed, and were compared with the substrate sample. Results showed that the coatings were adhesive well onto the substrate. More WC with fine crystals is retained in HVAF-WC coating due to low flame flow temperature, while WC of LC-WC coating is characterized by columnar crystals. The wear rate of HVAF-WC and LC-WC coating was 4.00 × 10-7 mm3/(N•m) and 3.47 × 10-6 mm3/(N•m), respectively, which was two and one orders of magnitude lower than SK5 steel with 3.54 × 10-5 mm3/Nm. HVAF-WC coating exhibited the best wear resistance because of significant fine grain strengthening, which wear mechanism is mainly dominated by abrasive wear. Thus, it was thought that HVAF-WC coating is more effective ways to improve the wear resistance of SK5 steel, comparing with LC-WC coating.

Formation of TiB2-MgAl2O4 Composites by SHS Metallurgy.

TiB2-MgAl2O4 composites were fabricated by combustion synthesis involving metallothermic reduction reactions. Thermite reagents contained Al and Mg as dual reductants and TiO2 or B2O3 as the oxidant. The reactant mixtures also comprised elemental Ti and boron, as well as a small amount of Al2O3 or MgO to serve as the combustion moderator. Four reaction systems were conducted and all of them were exothermic enough to proceed in the mode of self-propagating high-temperature synthesis (SHS). The reaction based on B2O3/Al/Mg thermite and diluted with MgO was the most exothermic, while that containing TiO2/Al/Mg thermite and Al2O3 as the diluent was the least. Depending on different thermites and diluents, the combustion front temperatures in a range from 1320 to 1720 °C, and combustion wave velocity from 3.9 to 5.7 mm/s were measured. The XRD spectra confirmed in situ formation of TiB2 and MgAl2O4. It is believed that MgAl2O4 was synthesized through a combination reaction between Al2O3 and MgO, both of which can be totally or partially produced from the metallothermic reduction of B2O3 or TiO2. The microstructure of the TiB2-MgAl2O4 composite exhibited fine TiB2 crystals surrounded by large densified MgAl2O4 grains. This study demonstrated an energy-saving and efficient route for fabricating MgAl2O4-containing composites.

Enhanced strength and ductility in a powder metallurgy Ti material by the oxygen scavenger of CaB6

• There exists a continuous oxide layer on the irregular HDH Ti powder surface. • CaB 6 addition promotes the improved sintered density and refines the grain size. • The scavenging of O by CaB 6 addition makes a high strength and superior ductility for α-Ti alloy. The challenge of producing a high-ductility titanium (Ti) material using inexpensive high-oxygen hydride-dehydride (HDH) Ti powder is hereby addressed by the incorporation of CaB 6 oxygen-scavenger. The oxygen-scavenging behaviour, microstructure evolution, mechanical behavior and improvement mechanism were systematically investigated. A continuous TiO 2 oxide layer with a thickness of approximately 9.3 nm is presented on the HDH Ti powder surface. The oxide layer will dissolve into Ti matrix during sintering, making the increase of c / a value and leading to the Ti-Ti bonds developing from plastic metal bonds toward brittle covalent bonds. The CaB 6 addition can scavenge O impurity and make a significant increase in tensile ductility for α-Ti matrix. A small addition of 0.2 wt.% CaB 6 provides a superior tensile elongation of 22.2% for Ti material, almost three times as high as that of pure Ti (7.5%). The increase of deformation twining activity and grain refinement are responsible for the improved ductility. Furthermore, the CaB 6 oxygen-scavenger can react with the surface oxide layer to in-situ form rod-like TiB and granular CaTiO 3 reinforcements, refining the coarse near equiaxed grain of α-Ti matrix into fine equiaxed crystals. The multiple mechanisms of grain-boundary strengthening, load-bearing strengthening of TiB and Orowan strengthening of CaTiO 3 nanoparticles work together to increase the tensile strength of Ti/CaB 6 composites. This work offers an effective method to fabricate high-performance Ti material using inexpensive high-oxygen HDH Ti powder.

Effect of Trace Amount Modified SiC Nanoparticles on Microstructures and Mechanical Properties of ZA27 Alloy

In order to modify the microstructure and enhance the mechanical properties, the influence of trace amount modified SiC nanoparticles on the as‐cast ZA27alloy is investigated. The results indicate that the original coarse and developed dendrites are refined gradually and turn into fine and uniform equiaxed crystals and spherical structures. The primary α(Al) phases, eutectoid(α + η) phases, and ε(CuZn4) phases are also refined. The planar disregistry calculations between 6H‐SiC and α(Al) show that 6H‐SiC is an effective heterogeneous nucleus substrate for α(Al). The refined mechanism of modified SiC nanoparticles on ZA27 alloy is also discussed. When the addition is 0.5%, the tensile strength is increased by 6.5% and elongation is increased by 12.7%. The yield strength of SiC nanoparticles reinforced ZA27 is discussed quantitatively to reveal the strengthening mechanisms.