High Temperature Mixing Research Articles

Melt- vs. Non-Melt Blending of Complexly Processable Ultra-High Molecular Weight Polyethylene/Cellulose Nanofiber Bionanocomposite.

The major hurdle in melt-processing of ultra-high molecular weight polyethylene (UHMWPE) nanocomposite lies on the high melt viscosity of the UHMWPE, which may contribute to poor dispersion and distribution of the nanofiller. In this study, UHMWPE/cellulose nanofiber (UHMWPE/CNF) bionanocomposites were prepared by two different blending methods: (i) melt blending at 150 °C in a triple screw kneading extruder, and (ii) non-melt blending by ethanol mixing at room temperature. Results showed that melt-processing of UHMWPE without CNF (MB-UHMWPE/0) exhibited an increment in yield strength and Young’s modulus by 15% and 25%, respectively, compared to the Neat-UHMWPE. Tensile strength was however reduced by almost half. Ethanol mixed sample without CNF (EM-UHMWPE/0) on the other hand showed slight decrement in all mechanical properties tested. At 0.5% CNF inclusion, the mechanical properties of melt-blended bionanocomposites (MB-UHMWPE/0.5) were improved as compared to Neat-UHMWPE. It was also found that the yield strength, elongation at break, Young’s modulus, toughness and crystallinity of MB-UHMWPE/0.5 were higher by 28%, 61%, 47%, 45% and 11%, respectively, as compared to the ethanol mixing sample (EM-UHMWPE/0.5). Despite the reduction in tensile strength of MB-UHMWPE/0.5, the value i.e., 28.4 ± 1.0 MPa surpassed the minimum requirement of standard specification for fabricated UHMWPE in surgical implant application. Overall, melt-blending processing is more suitable for the preparation of UHMWPE/CNF bionanocomposites as exhibited by their characteristics presented herein. A better mechanical interlocking between UHMWPE and CNF at high temperature mixing with kneading was evident through FE-SEM observation, explains the higher mechanical properties of MB-UHMWPE/0.5 as compared to EM-UHMWPE/0.5.

An experimental study on emission characteristics in compression ignition engine with silver and zinc coated catalytic converter

Effect of harmful emission like oxides of nitrogen (NOx) and smoke (or) particulate matter (PM) from automobile vehicles to the environment become an addressable topic nowadays. In general NOx and smoke levels are slightly higher in diesel engine compared to petrol engine due to excess Oxygen (O2) supply, high in-cylinder temperature & improper mixing (Heterogeneous mixture) of fuel & air. These emissions are normally controlling by either combustion or by after treatment process. To control these emissions in after treatment process, three-way catalytic converter coated with noble materials like platinum, palladium & rhodium is used in diesel as well as petrol engines. In this present work, various emission characteristics were studied in single cylinder, water cooled, four stroke direct injection diesel engine with and without silver & zinc coated catalytic converter. Experimental results shown that diesel engine with silver (Ag) & zinc (Zn) coated catalytic converter provide 70% of reduction in NOx, 60% of reduction in CO, 55% of reduction in HC and 40% of reduction in CO2 emissions respectively at the exhaust pipe in full load condition compared with conventional diesel engine.

SLES/CMEA mixed surfactant system: Effect of electrolyte on interfacial behavior and microstructures in aqueous media

In aqueous anionic sodium lauryl ether sulfate (SLES) solution, presence of nonionic cocamide monoethanolamine (CMEA) depicts intriguing interfacial and bulk properties. CMEA has poor water solubility but can be readily solubilized in SLES solution to form mixed micellar aggregates as revealed by surface tension measurements. Sphere-to-rod micellar transition in aqueous SLES-CMEA binary mixtures occurs at higher surfactant concentration (total surfactant concentration beyond 15 wt%), inducing a sharp growth in the viscosity (>1000 cP). Nevertheless, adding NaCl in SLES-CMEA mixtures, substantial growth in viscosity is perceived at much lower surfactant concentration (~5–10 wt%) attributed to the formation of intertwined worm-like micelles. Micellar sizes were obtained by dynamic light scattering (DLS) measurements and small-angle neutron scattering (SANS) investigations is used to determine micellar shapes and aggregation number for SLES-CMEA mixtures. Furthermore, it is observed that foaming behavior of SLES can be modulated by CMEA ascribed to the change in foam film rigidity. Corresponding experiments were also performed with nonethoxylated counterpart sodium lauryl sulfate (SLS) under analogous condition for comparison. The study reported here may prove to be an appropriate tactic to alter not only the rheology or foaming behavior of SLES-CMEA mixed surfactant system but also provide pre-solubilized composition of CMEA which could be highly beneficial for personal care products enabling CMEA blending at room temperature, which otherwise needs high temperature mixing.

Study on preparation and thermophysical characteristics of molten salt nanocomposite by microwave method

Molten salts are widely applied as heat transfer and thermal storage medium for solar thermal power. In order to research the effect of preparation conditions and the types of nanoparticles on the thermophysical properties of molten salt nanocomposite, different molten salt nanocomposites were developed by mixing the nitrates (Ca (NO3)2·4H2O–KNO3–NaNO3–NaNO2) with 1.0 wt% of SiO2, MgO, TiO2 and CuO nanoparticles using a microwave method, which was a new preparation process of molten salt nanocomposite based on high temperature mixing without water. The effect of different microwave heating temperature (250, 350 and 450 °C) and heating time (30, 60, 90 and 120 min) were experimentally studied. The melting point, latent heat and specific heat of the samples were analyzed by differential scanning calorimeter (DSC). The morphology was observed by scanning electron microscope (SEM). The results showed that the nanoparticles induced a decrease of the melting point of 0.1–2.4% while the latent heat decreased by 3.3–7.9%. Compared with other molten salt nanocomposites, the molten salt with the addition of SiO2 nanoparticles had the biggest increase in specific heat, which increased by 7.7% in solid state and 21.0% in liquid state after heating for 90 min at 250 °C. The total heat storage density could reach to 783.0 J/g between 30 and 500 °C, which was 13.3% higher than the base salt. In addition, according to the morphology of the samples, network nanostructures were observed in the molten salt nanocomposite doped with SiO2.

Effect of crystalline quality on the transport properties of ferromagnetic Weyl semimetal Co3Sn2S2

Co3Sn2S2 is predicted to host topological Weyl semimetal phase in ferromagnetic state. The realization of Weyl phase properties needs tuning of Fermi level which in turn depends on crystalline quality. Here we show that slight variation in high-temperature mixing protocol during crystal growth strongly affects the crystalline quality and resultant physical properties. The detailed crystal characterization reveals that a longer high-temperature mixing protocol yields better crystal quality in comparison to that of intermediate mixing. The crystal grown by long-duration high-temperature mixing (S1) has lower microstrain and low-angle structural grain boundaries due to stress relaxation while the crystal grown by intermediate mixing (S2) has large microstrain and enhanced unit cell volume due to intercalation of sulfur atoms. The transport results indicate ferromagnetic ordering in S1 at 174 ​K and in S2 at 178 ​K. Crystal S2 exhibits large positive magnetoresistance and strong thermal suppression of spin disorder in comparison to S1.

Effect of room-temperature annealing on structures and properties of SSBR/BR blends and SSBR/BR/SiO2 composites

Room-temperature annealing process lies between high-temperature mixing process and high-temperature vulcanization process in rubber processing technology, and definitely affects the performances of rubber composites. In this work, the influences of room-temperature annealing on the structures and properties of unfilled SSBR/BR blends and silica-filled SSBR/BR composites have been evaluated in detail. For the unfilled SSBR/BR vulcanizates, the tensile strength, tear strength and fatigue resistance deteriorate due to the reduced rubber matrix strength with lower crosslinking density and less chain entanglements with annealing time extending. While for the SSBR/BR/SiO2 vulcanizates with dual networks including filler-filler networks and polymer-polymer networks, the tensile strength and fatigue resistance reduce, the tear strength, dynamical properties concerning abrasion, heat built-up and rolling resistance improve obviously with extending annealing time, which are attributed to the enhanced filler-polymer interactions, severe silica flocculation, and reduced internal hysteresis loss with annealing time prolonging. This work is expected to provide fundamental understanding of the annealing process in the rubber processing technology for development of high-performance rubber composites.

The influence of the warm-mixed agent on the performance of Gussasphalt after superheated aging

Gussasphalt has been widely used in steel bridge deck and pavement in China, but it will lead to the pyrolysis aging of gussasphalt binder in the mixing process due to the high temperature and longtime mixing. The effect of improving the aging performance of Gussasphalt was studied by adding warm-mixed agent after superheat aging, and the aging performance between the matrix asphalt and the gussasphalt modified with Sasobit and RH were compared and analyzed. The results show that: RH warm-mixed agent has little effect on the penetration of Gussasphalt binder, while Sasobit warm-mixed agent has more influence on the penetration of Gussasphalt binder. Gussasphalt binder with of 2% RH warm-mixed agent or 1% Sasobit warm-mixed agent is the optimum mix dosage. The adding of 2% RH warm-mixed agent or 1% Sasobit warm-mixed agent can effectively decrease the mixing temperature of the mixture, and Sasobit’s effect is better.

Study on Improvement of Aging Performance for Gussasphalt Modified by Reclaiming Agent

Gussasphalt has been widely used in steel bridge deck and pavement in China, but it will lead to the pyrolysis aging of gussasphalt binder in the mixing process due to the high temperature and long time mixing. In this paper, the effect of ARA asphalt reclaiming agent on the main performance indexes of gussasphalt at five aging temperatures was studied. It was found that the indexes of penetration and ductility were greatly improved after the addition of the reclaiming agent, and the softening point was regularly reinforced. All the three indexes were improved to varying degrees, which indicates that ARA reclaiming agent had a significant effect on the performance recovery of the gussasphalt after superheat aging.

2.9 Ga magmatism in Eastern Hebei, North China Craton

We report the results of a comprehensive isotopic investigation of zircons from metamorphosed orthogneisses from Caochang village in the Zunhua Complex, Eastern Hebei, North China Craton (NCC). A detailed investigation of the internal structures of these zircons combined with SIMS U–Pb and ICP-MS Lu-Hf zircon analyses, as well as a whole-rock geochemical study, revealed a previously unknown ∼2.9 Ga magmatic event in Eastern Hebei. The identified Mesoarchean gneisses are mainly felsic gneisses and amphibolites. Amphibolites with positive εNd(t) values were derived from the depleted mantle, with some crustal contamination during ascent. Zircon Hf isotopes indicate that the high-silica gneisses originate from the high-temperature mixing of mafic magma derived from a depleted mantle source and the subsequent felsic magma derived from the melting of ancient crustal materials, with the subsequent high degree fractional crystallization of the parental magma. Some of the 2.9 Ga felsic gneisses may record an anatectic event at 2.5 Ga. The widespread ancient inherited and detrital zircons (>2.6 Ga) and the existence of Mesoarchean rocks imply a possible ancient continent in Eastern Hebei. It may also imply that the Mesoarchean era (especially at 2.9 Ga) represents another important magmatic event in the eastern block of the NCC. The identification of 2.9 Ga rocks indicates that the magmatic history of Eastern Hebei is far more complex than previously thought.

Heat capacity of nanofluids for solar energy storage produced by dispersing oxide nanoparticles in nitrate salt mixture directly at high temperature

Molten salts as phase change materials (PCMs) can be used as thermal storage media in concentrated solar power (CSP) plants. The addition of nanoparticles into a base fluid (producing the so called nanofluid) can enhance its thermal properties. The most common technique involves the use of water. We present a new procedure based on high temperature mixing. In particular, different nanofluids were developed by mixing NaNO3-KNO3 (60–40wt%) solar salt with 1.0wt% of SiO2, Al2O3 and a mix of SiO2/Al2O3 nanoparticles at 300°C using a twin screw micro-compounder. The effect of different screw speeds (100 and 200rpm) and mixing times (15 and 30min) were studied. The results showed that the nanoparticles induce an increase of the heat of fusion of 1.5–7.4% while the onset temperatures decrease for all the nanofluids independently from the processing conditions (up to 9.7°C). Moreover, an increase in the specific heat (Cp) is recorded mainly for the nanofluid with SiO2/Al2O3 with a maximum of 52.1% in solid phase and 18.6% in liquid phase after 30min of mixing at 200rpm. The same nanofluid showed the highest stored heat. Particle aggregation into clusters in solid state was detected by scanning electron microscopy (SEM) but smaller aggregates resulted for higher mixing times and screw speed related to the highest Cp. Moreover, smaller grains in the nanofluids were detected with respect to the base salt morphology. Thus, the nanofluid produced with SiO2/Al2O3 nanoparticles at 200rpm for 30min gives the best overall performances.This work showed that nanofluids with enhanced thermal properties can be obtained with an innovative mixing process directly at high temperature, eliminating the water evaporation step.

Rheology of Green Self-Consolidated Concrete (GSCC) with Ternary Blend under Coupled Effects of Temperature and Prolonged Mixing

The fresh quality of a concrete mixture subjected to high temperature and prolonged mixing is adversely affected. These harsh conditions would result in a stiff concrete that is hard to handle and place. This paper investigates the coupled effects of temperature and prolonged mixing on green self-consolidating concrete (GSCC) incorporating a ternary blend of fly ash and silica fume. This study was carried out in the construction material laboratory of Abu Dhabi University under an outdoor environment during the summer of 2014. The SCC mixtures were continuously mixed for 110 minutes at a temperature ranging from 25 to 40 °C to simulate the actual conditions of concrete during transporting to a construction site. The fresh properties were tested using BT2 portable rheometer, slump flow, T 50 and visual stability index (VSI). The results showed that the ternary blend of silica fume and fly ash enhanced the rheological properties of SCC mixtures under high temperature and prolonged mixing time.

Elucidating the effects of high temperature mixing method under hydrothermal condition (HTMM) on grain refinements and assembling structures

Crystal size and microstructure are of great importance in determining the physical and chemical properties of functional materials, and refine powders, especially their assembled porous structures have potential application in ceramic fabrication, absorption, catalysts and drug delivery, due to their characters of high activity and large specific surface area. Herein, high temperature mixing method under hydrothermal condition (HTMM) was adapted to synthesize barium strontium titanate [(Ba, Sr)TiO3, BST] powders with various Ba/Sr ratios (x=0.5, 1.0, 3.0 and 4.0). In comparison with conventional hydrothermal synthesis (CHS), the effects of HTMM on grain refinement and porous structure formation were exclusively investigated. XRD and SEM results indicated that, in the given condition, BST powders prepared by HTMM were much smaller than that by CHS, especially at a lower Ba/Sr ratio. Additionally, assembled porous architectures were constructed by HTMM. It's believed that the high temperature mixing process and continuous rotation contributed to the grain refinement and assembled porous structure, respectively. The assumption was further confirmed through the synthesis of sodium niobate (NaNbO3) powders by HTMM. It's demonstrated that HTMM is advantageous in preparation of refine powders and porous assembled architectures.

A novel material for in situ construction on Mars: experiments and numerical simulations

A significant step in space exploration during the 21st century will be human settlement on Mars. Instead of transporting all the construction materials from Earth to the red planet with incredibly high cost, using Martian soil to construct a site on Mars is a superior choice. Knowing that Mars has long been considered a “sulfur-rich planet”, a new construction material composed of simulated Martian soil and molten sulfur is developed. In addition to the raw material availability for producing sulfur concrete and a strength reaching similar or higher levels of conventional cementitious concrete, fast curing, low temperature sustainability, acid and salt environment resistance, 100% recyclability are appealing superior characteristics of the developed Martian Concrete. In this study, different percentages of sulfur are investigated to obtain the optimal mixing proportions. Three point bending, unconfined compression and splitting tests were conducted to determine strength development, strength variability, and failure mechanisms. The test results show that the strength of Martian Concrete doubles that of sulfur concrete utilizing regular sand. It is also shown that the particle size distribution plays an important role in the mixture’s final strength. Furthermore, since Martian soil is metal rich, sulfates and, potentially, polysulfates are also formed during high temperature mixing, which might contribute to the high strength. The optimal mix developed as Martian Concrete has an unconfined compressive strength of above 50MPa. The formulated Martian Concrete is simulated by the Lattice Discrete Particle Model (LDPM), which exhibits excellent ability in modeling the material response under various loading conditions.

Modelling the Kinetics of Jatropha Oil Transesterification

Kinetics of a chemical reaction provides an important means of determining the extent of the reaction and in reactor designs. Transesterification of jatropha oil with methanol and sodium hydroxide as a catalyst was conducted in a well mixed reactor at different agitation speeds between 600 and 800 rpm and temperature range between 35°C and 65°C. The effect of variation of temperature and mixing intensity on rate constants were studied. The initial mass transfer controlled stage was considered negligible using the above impeller speeds and second order mechanism was considered for the chemically controlled kinetic stage. Samples were collected from the reaction mixture at specified time intervals and quenched in a mixture of tetrahydrofuran (THF) and sulphuric acid. The mixture was centrifuged at 2000 rpm for 15 minutes and the methyl ester was separated from the glycerol. The ester was washed with warm water (50°C), dried and analysed using gas chromatography coupled with flame ionization detector (GC/FID) to determine free and total glycerine and methyl ester. A mathematical model was fitted using second order rate law. High temperature and high mixing intensity increased reaction rates. The model fitted well with a high correlation coefficient (R2) of 0.999.

Enhanced dispersion of cellulose nanocrystals in melt-processed polylactide-based nanocomposites

Dispersion and distribution of cellulose nanocrystals (CNC) in a thermoplastic matrix is one of the most important issues in the development of CNC-based high performance composites. During melt processing, agglomeration of CNC is prone to occur due to poor polymer wetting on the hydrophilic CNC surface and to strong particle–particle interactions. Because of the high temperature and intensive mixing involved in melt-processing, degradation of the CNC is also possible. To avoid these problems, solvent mixing followed by solvent casting is the main processing route used in the majority of studies on polymer–CNC composites. In this work, we have explored a novel two-step process where solvent-mixing and melt-mixing were carried out sequentially to improve the overall dispersion of the CNC. The first step consisted in forming a CNC suspension into a polyethylene oxide (PEO) aqueous solution. In the second step, water was removed by freeze-drying to form a water-free well dispersed PEO/CNC mixture. The final step consisted in melt-mixing the PEO/CNC mixture into PLA for the preparation of the composites. PEO and PLA are known to be miscible in certain molecular weight and composition ranges, thus leading to a composite where the CNC particles are well dispersed into a homogeneous mixture of PLA and PEO. Two different PEO molecular weights were investigated in this study, and several formulations were compared under the same processing conditions. Direct blending of CNC and molten PLA was also carried out for comparison purposes. CNC particles tended to agglomerate during blending but the agglomerates were smaller and their number was considerably decreased when the PEO content increased in the formulation. At the highest PEO/CNC ratio, no agglomerates were observed. Thermomechanical and rheological properties of the PLA-based nanocomposites were also investigated.

Fabrication of BaTiO3 nanoparticles and its formation mechanism using the high temperature mixing method under hydrothermal conditions

Barium titanate (BaTiO3) single-crystalline nanoparticles have been prepared via high temperature mixing method (HTMM) under hydrothermal conditions. The crystallized products were characterized by X-ray diffraction (XRD), filed emission scanning electron microscopy (FESEM), X-ray fluorescence (XRF), Raman spectra, transmission electron microscopy (TEM). The BaTiO3 nanoparticles can be prepared at dilute KOH as compared with the method mixed at room temperature. The results show that the stoichiometric BaTiO3 nanoparticles were synthesized at [Ba/Ti]solution=1. The high temperature will significantly narrow the solubility difference between the barium and titanium sources and leads to a burst nucleation from the solution. The defect mechanism is used to illustrate the time-dependent transformation from cubic to tetragonal phase.

In-melt transesterification of poly(lactic acid) and poly(ethylene-co-vinylalcohol)

Transesterification of poly(lactic acid) and poly(ethylene-co-vinylalcohol) was realized in-melt using different catalysts. Reactions were first conducted in an internal mixer and the different reaction parameters effect on exchange reactions and the obtained copolymers were optimized. Among the used catalysts, 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) and Tin(II) bis(2-ethylhexanoate) (Sn(Oct)2) were particularly efficient.In a second part, reactions were made by reactive extrusion. In most of reaction conditions, compatible blends were obtained with a fine micro phase separation. Only under extreme reaction conditions, high temperature and intensive mixing, nanostructured graft copolymers were obtained.

Synthesis and Characterization of K(Ta<SUB><I>x</I></SUB>Nb<SUB>1−<I>x</I></SUB>)O<SUB>3</SUB> Particles by High Temperature Mixing Method Under Hydrothermal and Solvothermal Conditions

KTa(x)Nb(1_x)O3 (KTN) particles with an orthorhombic perovskite structure were synthesized via a high temperature mixing method (HTMM) under hydrothermal and solvothermal conditions. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influences of alkaline concentration and Ta doping amounts on the phase structure and morphology of the obtained powders were investigated. The results showed that KTN powders could be solvothermally prepared when the KOH concentration is as low as 0.5 M. In comparison with the hydrothermal process, supercritical isopropanol plays an important role in synthesizing KTN particles under milder conditions. The KTa(0.4)Nb(0.6)O3 particles solvothermally synthesized in isopropanol are made of well crystallized and single crystalline particles with a size of about 100-200 nm. Room temperature PL studies excited at different wavelengths reveal five emission bands centered at about 421 nm, 446 nm, 468 nm, 488 nm, and 498 nm, respectively. The supercritical process proposed here provides a new potential route for synthesizing other perovskite-type materials.

Interactions between rhyolitic and basaltic melts unraveled by chaotic mixing experiments

Magma mixing may operate at any stage in the evolution of a magmatic system. The development of mixing is strongly controlled by fluid dynamics and its understanding requires a comprehensive physico-chemical approach in order to identify and interpret its occurrence in nature. Here, we experimentally study the physical and chemical interplays during the mixing of basaltic and rhyolitic natural melts from the Snake River Plains, USA. In particular, we present the results of the first high-temperature mixing experiments performed under controlled chaotic dynamic conditions, providing a new methodological approach to constrain the complexities of the mixing process between natural silicate melts.The mixing process is initially governed by the dynamics of stretching and folding of the melts, producing alternating flow bands. These bands increase the contact area between the end-members, which subsequently enhance chemical exchanges and thus contribute to the generation of regions with variable degrees of hybridization. We quantified the mobility of major and trace elements across contact areas, and analyzed the concentration variance decay induced by chemical diffusion. The analysis shows that elements diffuse with different efficiencies as the chemical gradient evolves and therefore, the achievement of hybrid compositions contrasts between elements. The approach introduced in this study can, in principle, be applied to mixing trends observed in nature in order to estimate the time-scales and degree of magma mixing evidenced across volcanic rocks/deposits.

Synthesis of (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders by high temperature mixing method under hydrothermal conditions

A facile hydrothermal route via high temperature mixing method was used to synthesize (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramic powders. The influence of Ta doping and K+/(K++Na+) molar ratios in the starting solution on the resultant powders were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscopy, and selected area electron diffraction. The Ta element was successfully doped into the alkaline niobate structure to form crystalline (K, Na) (Nb, Ta)O3 lead-free piezoelectric ceramics powder. The microstructure, piezoelectric, ferroelectric, and dielectric properties of the sintered (K, Na) (Nb, Ta)O3 ceramics from the obtained powders were investigated. The piezoelectric coefficient (d33), electromechanical coupling coefficient (kp), dielectric constant (ɛr), and remnant polarization (Pr) of the sample sintered at 1180°C show optimal values of 210pC/N, 34.0%, 2302, and 19.01μC/cm2, respectively.