Eutectic Components Research Articles

Simultaneous size and defect control of metal-organic framework by deep eutectic solvent for efficient perfluoroalkyl substances adsorption: Delving into mechanism

This study reports an environment-friendly protocol to prepare a metal–organic framework (MOF) with simultaneously controlled particle size and open metal site for adsorption removal of perfluoroalkyl substances (PFASs). The successful preparation of UiO-66 with defect and crystal size modulation was achieved using a green and straightforward method, adjusting the components and molar ratios of ammonium salt/glycolic acid deep eutectic solvents (DESs). The corresponding modulation mechanism primarily relied on the combined regulation of the deprotonation and competitive coordination abilities of the eutectic solvent components. The adsorption process was thoroughly examined using spectral analyses, adsorption behavior profiling, and ab initio molecular dynamics simulations. The results revealed that PFAS adsorption is driven by combined capturing effects, such as CF–π, acid/base coordination, C–F⋯Zr, hydrogen bonding, and hydrophobic interactions. Our findings were not thus that the smaller the crystal size of MOF and the higher the defect concentration in the material, the better the PFAS adsorption performance. The result demonstrated the combined effect of these adsorbent features on PFAS mixtures. Furthermore, they revealed unique differences in sorption properties between these targets with different carbon chain lengths. Extensive defects in DES-based UiO-66 led to larger pores, increasing the availability of many adsorption sites and aiding in PFAS adsorption and diffusion. Nevertheless, the surplus of larger pores in the substance increased the competitive adsorption, reducing the total quantity of PFASs absorbed. Furthermore, various interactions and a less restrictive configuration increased the contact of functional groups with adsorbates, substantially enhancing the adsorption. This study investigates the basic questions about how PFAS molecules are adsorbed on DES-based MOFs and the relationship among the structure, properties, and performance to improve the efficiency of this novel adsorbent.

Towards valorization of rice straw into bioethanol and lignin: Emphasizing critical role of deep eutectic solvent components in biorefining process

Deep eutectic solvents (DESs) offer a potential opportunity in biomass utilization industries. This work emphasized the impact of hydrogen bond donors (HBD) and acceptors (HBA) on deconstruction and valorization of rice straw. Acidity, alkyl chain length, hydrogen bonding ability and functional groups of HBD and HBA appeared to be important factors affecting the fractionated pulps and lignins, which further influenced ethanol fermentation. Among the candidate DESs, lactic acid/guanidine hydrochloride (LGH) was proved to be the most suitable one due to the excellent delignification and xylan removal. For the downstream fermentation process, 0.47 g g−1 of bioethanol with 0.55 g/L h−1 of productivity can be obtained from the LGH pulp’s hydrolysate. Mass balance showed 302.8 g bioethanol and 119.0 g technical lignin can be co-generated from 1 kg dried rice straw. This “green” valorization strategy offers a promising scheme in biorefinery of lignocelluloses.

Low-temperature cordierite ceramics with porous structure for thermal shock resistance products

This article shows the results of the study of low-temperature (1100−1150 °C) porous ceramics of cordierite composition. The technological manufacturing parameters, the features of the microstructural and phase composition of ceramics have been studied. A decrease in the sintering temperature is achieved by appending a part of components using eutectic glass of MgO–Al2O3–SiO2 pseudoternary system. The principle of reactive formation of the structure of the ceramic sample is implemented in the process of its low-temperature firing. The formation of α-cordierite occurs in the process of firing ceramics by means of intensive interaction between eutectic glass components and crystalline fillers, as well as in the result of glass crystallization. By means of the thin layers of the glassy phase, cordierite crystals form a hard base with a branched system of interconnected open pores (30.0−31.3 %). The cordierite-phase crystals, forming the structure of ceramics, have a particle size ranging from 0.2 to 0.3 μm to 1.0−2.0 μm. The specific surface area of the porous cordierite ceramics is in the range of 4.2–4.7 m2/g. The developed cordierite ceramics is characterized by its low coefficient of linear temperature expansion (1.7–2.6)·10−6 °С−1, which determines its high thermal shock resistance (1000−1150°С). The ceramics may be used as filtering elements in high-temperature filtering units, as well as catalyst carriers in the exhaust systems of combustion engines for discharging the sooty component.

Synthesis and characterization of pH-responsive deep eutectic solvent followed by HPLC for trace determination of bisphenol A in water samples.

A microextraction based on pH-responsive deep eutectic solvent combined with high-performance liquid chromatography was developed for the separation, preconcentration, and determination of bisphenol A in water samples. Five deep eutectic solvents were prepared using thymol (hydrogen bond acceptor) and 6-, 8-, 9-, 10-, and 12-carbon carboxylic acids (hydrogen bond donor), and were used as extraction solvent. Herein, by alkalinizing the environment, phase transition takes place, and by adding acid, phase separation and extraction of analytes occur simultaneously. Some important parameters on the extraction such as deep eutectic solvent type, molar ratio of deep eutectic solvent components, deep eutectic solvent volume, potassium hydroxide concentration, hydrochloric acid volume, extraction time, and salt addition were optimized. Under the optimum conditions, intra- and interday precisions of the method based on seven replicate measurements of 10μg L-1 of bisphenol A in water samples were 2.2% and 4.3%, respectively. The analytical performance of the method showed linearity over the concentration of 0.05-50μg L-1 with the detection limit of 0.02μg L-1 . The accuracy of the method was confirmed by spiking different concentrations of bisphenol A in real water samples and obtaining relative recoveries in the range of 92.5%-105.2%.

Thermodynamic analysis of the reactions of strontium anorthite formation during the firing of thermal shock resistance ceramics based on the eutectic glasses of the SrO–Al2O3–SiO2 systems

Thermal shock resistance ceramic materials must have a high degree of sintering to ensure the required mechanical strength, erosion resistance, and resistance to high-temperature oxidation. However, the search for effective ways to achieve a high degree of sintering of ceramic materials based on the SrO–Al2O3–SiO2 system at low temperatures requires a large amount of experimental research. The aim of this work is to analyze thermodynamically the reactions of strontium-anorthite phase formation at the points of triple eutectics of the SrO–Al2O3–SiO2 system under low-temperature firing conditions. The eutectic points were selected in the region of strontium anorthite crystallization and had a temperature not exceeding 14000C. It has been established that in the case of compliance with the stoichiometric ratio, the final product of the interaction of the components of eutectic glasses S-1 and S-2 with the charging components is the strontium anorthite phase. The most probable is the formation of strontium anorthite in the interaction of eutectic glass components with Al2O32SiO2, which is a product of kaolinite dehydration (Al2O32SiO22H2O). It has been found that the compounds SrOSiO2 and 2SrOAl2O3SiO2 are most active in the interaction with the charging components in the direction of formation of the strontium anorthite phase than SiO2 tridymite. As a result, the sintering of strontium-anorthite compositions at a temperature of 9000C causes a significant increase in the content of the crystalline phase of strontium anorthite. The determined patterns allow making a reasonable choice of glass in the SrO–Al2O3–SiO2 system for the further manufacture of low-temperature strontium-anorthite ceramics.

Novel reusable and switchable deep eutectic solvent for extraction and determination of curcumin in water and food samples

For the first time, a fast and easy extraction method based on a unique reusable and switchable deep eutectic solvent (made of octylamine, succinic acid, and water as precursors) was presented and utilized for the microextraction and determination of curcumin as a model analyte. The main factors used to induce a phase transition in the as-prepared deep eutectic solvent were solutions of NaOH and HCl. Among the standout characteristics of the suggested deep eutectic solvent are the removal of toxic organic solvents like THF, the lack of a need for centrifugation, and the ability to be reused in subsequent extractions. The influence of effective parameters (i.e., proportions of deep eutectic solvent structure components, volume of prepared deep eutectic solvent, volume and concertation of NaOH, volume of HCl, and salt effect) on the extraction procedure were investigated. The calibration curve also was linear in the range of 35–500 μg L−1 with coefficients of determination (R2) of 0.9976. Limit of detection (S/N = 3) 10.0 μg L−1, the limit of quantification (LOQ) of 35.0 μg L−1, the relative standard deviations (RSDs %) composed of intra-day RSD (4.7) and inter-day RSD (6.4), preconcentration factor of 40.0, enrichment factor of 38.68, and relative recovery of 92.6%–100.3 % were achieved. The reusable and switchable deep eutectic solvent based-dispersive liquid-liquid microextraction technique was proficiently employed to expedite easy and fast extraction of curcumin from water and food samples.

Biomimetic design of flexible wood film combined with thermochromism and self-luminescence for enhanced energy-saving

In this research, the layered bionic wood films were designed and constructed inspired by the “reinforced concrete”-like chemical structure of wood combined with the macrostructure of bark and phloem. Specifically, a simple strategy for immobilizing diol eutectic phase change components with intelligent discoloration/chromogenic leaching in wood by using delignification wood (DE) with capillary penetration was adopted. The “reinforced concrete” structure solves the problem of easy leakage and weak strength due to strong molecular bonding. The bionic wood film has a high phase change enthalpy (155.5 J/g) and suitable phase change temperature (29.9 °C). On this basis, combined with PVA/glycerol as a flexible matrix as the inner bark of wood and phloem connecting each layer, combined with PVA/glycerol/PLO-8C as a key self-luminescent energy-enriched material as the outer bark of wood, the flexible and self-luminescent energy-saving wood films were reconstructed in a biomimetic way with a high mechanical strength (65.53 MPa). Through the change of color, the phase transition process and the current ambient temperature can be intuitively judged. The surface morphology and luminescence intensity were also not affected after 50 cycles of absorption and luminescence. This study provides a broader development direction for the application of intelligent enhanced energy enrichment of PCM-based on bionic wood construction.

Thermodynamic calculations and experimental studies of ternary molten salts for high-temperature thermal energy storage

Chloride, fluoride, and carbonate salts act as potentially promising thermal storage media for high-temperature thermal energy storage (TES) systems. In this study, the eutectic components of three ternary molten salts; i.e., NaCl–KCl–LiCl, NaCl–KCl–NaF, and NaCl–KCl–Na2CO3 were first predicted by using thermodynamic calculations and the accuracy was further verified by differential scanning calorimetry. Next, the melting point, thermal conductivity, latent heat, specific heat, and TES density of the three eutectic salts were determined and calculated by thermal analysis methods and compared with those of Solar and Hetic salts. The results show that the eutectic salt NaCl–KCl–Na2CO3 exhibits the highest TES density, which is 1.87 and 1.31 times higher than that of the Solar salt and Hetic salt, respectively. Moreover, the costs of the three eutectic salts were calculated and analyzed herein, and the cost per unit TES density of the eutectic salt NaCl–KCl–Na2CO3 accounted for only 17.01 % and 29.75 % of the cost of the Solar salt and Hetic salt, respectively. The three eutectic salts exhibit good thermal stability even at a high temperature of 700 °C, and thus act as potential candidates for thermal storage materials for the next-generation concentrating solar power plants.

Hydration is not detrimental for Glycerol:Lactic acid deep eutectic mixtures

Natural deep eutectic solvents (NADES) have been proposed as eco-friendly alternatives to organic solvents. A trace amount of water is frequently unavoidable as a contaminant and may be also purposely added to the mixtures to reduce their problematically high viscosity and costly price. It is critical to understand the different effects of water on the characteristics of NADES, particularly for their use in procedures such as bioactives’ extraction, and enzymatic synthesis, among others. In this work, the effect of water on the physicochemical properties and structural features of glycerol:lactic acid (GLY:LAC) deep eutectic mixture was investigated. The structural changes after water addition were evaluated using FTIR-ATR and 1H NMR spectroscopy. The pH, conductivity, and polarity of the mixtures were also evaluated after the addition of different percentages of water. Molecular dynamics simulations (MD) were applied to assess the role of water on NADES components' distribution and properties, including the number of hydrogen bonds (HB), the radial distribution functions (RDF), and the spatial distribution functions (SDF). The results demonstrated that when water enters the system, the hydrogen bonds between the eutectic components break but new ones are formed creating strong interactions between them and the water. A ternary eutectic combination arises, leading to a melting point lower than the original counterparts, even with 90 % water, caused by the formation of stronger intermolecular interactions. The MD simulations indicate no phase separation regardless of the ratio of the components or the water content in the mixture, showing preservation of the eutectic behavior.Overall, these unprecedented results, in which the rupture of the HB between eutectic mixtures is never observed up to 90 % water, unravel the potential of these novel mixtures for multiple applications.

Комплексне модифікування сплаву AlSi9Cu3(Fe) кобальтом, ванадієм та молібденом

Aluminum casting alloys of the Al-Si and Al-Si-Cu systems are among the most widely used materials for machine building. Their wide use is associated with low cost, high manufacturability, excellent ability for multiple recycling and sufficient level of mechanical properties. Increasing of Al-Si-Cu alloys mechanical characteristics always remains as a relevant task, which is often solved by several components modification. Presented work is dedicated to investigation of Co, V and Mo complex influence on the structural phase state and mechanical properties of the widely used AlSi9Cu3(Fe) alloy. All modifying additives were added in the amount of 0.1-0.2 wt. %. At the same time, their total content did not exceed 0.5 wt. %. It is shown that the complex modification of AlSi9Cu3(Fe) with cobalt and vanadium contributes to a significant grain refinement and increasing strength of the alloy by more than 20% while maintaining plasticity. At the same time, cobalt mainly performs the function of a modifier of eutectic components, and vanadium plays the role of a grain refiner. Simultaneous modification of the alloy with vanadium and molybdenum ensures refining of all structural components and strength elevating. Both components perform the function of nucleation. The simultaneous addition of cobalt and molybdenum shows the effect of cobalt on eutectic components. Molybdenum actually does not have a nucleating effect and is mainly goes to iron-containing phases. As a result, average mechanical properties can be observed. Triple modification makes it possible to obtain maximum refining of all structural-phase components and increase the strength of the alloy. The highest microhardness of such alloys indicates potentially high level of mechanical properties at elevated temperatures. Keywords: cast aluminum alloys, modification, AlSi9Cu3(Fe), structure, phase composition, mechanical properties.

Структура, фазовий склад і властивості сплаву АК12М2МгН з підвищенням вмістом заліза, обробленого в рідкому стані електричним струмом

The possibility of replacing the piston eutectic alloy of the Al-Si-Cu system AK12M2MgN, which was produced at OJSC "Zaporizhsky Aluminum Combine" from primary aluminum, with AK12M2MgNZH with an increased iron content, which will allow expanding the raw material base of production due to the use of scrap and waste. It is proposed to solve this problem by introducing into the technological process of processing the melt with a unipolar pulsed electric current during pouring according to specially developed modes. To investigate this possibility, experiments were conducted on the effect of electric current on the microstructure, phase composition of AK12M2MgN and AK12M2MgNZH alloys and their mechanical properties at temperatures of 20 oC and 300 oC. The melt was treated with an electric current in the following modes: electric current density (j) 100 - 400 A/cm2, pulse frequency (ν) 50 - 2000 Hz. The phase composition of alloys is considered. It is shown that the main iron-containing phase of the AK12M2MgN alloy is (Fe,Mn)3Si2AI15 (α) in the form of branched eutectic crystals. The acicular β-FeSiAI5 phase is practically absent. Unlike AK12M2MgN, the composition of AK12M2MgNZH alloy includes β-FeSiAl5 intermetallic and primary coarse crystals of (Fe,Mn)3Si2AI15 phase. After treatment of alloys in the liquid state with pulsed electric current in different modes, their microstructure and phase composition change significantly. The degree of differentiation of eutectic components increases. In particular, the linear size of eutectic silicon crystals, depending on the density and frequency of the electric current, decreases by 2-3 times. Primary crystals of the intermetallic (Fe,Mn)3Si2Al15 are formed in the AK12M2MgN alloy, which in cross-section have the appearance of compact, close to globular crystals. X-ray spectral studies have shown that despite the same crystallographic structure, eutectic and primary crystals of the (Fe,Mn)3Si2Al15 phase differ in the higher concentration of iron, manganese, copper and nickel in the latter. In the composition of the AK12M2MgNZH alloy, there is practically no acicular intermetallic β-FeSiAl5, the formation of which is one of the main reasons for the decrease in mechanical properties. Similar to the AK12M2MgN alloy, compact crystals of the primary phase (Fe,Mn)3Si2Al15 and a significant amount of the π-FeMg3Si6Al8 phase appear. Such structural changes ensured an increase in the mechanical properties at 20 and 300 oC of both the AK12M2MgN alloy and AK12M2MgNZH. The highest properties of both alloys are achieved at j = 100 A/cm2; ν = 1000 ‒ 2000 Hz. The characteristics of mechanical properties increase from 25 % to 40 %. The structural and phase changes caused by the processing of the AK12M2MgNZH melt with an electric current according to experimentally established modes provide it with mechanical properties at the level of the AK12M2MgN alloy with several higher heat resistance indicators. In addition, treatment of the melt with electric current allows to reduce the consumption of sodium-potassium fluxes by 15-50%; time of heat treatment for T1 from 10-12 hours. up to 2-3 hours.

Modelling of mixed thermodynamic model based on new materials

In order to solve the problem of the performance of mixed alkane phase change energy storage materials, this paper proposes the modelling research of mixed thermodynamic model based on new materials. In this paper, the thermodynamic performance of binary mixed alkane system is studied, the influence of phase transition temperature, phase transition enthalpy and its composition on the mixed alkane system is explored, and its solid-liquid phase diagram is drawn. We used different thermodynamic models to predict the phase transition temperature and enthalpy in the melting process of binary mixed alkanes, which were mutually verified with the experimental results. The experimental results show that C9-C10 and C9-C11 systems exhibit eutectic behavior. The eutectic components are 88% (mass fraction, the rest is the same) C9-12% C10 and 90% C9-10% C11. The eutectic temperatures are 218.25 K and 215.15 K, respectively. The C8-C9 system has peritectic phenomenon, C10-C11 system shows complete mutual solubility, and their mini?mum melting points are 200.25 K and 234.35 K, respectively. Conclusion is that the C9-C10 and C9-C11 eutectic systems are suitable for low temperature phase change materials in the temperature range of 210-220 K, providing data reference for their application in low temperature energy storage.

Electroactivity of weak electricigen Bacillus subtilis biofilms in solution containing deep eutectic solvent components

Bacillus subtilis is a Gram-positive, spore-forming bacterium with a versatile and adaptable metabolism, which makes it a viable cell factory for microbial production. Electroactivity has recently been identified as a cellular characteristic linked with the metabolic activity of B. subtilis. The enhancement of B. subtilis electroactivity can positively enhance bioproduction of high-added value metabolites under electrofermentative conditions. Here, we explored the use of deep eutectic solvents (DESs) and DES components as biocompatible nutrient additives for enhancing electroactivity of B. subtilis. The strongest electroactivity was obtained in an aqueous choline chloride: glycerol (1:2 mol mol−1) eutectic mixture. At low concentration (50–500 mM), this mixture induced a pseudo-diauxic increase in planktonic growth and increased biofilm formation, likely due to a nutritional and osmoprotectant effect. Similarities in electroactivity enhancements of choline chloride-based eutectic mixtures and quinone redox metabolism in B. subtilis were detected using high performance liquid chromatography and differential pulse voltammetry. Results show that choline chloride-based aqueous eutectic mixtures can enhance biomass and productivity in biofilm-based electrofermentation. However, the specific mechanism needs to be fully elucidated.

Deep eutectic solvent-based ultrasound-assisted liquid–liquid microextraction of ibuprofen prior to HPLC-UV determination

ABSTRACT In this study, accurate and sensitive determination of ibuprofen in blood, urine, pharmaceutical tablet, syrup, and water samples was accomplished with the combination use of deep eutectic solvent-based ultrasound-assisted liquid–liquid microextraction (DES-UA-LLME) and high-performance liquid chromatography-ultraviolet visible detection system. The most important advantage of this method is that it can be used in the determination of ibuprofen without affecting the matrix environment of a wide range of samples. Ibuprofen in the sample phase was extracted to 500 µL of deep eutectic solvents phase (ChCl:Ph at 1:4 molar ratios) at pH 3.0. The influence of analytical parameters, such as pH of sample solution, the molar ratio of deep eutectic solvents components, tetrahydrofuran volume, and volume of DESs, were optimised in details. The preconcentration factor (PF), the detection limit (DL), intraday, and interday relative standard deviations (RSD, %) for the developed DES-UA-LLME/HPLC procedure were found as 30, 0.4 µg L−1, 1.74%, and 4.68%, respectively. The developed DES-UA-LLME was successfully used for the determination of ibuprofen in urine, blood, pharmaceutical tablet, syrup, and water samples.

Влияние модифицирующих элементов на структуру и механические свойства литейных Al-Si-сплавов

The state of scientific research on the modification of aluminum-silicon (Al-Si) alloy with strontium, sodium, phosphorus, which are widely employed in industrial alloys, and the modification of Al-Si alloy with intensively studied rare-earth elements (cerium, europium, samarium and others) was analyzed. Scientific articles related to the study of the effect of modifiers on the mechanical properties, mainly on the strength and ductility of hypoeutectic, eutectic and hypereutectic alloys was considered. On the basis of a literary data analysis, ways of improving the mechanical properties have been proposed by jointly modifying several elements, the possibility of forming the solely eutectic structure in the hypereutectic composition alloy 0.01 wt% strontium (Sr) modified and directionally crystallized at a rate that provides paired growth of the eutectic components is noted. This composition of Al-Si alloy has superfine-grained eutectic structure, its strength and ductility exceed the mechanical properties of Al-Si alloys obtained by other techniques.

Influence of modifying elements on the structure and mechanical properties of casting Al-Si alloys

The state of scientific research on the modification of aluminum-silicon (Al-Si) alloy with strontium, sodium, phosphorus, which are widely employed in industrial alloys, and the modification of Al-Si alloy with intensively studied rare-earth elements (cerium, europium, samarium and others) was analyzed. Scientific articles related to the study of the effect of modifiers on the mechanical properties, mainly on the strength and ductility of hypoeutectic, eutectic and hypereutectic alloys was considered. On the basis of a literary data analysis, ways of improving the mechanical properties have been proposed by jointly modifying several elements, the possibility of forming the solely eutectic structure in the hypereutectic composition alloy 0.01 wt% strontium (Sr) modified and directionally crystallized at a rate that provides paired growth of the eutectic components is noted. This composition of Al-Si alloy has superfine-grained eutectic structure, its strength and ductility exceed the mechanical properties of Al-Si alloys obtained by other techniques. Keywords: rare-earth elements, eutectic, microstructure, elongation, tensile strength.

Application of curcumin as a green and new sorbent in deep eutectic solvent-based dispersive micro-solid phase extraction of several polycyclic aromatic hydrocarbons from honey samples prior to gas chromatography-mass spectrometry determination.

A green, simple, and efficient dispersive micro-solid phase extraction method was developed for the extraction of polycyclic aromatic hydrocarbons from honey samples. In this method, for the first time, curcumin was used as an efficient and green sorbent to extract the analytes from the sample. After that the adsorbed analytes were eluted using a deep eutectic solvent prepared by mixing tetrabutylammonium chloride: ethylene glycol and analyzed by gas chromatography-mass spectrometry. Important experimental factors affecting adsorption and desorption steps of the method were optimized and under optimal experimental conditions, low limits of detection (0.14-0.37ng/g) and quantification (0.49-1.3ng/g), wide linear range (1.3-500ng/g) with a coefficient of determination ≥0.994 were obtained. Relative standard deviation values for intra- and interday precisions were ≤7.5% for all of the analytes at a concentration of 2ng/g for each analyte (n=6). Extraction recovery of the method was in the range of 72-81%. Finally, 20 honey samples were analyzed and the analytes were successfully detected. The method is environment friendly because of the use of curcumin as a sorbent. Also, biodegradability of the used deep eutectic solvent components is another advantage of the method.

Вплив магнію на високотемпературну структурно-фазову стабільність сплавів системи Al-Ni-La

The paper considers a relevance of the Al-Ni-La system cast alloys development as promising materials for application at elevated temperatures. The influence of magnesium on the structural-phase characteristics of alloys-representatives with a nickel content of about 2% wt. and lanthanum - about 5,5 and 11,5% wt. were studied in the cast condition and after annealing at 425 ° C for 5 hours. It is shown, that the addition of magnesium in the amount of 0,6 wt%. to alloys with a lanthanum content of 5,5 % wt. helps to increase the size of the lanthanum-containing eutectic component in the cast state, but stimulates its grinding after annealing. Since doubling the lanthanum content, magnesium has almost no effect on the structure of the eutectic in the cast state, but intensifies the process of changing its structure during annealing. In this case, the size of the eutectic components is almost unchanged and can be compared with an undoped alloy. Increasing the magnesium content twice to 1,2% wt. in the alloy with a lanthanum content of 11% wt. leads to a noticeable enlargement of Al11La3 intermetallics. After annealing, this structural component retains the characteristics of a fibrous structure and at the same time increases in size by about half. The magnesium content in the eutectic zones and in the solid solution hardly changes after annealing. The obtained data indicate the possibility of using magnesium as an additional alloying element of cast heat-resistant alloys of the Al-Ni-La system, which is able to simultaneously contribute to their strengthening both under normal conditions and at elevated temperatures. In this case, magnesium, in the amount of about 0,6% wt., also helps to preserve the fine structure of the eutectic components at high temperatures. Keywords: Al-Ni-La, Al-Ni-La-Mg, alloying, structural stability, heat resistance.

Microstructure evolution and toughening mechanism of Al2O3/YSZ directionally solidified eutectic ceramic

Al2O3/YSZ directionally solidified eutectic ceramics (DSECs) with a diameter of 10 mm were prepared via the induction heating zone melting (IHZM), and effects of the pulling rate of the crucible on the microstructure and mechanical properties were investigated. The eutectic components included α-Al2O3, t-ZrO2 and m-ZrO2 phases. The DSECs’ microstructure evolved from a mixture of discontinuous lamellar and round colony structure to the round colony structure, then to the faceted colony structure, and finally to a cell structure with increasing the pulling rate. The formation kinetics and growth process of the round colony structure were described and discussed in detail. The reason that the faceted colony structure formed could attributed to the large increase of solid-liquid interface curvature. When the pulling rate was 300 mm/h, the actual growth rate vg = 81.9 ± 17.5 mm/h was calculated from λ2v=37.7 corresponding to the intracolony; or vg = 99.5 ± 58 mm/h was calculated from with λ2v=631 corresponding to the intercolony. The DSECs’ hardness and fracture toughness increased with the pulling rate, and got the maximum values of 18.6 GPa and 9.39 MPa m1/2 at 300 mm/h, respectively, which could be attributed to the refinement of phases and the decrease of m-ZrO2 phase fraction.

Ultra-high local plasticity in high-strength nanocomposites

We subjected an aged Cu-24wt%Ag ingot to cold drawing to create a high-strength nanostructured composite wire with both Cu-rich proeutectic and Ag-rich eutectic components. During the drawing, a fine lamellar structure (average spacing 20 ± 6 nm) developed in the proeutectic component, which contained a high density of Ag fibers (average width below 5 nm) embedded in the matrix. In the eutectic component, a relatively coarse structure developed, with an average Ag grain size around 100 nm. The result of such a bimodal size of Ag fibers was ultra-high bending plasticity, i.e., the drawn wire tolerated 59% bending strain at the outermost edge, 15 times its tensile elongation (3.6%). During our bending test, dynamic recovery and partial recrystallization occurred more near the inner edge than near the outer edge and primarily in the eutectic component. High bending strain caused some of the thicker Ag fibers to become discontinuous and lose their original alignment. This structural evolution increased local plasticity, resulting in an unexpectedly high achievable bending strain, which is unusual in nano-sized, Ag-fiber-reinforced high-strength composites.