Interdiffusion Rates Research Articles

Significant enhancement in high temperature performance of TiAl matrix composites by a novel configuration design

Ti5Si3/TiAl composites were successfully prepared by pressure infiltration and subsequent reactive annealing. Final microstructure of Ti5Si3/TiAl composites was dependent on the reactive annealing temperature, which varied from 1350 °C to 1420 °C, two typical microstructures could be achieved: (i) An unique core-shell structure (Core: fully lamellar α2-Ti3Al/γ-TiAl with in-situ synthesized Ti5Si3 particles predominantly distributed at the interfaces of α2/γ lamellar colonies; Shell: equiaxed γ-TiAl with Ti5Si3 particles distributed in γ grain boundaries); And (ii) A novel quasi-network structure composed of fully lamellar α2/γ and a majority of Ti5Si3 particles with a quasi-network distribution. The formation of the two microstructures could be attributed to the chemical composition heterogeneity which was caused by the difference in interdiffusion rate of Ti and Al elements in different annealing temperatures. The comparative investigations on high temperature tensile properties and creep behavior showed that the core-shell Ti5Si3/TiAl composites exhibited a better specific strength (165 MPa⋅g−1⋅cm3) and higher ultimate tensile strength (633 MPa) at 800 °C, which was 12 % higher than that of the quasi-network Ti5Si3/TiAl composites. While the creep behavior analysis showed that in compassion with equiaxed γ phase, the slip distance of dislocations in fully lamellar α2/γ phase was shorter, impeding the motion of dislocations more effectively. And core-shell Ti5Si3/TiAl composites possessed a large number of grain boundaries concentrating in the shell which became weaker in the high temperature, facilitating the formation of creep pores in the shell and the final premature fracture. Hence, the quasi-network Ti5Si3/TiAl composites containing a higher content of fully lamellar α2/γ exhibited a better creep resistance than that of core-shell Ti5Si3/TiAl composites. More importantly, the steady state creep rate at 750 °C under the fixed stress of 250 MPa of quasi-network Ti5Si3/TiAl composites was relatively low, only 3.305 × 10−8 s−1, comparable to that of third-generation TiAl alloys.

Investigation of interdiffusion between compatible polymers under static and co‐extrusion processing conditions

AbstractWhen two compatible polymer melts are brought into contact, a diffuse interphase is formed that governs the adhesion between them. The degree of interdiffusion is defined mainly by the processing conditions and the physico‐chemical properties of the materials. Despite the great industrial relevance of co‐extrusion in manufacturing multilayer structures, little research has dealt with interdiffusion under these processing conditions, where polymer‐polymer interfaces are subject to shear load. In this work, procedures for investigating interdiffusion both under static and real co‐extrusion flow conditions were developed. Using various grades of poly(methyl methacrylate) and styrene‐co‐acrylonitrile copolymer, we studied both theoretically and experimentally the effects of interfacial contact time, temperature, material compatibility, and interfacial shear stress on interdiffusion. Spectroscopic analysis of the interfaces using confocal Raman microscopy showed that the general relationships between interdiffusion, time (Fick's law) and temperature (Arrhenius relationship) are identical under both static and co‐extrusion conditions. However, the interdiffusion rate is significantly higher under shear influence. Since the prediction of the interdiffusion process supports material selection and process design in multilayer manufacturing, a simple analytical model was developed to quantify the effects of aforementioned material properties and processing conditions on the apparent mutual interdiffusion coefficient.

Interfacial diffusion and Kirkendall voids evolution in the Copper-Zinc alloy binary interface revealed by in situ transmission electron microscopy

Investigating the diffusion behavior of binary system is crucial for understanding the solid-state diffusion in metallic joints, as it affects the interfacial reaction that forms intermetallic components (IMCs) and introduces Kirkendall voids that change the interfacial microstructures. In this study, we intuitively investigated the interfacial diffusion behavior of Copper-Zinc alloy binary interface by in situ transmission electron microscopy. Our findings revealed the interfacial diffusion of atoms, the growth processes of intermetallic phases, and the evolution of the Kirkendall voids during thermal diffusion. We observed that the Zn atoms diffuse rapidly into Cu and form the β phase at the onset of thermal diffusion at 200 ℃. Additionally, with increasing temperature, Cu atoms control the diffusion and the formation of IMCs due to their higher diffusion coefficient in the β and α phases, which are 2.09 ± 0.63 × 10−16 m2/s at 250 ℃ and 3.44 ± 0.44 × 10−17 m2/s at 300 ℃, respectively. Furthermore, we found that the interface significantly influences the interdiffusion rates of the IMCs and the formation of Kirkendall voids. The emergence of voids, which are formed at the initial defective site and the IMC layer at the temperature of 250 and 300 ℃, respectively, leading to a considerable decrease in interdiffusion at the binary interface of two orders of magnitude in comparison to unaffected regions. Moreover, we revealed the evolution of Kirkendall void, involving the formation and merging of holes, as well as the gradual thinning of atomic layers during diffusion. These findings are essential for understanding the formation and evolution of IMCs and Kirkendall void in binary interfaces.

Fe-Mn interdiffusion in aluminosilicate garnets

Precise determination of cation diffusivity in garnet can provide critical information for quantitatively understanding the timescales and thermodynamics of various geological processes, but very few studies have been performed for Fe-Mn interdiffusion. In this study, Fe-Mn interdiffusion rates in natural single crystals of Mn-bearing garnet with 750 ppm H2O are determined at 6 GPa and 1273–1573 K in a Kawai-type multi-anvil apparatus. Diffusion profiles were acquired by electron microprobe and fitted using Boltzmann–Matano equation. The experimental results show that the Fe-Mn interdiffusion coefficient (DFe-Mn) slightly decreases with increasing XFe. The experimentally determined DFe-Mn in Mn-bearing garnet can be fitted by the Arrhenius equation: DFe-Mnm2/s=D0XFenexp-E∗/RT, where E*=1-XFeEMn*+XFeEFe*, D0 = 8.06-6.04+9.87 × 10−9 m2/s, EMn*= 248 ± 27 kJ/mol, EFe*= 226 ± 59 kJ/mol, n = −1.36 ± 0.51. The comparing the present results with previous experimental data suggest that water can greatly enhance the DFe-Mn in garnet. Our results indicate that the time required for homogenization of the compositional zoning of a garnet is much shorter than previously thought.

The Effect of Non-Solvent Nature on the Rheological Properties of Cellulose Solution in Diluted Ionic Liquid and Performance of Nanofiltration Membranes.

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

Long term oxidation of NiCoCrAlY coated Ni-based superalloys: A comparison of observed and simulated interdiffusion

Lifetimes of MCrAlY-type coatings can easily surpass 25 kh when the criteria of ß-depletion is used. To reduce experimental effort, it’s necessary to develop models capable of simulating interdiffusion and oxidation. In the present study, NiCoCrAlY coatings were high velocity oxyfuel deposited on PWA 1483, MARM247, and CMSX-4 substrates, and samples were exposed at 900 °C for 5–20 kh in air+ 10 vol%H2O to study interdiffusion rates. Thermo-Calc/DICTRA was used to reproduce the observed differences, and microstructures were compared. Based on the agreement between calculated and observed rates, simulations were projected past the experimental exposures, utilizing ß-depletion as lifetime criteria.

Unveiling the Local Structure and Electronic Properties of PdBi Surface Alloy for Selective Hydrogenation of Propyne.

Building a reliable relationship between the electronic structure of alloyed metallic catalysts and catalytic performance is important but remains challenging due to the interference from many entangled factors. Herein, a PdBi surface alloy structural model, by tuning the deposition rate of Bi atoms relative to the atomic interdiffusion rate at the interface, realizes a continuous modulation of the electronic structure of Pd. Using advanced X-ray characterization techniques, we provide a precise depiction of the electronic structure of the PdBi surface alloy. As a result, the PdBi catalysts show enhanced propene selectivity compared with the pure Pd catalyst in the selective hydrogenation of propyne. The prevented formation of saturated β-hydrides in the subsurface layers and weakened propene adsorption on the surface contribute to the high selectivity. Our work provides in-depth understanding of the electronic properties of surface alloy structure and underlies the study of the electronic structure-performance relationship in bimetallic catalysts.

Gradient-tailored and heterointerface-rich architectures enable superior Li-ion storage performances of GeS2@NiS@N-doped carbon microspheres

The mesoporous compositional gradient nitrogen-doped carbon encapsulated germanium disulfide-nickel sulfide (abbreviated as “GeS2@NiS@NC”) microspheres have been synthesized. The Ni3Ge2O5(OH)4 microspheres precursor is firstly prepared by a hydrothermal mineralization process, which transforms to Ge3Ni5 microspheres by high temperature reduction. A thin polydopamine shell protects the microsphere architecture, which is converted into nitrogen-doped carbon layers. The GeS2@NiS@NC microspheres are finally fabricated via a high temperature interdiffusion vulcanization process induced by Kirkendall effect, during which the interdiffusion rate of Ni atoms is much faster than that of Ge atoms leading to the gradual composition changes from the exterior (NiS phase is rich) to the interior (GeS2 phase is rich) throughout a single microsphere. The GeS2@NiS@NC microspheres show unique structural advantage of the abundant heterogeneous interfaces, which accelerates the Li+ diffusion kinetics proved by density functional theory results. Besides, the in-situ XRD analyses reveal a continuous lithiation sequence as the compositional gradient from NiS to GeS2, during which the in-situ generated Ni clusters from NiS construct a continuous and penetrating e− transport channel throughout the microsphere. As a result, the GeS2@NiS@NC microspheres exhibit improved cycling stability and rate capability when employed as anodes for lithium ion batteries.

Composition-dependent interdiffusivity matrices of ordered bcc_B2 phase in ternary Ni–Al–Ru system at 1273∼1473 K

Abstract In this paper, 5 Ni–Al–Ru ternary and 2 NiAl/RuAl binary equilibrium alloys were prepared, and their lattice parameters were evaluated by using the X-ray diffraction technique. The relation between the lattice parameters and Ru content satisfies Vegard’s law, confirming that a continuous single bcc_B2 phase exists between NiAl and RuAl in the ternary Ni–Al–Ru system. After that, three diffusion couples located in the bcc_B2 phase region were prepared at 1273, 1373 and 1473 K, respectively. With the presently measured concentration profiles, the composition-dependent interdiffusivity matrices along the entire diffusion paths were efficiently determined by using the High-throughput Determination of Interdiffusion Coefficients (HitDIC) software. The obtained interdiffusivities show a good agreement with the limited experimental data in the literature. Furthermore, the present results show that the addition of Ru to bcc_B2 NiAl alloys can significantly inhibit the interdiffusion rate of Ni, indicating that the bcc_B2 Ru-containing NiAl bond coats can serve as a potential diffusion barrier for Ni-based superalloy substrate.

Kinetically Controlled Epitaxial Growth of Fe3GeTe2 van der Waals Ferromagnetic Films

We demonstrate that kinetics play an important role in the epitaxial growth of Fe$_3$GeTe$_2$ (FGT) van der Waals (vdW) ferromagnetic films by molecular beam epitaxy. By varying the deposition rate, we control the formation or suppression of an initial tellurium-deficient non-van der Waals phase (Fe$_3$Ge$_2$) prior to realizing epitaxial growth of the vdW FGT phase. Using cross-sectional scanning transmission electron microscopy and scanning tunneling microscopy, we optimize the FGT films to have atomically smooth surfaces and abrupt interfaces with the Ge(111) substrate. The magnetic properties of our high quality material are confirmed through magneto-optic, magnetotransport, and spin-polarized STM studies. Importantly, this demonstrates how the interplay of energetics and kinetics can help tune the re-evaporation rate of chalcogen atoms and interdiffusion from the underlayer, which paves the way for future studies of van der Waals epitaxy.

Reducing the amount of coalescing aid in high performance waterborne polymeric coatings

One of the objectives of the waterborne coatings industry is to reduce or eliminate solvents out of latex paints, maintaining or increasing the mechanical performance in a way that makes industrial adaptation as plain and economical as possible. This task has been tackled by the use of temporary oligomer plasticizers (TOP) in this work. The aim of TOPs is to use oligomers to achieve the plasticisation during film formation without changing significantly the final properties of the film. The incorporation of oligomers in the polymer particles is obtained by in-situ formation with the help of a chain transfer agent added in the reactor at the end of the main polymerization step. The TOP concept is translated as well from a conventional copolymer acrylic composition to a commercial formulation with promising results. On the other hand, a study of the role of the plasticizer during film formation is carried out by measuring the chain interdiffusion rate using the Pyrene Excimer Fluorescence (PEF) technique. The reduction of the amount of co-solvent needed to produce films at room temperature by the use of TOP is therefore associated to a faster diffusion of polymer chains in the presence of oligomers.

Effect of surface finish metallization layer on shearing fracture toughness of sintered silver bonded joints

In this paper, the effect of different surface finish metallization layers (Cu, Ni, Au and Ag) on the shearing fracture toughness of sintered Ag bonded joints under various sintering temperatures is investigated based on end-notch flexure (ENF) test. The results show that the shearing fracture toughness for different kinds of specimens all increase with the sintering temperature augment. The sintered Ag/Ag joint shows the highest shearing fracture toughness while the sintered Ag/Ni joint shows the lowest. The average shearing fracture toughness of the Ag/Cu joint is very close to the Ag/Au joint when sintered from 240 °C to 280 °C, whereas the former became much higher when sintered under 300 °C. By statistically analysis of crack propagation paths, interface microstructure characteristics, and interface reaction, it is found that the main factors affecting the discrepancy of the shearing fracture toughness for different metallized layers are the interface connection ratio and contact angle. A higher interface connection ratio and lower contact angle can increase the actual crack resistance and lower down stress concentration at the bonding interface, which leads to the discrepancy of shearing fracture toughness correspondingly. The different inter-diffusion rates for Ag and various metallization layers are also clarified. This study could deepen the understanding of the metallization layer effect on the shearing fracture behaviors of sintered silver bonded joints.

Preparation and Enhanced Isothermal Oxidation Resistance of a Low Diffusivity NiRePtAl Single-Phase Coating

A low diffusivity NiRePtAl single-phase coating was formed on a Ni3Al-based SC superalloy by electroplating and aluminizing treatments, in which the electroplating consisted of depositing Ni-Re and Pt layer. The isothermal oxidation test of the sample was evaluated at 1100 and 1200 °C; the results indicated that the low diffusivity NiRePtAl single-phase sample promoted the oxidation resistance due to a greater β-NiAl phases-enriched outer layer. The Re-base diffusion barrier could effectively refrain the outward diffusion of Mo. Low diffusivity NiRePtAl single-phase coating has a lower inter-diffusion rate to the superalloy, where the thickness of the secondary reaction zone decreased by 35%. Mechanisms responsible for improved oxidation resistance and decreased extent for the formation of secondary reaction zones are discussed in the present study.

Manipulation of Interfacial Diffusion for Controlling Nanoscale Transformation.

The unprecedented development of inorganic nanostructure synthesis has paved the way toward their broad applications in areas such as food science, agroforestry, energy conversion, and biomedicine. The precise manipulation of the nucleation and subsequent growth has been recognized as the central guiding principle for controlling the size and morphology of the nanostructures. However, conventional colloid syntheses based on direct precipitation reactions still have limitations in their versatility and extendibility. The crystal structure of a material determines the limited number of possible morphologies that its nanostructures can adopt. Further, as nucleation and growth kinetics are sensitive to not only the nature of the precipitation reactions but also ligands and ripening effect, rigorous control of reaction conditions must be established for every specific synthesis. In addition, multiple experimental parameters are entangled with each other, thereby requiring rigorous control of all reaction conditions. As a result, it is usually challenging to extend a synthetic recipe from one material to another. As an alternative method, the direct transformation of existing nanostructures into target ones has become an effective and robust approach capable of creating various complex nanostructures that are otherwise challenging to obtain using conventional methods. To this end, an in-depth understanding of nanoscale transformation toward the synthesis of inorganic nanostructures with diverse properties and applications is highly desirable.In this Account, we aim to reveal the critical effect of the interfacial diffusion on controlled nanoscale transformation. We first discuss how the interdiffusion rates determine the morphology and properties of bimetallic nanostructures. While equal interdiffusion rates lead to perfect mixing and generate fully alloyed nanostructures, interdiffusion at unequal rates creates vacancies in the fast diffusion side, which may cause dramatic morphological transformation to the nanostructures. Then, we introduce interfacial reactions, including the Kirkendall cavitation process, elimination reaction, and solid-state reaction, to promote the unbalanced interdiffusion and generalize nanoscale transformations in materials of various compositions, morphologies, and crystal structures. Finally, we discuss the use of capping ligands to inhibit the diffusion of atoms on one side of the interface in order to enable selective etching or transformation of the nanostructures. By modifying the nanostructured surface with specific capping ligands, the diffusion of surface atoms is restricted. When nanoparticles undergo chemical reactions (such as etching or heating), the outward diffusion of substances dominates, thereby successfully achieving chemical and morphological transformations. We believe that controlled interfacial diffusion can effectively manipulate nanoscale transformations, thus providing new strategies for the custom synthesis of multifunctional nanomaterials for various specific applications.

Fe–Mg interdiffusion in wadsleyite and implications for water content of the transition zone

Fe–Mg interdiffusion rates in polycrystalline wadsleyite aggregates have been determined as a function of water content (up to ∼0.345 wt.% H2O) at 16 GPa and 1373–1773 K in a Kawai-type multi-anvil apparatus. Pre-synthesized water-poor and -rich polycrystalline wadsleyite were used as starting materials. Diffusion profiles were obtained across the interface between Fe-free and -bearing diffusion couples, namely, Mg2SiO4 and (Mg0.9Fe0.1)2SiO4 aggregates by electron microprobe. Fe–Mg interdiffusivities by experiments yield DFe−Mg(m2/s)=D0XFenCH2Orexp⁡[−(E+αXFe+βCH2O)/RT], where D0 = 1.33−0.23+0.20× 10−11 m2/s, n = 0.19 ± 0.04, r = 0.29 ± 0.12, E = 92 ± 2 kJ/mol, α = −45 ± 12, and β = −134 ± 2. Our results indicate that water significantly enhances the rates of Fe–Mg interdiffusion in wadsleyite (a factor of 2.4 for fixed temperature and Fe concentration) compared to that in ringwoodite. Although under hydrous condition the transition zone shows the maximum Fe–Mg mixing efficiency as revealed by diffusivity-depth profile in the mantle, homogenization of existing chemical heterogeneity is still very limited at geological time scale only through solid-state diffusion. Combined with the Nernst–Einstein relation, the results suggest that the contribution of water to the electrical conductivity of wadsleyite or ringwoodite may be overestimated from Fe–Mg interdiffusion data at high water content. Further calculation demonstrates that ∼0.1–0.5 wt.% H2O is sufficient to account for the high conductivity values in the upper part (410–520 km) of the mantle transition zone as observed by electromagnetic induction studies.

Controlling the Self-Assembly of New Metastable Tin Vanadium Selenides Using Composition and Nanoarchitecture of Precursors.

In solid-state chemistry, the direct reaction of elements at low temperatures is limited by low solid-state interdiffusion rates. This and the limited number of processing parameters often prevent the synthesis of metastable compounds. Precisely controlling the number of atoms and nanoarchitecture of layered elemental precursors enabled the selective synthesis of two closely related metastable tin vanadium selenides via near-diffusionless reactions at low temperatures. Although the nanoarchitectures of the precursors required to form [(SnSe2)0.80]1(VSe2)1 and [(SnSe)1.15]1(VSe2)1 are very similar, controlling the local composition of the Sn|Se layers in the precursors enables the selective synthesis of either compound. The metastable alloy SnxV1-xSe2 was preferentially formed over [(SnSe2)0.80]1(VSe2)1, which has the identical composition, by modifying the nanoarchitecture of the precursor. Ex situ in-plane X-ray diffraction and X-ray reflectivity collected as a function of annealing temperature provided information on lateral and perpendicular growth of [(SnSe2)0.80]1(VSe2)1. The presence of Laue oscillations throughout the self-assembly provided atomic-scale information on the thickness of the [(SnSe2)0.80]1(VSe2)1 domains, giving insights into the self-assembly process. A reaction mechanism is proposed and used to rationalize how composition and nanoarchitecture control the reaction pathway through the free energy landscape.

Alteration rate of medieval potash-lime silicate glass as a function of pH and temperature: A low pH-dependent dissolution

Potash lime silicate glasses were extensively used during the Middle Ages as components of stained glass windows. Their external faces have been subjected to alteration in the atmospheric medium for centuries, leading to the development of thick alteration layers on the surfaces. This alteration is mainly caused by water in liquid (rainfall) or gaseous (vapor) form. In order to implement geochemical models simulating the long-term behavior of these glasses by coupling the different atmospheric factors, it is necessary to study mechanisms and kinetics of alteration induced by these different hygroscopic situations (rainfall and relative humidity). The aim of this study is here to evaluate the impact of liquid water on stained glass windows and especially to determine alteration rate laws of dissolution and interdiffusion as a function of pH and temperature. For that, a medieval model glass was altered in aqueous solution in batch experiments at different pH values (from 2 to 11), temperatures (from 5 to 70 °C) and saturation states of the solution. From the elemental concentrations in solution, the release rate of elements was calculated and the pH- and T-dependencies were determined. The dissolution and interdiffusion rate laws can now be used to simulate the alteration of a medieval glass submitted to a rainfall event. Moreover, this study highlights that the Si-K-Ca medieval glass presents a very low pH-dependency at alkaline pH, which can be explained by its composition.

The Influence of Porous Structure on the Interdiffusion Kinetics of Cu-Ni System During Spark Plasma Sintering

The interdiffusion kinetics of Cu-Ni system and the influence of porous structure on atomic diffusion kinetics during spark plasma sintering (SPS) were investigated. The interdiffusion coefficient of the Cu-Ni system annealed under SPS is much higher than that without current when the temperature exceeds 700 °C. By comparing the interdiffusion behaviors between Ni powder/Cu foil interface and Ni foil/Cu foil interface, the interdiffusion rate at the foil/powder interface was found to be significantly higher than that at the foil/foil interface during SPS. The diffusion process at the Ni powder/Cu foil interface shows two clearly identified stages: a high diffusion rate at the initial stage with high porosity and a slower diffusion rate at the mid-late stage with low porosity. The diffusion coefficient at the initial stage is nearly 5.2 times higher than that of the mid-late stage, demonstrating that the diffusion rate at the foil/powder interface decreases with the gradual reduction of porosity during the SPS densification process. The porous structure leads to an extremely high local current density at the neck area, which results in a high density of crystal defects at the diffusion interface and subsequently accelerates atomic diffusion.

Study of migration and diffusion during the mixing process of asphalt mixtures with RAP

The mixing degree of virgin and aged asphalt binders is one of the main factors that can significantly affect the performance of reclaimed asphalt pavement (RAP). On the other hand, an important factor that contributes to the mixing is diffusion, which dominantly determines the general performance of asphalt mixtures with RAP. In this study, twelve different lab-mixing conditions were deliberately adopted to investigate the impact on the diffusion between virgin and aged bitumen binders, including three mixing temperatures (110°C, 130°C, 150°C) and four mixing times (30 s, 60 s, 120 s, 240 s). Specially fabricated cubic aggregates were designed and deposited for collecting pure binders, so that virgin or aged binders can be tracked and the effect of chemical reagents be avoided. Based on the Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared Spectroscopy (FTIR) tests, the performance and blending rate of binders under various conditions were clearly shown. The results show that blending temperature can play a more crucial role in diffusion than mixing duration, which means the higher temperature is capable of accelerating the inter-diffusion rate between virgin and aged bitumen binders, thus increasing the efficiency of recycling ulteriorly. The blending degree investigated in this study could not achieve the complete mixed state with the highest value being around 50%. Furthermore, the Asymmetric Gaussian Model is proposed to mathematically describe the change of blending rate with the mixing time.

The Role of Isobutanol as a Precipitant of Cellulose Films Formed from N-Methylmorpholine N-Oxide Solutions: Phase State and Structural and Morphological Features

The process of film formation including the initial treatment of thin layers of cellulose solutions in N-methylmorpholine N-oxide with isobutanol followed by washing with water is investigated in detail, and the structural and morphological features of the obtained films are examined. The phase state of the N-methylmorpholine N-oxide–isobutyl alcohol system is studied by differential scanning calorimetry and optical interferometry, and a diagram describing the crystalline equilibrium and allowing determination of the temperature–concentration “window” of compatibility of components is constructed. The dependence of viscosity of N-methylmorpholine N-oxide solutions in isobutanol on temperature confirms the phase composition of the system. The process of film formation is modeled by analyzing the diffusion zone of the cellulose solution–isobutyl alcohol system. The IR study of the interaction of N-methylmorpholine N-oxide containing 13.3% water with isobutanol shows that the affinity of isobutanol for water is much higher than that for N-methylmorpholine N-oxide. For this reason, when the spinning solution is brought in contact with isobutanol, the redistribution of water between the interacting components occurs and the structure of the heterogeneous gel-like complex cellulose–N-methylmorpholine N-oxide–isobutanol “is frozen,” as proved by the X-ray diffraction study of the films. Complete removal of the solvent and isolation of cellulose from this film proceed only upon subsequent washing with water. The X-ray diffraction and optical interferometry study of the effect of temperature on the interaction of a hot cellulose solution with cold isobutanol suggests that at room temperature the film obtained from solution contains inclusions of the vitrified N-methylmorpholine N-oxide. Under isothermal conditions (at a temperature of 90°С), the rate of interdiffusion grows appreciably and the solution preserves the homogeneous structure. Thus, the precipitation of cellulose from the bicomponent solvent N-methylmorpholine N-oxide–water upon contact first with isobutanol and then with water proceeds via two stages: initially the system undergoes phase separation and a concentrated solution is formed in the isobutanol-N-methylmorpholine N-oxide blend, from which cellulose precipitates upon interaction with water. When the process of primary interaction of the solution with alcohol is conducted under the conditions of compatibility of isobutanol with N-methylmorpholine N-oxide, a more homogeneous morphology of the films can be obtained.