Ionic Interdiffusion Research Articles

The reinforcing mechanism of ionic interdiffusion on MgO–MgAl2O4 composites between structural densification and mechanical property

MgO–MgAl2O4 composites are arising as promising candidates for high-temperature industrial applications. For this reason, the in-situ synthesis of such types of composites with spinel structure has attracted the attention of the scientific community. Along these lines, in this work, magnesia and bauxite were used as raw materials to fabricate MgAl2O4 composites. The mass proportion in the composites was also adjusted by using the solid-phase sintering method at 1400–1650 °C to enhance its mechanical properties and densification. XPS and SEM measurements were conducted, indicating that the MA50 sample with the mass ratio of 50:100 (MgAl2O4:MgO + MgAl2O4) exhibited the best properties at 1550 °C, in terms of uniformity of the grains’ growth morphology, optimal densification of the matrix structure, and achieving a maximum flexural strength of 113.23 MPa. From our analysis, it was demonstrated that the non-equivalent displacement of Al3+ and Mg2+ could easily lead to the formation of the (Mg1-xAlx/2)Mgx/4O solid-solution during the similar crystal structure, which enhanced mechanical strengthening between the micro-grain and framework. Meanwhile, the existence of a certain liquid phase not only effectively increased the mass transfer during the processing of interdiffusion between Al3+ and Mg2+, but also promoted the distribution of crystallite and microstructure.

Assessment of in-vitro bioactivity, biodegradability and antibacterial activity of polymer-derived 3D printed åkermanite scaffolds

Reticulated åkermanite (Ca2MgSi2O7) 3D scaffolds were fabricated by direct ink writing of pastes based on a commercial silicone resin and fillers, such as calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2) microparticles, followed by heat treatment at 1100 °C in air. To form liquid phase upon firing and thus promote the ionic interdiffusion, borax (Na2B4O7·10H2O) or hydrated sodium phosphate (Na2HPO4·12H2O) were considered as alternative additives. Although leading to scaffolds with different strength-to-density ratio, the two additives did not lead to substantial differences in terms of biological response. All fabricated ceramics exhibited acellular in-vitro bioactivity upon immersion in simulated-body-fluid (SBF) as well as antibacterial activity against S. aureus and E. coli. Direct contact cell viability test, performed with a stromal-cell line from mouse bone marrow (ST-2 cells), indicated no cytotoxicity of both samples determined by the WST-8 assay.

Interfacial Engineering at Cathode/LATP Interface for High-Performance Solid-State Batteries

Solid-state rechargeable lithium batteries are considered as one of the promising energy storage technologies due to their safety and high energy density. While developing better solid-state batteries is hampered by the poor interfacial compatibility. In this work, one novel design of buffer layer using the Li1+xAlxTi2−x(PO4)3 (LATP) solid electrolyte is reported to address the poor compatibility and big migration gap at the electrode-solid electrolyte interface. Such a facile design works well on facilitating the interfacial ionic inter-diffusion by padding the gap of ionic conductivity between electrode and electrolyte, as well as passivating the electric activity of interface region to avoid the continuously interfacial degradation, hence makes the interface more homogeneous and intimate to deliver the superior electrochemical performance. Moreover, upon cycling, a new carbon-rich interphase is revealed from electron microscopy in the interface region, which probably plays an important role in stabilizing the structure and regulating the electron/ion fluxes. All these findings provide a rewarding avenue to resolve the interfacial issues of solid-state lithium ion batteries and the integrated electronic devices.

Ionic interdiffusion as interaction mechanism between Al and Si3N4

AbstractAl‐Si3N4 couples were heat‐treated at 850‐1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre‐coefficient of 5 × 10−9 m2/s, indicating that the interaction is diffusion‐dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al‐Si transfer through the solid solution (Si3‐xAlxN4‐y) at the interface of Al alloy and β‐Si3N4 grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al1‐xSixN1+y (viz., AlN). Next, the Al1‐xSixN1+y grains detach from the β‐Si3N4 grains and subsequently new Al‐Si3N4 interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics.

Numerical simulation of equilibrium ionic transport processes through permeable ion-exchange membranes in bi-ionic systems

This paper aims to numerically study the equilibrium characteristics of the ionic inter-diffusion processes in ion-exchange membrane systems under bi-ionic conditions as a function of the membrane fixed-charge concentration and the thickness of the diffusion boundary layers adjacent to the membrane. The considered particular system is constituted by a membrane with negative fixed charge and two identical diffusion boundary layers on both sides of the membrane. The system is bathed by two solutions with a common co-ion but different counter-ion. The ionic transport processes of a ternary electrolyte are described by the Nernst-Planck-Poisson equations not only in the membrane but also in the diffusion layers, including the electric double layers at the interfaces. The ionic concentrations and electric potential profiles have been numerically obtained using the network simulation method in a permeable membrane system where the co-ion flux is a significant fraction of the counter-ionic fluxes. The effect of the diffusion boundary layers on the equilibrium membrane potential, the ionic fluxes and the ionic concentration profiles inside the membrane have been analysed and discussed.

The stability of titania‐silica interface

AbstractSilica is very often the catalyst support of choice for transition metal oxides such as titania, and specially anatase. Titania is an excellent absorber and photocatalyst for many organic molecules degradation. In order to understand the chemical nature of the interaction between titania and silica, we have performed a theoretical study using density functional theory aiming to elucidate the role on the stability of the interface of the specific type of interactions, H‐bonding, covalent bonding of the pristine surfaces, and covalent bonding after silicon and titanium ions interdiffusion. The calculations were carried out for hydrogen and oxygen terminated surface, comparing the bonding types and the forces acting along the interface. The interface dynamics was studied for interfaces under applied stress in order to elucidate their stability and failure limits. The shearing forces and the mechanisms of interface failure were determined. Interfaces with interdiffused Si and Ti ions were studied to improve the interface stabilization. The results demonstrate that high‐temperature treatment leading to formation of SiOTi bonds at the interface is responsible for the formation of strong and flexible binding interaction between both oxides. At high strains, the SiOTi interface failure is observed due to lattice mismatch between the SiO2 and TiO2. The failure is a result of forces acting orthogonal to the interface shearing. In case of hydrogen terminated surface, the interface binding is a result of hydrogen bond network. Such interface is fragile at moderate shearing forces along the applied strain. The hydrogen bond network decreases the elastic properties and flexibility of the interface. The SiO2/TiO2 interface is further stabilized by Si/Ti ion interdiffusion. The ionic interdiffusion process also increases the interface flexibility. Thus, in order to obtain more stable anatase photocatalyst supported on silica, the synthetic routes should favor silicon and titanium ions interdiffusion along the interface.

Residual stress in ion-exchanged silicate glass: An analytical solution

The ion-exchanged residual stress profile influences both the strength and the wear-resistance of glass hence its description is of great importance. Currently, residual stress profiles of silicate glasses can only be estimated by numerical time-integration based on the known ionic concentration profile and the expected stress relaxation behavior of the glass. In this work, we derived and validated the constant coefficients analytical solution describing the residual stress profile in single-step ion-exchanged glasses. The proposed solution is based on Sane and Cooper's model and assumed that both the generalized Maxwell stress relaxation function applied and that a constant ionic inter-diffusion coefficient could accurately describe the behavior of the system. Furthermore, an analytical approximation for composition-dependent stress relaxation behavior of the glass was proposed. Examples of how the newly developed analytical description of the stress profile could be fitted through regression analysis to available residual stress data were also presented.

B-doped hardystonite bioceramics from preceramic polymers and fillers: Synthesis and application to foams and 3D-printed scaffolds

Highly porous hardystonite-based bioceramics, in the form of foams and 3D scaffolds, were obtained by the thermal treatment, in air, of silicone resins and engineered micro-sized oxide fillers. Besides CaO and ZnO precursors (CaCO3 and ZnO powders), calcium borate, in both hydrated and anhydrous form (Ca2B6O11·5H2O and Ca2B6O11, respectively), was added to commercial silicone resins, with a significant impact on the microstructural evolution. In hydrated form, calcium borate led to a substantial foaming of silicone-based mixtures, at low temperature (420°C); after dehydration, upon firing, the salt provided a liquid phase, favouring ionic interdiffusion, with the development of novel B-contaning hardystonite-based solid solutions (Ca2Zn1-xB2xSi2-xO7). Although fired at lower temperature than previously developed silicone-derived hardystonite cellular ceramics (950°C, instead of 1200°C), the newly obtained foams and scaffold exhibit substantial improvements in the mechanical properties.

Quantification of light-enhanced ionic transport in lead iodide perovskite thin films and its solar cell applications

Ionic transport in organometal halide perovskites is of vital importance because it dominates anomalous phenomena in perovskite solar cells, from hysteresis to switchable photovoltaic effects. However, excited state ionic transport under illumination has remained elusive, although it is essential for understanding the unusual light-induced effects (light-induced self-poling, photo-induced halide segregation and slow photoconductivity response) in organometal halide perovskites for optoelectronic applications. Here, we quantitatively demonstrate light-enhanced ionic transport in CH3NH3PbI3 over a wide temperature range of 17–295 K, which reveals a reduction in ionic transport activation energy by approximately a factor of five (from 0.82 to 0.15 eV) under illumination. The pure ionic conductance is obtained by separating it from the electronic contribution in cryogenic galvanostatic and voltage-current measurements. On the basis of these findings, we design a novel light-assisted method of catalyzing ionic interdiffusion between CH3NH3I and PbI2 stacking layers in sequential deposition perovskite synthesis. X-ray diffraction patterns indicate a significant reduction of PbI2 residue in the optimized CH3NH3PbI3 thin film produced via light-assisted sequential deposition, and the resulting solar cell efficiency is increased by over 100% (7.5%–15.7%) with little PbI2 residue. This new method enables fine control of the reaction depth in perovskite synthesis and, in turn, supports light-enhanced ionic transport.

Facile obtainment of luminescent glass-ceramics by direct firing of a preceramic polymer and oxide fillers

Rare-earth (RE) doped glass-ceramics represent very interesting luminescent materials. The thermal annealing of the glass precursor causes the controlled precipitation of several crystalline phases, in which RE may be variously distributed, also with different oxidation states, e.g. Eu2+ and Eu3+. The present investigation demonstrates the feasibility of preparation of RE-doped alumino-boro-silicate glass-ceramics by direct firing in air (at 1000–1200°C) of a preceramic polymer, filled with nano- and micro-sized particles, as an alternative to glass melting and annealing. In particular BaCO3 or SrCO3 micro-particles, mixed with nano-sized γ-Al2O3, were found to react with amorphous silica, available from the oxidative decomposition of a commercial silicone, yielding a strontium or a barium alumino-silicate phase. Boric acid micro-particles contributed both to the development of a liquid phase upon firing (promoting ionic interdiffusion) and to the formation of a La-borate phase, by interaction with La2O3 micro-particles. The blue and red luminescence of the obtained glass-ceramics is attributed to the incorporation of Eu2+ and Eu3+ ions, from nano-sized Eu2O3 filler, in alumino-silicate and borate phases, respectively.

Bioactive Wollastonite-Diopside Foams from Preceramic Polymers and Reactive Oxide Fillers

Wollastonite (CaSiO3) and diopside (CaMgSi2O6) silicate ceramics have been widely investigated as highly bioactive materials, suitable for bone tissue engineering applications. In the present paper, highly porous glass-ceramic foams, with both wollastonite and diopside as crystal phases, were developed from the thermal treatment of silicone polymers filled with CaO and MgO precursors, in the form of micro-sized particles. The foaming was due to water release, at low temperature, in the polymeric matrix before ceramic conversion, mainly operated by hydrated sodium phosphate, used as a secondary filler. This additive proved to be “multifunctional”, since it additionally favored the phase development, by the formation of a liquid phase upon firing, in turn promoting the ionic interdiffusion. The liquid phase was promoted also by the incorporation of powders of a glass crystallizing itself in wollastonite and diopside, with significant improvements in both structural integrity and crushing strength. The biological characterization of polymer-derived wollastonite-diopside foams, to assess the bioactivity of the samples, was performed by means of a cell culture test. The MTT assay and LDH activity tests gave positive results in terms of cell viability.

Studies on the use of microwave for enhanced properties of glass-ceramics produced from sewage sludge pyrolysis residues (SSPR)

SSPR (sewage sludge pyrolysis residues) were reused as main raw materials (up to 80%) for glass-ceramics. In the present work, glass-ceramics were synthesized by microwave and conventional processes with an objective of investigating the function of microwave radiation on enhancement in the properties and crystallization mechanisms of the two heating styles. The heat treatment schedule of the microwave glass (M-G) and conventional glass (C-G) was decided on the basis of differential scanning calorimetry (DSC) results. A control study of microwave glass (CM-G) was carried out following identical heat treatment schedule as was adopted by M-G under conventional heating process. X-ray diffraction (XRD) analysis revealed that the main crystalline phase of microwave glass-ceramics (M-GC) was anorthite (CaAl2Si2O8), and the main crystalline phases of both conventional glass-ceramics (C-GC) and control microwave glass-ceramics (CM-GC) were wollastonite (CaSiO3) and anorthite (CaAl2Si2O8). The difference of the main crystalline phase between the two heating styles was attributed to the improved ionic interdiffusion caused by microwave radiation. Scanning electron microscopy (SEM) analysis clearly indicated that M-GC possess finer and uniform microstructure. M-GC exhibited excellent properties in comparison to C-GC and CM-GC. The kinetics study indicates that microwave radiation decreased Ea about 76kJmol−1. The n values of M-G and C-G were in the range of 3.03–3.43 and 1.73–1.95, representing the crystallization mechanism of bulk nucleation and surface nucleation, respectively.

Ferroelectric/ferrimagnetic composite ceramics with depressed interfacial reaction and low dielectric loss

(1−x)BaTiO3/xNi0.5Zn0.5Fe2O4 (NZFO) ferroelectric/ferrimagnetic composite ceramics with restricted interfacial reaction were prepared by adopting fine NZFO precursors synthesized by combustion method. The dielectric dispersion, loss, and conductivity are significantly reduced at most compositions, particularly at concentrations below the percolation threshold. At x = 0.3, a frequency-stable permittivity of 2300 and a low loss of 0.04 at 1 kHz is realized. The recovery of the dielectric/electric properties is attributed to the interfacial amorphous phase introduced by the fine NZFO precursors, which can act as barrier for ionic inter-diffusion between the two phases and hopping conduction among ferrites.

Near Hydrothermal Alteration of Obsidian Glass: Implications for Long Term Performance Assessments

Abstract Obsidian glass alteration experiments under near hydrothermal conditions were performed to study mechanism and conditions of formation of altered minerals. X-ray diffraction patterns and cell dimensions of the specimens treated at 150, 200 and 3000C (pH = 8.03) revealed appearance of three main minerals - illite (9.5-10 Å), chlorite (7.04 Å) and halloysite (10.25Å). Further increase in the pH favours matrix dissolution with the formation of secondary altered layers. SEM-EDS study show that the alteration causes smoothing of the grain surfaces. These surfaces exhibits etch pits and series of depressions, formed by the process of dissolution. SEM - Back Scattered Electron images of obsidian specimens show thin laminae of smectite, with foliated bulky rims and cellular honeycomb texture, formed by precipitation from the solution as well as by direct transformation of glass during alteration. This mechanism is resulting from the alteration of alkalis by ionic inter-diffusion with H3O+ and H+ and inward diffusion of H2 O, leading to free diffusion of silica into solution and then to a local rearrangement of the glass framework. Thus, a direct transformation of glass into clay minerals is the major reaction mechanism as evidenced by the mechanism of glass dissolution and subsequent mineral precipitation.

Diffusion characteristics of mixed-cation ion-exchange membranes

Approaches are proposed for determining diffusion parameters of mixed-cation membranes. One of them is used to evaluate diffusion coefficients and effective ion-exchange constants in membranes containing both H+ and M+ (M = Li, Na, K, Rb) cations from ionic conductance and interdiffusion data for samples in equilibrium with solutions differing in the ratio of salt and acid concentrations.

Low-temperature cofiring behavior of ZnTiO3 dielectrics/NiZnCu ferrite composites

Abstract The low-temperature cofiring compatibility between ferrite and dielectric materials is the key issue in the production process of multilayer chip LC filters. In this paper, no camber and cracks multilayer composite samples were obtained by using restricted shrinkage sintering process. The cofiring interface, ionic interdiffusion between constituents and dielectric properties of cofired composites were investigated. The results show that interfacial reactions occur at the interface, which can strengthen combinations between ferrite layers and dielectric layers. Iron and titanium have a wide diffusion range. Due to their low-firing characteristics and realizable cofiring compatibility, ZnTiO3 dielectrics/NiZnCu hexagonal ferrite can serve as the promising medium materials in the multilayer LC filter.

Numerical simulation of diffusion ions in ZnTiO 3 dielectrics/NiZnCu ferrite composites using restricted shrinkage sintering process

No camber and cracks ZnTiO 3 dielectrics/NiZnCu hexagonal ferrite (abbreviated to ZT/NZC) composite samples were obtained by using restricted shrinkage sintering process. The cofiring interface and ionic interdiffusion between constituents of cofired composites were investigated. The interdiffusion of ZT/NZC composite can be regarded as the semi-infinite diffusion-couple model and based on this diffusion model, the numerical simulation for the ionic composition distribution was carried out by computer, which was in agreement with the experimental results. The diffusion coefficients and activation energies for the Zn 2+, Ti 4+, Ni 2+, and Fe 3+ were determined, respectively. The difference between the ionic diffusion coefficients and apparent activation energies was discussed in this article.

Interface and ionic interdiffusion in cofired ferroelectric/ferrite multilayer composites

Recently, the surface mount technology (SMT) has been rapidly developed for miniaturization of electric devices such as multilayer ceramic capacitor (MLCC) and multilayer chip inductor (MLCI). The trend of electronics has been for an increasingly compact design. Some characterizations of cofired devices such as ceramic-filled glass electronic package, and varistorcapacitor cofired multilayer device have been reported [1, 2]. Multilayer chip LC filter, which is combined with several capacitors and inductors by the production process of multilayer chip components, is a type of advanced surface mount devices (SMD). Lead based relaxor ferroelectrics, such as Pb(Mg1/3Nb2/3)O3, Pb(Ni1/3Nb2/3)O3 and Pb(Zn1/3Nb2/3)O3, are being widely used as MLCC due to their high dielectric constant and low sintering temperature [3–5]. And NiCuZn ferrite, which has excellent magnetic permeability and can be densified at low temperature, is an important material using for producing low temperature sintered MLCI [6–8]. They are promising materials for the multilayer chip LC filters. The key issue of manufacturing the multilayer chip LC filters is cofiring the capacitor and inductors together at low temperature. The interfacial interactions such as chemical reaction, ionic interdiffusion, are important for the production of devices. In the present study, the multilayer components were prepared by cofiring Pb(Ni1/3Nb2/3)O3-PbTiO3 (abbreviated as PNNT) ferroelectrics and NiCuZn ferrite. The cofiring interface and ionic interdiffusion between constituents were investigated. According to the diffusioncouple model, the interfacial diffusion coefficient for Pb2+, Nb5+, Ni2+, and Fe3+ had been estimated. The specimens were prepared by the conventional oxide-mixing technique. 99% pure reagent-grade PbO, NiO, Nb2O5, TiO2, Fe2O3, CuO, and ZnO oxides were weighed in the appropriate proportions and used as starting materials. Fe2O3, NiO, CuO and ZnO powders, according to the composition (Ni0.8Cu0.1Zn0.1)Fe2O4, were calcined at 720 ◦C for 4 h to fabricate NiCuZn ferrite. The dielectric material, according to the composition 0.8 Pb(Ni1/3Nb2/3)O3-0.2PbTiO3 with little amount of CuO and ZnO, were calcined at 800 ◦C for 4 h. The calcined mixtures were ground by ball milling for 12 h to a proper surface area. The ground powders were dried and added to PVA for the disk bodies. Firstly, ferroelectic and ferrite disks were separately prepared and sintered at 850–950 ◦C for 2 h, in order to measure characteristics such as phase structure and sintered densities. Secondly, the mixed calcined powders of ferroelectric and ferrite were laminated into a mold and compressed into a plate with the diameter of 12 mm, which was sintered at 950 ◦C for 2 h. The sintered densities were measured by the Archimedes method. The phase structure for the specimens were identified using X-ray diffractometer (XRD). For lead-based ferroelectrics, perovskite phase and pyrochlore phase always coexist. The relative amounts of perovskite and pyrochlore phases were determined by measuring the major X-ray peak intensities for perovskite and pyrochlore phases, i.e. (110) and (222), respectively. The percentage of perovskite phase was calculated by the following equation [9]:

III. Electrochemistry in Glasses and Melts. Glass electrodes: Why and how they function

AbstractSubsurface concentration profiling by Ion Bombardment for Spectrochemical Analysis (IBSCA) and Nuclear Reaction Analysis (NRA) combined with other methods yielded information on the ionic processes at and in glass electrode membranes and results in the mechanism (“dissociation mechanism”) of glass electrodes. The primary step is the formation of a phase boundary equilibrium between functional groups, e.g. siloxy, at the glass surface and hydronium or alkali ions in the solution. It determines the potential of the glass due to the charge density established at the glass surface by the dissociated form of the surface groups, e.g. SiO−, and the surface activities of the acidic or salt forms of the surface groups, e.g. SiOH and SiOM, respectively. This inseparable connection of solution‐dependent potential and “surface coverage” was verified by electrolytic migration experiments. The concentration gradients thus caused below the glass surface lead to an ionic interdiffusion in the subsurface glass range (if the ions attached to the surface groups are not hindered sterically to enter the glass), which is the first step of glass corrosion, and to a diffusion voltage, which is part of the overall membrane potential. Quantitative expressions are given, and it is shown that, in principle, the response of glass electrodes is below “ideal”, i.e. smaller than RT(In 10)/F, which explains the well known sub‐Nernstian response of pH glass electrodes. Two new sodium errors were found. Construction and operation of glass electrodes are briefly sketched as an introductory basis. The reason for the long existence of the purely thermodynamic “ion exchange theory” is analysed.

On the role of local electric field correlation effects on the ionic interdiffusion in soda-lime glass

The contribution of the local electric field to the interdiffusion process in glass is analyzed by means of numerical simulation methods. The results are compared with experimental data from secondary ion mass and Rutherford backscattering spectrometry data for a silver-sodium ion-exchanged soda-lime glass.