Barrier Material Research Articles

In-situ reactivation and reuse of micronsized sulfidated zero-valent iron using SRB-enriched culture: A sustainable PRB technology

Sulfidated zero-valent iron (S-ZVI) is an attractive material of permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. However, S-ZVI is prone to be passivated due to the oxidation of reactive and conductive iron sulfide (FeSx) shell and the formation of inactive and non-conductive ferric (hydr)oxides, which serve as electron transfer barriers to hinder the electron flow from Fe° core to contaminants. This study thus proposed a novel approach for in-situ reactivation and reuse of micronsized S-ZVI (S-mZVI) in PRB using sulfate-reducing bacteria (SRB) enriched culture to realize long-lasting remediation of Cr(VI)-contaminated groundwater. S-mZVI were passivated after reactions with Cr(VI) due to the formation of electron transfer barriers (mainly inactive and non-conductive Fe(III) (hyd)oxides, which increased the polarization resistance from 16.38 to 27.38 kΩ cm2 and hindered the electron transfer from the Fe° core. Interestingly, the passivated S-mZVI was efficiently reactivated by providing the SRB-enriched culture and organic carbon within 12 h, and the Cr(VI) removal capacity of S-mZVI in the three use cycles increased to 37.4 mg Cr/g, which was 2.1 times higher than that of the virgin S-mZVI. After biological reactivation, the Rp of reactivated S-mZVI decreased to 12.30 kΩ cm2. SRB-mediated reactivation removed the electron transfer barriers via biotic and abiotic reduction of Fe(III) (hyd)oxides. Especially, the microbial Fe(III) reduction mediated by FmnA-dmkA-fmnB-pplA-ndh2-eetAB-dmkB protein family enhanced the Fe2+ release from the surface and the subsequent re-formation of reactive and conductive FeSx shell. A long-term PRB column test further demonstrated the feasibility of in-situ biological reactivation and reuse of S-mZVI for enhanced Cr(VI)-contaminated groundwater remediation. Within 64 days, the Cr(VI) removal capacity of S-mZVI in the four use cycles increased by 3.2 times, compared to the virgin one. The bio-reactivation using the SRB-enriched culture and sulfate locally-available in groundwater will reduce the chemical and maintenance costs associated with the frequent replacement of reactive ZVI-based materials. The PRB technology based on the bio-renewable S-mZVI can be a sustainable alternative to the conventional PRBs for the long-lasting and low-cost remediation of groundwater contaminated by oxidative pollutants.

Nano boron nitride laminated poly(ethyl methacrylate)/poly(vinyl alcohol) composite films imprinted with silver nanoparticles as gas barrier and bacteria resistant packaging materials

AbstractHerein, nano boron nitride (BN) laminated poly(ethyl methacrylate) (PEMA)/poly(vinyl alcohol) (PVA) nanocomposite films are fabricated by using a simple in situ polymerization technique with incorporation of silver nanoparticles (Ag NPs). Structural investigations of PEMA/PVA/Ag@BN nanocomposite thin films are carried out by Fourier‐transform infrared spectroscopy, dynamic light scattering, X‐ray diffraction analysis, 1H nuclear magnetic resonance, 13C nuclear magnetic resonance, and mass spectrometry. The change in morphology of PEMA/PVA matrix due to the reinforcement of BN platelets are identified by electron microscopic studies. The unique tortuous paths are achieved by the dispersion of BN platelets by which gas penetration is restricted with enhancing the barrier properties of the material by 6.5 folds at 5 wt% BN content as compared with neat PEMA/PVA. Acid and alkali resistant along with biodegradability behavior of as‐synthesized nanocomposites are studied. From limiting oxygen index (LOI) results, it is found that the prepared materials are fire retardant in nature owing to effective reinforcement of BN layers. Antibacterial activities of PEMA/PVA/Ag@BN nanocomposite are studied by Xanthomonas citri or axonopodis pv. Citri, Escherichia coli, and Xanthomonas oryzae pv. Oryzae because of Ag NPs reinforcement. The substantial improvements in gas barrier, fire retardant, and antibacterial properties enable the materials for packaging application.

In-situ constructing hybrid cross-linked networks in brominated butyl rubber via amphiphilic graphene oxide cross-linkers: Retaining excellent gas barrier and mechanical properties after fatigue

Rubber/graphene nanocomposites as gas barrier materials have attracted great interest in recent years. However, it is still a challenge to construct strong covalent interfaces between nonpolar rubber matrix and graphene for retaining excellent gas barrier and mechanical properties of aircraft tires after fatigue. In this work, hybrid cross-linked networks in brominated butyl rubber (BIIR) are first proposed and in-situ constructed successfully via introducing the amphiphilic graphene oxide cross-linkers (R-aGO). R-aGO can participate in the curing of BIIR to form hybrid cross-linked networks, which can force R-aGO to move with BIIR synchronously during fatigue deformation due to strong interfaces between BIIR and R-aGO via covalent bonds. When R-aGO content is 3 phr, the BIIR/R-aGO nanocomposites show a 27 % improvement in gas barrier property, a 230 % increase in strength at 40 % strain (suffered deformation of aircraft tires), and a 229 % enhancement in tensile strength relative to conventional BIIR/aGO nanocomposites with interfacial modifiers. More importantly, BIIR/R-aGO nanocomposites still retain excellent gas barrier and mechanical properties even after 500,000 load cycles (40 % strain). This work provides a novel route to fabricate rubber/graphene nanocomposites with superior gas barrier and mechanical properties, especially after fatigue.

A study on the materials of smart barrier for selectively blocked TCE and TPH

Many barrier materials are used around industries, construction areas, livestock dump sites, waste landfills, and underground oil storage tanks. In the case of barriers, even if there is no inflow of contaminants, they do not provide selective permeability, develop water barrier properties, and hinder groundwater flow when contaminants encounter groundwater. Recently, contaminated sites that are difficult to resolve with current purification technologies continue to emerge. Pollutants flow into groundwater through the advection and diffusion by leaking. The pollutants introduced in this way cause pollution to the surrounding environment, and various types of severe underground environmental pollution problems occur depending on the type of pollutants leaked. Therefore, using a material that has the property of adsorbing organic contaminants and gelling them is harmless to the environment by penetrating groundwater under normal conditions. It has the property of selectively adsorbing the pollutant and gelling it upon contact with it underground. Therefore, the authors aim to study the applicability of polynorbornene and polyolefin as components of smart barrier materials that make barrier materials impermeable through the adsorption of pollutants, swelling, and coagulation behavior in this study. The components of smart barrier materials include Ottawa sand, organo-bentonite, polynorbornene, and polyolefin. Polynorbornene and polyolefin adsorb only organic pollutants selectively. Before applying polynorbornene and polyolefin to the barrier material, TCLP was performed to evaluate environmental hazards. As a result of heavy metal analysis, it was determined that there was no environmental hazard. The pH results are 7.27 for polynorbornene and 7.31 for polyolefin, indicating that both materials are slightly alkaline. In addition, as a result of testing with TCE (stock solution) and TPH (diesel crude oil) to confirm the swelling effect when in contact with organic pollutants, the efficiency of pollutant adsorption and swelling was found to be high when the ratio of polynorbornene: polyolefin = 6:4. Therefore, when using the material used in this study, it is expected that it can be applied as a component of a smart barrier material that selectively blocks pollutants.

Bioinspired triple-layered membranes for periodontal guided bone regeneration applications.

Barrier membranes have been used for the treatment of alveolar bone loss caused by periodontal diseases or trauma. However, an optimal barrier membrane must satisfy multiple requirements simultaneously, which are challenging to combine into a single material. We herein report the design of a bioinspired membrane consisting of three functional layers. The primary layer is composed of clay nanosheets and chitin, which form a nacre-inspired laminated structure. A calcium phosphate mineral layer is deposited on the inner surface of the nacre-inspired layer, while a poly(lactic acid) layer is coated on the outer surface. The composite membrane integrates good mechanical strength and deformability because of the nacre-inspired structure, facilitating operations during the implant surgery. The mineral layer induces the osteogenic differentiation of bone marrow mesenchymal stem cells and increases the stiffness of the membrane, which is an important factor for the regeneration process. The poly(lactic acid) layer can prevent unwanted mineralization on the outer surface of the membrane in oral environments. Cell experiments reveal that the membrane exhibits good biocompatibility and anti-infiltration capability toward connective tissue/epithelium cells. Furthermore, in vitro analyses show that the membrane does not degrade too fast, allowing enough time for bone regeneration. In vivo experiments prove that the membrane can effectively induce better bone regeneration and higher trabecular bone density in alveolar bone defects. This study demonstrates the potential of this bioinspired triple-layered membrane with hierarchical structures as a promising barrier material for periodontal guided tissue regeneration.

Appraising and comparing the role of autogenous periosteal graft as a barrier membrane in the treatment of intrabony defects in chronic periodontitis cases: A systematic review and meta-analysis.

Periodontal regeneration refers to procedures aimed at restitution of lost supporting tissue around the periodontally compromised tooth. Regenerative procedures very often include the use of barrier materials to encourage the growth of key surrounding tissues. The current study aimed to evaluate the effectiveness of autogenous periosteal graft as a barrier membrane for the treatment of intrabony defects in chronic periodontitis patients. A total of four data bases MEDLINE (by PubMed), Cochrane database, EBSCO, and Google Scholar were explored to identify the studies in English up to December 2022. An additional hand search of relevant journals was also done. A team of three independent reviewers screened the retrieved articles using the inclusion criteria. Randomized control trials (RCTs) evaluating the effectiveness of autogenous periosteal grafts in the treatment of intrabony defects in chronic periodontitis cases were included in the study. A total of six relevant articles were recognized for data procurement. A total of 117 patients with 68 sites with an age range between 18 years and 55 years were selected. Outcome variables examined were pocket depth (PD), clinical attachment level (CAL), radiographic bone defect fill (BDF), gingival recession (GR), plaque index (PI), gingival index (GI) and bleeding on probing (BOP). Data were analyzed using Revman 5.3 software. The mean differences and 95% confidence interval were used to illustrate the estimate of effect size. There is an equal effect in both groups for the PI, GI, and BOP reduction. For PD reduction, the result was in the favor of periosteal graft with open flap debridement (OFD) group. For CAL gain, radiographic BDF and GR, results also favored the periosteal graft, but no statistically significant difference was found amongst the groups. Within the limitation of the study, it seems that the autogenous periosteal graft can be used successfully along with OFD to treat intrabony defects in chronic periodontitis patients.

Evaluation of Desiccation Behavior in Basalt Microfiber–Reinforced Bentonite Clay for Geological Repositories of Nuclear Spent Fuel Using Digital Image Correlation

Abstract Secure storage of nuclear spent fuel (NSF) is of great concern for protecting public health and safety. The preferred long-term solution is underground containment in geological repositories, where one or more engineered barrier materials (EBM) encapsulate the NSF and separate it from the natural rock. Bentonite clay is commonly used as an EBM due to its many advantageous properties including low hydraulic conductivity, which ensures limitation of water infiltration to the system and the subsequent risk of corrosion in NSF canisters. However, bentonite clay subjected to heating from nuclear decay may form desiccation cracking. This study conducted disk-shaped free shrinkage tests and ring-shaped restrained shrinkage tests of bentonite clay samples reinforced with basalt microfibers. Digital image correlation was used as a noncontact full-field displacement measurement to track the time-evolving shrinkage and desiccation cracking phenomena and make quantified comparisons between plain bentonite and bentonite with varying contents of basalt microfibers (i.e., 0.0, 0.5, 1.0, and 1.5 % wt.). Results indicate that plain bentonite and basalt microfiber-reinforced samples showed similar free shrinkage behavior, while desiccation cracking behavior was significantly altered by adding basalt microfibers. Microfiber reinforcement effectively reduced major cracks through a “crack-bridging” effect while causing minor cracks to initiate earlier and at higher moisture contents than plain bentonite. Results infer that reinforcing plain bentonite with inorganic microfibers can potentially control desiccation cracking, leading to safer and improved nuclear waste management.

Effect of multi arm-PEG-NHS (polyethylene glycol n-hydroxysuccinimide) branching on cell adhesion to modified decellularized bovine and porcine pericardium.

Implanting physical barrier materials to separate wounds from their surroundings is a promising strategy for preventing postoperative adhesions. Herein, we develop a material that switches from an anti-adhesive surface to an adhesive surface, preventing adhesion in the early stage of transplantation and then promoting recellularization. In this study, 2-arm, 4-arm, and 8-arm poly(ethylene glycol) succinimidyl glutarate (2-, 4-, 8-arm PEG-NHS) were used to modify the surface of decellularized porcine and bovine pericardium. The number of free amines on the surface of each material significantly decreased following modification regardless of the reaction molar ratio of NH2 and NHS, the number of PEG molecule branches, and the animal species of the decellularized tissue. The structure and mechanical properties of the pericardium were maintained after modification with PEG molecules. The time taken for the PEG molecules to detach through hydrolysis of the ester bonds differed between the samples, which resulted in different cell repulsion periods. By adjusting the reaction molar ratio, the number of PEG molecule branches, and the animal species of the decellularized pericardium, the duration of cell repulsion can be controlled and is expected to provide an anti-adhesion material for a variety of surgical procedures.

Влияние сорбции на выход иода-129 из ближней зоны ПГЗРО

In terms of potential long-term radiation hazard, 129I is seen as a most problematic radionuclide, which is explained by its high mobility and long half-life. The paper explores its forms that may occur in VHLW from SNF reprocessing. It also overviews the studies focused on 129I sorption by engineered barrier materials considered typical for DGR sited in crystalline rocks, namely, bentonite and steel containers for vitrified high-level waste. The paper shows that when considered, the realistic coefficients for the interphase 129I distribution on bentonite and carbon steel corrosion products have little effect on its release beyond the DGR’s near field However, 129I release into the DGR’s near field is expected to be retarded in a quite considerable way if the empty space inside the insulating containers is filled with selective sorbents.

Predicting the behavior of engineered barrier materials based on molecular dynamics simulation

Predicting the behavior of engineered barrier materials based on molecular dynamics simulation

Исследование природных и археологических аналогов для материалов ИББ

Research data on natural, anthropogenic and historical analogues of materials used in engineered safety barrier (EBS) designs are viewed as sources of important information about their degradation, its conditions and dynamics supporting the safety assessments on the long-term stability of radioactive waste disposal facilities (RWDF). The article evaluates historical and natural analogues of safety barrier materials: bentonite, copper, iron, glass, concrete based on Portland cement. It establishes their reference degradation rates that can be recommended under the longterm safety assessments of RWDFs.

Suppression of Chemical Degradation By Gas Barrier Polymer Electrolyte Membranes

[Introduction]Polymer electrolyte fuel cell (PEFC) is one of the promising technologies for decarbonization. Especially, PEFC is suitable to power heavy-duty vehicles (HDV) because of its high efficiency and high fuel capacity. However, there are some serious technical challenges for PEFC application for HDV such as the durability. When we focus on the chemical degradation of polymer electrolyte membranes (PEMs), it happens due to attack by radical species. One of the radical formation mechanisms is the reaction at the anode side by the penetrated oxygen from cathode. Therefore, a promising mitigation strategy against chemical degradation is the suppression of oxygen permeability through the PEM.To verify this concept, we developed high gas barrier PEM. As a model gas barrier PEM, we made a sandwich type PEM with high oxygen barrier property. The sandwich PEM was prepared by depositing a thin interlayer consisting blended poly(vinyl alcohol) (PVA) as a gas barrier material and poly(vinyl sulfonic acid) (PVS) as a proton conductor in between two layers of Nafion 211 membranes. We evaluate chemical durability using the sandwich gas barrier PEM and discuss about the mechanism.[Experimental]To fabricate thin sandwich PEMs (15-20 µm), ethanol diluted Nafion dispersion solution (20 mg/ml) and PVA/PVS solution (10 mg/ml) were sprayed on a polytetrafluoroethylene (PTFE) sheet by a spray gun (Tamiya HG wide airbrush). The thickness of each layer was controlled by controlling the deposited weight. Then, membrane characterization procedures such as surface roughness, proton conductivity, and dimensional stability were performed. To evaluate fuel cell performance, the PEMs were mounted to a JARI cell with 1 cm2 active area. Chemically accelerated stress test was performed by open circuit voltage (OCV) holding test following NEDO protocol.[Results and Discussion]Several areal densities of PVA/PVS interlayer were successfully incorporated into Nafion membrane to make sandwich PEM. The sandwich PEM shows considerable fuel cell performance, and thin sandwich PEMs show higher performance than the 50 µm sandwich PEM, although it is lower than the thin sprayed Nafion. For example, the peak power density of 15 µm sandwich PEM was 0.44 W cm-2 compared to 0.30 W cm-2 and 0.50 W cm-2 for 50 µm sandwich PEM and 15 µm Nafion, respectively. Furthermore, the incorporation of interlayer to thin PEM can suppress the hydrogen crossover current density from 7.8 mA cm-2 to 5.5 mA cm-2 indicating superior gas barrier property. From the higher gas barrier property, it is predicted thin sandwich PEMs will have higher chemical durability than Nafion with similar thickness.

Performance of amorphization AlCrTiZrMo high entropy alloy barrier for copper metallization

A reliable ultra-thin diffusion barrier is required for Cu interconnection. High entropy alloy (HEA) films have received attention in the development of diffusion barrier materials due to their remarkable properties. Here, the dense and smooth 17 nm AlCrTiZrMo high entropy alloy amorphous film (HEAAF) is obtained by the cofilter cathode vacuum arc deposition. After annealing at 700 °C for 1 h, no Cu-silicide compounds are formed and the sheet resistance is 0.27 Ω/□, which indicated that AlCrTiZrMo HEAAF has excellent diffusion barrier performance. Such barrier temperature is comparable to some ceramic barriers. The excellent diffusion barrier performance of AlCrTiZrMo HEAAF is due to its good stability of amorphous structure and chemical stability at high temperature.

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material.

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress-strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm3 to 1.72 g/cm3 with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10-9 cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd2+, Mn2+ and Cu2+ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Qmax) of Cu2+, Cd2+ and Mn2+ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu2+, Cd2+, and Mn2+ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills.

Facile fabrication of shapeable three-component hydrogen-bonded covalent-organic aerogel as permeable reactive barrier material for efficient in-situ fluoroquinolone contaminated groundwater remediation

Fluoroquinolones (FQs) antibiotics found in groundwater pose hazardous impacts to organisms and humans. Moreover, permeable reactive barrier (PRB) is reckoned as an effective in-situ remediation technique for FQ-contaminated groundwater, in which PRB materials with high adsorption capacity and moldability are severely desired. Herein, a shapeable three-component hydrogen-bonded covalent-organic aerogel with sulfonic acid (SLEL-3) was fabricated based on a multiple-component method. The appraisal of SLEL-3 for the capture of levofloxacin (LVF) and ciprofloxacin (CIP) was evaluated systematically through kinetics and isotherms, which exhibited satisfactory adsorption performance in the following aspects: amended adsorption capacity, acceptable removal depth and resistance to ions and acidity/alkalinity. The proposed adsorption mechanisms involved a combination of pore filling effect, electrostatic effect, hydrogen bonding, π-π/n-π electron-donor–acceptor (π-π/n-π EDA), Lewis acid-base and hydrophobic/hydrophilic interaction. More importantly, in view of self-shaping ability, adaptability to harsh conditions, high swellability as well as felicitous hydraulic conductivity, novel PRB systems integrating SLEL-3 into 1-D column and 2-D tank in lab-scale study were developed for the capture of LVF, achieving impressive removal efficiencies of 86% and 92.65% over a 72-h period, respectively. Thus, this study provides a new notion of contriving a shapeable, eco-friendly and practicable covalent-organic polymer for potentially efficient in-situ remediation of FQ contaminated groundwater with a large area.

Применение оптимальных паро-теплоизоляционных материалов для повышения энергоэффективности зданий

Modern construction is not complete without complex, composite enclosing structures that consist of various elements and materials.
 The analysis of the energy efficiency of heat and vapor barrier materials in the USA and Kazakhstan is carried out, traditional materials such as mineral wool, expanded polystyrene, etc. are considered. The analysis of the possibility of using alternative materials to improve energy efficiency in Kazakhstan was also carried out. The properties and characteristics of steam-insulating materials are considered, the standards of the USA and Kazakhstan regulating the use of such materials in construction are presented.
 Considering several options of alternative steam-insulating materials for construction in Kazakhstan on the example of the city of Almaty, an analysis of its climate was carried out and based on the results obtained, the most suitable insulation materials for this region were determined.
 As the results, the advantages of using the selected materials were considered, and data on the characteristics of alternative steam-insulating materials were presented, where it can be noted that these materials can significantly increase the energy efficiency of buildings and reduce heating and cooling costs. Environmental aspects of the use of these materials were also considered.
 The use of alternative steam-insulating materials is an effective and more environmentally friendly option for improving the energy efficiency of buildings in Kazakhstan. These data may be of interest to specialists working in the field of energy efficiency of buildings and construction, as well as for manufacturing plants that are engaged in the production and sale of steam-insulating materials.
 Keywords: thermal insulation, standards, energy efficiency of thermal insulation materials.

Supplemental Material for Identity Management Processes, Contextual Supports and Barriers, and Substance Use Among Sexual Minority Workers: A Social Cognitive Lens

Supplemental Material for Identity Management Processes, Contextual Supports and Barriers, and Substance Use Among Sexual Minority Workers: A Social Cognitive Lens

Structural and optical characteristics of ∼ 1.65 μm-emitting quantum dots on InP substrate grown by selected area-MOVPE

Diblock co-polymer lithography and selected area metalorganic vapor phase epitaxy was used to fabricate quantum dots (QDs) on InP substrates for application in C- band communication. Initial structural and optical studies were carried out on three layered quantum dots with compressively strained In0.76Ga0.24As well and lattice-matched either In0.53Ga0.47As or In0.52Al0.48As as barriers. Photoluminescence studies at room temperature and at low temperature indicated weak carrier confinement in the QDs with In0.53Ga0.47As barrier, which leads to its broader PL linewidth, compared to QDs with In0.52Al0.48As barrier. This makes InAlAs a better choice for the barrier material in device applications. However, the higher growth rate of InAlAs inside the selected area and shape of the dots resulting from in-situ etching are some issues that need to be addressed to optimize the optical properties of QDs.

The Role of Polar Optical Modes in Wide Bandgap Semiconductor Quantum Structures

Abstract: In this paper, the interface polariton (IP), the confined (CF) modes in nanostructures made with wide bandgap semiconductors, as well as their contributions to the carrier scattering mechanism have been investigated. An asymmetric quantum well (AQW) made with ZnSe/CdSe/ZnS has been studied. More specifically, the dielectric continuum (DC) model has been employed to describe both the IP and the CF modes. Additionally, the Fermi golden rule has been used to estimate the electron transition rate within the asymmetric structure. Our numerical results show that the scattering rate for an electron which is localized at the bottom of the first subband above the well and drops within the quantum well, is characterized by regular peaks with an almost linear increase as the size of the QW increases. The emerge peaks are related to two different physical characteristics of the AQW system. These peaks are related to electron resonances and the threshold phonon emission (both CF and IP) called phonon resonances. The scattering rate of an electron which is localized at the bottom of the second subband above the well and makes transitions to all possible states within the quantum well gives only rise to phonon resonances. The research highlights the importance of the CF and IP modes on transition rates and their dependence on both the size of the quantum well and the asymmetry of the barrier materials.

Evolution of microstructure and properties of Ba(Mg1/3Ta2/3)O3 thermal barrier material exposed to CMAS corrosion

Calcium-magnesium-alumina-silicate (CMAS) resistance has become a key parameter to evaluate the properties of thermal barrier coating (TBC) materials. The CMAS corrosion behavior of BMT ceramic as a novel candidate material for TBC is poorly understood. In this paper, the solid-state sintering process was used to prepare the BMT bulks, and the evolution of microstructure, phase composition, thermophysical properties, and mechanical properties of the BMT bulks exposed to CMAS corrosion were studied. The results indicate that obvious elemental interdiffusion between the CMAS melt and BMT occurred at 1250 °C, which changed the original phase composition and formed multiple substances including Ba(Al, Ca)Si2O8, Ba2MgSi2O7, BaTa2O6, Ba2Si4O10, etc. The microstructure of BMT also underwent changes due to differences in the diffusion coefficients of different elements. As corrosion time prolongs, an obvious porous columnar reaction layer formed on the sample surface, causing the CMAS melt to sustainably corrode the deep BMT, resulting in intragranular corrosion. In terms of properties, the thermophysical and mechanical properties of the BMT bulks corroded by CMAS deteriorated. The thermal conductivity at 1100 °C increased from 1.43 W m−1 · k−1 to 1.67 W m−1 · k−1. The average coefficient of thermal expansion at 200–1400 °C decreased from 11.60 × 10−6 K−1 to 10.95 × 10−6 K−1. The hardness dropped by 21 % compared to the original BMT bulk. Therefore, it is necessary to improve the CMAS resistance of BMT ceramic in future studies.