Low Coefficient Of Thermal Expansion Research Articles

Biodegradable Dual-Network Cellulosic Composite Bioplastic Metafilm for Plastic Substitute.

With the escalating environmental and health concerns over petroleum-based plastics, sustainable and biodegradable cellulosic materials are a promising alternative to plastics, yet remain unsatisfied properties such as fragility, inflammability and water sensitivity for practical usage. Herein, we present a novel dual-network design strategy to address these limitations and fabricate a high-performance cellulosic composite bioplastic metafilm with the exceptional mechanical toughness (23.5 MJ m-3 ), flame retardance, and solvent resistance by in situ growth of cyclotriphosphazene-bridged organosilica network within bacterial cellulose matrix. The phosphorus, nitrogen-containing organosilica network, verified by the experimental and theoretical results, plays a triple action on significantly enhancing tensile strength, toughness, flame retardance and water resistance of composite bioplastic metafilm. Furthermore, cellulosic bioplastic composite metafilm demonstrates a higher maximum usage temperature (245 °C), lower thermal expansion coefficient (15.19 ppm °C-1 ), and better solvent resistance than traditional plastics, good biocompatibility and natural biodegradation. Moreover, the composite bioplastic metafilm have a good transparency of average 74 % and a high haze over 80 %, which can serve as an outstanding substrate substitute for commercial polyethylene terephthalate film to address the demand of flexible ITO films. This work paves a creative way to design and manufacture the competitive bioplastic composite to replace daily-used plastics.

Biodegradable Dual‐Network Cellulosic Composite Bioplastic Metafilm for Plastic Substitute

AbstractWith the escalating environmental and health concerns over petroleum‐based plastics, sustainable and biodegradable cellulosic materials are a promising alternative to plastics, yet remain unsatisfied properties such as fragility, inflammability and water sensitivity for practical usage. Herein, we present a novel dual‐network design strategy to address these limitations and fabricate a high‐performance cellulosic composite bioplastic metafilm with the exceptional mechanical toughness (23.5 MJ m−3), flame retardance, and solvent resistance by in situ growth of cyclotriphosphazene‐bridged organosilica network within bacterial cellulose matrix. The phosphorus, nitrogen‐containing organosilica network, verified by the experimental and theoretical results, plays a triple action on significantly enhancing tensile strength, toughness, flame retardance and water resistance of composite bioplastic metafilm. Furthermore, cellulosic bioplastic composite metafilm demonstrates a higher maximum usage temperature (245 °C), lower thermal expansion coefficient (15.19 ppm °C−1), and better solvent resistance than traditional plastics, good biocompatibility and natural biodegradation. Moreover, the composite bioplastic metafilm have a good transparency of average 74 % and a high haze over 80 %, which can serve as an outstanding substrate substitute for commercial polyethylene terephthalate film to address the demand of flexible ITO films. This work paves a creative way to design and manufacture the competitive bioplastic composite to replace daily‐used plastics.

Improved thermal properties and CMAS corrosion resistance of rare-earth monosilicates by adjusting the configuration entropy with RE-doping

The novel rare earth monosilicates (xRE1/x)2SiO5 (RE=Yb, Tm, Er, Y, Dy and Tb, x = 2–6) were prepared in order to establish the relationship between configurational entropy and lattice distortion, and the effect of configurational entropy on their properties was investigated. The results showed that the lattice distortion of (xRE1/x)2SiO5 increased gradually with the increase of configurational entropy, but the multi-principal component solid solution tended to form a highly symmetrical crystal structure when the configurational entropy was large enough, thus inhibiting the lattice distortion. (5RE1/5)2SiO5 had a maximum lattice distortion, which leaded to a relatively low thermal conductivity and coefficient of thermal expansion, and good CMAS corrosion resistance.

AlGaN High Electron Mobility Transistor for High Temperature Logic

We report on AlGaN HEMT-based logic development, using combined enhancement- and depletion-mode transistors to fabricate inverters with operation from room temperature up to 500°C. Our development approach included: (a) characterizing temperature dependent carrier transport for different AlGaN HEMT heterostructures, (b) developing a suitable gate metal scheme for use in high temperatures, and (c) over-temperature testing of discrete devices and inverters. Hall mobility data revealed the GaN-channel HEMT experienced a 6.9× reduction in mobility, whereas the AlGaN channel HEMTs experienced about a 3.1x reduction. Furthermore, a greater aluminum contrast between the barrier and channel enabled higher carrier densities in the two-dimensional electron gas for all temperatures. The combination of reduced variation in mobility with temperature and high sheet carrier concentration showed that an Al-rich AlGaN-channel HEMT with a high barrier-to-channel aluminum contrast is the best option for an extreme temperature HEMT design. Three gate metal stacks were selected for low resistivity, high melting point, low thermal expansion coefficient, and high expected barrier height. The impact of thermal cycling was examined through electrical characterization of samples measured before and after rapid thermal anneal. The 200 nm tungsten gate metallization was the top performer with minimal reduction in drain current, a slightly positive threshold voltage shift, and about an order of magnitude advantage over the other gates in on-to-off current ratio. After incorporating the tungsten gate metal stack in device fabrication, characterization of transistors and inverters from room temperature up to 500°C was performed. The enhancement-mode (e-mode) devices’ resistance started increasing at about 200°C, resulting in drain current degradation. This phenomenon was not observed in depletion-mode (d-mode) devices but highlights a challenge for inverters in an e-mode driver and d-mode load configuration.

High-performance epoxy nanocomposites via constructing a rigid-flexible interface with graphene oxide functionalized by polyetheramine and f-SiO2

Graphene oxide (GO) is an ideal reinforcement for improving mechanical properties of epoxy (EP) and reducing its coefficient of thermal expansion (CTE). However, the poor interfacial interaction between GO and polymer matrix seriously hinders the reinforcing effect of GO. To improve their interface, we first functionalized GO with flexible polyetheramine (PEA) and f-SiO2 rigid nanoparticles, obtaining PEA-GO and SiO2-PEA-GO hybrids, respectively. Then the PEA-GO and SiO2-PEA-GO were incorporated into EP to obtain nanocomposites with flexible interphases and rigid-flexible interphases, respectively. The interfaces were tuned by two PEA molecules (D230 and D2000) with different chain lengths. The effects of the different interface structures on the mechanical properties and CTE of the GO/EP nanocomposites with a 0.25 wt% filler loading were investigated. It was found that the effects of SiO2-PEA-GO on strengthening and toughening EP matrix and on reducing its CTE were much better than those of PEA-GO, because the rigid-flexible interfaces provided higher bonding strength and better energy dissipation mechanisms than the flexible interfaces. Moreover, the D230-GO/EP nanocomposite containing shorter PEA (D230) molecules exhibited higher strength but lower toughness and CTE than the D2000-GO/EP nanocomposite. However, the SiO2-D2000-GO/EP nanocomposite showed greater strength, toughness and CTE than the SiO2-D230-GO/EP nanocomposite. This indicated that the longer PEA molecules in rigid-flexible interphases produced higher improvement in strength and toughness but smaller decreases in CTE. This work provides a promising strategy of constructing an adjustable flexible-rigid interfacial structure and opens an avenue for developing GO/EP nanocomposites with high mechanical properties and low CTE.

Interfacial regulation and fracture mechanism of Al–Si/SiC composites infiltrated under super-gravity field

We reported a novel method to prepare Al–Si/SiC composites infiltrated under super-gravity field without Mg addition. Noted that centrifugal force acted as the main driving force to overcome the penetration resistance, making it feasible to obtain the Al–Si/SiC composite with high relative density (≥99.3 %). The interfacial reaction between Al and SiC was retarded by Si addition under super-gravity field. Interestingly, the rod-like eutectic Si was detected at Al–SiC interface with semi-continuous distribution, leading to the excellent bending strength (342.6 ± 1.0 MPa), enhanced thermal conductivity (173 W/m K at 373 K), and relatively low coefficient of thermal expansion (8.90 × 10−6 K−1 ranged from 323 to 373 K). The interfacial regulation and fracture mechanism were discussed in details.

Achieving high thermal conductivity of Al–50Si alloy through heat treatment and its microstructural evolution

Al–50Si alloys were prepared by powder extrusion and characterized for electronic packaging. The optimization of powder size, extrusion temperature, and heat treatment parameters was performed to enhance the microstructure and thermo-physical properties. The alloy exhibits a high relative density >99 %, a low coefficient of thermal expansion (CTE) < 10 × 10−6/K, and a good thermal conductivity (TC) ∼117 Wm−1K−1 achieved by employing a large size powder and high extrusion temperature during the extrusion process. Subsequent heat treatment of the optimized alloy at 550 °C for various time reveals a fluctuating increasing trend in TC during the heat treatment process. The TC values exhibit periodic fluctuations as they alternate between increments and decrements, primarily resulting from the recrystallization and secondary recrystallization of Al grains during heat treatment process. Notably, the maximum TC value (∼159.1 Wm−1K−1) at room temperature is obtained after heating the alloy to 550 °C for 26 h. Compared to the as-extruded alloy, the TC of heat-treated alloy increases by approximately 36 %, which can be attributed to the elimination of eutectic Si and growth of Si and Al grains within the alloy. The study may shed light on the mechanism underlying the improvement in thermal conductivity of Al–50Si alloy by microstructural evolution.

Elastic constants of equiatomic Fe–Ni Invar alloy single crystal

In a disordered fcc structure, the equiatomic Fe–Ni alloy is of great interest as a soft magnetic Invar alloy with a near zero or low thermal expansion coefficient. In the L10 ordered phase, it is of interest as a potential high-performance permanent magnet alloy. In this work, the first detailed measurements of the elastic constants in a [001]-oriented Fe-50 at. % Ni alloy single crystal under a no magnetic field condition were made using the resonant ultrasound spectroscopy technique. The elastic constants measured allow one to understand the nature of atomic bonding in a material and the mechanical response to applied stress. The single crystal sample having a rectangular parallelepiped shape was prepared from a single crystal grown using the vertical Bridgman technique. The elastic constants C11, C12, and C44 were obtained from the resonant frequencies observed over a frequency range of 100–900 kHz. Using these C11, C12, and C44 values, Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio were calculated to be 99.1 GPa, 73.4 GPa, 176.7 GPa, and 0.20, respectively. The large anisotropy factor of 3.29 highlights the strong directional dependence of the material’s mechanical behavior.

Fabrication of artificial nacre-like hexagonal boron nitride/lignocellulosic fiber composites with high thermal conductivity

The low thermal expansion coefficient, low dielectric constant, high thermal conductivity, high electrical resistivity, and excellent thermal stability of hexagonal boron nitride (hBN) make it an ideal filler for insulating and thermally conductive composite films. Its use has been suggested in insulating packaging systems to solve the heat dissipation problems in modern electronic equipment. Here, a novel strategy was proposed to construct superior thermally conductive networks via the vacuum-assisted filtration of hydroxyl-modified hexagonal boron nitride (BN-OH) and lignocellulosic fiber (LCF). The π–π interactions between the benzene ring of LCF and the hBN plane assist in the dispersal of BN-OH in aqueous solution. The abundance of functional groups such as hydroxyl and phenolic hydroxyl groups in the LCF structure allow for hydrogen bonding with the hydroxyl groups on the BN-OH surface, increasing interfacial interactions between BN-OH and LCF and reducing interfacial thermal resistance. In addition, the long-range one-dimensional structure of LCF can assist in the formation of a self-supporting, high-thermal-conductivity film with a high content of BN-OH. The through-plane thermal conductivity of BN-OH/LCF reached 5.34 W/(m⋅K) at 90 wt.% BN loading. This work provides inspiration for the green preparation of hBN thermally conductive composite films with high filler loadings.

Cyclic oxidation resistance and self-healing properties of HfB2-doped glass composite coatings at 900 °C

HfB2-doped glass coating exhibits superior cyclic antioxidative performance compared to pure glass coating. The HfB2 particles inhibit the precipitation of crystals with low thermal expansion coefficient, mitigating the risk of fish-scaling failure. In addition, the HfB2-doped glass composite coating, with high contents of amorphous phases, maintains its viscous flow properties even after multiple high temperature cyclic oxidations, which enables it to self-heal. Moreover, the oxidation product (B2O3) of HfB2 enhances network connectivity of the glass system, providing more unsaturated sites for the chemical bonding of the self-healing process.

Thermal expansion studies of Li2TiO3 by dilatometry and in-situ high-temperature X-ray diffraction

Li2TiO3 (lithium titanate) is a material of interest in the field of fusion reactors due to its potential application as a tritium breeder material. Because of the extreme working conditions and temperature gradients involved, thermal expansion properties are critical to consider when assessing a material for a fusion reactor. The reactor is subjected to severe neutron flux, high temperature and thermal cycling, which can cause significant stress on the material. A low coefficient of thermal expansion (CTE) of Li2TiO3 is important as it mitigates mechanical stress and minimized the risk of structural damage resulting from thermal cycling. Material degradation, cracking, or delamination might result from a mismatch in CTE between different materials in the reactor. Therefore the estimations of material's thermal expansion properties hold significance for the designing and fabrication of structural material. In this study, Li2TiO3 material was compacted into pellets and high-temperature X-ray diffraction (HT-XRD) was employed to obtain X-ray diffraction patterns from room temperature to 1273 K at 100 K intervals. The lattice parameters (a, b, and c) of Li2TiO3 polycrystals were determined and corresponding unit cell volumes were estimated at each temperature. The thermal expansion percentages for the lattice parameters a, b, and c between room temperature and 1273 K were found to be 1.21%, 1.84%, and 1.83% respectively. The calculated coefficient of thermal expansion (CTE) were determined as 12.5 × 10−6 K−1, 19 × 10−6 K−1, and 18.9 × 10−6 K−1for lattice parameters a, b and c respectively. The crystallographic density at room temperature was estimated to be 3.42 g/cm3. The molar volume was calculated to range between 32.12 and 33.72 cm3/mol from room temperature to 1273 K. Additionally, high-temperature dilatometry was employed to measure the thermal expansion of Li2TiO3, resulting in the estimation of coefficient of thermal expansion. From room temperature to 1290 K, the thermal expansion percentage and mean coefficient of thermal expansion were calculated to be 1.91% and 19.64 × 10−6 1/K, respectively. Furthermore, the temperature dependent mean and instantaneous thermal expansion values were also determined. The differential scanning calorimetry (DSC) method was used to estimate the temperature of the monoclinic to cubic transformation, which was determined to be 1416 K. This paper provides a comprehensive description of the conducted experiments, accompanied by the detailed analysis of the thermal expansion properties derived through the use of High-Temperature X-Ray Diffraction (HT-XRD) and HT-dilatometry (High-Temperature Dilatometry).

High-entropy (YErYbLu)2SiO5 ceramic aerogel: A potential ceramic insulator with low thermal conductivity

Conventional oxide aerogels have limitations in terms of structural damage and phase transformation at high temperatures. A novel high-entropy (YErYbLu)2SiO5 ceramic aerogel was synthesized by a combination of the sol-gel process, supercritical drying, and high-temperature calcination. The successful synthesis of a high-entropy (YErYbLu)2SiO5 ceramic aerogel in a single phase after calcination at 1250 °C was confirmed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The high-entropy ceramic aerogel (YErYbLu)2SiO5 still shows excellent structural and phase stability after annealing at 1400 °C. The structurally reconstructed samples (RSO) exhibit low densities ranging from 1.79 to 3.28 g/cm3, room-temperature thermal conductivities between 0.109 and 0.253 W·m-1 K-1, and fracture toughness values ranging from 0.61 to 9.70 MPa. Notably, the lowest thermal conductivity is less than 1/10 of that of the corresponding dense crystalline ceramics. Furthermore, the RSO has a low coefficient of thermal expansion within the temperature range of 360–1200 °C (ranging from 5.84 × 10−6 °C−1 to 7.36 × 10−6 °C−1). The RSO exhibits high residual strength retention after thermal shock testing. These properties position the high-entropy (YErYbLu)2SiO5 ceramic aerogel as a promising candidate for nano-thermal insulation as a porous ceramic material that undergoes structural reconstruction.

Design and synthesis of intrinsic black polyimide with full visible-light absorption and low coefficient of thermal expansion for black flexible copper clad laminates

With the rapid growth of microelectronics and optoelectronics, the demand for black polyimides (BPIs) with exceptional comprehensive performance has increased dramatically. 3,6-diaryl-2,5-dihydropyrrolo [3,4-c]pyrrole-1,4-dione (TDPP) is a well-known organic dye that has strong visible absorption. In this study, a novel diamine (DPPTPDA) containing TDPP-based chromophore was successfully synthesized, and an intrinsic BPI (DPPTPPI) was then obtained by the polymerization of DPPTPDA with pyromellitic dianhydride (PMDA). With the introduction of TDPP-based chromophores, the light absorption of DPPTPPI is significantly red-shifted and broadened, exhibiting complete absorption in the visible range. To explore the underlying electron nature of DPPTPPI, density functional theory calculations are carried out. The result shows that the outstanding light absorption of DPPTPPI is mostly owing to the electron transitions of HOMO→LUMO+1 that occur in the TDPP-based chromophores units. Meanwhile, DPPTPPI exhibits a low coefficient of thermal expansion and excellent electrical performances. The flexible copper clad laminate based on DPPTPPI films show high solder heat resistance and peel strength. The study provides theoretical implications for the molecular design of high-performance intrinsic BPI materials targeting practical microelectronic applications.

Novel Cr–Mn–Fe–Co–Ni oxide composites fabricated by in situ spark plasma sintering for high-temperature applications

Spinel composite is being considered for electrode materials in molten salt electrolysis, aiming to improve high-temperature stability and conductivity. Multi-phase composites with the general formula of (Fe1-3x-y Niy Cox Crx Mnx)3 O4 (x = 0.03, 0.06, 0.09, y = [1-2x]/3) were prepared via in situ SPS method. The composites were confirmed to consist of spinel and rock-salt phases through XRD and SEM analysis. Compared to the Ni–Fe–O system, the doping of Cr, Mn and Co improved the phase stability of the spinel during SPS, but hindered the shrinkage process. These composite exhibited low thermal diffusivity (1.236–2.481 m2/s, room temperature) and low coefficient of thermal expansion (9.8 - 14.4 × 10−6 K−1, 400–800 °C). Moreover, the composite with x = 0.06 and y = 0.29 exhibit 94.4 % lower permittivity, 7 times higher dielectric loss (at 40 Hz) and 26.6 % lower high-temperature conductivity (at 800 °C) than that of Ni–Fe–O system. This work demonstrates the enhanced thermal and electrical properties of spinel-based composites, which can provide inspiration to researchers and promote the development of high-temperature electrodes.

Computational discovery of novel U-N-C ternary phases as promising accident-tolerant fuels

Recently, uranium carbonitride solid solution has been recognized as a promising nuclear reactor fuel due to its excellent physicochemical properties. However, due to the complexity of U-N-C ternary system, the research on the structure and properties of uranium carbonitride is still insufficient. In this work, a series of promising accident-tolerant ternary compounds in the U-N-C system were predicted through a combination of first-principles calculations with an evolutionary algorithm. Fifteen dynamically and mechanically stable novel U-N-C ternary compounds with seven chemical compositions, including U-N-C solid solutions and new intermetallic structures, were suggested to be promising for experimental synthesis. For U-N-C solid solutions with rock-salt structures, it was revealed that the lattice expansion and bond length elongation caused by the substitution of carbon atoms for nitrogen atoms can lead to a decrease in elastic moduli and melting point and an increase in toughness. Moreover, two newly identified structures P63/mcm-U3N2C and P2/m-U4NC were considered to be very promising accident-tolerant fuels due to their high mechanical strength, excellent melting point, low thermal expansion coefficient, and high thermal conductivity. The larger atomic number density of P63/mcm-U3N2C enables a higher elastic modulus and a satisfactory melting point than those of rock-salt structures. While for P2/m-U4NC, its unique shorter and stronger U-N/C and U-U bonding leads to its highest mechanical strength and appropriate melting point. Furthermore, the linear thermal expansion coefficients of P2/m-U4NC and P63/mcm-U3N2C are comparable to those of UN and UO2, respectively, and their thermal conductivities increase with temperature, much higher than that of UO2.

Exploring the Relationship between the Structural Characteristics and Mechanical Behavior of Multicomponent Fe-Containing Phases: Experimental Studies and First-Principles Calculations.

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies and first-principles calculations. The results indicate that it is easier for Fe and Cr to substitute the Mn-12j site in α-AlMnSi in thermodynamics; Cr is preferred to Fe for substituting Mn-12j/k sites due to its lower formation enthalpy after single substitutions at Mn atom sites. The α-AlFeMnCrSi phase shows higher thermal stability, modulus and intrinsic hardness and a lower volumetric thermal expansion coefficient at different temperatures due to the strong chemical bonding of Si-Fe and Si-Cr. Moreover, the α-AlFeMnCrSi phase has a higher ideal strength (10.65 GPa) and lower stacking fault energy (1.10 × 103 mJ/m2). The stacking fault energy evolution of the different Fe-containing phases is mainly attributed to the differential charge-density redistribution. The strong chemical bonds of Si-Fe, Si-Mn and Si-Cr are important factors affecting the thermophysical and mechanical behaviors of the α-AlFeMnCrSi phase.

Investigation of deformation mechanism of SiC–CuNi composite thin film material nanochannels by molecular dynamics simulation

Semiconductor–metal composites are widely used in aerospace and automotive manufacturing, weapon production, and electronic packaging because of their high hardness and strength as well as low coefficient of thermal expansion. In this study, SiC–CuNi composite films produced by single-target and dual-target co-deposition were simulated using molecular dynamics. The films were subjected to high-temperature quenching to obtain an annealing model. The deformation behaviors of the deposition and annealing models during the nanoindentation process were investigated in detail. Then, a characterization method for inspecting the roundness of nanochannels was proposed. In the deposition model, the Ni–Cu model generated amorphous structures at the interface. However, the annealing treatment atomically rearranged the film, producing dense films with improved crystalline quality. Other deposition models are developed using complex twin structures, which play a role in stress distribution and strain diffusion during deformation. Comparative investigation shows that high-temperature quenching can effectively enhance the stiffness of composite films, tightly bonding the atoms at the semiconductor–metal interface. Hardness calculations were performed for all models and the result was that the Cu + Ni model had the highest hardness. Moreover, the formation of nanochannels is affected: the tighter the bond, the more uniform the nanochannels.

Synthesis, structure and thermal expansion of new complex phosphates of titanium and metals in the +2 oxidation state

The phosphates of the composition Ca0.5+xMxTi2-x(PO4)3 (M − Ni, Mg) were synthesized by a co-precipitating of salts in aqueous solutions followed by thermal treatment stages. The studied series formed limited NZP solid solutions within the regions 0 ≤ x ≤ 0.5 (Ni) and 0 ≤ x ≤ 1 (Mg). The Rietveld refinement of the Ca1.2Mg0.7Ti1.3(PO4)3 structure showed that its basis is framework formed by TiO6 and (Mg/Ti)O6 octahedra (together with PO4 tetrahedra), and the Ca2+ ions are situated in the cavities. Thermal expansion of the phosphates depending on their chemical composition was characterized in the temperature range from 173 to 473 K. There was a gradual decrease in the linear thermal expansion coefficients with x growth, so that average linear coefficients varied from (11.0–2.6)∙10−6 K−1. Low average thermal expansion coefficient and its low anisotropy allow the studied phosphate ceramics to withstand temperature changes.

Fabrication of textured cordierite ceramics with low thermal expansion coefficient and custom structure via vat photopolymerization

Owing to the orientation of grains, textured ceramics possess particular properties along a specific direction. In this study, combining reactive template grain growth (RTGG) and vat photopolymerization, the textured cordierite ceramics with low thermal expansion coefficient (CTE) and custom structure were prepared successfully. Initially, the generation mechanism of the oriented c axis of α-cordierite grains in the XY plane was revealed by analyzing the evolution of microstructure during the sintering process. Then, two printing models were used to investigate the anisotropic CTE of porous cordierite ceramics fabricated by vat photopolymerization, indicating the effect of oriented grains and microstructure on the CTE. Finally, based on the selected dominant model, the controllable oriented microstructure was achieved by altering the shear stress provided by the scraper. The results showed that the oriented α-cordierite grains and skeletons were originated from the oriented tabular talc particles. Owing to the c axis of α-cordierite grains oriented in the XY plane, the CTE of the test direction parallel to the XY plane is lower than that perpendicular to the XY plane. In addition, with decreasing the setting layer thickness to adjust shear force, the oriented degree of tabular talc particles and α-cordierite skeletons became controllable. When the layer thickness reached a minimum of 25 μm, the CTE of porous cordierite ceramic reached the lowest of 1.26 × 10−6 K−1.

Evaluation of high temperature oxidation behavior of LZ, CSZ, and LZ-CSZ composite thermal barrier coatings

La2Zr2O7 (LZ) compound is a promising candidate for the new generation of thermal barrier coatings (TBCs). Despite its unique properties, this material suffers from a quite low coefficient of thermal expansion (CTE) and also brittleness which restricts its potential application. In this study, LZ was modified with ceria stabilized zirconia (CSZ), and LZ-CSZ composite powders with different compositions were prepared and applied with the air plasma spraying (APS) method. The oxidation behavior of samples was studied at 1100 °C, and the tests were continued until coatings spallation. Microstructural studies showed that the thermally grown oxide (TGO) layer in all samples consists of alumina and mixed spinel oxide layers. Due to lower oxygen diffusivity, the samples with a higher fraction of LZ contain a narrower TGO layer with a small spinel phase. The inward oxygen penetration in coatings with higher CSZ percentages was considerable, that led to the evolution of Al-depletion zone in the bond coat area, and increased the portion of spinel oxides in the TGO. The 50CSZ-50LZ coating, due to its better combination of CTE compatibility, thermal stability, and fracture toughness, showed better oxidation resistance and collapsed after 264 h with a TGO thickness of 5.4 μm.