Compatible Coefficient Of Thermal Expansion Research Articles

Achieving Compatible p/n-Type Half-Heusler Compositions in Valence Balanced/Unbalanced Mg1-xVxNiSb.

In thermoelectric and other inorganic materials research, the significance of half-Heusler (HH) compositions following the 18-electron rule has drawn interest in developing and exploiting the potential of intermetallic compounds. For the fabrication of thermoelectric modules, in addition to high-performance materials, having both p- and n-type materials with compatible thermal expansion coefficients is a prerequisite for module development. In this work, the p-type to n-type transition of valence balanced/unbalanced HH composition of Mg1-xVxNiSb was demonstrated by changing the Mg:V chemical ratio. The Seebeck coefficient and power factor of Ti-doped Mg0.57V0.33Ti0.1NiSb are -130 μV K-1 and 0.4 mW m-1 K-2 at 400 K, respectively. In addition, the reduced lattice thermal conductivity (κL < 2.5 W m-1 K-1 at 300 K) of n-type compositions was reported to be much smaller than κL of conventional HH materials. As high thermal conductivity has long been an issue for HH materials, the synthesis of p- and n-type Mg1-xVxNiSb compositions with low lattice thermal conductivity is a promising strategy for producing high-performance HH compounds. Achieving both p- and n-type materials from similar parent composition enabled us to fabricate a thermoelectric module with maximum output power Pmax ∼ 63 mW with a temperature difference of 390 K. This finding supports the benefit of exploring the huge compositional space of valence balanced/unbalanced quaternary HH compositions for further development of thermoelectric devices.

A Systematical Ab Initio Study of Diffusivity and Ionic Conductivity of Ln2NiO4+ δ (Ln=La, Nd, Pr) Reversible Solid Oxide Cells (r-SOCs)

The Ln2NiO4+δ (Ln=La, Nd, Pr) reversible solid oxide cells (r-SOCs) exhibit a relatively high oxygen diffusivity and surface reaction activity, compatible thermal expansion coefficient with solid electrolyte, and oxygen over-stoichiometry enabling the transportation of oxygen ions. The atomistic simulation technique provides detailed information concerning the diffusion mechanisms of the materials. In the present study, we systematically investigated the vacancy formation energy, thermal expansion, diffusivity, and ionic conductivity of the Ln2NiO4 + δ (δ=0.125) compound through the ab initio approach. Especially considering the change of the oxygen transport properties caused by the thermal expansion effect, a combination of quasi-harmonic approximation (QHA) and a linear regression model is used to study and reproduce the temperature-dependent properties of the Ln2NiO4 + δ.

(Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 high-entropy ceramic with low thermal conductivity, tunable thermal expansion coefficient, and excellent resistance to CMAS corrosion

Low thermal conductivity, compatible thermal expansion coefficient, and good calcium—magnesium—aluminosilicate (CMAS) corrosion resistance are critical requirements of environmental barrier coatings for silicon-based ceramics. Rare earth silicates have been recognized as one of the most promising environmental barrier coating candidates for good water vapor corrosion resistance. However, the relatively high thermal conductivity and high thermal expansion coefficient limit the practical application. Inspired by the high entropy effect, a novel rare earth monosilicate solid solution (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 was designed to improve the overall performance. The as-synthesized (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 shows very low thermal conductivity (1.07 W·m−1·K−1 at 600 °C). Point defects including mass mismatch and oxygen vacancies mainly contribute to the good thermal insulation properties. The thermal expansion coefficient of (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 can be decreased to (4.0–5.9)×10−6 K−1 due to severe lattice distortion and chemical bonding variation, which matches well with that of SiC ((4.5–5.5)×10−6 K−1). In addition, (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 presents good resistance to CMAS corrosion. The improved performance of (Ho0.25Lu0.25Yb0.25Eu0.25)2SiO5 highlights it as a promising environmental barrier coating candidate.

High strength and high light transmittance sapphire/sapphire joints bonded using a La2O3-Al2O3-SiO2 glass filler

A novel La2O3-Al2O3-SiO2 (LAS) glass was used as filler to join transparent sapphire for obtaining high strength and high light transmittance joints. The results show that the LAS glass filler had compatible coefficient of thermal expansion (CTE) with sapphire and excellent wetting ability on sapphire. During the joining process, no interfacial reaction occurred and the brazing seams were in a completely amorphous state under fast cooling conditions (~50 °C/min). With increased joining temperature, the mutual dissolution and diffusion between sapphire and the LAS filler were enhanced. The flexural strength of joints first increased and then decreased with an increase in the joining temperature from 1400 °C to 1550 °C. The optimal flexural strength of joint reached 325 MPa, which almost was the same as the strength of sapphire substrate. At 500 nm, the in-line transmittance of this joint was 80.5%, which was close to that of sapphire (84.2%).

Fabrication and Evaluation of Low-Cost CrSi2 Thermoelectric Legs

CrSi2 is a promising thermoelectric material constituted of non-toxic and earth abundant elements that offer good perspectives for the mass production of inexpensive and reliable thermoelectric modules for waste heat recovery. Realization of robust metallic contacts with low electrical and thermal resistances on thermoelectric materials is crucial to maximize the conversion efficiency of such a device. In this article, the metallization of an undoped CrSi2 with Ti and Nb using a conventional Spark Plasma Sintering process is explored and discussed. These contact metals were selected because they have compatible thermal expansion coefficients with those of CrSi2, which were determined in this study by X-ray Diffraction in the temperature range 299–899 K. Ti was found to be a promising contact metal offering both strong adhesion on CrSi2 and negligible electrical contact resistance (&lt;1 μΩ cm2). However, metallization with Nb resulted in the formation of cracks caused by large internal stress inside the sample during the fabrication process and the diffusion of Si in the metallic layer. A maximum conversion efficiency of 0.3% was measured for a sandwiched Ti/CrSi2/Ti thermoelectric leg placed inside a thermal gradient of 427 K. The preliminary results obtained and discussed in this article on a relatively simple case study aim to initiate the development of more reliable and efficient CrSi2 thermoelectric legs with an optimized design.

The physical properties and effects of sintering conditions on rSOFC fuel electrodes evaluated by molecular dynamics simulation

Reversible solid oxide fuel cell (rSOFC) can produce and store energy through dual-mode operating, which is promising for balancing the conflicts between power supply and requirements. One crucial issue is to develop high performance of fuel electrode materials, in terms of materials costs, mechanical strength, mass production in commercialization. The reversible performance of the materials may be enhanced by electrode microstructure optimization in the preparation procedures. It is beneficial to understand the mechanisms of sintering process, in terms of the electrode particle interactions and sintered structure in the molecular/nanoparticle level. Accordingly, a molecular dynamics method is developed to simulate the sintering process for the LST/GDC nanoparticle systems. It is found that a high sintering temperature is beneficial for increasing triple-phase-boundary (TPB) length, but not for the effective surface area of catalyst particles. A mass fraction of 0.5–0.6 is predicted as the optimal LST composition for the TPB length, active surface area, and compatible thermal expansion coefficient. The heat capacity and thermal conductivity increase in the high sintering temperature and high mass fraction of LST conditions. The methodology and findings can provide a guideline on optimization of the sintering conditions for LST/GDC electrodes, which may promote the commercialization of rSOFC technology.

Effect of Ag/Cu matrix composition on thermal properties of diamond/Ag/Cu-Ti composites fabricated by pressureless sintering

• New strategy is proposed to design and synthesize diamond/Ag/Cu composites. • Diamond/Ag/Cu-Ti composites were fabricated via low-cost pressureless sintering. • TiC phase formed at interface demonstrates improved diamond–matrix wettability. • The thermal conductivity of composite is maximized at 40 at.% Cu in the matrix. • Diamond/Ag/Cu composites are promising thermal management materials. Diamond/Ag/Cu–Ti composites were fabricated by low-cost pressureless sintering with Ti addition to improve the diamond–metal matrix wettability and the effects of Ag/Cu matrix variation on the composites were investigated. Transmission electron microscopy identified the interfacial structure on the diamond (1 0 0) plane of the diamond/Ag/Cu–Ti composite with the 80 at.% Cu matrix as Cu–Ag/TiC/Ag–C/TiC/diamond. The thermal conductivity of the diamond/Ag/Cu–Ti composites was significantly enhanced upon increasing the Ag contents of the Ag/Cu matrix. The 60 vol% diamond/Ag/Cu–2 at.% Ti composite with 40 at.% Cu matrix content exhibited the maximum thermal conductivity of 826 W/m·K and the compatible coefficient of thermal expansion of 6.0 ppm/K. The diamond/Ag/Cu-Ti composites are promising low-cost thermal management materials for electronic device integration.

Thermal expansion coefficients of high thermal conducting BAs and BP materials

Recently reported very high thermal conductivities in cubic boron arsenide (BAs) and boron phosphide (BP) crystals could potentially provide a revolutionary solution in the thermal management of high power density devices. To fully facilitate such an application, the compatible coefficient of thermal expansion (CTE) between the heat spreader and the device substrate, in order to minimize the thermal stress, needs to be considered. Here, we report our experimental CTE studies of BAs and BP in the temperature range from 100 K to 1150 K, through a combination of X-ray single crystal diffraction and neutron powder diffraction. We demonstrated that the room temperature CTEs, 3.6 ± 0.15 × 10−6/K for BAs and 3.2 ± 0.2 × 10−6/K for BP, are more compatible with most of the semiconductors including Si and GaAs, in comparison with diamond, and thus could be better candidates for the future heat spreader materials in power electronic devices.

A novel phosphate-ceramic coating for high temperature oxidation resistance of Ti65 alloys

A novel phosphate-ceramic coating was developed for high-temperature oxidation protection of Ti65 titanium alloy. Aluminum phosphate binder was strategically mixed with Al2O3+SiC ceramic particles as the filler material and subsequently deposited on Ti65 titanium alloy by air spraying. High temperature oxidation behavior of the Ti65 substrate was studied in coated and un-coated state by performing series of isothermal oxidation and thermal shock tests at 650 °C. Microstructural and thermal evolutions under different conditions were investigated using scanning electron microscopy (SEM), electron-probe microanalysis (EPMA) and X-ray diffraction (XRD). It was revealed that under uncoated condition, the Ti65 alloy experienced severe oxidation and developed non-protective TiO2 oxide film. In contrast, phosphate-ceramic coated Ti65 alloy exhibited excellent oxidation resistance with small weight gain (0.35 mg/cm2) compared with that of the uncoated Ti65 alloy (1.05 mg/cm2). Microscopy results confirmed absence of TiO2 oxide scales at the coating-substrate interface. The significant enhancement in the oxidation resistance of the Ti65 alloy was attributed to the dense nature of the phosphate-ceramic protective coating with great thermal and chemical stability. Furthermore, the coating exhibited excellent thermal shock resistance for having compatible thermal expansion coefficient with the Ti65 alloy substrate.

Cobalt-Free Perovskite Oxide La0.6Sr0.4Fe0.8Ni0.2O3−δ as Active and Robust Oxygen Electrode for Reversible Solid Oxide Cells

Reversible solid oxide cells have received increasing attention due to high efficiency. Cobalt-free perovskite electrode has compatible thermal expansion coefficient matching with the electrolyte and the reversible operation to inhibit the segregation of Sr. Herein a novel cobalt-free La0.6Sr0.4Fe0.8Ni0.2O3−δ perovskite is developed and investigated as oxygen electrode for reversible solid oxide cells. The electrochemical performance of La0.6Sr0.4Fe0.8Ni0.2O3−δ oxygen electrode in fuel cell mode and electrolysis mode is investigated in detail. The maximum power density of 961 mW cm–2 and polarization resistance of 0.142 Ω cm2 at 800 °C can be achieved in fuel cell mode. While the cell is operated in electrolysis mode, the current density ranges from 0.53 A cm–2 at 750 °C to 1.09 A cm–2 at 850 °C with 50 vol % absolute humidity at 1.3 V, and the hydrogen generation rate can reach up to 1348.5 mL (cm2 h)−1 with 90 vol % absolute humidity at 800 °C. The reversible solid oxide cells show excellent reversibili...

A high-performance cobalt-free Ruddlesden-Popper phase cathode La1·2Sr0·8Ni0·6Fe0·4O4+δ for low temperature proton-conducting solid oxide fuel cells

Ruddlesden-Popper typological (R-P type) layered material La2NiO4 is known for the excellent ionic conductivity and fast oxygen kinetics, but limited by its electronic conductivity as a single-phase cathode for low-temperature proton-conducting solid oxide fuel cells (LT H-SOFC). Cobalt-doping can improve the electro-catalytic capability, accompanied with an increased thermal expansion coefficient (TEC), which would lead to the delamination at the cathode/electrolyte interface. In this assignment, strontium and iron co-doped R-P phase cathode La1·2Sr0·8Ni0·6Fe0·4O4+δ (LSNF), exhibiting fine oxygen conduction, sufficient electronic conductivity and compatible TEC with the electrolyte, is investigated thoroughly. The single cell with LSNF cathode based on BaZr0·1Ce0·7Y0·2O3-δ (BZCY) electrolyte achieves a maximum power density (MPD) of 781 mW cm−2 with the low interfacial polarization resistance (Rp) of 0.078 Ω cm2 at 700 °C. Interestingly, the single cell can also possess an eximious power output of 138.5 mW cm−2 at relatively low temperature of 500 °C. Moreover, the excellent long-term stability with no observable performance degradation for almost 100 h at 600 °C could also indicate that the single-phase R-P layered material LSNF is a preeminent cathode candidate for LT H-SOFC.

Tunable properties of (HoxY1-x)2SiO5 as damage self-monitoring environmental/thermal barrier coating candidates

RE2SiO5 with low thermal conductivity, compatible thermal expansion coefficients and excellent high-temperature reliability in harsh environments are excellent candidates as advanced environmental/thermal barrier coating materials for high-efficiency gas turbine engines. A series of rare earth silicates (HoxY1-x)2SiO5 are designed and their properties are comprehensively investigated in this paper. Through doping Ho into Y2SiO5, the thermal conductivity of Y2SiO5 is significantly decreased and the thermal expansion coefficient is also optimized closer to Si-based ceramics. High-temperature elastic stiffness and bending strength are increased with the enhancing of Ho content. Most important, doping Ho element provides (HoxY1-x)2SiO5 with tunable luminescence characteristic. (HoxY1-x)2SiO5 exhibit green, to yellow-green, then to orange-red luminescence color with increased Ho concentration. The results show that they can be used as damage self-monitoring environmental/thermal barrier coating materials for Si-based ceramics.

Al₂O₃-Cu Substrate with Co-Continuous Phases Made by Powder Sintering Process.

Ceramic-Al substrates with co-continuous ceramic and metal phases, which exhibit high thermal conductivity and compatible coefficient of thermal expansion (CTE), have been widely investigated through the process of die-casting. In this research, a kind of powder sintering process was proposed for fabricating ceramic-Cu composite substrates with co-continuous phases. Copper fiber (Cuf) has excellent thermal conductivity and large aspect ratio, making it an ideal material to form bridging network structures in the ceramic-Cu composite. To maintain the large aspect ratio of Cuf, and densify the composite substrate, ZnO-SiO2-CaO glass was introduced as a sintering additive. Both Al2O3/glass/Cuf and Al2O3/30glass/Cup composite substrates were hot-pressed at 850 °C under 25 MPa. Experimental results showed that the thermal conductivity of Al2O3/30glass/30Cuf composite substrate was as high as 38.9 W/mK, which was about 6 times that of Al2O3/30glass; in contrast, the thermal conductivity of Al2O3/30glass/30Cup composite substrate was only 25.9 W/mK. Microstructure observation showed that, influenced by hot press and corrosion of molten ZnO-SiO2-CaO glass, the copper fibers were deformed under hot-pressing, and some local melting-like phenomena occurred on the surface of copper fiber at 850 °C under 25 MPa. The molten phase originating from surface of Cuf welded the overlapping node of copper fibers during cooling process. Finally, the interconnecting metal bridging in ceramic matrix was formed and behaved as a rapid heat-dissipating channel, which is similar to substrates prepared through die-casting process by porous ceramic and melted Al.

Fabrication and oxidation resistance of mullite/yttrium silicate multilayer coatings on C/SiC composites

A tri-layer coating of mullite/Y2Si2O7/(70wt%Y2Si2O7+30wt%Y2SiO5) was prepared on carbon fiber reinforced silicon carbide (C/SiC) composite substrate through dip-coating route for the sake of improving oxidation resistance of C/SiC composites. An Al2O3–SiO2 sol with high solid content was selected as raw material for mullite, and a slurry of Y2O3 powder filled silicone resin was used to synthesize yttrium silicate. The microstructure, phase composition, and oxidation resistance of the coating were investigated. The as-fabricated coating shows high density and favorable bonding to C/SiC substrate. After oxidation at 1400 and 1500 °C for 30 min under static air, the flexural strengths of coated C/SiC composite were both increased by ~30%. The desirable thermal stability and the further densification are responsible for excellent oxidation resistance. With the additional help of compatible thermal expansion coefficients among substrate and sub-layers in coating, the coated composite retained 111.2% of original flexural strength after 12 times of thermal shock in air from 1400 °C to room temperature. The carbothermal reaction at 1600 °C between free carbon in C/SiC substrate and rich SiO2 in mullite resulted in severe frothing and desquamation of coating and obvious degradation in oxidation resistance.

As-casting performance of gold alloys and their de-bonding strengths in metal–ceramic systems

This study characterized noble gold casting alloys and evaluated the de-bonding strength of metal–ceramic composite structures. A casting metal plate was prepared from three commercial alloys with similar constitutions: BegoStar, Argedent 500 (Argen500), and Jelenko Cameo (Cameo). The physical properties of strengths, modulus and recovery angle were tested by three-points bending mode. Vickers microhardness of the cast alloys were measured across the samples. The de-bonding strengths of metal–ceramic composite structures and failure surfaces were also evaluated. The as-casting Argen500 alloy represented the more ductile, stronger and better porcelain bonding properties with highest values of the ultimate strength, yield strength, recovery angle, and lower coefficient of thermal expansion (CTE). An Indium (In) contained alloy (Argen500) possesses more compatible CTE and smaller grain size with higher hardness in the oxide effect layer would be an advantage to porcelain fused-to-metal alloys applied in fixed partial dentures.

RBa(Co, Ga)4O7 Cathodes with High-Temperature Phase Stability for Solid Oxide Fuel Cells

YBaCo4O7+δ-based materials have attracted much attention since last decade because of their potential applications as cathode materials in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The ideal matching of the relatively low thermal expansion coefficient (TEC) of YBaCo4O7+δ (7.5 × 10-6 K-1) with those of common oxide-ion electrolytes (10 – 12.5 × 10-6 K-1) in the temperature range of 300 – 900 °C alleviates the thermal stress during long-term operation in IT-SOFCs.1 However, the practical applications of this class of materials is impeded by the irreversible oxygen absorption and phase decomposition at 600 – 900 °C. The decomposition products, such as BaCoO3, Y2O3, and Co3O4, are easily found after heating YBaCo4O7+δ to the decomposition temperature region.2 With an aim to enhance the high-temperature phase stability, oxygen-storage capability, and electrocatalytic activity in IT-SOFCs, we present here the RBaCo4O7+δ-based samples with a co-substitution in the R site with Y, In, and Ca and Ga substitution in the Co site.3 All twenty-four examined compositions, includingYBaCo4-yGayO7+δ, Y1-xInxBaCo3.3Ga0.7O7+δ, Y1-xCaxBaCo3.3Ga0.7O7+δ, In1-xCaxBaCo3.3Ga0.7O7+δ, and Y0.5In0.5BaCo4-yGayO7+δ series of materials, have been synthesized by a solid-state reaction. The phase stabilities have been assessed by long-term testing at 600 – 800 °C for 120 h. The phase of pristine and high-temperature annealed samples was characterized by X-ray diffraction (XRD). The thermal behavior which includes oxygen absorption and desorption was evaluated by thermogravimetric analysis (TGA) from room temperature to 1000 °C in air. For the electrochemical performance assessment, composites consisting of a mixture of Ce0.8Gd0.2O2-δ (GDC) and the stabilized Ga-substituted RBaCo4O7+δ were applied as cathodes. The electrocatalytic activity for the oxygen reduction reaction in air was evaluated with a symmetric cell, which was fabricated by screen printing the composite cathodes onto two sides of a dense GDC pellet and co-sintering at 950 °C. The fuel cell performance of the composite cathodes was determined by an anode-supported single cell, which was made by a co-pressing method with NiO + GDC and GDC, respectively, as the anode and the electrolyte. Figure 1 indicates the stable compositions in which no impurity peaks appear in the XRD pattern after 120 h long-term tests at 600, 700, and 800 °C. The results reveal that the synergistic effect of In and Y co-dopants could enhance the stability and mitigates the phase decomposition at a certain Ga content. While decreasing the Ga content, Y0.5In0.5BaCo3.5Ga0.5O7+δ still remains single phase at all tested temperatures. However, Ca hinders the phase stability regardless of the other dopant on the R site, and there is no synergistic effect of In-Ca or Y-Ca co-dopants. The thermal behavior illustrates the reason for high-temperature decomposition with incomplete oxygen release at ~350 °C and continuous oxygen absorption above 400 °C. The TECs of the high-temperature stable materials are all in the range of 7.0 – 9.2 × 10-6 K-1 at 200 – 900 °C. In addition, these materials display adequate electrical conductivity (3 – 20 S cm-1) at 500 – 900 °C. Among the studied compositions, the symmetric cell with Y0.9In0.1BaCo3.3Ga0.7O7+δ + GDC composite cathode exhibits the lowest area-specific resistance of 0.07 Ω cm2 at 700 °C. The single cell and long-term performance with Y0.9In0.1BaCo3.3Ga0.7O7+δ + GDC composite cathode are shown in Figure 2. The maximum power density reaches 0.33, 0.56, and 0.91 W cm-2 at, respectively, 600, 650, and 700 °C. The voltage remains stable without a significant degradation with a constant current density of 0.7 A cm-2 at 650 °C in the 140 h long-term test. In summary, the compatible TECs, high maximum power performance, and stable long-term performance demonstrate the advantages of Y0.9In0.1BaCo3.3Ga0.7O7+δ as a potential cathode material for IT-SOFCs. REFERENCEs 1. W. H. Kan, K.-Y. Lai, A. Huq, and A. Manthiram, J. Power Sources, 307, 454–461 (2016). 2. J.-H. Kim and A. Manthiram, Chem. Mater., 22, 822–831 (2010). 3. K.-Y. Lai and A. Manthiram, Chem. Mater. (2016) DOI: 10.1021/acs.chemmater.6b04122. Figure 1

Capacity and mechanisms of plastic deformation in β-Lu2Si2O7

RE2Si2O7 disilicates are promising candidates for oxidation resistant interfacial phase in SiC fiber-reinforced SiC matrix composites due to their good damage tolerance, good phase stability and compatible thermal expansion coefficients with SiC. We herein investigate the capacity and mechanisms of plastic deformation in β-Lu2Si2O7 by a combination of Hertzian indentation experiment and transmission electron microscopy observation. A large amount of (1 1 0) deformation twinning, dislocations and slip bands are observed. For the common twinning mode, fewer atomic shuffle types, small shear strain, and low shear modulus in the twinning direction help explain the prevalence of this mode.

Nondestructive evaluation of the interface between ceramic coating and stainless steel by electromagnetic method

Protecting coatings as thermal barrier coating (TBC) are used for yield improvement of equipment working at high temperature. Zirconia doped with yttria ceramics are considered a good TBC material due of its low thermal conductivity, refractory, chemical inertness and compatible thermal expansion coefficient with metallic support. The paper proposes the use of an electromagnetic method for evaluation of coatings on stainless steel using a sensor with metamaterial lens and comparison of the results with those obtained by complementary methods.

Comparison of Physical, Thermal, and Thermomechanical Properties of Cotton/Epoxy Composite and Cotton/Vinyl Ester Composite Inhibitors

AbstractThe inhibition of a double‐base solid propellant is used to control and prevent the burning degree of the exposed area, which is due to longer burning time. In recent years, inhibition with cellulose derivatives has become popular, but these monolithic systems usually suffer from the drawback of a high erosion rate and demand high thickness and low burning time. In this research two composite inhibitors based on natural fibers were manufactured by filament winding technique and their physical, thermal, and thermomechanical properties were compared. In addition, a chlorinated flame retardant (CFR) as well as antimony trioxide were added in inhibitor compositions to control their burning processes. It was found that the cotton/epoxy composite inhibitor displays a compatible thermal expansion coefficient with the propellant and a high amount of residual char compared to cotton/vinyl ester composite. Also, it was understood that the moisture absorption resistance and thermal stability, i.e., initial decomposition temperature of cotton/vinyl ester specimen were better than cotton/epoxy specimen. Furthermore, density and the flame retardant performance of both composite inhibitors were similar. Additionally, the tan(δ) value obtained for cotton/epoxy composite was higher than that of cotton/vinyl ester composite indicating its good dissipation of vibrational energy.

Theoretical and experimental determination of the major thermo-mechanical properties of RE2SiO5 (RE = Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) for environmental and thermal barrier coating applications

X2-RE2SiO5 orthosilicates are promising candidate environmental/thermal barrier coating (ETBC) materials for silicon-based ceramics because of their excellent durability in high-temperature environments and potential low thermal conductivities. We herein present the mechanical and thermal properties of X2-RE2SiO5 orthosilicates based on theoretical explorations of their elastic stiffness and thermal conductivity, and experimental evaluations of the macroscopic performances of dense specimens from room to high temperatures. Mechanical and thermal properties may be grouped into two: those that are sensitive to the rare-earth (RE) species, including flexural strength, elastic modulus, and thermal shock resistance, and those that are less sensitive to the RE species, including thermal conductivity, thermal expansion coefficient, and brittle-to-ductile transition temperature (BDTT). The orthosilicates show excellent elastic stiffness at high temperatures, high BDTTs, very low experimental thermal conductivities, and compatible thermal expansion coefficients. The reported information provides important material selection and optimization guidelines for X2-RE2SiO5 as ETBC candidates.