Linear Thermal Expansion Coefficient Values Research Articles

Mechanical and thermodynamic behaviors of the second phases in Al–Zn–Mg–Cu alloys

The mechanical and thermodynamic behaviors of intermetallics in Al–Zn–Mg–Cu alloys are studied by first-principles calculations. All studied second phases have negative values of formation enthalpy and cohesive energy indicating their excellent thermodynamic stability. Al3Er_D0[Formula: see text] has the most significant metallic nature, while Mg2Si shows the least metallicity. TiAl3 shows the highest bulk, shear, and Young’s moduli. All Al3M polymorphs, Mg2Si and TiAl3 phases show covalent/metallic hybrid bonding. The mechanical anisotropic behaviors obey the trend of: MgZn[Formula: see text]Er_D0[Formula: see text]Sc_D0[Formula: see text]Sc_D0[Formula: see text]Er_D0[Formula: see text]Er_L1[Formula: see text]Sc_L1[Formula: see text]Si, where MgZn2 is the most mechanically anisotropic phase. The calculated room-temperature linear thermal expansion coefficient values for the studied phases are from [Formula: see text] K[Formula: see text] to [Formula: see text] K[Formula: see text]; where Al3Er_L12 has the highest value ([Formula: see text] K[Formula: see text], followed by Al3Sc_L12 ([Formula: see text] K[Formula: see text]; both of which are close to that of the Al matrix, thus making the relatively lower thermal misfit.

Linear thermal expansion behavior of compacted bentonite buffer materials

In a geological repository system, buffer is indispensable to ensure the safe disposal of high-level radioactive waste (HLW). Because heat generated from spent nuclear fuel in a canister is released to the surrounding buffers, thermal properties of such materials are fundamental in determining the overall disposal safety. Specifically, given that thermal expansion causes thermal stress to canisters and intact rock masses in the near-field location, it is imperative to evaluate the thermal expansion characteristics of the buffer, particularly when bentonite is used. This study investigates the linear thermal expansion properties of Kyeongju bentonite buffer, a type of Ca-bentonite produced in South Korea. The linear thermal expansion coefficient of dried bentonite was measured considering the heating rate, dry density, and temperature variation using dilatometer equipment. The linear thermal expansion coefficient values of the KJ bentonite buffers were found to be 4.0–6.2 × 10⁻⁶/°C. Based on test results, a numerical analysis was conducted, and the thermal strain values were similar between the test and numerical analysis. The overall linear thermal expansion coefficient of the KJ bentonite, considering radially confined or unconfined conditions and dried or saturated states, was predicted to be between 3.2 × 10⁻6/°C and 1.0 × 10⁻5/°C.

Processing and thermal characterization of polymer derived SiCN(O) and SiOC reticulated foams

Highly porous polymer-derived SiCN(O) and SiOC ceramics with low thermal conductivity were developed by replicating polyurethane (PU) foams. The PU templates were impregnated with polysilazane or polysiloxane precursor, followed by pyrolysis at different temperatures (1200 °C - 1500 °C) yielding SiCN(O) or SiOC ceramic foams, respectively. The swelling and cross-linking behavior of the used precursors had a significant impact on the morphology of the prepared foams. The samples had bulk densities ranging from 0.03 g.cm-3 to 0.56 g.cm-3 and a total porosity in the range from 75 to 98 vol%. Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) were employed to follow the structural evolution together with morphological characterization by scanning electron microscopy (SEM). The obtained ceramics were thermally stable up to 1400 °C, and the linear thermal expansion coefficient values of the porous SiCN(O) and SiOC components in the temperature range from 30 to 850 °C were found to be ~1.72 x 10-6.K-1 and ~1.93 x 10-6.K-1, respectively. Thermal conductivity (λ) as low as 0.03 W.m-1 K-1 was measured for the SiCN(O) and SiOC foams at room temperature (RT). The λ of the ceramic struts were also assessed by using the Gibson-Ashby model and estimated to be 2.1 W.m-1 K-1 for SiCN(O), and 1.8 W.m-1 K-1 for SiOC.

Effect of Melt Treatment with Water Vapor on Thermal Expansion of Alloy Al – 20–40% Si

The effect of melt treatment with water vapor on the microstructure and linear thermal expansion coefficient (LTEC) of Al–(20–40)% Si alloys is studied. LTEC values are determined in the temperature range of 50–450 °C. It is established that melt treatment with water vapor has not only a modifying effect on the structure of high-silicon silumins, but also affects the value and nature of the change in LTEC making it possible to reduce its values at test temperatures of 50–250 °C. The efficiency of melt treatment in a water vapor atmosphere depends on silicon content and decreases with the increase of its content in the alloy. A regime for alloy modification providing maintenance of water vapor at 1200 °C in the atmosphere for 1 hour may be used in the production of industrial alloys with low LTEC for objects of special instrument building.

Comparative Evaluation of Physical and Mechanical Characteristics of Composite facing Materials "Ceramage" and "Ultraglass"

In the oral cavity, mechanical loading and exposure to temperature leads to deformation of the frameworks of fixed prostheses and lining materials ensuring the proper level of their aesthetics. The increase of the isotropy of the material of the framework of a fixed prosthesis and the material that is facing it is one of the urgent problems in the field of orthopedic dentistry. In this paper, the linear thermal expansion coefficients (LTEC) of the facing materials “Ceramage Opaque Dentin”, “Ceramage Incisal”, produced by the Japanese company “Shofu”, and those of “UltraGlass” of the Russian firm “VladMiVa” were studied. The values of LTEC of facing materials were correlated with LTEC of cobalt-chromium alloy, used for making the frameworks of fixed prostheses. A comparative evaluation of the compressive strength, flexural strength, and modulus of elasticity of the specified composite materials used for facing the frameworks of fixed prostheses was also carried out.

Thermal expansion of organic superconductor κ-(D4-BEDT-TTF)2Cu{N(CN)2}Br. Isotopic effect

Linear thermal expansion coefficient (LTEC) of single crystal κ-(D4-BEDT-TTF)2Cu[N(CN)2]Br was studied across the crystal layers in the temperature range 2–290 K using the method of precise capacitive dilatometry. Below Tc = 11.6 K the LTEC of the sample had a small negative value, which is apparently due to the transition from the paramagnetic metal in the superconducting state. There was a bend of temperature dependence of the LTEC, which shows broad peak around 40 K and can be attributed to the elastic lattice anomaly around the end-point of Mott boundary. A sharp jump in the LTEC values and hysteresis was observed in the area of Tg ∼ 75–77 K, what is likely explained by the transition in a glass-like state. The isotope effect in the thermal expansion is discusses, which manifested itself in a shift of the phase transitions in comparison with fully deuterated BEDT-TTF sample.

The Study on Thermal Expansion of Ceramic Composites with Addition of ZrW2O8

The studies on structure, phase composition and thermal properties of (Al2O3 - 20 wt% ZrO2) - ZrW2O8 ceramic composites obtained using nanosized, initial powders were conducted. Homogeneously distributed white particles on the polished surface of composites were observed. Phase composition of the composites was represented with corundum, monoclinic ZrO2 and two modifications of ZrW2O8 (tetragonal and cubic). Linear thermal expansion coefficient values of the composites were determined. The difference in experimental and calculated coefficient of thermal expansion values for composites obtained may be attributed to phase transformations, features of the structure, internal stresses due to thermal expansion mismatch, which contribute significantly to thermal expansion of the ceramic composites.

Structure and Properties of the Bi<sub>0.85</sub>Nd<sub>0.15</sub>FeO<sub>3</sub>, BiFe<sub>0.85</sub>Mn<sub>0.15</sub>O<sub>3</sub>, and Bi<sub>0.85</sub>Nd<sub>0.15</sub>Fe<sub>0.85</sub>Mn<sub>0.15</sub>O<sub>3</sub> Multiferroics Solid Solutions

The Bi0.85Nd0.15FeO3, BiFe0.85Mn0.15O3, and Bi0.85Nd0.15Fe0.85Mn0.15O3 ferrites solid solutions were synthesized and their crystal structure, magnetic susceptibility, thermal expansion, electrical conductivity, thermo-EMF and dielectric properties were studied. It was found that Bi0.85Nd0.15FeO3 and BiFe0.85Mn0.15O3 had rhombohedral structure (space group R3c), but Bi0.85Nd0.15Fe0.85Mn0.15O3 one had orthorhombic structure (space group Pnma) and all the complex oxides studied were the antiferromagnetic semiconductors of p-type, which electrical conductivity values were larger than for unsubstituted bismuth ferrite BiFeO3, Neel temperature and thermo-EMF coefficient sharply decreased at partial substitution of iron by manganese and linear thermal expansion coefficient values varied within (10.0-13.4)·10 - 6 K -1 . The values of charge carriers transfer parameters in (Bi,Nd)(Fe,Mn)O3 phases were calculated.

Phase Study and Thermal Expansion of Yttria Stabilized Zirconia Doped with PuO2-x

Phase relations between PuO2 and yttria stabilized zirconia (YSZ, Pu/(Pu+YSZ)=0-0.5) were investigated in air, vacuum and H2 atmospheres. All samples prepared in air and vacuum were single-phase solid solutions with the fluorite structure while those prepared in H2 were single-phase either the fluorite (Pu/(Pu+YSZ)<0.3) or the pyrochlore structure (Pu/(Pu+YSZ)>0.3). The observed lattice parameter change of the fluorite solid solution with the Pu content was well explained by an ionic model where oxygen vacancies occurred preferentially to Zr4+ and the coordination number (CN) of Zr4+ reduced to 7 while the CN of the other metal ions remained 8. Thermal expansion of YSZ doped with PuO2 was also studied by high-temperature X-ray diffraction method at temperatures between room temperature and 1273 K in air. Linear thermal expansion coefficient values of the solid solution (Pu/(Pu+YSZ) = 0-0.25) fell in the range 6-12 x 10-6 K-1. Though there was no apparent relationship between thermal expansion coefficients and Pu content, it was seen that thermal expansion coefficients became small with increasing Pu content above 1000 K. The constant-pressure heat capacities of the solid solutions were also calculated from the thermodynamical relation.