Low-temperature Thermal Expansion Research Articles

High-pressure synthesis and low-temperature thermal expansion behavior of homogeneous phosphorus-rich pseudo-binary compound (V0.5Cr0.5)P4

A black phosphorus layered homogeneous phosphorus-rich compound – (V0.5Cr0.5)P4 is synthesized using a large volume press under conditions of P = 5 GPa, 1100 °C, and 1 h of heating. (V0.5Cr0.5)P4 has a monoclinic (C2/c) structure with lattice parameters and cell volume of a = 5.2307(3)Å, b = 10.861(4)Å, c = 5.8253(4)Å, β = 110.784°, and V = 309.41(4)Å3, respectively. The thermal expansion behavior above about 110K has been investigated by low-temperature synchrotron XRD. The coefficient of thermal expansion, α, was calculated to be αa = 0.57 × 10−5K−1, αb = 0.70 × 10−5K−1, αc = 0.92 × 10−5K−1, αβ = 0.13 × 10−5K−1 and αv = 2.10 × 10−5K−1 at 293K. This thermal expansion behavior presents an anisotropic expansion characteristic different from pure black phosphorus due to the V/Cr atom that bonded the black phosphorus layers together.

Low-temperature thermal drying-induced pore expansion effects of cellulosic fibers

Low-temperature thermal drying-induced pore expansion effects of cellulosic fibers

Study on typical temperature effect mechanism of multi-component coal during low-temperature thermal expansion

Liquid Nitrogen (LN2) cold shock on coal reservoir is a promising technology, and its complex fracture networks are directly related to the temperature effect of each component in coal caused by temperature change. Among them, the typical temperature effects include the expansion difference of different mineral particles, the evaporation of pore water and the volume expansion of gas heated, and the phase transition of water into ice. The above-mentioned effects will all occur in the process of cold shock and temperature returning of coal samples, and further influence the generation of fractures. In this paper, the relationship between minerals, moisture and porosity of six kinds of coals in the range of −30 °C–40 °C and the overall thermal expansion coefficient of coal samples is explored by using low-temperature thermal expansion coefficient tester, low-field nuclear magnetic resonance tester, XRD diffraction analyzer, CT scanner and muffle furnace industrial analyzer. It is found that the main minerals in coal are generally lower than the thermal expansion coefficient of the whole coal. The moisture and porosity of coals are proportional to the overall thermal expansion coefficient of coal samples. Among them, the porosity of small holes accounts for the highest proportion, and its internal moisture and gas have the greatest influence on the overall thermal expansion of coal, which indicates that the temperature effect of pore water evaporation and gas volume expansion in pores plays an important role in the process of coal temperature change.

Low temperature synthesis and thermal expansion study of nanocrystalline CaTiO3

We have successfully synthesized nanocrystalline calcium titanate (CaTiO3) at low temperature by wet chemical method. The prepared CaTiO3 was characterized by simultaneous Thermogravimetry-differential thermal analysis. The CaTiO3 nanoparticles at different annealing temperatures confirms the formation of the single-phase CaTiO3 at 700 °C for 1 h. The influence of annealing temperatures on the microstructures are investigated by SEM and TEM.The thermal expansion of sintered CaTiO3 in the range of 30 °C to 950 °C exhibits average linear thermal expansion coefficient (α) of 12.94 × 10−6 K−1. The nanocrystalline CaTiO3 powder pelletized and sintered at 1250 °C for 5 h has achieved density > 95 %.

Quantum effects in the low-temperature thermal expansion of fullerite C60 doped with a 4He impurity

The thermal expansion of fullerite C60 doped with a 4He impurity at T ∼2 K has been investigated by the method of low temperature precision dilatometry in the interval T = 2.2−24 K. The character and the derived values of the thermal expansion coefficients were strongly dependent on the concentration of the 4He impurity in fullerite. In the interval T = 2.2−5 K the thermal expansion of the 4Hex−C60 system is negative, which is attributed to the tunnel movement of the 4He atoms in the cavity system of the C60 crystal lattice and at the crystallite surface. The contribution of this process to the thermal expansion decreases as the impurity (4He) concentration increases and the probability of 4He tunneling between the crystal lattice cavities and the impurity-free areas of the grain surface diminishes. In the temperature interval T = 4.5−24 K the thermal expansion of the 4Hex−C60 system is influenced predominantly by the mutual transformations of different orientation glass modifications of fullerite. Owing to their tunnel character the transformations make a negative contribution to the process of thermal expansion entailing a hysteresis and other anomalies observed in this temperature interval. The intensity of the processes provoked by the tunneling-encouraged phase transformations of the orientational glasses of C60 increases with the 4He concentration in fullerite.

Low-temperature nanoscale heat transport in a gadolinium iron garnet heterostructure probed by ultrafast x-ray diffraction.

Time-resolved x-ray diffraction has been used to measure the low-temperature thermal transport properties of a Pt/Gd3Fe5O12//Gd3Ga5O12 metal/oxide heterostructure relevant to applications in spin caloritronics. A pulsed femtosecond optical signal produces a rapid temperature rise in the Pt layer, followed by heat transport into the Gd3Fe5O12 (GdIG) thin film and the Gd3Ga5O12 (GGG) substrate. The time dependence of x-ray diffraction from the GdIG layer was tracked using an accelerator-based femtosecond x-ray source. The ultrafast diffraction measurements probed the intensity of the GdIG (1 −1 2) x-ray reflection in a grazing-incidence x-ray diffraction geometry. The comparison of the variation of the diffracted x-ray intensity with a model including heat transport and the temperature dependence of the GdIG lattice parameter allows the thermal conductance of the Pt/GdIG and GdIG//GGG interfaces to be determined. Complementary synchrotron x-ray diffraction studies of the low-temperature thermal expansion properties of the GdIG layer provide a precise calibration of the temperature dependence of the GdIG lattice parameter. The interfacial thermal conductance of the Pt/GdIG and GdIG//GGG interfaces determined from the time-resolved diffraction study is of the same order of magnitude as previous reports for metal/oxide and epitaxial dielectric interfaces. The thermal parameters of the Pt/GdIG//GGG heterostructure will aid in the design and implementation of thermal transport devices and nanostructures.

Low-temperature thermal expansion of the topological material candidates [formula omitted]-PtBi[formula omitted] and [formula omitted]-PdBi[formula omitted

We report on the low-temperature (T< 120 K) thermal expansion of the bismuth-based topological semimetal β-PtBi2 and topological superconductor β-PdBi2 candidates. The linear thermal-expansion coefficient of tetragonal β-PdBi2 shows a pronounced anisotropy between the a- and c-axis while the volume thermal-expansion coefficient αV (β-PdBi2) is considerable larger than αV (β-PtBi2). The coefficient αV (β-PtBi2) nearly matches the experimental specific heat, from which a Debye temperature θD=199 K is obtained. On the other hand, αV (β-PdBi2) reasonably fits the Debye model with θD=138 K, extracted from the low-temperature specific heat. An almost constant Grüneisen parameter Γ≈ 2 is obtained for both compounds. No magnetostriction is observed in any of both compounds up to μ0H=16 T. We compare our results with other Bi-based topological materials.

Thermal expansion of FeNi Invar and zinc-blende CdTe from the view point of local structure

Thermal expansion of FeNi Invar and zinc-blende CdTe was investigated from the view point of local structure using the extended x-ray absorption fine structure (EXAFS) spectroscopic data and the path-integral effective classical potential (PIECP) Monte Carlo computational simulations. In this Review article, first the quantum statistical perturbation theory is intuitively described to see different character concerning thermal expansion between the quantum and classical theories. The diatomic Br2 molecule is employed as a simple example. Second, the PIECP theory is briefly described to note advantages and disadvantages of this simulation technique. Historical background is also discussed for the EXAFS investigation of thermal expansion based on the quantum statistical theories. The results of the FeNi Invar alloy are then summarized. The origin of zero thermal expansion in the FeNi alloy is ascribed to the so-called Invar effect that implies the variation of the electronic structure of Fe atoms depending on temperature. Zero thermal expansion at low temperature is however found to originate from the vibrational quantum effect. It is also noted that the interatomic distances of Fe-Fe, Fe-Ni, and Ni-Ni pairs are slightly but meaningfully different from each other, although the alloy exhibit a simple fcc crystal. Such a pair- dependent difference is also true for thermal expansion and we will discuss thermal expansion from the local point of view, which is interestingly different from the lattice thermal expansion significantly. Finally, the results of the zinc blende (or diamond) structure are presented. Although the origin of negative thermal expansion in these tetrahedral crystals is known as a result of classical vibrational anomaly within the Newton dynamics theory, the quantum statistical simulation is found to be essential to reproduce the negative thermal expansion of CdTe. It is emphasized that the vibrational quantum effect and classical anharmonicity are of great importance for the understanding of low-temperature thermal expansion as well as the elastic constants.

Study on Typical Temperature Effect Mechanism of Multi-Component Coal During Low-Temperature Thermal Expansion

Study on Typical Temperature Effect Mechanism of Multi-Component Coal During Low-Temperature Thermal Expansion

Size Effect on the High-Strength and Electrically Conductive Polyolefin/Reduced Graphene Oxide (RGO) Composites

Size-controlled alkylated reduced graphene oxide (M-LTRGO) with a narrow particle size distribution was synthesized in one step via a low-temperature thermal expansion strategy at a large scale. The physicochemical properties of the modified graphite oxide (M-GO) and M-LTRGO with changes in the particle size were characterized and discussed. After incorporation in low-density linear polyethylene (LLDPE) by melt blending, the composites have been characterized regarding their morphological, mechanical, and electrical properties to study the performance evolution of LLDPE/M-LTRGO with changing M-LTRGO size. The electrical properties of the LLDPE/M-LTRGO composites show the exact opposite trend with the M-LTRGO tablet, as the changing of the average M-LTRGO size. The opposite electrical phenomenon ascribes the small-size M-LTRGO resulting in a better dispersion in LLDPE matrix, which is determined by the mean surface-to-surface interparticle distance (IPD) from examination of scanning electron micrographs.

Architecture & functionalization evolution of RGO affect physicomechanical properties of polyolefin/RGO composites

This work was aimed to investigate how the architecture and functionalization of reduced graphene oxide (RGO) would affect the physicomechanical properties of polyolefin/RGO composites prepared by a melt blending route. Fine controllable alkylated RGO with designed exfoliation degree and modification degree was one-step synthesized through a modified low-temperature thermal expansion technology as the raw of gradient alkylated graphite oxide. The physicomechanical properties of the polyolefin/RGO composites were mainly determined by the interplay of two influence factors: exfoliation degree (specific surface area) and modification degree. Based on the alkyl modification to RGO, the exfoliation degree of RGO is decisive in the mechanical properties and thermal stability of polyolefin/RGO composites. The interaction between RGO sheets and the polyolefin matrix calculated from Raman spectrum is well consistent with the changes of specific surface area & modification degree.

Negative 2D thermal expansion in the halogen bonded acetone bromine complex

The complex formed between acetone and bromine shows both negative 2D thermal expansion at low temperature and colossal thermal expansion.

Features of low-temperature thermal expansion of n-type Bi2Se3 single crystals in magnetic field

Tensometric study of n-type Bi2Se3 single crystals in dc magnetic fields to 6 T in a temperature range of 7–23 K detected a weak negative thermal expansion (NTE) in the basal plane. The NTE increases with the field strength and depends on its orientation with respect to the trigonal c axis. In a magnetic field of 6 T, parallel to the c axis, the linear NTE coefficient reaches −7 · 10−7 K−1, and a minimum sample length is reached at a temperature of 13 K, where a Hall carrier concentration maximum is also detected. The found magnetoelastic anomaly can be associated with the topological insulator state.

High refractive index coating of phosphor-in-glass for enhanced light extraction efficiency of white LEDs

The coating of phosphor-in-glass with high refractive index was successfully fabricated for enhanced light extraction efficiency of white LEDs through a multilayer screen-printing and low-temperature sintering procedure. The effects of sintering temperature on the B2O3–SiO2–ZnO glass coating and YAG:Ce phosphor concentration on the phosphor-in-glass coating were investigated. The B2O3–SiO2–ZnO glass matrix possesses low glass transition temperature and appropriate thermal expansion coefficient. With the addition of La2O3 and WO3, high refractive index of 1.82 at 460 nm is acquired. The amorphous glass coating, sintered at 600 °C, yields an optimized transmittance of 50%. Furthermore, negligible thermal degradation is observed in the phosphor-in-glass coating, and the emission peak under the 460-nm excitation is at ~540 nm. When increasing the concentration of phosphor, luminous efficacy and correlated color temperature are both improved, but color rendering index is deteriorated. As the refractive index increases, the light extraction efficiency of white LEDs is enhanced due to the reason that the match of refractive index between the glass matrix and the phosphor decreases the total internal reflection at the interface.

Low-temperature abnormal thermal expansion property of Mn doped cubic NaZn13-type La(Fe, Al)13 compounds

Low-temperature abnormal thermal expansion (ATE) materials have been recently developed because of their significant applications for cryogenic engineering. However, the challenge still remains for the control of ATE effect at cryogenic temperature and adjustable ATE is of fundamental interest. In this paper, we report the isotropic ATE in La(Fe, Al)13 compounds over a wide adjusting temperature range by partially substituting Fe by Mn. It is found that all samples crystallize in the cubic NaZn13-type structure with the space group. The introduction of nonmagnetic Mn atoms reduces the Fe-Fe exchange interaction, therefore, the itinerant electron system needs less energy to break the magnetic order in ferromagnetic (FM) state at low temperature. The negative thermal expansion (NTE) operation-temperature window moves towards lower temperatures accompanied with the decrease of Curie temperature (TC) by increasing Mn elements. Moreover, the composite combining Mn 0 and Mn 57 broadens the zero thermal expansion (ZTE) behavior occurring in the whole tested temperature range. The present studies could be useful to control the thermal expansion, and indicate the potential applications of ATE materials in cryogenic engineering.

Accordion-like graphene by a facile and green synthesis method reinforcing polyolefin nanocomposites

Scalable synthesis of accordion-like graphene via low temperature (below 170 °C) thermal expansion exfoliation of alkylated graphite oxide without any auxiliary equipment.

Strong correlations, strong coupling, ands-wave superconductivity in hole-dopedBaFe2As2single crystals

We present a comprehensive study of the low-temperature heat capacity and thermal expansion of single crystals of the hole-doped Ba1-xKxFe2As2 series (0<x<1) and the end-members RbFe2As2 and CsFe2As2. A large increase of the Sommerfeld coefficient is observed with both decreasing band filling and isovalent substitution (K, Rb, Cs) revealing a strong enhancement of electron correlations and the possible proximity of these materials to a Mott insulator. This trend is well reproduced theoretically by our Density-Functional Theory + Slave-Spin (DFT+SS) calculations, confirming that 122-iron pnictides are effectively Hund metals, in which sizable Hund's coupling and orbital selectivity are the key ingredients for tuning correlations. We also find direct evidence for the existence of a coherence-incoherence crossover between a low-temperature heavy Fermi liquid and a highly incoherent high-temperature regime similar to heavy fermion systems. In the superconducting state, clear signatures of multiband superconductivity are observed with no evidence for nodes in the energy gaps, ruling out the existence of a doping-induced change of symmetry (from s to d-wave). We argue that the disappearance of the electron band in the range 0.4<x<1.0 is accompanied by a strong-to-weak coupling crossover and that this shallow band remains involved in the superconducting pairing, although its contribution to the normal state fades away. Differences between hole- and electron-doped BaFe2As2 series are emphasized and discussed in terms of strong pair breaking by potential scatterers beyond the Born limit.

Low-temperature thermal expansion behavior of the geometrically frustrated pyrochlore Tb2Ti2O7

Abstract The low-temperature lattice behavior of the pyrochlore magnet Tb 2 Ti 2 O 7 has been investigated by thermal expansion measurements. The thermal expansion coefficient of Tb 2 Ti 2 O 7 shows no anomaly except for a shoulder around 8 K, which can be explained by a Schottky type excitation arising from the energy gap between the ground-state and first excited CEF doublets. The analysis of the thermal expansion behavior combined with the heat capacity data indicates the lack of strong spin-lattice coupling in the thermal expansion at the low temperature region, where the spin liquid state emerges.

Influence of mechanical activation on MgO-Al2O3-SiO2 system in the presence of TeO2 additive

Cordierite 2MgO+2Al2O3+5SiO2 is frequently used ceramic material, that is commonly used as a carrier of electrical components due to its low dielectric constant (~ 5), and low temperature thermal expansion coefficient (20·10-7 oC-1). In order to accelerate the process of sintering, 5.00 mass% TeO2 was added to the starting mixtures. System was tested in two parallel mixtures, one with no additives, and the other one with TeO2. The mechanical activation of the both mixtures was performed in a highenergy ball mill in time intervals from 0 to 40 min with ball to powder mass ratio 1:40. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders as well as microstructures was analyzed by the means of X-ray diffraction method and SEM.

Optimization of Cutter Geometry Features to Minimise Cutting Force on Machining Polyetheretherketone (PEEK) Engineering Plastic

Machining of thermoplastic material poses several challenges due to its low melting temperature and high thermal expansion which directly related to cutting force. Thus, controlling the cutting force and temperature is desirable for machining polyetheretherketone (PEEK). The cutting force is dependent on friction and shearing action produced by the tool. It is indicated the cutting force is significantly affected by tool cutter geometry. This paper aims to control the cutting force by optimizing the cutter geometries especially rake, clearance and helix angle on machining PEEK. The two –flutes of solid carbide ball nose end mills were used to conduct the experiments and the cutting force acquired was measured using piezoelectric dynamometer. Response Surface Methodology (RSM) approach was applied to design and analyse the optimal combination of tool geometry feature for machining PEEK. Based on obtained results, the best optimal values of tool geometry which contribute to minimum of cutting force were 17° rake angle, 26° of helix angle and 10° of clearance angle. The best control of tool geometry ultimately improves the cutting performance and reduces defect caused by high cutting forces.