Thermal Expansion Compensation Research Articles

Giant auxetic behavior in remote-plasma synthesized few-layer tungsten semicarbide.

Auxetic crystals exhibiting highly positive lateral expansivity when stretched are an experimentally elusive class of two-dimensional (2D) materials with tremendous potential, for example in the direct transduction of electric signals and the compensation of thermal expansion at the nanoscale. 2D tungsten semi-carbide (W2C) was theoretically predicted to exhibit giant auxetic behavior, but has yet to be synthesized, as the corresponding full carbide (WC) is energetically favored under thermodynamic equilibrium synthesis processes such as furnace-based chemical vapor deposition. Here, we report on an ad hoc designed dual-zone remote plasma deposition system specially conceived to grow tungsten carbides out of thermodynamic equilibrium with well-tuned ratios of W and C precursors. We report on the specific conditions under which this system allowed for the synthesis of flakes of few-layer tungsten semicarbide (FL-W2C) which are 2D in nature due to retained periodicity at the mesoscopic level in a Stranski-Krastanov growth process. Under applied strain, FL-W2C 2D crystals exhibit the strongest auxetic behavior observed to date. This result suggests that the theoretically predicted high negative Poisson's ratio of single-layer W2C, also extends to thicker FL-W2C flakes that are retaining the periodicity of the 2D crystal at the mesoscopic level.

A Negative Thermal Expansion Metamaterial Inspired by the Sicilian and Manx Symbols

A negative thermal expansion (NTE) metamaterial is established herein by inspiration from the Sicilian and Manx symbols to form rigid units of the metamaterial. By attaching connecting material of positive thermal expansion to the rigid units, the resulting metamaterial exhibits NTE. Analytical forms for the effective coefficients of thermal expansions (CTE) were established using infinitesimal and finite deformation assumptions for small and large temperature changes, respectively. Results indicate that the negativity of this metamaterial’s thermal expansion is enhanced with the thickness of the connecting material but decreases with the dimensions of the rigid units. The transverse isotropy for this metamaterial’s CTE is useful if thermal expansion compensation is required in two orthogonal directions but zero thermal expansion is required in the remaining orthogonal direction.

Engineered colossal linear thermal expansion in nanocrystalline NiTi micropillars by stress

Materials with unusual large negative and positive thermal expansions are attractive for applications in high-precision actuation and thermal expansion compensation. So far, such unusual property has been reported in a variety of framework materials and polymers but it remains challenging to obtain in metals. Here, we report a colossal linear thermal expansion in single-phase nanocrystalline NiTi ferroelastic alloy under uniaxial compressive stress. By microscale isothermal severe plastic deformation, we fabricated fully austenitic and martensitic NiTi nanocrystalline micropillars that respectively possess high yield stresses of 2.65 GPa and 2.23 GPa and strong negative, and positive temperature dependence of Young′s modulus (dE/dT). We demonstrate that due to the large dE/dT, the coefficient of linear thermal expansion (CTE) of the austenitic and martensitic NiTi micropillars can be tailored to values of +106×10−6 K–1 and -88×10−6 K–1 by applying 2.5 GPa and 2.0 GPa compressive stress. Such tailored CTEs are approximately 10 times larger than the typical value (∼10×10−6 K–1) of metallic materials. Our work provides a mechanical route to obtain colossal positive and negative thermal expansion in single-phase nanostructured ferroelastic alloys at microscale.

Temperature dependent phase transition and negative thermal expansion of Hg2Cl2 compound: insights from first-principle DFT and Born-Oppenheimer on the fly molecular dynamics calculations

ABSTRACT The paper is aimed to understand the key phonon modes that are responsible for the temperature dependent structural phase transition and negative thermal expansion of Hg2Cl2 compound for the first time with the aid of density functional theory and Born-Oppenheimer on the fly molecular dynamics calculations. The phonon dispersion spectra, phonon density of states and Grüneisen parameters for the body-centered tetragonal and base-centered orthorhombic phases of the compound have been explored in detail. The order parameter associated with the phase transition and its nature has also been reported herewith. We believe that the present study will not only help for futuristic designs of improved functionalized systems with Hg2Cl2 compound but also can augment their applications in thermoelectric conversion systems, fibre-optic communications, thermal expansion compensators and in fuel cells.

Systematic Study on the Role of the Third Zn-Site Element in Zn<sub>2−</sub><i><sub>x</sub></i>Mg<i><sub>x</sub></i>P<sub>2</sub>O<sub>7</sub> Showing Giant Negative Thermal Expansion

For Mg-doped Zn2P2O7, this systematic investigation of co-doping onto Zn sites has elucidated specific effects on negative thermal expansion (NTE). The low-cost and low-environmental-impact NTE material Zn2−xMgxP2O7 shows large NTE in a temperature range including room temperature for x = 0.4. Although Mg doping broadens the operating-temperature window, it remains several dozen degrees wide. Moreover, the total volume change related to NTE becomes less than that of the Zn2P2O7 parent material. Findings obtained from this study demonstrate that co-doping of Mg and of another element onto the Zn site is effective for achieving simultaneous expansion of the operating-temperature window and maintenance of the volume change related to NTE. One illustrative case is that Zn1.64Mg0.30Al0.06P2O7 has a large negative coefficient of linear thermal expansion of about −65 ppm/K at temperatures of 300–375 K. In fact, at temperatures high above room temperature, Zn1.64Mg0.30Al0.06P2O7 powder shows better thermal expansion compensation capability than the composition without Al. The Al-doped phosphates are expected to have broad practical application because of their performance, cost, and environmental load characteristics.

Testing of ITER diagnostic pressure gauges in preparation of final design review

Hot cathode ionization gauges will measure neutral gas pressures in the vacuum vessel of ITER. Overall 52 gauge heads are distributed in the divertor, the equatorial ports and pumping ducts. Present design and prototype testing of diagnostic pressure gauge (DPG) heads is presented. Focus is on the development of a novel type of cathode, which is able to overcome major issues that emerged during the preliminary design phase. In comparison with the formerly employed yttria coated tungsten–rhenium filament, the operational stability of the present cathode, which uses an indirectly heated plate of zirconium carbide as the electron emitter, is enhanced in terms of needed heating current and accuracy. A major issue of filament deflection by electromagnetic forces was overcome through the rigid setup, which still allows for the compensation of differential thermal expansion and provides a high reproducibility in manufacturing. Reliable functioning for long periods was proven successfully in a superconducting magnet, covering the required pressure range. Prototype testing revealed an issue during permanent operation in hydrogen at high pressures: erosion can lead to limited life-time of the cathode. The introduction of interlayer foils can retard but not completely inhibit the process. A possible mechanism based on reaction and diffusion of carbon is proposed.

Temperature-compensated optical cavities for laser frequency stabilization

We propose a method for thermal expansion compensation of reference monolithic optical cavities for laser frequency stabilization. Two schemes of optical cavities are considered: a Fabry–Perot interferometer with a crimp ring and a whispering-gallery-mode cavity with a clamp. In each scheme, thermal expansion compensation is achieved due to the strained connection of the cavity with an element made of a material with a high coefficient of thermal expansion. The temperature range of the cavities’ optical length stabilization is estimated.

Multiple roles of negative thermal expansion material for high-performance fully-air processed perovskite solar cells

For fully-air-processed perovskite solar cells (PSCs), high-quality perovskite films and improved intrinsic stability are critical for high photovoltaic performance. However, strain, as a critical factor of perovskite instability, not only harms the efficiency of PSCs but also accelerates the degradation of the PSCs devices. In this report, we introduce a novel negative thermal expansion (NTE) material into perovskite film for the first time, growing a high-quality perovskite films with high crystallinity, large grain size and low defect density. More importantly, effective residual strain relaxation of perovskite films is achieved, the thermal expansion compensation properties of NTE materials reduces the overall thermal expansion coefficient for perovskite films. As a result, the fully-air processed PSC achieves a champion power conversion efficiency (PCE) of 22.40 %. Simultaneously, the unencapsulated device retains 93.78 % of its original PCE after storage in ambient air after 90 days. Furthermore, these devices also show excellent thermal stability and remarkable light stability. The present study not only provides insights into the multi role of NTE materials, but also provides a new path for the application of NTE materials in the photovoltaic field.

Tailoring Negative Thermal Expansion via Tunable Induced Strain in La-Fe-Si-Based Multifunctional Material.

Zero thermal expansion (ZTE) composites are typically designed by combining positive thermal expansion (PTE) with negative thermal expansion (NTE) materials acting as compensators and have many diverse applications, including in high-precision instrumentation and biomedical devices. La(Fe1-x,Six)13-based compounds display several remarkable properties, such as giant magnetocaloric effect and very large NTE at room temperature. Both are linked via strong magnetovolume coupling, which leads to sharp magnetic and volume changes occurring simultaneously across first-order phase transitions; the abrupt nature of these changes makes them unsuitable as thermal expansion compensators. To make these materials more useful practically, the mechanisms controlling the temperature over which this transition occurs and the magnitude of contraction need to be controlled. In this work, ball-milling was used to decrease particles and crystallite sizes and increase the strain in LaFe11.9Mn0.27Si1.29Hx alloys. Such size and strain tuning effectively broadened the temperature over which this transition occurs. The material's NTE operational temperature window was expanded, and its peak was suppressed by up to 85%. This work demonstrates that induced strain is the key mechanism controlling these materials' phase transitions. This allows the optimization of their thermal expansion toward room-temperature ZTE applications.

Front-end hybrid designs for the CMS Phase-2 Upgrade towards the production phase

Sixteen thousand 2S front-end hybrids and twelve thousand PS front-end hybrids will be produced for the CMS Tracker Phase-2 upgrade. The hybrids consist of flip-chips, passives and mechanical components mounted on a flexible substrate, laminated onto carbon-fibre stiffeners with thermal expansion compensators. In the prototyping phase, several critical issues have been solved to manufacture these complex circuits. Final designs are now reaching readiness for the full-scale production. Lessons learned during the prototyping phase and different improvements implemented for manufacturability will be presented in this contribution.

Structural phase transition and giant negative thermal expansion in pyrophosphate Zn2–xMgxP2O7

By tuning the structural phase transition in Zn2–xMgxP2O7, large negative thermal expansion (NTE) was achieved at room temperature. An earlier report described that Zn2P2O7 undergoes a structural phase transition at 405 K, accompanied by volume contraction of 1.8% on heating. Results showed that as Mg doping proceeds, the transition temperature decreases. Also, the volume change becomes gradual with respect to temperature. Particularly, Zn1.6Mg0.4P2O7 has a large negative coefficient of linear thermal expansion αL of −60 ppm/K at 280–350 K. Structural analysis using synchrotron radiation revealed that this dilatometric NTE is almost identical to that of crystallographic unit cells, indicating less dominant structural effects on NTE. We also verified thermal expansion compensation capabilities of powdered Zn1.6Mg0.4P2O7 by evaluating the thermal expansion of the epoxy resin matrix composites. The present phosphates are promising for use as practical thermal expansion compensators because they are free of toxic or expensive elements and can be fabricated in air using the simple solid-state reaction method.

Negative Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings.

A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.

Anisotropic elasticity drives negative thermal expansion in monocrystalline SnSe

Negative thermal expansion (NTE) materials have been at the center of attention for the past few decades as thermal expansion compensators in the fields of engineering, photonics, electronics, and medicine. Numerous crystalline materials exhibit NTE, wherein a combination of positive and negative linear thermal expansion coefficients results from their highly anisotropic elasticity. In this study, we selected SnSe, an anisotropic uniaxial NTE material as a model system where theoretical studies have linked its NTE along the $c$ direction to transverse phonons and to positive Gr\uneisen parameters along all crystallographic axes. However, the fundamental origin of NTE in SnSe have not been experimentally resolved. Here we performed temperature-dependent resonant ultrasound spectroscopy (between 295--773 K) on single-crystalline SnSe to experimentally measure all nine independent elastic constants (${C}_{11}, {C}_{22}, {C}_{33}, {C}_{44}, {C}_{55}, {C}_{66}, {C}_{12}, {C}_{13}, {C}_{23}$). Our data revealed a high degree of anisotropy in the temperature-dependent elastic constants with shear anisotropic factors show a contrasting pattern with increasing temperature. From this data we also deduced its material compressibility and negative Poisson's ratios in the major crystallographic directions that could explain its colossal linear thermal expansion coefficient along the $c$ direction, reaching $\ensuremath{\sim}--12\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at 773 K as reported in this study. Furthermore, we confirmed positive Gr\uneisen parameters along all the crystallographic axes and observe that SnSe behaves like a semicompressible parallelepiped with elastically coupled $a$ and $b$ axes, with the NTE being driven by the displacement of Sn atoms in the $c$ direction.

Large negative thermal expansion promoted by microstructure in hexagonal Fe1−xCoxS

Materials showing negative thermal expansion (NTE) can be used as thermal expansion compensators. Here, we report the NTE behavior in hexagonal Fe1−xCoxS (0 ≤ x ≤ 0.15) alloys. NTE appears near room temperature when x is increased to 0.09, shifts to lower temperature as x increases, and finally disappears for x ≥ 0.15. For x = 0.10, the inherent volumetric coefficient of thermal expansion (αV) measured by diffraction method is about − 29.8 ppm/K. However, the value obtained by dilatometric method is increased to − 97.2 ppm/K. The pores among the grains in polycrystalline sample are suggested to account for the extra NTE performance. The present study suggests that the NTE of the alloys with anisotropic lattice thermal expansion can be adjusted effectively by controlling the microstructure.

MATERIALS AM2О8 (А = Zr, Hf; М = W, Mo) WITH NEGATIVE THERMAL EXPANSION

The data on AM2О8 materials (А = Zr, Hf; M = Mo, W) exhibiting negative thermal expansion are reviewed. Synthesis methods, polymorphs, thermal properties, and the possibility of using these materials as thermal expansion compensators in composites are considered.

Enhanced negative thermal expansion of boron-doped Fe43Mn28Ga28.97B0.03 alloy

Enhanced negative thermal expansion (NTE) properties are achieved by introducing a little amount of boron in the Fe43Mn28Ga28.97B0.03 alloy. As a result, this alloy shows a giant NTE coefficient of αl = −79.7 × 10−6 K−1 in a wide temperature range from 277 K to 136 K. Compared to the NTE characteristics in Fe43Mn28Ga29, the NTE operation temperature window has expanded by 74% with the corresponding coefficient of thermal expansion increased by 57% within the NTE temperature window for the boron-doped Fe43Mn28Ga28.97B0.03. In-situ synchrotron high-energy X-ray diffraction results suggest that by boron substitution, the large unit cell volume change across martensitic transformation and the wide phase transition temperature interval are responsible for the pronounced NTE behavior in Fe43Mn28Ga28.97B0.03. Moreover, for the Fe43Mn28Ga28.97B0.03 NTE material, the compressive strength and strain are significantly improved compared with that of Fe43Mn28Ga29. The present study indicates that Fe43Mn28Ga28.97B0.03 with enhanced NTE across martensitic transformation may be used for practical application as thermal-expansion compensators.

E-Clutch Torque Control Including Compensation of Thermal Expansion Effects

The E-clutch considered is a dry clutch automated by means of a hydrostatic actuator, whose master cylinder is driven by an electric servomotor through a spindle drive. The paper deals with design of E-clutch open-loop torque control strategy which includes compensation of clutch thermal expansion effects. A series of experiments have been conducted by using a custom-designed E-clutch test rig, in order to characterize influence of thermal effects on clutch control performance. A comprehensive analysis of test data reveal a strong correlation of clutch torque reduction and E-clutch slave cylinder (CSC) position increase caused by clutch pack thermal expansion. The determined dependence, where CSC position measurement serves for quantification of thermal effects, is incorporated within the clutch torque control strategy for the sake of thermal effects compensation. Furthermore, it is found out that the CSC position can be effectively estimated based on clutch temperature inputs, thus implying that the CSC position sensor can be omitted, while still keeping the possibility of effective thermal expansion compensation. The proposed clutch control strategy is examined based on experimental data acquired for two clutch friction plates/materials.

Giant anisotropic thermal expansion actuated by thermodynamically assisted reorientation of imidazoliums in a single crystal

Materials demonstrating unusual large positive and negative thermal expansion are fascinating for their potential applications as high-precision microscale actuators and thermal expansion compensators for normal solids. However, manipulating molecular motion to execute huge thermal expansion of materials remains a formidable challenge. Here, we report a single-crystal Cu(II) complex exhibiting giant thermal expansion actuated by collective reorientation of imidazoliums. The circular molecular cations, which are rotationally disordered at a high temperature and statically ordered at a low temperature, demonstrate significant reorientation in the molecular planes. Such atypical molecular motion, revealed by variable-temperature single crystal X-ray diffraction and solid-state NMR analyses, drives an exceptionally large positive thermal expansion and a negative thermal expansion in a perpendicular direction of the crystal. The consequent large shape change (~10%) of bulk material, with remarkable durability, suggests that this complex is a strong candidate as a microscale thermal actuating material.

Evaluation of thermal residual stresses of thin-walled laminated composite pipes to characterize the effects of mandrel materials and addition MWCNTs

This research focuses on finding the effects of the addition of multi-walled carbon nanotubes (MWCNTs) and using various mandrel materials on the ply-level thermal residual stresses of thin-walled laminated filament-wound composite pipes. To accomplish this objective, a few specimens were made by considering two various weight fractions, containing 0 and 3%, for MWCNTs and two various mandrel materials, containing aluminum and steel. This study employed the incremental hole drilling method using integral inverse solution for measuring the thermal residual stresses within the structure. This method contains simulation and experimental parts, which both were explained in details entirely. This paper presents analytical discussions and the experimental results to clarify achievements. The results confirmed that adding MWCNTs, as a thermal expansion compensator, to the epoxy matrix modifies the thermal behavior of the epoxy matrix and reduces the thermal residual stresses in the composite pipes. Also, the results show that the residual stresses are strongly affected by the mandrel thermal expansion coefficient. In this case, for example, the specimen manufactured by the steel mandrel experiences less residual stresses compared to which manufactured by the aluminum mandrel.

Evaluation of open-loop linear drive accuracy achieved by calibration and linear thermal expansion compensation

The study is a part of the current work on the design and creation of a precision mechanism with parallel kinematics such as a space hexapod. The positioning accuracy and repeatability of the movable platform of the machine relative to its fixed base in the structure under consideration depends on the accuracy of the actuating elements of the hexapod – linear drives. The aim of the work is to assess the achievable accuracy of the linear drive, taking into account the main factors affecting the accuracy of its rod movement. The article describes the studies of the accuracy of the open-loop linear drive, which has no common feedback on the output coordinate. The main factors affecting the accuracy of movement are highlighted. The experimentally obtained estimates of the linear drive rod displacement errors are given. A technique is proposed for improving the linear drive accuracy by programmatically calibrating its ball screw drive and compensating for linear thermal expansion (LTE) when the drive is operating in a wide temperature range. An estimate of the calibrated linear drive rod movement accuracy with LTE compensation has been obtained.