Expansion Compensation Research Articles

Mixed anion control of enhanced negative thermal expansion in the oxysulfide of PbTiO3.

The rare physical property of negative thermal expansion (NTE) is intriguing because materials with a large NTE over a wide temperature range can serve as high-performance thermal expansion compensators. However, the applications of NTE are hindered by the fact that most of the available NTE materials show small magnitudes of NTE, and/or NTE occurs only in a narrow temperature range. Herein, for the first time, we investigated the effect of anion substitution instead of general Pb/Ti-site substitutions on the thermal expansion properties of a typical ferroelectric NTE material, PbTiO3. Intriguingly, the substitution of S for O in PbTiO3 further increases the tetragonality of PbTiO3. Consequently, an unusually enhanced NTE with an average volumetric coefficient of thermal expansion of V = -2.50 × 10-5 K-1 was achieved over a wide temperature range (300-790 K), which is in contrast to that of pristine PbTiO3 (V = -1.99 × 10-5 K-1, RT-763 K). The intensified NTE is attributed to the enhanced hybridization between Pb/Ti and O/S atoms by the substitution of S, as evidenced by our theoretical investigations. We therefore demonstrate a new technique for introducing mixed anions to achieve a large NTE over a wide temperature range in PbTiO3-based ferroelectrics.

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.

Negative thermal expansion mechanical metamaterial using the swastika shape

Materials and structures operating under thermal fluctuation encounter thermal expansion and/or thermal stresses, which require components that allow expansion compensation in certain directions and zero expansion in other directions. A 2D mechanical metamaterial with negative thermal expansion and zero thermal expansion in the in-plane and out-of-plane directions, respectively, is established herein by inspiration from the swastika shape. The swastika units are rigid and are interconnected to each other by positioning the connecting materials, which possess high thermal expansion, at the inner surfaces of the swastika arms. In this way, thermal expansion of the connecting materials tends to draw the swastika units towards each other, thereby generating an overall thermal contraction. Theoretical results indicate that the negativity of the thermal expansion is enhanced by the size of the connecting materials, but suppressed by the size of the swastika units. The results also reveal that the connecting material thickness and the swastika arm length exert major roles while the connecting material length and the swastika arm width play minor roles in influencing the effective thermal expansion coefficient of the metamaterial. These observations offer solutions for quick coarse-tuning and slow fine-tuning of the metamaterial’s CTE. Although swastikas have cultural, religious, and even political connotations, the author would like to clarify that the swastika considered herein has been used purely for its geometric shape. The author does not intend to convey any cultural or ideological meaning by its use in this article.

Piping riser isolation to prevent transmission of noise and vibration in high rise structures

Preventing the transmission noise and vibration in high rise construction through risers utilizing Spring Isolators is the easiest way to achieve the acoustic criteria for the structure and eliminate weak links (expansion compensators and flexible connectors) in the piping system. We first published literature on the topic in the late 1980s. By utilizing standard calculations for thermal expansion and contraction and selecting a proper anchorage point, isolating risers with spring mounts is simple. This paper is written as a design and installation guideline which addresses concept, design, estimating, and installation.

In-situ expansion compensation and repetitive self-healing of concrete using difunctional artificial aggregates

A difunctional artificial aggregate (DAA) was developed to address autogenous shrinkage caused by self-desiccation of concrete during early hydration in this study. Through in-situ combination with a tri-component healing agent, comprising ammonium acetate CH3CCONH4, ammonium bicarbonate NH4HCO3, and ammonium carbamate NH2COONH4, repetitive self-healing for cracks can be achieved. The expansion product can provide additional free calcium to enhance the self-healing process. Compensatory self-healing is triggered by exposing the internal tri-component to over-expansion, where both expansion compensation and repetitive self-healing are independent but interact with each other. At a 2% DAA dosage, appropriate compensation for hydration expansion was achieved while maintaining specimen volume integrity. The compensatory self-healing of the 4% group was effective for 60 days, while the 8% group exhibited the lowest self-desiccation effect and densest pore structure. In the twice self-healing experiment involving the 0% and 2% groups, various measurements were taken to evaluate healing efficiency, including sound velocity, compressive strength, and quantitative characterisation of calcium carbonate (CaCO3). Results showed a higher healing rate for the second self-healing compared to the first (167.13%, 37.76%, and 12.4% compared to 146.05%, 23.36%, and 7.2%, respectively). This confirmed that the self-healing efficiency increased with the regeneration of NH4HCO3, which increased with the number of self-healings.

CATS: A high‐performance software framework for simulating plant migration in changing environments

Abstract Considering local population dynamics and dispersal is crucial to project species' range adaptations in changing environments. Dynamic models including these processes are highly computer intensive, with consequent restrictions on spatial extent and/or resolution. We present CATS, an open‐source, extensible modelling framework for simulating spatially and temporarily explicit population dynamics of plants. It can be used in conjunction with species distribution models, or via direct parametrisation of vital rates and allows for fine‐grained control over the demographic and dispersal processes' models. The performance and flexibility of CATS is exemplified (i) by modelling the range shift of four plant species under three future climate scenarios across Europe at a spatial resolution of 100 m., and (ii) by exploring consequences of demographic compensation for range expansion on artificial landscapes. The presented software attempts to leverage the availability of computational resources and lower the barrier of entry for large‐extent, fine‐resolution simulations of plant range shifts in changing environments.

Increasing the static and dynamic accuracy of the parallel structure mechanism for space application

The article considers the control system of a parallel structure mechatronic device for space application such as a hexapod (Stewart platform). The solution of the inverse problem of kinematics is described and the necessity of solving the direct problem of kinematics by numerical methods is substantiated. During the research, it was revealed that the main source of positioning errors of the hexapod without the main feedback is its linear drives, which have systematic errors in the mechanical part of the linear transmission, gearbox, in the location of the motor windings; temperature errors due to changes in the dimensions of parts due to heating or cooling; errors caused by elastic deformations under load. To improve the static accuracy of the hexapod, a number of both design and software solutions are proposed: mechanical transmission preload, individual calibration of each drive, compensation for thermal expansion, etc. To improve the dynamic accuracy, it is proposed to use the method of controlling linear drives in the servo mode along with ensuring the trajectory of the platform with the limitation of the speed of its movement and derivatives of the speed. The use of these methods makes it possible to significantly improve the accuracy of the operation of the mechanisms of a parallel structure and, thereby, to approach the achievement of the limiting qualitative properties of onboard optical-electronic and information systems of spacecraft and stations.

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.

Lizard species on three islands off the Mexican Pacific Coast: effects of insularity

This study provides a descriptive panorama of the lizard communities on 3 islands and the mainland on the Pacific coast of Mexico, estimating the effect of insularity (ecological changes between lizards on the islands and on the mainland) on lizard populations. The panorama included the number of species, encounter frequency and age classes. The insularity effects were estimated by comparing these variables, as well as basking behavior, activity related to microclimate, and perch height among the islands and the mainland. Of 11 species recorded, 8 occurred on the islands; however, every insular community was composed of 3 to 5 species (4 are protected by Mexican law). The encounter frequency for all species ranged between 11 and 0.1 individuals per hour. Lizard communities were predominantly composed of adults. Only 2 lizard species, Aspidoscelis communis and A. lineattissima, were shared among all sites, showing no insularity effects on the encounter frequency nor basking behavior. There were signs of insularity, however, on age classes and a clear effect on perch height, suggesting niche expansion. The study contributes to the regional knowledge of lizard species, as well as to ecological theories such as niche expansion and density compensation.

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.

Особенности проектирования высокотемпературных пластинчатых теплообменников для малоразмерных газотурбинных двигателей

An increase in the fuel efficiency of small-sized gas turbine engines can be achieved by regenerating the heat of the turbine exhaust gases. A rational layout solution in this case is a turboshaft scheme, where the effective power is generated on the shaft of a free turbine, and the turbine exhaust gases are released into the environment without doing useful work. When creating a turboshaft engine with heat recovery, the concept of developing engine family on the base of unified gas-generator was considered. The concept involves the development of a modular system, where the addition or exclusion of individual large units allows changing the type of engine at minimal cost. The article presents the layout solution of a small-sized turboshaft gas turbine engine with heat recovery, developed on the basis of a unified gas-generator and using a gearbox to transfer effective power to a propeller or a rotor. A plate heat exchanger module with a corrugated heat exchange surface for a small-sized turboshaft gas turbine engine has been designed. The heat exchange matrix was developed using a complex techniques of computer-aided design, calculation and manufacture of plate heat exchangers. Some design features of high-temperature plate heat exchangers are identified, the most important of which is the non-uniformity of temperature fields in the heat exchange matrix. Taking into account the non-uniformity of temperature fields, the heat exchanger module is a collapsible structure allowing the replacement of the heat exchange matrix and providing compensation for thermal expansion of the heat exchanger elements. The designed plate heat exchanger module for a small turboshaft gas turbine engine will be manufactured and tested on the bench

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.