Near-zero Expansion Research Articles

Small organic molecules for aqueous zinc-ion batteries with stable structure and ultrafast H-ion and Zn-ion diffusion kinetics via coating

Aqueous Zn-ion batteries (AZIBs) with excellent electrochemical performance are achieved by using small organic molecules VO(acac)2 (IV) as cathode. The surface area and electrical conductivity of IV are increased by coating wrinkled rGO, thereby improving the electrochemical sluggishness of IV cathode. The VO(acac)2@rGO (IV@rGO) aqueous battery can display a high capacity of 327.2 mAh g−1 at 100 mA g−1. The Zn2+ and H+ con-insertion/extraction reactions within IV@rGO are a joint control of pseudocapacitance and diffusion process. The in-situ XRD combinded with ex-situ Raman and XPS reveal that the multivalent transition of vanadium and coordination reaction of organic functional groups (VO), and no significant volume change of IV structure implying near-zero expansion characteristic during charging/discharging process.

Near-Zero Thermal Expansion and High Heat-Resistance Polyimide Films Based on a Symmetric and Rigid Pyrazine Structure

Regarding the applications of polyimide (PI) films in emerging flexible devices and precision apparatus, their low coefficient of thermal expansion (CTE), especially near-zero expansion, is an urgent requirement for weakening the internal stress between the organic/inorganic layers. Other properties of PI films including the high heat-resistance and superior toughness are also demanded in actual scenarios. Herein, a set of PI films was developed by copolymerization of 2,5-bis(4-aminophenyl)pyrazine (PRZ) into a pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) system. The monocrystal analysis of the PRZ monomer reveals its rigid, symmetric, and nearly coplanar steric structure. Thanks to the synergy and balance of flexible ODA and rigid PRZ units in PI chains, the near-zero expansion, high heat-resistance, and optimal mechanical properties of the PI films are simultaneously achieved. Particularly, the PI film with ODA/PRZ = 4.5/5.5 presents a near-zero CTE of −0.41 ppm/K, high glass transition temperature (Tg) of around 417 °C, superior fracture strength of 191 MPa, and initial modulus of 3.83 GPa. Interestingly, via adjusting the ODA/PRZ ratios, the precise control of CTE values can be realized, enabling the thermal expansion matching of PI films on broad types of device substrates, e.g., Cu (15–17 ppm/K) and Si (3–5 ppm/K).

Chemiresistively sensitized SiOC structure for formaldehyde detection under thermal and pressure loading

Chemiresistive SiOC Negative Poisson's ratio structures for gas detection under thermal and pressure loading were constructed by vat photopolymerization and surface sensitization. Metal-organic framework-derived SnO2 nanocubes modification provided the structures with sensing capability, while the high deformation-resistant SiOC substrates protected the integrity and connectivity of the sensing layer. The resulting SnO2/SiOC sensing structures exhibited high selectivity to formaldehyde vapor and showed a response value of 3.6 to 100 ppm formaldehyde vapor. The structures also had a short sensing delay with the response and recovery times of 32 s and 41 s, respectively. Besides, the independent deformation of the units maintained the dimensional accuracy and avoided thermal fatigue failure of the structure at the working temperature by dispersing the thermal stress, at which the coefficient of thermal expansion reached 0.71 × 10−6/K, revealing a near-zero expansion behavior. Meanwhile, the mechanical performance can be adjusted by structure optimization, and the compressive strength and Young's modulus of the structure reached 51.25 MPa and 5.14 GPa, respectively. Taking advantage of the strengthened and self-adaptive design, the structure exhibited high load-carrying capacity and low thermal expansion performance, providing a facile strategy for highly stable gas detection under complex loading environments.

Highly porous LAS-SiC ceramic with near-zero thermal expansion prepared via aqueous gel-casting combined with adding pore-forming agents

The main problem during preparing high porosity ceramics via aqueous gel-casting is the large drying shrinkage of green bodies. In this work, carbon fibers with high aspect ratio were introduced into aqueous gel-casting processes, which significantly inhibited the drying shrinkage of green bodies by overlapping fibers. At the same time, exhaustible carbon fibers sintered in air also act as sacrificial templates to further improve the porosity. Through the above method, porous LAS/SiC ceramics with high porosity and near-zero expansion were prepared. Drying shrinkage of the green bodies was reduced from 25.2% to 5.7% with the increase of fibers. The porosity of the obtained LAS/SiC ceramic is as high as 76.2%. When the fibers content is 20 vol% and LAS to SiC volume ratio is 6: 4, the composite has maximum value of compression and bending strength (18.2 and 14.0 MPa) and near-zero CTE (0.9 × 10−6 /K).

Near-zero expansion of ceramics by 3D printing thermally induced torsional structures

Structural materials with high bearing capacity and low expansion have great application demand in precision instruments. Negative Poisson's ratio structure with thermally induced torsion ability is promising as the structure stretching, bending, and twisting can disperse the thermal stress. Besides, the thermal expansion performance can be further optimized by the coordinating control of macrostructure and composition. Herein, the work investigated the bearing capacity and expansion behavior of Negative Poisson's ratio structures fabricated by digital light processing (DLP) 3D printing. Negative expansive LiAlSiO4 was further introduced to reduce thermal expansion. The thermal shrinkage of the LiAlSiO4 compensated for the volume change caused by thermal expansion. Ultimately, the LiAlSiO4 infiltrated Negative Poisson's ratio structures with torsion angles of 120° had an average CTE of 1.90 × 10-6 /K. The compressive strength, Young’s modulus, and work of fracture reached 7.36 MPa, 19.65 GPa, and 1.61 KJ/m2, respectively, which had the potential in high bearing capacity and low expansion application.

A near-zero thermal expansion material: AlMoVO7

An orthorhombic AlMoVO7 was synthesized by solid-state method. Its phase, expansion property, and Raman spectra were analyzed in detail. Analysis showed that AlMoVO7 has near-zero expansion in 173–673 K. With increasing temperature, the librational and translational vibrations of [AlO6] and [MoO4] caused the Al-O-Mo chain bending. The thermal expansion of AlMoVO7 unit cell has an anisotropic and near-zero expansion. The thermal expansion performance of AlMoVO7 block depends on its unit cell structure and microstructure. Therefore, near-zero expansion in 173–673 K is shown.

Influence of high-energy milling and heat treatment on the thermal and mechanical properties of a ZrMgMo3O12p/2024Al composite

In this study, ZrMgMo 3 O 12particle (p) /2024Al composites were fabricated with 10 vol% of a near-zero expansion material, ZrMgMo 3 O 12 , as a reinforcement via high-energy milling followed by vacuum hot pressing (VHP). The influences of the milling conditions and the heat treatment on the hardness, thermal expansion properties and dimensional stabilities of the composites were studied. The results show that high-energy (HE) ball milling refined the ZrMgMo 3 O 12 particles and the grains of the α-Al matrix, increased the hardness and decreased the coefficients of thermal expansion (CTEs) of the ZrMgMo 3 O 12p /2024Al composites. Compared with those of the ZrMgMo 3 O 12p /2024Al composites prepared via low-energy (LE) milling, the hardness value increased to 183 HV from 91.8 HV and the CTE decreased to 16 × 10 −6 /°C (RT - 400 °C) from 22 × 10 −6 /°C (RT - 300 °C). Heat treatment of the solution for 24 h followed by ageing at 190 °C for 5 h (i.e., P2 process) further increased the hardness value to 277 HV and decreased the CTE to 13.4 × 10 −6 /°C (RT - 400 °C), which represent an increase of 83% and decrease of 39%, respectively, compared with those of the heat-treated LE ZrMgMo 3 O 12p /2024Al composites. High-energy ball milling and heat treatment could improve the dimensional stabilities of the composites as well. In particular, the HE ZrMgMo 3 O 12p /2024Al composites heat treated with the P2 process showed no variation in their hysteretic strain or CTEs during thermal cycling from RT to 400 °C. Therefore, the P2 HE ZrMgMo 3 O 12p /2024Al composites are in a thermostable state and have the best dimensional stabilities of the tested samples.

In Situ High-Temperature Crystallographic Evolution of a Nonstoichiometric Li2O·2SiO2 Glass

In this work, the high-temperature crystallographic evolution of crystalline phases in a complex lithium disilicate glass was investigated using synchrotron X-ray powder diffraction. The lattice parameters and unit cell volume of Li2SiO3 (LS), Li2Si2O5 (LS2), Li3PO4 (LP), and ZrO2 as a function of temperature were determined upon heating. It is found that the lattice parameter c of LS2 shows a "V"-shaped trend during heating. The crystallographic evolution of the LS2 phase has a close correlation with the LS phase, indicating the mutual interaction between LS and LS2 phases along the c axis during the nucleation/crystallization process. The phase evolution processes were different upon heating and cooling, and the unit cell volume of both LS and LP phases demonstrated different change rates. In this glass system, no LS2 was detected during cooling and the main phases formed during cooling process were LP, LS, β-cristobalite, and β-quartz. Interestingly, there were two forms of β-quartz with slightly different lattice constants, and the silica phases showed a near-zero expansion behavior. The crystallographic evolution mechanism is discussed.

Negative thermal expansion in Th 2O(PO 4) 2

High temperature X ray diffraction performed on recently discovered orthorhombic Th 2O(PO 4) 2 shows a continuous linear thermal contraction (−1.6 × 10 −6 °C −1) in 20–600 °C range and a near-zero expansion at higher temperatures resulting from a dual structural deformation involving oxygen oscillations and inter-cations repulsions. Although similar mechanisms were observed in isotypic Zr 2O(PO 4) 2 (+1.5 × 10 −6 °C −1) and U 2O(PO 4) 2 (−1.4 × 10 −6 °C −1), those observed in Th 2O(PO 4) 2 are particularly intense because of the high ionic radius of tetravalent thorium.

Crystal-chemical approach to predicting the thermal expansion of compounds in the NZP family

The general structural aspects of phosphates with {[L2(PO4)3]p–}3∞ frameworks (L = octahedral cation) are considered, and the possible isomorphous substitutions in NaZr2(PO4)3 (NZP) phosphates are analyzed. The available data on the thermal expansion of NZP materials in the range 293–1273 K, together with crystal-chemical data on their structure, are used to identify the processes underlying the thermal expansion of these materials. The results provide basic guidelines in designing NZP-based materials with controlled (ultralow) thermal expansion and near-zero expansion anisotropy.

On the Effective Coefficient of Thermal Expansion in Thermal Bending of Composites Undergoing Linear Heat Flow

It is suggested that the localized stresses and associated displacements resulting from the thermal conductivity mismatch of second-phase inclusions in dispersed phase-continuous matrix composites subjected to linear heat flow can contribute to the thermal bending (i.e., the curvature) of the composite at the continuum level. The original solutions of Tauchert for a single inclusion were used to derive an expression for the curvature and associated effective coefficient of thermal expansion of a matrix with spherical inclusions undergoing linear heat flow. The results are expressed in terms of the isothermal coefficient of thermal expansion, Young's modulus and thermal conductivity of the composite, which, in turn, depend on the relevant properties and volume fractions of the matrix and dispersed phase. Numerical examples are presented which indicate a significant effect. Thermal expansion mismatches between the matrix and dispersed phase are shown to play a particularly large role in either increasing or decreasing the degree of thermal bending, which may even become negative for matrices with near-zero expansion behavior. A numerical example based on a flat composite plate constrained from bending indicates that the above effect can have a large influence on the magnitude of maximum thermal stress.

NZP: A new family of low-thermal expansion materials

A new structural family of low-expansion materials known as NZP has been recently discovered and has generated great interest for wide-ranging applications such as fast ionic conductors, devices requiring good thermal shock resistance, hosts for nuclear wastes, catalyst supports in automobiles, etc. This family is derived from the prototype composition NaZr2P2O12 in which various ionic substitutions can be made leading to numerous new compositions. The bulk thermal expansion of these materials varies from low negative to low positive values and can be controlled and tailored to suit the needs for specific applications. In general, most of the NZP members demonstrate an anisotropy in their lattice thermal expansions, which is the main cause of the low-thermal expansion behavior of these materials. In CaZr4P6O24 and SrZr4P6O24 an opposite anisotropy has been observed which has led to the development of near-zero expansion crystalline solution composition. On the basis of the coupled rotations of the polyhedral network formed by ZrO6 octahedra and PO4 tetrahedra, a crystal structure model to interpret and explain the thermal expansion behavior has been discussed.

High-temperature crystal chemistry of phenakite (Be2SiO4) and chrysoberyl (BeAl2O4)

Thermal expansion and high-temperature crystal structures of phenakite and chrysoberyl have been determined by x-ray methods at several temperatures to 690° C. Phenakite (hexagonal, space groupR $$\bar 3$$ ) has slightly anisotropic thermal expansion; average expansions between 25 and 690° C perpendicular and parallel to thec axis are α⊥=5.2×10−6 °C−1 and α∥=6.4×10−6 °C−1, respectively. The unit cell volume of phenakite over this temperature range is given by the polynomial expression:V = 1102.9(2) + 0.010(2)T + 1.1(3) × 10-5 T 2. Chrysoberyl (orthorhombic, space groupPbnm) has nearly isotropic thermal expansion, with maximum expansivity 8.5×10−6 °C−1 parallel to theb axis, and minimum expansivity 7.4×10−6 °C−1 parallel toa. Thec axis expansivity is 8.3×10−6 °C−1. Chrysoberyl volume between 25° and 690° C may be represented by:V = 227.1(2) + 0.003(1)T + 4(2) × 10-6 T 2. The thermal expansion of beryllium, aluminum, and silicon cation coordination polyhedra in phenakite and chrysoberyl are similar to values found in previous studies of minerals in the BeO-Al2O3-SiO2 system. High-temperature structure studies of bromellite (BeO), beryl (Be3Al2Si6O18), phenakite and chrysoberyl all have beryllium tetrahedra that display the same near-zero expansion at room temperature, but increasing expansion at higher temperatures.

Composite route to ?zero? expansion ceramics

The use of diphasic or multiphasic composites, involving one negativeα phase to control and lower the thermal expansion of a ceramic for substrate, laser mirror and anti-thermal shock applications, was studied. The two phases thermodynamically stable with each other — one with negativeα and the second with positiveα were mixed, sintered and characterized for thermal expansion behaviour. The negative-α phase was selected from the [NZP] or [CTP] structural family. Specific systems including NaZr2P3O12, CaZr4P6O24 + Nb2O5, GdPO4, ZrSiO4, Mg3(PO4)2, MgO and ZnO were investigated. Several compositions exhibited a near-zero expansion profile over a wide temperature range.

CTP]: A new structural family of near-zero expansion ceramics

In this paper we report the discovery of a new structural family for use in ultra-low ‘α’ ceramics. The prototype composition is Ca 0.5Ti 2P 3O 12 abbreviated [CTP] after which the structural family is named. The importance of this family in contrast to the eucryptite-spodumene family is the enormous range of substitutions which are possible, permitting one to control ‘α’ continuously over a wide range of temperature. Different compositions exhibit near zero thermal expansion in different temperature ranges.