Low Expansion Coefficient Research Articles

Dispersion relations, knots polynomials, and the q -deformed harmonic oscillator

We show that the crossing symmetric dispersion relation (CSDR) for 2-2 scattering leads to a fascinating connection with knot polynomials and q-deformed algebras. In particular, the dispersive kernel can be identified naturally in terms of the generating function for the Alexander polynomials corresponding to the torus knot $(2,2n+1)$ arising in knot theory. Certain linear combinations of the low energy expansion coefficients of the amplitude can be bounded in terms of knot invariants. Pion S-matrix bootstrap data respects the analytic bounds so obtained. We correlate the $q$-deformed harmonic oscillator with the CSDR-knot picture. In particular, the scattering amplitude can be thought of as a $q$-averaged thermal two point function involving the $q$-deformed harmonic oscillator. The low temperature expansion coefficients are precisely the $q$-averaged Alexander knot polynomials.

Influence of metallization on the mechanical properties of polyimide films

The need to obtain and study the properties of metallized polymeric materials is associated with their wide application in space exploration, electronics, and the production of consumer goods. The main directions in the search for new materials are aimed at obtaining composite films with different distributions of the metal phase over the thickness while maintaining the mechanical characteristics. The most promising metallized polymer materials are polyimides with high thermal stability, good dielectric properties, and low expansion coefficient. Therefore, the study of viscosity, strength, and other mechanical characteristics of metallized polymeric materials, the determination of the effect of the coating structure on their mechanical behavior, and the development of methods for predicting their behavior are currently relevant and important tasks. Methods for improving the mechanical properties of polyimide films by silver plating have been studied. The thickness of the metal layer of the polyimide base, which is part of the structure, ranged from 1 to 5 μm. Surface coatings were 80–97% of comparable silver mirrors in the visible and infrared regions. The deformation of the samples was carried out at room temperature on an Instron 5982 universal testing machine in the uniaxial tension mode. As a result of the metallization of the films, a significant increase in mechanical characteristics was observed compared to a pure polyimide film. An increase in ultimate strength by ∆σ = 105 MPa and plasticity by ∆ε = 75% was obtained, which is associated with a change in the structure of metallized films and the conditions of their chemical treatment.

Bio-based trifunctional diphenolic acid epoxy resin with high Tg and low expansion coefficient: synthesis and properties

Bio-based trifunctional diphenolic acid epoxy resin with high Tg and low expansion coefficient: synthesis and properties

Three-dimensional porous tungsten via DLP 3D printing from transparent ink

Tungsten, an essential refractory metal material, has the characteristics of high melting and boiling points, high hardness, low expansion coefficient, and low vapor pressure. An indirect strategy to print three-dimensional (3D) refractory metal materials via digital light processing (DLP) followed by a post-treatment process was proposed. To analyze this strategy, a transparent ink with tungsten salts was developed, printed into a 3D precursor via DLP, and subsequently transited into 3D porous tungsten. The ultraviolet rheological properties and stability of the ink, transition process from the precursor to a 3D article, and the properties of the obtained 3D porous tungsten were investigated. This ink was preferable for DLP 3D printing, possessing consistency, stability and favorable absorbance at the wavelength of 385 nm. With increasing temperature, the weight of the tungsten salt in the 3D precursor decreased by 8.97% and was transited to tungsten oxide below 460 °C, reduced to pure nano-sized tungsten at approximately 700 °C, and finally sintered into porous articles. The organics initially contributed to polymerization during printing as well as reduction as a carbon reducer after pyrolysis. The pore size distribution of porous tungsten is nonlinear or multimodal, depending on the final sintering temperature. At 1200 °C, two distinct peaks are observed in the pore distribution curves of the products. At 1400 °C, the small pore as a whole decreases from approximately 100–1000 nm. Correspondingly, the relative density of the samples increased with temperature.

Ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics containing multiphase nanocrystals

AbstractLi2O–Al2O3–SiO2‐based glass–ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire‐safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O–MgO–Al2O3–SiO2 glass–ceramics were prepared by conventional melt‐quenching and subsequent heat‐treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass–ceramics was highly dependent on MgO/Li2O ratios in glass components and heat‐treatment temperatures, corresponding with the crystal phases in glass–ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass–ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy‐dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass–ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.

Crystallization behavior and properties of a novel rare-earth rich BaO–SiO2–La2O3 glass-ceramic for millimeter-wave technology

In this work, a novel low permittivity and high expansion coefficient rare-earth rich BaO–SiO2–La2O3 (BSL) glass-ceramic for millimeter-wave technology was systematically investigated by the network structure, crystallization the phase transformation, microstructure and microwave dielectric properties. With the decrease of the SiO2/BaO mol ratio from 3.75 to 0.9, the crystallization activation energy (Ec) of BSL glass calculated by the Kissiger equation continued to fall from 400.65 to 316.85 kJ/mol, and the crystal growth mode of all samples judging by Avrami parameter (n) was 1-D volume crystallization, implying that the crystallization ability of the BSL glass was enhanced. The main crystal phase of BSL glass-ceramic transformed from BaSi2O5 to BaSiO3 phase, coincided with a second phase Ba4La6O(SiO4)6. And then, the relative permittivity εr of BSL glass-ceramic had increased from 7.8 to 11, while quality factor (Q × f), temperature coefficient of frequency τf, and coefficient of thermal expansion (CTE) had decreased with the decrease of SiO2/BaO ratio. By adjusting the mol ratio of SiO2/BaO, the best comprehensive properties of 20BaO–75SiO2–5La2O3 glass-ceramic could be obtained with εr = 7.8, Q × f = 21000 GHz, CTE = 12.39 × 10−6/°C (30–800 °C), which was favorable properties for microwave dielectric applications.

Mechanical properties and microstructure evolution of MgO–Al–C slide plate refractories in presence of Al powder-modified magnesia aggregates

MgO–Al–C slide plate refractories were fabricated using sintered magnesia and modified sintered magnesia as aggregates, fused magnesia aggregates and fines, Al powder and carbon black (N220) as fines, and thermosetting phenolic resin as the binder. Al powder-modified magnesia aggregates were prepared and characterized and were introduced into the MgO–Al–C slide plate refractories. The effects of the modified aggregates on the properties, phase composition, and microstructure were investigated. 1) The Al powder-modified magnesia aggregates exhibited considerably high bonding strengths and low Al powder shedding ratios, thus meeting the preparation requirements of MgO–Al–C slide plate refractories. 2) At high temperatures, more needle-like and fibrous Al 4 C 3 , AlN and octahedral MgAl 2 O 4 were generated on the surface of the modified magnesia aggregates, which enhanced the bond between the matrix and the aggregates and increased the hot modulus of rupture of the material. 3) Non-oxide Al 4 C 3 and AlN phases were formed in situ and had high thermal conductivity and low coefficient of expansion; this could relieve the internal thermal stress of the material and create a toughening effect, improving the thermal shock resistance of the material.

Optimization of beam oscillation on macro/micro formation and mechanical property in low-expansion superalloy laser-welded joint

Low-expansion superalloys have been widely used in aerospace, ships, nuclear power fields due to the high strength and low expansion coefficient. Generally, laser beam oscillation was adopted to solve the defects including poor bead formation, inner pores, and solidification cracks in the weldment of GH909 low-expansion superalloys medium-thick plates. Therefore, the molten pool flow, joint formation, microstructure, and mechanical properties were systematically studied in this paper. Results showed that beam oscillation effectively stabilized the molten pool and keyhole inside, thus forming a well-formed joint without obvious pores. In tensile tests, the strength and elongation of the joint at 300 Hz were measured as 859.5 MPa and 38.6 %, significantly higher than those of laser joint (731.1 MPa and 17.9 %) with plenty of pores and cracks. The average microhardness of the fusion zone (FZ) using laser oscillating welding (LOW) was about 16 HV larger than that of single laser welding (SLW). In FZ, γ/Laves eutectic precipitated phase was distributed discretely without obvious solidification cracks. There existed coherent and incoherent interfaces between eutectic γ and Laves phases. Moreover, coherent interfaces were detected to account for 73.9 %, presenting a major fraction. The improvement of the mechanical properties of LOW joint was mainly caused by solid solution strengthening and precipitation strengthening. This research has a guiding reference for well-formed and high-quality low-expansion superalloy welding and relevant industrial application.

Computational screening of spinel structure cathodes for Li-ion battery with low expansion and rapid ion kinetics

Lithium ion batteries (LIBs) dominate the market of energy storage systems due to their high energy density and light weight. Spinels, a group of environmentally friendly, low cost and thermal stable materials, have been reported as high-performance cathode candidates of LIBs. In spinel LIBs, Mn-based spinels (LiMnO4) have been widely studied, and further reports have been carried out on the doping of LiMnO4 structures to suppress the disproportionation reaction of the Mn3+. However, the application of spinel cathodes in LIBs is still affected by the volume expansions and slow ion diffusion kinetics. In this work, we generated 62 spinel materials from the periodic table based on the widely studied LiB2X4 and LiMn1.5B0.5X4 structures (i.e., Mn-based spinel with doping of elements B), where the element B can be chosen from the Co, Cr Fe Ir, Mn, Mo, Ni, Pd, Pr, Rh, Ti, V, Ce, Tb, Ru or Ta while the element X can be an anion of O or S. Based on the density functional theory (DFT), the electronic conductivities, expansion coefficients and ion kinetics of the selected 62 spinel structures were predicted. Finally, we screened out 18 structures having excellent electronic conductivity (i.e., the band gap, Eg = 0), low expansion coefficient (<10%) and low diffusion energy barrier (<0.4 eV). In addition, 8 spinel structures were found to be superionic conductor with extremely high ionic conductivity (>10−4 S·cm−1). The proposed work not only filtered out the spinel electrode materials with the best performance for LIBs and found the superionic conductor based on lithium spinel, but also provided an efficient solution for the search of other excellent electrode materials with optimal structures.

Multiscale simulation on nonlinear mechanical properties of 3D printed cellulose composites

Polypropylene (PP), a major thermoplastic resin, is widely used in compression molding and injection molding due to its excellent mechanical properties and recyclability. In general, talc, an inorganic mineral product, is widely used as a reinforcing filler in PP. Talc has excellent chemical stability, electrical insulation, and affinity with organic materials. However, PP has a high coefficient of linear expansion, making it difficult to use with the fused deposition modeling 3D printers that have become increasingly popular in recent years because of warping of the printed structures. On the other hand, cellulose nanofiber (CNF) is a plant fiber that has been degraded to the nanoscale and is expected to be used as a reinforcing filler for composite materials because of its superior specific stiffness and specific strength. It is expected to reduce environmental impact compared to conventional reinforcing fillers due to its reduced CO2 emissions and high recyclability. In addition, the high aspect ratio and low coefficient of linear expansion of CNF can be expected to reduce thermal deformation of composite materials. In this study, the mechanical properties of PP composites reinforced by talc and CNF fillers were tested by multiscale finite element analysis. The contents of talc and CNF were changed, and the effects of adding each were clarified.

Pyrophyllite: An Economic Mineral for Different Industrial Applications

Pyrophyllite (Al2Si4O10(OH)2) is a phyllosilicate often associated with quartz, mica, kaolinite, epidote, and rutile minerals. In its pure state, pyrophyllite exhibits unique properties such as low thermal and electrical conductivity, high refractive behavior, low expansion coefficient, chemical inertness, and high resistance to corrosion by molten metals and gases. These properties make it desirable in different industries such as refractory; ceramic, fiberglass, and cosmetic industries; as filler in the paper, plastic, paint, and pesticide industries; as soil conditioner in the fertilizer industry; and as a dusting agent in the rubber and roofing industries. Pyrophyllite can also serve as an economical alternative in many industrial applications to different minerals as kaolinite, talc, and feldspar. To increase its market value, pyrophyllite must have high alumina (Al2O3) content, remain free of any impurities, and possess as much whiteness as possible. This paper presented a review of pyrophyllite’s industrial applications, its important exploitable properties, and the specifications required for its use in industry. It also presents the most effective and economical techniques for enriching low-grade pyrophyllite ores to make them suitable for various industrial applications.

Structure and Thermal Expansion of Cu−90 vol. % Graphite Composites

Copper–graphite composites are promising functional materials exhibiting application potential in electrical equipment and heat exchangers, due to their lower expansion coefficient and high electrical and thermal conductivities. Here, copper–graphite composites with 10–90 vol. % graphite were prepared by hot isostatic pressing, and their microstructure and coefficient of thermal expansion (CTE) were experimentally examined. The CTE decreased with increasing graphite volume fraction, from 17.8 × 10−6 K−1 for HIPed pure copper to 4.9 × 10−6 K−1 for 90 vol. % graphite. In the HIPed pure copper, the presence of cuprous oxide was detected by SEM-EDS. In contrast, Cu–graphite composites contained only a very small amount of oxygen (OHN analysis). There was only one exception, the composite with 90 vol. % graphite contained around 1.8 wt. % water absorbed inside the structure. The internal stresses in the composites were released during the first heating cycle of the CTE measurement. The permanent prolongation and shape of CTE curves were strongly affected by composition. After the release of internal stresses, the CTE curves of composites did not change any further. Finally, the modified Schapery model, including anisotropy and the clustering of graphite, was used to model the dependence of CTE on graphite volume fraction. Modeling suggested that the clustering of graphite via van der Waals bonds (out of hexagonal plane) is the most critical parameter and significantly affects the microstructure and CTE of the Cu–graphite composites when more than 30 vol. % graphite is present.

The Effect of Different Additives on the Hydration and Gelation Properties of Composite Dental Gypsum.

Dental mold gypsum materials require fine powder, appropriate liquidity, fast curing, and easy-to-perform clinical operations. They require low linear expansion coefficient and high strength, reflecting the master model and facilitating demolding. In this article, the suitable accelerators and reinforcing agents were selected as additives to modify dental gypsum. The main experimental methods used were to compare the trends of linear expansion coefficients of several commercially available dental gypsum products over 72 h and to observe the cross-sectional microstructure of cured bodies before and after dental gypsum modification using scanning electron microscopy. By adjusting the application of additives, the linear expansion coefficient of dental gypsum decreased from 0.26% to 0.06%, while the flexural strength increased from 6.7 MPa to 7.4 MPa at 2 h. Formulated samples showed good stability and gelation properties with linear expansion completed within 12 h. It is indicated that the performance of dental gypsum materials can be improved by adding additives and nanomaterials, which provided a good reference for clinical preparation of high-precision dental prosthesis.

Study of Ni&lt;sup&gt;(0)&lt;/sup&gt;/La&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; perovskite coated on monolith substrates as a promising catalyst for CO&lt;sub&gt;2&lt;/sub&gt; dry reforming with steam reforming of methane in syn-gas production

Coated monolith/foam catalysts are promising materials for chemistry applications due to structured reactor configuratiions providing low expansion coefficient, good thermal stability and low pressure loss. In this study, powedered Ni(0)/La2O3 catalysts in perovskite structures, were deposited on cordierite monolith substrates (2MgO-2Al2O3-5SiO2) by dip-coating method. The catalysts were characterized by N2 adsorption, XRD, TPR-H2 analysis. The activity of structured catalysts with various powder loadings (4, 8, 12, 20 and 30 wt %) were evaluated in combined Steam-CO2 reforming reaction (CH4/CO2/H2O = 2/1/2 vol%) at GHSV = 60.000 h-1. XRD and TPR results showed that the active phase LaNiO3 were mainly Ni and La2O3 distributed on the surface of cordierite channels after air calcination of 850oC, 3 hours and hydrogen reduction of 600oC, 2 hours . The conversion of methane and CO2 on monolith catalysts, with proper active sites loadings of 12 – 20 wt%, were close to 80 vol% at 800oC. At the same reaction amount of active sites, the feedstock conversion on LaNiO3/monolith (12 %wt LaNiO3/monolith) was significantly higher than on corresponding powdered type, respectively 1.6 times of CH4, 1.8 times of CO2 conversion.

Copolyamide-Imide Membrane with Low CTE and CME for Potential Space Optical Applications.

Polyimide diffractive membrane lens can be used in space optical telescope to reduce the size and mass of an imaging system. However, traditional commercial aromatic polyimide membrane is hard to meet the challenging requirements of dimensional stability and optical homogeneity for optical use. Based on molecular structure design and the optimization of fabrication process, the prepared copolyamide-imide membrane achieved the desired performance of membrane as an optical material. It showed a very low coefficient of thermal expansion (CTE), which is 0.95 ppm/°C over a temperature range of −150–100 °C and relatively low coefficient of moisture expansion (CME), which is only 13.30 ppm/% RH (0~90% RH). For the optical use, the prepared copolyamide-imide membrane (φ200 mm) achieved good thickness uniformity with wave-front error smaller than λ/30 (λ = 632 nm) in RMS (root mean square). Besides, it simultaneously meets the optical, thermal, and mechanical requirements for space telescope use. Copolyamide-imide membranes in this research with good comprehensive performance can be used as large aperture membrane optical system architectures.

Successful application of optical bench in Taiji-1 laser interferometer

As an important part of laser interferometry system, optical bench is one of the core technologies for the detection of spaceborne gravitational waves. As the first step of the space Taiji program, Taiji-1 provides the measurement accuracy of laser interferometry system better than 100 pm/Hz[Formula: see text](@10 mHz–1 Hz). Taiji-1 is required to be able to track the motion of test mass in inertial sensor. According to the requirements, four interfering optical paths were designed. By adopting an integrated satellite design and selecting the optical and mechanical materials with low linear expansion coefficient, the high stability of optical path was achieved. By using the DOE method, the alignment errors (position/attitude) of four optical paths were all reduced to below 50 [Formula: see text] m/100 [Formula: see text] rad. In the performance test, the accuracy of laser interferometry system was better than 100 pm/Hz[Formula: see text](@10 mHz–1 Hz), and the modulation signal of inertial sensor was successfully detected. The results show that all technical indexes of optical bench have met or exceeded the design requirements.

Mechanical and Thermal Properties of Harmonic Structured Composites by MM/SPS Process

Harmonic structured composites consist of a low fraction metal region like network and a dispersed another major metal region like island. The harmonic structured composites were produced via mechanical milling (MM) followed by spark plasma sintering (SPS), and its mechanical and thermal properties were investigated in detail. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM). The mechanical properties of the harmonic structured composites were evaluated using results of the Vickers hardness and the tensile tests. The thermal properties of a part of the harmonic structured composites were evaluated using results of thermo-mechanical analysis and laser flash method. High speed steel / mild steel harmonic structured composite exhibited high strength and enough ductility in spite of the trade-off relationship between strength and ductility. In addition, the high speed steel / mild steel harmonic structured composite also demonstrates a superior wear properties and low hardness simultaneously. On the other hand, molybdenum / copper harmonic structured composite demonstrate low coefficient of linear expansion and enough thermal conductivity compared to the conventional copper / molybdenum particle dispersed composite. The coefficient of linear expansion and thermal conductivity are the trade-off relation in this composite. In summary, the harmonic structure control is effective for improvement of the trade-off mechanical and thermal properties in the composite.

Pre-heating by defocusation of the CO2-Laser polishing beam: an experimental report from the lab-floor -INVITED

The laser beam polishing for glass and plastics is a purely thermal process and melts the ground or lapped structures to a depth of limited extent. This results in a smoothing of the surface, whereby the 1st - 4th order shape deviations can be corrected very well and transparent surfaces are created. The process is excellently suited for quartz glasses and other optical glasses with a low coefficient of expansion α. Furthermore, thermoplastics or metallic molds for injection molding and precision molding applications can also be polished with the laser beam. On the other hand, special measures are required for glasses with a high α, e.g. preheating of the component. For the investigations, a defocused laser beam was used for the defined preheating of glasses with high linear expansion coefficients. After reaching the material-specific preheating temperature, the laser beam was focused and the polishing process started. A defined cooling process follows again with a defocused beam. In this way, a ground biconvex lens made of boron crown glass was successfully polished. The laser-polished surfaces have an RMS value of 1- 3 nm. The polishing process can be used very flexibly. Likewise, very differently shaped optical components can be polished. The newly developed polishing regime is transferable to other optical glasses with high linear expansion coefficients.

Sol - gel method for producing of glass binding in the Li2O - Al2O3 - SiO2 system for ceramic materials

The results of glass binding obtaining in the Li2O — Al2O3 — SiO2 system for ceramic materials are presented in the article. The lithium aluminum silicate system was chosen taking into account the low temperature expansion coefficients of crystalline phases that form in it. This will allow controlling the thermal expansion of materials into which the glass binding will be introduced. A sol - gel method based on ethyl silicate and soluble salts of the corresponding oxides is proposed as a method for producing of glass binding. This method is more rational in comparison with the traditional method of glass melting due to low energy costs. Also, the method allows to obtain a more uniform and active product.&#x0D; The effect of glass binding on the properties of ceramic materials for various purposes has been investigated. As such materials, low-temperature electrotechnical porcelain, quartz ceramics, and engobe coatings were chosen. The glass binding was introduced into the raw material charge of these materials in an amount of 5 wt. %. Further, the properties of calcined product without additives and with additives under the same conditions were compared.&#x0D; The intense fluxing effect of glass binding during the formation of electrical porcelain has been established. The glass binding reinforces the effect of natural fluxes (pegmatites) that are present in the basic composition of the mass. This contributes to the material compaction during firing. The formation of eucryptite and spodumene helps to reduce the thermal expansion of material. The introduction of glass binding into the engobe led to a less intense compaction of its structure. This was observed due to an insufficient amount of the added glass binding for this type of material. In the composition of quartz ceramics, glass binding contributed to the material sintering, but the thermal properties were deteriorated.&#x0D; Thus, the sintering results of ceramic material with the introduction of glass binding in the charge composition are positive. However, sintering significantly depends on the material type. The glass binding stimulates the formation of a melt in which solid finely dispersed components of the ceramic mass dissolve. This contributes to the formation of a dense durable ceramic.

A well-balanced ADER discontinuous Galerkin method based on differential transformation procedure for shallow water equations

This article develops a new discontinuous Galerkin (DG) method on structured meshes for solving shallow water equations. The method here applies the one-stage ADER (Arbitrary DERivatives in time and space) approach for the temporal discretization and employs the differential transformation procedure to express spatiotemporal expansion coefficients of the solution through low order spatial expansion coefficients recursively. Numerical fluxes using the hydrostatic reconstruction together with a simple source term discretization results in a well-balanced method accordingly. Compared with the Runge-Kutta DG (RKDG) methods, the proposed method needs less computer memory storage due to no intermediate stages. In comparison with traditional ADER schemes, this method avoids solving the generalized Riemann problems at inter-cells. The differential transformation procedure used here is cheaper than the Cauchy-Kowalewski procedure in traditional ADER schemes. In summary, this method is one-step, one-stage, fully-discrete, and easily achieves arbitrary high order accuracy in time and space. Theoretically as well as numerically, the proposed method is verified to be well-balanced. Numerical results illustrate the high order accuracy as well as good resolutions for discontinuous solutions. Moreover, this method is more efficient than the Runge-Kutta DG (RKDG) method.