Thermal Expansion Characteristics Research Articles

Anomalous thermal expansion properties in perovskite Sm0.85Zn0.15MnO3

The multiple sintering compounds of perovskite Sm0.85Zn0.15MnO3, which are denoted as S1, S2, S3, S4, and S5, have been synthesized by a solid-state method. The analysis of their crystal structure and microstructure were conducted by X-ray diffractometer and scanning electron microscopy, respectively. The average particle size and porosity were counted by microscopic image analysis. The thermal-expansion behavior of the compounds was studied by a dilatometer and high-temperature XRD. Experimental results indicated that the once sintering sample (S1) of Sm0.85Zn0.15MnO3 possesses the negative thermal expansion (NTE) properties with a coefficient of thermal expansion of −8.40 × 10−6 K−1 in the range of 519–1023 K. By contrast, the thermal expansion behavior for the multiple sintering samples (S2–S5) is not same as that of S1. The porosity of the samples dramatically affects their thermal expansion behavior. The samples S1 and S2 exhibit the NTE characteristics as their porosity was larger than 9.5%, but the samples S3, S4, and S5 exhibit positive thermal expansion characteristics, as their porosity is less than 9.5%. In addition, anisotropy of thermal expansion plays a crucial role in the NTE mechanism. The mechanism underlying the NTE of Sm0.85Zn0.15MnO3 (S1) involves the coupling effect of the high porosity and the microstructural NTE effect caused by crystal grains with anisotropic thermal expansion and intercrystalline pores.

Anomalous thermal expansion behavior in Er1-xCaxMnO3

Perovskite Er1-xCaxMnO3 (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5) was synthesized using a solid-state method. Thermal expansion behavior was tested using a thermal dilatometer and high-temperature X-ray diffraction (XRD). The experimental results indicated the doping contents of Ca (x) in the Er1-xCaxMnO3 have a dramatic effect on their thermal expansion behavior. The samples of Er1-xCaxMnO3 (x = 0.1,0.2 and 0.25) exhibit positive thermal expansion (PTE) characteristics while Er0.7Ca0.3MnO3 (x = 0.3) exhibits a negative thermal expansion (NTE) property with a thermal expansion coefficient of −3.1 × 10−6 K−1 in room temperature (RT) −750 K. In addition, Er0.6Ca0.4MnO3 (x = 0.4) exhibits NTE properties only at RT–500 K, and Er0.5Ca0.5MnO3 (x = 0.5) exhibits PTE properties at RT–750 K. The thermal shrinkage mechanism is the Jahn–Teller effect of the Mn3+ ions and the double exchange of Mn3+–O–Mn4+ in Er0.7Ca0.3MnO3. This phenomenon causes Mn–O octahedral distortion and oxygen vacancy, causing Er0.7Ca0.3MnO3 to become anisotropic. This feature results in the elastic deformation of Er0.7Ca0.3MnO3 during heating, which consumes the void and displays NTE at macro level.

Mechanisms of thermal cycling damage in polycrystalline Sn-rich solder joints

Solder joints will experience elevated temperatures during operation due to resistive heating and ambient conditions. Device components have different thermal expansion characteristics, leading to straining of the solder joint and development of surface damage features. The anisotropic thermal expansion of βSn grains and discrepancy between the thermal expansion of intermetallic compounds causes degradation to be localized near grain boundaries and phase interfaces. Three experiments were conducted to investigate thermal effects on solder joint microstructure. Interrupted low temperature aging revealed the formation and movement of grain boundary ledges and uninterrupted thermal aging confirmed that the ledges formed during the cooling cycle of the experiment. Finally, high temperature thermal cycling demonstrated the acceleration of surface damage that accompanies an increase in peak temperature and cycling frequency. The orientation of the c-axis of the Sn matrix grains proved to be the critical feature controlling the direction of grain boundary ledge migration and type of surface deformation surrounding Cu6Sn5 intermetallic needles.

Study on the Thermal Expansion Performance of Gypsum in the Application of Precision Casting

Gypsum is a very important cementitious material in gypsum-based precision casting. The thermal expansion characteristics of gypsum have great influence on the adjustment of gypsum type precision casting powder formula. In this paper, the thermal expansion properties of different gypsums such as β-gypsum, natural gypsum-based α-gypsum, desulfurization gypsum-based α-gypsum, and the influence of temperature, heating rate/heating mode on the thermal expansion properties of α-gypsum are studied, which can provide references for the application of gypsum in the precision casting.

Measurement and Analysis of Silicone Oil Characteristics and Viscosity-Temperature Index

This paper introduces the shear resistance, viscous-temperature characteristics and thermal expansion characteristics of silicone oil. According to the physical and chemical properties of silicone oil, the viscosity of silicone oil is tested through experiments, and the viscous-temperature characteristic curve of the sample is obtained. The degree of the decrease of the viscosity of silicone oil with the increase of the temperature of silicone oil is quantified. It is important to study the calculation method of slip difference of silicone oil fan clutch and the surface temperature of the shell.

A framework for application of dynamic line rating to aluminum conductor steel reinforced cables based on mechanical strength and durability

Dynamic line rating can be described as a method of overloading the power line within reliability and safety limits. Power line’s loading limits can be increased, if its temperature is controlled to be below the maximum allowable conductor temperature, which is defined by the grid regulations. Dynamic rating brings additional uncertainties and risks to the grid operation due to high variability of weather conditions, which plays an essential role in determining real-time capacity limits. Power lines often are under the influence of risk factors related to power system performance, however, they could also be subjected to additional risks related to their mechanical structure. Overhead lines, which are composed of more than one stranded material, are exposed to increasing mechanical stress due to differences in thermal expansion characteristics of different materials. The reliability analysis of transient expansion/shrinkage of the material has identified the risks to the conductor mechanical strength that are associated with dynamic heating and cooling.This study determines an optimal dynamic line rating application, which not only would take into account electrical properties of the system and economic benefits, but would also minimize the aging of steel reinforced aluminum overhead lines. Alternatively to hourly line rating adjustment, 2 h, 3 h and 4 h ratings are suggested as possible way to decrease impact of DLR on conductor mechanical durability. Comparing the mechanical durability and cost benefits between different frequencies of loading limit adjustments, allows suggesting improvements to dynamic line rating application.

Synthesis, characterization and thermal expansion of the zinc-containing phosphates with the mineral-like framework structures

The new phosphates ZnxMg0.5+xE2−x(PO4)3 (E = Ti, Zr) were synthesized by the sol–gel method followed by heat treatment. Obtained samples were characterized with X-ray, IR, DTA and microprobe electron analyses. The ZnxMg0.5+xTi2−x(PO4)3 solid solution (0 ≤ x ≤ 0.5, kosnarite-type, sp. gr. R$$\bar{3}$$) is stable up to 1323 K. The ZnxMg0.5+xZr2−x(PO4)3 solid solution (0 ≤ x ≤ 0.5, Sc2(WO4)3-type, sp. gr. P21/n) is thermally unstable above 1273 K. The thermal expansion of ZnxMg0.5+xE2−x(PO4)3 solid solutions was studied in the temperature range 298–1073 K. The magnitudes of average volume thermal expansion coefficients vary from 1 × 10−5 to 5 × 10−6 K−1. The composition regulation of these medium- and high-expanding materials allows you to change the characteristics of thermal expansion in the required direction.

Applying Selective Laser Melting to Join Al and Fe: An Investigation of Dissimilar Materials

Combining aluminum and steel is a major goal of automobile manufacturers and other industries because the hybrid material reduces the weight of components. However, differences in chemical properties, thermal expansion, and physical characteristics of aluminum and steel are barriers to achieving this goal. In this article, selective laser melting (SLM), which is widely used in industrial fields, was applied to join dissimilar materials by printing aluminum on a steel substrate. Defects of joining during the SLM process, characteristics of the intermetallic reaction layer, and the effects of the process parameters were investigated. The analysis indicates that flake behavior could affect the quality of joining. The phases of the intermetallic layer found in this study were in agreement with other research, but the morphology of the layer was much different. A formula to estimate the join quality in terms of density energy is proposed. The results indicate that the SLM process is a promising method to manufacture a hybrid material.

Effects of TiO2 doping on microstructure and properties of directed laser deposition alumina/aluminum titanate composites

ABSTRACT Al2O3-based composite ceramics have excellent high temperature performance and are ideal materials for preparing hot end components. However, poor fracture toughness and thermal shock resistance limit its applications. Based on the excellent low thermal expansion characteristics and thermal shock resistance of Al2TiO5 ceramic, different composition ratios of Al2O3/Al2TiO5 composite ceramics were prepared by directed laser deposition (DLD) technology. Effects of TiO2 doping amount on microstructure and properties of the composite ceramics were investigated. Results show that α-Al2O3 phase is discretely distributed in the continuous aluminum titanate matrix when TiO2 doping amount between 2 and 30 mol%. With the increase of TiO2 doping amount, content of Al2O3 gradually decreases and its morphology changes from cellular to dendritic. When TiO2 doping amount reaches 43.9 mol%, the microstructure transforms into fine Al2TiO5/Al6Ti2O13 eutectic structure. Property test results show that Al2O3/Al2TiO5 composite ceramics have good comprehensive mechanical properties when TiO2 doping amount between 2 and 6 mol%.

Electroplating and Characterization of Invar Fe–Ni Alloy Films from Plating Baths Containing Organic Acids

Practical plating baths and plating conditions for preparing Fe–Ni alloy electroplated films with compositions in the Ni content range 36–100 mass% have been proposed. The addition of saccharin in sulfate-chloride bath is indispensable for preparation of Fe-30–45 mass% Ni alloy electroplated films, i.e., those in invar composition region. The addition of tartaric acid or malonic acid to Fe–Ni alloy plating baths (containing saccharin) prevents a reduction in the toughness of the plated film by masking Fe3+ generated by oxidation. It was possible to suppress the internal stress in invar Fe–Ni alloy electroplated films to low levels. Resultantly, the invar electroplated films obtained from these optimized plating baths show promise for electroforming. On the contrary, the addition of citric acid, which forms a more stable complex with Fe3+, causes very large internal stress in the resultant invar Fe–Ni alloy electroplated films, making them unsuitable as MEMS materials. It was confirmed that Fe–Ni alloy electroplated films with Ni contents of 45–100 mass% comprise a single-phase alloy having an fcc structure but the invar Fe-36–42 mass% Ni alloy electroplated film is a metastable bcc phase or a mixture of bcc and fcc phases. Therefore, to impart low thermal expansion characteristics to as-plated invar alloy films, it is necessary to induce phase transformation to an fcc phase, which is the equilibrium phase at high temperature, by the means of heat treatment.

Interesting Facets of Surface, Interfacial, and Bulk Characteristics of Perfluorinated Ionomer Films.

Ion-containing perfluorinated polymers possess unique viscoelastic properties, excellent proton conductivity, and nanophase-segregated structure all arising from the clustering of hydrophilic sulfonic acid groups within a matrix of hydrophobic fluorocarbons. When these ionomers are confined to nanothin films, a broad swathe of structural organization imparting a rich variety of surface, interfacial, and bulk characteristics can be expected. However, our understanding of perfluorinated ionomer thin film behavior is still in a rudimentary stage, and much of the research focus to date has been on its hydration-related structure and properties pertinent to electrochemical applications. Thus, many hidden gems-their interesting surface and interfacial properties-have been overlooked. In this Invited Feature Article, which is a summary of the key contributions by the author's group, including several collaborative publications on ionomer thin films, we unravel many of these facets. In addition, the article attempts to integrate knowledge acquired from a variety of investigations of different aspects of the ionomer thin films to refine and develop a consistent picture of their structure and behavior. First, we focus on the self-assembly of ionomers and show that dispersion media and hydrophobicity/hydrophilicity of the substrate can result in partial or even no coverage of substrates, shedding light on the complexity of polymer-substrate, polymer-solvent, and polymer-polymer interactions, an insight completely obscured when the spin-coating method is adopted for film creation. We demonstrate that the same ionomer can be used to create a variety of surfaces ranging from superhydrophilic to highly hydrophobic by controlling the film thickness or through the choice of substrate material. The ultrathin, hydrophilic surfaces of self-assembled Nafion ionomer films exhibit wettability switching behavior which opens the door to creating stimuli-responsive smart surfaces. The thermoresponsive behavior of the films is discussed in the context of surface (wettability) and bulk (thermal expansion) characteristics as well as a newly discovered vibrational mode. The substrate- and film thickness-dependent thermal expansion coefficients reinforce the importance of interfacial interactions and confinement on the structure/properties of these films. They also open up the potential of tuning ionomer bulk properties via substrate chemistry. The discovery of a vibrational mode that becomes thermally activated at high temperature has provided new insights into the origins of the molecular motions responsible for the α-relaxation of the Nafion ionomer as well as the underlying reason for wettability switching. Our recent neutron reflectometry study of different ionomers varying in side-chain composition/length on a platinum substrate shows that the interfacial hydration level is correlated to the side-chain length, which opens up the possibility of the controlling the interfacial electrochemistry. Finally, a systematic analysis of factors affecting proton conduction is presented to elucidate the yet-unresolved origins of the suppressed conduction of nanothin ionomer films compared to that of the bulk membrane. By revealing these interesting yet poorly understood facets of ionomer thin films, the article aims to stimulate further scientific pursuit on this topic.

Effects of Dynamic Line Rating on the Durability and Mechanical Strength of Aluminum Cable Steel Reinforced (ACSR) Conductors

Dynamic Line Rating (DLR) is an emerging technology, which provides better utilization of power lines, by using real-time information on the weather parameters to dynamically adjust line rating limits. The power line capacity is highly dependent on its heat balance. The heat balance is influenced by external factors such as wind speed, ambient temperature, humidity, solar radiation and load. DLR analyses have shown high economical and reliability benefits from power system perspective. However, the mechanical stress on the conductor due to differences in thermal expansion characteristics of Aluminum and Steel materials could lead to faster ageing and mechanical damages. The study aims to provide better understanding of the risks associated with DLR application, which can affect conductor’s mechanical lifetime. The reliability analysis of transient expansion and shrinkage of the material has identified the risks to the conductor mechanical strength that are associated with dynamic heating and cooling.

Electrical Properties and Thermal Expansion Characteristics of (1–x)Ba0.948Ca0.05Er0.002Ti0.94Zr0.06O3–(x)Pr Lead‐Free Piezoelectric Ceramics Sintered at a Low‐Temperature

(1 − x)Ba0.948Ca0.05Er0.002Ti0.94Zr0.06O3–(x)Pr (x = 0–0.75 mol%) ceramics are sintered at 1240 °C by conventional solid‐state reaction method using the as‐synthesized nanoparticles, which are prepared by a modified Pechini method. The structural, morphological, electrical, and thermal expansion properties as a function of varying x are systematically investigated. All samples feature rhombohedral phase, and their lattice parameters are accurately calculated by Rietveld refinement software. Volume of oxygen vacancies initially decreases and then increases with increasing x, leading to diversified electrical properties. Deteriorated electrical properties of the ceramics with excessive x are attributed to the increment of defect complexes with a large volume of oxygen vacancies. The coefficient of thermal expansion values of the ceramics that is influenced by phase evolution and structure defects under different temperature ranges are studied. The respective optimal electrical properties, that is, d33 = 186 pC N−1 and kp = 27.2% are obtained at x = 0.30 mol%. This research is believed to be insightful to practical application of the lead‐free multifunctional electron components.

High-Temperature Performance of Lining Concrete for Subsea Tunnel

To study the physical and mechanical properties of tunnel lining concrete under high-temperature combustion, concrete specimens were developed by consulting the concrete proportioning in Xiangan subsea tunnel lining. After combusting the specimens under high temperatures, two types of cooling methods were used, namely, natural cooling and water spraying. The thermal expansion and deformation characteristics, compressive strength, elastic modulus, and antipermeability of concrete after high temperature were analyzed. Results were as follows: (1) Water spray cooling had a significant effect on the thermal expansion of concrete at high temperatures, and natural cooling greatly influenced the elastic modulus and antipermeability level. (2) If the axial strain was the same, then the transverse strain increased with the increase in temperature when the temperature was below 600°C. However, when the temperature was higher than 600°C, the transverse strain decreased with the increase in temperature. (3) With the increase in temperature, a linear relationship existed between the compressive strength of concrete and the temperature under natural cooling condition. However, under the water spray cooling condition, a nonlinear relationship was observed.

Thermal Expansion and Electrical Characteristics of Ba(1−x)CaxTi0.92Zr0.08O3 Lead-Free Ceramics Prepared by a Modified Pechini Method

Ba(1−x)CaxTi0.92Zr0.08O3 (BTZ-xCa; x = 0–0.20) lead-free ceramics were prepared at a low temperature of 1210°C using as-synthesized nanoparticles through a modified Pechini method. The structure, permittivity, ferroelectricity, piezoelectricity, and thermal expansion characteristics of the ceramics that were influenced by varying calcium contents were studied in detail. X-ray powder diffraction and Raman results suggested that calcium could not induce the rhombohedral phase transition, and impurity phases were detected with excessive x. The electrical properties were basically elevated firstly in the room temperature direction of the temperature of phase transitions for orthorhombic-to-tetragonal with weaker internal stress, and then they apparently deteriorated with the shrunk octahedron size and strongly distorted structure with an increase of calcium content. The optimum electrical properties, i.e., d33, kp, and Qm of the BTZ-xCa ceramics were 261 pC/N, 24.9%, and 98 were obtained when the calcium content was 0.05, respectively. Additionally, the thermal expansion coefficient was studied for providing guidance on the ceramic materials production and usage.

Design and analysis of lattice cylindrical shells with tailorable axial and radial thermal expansion

Current periodical lattice structures with tailorable coefficient of thermal expansion (CTE) can be hardly used as engineering structures since these configurations are neither planar nor regular three dimensional geometries. Here, lattice cylindrical shells, which are widely in aerospace engineering, are originally devised and analyzed to exclusively achieve a wide range of tailorable CTEs in both axial and radial directions. The thermal expansion behaviors are systematically calculated by finite element analysis, and the expressions of CTEs for the devised lattice cylindrical shells are well established. Warp effects are found in lattice cylindrical shells winded from planar triangle and planar square due to the sparse arrangement mode, and with few circumferential triangles, the radial CTE is significantly larger than those of the corresponding planar lattices. Tailorable thermal expansion characteristics including zero, large positive and negative values are confirmed. Moreover, in case study with aluminum alloy, stainless steel and invar, a wide range of thermal expansion ranged from −64.6 to 88.0 ppm∕∘C, which are remarkably larger than those of constituents, can be easily achieved through the devised lattice cylindrical shells. The wide range of CTEs obtained here can promote these lattice cylindrical shells to be used as structures under temperature variation service environment for purpose of obtaining dimensional stability and thermal expansion compensation.

Lightweight composite lattice cylindrical shells with novel character of tailorable thermal expansion

Composite lattice cylindrical shells widely utilized in aerospace engineering are susceptible to experience large temperature excursions, and generate undesirable thermal deformation. Here, we devise novel composite lattice cylindrical shells which can exclusively present a wide range of negative, positive and especially zero coefficient of thermal expansion (CTE) through structural design and rational arrangement of commonly available positive CTE composites. Theoretical analysis figures out the thermal deformation mechanism, and clearly establishes the important relationship that with adequate circumferential triangle units, the CTEs of the lattice cylindrical shells closely approach to the CTEs of the corresponding triangle and planar lattice composites. Finite element analysis firmly confirms the tailorable thermal expansion characteristics. Furthermore, in practical design of lattice cylindrical shells with commonly available composites, a wide range of tailorable thermal expansion up to −2200 to 2200 ppm/∘C, which is substantially larger than those of available engineering materials, can be easily achieved. Such wide range of CTEs and lightweight feature enable these composite lattice cylindrical shells to be potentially used in aerospace engineering.

Parameters Evolution of Orthorhombic Martensite Lattice Ti-Mo-Al Alloys Studied by in Situ T-XRD

In-situ study of heating in an X-ray diffractometer of Ti-8Mo and Ti-3Al-7Mo alloys samples quenched from different temperatures of α+β and β-fields was carried out. The characteristics of anisotropy thermal expansion of orthorhombic martensite lattice were investigated. It is shown that there is a critical ratio of lattice parameters R = ⇃3a/b close to 1.11, after which either a reverse martensitic transformation occurs, or R of the martensite lattice decreases upon further heating.

Thermal and hygroscopic expansion characteristics of bamboo

The expansion and contraction of bamboo caused by temperature and moisture variations must be evaluated if bamboo is to be utilised as a building material. However, detailed expansion data, especially data in the ascent and descent processes of temperature and moisture are unexplored. The aim of this study is to investigate the expansion characteristics of Phyllostachys edulis (Moso bamboo) in ascent and descent processes of temperature and moisture. The measurement of linear thermal expansion and hygroexpansion of bamboo specimens were conducted with a dilatometer and a micrometer, respectively. The temperature range of the linear thermal expansion measurement was between 23 and 70°C. In the linear moisture expansion measurement, all specimens were measured at various relative humidity (RH) conditions including oven dry, 27, 54, 76 and 95%RH, and water soaking stages. Major findings include: the swell of bamboo specimens increases with RH, whereas the shrinkage of bamboo specimens decreases with RH. The hygroexpansion is much more significant compared with the linear thermal expansion. Both linear thermal expansion and hygroexpansion of the specimens from the longitudinal directions are smaller than those from the radial direction and tangential direction.

Experimental Study of Thermal Expansion Characteristics of Coaly Mudstone at High Temperatures

This study investigated the thermal expansion characteristics of coaly mudstone specimens at temperatures ranging from room temperature up to 800 °C. The experiments were performed by an MTS810 electro-hydraulic servo system and an MTS653.02 high-temperature furnace. Results revealed that mudstone experienced thermal expansion at high temperature, and that the relationship curve between thermal expansion strain and testing time could be divided into three stages. With increasing temperature, mudstone’s thermal strain and expansion coefficient exhibited an upward trend. With 400 °C as the critical temperature, the curve could be divided into (1) rapid increase stage, (2) flat stage, and (3) rapid increase stage. The major causes behind thermal expansion are changes in internal pores and fissure, as well as the thermochemistry effect of mineral components.