Insulation Coatings Research Articles

Emerging SiO2@ATO hierarchical submicron hollow microspheres with efficient photo-thermal shielding properties

Silicon dioxide/antimony doped tin oxide (SiO2@ATO) submicron hollow microspheres were prepared by hydrothermal method. The morphology and microstructure of the microspheres were characterized by XRD, SEM, EDS and HRTEM. The composite coatings were prepared by adding SiO2@ATO powders to acrylic matrix, and their photothermal shielding properties were investigated. In addition, the electronic structure and optical properties of SiO2@ATO heterojunction were calculated and analyzed using first principle. The results show that the interface binding energy of SiO2@ATO is ∼2.496 J/m2, which indicates that the interface can exist stably. The light transmittance of the acrylic matrix coating with 1.0 wt% submicron hollow SiO2@ATO microspheres can reach about 83 %. Moreover, it was found that the hollow double-shell SiO2@ATO/acrylic matrix coating lowered the indoor temperature of the homemade incubator by 11.5℃. In summary, the SiO2@ATO structure shows potential in the application of transparent thermal insulation coatings.

Waterborne novolac epoxy‐based thermal resistant and fire‐retardant thermal insulation coatings

AbstractWaterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance.

Study on damage of CRTS II slab tracks in coated-uncoated transition zones subjected to temperature and train loads

The CRTS II ballastless track is sensitive to temperature due to its longitudinal continuity. The application of reflective insulation coating can efficiently lower the temperature of the track slab, thereby decelerating track deterioration. Given the considerable length of high-speed railway lines, the application of reflective insulation coatings leads to numerous transitions between coated and uncoated sections. This study investigates the influence of reflective insulation coatings on the structural damage of coated-uncoated transition zones in railways. To this end, a CRTS II slab track model involving the bilinear cohesive zone model and the concrete plastic damage model is established. The model examines the combined impact of high temperature and train loading, aiming to investigate the damage patterns within the coated-uncoated transition zone of the track. The results indicate: (1) During high temperature loading, the center of the track slab layer is predisposed to warping compared to the sides. (2) If the cohesion parameter falls below 0.04 MPa, augmenting the cohesion model parameter effectively alleviates track slab arching. (3) In instances where the track slab lacks complete coverage of reflective insulation coatings, train loading may shift the location of the maximum vertical displacement and interface failure mode.

Selection of insulation coatings for industrial-grade FeSiBC amorphous soft magnetic composites based on dry particle coating method

Selection of insulation coatings for industrial-grade FeSiBC amorphous soft magnetic composites based on dry particle coating method

Influence of Bond Coat Roughness on Adhesion of Thermal Barrier Coatings Deposited by the Electron Beam–Physical Vapour Deposition Process

Thermal barrier coatings (TBCs) are effective protective and insulative coatings on hot section components of turbine engines. The quality and subsequent performance of the TBCs are strongly dependent on the adhesion between the coating and the metal substrate. The adhesion strength of TBCs varies depending on the substrate materials and coating, the coating technique used, the coating application parameters, the substrate surface treatments, and environmental conditions. Therefore, the roughness of the substrate surface has a significant effect on the performance of the TBC system. In this work, the roughness and microstructure of the 7YSZ (7 wt.% yttria-stabilised zirconia) top coat under different bond coat roughness treatments were studied. The purpose of this paper was to investigate the influence of the roughness of the bond coat on the adhesion of 7YSZ TBCs prepared by the electron beam–physical vapour deposition (EB-PVD) process. The VPA (vapour phase aluminium) bond coat was deposited on Inconel 718 nickel superalloy substrate using the above-the-pack technique. The ceramic top coat was applied to the bond coat using the EB-PVD process. The dependence between the TBC coating roughness and the bond coat roughness was determined. Adhesion strength measurements were performed according to the ASTM C 633 standard test method. The highest adhesion value observed in the tensile adhesion tests was 105 MPa. However, it was not determined whether the surface roughness of the bond coat affects the adhesion of the 7YSZ top coat.

Interdiffusion mechanism of hybrid interfacial layers for enhanced electrical resistivity and ultralow loss in Fe-based nanocrystalline soft magnetic composites

Soft magnetic composites (SMCs) composed of ferromagnetic particles and insulating binder are highly desired in energy-saving and high-efficiency devices for their high electrical resistivity and softer saturation characteristics. However, traditional insulation coatings are facing thermal instability, inhomogeneous distribution, and magnetic dilution, presenting a major challenge for the trade-off relationship between power loss and permeability. Here, the phosphate-coated FeSiBCuNb/SiO2 SMC is successfully fabricated by a unique interdiffusion effect in hybrid interfacial layers, which shows a combination of ultralow power loss of 135.8 kW/m3 (50 kHz/100 mT), high effective permeability of 80.6, and good temperature stability. The interdiffusion behavior between Si/O and Fe/P/O elements promotes the formation of ultrathin, uniform, and multilayer interface structure, which alleviates the magnetic dilution. Penetrating oxidation at the edge interface and elements interdiffusion effect contribute to a higher electrical resistivity induced by hot isostatic pressing with rapid quenching, leading to a low eddy current loss. Synergistic effect of isostatic pressures and rapid quenching facilitates the formation of high-density Cu clusters corresponding to ultrafine microstructure, which is beneficial for low coercivity and low hysteresis loss. This study involves the interdiffusion mechanism of hybrid interfacial layers and nanocrystalline behavior, providing a new strategy for the next-generation of high-performance SMCs.

Study on the thermal insulation property of lanthanum–cerium oxide coatings

Functional fillers with low thermal conductivity and high near-infrared reflectance play a vital role in high temperature thermal insulation coatings and make an outstanding contribution to achieving efficient comprehensive thermal insulation. In this work, the thermal insulation and bonding properties of lanthanum–cerium oxide (LCO) coatings were regulated by composition design. The effects of the La/Ce mole ratio on phase composition, the thermal conductivity and near-infrared reflectivity of LCO coatings were investigated systematically. The results showed that coating with a La/Ce mole ratio of 1:1 possess the excellent thermal insulation properties (ΔT ≈ 115°C) due to the formation of a LCO solid solution and a lanthanum phosphate mesophase with low thermal conductivity and high near-infrared reflectivity. In addition, the mortise and tenon structure was formed between the coating and the substrate, which led to the remarkable bonding properties. The LCO coating offers excellent thermal insulation properties and broad application prospects in the fields of high temperature and energy conservation.

Thermal properties of high-entropy fluorite (Zr0.2Hf0.2Pr0.2La0.2×0.2)O2-δ(X=Dy, Ho, Er, Y, Tm): A first-principles combined with experimental study investigating the influence of size and mass difference effect

The limited efficiency of traditional trial-and-error experiments has impeded the development and application of high-entropy fluorite oxides in thermal insulation coatings. To solve this problem, a novel entropy descriptor based on first principles is presented to help select candidate components for synthesizing high-entropy fluorite structure oxides. Results show that the compatibilities of 10 single-phase high-entropy fluorite oxides can be accurately predicted based on entropy formation ability. In the studied (Zr, Hf, Pr, La, X) O2-δ system, a correlation between thermal characteristics and size/mass differences was established by designing the size and mass of X. Specifically, we found that the thermal conductivity is more strongly correlated with the difference in atomic mass, while the coefficient of thermal expansion is strongly correlated with the difference in atomic size. X-ray photoelectron spectroscopy (XPS) analysis shows that the concentration of oxygen vacancy can effectively reduce the thermal conductivity of high-entropy fluorite oxides. In addition, the values of hardness, elastic modulus and thermal conductivity of five single-phase fluorite oxides are successfully predicted by first principles calculation, and the differences between these values and the experimental results are small, which provides a prospective significance for the performance prediction of high-entropy fluorite oxides. Our findings provide a strategy for customizing high-entropy fluorite single-phase oxides with suitable properties to meet the performance requirements of thermal barrier coatings (TBCs).

Fabrication of photothermal responsive dual-chamber microcapsules for self-healing epoxy anticorrosion coatings

It has been urgent that timely repair of microdamage generated during long-term service of metal insulation coatings. Hereby, we developed a novel self-healing dual-chamber microcapsule with particle size about 5 μm, in which furfuryl amine modified polystyrene-acrylic acid (PSAF) as shell material and photosensitizer Carbon dots (CDs) as Pickering emulsifier. The synthesized materials were characterized analytically, FTIR and DSC demonstrated the simultaneously existence of healing agent and curing agent in the resultant dual-chamber microcapsule. Experiments also showed microcapsules exhibited satisfying storage stability more than 20 d at room temperature as well as thermogenesis effect that allowing temperature of epoxy composite materials raised to 50 °C in 60s and fractures to be effectively minimized in time. The scratch tensile measurement results demonstrated that epoxy resin composites incorporated with 2 wt% microcapsules exhibited the optimal strength self-healing efficiency, modulus, toughness and anti-fatigue performance. Furthermore, surface characterization and EIS analysis also confirmed the long-lasting healing effect of EP/MC2% complex coating with outstanding corrosion resistance. Therefore, the photothermal responsive dual-chamber microcapsule designed in this work has application as self-healing material especially epoxy anti-corrosion coating.

NdAlO3-Nd2Zr2O7 composite with eutectic composition for advanced nanostructured thermal insulation coatings

Though numerous novel materials have been discovered as potential materials for thermal barrier coatings, their either relative poor strain tolerance or high thermal conductivity limited their further application. In the present work, a NdAlO3-Nd2Zr2O7 composite coating is prepared by air plasma spraying process. Glass phase appears in the composite coating and crystallizes after thermal exposure at 1000 °C for 5 h. This crystallization process leads to the severe reduction of the thermal expansion rate. Additionally, thermal conductivity of as-sprayed NdAlO3-Nd2Zr2O7 coating is about 1.0 Wm−1 K−1 but increases to 1.7 Wm−1 K−1 after heat treatment. A quite stable nanostructured thermal barrier coating is obtained after heat treatment. Remarkably, the NdAlO3-Nd2Zr2O7 composite coating exhibits a superior microstructure stability that the average grain size remains less than 100 nm, 175 nm, and 250 nm after calcined at 1100 °C, 1200 °C, and 1300 °C for more than 100 h, respectively. The fracture toughness of NdAlO3-Nd2Zr2O7 composite coating is one of the highest among the novel thermal barrier coatings owing to the existence of super-fine grains. The present study brings some new insight in designing advanced stable nanostructured thermal insulation coatings.

Using optical emission spectroscopy in atmospheric conditions to track the inflight reduction of plasma sprayed TiO2−x feedstock for thermoelectric applications

Thermal spray deposition (specifically Atmospheric Plasma Spraying, APS) is a well-established surface coating technology with a broad scope of applications (i.e., insulative coatings, tribological coatings, anti-corrosion coatings, etc.). In addition, there is a constant drive to introduce the APS process into new and emerging fields. One such niche application for APS would be sub-stoichiometric TiO2−x coatings with enhanced thermoelectric performance (compared to the bulk material). The APS process in this context has a unique ability—given the use of hydrogen as a plasma gas—to reduce TiO2−x material during processing. However, to this point, there is neither a reliable nor self-consistent method to assess (nor control by parametric optimization) the inflight reduction of molten oxide particles during processing. This study shows that using Optical Emission Spectroscopy (OES), it can be possible—even in atmospheric conditions—to identify characteristic emission peaks associated with the inflight reduction of TiO2 during APS. Using this OES data, the input spray processing parameters and their influence on coating microstructure and the degree of inflight reduction of the material will be shown. Results suggest under equilibrium conditions only a minimal amount of hydrogen gas is needed in the plasma to fulfill the TiO2 reduction.

Glass-like thermal conductivity and phonon transport mechanism in disordered crystals.

Solid materials with ultra-low thermal conductivity (κ) are of great interest in thermoelectrics for energy conversion or as thermal barrier coatings for thermal insulation. Many low-κ materials exhibit unique properties, such as weak or even insignificant dependence on temperature (T) for κ, i.e., an anomalous glass-like behavior. However, a comprehensive theoretical model elucidating the microscopic phonon mechanism responsible for the glass-like κ-T relationship is still absent. Herein, we take rare-earth tantalates (RE3TaO7) as examples to reexamine phonon thermal transport in defective crystals. By combining experimental studies and atomistic simulations up to 1800 K, we revealed that diffusion-like phonons related to inhomogeneous interatomic bonding contribute more than 70% to the total κ, overturning the conventional understanding that low-frequency phonons dominate heat transport. Furthermore, due to the bridging effects of interatomic bonding, the κ of high-entropy tantalates is not necessarily lower than that of medium-entropy materials, suggesting that attempts to reduce κ through high-entropy engineering are limited, at least in defective fluorite tantalates. The new physical mechanism of multimodal phonon thermal transport in defective structures demonstrated in this work provides a reference for the analysis of phonon transport and offers a new strategy to develop and design low-κ materials by regulating the inhomogeneity of interatomic bonding.

Determination of Thermal Conductivity of Nano-ceramic Thermal Insulation Coating on the Surface of a Heat Pipe

In the pursuit of conserving non-renewable fuel and energy resources and mitigating harmful emissions into the atmosphere, thermal insulation is commonly employed in practice for heated elements, including but not limited to building exteriors, boilers and furnaces, thermal power equipment, pipelines, and the like. The primary characteristic of any insulation material lies in its thermal conductivity, particularly under operational conditions. The research object is liquid nano-ceramic thermal insulation located on the surface of a round-section pipeline with a circulating heat carrier. The research subject is the thermal conductivity properties of the insulation material under operational conditions. The research aim is to determine the thermal conductivity coefficient of liquid nano-ceramic thermal insulation coating on the surface of the pipeline. The research method involves the laws of steady-state heat conduction and heat transfer for a two-layer cylindrical wall. Research findings indicate that for a steel pipeline measuring 76×3 mm with insulation thickness of 3.5 mm, the thermal conductivity coefficient of the liquid nano-ceramic thermal insulation material amounted to 0.0145 W/(m⋅K). Disregarding the radiative component, the thermal conductivity coefficient equals 0.0135 W/(m⋅K). Conclusions drawn suggest that the obtained value of the operational thermal conductivity coefficient of the liquid nano-ceramic thermal insulation material aligns with the manufacturer's claimed material thermal conductivity of 0.014 W/(m⋅K) and with the findings of other researchers. Minor discrepancies in magnitudes may be attributed to the extended period of insulation usage on the pipeline surface, which at the time of the conducted scientific investigations was approximately 1.5 years.

A simple and efficient in situ polymerization of silica xerogel-acrylic thermal insulation coatings

Thermal insulation coatings are an efficient thermal management material that can effectively prevent heat exchange between the building and outside world, realizing building energy efficiency. In this paper, a new thermal insulation coating was innovatively developed by synthesizing silica xerogel within acrylic emulsion via in situ polymerization. Compared to the pure acrylic coating, the thermal insulation coating with 30 % silane concentration forms a promising xerogel structure, resulting in a thermal conductivity of 0.07 W/(m·K), which is 61 % lower than that of pure acrylic coating. And the surface temperature of the thermal insulation coating with 30 % silane concentration was found to be 12.1 °C lower than pure acrylic coating after placing on the hot stage for some time. These findings indicate that silica xerogel network was effectively synthesized in the acrylic emulsion through in situ polymerization and that the thermal insulation coating displays low thermal conductivity and admirable thermal insulation qualities. The xerogel-acrylic composite coating produced by this research offers a novel form of thermal insulation coating, and the in situ polymerization of silica xerogel can also promote the synthesis of multifunctional composite coatings in various aqueous emulsions.

Exploring the electronic, mechanical, anisotropic and optical properties of the Sc-Al-C MAX phases from a first principles calculations

MAX phase series materials have the excellent thermal, electrical and mechanical properties and have great research potential. To achieve a comprehensive understanding of the utilization of Sc-Al-C MAX phases, the mechanical properties, electronic structures, elastic anisotropy and optical properties of these compounds were calculated by first-principles calculations. The lattice parameters and equilibrium volumes agree with the existing experimental data. The elastic constants show that these compounds are mechanically stable. In addition, the enthalpy of formation indicates that they are thermodynamically stable. The metallic properties of the phases are verified by the analysis of their density of states and band structures. ScAl3C3 has the largest shear and Young’s modulus because of its strong chemical bonding and the values are 150.91 GPa and 346.65 GPa, respectively. Sc2AlC shows the lowest degree of anisotropy due to the lack of strong direction in the bonding. The G/B ratio and ν values support that all these compounds are brittle materials. By calculating the absorption coefficient, it is shown that these compounds can be used as optoelectronic devices in the ultraviolet range. The reflectance images show that these compounds can be used as thermal insulation coatings.

Preliminary Investigation on Mechanical Properties of Hollow Glass Spheres

Hollow glass microspheres (HGM) have been employed in a wide range of applications such as thermal insulating coatings for construction and transportation applications and for acoustic insulation coatings. As such, it is expected for the HGM to exhibit an extremely high pressure tolerance in order to endure the harsh environment. In this present study, an effort has been made to investigate the mechanical properties of hollow glass microsphere. The glass sphere with diameters between 5-30 µm, 50-90 µm and 90-125 µm were used for this investigation. This study's objectives are to investigate the strength of HGM and gain an in-depth understanding of the mechanical characteristics of the sintered spheres.

Feasibility study on cooling scheme design of the concrete shielding for swimming pool-type low-temperature heating reactor

Elevating the operational parameters of Swimming Pool-type Low-Temperature Heating Reactors to augment heating capacity raises concerns about heightened water temperatures within the pool. Elevated water temperatures pose a significant challenge to the integrity and durability of the concrete shielding, necessitating innovative solutions for effective thermal insulation. Existing approaches, such as insulation coatings and static insulation water layers, have shown limitations in maintaining prolonged cooling efficiency under reactor operating conditions. In response to this challenge, our research introduced a novel approach: the implementation of a flowing water layer within the concrete structure. A specialized insulation water layer is integrated within the reactor to efficiently isolate high-temperature pool water from the surrounding concrete shielding. A comprehensive experimental setup is established to assess the insulation effectiveness, yielding insights into the water layer’s insulation performance. Results demonstrate a significant radial temperature difference of up to 14.31 °C between the cold and hot walls of the water layer within the experimental parameters. Investigation into critical experimental variables indicates that inlet positioning minimally affects insulation efficiency. This study not only verifies the viability of the insulation water layer approach but also furnishes crucial experimental data for future research endeavors about the cooling scheme of the Swimming Pool-type Low-Temperature Heating Reactor.

A hBN/B-Si-Al-O-glass composite coating growth on SiCp/Al composite using one-step PEO with nanoparticle addition for outstanding electrical insulation performance

A comprehensive study of the formation of electrical insulation coatings on SiCp/Al composite using plasma electrolytic oxidation (PEO) in an electrolytic system with hBN nanoparticles has been carried out. A complete coating can be formed under a high positive voltage (550–600 V) in a short period of time (3 min), and the coating is mainly composed of the hBN crystal phase as well as some amorphous phases. The high temperature of the local plasma in the PEO process impels these amorphous phases to form an amorphous B-Si-Al-O glass phase. As the treatment time goes on, the cross-sectional porosity of the coating first decreases rapidly and then increases slowly. This is attributed to the fact that the nanoparticles continuously deposit and sinter to repair the larger pores during the coating growth process, hence reducing porosity. Within 6 min, the coating thickness rapidly increases to 133.3 μm, showing excellent electrical insulation performance (with a breakdown voltage of 1460 ± 28 V, volume resistance of 5.52 ± 0.26 G·Ω, electrical resistivity of 4.18 × 1010 Ω∙cm) and high optical band gap value (above 5 eV), which is suitable for electronic packaging or dielectric materials.

Synthesis of low-VOC unsaturated polyester coatings for electrical insulation

Abstract The objective of this research is to develop an unsaturated polyester (UPE) varnish with low-volatile organic compounds (VOCs). Instead of using a solvent, the solvent-free varnish incorporates a reactive diluent to reduce viscosity and a catalyst to accelerate curing. To achieve this, vinyl toluene and 1,4-butanediol dimethacrylate were employed as curing agents. Sebacic acid (SA) and fumaric acid were utilized to create UPE coatings for electrical insulation. Various tests and measurements were made to evaluate the physical, thermal, and chemical structure determination, and electrical properties of the synthesized resins. Given the increasing demand for eco-friendly and low-VOC products, gas chromatography was employed to determine VOC levels. The study demonstrated that the electrical volume resistance of cross-linked coatings containing FA was 1.58 × 1015 Ω·cm, whereas coatings containing SA exhibited a measurement of 6.96 × 1011 Ω·cm. VOC levels in the UPE coatings were found to be in the range of 2.10–3.60%.

Magnetic Properties of Soft Magnetic Composites Based on Iron Powder with a Multilayer Insulating Coating

Magnetic Properties of Soft Magnetic Composites Based on Iron Powder with a Multilayer Insulating Coating