Preparation and characterization of transparent fluorocarbon emulsion doped with antimony tin oxide and TiO2 as thermal-insulating and self-cleaning coating

A transparent thermal insulation and self-cleaning coating was prepared from a fluorocarbon emulsion doped with antimony tin oxide (ATO) and anatase TiO₂ nanoparticles. The thermal insulation and self-cleaning properties of the coating film were optimized by adjusting the amount of ATO and anatase TiO₂ nanoparticles in the fluorocarbon emulsion. The fluorocarbon coating containing 2.0 wt% ATO and 0.1 wt% TiO₂ possessed good comprehensive properties of thermal resistance, self-cleaning, weathering resistance, etc. Compared with the blank glass substrate, the mean light transmittance of the coating film only decreased by about 12% in the visible range. The temperature in the chamber covered with the coated glasses decreased 7°C lower than the common glass chamber without coating. The methyl red painted on the coating was completely faded after three days of ultraviolet irradiation, so the coating film exhibited an excellent self-cleaning property. The transparent coating with excellent thermal insulation and good self-cleaning will be developed for a potential building glass paint used for energy saving and environmental protection.     

Thermal insulation and anti-vibration properties of MoSi2-based coating on mullite fiber insulation tiles

Thermal protection materials with excellent thermal insulation properties and high reliability are crucial for aerospace vehicle. Mullite fiber insulation tiles coated with MoSi₂-borosilicate glass (MFIT@MoSi₂) were prepared by a simple slurry method. Results shown that the surface temperature rapidly reached 1043.1 °C under the heat flux of 450 kW/m², while the cold-surface remained at room temperature. The adjusting effects of MoSi₂-based coating on the thermal response and transfer properties of MFIT were investigated systematically. Compared with MFIT, the surface and internal temperatures of MFIT@MoSi₂ were obviously suppressed, due to the existence of MoSi₂-based coating with high emissivity, which effectively enhanced the thermal radiation of the surfaces. Finally, the structural reliability under coupled environment of heating (q₀ = 450 kW/m²) and random vibration with high magnitude (20–2000 Hz, Grms = 20 g) was also investigated. Destructive cracking and peeling of the coating were not observed, due to the excellent bonding strength between the coating and the substrate. The results provided an important basis for the potential application of insulation tiles with mullite fibers in aerospace vehicles and the design of lightweight thermal protection systems.     

粉煤灰微珠-Ag复合颗粒的制备工艺和分析

采用化学镀的方法,以银氨溶液为镀液,甲醛为还原剂,按照一定的工艺过程对粉煤灰微珠进行表面镀银处理,得到了粉煤灰微珠-Ag复合颗粒。同时借助激光粒径分析仪、X射线衍射仪、场发射扫描电子显微镜、X射线能谱仪等检测设备对复合颗粒的粒径分布、化学成分、镀层表面形貌和结构进行了分析。对复合微珠进行保温隔热性能测试,掺镀银微珠的涂料比原微珠的涂料温度低约4℃。结果表明,按照设定的工艺过程,可以成功制备出具有保温隔热低辐射功能的粉煤灰微珠-Ag复合颗粒,作为一种功能性骨料有望用于建筑物外围护结构表面的砂浆或涂料中以降低对远红外热的辐射能力。     

Preparation and properties of TaSi2-MoSi2-ZrO2-borosilicate glass coating on porous SiCO ceramic composites for thermal protection

A TaSi₂-MoSi₂-ZrO₂-borosilicate glass (TMZG) coating was prepared by a slurry method on a carbon fibre-reinforced porous silicon oxycarbide (SiCO) ceramic composite for thermal protection. The coating was well adhered to the substrate and showed a uniform thickness of approximately 375?µm. After thermal cycling from 1873?K to room temperature six times (total oxidation time of 180?min), the shape and dimension of the TMZG remain almost unchanged with no cracking or peeling of the coating surface. The TMZG-coated sample exhibits good oxidation resistance because of a molten SiO₂ film with ZrSiO₄ particles distributed on the outer layer of the coating. After ablation testing under an oxyacetylene flame at 1927?K for 90?s, the linear ablation rate of the TMZG coated sample are 8.33?×?10^?4 mm/s. The whole coating retains integrity, preventing substrate ablation during the test. The TMZG coating with excellent temperature resistance shows broad applicability in thermal insulation materials.     

Studies on a novel bioactive glass and composite coating with hydroxyapatite on titanium based alloys: Effect of γ-sterilization on coating

A novel silicate based bioactive glass coating composition containing B₂O₃ and TiO₂ having matching thermal properties with that of Ti₆Al₄ V implants was developed and characterized. A conventional vitreous enamelling technique was used for coating small flat surface and curved surface of small rods. Hydroxyapatite (HAp) micro and nano-crystalline particles were used to prepare bioactive glass-HAp composite coating. Scratch testing was used to study the coating adhesion and its fracture behaviour under simulated conditions. As observed from scratch testing results, adhesion strength of the coating improved from 21 N normal load to 27 N and 32 N on addition of micro-HAp and nano HAp powder, respectively, to bioactive glass matrix. Further, sterilization of the coated samples with 25 kGy gamma irradiation substantially enhanced the adhesion of glass coating and HAp-composite coating.     

High thermal conductive shape-stabilized phase change materials based on water-borne polyurethane/boron nitride aerogel

Phase change materials (PCMs) applied in energy storage and temperature control system are important for energy conservation and environmental protection. In this work, structure-adjustable water-borne polyurethane (WPU)/boron nitride (BN) aerogels were synthesized via directional freeze-drying method, and used as supporting scaffolds to confine paraffin wax (PW) and obtain composite phase change materials. The three-dimensional (3D) porous thermal conductivity network of BN was derived by the in-situ ice crystal mound in aerogel, which endows the PW/WPU/BN composite PCM-2.5 with high thermal conductivity (0.96 W m^?1 K^?1) and high energy storage density (140.04 J/g). Shape-stabilized PCMs with high thermal conductivity and excellent electrical insulation prepared by the simple method have great potential for the thermal management of electronic products.     

聚碳酸酯型水性聚氨酯乳液的制备与性能

以聚碳酸酯二元醇和异佛尔酮二异氰酸酯为主要原料,采用预聚法合成了聚碳酸酯型水性聚氨酯( WPU) ,用傅里叶变换红外光谱表征了WPU,考察了不同NCO/OH( 摩尔比) 对WPU 乳液粒径及薄膜的耐水性、拉伸性能的影响,并研究了WPU 的热稳定性。结果表明,随着NCO/OH 值的增大,WPU乳液的粒径增大,稳定性降低,薄膜的耐水性和拉伸强度提高,扯断伸长率降低; WPU 薄膜的热分解速率较快,硬段的热分解温度为193 ℃,最大失重温度为287 ℃; 软段的热分解温度为321 ℃,最大失重温度为364 ℃左右。     

Research on microstructure and oxidation resistant property of ZrSi2-SiC/SiC coating on HTR graphite spheres

ZrSi₂-SiC/SiC coating was prepared on the surface of high temperature gas-cooled reactor (HTR) matrix graphite spheres by two-step pack cementation and sintering process. The microstructure, oxidation resistance and thermal shock resistance properties of the as-prepared coatings with different original powder mixtures were investigated. Results show that dense microstructure of the ZrSi₂-SiC/SiC coating and continuous ZrSiO₄-SiO₂-ZrO₂ glass phase generated during the oxidation process were the key factors for the outstanding thermal properties. When the mole ratio of Zr:Si:C reaches 1:7:3 in the second pack cementation powders, the coated graphite spheres have optimum oxidation resistant ability. The weight gain is only 0.6 wt% after 15 times thermal shock tests and 0.12 wt% after isothermal oxidation test at 1500 °C for 20 h in air. The oxidation resistant mechanism of the coating was also discussed. The dense inner SiC layer and the outer glass layer generated during the oxidation process could protect the ZrSi₂-SiC/SiC coating from further oxidation.     

Model-based analysis of thermal insulation coatings

Thermal insulation properties of coatings based on selected functional filler materials are investigated. The underlying physics, thermal conductivity of a heterogeneous two-component coating, and porosity and thermal conductivity of hollow spheres (HS) are quantified and a mathematical model for a thermal insulation coating developed. Data from a previous experimental investigation with hollow glass sphere-based epoxy and acrylic coatings were used for model validation. Simulations of thermal conductivities were in good agreement with experimental data. Using the model, a parameter study was also conducted exploring the effects of the following parameters: pigment (hollow spheres) volume concentration (PVC), average sphere size or sphere size distribution, thermal conductivities of binder and sphere wall material, and sphere wall thickness. All the parameters affected the thermal conductivity of an epoxy coating, but simulations revealed that the most important parameters are the PVC, the sphere wall thickness, and the sphere wall material. The model can be used, qualitatively, to get an indication of the effect of important model parameters on the thermal conductivity of an HS-based coating and thereby be used as a specification tool or as a help in the planning of relevant experiments to conduct. Further work with the model must involve additional experiments to secure a general verification of important underlying model assumptions.     

Electrochemical performance of pyrolytic carbon-coated natural graphite spheres

Natural graphite (NG) spheres were coated by pyrolytic carbon from the thermal decomposition of C₂H₂/Ar at 950 °C in a fluidized bed reactor. Scanning electron microscopy and secondary electron focused ion beam (FIB) images clearly showed that a pyrolytic carbon layer with a thickness of ∼250 nm was uniformly deposited on the surface of the NG spheres. Electrochemical performance measurements for the original and coated NG spheres as anode materials of a lithium-ion battery indicated that the first coulombic efficiency and cyclability were significantly improved in the coated sample. The reasons for this were investigated by analyzing structural characteristics, specific surface area, pore size distribution, and solid electrolyte interphase (SEI) film. Using a FIB workstation, we demonstrated, by cross-section imaging of a coated NG sphere that had experienced five electrochemical cycles, that the SEI film formed on the non-graphitic pyrolytic carbon surface became thinner (60-150 nm) and more uniform in composition compared with that on the surface of uncoated NG spheres; and the formation of an “internal SEI film” inside the NG spheres was also remarkably suppressed due to the uniform coating of pyrolytic carbon.     

Synthesis and characterization of waterborne polyurethane emulsions based on poly(butylene itaconate) ester

Waterborne polyurethane (WPU) prepolymer was synthesised by the reaction of poly(butylene itaconate) ester (PBI, Mn = 1109 g/mol), 1,6-hexanediol, dimethylol propionic acid (DMPA), 2,4-toluene diisocynate (TDI), hydroxyethyl acrylate (HEA), and absolute ethanol as blocking agent, triethylamine as neutralizer. Cross-linked WPU was synthesized by trimethylolpropane (TMP) as crosslinker. The influences of PBI, DMPA, and TMP content on WPU emulsions and films were investigated. The structure of WPU was determined by Fourier transform infrared (FTIR) spectra, thermal properties and glass transition temperature of WPU films were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively, and morphology of the emulsion particles was observed by transmission electron microscopy (TEM). Through TGA, the heat resistance of the cross-linked WPU film was better than WPU film. By DSC analysis, glass transition temperature of cross-linked WPU film (21 °C) was higher than WPU film (10 °C).     

Enhancing thermal insulation and mechanical strength of porous ceramic through size-graded MA Hollow Spheres

In this study, a series of porous ceramics were prepared using different ratios of small and large size MA hollow ceramic spheres as pore-forming agents, and their thermal insulation properties were investigated. The results showed that increasing the proportion of small size hollow ceramic spheres could effectively decrease the thermal conductivity and improve the compressive strength of the porous ceramics. The optimal porous ceramic was prepared with a ratio of 10∼50 of small and large size hollow ceramic spheres, which had a thermal conductivity of 0.368 W/(m·K) at 800 °C and a compressive strength of 22.43 MPa. Microscopic analysis indicated that the enhanced thermal insulation and mechanical properties were due to the improved pore structure and the enhanced bonding strength between the ceramic spheres and the matrix. The findings provide valuable insights for the development of high-performance thermal insulation materials.     

Amorphous silica-coated graphite particles for thermally conductive and electrically insulating resins

A thermally conductive and electrically insulating composite filler was produced by surfactant assisted sol–gel coating of amorphous silica on flake graphite. Amorphous silica-coated graphite (a-Si coated grp) obtained using a cationic surfactant showed the best enhancement of the insulating coating. The resulting a-Si coated grp/boehmite/polybutylene terephthalate polyester resin composite exhibited a high volume resistivity, exceeding 1.0 × 10¹⁴ Ω cm at an applied voltage of 500 V, and a thermal conductivity of 3.3 W/m K at 22.9 vol.% a-Si coated grp loading. The heat releasing performance of the developed resin composite in actual light-emitting diodes bulb housings was compared with conventionally used thermally and electrically conductive resin. This comparison revealed that the new composite released heat more effectively. This innovative technology, which may solve the trade-off between material properties and cost, will be available for a broad range of thermally conductive resin applications that simultaneously require thermal conduction and electrical insulation.     

A low-temperature prepared composite coating to protect SiC-coated C/C composites against oxidation in a wide temperature range for long-life service

To improve the oxidation resistance of carbon/carbon (C/C) composites in a wide temperature range (1173–1773 K), a composite coating containing rich B₂O₃ glass was prepared on SiC-coated C/C composites by slurry dipping-densifying at low temperature. Borosilicate and SiO₂ glasses acted as oxygen barriers at low and medium-high temperatures, respectively. Besides, Hf-oxides (HfO₂, HfSiO₄) ceramic particles improved the thermal stability of the glass and enhanced the crack resistance of glass layer. Therefore, the composite coating can effectively protect C/C composites against oxidation for 403 h at 1173 K, 723 h at 1473 K and 403 h at 1773 K with the mass gain of 3.77 g·m⁻², 21.41 g·m⁻² and 0.42 g·m⁻², respectively. After 50 times thermal cycles between room temperature and 1773 K, the mass gain of the coated sample was 3.95 g·m⁻² and the mass retention rate was up to 98.19 % during the thermos-gravimetric test from room temperature to 1773 K.     

A SiC–Si–ZrB2 multiphase oxidation protective ceramic coating for SiC-coated carbon/carbon composites

In order to improve the oxidation protective ability of SiC-coated carbon/carbon (C/C) composites, a SiC–Si–ZrB₂ multiphase ceramic coating was prepared on the surface of SiC-coated C/C composite by the process of pack cementation. The microstructures of the coating were characterized using X-ray diffraction and scanning electron microscopy. The coating was found to be composed of SiC, Si and ZrB₂. The oxidation resistance of the coated specimens was investigated at 1773 K. The results show that the SiC–Si–ZrB₂ can protect C/C against oxidation at 1773 K for more than 386 h. The excellent oxidation protective performance is attributed to the integrity and stability of SiO₂ glass improved by the formation of ZrSiO₄ phase during oxidation. The coated specimens were given thermal shocks between 1773 K and room temperature for 20 times. After thermal shocks, the residual flexural strength of the coated C/C composites was decreased by 16.3%.     

Oxidation protection of B4C modified HfB2-SiC coating for C/C composites at 1073–1473 K

B₄C modified HfB₂-SiC coating for C/C substrate was designed to expand the application of HfB₂-SiC based coating in low-medium temperature environment. The oxidation protection behavior of HfB₂-SiC based ceramic coatings with and without B₄C at 1073, 1273 and 1473 K was tested and analyzed. The experimental results reveal that the oxidative damage of HfB₂-SiC coated C/C reduces by over 20% after introducing B₄C, which may be due to the protection of borosilicate glass with more suitable viscosity during oxidation. Meanwhile, B₄C can improve the oxidation protection ability of HfB₂-SiC coating best at 1473 K. And the introduction of B₄C can reduce the mass loss of HfB₂-SiC coated C/C sample by 77.6% after oxidation for 58 h at 1473 K. The fluidity of glass film becoming better with temperature-rising, and the fluid borosilicate glass layer makes the coated samples have the best anti-oxidation properties at 1473 K among these three temperatures.     

Multilayered nacre-mimetic inspired flexible PEI film with high thermal conductivity and reliable dielectric performances

It is critically desired to integrate high in-plane thermal conductivity (TC) and distinguished electric insulation for thermal conductive film in modern electronic devices. Herein, integration of high TC and electric insulation in sandwich-like BNNSs@MWCNTs/PEI (S-BNNSs@MWCNTs/PEI) composite film has been successfully achieved by layer-by-layer spin coating and hot pressing inspired by highly ordered structure of natural nacre. The covalently bonded connections between BNNSs and MWCNTs are beneficial to create more efficient heat conduction path, which can partly decrease the interfacial thermal resistance and phonon scattering. The resultant S-BNNSs@MWCNTs/PEI composite films possess a high in-plane TC of 6.88 W m^?1K^?1. Meantime, benefiting from the alternating multilayer structure, the composite films exhibit satisfactory reliable dielectric performances with flexibility, which shows great potential in ceramics-filled polymer composite TIMs.     

Fabrication of insulated metal substrates with organic ceramic composite films for high thermal conductivity

Insulated metal substrates (IMSs) were fabricated and characterized using an organic ceramic composite as a coating mixture. Organic‐inorganic sol solutions were prepared by a sol‐gel process using TEOS (tetraethylorthosilicate), MTMS (methyltrimethoxysilane) and PhTMS (phenyltrimethoxysilane). Ceramic fillers were composed of aluminum oxide (1 and 4 µm) and silicon nitride. The optimal ratio of ceramic filler in the coating mixture was found to be 70 wt%. A thermal conductivity of 3.16 W/mK and a breakdown voltage of 4 kV with a leakage current of 0.17 mA/cm² were obtained for the 122 µm-thick film. A well-networked microstructure between the sol resin and filler in the organic ceramic composite films enhanced the properties of the IMS, such as thermal conductivity and electric insulation.     

Preparation,Morphology and Properties of Waterborne-Polyurethane/Silica

A series of waterborne-polyurethane/silica (WPU/SiO₂) were prepared from isophoronediisocyanate, polyester polyol, dimethylolpropionic acid, tetraethoxysilane and 3-glycidyloxypropyl trimethoxysilane. The WPU/SiO₂ dispersion had narrower particle size distribution than the pure WPU. The mechanical properties of WPU/SiO₂ films were improved than the pure WPU. WPU/SiO₂ films were characterized by FT-IR spectroscopy, SEM, TEM, AFM, XRD and UV-Vis spectroscopy. The results showed that WPU/ SiO₂ hybrid films were found to be smooth morphology, and had good thermal stability and tunable transparence with the silica fraction in the film. Through suitable adjustment of silica content, some thin films have potential applications as the specialty materials.     

The chain extender content and NCO/OH ratio flexibly tune the properties of natural rubber‐based waterborne polyurethanes

The effects of chain extender content (ethylene diamine, EDA) and NCO/OH ratio on the properties of natural rubber‐based waterborne polyurethanes (WPUs) were investigated experimentally. The particle size of WPU increased significantly with the NCO/OH ratio, in the presence of the EDA chain extender, while it was unaffected by the EDA content. The water uptake of WPU film increased with the EDA content, while the swelling in various solvents decreased. In a thermal analysis, the second decomposition stage of a WPU film increased with the EDA content and with the NCO/OH ratio that also positively affected the dynamic mechanical and mechanical properties. These factors in WPU films had no the effect on the T_g. The stress–strain curves clearly showed the change in WPU films from soft elastomeric materials to ductile and hard plastics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42505.