Thermostable heat-insulating composite materials based on hollow microspheres and solid phosphate binders: development and research

Thermostable composite materials based on solid magnesium phosphate and calcium phosphate, as well as hybrid calcium magnesium phosphate binders have been developed and investigated. Thermal and phase transformations of the phosphate composites have been studied. Strength characteristics of composite materials have been determined in the temperature range of 20–1000 °C. It is shown that the obtained phosphate composites have high strength properties (compressive strength reaches 120–130 MPa) and are characterised by high thermal stability in the temperature range up to 1000 °С. The low weight loss of the studied composites (no more than 10 %) and the absence of significant thermal effects indicate that they are promising for use as a thermostable matrix for obtaining functional composite materials.

Hollow microspheres are widely used in syntactic foam as a lightweight filling material. Hollow glass microspheres (HGM) and hollow phenolic microspheres (HPM) were added to the phenolic resin to prepare phenolic syntactic foams. Then the mechanical properties, thermal insulation properties, and thermal property stability of them were studied. The mechanical test result shows that the flexural strength of phenolic syntactic foam gradually decreases with the increasing volume fraction of microspheres at room temperature. When the volume fraction of HGM is 20%, the specific strength of phenolic syntactic foam can rise to 0.0334 Nm/kg. HGM reduces the density of the phenolic syntactic foam and remains at high strength. In addition, the thermal conductivity of phenolic syntactic foam decreases with the increasing volume fraction of the hollow microspheres, indicating that the microspheres can effectively improve the thermal insulation performance of the phenolic syntactic foam. Meanwhile, the thermal conductivity of phenolic syntactic foam also increases as the heat treatment temperature rises. In addition, the thermal insulation performance of phenolic syntactic foam containing HGM is better than that containing HPM. Thermal analysis experiments show that the thermal weight loss rate becomes slower as the content of HGM increases. Therefore, HGM improves the thermal stability of the containing phenolic syntactic foam. However, the HPM reduces the thermal decomposition temperature and the thermal stability of the phenolic syntactic foam. This work provides the technical basis for applying phenolic syntactic foam as a heat insulation material.

Tailoring of thermal and dielectric properties of LDPE-matrix composites by the volume fraction, density, and surface modification of hollow glass microsphere filler

In this study, a kind of novel heat-insulating material composed by the vinyl-functionalized polyborosiloxane (BSiO) and hollow glass microspheres (HGM) was successfully prepared. Under solvent-free condition, the BSiO was synthesized by reacting triethoxyvinylsilane (VTEOS) and boric acid by one-pot method and characterized by GPC, FT-IR, NMR-29Si, NMR-11B and TGA analysis. The results indicated that the monomer feed ratio of the reactant made a great difference on the molecular structure and thermal stability of the BSiO and the BSiO-2 showed the best thermal stability when the feeding ratio of VTEOS and BA was 1.5. Moreover, the ceramic conversion analysis indicated that the BSiO-2 tended to form the inorganic SiBOC nanocomposite. Properties, such as the microstructure, density, linear shrinkage, compressive strength and thermal conductivity, burning behavior and flame retardancy of the BSiO-2/HGM composites after different heat treatment, were studied. The SEM results showed that the BSiO-2 could effectively wet the surface of HGM and the HGM was glued together firmly. With the increase in heat treatment temperature, the density and thermal conductivity of BSiO-2/HGM composites reached the minimum value at 600 °C, while the compressive strength reached the maximum value. The result of flame retardancy study showed that the composites possessed high LOI value (> 50%) and hardly any smoke could be observed during the burning process. This indicated that the BSiO-2/HGM composites possessed excellent flame-retardant property and fire safety. This paper will provide ideas for the design and preparation of heat-insulating materials with polyborosiloxane as heat-resistant binder.

Four types of hollow glass microspheres, having the density of 0.125–0.60 g/cm3, were filled into epoxy-matrix, and volume fraction of hollow glass microsphere was varied from 0% to 60%. The thermal, dielectric and compressive properties of the composites were investigated. The results show that the thermal conductivity, dielectric constant (Dk) and loss (Df) and compressive modulus and strength of the composites show decreased trend with increasing hollow glass microsphere content or decreasing hollow glass microsphere density, which indicates that the properties of the composites are mainly dependent on the characteristics of hollow glass microsphere. By comparing the experimental data and theoretical predictions, it is found that the properties of the composites, especially for thermal conductivity, are also related to the voids in epoxy-matrix. To conveniently predict thermal conductivity and Dk in the investigated materials system, theoretical models reported in the literature are analyzed and compared with the experimental data. Finally, suitable models are recommended. In addition, the thermal conductivity and dielectric properties of the composites were investigated as a function of testing temperature. This work indicates that thermal, dielectric and compressive properties of epoxy-matrix composites can be tailored by adjusting hollow glass microsphere content and density, which makes hollow glass microsphere filled composites a promising candidate in related fields.

Research on compressive strength and thermal conductivity of lightweight phosphogypsum-based composite cementitious materials

ABSTRACTPorous polymeric composites containing hollow microspheres such as hollow organic microsphere (HOM) and hollow glass microsphere (HGM), respectively, up to 50 vol% were prepared by a UV-radiation photo-curing process. The non-porous sample was also prepared as a reference material. The comparative study on measured and theoretical thermal conductivity (k) revealed that HOM composites were in a category of the internal porous material (EMT model < k < parallel model) with spherical pore structure. In case of HGM composites which were considered as three-phasic material composed of bulk HPU matrix, thermal conductivity of HGM composites could be perfectly predicted by Felske model. From dynamic mechanical measurement, tensile and compression properties, it appeared that mechanical characteristics of hollow microspheres played an important role in storage modulus, Tg, and mechanical properties of composites. Especially, the incorporation of HGMs leaded to the reinforcement with increasing volume percentage of HGM in composites.

A syntactic foam was prepared from an epoxy resin matrix and modified hollow glass microsphere fillers. Modification by silane coupling agents with different molecular structures was analyzed, and the optimal content of the silane coupling agent was determined. The results demonstrated that all silane coupling agents enhanced the adhesion between the hollow glass microspheres and epoxy resin matrix, resulting in enhanced water absorption, compressive performance, tensile performance, and bending performance compared to those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end groups, the one with a sulfhydryl end group exhibited optimal modification for hollow glass microspheres. Among the silane coupling agents with different backbone structures, the one with silanol groups exhibited the optimal modification of hollow glass microspheres. Additionally, the performance of the syntactic foams was optimal when 6% of the silanol-containing coupling agent was used. The results demonstrated that syntactic foams prepared with hollow glass microspheres modified by silane coupling agents exhibited improvements in water absorption, compressive performance, tensile performance, and bending performance, compared with those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end structures, the one with a sulfhydryl group as end group showed the best modification effect on hollow glass microspheres. The water absorption was 0.35%, the compressive strength was 62.15 MPa, the tensile strength was 40.15 MPa, and the bending strength was 53.17 MPa. Among silane coupling agents with different backbone structures, the one with silanol groupsbonds showed the best results. Its compressive strength was up to 64.15 MPa, the tensile strength was 35.47 MPa, and the bending strength was 53.99 MPa.

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

Preparation of high-performance thermal insulation composite material from alkali-activated binders, foam, hollow glass microspheres and aerogel

Preparation and characterization of hollow glass microsphere ceramics and silica aerogel/hollow glass microsphere ceramics having low density and low thermal conductivity

This manuscript proposes a soft-chemistry method to develop superhydrophobic and highly IR-reflective hollow glass microspheres (HGM). The anatase TiO2 and a superhydrophobic agent were coated on the HGM surface in one step. TBT and PFOTES were selected as the Ti source and the superhydrophobic agent, respectively. They were both coated on the HGM, and after the hydrothermal process, the TBT turned to anatase TiO2. In this way, a PFOTES/TiO2-coated HGM (MCHGM) was prepared. For comparison, PFOTES single-coated HGM (F-SCHGM) and TiO2 single-coated HGM (Ti-SCHGM) were synthesized as well. The PFOTES and TiO2 coatings on the HGM surface were demonstrated through X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive detector (EDS) characterizations. The MCHGM showed a higher contact angle (153°) but a lower sliding angle (16°) than F-SCHGM, with a contact angle of 141.2° and a sliding angle of 67°. In addition, both Ti-SCHGM and MCHGM displayed similar IR reflectivity values, which were about 5.8% higher than the original HGM and F-SCHGM. Also, the PFOTES coating barely changed the thermal conductivity. Therefore, F-SCHGM, with a thermal conductivity of 0.0479 W/(m·K), was quite like the original HGM, which was 0.0475 W/(m·K). MCHGM and Ti-SCHGM were also similar. Their thermal conductivity values were 0.0543 W/(m·K) and 0.0543 W/(m·K), respectively. The TiO2 coating slightly increased the thermal conductivity, but with the increase in reflectivity, the overall heat-insulation property was enhanced. Finally, since the IR-reflecting property is provided by the HGM coating, if the coating is fouled, the reflectivity decreases. Therefore, with the superhydrophobic coating, the surface is protected from fouling, and its lifetime is also prolonged.

Dry density and compression strength of foam concrete are conflicting, there is a negative relationship between them. Hollow glass microsphere is a new lightweight material which is lightweight, high strength, low thermal conductivity and good thermal stability. In order to prepare lightweight and high-strength foam concrete, this paper researched the effects of different dosage on dry density and compressive strength of foam concrete through adding hollow glass microspheres. The results show that the thermal conductivity of foam concrete increased as the hollow glass microsphere increases, and the dry densities of foam concrete are between 120-200 kg•m-3, compressive strength reaches 0.1MPa.

In this study, hollow glass microspheres (HGM) and hollow polystyrene microspheres (HPSM) have been employed as fillers in epoxy resin to prepare the syntactic foam. A kind of good performance composite was prepared. The effects of presence of various hollow microspheres on the impact and compressive properties of syntactic foams are studied. Weight fraction of HPSM and HGM for the syntactic foams varies up to 2.0 wt% and 25 wt%, respectively. The results show that the coupling agent can induce the interfacial adhesion between the HGM and the resin and help HGM uniformly disperse in the resin and hence result in better mechanical properties of composite. On the other hand, the effect of HPSM for the composite density is greater than that of HGM. The addition of a small percentage of HPSM helps produce an important improvement in the low density of syntactic foam. The syntactic foam has uniform stability component and the excellent integrative performances. Fabricated syntactic foams had compression strength of 51.96 MPa and density of 0.671 g/cm3.

The vibration-reducing ability of construction materials is generally described by the damping ratio of the materials. Previously, many studies on the damping ratio of concrete have been done, such as the addition of rubber, polymer, fiber, and recycled aggregates in the concrete. However, the application of these materials in construction is limited due to their drawbacks. This paper investigated the effect of the replacement ratio and the size of the hollow glass microspheres (HGM), cenospheres (CS), and graphite flakes (GF) on the damping ratio of mortar. Furthermore, rubber particles (RP), aluminum powder (AP), and natural fiber (NF) were investigated to find if they have a combination effect with HGM. The half-power bandwidth method was conducted to obtain the damping ratio at 28 days of curing, and the compressive and flexural strength tests were also conducted to study the mechanical properties of mortar that contained HGM, CS, and GF. The results show that increases in the size of HGM and the replacement ratio of sand with HGM lead to an increase in the damping ratio. Moreover, RP and NF do not provide a combination effect with HGM on the damping ratio, whereas the application of AP results in a drastic compressive strength decrease even with an increase in damping ratio when incorporated with HGM. Besides, an increase in the replacement percentage of CS also leads to an improvement in the damping ratio, and a smaller size and higher replacement ratio of GFs can improve the damping ratio compared to other additives. As a result, CS and GF are more effective than HGM. 50% replacement ratio of CS slightly reduced the compressive strength by 6.4 MPa while improving the damping ratio by 15%, and 10% replacement ratio of samller GF can enhance the flexural strength by over 4.55% while increasing the damping ratio by 20.83%.