Surface Of Hollow Glass Microspheres Research Articles

Constructing ‘bayberry shape’ structure on HGMs surface using CNTs to enhance the mechanical properties of HGMs/epoxy composites

The lightweight composites, composed of epoxy resin (EP) and hollow glass microspheres (HGMs), have been widely applied in marine buoyancy materials, insulation for marine pipelines, and aerospace. However, achieving lower density often requires a significant addition of HGMs, leading to a compromise in mechanical properties. To address this problem, this paper proposes a method to enhance the mechanical properties of HGMs/EP composites without altering the HGMs content. Here, the ‘bayberry shape’ structure of HGMs was achieved by chemically grafting carbon nanotubes (CNTs) onto their surface through an esterification reaction. Subsequently, a lightweight CNTs-HGMs/EP composite with improved strength was fabricated using these ‘bayberry’ HGMs as fillers and EP as the matrix. The effect of different grafted-CNTs content on HGMs' surface on the mechanical properties of CNTs-HGMs/EP composites, along with the enhancement mechanism, were systematically analyzed. The tensile strength, flexural strength and compressive strength of CNTs-HGMs/EP composites demonstrated remarkable increases of 39.14%, 21.78% and 17.87%, respectively, compared to pure HGMs/EP composites. Our results demonstrate that surface modification of HGMs could significantly improved the mechanical properties of HGMs/EP composites without affecting their density. Moreover, this method was characterized by its simplicity in operation and batch preparation, which holds great significance for the efficient production of lightweight composites.

Preparation and performance of intumescent water-based coatings with both thermal insulation and flame retardant functions

Functional flame retardant polymer materials are of great strategic relevance in reducing energy consumption in the wake of accelerated advances in materials science. In this paper, boehmite sol was employed to modify the surface of hollow glass microspheres (HGMs), self-designed a new type of intumescent flame retardant with melamine polyphosphate and starch (M-S system), which subsequently achieved synergistic flame retardant effects and produced high-performance water-based HGMs@Al2O3/M-S composite coatings that could be successively manufactured. As revealed from findings, HGMs@Al2O3 retained the fundamental structure and characteristics of HGMs and enhanced the interfacial compatibility with the water-based polymer matrix. The thermal conductivity of 0.097 W/(m·K) was achieved at 7 wt% HGMs@Al2O3, which notably strengthened the fire resistance of the coating when compounded with 20 wt% M-S. HGMs@Al2O3 also acted as a catalyst for carbon formation and achieves self-extinguishing off fire when the LOI value reached 36 % and UL94 passed the V-0 test. The maximum pyrolysis temperature of the HGMs@Al2O3/M-S composite coatings was 410.1 °C. The results of conical calorimetry indicate that the HRR were reduced by 76.9 % and the THR by 83.8 %, the superior smoke suppression performance of the material. FPI and FGI were 0.21 m2s/kW and 3.02 kW/m2/s separately, indicating a significant improvement in the fire performance of the material, with high residual carbon strength. When burned, HGMs@Al2O3 migrates to the surface of the material and acts as a flame retardant. It demonstrates that the material is superior to previous resemble products and has tremendous potential for application and further industrialization.

Hydrophobic treatment on hollow glass microspheres for enhancing the flowability of lightweight high-performance cementitious composites

The use of hollow glass microspheres (HGMs) in a low water-to-binder matrix generally hinders the flowability of the composite due to the high water absorption capacity of HGMs. This study investigated the feasibility of improving the flow behavior of lightweight high-performance cementitious composites (L-HPC) by adding microspheres with hydrophobic treatment. The hydrophobic HGMs were prepared with a ball milling method using low-cost stearic acid. The successfully modified hydrophobic HGMs were then used for the preparation of L-HPC. The results show that the production, including milling for 2–8 h with a 4 wt% addition of stearic acid, can convert hydrophilic HGMs into hydrophobic ones, with the water contact angle increasing from 0° to 102–154° (as a function of processing time). The diffraction peaks and phase transition latent heat results also proved the modification of the surface of HGMs with a hydrophobic coating layer. Cement hydration monitoring demonstrated that the hydrophobic HGMs hardly absorbed water and did not show significant wetting behavior during mixing. Since more water was available for cement hydration due to the hydrophobic effect of HGMs, the formation of hydration products and flowability were significantly increased. The presence of stearic acid delayed the contact time between some cement particles and water, thereby slowing down the heat release rate, resulting in the prevention of potential early cracking with the maintenance of high strength exhibition even with the enhanced flowability.

Ultra low-temperature fabrication of hollow glass microspheres and polysilazane coating for enhanced thermal protection of carbon/epoxy composites

This investigation was aimed to develop high-temperature resistant coatings suitable for carbon fiber-reinforced epoxy composites at ultra low preparation temperatures. In the organic-inorganic coating, hollow glass microspheres were chosen as the filling phase, and polysilazane was selected as the film-forming material. Fourier transforms infrared spectra showed that polysilazane can be cross-linked and solidified at low temperatures, which provided the possibility for protecting the substrate from high-temperature damage. By modifying the surface of hollow glass microspheres, the coating dispersions were able to maintain good stability within 120 min. The coating exhibited good thermal vibration resistance and could stand at 220 °C for 30 min after 6 cycles without obvious cracking and peeling. After the static thermal test, the coated composites still maintained a flexural strength of 603.7±19.2 MPa (retention rate can reach 86.6%) at 250 °C, which was higher than that (593.3±14.8 MPa) of uncoated samples at 190 °C. The results indicated that the coating has the advantage of low curing temperature, convenient operation, and excellent thermal protection performance, which could further expand the potential application of carbon fiber-reinforced epoxy composites in firefighting unmanned aerial vehicles, hypersonic missiles, and other fields.

Endowing versatility and superamphiphobicity to composite coating via a bioinspired strategy

The strong adhesion by crude oil and the deposition of wax in petrochemical pipeline systems are notorious problems, which seriously threaten the safety and economic production of the petroleum industry. Superamphiphobic coatings that repel water/oil offer exciting opportunities to solve these problems, but there are formidable challenges in developing elaborate structures facilely. Herein, a springtail-inspired and multifunctional superamphiphobic coating (OCA = 152.1 ± 0.4°, OSA = 8.2 ± 0.8°) was prepared by a straightforward spraying technique. To emulate the cuticular characteristics of the springtail, the micro-/nano-hierarchical fillers prepared by loading silica nanoparticles on the surface of hollow glass microspheres and then chemical modification (F-HGM@SiO2) and the fluorinated nano-silica (F-SiO2) were simultaneously introduced into polyvinylidene fluoride (PVDF) to construct a micro-/nano-/nano-hierarchical structure on the PVDF/F-HGM@SiO2/F-SiO2 surface. Hence, a durable air layer was formed due to the suitable rough structure in conjunction with low-surface-energy groups, which endows the coating with outstanding crude-oil-repellency. Moreover, based on the self-designed test device, the coating showed an excellent anti-waxing deposition ratio (R = 82.76 %). Significantly, on the basis of the morphologies, wettability, and anti-waxing performance of the coatings, the main liquid-wettability, and anti-waxing mechanisms were illustrated, which revealed the inseparable relationship between them. The durability of the coating was investigated through mechanical/chemical damage tests (the OCA and OSA were kept above 140° and below 30°, respectively). Therefore, this bioinspired superamphiphobic coating is expected to open up new avenues for the design and fabrication of anti-waxing coating, which present enormous application value in oily/corrosive environments.

Surface modified hollow glass microspheres-epoxy composites with enhanced thermal insulation and reduced dielectric constant

The hollow glass microspheres (HGMs) are the important fillers in the thermal insulating composites due to the low density, high flowability and the low thermal conductivity. However, the high filling ratio of HGMs without phase separation is hard to be reached owing to the weak interface binding strength between the HGMs and the resin matrix in the composites. In this work, the surface of HGMs is modified with silane coupling agents (3-Glycidoxypropyltrimethoxysilane, KH560) to improve the interface binding strength. After the surface modification, the maximum filling ratio of the HGMs in the epoxy (EP) resin can reach 35 wt. % (67 vol. %). The highly improved filling ratio benefits the HGMs-EP composites with an improved thermal insulation with a low thermal conductivity 0.14 W·m−1·K−1. Moreover, a highly reduced permittivity Dk = 2.3 at the frequency of 110 MHz is also attained for the 67 vol. % HGMs filled composites, which should be promising for the 5G communication technology that requires low dielectric constant for reducing the signal delay and loss.

Eco-friendly poly(dopamine)-modified glass microspheres as a novel self-floating adsorbent for enhanced adsorption of tetracycline

Hollow glass microspheres (HGM), as a promising hollow spherical ultra-light material, have the advantages of uniform particle size, regular shape, high mechanical strength and stable physical and chemical properties. It has been widely utilized in many fields but its application in water treatment is yet to be developed. Herein, a novel self-floating composite adsorbent was obtained by forming a poly(dopamine) (PDA) biomass coating on the surface of HGM and introducing sulfonic acid groups. The hollow composite material (HGM@PDA-SO3H) was utilized in the adsorptive elimination of tetracycline (TC) from aqueous solutions. In addition to great adsorption performance, HGM@PDA-SO3H also exhibited satisfactory self-floating solid-liquid separation capability. Langmuir, pseudo second-order and Elovich models correlate isotherms and kinetic data relatively well, respectively. The theoretical saturated TC adsorption amount of HGM@PDA-SO3H evaluated by Langmuir model reached 333.70 mg g−1. Thermodynamic analysis confirmed the spontaneous exothermic property of the adsorption process. There was no serious decline in the adsorption of TC by the material after 5 adsorption cycles, and the adsorbent saturated with contaminants could be easily regenerated via solution desorption, reflecting its satisfactory renewability and stability. Based on the results of batch experiments and characterization analysis, it could be concluded that the corresponding adsorption mechanisms mainly involve electrostatic attraction, hydrogen bonding and π-π stacking interactions. This research aimed to decorate HGM with biomaterials and apply it in the adsorptive purification of TC-contaminated water, which brought some insights and inspiration for the environmental application of HGM, and proved its potential applicability.

A novel self-floating silica adsorbent for antibiotic ciprofloxacin and nickel (II) ion

A novel self-floating silica adsorbent was synthesized by introducing sulfonic acid groups onto the surface of hollow glass microsphere (HGM) through post-grafting technique. The obtained sulfonated HGM (SO3H-HGM) not only had satisfactory adsorption performance for ciprofloxacin (CIP) and heavy metal nickel (Ni2+), but also had stable self-floating capability. SO3H-HGM exhibited wide pH adaptability. Langmuir and Elovich models well fitted the adsorption isotherm and kinetic data, respectively. Under the optimal experimental conditions, the theoretical saturated adsorption capacities of SO3H-HGM for CIP and Ni2+ calculated by the Langmuir model reached 464.78 mg·g−1 and 19.65 mg·g−1, respectively. Thermodynamic calculation verified the spontaneous nature and feasibility of the adsorption processes. The saturated adsorbent could be easily desorbed and regenerated by the eluent, and after five adsorption cycles, there was no serious reduction in adsorption capacity, which proved the good reusability and stability of SO3H-HGM. The adsorption mechanism of CIP and Ni2+ by SO3H-HGM is mainly electrostatic interaction, followed by hydrogen bond, hydrophobic interaction and coordination. This research demonstrates that HGM is a potential and promising material for the adsorptive purification of water contaminated with CIP and Ni2+, and to realize self-floating solid–liquid separation.

Preparation and Performance of HGM/PPENK-based High Temperature-resistant Thermal Insulating Coatings

Novel high temperature-resistant coatings with high mechanical strength and thermal-insulating performance were prepared with poly(ether nitrile ketone) (PPENK) resin as matrix and hollow glass microspheres (HGMs) as thermal-insulating filler. The corresponding mechanical and thermal-insulating study indicated that the mechanical properties of the coatings decreased with the increase of HGM content, and were improved after surface modification of HGM by KH570 resulting in enhancement of interaction between HGM and PPENK resin. The thermal conductivity of HGM/PPENK thermal-insulating coating decreased with the increase of HGM content and coating thickness, along with the decrease of the true density. It also showed slight increase trend due to HGMs surface modification. The HGM/PPENK coating filled with modified HGMs showed better thermal resistance than that of unmodified HGM/PPENK coating. The thermal decomposition temperature at 5% weight loss of the coating containing modified HGMs was 10 °C lower than that of pure PPENK, and 40 °C higher than that of neat HGM/PPENK coating. The coating exhibited commendable appearance after 400 °C for 30 min. The merits of HGM/PPENK-based thermal coatings obviously demonstrated promising prospect in thermal protection fields.

Multi-functionalized self-floating microspheres for dyes capture: Amphoteric adsorption and rapid surface solid-liquid separation

With the rapidly increased discharges of various complex dyeing wastewaters, adsorbents are required to own more properties such as cost-effectiveness, amphoteric ability, and rapid solid-liquid separation ability, to treat dyeing wastewaters. A multi-functional adsorbent was synthesized by co-grafting m-phenylenediamine and sodium allyl sulfonate on the surface of a low-cost base-material: hollow glass microsphere (HGM). Characterization results indicated the surface roughness and –Si–OH groups of HGM were increased by NaOH corrosion; functional groups such as aromatic-rings, –NH2, and –HSO3− were grafted on the surface of HGM. The synthesized adsorbent showed amphoteric attraction abilities for anionic acid green 25 and cationic basic fuchsin dyes. Kinetics and isotherms studies suggested the PSO model and Langmuir model were most satisfactory for adsorption processes, the theoretical maximum adsorption capacities for acid green 25 and basic fuchsin reached 454.55 and 588.24 mg g−1, respectively. The mechanism investigations indicated the electrostatic attraction, π-π stacking, and hydrogen bonds were the potential interaction forces between dyes and adsorbents. The synthesized material owns self-floating ability due to the hollow structure of HGM, over 95.7% of adsorbents were collected at water surface via the self-floating process in 12 min, which was beneficial to the solid-liquid separation process and the reuse of adsorbents. The technologies developed by these research efforts can serve as templates for synthesizing multi-functional adsorbents for complex wastewaters decontaminations.

Heat-insulating materials with high-temperature resistance through binding hollow glass microspheres with vinyl-functionalized polyborosiloxane

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.

Preparation and Properties of Hollow Glass Microsphere/Silicone Rubber Composite Material with the Transition Layer of Silicone Resin

Hollow glass microsphere (HGM)/silicone rubber composite material was prepared by using silicone resin as the transition layer between silicone rubber and HGM. Silane coupling agent was hydrolyzed on the surface of HGM by in-situ polymerization to form the silicone resin layer. And then such modified HGM was added to the silicone rubber to prepare HGM/silicone rubber composite material. The curing process, mechanical property, morphology, thermal stability, and electrical property were studied. It is found that the transition layer of silicone resin can speed up the curing reaction. And the curing time becomes longer with the increase of HGM. The transition layer of silicone resin also improves the compatibility between HGM and silicone rubber. And the mechanical properties of the silicone rubber are reduced with the increase of HGM. The introduction of HGM can improve the thermostability of the silicone rubber. And HGM can obviously reduce the dielectric constant (from 3.4 to 2.6) and increase the dielectric breakdown strength (from 14.78 kV/mm to 16.71 kV/mm) of the samples.

Gradient structure design of lightweight and flexible silicone rubber nanocomposite foam for efficient electromagnetic interference shielding

Flexible and efficient electromagnetic interference (EMI) shielding materials are urgently needed to satisfy the requirements for electromagnetic (EM) protection with the rapid popularization of wearable and the second generation of flexible electronic technology. Herein, lightweight and flexible silicone rubber/silver (Ag) plated hollow glass microspheres (HGMs) EMI shielding composite foam with gradient structure was prepared through supercritical carbon dioxide (scCO2) foaming technology. The composite foam displays an EMI SE of 30.5 dB at thickness of 0.7 mm and exhibits excellent EMI shielding stability under 1000 times bending. The electrical conductivity of the composite foam can reach up to 279.3 S/m at the Ag content of only 0.51 vol% due to the density-induced effect and the effective decorating of Ag particles on the surface of HGMs, which results in the selective distribution of Ag particles on the upper surface of foam, thereby enhancing the conductive network. The ability of composite foam to consume EM wave was further improved and the reflection EMI shielding effectiveness (SE) and reflection power coefficient (R) were reduced by 3.4 dB and 0.22 respectively because of the magnetic loss caused by Fe3O4@MWCNTs nanoparticles and the absorption originated by multiple reflections inside the cells. Furthermore, the EMI SE of the three-layer composite foam is as high as 59.39 dB, while the R value is only 0.59 at thickness of 2.0 mm. The gradient structure design and selective dispersion of conductive fillers provide a new insight into the preparation of EMI shielding composites. These composite foams have great potential applications in the field of EMI protection in wearable, intelligent and precision electronic devices.

Preparation of the floating HGMs-Ag3PO4 composites and the visible-light photocatalytic properties

The hollow glass microspheres (HGMs) with low density were used as the support to obtain the floating visible-light photocatalysts (HGMs–Ag3PO4) composites, in which silver orthophosphate (Ag3PO4) was dispersed on the surface of HGMs via silane coupling agents. The morphology, crystal structure and optical property of the HGMs-Ag3PO4 composites were characterized and the contents of Ag3PO4 dispersed on the surface of HGMs were quantified by atomic absorption spectrometry (AAS). Methylene blue (MB) was selected as the typical organic pollutants to evaluate the photocatalytic activity of HGMs-Ag3PO4 composite photocatalysts. The photo-catalytic rate of the floating composites was larger than the sinking composites and even pure Ag3PO4. Ag3PO4 particles could be dispersed well on the HGMs. The floating composites has a larger light contact area and the increased photo-catalytic activity sites even at the low Ag3PO4 loading. This work may open up a new insight for the floating photocatalyst to degrade organic dye on account of the low density and high visible-light responsiveness.

Preparation of Hollow Glass Microsphere/Organic Silicone Resin Composite Material with Low Dielectric Constant by In-Situ Polymerization

Hollow glass microsphere (HGM) /organic silicon resin composite materials with different quantity of HGM were prepared by in-situ hydrolytic polymerization. The hydrolysis reaction of silicone resin was carried out at the same time with the surface treatment of HGM by the silane coupling agent. It has been found that HGM was treated by silane coupling agent and the silicone resin was hydrolyzed on the surface of HGM. Such in-situ polymerization method solves the poor compatibility between HGM and silicone resin. And then the composite materials were cured by hydrosilylation. The composite material has low dielectric constant (2.40) and good heat resistance. Such new HGM/organic silicone resin composite material is expected to be used for integrated circuit packaging material.

Controlled TiO2 coating on hollow glass microspheres and their reflective thermal insulation properties

Hollow glass microspheres (HGMs) have great potential in building energy-saving and industrial insulation. Anatase TiO2-modified HGMs were prepared by a sol‒gel method in acetic acid-ethanol solution. Scanning electron microscopy, X-ray diffraction, zeta-potential measurements, nitrogen-sorption measurements, and Fourier-transform infrared and ultraviolet-visible-near-infrared diffuse reflectance spectroscopies showed that the alkali modification of the HGMs greatly influenced the loading and microstructure of the TiO2 film. The TiO2 loading could be accurately controlled by ethanol addition and the TiO2 coating time. A mechanism for the TiO2 coating of the HGM surface is proposed. The synergistic action of hydrogen bonding and electrostatic forces resulted in close contact between the HGMs and TiO2 sol at pH 3.5. The effects of different TiO2 loading rates on the reflective and thermal insulation properties were studied. The near-infrared reflectance of 15.9% TiO2 coated on HGMs was 96.27%, and the inner surface temperature of the composite pigment coated on aluminum board was reduced by 22.4°C. The TiO2/HGM composite pigments exhibited excellent solar reflective and thermal insulation properties, so have potential in the construction of exterior walls and roofs.

A novel floating adsorbents system of acid orange 7 removal: Polymer grafting effect

Floating adsorbents are materials that can adsorb dissolved pollutants and float on the water surface stably, which enables rapid and efficient solid-liquid separation. In this study, by grafting silane coupling agent A-1100 and methacryloyloxyethyltrimethyl ammonium chloride on the surface of hollow glass microspheres, adsorbents with non-polymer graft and polymer graft were prepared which have the ability to adsorb anionic dye and can be easily separated by floating mechanism. The SEM, XPS, SBET, TG, XRD characterization results confirmed the successful grafting of silane coupling agent A-1100 and methacryloyloxyethyltrimethyl ammonium chloride. Adsorption experiments on acid orange 7 show that non-polymer grafting adsorbents have better adsorption performance and the adsorption capacity reaches 217.39 mg g−1, while polymer grafting adsorbents have stronger environmental adaptability.

Use of a floating adsorbent to remove dyes from water: A novel efficient surface separation method.

In this study, our group grafted 2-acrylamido-2-methylpropane sulfonic acid (AMPS) onto the surface of hollow glass microspheres (HGM) and successfully prepared AMPS grafted floating adsorbent (AFA). The prepared AFA carries a large amount of negative charges, and the adsorptions of cationic dyes are achieved under the action of strong electrostatic interaction. Furthermore, due to the unique shell structure of AFA, it has a stable self-floating ability, which may change the traditional separation method to make the adsorbent easier to enrich and separate from water surface. Characterizations of AFA by scanning electron microscope, energy dispersive spectrometry, X-ray photoelectron spectroscopy. Fourier transform infrared spectra, Brunauer-Emmett-Teller surface areas, thermogravimetric analysis, and X-ray diffractometer shows the successful grafting of AMPS. Adsorption experiments confirmed that the adsorption capacities of AFA for methylene blue, malachite green, basic fuchsin and crystal violet under optimum conditions were 436.8 mg g-1, 637.6 mg g-1, 457.8 mg g-1, and 399.4 mg g-1, respectively. At the same time, AFA has excellent recyclability, and its adsorption capacity can be maintained after 6 cycles of reuse.

Preparation of hollow glass microspheres@ZnSxSe1−x or copper-/indium-co-doped ZnSxSe1−x composite color pigments with enhanced near-infrared reflectance

To improve the near-infrared (NIR) solar reflectance of ZnSxSe1−x or copper-/indium-co-doped ZnSxSe1−x (ZnSxSe1−x:Cu/In) pigment with various colors, hollow glass microspheres (HGMs)@ZnSxSe1−x or ZnSxSe1−x:Cu/In composite pigments with a litchis-like core-shell structure were prepared with HGMs dispersed and surface-corroded in an alkali-solution under ultrasound and ZnSxSe1−x or ZnSxSe1−x:Cu/In particles deposited on HGMs surface via in-situ co-precipitation and subsequent sintering. The structure, particle size, morphology, color properties and thermal performance of the composite pigments were investigated by X-ray diffraction (XRD), Fourier transfer infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), laser diffraction particle size analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nitrogen gas adsorption method (BET), ultraviolet-visible-near-infrared (UV-VIS-NIR) spectroscopy and infrared irradiation image analysis. The results show that ultrasound can promote the corrosion of HGMs surface in alkali solution and form a mesh-pore structure, thus providing some heterogeneous nucleation sites on HGMs surface and favoring the nucleation of pigment precursors on HGMs surface in subsequent in-situ co-precipitation reaction. Compared to ZnSxSe1−x or ZnSxSe1−x:Cu/In pigments, HGMs@ZnSxSe1−x or ZnSxSe1−x:Cu/In composite pigments have a higher solar reflectance since the multiple layer reflections occur at the interface between the pigment particles and HGMs, thus leading to a better heat-reflective property. The NIR solar reflectance of HGMs@ZnSxSe1−x or ZnSxSe1−x:Cu/In composite pigments is 90.61 ± 0.052% or 73.13 ± 0.046%. The surface temperature of aluminum plate coated with HGMs@ZnSxSe1−x composite yellow pigment is 3.4 ± 0.2 °C or 9.6 ± 0.2 °C lower than that of aluminum plate coated or uncoated with ZnSxSe1−x pigment. This approach may shed a light on a promising composite structure design for high-performance solar reflective ‘cool materials’.

Roughening of hollow glass microspheres by NaF for Ni electroless plating

Roughening of non-conductive substrate ceramic materials with hydrofluoric acid (HF) is usually an essential step to enhance adhesion of the coating by electroless chemical plating. However, the violent reaction between HF and the hollow glass microspheres (HGMs) usually causes breakage and damage of the thin shells of HGMs. This paper proposes a modified roughening strategy for Ni electroless plating, i.e., eroding HGMS slowly with a mixture of sodium fluoride (NaF) and hydrochloric acid (HCl). The Na2SiF6 by-products from the reaction of NaF with SiO2 were erased by the following NaOH washing to expose the surface of HGMs without any obvious pores or breakage. Such a modified roughening and followed alkali washing strategy can thus not only reduce the surface corrosion, but also hinder the further damage of HGMs by covering Na2SiF6 sediments. The successive plating of uniform Ni nanoparticles on HGMs was conducted, and the related mechanism was discussed in detail.