Zinc Hydroxystannate/Carbon Nanotube Hybrids as Flame Retardant and Smoke Suppressant for Epoxy Resins.

Novel hybrid flame retardants containing zinc hydroxystannate and carbon nanotubes (ZHS-CNTs) were synthesized using the coprecipitation method, and the structure and morphology of ZHS-CNTs were investigate using an X-ray powder diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and thermogravimetric analyzer (TGA). Then, the ZHS, CNTs and ZHS-CNTs were incorporated into EP, respectively, and the flame-retardant and smoke inhibition performance of the composites were compared and studied. Among the three composites, the EP/ZHS-CNT composites have the highest improvements on the fire resistance and smoke inhibition properties. With only 2.0 wt.% ZHS-CNT hybrids, the pHRR of EP/ZHS-CNT composite materials is reduced by 34.2% compared with EP. Moreover, the release of toxic gases including CO, CO2 and SPR from the composites was also effectively inhibited. The mechanisms of flame retardant and smoke inhibition were investigated and the improved properties were generally ascribed to the synergistic flame-retardant effects between ZHS and CNTs, the catalyzing effect of ZHS and the stable network structure of CNTs.

Novel self-healing and recyclable fire-retardant polyvinyl alcohol/borax hydrogel coatings for the fire safety of rigid polyurethane foam.

Rigid polyurethane foam (RPUF) has attracted great attention as an insulation material, but its inherent flammability restricts its practical application. Developing a sustainable fire-retardant strategy that can improve its fire safety is particularly desirable and challenging. Herein, novel fire-retardant hydrogel coatings based on polyvinyl alcohol (PVA) and borax are proposed and applied in RPUF, and the self-healing, recyclability and flame retardant properties of the coatings are investigated. The dynamic and reversible cross-linked networks based on the borate ester bonds and hydrogen bonds endow the hydrogels with excellent repairability, recyclability, and elasticity. Compared with a neat RUPF, the coated RPUF exhibited improved fire-retardant properties without the inherent advantages being influenced and can be reflected by the 8% increase in the limiting oxygen index (LOI), 20% reduction in total heat release (THR), and 25% decrease in total smoke production (TSP) with the coatings, along with a rapid self-quenching behavior. The novel hydrogel coatings provide a new strategy for the development of flame-retardant coatings, demonstrating the potential of the next generation of self-healing hydrogel coatings to reduce the fire risk of the RPUF.

Dual char-forming strategy driven MXene-based fire-proofing epoxy resin coupled with good toughness.

It is challenging that the functionalized MXene-based nanofillers are designed to modify the inherent flammability and poor toughness of epoxy polymeric materials and further to facilitate the application of EP composites. Herein, silicon-reinforced Ti3C2Tx MXene-based nanoarchitectures (MXene@SiO2) are synthesized by simple self-growth method, and its enhancement effects on epoxy resin (EP) are investigated. The as-prepared nanoarchitectures realize homogeneous dispersion in EP matrix, indicating well performance-enhancing potential. The incorporation of MXene@SiO2 achieves improved thermal stability for EP composites with higher T-5% and lower Rmax values. Moreover, EP/2 wt% MXene@SiO2 composites obtain a 30.2% and 34.0% reduction in peak heat release rate (PHRR) and peak smoke production rate (PSPR) compared to those of pure EP, respectively, also achieving a 52.5% fall in smoke factor (SF) values and increased yield and stability of chars. The dual char-forming effects of MXene@SiO2 nanoarchitectures, including the catalytic charring of MXene and the migration of SiO2 to induce charring, are accounted for the results, as well as lamellar barrier effects. Additionally, EP/MXene@SiO2 composites achieve an enhanced storage modulus of 51.5%, along with improved tensile strength and elongation at break, compared to those of pure EP.

Determination of radiative and multiphonon non-radiative relaxation rates of upconversion materials.

The radiative and multiphonon non-radiative relaxation rates of lanthanide ions are intrinsic parameters to characterize the optical properties, which are the basic data for the theoretical model and numerical simulation of lanthanide upconversion systems. However, there are complex energy transfer processes, such as energy migration, energy transfer upconversion, and cross-relaxation in the lanthanide-doped upconversion materials, so it is difficult to accurately measure the intrinsic radiative and multiphonon relaxation rates. Therefore, a method to determine the relaxation rates of multi-level upconversion systems is proposed based on multi-wavelength excitation and level-by-level parameter calculations in this paper. For a dilute doped multi-level luminescence system excited at low powers, a model based on the measurements of steady-state emission spectra and luminescence decay curves is established through the macroscopic rate equations at multi-wavelength excitation, which can be used for the level-by-level calculation of the multi-level radiative and multiphonon relaxation rates. With the dilute doped ß-NaYF4:Er3+ six-level luminescence system as an example, the measurement method and the model are introduced in detail. Under the experimental conditions of neglecting the energy transfer effect between ions, the materials are excited by five lasers with central wavelengths of 1523 nm, 980 nm, 808 nm, 660 nm, and 520 nm to form five subsystems. The steady-state emission spectra and luminescence decay curves of the luminescence system excited by each wavelength were recorded. The intrinsic relaxation rates including 11 radiative relaxation rates and 4 multiphonon relaxation rates in the ß-NaYF4:Er3+ six-level system were determined based on the established model and method, which experimentally verified the applicability of the method proposed in this paper. This work will provide basic data for the analysis and regulation of the luminescence properties of lanthanide upconversion systems.

Metal-organic Framework ZIF-67 Functionalized MXene for Enhancing the Fire Safety of Thermoplastic Polyurethanes.

In this work, a novel functionalization strategy for ZIF-67-modified layered MXene was proposed, aiming at improving the fire safety of thermoplastic polyurethanes (TPU). The ZIF-67@MXene was verified by microscopic morphology, elemental composition, functional group species and crystal structure, and then the successfully prepared ZIF-67@MXene was introduced into the TPU material. When ZIF-67@MXene content was only 0.5 wt%, the peak heat release rate, total heat release rate, peak smoke release rate, total smoke release rate, and CO yield of the TPU/ZIF-67@MXene composites were reduced by 26%, 9%, 50%, and 22%, respectively, compared with the pure TPU. The thermogravimetric tests showed that the residual char of TPU/ZIF-67@MXene composites was the most in all samples. In short, the high-quality carbon layer of TPU/ZIF-67@MXene composites acts as a physical barrier to the transfer of heat and toxic gases, greatly improving the flame retardant properties of the TPU polymer.

DOPO/Silicon/CNT Nanohybrid Flame Retardants: Toward Improving the Fire Safety of Epoxy Resins.

Novel DOPO/silicon/CNT nanohybrid flame retardants (FR-CNTs) were synthesized and FR-CNTs were introduced into epoxy resins through thermal curing process. The SEM and TEM results indicate that CNTs distribute uniformly in epoxy resins due to the good dispersion of CNTs in DOPO/silicon/CNT nanohybrid flame retardants. The thermal stability and flame-retardant properties of EP/FR-CNTs composites are improved, which is attributed to the good dispersion of DOPO/silicon/CNT nanohybrid. The cone calorimeter results demonstrate that FR-CNTs can reduce peak heat release and the release of toxic gas effectively compared with EP/CNTs and EP/CNT/FR composites. The char-residue analysis indicates that the improved flame-retardant properties are due to the char-reinforcing effects and the catalyzing charring effect of FR-CNTs, which provides enough time for flame retardants to trap radicals. Generally, the char layers, which act as insulating barrier, can reduce the releasing of flammable gases and protect the underlying epoxy resins from the heat source.

Risk modelling and simulation of thermal safety in underground railway tunnel surrounding.

The temperature of surrounding rock of the underground railway tunnel is increasing year by year. This slowly changing thermal hazard not only has a prominent impact on the stability of tunnel surrounding structures, but also deteriorates the tunnel thermal environment, so the formation of the thermal hazard should be investigated. In this work, the thermal hazard model of tunnel surrounding rock was established under the superposition of ground atmospheric temperature wave and tunnel wind flow temperature wave. The corresponding simulation software was developed to estimate the thermal hazards. This dual periodic temperature boundary model (DPTB) was also investigated in comparison with the single periodic temperature boundary (SPTB) model that simplified the periodic ground atmospheric temperature to a constant. The results show that the overlying rock layer of the tunnel is more affected by the superposition of double periodic temperature waves, and its temperature will be significantly higher in autumn. For the calculation example, the average annual heat storage in the surrounding rock under the DPTB is 41,775 kJ/m2, reduced by 432 kJ/m2 compared to the SPTB. The average temperature rise in the shallow surface surrounding rock over 25 years under the DPTB is about 2.04 °C, which is 0.48 °C lower than that of the SPTB. These calculation results provide a reference for the thermal hazards control in underground railway tunnels.

Recent Advances in the Synthesis and Application of Three-Dimensional Graphene-Based Aerogels.

Three-dimensional graphene-based aerogels (3D GAs), combining the intrinsic properties of graphene and 3D porous structure, have attracted increasing research interest in varied fields with potential application. Some related reviews focusing on applications in photoredox catalysis, biomedicine, energy storage, supercapacitor or other single aspect have provided valuable insights into the current status of Gas. However, systematic reviews concentrating on the diverse applications of 3D GAs are still scarce. Herein, we intend to afford a comprehensive summary to the recent progress in the preparation method (template-free and template-directed method) summarized in Preparation Strategies and the application fields (absorbent, anode material, mechanical device, fire-warning material and catalyst) illustrated in Application of 3D GAs with varied morphologies, structures, and properties. Meanwhile, some unsettled issues, existing challenges, and potential opportunities have also been proposed in Future Perspectives to spur further research interest into synthesizing finer 3D GAs and exploring wider and closer practical applications.

Flame-retardant activity of ternary integrated modified boron nitride nanosheets to epoxy resin.

In order to improve the fire safety of epoxy resin, ZIF-8 nanoparticle in-situ decorated boron nitride nanosheet (BN-OH/ZIF-8) is fabricated via self-assembly method and then ternary integrated BN-OH/ZIF-8/PA hybrids are prepared through the chemical etching effect of phytic acid. FTIR, XRD, XPS, TEM and TGA measurements are used to characterize the structure and morphology of the nanohybrids. The researches show that BN-OH/ZIF-8/PA not only uniformly distributed in EP matrix, but also improve the thermal stability of EP. The peak heat release rate, peak smoke production rate, total smoke production values, the fire growth index and peak CO production rate obtained from cone test are significantly decreased, demonstrating the reduction of the fire hazards of EP composites containing BN-OH/ZIF-8/PA. The nano barrier effect and catalytic activity of BN-OH/ZIF-8/PA may be conducive to suppress the release of combustible volatile products and heat, facilitate the formation of graphitized carbon layer, and protect matrix from flame damage. The ternary integrated method developed in this study explores a new way to improve the flame retardant properties of EP, thereby promoting its application range.

Green, tough and highly efficient flame-retardant rigid polyurethane foam enabled by double network hydrogel coatings.

Designing eco-friendly fireproof rigid polyurethane foam (RPUF) that can completely stop fire ignition or spread has significant technological implications, which has been proved to be extremely challenging. Herein, a novel green strategy based on double network hydrogel coating was developed to enhance the flame retardancy of RPUF via a facile casting and curing process. This strategy can create a homogeneous hydrogel fire-resistant layer with strong adhesion on the outermost surface of the substrate. Due to good water holding capacity and excellent thermal management properties, the hydrogel coating showed excellent fire retardancy. As a proof-of-concept, polyacrylic-polydopamine (PAAm-PDA) double network hydrogel coating was applied to an extremely flammable RPUF substrate. Compared with the neat foam, the PAAm-PDA coated RPUF exhibited an overall improvement in fire-safety performance, including a rapid self-quenching behavior, a six-fold enhancement in time to ignition (TTI), and 39.7% and 42.2% decreases in the mean heat release rate (HRR) and total smoke production (TSP), respectively. Furthermore, the tough hydrogel-coated RPUF possessed enough mechanical properties to meet the requirement of its practical applications. Benefiting from its low cost, easy-to-process and eco-friendly characteristics, this hydrogel fireproof coating strategy provides a new direction for developing green and safe structural materials with widespread use.

Reusable Magnetic Nanoparticle Immobilized Nitrogen-Containing Ligand for Classified and Easy Recovery of Heavy Metal Ions.

Functionalized Tris[2-(dimethylamino) ethyl] amine (Me6TREN) ligands tethered-Fe3O4@Me6TREN nanoparticles (NPs) with a size of 150 nm were prepared to achieve classified and easy recovery of heavy metal ions in wastewater. The preparation of such NPs related to sequential silane ligand exchange and a following cure and Schiff base reactions for Fe3O4 NPs. Fe3O4@Me6TREN NPs as an effective nano-adsorbent of heavy metals exhibited significant differences in maximum adsorption capacity for Cr(III) (61.4 mg/g), Cu(II) (245.0 mg/g), Pb(II) (5.3 mg/g), and Cd(II) (1136.2 mg/g), in favor of classified removal of heavy metals from wastewater. Furthermore, Fe3O4@Me6TREN NPs can be regenerated by desorbing metal ions from NP surfaces eluted with ethylenediaminetetraacetic acid disodium salt (EDTA-Na2) aqueous, which endows such NPs promising potency as new nano-vectors for the removal of heavy metals.

The impact of building surface temperature rise on airflow and cross-contamination around high-rise building.

This paper numerically studies the characteristics of flow field around a high-rise building and the cross-contamination when the building surface is heated by the solar radiation. Firstly, the normalized concentration Kc is used to evaluate the dispersion characteristics under different source locations without surface temperature rise. Under iso-thermal condition, the near-wall pollutant dispersion features revealed by the predicted results are similar to our previous wind tunnel experiment. Then, the effect of wall surface temperature rise on the cross-contamination and the flow fields is evaluated based on the near-wall concentration distributions and the wake zone vortex core positions, respectively. When the building surface temperature rises, the location of vortex core obviously changes comparing with that under iso-thermal condition. The correction formula for the vortex core location with the leeward wall surface temperature rise below 15 K is developed. The windward wall surface temperature rise brings more serious pollutant accumulation. The near-wall concentrations increase with the rise of temperature when the pollutant is released from the bottom and middle of leeward wall surface, while the top-release scenario exhibited a contrary tendency. For the three interval ranges of generally recognized Richardson number Ri (Ri < 0.1; 0.1 < Ri < 10; Ri > 10), these results indicate that when Ri is less than 0.1, the effect of wall surface temperature rise on near-wall flow and cross-contamination of small-scale model cannot be ignored.

Functionalized CNTs with DOPO and Silicon Containing Agents: Effective Reinforcer for Thermal and Flame Retardant Properties of Polystyrene Nanocomposites.

DOPO and silicon containing agents modified multiwalled carbon nanotubes (MCNTs) were synthesized through sol-gel process and MCNTs are introduced into polystyrene (PS) through in situ polymerization. TEM observations and FTIR results of MCNTs demonstrated that the MCNT nanofillers were coated with the organic/inorganic flame retardant compound. Moreover, the TEM results of the composites indicate that MCNTs dispersed in polystyrene PS matrix uniformly due to the modification. The PS/MCNTs composites showed improved thermal stability as well as flame retardant properties in comparison with PS/CNTs composites, which are due to the good dispersion of MCNT in the PS matrix. MCNTs in the PS matrix can also reduce the peak heat release rate, total heat release and improve the smoke suppression performance. The improved flame retardant properties are attributed to the char reinforcing effect of CNTs, which can provide enough time for MCNTs and organic/inorganic compound to trap the degradation of polymer chains and catalyze the formation of char. The char layers can not only serve as an efficient insulating barrier to reduce the exposure of PS matrix to heat source but also retard the releasing of combustible gas.

CNT modified layered α-MnO2 hybrid flame retardants: preparation and their performance in the flame retardancy of epoxy resins.

In this paper, CNT modified layered α-MnO2 hybrid flame retardants (α-MnO2-CNTs) were synthesized through one-pot preparation. The structure and composition of the α-MnO2-CNTs hybrid flame retardants were investigated by X-ray diffraction, TEM and SEM. Subsequently, the α-MnO2-CNTs hybrids were then incorporated into epoxy resin (EP) to improve the fire safety properties. Compared with pure EP and the composites with CNTs or α-MnO2, EP/α-MnO2-CNTs composites exhibited improved flame retardancy and smoke suppression properties. With the incorporation of only 2.0 wt% of α-MnO2-CNTs hybrid flame retardants, the peak heat release rate and total heat release of the composites showed 34% and 10.7% reduction respectively. In addition, the volatile gases such as CO and CO2 were reduced and the smoke generation was also effectively inhibited. The improved fire safety of the composites is generally due to the network structures and the synergistic effect of α-MnO2 and CNTs, the catalyzing charring effect, smoke suppression and the physical barrier effect of α-MnO2 nanosheets.

Bending and Elastic Vibration of a Novel Functionally Graded Polymer Nanocomposite Beam Reinforced by Graphene Nanoplatelets.

A novel functionally graded (FG) polymer-based nanocomposite reinforced by graphene nanoplatelets is proposed based on a new distribution law, which is constructed by the error function and contains a gradient index. The variation of the gradient index can result in a continuous variation of the weight fraction of graphene nanoplatelets (GPLs), which forms a sandwich structure with graded mechanical properties. The modified Halpin-Tsai micromechanics model is used to evaluate the effective Young's modulus of the novel functionally graded graphene nanoplatelets reinforced composites (FG-GPLRCs). The bending and elastic vibration behaviors of the novel nanocomposite beams are investigated. An improved third order shear deformation theory (TSDT), which is proven to have a higher accuracy, is implemented to derive the governing equations related to the bending and vibrations. The Chebyshev-Ritz method is applied to describe various boundary conditions of the beams. The bending displacement, stress state, and vibration frequency of the proposed FG polymer-based nanocomposite beams under uniformly distributed loads are provided in detail. The numerical results show that the proposed distributions of GPL nanofillers can lead to a more effective pattern of improving the mechanical properties of GPL-reinforced composites than the common ones.

A modified thermal radiation model with multiple factors for investigating temperature rise around pool fire.

Hazardous chemical tanks are widely distributed in China, while tank fires occur frequently. Thermal radiation of pool fire plays a critical role in multi-points combustion and accident expansion, resulting in severe thermal damage to the surrounding targets. There are kinds of classical models used to predict the temperature rise of the target, but inaccuracies still exist in the application. In this work, we had conducted a series of pool fire tests in a full-size tunnel and open space for three petroleum products, and observed the temperature variations around the pool fire. A basic thermal radiation model with multiple factors was established first to predict the surrounding temperature rise, but its accuracy was still low. Subsequently, a correction approach of view factor and other aspects was proposed to accord with the experimental data, and the basic prediction model of temperature rise was then modified accordingly. Calculative results of the modified model agreed well with the experimental measuring temperatures, which verified the accuracy and reliability of the modified model. This modified model has a functional applicability to estimate the thermal radiation of pool fire on the surrounding objects.

Study in performance analysis of China Urban Emergency Response System based on Petri net.

Urban Emergency Response System (UERS) is a modernization symbol of a city. With acceleration of urbanization process and constant expansion of city size in China, China cities must respond to various emergencies timely and effectively to satisfy urban residents' needs for public security. In recent years, many China cities made trials and efforts in setting up and improving the UERS. At the same time, the China government began to build Emergency Response Systems (ERS) in some cities to deal with various possible emergencies. In this paper, using Petri net (PN), we study the performance of China typical UERS and establish its PN model for performance analysis. Based on the Markov chain (MC) of the model, the performance of China typical UERS is analyzed. Results from our simulation are in conformity with practical operation of China current UERS.

Two-color optical charge-coupled-device-based pyrometer using a two-peak filter.

A two-color optical charge-coupled-device (CCD)-based pyrometer was developed using a multipeak interference filter with a color CCD sensor to measure multicolor signals with specified wavelengths. The effective and simple method adjusts the fixed spectrum response characteristics of a color CCD to allow improved temperature measurements. This pyrometer system not only has the advantage of traditional two-color (two-wavelength) pyrometry, but also overcomes the restrictions of color CCDs that can only be applied in waveband measurements. The measurement performance of the system using a two-peak filter (λ(1)=643 nm, λ(2)=564 nm) was evaluated by blackbody experiments. The results show that the low temperature detection limit is increased about 200 K with an increase in the sensitivity of the measured signals compared with the original system without two-peak filter [Fu, et al., Opt. Laser Technol. 42, 586 (2010)]. And the effective temperature range is also increased when T > 1233 K. The measured ratio C(R)/C(G) is monotonically relative to the temperature, which simplifies the measurements. The temperature sensitivity of 2.49 is larger and more uniform than the temperature sensitivity of 1.36 in the previous original system. Thus, the measurement performance of the new system is greatly improved. Finally, as an application, the surface temperature distribution of stainless steel sample in hot environments was determined by this new CCD-based pyrometer. The results agree well with the spectrometer-based results and further verify the applicability of the new system.