Novel porous fiber-based composites with excellent sound-absorbing and flame-retardant properties

Abstract

Novel ultralight porous fiber-based composites are a very attractive subject in the material chemistry and are enabled to promise applications in the sound absorption fields. In this work, it reported a facile strategy to prepare the flame-retardant, sound-absorbing, and mechanical enhancement porous fiber-based composites (PFC-EM-x) by using natural cellulose fiber, glass fiber, and flame retardant. Subsequently, the expandable microspheres (EMs) were added to construct the well-defined porous microstructure of materials for the enhancement in sound-absorbing performance. The results demonstrated that the high EMs contents had a remarkable influence on the porous structure of the composites so that the composites achieved the outstanding sound-absorbing performance and acceptable mechanical properties compared with other reported materials, especially as-prepared PFC-EM-20 composite showed excellent sound absorption at a range of high frequencies with the maximum sound absorption coefficient of 0.781 and tensile strength of 1.07?kN/m. Moreover, the limiting oxygen index values of all the samples were more than 26, both V1 and V2 rating in UL-94 test were achieved, which indicated that the obtained PFC-EM-x composites displayed outstanding flame retardancy. In summary, this study provides a facile strategy to rationally construct mechanically robust, highly efficient sound-absorbing and flame retardant ultralight composites which have promising applications in the future as green engineering materials.     

孔隙率和孔径对陶粒吸声材料吸声性能的影响

用流阻法和显微分析法定量表征材料的孔隙状况,研究以陶粒为主要骨料的多孔吸声材料在不同有效孔隙率和中值孔径下的吸声性能.结果表明陶粒吸声材料的NRC随着流阻的增加先增后减,当流阻为1144.07Pa·s/m3,材料吸声性能达到最佳:材料的中值孔径在0.71～1.44mm这一范围,当其减少时,吸声性能降低:随着有效孔隙率的...     

Properties of Microstructure-Controllable Porous Yttria-Stabilized Ziroconia Ceramics Fabricated by Freeze Casting

Porous yttria-stabilized ziroconia (YSZ) ceramics were fabricated by freeze casting using aqueous ceramic slurries. Polyvinyl alcohol (PVA) was added to the slurry with the aim of controling the microstructures and properties of the porous YSZ ceramics. The experimental results indicated that the large and noninterconnected lamellar pores of YSZ ceramics without PVA transformed changed into small and interconnected lamellar pores with PVA addition. The porosities of YSZ ceramics with PVA addition were higher than those of YSZ ceramics without PVA addition. The compressive strength of porous YSZ ceramics is the range from 23.57 to 63.86 MPa. All specimens exhibit noncatastrophic failure behaviors.     

论功能型建筑陶瓷的作用及其应用

将建筑陶瓷功能化是陶瓷行业的主要发展方向之一。本文对功能型建筑陶瓷,如自洁陶瓷、抗菌陶瓷、太阳能陶瓷、远红外辐射陶瓷、防静电陶瓷、发光陶瓷、调湿陶瓷、负离子陶瓷、多孔隔热陶瓷、透水砖、吸声陶瓷、吸收电磁波陶瓷和吸收二氧化碳陶瓷等方面进行了归纳,并阐述了各种功能型瓷砖的原理、工艺和应用。     

The sound absorption performance of the highly porous silica ceramics prepared using freeze casting method

Highly porous silica ceramics with unidirectional pores were prepared using the freeze casting method. By adjusting the solid content and freezing temperature, the porosity of the ceramics was tailored in the range of 78.20%-84.59% and pore size in the range of 8.4-71.4 μm, respectively. Sound absorption properties of porous silica ceramics was studied and the effect of structural factors was systematically investigated. The results showed that higher porosity and smaller pores of the porous ceramics favored the sound absorption in the entire sound wave frequency. By backing the sample with small pore size porous ceramics, the sound absorption property was enhanced, particularly in the low and medium frequency range, thus the sound absorption peak shifted towards lower frequency. The presence of air gap in the back would also favor sound absorption in low and medium frequency range. The as-fabricated porous silica ceramics owed excellent sound absorption properties due to their unidirectional pores and low flow resistances.     

Highly porous silica foams prepared via direct foaming with mixed surfactants and their sound absorption characteristics

The highly porous silica ceramics were fabricated by direct foaming with mixed surfactants and the influence of silicon nitride addition and solid content on the microstructures and properties were investigated. The results showed that silicon nitride can impede the formation of cristobalite and facilitates the sintering of silica ceramics. When the addition of silicon nitride powders reached 15 wt%, the highest compressive strength of silica ceramic foams could be obtained. The porosity of silica ceramic foams was tailored in the range of 84.61%–91.35% by adjusting the solid content, and the compressive strength of the obtained ceramic foams ranged from 5.89 MPa to 0.94 MPa. Sound absorption characteristics of silica ceramics foams were investigated. With the porosity of ceramic foams increased from 84.61% to 91.35%, the sound absorption coefficients in the entire sound wave frequency were enhanced due to the reduction of flow resistances, besides, the sound absorption peak varied from 4200 Hz to 2300 Hz, and became more intense and sharper.     

Multi-functional mullite fiber-based porous ceramics with a multilevel pore structure assembled by alumina platelets and mullite whiskers

Mullite fiber-based porous ceramics have been widely used in the field of heat insulation. To further broaden their applications in other fields, such as filtration and sound absorption, mullite whiskers and alumina platelets were introduced as the secondary structural materials in mullite fiber-based porous ceramics by a sol-gel combining heat-treating method, and new fiber-based porous ceramics with a unique multilevel pore structure were developed. By adjusting the molar ratios of aluminium tri-sec-butoxide to aluminium fluoride and calcination temperature, these fiber-based porous ceramics not only presented the characteristics of lightweight (maximum density of 0.38 g/cm³) and good heat insulation (minimum thermal conductivity of 0.11 W/mK) comparable to traditional fiber-based porous ceramics, but also showed a superior specific surface area (up to 11.5 g/m²) and excellent sound absorption performance (average sound absorption coefficient as high as 0.728). Owing to these outstanding characteristics, the corresponding porous ceramics are expected to be promising multifunctional materials in diverse fields, especially thermal insulation and sound absorption.     

Facile synthesis of a novel flower-like BiFeO3 microspheres/graphene with superior electromagnetic wave absorption performances

In recent years, porous or layered magnetic materials have received increasing attention due to their low density and lightweight. In this work, porous BiFeO₃ microspheres and three-dimensional porous BiFeO₃ microsphere-reduced graphene oxide (RGO) composite (3D porous BiFeO₃/RGO) were prepared by one-step etching processing using pure BiFeO₃ particles as precursors. The precursor undergoes dissolution-recrystallization/reduction process, resulting in large amount of BiFeO₃ fragments and graphene hybrid product, which forms 3D porous BiFeO₃/RGO composite. Electromagnetic (EM) absorption performance measurements exhibit that at low thickness of 1.8?mm, porous BiFeO₃/RGO composite can achieve reflection loss (R_L) value up to ?46.7?dB and absorption bandwidth (defined by R_L <?10?dB) exceeding 4.7?GHz (from 12.0 to 16.7?GHz), testifying outstanding microwave absorbing performance. Compared with pure porous BiFeO₃, improved EM wave absorption ability of as-prepared porous BiFeO₃/RGO composite is attributed to interfacial polarization, multiple reflections, scattering, and appropriate impedance matching.     

Fibrous porous mullite ceramics modified by mullite whiskers for thermal insulation and sound absorption

In order to meet the demand for thermal insulation and sound absorption, fibrous porous mullite ceramics (FPMC) with high porosity and an interconnected pore structure were prepared, followed by a pore structure modification with in situ grown mullite whiskers on the three-dimensional framework of the FPMC. The resultant hierarchical material exhibited superior sound absorption performance in the low-to-medium frequency to most reported sound-absorbing materials, as well as a sufficient compressive strength of 1.26 MPa with low thermal conductivity of 0.117 W·m^?1·K^?1. Moreover, the effects of solid content and mullite whiskers on the microstructure and physical properties of the material were analyzed. The increase of solid content led to increased compressive strength and thermal conductivity and decreased frequency corresponding to the first sound absorption peak. The thermal conductivity and compressive strength of the material increased as the mullite whiskers grew, while the median pore size decreased.     

Hierarchically porous networks structure based on flexible SiO2 nanofibrous aerogel with excellent low frequency noise absorption

Environmental noise has been regarded as major noise pollution with severe hazards to human physical and mental health. The common commercial fiber sound-absorption materials have insufficient low frequencies wave absorbing and fire-resistant ability, limiting their wide application. To solve these problems, a novel strategy combining flexible nanofibers and rGO/MXene nanosheets was proposed to fabricate rGO/MXene/SiO₂ nanofibers composite aerogel with hierarchically porous structure, which possessed an extremely low density of 9.8 mg/cm³ and superior low-frequency sound absorption ability (NRC value of 0.51). The obtained composite aerogel possessed a large deformation up to 80% (corresponding compressive stress of 17 kPa) and quickly recovered. In addition, the as-prepared aerogel could be easily produced on a large scale, providing a reference for the development of new generation of sound-absorbing products.     

Near‐Net‐Shaped Porous Ceramics for Potential Sound Absorption Applications at High Temperatures

We present an interesting processing route for obtaining alumina/mullite‐based ceramics with controlled porosity and airflow resistance leading to promising microstructures for application as sound absorbers. The use of ceramic materials aims for potential applications where high temperatures or corrosive atmospheres are predominant, e.g., in combustion chambers of gas turbines. For the production of the porous ceramics we combined freeze gelation and sacrificial templating processes to produce near‐net‐shaped parts with low shrinkage (<3%) based on environmental‐friendly and low cost conditions. The obtained microstructure presents a bimodal pore size distribution, with small pores derived from the freeze gelation process (~30 μm) connecting large pores (2–5 mm diameter) originated from the expanded polystyrene template particles. These connections, called “windows” in this study, show a significant impact on the sound absorption properties, allowing the pressure diffusion effect to take place, resulting in a significant improvement of the sound absorption coefficient. By varying the template particle content and the slurry solid content, it is possible to control the sound absorption behavior at different frequencies of the open‐celled ceramics. These ceramics feature a high open porosity, from 77% to 82%, combined with sufficient compressive strength ranging from 0.27 to 0.68 MPa and sound absorption coefficients of 0.30–0.99, representing a highly promising combination of properties for noise control and reduction at corrosive environments and high temperatures.     

Sintering Behavior of Gehlenite. Part I: Self-Forming, Macro-/Mesoporous Gehlenite—Pore-Forming Mechanism, Microstructure, Mechanical, and Physical Properties

A novel kind of pore self-forming macro-/mesoporous gehlenite (2CaO·Al₂O₃·SiO₂) ceramic (abbreviated C₂AS) having a highest porosity of 80% corresponding to a volume expansion of 134% during sintering has been developed. The pore self-forming ability, microstructure, mechanical, and thermal physical properties of the porous ceramic are related to the sintering temperature. The gehlenite ceramic shows a very good pore self-forming ability over a very wide range of temperature from 900° to 1450°C. No vesicant is required and no hydrothermal treatment is needed, as is generally the case for other kinds of porous ceramics or glasses. The pore self-forming ability of the C₂AS porous ceramic can be attributed to the escape of the adsorbed water vapor during the sintering process, due to automatic hydration of the fine, amorphous, flakey-shaped starting C₂AS powder particles synthesized by the organic steric entrapment (PVA) method, as well as to their fine, porous microstructure. The pores of the ceramics can be either open or closed, and the average pore size ranges from 0.6 to 1.1 μm, corresponding to a porosity of 75%–80%, respectively. The porous ceramic can preserve nanometer-sized (26–50 nm) crystallites up to 1000°C. Sintered or thermally treated under different conditions, the porous ceramics exhibit relatively high flexural strengths ranging from 9.1 to 15.4 MPa, with a standard deviation of 0.3 and 4.2 MPa, respectively. Thermal properties of the porous ceramic up to 1000°C, including thermal expansion coefficient, thermal diffusivity, specific heat, and thermal conductivity, were investigated, and the stability of the porous ceramic in boiling water was also studied.     

碱式硫酸镁多孔吸声材料的制备及性能研究

针对青海盐湖地区弃置堆积的水氯镁石难以规模化消纳问题,制备了碱式硫酸镁（BMS）水泥基多孔吸声材料,研究了原料硫酸镁、引气剂十四烷基甜菜碱（C₁₄BE）和矿物掺合料粉煤灰（FA）等对材料的微观孔结构和性能的影响。结果表明,硫酸镁和C₁₄BE的浓度对溶液的起泡性能和泡沫稳定性影响显著,当二者浓度分别为2.4 mol/L（水灰比为1.1）和9.8 mmol/L时,所制得的BMS多孔材料的孔径大、开孔率高,抗压强度为2.0 MPa,降噪系数（NRC）可达0.70;FA掺杂使材料的孔壁增厚、力学性能提升,同时开孔率下降、吸声性能降低,但即使FA掺量增至40%,其NRC值仍然可达0.51。BMS多孔吸声材料的研制不仅为噪声控制领域提供了一种新型无机非金属材料,而且为盐湖镁资源的有效利用提供了一条新途径。     

Microstructure and electromagnetic wave absorption property of reduced graphene oxide-SiCnw/SiBCN composite ceramics

In this account, RGO-SiC_nw/SiBCN composite ceramics were fabricated using polymer derived ceramic (PDC) combined with chemical vapor infiltration (CVI) technology. Dielectric property of as-obtained RGO-SiC_nw/SiBCN composite ceramics was significantly enhanced thanks to established conductive pathway through overlapped nanoscale SiC_nw and micro-sized RGO. The minimum RC of composite ceramics with 0.5 wt% GO and 2.29 wt% SiC_nw at thickness of 3.6 mm reached -42.02 dB with corresponding effective absorption bandwidth (EAB) of 4.2 GHz. As temperature rose from 25 to 400 °C, permittivity increased with enhanced charge carrier density and then it decreased due to oxidation process of RGO from 400 to 600 °C. The minimum reflection coefficient (RC) was recorded as -39.13 dB and EAB covered the entire X-band at 600 °C. EMW absorption ability was evaluated after high-temperature oxidation experiment under protective effect of wave-transparent Si₃N₄ coating. RGO-SiC_nw/SiBCN composite ceramics maintained outstanding EMW absorption ability with minimum RC of -10.41 dB after oxidation at 900 °C, indicating RGO-SiC_nw/SiBCN composite ceramics with excellent EMW absorption characteristic even at high temperatures and harsh environments.     

Open-cell porous sound-absorbing ceramics prepared by a new procedure that combines foamed and templated methods

Low-grade nonmetal ore, mainly magmatic soil and tuff, was used to prepare porous sound-absorbing ceramics. A new processing method that combines the foaming and templating methods was used to produce open-cell porous ceramics. Silicon carbide and carbon powders were used as the foaming agent and template agent, respectively, and their effects on open-cell preparation and sound-absorption properties were also investigated. The results showed that sound-absorption performance was closely related to the apparent porosity (H). Compared with either foaming or template methods, the new method incorporating both processes increased the sound-absorption coefficient (α) and H by 51%-258% and 69%-728%, respectively. Optimum sound absorption of the ceramics, that is, α = 0.68, noise reduction coefficient (NRC) = 0.48, and H = 50.22%, were obtained at foaming agent contents (FACs) of 1.5 wt% and template agent contents (TACs) of 4 wt%. The Delany-Bazley and Voronina models were selected to simulate the sound-absorption coefficients and the latter one fitted well with our experimental results.     

An efficient route to a porous NiO/reduced graphene oxide hybrid film with highly improved electrochromic properties

A porous NiO/RGO hybrid film is prepared by the combination of electrophoretic deposition and chemical-bath deposition. The porous hybrid film exhibits a noticeable electrochromism with reversible color changes from transparent to dark brown, and shows high coloration efficiency (76 cm(2) C(-1)), fast switching speed (7.2 s and 6.7 s) and better cycling performance compared with the porous NiO thin film. The enhancement of electrochromic performances are attributed to the reinforcement of the electrochemical activity of the RGO sheets and the greater amount of open space in the porous hybrid film which allows the electrolyte to penetrate and shorten the proton diffusion paths within the bulk of NiO.     

多孔陶瓷材料的制备与应用研究进展

介绍了多孔陶瓷材料的特点,综述了近年来国内外在制备多孔陶瓷材料上的新理论、新进展,对多孔陶瓷的制备工艺,特别是原料的选取、成型工艺和成孔工艺进行了分析,并阐述了其在过滤、催化、吸音、保温等方面的应用。     

Acoustic properties of cellular vitreous carbon foams

The present work deals with acoustic properties of highly porous rigid foams derived from flavonoid tannins. Such cellular solids derived from renewable resources were investigated before and after pyrolysis, the latter leading to cellular, vitreous, carbon foams. It is demonstrated here that these lightweight materials have a high air flow resistivity, which depends on the density of the foam. Vitreous carbon foams, especially, have rather low performances for sound absorption. Using a simple model, their sound absorption coefficients were predicted and found to be in very good agreement with measurements in all the investigated frequency range, 50–4300 Hz. However, we have shown that carbon foams are very appropriate materials to apply the double porosity concept since they can produce a high permeability contrast. This paper shows how vitreous carbon foams can become excellent sound-absorbing materials in a targeted frequency range by using the double porosity concept.     

Porous ceramics based on high-thermal-stability Al2O3–ZrO2 nanofibers for thermal insulation and sound absorption applications

Al₂O₃ fibers are promising candidates for porous ceramics, but the sudden growth of grains in the fibers above 1200 °C will limit their applications for high temperature. Herein, we reported the successful fabrication of the Al₂O₃–ZrO₂ nanofibers by electrospinning and the nanofiber-based porous ceramics by a combination of gel-casting, freeze-drying and high-temperature sintering. Results show that the addition of Zr could greatly improve the thermal stability (up to 1400 °C) of the Al₂O₃-based nanofibers, owing to the inhibition of the sudden growth of the grains in the fibers at high temperature. The Al₂O₃–ZrO₂ nanofiber-based porous ceramics after sintering at 1100–1400 °C possessed a multi-level pore structure and exhibited high thermal stability, ultra-high porosity (97.79–98.04%), ultra-low density (0.075–0.091 g/cm³) and thermal conductivity (0.0474–0.0554 W/mK), and excellent sound absorption performance with the average sound absorption coefficient of 0.598–0.770. These porous ceramics are expected to be employed in the fields of high-temperature thermal insulation and sound absorption.     

Preparation and performance of lightweight porous ceramics using metallurgical steel slag

In this paper, porous ceramics with high porosity and low bulk density were prepared by using steel slag and kaolin as main raw materials and polyurethane sponge as template. The effects of steel slag particle size, zirconia addition, the solid content of the slurry, and the addition of polycarboxylic acid water-reducing agent on the properties of ceramics were studied. In addition, by adding a surfactant (Sodium dodecyl sulfate) to form fine pores on the original framework of the three-dimensional network porous ceramic, the shortcomings of the single as well as the uncontrollable density and porosity of the porous ceramic, which are produced by the template method, are improved. When the grinding time of steel slag is 90 min, the content of zirconia is 3% wt, the solid content of ceramic slurry is 64% wt, and 0.6% wt polycarboxylic acid water-reducing agent and 0.4% of surfactant are added, the prepared porous ceramic skeleton is clear and good. The porous ceramic has a low bulk density (as low as 157.869 kg/m³), high porosity (about 94.05%) and high compressive strength (0.2 MPa). The crystalline phase of it is mainly composed of anorthite, gehlenite, forsterite and quartz. The addition of zirconia, water-reducing agent and surfactant only changes the macrostructure of porous ceramics, and does not change its crystal phase composition. The preparation of porous ceramics from steel slag not only solves the recycling problem of steel slag, but also provides a good substitute for main raw materials of porous ceramics.