以煤矸石为原料制备Al2O3-SiO2气凝胶的工艺与性能

煤矸石作为固体废弃物虽然被用作发电燃料、煤矿填料与建筑材料,但其利用率仍然不高,如何提高煤矸石的高值化利用率成为了目前研究的热点。本文以山西煤矸石为原料,采用一步酸溶和溶胶-凝胶法,并经过常压干燥得到了Al₂O₃-SiO₂气凝胶粉体。在溶剂置换与改性过程中引入超声波,研究了其对气凝胶的制备与性能的影响。采用BET、XRD、SEM、FT-IR、TG-DSC及接触角测试对所得Al₂O₃-SiO₂气凝胶粉体的结构与性能进行表征。结果表明,超声波的引入加快了反应速率,缩短了气凝胶的制备周期,所制备的Al₂O₃-SiO₂气凝胶是一种具有纳米三维网络结构的介孔材料,堆积密度低至0.120 g/cm³,比表面积为635 m²/g,高温下收缩性小于传统水玻璃制备的SiO₂气凝胶,并具有较好的疏水性。     

耐高温Al2O3气凝胶隔热材料的研究进展

Al₂O₃气凝胶因轻质、耐高温、稳定性好的特性,在高温隔热领域具有极大的应用潜力。阐述了近年来Al₂O₃气凝胶的溶胶-凝胶法制备过程及机制,介绍了多种干燥工艺方法,总结了在疏水、增强和耐高温性能方面的改性工艺,展望了其未来的发展方向。     

氧化铝纤维增强氧化铝基复合材料研究进展

与传统金属材料相比，氧化铝纤维增强氧化铝基(Al₂O₃/Al₂O₃)复合材料因具有比强度高、密度低、耐高温和抗氧化等特点，已经成为新一代备受国内外学者关注的航空航天热结构复合材料。本文介绍了目前常用的氧化铝纤维及其基本性能，总结了Al₂O₃/Al₂O₃复合材料中常用的界面相及其对复合材料性能的影响规律，归纳了Al₂O₃/Al₂O₃复合材料的制备工艺及性能，指出了该材料未来的发展趋势，旨在为国内Al₂O₃/Al₂O₃复合材料的研究提供借鉴和参考，促进Al₂O₃/Al₂O₃复合材料在航空航天领域热端高温部件上的广泛应用。     

SiO2气凝胶纤维隔热复合材料的常压制备及性能表征

SiO₂气凝胶的力学性能较差,隔热性能较强,为了使其成为良好的隔热材料,本文提出一种SiO₂气凝胶纤维隔热复合材料的制备方法。以正硅酸乙酯(TEOS)为前驱体,玻璃纤维和陶瓷纤维为增强体,硅烷偶联剂KH550和KH570为纤维处理剂,在常压条件下制备SiO₂气凝胶纤维隔热复合材料,并对材料性能进行表征。结果表明:前驱体中十六烷基三甲基溴化铵(CTAB)含量越高,复合材料中SiO₂气凝胶导热系数越低,低至0.028 W/(m·K);使用硅烷偶联剂KH550时,基体和纤维之间结合的紧密程度更高;纤维的加入使SiO₂气凝胶的力学性能达到很高水平;当前驱体中TEOS与CTAB摩尔比为1∶0.022时,经KH550处理的玻璃纤维/SiO₂气凝胶复合材料导热系数为0.054 W/(m·K),力学性能良好,隔热性能最优。     

Al2O3含量对PbO-CaO-B2O3-SiO2系玻璃析晶行为与烧结性能的影响

PbO-CaO-B₂O₃-SiO₂系玻璃粉体是耐高过载低温共烧陶瓷(LTCC)生瓷带的主要组成部分。玻璃粉体的析晶行为影响烧结性能,进而决定基板的使用性能。本文研究了Al₂O₃含量对PbO-CaO-B₂O₃-SiO₂系玻璃析晶行为与烧结性能的影响。结果表明:向PbO-CaO-B₂O₃-SiO₂系玻璃中引入Al₂O₃可抑制玻璃析晶,防止高膨胀晶相的析出,并提高玻璃烧结密度;不含Al₂O₃的PbO-CaO-B₂O₃-SiO₂玻璃粉体析晶峰温度为862 ℃,烧结过程中析出方石英晶相,20~200 ℃的平均线膨胀系数高达260.8×10^-7 ℃^-1;引入2.1%(质量分数)Al₂O₃可显著抑制玻璃析晶,700 ℃烧结后膨胀系数降低至72.9×10^-7 ℃^-1,介电常数显著增大,由6.30提高至7.02。     

Ni/Al2O3-SiO2催化剂表面性质及顺酐加氢性能

以Al₂O₃质量分数为10%的Al₂O₃-SiO₂复合氧化物为载体,通过浸渍法制备一系列不同Ni负载量的Ni/Al₂O₃-SiO₂催化剂。运用BET、XRD、H₂-TPR和NH₃-TPD-MS方法研究催化剂表面性质随活性金属Ni负载量的变化规律,探讨催化剂表面性质的变化对其顺酐加氢活性、选择性及催化剂稳定性的影响。结果表明,Ni/Al₂O₃-SiO₂催化剂中的Ni质量分数由5.0%增加至12.5%时,γ-丁内酯收率由7.9%快速增至38.9%,进一步增加Ni质量分数至20.0%,γ-丁内酯收率增加趋于平缓。催化剂中Ni活性物种与催化剂酸性中心的数量是影响催化剂顺酐加氢活性的主要原因。     

二氧化硅气凝胶隔热复合材料的高温疏水改性及失效机制

SiO₂气凝胶隔热复合材料已经广泛应用于航空航天、石油化工等隔热保温领域,通过疏水改性可大幅拓展其应用场景。为了使SiO₂气凝胶隔热复合材料在更高温度仍保持良好的疏水性能,采用聚硅氧烷改性硅酸盐涂料对SiO₂气凝胶隔热复合材料进行表面刷涂疏水改性,然后研究了涂层厚度对裂纹扩张的影响以及涂层在高温下疏水性能的失效机制和刷涂改性前后复合材料的耐磨损性能。结果表明,当涂层厚度大约为13 μm时,所制备的涂层表面无裂纹,接触角可达(113±2)°,经450 ℃高温热处理1 800 s后接触角依然可以保持在105°左右,表现出良好的热稳定性,同时涂层显著提高了复合材料的耐磨损性能。     

Al2O3/ACF复合电极材料的制备及性能表征

以H₃PO₄预处理后的活性炭纤维(ACF)毡为原料,采用浸渍煅烧法制备Al₂O₃/ACF复合电极材料;通过扫描电镜(SEM)、比表面积及孔径分析仪(BET)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶红外光谱分析仪(FTIR)对负载Al₂O₃前后活性炭纤维的微观结构与电化学性能进行表征,利用自制的电吸附装置对NaCl模拟废水进行电吸附性能测试。结果表明,采用浸渍煅烧法成功制备了Al₂O₃/ACF复合电极材料,Al₂O₃/ACF复合体表面及孔道中有絮状或颗粒状的Al₂O₃存在,比表面积从1244.37 m²·g^-1降为974.59 m²·g^-1;同时,Al元素含量为1.06%,Al₂O₃以无晶相无定形态存在于纤维表面;Al₂O₃/ACF表面形成一些Al O键的官能团,其比电容比ACF提高76.5%。负载Al₂O₃后的ACF电极材料电吸附性能增强,除盐效率较ACF原样电极提升了2.3倍,且电极具有可再生性。Al₂O₃/ACF复合材料可以作为电极材料用于去除废水中的无机盐离子。     

纤维改善SiO2气凝胶的力学和隔热性能研究进展

纤维/SiO2气凝胶复合材料因良好的力学和隔热性能具有广泛的节能应用前景,是当今国内外建筑、能源及材料等领域的研究热点.根据尺寸及形貌特征将纤维分为常规束状纤维、预制件纤维和纳米纤维三种类型,分析概述了不同类型的纤维与SiO2气凝胶复合材料的制备工艺、形貌特征以及力学和隔热性能,讨论了纤维改善SiO2气凝胶性能所存在的问题,并对以后的研究和发展趋势进行了展望.     

La2O3的添加方式对Al2O3热稳定性的影响

采用3种不同添加方式制备La₂O₃改性的Al₂O₃材料La-Al₂O₃。La-Al₂O₃分别经500 ℃、1 000 ℃和1 200 ℃焙烧,采用物理吸附、X射线衍射和荧光光谱等对高温处理的La-Al₂O₃进行比表面积和结构表征。结果表明,La₂O₃的添加能有效抑制Al₂O₃在高温条件下向热力学稳定态α-Al₂O₃转变,同时提高高温处理后La-Al₂O₃比表面积,使Al₂O₃热稳定性得到明显提高。在3种La₂O₃添加方式中,La(NO₃)₃浸渍法效果最为显著,制得的La-Al₂O₃(N)材料经1 200 ℃焙烧4 h的比表面积为30 m²·g^－1,是未经改性的Al₂O₃样品经同等温度焙烧比表面积的2.2倍。     

二氧化硅气凝胶复合隔热材料研究进展

二氧化硅气凝胶具有高孔隙率、低热导率等特点,使其成为新型超级隔热材料。然而,二氧化硅气凝胶的柔韧性、整体性差,并且常温干燥制备的气凝胶在高温时热导率迅速上升,这些都大大限制了二氧化硅气凝胶的应用。近些年,通过原位溶胶-凝胶法和模压成型法制备得到的二氧化硅气凝胶复合隔热材料,在一定程度上提高了其韧性、整体性和高温隔热性能,使得二氧化硅气凝胶作为单独块体隔热材料成为可能。本文阐述了二氧化硅气凝胶隔热材料的隔热机理,综述了近年来抗辐射型、纤维增强型和聚合物增强型二氧化硅气凝胶复合隔热材料的研究现状,最后讨论了该领域今后研究趋势。     

Elytra-mimetic ceramic fiber aerogel with excellent mechanical,anti-oxidation,and thermal insulation properties

High-performance thermally insulating aerogel with low density, high porosity, and low thermal conductivity characteristics was widely used in heat insulation. However, the large-scale application of aerogel was still limited by its brittleness and infrared radiation transparency at high-temperature. Fiber composite aerogel had achieved significant progress, but its anti-oxidation ability was poor, and its thermal insulation required further improvement at ultra-high temperatures. Herein, inspired by the structure of elytra, nanoparticle fiber (NF) was prepared by electrospinning of coaxial fiber loaded with opacifier and antioxidant nanoparticles. The NF was incorporated into the SiBCN aerogel to prepare NF/SiBCN ceramic fiber aerogel. The mechanical properties were improved by fiber networks. The shell structure increased the antioxidant properties. Heat conduction and heat convection were suppressed by the aerogel, while heat radiation was reduced by the coaxial fiber. The results showed that the ceramic fiber aerogel exhibited superior mechanical, antioxidant, and ultra-low thermal conductivity properties.     

Fiber Reinforced Polyimide Aerogel Composites with High Mechanical Strength for High Temperature Insulation

Glass fiber/polyimide aerogel composites are prepared by adding glass fiber mat to a polyimide sol derived from diamine, 4,4′‐oxydianiline, p‐phenylene diamine, and dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride. The fiber felt acts as a skeleton for support and shaping, reduces aerogel shrinkage during the preparation process, and improves the mechanical strength and thermal stability of the composite materials. These composites possess a mesoporous structure with densities as low as 0.143–0.177 g cm^?3, with the glass fiber functioning to improve the overall mechanical properties of the polyimide aerogel, which results in its Young's modulus increasing from 42.7 to 113.5 MPa. These composites are found to retain their structure after heating at 500 °C, in contrast to pure aerogels which decompose into shrunken ball‐like structures. These composites maintain their thermal stability in air and N₂ atmospheres, exhibiting a low thermal conductivity range of 0.023 to 0.029 W m^?1 K^?1 at room temperature and 0.057to 0.082 W m^?1 K^?1 at 500 °C. The high mechanical strengths, excellent thermal stabilities, and low thermal conductivities of these aerogel composites should ensure that they are potentially useful materials for insulation applications at high temperature.     

Opacifier embedded and fiber reinforced alumina-based aerogel composites for ultra-high temperature thermal insulation

A novel method was developed to uniformly disperse sub-micron TiO₂ opacifier into fiber reinforcements using agar and silica as binders via freeze drying. TiO₂ opacifier/ fiber/ alumina-based aerogel ternary (TFA) composites with high strength and excellent high-temperature thermal insulation were successfully prepared by sol-gel route, impregnation process and supercritical fluid drying. The microstructure, mechanical and thermal insulation properties of TFA composites were investigated comprehensively. The results show that the mechanical property of TFA composites can be significantly enhanced by mullite fiber felt and the incorporation of SiO₂ binder. The effect of TiO₂ opacifier on the high-temperature thermal conductivity was studied by adjusting the content of TiO₂ from 0 to 15 wt%. The obtained TFA composites exhibit high Young's modulus of up to 3.58 MPa and low high-temperature thermal conductivities of 0.129 W/m·K at 800 °C and 0.168 W/m·K at 1000 °C, respectively. The mechanism of heat transfer in TFA composites at high-temperature was also analyzed.     

二氧化硅气凝胶及其在保温隔热领域应用进展

二氧化硅气凝胶是目前已知最轻的固体材料，具有热导率低、孔隙率高和比表面积大等优点，被誉为新型超级保温隔热材料。然而，二氧化硅气凝胶自身存在力学性能差和制备成本高的问题，大大限制了其在保温隔热领域大规模推广应用。本文简述了二氧化硅气凝胶合成技术和力学性能增强方法，从制备过程控制、老化条件优化、热处理、纤维复合和高分子聚合物复合等方面分析了其对气凝胶性能和工艺的影响，重点介绍了近年来二氧化硅气凝胶保温隔热材料应用在航空航天、军工领域、工业管道、建筑保温以及新能源汽车等领域的研究进展，总结了其在各领域应用的技术挑战。指出未来需进一步拓展二氧化硅气凝胶的使用温区，利用共前体和化学交联等方法增强高温下的隔热性能，同时解决气凝胶纤维复材“掉粉”和微米级粉体分散不均匀等难题，尤其是新能源汽车等新兴应用领域发展迅猛，未来仍需针对新的应用需求对其合成技术进行设计和优化。     

Preparation and high-temperature service performance of hierarchically pore-structured BN fiber aerogels

Multifunctional aerogels with high porosity and good thermal insulation have attracted much attention in the field of energy and aerospace engineering. In this work, a three-dimensional BN fiber aerogel with hierarchically porous structure was prepared through a freeze-drying combined with in-situ carbothermal reduction nitridation route. The synthesized BN fiber aerogel exhibits a specific surface area of 154.3 m²/g, a high porosity of 96.8% and hydrophobicity. Moreover, the BN fiber aerogel shows a low thermal conductivity of 0.051 W/(m·K) and excellent thermal insulation properties owing to its hierarchical porous structure. Particularly, the BN fiber aerogel still maintains its low thermal conductivity and a rather high mechanical strength after re-heated at 1473 K for 3 h in Ar atmosphere, suggesting excellent high-temperature service performance. The successfully developed multifunctional BN fiber aerogel holds promising potential in high-temperature thermal insulation fields.     

Nanofibers reinforced silica aerogel composites having flexibility and ultra-low thermal conductivity

For the sake of enhancing the performance of flexible silica aerogel in practical applications, flexible SiO₂/SnO₂ nanofibers (SSNF) reinforced flexible silica aerogel composites (abbreviated as SiO₂-SSNF) were successfully prepared. Firstly, the SiO₂/SnO₂ nanofibers with fine diameter (~320 nm) and excellent flexibility were prepared by electrospinning technology. Then the aerogel composites were synthesized by adding the flexible SSNF to the silica solution and through the sol-gel method and ethanol supercritical drying technology. The effects of different content of the nanofibers on thermal conductivity and Yong's modulus of SiO₂-SSNF aerogel composites were investigated. The SiO₂/SnO₂ nanofibers were randomly dispersed in the flexible silica aerogel and the great integrity of the material result in smaller linear shrinkage, better thermal protection, and mechanical properties compared with those pure SiO₂ aerogels. The final SiO₂-SSNF aerogel composites possess excellent thermal conductivity (0.025-0.029 W/(m∙K)) and higher Yong's modulus (70 kPa), which was twice than that of the pure silica aerogel. This prepared SiO₂-SSNF aerogel composites can be better used in thermal insulation due to its excellent flexible and thermal insulation property.     

二氧化硅气凝胶高温稳定性研究

二氧化硅气凝胶具有极高的孔隙率和非常低的热导率,在保温隔热领域应用前景十分广阔。探究了二氧化硅气凝胶在不同温度热处理条件下热导率的变化情况,并从微观结构角度解释了其变化机理。随着热处理温度升高,气凝胶热导率先降低后升高。当热处理温度低于400 ℃时,气凝胶的热导率随热处理温度的升高而降低,这是因为较低温度的热处理去除了气凝胶内部的大部分杂质,并且使气凝胶的内部孔隙结构更加均匀;当热处理温度处于400~700 ℃时,更高温度的热处理使得气凝胶内部的孔径明显增大,气凝胶颗粒增大,使得热导率随热处理温度的升高而增加;当热处理温度高于700 ℃时,气凝胶颗粒开始烧结,骨架结构坍塌,密度显著增大,热导率也急剧上升,此时已不具备气凝胶轻质多孔的典型特征,可以认为已经失效。实验结果对亲水型气凝胶的应用给出了一定的指导:为保证气凝胶绝热能力的最优化,可以对气凝胶在400 ℃的温度下进行一段时间的保温;工作温度应在700 ℃以下,温度的升高会轻微降低气凝胶的隔热能力;气凝胶在700 ℃以上时会失去其绝热能力,因此不宜用于温度高于700 ℃的环境。