Nano-silica modified lightweight and high-toughness carbon fiber/phenolic ablator with excellent thermal insulation and ablation performance

Lightweight and high-toughness carbon fiber/phenolic ablator(CFPA)is required as the Thermal Protection System(TPS)material of aerospace vehicles for next-generation space missions.To improve the ablative properties,silica sol with good particle size distribution prepared using tetramethoxysilane(TMOS)was blended with natural rubber latex and deposited onto carbon fiber felt,which was then integrated with phenolic aerogel matrix,introducing nano-silica into the framework of CFPA.The modified CFPA with a low density of 0.28—0.31 g/cm3exhibits strain-in-fracture as high as 31.2%and thermal conductivity as low as 0.054 W/(m·K).Furthermore,a trace amount of nano-silica could effectively protect CFPA from erosion of oxidizing atmosphere in different high-temperature environments.The oxyacetylene ablation test of 3000°C for 20 s shows a mass ablation rate of 0.0225 g/s,a linear ablation rate of 0.209 mm/s for the modified CFPA,which are 9.64%and 24.82%lower than the unmodified one.Besides,the long-time butane ablation test of 1200°C for 200 s shows an insignificant recession with mass and linear ablation rate of 0.079 g/s and 0.039 mm/s,16.84%and 13.33%lower than the unmodified one.Meanwhile,the fixed thermocouple in the test also demonstrates a good thermal insulation performance with a low peak back-face temperature of 207.7°C,12.25%lower than the unmodified one.Therefore,the nano-silica modified CFPA with excellent overall performance presents promising prospects in high-temperature aerospace applications.

The Influence of Carbon Nanotubes and Nano-Silica Fume on Enhancing the Damping and Mechanical Properties of Cement-Based Materials

This paper conducted experimental studies on the damping and mechanical properties of carbon nanotube-nanosilica-cement composite materials with different carbon nanotube contents. The damping and mechanical properties enhancement mechanisms were analyzed and compared through the porosity structure test, XRD analysis, and scanning electron microscope observation. The results show that the introduction of nanosilica significantly improves the dispersion of carbon nanotubes in the cement matrix. At the same time, the addition of nanosilica not only effectively reduces the critical pore size and average pore size of the cement composite material, but also exhibits good synergistic effects with carbon nanotubes, which can significantly optimize the pore structure. Finally, a rationalization suggestion for the co-doping of nanosilica and carbon nanotubes was given to achieve a significant increase in the flexural strength, compressive strength and loss factor of cement-based materials.

Performance evaluation of nano-silica and silica fume on enhancing acid resistance of cement-based composites for underground structures

This study aims to evaluate the performance of silica fume(SF)and nano-silica(NS)on enhancing the sulfuric acid resistance of mortar mixtures.The NS and SF were added as substitutions for cement at various dosages.The cured samples were immersed in the sulfuric acid solution with a pH of 2 for 75 d.A compressive strength test and absorption and voids tests were conducted before sulfuric acid immersion.It was found that the addition of SF and NS reduced the volume of permeable voids and increased compressive strength.A thermo-gravimetric analysis was carried out to investigate the hydration of mixtures.The mixtures with SF showed a higher level of pozzolanic reaction compared with mixtures with NS.After the 75 d of immersion,the mixtures with 5%SF and 1%NS showed the best resistance against sulfuric acid because they showed the lowest mass change and length change.

Road Performances of Mesoporous Nano-silica Modified Asphalt Binders

The objective of this paper was to find new modifier to improve the aging resistance and low temperature cracking resistance of asphalt. To investigate the aging resistance of modified asphalt binders, mesoporous nano-silica（doping Ti^（4＋）） was used as a asphalt modifier. Some physical properties including penetration, ductility, and softening point of asphalt were analyzed with RTFO（Rotating thin film oven） aging and ultraviolet aging. Moreover, the performances of high and low temperature of modified asphalt binders with pressure aging were tested by dynamic shear rheometer（DSR） test and bending beam rheometer（BBR） test. These results showed that the penetration decreased, low temperature ductility, and softening point increased when adding mesoporous nano-silica to base asphalt. After ultraviolet radiation aging, the penetration loss and ductility loss of modified asphalt decreased than that of original asphalt, the increase of softening point was also significantly reduced than that of base asphalt. Furthermore, The test results of DSR and BBR showed that the G＊sinδ and creep modulus‘s＇ of pressure aged asphalt decreased, but the creep rate ‘m＇ increased. It can be concluded that the aging resistance and cracking resistance of modified asphalt are improved by adding mesoporous nano-silica, especially the doping of Ti^（4＋） could improve the aging resistance obviously.

Synthesis of a Green Nano-Silica Material Using Beneficiated Waste Dunites and Its Application in Concrete

Nano-silica, one of the substances boosting the field of nanomaterials, can be produced by dissolving olivine in acid. The dissolution of olivine is a convenient alternative route to the existing methods of nano-silica production (neutralization of sodium silicate and flame hydrolysis) because the olivine dissolution is a low temperature process making this method cheaper and greener. Furthermore, this process can use waste olivine materials for the production of nano-silica. The produced nano-silica has a specific surface area between 100 and 400 m2/g;a primary particle size between 10 and 25 nm, which is agglomerated in clusters;and an impurity content below 5 wt.%. In addition, olivine nano-silica can be classified as a pozzolanic material with an activity index of 101%. The optimum replacement level of olivine nano-silica in conventional vibrated concrete is around 5% by volume resulting in: 1) a compressive strength increase of 20%;2) a CO2 emission reduction of 3%. Therefore, the use of the olivine nano-silica in CVC does not only improve the compressive strength but also reduce the CO2 emissions.

Colored Nano-Silica and Its Adsorption on Cellulosic Materials

Deep understanding has been achieved for nanotechnology,which has greatly advanced the development of technology.The adsorption property,as one of conventional properties of nanomaterials,is well known but has not been fully applied.In this paper,nanomaterials were used as adsorbents,and further their adsorption properties on substrates were studied.Spherical nano-silica was selected as a representative,which was labeled with a dye.The chemical bonding between the dye and nano-silica was confirmed by Fourier transform infrared(FTIR)spectroscopy.It was proved that the adsorption was a spontaneous,endothermic and entropy increase process.The adsorption model conformed to the Langmuir-type adsorption model.Reaction kinetic studies showed that the number of reaction stages in the adsorption process was about 1.45.The adsorption state was studied to verify the existence of nanomaterials as an adsorbent on the surface of the polymer,and then provided a demonstration for feasibility of the general polymer surface modification method.

Development and Evaluation of Nano-Silica Dispersed Polyurethane Based Coatings for Improved Anti-Graffiti and Scratch Resistance

Polyurethane based anti-graffiti coatings have been developed by incorporating varying amounts of OH-functional Silicone modified polyacrylate. Optimization of Silicone polyacrylate concentration in neat PU was done by testing its performance for graffiti resistance. Tests which include static contact angle measurements with water and spray paint, visual inspection of stain removal and color change measurements were performed. It was observed that 5 wt % of Silicone polyacrylate in the neat PU showed 95% stain removability. These coatings showed excellent graffiti resistance but poor mechanical properties. Hence modification of these coatings was done by nano-particle incorporation. Nano-silica particle concentration was optimized for surface mechanical properties such as surface hardness, elastic modulus and scratch resistance. FEG-TEM revealed that nano-silica particles were uniformly distributed over the surface. 5 wt % nano-silica particle additions in PU-5 wt % silicone polyacrylate base showed superior mechanical properties than other concentrations. Color change measurements showed that nano-silica particle addition had no effect on its graffiti resistance. Hence PU-5 wt % silicone polyacrylate, 5 wt % nano-silica showed excellent graffiti resistance and mechanical properties.

Optimizing the compressive strength of concrete containing micro-silica, nano-silica, and polypropylene fibers using extreme vertices mixture design

Many studies have evaluated the effects of additives such as nano-silica (NS), micro-silica (MS) and polymer fibers on optimizing the mechanical properties of concrete, such as compressive strength. Nowadays, with progress in cement industry provides, it has become possible to produce cement type I with strength classes of 32.5, 42.5, and 52.5 MPa. On the one hand, the microstructure of cement has changed, and modified by NS, MS, and polymers;therefore it is very important to determine the optimal percentage of each additives for those CSCs. In this study, 12 mix designs containing different percentages of MS, NS, and polymer fibers in three cement strength classes(CSCs)(32.5, 42.5, and 52.5 MPa) were designed and constructed based on the mixture method. Results indicated the sensitivity of each CSCs can be different on the NS or MS in compressive strength of concrete. Consequently, strength classes have a significant effect on the amount of MS and NS in mix design of concrete. While, polymer fibers don’t have significant effect in compressive strength considering CSCs.

Interface Enhancement of Glass Fiber/Unsaturated Polyester Resin Composites with Nano-Silica Treated Using Silane Coupling Agent

Nano-silica treated with different kinds of coupling agent （KH550, A-143, A-151） was used to modify the surface condition of glass fiber, and then, the modified glass fiber/unsaturated polyester resin （UPR） composites materials were prepared. Scanning electron microscopy （SEM）, dynamic mechanical analysis （DMA）, and impact test were used to characterize the composite materials＇ structure and properties. The morphology of composite materials shows that the adhesion between nano-silica and glass fiber is improved when silane coupling agent is added in. The DMA and impact test results show that silane coupling agent （especially KH550 and A-151） could effectively improve the composite＇s mechanical properties. When the dose of KH550 was 0.1% （m ： m）, the storage modulus and impact strength reached the maximum.

A comprehensive review of the application of nano-silica in oil well cementing

Oil and Gas Industry is a Multi-Billion Dollar Industry.Drilling a well is costly,right from exploration to drilling and production to Enhanced Oil Recovery(EOR).Nanotechnology has the potential to introduce revolutionary changes in several areas of the oil and gas industry,such as exploration,drilling,cementation,production,EOR,etc.Use of Nanotechnology in the cement slurry can also achieve solutions to some of the problems pertaining to oil well cementation.Nano-silica is a better alternative compared to conventional additives like calcium chloride and silica,because as compared to calcium chloride and silica,the amount of nano-silica to be added is very small.Nano-silica acts as a multi-functional additive.Upon addition of nano-silica to cement slurry,there is a decrease in the thickening time,an increase in the compressive strength,decrease in porosity and permeability within the cement and also a decrease in the fluid loss.Incorporation of nano-silica ensures proper cementation and greater integrity of the well.Nano-silica helps in decreasing the wait on cement(WOC)time and therefore reduces the overall capital cost.Nano-silica is highly recommended for deep offshore wells where high temperature and high pressure are often encountered.This paper discusses the behavior of Nano-silica at high temperatures and also reviews effects of Nano-silica on various properties of cement.

Grafting of Poly（lauryl acrylate） onto Nano-silica by ‘Click Chemistry’

Poly（n-alkyl acrylate） with long side groups,namely,poly（lauryl acrylate）（PLA） was synthesized by reversible addition-fragmentation chain transfer（RAFT） polymerization,and the trithioester terminal groups were converted to thiol by reducing reaction.Grafting of the obtained polymer onto nano-silica modified with 3-（methacryloxy）propyl-trimethoxysilane（SiO2-MPS） was conducted by thiol-ene ‘click chemistry＇.PLA was characterized by proton nuclear magnetic resonance（1H NMR） and gel permeation chromatography（GPC）.Fourier transform infrared（FTIR） spectrometry and thermogravimetric analysis（TGA） were used to demonstrate the grafting reaction,and the grafted hairy nano-silica（SiO2-g-PLA） was viewed under a transmission electron microscope（TEM）.According to TGA,grafting ratio and grafting density of SiO2-g-PLA are 30.27％ and 0.013 chain/nm2,respectively.The static water contact angle of SiO2-g-PLA is （80.10±2.97）°,which ensures its hydrophobicity.Dispersion experiment was carried out to confirm its dispersibility in mixed solvents,indicating its potential application in coatings or composites.

纳米金颗粒@介孔二氧化硅修饰钛种植体促进高糖条件下的成骨分化

背景:微纳米结构改性是钛种植体表面处理的热点研究领域。糖尿病高血糖环境会影响钛种植体与骨组织形成稳定的结合,探索通过表面微纳结构改性来提高钛种植体在高糖环境下的成骨活性是有必要的。目的:观察钛表面纳米金颗粒@介孔二氧化硅涂层对体外高糖条件下成骨分化的影响。方法:分别制备纳米金颗粒悬浮液与介孔二氧化硅,将二者按一定比例混合在去离子水中,制备纳米金颗粒@介孔二氧化硅悬浮液。取钛片,分3组处理:光滑组经过水砂纸打磨处理,纳米管组经过水砂纸打磨处理后采用阳极氧化技术制备二氧化钛纳米管涂层,实验组制备二氧化钛纳米管涂层后浸泡于纳米金颗粒@介孔二氧化硅悬浮液中,制备纳米金颗粒@介孔二氧化硅涂层,表征3组钛片表面的微观形貌、亲水性。将大鼠骨髓间充质干细胞接种于3组钛片表面,通过细胞活/死荧光染色及CCK-8实验检测细胞增殖,DAPI/鬼笔环肽染色检测细胞黏附。将大鼠骨髓间充质干细胞接种于3组钛片表面,加入高糖成骨诱导培养基培养,通过碱性磷酸酶与茜素红S染色检测成骨分化。结果与结论:(1)扫描电镜下可见光滑组钛片表面均匀平坦,纳米管组钛片表面排列紧密的二氧化钛纳米管阵列,实验组钛片在二氧化钛纳米管表面及内部均负载纳米金颗粒@介孔二氧化硅;纳米管组、实验组钛片亲水性均优于光滑组。(2)细胞活/死荧光染色结果显示,3组钛片表面的细胞活力均高于90%;CCK-8实验结果显示,实验组细胞增殖率高于光滑组、纳米管组;DAPI/鬼笔环肽染色结果显示,二氧化钛纳米管涂层、纳米金颗粒@介孔二氧化硅涂层更有利于细胞黏附。(3)碱性磷酸酶与茜素红S染色结果显示,实验组钛片表面细胞碱性磷酸酶活性与细胞外基质矿化程度均高于光滑组、纳米管组。(4)结果表明,纳米金颗粒@介孔二氧化硅涂层可增强钛表面生物活性,促进高糖环境下的成骨分化。

纳米硅溶胶改良辽宁台安砂土的抗液化性能研究

辽宁台安砂土属于易液化砂,提升其抗液化性能具有重要的工程意义。文章针对纳米硅溶胶(CS)对辽宁台安砂土抗液化性能的改良效果进行探究,通过不排水动三轴试验,对纯砂样和改良砂样的液化特性进行对比研究,分析CS浓度和固化时间两个参量对改良砂样动力特性的影响。研究结果表明:(1)CS能够显著提升台安砂土的抗液化性能,在动载作用下改良砂样均未发生液化破坏。(2)随CS浓度和固化时间的增加,试样动孔压u_(d)、动应变ε_(d)呈现先迅速下降后趋于平缓的发展规律;当CS浓度增至4%、固化时间达到3周后,试样抗液化性能的提升效果不再明显。(3)改良砂样的滞回曲线变得更加稳定。随CS浓度增加,阻尼先降低后趋于稳定,动弹性模量逐渐增大并趋于平缓,但伴随有一定的波动;随固化时间增大,阻尼呈减小趋势,动弹性模量呈增大趋势。研究成果可为辽宁台安地区砂土液化治理提供参考依据。

纳米硅溶胶−EVA−粉煤灰水泥基复合浆材配比正交优化及对其物性的影响

针对传统水泥基浆材不能满足煤矿大变形巷道注浆加固实际需求的难题,通过添加纳米硅溶胶、乙烯−醋酸乙烯共聚物(EVA)和粉煤灰对普通硅酸盐水泥进行改性获得高性能复合浆材。采用正交试验和极差分析法系统研究复合浆材物理力学性能的变化规律,确定最优配比,并进一步分析最优配比复合浆材与纯水泥的物性差异,构建复合浆材的水化反应机理模型,阐明其加固破碎岩石的力学特性。研究结果表明,复合浆材最优配比为:水灰比0.7,粉煤灰掺量15%,硅溶胶掺量2%,EVA掺量7.5%;相较于纯水泥,复合浆材流变性略有下降,但浆液稳定性、力学性能等均有显著提升,初凝时间缩短了38.9%,终凝时间缩短了53.8%,析水率降低了60%,结石率提高了3.3%,单轴抗压强度提高了39.1%,抗拉强度提高了97.2%,拉压比提高了41.7%;硅溶胶和粉煤灰在不同时期与Ca(OH)2发生火山灰反应生成更多水化硅酸钙(C-S-H)和水化铝酸钙(CA-H),促进复合浆材的水化反应,并加速EVA成膜,使结石体更加致密;复合浆材注入量和胶结体单轴抗压强度均随注浆压力的增大而增加,随Talbot指数的增加,抗压强度先增大后减小,破坏形式多呈鼓状,剪胀变形明显;当注浆压力大于2 MPa,Talbot指数为0.5时,胶结体强度较大,破坏较小。本研究为水泥基复合浆材早期强度、增韧改性提供了可行途径。

纳米二氧化硅负载丙烯酰胺型SAP内养护性能研究

设计制备了纳米二氧化硅(NS)负载丙烯酰胺型高吸水树脂(SAP),探究了不同NS负载量的SAP对砂浆自收缩、干燥收缩和力学性能的影响。结果表明,丙烯酰胺型SAP能够完全消除砂浆自收缩,而随着NS负载量增加,负载型SAP对自收缩的抑制作用降低,但仍保持在80%以上。SAP及额外水的引入增加了砂浆的干燥收缩,但随着NS负载量增加,负载型SAP对缓解干燥收缩有积极作用。SAP及额外水的引入降低了砂浆的力学性能,但随着NS负载量增加,负载型SAP显著改善了砂浆的力学性能。其中,负载50%(相对于丙烯酰胺的质量分数)NS的SAP对砂浆力学性能影响最小,试样在28 d龄期的抗压强度与抗折强度仅损失5.6%与2.2%。热重(TG)以及背散射扫描电子显微镜(BSE)结果表明,随着NS负载量增加,负载型SAP内养护试样的水化程度显著提高,微观结构明显改善。

新型高效无氟泡沫灭火剂的制备及其性能表征

提出了一种由黄原胶、纳米二氧化硅颗粒和复配表面活性剂组成的新型环保型泡沫灭火剂,用于迅速扑灭易燃液体火灾。利用荧光分光光度计、液滴形状分析仪、润滑油抗泡沫特性测试仪以及双目透射偏光显微镜等试验研究了泡沫灭火剂的表面性能、聚集特性和发泡行为。结果表明,黄原胶以及二氧化硅纳米颗粒的加入使得10 min之内的泡沫稳定性保持在85%以上。通过泡沫性能测试,配比出最优异的泡沫性能,初始泡沫体积为905 mL,25%排水时间为300 s,10 min之内的排水量为105 mL,显著提升了泡沫的起泡性能和泡沫稳定性。随后使用该配方进行小型灭火试验,灭火时间为18 s,抗烧时间为650 s。

改性二氧化硅封堵剂的制备及性能评价

为了降低水基钻井液滤液对储层的扰动,以丙烯酰胺、苯乙烯、乙烯基三甲氧基硅烷对纳米SiO_(2)进行表面改性,将柔性链聚合物接枝在纳米刚性SiO_(2)粒子表面,形成一种新型的有机-无机复合封堵剂。实验结果发现:该封堵剂提高了泥饼的致密性和封堵性能,并对岩心孔隙进行了有效封堵,有效抑制岩屑水化现象,为水基钻井液在低渗-致密储层开发过程中的应用提供技术支持。

纳米纤维融合改性建筑结构胶制备及性能测试

为提高建筑结构胶性能,通过在传统建筑结构胶中加入纳米纤维材料,制备了一种具有较高应用性能的新型建筑用结构胶。新型建筑结构胶通过在微硅粉和纳米二氧化硅中加入纳米碳酸钙和纳米白炭黑,实现了对建筑结构胶环氧树脂结构胶的改性。当掺入的固定剂质量分数为50%,偶联剂4%,稀释剂10%,组合填料掺量为5%时,可获得抗压强度、抗拉强度等力学指标最佳的建筑结构胶。相对于加入传统的纳米二氧化硅,试验加入的组合填料对结构胶的改性更好。

海胆状纳米二氧化硅增强水凝胶的制备与性能研究

利用溶胶-凝胶法制备海胆状的二氧化硅纳米颗粒(USN),并将其作为共价交联中心增强聚丙烯酰胺(PAM)水凝胶。利用硅烷偶联剂(3-(异丁烯酰氯)丙基三甲氧基硅烷)对USN进行表面改性,通过原位引发自由基聚合得到USN增强的聚丙烯酰胺水凝胶。利用傅里叶变换红外光谱(FTIR)、动态光散射(DLS)和透射电子显微镜(TEM)对改性前后的USN进行表征,考察了USN加入量对水凝胶溶胀性能和压缩性能的影响。结果表明:与纯聚丙烯酰胺水凝胶相比,掺杂USN后,水凝胶溶胀率由约70%降低到约30%,显示出明显的抗溶胀性能;在应变为90%的条件下,水凝胶的最大压缩应力由298.8 kPa增大到566.4 kPa。

纳米SiO_(2)颗粒稳定非水相泡沫的排液行为研究

非水相泡沫在石油化工、食品化工、日用化工和生物医药等行业有着广泛的应用,但非水相溶剂本身的低表面张力和低介电常数决定了其难以形成稳定的泡沫,而纳米Si O_(2)颗粒在发泡及稳泡领域的独特优势正得到越来越多的关注。本文通过二氯二甲基硅烷(DCDMS)对14 nm的Si O_(2)颗粒进行表面润湿性改性,研究纳米Si O_(2)颗粒润湿性对非水相泡沫排液行为的影响。研究发现:随纳米Si O_(2)颗粒表面润湿性的增大,在非水相溶剂中形成的泡沫体积呈现先增大后减小的趋势;非水相溶剂极性的增强,其发泡性能呈现逐渐增强的趋势,但在非极性溶剂中不能形成有效的泡沫。所形成的非水相泡沫排液过程分为排液初期、中期、末期三个阶段,随纳米Si O_(2)颗粒表面润湿性的增大,泡沫消泡半衰期呈现先增大后减小的趋势;强极性溶剂泡沫排液半衰期可达45 min,中等极性溶剂泡沫排液半衰期可达60 min,且在光学显微镜下观察到随排液时间的增加,泡沫粒径逐渐增大,形状逐渐趋于多边形。