膨胀石墨孔隙结构及表征方法研究进展

膨胀石墨是制备柔性石墨材料及相关制品的原料,其微观结构特性对柔性石墨制品有重要影响。本文简述了膨胀石墨中宏观-介观-微观多尺度的孔隙分布、孔隙尺寸、孔隙形貌等孔隙结构,论述了石墨粒度、氧化插层工艺、氧化程度、水洗工艺、膨化方式、破碎等加工处理对孔隙结构的影响,介绍了低温N2吸附法、压汞法(MIP)、扫描电子显微镜(SEM)等膨胀石墨孔隙结构传统表征技术的基本原理,总结了小角度X射线散射法(SAXS)、原子力显微镜法(AFM)、差示扫描热孔计法(DSCT)、核磁共振冷孔计法(NMRC)等表征方法的优缺点,提出今后应结合多种表征技术重点探索膨胀石墨介微观孔隙结构,以此为切入点探讨膨胀石墨的理化性能,有助于推动膨胀石墨孔隙结构的深入研究及在其他领域的应用。     

抗氧化低硫柔性石墨材料的研究

针对目前石墨类密封制品抗氧化性能差,密封性能不高,易泄漏等问题,选用高锰酸钾和浓硫酸作混合氧化剂,三氯化铁作催化插入剂,少量过氧化氢作催化剂,采用半固相浸渍法制备膨胀石墨,再将其用蔗糖硼酸脂溶液浸渍、脱水、低温干燥、高温膨胀后压制成高抗氧化低硫柔性石墨复合密封材料。制品含硫量低于5.0×10-4,抗氧化能力增强一倍以上,在预紧力70MPa,介质压力10.0MPa的情况下泄漏率小于0.0001。研究结果表明采用这种新工艺可以改善石墨复合密封材料性能,从而更好地满足使用要求。     

过氧乙酸用量对石墨插层效果的影响及其氧化插层机理

以过氧乙酸为氧化剂,通过化学氧化法制备了不同插层效果的可膨胀石墨。利用XRD、FT-IR、SEM等对样品结构、氧化程度、微观形貌进行表征。结果表明,过氧乙酸对石墨有显著的氧化插层效果,在石墨与过氧乙酸体积比为1∶3时制备的可膨胀石墨的膨胀容积达到200 m L/g,其主要技术指标优于国标GB 10698—89中KP 180-Ⅲ型优等品的要求。过氧乙酸氧化机理在于其—COO^-可从石墨层夺取电子,导致石墨被氧化,打开石墨层,插层剂因静电作用进入石墨层间,形成可膨胀石墨。该方法所采用的过氧乙酸由于其成本低、环保等特点,有望应用于膨胀石墨的生产。     

添加剂硼酸对柔性石墨性能的影响

初步探讨了制造柔性石墨材料过程中加入添加剂硼酸的方法，并就硼酸的加入量对其膨胀倍数、抗氧化性、电阻率、抗拉强度等的影响进行了比较和分析。实验表明，添加剂硼酸使柔性石墨材料在抗氧化性方面具有明显的优越性，抗拉强度有所增加，而对其它性能的影响不大。     

聚苯硫醚树脂浸渍炭材料耐甲醇的研究

石墨材料经聚苯硫醚树脂浸渍固化后,机械强度有所提高,其耐甲醇性也得到明显提高。研究了聚苯硫醚树脂耐甲醇的效果,以及聚苯硫醚浸渍炭材料对其气孔率和力学性能的影响。通过液体树脂先浸渍石墨再压制烧结的方式,能提高浸渍炭材料的各种力学性能。在压力35 MPa下压制,300℃烧结时各项力学性能及耐甲醇性最优。     

氧化石墨改性酚醛泡沫材料的制备及其表征

采用原位聚合法制备了氧化石墨改性酚醛树脂,并以其为主要原料制备酚醛泡沫材料。通过红外光谱仪、万能试验机、热重分析仪、扫描电子显微镜等测试手段对改性酚醛泡沫材料的力学性能、热稳定性以及微观结构进行表征。结果表明,与未改性的酚醛泡沫塑料相比,添加1.0%氧化石墨改性酚醛泡沫材料泡孔尺寸更加均匀,压缩强度比未改性的酚醛泡沫塑料提高65.0%,表面粉化率显著降低,氧化石墨对酚醛泡沫材料的强度、韧性及热稳定性均有显著的提高。     

膨胀石墨压块的制备及其导热性能研究

为探索和优化微波法制备膨胀石墨及石墨压块成型工艺,利用激光粒度仪、扫描电镜对膨胀石墨及其压块的形貌、孔隙结构等微观结构进行表征,并进行正交试验分析研究了微波功率、微波时间、膨胀石墨粒径、压块成型压力、单次膨胀量等因素对压块导热性能的影响.结果 表明,微波功率和微波时间对压块导热性能有显著影响,功率过低和时间过短会导致石墨膨胀不充分,而功率过高和时间过长则会导致石墨蠕虫被过度灼烧而断裂,膨胀石墨粒径、压块成型压力、单次膨胀量对压块导热率无显著影响.依据实验和分析,以压块导热系数为目标确定了膨胀石墨压块最优制备条件:微波功率为700 W、微波时间为70 s、膨胀石墨粒径为80 ～ 100目、单次膨胀量为6.0g、压块成型压力为200 MPa,该条件下压块导热系数达到5.78 W/(m·K).     

微扩层改性对煤基石墨微观结构和储锂性能的影响

以自制煤基石墨为前体，浓硫酸为插层剂，高锰酸钾为氧化剂，采用液相氧化插层-热处理工艺对煤基石墨进行微扩层改性处理，制备出微扩层煤基石墨。利用X射线衍射仪、扫描电子显微镜、透射电子显微镜、拉曼光谱测试、低温氮气吸附和X射线光电子能谱等手段分析不同微扩层煤基石墨的微观结构，并测试其用作锂离子电池负极材料的电化学储锂特性，系统研究微扩层改性对煤基石墨微观结构和储锂性能的影响。研究表明，微扩层改性处理不仅可增加石墨微晶片层的层间距，还可以在石墨基体中引入纳米孔道和C==O、C—O—H及C—O—C等含氧官能团。氧化剂用量是影响微扩层煤基石墨微观结构的重要因素。通过调节氧化剂用量可实现微扩层煤基石墨微晶层间距、纳米孔道和表面官能团等微观结构的有效调控。当氧化剂用量为煤基石墨的0.30倍时，微扩层煤基石墨的层间距为0.3374nm，其纳米孔道主要由1～2nm微孔和2～6nm中孔组成，比表面积为24.6m2/g，且富含C==O、C—O—H及C—O—C等含氧官能团。微扩层煤基石墨用作锂离子电池负极材料展现出优异的电化学储锂性能，其在0.1C低电流密度下的可逆比容量最高可达511.1mAh/g，在5C高电...     

喷射混凝土渗透性、孔结构和力学性能关系研究

以喷射混凝土衬砌隧道结构为研究背景,开展喷射混凝土渗透性、孔结构及力学性能试验,采用AutoClam、非稳态氯离子快速测定法(RCM)、直线导线-线性回归法(ASTM C457)、压汞测孔法等,对喷射混凝土渗透性(透气性、透水性和氯离子迁移)、孔结构(砂浆孔结构和表面孔结构)及力学性能(抗压强度和劈裂抗拉强度)进行测试,研究喷射混凝土配合比对喷射混凝土能性的影响以及三者之间的相互关系.结果表明,喷射混凝土水胶比、粉煤灰及钢纤维对其渗透性、孔结构参数和力学性能具有直接影响,低水胶比、高钢纤维掺量对喷射混凝土性能的提高有利,粉煤灰可促进喷射混凝土性能优化,但过高的掺量会造成性能劣化.通过分析喷射混凝土渗透性、孔结构和力学性能之间的关系,认为喷射混凝土孔结构组成决定其渗透性和力学性能,随着孔隙率的增大,喷射混凝土渗透性提升、力学性能下降,孔隙率与渗透性及抗压强度之间呈指数关系.     

水胶比对混凝土性能及气孔结构的影响分析

通过试验,对不同水胶比下混凝土28 d龄期的抗压强度、氯离子电通量及微观方面的气孔结构和气孔特征参数进行了对比分析,研究了水胶比对混凝土宏观性能及微观孔结构的影响.结果表明:过量的自由水会在混凝土内部产生毛细孔,增大水胶比相当于变相增多了混凝土内部的孔隙数量,能够显著降低混凝土的抗压强度,但较大的水胶比又能够增强局部的水泥水化反应.对氯离子电通量而言,水胶比越大,毛细孔越多,孔含量越多,相对增大了连通孔隙的数量,氯离子电通量会呈现出增大的现象.随着水胶比的减小,孔径分布也有向小孔径方向发展的趋势.此外,抗压强度与较小孔径的孔含量及孔隙率的关联度计算结果较大,氯离子电通量与气孔间距系数的关联度计算结果较大,这说明小孔含量及孔隙率能够用来表征混凝土的抗压强度,气孔间距系数也能在一定程度上表征混凝土的耐久性.     

超细粉制备高密高强炭素材料

以超细焦炭粉和球形石墨为原料，以CJF-43和FB为粘结剂，通过特定工艺制备高密度高强度炭素材料。测试其体积密度、抗压强度、电阻率、肖氏硬度等性能，研究树脂种类及含量、细颗粒含量、球形石墨的含量、成型压力对其性能的影响。结果表明，FB的粘结效果好；随着球形石墨含量的增加，样品密度提高，机械强度降低；随着细颗粒的增加，样品的密度和硬度提高；其他工艺条件不变，在100MPa下样品的成型效果好。     

Creep of a Nextel™720/alumina ceramic composite containing an array of small holes at 1200°C in air and in steam

Tensile stress-strain and tensile creep behaviors of an oxide-oxide composite containing an array of small circular holes were evaluated at 1200°C. The composite consists of Nextel™720 alumina-mullite fibers in a porous alumina matrix. Test specimens contained an array of 17 holes with 0.5-mm diameter drilled using a CO₂ laser. The presence of holes caused reduction in tensile strength and modulus. Tensile creep tests were conducted at 1200°C in air and in steam at creep stresses ranging from 38 to 140 MPa. Primary, secondary, and tertiary creep regimes were noted in air and in steam. The presence of the laser-drilled holes accelerates the steady-state creep rates. Creep run-out, defined as 100 hours at creep stress, was attained for stress levels <60 MPa in air and for stresses <40 MPa in steam. The presence of the laser-drilled holes significantly degrades creep resistance of the composite. The retained tensile properties of all specimens that attained run-out were determined. Composite microstructure was examined; the damage and failure mechanisms were considered. The degradation of tensile properties and creep resistance are attributed to damage caused to composite microstructure by laser drilling.     

Mechanical and viscoelastic properties of soybean oil thermoset reinforced with jute fabrics and carded lyocell fiber

Composites and hybrid composites were manufactured from renewable materials based on jute fibers, regenerated cellulose fibers (Lyocell), and thermosetting polymer from soybean oil. Three different types of jute fabrics with biaxial weave architecture but different surface weights, and carded Lyocell fiber were used as reinforcements. Hybrid composites were also manufactured by combining the jute reinforcements with the Lyocell. The Lyocell composite was found to have better mechanical properties than other composites. It has tensile strength and modulus of about 144 MPa and 18 GPa, respectively. The jute composites also have relatively good mechanical properties, as their tensile strengths and moduli were found to be between 65 and 84 MPa, and between 14 and 19 GPa, respectively. The Lyocell‐reinforced composite showed the highest flexural strength and modulus, of about 217 MPa and 13 GPa, respectively. In all cases, the hybrid composites in this study showed improved mechanical properties but lower storage modulus. The Lyocell fiber gave the highest impact strength of about 35 kJ/m², which could be a result of its morphology. Dynamic mechanical analysis showed that the Lyocell reinforced composite has the best viscoelastic properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

用于北方满族民居墙体的再生混凝土性能研究

通过试验研究了再生混凝土作为北方满族民居建造材料的可行性。研究重点:再生骨料的物理性质测定、再生混凝土基本力学性能试验,以及粉煤灰、聚丙烯纤维以及附加水对其力学性能的影响。通过试验得到,再生混凝土立方体抗压强度最高应力达37.1 MPa、轴心抗压强度平均应力28.4 MPa、静力受压弹性模量平均应力22 300 MPa、抗折强度平均应力3.8 MPa、劈裂抗拉强度平均应力1.68 MPa。结果表明:在再生混凝土中加入粉煤灰和聚丙烯纤维都对立方体抗压强度有所提高,但附加水的加入对立方体抗压强度产生了降低作用。整体来说,再生混凝土各方面的力学指标都能满足一定的强度要求。因此可以作为北方满族民居的建设材料。     

碳纤维含量对PMMA-PMA基复合材料显微结构及力学性能的影响(英文)

以甲基丙烯酸甲酯(polymethyl methacrylate,PMMA)和丙烯酸甲酯(polymethyl acrylate,PMA)为原料、短切碳纤维(Cf)为增强相,采用悬浮聚合法制备碳纤维增强聚甲基丙烯酸甲酯-聚丙烯酸甲酯基复合材料(carbon fiber-reinforced polymethyl methacrylate-polymethyl acrylate matrix composites,Cf/PMMA-PMA)。研究碳纤维含量(质量分数,下同)对Cf/PMMA-PMA显微结构及力学性能(抗折强度、抗压强度和拉伸强度)的影响。结果表明:随碳纤维含量增加,Cf/PMMA-PMA的挠度呈线性增长,而抗折强度、抗压强度和拉伸强度呈先增大后减小趋势。当碳纤维含量为15%时,Cf/PMMA-PMA的抗折强度、抗压强度和拉伸强度分别达到最大值115.5、244.6MPa和158.6MPa。     

Physical and mechanical properties of materials prepared using Class C fly ash and soybean oil

In present work; epoxidized soybean oil (ESO), fly ash (FA) and natural clay (C) are used to produce 45 kinds of biocomposite materials and by analyzing the physical–mechanical properties of these novel materials, their use as an insulation material is investigated. The compressive strength, tensile strength, abrasion loss, thermal conductivity and oven-dry mass of each sample are measured. The minimum thermal conductivity of 0.273 W/mK is observed with the samples containing ESO–FA–C. It is increased with the decrease of ESO and FA. The compressive and tensile strengths are varied from 13.53 to 6.31 MPa and 1.287 to 0.879 MPa, respectively.     

Hybrid effect,mechanical properties and enhancement mechanism of oil-well cement stone with multiscale silicon carbide whisker

Cement-based materials typically have a relatively high compressive strength and a relatively low tensile strength. In this paper, multiscale silicon carbide whiskers (SW) were used to improve mechanical properties of oil-well cement stone. The structure and properties of whisker cement stone were analyzed via mechanical testing and cement sheath integrity. The results demonstrated that multiscale SW mixing showed a positive hybrid effect and could effectively improve the compressive strength, the flexural strength, and the splitting tensile strength of oil-well cement stone by 8.96%, 137.44% and 27.96%. The modulus and porosity of the whisker cement stone significantly reduced. The filling effect, whisker pinning, the pullout, and the whisker bridging were regarded as effective mechanisms for the addition of SW when improving the mechanical properties and microstructures of oil-well cement stone.     

To drill or not to drill? Creep of an oxide-oxide composite with diamond-drilled effusion holes at elevated temperature

Ceramic matrix composites (CMCs) are prime candidates for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. Film cooling technique requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep performance of an oxide-oxide CMC consisting of Nextel 720 alumina-mullite fibers in a porous alumina matrix were evaluated at 1200°C. Test specimens included 17 holes with a .5 mm diameter in the gage section. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled holes noticeably lowered tensile properties and degraded creep performance of the CMC. Our earlier study considered the effects of small holes drilled using a CO₂ laser on the tensile properties and tensile creep resistance of this composite. The presence of laser-drilled holes also considerably lowered the creep resistance of the Nextel 720/alumina CMC. In both cases the reductions in tensile strength and creep resistance are due to damage caused to composite microstructure by hole drilling. However, different drilling techniques result in different microstructure degradation mechanisms. Damage to the CMC microstructure caused by these two drilling techniques and implications for mechanical performance and durability are discussed.     

地质聚合物合成中铝酸盐组分的作用机制

在对铝、硅酸盐离子团中离子的部分电荷计算的基础上,研究了铝组分在地质聚合物合成中的作用机制,并通过实验进行了初步验证。研究表明：铝组分对地质聚合物的合成中缩聚反应有显著的促进作用,因而在合成地质聚合物时原料中铝组分的溶解性至关重要。实验结果表明：由具有较小颗粒度的煅烧高岭土为原料合成的地质聚合物具有较短的固化时间,更均匀的显微结构和更高的机械强度。如由较粗的煅烧高岭土为原料合成的地质聚合物的抗压强度为54MPa,而由较细的煅烧高岭土为原料合成的地质聚合物的抗压强度则能达到74MPa。