石墨表面Si-SiC-ZrB_2抗氧化复合涂层的制备及性能表征

为了防止石墨材料在高温下氧化,采用尺寸为10mm×10mm×5mm的高强石墨为基体,以d_(50)为0.5、10μm的SiC,d50为3μm的ZrB_2,粒度为5~10mm的硅块为涂层主要原料,通过反应浸渗法,在真空状态下于1650℃保温30min进行气相渗硅,在石墨表面制备了Si-SiC-ZrB_2复合抗氧化涂层;利用XRD、SEM研究了涂层的相组成与微观形貌。结果表明:反应浸渗后涂层的主晶相为Si、SiC和ZrB_2,涂层与基体之间具有过渡结构。抗氧化试验表明:由反应浸渗法制备的Si-SiC-ZrB_2复合涂层结构致密,无裂纹,具有良好的抗氧化性能;在1500℃空气条件下循环氧化3次(48h)后,未发现石墨基体被氧化的痕迹,试样质量仅增加0.84%;氧化试验后的涂层由两部分组成,即含有ZrO_2、ZrSiO_4的氧化层以及致密的Si-SiC-ZrB_2涂层。     

自愈合基体改性SiC/SiC复合材料的制备与性能研究

为了提高SiC/SiC复合材料的自愈合性能,借助扫描电镜、X射线衍射及抗氧化性能测试等手段分别对硼硅酸盐改性SiC/SiC复合材料进行微观形貌、相组成分析及抗氧化性能分析。研究结果表明:在1100℃下氧化30h后,通过ZnO:B_2O_3:SiO_2含量比为4:2:4的硼硅酸盐改性后试样失重率由未改性的2.41%降为0.89%,硼硅酸盐玻璃表面出现明显的裂纹自愈合现象,基体内部也存在自愈合基体包裹纤维的现象,但其弯曲强度由未改性的240 MPa降为225 MPa。     

基体改性剂含量对C/C复合材料抗氧化性能的影响

采用氧化烧蚀试验研究了改性剂硼玻璃含量对Ｃ／Ｃ复合材料抗氧化性能的影响,通过扫描电镜（ＳＥＭ）观察分析了其抗氧化机理。结果表明：随着改性剂硼玻璃含量的增加,基体改性Ｃ／Ｃ复合材料的显气孔率逐渐降低,抗氧化能力逐渐增强,当硼玻璃的含量超高９．０ｗｔ％后,Ｃ／Ｃ复合材料抗氧化能力的提高趋于平缓;在基体改性Ｃ／Ｃ复合材料的氧化过程中,改性剂硼玻璃起到了内外涂层的作用,使其抗氧化能力大大提高。     

SiC改性涂层石墨基体表面抗氧化性能研究

以Si粉和碳粉为包埋粉,通过包埋法在石墨基体材料表面制备了SiC抗氧化涂层,但发现涂层疏松多孔、不连续,导致其氧化防护能力弱,为了提高石墨基体材料的高温抗氧化性,分别在包埋粉中掺杂Cr粉和W粉,对涂层进行改性。结果表明,经Cr粉改性后的涂层致密连续,表面平整,制备涂层后的试样在1650℃下进行2h氧化实验,未掺杂金属粉的试样氧化失重率为0.46%;经Cr粉改性后,试样的氧化失重率为0.08%,涂层抗氧化性得到显著提高。但经W粉改性后的试样,由于W粉的热膨胀系数较大,且改性过程是物理改性导致其氧化失重率达到1.34%。     

基体改性对SiC/SiC复合材料高温抗氧化性能的影响

采用先驱体浸渍-裂解工艺结合三种基体改性方式制备了SiC/SiC复合材料,通过形貌分析和力学性能测试,分析了基体改性对Si C/SiC复合材料高温抗氧化性能的影响。研究表明,经1200℃静态空气氧化100h后,三种基体改性的复合材料弯曲强度几乎没有下降,氧化200h后,弯曲强度保留率均可达到80%;氧化300h后,复合材料内部结构没有氧化现象,表面区域界面层的氧化程度降低。改性基体中的B元素氧化生成液相封填SiC涂层表面,延缓了SiC涂层的氧化进程,并阻止氧化介质进入复合材料内部,保护纤维和界面层,从而使SiC/SiC复合材料的长时静态高温抗氧化性能明显提高。     

改性活性炭强化催化臭氧氧化降解草酸

对工业活性炭进行酸预处理、硝基化和氨基化表面改性,并在半连续反应器中研究其催化臭氧氧化降解草酸的活性. 结果表明,酸预处理的活性炭比表面积、等电点pH值(pHpzc)和碱性官能团含量提高了5%~10%,但催化降解草酸效率降低15.6%,氨基化活性炭的pHpzc和碱性官能团含量分别由2.6和234.8 mmol/g升至7.0和764.5 mmol/g,而硝基化活性炭的pHpzc和表面碱性官能团含量均降低. 在中性和酸性溶液中,两种改性活性炭降解草酸的活性均高于预处理活性炭. 在pH=7的溶液中,氨基化活性炭在45 min内催化降解草酸降解率为42.4%. 加入叔丁醇会抑制活性炭催化降解草酸,活性炭催化臭氧氧化草酸主要是羟基自由基起作用.     

改性氧化铁脱硫剂脱除羰基硫性能的研究

制备了一种采用碳酸盐活性组分浸渍改性的氧化铁脱硫剂,考察了活性组分负载量、原料气空速、水汽含量以及氧气含量对改性脱硫剂活性的影响.结果表明,在室温(10～30℃)、常压、原料气空速1000 h-1、原料气中水汽含量1%以及无氧的条件下,改性后氧化铁脱硫荆的COS硫客达到3%,且改性后脱硫剂对硫化氢和二硫化碳的脱除能力也有一定的提高.对新鲜和失活脱硫剂进行红外光谱表征,结果表明,COS在脱除过程中氧化生成的硫酸盐毒化了表面碱性羟基活性住是脱硫剂失活的直接原因.     

活性炭负载磷钨酸用于烟气脱硝抗水性能实验研究

通过硝酸活化和高温水热活化方法对活性炭进行表面改性,之后在改性活性炭上负载不同含量的磷钨酸考察催化剂在有水蒸汽条件下的催化氧化脱硝催化活性,初始反应条件为：温度80 ℃,空速800 h^-1,O₂体积分数为5%、H₂O体积分数为4.2%、NO含量为443 mg·m^-3。通过FT-IR表征制备的催化剂评价前后表面有机活性基团的变化,将不同磷钨酸负载量下活性炭催化剂的脱硝活性评价结果和红外光谱结合,结果表明,湿气条件下,磷钨酸负载质量分数为10%时制备的催化剂能够较好地保持催化氧化脱硝稳定性,NO脱除效率约40%。考察不同操作参数,如温度、水蒸汽含量、O₂含量和空速对负载质量分数10%磷钨酸的活性炭催化剂催化氧化脱硝抗水性能的影响,最优操作条件：温度120 ℃,O₂体积分数8%,水蒸汽体积分数6%,空速1 000 h^-1,催化氧化反应的NO转化率达62%。     

新疆杏核壳活性炭的改性对含氧官能团的影响

采用浓硝酸对活性炭进行表面氧化处理,用Boehm滴定法对改性活性炭表面酸性基团的含量进行测定,研究改性对活性炭吸附性能的影响,同时通过FT-IR加以验证。结果表明:活性炭与20%硝酸溶液按1∶10料液比混合,在70℃下氧化处理2 h后,活性炭表面酸性基团发生了显著变化,和未改性前相比,羧基的含量增加了8~9倍。     

改性活性炭用于三氟二氯乙烷的催化氧化

使用氧化试剂HNO_3和H_2O_2对活性炭进行改性处理,考察了改性处理对活性炭催化性能的影响,并对改性前后的活性炭进行表征。结果表明,改性后活性炭催化活性提高,用HNO_3处理比H_2O_2效果好,活性炭活性不仅与氧化试剂有关,还与活性炭的原料来源有关。     

Novel C/SiC porous ceramic with controllable properties served as transpiration cooling material

Transpiration cooling has been gradually regarded as one of the most efficient and potential thermal protection technologies for the high temperature hot-end components of future hypersonic vehicle. The cooling performance of this technology profoundly depends on the properties of porous medium. This paper exhibits a novel C/SiC porous ceramic with controllable properties adjusted by molding pressure and carbon fiber content in the grinding-mold pressing-sintering process, and investigates the transpiration cooling performance using this ceramic with liquid water. Molding pressure improves from 50 MPa to 100 MPa, the compressive strength has increased by 52.9% and 67.9%, and the permeability decreases about 38% and 39.5% respectively corresponding to fiber content of 6% and 10%. The surface temperatures and back-side temperatures of porous ceramic with the largest molding pressure reaches the highest due to the lowest porosity which can reduce the heat exchange area between cooling water and porous ceramic skeleton. This novel porous ceramic with controllable characteristics can optimize the design of the transpiration cooling system.     

Improved gas sensing of electrospun carbon fibers based on pore structure, conductivity and surface modification

A polyacrylonitrile and carbon black complex was fabricated as a gas sensor using an electrospinning method. The electrospun fibers were thermally treated to obtain carbon fibers, which were then chemically activated to improve the active sites for gas adsorption. The surface of the activated sample was modified by a fluorination treatment. The electrical conductivity was improved by the inclusion of carbon black additives. The activation process improved the porous structure, increasing the specific surface area around 100 times. The gas sensing ability was improved by the developed porous structure and induced functional groups. This treatment improves each of the three steps in the gas sensing mechanism. First, the induced functional groups attracted the target gas to the surface of the gas sensor through induced functional groups. Second, the pore structure significantly increased the amount of adsorbed gas. Third, the electrically conductive carbon black additives resulted in an efficient transfer of the resistive response from the surface of the gas sensor to the electrode. In total, the sensor sensitivity for NO and CO gases was improved about five times based on the effects of chemical activation, carbon black additives, and fluorination treatments.     

具有多级孔道结构的高比表面多孔炭活化策略及VOCs吸附性能

以废弃榛壳为前体,采用不同活化策略制备多孔炭,探究活化策略和活化温度对多孔炭挥发性有机化合物（VOCs）吸附性能的影响,以及多孔炭的结构、表面性质与VOCs吸附性能的构效关系。结果表明,H₃PO₄法制备的多孔炭介孔体积大,且炭结构缺陷较少,吸附位点较少; KOH法获得的微孔体积较大,孔径集中在0.5~0.7nm的微孔,不利于VOCs分子吸附位点的有效利用。H₃PO₄-KOH分步法在850℃下制备具有高比表面积,孔径集中在0.5~1nm的宽微介孔分布,且炭结构高度无序并含有丰富缺陷位的多孔炭,为VOCs吸附提供了充足的吸附位点并提高了吸附位点了利用率,相比于H₃PO₄与KOH活化法制备的多孔炭的VOCs饱和吸附量显著提升,特别是对于弱极性VOCs。另外,H₃PO₄-KOH分步法制备的多孔炭表面官能团含量较低,极性较低,对非极性VOCs的吸附量远大于极性VOCs。因此,H₃PO₄-KOH分步活化策略是制备具有高比表面积、高VOCs吸附性能多孔炭的最优策略与方案。     

Effect of surface oxygen content and roughness on interfacial adhesion in carbon fiber–polycarbonate composites

The effect of surface chemistry and rugosity on the interfacial adhesion between Bisphenol-A Polycarbonate and a carbon fiber surface subjected to surface treatment to add surface oxygen groups was investigated. The surface oxygen content of PAN based intermediate modulus IM7 carbon fibers was varied by an oxidative surface treatment. The oxygen content of the carbon fiber surface increased from 4 to 22% by changing the degree of surface treatment from 0 to 400% of nominal commercial surface treatment levels. The oxidative surface treatment also causes an increase in surface roughness by creating pores and fissures in the surface by removing carbon from the regions between the graphite crystallites. To decouple the effects of surface roughness and the surface oxides on the interfacial adhesion, the oxidized fiber surface was passivated via hydrogenation at elevated temperature. Thermal hydrogenation removes the oxides on the surface without significantly altering the surface topography. The results of interfacial adhesion tests indicate that an increase in the oxygen content of the fiber does not increase the fiber-matrix interfacial adhesion significantly. Comparing adhesion results between oxidized and hydrogen passivated fibers shows that the effect of the surface roughness on the interfacial adhesion is also insignificant. Overall, dispersive interactions alone appear to be the primary factor in adhesion of carbon fibers to thermoplastic matrices in composites.     

炭纤维硼改性的研究进展

详细论述了炭纤维渗硼的各种方法及其优缺点,并讨论了渗硼处理对炭纤维力学性能、微观结构的影响。对于ＰＡＮ 基炭纤维,渗硼处理后强度和模量都有一定的改善。扫描电镜观察发现,硼处理前后纤维表面没有明显区别。透射电镜分析表明,硼处理后纤维近表面区域的有序程度更高。利用光电子能谱测定了纤维中硼的存在形式,结果表明,硼主要以碳化硼形式存在,也有少部分单质硼。Ｘ－ｒａｙ 衍射分析表明,渗硼处理减小了层间距,增大了微晶尺寸（Ｌａ ,Ｌｃ）。     

Surface modification and adsorption of eucalyptus wood-based activated carbons: Effects of oxidation treatment, carbon porous structure and activation method

The incorporation of oxygen functional groups onto the surface of eucalyptus activated carbon and its surface chemistry were investigated as a function of oxidation conditions, carbon porous properties and carbon preparation method. Under all treatment conditions of increasing time, temperature and oxidant concentration, liquid oxidation with HNO₃, H₂O₂ and (NH₄)₂S₂O₈ and air oxidation led to the increase of acidic group concentration, with carboxylic acid showing the largest percentage increase and air oxidation at the maximum allowable temperature of 350 °C produced the maximum content of both carboxylic acid and total acidic group. Nitric acid oxidation of chemically activated carbon produced higher total acidic content but a lower amount of carboxylic acid compared to the oxidized carbon from physical activation. The increased contents of acidic groups on oxidized carbons greatly enhanced the adsorption capacity of water vapor and heavy metal ions.     

Surface-Treated Activated Carbon for Removal of Phenol from Water

Abstract

Adsorption of phenol from dilute solutions has been studied on porous and nonporous carbons, as well as on ion-exchange resins. At a given equilibrium concentration, uptake of phenol on nonporous carbons per unit area is determined by the nature of the carbon surface. Phenol uptake on porous activated carbons decreases sharply upon surface oxidation. However, progressive elimination of chemisorbed oxygen from the oxidized carbon upon heat treatment at increasing temperatures in N₂ increases the phenol adsorption capacity. The capacity is further enhanced if following heat treatment in N₂ at 950 [ddot]C the samples are reacted with H₂ at 300 [ddot]C. The mechanism of phenol adsorption on carbons has been discussed. Activated carbons are more effective adsorbents for phenol than commercial ion-exchange resins.     

活性炭微波改性及对偏二甲肼中氧化杂质的吸附

研究了活性炭微波改性后表面性质的变化及对偏二甲肼中氧化杂质吸附的性能.结果表明:微波法改性使活性炭表面的含氧基团有明显的减少,孔隙结构更为丰富;随着微波功率的提高,吸附率有明显的提高,微波照射时间对吸附效果的影响与功率有关;微波改性后的活性炭对偏二甲肼中的氧化杂质有更大的平衡吸附量及较小的等量微分吸附热.     

Inhibition of catalytic oxidation of carbon/carbon composites by boron-doping

The inhibition effect of high temperature boron-doping on the catalytic oxidation of carbon/carbon composites was investigated. Boron-doping at 2500 °C was found to improve the oxidation resistance of catalyst-loaded composites. Evident inhibition mechanisms include the reduction of active site number by increasing the crystallite size and the site blockage by formed boron oxide. Boron-doping at less than 1.0 wt.% was found to almost completely suppress the catalytic effect of calcium acetate after a slight carbon conversion. This inhibition effect was much less significant in the case of potassium-catalyzed oxidation where only a slight inhibition effect was observed. This is believed to be the essential result of the unique properties of potassium catalyst. Due to its wetting ability and mobility, potassium catalyst could form and maintain good interfacial contact with any exposed carbon surface regions.     

Preparation of porous carbons from petroleum coke by different activation methods

Porous carbons were prepared from Shengli petroleum coke (SPC) and Minxi petroleum coke (MPC) by different activation methods with H₂O, KOH and/or KOH+H₂O as active agents. The porous carbons were characterized by nitrogen adsorption at 77 K. It has been found that activation method and component of petroleum coke, of which different kinds of transitional metals on petroleum coke are crucial for preparing high quality porous carbons. Under the identical experimental conditions, the co-activation with KOH and H₂O as active agents in the same activation process, which has been rarely reported in literature, is the easiest method for the preparation of porous carbons with high surface area. The sequence of active agents in terms of difficulty in the preparation of porous carbons with high surface area is as follows: KOH+H₂O>KOH>H₂O. A drawback of KOH+H₂O activation in the preparation of porous carbon in this work is found to be its low carbon yield in comparison to KOH activation. Compared with the SPC coke, the MPC coke with higher contents of transitional metal and carbon and lower content of nitrogen is more suitable for making high surface area porous carbons, which is believed to be mainly due to the difference in the contents of transitional metals. Porous carbon with surface area around 2500–3000 m²/g and carbon yield about 25–30% has been obtained from MPC coke by KOH+H₂O activation with less KOH and shorter activation time in comparison to the traditional methods.