【作者】 肖丽；

【导师】 金为群；

【作者基本信息】 吉林大学 ， 材料学， 2004， 硕士

【摘要】 石墨插层复合材料——膨胀石墨是用天然鳞片石墨与其它无机、有机物人工复合而成的一类新型功能材料，广泛应用于石油、化工、冶金、电力、机械、制药、汽车、航天、核能等领域。天然鳞片石墨为层状结构，由于层间作用力较弱，可插入一些物质，形成石墨层间化合物，制成一种新的复合材料。这种材料既保留了天然石墨的耐高温，耐腐蚀，耐辐射，导电性等优良性质，又具有天然石墨所没有的柔软性，回弹性，自粘性，不渗透性，吸附性和低密度等特性。由于以往国内生产的产品常用浓硫酸作插入物，在作密封材料时制品中含有的残余硫会腐蚀金属，影响密封效果。因此，人们尝试选用不同的插层剂，所合成的产品具有不同的特性。本文采用磷酸作为插层剂，硝酸、高锰酸钾做氧化剂合成石墨插层复合材料——膨胀石墨，讨论了其最佳合成工艺条件，并且与选用不同的无机物和有机物作为插层剂所制得的产品进行比较，测定了该系列产品的PH、灰分、抗氧化性、水溶液中的电导率、吸附性。合成膨胀石墨的工艺过程为：在鳞片石墨中加入浓硝酸和高锰酸钾(氧化剂)，混合均匀后，加入插层剂，在一定温度下反应，洗涤至PH为5左右，100℃以下干燥，900℃膨化30S。氧化剂的作用是使鳞片石墨被氧化，这是生成层间化合物的第一步。氧化剂用量过小，碳原子被氧化得不够，层间化合物较少，膨胀容小；用量过大，灰分增加，产品质量下降。对于硝酸用量的选择，首先，硝酸在反应中起两方面的作用：一是在酸性条件下，提高氧化剂的氧化能力；二是作为插层物质进入石墨层间，然而硝酸的用量也不宜过大，过量会导致含水量增加，膨胀容下降。所以开始时，膨胀容随硝酸的加入量增大而增加，但是<WP=65>当硝酸过量到一定的程度时，膨胀容反而随硝酸的增加而降低。对于高锰酸钾用量的选择，开始时随着高锰酸钾加入量的增加，反应进行的越来越完全，直至达到最大，其后当再增加高锰酸钾的用量时，就会增加产品的灰分，从而影响到产品的质量。对于磷酸用量的选择，由于磷酸的用量过大会增大产品的灰分，所以在保证膨胀容较大的前提下，应尽量降低磷酸的用量。在不同的反应时间和温度下，反应时间越长，反应温度越高，反应越完全，膨胀容也就越大，但成本也越高。对于不同的膨化时间，膨化时间越长，插层剂的气化越充分，膨胀容积也越大，但时间过长，则会引起产品的氧化，导致产品质量降低。因此，综合考虑以上因素，用磷酸制备膨胀石墨的最佳工艺条件为：石墨(g)，硝酸(ml)，高锰酸钾(g)，磷酸(ml)的用量比为1：2.4：0.06：0.3。反应温度为70℃，反应时间为1h，膨化时间为30s。通过测量产品的水溶液的电导率，可以初步确定其层间化合物的成分。可以看出，用硫酸做插层剂的产品在水溶液中电导率较高，可以推测NO3－、HSO4－作为插层离子进入层间，所以用硫酸合成的产品在水溶液中的电导能力较强，反应式为：n石墨 + nHNO3+ nH2SO4 + n/2[O] →[石墨 +·NO3－·HSO4－]n+n/2H2O以磷酸、磷酸酐做插层剂的产品电导率居中，这说明插层物质除NO3－外，磷酸是以分子形式进入了层间，所以用磷酸、磷酸酐做插层剂的产品在水溶液中的电导能力居中，反应式为：n石墨 + nHNO3+ nH3PO4+ n/2[O] →[石墨 +·NO3－·H3PO4]n+ n/2H2O以乙酸、乙酸酐做插层剂的产品电导率较低，说明插层物质除NO3－外，大部分插层物质是乙酸分子，因此用乙酸、乙酸酐合成的产品在水溶液中的电导能力较弱，反应式为：n石墨 + nHNO3 + nCH3COOH + n/2[O]→[石墨 +·NO3－·CH3COOH]n + n/2H2O由于插入层间的物质不同，导致了产品性质上的差别。层间<WP=66>化合物的化学通式[graphite+·NO3－·B]，用硫酸插层，B代表硫酸氢根离子，这种层间化合物，高温膨化时，能放出二氧化硫和氮氧化合物，所以灰分比磷酸类层间化合物小，但含硫量高，腐蚀性强。用硝酸插层，成本低，但膨胀容小。用乙酸，乙酸酐作为插层剂，插入石墨层间的为乙酸分子和一少部分硝酸根离子，B代表乙酸分子，在高温膨胀时，能放出二氧化碳和一小部分氮氧化合物，因为有机物易挥发，因此灰分较小，纯度高，但膨胀容小。而以磷酸和磷酸酐制备时，B则代表磷酸分子，虽然灰分较大，但含硫量低，膨胀容大。由于各种材料性质不同，所以使用时应根据需要选择产品。对于系列产品的抗氧化性的实验，通过失重率随时间的变化和随温度的变化来进行比较。由于膨胀石墨比表面积大，在高温下的抗氧化性较天然石墨弱。用乙酸、乙酸酐作为插层剂，产品的抗氧化性较弱，用磷酸、磷酸酐插层的膨胀石墨抗氧化性要强于其它产品。膨胀石墨的结构疏松多孔，有较大的比表面积，一般可达50-200m2/g，孔径基本以中、大孔为主，因此易于吸附非极性有机大分子物质，特别是油类物质。通过对产品的吸附性的研究，膨胀石墨对有机油类大分子表现出优良的吸附能力，优于活性炭和棉花，而且是其它吸附产品无法比拟的。膨胀石墨具有低密度、轻质、高化学稳定性和无毒的特点，对比活性炭、棉花，其大孔结构及其独特的压延柔性，将使其成为一种新型的吸附材料，并会在化工、环保等领域具有非常广阔的应用前景。在环?更多还原

【Abstract】 Graphite intercalation composite is a new kind of technology material which is prepared with different kinds of inorganic and organic compound and graphite. It is widely used in many fields such as petrochemical industry, metallurgical industry, electric utility industry, mechanical industry, pharmacy industry, auto industry, aerospace industry and nuke industry. Natural squama graphite has layer structure. It can be compounded into graphite intercalation compounds (GIC) after some materials are intercalated into layers because of the weak binder and be produced into a new kind of composite. This kind of material has not only the good properties of natural graphite such as high-temperature, corrosion and radiation resistance, electrical conductivity, but also the characters of flexibility, resilience, self-adhesion, impermeability, adsorption, low density which natural graphite has not.Because of H2SO4 as inset in the old process of expanded graphite, there are remainder sulfur in the product which corrupt metal and affect the result of sealing. Therefore, different kinds of insets had been tried, the product being compounded have different characters.Graphite intercalation composite ——expanded graphite is prepared with HNO3,KMnO4 as oxidant and H3PO4 as intercalation in this paper. The conditions of optimum synthetic processing are discussed, too. The production is compared with the other kinds of productions prepared with different inorganic and organic compound. This series of productions’ PH, ash content, anti-oxidation, conductivity of solution, adsorption are studied and compared. <WP=68>The craft process of preparing expanded graphite: HNO3, KMnO4 (oxidant) and inset are added into squama graphite, the mixture is puddle into mash. The materials are kept at certain temperature, washed to PH=5,and dried at maximum of 100℃.Finally, they are exfoliated at 900℃ for 30s.The function of oxidant is to make squama graphite oxygenated, which is the first step of the preparation of GIC. If the quantity of oxidant is too low, the carbon atom is less oxygenated and less GIC are compounded, so the expand volume of product is low; If the quantity of oxidant is too large, the ash content of the product would increase, the quality of the product would decrease. According to the option for HNO3 quantity, first, there are two function in the reaction about HNO3: 1, HNO3 prompt the oxidation ability of oxidant; 2, the quantity of HNO3 is not too large when HNO3 is intercalated into the layers, otherwise, the water content would increase and expand volume would decrease. So, at the beginning, the expand volume increase as the increase of HNO3 quantity, but the expand volume decrease as the increase of HNO3 quantity when the HNO3 quantity increase at certain limit. According to the option for KMnO4 quantity, at the beginning, the mixture react more completely as the increase of KMnO4 quantity, The ash content would increase and the quality would be effected when the KMnO4 quantity increase out of certain limit. According to the option for H3PO4 quantity, the ash content would increase if H3PO4 quantity is too large, so H3PO4 quantity is decreased to the least in order to keep expand volume relatively large. The mixture react more completely and the expand volume is larger when the reaction time and the reaction temperature increase, but the cost would much more. According to different exfoliation time, inset is more fully gasified and expand volume would be larger when the exfoliation time increase, the product will be oxygenated and the <WP=69>quality of the product would decrease if the exfoliation time is too long. Therefore, we take all these factors into account and get the best condition of preparing expanded graphite with H3PO4 is: graphite(g): HNO3(ml): KMnO4(g): H3PO4(ml)= 1：2.4：0.06：0.3.The reaction temperature is 70℃, the reaction time is 1 hour, The exfoliation time is 30s.According to the conductivity of solution of the products, the component of GIC would be presumed. The conductivity of soluti更多还原