环保型铝用冷捣糊的研究

【作者】 田林；

【导师】 谢刚；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2012， 博士

【摘要】 随着铝工业的发展和进步,特别是石墨质阴极炭块的使用,铝电解槽的寿命已有了很大的提高,因此,制约铝电解槽寿命的关键材料已由传统的阴极炭块逐渐地向炭块间的捣固糊转变。传统的捣固糊则主要以煤沥青为黏结剂制备的热捣糊和温捣糊,由于这两种糊料在施工捣固前,均需预热,因此会释放出对人体和环境都有害的沥青烟气体,操作环境恶劣,工人劳动强度高,且捣固的糊料易分层,局部出现缺陷的可能性很大,影响糊料自身的使用。冷捣糊室温下即可施工捣固,不存在上述情况。但冷捣糊的生产主要掌握在挪威埃肯公司、法国铝业等一些发达国家手中,因此,我国独立自主研究开发一种铝用冷捣糊,对于打破国际先进水平对冷捣糊的垄断,提高我国铝业的科技进步和国际竞争力,努力使我国成为铝业强国,将具有重要意义。本文以树脂为主要黏结剂,添加适量的混合煤沥青成功制备了一种环保、节能的铝用冷捣糊,且常规性能达到了国家工业标准,部分非常规性能也较适宜,主要研究内容和结论如下：(1)采用最紧密堆积中的Dinger-Funk方程从理论上计算了不同颗粒分布系数下的粒度分布,通过测定制备糊料的空隙率、电阻率、抗压强度等,确定了骨料的最佳颗粒配比即5-3mm为20.87%,3-1mm为31.49%,1-0.074mm为33.90%,<0.074mm为13.74%。(2)分别研究了以改质煤沥青、中温煤沥青、环氧树脂、呋喃树脂、酚醛树脂及复合黏结剂为黏结剂或主要黏结剂,以电锻煤、石墨或二硼化钛、碳纤维为骨料,经过配料、混料、混捏等工序制备了铝用冷捣糊,通过黏结剂的改性,对制备的糊料进行了相应改进,采用电子万能试验机、电阻率仪等测定了制备冷捣糊的常规理化性能,扫描电镜和能谱仪(SEM-EDS)对制备糊料的微观形貌及钠渗透后糊料的微观形貌及渗透的元素进行了分析,应用红外技术(FT-IR)及X衍射仪(XRD)分析了碳化后黏结剂的结构变化和石墨化程度,还利用热重-差热分析仪(TG-DSC)研究了制备冷捣糊在焙烧过程中各个阶段的质量变化和热量变化。结果表明：以煤沥青和葸油为黏结剂制备的冷捣糊,在焙烧过程分为三个阶段,但该黏结剂黏结性较差,制备的糊料疏松多孔,且其保鲜性较差,硫和苯甲醛对煤沥青结焦值的提高较明显,制备的糊料也得到改进。以酚醛树脂为糊料的12.5%时,制备冷捣糊的表观性状和常规理化性能最优,它在焙烧过程中分为四个阶段。苯甲醛改性酚醛树脂结焦值提高最明显,且改性后酚醛树脂制备的冷捣糊常规理化性能得到了提高。复合黏结剂为制备冷捣糊的黏结剂时,以复合黏结剂A3为糊料的12.5%时,制备的冷捣糊表观性状和常规理化性能较好,以2%苯甲醛为复合黏结剂A3的改性剂对制备的糊料进行改进,改进后的糊料常规性能最优,部分非常规性能也较合适,它在焙烧过程中分为五个阶段。其中复合黏结剂A3为酚醛树脂：混合煤沥青(中温煤沥青：蒽油=65：35)=80：20,骨料为电锻煤、石墨、碳纤维,它们分别为骨料的54.7%、45%和0.3%。(3)采用气相色谱-质谱仪(GC-MS)测定了制备糊料在焙烧过程中多环芳烃(PAH)的释放量,得出以2%苯甲醛为复合黏结剂A3的改性剂制备的铝用冷捣糊在施工捣固及捣固后糊料焙烧过程都具有环保的特点。(4)利用TG热分析方法研究了苯甲醛改性后复合黏结剂A3在焙烧过程的质量变化,选取失重较为明显的两段进行研究,采用热分析方法中积分法(Flynn-Wall-Ozawa方程)和微分法(Friedman方程)模拟其焙烧过程。结果表明,第一段(130-190℃)热解过程是由多步复杂的反应组成,这阶段主要是树脂固化过程中及黏结剂中一些小分子有机物的挥发；第二段(390-600℃)热解过程可分为两步过程,第一步则在转化率a为0.55-0.60间,平均表观活化能E为43.28kJ·mol-1,平均InA为1.3291s-1,第二步则在α为0.65-0.80间,此步E为168.34kJ·mol-1,平均InA为17.06s-1。但两步的机理函数相同即f(α)=3/2(1-α)4/3[(1-α)-1/3-1]-1.(5)采用红外和核磁共振(1H-NMR)分析了苯甲醛对复合黏结剂A3的改性机理,其机理反应为苯甲醛与酚醛树脂和混合煤沥青中活性小分子发生了亲电反应,使得酚醛树脂和混合煤沥青中的活性小分子缔结为大分子有机物,从而提高了它们的结焦值。更多还原

【Abstract】 Life of aluminum electrolysis cell has been prolonged with the development and progress of aluminum industry, expecially use of graphitic cathode carbon block. So the key material to restrict life of aluminum electrolysis cell is transforming from cathode carbon block to ramming paste. Contraditonal ramming paste is hot or tepid with coal tar pitch as main binder. Both of pastes are needed to be preheated before tamping, so many genotoxic polycyclic aromatic hydrocarbons (PAHs) are released during tamping, which are hazardous for health and environment. What’s more, the possibility of layers and defects of tamped paste is high in the local area, affecting their use. The above disadvantages doesn’t exist in cold ramming paste because of its room tamping temperature, but production of cold ramming paste is controlled by developed countries such as Norway AIkem, French Aluminum Industy and etc. So it is of great significance to independently research and develop a cold ramming paste for aluminum industy, which can break the international developed countries’ monopoly, enhance scientific and technological progress and international competitiveness of Chinese aluminum industry and make our country become a powerful aluminum industry. An eco-friendly and energy-efficient cold ramming paste for the aluminum electrolysis cell is prepared with resin and a spot of mixed coal tar pitch as binder. Additionally, its conventional properties can reach the national industry standard and some unconventional properties are very suitable. Main contents and conclusions of this paper are as follows:(1) Particle size distributions were calculated in theory using Dinger-Funk equation in closest packing models at different particle distribution coefficients and then optimal particle proportion (5-3mm20.87%,3-1mm31.49%,1-0.074mm33.90%,<0.074mm13.74%) was determined through measment of porosity, electrical resistivity, compressive strength of the prepared paste.(2) The cold ramming pastes for aluminum electrolysis cell were prepared through burden, mixing, kneading, etc, with high temperature coal tar pitch, mid-temperature coal tar pitch, epoxy resin, furan resin, phenol-formaldehyde (PF) resin and composite binders as binder or main binder, respectively, electro-calcined anthracite, graphite or TiB2, carbon fiber as aggregate. Additionally, the prepared pastes were improved by binder modification. Conventional properties of prepared pastes were measured by electronic universal testing machine, electrical resistivity and so on. Micro-morphology of prepared paste before and after sodium pentration and pentrated elements were analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS). Structure change and graphitization degree of carbonized binders were observed by Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray diffraction (XRD). Heat and mass chang of prepared paste in every stage during the roasting were researched by Thermo Gravimetry-Differential Scanning Calorimetry (TG-DSC). The results show that the prepared paste used coal tar pitch as main binder can be devided into three stages during roasting process, which is loose and porous and its adhesion and shelf life are poor. Sulfur and benzaldehyde can obviously increase coking value of coal tar pitch. The prepared paste with coal tar pitch modified by sulfur and benzaldehyde as main binder can be improved. Apparent characters and conventional properties of the prepared paste used resin as binder is the best in a mass ratio of12.5%PF resin. This paste can be devided into three stages during roasting process. The coking value of PF resin modified by benzaldehyde is increased most obviously, what’s more, the conventional propertie of cold ramming paste prepared by PF resin modified by benzaldehyde are improved. Apparent characters and conventional properties of the prepared paste used composite binder as binder is better in a mass ratio of12.5%composite binder A3. The paste prepared with composite resin A3modified by benzaldehyde in a mass ratio2%is improved and its conventional properties is the best, additionally, the paste can be devided into three stages during roasting process and its unconventional properties is very suitable. Composite resin A3contains PF resin and mixed coal tar pitch in a mass ratio of80:20and mixed coal tar pitch contains mid-temperature coal tar pitch and anthracene oil in a mass ratio of65:35. The aggregate contains electro-calcined anthracite, graphite and carbon fiber in a mass ratio of54.7%,45%,0.3%, respectively.(3) PAHs of the prepared paste were measured during the roasting process using Gas Chromatography-Mass Spectrometry (GC-MS) was calculated. It is concluded that an eco-friendly cold ramming paste for the aluminum electrolysis cell in the tamping and roasting processes is prepared with composite binder A3modified by benzaldehyde in a mass ratio of2%as binder.(4) The mass change of composite binder A3modified by benzaldehyde during roasting process was studied through TG. Two of the more obvious weight loss temperature stages were studied using thermal analysis of the integral method (Flynn-Wall-Ozawa equation) and differentiation (Friedman equations) to simulate the roasting process The results show that the first pyrolysis process (130-190℃) can include many complex reactions and volatilization of some small volatile organic molecules in the curing resin binder and binder occur during this process. The second pyrolysis process can be devided into two steps. Conversion of the first step is ranged from0.55to0.60, and average apparent activation energy (E) and lnA are43.28kJ-mol-1and1.3291s-1, respectively. Conversion of the second step is between0.65and0.80, and average apparent activation energy (E) and lnA are168.34kJ-mol-1and17.06s-1, respectively. However, the mechanism functions of both steps are the same (f(α)=3-2(1一α)4/3[(1-α)-1/3-1]-1).(5) Modification mechanism of composite binder A3modified by benzaldehyde was analyzed by IR and Nuclear Magnetic Resonance (H-NMR). The result shows that electrophilic reaction occurs between benzaldehyde and active small molecules of PF resin and mixed coal tar pitch, which makes these active small molecules react into large molecule organic compounds and increase coking value.更多还原