【作者】 陆彩云；

【导师】 陈敏； 于景坤；

【作者基本信息】 东北大学 ， 钢铁冶金， 2008， 博士

【摘要】 MgO-Cr2O3耐火材料具有耐火度高、抗侵蚀性和抗热震性好等优点而广泛应用于水泥回转窑和冶金炉外精炼等设备,但MgO-Cr2O3耐火材料因Cr6+引起的环境问题越来越引起人们的普遍关注。欧美及日本等发达国家水泥回转窑用MgO-Cr2O3耐火材料替代品的开发已经取得了很大的进步目前有60%-70%水泥回转窑已经实现了无铬化。我国在这方面的研究尽管起步较早,但进展相对比较缓慢。但随着政府对环境问题的重视和相关法规的完善,我国MgO-Cr2O3耐火材料替代品的开发也必将取得长足进步。MgO-CaO耐火材料具有耐火度高,抗水泥熟料侵蚀性好,易于挂窑皮等优点,是代替MgO-Cr2O3耐火材料的一个重要发展品种,但MgO-CaO耐火材料因抗热震性差、抗水化性差等问题,使其实际应用受到很大限制。为此,欧美等国家通过添加ZrO2对MgO-CaO耐火材料进行改性形成MgO-CaO-CaZrO3耐火材料,有效地提高了MgO-CaO耐火材料的性能。但添加ZrO2后因大幅度增加耐火材料的生产成本,严重制约了这种耐火材料的推广应用。目前国外MgO-CaO-CaZrO3耐火材料中高达10%以上的ZrO2添加量引起的价格问题难以为国内目前状况所接受。通过少量ZrO2添加能够达到显著改善MgO-CaO耐火材料性能的效果的研究是当前国内外密切关注的一项前沿课题,该研究对降低耐火材料生产成本,促进MgO-CaO-CaZrO3耐火材料推广具有十分重要的意义目前国内关于添加ZrO2的MgO-CaO耐火材料的研究方法主要是采用颗粒或微粉ZrO2为添加剂合成MgO-CaO-CaZrO3耐火材料,研究内容主要集中于考查原料条件和烧成制度对耐火材料烧结、组织结构及性能的影响,尚处于开发MgO-CaO-CaZrO3耐火材料研究的初级阶段,与国外相比存在较大差距。纳米技术近年在耐火材料领域的应用十分活跃,利用纳米粉体的小尺寸效应等特性,能够显著地提高耐火材料的性能。此外,作为MgO-CaO-CaZrO3耐火材料主要原料的菱镁矿,我国资源丰富,但生产MgO-CaO熟料等镁质耐火原料均以高品位菱镁矿为原料,存在低品位矿和粉矿利用率低等问题,影响我国菱镁资源高效综合利用。因此,结合我国MgO-CaO熟料的生产现状和MgO-CaO-CaZrO3耐火材料的开发现状,本研究采用新型工艺以天然菱镁矿和碳酸钙为原料合成高纯MgO-CaO熟料,研究工艺条件对提纯效果和MgO-CaO熟料烧结性能的影响,并以实验室合成的及厂家提供的MgO-CaO熟料为主要原料,以微米和纳米Zr02粉末为添加剂,合成MgO-CaO-CaZrO3耐火材料,研究纳米Zr02添加对MgO-CaO-CaZrO3耐火材料烧结、显微结构和性能的影响规律及其作用机理,并得出以下结论：(1)以天然菱镁矿和碳酸钙为原料,采取水化碳酸化工艺可以实现良好的提纯效果,并利用碳酸镁和碳酸钙微粉的烧结活性,可以制得高纯致密的MgO-CaO熟料。采用这种工艺,实验过程无粉尘产生,环境污染小,特别适宜利用菱镁矿粉矿和低品位菱镁矿,能够有效地促进我国菱镁资源的高效综合利用。(2)MgO-CaO-CaZrO3耐火材料的致密度随煅烧温度的升高和保温时间的延长而增大,在1600℃×3h下可获得烧结致密的MgO-CaO-CaZrO3耐火材料。Zr02添加使MgO-CaO耐火材料的致密度显著提高,这是由于添加的Zr02与CaO反应生成的尺寸很小、晶格缺陷较多的CaZrO3具有很高的烧结活性,能有效地促进材料烧结；纳米Zr02添加剂本身具有的特性使其对MgO-CaO耐火材料的致密化效果比微米的明显(3)Zr02添加使MgO-CaO耐火材料中新生成的CaZrO3引发了大量的显微裂纹,材料的韧性增大,且ZrO2添加使材料内部的直接结合程度增大,从而材料的常温耐压强度和抗折强度增大、抗热震性能提高。添加纳米Zr02诱发了材料的穿晶断裂,且形成的CaZrO3更均匀地分散在材料内部,更有效地提高材料的常温耐压强度、抗折强度和抗热震性,有效地降低Zr02的添加量(4)Zr02添加使MgO-CaO耐火材料中游离的CaO减少、材料的致密度增大且改善了材料的显微结构,所以材料的抗水化性得以明显改善。纳米Zr02具有更高的活性,使其对改善材料抗水化性能的效果更显著(5)ZrO2添加使MgO-CaO耐火材料中低熔点物相的生成量大大减少,材料的直接结合程度增大,且ZrO2添加有利于在耐火材料表面形成一层保护膜,使耐火材料的抗侵蚀性提高。由于MgO-CaO-CaZrO3耐火材料中的CaO组分可以与水泥熟料中的2CaO·SiO2反应生成3CaO·SiO2,同时,CaZrO3的生成使材料中颗粒间的结合强度增大,材料的挂窑皮性能提高(6)实验室合成的MgO-CaO熟料的纯度很高,杂质含量很小,材料内部晶粒之间直接结合率很高,故由其合成的MgO-CaO-CaZrO3耐火材料各方面的性能都比较好。(7)ZrO2添加使MgO-CaO耐火材料的性能显著提高,纳米ZrO2具有的小尺寸等特殊效应使其对MgO-CaO耐火材料性能的改善效果更明显少量添加即可对材料的性能起到显著的改善作用。更多还原

【Abstract】 MgO-Cr2O3 refractories have been widely used in cement rotary kilns and secondary refining vessels in metallurgical industries for their excellent properties such as high refractoriness, excellent slag corrosion resistance and thermal shock resistance. Whereas, the environment problems which caused by toxic hexavalent chromate have been attracting people to pay much attention on this subject. Many studies have been carried out by developed countries on developing new type environmental friendship chrome-free refractories to substitute MgO-Cr2O3 refractories, and the chrome-free refractories have been used in 60%-70% cement rotary kilns. Study on developing the substitution of MgO-Cr2O3 refractories was carried out early in our country, but this subject progressed at a slower rate. However, the development of the substitution of MgO-Cr2O3 refractories in our country would progress at a rapid rate with the increase in environmental concerns and the establishment of correlative laws by state.MgO-CaO refractories were considered to be one type of chrome-free refractories to substitute MgO-Cr2O3 refractories for their properties of excellent stability at high temperatures, excellent corrosion resistance to alkalinity slag and adherence ability. However, their application has been inhibited for their poor thermal shock resistance and hydration resistance. It has been reported that the addition of ZrO2 can appreciably improve the properties of the MgO-CaO refractories, but the addition of ZrO2 causes the price of product appreciably rising, and then the application of these refractories was inhibited. At present, the content of ZrO2 in MgO-CaO-CaZrO3 refractories in overseas was more than 10%, which was too expensive to our country. Therefore, it was important for all refractory researchers to decrease the amount of ZrO2 for the purpose to improve the properties of the MgO-CaO refractories, resulting to the cost of the refractories appreciably reduced and the application of MgO-CaO-CaZrO3 refractories promoted.At the present time, the research technique on MgO-CaO refractories with ZrO2 addition in our country was focused on the synthesis of MgO-CaO refractories with granule or micro powder ZrO2 addition, the effect of the starting materials and burning system on sintering, microstructure and perforemance of MgO-CaO-CaZrO3 refractories was studied. This study was still at the primary stage with a wide gap between developed countries and us.Recently, the application of nano-technology in refractories was very active, the nano-sized additives could appreciably promote the performance of refractories due to the special characteristic such as size effect. In addition, magnesite, which was used as the main starting material to synthesize MgO-CaO-CaZrO3 refractories, is aboundant in our state. However, the MgO-CaO clinker was always synthesized from high-grade magnesite, it would caused the problem that the utilization ratio of low-grade magnesite and magnesite powder was very low. Due to the manufacturing status of MgO-CaO clinker and the researching status of MgO-CaO-CaZrO3 refractories, raw magnesite and calcium carbonate were used as starting materials to synthesize MgO-CaO clinker, in this paper, the effect of technological conditions on purification and the sintering of MgO-CaO clinker was studied, and then the as-received and synthesized MgO-CaO clinker were used as the main materials while micro-sized and nano-sized ZrO2 as additives to synthesized MgO-CaO-CaZrO3 refractories, the contrast between the different effect and mechanism of micro-sized and nano-sized ZrO2 on the sintering, microstructure and performance of MgO-CaO refractories were studied. The main conclusions were listed as following:(1) High-density and high-purity MgO-CaO clinker was synthesized through hydrous carbonation craft measures and special designment while using the natural low-cost raw materials such as magnesite and calcium carbonate as the main composition. No mill dust was generated during the experiment, and caused little environmental problem. It was an appropriate craft to put fine ore and low-grade magnesite to rational use.(2) The densification of MgO-CaO-CaZrO3 refractories was promoted when the sintering temperature was increased and the soaking time was prolonged. The MgO-CaO-CaZrO3 refractories were dense when sintered at 1600℃×3h. Owing to the formation of small sized CaZrO3, formed by the reaction of CaO and ZrO2, facilitated to sintering, the densification of the MgO-CaO refractories was appreciably promoted with ZrO2 addition, and the addition of nano-sized ZrO2 was more effective.(3) The cold crushing strength, bending strength and the thermal shock resistance of the MgO-CaO refractories with ZrO2 addition were increased due to the toughness and the direct-bonding of the grains were increased. The addition of nano-sized ZrO2 was more effective attributed to its well dispersion.(4) The slaking resistance of the MgO-CaO refractories was appreciably improved by addition of ZrO2 due to its effect on decreasing the amount of free CaO in the refractories, promotion of densification as well as modification of microstructure. The nano-sized ZrO2 addition was more effective due to its higher activity.(5) The slag corrosion resistance of the MgO-CaO refractories was enhanced by addition of ZrO2 due to the formation of self-protective coatings on the surface of the refractories and the increase of the viscosity of the liquid phase and thus inhibited further penetration of slag at elevated temperatures. Due to the reaction of CaO and 2CaO·SiO2 to form 3CaO·SiO2 and the increase of direct-bonding of the MgO-CaO refractories with ZrO2 addition, the aherence ability of the MgO-CaO refractories was promoted with ZrO2 addition, and the nano-sized ZrO2 addition was more effective.(6) Since the high purity of the synthesized MgO-CaO clinker, barely low melting point phases existed in the microstructure of the materials, and then the performance of the MgO-CaO refractories with ZrO2 addition was promoted further.(7) The performance of MgO-CaO refractories was appreciably promoted by ZrO2 addition, the effect of nano-sized ZrO2 addition was more effective than the micro-sized one due to the special effect of the nano powder, the performance of MgO-CaO refractories was appreciably promoted by less nano-sized ZrO2 addition.更多还原