【作者】 张文政；

【导师】 刘正；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2012， 博士

【摘要】 泡沫陶瓷是一种具有三维多孔结构的特殊材料，同时保持了陶瓷自身的优良特性，使其在过滤液态金属领域具有明显的优势。采用聚氨酯有机泡沫浸渍法制备的、用于过滤镁液的MgO泡沫陶瓷过滤器，具有制备工艺简单、操作方法简便、原料成本低廉的优势，因此拥有广阔的应用前景。镁合金具有高的比强度，比刚度和比弹性模量，以及阻尼抗震性好等优点，因此在交通运输、航空航天、电子通讯等领域应用广泛。然而，无论采用电解法还是采用还原法生产的纯镁中都含有多种夹杂物，这些夹杂物对材料的力学、耐腐蚀等性能有极大危害，需要进一步净化处理才能达到使用要求，因而阻碍了镁金属材料应用范围的拓展。同目前已系列化的Al₂O₃、ZrO₂、SiC、Si₃N₄等泡沫陶瓷相比，采用MgO泡沫陶瓷净化镁液具有除杂效率高、成本低、操作简便等优点，是一种很好的物理净化镁液的方法。它是利用机械过滤的方法，借助陶瓷网络自发吸附镁液中液态熔剂夹杂物和固态颗粒夹杂物，而其本身在镁液中保持化学性质稳定，不污染镁液，特别适合于镁液净化。但目前有关采用MgO泡沫陶瓷净化粗镁的系统性报导很少，因此，本课题旨在探寻适用于粗镁过滤净化的MgO泡沫陶瓷的制备方法及净化工艺，这对于提高镁金属的性能、拓展其应用领域显然具有重大的意义。我们围绕着上述目的，进行了一些探索工作，得出了以下结论：由于制备泡沫陶瓷的原料MgO极易与分散介质水发生水化反应，生成密度更小的Mg（OH）₂，将其加热到350℃以上又会分解生成MgO，这一过程变化会产生体积收缩，由此产生的裂纹会导致制品物理性能恶化。因此我们采用添加抗水剂的方法对MgO粉体进行抗水化处理。研究发现：经硅烷偶联剂KH-550处理的MgO粉体，在25℃下水化180min之后，粉体的水化率从未处理时的54.36%下降到17%，说明硅烷偶联剂KH-550达到了部分抑制MgO水化的目的。我们还根据Arrhenius方程log（k₁/k₂）=E_a/R（1/t₁-1/t₂）计算出经抗水剂磷酸铵（AP）和硅烷偶联剂KH-550处理获得的两种改性MgO粉体的水化反应活化能，计算结果分别是Ea（AP）=78.95kJ/mol，Ea（KH-550）=81.17kJ/mol，根据Bebson的活化能判据可知MgO的这两种水化过程都是由化学反应控制，而非扩散过程控制，结果表明经KH-550处理的MgO粉体更难水化。通过选用分散剂和进行颗粒级配的方法，我们获得了低粘度高固含量的MgO浆体。当聚羧酸盐型分散剂SN5040的添加量介于0.1-0.2%之间时，MgO浆料的厚化度和相对黏度分别介于1.024-1.034和1.058-1.083之间，MgO浆料的厚化度和相对黏度可以在该添加量范围内同时达到最佳值，这说明在相同固含量条件下，SN5040的分散性优于分散剂PAM和分散剂CMC-Na；采用双组分颗粒级配可以使MgO制品的抗弯强度和相对密度从未级配时的3.35MPa和0.42提高到5.12MPa和0.55，但采用三组分颗粒级配时抗弯强度和相对密度则又下降到4.78MPa和0.52。另外，有机泡沫前驱体经酚醛树脂乙醇溶液表面改性后，挂浆量更大且均匀，堵孔少，有机泡沫增重倍率从未处理之前的5倍提高到处理后的9倍；粉体颗粒在有机泡沫网络上粘附的更加牢固；处理后的有机泡沫耐高温性能更好，减少了素坯在烧结过程中的塌陷。我们还发现：通过向电熔MgO中添加烧结助剂MgF₂的方法可以使MgO的烧结温度从1500℃下降到1200℃左右，低温烧结而成的陶瓷制品尺寸稳定性更好。通过对比粗镁的不同过滤方式，发现MgO泡沫陶瓷可有效的清除镁液中的MgO等夹杂物，对精炼剂的吸附是一个自发的过程，减少了熔剂夹杂。MgO泡沫陶瓷的孔径越小，清除镁液中夹杂物和熔剂的能力越强，所得镁金属中所含的杂质越少，晶粒生长的就更加均匀和完善。根据粗镁过滤体系的自身特点，建立了MgO泡沫陶瓷过滤净化粗镁液中夹杂物的过滤效率判别式，随着过滤的不断进行，泡沫陶瓷网络表面拦截夹杂物将不断增多，泡沫陶瓷的孔隙率和流经泡沫陶瓷网络的熔体速度都将下降，导致过滤效率下降。我们还推导了泡沫陶瓷网络表面夹杂物厚度增长方程，为确保浇铸过程顺利进行提供了一定的理论依据，为MgO泡沫陶瓷过滤粗镁的工业应用奠定了初步的理论基础。更多还原

【Abstract】 Foam ceramics （FC）, a kind of special materials with the 3D porous structures andexcellent texture properties, have showed superiority in the field of molten metal filtration.The advantage of process of foam ceramics processed by impregnation of an open-cellpolyurethan（ePU）foam by immersion into a ceramic slurry have a promising prospect, dueto its simple process, low cost and prepared easily.Recently, Magnisium have been used widely in the field of transportation, aerospaceand communication for its properties of high specific strength, specific rigidity and specificelastic modulus, good damping resistance properties. However, the magnesium made fromboth electrolytic method and reduction method have a varity of inclusions which havenegative effects on products, such as worse mechanical and anticorrosion properties.Compared with some foam ceramic filter, such as Al₂O₃、ZrO₂、SiC、Si₃N₄, MagnesiumOxide（MgO） foam ceramic filter can absorb flux and clean up fine inclusions efficiently inmolten magnesium spontaneously as well as can not react with molten magnesium itself,so it is a better candidate to purify molten magnesium. But until now there are not reporton MgO foam ceramic filter to filter molten crude magnesium in detail. So our work is toexplore ways of making MgO foam ceramics and of purifying technologies of moltenmagnesium so as to improve the fineness of magnesium. We carry out a series ofexperiments for the purpose above, and draw some conclusions as following:Magnesia hydration is a key concern in refractory castable processing, the reasonabove can result in cracks or even explosion during the first heating-up，so we use differentadditives to inhibit MgO hydration. The hydration degree of MgO powder modified byKH-550 decrease from 54.36% to 17% compared with unmodified MgO powder whenMgO powders react with water in 25℃for 180min, that is to say, coupling agent KH-550have partial effect on inhibiting MgO hydration.We have studied the hydration kinetic equations of MgO powders treated byammonium phosphate（AP） and KH-550, respectively. According to the ArrheniusEquation,we obtained the datum of MgO hydration activation energy was Ea（AP）= 78.95kJ/mol and Ea（KH-550）=81.17kJ/mol,respectively. Hydrated rates of both of them arecontrolled by chemical reaction instead of diffusion. The results showed hydration reactionof MgO powder treated by KH-550 is more difficult to hydrate than that of MgO powdertreated by AP.When the dosage of SN5040, a kind of polyacrylic salt dispersants, is between 0.1%and 0.2%, the thick degree and relative viscosity of MgO slurry are 1.024-1.034 and1.058-1.083, respectively, the values of them are optimum simultaneously. Theexperimental results showed SN5040 is the optimum dispersant for dispersing MgOpowders in water than PAM and CMC-Na.Our experiment results prove that the design ofbicomponent composition is beneficial to improve the sample’s compressive strength andrelative density, and the values of compressive strength and relative density of sampleincrease from 3.35MPa and 0.42 to 5.12MPa and 0.55, respectively. Nevertheless, thevalues of compressive strength and relative density of sample come down in the conditionof tricomponent composition.The volume of slurry coating of MgO on PU foams is largerand more uniform than that of those untreated when PU foams immersed in phenolicresin-ethanol solution. The slurry weight on PU foam after modified is 9 times than theweight of PU foam while the slurry weight on PU foam unmodified is only 5 times thanthe weight of PU foam; The powder is adhere to the surface of foam more firmly and thetemperature resistant of PU foam is improved and the shrinkage collapse probability ofgreen foam ceramics decrease.The sintering temperature of MgO foam ceramics candecrease from 1500℃to 1200℃or so on the condition of adding a capful of sinteringadditive MgF₂to MgO powders, and the sintered fused MgO ceramics on the condition oflower temperature have a stable 3D structure and the little defect in them.Compared with different filtration methods of molten magnesium, we can draw aconclusion that MgO foam ceramics can clean MgO inclusions and flux effectively. Theresearch result indicates that filtrating ability are raised, inclusions and flux are less andgrains are more uniform and perfect by decreasing hole dimension of MgO foamceramics.Based on the characteristic of filtration system of molten magnesium, a moltenmagnesium purifying efficiency equation relative to foam ceramics filtration wasestablished.The experiment result indicates that the purifying efficiency of the foamceramics could be reduced with the increase of the inclusions on the network surface offoam ceramics because of smaller 3D sizes of holes and slower flow velocity of molten magnesium in foam ceramics.We analyzed some influencing factors on equation toinclusion thickness on the network surface of foam ceramics, for it is helpful to guaranteethe cast process goes well, so this will be helpful for extending the industrial application ofMgO foam ceramics to filter molten magnesium.更多还原