【作者】 杨晓洁；

【导师】 李胜利；

【作者基本信息】 山东大学 ， 材料学， 2007， 硕士

【摘要】 本研究的目的是开发一种成本低、制备温度较低、对基材形状要求小（如大面积、复杂形状等）的涂层工艺。选择两种方法（复合溶胶-凝胶和传统溶胶-凝胶法）在不同基体上制备钙钛矿型陶瓷涂层，并用热重分析（TG）、差示扫描量热分析（DSC）、X射线衍射分析（XRD）、扫描电镜（SEM）等手段系统研究了涂层制备工艺和组织，另外，还对不同工艺制得涂层的硬度、结合强度和电性能进行了研究。研究结果表明：用复合溶胶-凝胶法在烧结氧化铝基底上制备La_0.8Sr_0.2MnO₃涂层是完全可行的。优化后涂层工艺为：将La_0.8Sr_0.2MnO₃粉体混入同组分溶胶中制得稳定的浆料；用丙酮和酒精对氧化铝基底进行超声清洗后将基底浸渍在浆料中用提拉法进行涂覆，提拉速度为1cm·min^-1；涂覆后的试样在120℃恒温箱中干燥5min，再经600℃预烧10min。重复以上浸渍、干燥、预烧过程直到得到一定厚度的涂层。最后在800℃煅烧1-4h使剩余有机物分解，使钙钛矿相晶化完全。随炉冷却后用La_0.8Sr_0.2MnO₃溶胶进行封孔致密化，具体工艺为涂层在溶胶中浸渍、干燥后600℃预烧10min，再经800℃煅烧1h。XRD、SEM等表征结果证明，用复合溶胶-凝胶工艺在氧化铝基体上制备的涂层由La_0.8Sr_0.2MnO₃单相组成。粉体的加入显著改善了涂层表面质量，消除了由纯溶胶制得涂层中的裂纹。随粉体加入量和浸渍次数增加，涂层厚度增加；粉体加入量为0.6g时，涂层表面和截面连续、平整。另外，随粉体加入量和浸渍次数增加，涂层电阻减小；随Sr掺杂量增加，La_1-xSrxMnO₃电阻减小，当x=0.3时达最小值。用溶胶-凝胶工艺在碳钢基底制备La_1-xCa_xCrO₃涂层的优化工艺为：将预处理后的碳钢基底（20G钢）浸渍到前驱体溶液中一定时间，以1cm·min^-1速度取出，经80℃充分干燥，先400℃预烧10min，重复浸渍，最后放入箱式炉中800℃煅烧1h。XRD、SEM等表征结果证明，20G钢的表面涂层由陶瓷层和氧化物层两部分组成，陶瓷层由La（0.7）Ca_0.3CrO₃单相组成，厚度为12.5～25μm；氧化物层厚度为25～50μm。氧化物层的存在影响了涂层与基体间的结合强度。随前驱体溶液浓度增大涂层微孔和粗糙度增加，均匀性变差，缺陷增多。随pH值增加涂层孔隙率显著增加，组织明显疏松。随浸渍次数增加涂层中的孔洞不断被填充，孔隙率大大减小，涂层更加致密均匀；另外，浸渍次数增加时涂层厚度和结合强度也相应增加，但浸渍次数太多会降低生产效率。当前驱体溶液浓度为0.3mol·L^-1浸渍次数为6时，可以得到致密均匀的涂层。更多还原

【Abstract】 The purpose of this thesis is to develop a technique, which is simple, economical and applicable for preparing coatings on any surface （such as large surface, complex shapes） and can be synthesized at low temperature. Two kinds of technology were used, composite sol-gel route and conventional sol-gel method, to prepare perovskite-type ceramic coatings on different substrates. The fabrication process and microstructure were systematically investigated by means of thermogravimetric analysis （TG）, differential scanning calorimetry （DSC）, X-ray diffractometer （XRD） and scanning electronic microscopy （SEM）. The hardness, bonding intensity and electrical properties of coatings prepared from different processes were also investigated.The results indicated that the preparation of La_0.8Sr_0.2MnO₃ coating by composite sol-gel route was feasible. The optimized process was as follows: La_0.8Sr_0.2MnO₃ powders were added to precursor sol with the same composition to form a stable slurry; After being cleaned ultrasonically in acetone and alcohol, alumina substrates were dipped into the composite slurry and pulled out at a linear speed of 1 cnvmin^-1; The coated samples were then dried at 120℃for 5 min, and pre-fired at 600℃for 10 min. This dipped, dried and pre-fired step was repeated several times to achieve the desired thickness. And then, the coatings were calcined at 800℃for 1-4 h to decompose residual organic matter and crystallize the perovskite phase. Finally, the coatings were densified with La_0.8Sr_0.2MnO₃ precursor sol. The densification process was as follows: the deposited coatings were dipped into La_0.8Sr_0.2MnO₃ precursor sol, dried, pre-fired at 600℃for 10 min, and finally calcined at 800℃for 1 h.It was shown by XRD and SEM that a single La_0.8Sr_0.2MnO₃ perovskite phase was obtained on alumina substrate. The microstructure of coatings was significantly modified and cracks were eliminated by adding La_0.8Sr_0.2MnO₃ powders to the precursor sol. The thickness of coatings increased with increasing the amount of La_0.8Sr_0.2MnO₃ powders and the number of coating applications. The results also suggested that a smooth and continuous coating in both surface and cross-section can be obtained when the powder content increased to 0.6 g. Furthermore, the sheet resistance of coatings decreased as the amount of La_0.8Sr_0.2MnO₃ powders and the number of coating applications increased. The sheet resistance of coatings also decreased with the content of Sr-doping, and the minimial value was obtained when x=0.3.In the case of La_1-xCa_xCrO₃ coating, the optimized process was as follows: 20G substrate was dipped into precursor sol for certain minutes, withdrawn at a constant rate of 1 cm·min^-1, dried at 80 °C, pre-fired at 400 °C for 10 min, then this step was repeated several times, and finally calcined at 800 °C for 1 h in air.It was shown by XRD and SEM that coatings on 20G substrates consisted of two parts, i.e. ceramic layer which was composed of single La_0.7Ca_0.3CrO₃ perovskite phase, and oxide layer. The thickness of ceramic and oxide layer was approximately 12.5～25μm and 25～50μm respectively. It was also found that the bond strength of coatings to substrates was influenced by the oxide layer. The microporosity, roughness, inhomogeneity and defect of the coatings increased with the precursor concentration. The porosity increased and microstructure became porous as the pH value of precursor sol increased. Coatings showed denser and more homogeneous microstructure with reduced porosity as the number of coating applications increased, which was the result of the filling of pores. Moreover, the thickness and bond strength of coatings increased with increasing the number of coating application. However, the efficiency will be decreased. A dense and homogeneous coating could be obtained when the precursor concentration was 0.3 mol·L^-1 and the dipped, dried and pre-fired step was repeated six times.更多还原