水热介质pH值对纳米(Ce)ZrO_2晶粒制备的影响

用水热法制得纳米 (Ce)ZrO2 粉体 ,其晶粒粒度为 3～ 7nm ,而且为单一分散。用XRD、TEM分析了水热媒介pH值对粒度、m相含量、晶粒形貌的影响关系。结果表明 :水热煤介 pH值增大 ,ZrO2 晶粒也增大 ;pH值减小至酸性时 ,ZrO2 晶粒中出现部分m相 ,且晶粒易团聚     

反相胶束法制备纳米ZrO2粉体

利用NA/煤油-n-C6-OH/NH3@H2O反胶束体系,制备了纳米ZrO2粉体.采用TG-DTA、TEM、XRD等手段对粉体及前驱体进行表征粉体粒度分布均匀,无硬团聚,平均粒度为20～40nm.并且研究了反相胶束中的溶水量对ZrO2粒径的影响以及pH值对ZrO2晶型的影响.并推测20～40nmZrO2的单斜晶(m)与四方晶(t)可能的相转变温度为723℃,比相应的体相材料降低了近450℃.     

用水热反萃法制备氧化铁粉末

用水热反萃法制备了氧化铁粉体，采用TEM与XRD方法对其进行了表征，结果表明，有机相中的铁浓度，水热反萃温度的提高和水相pH值的降低均有利于晶粒粒度的增大，杂质H2PO4^-的引入大幅度降低了氧化铁粉末粒度，用水热反萃法可以直接获得组成均一、粒度小．结晶完好的α-Fe2O3。     

三异辛醇氧基铝水解法制备超细γ-Al_2O_3粉体

以自制三异辛醇氧基铝为原料,采用醇盐水解法制备γ-Al2O3粉体,利用X射线衍射、扫描电镜以及激光粒度分析等手段,着重探讨pH值、分散剂添加量两个工艺条件对最终产物的相组成、结晶形貌以及粉体粒度的影响。结果表明,制备的样品均为立方相γ-Al2O3,无其它杂质相,结晶纯度较高;pH值和分散剂添加量的调整对产物的相组成影响不大,但对结晶强度却有一定的影响;采用醇盐水解法制备的γ-Al2O3超细粉体粒度分布均匀,粒度为1～15μm,pH和分散剂添加量过大或过小均会导致粉体粒度增大。     

高温固相法制备锆英石工艺研究

为研究高温固相法制备锆英石的最佳工艺条件,以不同粒度的SiO2和ZrO2粉体为原料,在1 500℃条件下通过不同的保温时间进行锆英石的制备。利用激光粒度分析、X射线衍射、扫描电镜等手段对原料的粒度、物相与结构和微观结构进行表征。结果表明:不同粒度的SiO2和ZrO2粉体在1 500℃条件下通过保温1.5、3、4.5、6 h均可制备出锆英石,但d50=2.125μm的原料通过保温4.5、6 h所制备出的样品效果最好。利用高温固相法进行锆英石的工业化生产,原料的d50控制在2μm左右,在1 500℃条件下保温4.5 h的生产工艺比较合适,所制备样品的晶粒度主要集中在0.2~1.5μm之间。     

溶胶共沉淀法制备氧化锆氧化铝复合粉体

用溶胶共沉淀法辅以共沸蒸馏法工艺制备ZrO2/Al2O3复合粉体,研究了pH值和锆与铝的离子比对复合粉体和用这种复合粉体制备的瓷体的力学性能的影响.结果表明:随着溶胶体系pH值的增大,粉体粒径也相应增大.在制备粉体的混合溶液的pH值为8.6左右时,粉体没有明显的团聚且粒径分布均匀.随着氧化铝相对含量的提高,高弹性模量的Al2O3在烧结过程中起钉扎作用,阻碍Zr4 (Y3 )扩散传质的进行和晶界的移动,从而抑制了ZrO2晶体的生长,细化了ZrO2晶粒,表现为氧化锆的结晶温度、烧结体密度和复合陶瓷强度的提高.     

Zn-ZrO_2复合镀层的性能

复合镀层具有良好的性能,在氯化铵镀锌溶液中加入ZrO2,制备出了Zn-ZrO2复合镀层.讨论了阴极电流密度、镀液pH值对镀层中ZrO2含量的影响,采用扫描电镜对镀层的表面形貌进行了分析.结果表明:当阴极电流密度低于4 A/dm2时,镀层不存在ZrO2微粒,当阴极电流密度为10 A/dm2、pH值为2.5时,镀层中ZrO2的质量分数为2.47%;纯锌镀层晶粒粗大,晶粒间距较大,而Zn-ZrO2复合镀层不仅晶粒细小,平整,且组织均匀、致密;Zn-ZrO2复合镀层在5%NaCl溶液中比纯锌镀层具有更好的耐蚀性能,镀层与基体结合良好.     

注凝成型超细二氧化锆悬浮体的制备

研究了注凝成型超细ZrO2粉体(d0.5=0.199μm)悬浮体的特性及制备工艺.研究表明:采用A型分散剂(聚丙烯酸盐),分散剂用量为ZrO2粉体体积的2%～2.5%;料浆pH值为10～11;研磨时间为12h,可制备出固相体积分数达到54%的料浆悬浮体,料浆黏度为0.952 Pa*s,能够满足凝胶注成型的要求.并且可得到素坯弯曲强度达到50.09MPa的坯体,1550℃保温2h获得了结构致密、晶粒细小均匀的ZrO2陶瓷烧结体.     

负载型纳米TiO2的制备及其催化活性研究

以硅胶为载体、钛酸丁酯为原料,通过微乳液法制得平均晶粒度为6.3nm的锐钛矿型纳米TiO2负载催化剂.研究了焙烧温度、m(TiO2):m(硅胶)、溶液pH对紫外光照射下纳米TiO2降解溶液中苯酚的光催化活性的影响.结果表明,焙烧温度从400℃提高到700℃时,TiO2晶粒度从6.3nm增加到的83.2nm,而催化活性先增大后降低,在450℃时催化活性最大,苯酚的去除率45.6%;随着m(TiO2):m(硅胶)的减小,催化剂活性先增加后降低,在TiO2:硅胶(质量比)为0.05/1000时催化剂活性达到最大;溶液pH值小于6时,苯酚去除率随pH值减小而增大,但变化并不太明显;pH值大于6时,苯酚去除率随pH值增大而增大.     

均匀沉淀-水热法制备稳定Y-Ce-ZrO2纳米粉体

以尿素为沉淀剂,采用均匀沉淀-水热法成功地制备了2mol%Y2O3-5.5mol?O2稳定的纳米四方相ZrO2.研究了溶液的浓度、水浴时间、水热时间对ZrO2粉体的晶型和形貌的影响.结果表明在一定工艺条件下可制备平均粒径在10-20nm,粒度分布窄,分散性好的纳米稳定Y2O3-CeO2-ZrO2粉体.     

Fabrication and mechanical properties of homogeneous zirconia toughened alumina ceramics via cyclic solution infiltration and in situ precipitation

Alumina ceramic composites toughened with various contents of fine-sized zirconia particulates were fabricated via cyclic infiltrating pre-sintered alumina preforms with zirconium oxychloride solution and immersion in ammonia solution to induce in situ precipitation. Homogeneous distribution of zirconia throughout the bulk material has been substantiated by line-scan analysis and backscattering images taken from sections with different distances from surface. It was found that a higher drying temperature and increase in infiltration numbers lead to a greater zirconia content and bigger grain size. The hardness of fabricated zirconia toughened alumina composite was firstly improved probably due to the microstructure refining effect, while a further increase in zirconia content results in the decrease of hardness. A significantly higher indentation toughness has been observed for samples containing >10 wt.% zirconia compared with other specimens, which could be attributed to the coarser zirconia grain size and the related greater tendency to transformation into monoclinic phase.     

液相包覆制备Ce-TZP陶瓷的力学性能与稳定行为

采用XRD、SEM、TEM等分析手段对由液相包覆工艺制备的Ce—TZP陶瓷的微结构进行了研究，并和共沉淀粉体制备的Ce—TZP陶瓷进行了对比分析．力学性能表明，同共沉淀粉体制备的Ce—TZP陶瓷相比，由液相包覆工艺制备的Ce—TZP陶瓷虽硬度下降，但断裂韧性改善；液相添加少量Al2O3硬度随之增加、断裂韧性显著提高．电镜分析表明，液相包覆工艺制备的Ce—TZP陶瓷晶粒尺寸分布宽化，一部分晶粒尺寸较大但CeO2含量低、易发生马氏体相转变晶粒的存在是断裂韧性改善的主要原因．陶瓷体中单斜相大晶粒与四方相之间的残余应力、添加少量Al2O3在晶界上易形成薄的非晶包裹层，是增加可相变四方相数量，提高断裂韧性的其它机制。     

纳米级CaO－ZrO_2复合氧化物粉体的制备与表征

采用化学共沉淀─超临界干燥技术制备ＣａＯ－ＺｒＯ２纳米粉体，并详细考察了主要制备参数──共沉淀过程的ｐＨ值对产品粉体性能的影响。实验表明，超临界流体干燥法能很好地保留初始湿凝胶的结构，有效地防止凝胶干燥过程中粒子间硬团聚现象的发生，该法合成的纳米粉体具有粒径小、粒度分布范围窄、比表面大等特点；此外，实验还发现，水合凝胶体系的ｐＨ值会很大程度上影响产品粉体的性能，在实验范围内，随着体系ｐＨ值的增大，粉体的粒径逐渐减小，粉体中单斜相（ｍ）的含量降低，四方相（ｔ）及立方相（ｃ）的含量逐渐升高。     

R-curve behaviour of 9Ce-TZP zirconia ceramics

Stabilised zirconia ceramics may undergo a stress-induced tetragonal-to-monoclinic phase transformation. At crack tips, a transformation zone with compressive stresses develops, leading to an increase in fracture toughness, which depends on the size and geometry of the transformation zone. The influence of grain size on the R-curve behaviour and transformation zone size is investigated for five 9Ce-TZP zirconia ceramic materials of variable grain size.     

并流共沉淀法合成Dy_(2)O_(3)-ZrO_(2)纳米粉体EI北大核心CSCD

采用并流化学共沉淀法合成了Dy_(2)O_(3)掺杂ZrO_(2)(DySZ)纳米粉体材料,系统研究稳定剂掺杂量、阳离子浓度、反应系统pH值和煅烧温度对粉体材料物相组成、晶体结构和微观形貌的影响。结果表明:不同合成工艺条件下,DySZ粉体材料均具有纳米尺度特征,球形颗粒尺寸为10~30 nm,Dy_(2)O_(3)的掺杂可以起到稳定晶型的作用;稳定剂掺杂量对DySZ粉体的物相组成具有明显影响,掺杂量为10%(质量分数)时可合成单一四方相结构的DySZ粉体;DySZ粉体材料的四方度和微观形貌对稳定剂掺杂量、阳离子浓度、反应体系pH值和煅烧温度均不敏感,但其平均晶粒尺寸随稳定剂掺杂量、阳离子浓度和反应体系pH值的升高略有降低,随煅烧温度的提高而显著增加。     

Effect of stress-induced phase transformation on the properties of polycrystalline zirconia containing metastable tetragonal phase

Polycrystalline zirconia containing a high content of metastable tetragonal phase shows high strength ( 700 MPa), high fracture toughness (K _c = 6 to 9 MN m^–3/2) and small grain size (<0.3jm). The strength and grain size remain nearly constant over a wide range of tetragonal phase content (100 to 30%). At a low concentration of tetragonal phase <30%, there is a rapid decrease in strength accompanied by a rapid increase in grain size. These results are explained by means of a stress-induced phase transformation in the metastable tetragonal phase.     

Preparation of novel calcia-stabilized TZP ceramics

The preparation of tetragonal zirconia polycrystal (TZP) ceramics stabilized by the addition of calcia is presented. These novel ceramics were obtained by means of a fast-firing treatment applied to compacts of nanocrystalline powders with a composition of ZrO₂ — 4 mol% CaO. Powders were synthesized by a nitrate-citrate gel-combustion process and they exhibited the tetragonal phase at room temperature due to their small crystallite size (12–13 nm). These powders were compacted by uniaxial pressing and fired at 1400–1500 °C for 3–5 min, obtaining fine-grained, dense ceramics, which also retained the metastable tetragonal phase. Longer heat treatments increased the average grain size leading to large amounts of the monoclinic phase. It was also found that the critical grain size for the tetragonal-to-monoclinic transformation is about 150 nm for this composition. This small value explains the necessity of a fast-firing treatment of the samples, allowing densification but avoiding a significant grain growth.     

Effect of Yttria content and alumina addition on the formation of a textured microstructure during the surface nitridation of Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP)

The condition for the production of a textured microstructure was investigated in the process of nitridation of yttria-stabilized zirconia. The nitrided surface layer was composed of either columnar or equiaxed cubic grains. The amount of the cubic phase in the matrix, which was determined by yttria content and the sintering temperature, was the principal parameter that affected the morphology of the nitrided layer. With the increase in the cubic phase in the matrix, the chances of finding columnar grains decreased. The driving force of growth, which was provided by the free energy difference determined by the phase and grain size, decreased with the increase in the cubic phase in the matrix, and eventually led to the suppression of the growth of columnar grains. The cubic zirconia in the matrix also played the role of a transient pinning center due to its chemistry and lattice parameter that were dissimilar to those of the columnar grain. Such role of the cubic phase could be mimicked by the introduction of Al₂O₃ particles as an intended pinning center. With the introduction of the pinning center, the growth rate of the texture was suppressed and equiaxed grains appeared at the front of the texture. Therefore, by preparing the matrix with the utmost tetragonal phase, successful texturing of zirconia during nitridation could be achieved.     

Fracture variability and R-curve behavior in yttria-stabilized zirconia ceramics

An assessment of fracture origins is conducted in yttria-stabilized zirconia ceramics containing different grain sizes. As the microstructure coarsens due to the application of heat treatments, fracture origins change from single pores to transformed regions at the free surface which are induced by the applied stress. The observation of an increasing size of failure origins with microstructural coarsening lies as the underlying reason for the finding that specimens containing coarser microstructures and a more pronounced R-curve behavior do not fail at larger stresses. A fracture model is used to link the strength variability of a fully tetragonal zirconia containing a small grain size to its pore size distribution. The increased transformability of zirconia ceramics with coarser tetragonal grains is evaluated by means of quantitative phase analysis, characterizations of fracture surface morphology, and R-curve assessments. It is confirmed that tetragonal grains of up to 4 m may not necessarily undergo a spontaneous t–m transformation upon cooling from sintering.