溶胶-凝胶法制备ZrO_2粉的工艺研究

为了制备粒度更小、四方相更能稳定地存在至室温的氧化锆粉,以八水氧氯化锆(ZrOCl2·8H2O)为原料,以氨水(NH3·H2O)和氢氧化钠(NaOH)溶液为沉淀剂,采用溶胶-凝胶法制备氧化锆粉。主要研究了溶胶-凝胶体系pH(分别为9和13)、氢氧化锆湿凝胶洗涤工艺(分别为水洗和NaOH碱洗)、是否添加Y_2O_3等工艺因素对氢氧化锆干凝胶粉粒度以及氧化锆粉的Na2O含量、晶粒尺寸、物相组成和显微结构等的影响。结果表明:1)在溶胶-凝胶体系pH同为13的情况下,经碱洗工艺制得的氢氧化锆干凝胶粉的粒度和氧化锆粉的平均晶粒尺寸都比经水洗工艺制得的小,而经600℃煅烧制得的氧化锆粉中的四方相含量则比经水洗工艺制得的多很多;2)补加氢氧化钠溶液提高溶胶-凝胶体系pH以及碱洗,均使制得的氧化锆粉的Na2O含量升高;3)加入稳定剂Y_2O_3可提高四方相的稳定性,经1 000℃煅烧制得的氧化锆粉中的四方相含量仍可达45.8%(w)。     

微乳液法制备高分散性纳米氧化锆

利用微乳液法,在表面活性剂(TX-10)-正己醇-环己烷(体积比为1.0∶1.3∶7.7)组成的微乳液体系中,控制反应物浓度为0.02 mol/L,乙醇置换水量为200 mL,焙烧温度为450℃,制得高分散性纳米氧化锆。氮气吸附试验结果表明,纳米氧化锆颗粒表面的孔径分布与其分散性之间存在对应关系。XRD分析显示,产物最初为无定形ZrO2,经450℃焙烧3 h后,氧化锆主要以四方晶相为主,伴随少量单斜晶相,焙烧温度升高至750℃后,得到单一纯净的单斜晶相氧化锆。     

粉末注射成形不同混料工艺氧化锆喂料的制备及成型研究

通过捏合机和转矩流变仪两种不用混料工艺制备包含以石蜡(SW)、硬脂酸(SA)、聚丙烯(PP)为主的高分子粘结体系和氧化锆粉料的喂料,来研究氧化锆粉末的注射成型工艺。对不同混料工艺制备的喂料进行注射成型、脱脂、烧结和一系列的测试,分析了高分子粘结体系在混料过程中的分散情况和作用。此外,研究了喂料的内部混合形态和分散情况态对注射成型、溶剂脱脂及烧结致密化的影响。     

电纺制备氧化锆空心微球的工艺研究

为了获得直径较为均一、空心率较大的氧化锆空心微球,以八水氯氧化锆为原料,六水硝酸钇为稳定剂,聚乙烯吡咯烷酮(PVP)为助纺剂,无水乙醇和N,N-二甲基甲酰胺(DMF)为溶剂,采用电纺法制备出氧化锆-PVP前驱体球,经1 000℃煅烧后得到氧化锆空心微球。研究了PVP用量(加入质量分数分别为10%、15%和20%)、电纺电压(分别为15、20和25 k V)以及DMF与乙醇体积比(分别为1.675、0.618、0.2、0.1和0.05)对所制备氧化锆空心微球物相组成和显微形貌的影响。结果表明:仅以乙醇为溶剂制备的氧化锆空心球空心率较大,但直径分布不均匀。随PVP用量增大,试样获得纯的t-Zr O2晶相,PVP用量为10%(w)时出现m-Zr O2晶相;电纺电压过小会导致空心球的粘连,过大则生成了粒状的氧化锆颗粒。当电纺电压为20 k V,PVP用量为15%(w)时,制备出高纯t-Zr O2空心球。随着DMF与乙醇比例的减小,氧化锆空心球的球形度变好,直径变得均一;DMF与乙醇体积比为0.1时,制备出的氧化锆空心球直径约350 nm,壁厚和内径分别约为84和266 nm,具有明显空心结构。     

ZrO2基Al2O3-ZrO2-C质高温陶瓷材料抗渣性能研究

以板状刚玉、活性α—氧化铝、氧化锆(PSZ)、碳黑为主要原料,以金属硅和碳化硼作为添加剂,以热固性酚醛树脂作为结合剂,制备了ZrO2基Al2O3-ZrO2-C质材料。实验证明添加稳定氧化锆的Al2O3-ZrO2-C质高温陶瓷材料的抗渣性能优于添加单斜氧化锆、纳米氧化锆、金属铝的Al2O3-ZrO2-C质高温陶瓷材料。     

钇稳定氧化锆的反向共沉淀制备及固溶体晶型研究

以氯氧化锆为锆源,采用反向共沉淀法制备了钇稳定四方氧化锆(YSZ)。研究了多种沉淀剂、不同pH值和煅烧温度对钇稳定氧化锆晶型的影响,着重探讨了多种因素协同作用对产物晶型的影响。结果表明,pH≤7时,钇稳定氧化锆中有氧化钇晶型存在,pH=9时,易形成钇稳定氧化锆的固溶体。以碳酸氢铵、二乙胺为沉淀剂会阻碍钇稳定氧化锆的生成,氨水作为沉淀剂得到钇均匀分布的稳定氧化锆固溶体,其一次粒径约25 nm,团聚体粒径为200 nm。     

熔融盐对氧化锆纳米片合成的影响EI北大核心CSCD

以四氯化锆为锆源,乙醇为溶剂,采用溶剂热辅助熔盐法低温煅烧制备氧化锆纳米片。研究并讨论了熔盐种类和用量对氧化锆晶体生长和形貌的影响。结果表明:以NaCl和Na3PO4的混合物为熔盐,且m(前驱体):m(NaCl):m(Na3PO4)=10:10:1时,可以得到平均边长超过1.8μm,厚约70 nm,宽厚比大于10:1的单斜氧化锆纳米片。纳米片为单晶结构,无明显缺陷,主要暴露面为(001)晶面,其在熔盐中的形成符合自聚焦机理,包括溶解、扩散、吸附和生长过程,(001)面主导的氧化锆纳米片与表面能的理论计算结果吻合。     

研磨设备和工艺参数对氧化锆粉体粒度的影响

为了研究不同研磨设备及研磨工艺参数对粉体团聚体的解聚效果,以d50=1.355μm的氧化锆粉体为研究对象,研究了研磨设备和工艺参数对氧化锆料浆粒度的影响。首先,分别采用立式球磨机、立式珠磨机和卧式砂磨机为研磨设备,以φ2 mm的氧化锆球作为研磨介质,以m介质∶m物料=5∶1的介质物料比研磨15 h后,检测研磨后氧化锆料浆的粒度。结果表明,卧式砂磨机的研磨效果最优,研磨后氧化锆料浆的d50=0.303μm。然后,采用卧式砂磨机为研磨设备,以φ2 mm的氧化锆球作为研磨介质,选择介质物料比(m介质∶m物料)、料浆固含量(w)、线速度和研磨时间作为试验因素,进行四因素三水平(m介质∶m物料分别为4∶1、5∶1和6∶1,料浆固含量(w)分别为35%、45%和55%,线速度分别为5、10和15 m·s-1,研磨时间分别为20、25和30 h)正交试验,检测研磨后氧化锆料浆的粒度。结果表明:采用卧式砂磨机为研磨设备,当介质物料比(m介质∶m物料)为4∶1,料浆固含量(w)为45%,线速度为10 m·s-1,研磨时间为25 h时,研磨效果最佳,研磨后氧化锆料浆的d50约为0.3μm。     

纳米级超细氧化锆的合成及其除氟性能研究

该研究以氧化锆对F的专属吸附为理论基础、以乙二醇为分散剂,采用反滴定法制备出一种新型nHZO(纳米级超细氧化锆粉末)。研究结果表明,nHZO对氟的最大吸附量为19.78 mg/L较MHZO(普通粒径氧化锆粉末)有明显的提升,同时该材料表现出对氟良好的吸附选择性能,共存离子促进了氟在HZO中的吸附,并且阳离子的促进作用大于阴离子的抑制作用,pH探究实验表明,中性偏酸条件有利于nHZO对氟的吸附。     

熔融盐对氧化锆纳米片合成的影响

以四氯化锆为锆源,乙醇为溶剂,采用溶剂热辅助熔盐法低温煅烧制备氧化锆纳米片。研究并讨论了熔盐种类和用量对氧化锆晶体生长和形貌的影响。结果表明:以NaCl和Na₃PO₄的混合物为熔盐,且m(前驱体):m(NaCl):m(Na₃PO₄)=10:10:1时,可以得到平均边长超过1.8μm,厚约70 nm,宽厚比大于10:1的单斜氧化锆纳米片。纳米片为单晶结构,无明显缺陷,主要暴露面为(001)晶面,其在熔盐中的形成符合自聚焦机理,包括溶解、扩散、吸附和生长过程,(001)面主导的氧化锆纳米片与表面能的理论计算结果吻合。     

Effect of nano-TiO2 on properties of 3 mol% yttria-stabilized zirconia ceramic via layered extrusion forming

Layered extrusion forming (LEF), as an additive manufacturing technology, can freely form ceramic components. In this paper, 3 mol% yttria-stabilized zirconia (3YSZ) ceramic powder, nano-TiO₂ dispersion solution and methylcellulose were used as raw materials to prepare water-based ceramic slurry with 84 wt.% solid content. The ceramic green body was then prepared by the LEF technology, following by drying, degreasing and sintering to obtain ceramic components. The effects of addition amount of nano-TiO₂ dispersion solution and sintering temperature on properties of the 3YSZ ceramic were investigated. The optimal comprehensive performance of the 3YSZ ceramic was obtained when the content of nano-TiO₂ dispersion solution was 4.35 wt.% and sintering temperature was 1550 ℃, and the bending strength, linear shrinkage, apparent density were 328 ± 5 MPa, 18.31 %, 5.9 g/cm³, respectively. Moreover, the mechanisms of performance improvement were investigated. Finally, 3YSZ ceramic components with complex structure were fabricated by using the optimal process scheme.     

Strengthening of Porous Mullite and Zirconia CMC Matrices by Evaporation/Condensation

A processing method using evaporation/condensation sintering in an HCl atmosphere was developed for strengthening porous materials without shrinkage. Strengthening without shrinkage is useful in preventing voids and cracks that might be formed during constrained densification, e.g., a porous matrix in a continuous fiber reinforced ceramic composite. Mixtures of mullite and zirconia (monoclinic, tetragonal (3 mol% Y₂O₃), and cubic (8 mol% Y₂O₃)) were studied and exposed to HCl vapor at temperatures up to 1300°C. It was observed that the evaporation–condensation mass transport process produced a porous material with minimal shrinkage. As the crystal structure of the starting tetragonal and cubic zirconia powders did not change after extensive coarsening, it appeared that zirconium and yttrium were transported in the same proportion via evaporation/condensation. The process produced significant coarsening of the zirconia grains, which made the material resistant to densification when heated to 1200°C in air. Because the sintering produced coarsening without shrinkage, the pores also coarsened and a porous microstructure was retained. Mixtures of mullite and zirconia were used because mullite does not densify under the processing conditions used here, namely, heat treatments up to 1300°C. The mullite particles acted as a non-densifying second phase to further inhibit shrinkage when the mullite/zirconia composite was heated up to 1200°C in air. The coarsened cubic zirconia plus mullite mixture had the least densification after heat treatments in air of 100 h at 1200°C.     

Improving the properties of binder jetted ceramics via nanoparticle dispersion infiltration

To improve the dimensional accuracy, surface quality, and mechanical properties of binder jet additive manufactured ceramic parts, in this work, nanozirconia dispersion and binder were used to prepare a jet solution to investigate the effect of nanozirconia content of the jet solution on the properties of zirconia ceramic green and sintered bodies. When the nanozirconia content of the jet solution increased from 0 to 20 wt%, the forming precision of the zirconia ceramic green bodies improved, the surface roughness decreased, and the density increased. After sintering at 1400 °C for 2 h, linear shrinkage along the height, width, and length of the zirconia ceramics decreased by 6.27%, 10.20%, and 5.45%, respectively, while the surface roughness decreased by 42.87%, and the bending strength increased by 145.60%. With increasing nanozirconia content of the jet solution, the spreading and infiltration distance of the jetted solution in the powder layer decreased, the thickness of the deposition layer of nanozirconia on the surface of the zirconia particles in the powder layer increased, and the pore size of the powder layer decreased significantly. This increased the density of the green bodies; thus, improving the sintering properties of the zirconia ceramics.     

刚玉–莫来石–镁铝尖晶石复合陶瓷的原位合成及热震行为

以α-Al2O3、苏州土、滑石和石英为主要原料,采用无压烧结制备了刚玉–莫来石–镁铝尖晶石多相复合陶瓷,研究了烧结温度对样品的体积密度、线性收缩率和吸水率等烧结性能以及机械性能的影响。通过X射线衍射和扫描电子显微镜分析了复相陶瓷热震前后的物相组成和显微结构。结果发现：经1480℃烧结的样品吸水率为0.19%,体积密度为3.06g/cm3,抗折强度达99.59MPa,复合材料有较好的热震性能,1100℃空冷热震损失率仅6.9%,可耐受17次热冲击。该复相陶瓷可作为潜在的太阳能热发电材料。     

Investigation of the sintering of zirconia

Conclusions We investigated the sintering of zirconium dioxide as a function of the activity of the starting material. It was shown that preliminary firing or stabilization of zirconium dioxide reduces its capacity for densification at temperatures of up to 1500°C, while stabilizing it directly during sintering intensifies this capacity. The prestabilized zirconia has the lowest sintering rate.Introducing monoclinic unfired zirconia into the prestabilized material intensifies sintering; the optimal addition is 30%.It is established that the zirconia is sintered by volume diffusion of vacancies.We investigated the sintering of active zirconia obtained by decomposing zirconium nitrate. The greatest degree of densification is obtained with a preliminary short heat processing of the nitrate at 400°C. Activation is connected with the formation of metastable tetragonal and cubic modifications with defect crystal lattices. Increasing the heat-process temperature of the nitrate or prolonging the soak at 400°C, leading to the formation of stable monoclinic ZrO₂ with an ordered crystalline lattice, impairs sintering.Incorporating small additions of active ZrO₂ in the industrial material, and providing rapid firing in an oxidizing atmosphere, greatly increases the degree of sintering. Introducing stabilizing additives intensifies sintering. The maximum densification is obtained by the formation of 60–70% solid solution. Further increase in these additions reduces the shrinkage and densification of the specimens.Translated from Ogneupory, No. 6, pp. 33–40, June, 1968.     

Differential sintering in ceramic injection moulding: particle orientation effects

The sintering shrinkage in three orthogonal directions was measured in sections cut from large rectangular injection moulded ceramic blocks. Two powders were used: a comminuted alumina and a chemically-derived zirconia. Pronounced anisotropy of shrinkage was observed in the former whereas the equiaxed zirconia showed uniform shrinkage throughout the moulding. The pattern of shrinkage anisotropy was consistent with that observed by other investigators and indicates that slight particle anisotropy can introduce differential sintering. The sintering shrinkage in the alumina powder was found to be most pronounced perpendicular to the main flow direction.     

Densification and grain growth of 8YSZ containing NiO

The effects of NiO addition on sintering yttria-stabilized zirconia were systematically studied to understand the role of the additive in the sintering process of the solid electrolyte. Specimens of 8 mol% yttria-stabilized zirconia with NiO contents up to 5.0 mol% were prepared using different Ni precursors and sintered at several dwell temperatures and holding times. Densification and microstructural features were studied by apparent density measurements and scanning electron microscopy observations, respectively. The sintering dynamic study was carried out by following the linear shrinkage of powder compacts containing 0-0.75 mol% NiO. Small (up to 1.0 mol%) NiO addition was found to improve the sinterability of yttria-stabilized zirconia. The activation energy for volume diffusion decreases with increasing NiO content, whereas the grain boundary diffusion seems to be independent on this additive. The grain growth of yttria-stabilized zirconia is found to be enhanced even for small NiO contents.     

硅线石含量对轻质莫来石-刚玉耐火材料的显微结构与性能的影响

以多孔球形莫来石为骨料,板状刚玉细粉、硅线石和粘土为基质,经1400 ℃、1500 ℃和1600 ℃保温3 h烧成,制备了四组轻质莫来石-刚玉耐火材料.采用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对试样的物相组成和显微结构进行表征,研究了烧成温度及硅线石含量(4%、6%、8%和10%)对试样常温物理性能和显微结构的影响.结果表明:(1)当硅线石含量不变时,随着烧成温度的升高,试样的显气孔率逐渐减小,体积密度逐渐增大,线收缩率逐渐增加,常温耐压强度先降低后升高;(2)当硅线石的含量从4%增加到8%时,经1400 ℃烧后,试样的显气孔率和体积密度变化不大,当硅线石含量超过8%时耐压强度显著下降;经1600 ℃烧后,随硅线石含量的增加,试样的体积密度减小,强度降低,线收缩率也由2.5%减小到1.5%;(3)当硅线石含量为6%、烧成温度为1400 ℃时,试样的线收缩率为0.86%,耐压强度为36.1 MPa,热导率为0.249 W/(m·K)(300 ℃),试样基质中气孔的d50为46.7 μm.     

Al2TiO5添加量对MgO-Al2TiO5复合陶瓷烧结及抗热震性的影响

以纳米MgO粉为原料,选用以纳米Al2O3粉和纳米TiO2粉经1500℃保温3 h烧结制备的Al2TiO5为添加剂,采用固相烧结法经1500℃保温3 h制备了Al2TiO5质量分数分别为0、5%、10%和20%的MgO-Al2TiO5复合陶瓷,并采用XRD、SEM和EDS等研究了Al2TiO5添加量对MgO-Al2TiO5复合陶瓷烧结性能及抗热震性能的影响。结果表明:添加Al2TiO5有利于促进复合陶瓷的烧结,其体积密度和线收缩率随Al2TiO5添加量的增加而增大,当Al2TiO5添加量为20%(w)时,其体积密度和线收缩率分别为3.68 g·cm-3和22.07%;当Al2TiO5添加量为10%(w)时,其抗热震性能最佳。Al2TiO5位于方镁石晶粒交界处,抑制方镁石晶粒生长,阻碍裂纹扩展,使MgO-Al2TiO5复合陶瓷的抗热震性能得到改善。     

担载膜受限烧结孔结构模型的改进及验证

针对担载膜受限条件下,复杂的堆积方式及垂直膜面方向出现的加速收缩将影响孔径的问题,对前期建立的担载膜孔结构预测模型进行了改进,从两个方面对模型的关键参数进行定量修正。考虑制备过程中颗粒可能形成的软团聚体对初始堆积方式的影响,对模型重要参数——初始孔隙率进行调整;并结合受限烧结应力模型计算担载膜在垂直膜面方向上的收缩速率和收缩率,研究该方向加速收缩对孔径的影响。在此基础上,采用改进的模型对ZrO2担载膜在800～1200℃烧结后,孔径、孔隙率、膜厚等微结构进行了预测。结果表明:与原模型相比,改进模型具有更好的适应性以及更高的计算精度,能更准确地预测不同烧结温度制备的担载膜的孔径和膜厚,为陶瓷膜孔径的预测与定量控制提供了有效的工具。进一步将模型计算值代入Hagen-Poiseuille方程,可以预测膜的纯水渗透通量。