反应条件对氢氧化钇及氧化钇形貌的影响

以氨水和硝酸钇为原料制备氧化钇前驱体,考察表面活性剂及其用量对晶粒形貌和尺寸的影响;并在水热条件下研究体系pH、温度及时间对沉淀重整效果的影响.用XRD,SEM技术检测样品的晶型、尺寸和形貌.结果显示,阴离子型表面活性剂的浓度对一级晶粒的尺寸有较明显的影响,而阳离子型表面活性剂和非离子型表面活性剂的浓度对一级晶粒的尺寸的影响不明显.水热条件下对沉淀进行重整,可制备氢氧化钇纳米棒,溶液的碱浓度、温度及时间影响纳米棒的直径和长度.样品经600 ℃焙烧2 h,可制得立方晶相氧化钇,一级晶粒7～20 nm;氢氧化钇纳米棒焙烧后形成的氧化钇仍具有棒状结构.     

纳米氧化钇的制备与表征

以Y(NO3)3为原料,聚乙烯醇为分散剂,采用碳酸氢铵沉淀工艺制备了氧化钇前驱体。用FTIR、TG-DTA分析了沉淀前驱体的成分及其热分解过程。结果表明,前驱体为NH4Y(OH)2CO3。对形成前驱体的机理进行了初步探讨。用XRD、UV-Vis和TEM分析了不同温度下煅烧所得粉体的结构和形貌,结果表明,前驱体在750℃保温2h,得到分散性良好、纯度高、立方体型的氧化钇,平均颗粒尺寸20nm左右。实验证明,适量的分散剂和(NH4)2SO4的添加对氧化钇颗粒形貌和粒径有显著影响。     

球形纳米氧化钇的制备与表征

以尿素为沉淀剂,硝酸钇为钇源,十六烷基三甲基溴化铵为分散剂,采用均相沉淀法制备球形纳米氧化钇粉体,研究了反应物浓度比、表面活性剂用量、反应时间、搅拌转速、反应温度对氧化钇形貌及粒径的影响。通过激光粒度分析、X射线衍射（XRD）分析、扫描电镜（SEM）分析、傅里叶红外光谱（FTIR）分析等手段对样品进行表征。结果表明,反应物浓度比、反应时间、搅拌转速、反应温度会影响粉体的尺寸,适量CTAB的加入可显著降低氧化钇的粒径;在最佳工艺条件下,可制得粒径大小为110~130 nm的球形氧化钇粉体。     

超细氧化钇粉体的研究进展

综述了氧化钇纳米粉体的应用及研究现状,着重介绍了共沉淀法、喷雾热解法、溶胶一凝胶法以及近几年开发的高分子网络凝胶法等7种制备氧化钇粉体的方法。     

含脲柠檬酸钇燃烧法制备纳米氧化钇粉

以柠檬酸钇为先驱体化合物，并将脲加到柠檬酸钇中，得到一种新的含脲柠檬酸钇先驱体。两种先驱体分别经500，600，700℃和800℃煅烧，可得到纳米氧化钇粉。通过TEM和XRD研究，结果表明；Y2O3的大小是由 煅烧温度决定，随着温度升高颗粒变大；此外，在相同温度下，含脲柠檬酸钇比柠檬酸钇得到的纳米氧化钇更细。     

花状ZnO的水热合成与表征

以金属锌为原料,引入偶联表面活性剂作为晶体生长控制剂,在温和的水热条件(150℃)下一步合成了花状纳米结构的ZnO.使用XRD,TEM,SEM,SAED等测试手段,对产物的化学组成和形貌特征进行了分析和表征.结果表明,花状ZnO纳米结构由ZnO纳米棒组成,该ZnO纳米棒为六方晶系且表现为单晶性质.ZnO纳米棒纯度高、粒径较小、长直、光滑而且大多一端聚集而另一端向四周放射性分布,呈较完美的花状结构.初步探讨了ZnO单晶纳米棒和花状ZnO纳米结构的形成机理.分析表明,ZnO纳米棒及其花状结构的形成与偶联表面括性剂特殊的性质及分子结构有关.     

超细氧化钇粉体的制备

湿化学法制备超细粉体时，反应、分离、干燥以及灼烧都不同程度地影响粉体的粒径及团聚。在传统的草酸沉淀法制备氧化钇基础上对溶液的浓度、pH值以及表面活性剂的选择和用量、颗粒的表面电位进行了考察研究，确定了反应过程中影响粉体粒径的各个因素，得到一次粒径50－100nm，平均粒径0.521μm，晶型良好且具有单分散趋势的超细氧化钇。     

氧化钇稳定二氧化锆的制备及表征

以氯氧化锆为前躯体,尿素为沉淀剂,采用溶胶-凝胶法结合超临界CO2干燥进行了氧化钇稳定二氧化锫的制备。并通过XRD、TG—DTA、BET、FT—IR等方式对所制备的样品进行表征。结果显示,经过不同温度煅烧的样品都呈现出四方相氧化锆特性。400℃煅烧样品的比表面积高达120．25m^2／g。     

“一步法”合成改性纳米碳酸钙及表征

通过直接沉淀法、微乳液法和水热法合成并改性了纳米CaCO3。3种方法均有表面活性剂的介入,目的在于表面活性剂在控制碳酸钙晶粒生长的同时可使纳米CaCO3表面得到改性。采用X射线衍射(XRD)、红外光谱(FTIR)、透射电镜(TEM)等分析测试方法对产物的物相、形貌及颗粒大小进行表征。结果表明,采用水热法在十二烷基磺酸钠(SDS)和EDTA共同作用下得到粒径为20~50 nm的方解石型纳米CaCO3,通过表面活性剂与纳米CaCO3表面的化学吸附实现表面改性的目的。     

干燥及煅烧过程中引入表面活性剂控制ZrO2超细粉末团聚的研究

一、引言液相沉淀法制备氧化物超细粉末过程中,团聚体起源于沉淀反应过程.沉淀反应生成的聚集体内含有丰富的自由水,吸附水,结构配位水和非架桥羟基.在后续的热处理过程中,首先失去的是渗透在胶粒与胶粒之间的毛细管内的自由水.在水的表面张力的作用下,胶粒之间距离缩短,并相互接触,形成聚集.随着温度的升高,吸附水,结构配位水被排除.这些水分子具有比普通自由水高几倍至几十倍的表面张力,因而引起胶粒     

Synthesis of yttria nanopowder with poly acrylic acid as dispersant for highly transparent yttria ceramics

Highly pure and well-dispersed yttria nanocrystalline powders were synthesized with a modified coprecipitation method that uses mixed ammonium hydroxide-carbonate solution as the precipitant and poly acrylic acid (PAA) as the dispersant. Comparing with the yttria powders synthesized using the same route but without PAA dispersant, the PAA-assisted powders exhibit lower level of agglomeration and better sinterability. Sintering trajectories of the powders with and without PAA dispersant were investigated. Y₂O₃ ceramics sintered with the PAA-assisted powders exhibited smaller grain size, homogeneous microstructure, and higher in-line optical transmittance. The result suggests that the polymer-assisted coprecipitation could be used to synthesize yttria nanopowders for fabricating high optical quality transparent ceramics.     

Preparation and characterization of blend membranes of polyurethane and superfine chitosan powder

A novel kind of asymmetric blend membranes with superfine chitosan powder (SCP) and biomedical polyurethane was prepared by immersion precipitation phase inversion method. Effects of different SCP content on the morphology and properties of the blend membranes were investigated. The result showed that SCP content had little influence on the cross-section structure of the blend membranes, and the cross-section presented a cellular structure. WAXD results revealed that the aggregated structure of SCP remained. With an increment of SCP content, the pore diameter and porosities of blend membranes increased firstly, and then decreased. While, the water absorption rate and water vapor transmission rate were improved remarkably with increasing SCP content. The mechanical testing results indicated that with an increment of SCP ratio, mechanical properties presented a descending trend, whereas all blend membranes exhibited the good elasticity.     

Synthesis,sintering and electrical properties of yttria–calcia-doped ceria

Crystalline yttria and calcia doped ceria powder, with a composition of Ce_0.8Y_0.18Ca_0.02O_2?δ has been prepared by a coprecipitation procedure from the corresponding nitrates of component cations. Nanopowder was obtained after thermal treatment at 700 °C 2 h of the coprecipitated mixtures. Specific surface area was 45 m²/g. Isostatically and uniaxially pressed pellets were prepared from the powder. Sintering behaviour was followed by CHR dilatometer. Isothermal sintering was carried out between 1100 and 1300 °C. Apparent density as high as 98% D_th was attained by firing isostatically pressed pellets at 1150 °C 4 h. Uniaxially pressed pellets attained the same apparent density at 1275 °C 2 h, being in both cases very low the densification temperatures. Microstructure was observed by scanning electron microscopy (SEM). Ionic conductivity was determined by complex impedance spectroscopy. Bulk and grain boundary conductivities have similar values, and the total conductivity attains good value compatible with the use as electrolyte in solid oxide fuel cell (SOFC).     

高分子蜡乳液对白炭黑的改性与表征

采用自制的高分子蜡乳液对白炭黑进行改性处理.研究了改性剂的加入量对吸油值及表观密度的影响,利用扫描电镜(SEM)和热重-差热分析(TG-DSC)对改性前后的白炭黑的性能进行表征.研究表明,随着改性剂用量的增加,白炭黑吸油值明显减小,当添加量达到一定值时吸油值不再减小,表观密度随改性剂用量的增加呈增大趋势;改性剂加入量为5.0%(质量分数,下同)和7.5%时,改性后的白炭黑颗粒均匀,分散性好.研究结果表明,自制的高分子蜡乳液对白炭黑改性效果良好.     

Synthesis and encapsulation of yttria stabilized zirconia particles in supercritical carbon dioxide

Nanocrystalline oxide powders synthesized in supercritical CO₂ (SC-CO₂) generally consist in nanoparticle agglomerates, which are difficult to handle. In this work a particle encapsulation method in SC-CO₂ was developed to overcome this problem. By performing both the synthesis and encapsulation steps in the supercritical fluid, the agglomeration of particles can be limited, their handling can be improved and the powder behavior can be modified depending on the selected encapsulation agent. Poly(dimethylsiloxane)-graft-polyacrylate (PDMS-g-PA) phase separation method and methylmethacrylate (MMA) polymerization on particle surface are typical encapsulation processes usable in batch mode, with SC-CO₂ as a solvent, for ceramic powder encapsulation. This paper describes preliminary results concerning the synthesis of yttrium stabilized zirconia (YSZ) in SC-CO₂ and its encapsulation with PDMS-g-PA or PMMA in SC-CO₂. It has been shown that both phase separation and polymerization allow coating of the oxide particles, and clearly modify their properties. On the other hand, the use of a surfactant like PDMS-g-PA allows anchoring of MMA monomer and promotes polymerization on the particle surface. The choice of the surfactant is considered as a key parameter for a successful encapsulation process. This preliminary work offers new perspectives for synthesis and encapsulation of ceramic powders in SC-CO₂.     

机械法制莫来石微粉的性能与烧结

利用环缝磨、搅拌磨制得了Ｄ０．５达μｍ左右的莫来石微粉。该粉体粒度分布窄，机械力化学活性高。用此微粉与细粉进行压坯烧结试验表明，其粒径比和体积比对烧结有很大影响。在粒径比相差不大的情况下，对应每一烧结温度均存在一个微粉最低有效加入量，且烧结温度越高，该加入量越小；当粒径比相差很大时，此加入量值变得不太明显，但少量微粉引入即可显著提高坯体的烧结性能。     

有机酸催化合成微细级磷酸锌

为了改善磷酸锌的分散性，利用有机酸作为催化剂，常温条件下直接合成了磷酸锌。试验结果表明：合成的磷酸锌不用粉碎，粒径直接达到38μm以下，产品粒度分布均匀，白度比普通直接法生产的磷酸锌提高2％，其他各项指标均达到中国的企业标准要求。该工艺无需加热，减少了粉碎工序，节约了能源。     

Preparation and characterization of plasma-sprayed yttria stabilized zirconia as a potential substrate for NOx sensor

Fully stabilized zirconia containing 8 mol% of yttria was synthesized by solid state reaction method and deposited as a thick film by plasma spray coating. The crystal structure and phases developed were characterized by X-ray diffraction (XRD). The surface structure, surface morphology and microstructure developed were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The actual doping content was measured by electron probe micro-analyzer(EPMA). The plasma sprayed YSZ was characterized for its electrolytic properties by ac and dc conductivity measurements. The maximum conductivity for plasma sprayed YSZ was found to be −1.62 Scm⁻¹, which was lesser than the conductivity of standard 8YSZ of −1.03 Scm⁻¹ at pO₂=0.21 atm. However; conductivity trends in the arrhenius plot was observed to be similar for entire YSZ's, suggesting that the conductivity mechanism is same and dominated by oxygen ion conductivity independent of oxygen partial pressure. These promising electrolytic properties of thermal sprayed YSZ suggest that the thermal spray coating method may lead to be used as a potential method for the fabrication of NOx sensor.     

Synthesis of nanocrystalline ytterbium-doped yttria by citrate-gel combustion method and fabrication of ceramic materials

Nanosized ytterbium doped yttria powders were prepared by citrate-gel combustion techniques. As-synthesized precursor and calcined powders were characterized for their crystalline structure, particle size and morphologies. Nanocrystalline Yb³⁺:Y₂O₃ powders with pure cubic yttria crystal structure were obtained by calcination of as-prepared precursors at 1100 °C for 3 h. Powders obtained were well dispersed with an average particle size of 60 nm. By using the obtained powders, nearly full dense Yb³⁺:Y₂O₃ ceramics were produced by vacuum sintering at 1800 °C for 12 h. The emission spectrum of the sintered ceramics under the excitation wavelength of 905 nm illustrates that there are three fluorescence peaks locating at 976 nm, 1030 nm and 1075 nm respectively, all corresponding to the ²F_5/2 → ²F_7/2 transitions of ytterbium ion.     

Synthesis of the superfine high-entropy zirconate nanopowders by polymerized complex method

The high-purity and superfine high-entropy zirconate nanopowders, namely(Y_0.25La_0.25Sm_0.25Eu_0.25)₂Zr₂O₇ nanopowders, without agglomeration, were successfully synthesized via polymerized complex method at low temperatures for the first time. The results showed that the crystallinity degree, lattice strain, and particle size of the as-synthesized powders were gradually enhanced with the increase of the synthesis temperatu...