KINETICS OF CALCIUM OXIDE CHLORINATION AND PORE CLOSURE MODELS

The chlorination of cylindrical lime pellets was studied using thermogravimetric analysis by varying the chlorine concentration, pellet size and temperature. It was determined that the reaction is first order with respect to Cl₂. The intrinsic activation energy, E₁, is estimated to be 8.09 kcal/gmol in the temperature range of 333°C to 472°C.

A two-dimensional expanding grain model that accounts for bulk flow was developed and successfully applied to the lime chlorination system. The effect of varying the chlorine concentration, pellet size, and temperature can be explained in terms of the model. In addition, the modeling results seem to imply that even for a system with solid product expansion, the surface porosity remains finite after the maximum conversion is obtained.

     

KINETICS OF CALCIUM OXIDE CHLORINATION AND PORE CLOSURE MODELS

The chlorination of cylindrical lime pellets was studied using thermogravimetric analysis by varying the chlorine concentration, pellet size and temperature. It was determined that the reaction is first order with respect to Cl₂. The intrinsic activation energy, E₁, is estimated to be 8.09 kcal/gmol in the temperature range of 333°C to 472°C.

A two-dimensional expanding grain model that accounts for bulk flow was developed and successfully applied to the lime chlorination system. The effect of varying the chlorine concentration, pellet size, and temperature can be explained in terms of the model. In addition, the modeling results seem to imply that even for a system with solid product expansion, the surface porosity remains finite after the maximum conversion is obtained.     

Ta2O5与Nb2O5对TiO2基压敏陶瓷电性能的影响

研究了Ta2O5与Nb2O5对TiO2基压敏陶瓷电性能的影响.按照配方TiO2+0.003(按摩尔计)(SrO+Bi2O3+SiO2)+x Ta2O5+yNb2O5配制3种组分的圆片试样,各组分摩尔量分别为x=0.000 75,y=0;x=0.000 375,y=0.000 375及x=0,y=0.000 75.采用电流-电压、电容测量、阻抗分析和势垒高度测量等实验手段,分析了Ta2O5和Nb2O5的作用机理.结果发现,x=0.000 75的样品显示出最低的压敏电压梯度(E10 mA=7.9 V/mm)和最大的表观介电常数(εra=5.88×104),y=0.000 75的样品显示出最高的压敏电压梯度(E10mA=48.9 V/mm)和最小的表观介电常数(εra=1.39×104).这表明,掺Ta2O5可有效地降低压敏电压,提高介电常数.     

含Nb2O5和La2O3系统玻璃形成区

用新的玻璃形成区探索方法研究了Ｌａ２Ｏ３的质量分数分别为１％,５％,１０％时含Ｎｂ２Ｏ５,Ｌａ２Ｏ３系统玻璃的形成区（玻璃生成体分别为Ｐ２Ｏ５,ＳｉＯ２,Ｂ２Ｏ３,ＴｅＯ２＋ＧｅＯ２,修饰体为ＢａＯ,ＺｎＯ）,这些系统可作为激光激活离子Ｎｄ＾３＋,Ｙｂ＾３＋,Ｈｏ＾３＋,Ｔｍ＾３＋,Ｅｒ＾３＋等掺杂的理想基质。     

合成三聚氯氰的氯化和聚合反应宏观动力学研究

利用非等温固定床反应器，研究了三聚氯氰合成的氯化和聚合反应宏观动力学，实验表明氢氰酸与氯气的氯化反应为气相均相反应，而氯氰的聚合反应为吸附在活性炭表面上的氯氰表面反应为控制步骤的气固催化反应。实验测得氯化反应的宏观反应动力学方程为对氢氰酸的一级反应，即（－ｒＡ）１＝２．４５×１０７ｅｘｐ（－２．９０×１０４／ＲＴ）ｃＡ测得聚合反应的宏观动力学方程为（－ｒＡ）２＝ｋ［ｐ３Ａ－ｐＲ／Ｋｐ］／［１＋ＫＡｐＡ＋ＫＲｐＲ］３ｋ＝４．０×１０７ｅｘｐ（－４．３５×１０４／ＲＴ）Ｋｐ＝６．７６×１０－２３ｅｘｐ（３．５２×１０５／ＲＴ）ＫＡ＝４．０×１０３ｅｘｐ（－３．３９×１０４／ＲＴ）ＫＲ＝１．０５×１０３ｅｘｐ（－５．０２×１０４／ＲＴ     

Precipitation-induced healing of Nb2O5

Precipitation-induced stimulated-healing of Nb₂O₅ was carried out through the extrinsic addition of silver oxide nanoscale elemental inclusions to form ternary oxides at the crack site. Nb₂O₅ cylindrical pellets, 13 mm in diameter and 10 mm in length, were produced from powders using a cold isostatic press. The pellets were subsequently sintered at 1100 °C. A scratch was created in the sintered Nb₂O₅ pellets and was subsequently filled with Ag₂O. The pellets were annealed to stimulate the self-healing process. X-ray diffraction was used to explore the evolution of phases, chemical compositions, and structural properties of the sintered samples before and after the stimulated-healing process. Energy dispersive X-ray spectroscopy revealed the elemental composition in the healed region. The on-site composition of the healed sample was determined by Raman spectroscopy and was compared to the spectrum outside of the scratch. Raman spectroscopy confirmed that precipitation proceeded via the following chemical reaction which was facilitated at elevated temperature: Nb₂O₅ + Ag₂O → 2AgNbO₃. In addition, a 3D reconstructed stylus profilometry image of the crack region confirmed that healing occurred. Healing by recovering 89% of the original material strength was confirmed using the three-point bend test.     

Nb2O5掺杂对BaTiO3陶瓷介电常数的影响

BaTiO3陶瓷以其优异的铁电、压电和绝缘性能广泛应用于体积小、容量大的电子器件材料,但其在一定的工作温度区间介电常数却呈现不稳定变化。对其常用的改性方法进行了分类和阐述,同时对Nb2O5掺杂改性对BaTiO3陶瓷介电性能的影响作了简单介绍,最后讨论了Nb2O5在多层陶瓷电容器制备领域的应用和重要性。     

Raman investigations of NH3 adsorption on TiO2, Nb2O5, and Nb2O5/TiO2

A study has been carried out of the interactions of NH₃ with TiO₂, Nb₂O₅, and Nb₂O₅/TiO₂. Raman spectroscopy was used to characterize the structure of the adsorbed NH₃ and perturbations of species present at the surface of the adsorbent. On each oxide, NH₃ adsorbs predominantly at Lewis acid sites. Hydrogen-bonding occurs between the adsorbed NH₃ and OH groups present on the surface of TiO₂. A small concentration of NH ₄ ⁺ is observed, consistent with the relatively low concentration of Brønsted acid sites compared to Lewis acid sites on each of the samples investigated. Exposure of Nb₂O₅/TiO₂ to NH₃ at temperatures up to 500°C does not result in partial reduction of the supported niobia.     

Zn含量高的Nb2O5-ZnO-Bi2O3系高频介质陶瓷

研究Ｚｎ含量高的Ｎｂ２Ｏ５－ＺｎＯ－Ｂｉ２Ｏ３系高频介质陶瓷,实验结果表明,组成的特征为混合多相结构,除了主晶相为立方焦绿石相之外,随组成变化,尚能生成ＺｎＯ,ＺｎＮｂ２Ｏ６,Ｚｎ３Ｎｂ２Ｏ８,ＢｉＮｂＯ４等相,立方焦绿石相具有高的εＺｒＯ相约出现降低ε及增大ｔａｎδ而ＺｎＮｂ２６,ＢｉＮｂＯ４等相的出现使ε,ｔａｎδ同时降低,并改善电容温度系数。     

低温烧结CuO-V_2O_5-Bi_2O_3掺杂Zn_3Nb_2O_8陶瓷的微波介电性能

研究了CuO–V2O5–Bi2O3作为烧结助剂对Zn3Nb2O8陶瓷的烧结特性、微观结构、相结构及微波介电性能的影响。CuO–V2O5–Bi2O3复合掺杂可以将Zn3Nb2O8陶瓷的烧结温度从1150℃降到900℃。在900℃烧结4h的Zn3Nb2O8–0.25%(质量分数,下同)CuO–1.5%V2O5–1.5%Bi2O3陶瓷的密度达到了理论密度的98.1%,相对介电常数为18.8,品质因数与谐振频率之积为39442GHz。该体系的介电性能和陶瓷的致密度与烧结助剂的含量及烧结温度密切相关,陶瓷的致密度和相对介电常数随CuO–V2O5–Bi2O3烧结助剂含量的增加而增加,同样陶瓷的致密度和相对介电常数也随烧结温度的升高而提高。     

Effect of Nb2O5 and MgO/Nb2O5 doping on densification,microstructure and wear resistance of alumina

In this paper, the influence of Nb₂O₅ single-doping and MgO/Nb₂O₅ co-doping on the densification, microstructure and wear resistance of Al₂O₃ has been investigated. The results show that Nb₂O₅ single-doping can increase the density of alumina effectively, but excessive Nb₂O₅ will lead to abnormal grain growth. Comparing with Nb₂O₅ single-doping, MgO/Nb₂O₅ co-doping can further increase the density and suppress the abnormal grain growth of the alumina. Meanwhile, the co-doped samples also show much lower wear rates. Typically, when 500 ppm MgO/1000 ppm Nb₂O₅ co-doped, the alumina ceramics has a minimum wear rate of 0.01‰, which is about 1/5 of the alumina ceramics with 1000 ppm Nb₂O₅ single-doped. The inhibiting effect of co-doping on abnormal grain growth and the reasons for the decrease of wear rate are also discussed.     

Fabrication of high-quality flexible transparent conductive thin films with a Nb2O5/AgNWs/Nb2O5 sandwich structure

Different sandwich structures of flexible transparent conductive thin film (TCFs) composed of Nb₂O₅ layers and Ag nanowires (AgNWs) have been prepared onto flexible polyethylene terephthalate (PET) substrate at room temperature to develop an indium-free TCF. The AgNWs are synthesized by a modified polyol method and inserted into the Nb₂O₅ layers that are prepared by radio frequency magnetron sputtering. The optical and electrical properties can be modified by changing the number of spin-coating cycle of AgNW suspension. At optimized condition, we achieve a flexible Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film with a low sheet resistance of 9.61 Ω/square and a high optical transmittance of 84.3%. Meanwhile, the resistance remains nearly constant after 30 tape tests, suggesting a strong adhesion to the PET substrate. The sandwich thin films show high long-term stability to oxidation, humid heat, and chemicals compared with that of AgNW networks, which can be attributed to the effective covering of Nb₂O₅ layer on the AgNWs. In addition, the Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin films show good stability after repeated bending. This Nb₂O₅/AgNWs/Nb₂O₅ sandwich thin film can therefore serve as a high-performance transparent conductive electrode for numerous flexible electronic devices.     

Nb2O5薄膜的制备及性能研究

以NbCl5作为前驱物,用微波催化的溶胶-凝胶法制备了Nb2O5薄膜,并在不同温度下进行热处理。经透过率测试及用X射线衍射分析仪和原子力显微镜对薄膜的相结构和表面形貌进行测试分析,测试结果表明：制得的薄膜主晶相为假六方Nb2O5晶相（TT-Nb2O5晶相）。薄膜厚度具有良好的透光率、良好的空架结构。     

Oxidative dehydrogenation of ethane to ethylene over V2O5/Nb2O5 catalysts

V₂O₅/Nb₂O₅ catalysts with various V₂O₅ contents were prepared by impregnation and characterized by various techniques in detail. Oxidative dehydrogenation of ethane was carried out in a fixed bed quartz reactor at 500–600 °C. XPS analysis indicated a clear enrichment of vanadium on the near-surface-region and UV–vis diffuse reflectance spectroscopy revealed the nature of VO_x structures formed. 10 wt.% V₂O₅/Nb₂O₅ catalyst has displayed the best performance (X = 28%, S = 38% at 600 °C) due to enrichment of vanadium in the near-surface-region and formation of optimum amount of monomeric/oligomeric VO_x species.     

Nb2O5掺杂Co2Z 六角铁氧体的烧结行为和电磁特性

采用固相反应法制备Nb2O5掺杂Co2Z六角铁氧体[Ba3(Co0.4Zn0.6)2Fe24O41,Z-型].通过显微结构观察和电磁性能的测试分析,研究了不同Nb2O5掺量对Z-型铁氧体烧结特性和电磁特性的影响.结果表明:由于Nb5 固溶于铁氧体中,增加了空穴浓度,使体扩散加剧,进而促进材料的烧结.适当添加Nb2O5可提高样品的致密化程度,改善Z-型六角铁氧体的显微结构和电磁特性.在Nb2O5掺量为Co2Z一次预烧料质量(下同)的0～0.8%内,随Nb2O5掺量增加,在Z-型六角结构相生长的同时,伴生M-相六角结构.六角结构致密度增加,磁导率增大,铁磁共振频率点移向低频.掺量为0.8%Nb2O5的样品在1 260℃烧结6 h,得到材料的相对密度为95%左右,起始磁导率为33,高μQ积,低损耗角tgδ矫顽力Hcb.     

Phase evolution in plasma sprayed Nb2O5 coatings

Nb₂O₅ polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb₂O₅ is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb₂O₅ coatings, and its effect on their morphology and properties. Phase evolution from H-Nb₂O₅ in the feedstock, to T-Nb₂O₅, TT-Nb₂O₅, N-Nb₂O₅, H-Nb₂O₅, Nb₁₂O₂₉ and NbO₂ in the coatings depends on the plasma Ar/H₂ ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb₂O₅ or TT-Nb₂O₅. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb₂O₅ incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.     

Nb2O5薄膜的溶胶—凝胶法制备

以金属醇盐为前驱体获得涂膜液，采用浸渍－提拉法制备Ｎｂ２Ｏ５薄膜，研究了不同催化环境对涂膜液溶胶的影响，不同涂膜次数样品的反射透过情况。并由此推算了薄膜的厚度及折射率。ＸＲＤ结果表明：５６０℃热处理１ｈ后得到正交晶相的Ｎ２Ｏ５薄膜；Ｎｂ２Ｏ５薄着色为淡黄色。     

Synthesis of Nb2O5 and Ta2O5 nanopowders by means of an endo-templating method

Finding efficient templates for the nanostructuring of materials is a key point. Here, the niobium (V) - and tantalum (V) oxide ceramics nanopowders have been synthesized by a hard-templating approach by using the tricalcium phosphate biomaterial (Ca₃(PO₄)₂.xH₂O) as template agent. The oxide ceramics were investigated by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, nitrogen physisorption and Scanning Electron Microscopy (SEM). It was observed that the surface properties (specific surface areas, pore volumes) of the Nb₂O₅ and Ta₂O₅ powders were strongly dependent of the amount of the Ca₃(PO₄)₂.xH₂O template previously used in the preparation of the [oxide ceramics/template] composites. For instance, with a Ca₃(PO₄)₂.xH₂O/ceramic salt weight ratio ranging from 0 to 1, the specific surface areas of Nb₂O₅ and Ta₂O₅ were gradually enhanced of 48–166 m²/g and 5–84 m²/g, respectively. The pore volumes were increased as well. The use of the eco-friendly tricalcium phosphate material (Ca₃(PO₄)₂.xH₂O) as template in the hard-templating approach may be suitable and efficient in the aim of synthesizing materials with enhanced surface properties.