Nanostructured Ca-based sorbents with high CO2 uptake efficiency

Calcium-based carbon dioxide sorbents were made in the gas phase by scalable flame spray pyrolysis (FSP) and compared to the ones made by calcination (CAL) of selected calcium precursors. Such flame-made sorbents consisted of nanostructured CaO and CaCO₃ with twice as much specific surface area (40-60 m²/g) as the CAL-made sorbents. All FSP-made sorbents exhibited faster and higher CO₂ uptake capacity than all CAL-made sorbents at intermediate temperatures. CAL of calcium acetate monohydrate resulted in sorbents with the best CO₂ uptake among all CAL-made ones. At higher temperatures both FSP- and CAL-made sorbents (esp. from CaAc₂·H₂O) exhibited very high initial molar conversions (95%) but sintering contributed to grain growth that reduced the molar conversion down to 50%. In multiple carbonation/decarbonation cycles, the nanostructured FSP-made sorbents demonstrated stable, reversible and high CO₂ uptake capacity sustaining maximum molar conversion at about 50% even after 60 such cycles, indicating high potential for CO₂ uptake. The top performance of flame-made sorbents is best attributed to their nanostructure (30-50 nm grain size) that allows operation in the reaction-controlled carbonation regime rather than in the diffusion-controlled one when sorbents made with larger particles are employed.     

利用廉价高岭土制备纳米氧化铝的工艺研究

以我国大储量的高岭土为原料，采用化学沉淀法制备超精细的氧化铝粉末。通过对比试验和SEM等设备的检测结果．考察制备过程中溶液浓度，分散剂，防团聚技术对最终产品的影响，探索出了一套适合工业生产纳米氧化铝的工艺。     

Mg gas infiltration for the fabrication of MgB2 pellets using nanosized and microsized B powders

MgB₂ superconductor pellets were synthesized through Mg gas infiltration method using nanosized- and microsized B powders. There was a marked difference in the superconducting properties of the two samples, particularly in the pinning force and dominant pinning mechanism. The microstructures of the samples were observed using HR-TEM and STEM-HAADF, and the results showed that the primary reason for the difference in the superconducting properties is the distribution of the nanosized second-phase particle MgO. Additionally, a feasible reaction model for the Mg gas infiltration method was established. Compared to the Mg liquid infiltration method, the gas infiltration showed better penetrability ability with a small amount of residual Mg. This study presents a novel synthesis process to fabricate an MgB₂ pellet with superior density and superconducting properties. This method can be used in multiple applications such as superconducting bearings, compact superconductor magnets, and magnetic shielding.     

Svnthesis and Characterization of Nanoscale Mullite Powder

Nanoscale mullite powder were synthesized via Solgel-SCFD and middle temperature treatment by using AIP( aluminum-isopropoxde ) and TEOS ( tetraethyl orthosdicate) as starting materials. Both of the binary aerogel of alumina-silica and calcined nanoscale materials were investigated by using TG-DSC (thermogravimetry-differential scanning calorimeter), TEM (transmission electron microscope), XRD ( X-Ray diffractometer ) and specific surface area and porosimetry. TG-DSC indicated the removal of most of the volatiles , i. e. 15.98% up to about 700℃ ,and in the DSC curve, existence of two exothermic peak at about 445℃ and 1015℃ may be due to the crystallization of Si-O-Al-O in diphasic gels and mullitization and a small endothermic peak at about 805℃ indicated the decomposition of structural water molecules. On the colligation of the results of TG- DSC, XRD and TEM , the beginning temperature of mullitization in Al2 O3-SiO2 aerogel system can be confirmed at about 1015℃. XRD results also showed the formation of mullite at the range 1100 ～1200℃. TEM and surface area and porosimetry results showed that the nanosized mullite were calcinated at 1100and 1200℃ exhibited size 30nm and 50nm, specific surface area 138.91m2/g and 95.81m2/g.     

Low temperature behaviour of TiO2 rutile as negative electrode material for lithium-ion batteries

High surface nanosized rutile TiO₂ is prepared via a sol-gel method from an ethylene glycol-based titanium-precursor in the presence of a non-ionic surfactant, at pH 0. Its electrochemical behaviour has been investigated at low temperature using two different potential windows. Typically, the potential window of the rutile system is 1-3 V but the use of an enlarged potential window (0.1-3 V), leads to an excellent reversible capacity of 341 mAh g⁻¹ which is comparable to graphite anodes. The electrochemical performance was investigated by cyclic voltammetry and galvanostatic techniques at temperatures ranging from −40 to 20 °C. Nanosized TiO₂ exhibits excellent rate capability (341 mAh g⁻¹ at 20 °C, 197 mAh g⁻¹ at −10 °C, 138 mAh g⁻¹ at −20 °C, and 77 mAh g⁻¹ at −40 °C at a C/5 rate) and good cycling stability. The superior low-temperature electrochemical performance of nanosized rutile TiO₂ may make it a promising candidate as lithium-ion battery material.     

Nanostructured Si/TiC composite anode for Li-ion batteries

Si/TiC nanocomposite anode was synthesized by a surface sol-gel method in combination with a following heat-treatment process. Through this process, nanosized Si was homogeneously distributed in a titanium carbide matrix. The electrochemically less active TiC working as a buffer matrix successfully prevented Si from cracking/crumbling during the charging/discharging process. The interspaces in the Si/TiC nanocomposite could offer convenient channels for Li ions to react with active Si. The Si/TiC composite exhibited a reversible charge/discharge capacity of about 1000 mAh g⁻¹ with average discharge capacity fading of 1.8 mAh g⁻¹ (0.18%) from 2nd to 100th cycle, indicating its excellent cyclability when used as anode materials for lithium-ion batteries.     

Influence of Different Substrates on the Detectivity of Pyroelectric Sensors

Nanosized lead titanate doped with calcium and lanthanum (PCLT) powder obtained by the sol-gel method was homogeneously mixed with vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] to form nanocomposites. Several pyroelectric sensors were prepared on porous silicon dioxide, on poly(ethylene terephthalate) (PET) film and on bulk silicon substrates, respectively. The nanocomposite PCLT/P(VDF-TrFE) sensing film was deposited by spin-coating and Ni-Cr film was deposited as the top electrode and absorption layer. Experimental results showed that the substrate of the pyroelectric sensor could significantly affect the specific detectivity. The porous silicon dioxide and PET plastic film substrates could effectively decrease the thermal conductivity and the thermal fluctuation noise of the pyroelectric element, increase the voltage responsivity and the specific detectivity. The results indicated that the specific detectivity of PCLT/P(VDF-TrFE) pyroelectric sensors based on porous silicon dioxide and PET plastic film substrates reached 4.2E6 and 3.4E7 cmHz 1/2 W m 1 respectively, which is about 1-2 orders of magnitude higher than that of the sensors formed under the same condition on the bulk silicon substrate.     

Synthesis of NdAlO3 with good microwave dielectric properties by stearic acid method

In this study, NdAlO₃ with perovskite structure was synthesized by the stearic acid method at relatively low temperature. The structural characteristics of the as-synthesized product were identified by TG–DSC, XRD, FT–IR, SEM, and TEM techniques. Using the powders as starting materials, NdAlO₃ bulk microwave ceramics were prepared, and the corresponding densification process, microstructural and dielectric properties were studied. The XRD and FI–IR results confirmed that single phase NdAlO₃ could be prepared at low temperature by the stearic acid method. A unique two-dimensional platelike morphology with an unevenly dispersed bubble shape structure was observed in the calcined powder. However, the TEM result revealed that the powder calcined at 800 °C had a good dispersity accompanied with narrow particle size distribution within a range of 20–35 nm. The average particle size of 27.3 nm was in accordance with that calculated from the XRD data. Using the powder calcined at 800 °C as raw materials, the as-obtained NdAlO₃ ceramics sintered at 1500 °C for 4 h possessed the highest density and favorable combined microwave dielectric properties (i.e., ε_r = 23.02, Q × f = 65320 GHz, and τ_f = −32.4 ppm/^°C). The present work developed a fast, energy-efficient approach to synthesize NdAlO₃ powder used as promising raw materials of microwave dielectric ceramics.     

Nanosized corundum synthesis

 Alumina continues to play an important role in the materials industry with the Bayer process still providing alumina after a 100 years of continuous processing. In addition to traditional applications of alumina, alumina is being advanced as a major part of the new frontier on nanophase materials and nanophase technology. High surface area corundum has been synthesized using a rapid totally ”green” hydrothermal process for forming nanosized diaspore precursor to nanosized corundum. Surface areas of the nanosized corundum are in excess of 160 square meters per gram. High temperature solution calorimetry show that gamma alumina becomes the energetically stable phase relative to corundum at specific surface areas greater than 125 square meters per gram. These data provide a thermodynamic basis for the equilibrium relationships among the alumina phases in the nanocrystalline region. Received: 19 November 1997 / Accepted: 22 December 1997     

纳米硫酸钡增强增韧尼龙66

通过熔融共混法制备了纳米硫酸钡增强增韧尼龙66复合材料。研究了纳米硫酸钡含量对增强增韧尼龙66复合材料力学性能的影响。结果表明，纳米硫酸钡对尼龙66有显著的增强增韧作用。尼龙66的韧性、刚性和强度随着纳米硫酸钡含量的增加先增后减，在纳米硫酸钡质量分数为3％时，力学性能最优；对比空白样，缺口冲击强度提高了17．1％，弯曲强度和模量分别提高了5．74％和11．57％，拉伸强度和模量稍有提高。