Effect of drying technique on the physicochemical properties of sodium silicate-based mesoporous precipitated silica

The conventional drying (oven drying) method used for the preparation of precipitated mesoporous silica with low surface area (>300 m²/g) and small pore volume is often associated with a high production cost and a time consuming process. Therefore, the main goal of this study was to develop a cost-effective and fast drying process for the production of precipitated mesoporous silica using inexpensive industrial grade sodium silicate and spray drying of the precipitated wet-gel silica slurry. The precipitated wet-gel silica slurry was prepared from an aqueous sodium silicate solution through the drop-wise addition of sulfuric acid. Mesoporous precipitated silica powder was prepared by drying the wet-gel slurry with different drying techniques. The effects of the oven drying (OD), microwave drying (MD), and spray drying (SD) techniques on the physical (oil, water absorption, and tapping density), and textural properties (specific BET surface area, pore volume, pore size, and % porosity) of the precipitated mesoporous silica powder were studied. The dried precipitated mesoporous silica powders were characterized with field-emission scanning electron microscopy; Brunauer, Emmett and Teller and BJH nitrogen gas adsorption/desorption methods; Fourier-transform infrared spectroscopy; thermogravimetric and differential analysis; N₂ physisorption isotherm; pore size distribution and particle size analysis. There was a significant effect of drying technique on the textural properties, such as specific surface area, pore size distribution and cumulative pore volume of the mesoporous silica powder. Additionally, the effect of the microwave-drying period on the physicochemical properties of the precipitated mesoporous silica powder was investigated and discussed.     

表面修饰的钛酸钡纳米粉体的制备

采用水热法制备出表面包裹有硬脂酸的钛酸钡钠米粉体,并运用一系列手段对其微结构进行了表征。结果表明：产物粒径较小,粒度分布较窄,单分散性较好,其表面为非极性,同时表现出良好的流动性能。认为钛酸钡纳米粉体表面极性的改变是由于其表面包裹了一层硬脂酸,并且包裹层降低了粉体间的相互作用力,从而提高了粉体的流动性。     

Synthesis,forming and characterization of ceramic materials for the planar solid oxide fuel cell (SOFC)

Chemically-homogeneous and well-characterized ceramic powders have been used for the preparation and investigation of the SOFC components. The powders were synthesized by spray drying and subsequent calcination. The resulting powders were characterized with regard to the crystalline phases, chemical analysis, specific surface area, particle size and particle size distribution, morphology and particle agglomerates. These parameters are very important for forming thin, flat ceramic sheets and components by tape-casting and screen-printing technology. Forming process, sintering, electrical conductivity and compatibility are discussed. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994     

Impact of the Granulation Process on Color Texture of Compacts

This paper examines the effect of the granulation process on the color texture of compacted powders and granules. The objective is to obtain information to provide for a better comprehension of granulation mechanisms by using a pigment as a texture marker. This requires the establishment of a methodology both to qualify and quantify the spatial variation of color on the compact surface. This is achieved by color image analysis accompanied by both a statistical and a spatial treatment of the color content in the images.     

Effect of alkali metal on the properties of Bi-based glass powders prepared by spray pyrolysis

Bismuth-based glass powders with different quantities of Li₂O were directly prepared by high-temperature spray pyrolysis. The bismuth-based glass powders were completely spherical and submicron in size irrespective of the quantities of the Li₂O additive. The high optical transmittances of the dielectric layers formed from the glass powders obtained by spray pyrolysis were due to the decrease in the glass-transition temperatures of the glass powders with the addition of Li₂O. The ‘yellowing phenomenon’ was not observed in the dielectric layers formed from the glass powders obtained by spray pyrolysis, whereas it occurred in the dielectric layers formed from the glass powders obtained through the conventional melting process. PACS 42.70.Ce; 85.60.Pg; 71.55.Jv     

Ferroelectricity and ferromagnetism in fine-grained multiferroic BaTiO3/(Ni0.5Zn0.5)Fe2O4 composites prepared by a novel hybrid process

Dense, homogeneous, and fine-grained multiferroic BaTiO₃/(Ni_0.5Zn_0.5)Fe₂O₄ composite ceramics are synthesized by a novel powder-in-sol precursor hybrid processing route. This route includes the dispersion of nanosized BaTiO₃ ferroelectric powders prepared via conventional sold-state ceramic process into (Ni_0.5Zn_0.5)Fe₂O₄ ferromagnetic sol-gel precursor prepared via a sol-gel wet chemistry process. The composite ceramics show coexistence of obvious ferroelectric and ferromagnetic hysteresis loops at room temperature. Very low dielectric loss of about 0.02–0.0067 in the range of 10 kHz–10 MHz can be achieved, which is about an order of magnitude lower than the results of many reports using conventional processes at room temperature. The combination of high permeability and permittivity with low losses in the ceramics enables significant miniaturization of electronic devices based on the ceramics.     

The effects of high purity MgO nano-powders on the electrical properties of AC-PDPs

A major goal in plasma display panel technology is to reduce power consumption and increase efficiency. A candidate method to accomplish this goal is to increase the Xe content in discharge gases. However, this method has the weak point of increasing discharge voltages. High purity MgO powders made by the self-reaction method are adopted to overcome this disadvantage. From scanning electron microscope analysis, particles of the powders were observed to have very sharp edges, and the impurity content is very low according to inductively-coupled plasma mass spectrometry analysis. Moreover, the powders show a very high photo-induced electron emission and exo-electron emission, and have a very low concentration of oxygen vacancies by cathodoluminescence. Finally, the discharge voltage of high purity MgO powder-adopted films is reduced by about 34% compared to that of conventional films.     

Plasma spraying-an innovative coating technique: process variantsand applications

The use of plasma processing for spraying is reviewed, with emphasis on the material used, their sprayed structure, and successfully applied coatings. It is noted that new and further developments in plasma spray processes, spray devices, and spray materials have led to advantages in the realization of functional coatings and applications ranging from conventional to highly specialized industries. Different functions of the sprayed coatings can be achieved by choosing various plasma-process variations and any of a high number of useful coating materials. The plasma-spray process can be regarded as almost universal because of its inherently high process temperature, which allows almost unlimited combinations of coating and base material to be used     

Disodium terephthalate/multiwall-carbon nanotube nanocomposite as advanced anode material for Li-ion batteries

Organic small molecule materials have attracted extensive attention due to their environmentally friendly, sustainability, and low cost which can be obtained from biomass and recyclable resources for Li/Na-ion batteries. However, the intrinsic poor electronic conductivities and the dissolution in organic liquid electrolyte lead to poor electrochemical performance, thus preventing them from practical application. To tackle these issues, herein, we take disodium terephthalate (Na₂TP) as an example and report an organic/multiwall-carbon nanotube nanocomposite via a simple spray drying methodology as an anode material for Li-ion battery. It delivers improved electrochemical performance compared to the pristine Na₂TP microspheres produced by the same spray drying method and the bulk microsized Na₂TP prepared by a conventional water-crystallization method. This is mainly due to the as-prepared nanocomposite can shorten the Li-ion diffusion distance, form highly conductive network and slow the dissolution rate. Our simple methodology could be of interest designing newly organic composites.     

Bi-2223喷雾热分解粉末热处理工艺优化

Bi-2223 带材目前在电流引线、 超导电机、 超导电缆、 超导限流器等领域实现了许多示范性应用, 载流性能是表征其性能的重要指标, 而高质量的前驱体粉末是最终带材性能的关键保障. 本文选用具有工艺简单、 粉末效率高、 批次稳定性好等优点的喷雾热分解法制备的Bi-2223 前驱体粉末, 利用 TG-DSC、XRD、SEM 等测试手段对低氧条件下不同保温时间烧结的粉末进行分析, 并结合最终带材的载流性能测试结果, 获得了最优粉末烧结参数, 为后续喷雾热分解粉末的进一步生成 Bi-2223 相以及高性能粉末的制备提供了依据.     

High Pressure-Temperature Processing as an Alternative for Preserving Basil

In this study the effect of sterilisation by high pressure (HP) on the quality of basil was compared to conventional processing techniques. By means of freezing, or blanching followed by drying, microbial reduction of spores was maximal one-log. Pulsed HP-temperature treatment yielded a reduction of the natural occurring flora of more than 3 log CFU/g product. The essential oil content in basil consisted mainly of methylchavicol and linalool. HP sterilisation preserved these compounds in contrast to the equivalent conventional heat sterilisation process, which reduced the linalool and methylchavicol content to respectively 21 and 3% of the original amount. Drying and freezing also resulted in a significant reduction of the essential oil content.     

Effects of microwave drying on the microstructure and photocatalytic activity of bimodal mesoporous TiO2 powders

Bimodal nanocrystalline mesoporous TiO₂ powders with highly photocatalytic activity were prepared by a hydrothermal method using tetrabutylorthotitanate as precursor, and then dried in microwave oven. The prepared samples were characterized by XRD, SEM, TEM, HRTEM and N₂ adsorption-desorption measurement. The photocatalytic activity was evaluated by the photocatalytic degradation of acetone in air under UV light irradiation at room temperature. The effects of microwave drying on the microstructures and photocatalytic activity of the TiO₂ powders were investigated and discussed. The results show that microwave drying not only promotes the growth of the pores but also greatly reduces the state of agglomeration within the powders. All the microwave-dried TiO₂ powders show higher photocatalytic activity than Degussa P-25 (P25) and the TiO₂ powders dried by conventional method.     

Improvement of the properties of MnZn ferrite power cores through improvements on the microstructure of the compacts

In the present work freeze drying and wet-pressing technologies are applied and evaluated in the manufacturing process of functional ceramics such as MnZn power ferrites. In particular, the implementations of freeze drying instead of spray drying and the implementation of wet pressing instead of dry uniaxial pressing are investigated. It appeared that at high frequencies there is almost 25% power loss reduction by the implementation of freeze drying instead of spray drying. At low frequencies there is almost 23% power loss reduction by the implementation of wet pressing instead of dry pressing. By introducing wet pressing technology, MnZn ferrite materials exhibiting power losses of 210 mW cm⁻³ (100 kHz, 200 mT and 100 °C) could be synthesized. This is one of the lowest power loss values reported in the scientific or patented literature.     

Effects of powder flowability on the alignment degree and magnetic properties for NdFeB sintermagnets

The magnetic powders for sintered NdFeB magnets have been prepared by using the strip casting (SC), hydrogen decrepitation (HD) and jet milling (JM) techniques. The effects of powder flowability and addition of a lubricant on the alignment degree and the hard magnetic properties of sintered magnets have been studied. The results show that the main factor affecting powder flowability is the aggregation of magnetic particles for powders in a loose state, but it is the friction between the powder particles for powders that are in a compact state. The addition of a lubricant with suitable dose can slightly prevent the congregating of powders, obviously decrease the friction between the powder particles, improve the powder flowability, and increase the alignment degree, remanence and energy product density of sintered magnets. Mixing a suitable dose of lubricant and adopting rubber isostatic pressing (RIP) with a pulse magnetic field, we have succeeded in producing the sintered NdFeB magnet with high hard magnetic properties of B_r=14.57 KG, _jH_c=14.43 KOe, (BH)_max=51.3 MGOe.     

The effect of La-substitution on magnetic properties of nanosized Sr1−xLaxTi0.05Zn0.2(Fe)11.75−δ(Fe)δO19 powders

A series of La-substituted M-type Sr hexaferrite powders Sr_1−xLa_xTi_0.05Zn_0.2Fe³⁺_11.75O₁₉, wherein x ranges from 0.1 to 0.5 with a step of 0.1, have been prepared by the conventional ceramic method and were then milled in a high energy mill to prepare nanosized powders. XRD investigation of the calcined and the milled powders shows that single phase hexaferrite structure has been formed after calcining and has not changed after milling. The lattice parameters and the mean crystallite sizes of the samples have been determined from the XRD data and Scherrer's formula. The results show that the lattice parameters (“а” and “c”) decrease with increase in La-substitution and the mean crystallite size of the milled powders is about 17 nm. Coercivities and magnetizations of the samples in a magnetic field of 16 kOe have been determined from the room temperature hysteresis loops. It was found that both parameters increase with La substitutions up to 0.3 and then decrease for higher substitutions. These variations were attributed to the enhancement of hyperfine field and spin-canting magnetic structure when La content increases. In addition, the magnetizations were smaller for the nanosized samples in comparison with those of bulk ones, which were discussed according to the core-shell model. Also the results show that annealing of the nanosized samples up to 500 °C can enhance coercivity and magnetization of the samples, which is discussed based on crystallite size growth.     

Sintering properties of nanosized 90W–7Ni–3Fe composite powder

In order to study the sintering properties of nanosized 90W–7Ni–3Fe composite powder synthesized by spray drying-hydrogen reduction process, melting point and phase changes of nanometer 90W–7Ni–3Fe composite powder whose average particle sizes were in the range from 60 to 91 nm were measured by DTA, and sintering characteristic of specimens was studied at different sintering temperatures and times. Fracture morphology and W grain sizes of sintered specimens were measured by SEM and optical micrograph, respectively. Relative density, tensile strength and elongation of sintered specimens were also measured and analysed. The sintering temperature is lower than 80 °C in comparison traditional 90W–Ni–Fe powder. Mechanical properties are low because of appearance of cavities and vapour due to high oxygen content of nanosized 90W–7Ni–3Fe composite powder during liquid sintering.     

Effect of Dihydromyricetin on the Stability of Polypropylene in Natural Weathering Tests

Effects of dihydromyricetin (DMY), extracted from Ampelopsis grossedentata, on the antioxidantive properties of polypropylene were evaluated by investigating differences in mechanical properties and melt flowability between pre- and post-natural weathering tests. For comparison purposes, the effects of a synthetic phenolic commercial antioxidant (Irganox 1010) were also analyzed. The results showed that reduction in mechanical properties and increment in melt flowability of polypropylene containing DMY were slower than that of unstabilized reference during the aging process, which implies that DMY exhibits high efficiency as a thermal antioxidant for polypropylene. On the other hand, samples that contained Irganox 1010 obtained further improved stability over the samples containing DMY during 105 days; however, the effectiveness of DMY lasted longer than that of Irganox 1010. DMY has a characteristic of being harmless and having high activity, good stability, and abundant resources to be a good natural antioxidant.     

Synthesis of nanosized Si composite anode material for Li-ion batteries

A simple method was proposed to prepare nanosized Si composite anode materials for lithium-ion (Li-ion) batteries. The preparation started with the shock-type ball milling of silicon in liquid media of polyacrylonitrile (PAN)/dimethylformamide (DMF) solution, forming slurry where the nano-Si particles were uniformly dispersed, followed by the drying of the slurry to remove DMF. The nanosized Si composite anode material was obtained after the pyrolysis of the mixture at 300 °C where the pyrolyzed PAN provided a conductive matrix to relieve the morphological change of Si during cycling. As-prepared composite presented good cyclability for lithium storage. The proposed process paves an effective way to prepare high performance Si, Sn, Sb and their alloys based composite anode materials for Li-ion batteries.     

Characteristics and heat treatment of cold-sprayed Al-Sn binary alloy coatings

In this study, Al-Sn binary alloy coatings were prepared with Al-5 wt.% Sn (Al-5Sn) and Al-10 wt.% Sn (Al-10Sn) gas atomized powders by low pressure and high pressure cold spray process. The microstructure and microhardness of the coatings were characterized. To understand the coarsening of tin in the coating, the as-sprayed coatings were annealed at 150, 200, 250 and 300 °C for 1 h, respectively. The effect of annealing on microstructure and the bond strength of the coatings were investigated. The results show that Al-5Sn coating can be deposited by high pressure cold spray with nitrogen while Al-10Sn can only be deposited by low pressure cold spray with helium gas. Both Al-5Sn and Al-10Sn coatings present dense structures. The fraction of Sn in as-sprayed coatings is consistent with that in feed stock powders. The coarsening and/or migration of Sn phase in the coatings were observed when the annealing temperature exceeds 200 °C. Furthermore, the microhardness of the coatings decreased significantly at the annealing temperature of 250 °C. EDXA analysis shows that the heat treatment has no significant effect on fraction of Sn phase in Al-5Sn coatings. Bonding strength of as-sprayed Al-10Sn coating is slightly higher than that of Al-5Sn coating. Annealing at 200 °C can increase the bonding strength of Al-5Sn coatings.     

Sensible design of open-porous spherical architectures for hybrid supercapacitors with improved high-rate capability

Hybrid supercapacitors show high energy densities with good long-term cycling stability when used as energy sources. However, their poor rate performance as a consequence of their low ionic diffusion capability at high currents during cycling should be improved. Here, we propose using a spray-drying process to fabricate a novel structure comprising open-porous spherical lithium manganese oxide as an electrode material for hybrid supercapacitors. The resultant hybrid supercapacitor comprising full-cell systems shows a high specific capacitance (33.8 F cm⁻³ at a current of 1 A) and remarkable high-rate performance (25.6 F cm⁻³ at a current of 16 A). Moreover, outstanding cycling stability of 83% was attained at a current of 2 A after 5400 cycles. Our new strategy provides a useful methodology to increase the abundance of electrochemically active sites by fabricating a spherical structure using nanosized primary particles, which also leads to shorter diffusion pathways and to improved ionic electron transport because of the open-porous structure of the electrode materials.