无机盐对4A沸石晶化过程的影响

研究了添加无机盐氯化钠(NaCl)对4A沸石晶化速度以及粒度的影响。结果表明,添加一定量的NaCl并且随着NaCl加入量的增加,能够缩短4A沸石的晶化诱导期,加快晶化速率,减小4A沸石的粒度,使其粒度分布变窄。从电镜照片可以看出,加入NaCl合成的4A沸石晶体为正方形,晶体粒度比不加NaCl合成的4A沸石粒度小,并且随着NaCl加入量的增加,4A沸石晶体粒度明显减小。     

Microwave-assisted hydrothermal synthesis of zeolite films on ceramic supports

Zeolite films were formed on ceramic supports by a novel microwave-assisted hydrothermal method and were characterized by XRD, SEM, FTIR and BET surface area. The two-stage synthesis technique consists of microwave heating of supports saturated with precursor solution to form a thin layer of zeolite nano-seeds, followed by hydrothermal treatment to crystallize MFI zeolite. The resulting zeolite formation time was drastically reduced and the BET surface area of the product was double that obtained using conventional hydrothermal method. The dipping time, microwave heating time, power and hydrothermal heating time influence the amount of zeolite formation, the BET surface area and preferred orientation of the zeolite film. This new method of seed-film growth using a simple domestic microwave oven has the advantages of a two-stage synthesis technique, allowing independent control of nucleation and crystallization to obtain an optimum zeolite film and reduce the synthesis time.     

Optimization of crystal growth of hierarchical porosity ZSM-5 zeolite based on coal fly ash “waste utilization”

In this study, ZSM-5 zeolite with hierarchical porosity structure was synthesized by hydrothermal method using Al(OH)₃, SiO₂ extracted from coal fly ash as aluminum source and silicon source. The optimal synthesis parameters of ZSM-5 zeolite were determined via an orthogonal analysis table. The optimum synthesis conditions were: SiO₂/Al₂O₃/Na₂O/hexadecyltrimethylammonium bromide/tetrapropyl ammonium bromide/H₂O = 1/0.08/0.25/0.05/0.17/50, and the optimum crystallization temperature and crystallization time were 160 °C and 48 h, respectively. Scanning electron microscopy showed that the synthesized ZSM-5 zeolite exhibited a spherical shape. Nitrogen adsorption-desorption and Brunauer-Emmett-Teller measurement analysis displayed that the best sample ZSM-5 molecular sieve showed a typical type IV isotherm, and the micropores and mesopores coexisted in the sample, indicating the successful preparation of ZSM-5 zeolite with hierarchical porosity structure. The crystal growth of ZSM-5 under different hydrothermal conditions follows the “S” adjustment.     

Preparation and characterization of nano-NaX zeolite by microwave assisted hydrothermal method

In the present work, nano-NaX zeolite crystals were synthesized via microwave and conventional hydrothermal methods. The effects of reaction time, temperature and heating method on the characteristics of zeolite nanoparticles such as particle size, crystallinity, morphology, size distribution and surface area were investigated. The prepared NaX zeolite nanoparticles were characterized by the XRD, SEM, DLS, BET and XRF analysis. The results showed that both heating methods produced the NaX zeolite crystals with nano-in size. The microwave heating produced smaller zeolite nanoparticles with relatively narrower particle size distribution, required much shorter heating times and did not significantly change composition or crystallinity, compared with the conventional heating method. It was also observed that the time and temperature of microwave heating had significant effects on the prepared zeolite particles and the pure zeolite X nanoparticles or a mixture of zeolite X and A can be synthesized using the microwave heating method by control of the crystallization time and temperature.     

Crystallization behavior of phosphate glasses and its impact on the glasses’ bioactivity

The crystallization behavior of phosphate glasses of the composition 50P₂O₅–(40?x)CaO?xSrO–10Na₂O with x = 0, 20, and 40 was investigated using non-isothermal differential thermal analysis. The study was performed on three different size fractions (fine powder (<45 μm), intermediate (300–500 μm), and coarse particles (>500 μm)). The DTA thermograms recorded for all glasses exhibited a single and symmetrical crystallization peak. The position and shape of the crystallization varies with the particles size. The activation energy for crystallization, E _c, was calculated using equations proposed by Kissinger and Friedman. The calculated E _c values were similar for both techniques. E _c decreased with increasing the particle size for all glass compositions. The Johnson–Mehl–Avrami exponent n expressing the crystal growth dimensionality was quantified using the methods proposed by Augis–Bennett (AB) and Ozawa. In general, the AB method gave higher value than the Ozawa technique. For all glass composition the n value for the coarse powder suggested bulk crystallization whereas with decreasing particle size, the value of n indicated a complex surface crystallization. Glass monoliths were heat treated in electric oven at several temperatures for various times. XRD suggested crystallization of two phases: Ca(PO₃)₂ and NaCa(PO₃)₃ for the glass with x = 0, Sr(PO₃)₂ and NaSr(PO₃)₃ for the glass with x = 40, and a solid solution of (Ca,Sr)(PO₃)₂ and Na(Ca,Sr)(PO₃)₃ for the glass with x = 20. All crystals were found to preferentially nucleate and grow from the surface. Partially to fully crystallized glass particles were immersed in simulated body fluid for 24, 48, and 72 h. SEM/EDS of the particles and changes in the pH and ion concentrations of the solution (ICP-OES) suggested that crystallization prevents the CaP layer formation for all partially crystallized glasses.     

Size-controlled hydrothermal synthesis of monodispersed BaZrO3 sphere particles by seeding

Monodispersed barium zirconate (BaZrO₃) fine particles with a spherical shape have been synthesized by hydrothermal reactions using barium hydroxide and a Zr-triethanolamine (TEOA) complex. The particle mean diameter was gradually controlled in a range from 0.20 μm to 3.5 μm by change in the added amount of seed nanoparticles. The mechanistic characterization of the seed-mediated BaZrO₃ sphere synthesis revealed that the particle growth obeyed a simple seed growth mechanism. In the present system, utilization of the Zr-TEOA complex played an important rule to prevent uncontrollable nucleation to form the uniform BaZrO₃ fine particles with narrow size distributions.     

Facile synthesis and morphology control of zeolite MCM-22 via a two-step sol–gel route with tetraethyl orthosilicate as silica source

MCM-22 zeolite was synthesized via a two-step sol–gel route (low pH sol–gel reaction followed by high pH crystallization) under static hydrothermal conditions using tetraethyl orthosilicate (TEOS) as silica source. Various parameters that significantly influence the synthesis results during both the hydrolysis reaction of TEOS in acid media and the hydrothermal reaction in base media were investigated in detail. The produced samples were characterized by XRD, ICP, and SEM techniques. It is found that pure MCM-22 with high crystallinity can be obtained via the novel two-step sol–gel route in a broad window of reaction conditions. The increase of temperature and pH value for the hydrolysis of TEOS favors the shortening of crystallization time and decreasing of MCM-22 particle size. Moreover, by adjusting the hydrothermal reaction parameters, such as increasing the crystallization temperature, increasing the alkalinity of the synthesis gel mixture, and decreasing the SiO₂/Al₂O₃ ratio, the crystallization is accelerated substantially. Also, rose-like or lamellar-like morphologies of MCM-22 particles with different sizes can be achieved by changing these reaction parameters. Using this two-step sol–gel route, MCM-22 is able to be well produced in a wide range of the SiO₂/Al₂O₃ ratio from 20 to 100.     

Rapid synthesis of pure DD3R zeolite using ball-milled Sigma-1 seeds under static conditions

Deca-Dodecasil 3 Rhombohedral (DD3R) zeolite has great potential applications in the separation of gases with small molecular size; however, the extremely long crystallization time and the generated impure phases such as Sigma-Two (SGT) and Dodecasil 1H (DOH) have been the main obstacles for commercial utilization. In this work, ball-milled Sigma-1 was used as seeds for the first time to induce the crystallization of DD3R crystals. Pure DD3R zeolite was successfully produced under static conditions with drastically reduced crystallization time of ca. 9 h. The new synthesis approach showed 100 % of repeatability to obtain pure DD3R zeolite.     

Utilization of natural zeolite in aerated concrete production

In this study, natural zeolite (clinoptilolite) was used as an aggregate and bubble-generating agent in autoclaved aerated concrete (AAC) production. The crushed and grinded samples were classified into two different particle sizes: 100 μm (fine-ZF) and 0.5–1 mm (coarse-ZC) before using in AAC mixtures. The effects of particle size, replacement amount (25%, 50%, 75% and 100% against quartz) and curing time on the AAC properties were experimentally investigated. It was found that usage of natural zeolite, especially with a coarser particle size, has beneficial effect on the physical and mechanical properties of AAC. The optimum replacement amount was determined as 50% and at this rate the compressive strength, unit weight and thermal conductivity of AAC were measured as 3.25 MPa, 0.553 kg/dm³ and 0.1913 W/mK, respectively. Scanning electron microscopy analysis also confirmed the above findings. Denser C–S–H structures were obtained up to a replacement amount of 50%. Finally, the test results demonstrated that calcined zeolite acts as both an aggregate and a bubble-generating agent, and that AAC with a compressive strength of 4.6 MPa and unit weight of 0.930 kg/dm³ can be produced without aluminum powder usage.     

在泡沫碳化硅载体上原位生长silicalite-1型沸石晶体

以多晶硅颗粒为硅源, 在泡沫碳化硅载体上原位水热合成silicalite--1型沸石晶体。研究了硅颗粒加入量、NaOH浓度以及合成时间等因素对沸石晶体的负载量、晶体尺寸和沸石晶体/泡沫碳化硅复合材料比表面积的影响。结果表明,
以多晶硅颗粒为硅源控制硅酸根的释放速度, 使沸石晶体在碳化硅载体表面异质界面形核, 从而实现沸石晶体在泡沫碳化硅载体表面的连续生长; 当多晶硅量过少时, 溶液中的硅酸根浓度过低, 不能在载体表面形成连续生长的沸石层;
而当多晶硅量过大时, 溶液中硅的浓度过高, 部分沸石晶体在溶液当中形核, 使沸石晶体在载体表面的负载量下降; 提高溶液中NaOH的浓度, 加快硅的溶解, 使溶液中硅的饱和浓度升高, 沸石晶体的形核率也随之升高, 使沸石晶体的负载量增加。在最优条件下制备的silicalite--1/泡沫碳化硅复合材料其沸石晶体的比表面积为81.28 m²g^-1。     

Behavior of osteoblast-like cells on calcium-deficient hydroxyapatite ceramics composed of particles with different shapes and sizes

In designing the biomaterials, it is important to control their surface morphologies, because they affect the interactions between the materials and cells. We previously reported that porous calcium-deficient hydroxyapatite (HA) ceramics composed of rod-like particles had advantages over sintered porous HA ceramics; however, the effects of the surface morphology of calcium-deficient HA ceramics on cell behavior have remained unclear. Using a hydrothermal process, we successfully prepared porous calcium-deficient HA ceramics with different surface morphologies, composed of plate-like particles of 200–300, 500–800 nm, or 2–3 μm in width and rod-like particles of 1 or 3–5 μm in width, respectively. The effects of these surface morphologies on the behavior of osteoblast-like cells were examined. Although the numbers of cells adhered to the ceramic specimens did not differ significantly among the specimens, the proliferation rates of cells on the ceramics decreased with decreasing particle size. Our results reveal that controlling the surface morphology that is governed by particle shape and size is important for designing porous calcium-deficient HA ceramics.     

High-temperature and short-time hydrothermal fabrication of nanostructured ZSM-5 catalyst with suitable pore geometry and strong intrinsic acidity used in methanol to light olefins conversion

High temperature hydrothermal synthesis method was developed to preparation of nanostructured ZSM-5 molecular sieves at short crystallization time. A series of catalysts were synthesized at various temperatures and crystallization times for achievement of pure ZSM-5 phase with MFI structure. The synthesized catalysts were investigated with XRD, FESEM, EDX, BET-BJH, FTIR and TPD-NH₃ techniques. The results revealed that hydrothermal synthesis conditions generally affected the nucleation rate, particle size, textural properties and acidic nature of ZSM-5 catalysts. It was found that pure ZSM-5 materials with high crystallinity could be obtained at specific crystallization conditions of about 300?°C for 1.5?h and also 350?°C for 0.5?h. Increasing the hydrothermal temperature to 350?°C and decreasing the crystallization time to 0.5?h led to the formation of small particles with high specific surface area of 392?m²/g. Furthermore, ammonia TPD spectra showed that ZSM-5(300-1.5) catalyst contained higher amount of acid sites and less acid strength compared to ZSM-5(350-0.5) catalyst. The catalytic performance of samples was studied for conversion of methanol to light olefins under different reaction conditions. Interestingly, the proper pore geometry along with the strong intrinsic acidity resulted in a tendency for excessive production of light olefins for ZSM-5(350-0.5) catalyst. The selectivity of light olefins over this catalyst was increased about 94% in the long time on stream (2100?min). Also, the possible reaction pathway for ZSM-5 synthesis at high temperatures was discussed in details.     

Particle size distribution control and related properties improvements of tungsten powders by fluidized bed jet milling

Fine grinding process of different particle size tungsten powders was carried out by fluidized bed jet milling. The results showed that the jet milling treatment caused deagglomeration of tungsten powders, which led to particles sufficient dispersion and narrow particle size distribution. Grinding gas pressure of 0.70 Mpa made the particles achieve high speed which promoted the particles collision contributing to particle dispersion and shape modification. For tungsten powder with particle size of 3 μm FSSS, a higher packing density with 5.54 g/cm³ was obtained, compared with the 3.71 g/cm³ of the original powder. For tungsten powder with particle size of 1 μm FSSS, the big agglomerates disappeared and the particle size distribution become narrower, while small aggregates about 2–3 μm still exist after the jet milling process. For tungsten powder with particle size of 5 μm and 10 μm FSSS, different medium diameter particle size and narrow particle size distribution of monodisperse tungsten powders can be produced by the optimized jet milling parameters. More important, the effective dispersion, favorable shape modification and precise classification have been achieved in the simple process.     

Sodium dodecyl benzene sulfonate-assisted synthesis through a hydrothermal reaction

The effects of the anionic surfactant on the morphology, size and crystallization of NiSe precipitated from NiCl₂·6H₂O and SeCl₄ in presence of hydrazine (N₂H₄·H₂O) as reductant were investigated. The products have been successfully synthesized in presence of sodium dodecyl benzene sulfonate (SDBS) as surfactant via an improved hydrothermal route. A variety of synthesis parameters, such as reaction time and temperature, capping agent and amount of reducing agent have a significant effect on the particle size, phase purity and morphology of the obtained products. The sample size became bigger with decreasing reaction temperature and increasing reaction time. In the presence of 2 ml hydrazine, the samples were found to be the mixture of Ni₃Se₂ and NiSe. With increasing the reaction time and amount of hydrazine a pure phase of hexagonal NiSe was obtained. X-ray diffraction analysis (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM) images indicate phase, particle size and morphology of the products. Chemical composition and purity of the products were characterized by X-ray energy dispersive spectroscopy (EDS). Photoluminescence (PL) was used to study the optical properties of NiSe samples.     

Recovery and removal of fluoride from fluorine industrial wastewater by crystallization process: a pilot study

Recovering fluoride from wastewater has large economic and environmental significance within the fluorine industry. A novel crystallization process was proposed for the recovery and the removal of fluorine-containing industrial wastewater by steps. A pilot-scale reaction-separation integrated reactor was used to recover the sandy cryolite via crystallization. A pilot-scale fluidized bed reactor was used to recover the sandy calcium fluoride via crystallization. The results showed that the recovery rate of cryolite was greater than 70%, with a purity of more than 89%. The qualities of cryolite products could meet the national standard for synthetic cryolite in China. The purity of the calcium fluoride was greater than 71%, with a particle size of 153.1 μm, and a water content of 27%. The qualities of calcium fluoride products could meet the national standard of comminuted fluorspar in China. Both the cryolite products and the calcium fluoride products could be reused as raw materials. The fluoride concentration of the wastewater was less than 10 mg/L, which met the national discharge standard in China.     

Dependence of thermal conductivity in micro to nano silica

This work presents the measurement of thermal conductivity of nano-silica particles using needle probe method. The validation test of thermal probe was conducted on ice and THF hydrates using our experimental set up and the results are satisfactory when compared with the literature data. The nano silica used in this study is with particle sizes in the range 50–1000 nm. The sand powders sieved in different sizes ?<75 and 75  μ m ?>? d ?>? 250  μ m were also studied to probe the particle size dependence on thermal conductivity. Thermal conductivity decreased by about 70% in silica nano powders.     

以聚乙二醇为模板凝胶转化制备介孔ZSM-5沸石及其催化性能

以聚乙二醇为介孔导向剂, 通过凝胶转化制备了介孔ZSM-5沸石。研究表明, 在TPA⁺/SiO₂=0.1时经过9~15 h溶剂挥发制得的凝胶, 在160℃处理24 h可得到介孔ZSM-5沸石; 挥发时间太短或太长会得到纯的ZSM-5沸石或介孔材料, 说明在凝胶的制备过程中, 通过控制溶剂的挥发程度, 既可为沸石生长过程提供所需的水分, 又能避免沸石晶体形成过程中无定型相的产生, 从而在较低的TPA⁺浓度下获得介孔ZSM-5沸石。与传统的ZSM-5沸石相比, 利用该方法制备的介孔ZSM-5沸石不仅具有微孔/介孔多级孔结构, 同时具有沸石材料较强的酸性、较高的水热稳定性和择形催化性能, 使其在苯甲醛与正丁醇的大分子醇醛缩聚反应中能有效地克服传统沸石孔径限制的缺点, 收率高达42.4%。     

Synthesis of superparamagnetic ZnFe2O4 nanoparticle by surfactant assisted hydrothermal method

Zinc ferrite (ZnFe₂O₄) ultrafine powder was synthesized by hydrothermal method using various amounts of cetyltrymethylammonium bromide (CTAB) as a surfactant. The phase purity, thermal stability, morphology, size and magnetic properties of the final products were studied. All the synthesized products were possessing normal spinel structure without any impurities. The crystalline size of synthesized products decreased with the increasing amounts of surfactant. Particles had narrow size distribution with an average particle size of 6.5 nm for 1.5 g of CTAB. Magnetic characterizations revealed that the synthesized products were superparamagnetic in nature.     

Microstructural, electrical, and mechanical characterization of Bi2Cu0.1V0.9O5.35 (BICUVOX) ceramics fabricated from co-precipitated precursor powders

Copper-doped bismuth vanadate (Bi₂Cu_0.1V_0.9O_5.35, BICUVOX) was synthesized by a co-precipitation process which resulted in a homogenous, fine-grained powder with an average particle size of ~0.45 μm. The consolidated BICUVOX powder was sintered at temperatures between 625 and 800 °C for 0–8 h in air. The correlation between the thermal processing schedule and the final microstructure were completed for all conditions through stereological analysis of the resultant cross-sectional scanning electron microscope images. From this work, the sintering schedule of 675 °C for 1 h resulted in acquiring a BICUVOX ceramic microstructure that displayed ~97 % relative density with an average grain size of ~1.29 μm. This processing condition was ~75–125 °C lower than typical sintering temperatures for the same density, and resulted in a final grain size that is ~5–10 μm smaller in size. The four-point conductivity testing of the BICUVOX ceramics in air showed values of ~0.003–0.007 and ~0.07–0.12 S/m at 300 °C and 500 °C, respectively, depending upon the thermal processing schedule. The average flexure strength of the same BICUVOX membrane was measured using a ring-on-ring configuration, and this measurement showed flexural strengths as high as 159.3 MPa. This strength is ~92 % greater than previously reported values for BICUVOX membranes.     

Preparation of surfactant templated nanoporous silica spherical particles by the Stöber method. Effect of solvent composition on the particle size

Monodispersed nanoporous silica spherical particles with the particle size ranges from 0.01 μm to 1.5 μm were successfully prepared by the Stöber method combined with supramolecular templating approach. The particles formed from homogeneous solutions containing tetraethoxysilane, cetyltrimethylammonium chloride, methanol, and aqueous ammonia solution at room temperature. In the present study, methanol/tetraethoxysilane ratio was the factor to control the particle size. With increasing the methanol/tetraethoxysilane ratios from 1,125 to 6,000, particle size decreased from 1.5 μm to 0.01 μm. The calcination of the particles resulted in the spherical porous silicas with the average pore sizes of around 2.0 nm irrespective of the particle size. The particle morphology retained after the calcination.