Preparation and characterization of some multicomponent silicate glasses and their glass–ceramics derivatives for dental applications

The chemical corrosion and UV–vis absorption and infrared absorption spectra of binary and multicomponent lithium silicate glasses and corresponding glass–ceramics were investigated. The chemical durability of the glasses and derived glass–ceramics was found to be excellent to all leaching media. The IR absorption spectra of the glass and glass–ceramic samples reveal absorption bands of characteristic groups mainly due to major silicate network besides the possible sharing of network units due to some involving oxide constituents. X-ray analysis of glass–ceramics indicates the separation of lithium disilicate phase as the main constituent beside other phases according to the specimen chemical constituents. The obvious promising investigated chemical and physical properties are correlated with the presence of multioxides such as Al₂O₃, TiO₂, MgO and ZrO₂. Transmission and reflectivity properties reveal acceptable data. The prepared glass–ceramics are recommended for dental applications.     

Fabrication,characterization and cellular biocompatibility of porous biphasic calcium phosphate bioceramic scaffolds with different pore sizes

Facile wet-chemical methods are applied to synthesize hydroxyapatite and β-tricalcium phosphate nanoparticles, respectively. Porous biphasic calcium phosphate (BCP) bioceramic scaffolds are then fabricated using as-prepared HA and β-tricalcium phosphate nanoparticle powders. The macro pore diameter of BCP bioceramic scaffolds can be controlled by adjusting the amount of surfactants. The average diameter of the macro pores in BCP bioceramic scaffolds increases from 100 to 600 µm with the decrease amount of sodium dodecyl sulfate from 0.8 to 0.5 g, respectively. The BCP bioceramic scaffolds gradually degrade and the calcium-phosphate compounds fully deposit when soaking in simulated body fluid solution. Moreover, The BCP bioceramic scaffolds have outstanding biocompatibility to promote the cellular growth and proliferation of human dental pulp stem cells (hDPSCs). The hDPSCs also demonstrate favorable cellular adhering capacity on the pore surface of scaffolds, especially on the scaffolds with 100–200 µm pore diameter. The porous BCP bioceramic scaffold with inter-connected pore structure, outstanding in vitro cellular biocompatibility, favorable cell viability and adhesion ability will be a promising biomaterial for bone or dentin tissue regeneration.     

Improved mechanical strength and thermal resistance of porous SiC ceramics with gradient pore sizes

Thermal insulation applications of porous SiC ceramics require low thermal conductivity and high mechanical strength. However, low thermal conductivity and high mechanical strength possess a trade-off relationship, because improving the mechanical strength requires decreasing the porosity, which increases the thermal conductivity. In this study, we established a new strategy for improving both the mechanical strengths and thermal resistances of porous SiC ceramics with micron-sized pores by applying a double-layer coating with successively decreasing pore sizes (submicron- and nano-sized pores). This resulted in a unique gradient pore structure. The double-layer coating increased the flexural strengths and decreased the thermal conductivities of the porous SiC ceramics by 24–70 % and 29–49 % depending on the porosity (48–62 %), improving both their mechanical strengths and thermal resistances. This strategy may be applicable to other porous ceramics for thermal insulation applications.     

不同孔径Ni-MCM-41催化剂及用于甲烷部分氧化反应的研究

通过添加1,3,5-三甲苯(TMB)溶胀剂制备不同孔径的Ni-MCM-41催化剂,采用XRD、N_2吸附-脱附、H_2-TPR、FTIR、TGA对制备的催化剂进行表征,并考察孔径大小对甲烷部分氧化制合成气催化性能的影响。结果表明,在四种不同孔径中,TMB/CTAB=3时,更有助于提高催化剂的抗积碳能力。在温度750℃,空速18 L/(g·h)的条件下,3TA的催化剂在反应中的催化效果最佳,CH_4转化率达90%,CO选择性达89%。     

不同孔径Ni-MCM-41催化剂及用于甲烷部分氧化反应的研究

通过添加1,3,5-三甲苯(TMB)溶胀剂制备不同孔径的Ni-MCM-41催化剂,采用XRD、N_2吸附-脱附、H_2-TPR、FTIR、TGA对制备的催化剂进行表征,并考察孔径大小对甲烷部分氧化制合成气催化性能的影响。结果表明,在四种不同孔径中,TMB/CTAB=3时,更有助于提高催化剂的抗积碳能力。在温度750℃,空速18 L/(g·h)的条件下,3TA的催化剂在反应中的催化效果最佳,CH_4转化率达90%,CO选择性达89%。     

Interactions of dynamic supercritical CO2 fluid with different rank moisture-equilibrated coals:Implications for CO2 sequestration in coal seams

The interactions between CO2 and coals during CO2-ECBM (CO2 sequestration in deep coal seams with enhanced coal-bed methane recovery) could change pore morphology and chemistry property of coals,thereby affecting adsorption,diffusion and flow capability of CO2 and CH4 within coal reservoirs.To sim-ulate CO2-ECBM process more practically,the dynamic interactions of supercritical CO2 (scCO2) and moisture-equilibrated coals were performed at temperature of 318.15 K,pressure of 12.00 MPa,and duration of 12.00 h.The impacts of the interactions on physicochemical properties of coals were inves-tigated.Results indicate that scCO2/H2O exposure shows minor effect on micropores of coals.However,the exposure significantly decreases the mesopore surface area of bituminous coals,while increases that of anthracites.The mesopore volume and the average mesopore diameter of all the coals after scCO2/H2O exposure decrease.The multi-fractal analysis verifies that the scCO2 exposure can enhance the pore con-nectivity of various rank coals.Apart from the pore morphology,the exposure of scCO2/H2O also affects the oxygenic functional groups on coal surface.Particularly,the exposure of scCO2/H2O reduces the con-tent of C-O and C=O of coals.The content of COOH of low rank coals including Hehua-M2# coal,Zhongqiang-4# coal,Buliangou-9# coal and Tashan-5# coal decreases,while the high rank Laochang-11# coal and Kaiyuan-9# coal witness a growth in COOH.The content of total oxygenic functional groups of all coals after interaction with scCO2/H2O decreases;on the contrary,that of C-C/C-H of all coals after SCCO2/H2O exposure increases.In summary,the interaction with SCCO2/H2O significantly changes the pore system and oxygenic functional groups of various rank coals,which needs further attention regard-ing CO2-ECBM.     

Preparation of microporous chlorinated poly(vinyl chloride) membrane in fabric and the characterization of their pore sizes and pore‐size distributions

Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, d_p, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (R_m) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002     

Preparation of carbon aerogels with different pore structures and their fixed bed adsorption properties for dye removal

Controlled porosity carbon aerogels are prepared by a sol–gel polymerization method and the prepared materials are used as fixed bed adsorbents for dye removal. The influences of operating conditions and preparation factors on the adsorption of C. I. Reactive Red 2, as a model compound, from aqueous solution were investigated. Many column parameters were estimated at different stages and the Bed-Depth-Service-Time model was used to analyze the experimental data. The results showed that the adsorption bed capacity increased with increasing bed height, decreasing liquid flow rate and decreasing initial dye concentration. Moreover, the work indicated that the adsorption ability of the carbon aerogel could be controlled by adjusting the molar ratio of resorcinol to surfactant and carbonization conditions. In addition, the adsorption capacity could be improved when the carbon aerogel was activated by CO₂. The reasons for the difference in adsorption ability could be related to the different pore structure characteristics of various samples.     

Experimental study of CO2 hydrate formation in porous media with different particle sizes

To investigate the effect of the particle size of porous media on CO₂ hydrate formation, the formation experiments of CO₂ hydrate in porous media with three particle sizes were performed. Three kinds of porous media with mean particle diameters of 2.30 μm (clay level), 5.54 μm (silty sand level), and 229.90 μm (fine sand level) were used in the experiments. In the experiments, the formation temperature range was 277.15–281.15 K and the initial formation pressure range was 3.4–4.8 MPa. The final gas consumption increases with the increase in the initial pressure and the decrease in the formation temperature. The hydrate formation at the initial formation pressure of 4.8 MPa in 229.90 μm porous media is much slower than that at the lower formation pressure and displays multistage. In the experiments with different formation temperatures, the gas consumption rate at the temperature of 279.15 K is the lowest. In 2.30 and 5.54 μm porous media, the hydrate formation rates are similar and faster than those in 229.90 μm porous media. The particle size of the porous media does not affect the final gas consumption. The gas consumption rate per mol of water and the final water conversion increase with the decrease in the water content. The induction time in 5.54 μm porous media is longer than that in 2.30 and 229.90 μm porous media, and the presence of NaCl significantly increases the induction time and decreases the final conversion of water to hydrate.     

Preparation of cellulose adsorbents with ionic liquid and pore expansion for chromatographic applications

Chromatography is a widely used technique in protein separation, and the adsorbents are essential to separate target proteins from raw mixtures. In this study, porous cellulose beads were prepared with a direct dissolution of microcrystalline cellulose (MCC) using an ionic liquid solvent 1‐butyl‐3‐methylimidazolium chloride. Pore expanding agents (cassava starch and cyclohexane) were added in MCC solutions to change the pore structure of the cellulose beads. The results showed that the mean pore size of cellulose beads increased after the application of pore expanding agents, whereas the wet density and the specific surface area were decreased. Residence time distribution studies indicated that the beads prepared with the addition of cyclohexane had the best performance for a series of molecules with different molecular weights. The cellulose beads were coupled with diethylaminoethyl and the adsorption properties with bovine serum albumin as a model protein showed that the beads prepared with cyclohexane had the best protein adsorption capability. The chromatographic results demonstrated that ionic liquids are effective solvents for cellulose dissolution and pore expanding agents can be used to enhance the pore structure of cellulose beads. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40060.     

Preparation and characterization of aluminum borate whiskers reinforced ceramics with MnO2 addition

Ceramics with aluminum borate whiskers (ABWs) were prepared from H₃BO₃ and Al₂O₃ reagent, with and without 6 wt% MnO₂ used as an addition. The microstructures, phase composition, and crystal structure of the ceramics were analyzed via scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction, respectively. The results show that MnO₂ is an effective addition for enhancing the flexural strength of ceramics. The MnO₂ could lead to the distortion of lattice, and improve the mechanical strength via a solid solution strengthening mechanism. Moreover, the content of H₃BO₃ and the sintering temperature were also key factors in the manufacture of optimal ceramics. The ceramic made from 6 wt% MnO₂ addition, 25 wt% H₃BO₃, and sintered at 1200°C, showed the highest flexural strength of 88.5 (±1.9) MPa, and had a bulk density of 1.64 g/cm³ and porosity of 44.2%.     

ZrO2 ceramics with aligned pore structure by EPD and their characterisation by X-ray computed tomography

Using the electrolytic gas generation during the electrophoretic deposition (EPD) from aqueous suspensions, planar zirconia green bodies with unidirectionally aligned pore channels were produced. Number, diameter distribution, and arrangement of the pore channels could be controlled by the experimental conditions such as the electrolyte content of the suspension, the applied electric field strength, and the kind of the deposition electrode. The green bodies were sintered at 1450 °C in air. Besides optical microscopy and mercury porosimetry, X-ray computed tomography was used for characterising the porous samples. The CT investigations were well suited for this purpose because they enabled a three-dimensional characterisation of the pore structure by a non-destructive method.     

Preparation and characterization of transparent magneto-optical Ho2O3 ceramics

Transparent magneto-optical Ho₂O₃ ceramics were successfully prepared with an in-line transmittance of ~73% at the wavelength of 1000 nm (~90% of the theoretical transmittance of Ho₂O₃ single crystal) and an average grain size of ~28 μm. The ceramics were fabricated using sulfate-exchanged nitrate-type layered rare-earth hydroxide as the precipitation precursor at a relatively low sintering temperature of 1700°C. The layered compound exhibited nanosheet morphology and fully collapsed into a round oxide powder with an average particle size of ~48 nm by pyrolysis. Calcination temperature for Ho₂O₃ powder significantly affected the optical quality of the sintered body and the optimum calcination temperature was found to be 1050°C. The transparent magneto-optical Ho₂O₃ ceramics displayed wavelength-dependent Verdet constants of −180, −46, and −20 rad/Tm at 632, 1064, and 1550 nm, respectively. Thus, the Ho₂O₃ ceramics show good potential for applications in high-power laser systems.     

Collection efficiency of airborne fibers on nylon mesh screens with different pore sizes and configurations

Aerodynamic behavior of airborne fibers including high-aspect ratio particles plays an important role in aerosol filtration and lung deposition. Fiber length is considered to be an important parameter in causing toxicological responses of elongate mineral particles, including asbestos, as well as one of the factors affecting lung deposition. In order to estimate the toxicity of fibers as a function of fiber length, it is required to separate fibers by length and understand mechanisms related to fiber separation for use in toxicology studies. In this study, we used nylon mesh screens with different pore sizes as a separation method to remove long fibers and measured screen collection efficiency of glass fibers (a surrogate for asbestos) as a function of aerodynamic diameter with the aim to prepare toxicology samples free of long fibers and/or harvest long fibers from the screen. Two screen configurations ([i] without a laminar flow entrance length, and [ii] with the entrance length) were tested to investigate the effect of screen pore size (10, 20, and 60 µm) and screen configuration on collection efficiency of fibers. Screen collection efficiency (η) was obtained based on measurements of downstream concentrations of a test chamber either without or with a screen. The results showed that screen collection efficiency increases as screen pore size decreases from 60 to 10 µm for both cases with and without entrance lengths. For the screen configuration without entrance length, higher collection efficiency was obtained than the case with entrance length probably due to increased impaction caused by the close proximity of inlet to screen. In addition, the difference between the collection efficiencies for the different configurations was small in the aerodynamic size range below 3 µm while it increased in the size range from 3 to about 7 µm, indicating that as large aerodynamic diameter is associated with longer fibers, some differential selection of fibers is possible. Modified model collection efficiency for 10 and 20 µm screens based on the interception predicts well the measured data for the case with entrance length, indicating that the fiber deposition on these screens occurs dominantly through the interception mechanism in the micrometer size range under a given flow condition.     

Preparation and characterization of GDC-Li2SO4/Li2CO3 nanocomposite electrolytes for applications in intermediate solid oxide fuel cells

Gd_0.1Ce_0.9O_1.95/Li₂CO₃-Li₂SO₄ (GDC/LCS) nanocomposite electrolytes were prepared through nano-powders mixing, prefiring and sintering operations. The phase components and microstructures of the as-prepared nanocomposite were characterized by XRD, FESEM, TG-DSC and IR spectroscopy. AC impedance spectroscopy and DC polarization method were utilized to measure their electrical conductivities under different conditions. It has been found that the GDC/LCS nanocomposite have a very homogeneous microstructure, where the LCS is mostly in amorphous state due to the strong interfacial interactions between the GDC and LCS. In addition, their overall electrical conductivity was found to increase with temperature in air, featured with a sharp activation energy change from 1.01 to 0.30 eV around 520 °C, and reach 108.7 mS/cm at 600 °C, while their protonic and oxide ionic conductivities were 16 mS/cm in H₂ and 5 mS/cm in air at the same temperature, respectively. The single cell built up of the GDC/LCS nanocomposite showed an open-circuit voltage of 1.01 V and peak power density of 272 mW/cm² at 600 °C.     

Preparation and characterization of corundum ceramics doped with Fe2O3 and TiO2 for high temperature thermal storage

High-temperature thermal storage materials have received urgent attention for efficient thermal transfer in solar thermal power generation. Corundum ceramics doped with Fe₂O₃ and TiO₂ were prepared via a pressureless sintering. A Fe₂O₃–TiO₂ system with different Fe₂O₃/TiO₂ ratios was applied to corundum ceramics. Phase composition, microstructural evolution, sintering properties, high temperature resistance and thermophysical properties were evaluated. The results indicated that Fe₂O₃ and TiO₂ rendered the grains highly active and enhanced the bonding between grains due to existing stably in the lattice of corundum. In addition, decrease in the Fe₂O₃/TiO₂ ratio led to a new phase of FeAlTiO₅, which refined the grains. These effects gave the samples good sintering properties and thermal shock resistance, but the thermal expansion coefficient mismatch between FeAlTiO₅ and corundum deteriorated the high-temperature (1300 °C) stability. Formula C1 (Fe₂O₃/TiO₂ ratio of 9:1) sintered at 1600 °C had the optimum comprehensive properties, possessing a bending strength loss rate of 1.54% after 30 cycles of thermal shock (1100 °C-room temperature, air cooling) and a constant strength retention rate of approximately 71.34% after 90 h high-temperature cycle. The corresponding thermal conductivity and specific heat capacity were 18.81 W/(m·K) and 1.02 J/(g·K) at 25 °C, which was suitable as a high-temperature thermal storage material.     

Ultralow temperature cofired BiZn2VO6 dielectric ceramics doped with B2O3 and Li2CO3 for ULTCC applications

In this paper, BiZn₂VO₆ doped with sintering aids of B₂O₃ and Li₂CO₃ is investigated in order to broaden the options for ultralow temperature cofired ceramics (ULTCC). The sintering behavior, microstructure, and microwave dielectric properties are studied. In combination with 1 wt% B₂O₃ and 5 wt% Li₂CO₃ dopants, the sintering temperature of the BiZn₂VO₆ ceramics was reduced from 780°C to 600°C. The co-doped BiZn₂VO₆ ceramics exhibited a low relative permittivity (ε_r) of 8.9 and a quality factor (Q × f) of 13 000 GHz at a microwave-range frequency of 9 GHz. The temperature coefficient of resonant frequency (τ_f) was measured to be −97 ppm/°C. The average linear coefficient of thermal expansion (CTE) was 7.2 ppm/°C. With the low sintering temperature, the co-doped BiZn₂VO₆ ceramics are compatible to be cofired with cost-effective aluminum electrodes. This was proven in a reaction test between the BiZn₂VO₆-B₂O₃-Li₂CO₃ and aluminum powders, in which no chemical interaction could be detected. These promising properties make the B₂O₃-Li₂CO₃ co-doped BiZn₂VO₆ an ideal candidate for ULTCC applications.     

Preparation of porous Y2SiO5 ceramics with high porosity and extremely low thermal conductivity for radome applications

It is well known that aqueous gel-casting is challenging to prepare high-porosity ceramics due to the considerable drying shrinkage, cracking, and deformation of green bodies during drying caused by the high surface tension of water. Porous Y₂SiO₅ ceramics with high porosity were prepared by introducing carbon fibers as a support material in the drying process of aqueous gel-casting to reduce shrinkage during drying. Burning out the carbon fibers after drying does not negatively affect the properties of the porous ceramic. As prepared green bodies by aqueous gel-casting have low shrinkages of 8.69%–6.81% during drying processes and high compressive strength of 13.73 ± 1.55–10.66～0.49 MPa. The higher compressive strength of the green body has a positive significance for processing porous ceramics into special-shaped structures. As prepared porous Y₂SiO₅ ceramics have high porosity of 73.94%–87.71%, lightweights of 1.16–0.55 g?cm³, extremely low thermal conductivities of 0.134 ± 0.006 to 0.051 ± 0.001 W?m^?1?k^?1, relatively low dielectric constants of 2.34–1.58, and tan δ are lower than 1.25 × 10^?3. Porous Y₂SiO₅ ceramics with excellent dielectric properties and thermal insulation properties meet the requirements of thermal insulation and wave transmission integration of radome materials. Aqueous gel-casting also enriches the preparation methods of high-porosity Y₂SiO₅ ceramics.     

Preparation of Nd-doped Ba2Ti9O20 ceramics for use in microwave applications

Densification behaviour, the resulting microstructure and dielectric properties of Nd-doped Ba₂Ti₉O₂₀-based ceramics were investigated. It was observed that with Nd-doping reaction sintering resulted in lower porosities than with normal two-stage processing. The phases identified at all levels of Nd-doping, for both prefired and reaction sintered materials, namely 0·5, 2·6, 5·0 and 10 wt%, could be classified into three main categories—BaTi₄O₉ (BT₄, Ba₂Ti₉O₂₀ (B₂T₉) and the Nd-rich phases. The changes in the dielectric properties caused by Nd-doping can be interpreted as a consequence of the different properties of this Nd-rich phase. Increasing the Nd-content resulted in an increase of the positive temperature coefficient of the resonant frequency, a higher dielectric constant, and also a lower Q-value. Products made without the prefiring stage were found to contain a substantially larger number of flaws and microcracks, and hence are not best suited for use as dielectric materials.