Fumed silica is one of the most commonly used fillers for dental resin adhesives. However, fumed silica produced by flame hydrolysis of chlorosilanes are typically agglomerated aggregates instead of isolated primary particles. The fumed silica aggregates may affect the dispersion of fillers in the resin matrix, thus affect the bonding performance of the dental adhesives. In this study, fumed silica fillers chemically treated with methacrylsilane were loaded into an etch & rinse model dental adhesive. Filler 1 was only chemically pre-treated, while Filler 2 was combined chemically and mechanically pre-treated to break the agglomerated aggregates. The experiment result indicated that Filler 1 has faster rheology control effect than Filler 2 on the handling property of the filled resin adhesive showing as the rapid increased viscosity, which may due to the fast inorganic phase growing in the Filler 1 filled resin matrix. As for the mechanical properties, neither Filler 1 nor Filler 2 has an positive effect on the micro-tensile bond strength in short term and long term, despite of the fact that lower weight percent of Filler 2 loading is favourable to the penetration of the experimental adhesive into dentin substrate. In conclusion, mechanically pre-treatment to break the agglomerated fumed silica is helpful to increase the limit of filler loading percent while maintaining appropriate handling property, but the chemically and mechanically pre-treatment cannot provide positive effect on bonding performance within the range of this study. 相似文献
MgO–Al–C slide plate refractories were fabricated using sintered magnesia and modified sintered magnesia as aggregates, fused magnesia aggregates and fines, Al powder and carbon black (N220) as fines, and thermosetting phenolic resin as the binder. Al powder-modified magnesia aggregates were prepared and characterized and were introduced into the MgO–Al–C slide plate refractories. The effects of the modified aggregates on the properties, phase composition, and microstructure were investigated. 1) The Al powder-modified magnesia aggregates exhibited considerably high bonding strengths and low Al powder shedding ratios, thus meeting the preparation requirements of MgO–Al–C slide plate refractories. 2) At high temperatures, more needle-like and fibrous Al4C3, AlN and octahedral MgAl2O4 were generated on the surface of the modified magnesia aggregates, which enhanced the bond between the matrix and the aggregates and increased the hot modulus of rupture of the material. 3) Non-oxide Al4C3 and AlN phases were formed in situ and had high thermal conductivity and low coefficient of expansion; this could relieve the internal thermal stress of the material and create a toughening effect, improving the thermal shock resistance of the material. 相似文献
The shear strength parameters property of rock-soil aggregates in embankment slope of reservoir, that is, the relationship
between cohesion and gravel content, between friction angle and gravel content, and the relationship between cohesion and
water content, between friction angle and water content, is studied based on the direct shear test results, the shear strength
change law of the rock-soil aggregates is given, and the unsaturated shear strength formulation of rock-soil aggregates that
could consider suction and saturation degree influence is put forward in this paper, through which the sliding or failure
physical mechanism of this type of slope under the condition of rainfall infiltration is studied. Also the 3D unsteady saturated-unsaturated
seepage field and its FEM resolving mode are established based on the analysis of the slope rainfall infiltration process.
Case study with this method indicates that the minimum safety factor of the accumulated rock-soil aggregates dose not arrive
at the moment of rainfall cessation, but appears several hours after the rainfall cessation, this phenomenon is in accordance
with the practical slope engineering’s failure process and could explain appropriately the slope failure caused by rainfall
infiltration. Research results in this paper have an important reference value for the research on stability of the accumulated
rock-soil aggregates in embankment slope of reservoir, and can enrich the stability analysis method and relevant theory of
reservoir embankment slope.
Supported by the National Natural Science Foundation of China (Grant Nos. 50539010, 50539110, 50809025, 50539030-1-3), National
Science and Technology Support Plan of China (Grant Nos. 2006BAC14B03, 2008BAB29B06, 2008BAB29B03), Opening Fund of Geotechnical
Mechanic and Engineering Key Laboratory of the Ministry of Water Recourses of China (Grant No. G07-03), Science and Technology
Support Project of China Hydropower Engineering Consulting Group Co. (Grant No. CHC-KJ-2007-02), Special Scientific Research
Fund of Doctor Subjects of Colleges and Universities: Research on Diagnosis Method of Concrete Dam Crack Transferring 相似文献
Water-soluble polyaramides have been prepared from 2,5-diaminobenzene-sulphonic-acid activated by TMSCl and terephthalic-acid-chloride. Using this method, we achieved molecular weights of our polymers up to 18,000 g mol−1. Two model compounds were synthesized in order to establish the effect of trimethylsilyl-chloride, which was used as the activating agent for this reaction. The resulting sulphonated poly-aramides were characterized by: inherent viscosity measurements, size exclusion chromatography (SEC), DMA, TGA, flame absorbance atomic spectroscopy (FAAS), NMR spectroscopy and optical polarisation microscopy. In all cases, the polymers were easily soluble in hot water up to concentrations of 20 wt%. Upon cooling lyotropic alignment of molecular aggregates is observed at low polymer concentrations, typically 2–5 wt%. Polymers with low molecular weights do not show this behaviour. Films made from these sulphonated aramide polymers showed good thermal stability, and have interesting mechanical properties. Our results indicate the presence of a structure consisting of molecular aggregates. 相似文献
In this paper, we report the development of a java application for the Superposition T-matrix code, JaSTA (Java Superposition T-matrix App), to study the light scattering properties of aggregate structures. It has been developed using Netbeans 7.1.2, which is a java integrated development environment (IDE). The JaSTA uses double precession superposition codes for multi-sphere clusters in random orientation developed by Mackowski and Mischenko (1996). It consists of a graphical user interface (GUI) in the front hand and a database of related data in the back hand. Both the interactive GUI and database package directly enable a user to model by self-monitoring respective input parameters (namely, wavelength, complex refractive indices, grain size, etc.) to study the related optical properties of cosmic dust (namely, extinction, polarization, etc.) instantly, i.e., with zero computational time. This increases the efficiency of the user. The database of JaSTA is now created for a few sets of input parameters with a plan to create a large database in future. This application also has an option where users can compile and run the scattering code directly for aggregates in GUI environment. The JaSTA aims to provide convenient and quicker data analysis of the optical properties which can be used in different fields like planetary science, atmospheric science, nano science, etc. The current version of this software is developed for the Linux and Windows platform to study the light scattering properties of small aggregates which will be extended for larger aggregates using parallel codes in future. 相似文献
The cover image is based on the Research Article Cross-linked enzyme aggregates of recombinant cyclodextrin glycosyltransferase for high-purity β-cyclodextrin production by Jianguo Zhang et al., DOI: 10.1002/jctb.5912 .
The structure of amphiphilic low-dimensional copolymer electrolytes I of similar overall composition but prepared by different synthetic procedures X and Y are described. I are copolymers of poly[2,5,8,11,14-pentaoxapentadecamethylene(5-alkyloxy-1,3-phenylene)] (CmO5) and poly[2,-oxatrimethylene(5-alkyloxy-1,3-phenylene)] (CmO1) where the alkyl side chains having m carbons are hexadecyl or mixed dodecyl/octadecyl (50/50). 1H NMR shows that the copolymers have 50% (m = 16) or only 18 and 13% of CmO5 units and DSC indicates that the copolymers have ‘block’ sequencing of CmO1 and CmO5 segments. Molecular dynamics modelling indicates that in CmO5 Li+ and BF4− ions are separated by Li+ encapsulation in tetraethoxy segments but in ionophobic CmO1 units the salt is mostly present as neutral aggregates decoupled from the polymer. Conductivities of these microphase-separated mixtures with salt-bridge amphiphilic polyethers II and III of each system are similar. They have low temperature dependence over the range 20 °C to 110 °C at ∼10−3 S cm−1. 7Li NMR linewidth measurements confirm high lithium mobilities at −20 °C. A conduction mechanism is proposed whereby Li+ hopping takes place along rows of decoupled aggregates (dimers/quadrupoles) within an essentially block copolymer structure. Subambient measurements to −10 °C gave a conductivity of 4 × 10−5 S cm−1. 相似文献