The granary weevil, Sitophilus granarius (L.), is one of the most important internal feeders of stored grain. Nanotechnology has become one of the most promising new approaches for pest control in recent years. In our screening program, laboratory trials were conducted to determine the effectiveness of silica nanoparticles (SNPs) and zinc nanoparticles (ZNPs) against the larval stage and adults of S. granarius on stored wheat. Nanoparticles of silica and zinc were synthesized through a solvothermal method. They were then used to prepare insecticidal solutions of different concentrations and tested on S. granarius. Silica nanoparticles (SNPs) were found to be highly effective against S. granarius causing 100% mortality after 2 weeks. ZNPs were moderately effective against this pest.
Describes how to obtain a soluble sodium silicate with a density of 1.40 g/cm3, 1.45 g/cm3, 1.50 g/cm3, and silica module M = 2.1 obtained from the silica- sodium glass with module M = 3.3 and M = 2.1. Residual (final) strength of molding samples made with these binders, were determined at temperatures corresponding to the characteristic temperatures of phase and temperature transitions of silica gel. Indicated the type of soluble sodium silicate capable of obtain the smallest value of the final strength of molding sand in the specified range of temperatures.
Alkali-aggregate reactivity (AAR) is one of the major causes of damage in concrete. Potential susceptibility of aggregates to this reaction can be determined using several methods. This study compares gravel alkali reactivity results obtained from different tests conducted on coarse aggregates with complex petrography. The potential for the reactivity in the aggregates was revealed in the chemical test using treatment with sodium hydroxide. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to identify the reactive constituents. The expansion measured in the mortar bars test confirmed that the aggregate was potentially capable of alkali silica reactivity with consequent deleterious effect on concrete.
The goal of this article is to application of non-silica sands based on alumininosilicates as an alternative of traditionally used chromite sand for alloyed steel and iron castings. Basic parameters as bulk density, pH value of water suspension, refractoriness, grain shape of the testing sands were evaluated. Also mechanical properties of furan no-bake moulding mixtures with testing sand were determined. Finally, the influence of non-silica sand on casting quality was evaluated via semi-scale under normal casting production for sand characterization Optimization of production process and production costs were described.
The effects of silica additive (Poraver) on selected properties of BioCo3 binder in form of an aqueous poly(sodium acrylate) and dextrin (PAANa/D) binder were determined. Based on the results of the thermoanalytical studies (TG-DTG, FTIR, Py-GC/MS), it was found that the silica additive results in the increase of the thermostability of the BioCo3 binder and its contribution does not affect the increase in the level of emissions of organic destruction products. Compounds from group of aromatic hydrocarbons are only generated in the third set temperature range (420-838°C). The addition of silicate into the moulding sand with BioCo3 causes also the formation of a hydrogen bonds network with its share in the microwave radiation field and they are mainly responsible for maintaining the cross-linked structures in the mineral matrix system. As a consequence, the microwave curing process in the presence of Poraver leads to improved strength properties of the moulding sand (���� �� ). The addition of Poraver's silica to moulding sand did not alter the permeability of the moulding sand samples, and consequently reduced their friability. Microstructure investigations (SEM) of microwave-cured samples have confirmed that heterogeneous sand grains are bonded to one another through a binder film (bridges).
Moulding sands containing sodium silicate (water-glass) belong to the group of porous mixture with low resistance to increased humidity.
Thanks to hydrophilic properties of hardened or even overheated binder, possible is application of effective methods of hydrous
reclamation consisting in its secondary hydration. For the same reason (hydrophilia of the binder), moulds and foundry cores made of
high-silica moulding sands with sodium silicate are susceptible to the action of components of atmospheric air, including the contained
steam. This paper presents results of a research on the effect of (relative) humidity on mechanical and technological properties of
microwave-hardened moulding mixtures. Specimens of the moulding sand containing 1.5 wt% of sodium water-glass with module 2.5
were subjected, in a laboratory climatic chamber, to long-term action of steam contained in the chamber atmosphere. Concentration of
water in atmospheric air was stabilized for 28 days (672 h) according to the relative humidity parameter that was ca. 40%, 60% and 80% at
constant temperature 20 °C. In three cycles of the examinations, the specimens were taken out from the chamber every 7 days (168 h) and
their mechanical and technological parameters were determined. It was found on the grounds of laboratory measurements that moulds and
cores hardened with microwaves are susceptible to action of atmospheric air and presence of water (as steam) intensifies action of the air
components on glassy film of sodium silicate. Microwave-hardened moulding sands containing sodium silicate may be stored on a longterm
basis in strictly determined atmospheric conditions only, at reduced humidity. In spite of a negative effect of steam contained in the
air, the examined moulding mixtures maintain a part of their mechanical and technological properties, so the moulds and foundry cores
stored in specified, controlled conditions could be still used in manufacture.
In the paper, presented is a research on effectiveness of absorbing electromagnetic waves at frequency 2.45 GHz by unhardened moulding
sands prepared of three kinds of high-silica base and a selected grade of sodium silicate. Measurements of power loss of microwave
radiation (Pin) expressed by a total of absorbed power (Pabs), output power (Pout) and reflected power (Pref) were carried-out on a stand of
semiautomatic microwave slot line. Values of microwave power loss in the rectangular waveguide filled with unhardened moulding sands
served for determining effectiveness of microwave heating. Balance of microwave power loss is of technological and economical
importance for manufacture of high-quality casting moulds and cores of various shapes and sizes. It was found that relative density
influences parameters of power output and power reflected from samples of moulding sand placed in a waveguide. Absorption expressed
by the parameter Pabs is not related to granularity of high-silica base: fine, medium and coarse. It was found that the semiautomatic
microwave slot line supports evaluation of effectiveness of microwave absorption on the grounds of power loss measurements and enables
statistic description of influence of relative density of the sandmix on penetration of electromagnetic waves in unhardened moulding sands.
The study presented research on the possibility of using acoustic emission to detect and analyze the development of the alkali-silica reaction (ASR) in cement mortars. The experiment was conducted under laboratory conditions using mortars with reactive opal aggregate, accelerating the reaction by ensuring high humidity and temperature, in accordance with ASTM C227. The progress of corrosion processes was monitored continuously for 14 days. The tests were complemented with measurements of the expansion of the mortars and observations of microstructures under a scanning electron microscope. The high sensitivity of the acoustic emission method applied to material fracture caused by ASR enabled the detection of corrosion processes already on the first day of the test, much sooner than the first recorded changes in linear elongation of the specimens. Characteristic signal descriptors were analyzed to determine the progress of corrosion processes and indicate the source of the cracks. Analysis of recorded 13 AE parameters (counts total, counts to peak, duration, rise time, energy, signal strength, amplitude, RMS, ASL, relative energy, average frequency, initial frequency and reverberation frequency) indicates that the number of counts, signal strength and average frequency provide most information about the deleterious processes that occur in the reactive aggregate mortars. The values of RA (rise time/amplitude) and AF (average frequency) enabled the classification of detected signals as indicating tensile or shear cracks. The acoustic emission method was found suitable for monitoring the course of alkali-aggregate reaction effects.
In this study, agar-based nanocomposite films containing ultra-porous silica aerogel particles were fabricated by gel casting using an aqueous agar/silica aerogel slurry. The silica aerogel particles did not show significant agglomeration and were homogeneously distributed in the agar matrix. Transmission electron microscopy observations demonstrated that the silica aerogel particles had a mesoporous microstructure and their pores were not incorporated into the agar polymer molecules. The thermal conductivities of the agar and agar/5 wt.% silica aerogel nanocomposite films were 0.36 and 0.20 W·m–1·K–1, respectively. The transmittance of the agar films did not decrease upon the addition of silica aerogel particles into them. This can be attributed to the anti-reflection effect of silica aerogel particles.
The paper analyses the influence of chemical composition of silicone-based composites on their properties in the aspect of using them as long-term soft denture lining materials. Different concentrations of filler and methylhydrosiloxane-dimethylsiloxane copolymer were used. The filler was introduced into the composite with mechanical mixing combined with ultrasonic homogenization. Scanning electron microscopy was used to investigate the quality of filler dispersion. Shore A hardness, tensile strength, sorption, solubility and tensile bond strength to poly(methyl methacrylate) were measured. Tests show satisfactory results for some experimental composites, which met all the requirements for such materials.
Macroporous silica fibers having spherical cavities were fabricated by electrospinning using the spinning solution prepared from the mixed dispersion of tetraethylorthosilicate (TEOS) and polystyrene nanospheres as precursor and sacrificial templates, respectively, by injection through metallic nozzle. By applying electric field, the electro-spun fibers obtained by evaporation-driven self-assembly were collected on flat substrate or rotating drum, followed by the removal of the templates by calcination. The sound absorption coefficient of the porous fibers was measured by impedance tube, and the measured value was larger than 0.9 at high frequency region of incident waves. The surface of the resulting fibers was modified using fluorine-containing silane coupling agent to produce superhydrophobic fibrous materials to prevent the infiltration of humidity.
The effect of additives on the densification behavior and mechanical properties of pure and additive (Zr, B and Mg)-added silica ceramics were investigated for their application to the matrix phase of a silica fiber reinforced silica (SiO2/SiO2f) composite. The additives affected the rate of densification and crystallization (or transformation) of the amorphous silica. Among the compositions, pure silica ceramics sintered at 900°C for 1 h showed the maximum flexural strength. Based on the results, SiO2/SiO2f was fabricated by a repeated vacuum-assisted infiltration method followed by the heat treatment at 900°C for 1 h. The relative density of the composite was 78.2% with a flexural strength of 22.4 MPa. Fractography revealed that the composite was damaged by strong bonding at the fiber/matrix interface and the fracture of fiber.
We have numerically studied different designs of technologically feasible microstructured fibers with a germanium-doped core in order to obtain normal dispersion reaching possibly far in the mid infrared. Hexagonal, Kagome and the combination of both geometries were numerically examined with respect to different constructional parameters like pitch distance, filling factor of air holes, number of layers surrounding the core, and level of germanium doping in the core. Our analysis showed that the broadest range of normal dispersion reaching 2.81 μm, while keeping an effective mode area smaller than 30 μm2, was achieved for a hexagonal lattice and a 40 mol% GeO2 doped core. The proposed fibers designs can be used in generation of a normal dispersion supercontinuum reaching the mid-IR region.
Foundry sand waste can be utilized for the preparation of concrete as a partial replacement of sand. The strength properties of M25 grade concrete are studied with different percentages of replacement of fine aggregates by foundry sand at 0%, 10%, 20%, 30%, 40%, and 50%. The optimum percentage of foundry sand replacement in the concrete corresponding to maximum strength will be identified. Keeping this optimum percentage of foundry sand replacement as a constant, a cement replacement study with mineral admixtures such as silica fume (5%, 7.5%, 10%) and fly ash (10%, 15%, 20%,) is carried out separately. The maximum increase in strength properties as compared to conventional concrete was achieved at 40% foundry sand replacement. Test results indicated that a 40% replacement of foundry sand with silica fume showed better performance than that of fly ash. The maximum increase in strengths was observed in a mix consisting of 40% foundry sand and 10% silica fume. SEM analysis of the concrete specimens also reveals that a mix with 40% foundry sand and 10% silica fume obtained the highest strength properties compared to all other mixes due to the creation of more C-H-S gel formations and fewer pores.