With the miniaturization of current electronic products, ceramic/polymer composites with excellent thermal conductivity have become of increasing interest. Traditionally, higher filler fractions are ...required to obtain a high thermal conductivity, but this leads to a decrease in the mechanical properties of the composites and increases the cost. In this study, silicon nitride nanowires (Sisub.3Nsub.4NWs) with high aspect ratios were successfully prepared by a modified carbothermal reduction method, which was further combined with AlN particles to prepare the epoxy-based composites. The results showed that the Sisub.3Nsub.4NWs were beneficial for constructing a continuous thermal conductive pathway as a connecting bridge. On this basis, an aligned three-dimensional skeleton was constructed by the ice template method, which further favored improving the thermal conductivity of the composites. When the mass fraction of Sisub.3Nsub.4NWs added was 1.5 wt% and the mass fraction of AlN was 65 wt%, the composites prepared by ice templates reached a thermal conductivity of 1.64 W·msup.−1·Ksup.−1, which was ~ 720% of the thermal conductivity of the pure EP (0.2 W·msup.−1·Ksup.−1). The enhancement effect of Sisub.3Nsub.4NWs and directional filler skeletons on the composite thermal conductivity were further demonstrated through the actual heat transfer process and finite element simulations. Furthermore, the thermal stability and mechanical properties of the composites were also improved by the introduction of Sisub.3Nsub.4NWs, suggesting that prepared composites exhibit broad prospects in the field of thermal management.
In this work, Agsub.2COsub.3 was prepared via a solution-based method and was further characterized by XRD, Raman spectroscopy, SEM/EDS analysis, and UV-VIS spectroscopy. SEM results revealed the ...formation of micro-sized particles with a rectangular shape. The photocatalytic activity of the catalyst was evaluated in the degradation of 4-tert-butylphenol (4-t-BP) under simulated solar light irradiation. The effects of 4-t-BP initial concentration (2.5-10 ppm), catalyst dosage (100-300 mg/L), different types of lamp sources, and water matrix were investigated. Complete 4-t-BP (5 ppm) degradation was achieved after 60 min by Agsub.2COsub.3 (200 mg/L). The effect of anions such as COsub.3 sup.2−, HCOsub.3 sup.−, NOsub.3 sup.−, and Clsup.- in the concentration range of 100-300 mg/L was also studied. COsub.3 sup.2− promoted the photocatalytic degradation process, while HCOsub.3 sup.− and NOsub.3 sup.− exhibited an inhibition effect, which was marked with increasing HCOsub.3 sup.− and NOsub.3 sup.− concentrations. The presence of Clsup.− at the concentration of 100 mg/L increased 4-t-BP degradation, but higher concentrations inhibited the photocatalytic reaction. Cyclic experiments showed that the catalyst practically retained its catalytic activity toward 4-t-BP degradation after three successive experimental runs.
WO.sub.x has good performance in olefin epoxidation, however, the presence of a large amount of Brönsted acid on WO.sub.x affects the selectivity of epoxy products. In this paper, broken carbon ...spheres (b-C spheres) treated with nitric acid were used as support to anchor WO.sub.x in dynamic solvothermal process. Based on GC-MS and GC-IR detection, the obtained WO.sub.x/C greatly increased selectivity of 1,2-epoxyhexane from 16.0% (pure WO.sub.x) to 92.1% in epoxidation of 1-hexene. The improvement of WO.sub.x performance is attributed to the reduction of Brönsted acid sites and electron cloud density after loading, which may all result from interaction between WO.sub.x and oxygen-containing functional groups of b-C spheres. Above changes not only effectively inhibit the hydrolysis of 1,2-epoxyhexane, but also are conducive to nucleophilic reaction of H.sub.2O.sub.2 to WO.sub.x, which is beneficial to the activation of H.sub.2O.sub.2. Finally, an epoxidation mechanism with oxygen vacancies as the main route under WO.sub.x/C catalysis is reasonably proposed.
Aim of the work
The purpose of this study was to compare stress induced by the conventional design of lower unilateral free-end saddle and side plate with extra-coronal attachment (OT Cap attachment) ...and record the micro-strains induced by this stress.
Materials and methods
Strain gauge technology was used for strain analysis. A two-layer epoxy resin model with a unilateral distal extension base was used in this study with the second premolar as the last standing abutment. Model A: A lower metallic partial denture was made with an RPI clasp as a direct retainer on the second premolar and a double Aker clasp for cross-arch stabilization on the 1st and 2nd molars of the dentulous side, and the lingual plate served as a major connector. Model B: Lower metallic partial denture was made with the extra-coronal attachment (OT Cap attachment) as a direct retainer on the second premolar splinted with the first premolar by crowns. Stresses were measured vertically and obliquely at the buccal and lingual sides of the lower 2nd premolar, the edentulous ridge in the lower 2nd molar, and the double Aker in the dentulous side of model A. However, stresses were measured vertically and obliquely at the buccal and lingual side of the lower 2nd premolar and the edentulous ridge in the lower 2nd molar of model B. Data were collected, tabulated, and statistically analyzed using the SPSS software program.
Results
The present study revealed that stresses recorded at the abutment teeth and the ridge in the area of the lower second molar were higher in the case of conventional RPD than in OT attachment and the micro strains recorded around the abutment tooth were much more than micro-strains recorded around the residual ridge.
Conclusions
Mandibular partial denture using OT attachment can be considered as a prosthetic option for the management of class II Kennedy classification as it can improve the integrity of the alveolar bone of the abutment tooth and the residual ridge. Splinting of abutments reduces the stresses located in the buccal and lingual aspects of the abutment connection between the abutment and the OT attachment allowing better distribution of the stresses between the abutment tooth and the ridge vertically and obliquely.
Gd@Csub.82Osub.xHsub.y endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a ...mixture of graphite and Gdsub.2Osub.3 oxide. The Gd@Csub.82 endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@Csub.82Osub.8(OH)sub.20. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole Csub.82 cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the Csub.82 cage causes the formation of Gd@Csub.82Osub.28Hsub.20, with a breakdown of the integrity of the parent Csub.82 cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@Csub.82Osub.6(OOH)sub.2(OH)sub.18 endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.
Geranylacetone and nerylacetone are natural sesquiterpenoids, which play various roles in plant-insect interactions, including the deterrent and repellent effects on herbivores. The structural ...modifications of natural compounds often change their biological activities. The aim of the study was to evaluate the effect of geranylacetone, nerylacetone and their epoxy-derivatives on the probing and settling behavior of Myzus persicae (Sulz.) (Hemiptera: Aphididae). The no-choice test using the Electrical Penetration Graph (EPG) technique showed that the probes before the first phloem phase were usually shorter than 3 min, which means that they were terminated within the epidermis and/or outer layers of mesophyll. This resulted in a tendency to delay the initiation of the phloem phase in aphids, which reflects a weak preingestive deterrent activity of the studied compounds at the level of non-vascular tissues. Most M. persicae showed bouts of sustained phloem sap ingestion. However, the 24-h free-choice test demonstrated that aphids did not settle on the leaves treated with geranylacetone, nerylacetone, and their epoxy-derivatives. The refusal to settle after the consumption of phloem sap on treated plants indicated that the studied compounds had postingestive deterrent activity. The epoxidation of geranylacetone and nerylacetone did not evoke significant changes in their activity profiles.
Functionalized aluminosilicate materials were studied as catalysts for the conversion of different cyclic carbonates to the corresponding epoxides by the addition of COsub.2. Aluminum was ...incorporated in the mesostructured SBA-15 silica network. Thereafter, functionalization with imidazolium chloride or magnesium oxide was performed on the Al_SBA-15 supports. The isomorphic substitution of Si with Al and the resulting acidity of the supports were investigated via sup.27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and NHsub.3 adsorption microcalorimetry. The Al content and the amount of MgO were quantified via inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. The anchoring of the imidazolium salt was assessed by sup.29Si and sup.13C MAS NMR spectroscopy and quantified by combustion chemical analysis. Textural and structural properties of supports and catalysts were studied by Nsub.2 physisorption and X-ray diffraction (XRD). The functionalized systems were then tested as catalysts for the conversion of COsub.2 and epoxides to cyclic carbonates in a batch reactor at 100 or 125 °C, with an initial COsub.2 pressure (at room temperature) of 25 bar. Whereas the activity of the MgO/xAl_SBA-15 systems was moderate for the conversion of glycidol to the corresponding cyclic carbonate, the Al_SBA-15-supported imidazolium chloride catalysts gave excellent results over different epoxides (conversion of glycidol, epichlorohydrin, and styrene oxide up to 89%, 78%, and 18%, respectively). Reusability tests were also performed. Even when some deactivation from one run to the other was observed, a comparison with the literature showed the Al-containing imidazolium systems to be promising catalysts. The fully heterogeneous nature of the present catalysts, where the inorganic support on which the imidazolium species are immobilized also contains the Lewis acid sites, gives them a further advantage with respect to most of the catalytic systems reported in the literature so far.
The development of novel catalysts for the synthesis of cyclic carbonates under mild conditions remains a challenge. Herein, we designed the strategy of immobilizing DBU-based ionic liquid on ...mesoporous SBA-15 (DBU@SBA-15), due to the cooperative effect between silanol and bromide anion, DBU@SBA-15 exhibits high CO.sub.2 catalytic performance under solvent-free and metal-free and additive-free conditions. Typically, the yield of chloropropene carbonate was close to 100% from the reaction of epichlorohydrin and CO.sub.2 within 12 h at 80 °C and 2 MPa. Notably, the product yield could achieve 64.8% even at ambient pressure, and DBU@SBA-15 was recycled four times without significant loss of catalytic activity. Additionally, DFT studies revealed that the nucleophilic effect and the strong hydrogen bond together promote the ring-opening of epoxides, which was consistent with the possible reaction mechanism proposed based on experiments.
PDF
