Advanced Materials Research Vols. 306-307

Abstract: In this paper we studied the feasibility of baking-free bricks which were produced in condition of high pressure and natural curing. Studied the influence of shaping pressure, molding water on performances of baking-free bricks, and the active probability of activating agents which contain phosphogypsum, and lime of different amounts. The experiments showed that the best shaping pressure is 20MPa, the preferable molding water is 14-18%, and the best raw material composition is 50% fly ash, 33% stone clips, 4% phosphogypsum, 3% lime, and 10% cement. SEM was used to study the relationship between structure and performance.

Abstract: Self-assembled monolayer of n-tetradecanoic acid (CH₃(CH₂)₁₄COOH) are formed on the native oxide surfaces of Fe₃Al. The structure of the monolayer is probed with contact angle measurement and SEM. The results (indicate) that the structure of the adsorbed film like lotus structure and the contact angle are larger than 150° for seawater. Moreover, the corrosion behavior of bare Fe₃Al and Fe₃Al with super-hydrophobic surface, with two different surface microstructure, in seawater(pH=8.02), has been investigated using electrochemical impedance spectroscopy (EIS) and weight loss measurements. Both methods reveal that corrosion rate of Fe₃Al with Super-hydrophobic surface sample decreases dramatically because of its special microstructure. These results indicate that the super-hydrophobic surface formed on the Fe₃Al can improve corrosion resistance of Fe₃Al in seawater significantly.

Abstract: Accelerated aging procedure and SIC test method have been used to determine the mechanical property of glass fiber reinforced magnesium oxychloride cement (GRMC). Hydration product, microstructure and corrosion degree of glass fibers have been analyzed by XRD and SEM in the oxychloride magnesium cement matrix. The mechanism of mechanical property degradation has been concluded based on the analysis of testing data. For ordinary GRMC sample, the main hydration product 5Mg(OH)₂·MgCl₂·8H₂O (5·1·8) hydrolyzed to Mg(OH)₂ easily in water. Mechanical property degraded because of the formation of leptophyllous Mg(OH)₂, the looseness of interface region of matrix and glass fiber and corrosion of glass fiber. However, the extended mechanical performance was excellent due to the steadily exsit of 5·1·8 in high performance GRMC sample. It could be concluded that the 5·1·8 existing steadily in oxychloride magnesium cement matrix was the basilic premise for glass fiber which could not be corrupted easily.

Abstract: Steel slag and carbon dioxide were used as raw materials to prepare building material by carbonation. Effects of forming pressure on carbonation of steel slag and carbonated depth were studied by pore structural changes before and after carbonation and carbonated region. The results showed that these were visible pore structural changes between non-carbonated and carbonated steel slag, and after carbonation, the porosity of steel slag samples were decreased, the number of fine pore was increased and large pore was opposite. Carbon dioxide gas which was sequestrated by Ca(OH)₂ and C₃S were combined in CaCO₃ crystal, and this process was form surface to interior. Clustered granular crystals were generated in the surface and 12 mm depth of samples, while none in the 20 mm depth of samples, no obvious granular crystal growth. The granular crystals which produced by carbonation filled the pores of the sample, in particular the arrangement of dense granular surface of crystal layer, which may impede the spread of CO₂ gas to the depths, and carbonation reaction focused on the surface to 12 mm depth region.

Abstract: This paper deals with the effects of mechanical behavior of adhesives on the shear stress distributions of single-lap adhesive joints under tension using the three-dimensional finite element analysis (FEA) technique. Numerical examples are provided to show the influence on the shear stresses of the joints using adhesives of different characteristics which encompass the entire spectrum of viscoelastic behavior. FEA solutions of the shear stress distributions in the adhesive layer have been obtained for four typical characteristics of adhesives. The results indicate that Young’s modulus and Poisson’s ratios of adhesives strongly affect the shear stress distributions of the joints.

Abstract: Luminescence properties of blue emission InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs), grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD), were studied by time-resolved photoluminescence (TRPL) spectroscopic technique. Samples involved have similar basic structures of three QWs but different well-composition and barrier/well dimensions. TRPL results show that PL intensity and decay time increase with the number of QWs and the indium composition. Correlation of physical properties with crystalline perfection open the way for optimized designs of InGaN MQW LED, with controlled the indium composition and QW numbers.

Abstract: Removing water excessively could result in the formation of sphere-like agglomerates of TiO₂ precursor with 1-2 μm in size, which was used to prepare TiO₂ nanoparticles by detonation method. Different temperature distributions of TiO₂ precursor agglomerates influenced the components of detonation products. In order to obtain the temperature distributions, a mathematic model was introduced to study the heat transfer behaviors of the TiO₂ precursor agglomerates during the detonation process. The temperature history at spherical center with different spherical radiuses and time was also studied. The calculation results were in good agreement with the experimental results. The heat transfer analysis laid the foundation for the synthesis mechanism research of TiO₂ nanoparticles, and it was also helpful to design and optimize experimental procedure.

Abstract: A novel crystalline precursor for preparing Y₃Al₅O₁₂ (YAG) nanocrystallite was synthesized via a co-precipitation method using (NH₄)₂CO₃ solution as the precipitator. The precursor was characterized by means of powder X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), thermal gravimetry (TG), differential thermal gravimetry (DTG) and differential scanning calorimetry (DSC), respectively. The empirical chemical formula of the crystalline precursor can be expressed as 5[(NH₄)₂Al₆(CO₃)₃(OH)₁₄]×9[Y₂(CO₃)₃×3H₂O] according to the test results. The measured weight loss of 46.7% of the precursor without consideration of the absorbed water is in accord with the calculated value of 47.5% according to the above empirical formula. The phase-pure YAG nanocrystallites were obtained by calcining the above precursors at 900°C for 2 hours in air atmosphere. Transmission electronic microscopy (TEM) result showed that the particle size of YAG nanocrystallites is 40-80 nm. The mechanism of themal decomposition of the crystalline precursor was also presented.

Abstract: The composite electrodes of cobalt oxide and multi-wall carbon nanotubes (MWCNTs) are prepared by a simple low-temperature solid-phase synthesis method with the assistance of polyethylene glycol and their pseudocapacitive performances are investigated in alkaline solution by cyclic voltammetry and galvanostatic charge/discharge tests, respectively. Transmission electron microscope images show that cobalt oxide is uniformly coated on multi-wall carbon nanotubes and the homogeneous hybrid nanostructure are considered to be responsible for their preferable electrochemical performances. The electrochemical tests further reveal that the composite can deliver a maximum specific capacitance of 217 F/g with a biggest utilization of Co element when the content of MWCNTs increases to 50 wt.%.

Abstract: The manganese oxide (MnO₂) nanocrystals were formed on the surface of graphene oxides (GOs) and multi−walled carbon nanotubes (MWCNTs) through a facial hydrothermal route, respectively. It is found that the similar flower−like MnO₂ nanocrystals covered on both conductive supports. Moreover, more dense and less size of MnO₂ nanocrystals appeared on the surface of MWCNTs, whereas more perfect crystal structures for MnO₂/GOs. Electrochemical measurements showed that both the nanocomposite electrodes exhibited nearly ideal capacitive behavior, and large capacitive value can be obtained for MnO₂/GOs, while high stability for MnO₂/MWCNTs. The high capacitance performance arises from the unique nanostructure of the nanocrystals, which facilitate the contact of the electrolyte and the active materials, and carbon−based materials provide an effective support for the formation of the nanocrystals and conductive pathway for the nanocomposite electrodes.