Key Engineering Materials Vol. 633

Abstract: Based on the need of calorimeter for dark matter search in China, 600 mm BGO crystals were investigated on longitudinal transmission and light response uniformity of crystal. In the analysis of the data obtained, a strong correlation between the crystal light response uniformity and their longitudinal transmission in the range 435 nm has been noticed. As a consequence, the transmission measurement alone can be used to help classification of crystal and identify crystals requiring uniformization. In the following the outcome of this analysis and the results that can be achieved will be discussed.

Abstract: In order to explain the deterioration mechanism of air entrained concrete subjected to freeze-thaw cycles in water, NaCl, Na₂SO₄ and composite solution, The damage of concrete and ice-formation expansion of salt corrosion solution are tested. The experimental results show that the damage degree of concrete under salt frost is NaCl solution>composite solution>water>Na₂SO₄ solution. Considering the chloride penetrated into concrete and following 2^nd Fick’s Law, the ice-formation expansion resulted by NaCl solution in surface layer of concrete is higher than that in inner, and the expansion stress at outer layer is 1.73 times of that at inner layer according to the proposed function. The expansion stress difference between the internal and external layer causes spalling damage of concrete in chloride salt frost. The ice-formation expansion of Na₂SO₄ solution increases with its raising concentration and it is higher than that of NaCl solution at the same temperature. However, the corrosion products are ettringite and gypsum after sulfate salt frost, and the volume of solid corrosion products is barely change, or even reducible.

Abstract: Objective: To evaluate the fracture resistance of endodontically treated teeth reinforced with cast titanium posts and prefabricated glass-fiber posts with different diameters. Materials and Methods: 50 recently extracted human maxillary central incisors were endodontically treated and randomly divided into 5 groups of 10 specimens each: Group A: 1.35mm diameter of cast titanium post; Group B: 1.5mm diameter of cast titanium post; Group C: 1.375mm diameter of prefabricated fiber post; Group D: 1.5mm diameter of prefabricated fiber post; Group E: resin restoration. All specimens were subjected to fracture resistance testing in a universal testing machine, statistical analysis was performed and the fracture modes were analyzed. Results: The mean fracture resistance of five groups as follows: 404.22±73.92N for group A, 488.17±78.68N for group B, 280.32±45.23N for group C, 317.53±50.87N for group D, 222.76±38.67N for group E. The fracture resistance of restored teeth between group C and group D had no significant difference (P>0.05). The fracture resistance of the rest pairwise group comparisons had significant difference (P<0.05). Most of cast post samples fractured at the root middle or apical portion, while most of the fiber post samples fractured at the root cervical or post fracture, which could be retreated. Conclusion: Human maxillary central incisors restored with cast posts could bear higher fracture load and fiber post could protect the root from fracture preferably.

Abstract: To investigate the effect of annealing temperature on the structures and properties of Bi_4.15Nd_0.85Ti₃FeO₁₅ (BNTF), their thin films with four perovskite slabs were deposited on Pt/Ti/SiO₂/Si substrates by the metal-organic decomposition method. Good remanent polarization and excellent fatigue resistance were observed at room temperature. The BNTF thin films annealed at 780°C presented better ferroelectricity than those annealed at 700°C-780°C. Ferromagnetic of BNTF thin films was not observed at room temperature.

Abstract: The low grade quartz sands is the main raw material to prepare the unfired porous brick through adjusting the maitenance technology. The compressive strength of brick is higher with the maitenance temperature for 40¡æ. The compressive strength of brick is higher with the longer maitenance time. The high performance brick is prepared via the third technology, the pore of brick is more and uniform, it is bowl shape, that is close pore, which provide the reference for preparing the heat insulating materials. The compressive strength of brick is 1.9MPa, the density is 0.628 g/cm³.

Abstract: The masonries with a square of 2m×3m of 3 different aerated concrete blocks were built respectively, and plastered with plastering mortar. The shrinkage-cracking property and other performances of different aerated concrete masonries were studied in natural condition. The results showed that, there were less cracks and smaller crack width in the masonry of aerated concrete with low water absorption, the condition of aerated concrete cracking can be improved by plastering with plastering mortar; the shrinkage of aerated concrete block masonry with low water absorption is smaller, the shrinkage of aerated concrete masonry plastered by special plastering mortar is smaller.

Abstract: TiO₂ was added in Zn-Bi based varistors to enhance the grain growth of ceramics and the effects of TiO₂ addition on the microstructure, I-V, flow and aging characteristics of Zn-Bi varistors were studied. The voltage-gradient of samples decreased to minimum value of 30.6 V/mm when the TiO₂ content was 0.6 mol%, but increased with further increasing TiO₂ content. The variation trend of average grain size was just the opposite of the voltage-gradient. 0.6 mol% TiO₂ added samples have a more unify microstructure and excellent three parameter values with I_L=5.7μA, E_1mA=30.6V/mm, α=25.8. After Dc aging at 125 ^oC for 7h, the voltage variation of samples is very slow (~-4.1%).

Abstract: ZnO-Pr₆O₁₁-Co₃O₄-Cr₂O₃-SnO₂ varistors with different doping levels of Pr₆O₁₁ (0.25-2 mol%) were prepared at 1300 °C with conventional ceramic processing, and the effect of Pr₆O₁₁ doping on the microstructure and electrical properties of the varistor materials were investigated. The results indicated that the doped Pr₆O₁₁ basically existed at the boundary of ZnO grains in the varistor ceramics, and SnO₂ might enter into the lattice of ZnO grains or precipitate in reaction with Pr₆O₁₁ into Pr₂Sn₂O₇ at the gain boundaries particularly where there were three or more ZnO grains. The analysis of scanning electron microscopy further revealed that Pr₆O₁₁ doping would inhibit the growth of ZnO grains, resulting in decreasing ZnO grain size with increasing doping level of Pr₆O₁₁. The measured electric-field/current-density characteristics of the samples showed that the varistor voltage increased with increasing doping level of Pr₆O₁₁ when the doping level was no more than 1.5 mol%, and the nonlinear coefficient of the varistors increased with increasing doping level of Pr₆O₁₁ up to no more than 1.0 mol% in the varistors, respectively.

Abstract: The damage experiments of reinforced concrete (RC) samples under synergistic effects of cyclic freeze-thaw, deicing-salt attack, rebar corrosion and bending stress were investigated using a comprehensive experimental method. Synergistic effects of these factors on the damage evolvement of RC were studied by measuring the change of dynamic modulus of concrete, rebar strain and concrete strain. Experimental results showed similar rule in damage evolvement but different damage rate between the normal-strength concrete (C45, the 28-day compressive strength of 52 MPa) and the high-strength concrete (C70, the 28-day compressive strength of 77 MPa). The dynamic modulus of the reinforced concrete degraded with increasing effecting factors.

Abstract: This study selected high alkali aluminosilicate glass as the research object. It’s belongs to the SiO₂-Al₂O₃-RO-R₂O glass system. By changing the content of Al₂O₃ in the SiO₂-Al₂O₃-RO-R₂O glass system, designed five basic glass formula. Using conventional melting method prepared the high alkali aluminosilicate glass. In the case of the same heat treatment, the glass formulations are the most important factor in the glass surface tension. Using the glass surface tension measuring instrument, focus on the content of Al₂O₃ on the glass surface tension’s effects law. The results show that the high alkali aluminosilicate glass’s surface tension are increase with the increase of Al₂O₃ content. The relation between glass surface tension and the content of Al₂O₃ conforms to the formula Y=290+6.5W_Al2O3, Al₂O₃ factors influence the surface tension of the glass is 6.5.