Substitution of Sodium and Silicon in Tricalcium Aluminate

Four types of tricalcium aluminate solid solutions with different concentrations of Na₂O and SiO₂ were prepared and examined using an electron probe microanalyzer. The atomic ratios, including those determined in a previous study, were derived from the oxide compositions and provided excellent correlations between Ca and Na + Si (i.e., Ca = 3.003 − 0.48[Na + Si]), and Al and Si (Al = 1.997 − 1.02Si). Because the replacement reactions, Ca²⁺↔ 2Na⁺ and Ca²⁺+ 2Al³⁺↔ 2Si⁴⁺, independently occur within the same crystal, these reactions have been simply combined together to generate a new formula, Na_{2 x} Ca_{3− x − y} (Al_{1− y} Si _y )₂O₆, where x is the amount of Ca substituted by Na, and y is the amount of Al substituted by Si. This formula leads to the equations Ca = 3 − 0.5[Na + Si] and Al = 2 − Si, which nicely account for the constrained chemical variation of the actual solid solutions with 0 ≤ x < 0.049 and 0 ≤ y < 0.073.     

Durable aluminate toughened zirconate composite thermal barrier coating (TBC) materials for high temperature operation

Research on advanced thermal barrier coating (TBC) materials capable of operating beyond 1200°C has primarily focused on the rare earth zirconate pyrochlores, particularly gadolinium zirconate (Gd₂Zr₂O₇ – GZO). The drawback of this material is a significant reduction in durability due to a low fracture toughness. This study investigates utilization of a thermodynamically compatible gadolinia alumina perovskite (GdAlO₃ – GAP) toughening phase to improve the durability of GZO. Dense pellets were fabricated to assess the material properties with minimal microstructural influence. Thermal stability, elastic modulus, hardness, indentation fracture resistance and erosion durability were evaluated for GZO, GAP, and composite pellets containing 10, 30, and 50 wt.% GAP. It was demonstrated that GAP and GZO are thermodynamically compatible through 1600°C and thus capable of operating well beyond the limits of traditional 7 wt.% yttria stabilized zirconia (YSZ). Grain sizes are maintained due to a lack of diffusion, and thus microstructural stability is enhanced. The GAP fracture toughness was shown to be over 2X that of GZO while exhibiting a lower elastic modulus and similar hardness. The 50:50 GZO-GAP composite exhibited a 63% reduction in the absolute erosion rate, demonstrating the immense toughening capabilities of this system. The implications for composite TBCs utilizing this system are discussed, along with future work.     

Synthesis of Pure Monolithic Calcium, Strontium, and Barium Hexaluminates for Catalytic Applications

Calcium, strontium, and barium hexaluminates have been prepared via a chemical route. In light of their interest as catalytic substrates the relation between attrition-milling time and density was studied, with the scope of obtaining fired bodies with suitable pore structure. It was found that all hexaluminates grew in elongated structures; longer milling times resulted in higher aspect ratios for calcium hexaluminate, with less than 75% of the theoretical density. Strontium and barium hexaluminates were prepared with even lower densities, but the reason is the inherent poor densification, and not the growth of mutually interfering elongated structures, as in the case for calcium hexaluminate.     

Preparation of Phosphors MAl_2O_4∶Eu~(2 )(M=Ca,Sr,Ba) by Microwave Heating Technique and Their Phosphorescence

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Self heat generating synthesis of tri-colour lamp phosphors

The simple method for the preparation of phosphors such as aluminates, Y₂O₃, YVO₄ and LaPO₄ by the combustion synthesis described earlier in the literature is reported. It is shown here that the phosphors prepared by such synthesis do not possess all the required characteristics. Suitable modifications by way of annealing at >1200°C in controlled atmospheres, however, can yield the phosphors with characteristics which may fulfil the demands of lamp industry.     

Green EuAlO3:Eu2+ nanophosphor for applications in WLEDs

Green-emitting aluminate nanophosphors fabricated by a pressure-assisted combustion synthesis (P₀ = 1.4, 2.8 and 3.4 MPa) and annealed in pure H₂ is reported. The XRD analysis indicates the formation of the EuAlO₃ orthorhombic phase. Transmission electron microscopy (TEM) shows coalesced irregular grains with lengths in the range of 35–140 nm. In addition, the nanophosphor synthesized at an initial pressure of 3.4 MPa produced the highest green luminescence centered at 530 nm, which was associated to 4f⁷–4f⁶5d¹ allowed transitions of the Eu²⁺ located into the EuAlO₃:Eu²⁺ compound. A weak red emission peak corresponding to Eu³⁺ was also observed by cathodoluminescence. The CIE coordinates for green emission are x = 0.2613 and y = 0.3892, and the luminance produced from nanophosphors when they are excited with a commercial UV-396 nm LED (8.0 μW) was 285 ± 4.3 Cd/m².     

Q345钢精炼过程夹杂物成分的变化

通过工业试验研究了Q345钢在钢包精炼过程和RH处理过程中夹杂物成分的变化。结果表明:通过与高碱度、低氧化性渣的反应,钢水中的大部分Al2O3夹杂物转变为具有较低熔点的CaO-Al2O3-MgO夹杂物。研究了RH处理后钙的加入量对夹杂物成分的影响。结果表明:当钢包顶渣的成分控制在w(CaO)=50%～55%、w(CaF2)=5%～8%、w(Al2O3)=25%～30%、w(SiO2)=5%～8%、w(MgO)=5%～10%、w(FeO)<1%,经过钢包精炼和RH处理,每吨钢水中加入0.12 kg钙后,钢水中夹杂物的平均成分处于低熔点(≤1 500℃)区。     

长余辉发光Lyocell纤维的制备与性能研究

通过采用不同偶联剂对长余辉发光粉末进行表面处理,比较其在NMMO水溶液中的沉降性变化,优选出合适的钛酸酯偶联剂以提高发光粉在NMMO水溶液中的分散稳定性,并采用干湿法纺丝,成功制备了长余辉绿色发光Lyocell纤维。结果表明,通过对发光粉的偶联剂处理,所得发光Lyocell纤维强度略有提高。随着发光粉含量的增加,纤维的热性能和结晶度有所降低,初始发光亮度提高。当发光粉含量>10%(质量分数)时,纤维的衰减时间常数迅速增大,余辉性能提高。     

稀土光致发光安全涂料的制备

采用稀土元素掺杂的碱土铝酸盐光致发光材料研制丙烯酸乳液型发光涂料。乳液型光致发光涂料通过吸收各种可见光实现自动发光功能,本涂料以天然物质为发光材料,以丙烯酸乳液为基料,配合各种颜料、填料及添加剂而成。讨论了这种涂料的发光机理、发光时间。     

Preparation and luminescent properties of CaAl_2O_4:Eu~(3+),R~+(R=Li,Na,K) phosphors

CaAl2O4:Eu3+,R+(R=Li+,Na+,K+) red phosphors were synthesized by solid state reaction method.X-ray diffraction(XRD) and photoluminescence(PL) were employed to characterize their structural and luminescent properties.It was found that the optimal sintering temperature and sintering time were 1200 °C and 4 h,respectively.The optimal concentration of doped Eu3+ was 3 mol.%.Furthermore,under ultraviolet excitation with a wavelength of 254 nm,these samples showed red luminescence which were probably attributed to the transitions from 5D0 excited state to 7FJ(J=0-4) ground states of Eu3+ ions.The feature and the high intensity of hypersensitive transition from 5D0→7F2 indicated that Eu3+ preferred to occupy a low symmetry site.The incorporation of alkali metal ions greatly enhanced the luminescence intensity probably due to the influence of charge compensation of alkali metal ions.