Amphoteric behavior of alumina in viscous flow and structure of CaO-SiO<Subscript>2</Subscript> (-MgO)-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> slags

The viscosity of CaO-SiO₂ (-MgO)-Al₂O₃ slags was measured to clarify the effects of Al₂O₃ and MgO on the structure and viscous flow of molten slags at high temperatures. Furthermore, the infrared spectra of the quenched slags were analyzed to understand the structural role of Al₂O₃ in the polymerization or depolymerization of silicate network. The Al₂O₃ behaves as an amphoteric oxide with the composition of slags; that is, the alumina behaves as a network former up to about 10 mass pct Al₂O₃, while it acts as a network modifier, in parts, in the composition greater than 10 mass pct Al₂O₃. This amphoteric role of Al₂O₃ in the viscous flow of molten slags at the Newtonian flow region was diminished by the coexistence of MgO. The effect of Al₂O₃ on the viscosity increase can be understood based on an increase in the degree of polymerization (DOP) by the incorporation of the [AlO₄]-tetrahedra into the [SiO₄]-tetrahedral units, and this was confirmed by the infrared (IR) spectra of the quenched slags. The influence of alumina on the viscosity decrease can be explained on the basis of a decrease in the DOP by the increase in the relative fraction of the [AlO₆]-octahedral units. The relative intensity of the IR bands for the [SiO₄]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO₄]-tetrahedra with high NBO/Si increased with increasing Al₂O₃ content greater than the critical point, i.e., about 10 mass pct in the present systems. The variations of the activity coefficient of slag components with composition indirectly supported those of viscosity and structure of the aluminosilicate melts.     

27Al quadrupole interaction in zeolites loaded with probe molecules--a quantum-chemical study of trends in electric field gradients and chemical bonds in clusters

The electric field gradient (EFG) has been calculated in zeolite clusters at the aluminium site surrounded by four SiO4 tetrahedra. Density functional theory (DFT) with the 6-31G** basis set has been employed. Formation of a Br?nsted acid site by protonation of one oxygen atom of the AlO4 tetrahedron perturbs the coordination of aluminium, i.e., the corresponding Al-O bond is considerably weaker than in the unprotonated case. This leads to a large EFG, and the calculated quadrupole coupling constant (QCC) for 27Al is 18.2 MHz. Different probe molecules were adsorbed on the Br?nsted site. The hydrogen bond formed between the acid proton and the probe molecule weakened the zeolitic O-H bond. For conservation of the overall bond order of the oxygen atom, its bonds to the neighboring tetrahedral atoms (Si, Al) become stronger. As a consequence, the perturbation of the AlO4 tetrahedron and the EFG at the aluminium position decrease depending on the strength of the hydrogen bond. Perturbation of an oxygen atom of the AlO4 tetrahedron by accepting a hydrogen bond from the base molecule also affects the corresponding Al-O bond order. A linear correlation is found between the calculated QCC constants for 27Al and the Al-O bond orders of the oxygen atoms which are perturbed by protonation or by hydrogen bonds. A geometrical shear strain parameter and a simple electrostatic point charge model are less successful at predicting the trends in EFG which clearly shows the importance of the chemical bonds.     

Optimization of BaMgAl₁₀O₁₇:Eu²⁺ phosphors by the substitution of Si-N bonds for Al-O bonds

We proposed a simple method to improve the thermal stability of BaMgAl10O17:Eu2+(BAM) phosphors by the substitution of Si-N bonds for Al-O bonds in the host lattice.Both photoluminescence properties and thermal stability under ultraviolet(UV) and vacuum ultraviolet(VUV) excitation could be significantly improved through Si-N incorporation.After thermal degradation at 600 °C for 1 h in air atmosphere,the Si-N doped sample(Ba0.88Eu0.12MgAl9.97Si0.03O16.97N0.03) had the highest emission intensity which was 22% and 40% stronger than that of as-received sample under UV and VUV excitation,respectively.This could be attributed to the stable local structure surrounding the Eu2+ ions and the lower electronegativity of nitrogen.     

Upconversion properties of Y2O3：Er films prepared by sol-gel method

Y2O3:Er3+ films were prepared by a simple sol-gel process. The structural properties of Y2O3:Er3+ flints were characterized with X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. The results indicated that the Y2O3:Er3+ f'rims might have high upconversion efficiency because of their low vibrational energy. Under 785 and 980 nm laser excitation, the samples showed green (2H11/2→4I15/2, 4S3/2→4I15/2) and red (4F9/2→4I15/2) upconversion emissions. The upconversion mechanisms were stud-led in detail through laser power dependence. Excited state absorption and energy transfer process were discussed as possible upconversion mechanisms. The cross relaxation process in Er3+ was also investigated.     

Form of fluorine in Na2O-NaF-SiO2 slags determined by infrared spectroscopy

Abstract

The form of fluorine in Na₂O-NaF-SiO₂ slags has been investigated using Fourier transform infrared spectroscopy. Additions of NaF shifted absorption peaks for stretching modes of Si O bonds to higher wavenumbers, where the basicity of (mol-%Na₂O)/ (mol-%SiO₂ ) was kept constant, and the shift became larger with an increase in the concentration of NaF. This shift can be explained by the change from Si-O to Si-F bonds, with reference to harmonic oscillation theory of diatomic molecules. It is likely that added NaF depolymerises the silicate network to form Si-F bonds in Na₂O-NaF-SiO₂ slags.     

The effect of CaF2 on the viscosities and structures of CaO-SiO2(-MgO)-CaF2 slags

The viscosities of CaO-SiO₂(-MgO)-CaF₂ slags were measured to clarify the effect of CaF₂ on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. Furthermore, the infrared (IR) spectra of the quenched slags were analyzed to understand the structural role of CaF₂ in the modification of slag structure. The CaF₂ affects the critical temperature (T _CR) of the slags; that is, the higher the content of CaF₂, the lower the T _CR of the slags. It is suggested that some extent of undercooling as a driving force is needed for the precipitation of solid particles in the melt. In the composition of B (≡(mass pct CaO)/(mass pct SiO₂)) = 1.0, the T _CR was decreased about 150 to 200 K by addition of 10 mass pct MgO, while the T _CR was increased about 100 K by MgO addition at B = 1.3. The effect of CaF₂ on the viscous flow of molten slags can be understood based on a decrease in the degree of polymerization by F⁻ as well as by O²⁻ ions and this was confirmed by the IR spectra of the quenched slags. The relative intensity of the IR bands for [SiO₄]-tetrahedra with low NBO/Si decreased, while that of the IR bands for [SiO₄]-tetrahedra with high NBO/Si increased with increasing CaF₂ content. The decrease in viscosity of the CaO-SiO₂-MgO-CaF₂ (B = 1.0) system by CaF₂ addition was negligible, while the effect of CaF₂ on the viscosity was significant in the more basic system (B = 1.3).     

CaO-SiO_2-B_2O_3熔渣的热力学计算模型

根据CaO-SiO2、CaO-B2O3和SiO2-B2O3二元相图确定了熔渣的结构单元,利用熔渣的分子离子共存理论建立了CaO-SiO2-B2O3三元熔渣活度模型。通过对模型求解,可以计算出熔渣中CaO、SiO2、B2O3、CS、C2S、C3B、C2B、CB和CB2的组分活度。分析了熔渣碱度、B2O3含量及温度对熔渣组分活度的影响,其中熔渣碱度的影响最大,B2O3含量的影响次之,温度的影响最小。     

Photoluminescence study of SiO₂ coated Eu³⁺:Y₂O₃ core-shells under high pressure

Uniform core-shell Eu3+:Y2O3/SiO2 spheres were synthesized via precipitation and the Stber method.The structural transition of core-shell Eu3+:Y2O3/SiO2 was studied by using high pressure photoluminescence spectra.With pressure increasing,the emission intensities of 5D0→7F0,1,2 transitions of Eu3+ ions decreased and the transition lines showed a red shift.The relative luminescence intensity ratio of 5D0→7F2 to 5D0→7F1 transitions decreased with increasing pressure,indicating lowering asymmetry around Eu3+ ions.During compression,structural transformation for cores in the present core-shell Eu3+:Y2O3/SiO2 sample from cubic to monoclinic took place at 7.5 GPa,and then the monoclinic structure turned into hexagonal above 15.2 GPa.After the pressure was released,the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.     

Role of B2O3 on the Viscosity and Structure in the CaO-Al2O3-Na2O-Based System

The effect of B₂O₃ on the viscosity and structure in the calcium-aluminate melt flux system containing Na₂O was studied. An increase in the B₂O₃ content at fixed CaO/Al₂O₃ ratio lowered the viscosity. Higher CaO/Al₂O₃ ratio at fixed B₂O₃ content also decreased the viscosity. The alumino-borate structures were confirmed through Fourier transformed infrared (FTIR) and Raman spectroscopy and consisted of [AlO₄]-tetrahedral structural units, [BO₃]-triangular structural units, and [BO₄]-tetrahedral structural units, which could be correlated to the viscosity. At fixed CaO/Al₂O₃ ratio, B₂O₃ additions decreased the [AlO₄]-tetrahedral structural units and transformed the 3-D network structures such as pentaborate and tetraborate into 2-D network structures of boroxol and boroxyl rings by breaking the bridged oxygen atoms (O⁰) to produce non-bridged oxygen atoms (O^?) leading to a decrease in the molten flux viscosity. At fixed B₂O₃ contents and higher CaO/Al₂O₃ ratio, 3-D complex network structures become 3-D simple and 2-D isolated network structures, resulting in lower viscosities. The apparent activation energy for viscous flow varied from 132 to 249 kJ/mol according to the composition of B₂O₃ and CaO/Al₂O₃ ratio.     

A Study on the Effect of Na2O on the Viscosity for Ironmaking Slags

The viscosities of CaO‐SiO₂‐10wt%MgO‐20wt%Al₂O₃‐Na₂O slags (CaO/SiO₂ = 0.8–1.2, wt%Na₂O = 0–10) were measured to estimate the effect of Na₂O on the viscous behavior at elevated temperatures. The slag viscosity at 1773 K decreased with increasing Na₂O contents, which is observed in a basic oxide component. However, the FT‐IR spectroscopic analysis of the slag structure seemed to verify that [AlO₄]‐tetrahedra depolymerized more readily than [SiO₄]‐tetrahedra due to ionic charge compensation which has a tendency to be more effective on [AlO₄]‐tetrahedra. Hence, for the present slag system, the viscosity decreased with additions of Na₂O by providing network breaking O^2‐ ions, and the charge balance by Na⁺ ions independently contributed to the depolymerization of the network structure of the molten slag. In addition, Na₂O also lowered the critical temperature (T_CR) resulting in a larger temperature difference between the operating temperature (T_OP) and T_CR, which can enhance operational stability.     

Y2O3对超细Mo复合粉末烧结性能与显微组织的影响

以仲钼酸铵(NH<,4>)<,6>Mo<,7>O<,24>·4H<,2>O和硝酸钇Y(NO<,3>)<,3>6H<,2>O为原料,采用喷雾干燥-煅烧-热还原工艺制备含Y的超细Mo复合粉末,粉末经成形、预烧和高温烧结制备细晶Mo合金,研究Y<,2>O<,3>对超细Mo复合粉末烧结性能与显微组织的影响.结果表明:热还原后稀...     

Citric Gel Synthesis and Luminescent Properties of Ce^3＋-Activated SrGa2O4 Phosphor

Ce^3＋-activated SrGa2O4 phosphor was synthesized by a method of citric gel,wherein citric acid served as a chelate agent,and the as-synthesized powder was calcined in a slightly reduced ambient.The crystallization characteristics of the sample varied with the calcining temperature.Compared with the phosphor prepared by the solid-state reaction,the phosphor synthesized by citric gel was calcined at a relatively lower temperature.Consequently,the volatilization of Ga2O3 during high-temperature calcining process was avoided.The typical double-peak emission of Ce^3＋ originated from 2D（5d）→4F5/2（4f）,and 2D（5d）→4F7/2（4f）was observed,and the intrinsic emission of SrGa2O4 host was much restricted.The emission intensity varied with the calcining temperature because the different crystallinity and the optimal concentration of Ce-dopant was determined at 3%.     

Optimization of BaMgAl10O17:Eu2+ phosphors by the substitution of Si-N bonds for Al-O bonds

We proposed a simple method to improve the thermal stability of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphors by the substitution of Si-N bonds for Al-O bonds in the host lattice. Both photoluminescence properties and thermal stability under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation could be significantly improved through Si-N incorporation. After thermal degradation at 600 °C for 1 h in air atmosphere, the Si-N doped sample (Ba_0.88Eu_0.12MgAl_9.97Si_0.03O_16.97N_0.03) had the highest emission intensity which was 22% and 40% stronger than that of as-received sample under UV and VUV excitation, respectively. This could be attributed to the stable local structure surrounding the Eu²⁺ ions and the lower electronegativity of nitrogen.     

均匀共沉淀法合成纳米Gd_2O_3:Eu粉体及其发光特性

以六次甲基网胺(hexamethylenetetramine,(CH2)6N4,HMT)为沉淀剂,在GdCl3和EuCl3混合溶液中,利用均匀共沉淀法制得了纳米颗粒.结果表明,获得的Gd2O3:Eu纳米颗粒近似为球形,尺寸均匀,平均粒径为100 nm,且每个球形颗粒由平均粒径为20 nm的微晶聚并而成.Gd2O3:Eu荧光粉在波长612 nm的红光发射来自Eu3+的5D0-7F2电偶极跃迁,发光强度随煅烧温度提高而增强,随Eu3+掺杂摩尔分数的提高而增强.Eu3+掺杂摩尔分数超过7%时,发生浓度淬灭,发光强度减弱.     

Effect of Slag Composition on the Concentration of Al2O3 in the Inclusions in Si-Mn-killed Steel

The thermodynamic equilibria between CaO-Al₂O₃-SiO₂-CaF₂-MgO(-MnO) slag and Fe-1.5 mass pct Mn-0.5 mass pct Si-0.5 mass pct Cr melt was investigated at 1873 K (1600 °C) in order to understand the effect of slag composition on the concentration of Al₂O₃ in the inclusions in Si-Mn-killed steels. The composition of the inclusions were mainly equal to (mol pct MnO)/(mol pct SiO₂) = 0.8(±0.06) with Al₂O₃ content that was increased from about 10 to 40 mol pct by increasing the basicity of slag (CaO/SiO₂ ratio) from about 0.7 to 2.1. The concentration ratio of the inclusion components, \( {{X_{{{\text{Al}}_{2} {\text{O}}_{3} }} \cdot X_{\text{MnO}} } \mathord{\left/ {\vphantom {{X_{{{\text{Al}}_{2} {\text{O}}_{3} }} \cdot X_{\text{MnO}} } {X_{{{\text{SiO}}_{2} }} }}} \right. \kern-0pt} {X_{{{\text{SiO}}_{2} }} }} \) , and the activity ratio of the steel components, \( {{a_{\text{Al}}^{2} \cdot a_{\text{Mn}} \cdot a_{\text{O}}^{2} } \mathord{\left/ {\vphantom {{a_{\text{Al}}^{2} \cdot a_{\text{Mn}} \cdot a_{\text{O}}^{2} } {a_{\text{Si}} }}} \right. \kern-0pt} {a_{\text{Si}} }} \) , showed a good linear relationship on a logarithmic scale, indicating that the activity coefficient ratio of the inclusion components, \( {{\gamma_{{{\text{SiO}}_{2} }}^{i} } \mathord{\left/ {\vphantom {{\gamma_{{{\text{SiO}}_{2} }}^{i} } {\left( {\gamma_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{i} \cdot \gamma_{\text{MnO}}^{i} } \right)}}} \right. \kern-0pt} {\left( {\gamma_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{i} \cdot \gamma_{\text{MnO}}^{i} } \right)}} \) , was not significantly changed. From the slag-steel-inclusion multiphase equilibria, the concentration of Al₂O₃ in the inclusions was expressed as a linear function of the activity ratio of the slag components, \( {{a_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{s} \cdot a_{\text{MnO}}^{s} } \mathord{\left/ {\vphantom {{a_{{{\text{Al}}_{2} {\text{O}}_{3} }}^{s} \cdot a_{\text{MnO}}^{s} } {a_{{{\text{SiO}}_{2} }}^{s} }}} \right. \kern-0pt} {a_{{{\text{SiO}}_{2} }}^{s} }} \) on a logarithmic scale. Consequently, a compositional window of the slag for obtaining inclusions with a low liquidus temperature in the Si-Mn-killed steel treated in an alumina ladle is recommended.     

A structural model for binary silicate systems

A structural model is presented for binary silicate systems of the typeMO-SiO₂, whereMO is a basic oxide, in which silicate tetrahedra and oxygen “bridges” are treated as structural units. One single formalism applies over the entire composition range from pureMO, where the model reduces to a simple orthosilicate anion model, to pure SiO₂, where the model reduces to a simple model of the breaking of oxygen “bridges” upon the addition ofMO. At intermediate compositions, chain length distributions for silicate polymer chains can be calculated from the model, even though these polymeric chains are not explicitly treated as structural units of the model. The calculated chain length distributions are in very good agreement with those calculated from the polymeric model of Masson for all systems studied. Furthermore, two dimensional (cyclic) and three dimensional (network) polymeric structures are accounted for by the present model. The model accounts well for available enthalpy, entropy, activity, and phase diagram data in the binary liquid systemsMO-SiO₂ whereM = Ca, Mg, Mn, Fe, or Pb. The observed variations of ΔH with composition and from system to system are explained in terms of the energies of the various bonds and are represented by a three parameter equation. Although the model has been tested here only for liquid slags, it should be useful in understanding the structure of silicate glasses as well.     

Activity Calculation by Application of Sub-Regular Solution Model in Binary Oxide Systems

 To confirm sub-regular solution model valid for predicting the activity of component in binary oxide systems, seven systems in the whole concentration and twelve systems presenting saturation concentration have been studied. The total average relative errors of component 1 and 2 are 3.2% and 4.1% respectively by application of the sub-regular solution model into the systems within the whole concentration. However, the total average relative errors are 16% and 1088% in the systems presenting saturation concentration. The results show that sub-regular solution model is not good for predicting the systems presenting saturation concentration, especially for the systems containing acidic or neutral oxide. The reason may be that the influence of the two types of oxide on the configuration is greater in binary oxide systems. These oxides can be present in the form of complex anion partly, Si-O, Al-O, Ti-O and so on, for example (SiO4)4-. That is contrary to sub-regular solution model which is supposed that the oxide systems consist of cation and O2-. But compared with regular solution model and quasi-regular solution model, sub-regular solution model is closer to the characteristics of actual solution and the calculated results are superior.     

Structural analysis by Rietveld refinement of calcium and lanthanum phosphosilicate apatites

Britholites with the general formula Ca10-xLnx(PO4)6-x(SiO4)xF2, (0≤x≤6) are considered to be promising matrices for the confinement of the by-products in the nuclear industry. A thermodynamic study sh...     

CaO－Al_2O_3－SiO_2渣系氮的溶解热力学

根据炉渣结构的共存理论，推导了ＣａＯ－Ａｌ_２Ｏ_３－ＳｉＯ_２熔渣的作用浓度计算模型。模型计算得出的各组元的作用浓度值与文献报道的活度值非常一致。在此基础上，进一步采用回归分析法找出了ＣａＯ－Ａｌ_２Ｏ_３－ＳｉＯ２渣系中溶解的氮含量以及与此渣系相平衡的钢中氮含量及氮的分配比随渣中各组元作用浓度之间变化的定量关系，理论计算结果与实验值非常符合。     

The macrophage cell surface glycoprotein F4/80 is a highly glycosylated proteoglycan

Molecules whose expression is limited to particular leukocyte populations are of interest since they may perform unique functions for these cells. We therefore examined the biochemical nature of the F4/80 molecule, which is expressed solely on macrophage and dendritic cell subpopulations. Our study clearly indicates that post-translational modifications, which can influence both a protein's structural and functional features, constitute a major component of the 160-kDa cell-surface F4/80 molecule. The F4/80 molecule is synthesized as a single polypeptide chain which acquires numerous intramolecular disulfide bonds and requires an extended time period (T1/2 = 60 min) for transport to an endoglycosidase H-resistant form. The F4/80 molecule contains extensive N-linked glycosylation which contributes approximately 40 kDa to the mature molecule. The N-linked carbohydrates are of the branched, complex type, containing repeating N-acetylglycosamine or N-acetyllactosamine units which mediate the reactivity of the F4/80 molecule with Datura stramonium lectin. O-linked glycosylation is also present and contributes approximately 10 kDa to the F4/80 molecule. Furthermore, the sialic acid modifications of the F4/80 molecule are primarily through alpha 2-6 linkages to galactose. Finally, we demonstrate that the F4/80 molecule is a proteoglycan modified by chondroitin sulfate glycosaminoglycans. In addition to clarifying the nature of the F4/80 molecule biochemically, these post-translational modifications have specific implications for molecular recognition processes. We conclude that the modifications of the F4/80 molecule may mediate cell-cell recognition, cell adhesion, or ligand binding independently of the F4/80 molecule protein core.