ICP-AES同时测定铬质引流剂中的Cr2O3、Al2O3、Fe2O3和MgO

探讨了电感耦合等离子体-原子发射光谱法(ICP-AES)测定铬质引流剂中Cr2O3、Al2O3、Fe2O3和MgO的分析条件.试样经过氧化钠熔融分解,盐酸酸化,采用内标加入法,利用ICP光谱仪于所推荐的波长处,测量溶液中铬、铝、铁、镁元素对钇内标元素的相对强度,根据标准溶液绘制的校准曲线计算出待测元素氧化物的质量分数.对该方法进行精密度试验,相对标准偏差(RSD,n=8)均小于1.0％,本测试方法简单、快速、精度高,将该方法用于铬质引流剂中Cr2O3、Al2O3、Fe2O3和MgO含量的测定,取得满意效果.     

XPS and auger spectroscopy studies on mixtures of the oxides SiO2, Al2O3, Fe2O3 and Cr2O3

X-ray photoelectron Spectroscopy (XPS) and X-ray-induced Auger Spectroscopy were utilized to examine qualitative and quantitative aspects involved in the surface analysis of mechanical mixtures of the title oxides. Consideration of O1s and OKVV bands of the mixtures makes it possible to distinguish between the single oxide components. The energy shift between the Fe₂O₃ and SiO₂ (or Al₂O₃) components is about twice as large in the OKVV region as in the O1s region. By way of contrast, Auger Spectroscopy analysis of the mixtures does not appear to enable a quantitative distinction between the constituent oxides to be made. Conversely, XPS analysis provides instead quantitative results, although these are affected by a relative error of ± 10%. A simple approach, based on intensity ratio measurements of the single O1s components, enables relatively accurate quantitative results to be obtained.It is shown that analysis of appropriate mixtures is a useful case study for investigations on surface and interface properties of real materials. Argon ion etching effects on the mixtures and on the title oxides analyzed separately are reported.     

Growth,electronic properties and thermal stability of the Fe/Al2O3 interface

Soft X-ray photoelectron spectroscopy and resonant photoemission have been used to study the growth and electronic properties of Fe ultrathin films deposited on Al₂O₃ substrates. A simultaneous multilayer growth mode has been found for Fe growth at room temperature. For iron coverages below 1 ML, Fe²⁺ species are formed at the Fe/Al₂O₃ interface, followed by the formation of a metallic iron overlayer. The bonding of Fe at very low coverages occurs by charge transfer from Fe to surface oxygen atoms, and neither hybridisation of Fe and Al states nor reduction of the Al₂O₃ substrate are observed. The thermal stability of the interface has been also studied in the range 673–873 K. Annealing produces Fe agglomeration in such a way that some areas of the Al₂O₃ substrate become fully Fe-depleted. In these Fe-depleted areas, Fe²⁺ completely disappears and Al⁰ reduced species are formed. This behaviour would explain the decrease in the magnetoresistance performance of magnetic tunnel junctions after annealing above 573 K.     

Effect of Fe2O3 and Cr2O3 on the Processes of Pyroxene Formation in Silicate Glasses

We have investigated the processes of pyroxene formation in crystallization of glasses of the system SiO₂–Al₂O₃–CaO–MgO–Na₂O stimulated with chromium and iron oxides introduced together. It is found that sharp activation of the processes of pyroxene formation occurs in the temperature interval of thermal treatment 850–900°C. Interpretation of the absorption bands is carried out and conclusions are drawn on the structural role of the iron and aluminum ions in the process of formation of a pyroxene solid solution.     

XRD and Mössbauer spectroscopy investigation of Fe2O3–Al2O3 nano-composite

Fe₂O₃–Al₂O₃ nano-composites were synthesized by sol–gel means. The properties of samples sintered at various thermal treatment temperatures were investigated by X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The experimental results show that the γ- to α-Al₂O₃ transformation occurs at lower temperature after iron oxide doping. The samples obtained at 1173 K contained poorly crystallized γ-Al₂O₃ phase and an amorphous iron oxide. When the temperature of heating was increased to 1373 K, the sample was composed of α-Fe₂O₃/α-Al₂O₃ nano-composite and some solid solution. A superparamagnetic phenomenon was observed until the thermal treatment temperature reached 1373 K.     

Auger electron spectroscopy study on the Cr/Al2O3 interfacial reactions

Interfacial reactions of evaporated chromium with surface has been studied using Auger electron spectroscopy (AES). The results reveal that the interfacial region consists of a mixture, which is a double oxide of Cr and Al or two separated oxides. After annealing, the chromium oxide and the metallic Al produced by reduction of the Al³⁺ ions were easily detected by AES at the interface. We suggest that the interfacial reaction occurs mainly by the charge transfer from the 3d electrons of Cr atoms to O 2p orbitals of the Al₂O₃ substrate. The annealing at higher temperature (973 K) is favourable to promote the interfacial reaction between the surface oxygen and the initial few atomic monolayers of the deposited chromium. The results also showed that the change of the relative Auger peak-to-peak height (APPH(%)) of the Cr LMM group peaks can be used as an index to identify the oxidation states of chromium at the Cr/Al₂O₃ interface.     

Cr3+ doped Al2O3 nanoparticles: Effect of Cr3+ content in intensifying red emission

Cr³⁺-doped α-Al₂O₃ nanoparticles (Al_2−xCr_xO₃, 0.005 ≤ x ≤ 0.05) were synthesized by co-precipitation method. X-ray diffraction (XRD) patterns of Cr³⁺:Al₂O₃ nanoparticles revealed the crystallite size of ∼53 nm and electron microscopy (SEM & TEM) confirmed the spherical nanoparticle formation. Diffuse reflectance spectra (DRS) displayed peaks at 406 and 558 nm corresponding to the Cr³⁺ transitions which became prominent with the increase in Cr³⁺ concentration which was also evidenced by the gradually increasing pink coloration of the samples. Photoluminescence (PL) studies showed the sharp red emission at 694 nm (ruby line) which was observed for all samples. The Dq/B value for all samples was found to be greater than 2.3 confirming the presence of Cr³⁺ ions in the octahedral sites. Chromaticity diagrams displayed the maximum red appearance for the sample with x = 0.01 and a lifetime of 4 ms. The synthesized Cr³⁺:Al₂O₃ nanoparticles with smaller crystallite sizes and narrow near monochromatic emission can be used in various applications including sensing, lasing, and bioimaging applications.     

Cr4+在Al2O3多晶体中的光谱性能研究

采用传统无压烧结工艺制备Cr:Al2O3透明多晶陶瓷.测定了其退火前后的吸收光谱和荧光光谱,发现在Al2O3六配位的八面体结构中,Cr4+的荧光发射也处在1100-1600 nm波段的红外区间,荧光发射峰位于1223 nm附近,类似Cr4+在四面体中的发光行为.同时由于氧化铝晶格常数较小,晶体场强较强,使Cr4+:Al2O3荧光发射峰相对其他Cr4+掺杂的晶体发生蓝移.由于Cr4+:Al2O3中Cr4+是位于八面体配位结构中,其荧光发射峰较窄,半高宽Δλ仅为37 nm.     

Cr3+:Al2O3透明多晶陶瓷光谱特性分析

对透光性良好的Cr3+:Al2O3透明多晶陶瓷的光谱性能进行了研究,其吸收光谱中吸收峰与单晶红宝石相一致,按吸收光谱和Tanabe-Sugano能级图,算出其晶场强度参数Dq及Racah参数B分别为1792cm-1,689cm-1,Dq/B=2.6,陶瓷中Cr3+离子所处格位的晶体场强比单晶弱一些,但Cr3+:Al2O3透明陶瓷仍属于强场晶体材料;当Cr3+掺杂浓度到达0.8wt%时,陶瓷的发射谱仍保持较好的R线发射;随Cr3+掺杂浓度的增大,激发峰位发生"红移".在Cr3+:Al2O3透明多晶陶瓷的荧光谱上,发现一个波长为670nm的发射峰,经激发谱确认为Cr3+的发射峰.     

Strain wave in Cr rich CrFe alloys

Satellite reflections due to the strain wave were observed in Cr rich CrFe alloys by X-ray diffraction. The magnitude of the wave number vector of the strain wave decreases whenever the temperature approaches the ISDW-CSDW transition. From the temperature and concentration dependences of the strain wave and the lattice parameter observed by X-ray diffraction the magnetic phase diagram of CrFe was determined.     

Mössbauer studies of granular Fe/Al2O3 films

Results from low temperature Mössbauer measurements upon several samples of dispersed small Fe particles in an alumina matrix are presented. The nature and population of the various iron species are deduced and discussed in relation to the particle mean diameters. An evaluation of the blocking temperature for one sample has been attempted.     

Activation of Al2O3 by a long-ranged chemical bond mechanism

On the basis of density functional theory calculations, a novel bond mechanism with chemical strength but of long-ranged character is proposed. As compared to adsorption on a sole oxide or metal, the mechanism is found to enhance the bond strength between an adsorbate and an oxide in contact with a metal. As a model system, NO2 adsorption on alpha-Al2O3(0001) either in contact with Ag(111) or small Agn clusters is used. The observed phenomenon rests on charge transfer and modification of the oxide-metal interface. The mechanism is general in nature and the implication for heterogeneous catalysis is discussed.     

Cr3+掺杂的Ca3Al2Ge3O12石榴石的光谱性质

在此报告钙铝锗石榴石Ca₃Al₂Ge₃O₁₂中Cr³⁺离子的光谱特性,依据不同浓度的样品在不同温度下发射光谱的实验结果,分析了不等价Cr³⁺发光中心零声子线R₁,R₂的位置变化情况。通过对Cr³⁺吸收和发射光谱的分析,估算了Cr³⁺所处格位的晶场强度参数Dq和Racah参数,同时,对低温下Cr³⁺R线边带振动光谱的精细结构的起因进行了分析和指认。在室温和低温下测得Cr³⁺的⁴T₂→⁴A₂和²E→⁴A₂能级跃迁的荧光衰减为单指数规律。     

Fe3+ ions in amorphous solids: EPR on mechanically and chemically amorphized Al2O3

Stepwise amorphization of a low-level doped α-Al₂O₃ single crystal yielded powders without changes of the concentration and chemical nature of the dopants. Kind and degree of disturbances could be unambiguously monitored by the allowed and forbidden transitions of the Fe³⁺-cw-EPR in X-band using a Bruker bimodal cavity. Based on simulations diagonalizing the spin Hamiltonian forS = 5/2 it was possible to discriminate between regions as well as samples of structural order and disorder. The spectral pattern of the allowed and forbidden transitions of Fe³⁺ ions together with the field-position-dependent saturation behaviour (4.2 K) allowed us to differentiate between crystalline and amorphous components or regions of a sample.     

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au³⁺ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.     

Growth mechanism of ZnO nanorod/Fe3O4 nanoparticle composites and their photocatalytic properties

ZnO nanorods/Fe₃O₄ nanocomposites as the recyclable photocatalyst were synthesized by a co-precipitation method, with microwave assistant by dropping alkaline solution with Fe₃O₄ nanoparticles into the aqueous of zinc salt. These Fe₃O₄ nanoparticles were the nucleated centers for the ZnO nanorods growth so that these nanorods ended with aggregated Fe₃O₄ nanoparticles. The growth processes and mechanism are explained as those insoluble zinc hydroxides prefer to nucleate on the surface of Fe₃O₄ nanoparticles (heterogeneous nucleation) rather than nucleated as isolated ZnO nanostructures (homogeneous nucleation). These nanocomposites have strong photocatalytic ability to reduce RhB and moderate magnetization, which make them being good recyclable photocatalysts.