MgO is a crystalline solid with significant practical and theoretical value in many fields. Brillouin scattering has long been regarded as a reliable method for accurately measuring the elasticity and photoelasticity of crystals; however, its practical application in photoelasticity has been stagnant. In this paper, three independent photoelastic constants of MgO have been measured for the first time by polarized Brillouin scattering spectroscopy and we have defined a scattering factor containing three photoelastic constants to connect with the Brillouin peak intensity. Accordingly, the ratios of |p11/p44| = 2.87 (1), |p12/p44| = 0.53 (2), and |p12/p11| = 0.18 (1) were accurately determined by comparing the intensities of transverse and longitudinal acoustic modes within the same spectrum. Then, a standard sample of CaF2 crystals was adopted to calculate the corresponding peak intensity of MgO to achieve the absolute values (|p44| = 0.085 (1), |p11| = 0.244 (4) and |p12| = 0.045 (3)). Finally, all three constants were confirmed to be negative. These first-hand Brillouin scattering results can eliminate the long-standing discrepancies of the photoelastic constants of MgO. A standard process for the simultaneous measurement of elasticity and photoelasticity through Brillouin scattering was also constructed.
The local structure around germanium is a fundamental issue in material science and geochemistry. In the prevailing viewpoint, germanium in GeO2 melt is coordinated by at least four oxygen atoms. However, the viewpoint has been debated for decades due to several unexplained bands present in the GeO2 melt Raman spectra. Using in situ Raman spectroscopy and density functional theory (DFT) computation, we have found a [GeOØ2]n (Ø = bridging oxygen) chain structure in a GeO2 melt. In this structure, the germanium atom is coordinated by three oxygen atoms and interacts weakly with two neighbouring non-bridging oxygen atoms. The bonding nature of the chain has been analyzed on the basis of the computational electronic structure. The results may settle down the longstanding debate on the GeO2 melt structure and modify our view on germanate chemistry.
In situ high temperature Raman spectra of xK2O-(100-x)GeO2, samples containing 0, 5, 11.11, 20, 25, 33.3, 40, and 50 %mol K2O, were measured. The structure units and a series of model clusters have been designed, optimized, and calculated by quantum chemistry ab initio calculations. The computational simulation in conjunction with the experiments put forward a novel method to correct the experimental Raman spectra of the melts. Deconvolution of the stretching vibrational bands of nonbridging oxygen of [GeO4] tetrahedra of Raman spectra by Gaussian functions was carried out, and the quantitative distribution of different Qn species in molten binary potassium germanates was obtained. The result on all molten samples show that four-fold coordinated germanium atoms occupy a dominant position in the melt and only four-fold coordinated exists in the melt when the K2O content exceeds a certain amount. For melts with high GeO2 content, with the increasing K2O content, the structure of [GeO4] tetrahedra gradually changes from a three-dimensional network consisting of both six-membered and three-membered rings to a three-dimensional network that presents all three-membered rings.
Aluminum nanowires with irregular morphologies were prepared by template-free electrodeposition from a room-temperature chloroaluminate ionic liquid. The effects of the diffusion condition and deposition potential on the morphologies of Al nanowires were investigated. The decrease of diffusion flux leads to the formation of particular segmented morphologies of Al nanowires. A dynamic equilibrium between the electrochemical reaction and the diffusion of Al2Cl7- results in the current fluctuation and the periodical variation of diameters in the Al nanowires growth period. Al nanowires with several kinds of morphologies can be controllably electrodeposited under a restricted diffusion condition, without using a template. Increasing the overpotential shows the similar influence on the morphology of Al nanowires as the decrease in diffusion flux under the restricted diffusion condition. Most of the segmented Al nanowires have a single crystalline structure and grow in the [100] orientation. This work also provides a new strategy for the fabrication of nanowires with highly controllable irregular morphologies.
In situ high-temperature Raman spectra of polycrystalline KBi(MoO4)2 were recorded from room temperature to 1073 K. Thermal stability of the monoclinic KBi(MoO4)2 was examined by temperature-dependent XRD. The monoclinic phase transformed into the scheelite tetragonal structure at 833 K, and then to the monoclinic phase at 773 K. Quantum chemistry ab initio calculation was performed to simulate the Raman spectra of the structure of KBi(MoO4)2 high-temperature melt. The experimental Raman band at 1023 K was deconvoluted into seven Gaussian peaks, and the calculated results were in good agreement with the experimental data. Therefore, the vibrational modes of Raman peaks of molten KBi(MoO4)2 were assigned. It was confirmed that the isolated structure of [Bi(MoO4)2]- monomer, consisting of Mo6+ centers and Bi3+ sub-centers connected by edge-sharing, mainly exists in the melt of KBi(MoO4)2.
In this study, vacuum low-pressure carburizing heat treatments were carried out on 18Cr2Ni4WA case-carburized alloy steel. The evolution and phase transformation mechanism of the microstructure of the carburized layer during low-temperature tempering and its effect on the surface hardness were studied. The results showed that the carburized layer of the 18Cr2Ni4WA steel was composed of a large quantity of martensite and retained austenite. The type of martensite matrix changed from acicular martensite to lath martensite from the surface to the core. The hardness of the carburized layer gradually decreased as the carbon content decreased. A thermodynamic model was used to show that the low-carbon retained austenite was easier to transform into martensite at lower temperatures, since the high-carbon retained austenite was more thermally stable than the low-carbon retained austenite. The mechanical stability-not the thermal stability-of the retained austenite in the carburized layer dominated after carburizing and quenching, and cryogenic treatment had a limited effect on promoting the martensite formation. During low-temperature tempering, the solid-solution carbon content of the martensite decreased, the compressive stress on the retained austenite was reduced and the mechanical stability of the retained austenite decreased. Therefore, during cooling after low-temperature tempering, the low-carbon retained austenite transformed into martensite, whereas the high-carbon retained austenite still remained in the microstructure. The changes in the martensite matrix hardness had a far greater effect than the transformation of the retained austenite to martensite on the case hardness of the carburized layer.
Thallium is an emerging pollutant reported in wastewater along with the increasing mining and smelting of thallium-containing ores in recent years. The complete removal of Tl(I) from wastewater is of significant emergency due to its high toxicity and mobility, however, Tl(I) removal is always confronted with numerous technical difficulties because of the extremely low Tl(I) concentration in wastewater and the disturbances of many accompanying impurity ions. Adsorption is currently the most widely used method for Tl(I) removal on industrial scale and varied kinds of adsorbents such as Prussian blue analogues, biosorbents, and metal oxides have been developed. However, the adsorption process of Tl(I) is always affected by the co-existing cations, resulting in low Tl(I) removal efficiency. Recently, the development of a variety of novel adsorbents or ion sensors based on macrocyclic compounds for enrichment and accurate determination of trace Tl(I) in aqueous solutions exhibits great potential for application in Tl(I) removal from wastewater with high selectivity and process efficiency. This paper provides an overview of the adsorption methods for Tl(I) removal from wastewater with emphasis on complexation properties between varied types of adsorbents and Tl(I). Future directions of research and development of adsorptive Tl(I) removal from industrial wastewater are proposed.
Sodium orthosilicate was synthesized by a wet chemical method with further calcination at 600 °C. Mixtures of Na4SiO4 and alkali (Li/Na/K) carbonates were prepared by a mechanical mixing method. The CO2 capture performance of the samples was characterized by dynamic thermogravimetric analyses and in situ XRD and Raman spectroscopy in 80 vol% CO2 mixed with 20 vol% N2. It was found that sodium orthosilicate could be used for CO2 sorption, and its maximum capacity could reach up to 19.2 wt%. The addition of alkali carbonates, which serve as promoters, led to the enhancement of the CO2 capture performance of Na4SiO4, especially at low temperatures, because of the formation of C2O52-. The existence of C2O52- in the mixture exposed to 80 vol% CO2 was confirmed by in situ Raman spectra, and its geometric structure was presented by DFT calculations. The formation of C2O52- within carbonates exhibited a positive influence on the CO2 capture at low temperatures and the enhancement of CO2 diffusion by Grotthuss-like transport through the carbonate product shell at high temperatures besides the formation of eutectic carbonate melts.
Knowledge of the molecular-level structure of the Li2GeO3 melt is essential to understand its basic physicochemical properties. In this work, in situ Raman spectroscopy, factor group analysis, and density functional theory (DFT) calculations were applied to investigate the Li2GeO3 crystal Raman spectrum and its transformation during the crystal melting process. Finally, the Li2GeO3 melt structure was determined. The Li2GeO3 lattice phonons were fully analyzed by the factor group. The DFT calculations confirmed the analysis results and assigned all of the experimental Raman bands. There are two characteristic Raman bands in the experimental spectrum. The 495 cm-1 band (mid-frequency band) is attributed to the symmetric bending vibration of the Ge-O-Ge bond, and the 814 cm-1 band (high-frequency band) arises from the symmetric stretching vibration of the O-Ge-O bond. The mid-frequency band anomalously shifted to a higher frequency and the high-frequency band normally shifted to a lower frequency when the crystal melted. The DFT method was employed to investigate two possible Li2GeO3 melt structures, one consisting of the [GeO2Ø2] n (Ø = bridging oxygen) chain and the other consisting of the [Ge3O9] ring. The chain-type structure was demonstrated to provide a better description of the Li2GeO3 melt than the ring-type structure. The anomalous shift of the mid-frequency band is related to the shrinkage of the [GeO2Ø2] n chain. On the basis of the chain-type structure, the high viscosity of the Li2GeO3 melt and the growth phenomena of the Li2GeO3 crystal were explained.
In situ high temperature X-ray diffraction and Raman spectroscopy were used to investigate the temperature dependent micro-structure of KAlF4. Density functional theory was applied to simulate the structure of crystalline KAlF4 while a quantum chemistry ab initio simulation was performed to explore the structure of molten KAlF4. Two crystal polymorphs demonstrated to be present in solid KAlF4. At the temperature below 673 K, it belongs to the tetragonal crystal system within the P4/mbm space group, while the high temperature phase is attributed to the monoclinic crystal system within the P21/m space group. Both polymorph KAlF4 phases are characterized by a layered structure consisting of K⺠and [AlF6]3- octahedra, each of the [AlF6]3- octahedra equivalently shares four corners with other four [AlF6]3- octahedra along the layer. The layered structure became unstable at higher temperatures and crashed when the temperature exceeded the melting point. It demonstrated that the molten KAlF4 consisted of predominant [AlF4]- and a small amount of [AlF6]3-. The Raman spectrum of molten KAlF4 simulated by using a quantum chemistry ab initio method agreed well with the experimental Raman spectrum.
The quantitative distribution of different species ( Q ijklm and H ijklmno) in binary potassium molybdate melts has been investigated by in situ high temperature Raman spectroscopy in conjunction with quantum chemistry (QC) ab initio calculations. The symmetric stretching vibrational wavenumbers of molybdenum nonbridging oxygen bonds in high wavenumber range and their respectively corresponding Raman scattering cross sections were determined and analyzed. Deconvolution of the stretching bands of molybdenum nonbridging oxygen bonds of molten Raman spectra by using the Voigt function was carried out. The six-coordinated molybdenum oxygen octahedra [MoO6]6- have been proposed to be present in molten molybdates, apart from the well-known existence of the four-coordinated [MoO4]2- tetrahedra. The quantitative analysis of different species in the molten K2MoO4-MoO3 system and their dependence on the content of MoO3, as well as the relationship with the viscosities of the melts, were also discussed. The quantitative results have been integrated with published data on physical and chemical properties of the melts.
The Li2Mo4O13 melt structure and its Raman spectral characteristics are the key for establishing the composition-structure relationship of lithium molybdate melts. In this work, Raman spectroscopy, factor group analysis, and density functional theory (DFT) were applied to investigate the structural and spectral details of the H-Li2Mo4O13 crystal and a Li2Mo4O13 melt. Factor group analysis shows that the crystal has 171 vibrational modes (84Ag + 87Au), including three acoustic modes (3Au), six librational modes (2Ag + 4Au), 21 translational modes (7Ag + 14Au), and 141 internal modes (75Ag + 66Au). All of the Ag modes are Raman-active and were assigned by the DFT method. The Li2Mo4O13 melt structure was deduced from the H-Li2Mo4O13 crystal structure and demonstrated by the DFT method. The results show that the Li2Mo4O13 melt is made up of Li+ ions and Mo4O132- groups, each of which is formed by four corner-sharing MoO3Ø/MoO2Ø2 tetrahedra (Ø = bridging oxygen). The melt has three acoustic modes (3A) and 54 optical modes (54A). All of the optical modes are Raman-active and were accurately assigned by the DFT method.
This study explores the effect of introducing additional alloy elements not only in a different order but also at different stages of the Ruhrstahl-Heraeus (RH) process of low-carbon silicon steel production. A more economical method, described as "pre-alloying", has been introduced. The evolution of MnO-FeO inclusions produced by pre-alloying was investigated. Results show that spherical 3FeO·MnO inclusions form first, then shelled FeO·zMnO (z = 0.7-4) inclusions nucleate on the surface of pre-existing 3FeO·MnO. Spherical FeO·zMnO (z = 3-5) is further evolved from shelled 3FeO·MnO by diffusion. Because these MnO-FeO inclusions float up into the slag before degassing, the pre-alloying process does not affect the quality of the melt in the end. Both carbon content and inclusion size conform to industry standards.
Recent interest in optimizing composition and synthesis conditions of functional crystals, and the further exploration of new possible candidates for tunable solid-state lasers, has led to significant research on compounds in this family MIMIII(MVIO4)2 (MI = alkali metal, MIII = Al, In, Sc, Fe, Bi, lanthanide; MVI = Mo, W). The vibrational modes, structure transformation, and Al coordination of crystalline, glassy, and molten states of KAl(MoO4)2 have been investigated by in-situ high temperature Raman scattering and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, together with first principles density functional simulation of room temperature Raman spectrum. The results showed that, under the present fast quenching conditions, Al is present predominantly in [AlO6] octahedra in both KAl(MoO4)2 glass and melt, with the tetrahedrally coordinated Al being minor at approximately 2.7%. The effect of Kâº, from ordered arrangement in the crystal to random distribution in the melt, on the local chemical environment of Al, was also revealed. The distribution and quantitative analysis of different Al coordination subspecies are final discussed and found to be dependent on the thermal history of the glass samples.
In-situ high temperature Raman spectroscopic (HTRS) technique in combination with density functional theory (DFT) analysis has been adopted to investigate the micro-structure of solid and molten A2W2O7 (A=Li, Na, K). The [WO6] octahedra were found to be connected to each other by corner and edge sharing in the crystalline Li2W2O7 and K2W2O7 compounds. In the crystal lattice of Na2W2O7, on the other hand, the [WO4] tetrahedra and [WO6] octahedra were found to coexist and paired by corner sharing. Although the structural diversity has clearly led to distinct Raman spectra of the crystalline A2W2O7 compounds, the spectra of their melts tended to be analogous, showing the typical vibration modes of (W2O7)2- dimer. A mechanism was then proposed to explain the structure evolution occurring during the melting process of A2W2O7. The effect of A+ cation on the Raman bands of (W2O7)2- dimer in molten A2W2O7 has also been investigated. Both the wavenumber and full width at half-height (FWHH) of the characteristic band assigned to the symmetrical stretching vibration mode of WOnb (non-bridging oxygen) in (W2O7)2- were found to decrease in the sequence of Li+, Na+ and K+, indicating the cation effect on the mean bond length and its distribution range of WOnb. In addition, the relative intensity of this band was also influenced by the cation and it was increased in the order of Li2W2O7, Na2W2O7 and K2W2O7, which has been explained by the charge transfer process and confirmed by Mulliken overlap population analysis.
LiB3O5 is the most widely used nonlinear optical crystal. Li2Mo3O10 (a nominal composition) is a typical flux used to produce large-sized and high-quality LiB3O5 crystals. The structure of the LiB3O5-Li2Mo3O10 high-temperature solution is essential to understanding the flux behavior of Li2Mo3O10 but still remains unclear. In this work, high-temperature Raman spectroscopy combined with density functional theory (DFT) was applied to study the LiB3O5-Li2Mo3O10 solution structure. Raman spectra of a LiB3O5-Li4Mo5O17-Li2Mo4O13 polycrystalline mixture were recorded at different temperatures until the mixture melted completely. The solution structure was deduced from the spectral changes and verified by DFT calculations. When the mixture began to melt, its molybdate component first changed into the Li2Mo3O10 melt; meanwhile, the complicated molybdate groups existing in the crystalline state transformed into Mo3O102- groups, which are formed by three corner-sharing MoO3Ø-/MoO2Ø2 (Ø = bridging oxygen atom) tetrahedra. When LiB3O5 dissolved in the Li2Mo3O10 melt, the crystal structure collapsed into polymeric chains of [B3O4Ø2-]n. Its basic structural unit, the B3O4Ø2- ring, coordinated with the Mo3O102- group to form a MoO3·B3O4Ø2- complex and a Mo2O72- group. On the basis of the LiB3O5-Li2Mo3O10 solution structure, we discuss the LiB3O5 crystal growth mechanism and the compositional dependence of the solution viscosity.
Melt structures are essential to understand a variety of crystal growth phenomena of alkali-metal triborates, but have not been fully explored. In this work, Raman spectroscopy, coupled with the density functional theory (DFT) method, has been used to solve the CsB3O5 (CBO) melt structure. When the CBO crystal melts, the extra-ring B4-Ø bonds (the B-Ø bonds of BØ4 groups, Ø = bridging oxygen atom) that connect two B3O3Ø4 rings (the basic boron-oxygen unit in the CBO crystal structure) break. As a result, the three-dimensional boron-oxygen network collapses to unique polymer-like [B3O4Ø2]n chains. On the basis of the optimized [B3O4Ø2]n chain model, the CBO melt Raman spectrum was calculated by the DFT method for the first time and the calculated results confirm that the [B3O4Ø2]n chain is the primary species in the CBO melt. These results also demonstrate the capability of the combined Raman spectral and DFT method for analyzing borate melt structures.
Comprehensive experimental as well as theoretical methods were applied to investigate the structure evolution of jadeite in the hot-melt process, especially on the variation of aluminium coordination number. In-situ high temperature Raman spectroscopic technique was used to record the characteristic Raman spectra of jadeite and its melt with the increasing temperature, consequently, density function theory and ab initio calculation methods were applied to analyze the related micro-structures and aluminium coordination number and simulate the Raman spectra. Results showed that aluminum in jadeite crystal is all six-fold and would transform into four-fold coordination at 1 293K while jadeite being melting. Aluminum is prominently in four-fold coordination in the melt, in which TO4 (T = Si, Al) connects to each other as the network of multiple rings. Five-fold coordinated aluminum emerges and it appears the trend of phase separation while the melt transformed into glass by the processing of fast cooling.
Temperature dependent Raman spectra of BiB3 O6 crystal and its melt were recorded and the microstructure of BiB3 O6 melt was predicted. Multiple theoretical methods including quantum chemistry ab initio calculation and DFT (Density Function Theory) methods were applied to simulate the BiB3 O6 crystal and melt structure and Raman spectra. It was demonstrated that B-O triangles and Bi lattice in the crystal reveal little affected in structure while B-O tetrahedra shows severe distortion with increasing temperature, especially B-O tetrahedra disappears after being completely melt. The microstructure of BiB3 O6 melt consists of six-member ring, [B6 O12](6-), which varies in bond lengths and angles individually. Cation Bi behaves to balance the charge of anion cluster, and the oxygen coordination number of cation Bi is 3, different from the crystal situation in which cation Bi is coordinated with 6 oxygens.
A calibration method for Raman spectroscopic quantitative analysis of binary alkaline silicate glasses is proposed. By applying ab initio quantum chemistry simulation, Raman optical activities (ROA) of various cluster units consisting of silicon-oxygen tetrahedra (SiOT) with different number of non-bridging oxygen (NBO) can be obtained. Thus, experimental results could be calibrated in order to reflect and represent directly the true relative density of various silicon-oxygen tetrahedra existing inside the silicate glasses. Cation effect on the intensity of Raman bands was also observed and discussed.
