Absence Of Crystalline Phases Research Articles

Vitrification of a Simulator of Vat Residues from Liquid Radioactive Waste

The study on the posibility of the use of the optimal glass compositions for vitrification of an imitator of vat residues of liquid radioactive waste from nuclear power plants with VVER-1000 reactors was carried out. The main process parameters such as vitrification temperature, strength, corrosion resistance, absence of crystalline phases, minimization of glass-forming additives and inclusion the maximum amount of waste were analyzed. It has been established that the melting temperature of lead-borosilicate glass matrices was 1150 °C, which satisfies the requirements for vitrification of low- and medium-level waste. The ultimate compressive strength of the obtained samples of glass matrices was 136.0 MPa. In addition, it has been shown that lead-borosilicate glass matrices are the most resistant to leaching. The cesium leaching rate was 1.5·10-5 g/cm2·day.

Effect of Gamma Irradiation on Dielectric and AC Conductivity Studies of Bismuth Borate Glasses Doped with V2O5

Objectives: To study gamma ray irradiation effect on dielectric and AC conductivity of V2O5 doped bismuth borate glasses designed with the compositions 50B2O3-(50-X)Bi2O3-XV2O5 where, X = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and establishing the conduction mechanism. Methods: Glasses were synthesized by traditional melt quenching technique at 1323K. The prepared samples were subjected to annealing at 623K, which helps to remove strain in the samples. Absence of crystalline phases in the samples was confirmed by X-ray diffraction studies. An independent measurement of dielectric constant, dielectric loss and AC conductivity was carried out for temperature range from 300Kto 493K by impedance analyzer. Findings: The physical properties of glass were achieved by studying the density and the molar volume. Dielectric constant (e ’) and dielectric loss (e ”) were measured as a function of temperatures in the range from 300K to 493K, over the frequencies 102 Hz – 106 Hz before and after gamma ray irradiation. AC conductivity (s AC) of the glasses was measured as a function of frequency for different temperatures before and after gamma ray irradiation. Novelty: For the first time, it was attempted that the effect of gamma ray irradiation on dielectric and AC conductivity properties of bismuth-borate glasses doped with vanadium oxide has been investigated. Here we have observed the change in the variation of dielectric constant, dielectric loss and AC conductivity with frequency and temperature before and after gamma ray irradiation. The borate network becomes more compact after being exposed to gamma rays, and the energy band gap may even narrow. Furthermore, it has been found that the composition of the glass influences how radiation impacts conductivity. Keywords: Oxide Glasses; XRD; Gamma Ray Irradiation; Dielectric Properties; AC Conductivity

Evaluation of HNa[Cu2(Ac)6] As a Cathode Material for Li-Ion Batteries

Cathode materials in currently commercialized rechargeable Li-ion batteries (LIBs) use transition metal ions such as Mn, Fe, Co, and Ni as the redox centres. Such electrode materials include LiMn2O4, LiFePO4, LiNi0.8Co0.15O2, and LiCoO2.1 As the market for LIBs has expanded exponentially, the needs for such species have increased significantly despite their continuously dwindling natural reserves, leading to the cost increases for the electrode materials. Therefore, the search for alternative cathode materials using earth-abundant and nontoxic Cu ions has been going on for decades albeit with limited success possibly mainly due to two reasons. First, Cu2+/Cu+ tend to get reduced to metallic Cu, resulting in the framework collapses and cycling instability. Second, many Cu2+/Cu+-based inorganic frameworks tend to have their electrochemical potentials in the anode ranges. Few successful exceptions include Cu(2,7-AQDC) (AQDC = Anthraquinone -dicarboxylate)2 and a core-shell structure with K0.1Cu[Fe(CN)6]0.7·3.8H2O as the core.3 However, the previous case uses a large ligand with a large molecular mass, leading to a lower theoretical capacity and the inclusion of solvent molecules into the framework and slow Li-ion diffusion in cycling. The latter uses toxic CN- ligand and the core needs to be stabilized by the K0.1Ni[Fe(CN)6]0.7·4.1H2O shell. The Cu2+/ Cu+ in these two cases are coordinated by four O atoms and five N atoms, respectively. Here we report the evaluation of a metal-organic framework, namely HNa[Cu2 (Ac)6] (HAc = Acetic acid) as a nontoxic cathode material for LIBs. A hydrothermal reaction between Cu(Ac)2 and NaAc at 105 ºC for 24 h gave deep blue single crystals of HNa[Cu2(Ac)6] that were selected for single crystal structural analysis. HNa[Cu2(Ac)6] contains discrete binuclear paddle-wheel [Cu2(Ac)6]2- anions (Fig. 1a). In each [Cu2(Ac)6]2-, four acetate (i.e. Ac-) groups connect two Cu2+ as paddles with two additional Ac- groups to occupy the two axial sites of Cu2+. Such paddlewheel exists in Cu(2,7-AQDC) as [Cu2(COO)4] that uses the COO- groups to connect to each other via organic groups. Here each Cu2+ is five- coordinated with a distorted square pyramidal {O5} donor set in which each of the five O atoms is from the five Ac- groups. Packings of the [Cu2(Ac)6]2- anions (Fig. 1b–c) show they are separated and charge-balanced by Na+ and H+ ions. Each Na+ is weakly coordinated by six O atoms from six Ac- groups with a distorted octahedral coordination polyhedron. Powder X-ray powder diffraction (PXRD) analysis confirms the product is pure (Fig. 1d). In the first discharge, HNa[Cu2(Ac)6] delivers more than 90 mAh/g at the 1.85 V plateau and a total of 150 mAh/g (Fig. 2a). Its discharge capacity being higher than its theoretical capacity (106 mAh/g; Mw = 505.34) based on reversible Cu2+/+ redox pair suggests at least partial reduction of Cu2+ to metallic Cu. To understand the mechanism, ex-situ PXRD analysis (Fig. 2b) was used to track the electrode during cycling. When it was discharged to 1.85 V, all the main PXRD peaks from HNa[Cu2(Ac)6] remained with the relative intensities of some peaks changed, possibly mainly due to the insertion of Li+ into the framework and the accompanied structural rearrangement. There were no apparent new phases coming from the decomposition, indicating the metallic copper may be amorphous or leave the electrodes. Similar partial reduction to form metallic Cu during the initial insertion of Li+ into the framework is also observed in Cu3(PO4)2.4 When HNa[Cu2(Ac)6] was further discharged to 1.5 V, all the PXRD peaks related to the framework disappeared and the electrode material was amorphous. Interestingly, when HNa[Cu2(Ac)6] was charged to 3.5 V, ca. 60% of the framework was recrystallized back judging from the relative intensity of the (110) peak at 8.34°. Thereafter, the discharge and charge capacities during the second cycle were 78 and 91 mAh/g. During the fifth cycling, the capacities were 35 mAh/g and its PXRD pattern indicates the absence of crystalline phase and the complete decomposition of the framework. Investigations on correlating the framework structures and the coordination environments of Cu2+ with their electrochemical performances toward Li+ insertion-removal are ongoing. References Blomgren, G. E. J. Electrochem. Soc. 2017, 164, A5019–A5025.Zhang, Z. Y.; Yoshikawa, H.; Awaga, K. J. Am. Chem. Soc. 2014, 136, 16112–16115.Asakura, D.; Li, C. H.; Mizuno, Y.; Okubo, M.; Zhou, H. S.; Talham, D. R. J. Am. Chem. Soc. 2013, 135, 2793–2799.Zhong G. M.; Bai, J. Y.; Duchesne, P. N.; McDonald, M. J.; Li, Q. et al. Mater., 2015, 27, 5736–5744. Figure 1

The properties and structure of Ge[sbnd]Se[sbnd]Te glasses and thin films

Ge30Se70−xTex bulk glasses and thin films for x=0, 10 and 20 were prepared. The properties and structure were characterized by differential scanning calorimetry (DSC), Raman spectroscopy and also by 77Se and 125Te MAS NMR spectroscopy. The optical properties were also measured. The absence of crystalline phases was verified by XRD, while DSC indicated that the glasses were not phase separated. Although the glass transition temperature of both Ge30Se70 glass and thin film is the same, different ΔCp reveal a higher disorder of the thin film. Both the glass transition temperature and ΔCp of Te glasses as well as crystallization temperatures decrease when Te increases due to increasing GeTe2/2 instead of GeSe4/2 structural units thereby reducing 3D interconnection of the glassy network. Based on the 77Se MAS NMR results, the short-range order model was determined as a suitable structural model for Ge30Se70 glass. 77Se and 125Te MAS NMR confirmed that Ge in alloys with Te only reaches oxidation state +II in agreement with GeTe phase diagram and therefore no GeTe4/2 tetrahedra can be present in these glasses and/or films. Raman spectroscopy confirmed that the short-range order of glasses and films is basically the same. The refractive index of thin films increases with tellurium content. The optical band gap of the thin films strongly decreases from 2.02eV to 1.36eV with increasing Te content and simultaneously the increasing structural disorder and width of the band tails increase. Reduction of the oxidation state of germanium to GeII caused by a reaction with tellurium ultimately leads to a reduction in 3D connectivity of the non-crystalline matrix and the loss of the glass-forming ability of the GeSeTe system.

Dielectric and AC conductivity studies in Li2O-CoO-B2O3-TeO2 glasses

CoO and Li2O mixed with borotellurite glasses in the compositions, (B2O3)0.2-(TeO2)0.3-(CoO) x -(Li2O)0.5−x, where x = 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50 were synthesized by fast cooling the melt to room temperature. Absence of crystalline phases in the samples was confirmed by X-ray diffraction studies. Changes in dielectric properties with frequency and temperature over wide ranges have been measured. Dielectric constant and loss increased with increase in CoO content. AC conductivity has been analyzed using Mott’s small polaron model and activation energy was determined. Activation energy decreased and conductivity increased with increase in CoO content up to 0.3 mole fractions, and they behaved oppositely for higher concentration of CoO. This observed change of trend in activation energy and conductivity at 0.3 mole fraction of CoO ascribed to switch over of conduction mechanism occurring from predominantly ionic to electronic regime. For the first time, a transition of conduction mechanism is observed in borotellurite glasses. Temperature and composition independent relaxation mechanism in these glasses has been confirmed by plotting the scaled conductivity master curves. Hunt’s model has been invoked to understand the frequency dispersion of conductivity.

Embedded argon as a tool for sampling local structure in thin plasma deposited aluminum oxide films

Al2O3 thin films, either amorphous or of varying degrees of crystallinity, were deposited by two-frequency radio-frequency magnetron sputtering. Film crystallinity was investigated by Fourier transform infrared spectroscopy and X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the amount of Ar naturally trapped within the films during the deposition process. A clear correlation was found between the existence of crystalline phases, as determined by XRD, and a shift towards lower binding energy positions of the Ar2p core levels of embedded gas. The shift is due to differences in the local Al2O3 matrix (amorphous or crystalline) of the embedded gas, thus, providing an XPS fingerprint that can be used to qualitatively determine the presence or absence of crystalline phases in very thin films.

Electronic Waste: Characterization of the Glass of Cathode Ray Tube Computer for Making Decorative Pieces by Recycling

The vigorous industrialization of the modern world and the incorporation of new consumption habits of society made appears electronic waste. This work had as objective to collect and characterize vitreous residues originating from Cathode Ray Tubes or, popularly, "image tubes", identified for the acronym CRT, which integrate computers monitors that will be recycled in the production of handicrafts. For its characterization were used techniques: X-Ray Fluorescence, Granulometric Analysis, X-Ray Diffraction. After analyses it was observed that glasses of the screen and of the funnel presented different chemical compositions, being silicium oxide (SiO2) the component of larger percentage in these glasses, 59.89% and 48.63%, for screen and funnel, respectively. Funnel presented 29.47% of lead oxide (PbO) while this oxide is absent in the screen. Screen presents significant amounts of barium oxide (10.75%) and strontium oxide (7.71%). Vitreous samples X-ray diffractions of residues of the funnel and the screen are to each other similar, presenting an amorphous band that indicates silica presence, with absence of crystalline phases. Through the presented results can be concluded that computer monitors CRTs has potential for be recycled, because present great amounts of SiO2, oxide that forms the vitreous net.

Structural Investigation of Polyurethane Based Gel Polymer Electrolytes Using Small Angle X-ray Scattering (SAXS)

Cross linked polymers PU (polyurethane) gel electrolytes have been synthesized from polyethylene oxide triol (PEO triol) and 4,4-methylenediphenyl diisocyanate (MDI). The minimum and maximum intake of liquid electrolyte by this gel is 35 and 65 wt % respectively. WAXD patterns for PU gel electrolytes shows featureless behaviour indicating absence of crystalline phase. SAXS pattern of polyurethane gel exhibits a broad peak at lower q value (∼0.7 nm -1 ) that is attributed to the presence of two phases, namely hard domains and soft domains. The structure of the gel was inferred as a continuous soft phase with dispersed hard domains. The shape and interface of the hard domains were determined from the slope of the curve in log ( I ( q )) versus log ( q ) plot. The slope of the curve decreases with increase in propylene carbonate (PC) content. The decrease in slope from -1.5 to -0.2 suggest that the shape of the hard domains changed from diffused ellipsoidal to the diffused spherical when the PC content was increased from 35 to 60 wt % in gels. PU-PC(60 wt %) gel electrolyte shows the maximum conductivity 2.53 ×10 -3 S/cm at room temperature.

SURFACE MORPHOLOGIES ON THE ADDITION OF TiO2 TO CALCIUM PHOSPHATE BIO-GLASS

Titanium dioxide is added into calcium phosphate bio-glass (CPG) to have crystalline phases of titanium phosphoric ( TiP 2 O 7) and calcium phosphoric ( CaP 2 O 7) on its surfaces. The bio-glass synthesis with the addition of titanium dioxide herein is denoted as TCPG. To elucidate their surface morphologies, both specimens of CPG and TCPG were immersed in Hanks' solution for two days before soaking in the mixed solutions of ( NH 4)2 HPO 4 and Ca ( NO 3)2 at 70°. Crystalline layers of titanium phosphoric were observed on the surfaces of TCPG from immersing in Hanks' solution. After which calcium pyrophosphate appeared on the second step of soaking process from the calcium ion contained solutions. Due to the absence of crystalline phases on the surfaces of CPG specimen, it can be deduced that the addition of titania ( TiO 2) causes the hydroxyapatite formation on the surface of bio-glass.

SURFACE MORPHOLOGIES ON THE ADDITION OF TiO2 TO CALCIUM PHOSPHATE BIO-GLASS

Titanium dioxide is added into calcium phosphate bio-glass (CPG) to have crystalline phases of titanium phosphoric (TiP2O7) and calcium phosphoric (CaP2O7) on its surfaces. The bio-glass synthesis with the addition of titanium dioxide herein is denoted as TCPG. To elucidate their surface morphologies, both specimens of CPG and TCPG were immersed in Hanks' solution for two days before soaking in the mixed solutions of (NH4)2HPO4 and Ca(NO3)2 at 70°. Crystalline layers of titanium phosphoric were observed on the surfaces of TCPG from immersing in Hanks' solution. After which calcium pyrophosphate appeared on the second step of soaking process from the calcium ion contained solutions. Due to the absence of crystalline phases on the surfaces of CPG specimen, it can be deduced that the addition of titania (TiO2) causes the hydroxyapatite formation on the surface of bio-glass.

Structural and Electrical Characterizations of Yttrium Oxide Films after Postannealing Treatments

We investigated annealing effects on yttrium oxide films elaborated at by pulsed injection plasma-enhanced metallorganic chemical vapor deposition. A certain amount of carbon is present in the as-deposited layers due to incomplete metallorganic precursor decomposition. Because the carbon is known to be disadvantageous for the dielectric permittivity, several annealing post-treatments (under Ar or at and under at during at atmospheric pressure) were performed. Chemical modifications in the yttrium oxide layer and also at the interface were investigated combining several analyses [as infrared spectroscopy, (angle-resolved) X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, electron energy loss spectroscopy, and Rutherford backscattering spectrometry] carried out on thick and thin films (respectively, and ). High-temperature post-treatments result in a significant reduction of carbon content. However, the presence of oxygen at high temperature (even for low residual oxygen partial pressure) involves formation at the interface and leads to the transformation of the yttrium oxide into Y-based silicates, which, for the thin films, results in the absence of crystalline phase. The anneal does not modify the film's chemical nature except for a significant reduction of hydrogen content. After annealing under , a strong improvement of the capacitance behavior is observed, especially on the thin films.

The Application of X-Ray Diffraction for Glass Batch Homogeneity Determination

AbstractAn X-ray diffraction (XRD) technique is employed to determine the presence or absence of crystalline phases in glass batch and to determine its homogeneity qualitatively and quantitatively.Sample preparation problems are discussed, and promising techniques for sample preparation are presented. Qualitative batch homogeneity determination is accomplished by comparing the integrated intensity of a particular reflection of the reference sample to that of the unknown sample. Quantitative batch determination is accomplished by using the internal standard method. Three replicated data sets indicate that the standard deviation of kaolinite and colemanite are higher than those of quartz and calcite. However, the overall data from the quantitative analyses lie within an acceptable range of precision and accuracy.