Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB₂O₃-(40−x)Fe₂O₃-60P₂O₅ (x = 2-20, mol%) and xB₂O₃-(100−x)[Fe₂O₃-60P₂O₅] (x = 2-20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. T_g increased with increasing B₂O₃ content for the glasses in the first series which indicates that the addition of B₂O₃ increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10⁻⁹ gr/cm² min which are comparable to that of the base iron phosphate glass. When the B₂O₃ content was above 14%, new bands related to BO₄ tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe²⁺ ions in glasses (Fe²⁺/∑(Fe²⁺ + Fe³⁺)) was found to be 23% for the base glass while it was 10-22% for the boron doped glasses.     

The influence of controlled electron-seeking addition agents of the melt on stilbene single crystal structure and radioluminescence properties

The study of certain radioluminescence characteristics of stilbene single crystals is performed. Doping the stilbene melt with electron-seeking (ES) addition agents of benzol and benzophenone halogen derivatives allowed to control the structure perfection of the crystal grown. The root-mean-square random orientation of single crystal mosaic structure, and concentration of the deep traps of charge carriers and excitons were minimum for the single crystals grown from the melt containing 0.1 mol% ES addition agent. Doping the melt with ES addition agents did not cause the appearance of additional luminescence impurity centres or quench luminescence centres in the single crystals grown.     

Effects of Ge addition on the optical and electrical properties of eutectic Sb70Te30 films

The aim of this work is to study the influence of Ge addition on the optical and electrical properties in eutectic SbTe thin films (with the compositions: Sb₇₀Te₃₀, Ge₂Sb₇₀Te₂₈, Ge₅Sb₇₀Te₂₅ and Ge₁₀Sb₆₅Te₂₅) using visible optical reflectance, ellipsometry measurements, near infrared transmittance spectra, and four probe electrical resistivity measurements. From near infrared transmittance measurements the optical band gap was determined using Tauc’s expression for amorphous materials, a value of about 0.47 eV was obtained without any clear dependence on the Ge content. All amorphous films have approximately the same reflectance value, however the contrast ratio between the crystalline and amorphous phases decrease with increase of Ge. Using in situ four probe measurements versus temperature the dependence of the activation energy of conductance and the onset of the crystallization temperature have been determined for different materials. Four probe measurements have shown that the resistivity of amorphous films increases with increase of Ge. The results obtained have shown that optical and electrical properties of SbTe films with near eutectic composition change with the Ge content and depending on the application, in either optical or electrical memory devices, the most suitable composition needs to be determined.     

Effects of dimethyldiethoxysilane addition on the sol-gel process of tetraethylorthosilicate

The effects of dimethyldiethoxysilane (DDS) addition on the sol-gel process of tetraethylorthosilicate (TEOS) were investigated by varying the addition-time of DDS to acid-catalyzed TEOS solutions in different water contents. At a low water content, the solution is transparent until gelation takes place, while at a high water content, phase separation occurs and leads to hydrophobic particles which, according to scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) and thermogravimetric (TG) analysis, show different morphology and thermal behavior. The reaction between TEOS and DDS in different water contents and the structure of final polymers are discussed.     

Anelastic indentation recovery of bioglass at room temperature

Using the microindentation technique, micro-indentations were made on bioglass 45S5 by a spherical diamond indenter for the indentation loads in the range of 50-500 mN at room temperature. Complete anelastic recoveries of the indentation depths and the impression marks were observed for the first time. The recovery rate of the indentation depth decreased with increasing the indentation load. A phenomenological model was proposed to explain the indentation recovery. It found that the recovery rate of the indentation depth was a power-function of the indentation load as supported by the experimental results.     

Effects of CaO addition on growth of YVO4 single crystals

YVO₄ single crystals doped with CaO are grown by the floating zone method in nitrogen atmosphere. The crystal is colorless and transparent after annealing in oxygen atmosphere. The effects of CaO addition are discussed. The Ca²⁺ ions can substitute for Y³⁺ at Y-sites in the YVO₄ structure to form oxygen vacancies via which oxide ions can easily diffuse and, consequently, yield transparent crystals.     

Effect of BaO addition on the structural aspects and thermophysical properties of sodium borosilicate glasses

Sodium borosilicate glasses containing different amounts of BaO were prepared by a conventional melt quench method and characterized for their structural aspects by ²⁹Si, ¹¹B NMR and IR spectroscopy. From ²⁹Si MAS NMR studies, it has been inferred that these glasses consist of Q² and Q³ structural units of silicon and that the addition of BaO results in the marginal conversion of Q³ to Q² structural units. There is no direct interaction between Ba²⁺ ions and boron structural units, as revealed by the identical values of the relative concentration of BO₃ and BO₄ structural units and quadrupolar coupling constant values for the BO₃ structural units. The identical values of glass transition temperature and vibrational frequencies corresponding to Si–O–Si/Si–O–B and B–O linkages of all the samples further support this. As the borosilicate network is unaffected, the systematic increase in the values of thermal expansion coefficient with increase in BaO content has been attributed to the increase in the relative concentration of less rigid Ba–O linkages compared to the more rigid Si–O and B–O linkages in the glass. Such studies will be useful for the development of matrices for the management of nuclear waste generated during the reprocessing of the spent fuel from thoria based reactors.     

The effect of copper ions addition on structural and optical properties of zinc borate glasses

Glasses in the ternary system xCuO?(100 ? x)[55B₂O₃·45ZnO] (0 ≤ x ≤ 20 mol%) have been prepared by melting at 1200 °C and rapidly cooling at room temperature. The effect of copper ions addition in 55B₂O₃·45ZnO glass matrix together with the matrix effect on paramagentic behavior has been investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA), electron paramagnetic resonance (EPR), ultraviolet–visible (UV–VIS) spectroscopy and density measurements. The increase of the number of non-bridging oxygen (NBO) atoms as a function of CuO content in these glasses leads to the decrease of glass polymerization which reduces the stability of the glasses and favors the association of copper ions in clusters. This leads to the major changes of structural and optical properties of the studied glasses as can be seen from the data obtained by FTIR and EPR spectroscopies.     

Electrical properties of nitrogen implanted GaSe single crystal

N‐implantation to GaSe single crystals was carried out perpendicular to c‐axis with ion beam of 6 × 10¹⁵ ions/cm² dose having energy values 30 keV and 60 keV. Temperature dependent electrical conductivities and Hall mobilities of implanted samples were measured along the layer in the temperature range of 100‐320 K. It was observed that N‐implantation decreases the resistivity values down to 10³ Ω‐cm depending on the annealing temperature, from the room temperature resistivity values of as‐grown samples lying in the range 10⁶‐10⁷ Ω‐cm. The temperature dependent conductivities exhibits two regions (100‐190 and 200‐320 K) with the activation energies of 234‐267 meV and 26‐74 meV, for the annealing temperatures of 500 and 700 °C, respectively. The temperature dependence of Hall mobility for the sample annealed at 500 °C shows abrupt increase and decrease as the ambient temperature increases. The analysis of the mobility‐temperature dependence in the studied temperature range showed that impurity scattering and lattice scattering mechanisms are effective at different temperature regions with high temperature exponent. Annealing of the samples at 700 °C shifted impurity scattering mechanism toward higher temperature regions. In order to obtain the information about the defect produced by N‐implantation, the carrier density was analyzed by using single donor‐single acceptor model. We found acceptor ionization energy as E_a = 450 meV, and acceptor and donor concentration as 1.3 × 10¹³ and N_d = 3.5 × 10¹⁰ cm⁻³, respectively. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of boron addition on texture and structure of NiMo/Al2O3 catalysts

The effect of support (Al₂O₃) modification with borate ions and the effect of their concentration on the texture and structure of nickel-molybdena catalysts were studied. The surface area and pore volume of the samples were determined using the BET method, whereas pores distribution – besides the BET method also by mercury porosimetry. FT-IR, derivatographic, and diffractometric studies were also performed. Modification with borate ions does not bring about any change in the type of the support pores, nor does it change its crystallic structure. However, a considerable decrease in the surface area of the support was observed. It was shown that modification with borate ions leads to a decrease in thermal stability of catalysts, yet increase in concentration of borate ions raises the thermal stability of the samples. It was found that on the catalyst surface borate ions form a well-dispersed monolayer structure.     

Effects of modifier additions on the thermal properties,chemical durability,oxidation state and structure of iron phosphate glasses

Modified iron phosphate glasses have been prepared with nominal molar compositions [(1?x)·(0.6P₂O₅–0.4Fe₂O₃)]·xR_ySO₄, where x = 0–0.5 in increments of 0.1 and R = Li, Na, K, Mg, Ca, Ba, or Pb and y = 1 or 2. In most cases the vast majority or all of the sulfate volatalizes and quarternary P₂O₅–Fe₂O₃–FeO–R_yO_z glasses or partially crystalline materials are formed. Here we have characterized the structure, thermal properties, chemical durability and redox state of these materials. Raman spectroscopy indicates that increasing modifier oxide additions result in depolymerization of the phosphate network such that the average value of i, the number of bridging oxygens per –(PO₄)– tetrahedron, and expressed as Qⁱ, decreases. Differences have been observed between the structural effects of different modifier types but these are secondary to the amount of modifier added. Alkali additions have little effect on density; slightly increasing T_g and T_d; increasing α and T_liq; and promoting bulk crystallization at temperatures of 600–700 °C. Additions of divalent cations increase density, α, T_g, T_d, T_liq and promote bulk crystallization at temperatures of 700–800 °C. Overall the addition of divalent cations has a less deleterious effect on glass stability than alkali additions. ⁵⁷Fe Mössbauer spectroscopy confirms that iron is present as Fe²⁺ and Fe³⁺ ions which primarily occupy distorted octahedral sites. This is consistent with accepted structural models for iron phosphate glasses. The iron redox ratio, Fe²⁺/ΣFe, has a value of 0.13–0.29 for the glasses studied. The base glass exhibits a very low aqueous leach rate when measured by Product Consistency Test B, a standard durability test for nuclear waste glasses. The addition of high quantities of alkali oxide (30–40 mol% R₂O) to the base glass increases leach rates, but only to levels comparable with those measured for a commercial soda-lime-silica glass and for a surrogate nuclear waste-loaded borosilicate glass. Divalent cation additions decrease aqueous leach rates and large additions (30–50 mol% RO) provide exceptionally low leach rates that are 2–3 orders of magnitude lower than have been measured for the surrogate waste-loaded borosilicate glass. The P₂O₅–Fe₂O₃–FeO–BaO glasses reported here show particular promise as they are ultra-durable, thermally stable, low-melting glasses with a large glass-forming compositional range.     

Hydrolysis and condensation of silicates: Effects on structure

The hydrolysis and condensation reactions of monomeric alkoxysilanes and organylalkoxysilanes utilized in sol-gel processing are reviewed. Both reactions occur by acid or base-catalyzed bimolecular displacement reactions. The acid-catalyzed mechanisms are preceded by protonation of OH or OR substituents attached to Si, whereas under basic conditions hydroxyl or silanolate anions attack Si directly. Many of the observed structural trends are understood on the basis of the pH and [H₂O] dependence of the hydrolysis, condensation, and dissolution reactions.     

Effect of B2O3 addition on the thermal properties and density of barium phosphate glasses

Variations in glass transition temperature, onset of crystallization, thermal expansion coefficient, density and molar volume with B₂O₃ concentration were studied in a series of xB₂O₃–(100 − x)Ba(PO₃)₂ glasses with 0–10 mol% B₂O₃. DTA analysis and isothermal treatments for powdered glass samples reveal that ⩾7.5 mol% B₂O₃ addition suppresses surface crystallization during softening process. Raman spectroscopy suggests that the properties are related to the glass structure consisting of PO₄ Q² units with diborate and PO₄–BO₄ groups.     

Effects of Sn addition on the glass forming ability and crystallization behavior in Ni-Zr-Ti-Si alloys

The effect of Sn substitution for Si on the glass forming ability (GFA) and crystallization behavior has been studied in Ni₅₉Zr₂₀Ti₁₆Si_5 − xSn_x (x=0, 3, 5) alloys. A bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy with diameter up to 3 mm can be fabricated by injection casting. Partial substitution of Si by Sn in Ni₅₉Zr₂₀Ti₆Si_5 − xSn_x alloys improves the glass forming ability. The improved GFA of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy is can be explained based on the lowering of liquidus temperature. The crystallization sequence becomes completely different with addition of Sn. The amorphous Ni₅₉Zr₂₀Ti₁₆Si₅ alloy crystallizes via precipitation of only a cubic NiTi phase in the first crystallization step, whereas the amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy crystallizes via simultaneous precipitation of orthorhombic Ni₁₀(Zr,Ti)₇ and cubic NiTi phases. Addition of Sn in the Ni₅₉Zr₂₀Ti₁₆Si₅ alloy suppresses the formation of the primary cubic NiTi phase. The bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy exhibits high compressive fracture strength of about 2.7 GPa with a plastic strain of about 2%.     

Effect of iron oxide addition on structural properties of calcium silico phosphate glass/glass-ceramics

Glasses with nominal composition 34SiO₂–(45 ? x) CaO–16 P₂O₅–4.5 MgO–0.5 CaF₂–x Fe₂O₃ (where x = 5, 10, 15, 20 wt.%) have been synthesized by melt quench technique. These have been investigated for structural features by using Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Results have shown an increase in fraction of non‐bridging oxygen in glasses with an increase in iron oxide content up to 15 wt.% and subsequently decreases with further increase in iron oxide content to 20 wt.%. These effects are originated by the incorporation of Fe₂O₃ into the silica network. Iron oxide behaves as a network modifier at low concentration and stabilizes the glass network at higher content. The glass-ceramics exhibit an increase in the formation of magnetite phase with an increase in iron oxide. The glass phase in the glass-ceramics matrix, controls the surface dissolution, which in turn decides the response of the material in-vitro. The glass-ceramics with 15 wt.% iron oxide has shown optimum response in simulated body fluid.     

Influence of thermal history on the structure and properties of silicate glasses

We studied a set of float glass samples prepared with different fictive temperatures by previous annealing around the glass transition temperature. We compared the results to previous measurements on a series of amorphous silica samples, also prepared with different fictive temperatures. We showed that the modifications on the structure at a local scale are very small, the changes of physical properties are moderate but the changes on density fluctuations at a nanometer scale are rather large: 12% and 20% in float glass and silica, for relative changes of fictive temperature equal to 13% and 25% respectively. Local order and mechanical properties of silica vary in the opposite way compared to float glass (anomalous behavior) but the density fluctuations in both glasses increase with temperature and fictive temperature.     

Crystal structure and spectroscopic properties of glycinium monophenylphosphate

The crystal structure of glycinium monophenylphosphate [NHsk3/+CH₂COOH·C₆H₅OPO₃H^– has been determined. The crystals are orthorhohombic:Pbca (NO. 61),a=26.001(3),b=7.423(2),c=11.273(2) Å,Z=8. The structure was solved by direct methods, are refined toR=0.035 for 1499 independent reflections. The crystal structure is stabilized by a three-dimensional network of hydrogen bonds. The phosphate group is involved in five H bonds: three NO and two OO bonds, with the shortest distances 2.745(3) and 2.608(2) Å, respectively. The glycine cation is entirely planar, and a cationo-anionic form of the title compound has also been confirmed in solution byIR studies.     

Elastic properties and structure of alkaline-earth silicate glasses

The densities and elastic properties of RO · SiO₂ and RO · 2 SiO₂ glasses (R = Mg, Ca, Sr, Ba or their mixtures) have been determined to obtain the compositional dependences of volume and bulk modulus of alkaline-earth silicate glasses. The mean atomic volume was found to vary almost linearly with glass composition for a series of RO · SiO₂ or RO · 2SiO₂ glasses, although there exists a slight negative deviation from the linearity for RO · 2SiO₂ glasses when two kinds of alkaline-earth oxides were mixed. The change in glass volume agreed fairly well with the value calculated on the basis of the difference in ionic size of alkali-earth ions being subtituted each other. The bulk moduli of RO · SiO₂ and RO · 2Si_O2 glasses were found to vary in reciprocal proportion to the four-thirds power of the volume when R was changed from one kind to another, indicating that the difference in internal energy of glass arises mainly from the change in Coulombic attraction due to their size difference. These results seemed to show that the glass structure of a series of RO · 2SiO₂ or RO · 2SiO₂ glasses remains almost unchanged except the local a change around R ions when R is subtituted from one kind to another.     

Control of the thermal properties of slow bioresorbable glasses by boron addition

This work studied the properties of glasses with the molar composition 63.8SiO₂-(11.6-x)Na₂O-(0.7 + x)B₂O₃-19.2CaO-3MgO-1.5Al₂O₃-0.2P₂O_5, in which x = 0, 1, 2, 3. These glasses are of interest for the development of slowly dissolving fibers to be incorporated in composites for medical applications. The thermal properties were recorded using hot stage microscopy, differential thermal analysis, and heat treatments in the range of 800°-1000 °C. The glass crystallization behavior was determined based on calculated values of the activation energy of crystallization and the Johnson-Mehl-Avrami exponent. The structural units in the glass network were identified using infrared spectroscopy. Finally, in vitro dissolution was tested in SBF solution.The addition of B₂O₃ increased the glass transition temperature and reduced the working temperature. When heat treated at 900 °C, the glass with the smallest amount of B₂O₃ formed two crystalline phases: magnesium silicate MgSiO₃ and wollastonite CaSiO₃. In the other compositions, only CaSiO₃ was observed after heat treatment at 950 °C. All the glasses crystallized preferentially from the surface. Changes in the liquidus and crystallization temperatures were related to changes in the glass structure. The formation of [BO₃] units led to glasses with improved resistance to crystallization and decreased liquidus temperature. In the glasses with 2.7 and 3.7 mol% B₂O₃, [BO₃] units were transformed into [BO₄] units. The formation of [BO₄] led to an increase in fragility and a decrease in resistance to crystallization. All the glasses dissolved slowly in simulated body fluid.     

Effects of graphite additive on dielectric properties and microwave absorption properties of zinc-containing foam glass

This paper reports effects of graphite additive on dielectric properties and microwave absorption performances of zinc-containing foam glasses. Changes of pore structure of porous glass are analyzed. One-dimensional zinc oxide crystal whiskers on walls of foam glass are observed. With the graphite additive increases, both real (ε′) and imaginary (ε″) parts of complex permittivity increase from ~ 3.25 and ~ 0.2 to ~ 7.5 and ~ 2.8, respectively. Microwave reflection loss of porous glass was calculated based on the permittivity in the range of 8.2–12.4 GHz(X-band). Reflection loss of foam glass decreases as graphite additive and the sample with 2.0 wt% graphite additive achieve reflection loss less than ? 10 dB in whole X-band with thickness ranging from 2.3 to 3.5 mm. Linear relation between reduction of reflectivity and increase of graphite content is achieved. The results show that changing foaming agent additive is an efficient way to design dielectric and microwave absorption properties of foam glass. Foam glass with 1.0 wt% graphite additive may find application in photocatalytic degradation of many environmental pollutants due to its considerable zinc oxide whiskers.