The effect of nitrogen addition on certain properties and structure of fluorozirconate glasses

The effect of nitrogen on the properties and structure of fluorozirconate glasses in the system ZrF₄-BaF₂-LaF₃-AlF₃ (ZBLA) was investigated. Nitrogen was introduced by means of aluminium nitride. The substitution of fluorine by nitrogen in ZBLA glasses resulted in a considerable increase of microhardness, reduction of the linear expansion coefficient, and a small increase in characteristic temperatures. Structural investigations comprised RDF and Fourier transform-infrared (FT-IR) examinations. From radial distribution function (RDF) it followed that the introduction of nitrogen caused an increase of the mean distances Zr-F(N), Ba-F(N), La-F(N). From FT-IR spectra, it followed that nitrogen became incorporated into the bridging fluorine atoms which was evinced by a shifting of bands deriving from the bending vibrations between the [ZrF₆]^2– octahedra towards higher wave numbers.     

Properties of glasses in the ZrF4-AlF3-BaF2-RF (R = Li,Na or K) system

Densities, molar volumes, refractive indices, molar refractivities, glass transition temperatures and elastic constants of glasses with compositions (100–x) (0.6ZrF₄ · 0.1 AlF₃ · 0.3BaF₂) · xRF, where R = Li, Na or K, were studied. All the properties vary continuously with increasing RF concentration for all three alkali atoms. The calculated molar refractivities of LiF, NaF and KF are constants which are very close to the values of the crystalline compounds LiF, NaF and KF, respectively, throughout the composition range studied, suggesting that no change occurs in the coordination state of the alkali ions by fluorine atoms. The comparison with crystalline compounds suggests that Li⁺, Na⁺ and K⁺ ions are all coordinated by six fluorine atoms.     

Filamentary preforms of Al-13wt % Si alloy reinforced with TiC-coated and pre-treated carbon fibres

Filamentary preforms of aluminium-13 wt % Si alloy reinforced with TiC-coated carbon fibres were obtained by liquid metal infiltration using K₂ZrF₆ as wetting agent. The interfacial structure was investigated using analytical electron microscopy (TEM, SEM) and the fibre strength measured following each step of processing. The reaction between the K₂ZrF₆ deposit and the molten alloy is discussed on the basis of the reaction products formed at the fibre-matrix interface, which mainly consisted of fluoride compounds (K₃AlF₆), different zirconium-rich suicides (Si₂Zr, SiZr (Al), (Al, Si)₂Zr) and crystalline -alumina. Large amounts and/or inhomogeneous distributions of the K₂ZrF₆ deposit should be avoided, because the massive precipitation of colonies of intermetallics around fibres is conducive for the formation of harmful aluminium carbides and favours brittle fracture of the composite. The utilization of TiC-coatings formed by the reactive chemical vapour deposition process gave satisfactory results, both in terms of composite elaboration and fibre protection during liquid infiltration.     

Wetting improvement of carbon or silicon carbide by aluminium alloys based on a K2ZrF6 surface treatment: application to composite material casting

A surface treatment with aqueous solutions of K₂ZrF₆ has been carried out to improve, in dramatic manner, the wetting of carbon (or SiC)-base ceramics by liquid light alloys at low temperatures (i.e. within the 700 to 900°C range). The mechanism which is thought to be responsible for the wetting improvement involves two steps: (i) K₂ZrF₆ reacts with aluminium with the formation of K₃AlF₆, other complex fluoride species and intermetallics, (ii) K₃AlF₆ dissolves the alumina thin layer, coating the liquid light alloy and enables the wetting of the ceramics. The mechanism has been worked out from sessile drop experiments, solid state chemistry experiments and composite casting. The K₂ZrF₆ surface treatment appears to be particularly suitable for processing composite materials made of carbon (or SiC) fibrous preforms and aluminium-base matrices according to techniques directly derived from the light alloy foundry.     

A detection system for energetic light heavy ions

A light heavy ion detection system which consists of a gas-filled ionization chamber (IC) connected to a scattering chamber via a time-of-flight (TOF) system has been constructed. The entrance window of the IC has an area of 14 × 40 cm², the active depth is 115 cm. Filled with CF₄ at a pressure of 350 Torr, the energy range for ¹²C and ⁴⁰Ar is 5–20 MeV/A and 6–30 MeV/A, respectively. The TOF system consists of two parallel plate avalanche counters with a flightpath of 70 cm in between. The IC has been tested with ¹²C ions at an energy of 39 MeV. The energy resolution of the IC (1.1%) is mainly determined by the energy straggling in the foils of the TOF system and the ionization chamber. The energy-loss resolution is 3.5%, the horizontal position resolution varies between 6 and 20 mm and the vertical position resolution is 2 mm. The time resolution of the TOF system ranges from 800 ps for ⁴He at 5.0 MeV, to 280 ps for ²⁸Si at 55 MeV.     

Preparation and properties of fluorozirconate glasses containing divalent europium

The glass forming region of the (ZrF₄BaF₂ThF₄)EuF₂ system has been studied. EuF₂ was found to replace up to about 85% of the BaF₂ in a glass with a composition .615 ZrF₄, .32BaF₂, .07ThF₄. The glass transition temperature is seen to increase with the EuF₂ concentration. The 4f⁷→ 4f⁶5d¹ transition of the Eu⁺² ion in the glass matrix was studied by optical absorption and compared with data taken on crystalline compounds containing Eu⁺² in different environments. It is concluded from these results that the Eu⁺² ion - and also the Ba⁺² ion - is coordinated by 12 fluorides in the glass.     

A TEM study of the interfaces and matrices of SiC-coated carbon fibre/aluminium composites made by the K2ZrF6 process

Carbon fibre-reinforced aluminium composites were pressurelessly cast by using K₂ZrF₆ as the wetting promotion agent. Transmission electron microscopy (TEM) and energy dispersed analysis of X-rays, (EDAX) were used. The results showed that interfacial reactions were very active after K₂ZrF₆ treatment. This was caused by the diffusion and reaction of zirconium in the surface of carbon fibres or in the SiC coating. Silicon alloying of aluminium could suppress the interfacial reactions by decreasing the activity of zirconium and changing intermetallic Al₃Zr to Zr₃Al₄Si₅, and building up the phase equilibrium between SiC, aluminium and silicon. The requested silicon content was higher than the equilibrium content of Al-Si-SiC system to suppress the SiC/Al interfacial reaction. A perfect interface was achieved in SiC-coated carbon fibre Al-12 wt% Si composite.     

Determination du coefficient d'extinction molaire de OH− dans les verres fluores a base de metaux lourds

The extinction coefficient ? at 2.9 μm for OH in fluoride glasses is measured by determining the amount of HF evolved during heating of the glass under steam and the corresponding intensity of the OH absorption band. This coefficient is respectively equal to 31 litre mole^?1 cm^?1 for BTYbZ glass (15 BaF₂ - 29 ThF₄ - 28 YbF₃ - 28 ZnF₂) and 19.5 litre mole^?1 cm^?1 for BALLA glass (34 BaF₂ - 57 ZrF₄ - 4 AlF₃ - 5 LaF₃).     

High-resolution short range ion detectors based on 4H-SiC films

The energy resolution of SiC detectors has been studied in application to the spectrometry of α particles with 5.1–5.5 MeV energies. The Schottky barrier structure of the detector was based on a CVD-grown epitaxial n-4H-SiC film with a thickness of 26 μm and an uncompensated donor concentration of (1–2)×10¹⁵ cm^?3. An energy resolution of 0.5% achieved for the first time with SiC detectors allows fine structure of the α particle spectrum to be revealed. The average energy of the electron-hole pair formation in 4H-SiC is estimated at 7.71 eV.     

BF2 ion implantation in silicon through surface oxides,behaviour of the fluorine with rapid thermal annealing

BF₂ ion implantation through surface oxides has been investigated to form shallow p⁺/n junctions. BF₂ ion implantation was performed at 25 keV at a dose of 5.4 × 10¹⁴cm⁻² through surface oxides of different thicknesses into crystalline silicon. Rapid thermal annealing (1000°C/10 s) was used for dopant activation and radiation damage removal. Secondary ion mass spectroscopy (SIMS) was used to obtain the boron and fluorine distribution profiles. p⁺/n junctions as shallow as 0.12 μm were formed with reasonable sheet resistance. The study shows that, as expected, dopant loss in the surface oxide during ion implantation results in higher values of sheet resistance. Out-diffusion of fluorine during RTA resulted in a fluorine loss of 50 to 65% from the silicon. Also, fluorine was found to segregate at the oxide/silicon interface.     

Aqueous corrosion studies of a fluorozirconate glass

The effects of aqueous corrosion on a fluorozirconate glass containing ZrF₄, BaF₂, AlF₃, LaF₃ and LiF were investigated using soaking solution analysis, infrared transmission and reflectance spectroscopy and scanning electron microscopy. The dissolution of the glass was nearly congruent. The leached surface of the glass was covered with hydroxide crystals of Zr and Ba. The outer leached layer was thick, highly hydrated and cracked while the glass below was also hydrated and cracked indicating that no protective surface layer was formed. Drying studies of leached samples showed the appearance of an infrared absorptance peak at 7 μm (1440 cm^?1) caused by bridging oxygen bonds formed during dehydration.     

Verres fluores dans le systeme ZrF4ThF4MF3 (M = Y,Lu, Sc,Al)

The glass forming area has been precised in the ZrF₄ThF₄YF₃ ternary system. It is smaller than in the ZrF₄ThF₃LaF₃ system and corresponds to the limits: 45–70 % ZrF₄, 30–50 % ThF₄, 0–12 % YF₃. A series of glass samples with molar composition 0.5 ZrF₄, 0.43 ThF₄, 0.07 MF₃ (M : La, Y, Lu, Sc, Al) has been prepared and the linear evolution of T_G, molar refractivity and anionic compactness versus the ionic radius of M³⁺ is shown. The thermomechanical properties are better than for previous fluorozirconate glasses including barium. The average values are 480° C for T_G, 580° C for T_C, 800° C for T_F, 1.54 for n_D, 90.10^?7 K^?1 for thermal expansion coefficient. The U.V. absorption edge is improved by comparison with standard ZrF₄ -and AlF₃- based glasses. The potential application to I.R. optical fibres is discussed.     

ERD facility for analysis of hydrogen and deuterium in solids

Hydrogen is the lightest element in nature, and so, its detection and quantitative analysis is difficult by the conventional methods utilized for other elements. In the recent years the technique of elastic recoil detection analysis (ERD) using 1–2 MeV He⁺ beam has been developed to quantitatively and simultaneously analyze hydrogen and its isotopes in solids. Such a facility has been set up using the 2 MeV Van-de-Graaff accelerator at IIT Kanpur. It facilitates H and D analysis in a material up to a depth of ∼ 1μm with a detection sensitivity of 0·1 at.% and depth resolution of about 300 ?. The application potential of this setup is illustrated by presenting the results of measurements performed on Al:H:D systems prepared by plasma source ion implantation and highT _c YBCO pellets exposed to humid atmosphere.     

Spectroscopic properties and energy transfer process in Er doped ZrF4-based fluoride glass for 2.7 μm laser materials

Intense 2.7 μm emission from Er³⁺ doped in a new type of ZrF₄-based fluoride glass is reported. 2.7 μm emission characteristics and energy transfer process upon excitation of a conventional 980 nm laser diode are investigated. Based on the absorption spectra, the Judd-Ofelt parameters and radiative properties were calculated and compared with those of other glass hosts. The prepared glass possesses higher predicted spontaneous transition probability (29.04 s⁻¹) along with larger calculated emission cross section (9.16 × 10⁻²¹ cm²). Besides, the energy transfer coefficient of laser upper level (⁴I_11/2) can reach as high as 6.56 × 10⁻³⁹ cm⁶/s. Hence, these results indicate that this Er³⁺ doped ZrF₄-based fluoride glass has potential applications in 2.7 μm laser.     

Characterization of ZBGAN glasses

The physical and electrical properties of a ZrF₄-BaF₂-GdF₃-AIF₃-NaF (ZBGAN) glass have been studied. The addition of NaF increases the glass-forming ability of the base composition glass yet does not degrade the optical characteristics. The viscosity decreased with increasing NaF, suggesting that the increased glass-forming ability was due to the confusion principle. The electrical conductivity decreased with increasing NaF for low temperatures but increased at higher temperatures. The activation energy showed an increase with increasing NaF. The data suggest that the conductivity is not due to the total fluorine ion concentration.     

PIXE detection limits for dental enamel from some human teeth by excitation with protons and He ions from a 3 MeV Van der Graaff accelerator

A technique has been developed to measure elemental content in human teeth using H⁺ and ⁴He²⁺ ion beam analysis. Teeth of Oradea inhabitants were sampled in two stomatological clinics in Oradea in the period of 2004 and 2005 years. Tooth samples were irradiated in vacuum with 2 MeV proton and 3 MeV alpha beams from a Van der Graaff electrostatic accelerator of EG-5 experimental facility in FLNP, JINR. The particle induced X-ray emission (PIXE) analysis, apart from determination of Ca, allowed an optimised detection of Cr, Cu, Fe and Zn above the detection limits by the use of Al and Mylar filters. The detection limits for K_α X-rays using proton and alpha beams are determined and discussed.     

Light scattering investigation on a fluorozirconate glass

Light scattering characteristics for a fluorozirconate glass, ZrF₄(60)-BaF₂(32)-GdF₃(4)-AlF₃(4mol%), were measured. It was clarified that the light scattering depended remarkably upon the melt cooling rate through the crystallization temperature. In case of the low cooling rate, the glass had enormous Rayleigh's ratio, R₉₀o, with strong forward scattering and exhibited a large anisotropic light scattering. AlF₃ segregation was presumed to be an origin for the strong forward scattering. While, as the melt cooling rate was increased up to 33 °C/min., almost Rayleigh scattering aspect was observed and a relatively small Rayleigh's ratio R₉₀o = 5.34×10^?6 cm^?1 was obtained at 0.633 μm, which was comparable to those for some optical glasses. Based on the Rayleigh's ratio measured here, it is suggested that the scattering loss estimated by the $\text{1}\text{λ}{}^4$ law becomes less than 0.1 dB/km at the 3 μm band.     

Extremely deep profiling analysis of the atomic composition of thick (>100 μm) GaAs layers within power PIN diodes by secondary ion mass spectrometry

A new opportunity to analyze the atomic composition of thick (>100 μm) epitaxial GaAs layers by SIMS with lateral imaging of the cross section of a structure is demonstrated. The standard geometry of ldepth analysis turns out to be less informative owing to material redeposition from the walls of a crater to its floor occurring when the crater depth reaches several micrometers. The profiles of concentration of doping impurities Te and Zn and concentrations of Al and major impurities in PIN diode layers are determined down to a depth of 130 μm. The element sensitivity is at the level of 10¹⁶ at/cm³ (typical for depth analysis at a TOF.SIMS-5 setup), and the resolution is twice the diameter of the probing beam of Bi ions. The possibility of enhancing the depth resolution and the element sensitivity of the proposed analysis method is discussed.     

Synthesis and luminescent properties of alkali-metal and ammonium fluorosulfatozirconates and fluorosulfatohafnates

We have synthesized a variety of alkali-metal and ammonium fluorosulfatometallates (titanates, zirconates, and hafnates). The alkali fluorosulfatozirconates and fluorosulfatohafnates have been shown to exhibit efficient roentgenoluminescence (RL) in the UV through visible spectral region, with a maximum at 390–440 nm. Their RL spectra depend significantly on their composition (cation, anion, and water content), coordination of KF and K₂SO₄, and relative amounts of fluorine and SO₄ groups. We have examined the effect of heat treatment on the RL of these compounds. The rubidium and cesium fluorosulfatozirconates Rb₃Zr₂F₉SO₄ · 2H₂O, Cs₂ZrF₂(SO₄)₂ · 2H₂O, Cs₈Zr₄F₂(SO₄)₁₁ · 16H₂O, and Cs₂ZrF₄SO₄ offer the most efficient RL.     

A neutron polarimeter for the (p,n) reaction at Ep=50–80 MeV

A conventional type of neutron polarimeter consisting of three 12.5 × 12.5 cm cylindrical liquid scintillators and two 12.5 × 12.5 cm cylindrical plastic scintillators has been used to measure the transverse polarization transfer coefficient K_y^y in the (p, n) reaction in the energy range 50 < E_{p < 80 MeV}. The effective analyzing powers of this polarimeter have been obtained empirically by observing neutrons from the ⁶Li(p, n)⁶Be reaction at θ = 0° and E_p = 50,65 and 80 MeV whose polarizations are deduced from the K_y^y values of the ⁶Li(p,p′)⁶Be¹ (0⁺ reaction by utilizing the analogue relation. Observed effective analyzing powers are significantly reduced particularly at high energy, most likely due to the ¹²C(n,np)¹¹B reaction process. The double scattering efficiencies are 6 × 10⁻⁴ and 3 × 10⁻⁴ with effective analyzing powers of 0.14 and 0.11 at E_{n = 45} and 75 MeV, respectively.