Martine Cambon’s research while affiliated with French National Centre for Scientific Research and other places

Phenylacetylene was inserted and polymerized in 5 nm diameter silica nanotubes under high pressure – high temperature conditions of 0.5 GPa and 437 K in an inert gas. The resulting nanocomposite was characterized by infrared and Raman spectroscopy and scanning and transmission electron microscopy. The vibrational spectroscopic data confirmed the formation of π-conjugated polyphenylacetylene and the absence of crystallization of the amorphous nanotubes. Scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, STEM-EDX, measurements confirmed the insertion of the polymer in the channels of the nanotubes and electron diffraction confirmed the amorphous nature of both the polymer and the host SiO2 nanotubes. The obtained nanocomposite is a candidate material for gas sensing applications.

High temperature, high pressure conditions were used to insert liquid bismuth in 4–6 nm diameter amorphous silica nanotubes. A combination of transmission electron microscopy and neutron powder diffraction indicate that the final composite consists in 5–6 nm semi-conducting Bi nanowires confined in insulating mesoporous α-quartz. Such a nanostructured material could be of considerable interest for thermoelectric applications.

GaAsO4 is the highest performance piezoelectric material of the MIIIXVO4 alpha-quartz type group. First principles based calculations of the pure FeAsO4 show that the piezoelectric properties are strongly improved by replacing Ga³⁺ by a chemical element of the d-bloc like Fe³⁺. For GaAsO4, our calculations give, d11 = 7.08 and d14 = 5.76 pC/N, while these values are significantly higher in FeAsO4 to reach d11 = 18.77 and d14 = 13.78 pC/N; about a factor of three greater than in GaAsO4 due to the increase of the elastic compliances of FeAsO4 with respect to GaAsO4. These results show that the electronic configuration and particularly the involvement of the d-orbitals in the M-O bonds in the MIIIO4 tetrahedron could be at the origin of this increasing. By considering a linear dependence of d11 or d14 between the parent compounds, GaAsO4 and FeAsO4, we get the following equations for the Ga(1-x)FexAsO4 solid solution: d11 [pC/N] = 11.689 xFe + 7.082 and d14 [pC/N] = 8.021 xFe + 5.762. These predictions motivated the first synthesis of mixed Ga(1-x)FexAsO4 solid solutions with x = 0,09; 0,18 and 0,45. The hydrated compounds, Ga1-xFexAsO4,2H2O, were obtained by hydrothermal synthesis and the alpha-quartz phases Ga1-xFexAsO4 were crystallized with a thermal treatment in an oven at 600 °C for 24h. XRD patterns show that the cell parameters are in accordance with a Vegard's law for the orthorhombic hydrated phases (Pbca space group) and for the trigonal dehydrated alpha-quartz phases (P3121 space group). Raman spectroscopy data obtained for the hydrated phases confirm the results of the literature on FeAsO4·2H2O, GaAsO4·2H2O and other arsenate analogues as well as their substituted analogues on the M and X sites. For the dehydrated alpha-quartz phases, all the main peaks observed in Raman spectra have been observed and the assigned by analyzing the experimental spectra measured in solid solutions and the calculated spectra in the parent end-member compounds. DFT calculations were used to identify the Raman vibrational modes. As in the case of GaAsO4, no libration mode of oxygen atoms is present for FeAsO4 that could lead to a very high thermal stability. These results prove the interest of α-quartz type FexGa1-xAsO4 solid solutions.

At the present time, hazardous waste management is a major problem, like the waste containing asbestos. The development of a process for eradicating all types of asbestos waste is a real challenge. In this study, several usefully analysis techniques (XRD, SEM–EDX, and TEM) have been used to determine what kind of asbestos is present in the waste (amphiboles and/or chrysotile). The chrysotile-containing wastes were treated with nitric acid solution (HNO3) leading to obtain pure silica and an acidic solution. Alkaline treatment using sodium hydroxide (NaOH) was also used in the case of waste-containing amphiboles. A basic solution of silica was then obtained. Finally a first valorization route was proposed with the precipitation of the ions dissolved in the acid solution and a second with the synthesis of a zeolite using the solid silica resulting from the acid treatment and the solution coming from the alkaline treatment of the amphiboles as sources of silicon. This paper describes the implementation of a complete process adapted to chemically dissolve each type of waste (according to their composition, density and fiber content) and to transform or recover all the by-products of the process.

The invention relates to an asbestos waste destruction and valorization method, comprising the steps of: a) determining the asbestos mineralogical species contained in the waste; b) treating said waste, said treatment comprising an acid treatment when the waste comprises only chrysotile, a base treatment when the waste comprises only amphibole, or acid treatment followed by base treatment when the asbestos waste comprises a mixture of chrysotile and amphibole; and c) valorizing at least one of the products resulting from treatment step (b). The invention also relates to the treatment of chrysotile waste by means of acid treatment followed by a heat treatment.

Abstract Single crystals of α-quartz type Si1-xGexO2 with x<0.2 were grown in 0.05M NaOH solutions. Infrared measurements confirmed that crystals grown at high pressure and high temperature have a low –OH group defect content. After a few millimeters of crystal growth under these conditions, α3500 reaches 0.1cm-1 and no free –OH are present.. The d11 value measured on an X-cut from crystal with x=0.0375 is 3.08 pC/N (+/- 0.15), in a good agreement with the value of 2.97 pC/N obtained using density functional theory based calculations. Piezoelectric measurements were performed on a Si1-xGexO2 crystal with x=0.0375, both at room temperature and after annealing at various temperatures. The piezoelectric signal of the crystal with x= 0.0375 and pure SiO2 disappears after annealing at 635°C and 545°C, respectively. Nonlinear optical (NLO) properties of Si1-xGexO2 crystals were measured by Maker’s fringes technique on Z-cuts χ_11^((2) ) and their corresponding values for x = 0.023 and 0.028 are 1.3(2) pm/V and 1.6(2) pm/V, respectively. These values are in a good agreement with density functional theory based calculations. The light induced damage threshold values measured on Si1-xGexO2 crystals with x= 0.023 and 0.028 are very similar to that of α-quartz.

GaAsO4 crystals were grown by a hydrothermal epitaxial process. Microcrystalline GaAsO4 powder was first synthesized by hydrothermal methods by using GaAs as a starting material in a sulfuric acid solvent under oxidizing conditions. Experimental conditions were optimized and the yield of the nutrient synthesis reached 88%. GaAsO4 powder was then used as the nutrient for growing GaAsO4 single crystals by epitaxy on (21¯0) oriented GaPO4, AlPO4 and GaAsO4 plates. Crystal growth was performed in a horizontal PTFE-lined autoclave divided into two parts using sulfuric acid as the solvent under a slow heating gradient. Hydrothermal conditions were optimized in order to improve the crystal quality. The influence of the nature and orientation of the seeds on the growth rate was studied. From the solubility curve, the solute supply ΔS as a function of temperature during the growth process was calculated. Transparent crystals were obtained with ΔS between 0.002 and 0.009 mol/L. Large crystals (3.9×1.8×1.4 cm3) of gallium arsenate were obtained. These crystals were cut into (21¯0), (010) and (001) plates. Mapping using Raman spectroscopy was performed in order to study the growth recovery on the seed. GaAsO4 crystals were characterized by infrared spectroscopy in order to quantify the amount of OH groups in the crystal structure. A low value of the absorption coefficient α at 3300 cm−1 was measured 0.067 cm−1 indicating a good crystal quality. Optical measurements were performed on GaAsO4 crystals by UV–vis–NIR spectrophotometry. Gallium arsenate exhibits the highest value of birefringence in the α-quartz group with Δn=0.033. The transmission in the spectral region above 250 nm yields a bandgap of 5.85 eV. Piezoelectric properties were measured on resonators. An electromechanical coupling coefficient of 20% was measured which is the highest in the α-quartz group. A quality factor QF of 3.2×1010 was obtained on a Y-cut plate. The C66 elastic constant was found to be 20 GPa.

The dissolution of Si(1-x)Ge(x)O(2) solid solutions under hydrothermal conditions was studied by in situ X-ray absorption spectroscopy. Experiments were performed at the Ge K-edge using a high-pressure cell mounted on the FAME beamline of the European Synchrotron Radiation Facility. Spectra in both transmission and fluorescence mode were collected in isobaric conditions (100 and 150 MPa) up to 475 °C. The local atomic structure around the Ge atom was investigated as a function of the temperature and in pure water and sodium hydroxide solutions. In pure water, the solubility of the cristobalite-type Si(0.8)Ge(0.2)O(2) increases with the temperature and the Ge atom is in 4-fold coordination. In a sodium hydroxide aqueous solution, a complex between Ge and Na atoms forms and gives rise to precipitation of sodium germanates. Under these conditions, the Ge content in the solution decreases with increasing temperature. These results show that a sodium hydroxide aqueous solution, usually used for quartz crystal growth, is not suitable for Ge-containing crystals. The dissolution kinetics and phase transformation of the solid solution were studied as a function of the atomic fraction of Ge. Ge-rich solid solutions dissolve and transform to stable phases faster than Ge-poorer composition, giving rise to important variations of the Ge content in solution.

Single crystals of α-quartz type Si1-xGexO2 are prepared by the temperature gradient hydrothermal method in Ni—Cr autoclaves using pure water and crystobalite-type Si0.8Ge0.2O2 (<200 MPa, <400 °C) or Si0.7Ge0.3O2 glass (<200 MPa, <400 °C) as source.

The substitution of germanium in the α-quartz structure is a method investigated to improve the piezoelectric properties and the thermal stability of α-quartz. Growth of α-quartz type Si(1-x)Ge(x)O(2) single crystals was performed using a temperature gradient hydrothermal method under different experimental conditions (pressure, temperature, nature of the solvent, and the nutrient). To avoid the difference of dissolution kinetics between pure SiO(2) and pure GeO(2), single phases Si(1-x)Ge(x)O(2) solid solutions were prepared and used as nutrients. The influence of the nature (cristobalite-type, glass) and the composition of this nutrient were also studied. Single crystals were grown in aqueous NaOH (0.2-1 M) solutions and in pure water. A wide range of pressures (95-280 MPa) and temperatures (315-505 °C) was investigated. Structures of single crystals with x = 0.07, 0.1, and 0.13 were refined, and it was shown that the structural distortion (i.e., θ and δ) increases with the atomic fraction of Ge in an almost linear way. Thus, the piezoelectric properties of Si(1-x)Ge(x)O(2) solid solution should increase with x, and this material could be a good candidate for technological applications requiring a high piezoelectric coupling factor or high thermal stability.