Pascal G. Yot

Large breathing of the MOF MIL-47(VIV) under mechanical pressure: a joint experimental–modelling exploration

A joint experimental–modelling study has demonstrated a large flexibility of the MIL-47(VIV) upon mechanical pressure which strongly deviates from its rigid behaviour in presence of guest molecules. A structural transition suspected by mercury intrusion and further confirmed by X-ray powder diffraction and molecular dynamics simulations, leads to a closed MIL-47(VIV) form never observed so far corresponding to a cell contraction of up to 43%. The microscopic key features that govern this transition are then elucidated from complementary Raman experiments.

Lead extraction from waste funnel cathode-ray tubes glasses by reaction with silicon carbide and titanium nitride

As a possibility to clean waste CRT glass, treatment of lead-containing glass with a reducing agent, SiC or TiN, leads to a porous material containing metallic lead, Pb(0), located on the surface of the pore, and unreduced lead, Pb(II). The influences of reducing agent content, of the time, and at last of the temperature on lead reduction were analysed. Our investigations have pointed out significant differences as a function of the used reducing agent. CRT glass heat treated with SiC lead to less Pb(0), compared to TiN as shown by X-ray diffraction, and differential scanning calorimetry (DSC). It has been also evidenced that lead reduction occurs on randomized zones inside the sample leading to macroscopic lead beads inside glassy samples. XPS and XAS measurements were also carried out to investigate the local structure of lead and have evidenced a change of role of lead inside the glassy framework in function of the used conditions.

Characterization of lead, barium and strontium leachability from foam glasses elaborated using waste cathode ray-tube glasses

Foam glass manufacture is a promising mode for re-using cathode ray tube (CRT) glasses. Nevertheless, because CRTs employ glasses containing heavy metals such as lead, barium and strontium, the leaching behaviour of foam glasses fabricated from CRTs must be understood. Using the AFNOR X 31-210 leaching assessment procedure, the degree of element inertization in foam glasses synthesized from waste CRT glasses (funnel and panel glasses, containing lead and barium/strontium respectively) were determined. The amount of leached lead from foam glasses prepared from funnel glass depends on the nature and concentration of the reducing agent. The effects of the reducing agents on the generation of cellular structure in the fabrication of foam glass were studied. The fraction of lead released from foam glass was less than those extracted from funnel glass and was lower than the statutory limit. Leached concentrations of barium and strontium were found to be approximately constant in various tests and were also below regulatory limits.

Toward Understanding the Influence of Ethylbenzene in p-Xylene Selectivity of the Porous Titanium Amino Terephthalate MIL-125(Ti): Adsorption Equilibrium and Separation of Xylene Isomers

The potential of the porous crystalline titanium dicarboxylate MIL-125(Ti) in powder form was studied for the separation in liquid phase of xylene isomers and ethylbenzene (MIL stands for Materials from Institut Lavoisier). We report here a detailed experimental study consisting of binary and multi-component adsorption equilibrium of xylene isomers in MIL-125(Ti) powder at low (≤0.8 M) and bulk (≥0.8 M) concentrations. A series of multi-component breakthrough experiments was first performed using n-heptane as the eluent at 313 K, and the obtained selectivities were compared, followed by binary breakthrough experiments to determine the adsorption isotherms at 313 K, using n-heptane as the eluent. MIL-125(Ti) is a para-selective material suitable at low concentrations to separate p-xylene from the other xylene isomers. Pulse experiments indicate a separation factor of 1.3 for p-xylene over o-xylene and m-xylene, while breakthrough experiments using a diluted ternary mixture lead to selectivity values of 1.5 and 1.6 for p-xylene over m-xylene and o-xylene, respectively. Introduction of ethylbenzene in the mixture results however in a decrease of the selectivity.

Growth and dielectric characterization of large single crystals of GaAsO4, a novel piezoelectric material

AbstractGallium arsenate (GaAsO 4 )isanew α -quartz-type piezoelectric material. Large single crystals (8 mm along the c -direction) were grownfor thefirst timeby hydrothermal methods. The different crystal faces wereindexed by X-ray diffraction. The crystal quality was characterizedby infrared measurements. X -and Z -cut crystals were prepared in order to perform dielectric measurements. The dielectric constants ofGaAsO 4 ( e 11 =8 . 5, e 33 = 8 . 6) are the highest found among α -quartz type materials. A linear relationship has been established between astructural property, the tetrahedral tilt angle δ , and the dielectric constants for the well-known α -quartz homeotypes. These results indicatethat gallium arsenate should have the highest piezoelectric coupling coefficient of any material of this family.  2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved. 1. IntroductionQuartz material is currently the most used piezoelectricmaterial. Nevertheless, its properties are limited for certainapplications due to its low electromechanical couplingcoefficient. GaAsO

Advances in crystal growth and characterizations of gallium orthophosphate, GaPO4

Abstract Gallium orthophosphate, GaPO 4 , is a piezoelectric material isostructural with α -quartz, SiO 2 , with better piezoelectric characteristics: higher coupling coefficient for its temperature compensated cut and wider thermal stability (up to 933°C). A new investigation of the solubility of GaPO 4 in different acids and their mixtures allows to determine the metastable zone of which the knowledge is primordial for a good growth restart. The comparison of experimental growth results obtained in horizontal glass vessels ( T c T c >170°C) leads to specify a necessary minimum value of the solute supply at the interface crystal/solution. On the other hand, natural large seeds being not available, the seed lengthening is carried out with the splicing technique followed by crossed crystal growths to decrease the density of structural defects. At the same time, characterizations of crystals have been undertaken to check: the OH content by infrared spectroscopy; the crystalline quality (specially crystals after splicing) and the growth restart by X-ray topography; the piezoelectric properties.

Crystal growth of GaPO4, a very promising material for manufacturing baw devices

GaPO4 cystals were obtained by hydrothermal solution crystal growth. The retrograd solubility of the material was investigated in different solvents. In static growth vessels, good quality crystals can be obtained only if the solute supply is higher than about 0.06M/L. Crystal characterization by infrared spectroscopy showed that dilute solvents at high temperature decrease the “-OH” group content. Seed lengthening by splicing along the Y-axis was designed. The AT cut angle and the C44 elastic constant were determined. Compared to quartz-type materials, the C0/C1 calculation shows the high ability of GaPO4 for manufacturing BAW devices.

Key study on the potential of hydrazine bisborane for solid- and liquid-state chemical hydrogen storage.

Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during dehydrogenation) but can be used for the synthesis of derivatives with improved dehydrogenation properties. In liquid-state chemical hydrogen storage, it can be studied for room-temperature dehydrogenation, but this requires the development of an active and selective metal-based catalyst. HBB is a thus a candidate for chemical hydrogen storage.

Mechanical properties of a gallium fumarate metal–organic framework: a joint experimental-modelling exploration

A gallium analogue of the commercially available Al-fumarate MOF A520 – recently identified as isotypic to MIL-53(Al)-BDC – has been synthesized for the first time and further characterized in its hydrated and dehydrated forms. The structural response under applied mechanical pressure of this MIL-53(Ga)-FA solid was investigated using advanced experimental techniques coupled with computational tools. Hg porosimetry and high-pressure X-ray powder diffraction (XRPD) experiments evidenced that the pristine dehydrated large pore form undergoes an irreversible structure contraction upon an applied pressure of 85 MPa with an associated volume change of ∼14% which makes this material promising for mechanical energy storage applications, in particular as a shock absorber. The breathing behavior was further rationalized by performing a series of periodic Density Functional Theory (DFT) calculations with the construction of an energy profile as a function of volume for both MIL-53(Ga)-FA and its aluminium analogue. As such we unravelled the microscopic origin of the difference in pressure-induced behavior for the aluminium and gallium fumarate based materials.

Chemical vapor deposition growth of boron–carbon–nitrogen layers from methylamine borane thermolysis products

This work investigates the growth of B-C-N layers by chemical vapor deposition using methylamine borane (MeAB) as the single-source precursor. MeAB has been synthesized and characterized, paying particular attention to the analysis of its thermolysis products, which are the gaseous precursors for B-C-N growth. Samples have been grown on Cu foils and transferred onto different substrates for their morphological, structural, chemical, electronic and optical characterizations. The results of these characterizations indicate a segregation of h-BN and graphene-like (Gr) domains. However, there is an important presence of B and N interactions with C at the Gr borders, and of C interacting at the h-BN-edges, respectively, in the obtained nano-layers. In particular, there is a significant presence of C-N bonds, at Gr/h-BN borders and in the form of N doping of Gr domains. The overall B:C:N contents in the layers is close to 1:3:1.5. A careful analysis of the optical bandgap determination of the obtained B-C-N layers is presented, discussed and compared with previous seminal works with samples of similar composition.