I15-Extreme Conditions
|
Diamond Proposal Number(s):
[11823, 11658]
Abstract: The effect of pressure on the room temperature solubility of hydrogen in Zircaloy-4 was examined using synchrotron X-ray diffraction on small ground flake samples in a diamond anvil cell at pressures up to 20.9 GPa. Different combinations of hydrogen level/state in the sample and of pressure transmitting medium were examined; in all three experiments, it could be concluded that pressure resulted in the dissolution of δ hydrides and that interstitial hydrogen seemingly retards the formation of ω Zr. A pressure of around 9 GPa was required to halve the hydride fraction. These results imply that the effect of pressure is thermodynamically analogous to that of increasing temperature, but that the effect is small. The results are consistent with the volume per Zr atom of the α, δ and ω phases, with the bulk moduli of α and δ, and with previous measurements of the hydrogen site molar volumes in the α and δ phases. The results are interpreted in terms of their implication for our understanding of the driving forces for hydride precipitation at crack tips, which are in a region of hydrostatic tensile stress on the order of 1.5 GPa.
|
Jul 2019
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[8724]
Abstract: We have studied the compressibility and stability of different β-titanium alloys at high pressure, including binary Ti–Mo, Ti–24Nb–4Zr–8Sn (Ti2448) and Ti–36Nb–2Ta–0.3O (gum metal). We observed stability of the β phase in these alloys to 40 GPa, well into the ω phase region in the P–T diagram of pure titanium. Gum metal was pressurised above 70 GPa and forms a phase with a crystal structure similar to the η phase of pure Ti. The bulk moduli determined for the different alloys range from 97 ± 3 GPa (Ti2448) to 124 ± 6 GPa (Ti–16.8Mo–0.13O).
|
Apr 2017
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Diamond Proposal Number(s):
[10503]
Abstract: We report a powerful new technique: hyphenating synchrotron X-ray powder diffraction (XRD) with differential scanning calorimetry (DSC). This is achieved with a simple modification to a standard laboratory DSC instrument, in contrast to previous reports which have involved extensive and complex modifications to a DSC to mount it in the synchrotron beam. The high-energy X-rays of the synchrotron permit the recording of powder diffraction patterns in as little as 2 s, meaning that thermally induced phase changes can be accurately quantified and additional insight on the nature of phase transitions obtained. Such detailed knowledge cannot be gained from existing laboratory XRD instruments, since much longer collection times are required. We demonstrate the power of our approach with two model systems, glutaric acid and sulfathiazole, both of which show enantiotropic polymorphism. The phase transformations between the low and high temperature polymorphs are revealed to be direct solid–solid processes, and sequential refinement against the diffraction patterns obtained permits phase fractions at each temperature to be calculated and unit cell parameters to be accurately quantified as a function of temperature. The combination of XRD and DSC has further allowed us to identify mixtures of phases which appeared phase-pure by DSC.
|
Sep 2016
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Diamond Proposal Number(s):
[10503, 12735]
Open Access
Abstract: The design of a melt synthesis of the first air-stable formulation of the metastable form III of paracetamol is derived from thermo-spectroscopic and thermo-diffraction experiments. Melt crystallisation in the presence of β-1,4-saccharides produces form III selectively and the excipients appear to act as stabilising ‘active’ templates of the metastable polymorph.
|
Sep 2016
|
|
I19-Small Molecule Single Crystal Diffraction
|
Abstract: Reaction of α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-p-xylene (p-L1H4) with two equivalents of [VO(OR)3] (R = nPr, tBu) in refluxing toluene afforded, after work-up, the complexes {[VO(OnPr)(THF)]2(μ-p-L1)}·2(THF) (1·2(THF)) or {[VO(OtBu)]2(μ-p-L1)}·2MeCN (2·2MeCN), respectively in moderate to good yield. A similar reaction using the meta pro-ligand, namely α,α,α′,α′-tetrakis(3,5-di-tert-butyl-2-hydroxyphenyl)-m-xylene (m-L2H4) afforded the complex {[VO(OnPr)(THF)]2(μ-p-L2)} (3). Use of [V(Np-R1C6H4)(tBuO)3] (R1 = Me, CF3) with p-L1H4 led to the isolation of the oxo–imido complexes {[VO(tBuO)][V(Np-R1C6H4) (tBuO)](μ-p-L1)} (R1 = Me, 4·CH2Cl2; CF3, 5·CH2Cl2), whereas use of [V(Np-R1C6H4)Cl3] (R1 = Me, CF3) in combination with Et3N/p-L1H4 or p-L1Na4 afforded the diimido complexes {[V(Np-MeC6H4)(THF)Cl]2(μ-p-L1)}·4toluene (6·4toluene) or {[V(Np-CF3C6H4)(THF)Cl]2(μ-p-L1)} (7). For comparative studies, the complex [(VO)(μ-OnPr)L3]2 (8) has also been prepared via the interaction of [VO(nPrO)3] and 2-(α-(2-hydroxy-3,5-di-tert-butylphenyl)benzyl)-4,6-di-tert-butylphenol (L3H2). The crystal structures of 1·2THF, 2·2MeCN, 3, 4·CH2Cl2, 5·CH2Cl2, 6·4toluene·THF, 7 and 8 have been determined. Complexes 1–3 and 5–8 have been screened as pre-catalysts for the polymerization of ethylene in the presence of a variety of co-catalysts (with and without a re-activator), including DMAC (dimethylaluminium chloride), DEAC (diethylaluminium chloride), EADC (ethylaluminium dichloride) and EASC (ethylaluminium sesquichloride) at various temperatures and for the co-polymerization of ethylene with propylene; results are compared versus the benchmark catalyst [VO(OEt)Cl2]. In some cases, activities as high as 243400 g mmol−1 V−1 h−1 (30.43 kgPE mmol V−1 h−1 bar−1) were achievable, whilst it also proved possible to obtain higher molecular weight polymers (in comparable yields to the use of [VO(OEt)Cl2]). In all cases with dimethylaluminium chloride (DMAC)/ethyltrichloroacetate (ETA) activation, the activities achieved surpassed those of the benchmark catalyst. In the case of the co-polymerization of ethylene with propylene, complexes 1–3 and 5–8 showed comparable or higher molecular weight than [VO(OEt)Cl2] with comparable catalytic activities or higher in the case of the imido complexes 6 and 7.
|
Oct 2015
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Asma
Buanz
,
Tim
Prior
,
Jonathan
Burley
,
Bahijja Tolulope
Raimi-Abraham
,
Richard
Telford
,
Mike
Hart
,
Colin C.
Seaton
,
Philip J.
Davies
,
Ian J.
Scowen
,
Simon
Gaisford
,
Gareth
Williams
Diamond Proposal Number(s):
[7782]
Abstract: A comprehensive study of the thermal behavior of the 1:1 and 2:1 benzoic acid/isonicotinamide cocrystals is reported. The 1:1 material shows a simple unit cell expansion followed by melting upon heating. The 2:1 crystal exhibits more complex behavior. Its unit cell first expands upon heating, as a result of C–H···π interactions being lengthened. It then is converted into the 1:1 crystal, as demonstrated by significant changes in its X-ray diffraction pattern. The loss of 1 equiv of benzoic acid is confirmed by thermogravimetric analysis–mass spectrometry. Hot stage microscopy confirms that, as intuitively expected, the transformation begins at the crystal surface. The temperature at which conversion occurs is highly dependent on the sample mass and geometry, being reduced when the sample is under a gas flow or has a greater exposed surface area but increased when the heating rate is elevated.
|
May 2015
|
|
I19-Small Molecule Single Crystal Diffraction
|
Diamond Proposal Number(s):
[8521, 11238]
Abstract: Reaction of the pro-ligand α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L1H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L1)}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L1)}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L1)}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α′,α′tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L2H4) only the use of [Nb(O)Cl3(NCMe)2] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L2H2)2]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L2H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1–4 and the tetraphenols L1H4 and m-L2H4·2MeCN have been determined. Complexes 1–4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat).
|
Feb 2015
|
|
I15-Extreme Conditions
|
Diamond Proposal Number(s):
[6833]
Abstract: Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning
electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped
boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that
the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.
|
Jan 2015
|
|
I19-Small Molecule Single Crystal Diffraction
|
Dave
Allan
,
Daniel/dan
Bailey
,
Nigel
Bird
,
Alexander J.
Blake
,
Neil R.
Champness
,
Deguang
Huang
,
Conal P.
Keane
,
Jonathan
Mcmaster
,
Tim
Prior
,
Jeremiah
Tidey
,
Martin
Schröder
Diamond Proposal Number(s):
[1022, 1216, 3031, 6409, 7532]
Abstract: The mononuclear macrocyclic Pd-II complex cis[PdCl2([9]aneS(3))]([9]aneS(3) = 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur-metal interaction and an intermolecular equatorial sulfur-metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl2([9]aneS(3))], [PdBr2([9]aneS(3))], [PtBr2([9]aneS(3))], [PdI2([9]aneS(3))] and [PtI2([9]aneS(3))] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl2([9]aneS(3))] undergoes a phase change. Pressure-induced I center dot center dot center dot I interactions were observed for [PdI2([9]aneS(3))] and [PtI2([9]aneS(3))] at 19 kbar, but the corresponding Br center dot center dot center dot Br interactions in [PdBr2([9]aneS(3))] and [PtBr2([9]aneS(3))] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur-metal interactions.
|
Jun 2014
|
|
I12-JEEP: Joint Engineering, Environmental and Processing
|
Diamond Proposal Number(s):
[1966]
Abstract: This paper reports a number of recent developments in the intercalation chemistry of Al(OH)3. From Rietveld refinement and solid-state NMR, it has been possible to develop a structural model for the recently reported [MIIAl4(OH)12](NO3)2·yH2O family of layered double hydroxides (LDHs). The M2+ cations occupy half of the octahedral holes in the Al(OH)3 layers, and it is thought that there is complete ordering of the metal ions while the interlayer nitrate anions are highly disordered. Filling the remainder of the octahedral holes in the layers proved impossible. While the intercalation of Li salts into Al(OH)3 is facile, it was found that the intercalation of MII salts is much more capricious. Only with Co, Ni, Cu, and Zn nitrates and Zn sulfate were phase-pure LDHs produced. In other cases, there is either no reaction or a phase believed to be an LDH forms concomitantly with impurity phases. Reacting Al(OH)3 with mixtures of MII salts can lead to the production of three-metal MII-MII-Al LDHs, but it is necessary to control precisely the starting ratios of the two MII salts in the reaction gel because Al(OH)3 displays selective intercalation of M nitrate (Li > Ni > Co ≈ Zn). The three-metal MII-MII-Al LDHs exhibit facile ion exchange intercalation, which has been investigated in the first energy dispersive X-ray diffraction study of a chemical reaction system performed on Beamline I12 of the Diamond Light Source.
|
May 2011
|
|