Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD

<p>Chemical signatures of magnetite are commonly used to track the evolution of mineralizing systems in many geological settings. However, the impact of deformation processes on magnetite chemistry remains still underexplored. Here, we report a rare case of composite crystals consisting of magnetite and magnesioferrite recording different degrees and styles of deformation in order to evaluate how deformation promotes chemical modification. The samples employed in this study come from two different Mg-skarn iron deposits (i.e., El Robledal and San Manuel) from the Serranía de Ronda (SW Spain). Chemical data acquired by Electron Probe Microprobe Analyzer (EPMA) and Field Emission Scanning Microscopy (FESEM) are contrasted against microstructural data obtained by using Electron Back-Scattered Diffraction (EBSD). Our results show that magnesioferrite crystals [Fe<sup>2+</sup># (Fe<sup>2+</sup>/Fe<sup>2+</sup>+Mg<sup>2+</sup>) = 0.22-0.46 and Fe<sup>3+</sup># (Fe<sup>3+</sup>/Fe<sup>3+</sup>+Al<sup>3+</sup>) = 0.99-1.00] from El Robledal deposit are characterized by a ductile deformation that led to different crystallographic orientation domains along with the replacement of magnesioferrite by magnetite (Fe<sup>2+</sup># (Fe<sup>2+</sup>/Fe<sup>2+</sup>+Mg<sup>2+</sup>) = 0.51-0.99 and Fe<sup>3+</sup> (Fe<sup>3+</sup>/Fe<sup>3+</sup>+Al<sup>3+</sup>) =0.98-1.00] via coupled dissolution – reprecipitation. A replacement of magnesioferrite [Fe<sup>2+</sup># (Fe<sup>2+</sup>/Fe<sup>2+</sup>+Mg<sup>2+</sup>) = 0.43-0.64 and Fe<sup>3+</sup> (Fe<sup>3+</sup>/Fe<sup>3+</sup>+Al<sup>3+</sup>) = 0.99-1.00] by magnetite Fe<sup>2+</sup># (Fe<sup>2+</sup>/Fe<sup>2+</sup>+Mg<sup>2+</sup>) = 0.78-1.00 and Fe<sup>3+</sup># (Fe<sup>3+</sup>/Fe<sup>3+</sup>+Al<sup>3+</sup>) = 0.98-1.00] via a coupled dissolution – reprecipitation mechanism is also preserved in the composite (i.e., zoned) crystals from the San Manuel deposit, which was additionally overprinted by an additional recrystallization event as a result of grain boundary migration recrystallization. Our results show that deformation in a fluid-assisted deformation regime has induced chemical modification of the original magnesioferrite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of Mg-Fe oxides, utilizing their microstructurally controlled variation or lack thereof.</p>

Multilevel Strategies for Composition and Formation of DAAF/HNIW Composite Crystals

Insensitive energetic material is still a great challenge for the potential applications. In order to study the performance of (3,3'-diamino-4,4'-azoxyfurazan/2,4,6,8,10,12-hexa-nitrohexaazaisowurtzitane, often referred to as CL-20) DAAF/HNIW, DAAF/HNIW composite crystals with...

Compositely modulated structures of phosphor materials Sr x Li2+x Al2–x O4:Eu2+

Composite crystals Sr x Li2+ x Al2−x O4:Eu2+ were synthesized and their structures were determined using single-crystal X-ray diffraction. The commensurate structure with a modulation wavevector q = 5c*/6 was analyzed in a conventional manner in 3D space, while a structure model in (3+1)-dimensional superspace was used for the other two crystals with modulation wavevectors slightly differing from 5c*/6. The superstructure of the commensurate phase was described using the space group P4/n and a common superspace group I4/m(00γ)00 was used for the (3+1)D structures of all three crystals. The whole structure of each crystal consists of two substructures. Basis vectors a and b are common, but c is different for the two substructures. The first substructure is a host framework constructed by (Li/Al)O4 tetrahedra sharing edges. A linear connection of cavities is seen to be channel-like, in which Sr ions locate as guest cations forming the second substructure. The crystal of q = 5c*/6 contains five Sr ions per six cavities in a channel. Sr ions are distributed at seven sites, some of which are partially occupied. Statistical disorder of local structure models for the location of Sr ions in the channel was assumed to explain the results. Such a partially disordered character was also seen in the incommensurate phases and properly embodied by a (3+1)D model containing an atomic domain of the Sr ion with occupational modulation. Plots of the occupation factor, interatomic distances and the bond valence sum at each metal site as functions of t (= x 4 − q·r) are roughly identical in the three crystals, which are considered as members of the same series of composite crystals.

Finite Element Analysis of Thermal Effects in Diode End-Pumped Solid-State Lasers

Thermal effects are the main obstacle to getting high power and good beam quality in diode end-pumped solid-state lasers. In this work, a theoretical investigation of thermal effects in single and dual end-pumped solid-state lasers is carried out using finite element analysis (FEA) for a selected number of widely used laser producing materials, namely, Nd:YAG, Yb:YAG, and Nd:KGW. Crystals with different dimensions are also investigated both in single and in dual end-pumped configuration. Finally, the effect of using composite crystals on thermal lensing is investigated. An experiment to measure the thermal focal length for two different crystals was carried out and a comparison with FEA computed focal length of the thermal lens is made. In all cases studied in this work, results show clear effects of thermal lensing with some differences depending on crystal type, pump power, and size.