Stacking faults in a layered cobalt tellurium phosphate oxochloride

The new compound Co₂Te₃(PO₄)O₆Cl was synthesized by chemical reactions in a sealed and evacuated silica tube. The crystal structure was solved from single crystal diffraction data and is made up by charge neutral layers. Within the layers two types of chains are made up by edge sharing [CoO₆] and [CoO₅Cl] polyhedra respectively. The chains are separated by tellurium oxide and phosphate building blocks. There are only weak Van der Waals interactions in between the layers and severe diffuse scattering is observed due to faulted stacking of the layers. Structure solutions in a P-1 triclinic cell and a larger monoclinic cell in P2₁/c are discussed and compared to a computer generated model. The reasons for the stacking faults may be due to that there are two positions available for each layer that results in similar connectivity to the next layer in addition to the relatively wide channels in between the layers that reduce the Van der Waals interactions in between them.     

Comparison of two vibrational procedures for the direct determination of mancozeb in agrochemicals

The direct determination of mancozeb in agrochemicals has been made by diamond attenuated total reflectance (ATR) Fourier transform infrared spectroscopy in the middle range (DATR-MIR) and diffuse reflectance infrared Fourier transform spectroscopy in the near range (DR-NIR) methods using in both cases a previous identification of the samples using a dendrographic classification and an appropriate partial least squares (PLS) calibration established from a set of nine external standards and optimized for each type of sample. It was analyzed a heterogeneous population of 11 samples obtained from the Spanish market, containing different co-formulated products, such as fosetyl-Al, copper oxychloride, metalaxyl or cymoxanil. High performance liquid chromatography (HPLC) was used as reference method for validation of both vibrational strategies. The close agreement between values found for both, DATR-MIR and DR-NIR methods, and reference HPLC values indicates the accuracy and reliability of the proposed techniques for the direct determination of mancozeb in commercially available formulations.     

Increasing the cold atom density in an integrating spherical cavity

A novel method of angled incidence for diffuse laser cooling of ⁸⁷Rb is presented to improve the distribution of cold atom density in an integrating sphere. The angled injection scheme could cool more atoms in the middle of the sphere compared to the previous normal injection scheme. The loading time of the cold atoms for the angled injection scheme is twice as that of the normal injection scheme. The SNR and the contrast of the detected signal would be improved in the angled injection scheme.     

A sharp-interface interpretation of a continuous density model for homogenization of gravity-driven flow in porous media

We examine homogenization methods applied to sharp-interface and diffuse-interface models for gravity-driven flow in heterogeneous porous media. Our work specifically examines a matrix of models that includes (1) a variable media, diffuse-interface model, (2) a variable media, sharp-interface model, (3) a homogenized media, diffuse-interface model and (4) a homogenized media, sharp-interface model. We connect all four of these models via homogenization theory and sharp-interface limits. We show that existing results based on homogenization methods applied to sharp-interface models can be recovered by a less direct but more rigorous approach involving well-established homogenization theory and sharp-interface limits.     

Discoloration of celluloses treated with amino compounds

Degradation and discoloration of celluloses treated with different amino compounds, including primary amines and hexamethylenetetramine (HMTA), were studied using spectroscopic techniques. The colour generation was measured using standard colorimetry and the degradation and discoloration were characterized using diffuse reflectance FTIR spectroscopy and diffuse reflectance UV-visible spectroscopy. The colour of all the treated celluloses was due to the same chromophores, thus revealing that the discoloration mechanism was essentially the same. The most important reaction was the condensation between carbonyl and amino groups to form coloured imines, and secondary processes were detected at high temperatures and long heating times. The discoloration of celluloses modified with primary amines followed first-order kinetics. However, the discoloration of HMTA-treated cellulose showed an induction period which was related to the thermal decomposition of HMTA.     

Three inorganic-organic hybrids of bismuth(III) iodide complexes containing substituted 1,2,4-triazole organic components with charaterizations of diffuse reflectance spectra

The reactions of two kinds of substituted 1,2,4-triazoles with BiI₃ yielded three inorganic-organic hybrids: [HL1]₄[Bi₆I₂₂]·[L1]₄·4H₂O (1) (L1=3-(1,2,4-triazole-4-yl)-1H-1,2,4-triazole); [HL2]₄[Bi₆I₂₂]·6H₂O (2); [HL2]₂[Bi₂I₈]·[L2]₂ (3) (L2=(m-phenol)-1,2,4-triazole). Both 1 and 2 have polynuclear anions of [Bi₆I₂₂]^4- to build up the inorganic layers and substituted 1,2,4-triazoles as the organic layers. Hybrid 3 consists of two BiI₅ square pyramids as inorganic layers. There exist hydrogen bondings and I?I interactions in the structures of 1, 2 and 3. Optical absorption spectra of 1, 2 and 3 reveal the presence of sharp optical gaps of 1.77, 1.77 and 2.07 eV, respectively, suggesting that these materials behave as semiconductors.     

Mechanisms and Kinetics of Recrystallisation: A Two Dimensional Vertex Dynamics Simulation

The recrystallisation process in single phase materials is investigated using a vertex dynamics simulation. The situation is idealised (two dimensional and isotropic) to better understand the role of physical parameters (energy and mobility of subgrain and grain boundaries, shape and relative size of grains) on the competition between recrystallisation and recovery. Simulations show that subgrain growth can be very heterogeneous in the vicinity of grain boundaries, i.e. that recrystallisation develops following the bulging mechanism. Bulging is enhanced for low mobilities of subgrain boundaries, high relative desorientation and small relative sizes. The recrystallisation kinetics is well described by an Avrami law of low exponent.     

Microscopic in situ diffuse reflectance spectroelectrochemistry of solid state electrochemical reactions of particles immobilized on electrodes

An instrumental setup is described which allows electrochemical measurements to be performed with solid particles immobilized on the surface of a graphite electrode with in situ recording of diffuse reflectance spectra under an incident light microscope. The instrument used includes a special electrochemical cell and a microscope which is interfaced by a light␣guide to a transputer-integrated photodiode-array spectrometer allowing measurements ranging from 320 to 950 nm with a resolution of 3.2 nm/pixel and a PC-interfaced potentiostat. The ₀R₀ geometry of the optical arrangement and the use of crossed polarization filters for blocking specular reflectance makes it possible to use the Kubelka-Munk function for quantifying the optical measurements. The above instrument has been used for the study of the electrochromic system of solid silver octacyanomolybdate(IV/V) adjacent to a silver nitrate solution. The in situ diffuse reflec tance spectroelectrochemical measurements prove that the electrochemical reaction starts at the graphite/sample interface and then advances into the bulk of the sample towards the sample/electrolyte interface. The ratios Red:Ox determined by spectrometry and chronocoulometry as a function of electrode potentials are identical.