Evidence of quasi-intramolecular redox reactions during thermal decomposition of ammonium hydroxodisulfitoferriate(III), (NH4)(2)[Fe(OH)(SO3)(2)]center dot H2O

Synthesis of ammonium hydroxodisulfitoferriate(III), (diammonium catena-{bis(mu (2)-sulfito-kappa O,kappa O)-mu (2)-hydroxo-kappa O-2}ferrate(III) monohydrate) (NH4)(2)[Fe(OH)(SO3)(2)]center dot H2O (compound 1) and its thermal behavior is reported. The compound is stable in air. Its thermal decomposition proceeds without the expected quasi-intramolecular oxidation of sulfite ion with ferric ions. The disproportionation reaction of the ammonium sulfite, formed from the evolved NH3, SO2 and H2O in the main decomposition stage of 1, results in the formation of ammonium sulfate and ammonium sulfide. The ammonium sulfide is unstable at the decomposition temperature of 1 (150 A degrees C) and transforms into NH3 and H2S which immediately forms elementary sulfur by reaction with SO2. The formation and decomposition of other intermediate compounds like (NH4)(2)SnOx (n = 2, x = 3 and n = 3, x = 6) results in the same decomposition products (S, SO2 and NH3). Two basic iron sulfates, formed in different ratios during synthesizing experiments performed under N-2 or in the presence of air, have been detected as solid intermediates which contain ammonium ions. The final decomposition product was proved to be alpha-Fe2O3 (mineral name hematite)

The crystal structure of caratiite

ABSTRACT. The crystal structure of caratiite, K4CU402 (S04)4MeCI (a 13.60(2), c 4.98(I)A, Z = 2) was solved in space group 14 from single crystal data, and refined to R = 0.035 for 654Fo > 6u(Fo). The atomic arrangement is characterized by CU20(S04)2 chains parallel to [001], with Cu in (4+ 1) co-ordination and°surrounded tetrahedrally by four Cu atoms. These chains are interconnected by K atoms to a framework, the channels of which house theMe and CI atoms. The nature of the Me atoms is not completely clear; most probably the position is half occupied by Cu, fully occupied by Na, or occupied by a mixture of the two

Re-Examination of Berlinite (AlPO\u3csub\u3e4\u3c/sub\u3e) from Cioclovina Cave, Romania

Berlinite is a mineral indicative of high-temperature formation and, therefore, it would not be expected to be present in a sedimentary environment. In this study, we review the characteristics of a berlinite-bearing deposit and present a single-crystal structure investigation based on X-ray data: the refinement converged at R1(F) = 0.0276, wR2(F2) = 0.0657 for 677 reflections (2θMoKα ≤ 70°) and 31 variables in space-group P3121 [a = 4.9458(10), c = 10.9526(20) Å, V = 232.0 Å3, Z = 3{AlPO4}]. The average bond distances within the two crystallographically unique TO4 tetrahedra are 1.734 and 1.526 Å, respectively. From the scattering power at these T sites and the stereochemistry, the presence of an AlO4 tetrahedron linked to a PO4 tetrahedron is established. Consequently, the sample from Cioclovina Cave is verified as AlPO4 (modification berlinite), reconfirming the first description of this mineral from a sedimentary occurrence, which underwent an obvious natural heating process

Trigonal B₂O₃ with Higher Space-Group Symmetry: Results of a Reevaluation

A new crystal structure refinement based on published X-ray diffraction data [1] of the normal pressure modification of B2O3 (B2O3 form I) shows that the correct space group is (152) P3121 instead of (144) P31 within limits of error

Experimental investigation of the Cd-Pr phase diagram.

The complete Cd-Pr equilibrium phase diagram was investigated with a combination of powder-XRD, SEM and DTA. All intermetallic compounds within this system, already reported in literature, could be confirmed: CdPr, Cd2Pr, Cd3Pr, Cd45Pr11, Cd58Pr13, Cd6Pr and Cd11Pr. The corresponding phase boundaries were determined at distinct temperatures. The homogeneity range of the high-temperature allotropic modification of Pr could be determined precisely and a limited solubility of 22.1 at.% Cd was derived. Additionally, single-crystal X-ray diffraction was employed to investigate structural details of Cd2Pr; it is isotypic to the AlB2-type structure with a z value of the Cd site of 0.5. DTA results of alloys located in the adjacent two-phase fields of Cd2Pr suggested a phase transformation between 893 and 930°C. For the phase Cd3Pr it was found that the lattice parameter a changes linearly with increasing Cd content, following Vegard's rule. The corresponding defect mechanism could be evaluated from structural data collected with single-crystal XRD. Introduction of a significant amount of vacancies on the Pr site and the reduction in symmetry of one Cd position (8c to 32f) resulted in a noticeable decrease of all R-values

Pathogenicity and histopathology of Pratylenchus thornei populations on selected chickpea genotypes

Four populations of Pratylenchus thornei from different locations were tested for reproductive fitness in axenic carrot disc cultures and for pathogenicity to chickpea cultivars JG 62 and UC27 and lines K850 and ILC 1929. Parasitism and histopathology on selected chickpea genotypes (JG 62, UC27 and lines ILC 482, ICC 11324 and ICC 12237) were also investigated. Reproductive fitness, assessed as the ratio of the final number of nematodes per carrot disc to the number of nematodes inoculated, was similar among the populations tested and the four populations reproduced to a similar extent in a given chickpea genotype. However, the extent of reproduction was significantly affected by the chickpea genotype, JG 62 and UC27 being the best and poorest hosts, respectively. Pathogenicity to chickpea genotypes was assessed by the difference in fresh root and dry shoot weights between infected and uninfected plants 90 days after inoculation. Plant growth was significantly reduced by the four nematode populations in all chickpea genotypes, with the exception of cv. JG62, which was tolerant of P. thornei. Severity of root necrosis caused by nematode infection was similar for all populations. Histopathological studies of chickpea genotypes infected by P. thornei showed that all were suitable hosts according to nematode reproduction and host reaction. P. thornei always migrated through epidermal and cortical cells by breaking down cell walls along the nematode pathway. In the most susceptible lines (ILC 482 and JG 62), damage to endodermal cells adjacent to nematode feeding sites was occasionally observed.Research was supported in parts by grant AGF97-1479 from Comisión Interministerial de Ciencia y Tecnología (CICYT) of Spain, and Joint Research Program Consejo Superior de Investigaciones Científicas (CSIC)–Consiglio Nazionale delle Ricerce (CNR) for 1995–96. The authors thanks Drs N. Greco and M. Di Vito, CNR, Bari, Italy, for providing us with the population of P. thornei from Syria.Peer reviewe

High-temperature and “exotic” minerals from the Cioclovina Cave, Romania: a review

This paper reports on the identification of four rare minerals in the phosphate deposit in Cioclovina Cave, Romania. Berlinite, AlPO4 and hydroxylellestadite, Ca5[(Si,P,S)O4]3(OH,F,Cl) are minerals that can form only at high temperatures, and would not be expected in a sedimentary environment. In this study we review the characteristics of berlinite and hydroxylellestadite from a heated sedimentary sequence in Cioclovina Cave (Romania) and refine their structure from single-crystal X-ray data. Two other minerals, churchite-(Y), YPO4⋅2H2O and foggite, CaAl(PO4)(OH)2⋅H2O are, for the first time, described from a cave environment. The minerals were documented by means of single-crystal X-ray investigations, X-ray powder diffraction, and electron-microprobe (EMPA) analyses. In addition, laboratory synthesis of berlinite was conducted and vibrational spectroscopy data were collected for hydroxylellestadite and churchite-(Y). Based on these investigations, we suggest that locally the heavily compacted phosphate-bearing clay sediments underwent a natural heating process. It is likely that in-situ bat guano combustion is responsible for generating the high-temperature environment needed for the genesis of berlinite and hydroxylellestadite. The occurrence of churchite-(Y) and foggite is related to guano-leaches that reacted with subjacent limestone and different allogenic cave sediments