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[en] TL properties of barite occuring in Yugoslavia are investigated from room temperature up to 4000C. The samples taken from Foca and V. Kladusa localities show only one peak on TL curves as predicted by the theory of Tl processes in ideal crystallophosphors with one level of capture centres. The samples from other localities show two and more peaks indicating them to be policomponent systems. Using the criteria of Luscik, the basic parameters of the capture centres are determined: the energy of thermal activation (Esub(T)) and the frequency factor (p0) for samples with one peak on TL curve. The shift of Tsub(m) for quoted samples is attributed to different effects, including also thermal effects during geological history of the mineral. Radicals SO4-, SO3-, and SO2- formed in barite are the traps of electrons and holes. By heating, the holes are released from the traps and they recombine with recombination centres. The light energy radiated in this process is emitted by luminescence centres
[en] Bimineralic, polycrystalline rocksalt specimens ranging in composition from pure halite to pure anhydrite have been fabricated in hydrostatic compression at 150 MPa and 1000C for 15 minutes. Resulting porosities of the compacted samples increased with increasing anhydrite content, ranging from .02 for pure halite to .14 for pure anhydrite. Twenty-three compacted samples were then deformed in triaxial compression experiments at confining pressures of 10, 100, and 200 MPa, a nominal strain rate of 10-4 sec-1 and a temperature of 2000C. Sample strength at 10 percent axial strain was directly related to both anhydrite content and pressure. Relatively small strength increases were observed for increases in anhydrite content up to 75 percent, by weight, and for all pressure increases. Much larger increases in strength were observed when the anhydrite content was increased from 75 to 100 percent. Ductilites of less than 10 percent were seen in only two sets of data, the 100 and 75 percent anhydrite samples run at 10 MPa confining pressure, and these data indicated a trend of increasing ductility with increasing halite content and/or confining pressure. All samples exhibited strain hardening except for the 75 percent halite samples at all three pressures and the 50 percent sample of 10 MPa, which exhibited slight strain softening
[en] In this paper, properties of composite materials containing ternary binders are determined. Except gypsum, ternary binders containing also pozzolans and alkaline component, which serve as an activator of pozzolanic reaction. The main aim of this research was to investigate changes in physical and chemical properties and pore structural characteristics due to additions of ternary binders. Experimental results showed that changes in the properties of the composite depend not only on the amount of the addition, but also on the kind of pozzolan. (paper)
[en] A process is described for reducing the radioactive contamination in waste product gypsum in which waste product gypsum is reacted with a dilute sulfuric acid containing barium sulfate to form an acid slurry at an elevated temperature, the slurry is preferably cooled, the acid component is separated from the solid, and the resulting solid is separated into a fine fraction and a coarse fraction. The fine fraction predominates in barium sulfate and radioactive contamination. The coarse fraction predominates in a purified gypsum product of reduced radioactive contamination
[en] The sulfur species existing in different size aerosol particles were determined based on the 'white line' energy shift and the features of post edge structure of sulfur K-edge XANES (X-ray Absorption Near Edge Structure). The results indicated that sulfates were dominant sulfur species in aerosol particles. However, small amount of reductive sulfur species were also found in the ultrafine aerosol particles(<0.1 μm). Sulfates in aerosols mostly exhibited as (NH4)2SO4 and gypsum. Most (NH4)2SO4 distributed in aerosol particles finer than 0.952 μm, while gypsum was the dominant sulfate in coarse aerosols. (authors)
[en] The binder gypsum is firstly mixed with water glass in a ratio of 1 kg/100-500 ml and then the aqueous solution with HF, H2SO4, HClO4, HCl, HNO3 or KOH, NaOH, NH3 and CaOH to a content of 40 wt.% is added. (DG)
[de]Das Bindemittel Gips wird zunaechst mit Wasserglas im Verhaeltnis 1 kg/100-500 ml vermischt und dann erst die waessrige Loesung mit HF, H2SO4, HClO4, HCl, HNO3 oder KOH, NaOH, NH3 und CaOH bis zu einem Gehalt von 40 Gew.-% zugegeben. (DG)
[en] The crystal structure of gypsum, CaSO4.2H2O, has been refined to Rsub(w) = 0.023 and R = 0.036 for 610 neutron diffraction intensities collected at room temperature (294 K) for a unit cell with a = 5.679(5), b = 15.202(14), c = 6.522(6) A, β = 118.43(4)0, and space group I2/a, Z = 4, V = 495.2 A3, dsub(c) = 2.3 g cm-3. The refinement was based on a model with anisotropic thermal motion for all atoms, and an isotropic secondary-extinction coefficient. The O-H bonds of the water molecule are 0.942(3) and 0.959(3) A and hence significantly different. The difference 0.017(4) A, is in accordance with spectroscopic stretching-frequency differences for the two O-H bonds. The water molecule donates two hydrogen bonds of 1.856(2) and 1.941(2) A to sulfate O atoms. The shortest hydrogen bond is not linear, the O-H...O angle being 170.9(2)0, whereas the other bond has an angle of 177.2(2)0. H-H is 1.533(3) A and H-O-H 107.5(2)0. The sulfate ion is definitely not a regular tetrahedron. The S-O distances are equal [1.474(1) and 1.471(1) A], but the O-S-O angles are not [111.1(1), 111.0(1), 111.1(1) and 106.3(1)0], leading to differences in the O-O tetrahedral edges [2.429(1), 2.432(2), 2.426(2) and 2.357(1) A]. The shortest edge is shared between the sulfate tetrahedron and the square-bipyramidal CaO8 group. (Auth.)
[en] The quality of secondary materials is imperative to promote a circular economy. In order to improve the way in which the quality of recycled gypsum is assessed, European guidelines on recycled gypsum (RG) quality criteria have been outlined in the framework of the Life+ Gypsum to Gypsum (GtoG) project. Such GtoG guidelines, along with the European Standard on gypsum plasterboard EN 520, provided the basis for this study. During the GtoG project, gypsum recycling and plasterboard manufacturing processes were monitored by testing the gypsum feedstock and the plasterboard produced. The aim of this paper is to discuss the results obtained on relevant parameters that characterize gypsum as a secondary raw material, as well as the resulting product. The minimum requirements were fulfilled by 56% of the RG samples and 86% of the plasterboard with increased RG.
[es]La calidad de las materias primas secundarias es fundamental para promover una economía circular. En el marco del proyecto Life+ Gypsum to Gypsum (GtoG), y con el objeto de mejorar el análisis de la calidad del yeso reciclado, se han desarrollado orientaciones en cuanto a los criterios de calidad del material. Estas directrices voluntarias, junto a la norma europea EN 520, son la base del presente trabajo. Los procesos de reciclaje y fabricación se monitorizaron durante el proyecto GtoG, mediante el ensayo de materias primas y placas de yeso laminado. El objetivo del presente artículo es discutir las propiedades del yeso como materia prima secundaria, así como del producto obtenido. Un 56% de las muestras de RG y un 86% de las placas con aumento de contenido de RG cumplieron los requisitos mínimos establecidos.