Search Results

You are looking at 51 - 60 of 2,209 items for :

  • "treatment" x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All
Journal of Thermal Analysis and Calorimetry
Authors: N. Lahav, D. Ovadyahu, A. Gutkin, E. Mastov, T. Menjeritzki, A. Adin, L. Rubinstein, D. Tropp, and S. Yariv

Abstract  

A device was constructed in which a clay suspension is hermetically heated at 220°C for a few minutes. This thermal treatment is accompanied by a pressure increase in the cell. Once the valve is opened, there is a fast release of the pressure inside the cell and a sudden evolution of the interparticle water. This shock leads to a quasi explosion of the clay particle. This technique was named thermal vapour pressure shock explosion (TSE). The effect of TSE treatment on the properties of palygorskite suspensions was investigated. Palygorskite suspensions in water are rather unstable and particles smaller than 3 μm in size are not found before a TSE treatment. Stabilization of the suspension can be obtained by TSE treatments and/or by using a dispersing agent such as pyrophosphate, or both. As a result of TSE treatments smaller particles are obtained, the dispersiveness of the particles is improved and electrophoretic mobility is increased. Electron microscopy scans showed that the aggregates of needles which form the palygorskite fibres, disintegrate to separated thin needles as a result of the TSE treatment.

Restricted access

Summary Mechanical mixtures containing zirconia xerogel and increasing amount of crystalline yttria up to 40 mol%, were hydrothermally treated by microwave route at 110°C for 2h. All the treatments were performed in the presence of (KOH+K2CO3) mineralizer solution at concentration 0.2 M. Amorphous and hydrated ZrO2-Y2O3 solid solutions with yttria content up to 33.3 mol% (corresponding to Zr/Y molar ratio equal to 1), resulted after the hydrothermal treatments. A remarkable reduction of the surface area has been detected at increasing yttria content of the amorphous phases with a corresponding increase of the exothermic peak of crystallization. A mechanism of reaction for the formation of the amorphous solid solutions has been proposed.

Restricted access

Products of hydrothermal treatment of the initial amorphous system MnxFe2−2x(OH)6−4x for 0≤x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400‡C, was present at 0.5≤x≤0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT≥900‡C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn5O8 and partritgeite.

Restricted access

Abstract

Controlled heating (in air) of clay minerals leads to transformations into disordered structures and recrystallization into new phases at high temperatures. These phase transformations are of topotactic nature. On the other hand, prolonged dry-grinding treatments of the same silicates causes structural amorphization with no recrystallization into new phases. The mechanical energy relaxation mechanism, invoked to explain these differences, accounts for the particle size changes and the large growth of dislocations. The latters affect sensibly the reactivity of the materials submitted to such solid-state treatments.

These processes are monitored mostly by XRD, DTA and IR spectroscopy. The latter method allows to study in some silicates submitted to progressive grinding the location and nature of OH groups and water molecules.

Restricted access

Abstract  

The use of non-aqueous deacidification procedures as a preventive conservation measure to assist in retarding the deterioration of painting canvases has been suggested by the Conservation Department of the Tate Gallery [1]. The reverse sides of paintings are treated with commercially available MMC solution (methoxy magnesium methyl carbonate). The aim of this paper is to describe how dynamic mechanical thermal analysis can be used to evaluate the effects of this treatment. Measurements are described on modern commercially primed canvas samples [2] which show that the MMC treatment does cause an increase in the modulus or stiffness of the primed canvas materials but that the effect on theT g is minimal. The response of the treated materials to variations in relative humidity has also been studied and indications are that the response of treated canvases to variations in relative humidity differs from those of the untreated canvases.

Restricted access

Abstract  

Via the thermal treatment of natural phosphates and their analysis, it was proved that the decrease in their solubility in the interval 400–550C is an indication of the degree of incorporation of OH groups into the apatite structure of phosphates, whereas the solubility at 950C is an indication of the degree of incorporation of the non-volatile components. The higherR 950, the more extensive this substitution, and the more reactive the natural phosphate.

Restricted access

Abstract  

A natural laumontite from the Isle of Skye, Scotland has been examined as a candidate material for aqueous nuclear waste treatment, and its fully Ca exchanged form has been shown to be Sr selective. Laumontite has a good pH stability in acid and alkaline media. The materials used have been characterized by wet chemical analysis, XRD and thermal analysis. The studies include both ion exchange kinetics and equilibrium isotherm studies which tend to confirm simple Kd tests.

Restricted access

Abstract  

Fixation of137Cs,144Ce,60Co,90Sr,240Th and233U from aqueous and phosphate media on bentonite clay was studied. The fixation of the radioactive ions on bentonite surfaces was dependent on the pH behavior of the metal ions. A method was proposed to use bentonite as an absorbent of ions from simulated radioactive waste as a treatment step.

Restricted access

Abstract  

Radionuclide concentrations in digester sludge and effluent samples from Hamilton and Dundas sewage treatment plants, located at the western tip of Lake Ontario, have been determined by high-resolution γ-ray spectrometry. The radionuclides51Cr,75Se and131I, which are used in nuclear medicine procedures, were found in sludge samples. Very low concentrations of51Cr, entering Lake Ontario through the Hamilton plant effluent discharge, have little effect on lake water quality.

Restricted access

Abstract  

Gamma-irradiation of treated piggery slurry was studied as a possible way of posttreatment. Biologically non-degradable substances (cellulose, lignin, etc.) were almost completely oxidized at 90–100 kGy radiation doses. TOC values indicated complete oxidation of organic carbon to CO2. Radiation doses of 10 and 50 kGy have not changed the biodegradability of irradiated substances. By -irradiation after chemical and biological treatment it is possible to get highest quality effluent with COD values lower than 40 mg.l–1.

Restricted access