Search results for "RAV"

A new approach to the synthesis of intermetallic compounds: mild synthesis of submicrometric CoxMy (M = Mo, W; x∶y = 3∶1 and 7∶6) particles by direct…

2002

A simple processing route to cobalt–molybdenum and cobalt–tungsten intermetallics (CoxMy, where M = Mo and W, and x∶y = 3∶1 and 7∶6) has been developed, on the basis of the use of precursors resulting from freeze-drying of aqueous solutions of the appropriate common metal salts. The influence of the preparative variables on the outcomes of this procedure is examined. These compounds are prepared as single phases by thermal reduction of amorphous freeze-dried powders under a hydrogen–argon atmosphere (8% H2), followed by slow cooling of the samples. The materials have been characterised by X-ray powder diffraction, metal analysis, scanning electron microscopy and thermogravimetry under an ox…

Cadmium(II) complexes of cytosine

1990

Complexes of cadmium(II) with cytosine obtained from aqueous or physiological solutions at room temperature are reported. The complexes were characterized by spectroscopic, conductometric,1H-NMR, and13C-NMR measurements and also by thermogravimetry.

Synthesis of new vanadium–chromium and chromium–molybdenum oxynitrides by direct ammonolysis of freeze-dried precursors

2000

Interstitial vanadium–chromium and chromium–molybdenum oxynitrides in the solid solution series V1 − zCrz(OxNy) and Cr1 − zMoz(OxNy) (z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) have been obtained by direct ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the appropriate metal salts. A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the V1 − zCrz(OxNy) series are prepared as single phases by nitridation at 1073 K, followed by fast cooling of the samples. Compounds in the Cr1 − zMoz(OxNy) series are prepared as nearly single phases by nitridation at different temperatures, optimized for each composi…

Influence of drying to the structure of lactitol monohydrate

1997

The purpose of this study is to find out the effect of the crystal water content on the crystal structure of lactitol monohydrate. Crystal water was removed by drying over silicagel at 40°C and by using phosphorus pentoxide as drying agent at 20°C. The amouts of water removals were identified by thermogravimetry, the melting points and the heat of fusions were calculated from the results of differential scanning calorimetry measurements and the structure of samples were identified by X-ray powder diffraction method. Over 23 w/w% of total water content could removed by gently drying until significant structural changes could be detected. The melting point of anhydrous lactitol obtained by dr…

Effect of some additives on the reactions in fly ASH-Ca(OH)2system

2004

Differential thermal analysis and thermogravimetry were used to evaluate the effect of some additives, such as CaSO4, CaCl2 and silica fume amorphous silica from ferrosilicon synthesis on the mechanism and kinetics of reactions occurring in fly ash-Ca(OH)2 system. The accelerating role of these additives was demonstrated from the data relating to Ca(OH)2 consumption in hydrated pastes, determined by TG measurements.

Gravimetric characterisation of the surface properties of a porous drug carrier

1995

The gas adsorption method is the most common means to characterise the topology of solid surfaces with regard to its use as an adsorbent. Adsorption isotherms are determined advanta-geously using a vacuum microbalance: Thermogravimetric techniques allow the observation of sample degassing and its optimization. The dry mass is determined in situ, the mass of gas adsorbed is measured directly and different gases can be used without calibration. From the isotherm the pore size distributions, specific surface area, fractal dimension and density can be derived. Commercially available gravimetric sorption apparata and vacuum balances as well as software for data evaluation are reviewed in tables.…

Gravimetric and FTIR study of the interaction of tetramethylethylene on a MFI zeolite

2005

The adsorption of tetramethylethylene on a high siliceous ZSM-5 zeolite was performed by thermogravimetry, in situ FTIR spectroscopy and molecular dynamics simulation. Sorption and spectroscopic data were analysed as a function of loading and compared with molecular dynamics simulated results to characterize the adsorption process. The isotherm at 298 K does not show any deviation from the type I behaviour. The presence of admolecules in micropores does not or weakly affect zeolite framework vibration bands but induces an additional band at around 1715 cm−1 mainly due to a contribution of the microporous surface of the adsorbent. A confinement effect of the adsorbate is characterized during…

Some comments on the history of thermogravimetry

1990

Abstract In a review of the authors about the history of vacuum microbalance techniques (including a chronology in table form), also published in Thermochimica Acta, (ref. 1) it uas pointed out, that also some corrections are to be made on the history of therinogravimetry. The first findings of balances are dated to about 3000 B.C. A gravimetric hygrometer is mentioned by Nicolaus Cusanus in 1450. In the 19th century chemical reactions at variable temperatures uere investigated using balances. The very beginning of the thermogravinietry is antedated to the work of Talabot who in 1833 at Lyon equipped a laboratory with thermobalances for quality control of Chinese silk.

Solubility of some calcium-carboxylic ligand complexes in aqueous solution

1994

Insoluble species were identified in the systems Ca(2+)-hemimellitate, Ca(2+)-1,2,3,4-butanetetracarboxylate and Ca(2+)-citrate, and their solubilities were determined in aqueous solution at T = 25 degrees C. Values of pK(s0) were obtained for the species CaLH (L = benzene-1,2,3-tricarboxylate or hemimellitate), Ca(2)L (L = 1,2,3,4-butanetetracarboxylate), CaLH and Ca(3)L(2) (L = citrate), together with their dependence on ionic strength. Solid compounds were also characterized by thermogravimetry. The complex formation in solution for the system Na(+) - and Ca(2+)-hemimellitate was studied too.

1989

Polymides 3a and 3b with stiff-chains bearing trioxaoctyl or tetraoxaundecyl side chains were synthesized and characterized. The polycondensation was done with pyromellitic anhydride and N,N′-bis(1-imidazolylcarbonyl)-2,5-(1,4,7-trioxaoctyl)- or 2,5-(1,4,7,10-tetraoxaundecyl)-1,4-phenylenediamine (2a or 2b). 3b, being sufficiently soluble, was characterized by 13C NMR spectroscopy. The results of IR and 13C NMR spectroscopy prove the presence of the correct imide structure. In solid state 3a and 3b form layered structures with the side chains being in a disordered state.