Volume 60, Issue 2

Macrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both 27Al and 31P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO3. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue.

A novel carbonized clinoptilolite-rich tuff was studied for phenol removal from water. Zeolite sample carbonization was accomplished in a plasmachemical reactor (pyrolytic chamber) using several types of waste, here specifically waste vegetable residues and starch. Phenol adsorption experiments were performed in the batch system. An industrial activated charcoal and a clinoptilolite-rich tuff hydrofobized with an organic ammonium base were used as the related materials to compare phenol removal efficiency.

The flame retardant property of aerosols formed from 18 different nanopowders has been studied. The diameter of nanocrystalline powders was determined by XRD and TEM. The concentration of combustible gas was determined by gas chromatography. It was found that ZrO2 nanocrystalline powdered aerosol can effectively retard the burning of CH4. The flame retardation caused by ZrO2 toward the combustion reaction of methane is through an inhibitory mechanism, which was further confirmed by contrasting it with Halon extinguishing agent and flame retardant property of ZrO2-aerosol toward CH3CH2CH3 or CO. The type of nanopowder aerosols as anti-explosion and fireproof agents was researched preliminarily in theory, too. The current ZrO2-aerosol study will find extensive applications in the field of fire-extinguishing and anti-explosion agents used in case of combustible gas.

A simple and sensitive electroanalytical method was developed for microvolume trace elements determination. Commercially available interdigitated microelectrodes (IDA) from ALS Japan Inc. based on a thin carbon film technology were used. Anodic stripping voltammetry with collection at IDA was applied. Carbon IDA microbands were coated with a pre-deposited mercury film for better performance. The method with this sensor enables analysis of some heavy metals in total sample volumes as small as 0.05 cm3. The method was applied to Pb in blood samples determination by a standard addition method.

Efficiency of the suggested tandem technique of Marinković burner was studied in terms of the influence of the PC-controlled DC arc of the different intensities (10 A, 15 A, 20 A, 25 A) on the evaporation process. Higher intensities than 25 A did not allow to use the given experimental equipment since they cause plasma instability and periodic plasma quenching. The suggested method was evaluated by the determination of the half (t 50%) and total (t 100%) evaporation time and by determination of the signal/background ratio for the chosen elements (Al, Ca, Cr, Fe, Mg, Ni, Si, and V) in the model graphite matrix.

A method for the extraction of bioavailable iron from soils from various parts of Slovakia using a buffered diethylenetriaminepentaacetic acid (DTPA) solution was utilized. The extractant consists of 0.005 mol dm−3 DTPA, 0.1 mol dm−3 CaCl2, and 0.1 mol dm−3 triethanolamine with pH of 7.3. DTPA was selected as the chelating agent because it can effectively extract micronutrient metal, iron. Distribution of iron in the horizons of various types of soils with respect to bioavailable iron was evaluated. The bioavailable iron in the extracts was determined by flame atomic absorption spectrometry. The calibration standards were prepared in the same surroundings as the extracts. Comparing to the average of 2.7–3.7 % total iron contents in Slovak soils, the available amounts of iron represent in average only very small amounts, approximately 0.3 % in comparison to total amounts.

Three methods have been used for the determination of 99Tc in soils and solid radioactive wastes using 99mTc as a yield monitor. In the method one and three the samples were leached in low concentrated nitric and sulphuric acid. Many contaminants were then co-precipitated with Fe(OH)3 in alkali media and Tc in the supernatant was separated using anion-exchange extraction chromatography. There were made also some studies how to improve the chemical recovery of 99mTc in the process of chromatography. In the method two the sample was ashed and then leached in 8 mol dm−3 HNO3 and after iron precipitation, technetium was separated on chromatographic column. The chemical recovery of 99mTc was optimized in the process of chromatography and leaching. Typical recoveries of technetium determined with 99mTc tracer for all these methods were in the range 39 %–87 %. The 99Tc activity was measured using proportional low-background beta detector after one week of staying to allow decay of 99mTc activity. 99Tc was also determined by the non-radiometric method using inductively coupled plasma mass spectrometer.

Seven rare-earth complexes with salicylic acid RE(HSal)3·nH2O (HSal = C7H5O3; RE = La-Sm, n = 2; RE = Eu, Gd, n = 1) were synthesized and characterized by elemental analysis, the IR spectrum, and cyclic voltammetry. The constant-volume combustion energies of complexes, Δc U, were determined by a precise rotating-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δc H mo, and standard molar enthalpies of formation, Δf H mo, were calculated.

A new sensitive spectrophotometric method for the determination of nickel(II) with 3-(2-hydroxy-5-acetyl-(L1),-5-ethoxycarbonyl-(L2),-5-methyl-(L3),-5-formyl-(L4),-5-bromophen-1-ylazo)-1,2,4-triazole (L5), and 3-(2,4-dihydroxyphen-1-ylazo)-1,2,4-triazole (L6) in aqueous media containing 40 vol. % methanol has been developed. The method is based on the formation of stable coloured Ni(II) complexes with stoichiometric ratios 1: 1 and 1: 2 (n(M): n(L)). Linear calibration graphs are obtained up to 7.04 µg cm−3 of nickel(II) under optimum conditions attained from investigation of complex formation. The absorption maxima varied from 485 nm to 545 nm and the molar absorptivities ranged from 0.84 × 104 to 4.65 × 104 dm3 mol−1 cm−1 for 1: 1 and 1: 2 (n(M): n(L)) complexes with varying the substituent on the phenolic ring. The optimum ranges for the direct determination of nickel(II) (Ringbom) and the stability constants of the formed complexes are determined. The developed method was applied to the spectrophotometric determination of nickel(II) in some samples with satisfactory results.

5-[p-(R-Sulfonyl)phenylazo]-1,10-o-phenanthroline (L) and its octahedral complexes of the type [Ni(R2dtp)2(L)] (where R2dtp = diethyl-or dipropyldithiophosphate) with the core NiN2S4 have been prepared and characterized by spectral, magnetic, and thermogravimetric methods. The thermal decomposition mechanism of the compounds was proposed and the kinetic parameters of decomposition were calculated making use of the Coats—Redfern and Horowitz—Metzger equations.

The effects of the complexes of the type M(L)2(nia)2 (M = Cd or Zn; L = acetate (ac) or NCS−; nia = nicotinamida) on reduction of chlorophyll content in suspensions of Chlorella vulgaris and inhibition of photosynthetic electron transport in spinach chloroplasts were investigated. The inhibitory effects of the studied compounds depended on the central metal atom as well as on the structure of L ligands. In general, the toxicity of M(NCS)2(nia)2 was higher than that of M(ac)2(nia)2 and the compounds containing cadmium were more toxic than those with Zn. Dry mass of plants cultivated in the presence of the studied complexes (c = 100 µmol dm−3) showed a decrease related to control plants. The uptaken metal (Cd or Zn) was accumulated mainly in the roots. In general, application of M(ac)2(nia)2 compounds led to higher accumulated metal content in dry mass of plant organs (in mg g−1) related to M(NCS)2(nia)2 administration. In plants treated with Zn(NCS)2(nia)2 lower content of essential metals Mn and Cu was found than in those treated with Zn(ac)2(nia)2. Toxic effects of the studied M(L)2(nia)2 compounds could be caused by exchange of their ligands with potential “biotic S-, O-, and N-donor ligands” occurring in the plant cells.

Ethanol-tolerant and thermo-tolerant yeast strain Saccharomyces cerevisiae C11-3 cells immobilized in calcium pectate and calcium alginate gels were used for ethanol fermentation in a three-reactor system with a gradient temperature control. The fermentation process has been tested in a fixed-bed and a gas-lift arrangement. The gas-lift system was more efficient due to a better mass transport between the phases. Abrasion was more evident in calcium alginate particles, while calcium pectate beads were not significantly damaged. Two different concentrations of alginate were tested and calcium pectate gel was demonstrated to be more suitable as an immobilization material in comparison with calcium alginate due to its mechanical resistance and favourable diffusion parameters, providing an ethanol production of more than 7.5 g dm−3 h−1 over a period of 630 h.