Effect of the ionizing radiation on the kinetics of the reduction by hydrogen of NiO-Fe2O3 mixed oxides of various genesis

1986 ◽  
Vol 51 (8) ◽  
pp. 1561-1570 ◽  
Author(s):  
Milan Pospíšil ◽  
Jan Topinka
Keyword(s):  
Radiation Effects ◽  
Mixed Oxides ◽  
Chemical Properties ◽  
Fast Neutrons ◽  
Chemisorbed Oxygen ◽  
First Case ◽  
Different Temperatures ◽  
Negative Effect ◽  
Order Of Magnitude ◽  
Kinetics Of

The kinetics of the reduction by hydrogen of two series of NiO-Fe2O3 mixed oxides of different composition was studied in the temperature range 320 - 410 °C using thermogravimetry. Both series were prepared from different precursors that were thermally decomposed at different temperatures. The oxidizing ability of the surface ( the content of chemisorbed oxygen) is the only parameter from all physico-chemical properties studied that changed significantly during the pre-irridation of the system by 60Co gamma radiation (dose 505 kGy), by fast neutrons from the 252Cf source (dose Dn = 110 Gy) and by accelerated electrons (3 MeV, dose 500 kGy). A positive radiation effect was observed in the first case while the irritation by neutrons and electrons resulted in a negative effect. The magnitude of the effect depends on the composition and genesis of the system and it decreases in the sequence γ, e-, n. The radiation induced changes in the reduction kinetics of mixed oxides change their magnitude and sign in dependence on the composition and genesis. Not only the increase by an order of magnitude of the rate of the initial phase of the reduction which was ascribed to the partial reduction of hematite to magnetite but also the acceleration of the second step (reduction of Fe3O4 to Fe) was observed after the exposure to photons or fast neutrons. The radiation changes induced by electrons are limited only to the surface of the irradiated solid and they affect only the first step of the reduction. The maximum positive effect was observed in the region of high excess of hematite and its magnitude decreases with the increasing content of nickel oxide. The radiation effects decrease with the increasing temperature of the reduction and at about 400 °C the effect of irradiation is completely annealed.

Reduction of NiO-Mn2O3 mixed oxides with hydrogen and its affecting by ionizing radiation

1980 ◽  
Vol 45 (6) ◽  
pp. 1754-1765 ◽  
Author(s):  
Milan Pospíšil ◽  
Jan Topinka
Keyword(s):  
Mixed Oxides ◽  
Morphological Changes ◽  
Reduction Rate ◽  
Inert Atmosphere ◽  
Fast Neutrons ◽  
Nickel Metal ◽  
Chemisorbed Oxygen ◽  
Negative Effect ◽  
Positive Effect ◽  
Complex Influence

Reduction of NiO-Mn2O3 mixed oxides with hydrogen was studied thermogravimetrically at 350-440°C; in the entire composition region, 0-100% of one component, total reduction with the formation of a heterogenous Ni-MnO system was observed. The character of the kinetic curves of reduction of Mn2O3 is affected by the way of preparation and heat treatment of the samples before their reduction in inert atmosphere. In the mixed oxide, nickel accelerates the reduction of manganese sesquioxide, proceeding via Mn3O4 intermediate product. The mutual interaction of the two components appears in the pronounced dependence of the reaction rate on the composition, correlable with the analogous dependence of the apparent activation energy of reduction. The extent of the interaction, morphological changes, and some physicochemical parameters depend upon the degree of dispersion of the two oxides, which is also a function of the composition. A prior irridation of the samples by gamma radiation, dose 8 . 105 Gy, or fast neutrons, fluency 6.8 . 1015 n/m2 (Dn = 28.1 Gy), brings about a substantial increase in the content of the chemisorbed oxygen, particularly in the range of excess Mn2O3. The gamma irradiation results in an acceleration of the reduction of the mixed oxides; the extent of this positive effect is a nonmonotonic function of the composition and depends markedly on the temperature. The complex influence of fast neutrons appears as a negative effect (lowering of the reduction rate) resulting from the destruction of the existing centres (the polishing effect); in dependence on the composition the effect inverts into a positive one on the generated and stabilized new centres, which affect the rate of nucleation of the nickel metal phase.

Study of nickel-molybdenum catalysts for methanation of carbon monoxide

1980 ◽  
Vol 45 (3) ◽  
pp. 783-790 ◽  
Author(s):  
Petr Taras ◽  
Milan Pospíšil
Keyword(s):  
Carbon Monoxide ◽  
Catalytic Activity ◽  
Mixed Oxides ◽  
Minor Component ◽  
Fast Neutrons ◽  
Scanning Calorimetry ◽  
Low Concentrations ◽  
Γ Rays ◽  
Molybdenum Catalysts ◽  
Kinetics Of

Catalytic activity of nickel-molybdenum catalysts for methanation of carbon monoxide and hydrogen was studied by means of differential scanning calorimetry. The activity of NiMoOx systems exceeds that of carrier-free nickel if x < 2, and is conditioned by the oxidation degree of molybdenum, changing in dependence on the composition in the region Mo-MoO2. The activity of the catalysts is adversely affected by irradiation by fast neutrons, dose 28.1 Gy, or by γ rays using doses in the region 0.8-52 kGy. The system is most susceptible to irradiation in the region of low concentrations of the minor component (about 1 mol.%). The dependence of changes in catalytic activity of γ-irradiated samples on the dose exhibits a maximum in the range of 2-5 kGy. The changes in catalytic activity are stimulated by the change of reactivity of the starting mixed oxides, leading to different kinetics of their reduction and modification of their adsorption properties. The irradiation of the catalysts results in lowered concentration of the active centres for the methanation reaction.

The effect of origin and physico-chemical properties on the kinetics of reduction of mixed NiO-Fe2O3 oxides with hydrogen

1986 ◽  
Vol 51 (10) ◽  
pp. 2098-2108 ◽  
Author(s):  
Milan Pospíšil ◽  
Jan Topinka
Keyword(s):  
Mixed Oxides ◽  
Mutual Influence ◽  
Spinel Phase ◽  
Chemical Properties ◽  
Inhibitory Effect ◽  
Chemical Parameters ◽  
Physico Chemical ◽  
Preliminary Annealing ◽  
Kinetics Of ◽  
Kinetics Of Reduction

We investigated the effect of origin and some physico-chemical parameters on the kinetics of reduction with hydrogen of two series of mixed NiO-Fe2O3 oxides differing by their composition, the character of their precursors (mixed crystalline nitrates and coprecipitated hydroxides) and their decomposition temperature.This effect manifested itself by different magnitudes of specific surfaces of the mixed oxides and coherent regions of present phases as well as by different oxidizing abilities of the surface and differences in morphology and phase composition of corresponding samples in both series investigated. Nonlinear or nonmonotonous composition dependences of physico-chemical parameters investigated point to a mutual influence of individual components, which is also a function of the system origin and which modifies its reactivity during its reduction with hydrogen. The kinetics of the reduction was studied thermogravimetrically at 320-410 °C. The reduction of oxides of the hydroxide origin is catalytically accelerated by primarily reduced nickel, whereas in corresponding samples of the nitrate series, the total NiO is bound to the spinel phase and the reduction is delayed. Experimental IR spectra, the effect of preliminary annealing and DTA of the mixed oxides point to an inhibitory effect of water, which is constitutionally bound in trace admixtures of the goethite phase, on the kinetics of reduction of samples in the hydroxide series.

Preparation of modified sorbents from rehydrated clay materials

Clay Minerals ◽  
2012 ◽  
Vol 47 (2) ◽  
pp. 251-258
Author(s):  
M. Lhotka ◽  
V. Machovič ◽  
B. Doušová
Keyword(s):  
Chemical Properties ◽  
Solution Ph ◽  
Adsorption Capacities ◽  
Modification Method ◽  
Different Temperatures ◽  
Kinetics Of ◽  
Modified Sorbents ◽  
Highly Porous ◽  
Clay Materials

AbstractThe use of clay materials as selective sorbents for different contaminants requires very efficient methods. A natural kaolinite was calcined to metakaolinite and than rehydrated at different temperatures to produce a highly porous sorbent. The kinetics of this process were measured, with subsequent IR characterization of the phases formed. The surface and pore distribution of new phases were also assigned. In addition, the kaolinite obtained was pre-treated with Fe3+ ions to improve its sorption affinity for anionic particles. The rehydrated kaolinite and its Fe-modification were used for the adsorption of toxic cations (Zn, Cd, Pb) and anions (As, Se). Adsorption capacities depending on the physical chemical properties of the initial solution (pH, concentration of toxic ions) and the surface properties of the sorbent (specific surface area, modification method) were investigated. The adsorption properties of the sorbents were defined by the Langmuir model.

scholarly journals Kinetics of Oxidation of Metochlopramide withChloramine-T in HClO4 Medium

2009 ◽  
Vol 6 (2) ◽  
pp. 545-552 ◽  
Author(s):  
K. M. Meenakshi ◽  
K. Vasant Kumar Pai
Keyword(s):  
Thermodynamic Parameters ◽  
Fractional Order ◽  
Reaction Rate ◽  
Oxidation Products ◽  
Perchloric Acid Solution ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Different Temperatures ◽  
Negative Effect ◽  
Kinetics Of

The kinetics of oxidation of metochlopramide hydrochloride (MCP) with sodiumN-chlorop-toluenesulfonamide (CAT) in perchloric acid solution has been studied at 313K. The reaction rate shows a first order dependence on [CAT], fractional order on [MCP] and inverse fractional order on [H+]. There is a negative effect of dielectric constant of the solvent. The addition of the reduction product of CAT has no significant effect on the rate. The rate remained unchanged with the variation in the ionic strength of the medium. The reaction fails to induce the polymerization of acrylonitrile. Thermodynamic parameters have been computed by Arrhenius plot. The stoichiometry of the reaction was found to be 1:2 and oxidation products were identified. The Michaelis-Menten type of kinetics has been proposed. CH3C6H4SO2NHCl have been assumed to be the reactive oxidizing species. Thermodynamic parameters were computed by studying reactions at different temperatures. A mechanism consistent with observed kinetics is proposed.

Kinetics of Urethan Cleavage in Crosslinked Polyurethans

1967 ◽  
Vol 40 (4) ◽  
pp. 1230-1237
Author(s):  
Ajaib Singh ◽  
Leonard Weissbein
Keyword(s):  
Stress Relaxation ◽  
Relaxation Data ◽  
Network Chain ◽  
Transient Stress ◽  
Precise Control ◽  
Positive Identification ◽  
Thermodynamic Constants ◽  
Different Temperatures ◽  
Order Of Magnitude ◽  
Kinetics Of

Abstract A series of clean, well defined polyurethan networks was synthesized from polyester glycols, 2, 4-tolylene diisocyanate, and 1, 1′, 1″-trimethylolpropane by means that afforded precise control over the content of urethan groups per network chain. The thermal cleavage of these networks was studied using the technique of stress relaxation. Analysis of the stress relaxation data on each network structure revealed two exponential decay processes differing in rate by about an order of magnitude. The rate of the slower process, which dominates the overall stress decay, was shown to be directly dependent on the content of urethan groups per network chain. Positive identification of this process with urethan cleavage was thereby established. The kinetic and thermodynamic constants associated with urethan cleavage were then calculated from data on this process at different temperatures. The more transient stress decay process was not uniquely definable, but probably originated from the cleavage of one or more types of weak linkages found in small but variable proportions in the different polyurethan networks. The nature and origin of these weak linkages was discussed.

Effect of ionizing radiation on the kinetics of reduction of NiO-MgO mixed oxids with hydrogen

1979 ◽  
Vol 44 (4) ◽  
pp. 1023-1033 ◽  
Author(s):  
Milan Pospíšil ◽  
Miroslav Tvrzník
Keyword(s):  
Nickel Oxide ◽  
Magnesium Oxide ◽  
Reaction Rate ◽  
Mixed Oxides ◽  
Reduction Rate ◽  
Inert Atmosphere ◽  
Fast Neutrons ◽  
Mixed System ◽  
Degree Of Reduction ◽  
Kinetics Of

The low-temperature reduction of the mixed system nickel oxide-magnesium oxide with hydrogen was studied thermogravimetrically in the region 260-470 °C. The two oxides form in the whole composition region solid solutions, some physicochemical parameters of which vary nonmonotonically with the sample composition. The kinetics and degree of reduction of nickel oxide are appreciably affected by the presence of the unreduced magnesium oxide, in higher concentrations lowering the reaction rate. The kinetics of the reduction can be quantitatively described by the equation 1-(1-α)1/3 = kt, valid in dependence on the composition in differently wide ranges of the degree of reduction α. The reaction rate can be varied, particularly for samples with low contents of magnesium oxide, by heat treatment in inert atmosphere at 700 °C, and for all samples by irradiation by gamma rays or fast neutrons. The reduction rate grows with the increasing content of magnesium oxide up to a constant value. The positive effect increases with the increasing gamma dose and, according to the kind of radiation, in the order γ, n. The variation of the reactivity of irradiated or thermally treated mixed oxides is due predominantly to the shift of the equilibrium of the lattice defects, formation and stabilization of new centres, which affect the rate of nucleation of the forming metal phase.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

KARAKTERISTIK TANAH DAN PERBANDINGAN PRODUKSI KELAPA SAWIT (Elaeis guineensis Jacq.) DENGAN METODE TANAM LUBANG BESAR DAN PARIT DRAINASE 2:1 PADA LAHAN SPODOSOL DI KABUPATEN BARITO TIMUR PROPINSI KALIMANTAN TENGAH - INDONESIA

2015 ◽  
Vol 2 (2) ◽  
pp. 148-158
Author(s):  
Surianto
Keyword(s):  
Soil Texture ◽  
Oil Palm ◽  
Soil Profile ◽  
Chemical Properties ◽  
Exchangeable Cations ◽  
Soil Horizon ◽  
Soil Profiles ◽  
Negative Effect ◽  
Hole Profile ◽  
And Chemical Properties

Spodosol soil of Typic Placorthod sub-group of East Barito District is one of the problem soils with the presence of hardpan layer, low fertility, low water holding capacity, acid reaction and it is not suitable for oil palm cultivation without any properly specific management of land preparation and implemented best agronomic practices. A study was carried out to evaluate the soil characteristic of a big hole (A profile) and no big hole (B profile) system and comparative oil palm productivity among two planting systems. This study was conducted in Spodosol soil at oil palm plantation (coordinate X = 0281843 and Y = 9764116), East Barito District, Central Kalimantan Province on February 2014, by surveying of placic and ortstein depth and observing soil texture and chemical properties of 2 (two) oil palm's soil profiles that have been planted in five years. Big hole system of commercial oil palm field planting on the Spodosol soil area was designed for the specific purpose of minimizing the potential of a negative effect of shallow effective planting depth for oil palms growing due to the hardpan layer (placic and ortstein) presence as deep as 0.25 - 0.50 m. The big hole system is a planting hole type which was vertical-sided with 2.00 m x 1.50 m on top and bottom side and 3.00 m depth meanwhile the 2:1 drain was vertical-sided also with 1.50 m depth and 300 m length. Oil palm production was recorded from the year 2012 up to 2014. Results indicated that the fractions both big hole profile (A profile) and no big hole profile (B profile) were dominated by sands ranged from 60% to 92% and the highest sands content of non-big hole soil profile were found in A and E horizons (92%). Better distribution of sand and clay fractions content in between layers of big hole soil profiles of A profile sample is more uniform compared to the B profile sample. The mechanical holing and material mixing of soil materials of A soil profile among the upper and lower horizons i.e. A, E, B and C horizons before planting that resulted a better distribution of both soil texture (sands and clay) and chemical properties such as acidity value (pH), C-organic, N, C/N ratio, CEC, P-available and Exchangeable Bases. Investigation showed that exchangeable cations (Ca, Mg, K), were very low in soil layers (A profile) and horizons (B profile) investigated. The low exchangeable cations due to highly leached of bases to the lower layers and horizons. Besides, the palm which was planted on the big hole system showed good adaptation and response positively by growing well of tertiary and quaternary roots that the roots were penetrable into deeper rooting zone as much as >1.00 m depth. The roots can grow well and penetrate much deeper in A profile compared to the undisturbed hardpan layer (B profile). The FFB (fresh fruit bunches) production of the non-big hole block was higher than the big hole block for the first three years of production. This might be due to the high variation of monthly rainfall in-between years of observation from 2009 to 2014. Therefore, the hardness of placic and ortstein as unpenetrable agents by roots and water to prevent water loss and retain the water in the rhizosphere especially in the drier weather. In the high rainfall condition, the 2:1 drain to prevent water saturation in the oil palm rhizosphere by moving some water into the drain. Meanwhile, the disturbed soil horizon (big hole area) was drier than un disturbance immediately due to water removal to deeper layers. We concluded that both big hole and 2:1 drain are a suitable technology for Spodosol soil land especially in preparing palms planting to minimize the negative effect of the hardpan layer for oil palm growth.

scholarly journals Effects of serpentinite fertilizer on the chemical properties and enzyme activity of young spruce soils

2016 ◽  
Vol 30 (4) ◽  
pp. 401-414 ◽  
Author(s):  
Ewa Błońska ◽  
Kazimierz Januszek ◽  
Stanisław Małek ◽  
Tomasz Wanic
Keyword(s):  
Enzyme Activity ◽  
Chemical Properties ◽  
Molar Ratio ◽  
Tree Roots ◽  
Forest Zone ◽  
Negative Effect ◽  
Phosphorus And Potassium ◽  
One Year ◽  
Nitrogen Phosphorus ◽  
Experimental Plots

AbstractThe experimental plots used in the study were located in the middle forest zone (elevation: 900-950 m a.s.l.) on two nappes of the flysch Carpathians in southern Poland. The aim of this study was to assess the effects of serpentinite in combination with nitrogen, phosphorus, and potassium fertilizers on selected chemical properties of the soil and activity of dehydrogenase and urease in the studied soils. All fertilizer treatments significantly enriched the tested soils in magnesium. The use of serpentinite as a fertilizer reduced the molar ratio of exchangeable calcium to magnesium, which facilitated the uptake of magnesium by tree roots due to competition between calcium and magnesium. After one year of fertilization on the Wisła experimental plot, the pH of the Ofh horizon increased, while the pH of the mineral horizons significantly decreased. Enrichment of serpentinite with nitrogen, phosphorus, and potassium fertilizers stimulated the dehydrogenase activity in the studied organic horizon. The lack of a negative effect of the serpentinite fertilizer on enzyme activity in the spruce stand soil showed that the concentrations of the heavy metals added to the soil were not high enough to be toxic and indicated the feasibility of using this fertilizer in forestry.

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