P.J. Pomonis

Preparation of hydroxyapatite via microemulsion route.

Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1).

Variation of surface properties and textural features of spinel ZnAl2O4 and perovskite LaMnO3 nanoparticles prepared via CTAB-butanol-octane-nitrate salt microemulsions in the reverse and bicontinuous states.

Two binary oxides, a spinel, ZnAl2O4, and a typical perovskite, LaMnO3, have been prepared via CTAB-1-butanol-n-octane-nitrate salt microemulsion in the reverse and bicontinuous states. The exact point of the reverse and bicontinuous states of the microemulsion used in the synthesis was determined by conductivity experiments. The materials obtained after heating at 800 degrees C were characterized by XRD analysis for their crystal structure, N2 porosimetry for their surface area and porosity, and SEM and TEM photography for their texture. The ZnAl2O4 spinel obtained via the reverse microemulsion appears in SEM in a more fragmented form and with a higher specific surface area (143.7 m(2)g(-1)), compared to the corresponding solid prepared via the bicontinuous microemulsion, which appears more robust with lower surface area (126.7 m(2)g(-1)). Nevertheless both materials reveal in TEM a sponge-like structure. The perovskite materials LaMnO3 prepared via the reverse microemulsion showed in SEM a peculiar doughnut-like texture, each doughnut-like secondary particle having a diameter of 2 microm. The corresponding sample developed via the bicontinuous microemulsion showed in SEM uniform secondary particles of size approximately 0.2 microm. Both perovskite samples LaMnO3 appear well crystallized with relative low surface areas, 23.7 m(2)g(-1) for the reverse sample and 10.9 m(2)g(-1) for the bicontinuous one. The TEM photographs reveal that both of them, of reversed and bicontinuous origin, are made up of primary nanoparticles in the size range 40-100 nm. In SEM those materials showed a different secondary structure.

Seasonal fluctuations of organochlorine and triazines pesticides in the aquatic system of Ioannina basin (Greece)

Abstract For the period September 1984 to November 1985 water samples from the aquatic system of Ioannina basin were analyzed every second month for organochlorine and triazines pesticides. The detected compounds were found to follow a seasonal pattern, with an increment during summer followed by a decrease during winter and an increase again during late spring. This pattern was apparent for Ioannina lake as well as for the Kalamas river connected to it through the Lapsistas canal and tunnel. The results are discussed in terms of the amounts of the detected pesticides used for farming in the vicinity of the Ioannina basin and the seasonal rainfall.

Organophosphorous and carbamates pesticide residues in the aquatic system of Ioannina basin and Kalamas river (Greece)

Abstract Organophosphorus and carbamates pesticide residues have been monitored in the aquatic system of Ioannina basin and its natural outlet, Kalamas river, for the period September 1984, to October 1985. The concentrations of detected molecules of azinphos-methyl, parathion-methyl, diazinon, carbofuran and carbaryl were found to follow a seasonal fluctuation with maxima during summer and minima during winter months. The results are discussed in relation to the ammounts of those pesticides used for farming as well as the seasonal rainfall in the vicinity of Ioannina basin.

Movement of methyl parathion, lindane and atrazine through lysimeters in field conditions

The movement of pesticides methyl parathion, lindane and atrazine due to leaching by rainfall was studied in lysimeters containing different types of soil from the loannina area of Greece. For a period between October 1985 to June 1986 the amount of pesticides was analysed in water samples from rainfall concentrated after filtration through the soils to a depth of 100 cm. The total amounts of each pesticide transported in this way were 0.15–0.26% for methyl parathion, 0.15–0.19% for lindane and 0.54–0.66% for atrazine of the initial amounts.

THE ACTIVITY PATTERNS OF THE RARE EARTH OXIDES IN HETEROGENEOUS CATALYSIS

The catalytic activity of rare earth oxides for simple catalytic reactions show patterns which broadly resemble each other and also reactions in which the number of 4f-electrons changes. If simple concepts of electron transfer are augmented, it emerges that any rate controlling step which involves the adsorption of a species by electron transfer to it, leads to an activity pattern with maxima for f0 and f7 and f14 structures.AbstractКаталитическая активность окислов редкоземельных элеметнов в простых каталитических реакциях имеет ходы, прибоизительно подобные друг другу а также реакции, в которых изменяется число 4f-электронов. Принимая простые представления переноса электрона, было заключено, что любая ступень, контроллирующая скорость и включающая в себя адсорбцию частиц путем переноса электрона на них, приводит к ходу активности с максимумами в f1 и f8 структурах и с минимумами в f0, f7 и f14 структурах.

The influence of fly ash on 2,4-dichlorophenoxy-acetic acid persistence in corn cultivation and soil

Abstract The influence of fly ash (raw material ignite from thermal station, pH = 11.2) in the fate of 2,4-dichlorophenoxy-acetic acid (2,4-D) was studied in an experimental corn cultivation, under environmental conditions of Ioannina region (N.W. Greece). An amount of fly ash equal to 0.15% p.w. of soil for a depth 0–10 cm was used in a sandy-clay-loam soil on the 18th of May 1988 when the sowing of the corn took place and the herbicide was applied after 21 days. Analyses of soil samples for 220 days, in a period between June 8, 1988 and January 14, 1989 showed that the addition of fly ash decreases the half-life of 2,4-D, from 25.5 to 19 days. The final results of fly ash addition showed a decrement of 2,4-D residues of about 24% in soil without corn cultivation and 41% in soil with corn after 129 days. For the 2,4-D residues in corn plants the corresponding decrements were 17.6% after 18 days and reach 37.5% after 114 days.

The influence of fly ash on hydrolysis, degradation and adsorption of methyl parathion in aqueous soil suspensions

The hydrolysis, degradation and adsorption of methyl parathion were studied in aquatic suspensions of two soils and their mixtures with small amounts (0.1–0.5%) of fly ash. For a concentration range of methyl parathion between 2–30 ppm the addition of fly ash up to 0.5% in a sandy clay loam (SCL) soil resulted in an increment of insecticide hydrolysis by 1.5% and of degradation by 8.5% on the average, and a decrease in adsorption by 1.8%. In the case of a clay (C) soil the addition of fly ash up to 0.5% resulted in an increment of insecticide hydrolysis by 1.2% and of degradation by 10.6% and a decrease in adsorption by 4.3% on the average. So the addition of fly ash in soil in fertilization levels act beneficial for their detoxification of methyl parathion residues.

Kinetics of disappearance of Metolachlor, Atrazine and Cyanazine residues in corn cultivation soil under the influence of fly ASH

The influence of fly ash, the lignite after burning remaining in thermal stations, on the fate of metolachlor, atrazine and cyanazine was studied in an experimental corn cultivation soil, under environmental conditions of Ioannina region (N.W. Greece). An amount of fly ash equal to 0.15% p.w. of soil for a depth 0–10 cm was used in a clay soil on the 18th of June 1991 when the sowing of the corn took place. The herbicides metolachlor, atrazine and cyanazine were applied six days later. Analyses of soil samples for 202 days period, between June 24 1991 and January 12 1992 made it possible to study the kinetics of decrease which is described satisfactorily employing a first order equation. The results showed that corn plantation and the addition of fly ash decreases the half life of herbicides as compared to the control fields as follows: For metolachlor from 45 to 34 and further to 25 days, for atrazine from 73 to 67 and further to 55 days and for cyanazine from 28 to 22 and further to 18 days. The percent...

The influence of fly ash on atrazine and alachlor persistence in corn cultivation soil

The influence of fly ash (raw material lignite from thermal station, pH = 11.2) in the fate of atrazine and alachlor was studied in an experimental corn cultivation soil, under environmental conditions of Ioannina region (N.W. Greece). An amount of fly ash equal to 0.15% p.w. of soil for a depth 0–10 cm was used in a sandy‐clay‐loam soil on the 18th of May 1988 when the sowing of the corn and the application of two herbicides took place. Analyses of soil samples for 240 days, in a period between May 18, 1988 and January 14, 1989 showed that the addition of fly ash decreases the half life of atrazine, from 54 to 47 days and of alachlor from 25 to 22 days. The final results of fly ash addition showed a decrement of atrazine residues of about 42.6% in soil without corn cultivation and 46.6% in soil with corn after 240 days. For the alachlor residues the corresponding decrements were 40.6% in the reference soil and 52.8% in corn cultivation soil, after 118 days.