In the construction industry carbonate aggregates are commonly used in processes such as concrete production. Aggregates which contain (in their mineral composition) dolomite and an admixture of clay minerals and amorphous silica , can react with alkalis. These reactions can lead to a destructive expansion in concrete. This article explains the mechanisms and the essence of this phenomenon. What is more, some effective and fast methods of the estimation and evaluation of Polish aggregates consisting of carbonate rocks suggests effective methods to determine the usefulness of Polish carbonate aggregates in concrete production are discussed in the paper. Underneath the quality criteria to determine the reactivity of the aggregates will be given. It has been agreed that alkaline reaction and expansion are two separate phenomena related to each other genetically. The aggregates in which reactions caused by clay-siliceous admixtures occur are subjected to expansion. Mineral composition of expansive aggregates as well as their texture indicate that epigenetic dolomites with a distinctive texture are the most reactive. The phase transformations do not end with a complete disintegration of dolomite. They have a cyclical character. They consist of interchangeable reactions of dedolomitization and dolomitization of secondary calcite formed as a result of dolomite's disintegration. The secondary calcite can be effected by Mg+2 ions from pores' solutions and it can form a secondary dolomite. The Mg2+ ions originate from brucite [Mg(OH)2], created in dolomitization process. As a consequence of its reaction with silica, brucite can dissolve and enrich secondary calcite with magnesium. Therefore the reactions which take place in reactive carbonate aggregates and concrete that ismade of it are in fact ongoing processes which consist of dolomite's changes into calcite and vice versa. They are reactions between dedolomitization products (brucite, silica) and products from outside (water, alkalis). The described dedolomitization reactions are a phase of the process that enables expansion due to formation of pressure in inter-granular cracks, with pressure being a result of dry clay-minerals' expansion under the influence of water solutions. Loosening of the aggregate's structure as an effect of dedolomitization reaction makes it easier for water solutions to migrate far into the aggregate's grains followed by their contact with clay minerals.
The work concerns the dynamic behaviour of a porous, isothermal catalyst pellet in which a simultaneous chemical reaction, diffusion and adsorption take place. The impact of the reactant adsorption onto the pellet dynamics was evaluated. A linear isotherm and a non-linear Freundlich isotherm were considered. Responses of the pellet to sinusoidal variations of the reactant concentration in a bulk gas were examined. It was demonstrated that the dynamics of the pellet is significantly affected both by accounting for the adsorption and by the frequency of the bulk concentration variations. The sorption phenomenon causes damping of the concentration oscillations inside the pellet and damping of its effectiveness factor oscillations. Depending on the frequency of the concentration oscillations in the bulk, the remarkable oscillations can involve an entire volume of the pellet or its portion in the vicinity of the external surface.
Alkali-aggregate reactivity (AAR) is one of the major causes of damage in concrete. Potential susceptibility of aggregates to this reaction can be determined using several methods. This study compares gravel alkali reactivity results obtained from different tests conducted on coarse aggregates with complex petrography. The potential for the reactivity in the aggregates was revealed in the chemical test using treatment with sodium hydroxide. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to identify the reactive constituents. The expansion measured in the mortar bars test confirmed that the aggregate was potentially capable of alkali silica reactivity with consequent deleterious effect on concrete.
This scientific paper presents the research on influence of austenitizing temperature on kinetics and evolution of the spheroidal plain cast
iron during eutectoid reaction in isothermal conditions. The cast iron has been austenitized in temperatures of 900, 960 or 1020°C. There
were two temperature values of isothermal holding taken into consideration: 760 or 820°C. The order of creation of reaction products and
their morphology have been analyzed. The particular attention has been paid to the initial stage of transformation. The qualitative research
has been executed using the transmission electron microscope (TEM), as well as quantitative research (LM). The influence of austenitizing
temperature has also been determined on transformation kinetics and structural composition. It was found that the increase of austenitizing
temperature is conductive to the initial release of structures by metastable system. A reduction of time was observed of the initial stage of
transformation at temperature close to Ar12 with its simultaneous elongation at temperature close to Ar11, with an increase of austenitizing
temperature. The dependences obtained by the metallographic method confirm the prior results of dilatometric research of eutectoid
reaction.
Honesty and transparency in vaccination safety – monitoring adverse reactions to vaccines
Sperm-mediated gene transfer (SMGT) is based on the ability of spermatozoa to bind exoge- nous DNA and transfer it into oocytes by fertilization. However, SMGT is still undergoing opti- mization to improve its efficiency to produce transgenic animals. The acrosome reaction is neces- sary for spermatozoa to carry the exogenous DNA into oocytes. In this study, the effect of the acrosome reaction on the efficiency of spermatozoa carrying exogenous DNA was evalua- ted. The results showed that the efficiency of the acrosome reaction was significantly higher (p<0.05) after incubation with 50 μmol/L progesterone compared to incubation without proges- terone. It was significantly higher (p<0.05) in the 20, 40, and 60 min of progesterone treatment groups than in the 0 min treatment group. The spermatozoa were further incubated with cyanine dye Cy5 labeled DNA (Cy5-DNA) for 30 min at 37°C, and positive fluorescence signals were detected after the acrosome reaction was induced by progesterone at concentrations of 0 and 50 μmol/L for 40 min. The percentage of positive Cy5-DNA signals in spermatozoa was 96.61±2.06% and 97.51±2.03% following exposure to 0 and 50 μmol/L progesterone, respective- ly. The percentage of partial spermatozoa heads observed following combination with Cy5-DNA was 39.73±3.03% and 56.88±3.12% following exposure to 0 and 50 μmol/L progesterone, respec- tively. The ratio of positively stained spermatozoa combined with exogenous DNA showed no reduction after the acrosome reaction. These results suggest that the acrosome reaction might not be the key factor affecting the efficiency of SMGT.
In this paper, the kinetics of the platinum(IV) chloride complex ions reduction reaction was studied. It was shown that the mechanism exhibits autocatalytic character. The presence of metallic platinum in the system significantly increases the reaction rate. The influence of the initial concentration of precursor, reductant, ionic strength, initial concentration of the chloride ions as well as the temperature on the process rate was investigated. The activation energy was determined and is equal to 93.57 kJ/mol. Moreover, the obtained metallic phase was analyzed, and it was observed that it has a micrometric size.
Our scientific research is based on oxidation reactions and monitoring of chemical reaction kinetics in the Velekinca groundwaters plant in Gjilan municipality, Kosovo. The GW of this plant contains high concentration of manganese so we need to use potassium permanganate (KMnO4) as one of the most power oxidants in the water treatment plant. In our re-search the high concentration of Mn in groundwaters is 0.22–0.28 mg∙dm–3 and this concentration is not in accordance with the WHO. Chlorine is one of the most common disinfectants used in the water treatment industry because it has a low cost and immediate effect on the destruction of microorganisms, the concentration of chlorine (Cl2) in our research is 0.1–0.32 mg∙dm–3. The speed of chemical reactions in the technology of GW is extremely important because sometimes in the elimi-nation of chemical pollutants using oxidizing agents often form intermediate species. The speed of reactions indicates how fast chemical bonds are formed in the creation of a product, and this depends on the rate of reaction (XA). The focus for the research is to study the potassium permanganate and chlorine gas reactions in water if it forms intermediate products (in-termediate species) due to the high speed of reactions. Scientific research conclusion, intermediate species in the oxidation reactions of Mn and water disinfection with Cl2(g) it is impossible to cause a high rate of chemical reactions from the reac-tion rate (XA = 1%) to the reaction rate (XA = 99%). The maximum speed at the highest XA Cl2 is from 4.405∙10–11 to 8.87∙10–10 mol∙dm–3∙s–1, while at Mn is (2.030–4.034)∙10–7 mol∙dm–3∙s–1.
Pseudomonas syringae pv. syringae (Pss) constitutes a diverse group of bacterial strains that cause canker of stone fruits, blight of cereals and red streak of sugarcane. The purpose of this study was to determine how diverse Iranian strains of Pss are when they come from different hosts. We compared a total of 32 Pss strains isolated from stone fruits, barley, wheat and sugarcane from different geographical regions of Iran based on their phenotypic and molecular properties. Strains showed some variation regarding carbon and nitrogen utilization. Pss strains were similar in their protein banding patterns. Additional bands were found in sugarcane strains. Most strains showed one indigenous plasmid DNA and a few had two and some none. The genes of syrB and syrD encoding syringomycin synthesis and secretion, respectively, were amplified using specific primers in polymerase chain reaction. Syringomycin, producing strains amplified two DNA fragments of 752 and 446 bp representing syrB and syrD genes, respectively. Primer specificity was shown for Pss using various genera. Based on the results of this study, it is suggested that Pss strains from different hosts and geographical regions show diversity in phenotypic and molecular characters. It is thought that phenotypic variation is due to adaptation to specific hosts and niches for survival and pathogenicity.
Cucumber mosaic virus (CMV; family Bromoviridae, genus Cucumovirus) is the most cosmopolitan plant virus occurring worldwide. In the present study, leaf samples showing deformations, mosaics, and chlorotic spots symptoms were collected from naturally infected Basella alba, Telfairia occidentalis and Talinum fruticosum in a home yard garden in Ibadan, Nigeria. Total nucleic acid was extracted from leaves and used as template for cDNA synthesis. RT-PCR was carried out using CMV-specific primers targeting RNA-1 segment. Samples were also tested by RT-PCR using Potyvirus and Begomovirus genusspecific primers. DNA fragments with the expected sizes of ~500 bp were amplified by using CMV-specific primers; however, the expected amplicons were not produced using specific primers used for the detection of potyviruses and begomoviruses. The nucleotide and deduced amino acid sequences obtained for the isolates studied contained 503–511 nt and 144 aa, respectively. The isolates shared 81.9–85.3% nucleotide and 74.3–77.8% amino acid sequence identities with each other. The results of BLASTN analyses showed the highest identities of the isolates (80–93%) with CMV strains from Japan, USA and South Korea. Alignment of deduced partial protein revealed multiple amino acid substitutions within the three isolates and high identities with CMV subgroup I. Phylogenetic analyses putatively categorized the isolates in close association with subgroup IB isolates. The three isolates clustered together into a separate subclade, indicating possible new CMV strains. The results provide the first molecular evidence for CMV infections of T. fruticosum and B. alba in Nigeria and seem to show the possible presence of new strain(s). These findings also add three new hosts to the list of natural host range of the virus in Nigeria.
The paper presents current reports on kinetics and mechanisms of reactions with mercury which take place in the exhaust gases, discharged from the processes of combustion of solid fuels (coals). The three main stages were considered. The first one, when thermal decomposition of Hg components takes place together with formation of elemental mercury (Hg0). The second one with homogeneous oxidation of Hg0 to Hg2+ by other active components of exhaust gases (e.g. HCl). The third one with heterogeneous reactions of gaseous mercury (the both - elemental and oxidised Hg) and solid particles of fl y ash, leading to generation of particulate-bound mercury (Hgp). Influence of exhaust components and their concentrations, temperature and retention time on the efficiency of mercury oxidation was determined. The issues concerning physical (gas-solid) and chemical speciation of mercury (fractionation Hg0-Hg2+) as well as factors which have influence on the mercury speciation in exhaust gases are discussed in detail.
The homogeneous stirred reactor designed for kinetic studies of the combustion of hydrocarbons with intensive internal recirculation in high temperature combustion chamber is described. The originality of our reactor lies in its construction which allows to intensively mix fuel and flue gases, measure gas temperature as well as obtain samples which can be used to investigate diffusion flames. The cylindrical construction enables to use the reactor in laboratory cylindrical electrically heated ovens. The CFD analysis of the reactors, the mixing parameters (turbulent Peclet number and mixing level) and the volume average temperature in the reactors were elaborated on the basis of the typical dimensions of classical reactors to kinetics research as well as the own reactor design. The results of the analysis allow to reveal advantages of our construction.
The kinetics of the reaction between CO2 and methyldiethanolamine in aqueous solutions have been studied using the stopped-flow technique at 288, 293, 298 and 303 K. The amine concentration ranged from 250 to 875 mol·m-3. The overall reaction rate constant was found to increase with amine concentration and temperature. The acid base catalysis mechanism was applied to correlate the experimentally determined kinetic data. A good agreement between the second order rate constants for the CO2 reaction with MDEA computed from the stopped-flow data and the values reported in the literature was obtained.
The aim of the presented research was to test different carbon supports, such as graphene oxide (GO), graphene oxide modified with ammonia (N-GO), and reduced graphene oxide (rGO) for catalysts used in a low-temperature fuel cell, specifically a proton exchange membrane fuel cell (PEMFC). Modification of the carbon supports should lead to different catalytic activity in the fuel cell. Reduction of GO leads to partial removal of oxygen groups from GO, forming rGO. Modification of GO with ammonia results in an enrichment of GO structure with nitrogen. A thorough analysis of the used supports was carried out, using various analytical techniques, such as FTIR spectroscopy and thermogravimetric (TGA) analysis. Palladium and platinum catalysts deposited on these supports were produced and used for the oxygen reduction reaction (ORR). Catalytic activity tests of the prepared catalysts were carried out in a home-made direct formic acid fuel cell (DFAFC). The tests showed that the enrichment of the GO structure with nitrogen caused an increase in the catalytic activity, especially for the palladium catalyst. However, reduction of GO resulted in catalysts with higher activity and the highest catalytic activity was demonstrated by Pt/rGO, because platinum is the most catalytically active metal for ORR. The obtained results may be significant for low-temperature fuel cell technology, because they show that a simple modification of a carbon support may lead to a significant increase of the catalyst activity. This could be useful especially in lowering the cost of fuel cells, which is an important factor, because thousands of fuel cells running on hydrogen are already in use in commercial vehicles, forklifts, and backup power units worldwide. Another method used for lowering the price of current fuel cells can involve developing new clean and cheap production methods of the fuel, i.e. hydrogen. One of them employs catalytic processes, where carbon materials can be also used as a support and it is necessary to know how they can influence catalytic activity.
This work presents the qualitative and quantitative changes in the products of isothermal transformation (reaction) in a ductile cast iron
austenite after supercooling to the temperature range Ar1. The austenitizing temperature considered in this work was 900, 960 or 1020°C.
The eutectoid reaction was investigated by metallographic examination at a holding temperature right below Ar11 (820°C) or right below
Ar12 (760°C). The quantitative metallographic examination was carried out with a light microscope (LM). The initial transformation stage
products were identified with a transmission electron microscope (TEM). The selected samples were studied for chemical
microsegregation of manganese, silicon, phosphorus, and carbon with an X-ray microanalyser (MAR). The tested cast iron material was
found to predominantly feature a eutectoid reaction in the metastable system the ratio of which was increasing with the austenitizing
temperature. The austenitizing temperature was found to be conducive to the evolution kinetics of individual phases and to the
graphitization kinetics of the eutectoid cementite that was formed during the contemplated reaction.