Corona discharge experiments in admixtures of N2 and CH4: a laboratory simulation of Titan's atmosphere

A positive corona discharge fed by a N2:CH4 mixture (98:2) at atmospheric pressure and ambient temperature has been studied as a laboratory mimic of the chemical processes occurring in the atmosphere of Titan, Saturn's largest moon. In-situ measurements of UV and IR transmission spectra within the discharge have shown that the main chemical product is C2H2, produced by dissociation of CH4, with small but significant traces of ethane and HCN, all species that have been detected in Titan's atmosphere. A small amount (0.2 %) CH4 was decomposed after 12 minutes of treatment requiring an average energy of 2.7 kWh/g. After 14 minutes the discharge was terminated due to the formation of a solid yellow deposit on the central wire electrode. Such a deposit is similar to that observed in other discharges and is believed to be an analogue of the aerosol and dust observed in Titan's atmosphere and is composed of chemcial species commonly knonw as 'tholins'. We have also explored the electrical properties of the discharge. The admixture of methane into nitrogen caused an increase in onset voltage of the discharge and consequently led to a reduction in the measured discharge current

Current knowledge of external sulfate attack

This paper offers an update of the current understanding of sulfate attack, with emphasis on the sulfates present in an external water source percolating through, and potentially reacting with, the cement matrix. The paper considers the explanations put forward to explain sulfate attack, both from a chemical and microstructural perspective. Similarly, this paper reviews work on the physical damage caused by the precipitation of sulfate salts in porous materials. With the increased use of binary and ternary blends, this paper also considers the impact of binder composition on sulfate resistance, and similarly reviews how the nature of the sulfate species can affect the nature and extent of any deterioration. This then leads on to the important consideration of differences between field- and lab-based studies; reviewing the effect of various experimental parameters on sulfate resistance. This latter topic is of great importance to anyone who wishes to carry out such experiments

Hair Trace Element and Electrolyte Content in Women with Natural and In Vitro Fertilization-Induced Pregnancy

The objective of the present study was to perform comparative analysis of hair trace element content in women with natural and in vitro fertilization (IVF)-induced pregnancy. Hair trace element content in 33 women with IVF-induced pregnancy and 99 age- and body mass index-matched control pregnant women (natural pregnancy) was assessed using inductively coupled plasma mass spectrometry. The results demonstrated that IVF-pregnant women are characterized by significantly lower hair levels of Cu, Fe, Si, Zn, Ca, Mg, and Ba at p < 0.05 or lower. Comparison of the individual levels with the national reference values demonstrated higher incidence of Fe and Cu deficiency in IVF-pregnant women in comparison to that of the controls. IVF pregnancy was also associated with higher hair As levels (p < 0.05). Multiple regression analysis revealed a significant interrelation between IVF pregnancy and hair Cu, Fe, Si, and As content. Hair Cu levels were also influenced by vitamin/mineral supplementation and the number of pregnancies, whereas hair Zn content was dependent on prepregnancy anthropometric parameters. In turn, planning of pregnancy had a significant impact on Mg levels in scalp hair. Generally, the obtained data demonstrate an elevated risk of copper, iron, zinc, calcium, and magnesium deficiency and arsenic overload in women with IVF-induced pregnancy. The obtained data indicate the necessity of regular monitoring of micronutrient status in IVF-pregnant women in order to prevent potential deleterious effects of altered mineral homeostasis

The role of water and oxygen impurities on ozone production in a negative corona discharge of CO2

The production of ozone in a negative corona discharge fed by carbon dioxide with embedded traces of oxygen and water has been studied. The presence of traces of oxygen in both pure and dry CO2 leads to an increase in nascent ozone concentrations. In contrast, traces of water vapour (0-800 ppm) are shown to rapidly suppress ozone concentrations with the largest decreases being observed at lowest gas pressures in the discharge (300 Torr). The presence of water vapour did not considerably affect the electrical properties of negative dc corona suggesting that a chemical process is responsible for the ozone loss. We have shown that the addition of water up to a concentration of 1500 ppm has only a marginal effect on the processes of ozone formation but the catalytic cycle of ozone destruction involving OH radicals can be the reason for observed decrease in the total ozone concentration with increasing water concentration

Positive and negative corona discharges in flowing carbon dioxide

The effect of the gas flow rate (10–320 cm3 min-1) on the process of ozone formation in both positive and negative corona discharges has been studied using a coaxial cylindrical system of electrodes fed by dry CO2. The source of ozone is electron impact dissociation of carbon dioxide to liberate oxygen atoms and their subsequent formation of oxygen molecules, which may then form ozone by the well-known Chapman mechanism. Small increases in flow rate were found to cause a major increase in the discharge current measured in the negative corona discharge. This effect was found to correspond to observed changes in the ozone concentration within the discharge and is a consequence of dissociative electron attachment to ozone leading to negative ion formation in the discharge. In contrast no direct effect of ozone on the positive corona discharge current was observed. The observed increase in average positive ion mobility in the positive corona is ascribed to the conversion of ions into more mobile ions. Considerably higher ozone concentrations (up to 100 ppm) were found in the negative corona discharge. The effect of the geometry of the system was also explored by using three different stainless steel outer electrodes with diameters of 10, 15 and 27 mm. Ozone concentrations were found to decrease significantly with increasing radius of the outer electrode at the same average input energy density

A Study of the physical and chemical processes active in corona discharges fed by carbon dioxide

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO2 has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona

An analysis of mass spectrometric study of negative ions extracted from negative corona discharge in air

In this paper we report the detection and mass analysis of negative ions formed in a negative corona discharge using both dry and ‘wet’ air at pressures between 5 and 27 kPa. The yield of individual ions is strongly affected by trace concentrations of ozone, nitrogen oxides and water vapour. In dry air the dominant ion is CO3−. In presence of water this is converted very efficiently to cluster ions containing one and more water molecules. If ozone and nitrogen oxides are added, or are produced in discharge in sufficient concentrations, NO3− ions and NO3− hydrated clusters are formed. Ozone concentrations greater than 25 ppm are sufficient to completely suppress the appearance of O2− ions and its clusters both in dry and wet air. Such observations allow a comprehensive review of the physical and chemical processes within the discharge

Influence of the outer electrode material on ozone generation in corona discharges

The effect of the outer electrode material on negative corona discharge current and the process of ozone formation have been studied in coaxial cylindrical system of electrodes fed by dry oxygen. Three materials (brass, duralumin, stainless steel) were tested in experiments. The probability coefficient of ozone decomposition was found be slightly higher compared with known data. The coefficient of probability of ozone decomposition is decreasing with the time of exposition of the metal surface to mixture of oxygen and ozone. The effect of the electrode material on the current voltage characteristic of the discharge was marginal. In contrast to this at average energy density η higher than 10 J/cm3 the ozone concentration is affected by material of the outer electrode. A strong influence of the temperature of metal electrode on the probability coefficient of ozone decomposition was illustrated from the decrease of the ozone production

Ozone generation in a negative corona discharge fed with N₂O and O₂

Ozone production in a negative corona discharge has been studied experimentally at atmospheric pressure in mixtures of N2O+O2 at ambient temperature. Ozone formation was found to be dramatically reduced with increase in the content of N2O in the mixture. The reaction of O(1D) with nitrous oxide is the most likely process reducing the rate of ozone generation. A considerable decrease in the mean discharge current at a constant voltage was also observed with increasing content of nitrous oxide in the mixture and is attributed to the formation of anions in the discharge. The low values of the calculated mobility of negative charge carriers in the drift region of the discharge is caused by the formation of O− · (N2O)n and NO−·(N2O)n cluster anions in the drift region of the negative corona discharge