Mixing Volume Ratio Research Articles

Synthesis, characterization and analytical application of nano-composite cation-exchange material, poly-o-toluidine Ce(IV) phosphate: Its application in making Cd(II) ion selective membrane electrode

An organic-inorganic composite, poly-o-toluidine Ce(IV) phosphate was chemically synthesized by mixing ortho-toluidine into the gel of Ce(IV) phosphate in different mixing volume ratios. Effect of eluant concentration, elution behavior and pH-titration studies were carried out to understand the ion-exchange capabilities. The physico-chemical properties of the material were determined using AAS, CHN elemental analysis, UV–VIS spectrophotometry, FTIR, SEM/EDX, TGA–DTA, TEM (Transmission electron microscopy), XRD and SEM studies. The distribution studies revealed that the cation-exchange material is highly selective for Cd(II). Due to selective nature of the cation-exchanger, ion selective membrane electrode was fabricated for the determination of Cd(ІІ) ions in solutions. The analytical utility of this electrode was established by employing it as an indicator electrode in electrometric titrations.

Influence of surface modification of LiCoO2 by organic compounds on electrochemical and thermal properties of Li/LiCoO2 rechargeable cells

LiCoO2 is the most famous positive electrode (cathode) for lithium ion cells. When LiCoO2 is charged at high charge voltages far from 4.2V, cycleability of LiCoO2 becomes worse. Causes for this deterioration are instability of pure LiCoO2 crystalline structure and an oxidation of electrolyte solutions LiCoO2 at higher charge voltages. This electrolyte oxidation accompanies with the partial reduction of LiCoO2. We think more important factor is the oxidation of electrolyte solutions. In this work, influence of 10 organic compounds on electrochemical and thermal properties of LiCoO2 cells was examined as electrolyte additives. As a base electrolyte solution, 1M (M: molL−1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio=3:7) was used. These compounds are o-terphenyl (o-TP), Ph-X (CH3)n (n=1 or 2, X=N, O or S) compounds, adamantyl toluene compounds, furans and thiophenes. These additives had the oxidation potentials (Eox) between 3.4 and 4.7V vs. Li/Li+. These Eox values were lower than that (6.30V vs. Li/Li+) of the base electrolyte. These additives are oxidized on LiCoO2 during charge of the LiCoO2 cells. Oxidation products suppress the excess oxidation of electrolyte solutions on LiCoO2. As a typical example of these organic compounds, o-TP (Eox: 4.52V) was used to check the fundamental properties of these organic additives. Charge–discharge cycling tests were carried out for the Li/LiCoO2 cells with and without o-TP. Constant current charge at 4.5V is mainly used as a charge method. Cells with 0.1wt.% o-TP exhibited slightly better cycling performance and lower polarization than those without additives. Lower polarization arises from a decrease in a resistance of interface between electrolyte solutions and LiCoO2 by surface film formation resulted from oxidation of o-TP. Oxidation products were found by mass spectroscopy analysis to be mixture of several polycondensation compounds made from two to four terphenly monomers. Thermal stability of LiCoO2 with electrolyte solutions did not improve by addition of o-TP. Slightly better charge–discharge cycling properties were obtained by using organic modifiers. However, when industrial applications were considered, drastic improvements have not been obtained yet. One of reasons may be too large influence of the deterioration of stability of pure LiCoO2 structure at high voltage charging for industrial use. We hope to realize the tremendous improvements of high energy, long cycle life and safe lithium cells by the combination of both LiCoO2 with more stable structure such as LiCoO2 treated with MgO and new organic additives with molecular structure more carefully designed.

Synthesis, Characterization and Ion Exchange Behavior of Polyaniline Stannic Silicomolybdate, an Organic–Inorganic Composite Material: Quantitative Separation of Pb2+ Ions from Industrial Effluents

Polyaniline stannic silicomolybdate, an organic–inorganic composite material was synthesized by mixing polyaniline, an electrically conducting organic polymer into the matrices of inorganic precipitate of stannic silicomolybdate. The experimental parameters such as mixing volume ratio and pH were established for the synthesis of the material. The material was found granular, thus suitable for column operations. Polyaniline stannic silicomolybdate shows better ion exchange capacity and thermal stability. The exchanger was characterized on the basis of instrumental techniques such as FTIR, TGA, DTA XRD and SEM. The X-ray diffraction study showed semi-crystalline nature. The elution behavior of the material was also examined. The SEM micrographs show the difference in surface morphology of inorganic component and the composite material. Distribution coefficient studies were performed for different metal ions in varied solvent systems such as Triton X-100, trichloroacetic acid and acetic acid. The effect of temperature on the distribution coefficient was also studied. It was found that 40 °C appeared to be the most suitable temperature. The material was found to be selective for Pb2+ ion. On the basis of distribution coefficient values, some analytically important binary separations of metal ions viz. Mg2+–Pb2+, Zn2+–Pb2+, Cd2+–Pb2+ and Mg2+–Cu2+ were achieved on polyaniline stannic silicomolybdate columns. The practical utility of polyaniline stannic silicomolybdate was explored by achieving quantitative separation of Pb2+ in industrial waste effluents from battery manufacturing units.

Ion-exchange studies on poly-o-anisidine Sn(IV) phosphate nano composite and its application as Cd(II) ion-selective membrane electrode

Abstract An organic-inorganic composite, poly-o-anisidine Sn(IV) phosphate, was chemically synthesized by mixing ortho-anisidine into gels of Sn(IV) phosphate with different mixing volume ratios. Studies on the effect of eluant concentration, elution behavior and separation of metal ions were carried out to understand the ion-exchange capabilities. Due to Cd(II) selective nature of composite, revealed by distribution studies, Cd(II) ion selective membrane electrode was fabricated. The analytical utility of the electrode was established by employing it as an indicator electrode in electrometric titrations having fast response time, 3–5s, and long life span of six months. Some physical parameters like self-diffusion coefficient (D0), activation energy (Ea) and entropy of activation (ΔS0) have been evaluated under conditions favoring a particle diffusion-controlled mechanism by studying ion-exchange kinetics.

Effect of Diameter Ratio of 2-component Silica Particle on Coagulation State in a Liquid Fluid Field

In order to obtain knowledge for designing a particle hetero-coagulation in a liquid flow field, effects of the median diameter ratio in 2-component silica particles on particle distribution in various Reynolds number and pH conditions were investigated. The diameter ratio was 0.9-45.8 and the mixing volume ratio was constant at 1 : 1. As evaluation values, (1) amount of coagulation, (2) coagulation diameter and (3) constituting particle diameter of coagulation were calculated. As a result, when the diameter ratio was relatively large, greater or equal 11.2, coagulation was prevented. On the other hand, when the diameter ratio was relatively small, less or equal 1.5, the coagulation diameter and constituting particle diameter can be controlled by Reynolds number. The possible causes of the effects were discussed by focusing on a hetero-coagulation theory and a particle behavior in a flow field.

A new electron exchange material Ti(IV) iodovanadate: Synthesis, characterization and analytical applications

Abstract A new inorganic cation exchange material Ti(IV) iodovanadate has been synthesized under a variety of conditions. The experimental parameters such as mixing volume ratio, order of mixing and pH established for the synthesis of the material. The most stable sample has been prepared by adding aqueous mixture of 0.1 M potassium iodate and 0.1 M sodium vanadate into 0.1 M solution (CCl 4 medium) of titanium chloride at pH 1. The material is characterized using various analytical techniques like XRD, FTIR, TGA–DTA and SEM. A tentative structural formula has been proposed on the basis of chemical composition, pH titration, FTIR and thermogravimetric analysis. The ion exchange capacity and distribution coefficients of various metal ions have been determined to understand the cation exchange behavior of the material. On the basis of distribution studies, the material was found to be selective for Pb 2+ ion. Its selectivity has been examined by achieving some important and analytically difficult binary separations, viz. Cr 3+ –Pb 2+ , Fe 3+ –Pb 2+ , Zn 2+ –Pb 2+ , Cd 2+ –Pb 2+ , etc. The material has bee also used as an electron exchange material. The oxidation of Fe(II) to Fe(III) has been achieved by batch-equilibrium technique successfully. The decomposition of hydrogen peroxide by the material has also been studied. The practical utility of Ti(IV) iodovanadate has been demonstrated by separating metal ions quantitatively from a synthetic mixture using the packed column of Ti(IV) iodovanadate.

Carbonate-modified siloxanes as solvents of electrolyte solutions for rechargeable lithium cells

Influence of mixing carbonate-modified siloxanes into LiPF 6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) mixed solvent electrolytes on charge–discharge cycling properties of lithium was examined. As the solute, 1 M (M: mol L −1) LiPF 6 was used. As siloxanes, 4-(2-trimethylsilyloxydimethylsilylethyl)-1,3-dioxolan-2-one and 4-(2-bis(trimethylsilyloxy)methylsilylethyl)-1,3-dioxolan-2-one were investigated. These siloxanes are derivatives of butylene cyclic carbonate or vinyl ethylene carbonate. Charge–discharge cycling efficiencies of lithium metal anodes improved and an impedance of anode/electrolyte interface decreased by mixing siloxanes, compared with those in 1 M LiPF 6-EC/MEC alone. Slightly better cycling behavior of natural graphite anode was obtained by adding siloxanes. Si–C/LiCoO 2 cells exhibited better anode utilization and good cycling performance by using 1 M LiPF 6-EC/MEC + siloxane electrolytes. Thermal behavior of electrolyte solutions toward graphite–lithium anodes was evaluated with a differential scanning calorimeter. By adding siloxanes, temperature starting the large heat-output of graphite–lithium anodes with 1 M LiPF 6-EC/MEC electrolyte solutions shifted to higher temperature about 100 °C. However, amount of heat-output did not decrease by adding siloxanes.

Intermolecular Interaction between W(CO)6 and Alkane Molecules Probed by Ultrafast Vibrational Energy Relaxation: Anomalously Strong Interaction between W(CO)6 and Decane

The rate of vibrational energy relaxation (VER) is a valuable probe of microscopic intermolecular interaction. In the present article, the VER rate of the T(1u) CO stretch of W(CO)(6) is measured in binary solutions composed of an alkane (hexane, decane, tetradecane) and cyclohexane or CCl(4), with seven mixing volume ratios. The volume ratio dependence indicates that, among the three alkane-cyclohexane solutions, only decane shows an exceptionally strong contribution to the VER process. It is strongly suggested that decane forms a specific solute-solvent complex with W(CO)(6). The "V-shaped" dependence of the VER rate on the number of carbons in alkane solvents (Banno, M.; Sato, S.; Iwata, K.; Hamaguchi, H. Chem. Phys. Lett. 2005, 412, 464.) is explained by the solute-solvent complex model. There are no experimental results that suggest the formation of the specific solute-solvent complex in alkane-CCl(4) solutions.

Electrochemical properties and lithium ion solvation behavior of sulfone–ester mixed electrolytes for high-voltage rechargeable lithium cells

Sulfone–ester mixed solvent electrolytes were examined for 5V-class high-voltage rechargeable lithium cells. As the base-electrolyte, sulfolane (SL)–ethyl acetate (EA) (1:1 mixing volume ratio) containing 1M LiBF4 solute was investigated. Electrolyte conductivity, electrochemical stability, Li+ ion solvation behavior and cycleability of lithium electrode were evaluated. 13C NMR measurement results suggest that Li+ ions are solvated with both SL and EA. Charge–discharge cycling efficiency of lithium anode in SL–EA electrolytes was poor, being due to its poor tolerance for reduction. To improve lithium charge–discharge cycling efficiency in SL–EA electrolytes, following three trials were carried out: (i) improvement of the cathodic stability of electrolyte solutions by change in polarization through modification of solvent structure; isopropyl methyl sulfone and methyl isobutyrate were investigated as alternative SL and EA, respectively, (ii) suppression of the reaction between lithium and electrolyte solutions by addition of low reactivity surfactants of cycloalkanes (decalin and adamantane) or triethylene glycol derivatives (triglyme, 1,8-bis(tert-butyldimethylsilyloxy)-3,6-dioxaoctane and triethylene glycol di(methanesulfonate)) into SL–EA electrolytes, and (iii) change in surface film by addition of surface film formation agent of vinylene carbonate (VC) into SL–EA electrolytes. These trials made lithium cycling behavior better. Lithium cycling efficiency tended to increase with a decrease in overpotential. VC addition was most effective for improvement of lithium cycling efficiency among these additives. Stable surface film is formed on lithium anode by adding VC and the resistance between anode/electrolyte interfaces showed a constant value with an increase in cycle number. When the electrolyte solutions without VC, the interfacial resistance increased with an increase in cycle number. VC addition to SL–EA was effective not only for Li/LiCoO2 cell with charge cut-off voltage of 4.5V but also for Li/LiNi0.5Mn1.5O4 cells even with high charge cut-off voltage of 5V in Li/LiNi0.5Mn1.5O4 cells.

Dependence of Blast Attenuation on Weight of Barrier Materials

The attenuation effect of barrier materials, which covers an explosive completely, on blast waves was studied. The density of the barrier materials was examined to make the barrier materials light and low in volume. Water gel, small spheres of foam polystyrene, and mixtures of these two materials were used as the barrier materials, and the density of the mixture was varied from 0.12 g•cm-3 to 1.0 g•cm-3 by changing the mixed volume ratio. Natural silica sand was also tested for comparison. A spherical PMMA container was filled with the barrier materials and a spherical pentolite (100 g) was ignited at the center of container. The blast pressure around the container was measured. The mixture of the density of approximately 0.55 g•cm-3 maximized the attenuation of the blast wave for the same volume. The attenuation effect depends not only on the weight of the barrier materials but also on the porosity. A mixture of a density of approximately 0.13 g•cm-3 maximized the attenuation of the blast wave for the same weight. Using porous materials, relatively light barrier materials can attenuate the blast wave effectively, if the volume is not restricted. The attenuation effect of sand was greater than that of water gel and a mixture for the same volume.

Preparation and characterization of a new organic–inorganic nano-composite poly- o-toluidine Th(IV) phosphate: Its analytical applications as cation-exchanger and in making ion-selective electrode

An organic–inorganic hybrid poly- o-toluidine Th(IV) phosphate was chemically synthesized by mixing ortho-tolidine into the gel of Th(IV) phosphate in different mixing volume ratios, concentration of inorganic reactant with a fixed mixing volume ratios of organic polymer. The physico-chemical characterization was carried out by elemental analysis, TEM, SEM, XRD, FTIR and simultaneous TGA–DTA studies. The ion-exchange capacity, chemical stability, effect of eluant concentration, elution behavior and pH titration studies were also carried out to understand the ion-exchange capabilities. The distribution studies revealed that the cation-exchange material is highly selective for Hg 2+, which is an important environmental pollutant. Due to selective nature of the cation-exchanger ion-selective membrane electrode was fabricated for the determination of Hg(II) ions in solutions. The analytical utility of this electrode was established by employing it as an indicator electrode in electrometric titrations.

Poly-ether modified siloxanes as electrolyte additives for rechargeable lithium cells

Influence of four poly-ether modified siloxanes as electrolyte additives on charge–discharge cycling properties of lithium was examined. As siloxanes, diethylene glycol methyl-(3-dimethyl(trimethylsiloxy)silyl propyl)ether (sample A), diethylene glycol methyl-(3-dinethyl(trimethylsiloxy)silyl propyl)-2-methylpropyl ether (sample B), diethylene glycol methyl-(3-bis(trimethylsiloxy)silyl propyl)ether (sample C) and diethylene glycol-(3-methyl-bis(trimethylsiloxy)silyl-2-methylpropyl)ether (sample D) were investigated. As a base electrolyte solution, 1 M (M, mol L −1) LiPF 6-ethylene carbonate (EC)/methylethyl carbonate (MEC) (mixing volume ratio = 3:7) was used. As the anodes, lithium metal, natural graphite carbon and silicon–SiO 2–carbon (Si–C) composite electrodes were used. Lithium cycling efficiencies of these three anodes improved and an impedance of anode/electrolyte interface decreased by adding poly-ether modified siloxanes. Graphite/LiCoO 2 and Si–C/LiCoO 2 cells exhibited better anode utilization and good cycling performance by using 1 M LiPF 6–EC/MEC + siloxane electrolytes. It was also found that thermal stability of the electrolyte solutions improved by adding siloxanes. Thermal decomposition temperature of 1 M LiPF 6–EC/MEC shifted to higher temperature by adding siloxanes. Amount of heat-output of graphite–lithium anodes with M LiPF 6–EC/MEC electrolyte solutions decreased and the temperature starting the heat-output shifted to higher temperature by adding siloxanes. Among siloxanes examined here, samples B and D exhibited much better performance.

Synthesis of Nickel Powders by the Reduction of Hydrazine from Diethanolamine Solution

Nickel powders were synthesized by the reduction of hydrazine of nickel salts from diethanolamine (DEA) solution, and the morphological characteristics of nickel powders were investigated with various process conditions such as the addition of hydrazine, reaction temperature, the composition of mixed solvents. The addition of hydrazine in DEA solution largely affected the size control of nickel powders. Under N2H4/Ni2+molar ratio= 1.5 and 2.0 conditions, spherical nickel powders in the submicron range were obtained owing to higher the reduction rate. An increase of temperature increased the size of nickel particles. At 220°C for 40min, the nickel powders were composed of polyhedral particles with a high crystalline in the submicron range. The mixed volume ratio of TEA to DEA solvent improved the inhibition of agglomerate between particles.

Synthesis, ion exchange properties and analytical applications of stannic silicomolybdate: Effect of temperature on distribution coefficients of metal ions

Stannic silicomolybdate was synthesized at pH 0.63 .The experimental parameters such as order of mixing, mixing volume ratio, pH, stirring time, drying temperature were established for the synthesis of the material. The ion exchange capacity of Ca 2+ was improved from 0.53 to 1.73 meq/g for this newly synthesized material. The reproducibility of the product formed was checked. The exchanger was characterized on the basis of chemical composition, thermal and chemical stability, FTIR, TGA, DSC, X-ray and SEM analysis. The scanning electron microscopy of the material shows a regular diamond shape morphology. The presence of uniform morphology also indicated the absence of impure phases. The X-ray diffraction study showed the amorphous nature. Distribution coefficient studies of the metal ions on this material were performed in solvents having different acid dissociation constants namely trichloroacetic acid, formic acid and acetic acid. The effect of dielectric constants of solvents was studied by using dimethylsulfoxide; formic acid, acetic acid and trichloroacetic acid. The effect of temperature on the distribution coefficient was explored. It was finally concluded that 45 °C appeared to be the most favorable temperature. Important quantitative separations of metal ions in ternary mixtures included Ni 2+–Co 2+–Pb 2+, Cu 2+–Cr 3+–Pb 2+, Cu 2+–Fe 3+–Pb 2+, Th 4+–Zr 4+–Sn 4+, Cr 3+–Ni 2+–Fe 3+, Cu 2+–Ni 2+–Ag + and Fe 3+–Zn 2+–Al 3+. The practical potential of stannic silicomolybdate was explored by separating Cu 2+ and Zn 2+ quantitatively in synthetic mixtures as well as in commercially available brass samples.

DEA 용액에서 암모니아를 함유한 염화니켈 수용액으로부터 니켈 분말의 입경 제어

Nickel powders were synthesized by the hydrazine reduction of nickel chloride solution containing ammonia in DEA solutions. The size distribution of nickel powders were investigated as a function of ammonia concentration, hydrazine concentration and the mixed composition ratio of diethanolammine (DEA) and triethanolammine (TEA). Nickel powders with the size in submicron range were obtained at <TEX>$185^{\circ}C$</TEX> for 45 minutes by hydrazine reduction of nickel chloride solution in DEA solutions. The hydrazine concentrations showed significant effects on the particle size and shape distribution of nickel powders under <TEX>$NH_3/Ni^{2+}$</TEX> molar ratio of 2.0 condition. As the mixed volume ratio of TEA and DEA increased, nickel powders with relatively larger particle size and low agglomeration were obtained. Nickel powders with particle size in the ranged from 0.4 to <TEX>$0.9\;{\mu}m$</TEX> were obtained at the 50 <TEX>$vol.%$</TEX> of TEA.

DEA 용액으로부터 히드라진의 환원 반응에 의한 니켈 분말 제조

Nickel powders synthesized by the reduction of hydrazine of nickel salts from diethanolamine(DEA) solution, and investigated the morphological characteristics of nickel powders with the addition of hydrazine, reaction temperature, the composition of mixed solvents. The addition of hydrazine in DEA solution largely affected on size control of nickel powders. Under N₂H₄/Ni 2+ molar ratio=1.5 and 2.0 conditions, spherical nickel powders in the submicron range obtained, owing to higher the reduction rate. An increase of temperature increased the size of nickel particles. At 220℃ for 40 min, the nickel powders composed of polyhedral particles with high crystalline in the submicron range. The mixed volume ratio of TEA to DEA affected on the increase of particle size and the inhibition of agglomerate between particles.

The effects of chlorine depletion of antioxidants in PE

In this work, we studied several manufacture characteristics of various metal catalysts of Ni, Co, Cu, and Fe for the catalytic decomposition of a sodium hypochlorite solution. The metal oxide, metal hydroxide, and metal oxide–hydroxide forms were prepared and compared. Ultimately, a bead-type catalyst impregnated with a metal oxide–hydroxide mixture was manufactured and evaluated. The metal ions were oxidized and precipitated in the form of metal oxide–hydroxide or metal oxide in a hypochlorite solution, and the precipitates could decompose the hypochlorite in solution. The Ni oxide–hydroxide catalyst showed the best hypochlorite decomposition performance and was the most stable among the other metal catalysts as well as the Ni hydroxide and Ni oxide catalysts. When the Ni oxide–hydroxide catalyst was manufactured in a hypochlorite solution, an optimal mixing volume ratio of hypochlorite solution to the metal ion solution was achieved. A column packed with Ni oxide–hydroxide beads was confirmed to continuously and effectively decompose hypochlorite in seawater.

Ethylene carbonate/propylene carbonate/2-methyl-tetrahydrofuran ternary mixed solvent electrolyte for rechargeable lithium/amorphous V 2O 5-P 2O 5 cells

We have been studying a cell system which consists of an amorphous (a-) V 2O 5-P 2O 5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte by fabricating an AA-size prototype cell. In a previous study, we reported the influence of the mixing ratio of ethylene carbonate (EC) and propylene carbonate (PC) solvents, in EC/PC binary mixed solvent systems incorporating LiAsF 6 as the solute, on the cell performance and safety of Li/a-V 2O 5-P 2O 5 cells. In this paper, we examine the influence of LiAsF 6-EC/PC/2-methyl-tetrahydrofuran (2MeTHF) (solvent mixing volume ratio; 15:70:15) ternary mixed solvent electrolyte on the properties of AA-size Li/a-V 2O 5-P 2O 5 cells. The goals are to improve the cycle life of Li/a-V 2O 5-P 2O 5 cells while ensuring their safety and controlling their cost. Cell performance includes rate capability and charge-discharge cycle life. The abuse tests carried out on the Li/a-V 2O 5-P 2O 5 cells consist of a heating test at 130 °C and an external short circuit test at 25 °C. Cells with a ternary mixed solvent electrolyte have a longer cycle life than cells with EC/PC binary mixed solvent electrolytes. In addition, these cells are much less likely to suffer from soft shorting at low discharge rate cycles than cells with EC/PC binary mixed solvent electrolytes. This improvement in the cycle life is thought to result from an improvement in the Li anode cycling efficiency based on Li-half cell cycling test results. In addition, the abuse tests ensure the fundamental safety of cells containing ternary mixed solvent electrolyte.

The 10 μm feature of aggregates in comets

Thermal emission form cometary dust grains has been examined using model calculations of aggregates with fractal structure consisting of two components, namely silicate (olivine) and absorbing mateial (magnetite). Calculations of the thermal emission have been performed by using the discrete dipole approximation for small aggregates, and Mie theory with the Maxwell-Garnett rule for large aggregates. We have used the size distribution of the aggregates converted from the mass distribution of grains detected in comet P/Halley (Mazets et al., Nature 321, 276, 1986), taking into account the fractal aggregate model for cometary grains. It is found that the spectral feature at about 10 μm wavelength is mainly controlled by a fractal dimension D of the aggregates, wheras the temperature of the aggregates strongly depends on a mixing volume ratio M of magnetite to a whole volume, i.e. M = (magnetite (olivine — magnetite)). When the cometary dust grains consist of the fractal aggregates with D ≅ 2 and M = 0.15, a remarkable twin-peaked structure in the 10 μm silicate band apears even when large aggregates contribute to the infrared spectral feature. We can also expect a weak twin peak even when D ≅ 3. Furthermore, such grain model can predict a reasonable temperature of about 390 K at a Sun-comet distance of 0.79 AU, which gives a good fit to that reported in comet P/Halley (Campins and Ryan, Astrophys, J., 341, 1059, 1989). We conclude that the model calculations support an interpretation of the observational data in terms of porous particles consisting of different materials.

Methemoglobin production by nitric oxide in fresh sheep blood

As nitric oxide (NO) inhalation is used therapeutically, we studied the production of methemoglobin (metHb) by NO in fresh adult sheep blood. NO solutions were prepared by bubbling a 10% NO-90% N 2 gas mixture in phosphate-buffered saline (pH = 7.41 at 20°C) for at least 60 min. Fresh blood samples were obtained from catheterized femoral arteries or veins just prior to mixing with NO solution. Measurements of metHb were made at times 0, 30 sec, 2 min and 5 min after mixing of NO-containing buffer and blood using a Radiometer OSM-3 hemoximeter. Mixing was performed using two syringes connected via a stopcock. The reaction of NO with blood occurred rapidly after mixing since data values for each of the time points after 30 sec were unchanged for all mixtures. The mixing volume ratio of NO-containing buffer to blood was either 1:1 (protocol A) for comparisons of arterial vs venous blood, or the ratios were randomized (protocol B) to investigate effects of Hb oxygenation. Protocol A elicited only slight increases of metHb in arterial and venous blood which did not differ significantly. In protocol B, an increase of metHb was associated with a relative decline of deoxyhemoglobin (deoxyHb). A higher molar ratio of NO/deoxyHb yielded greater amounts of metHb. Therefore, in fresh sheep blood, deoxyHb is converted to metHb in the presence of NO. This reaction is not affected by the presence of oxyhemoglobin.