The Bayer process for the production of alumina (A1203) from bauxite involves a perennial gibbsite (y-Al(OH)3) precipitation step, relating to an inherently slow crystal growth from supersaturated sodium aluminate solutions (pregnant Bayer liquors). The kinetics and mechanisms involved in the transformation of the tetrahydroxo, Al(III)-containing species in solution into octahedrally-coordinated Al(OH)3 crystals in the presence of NA+ and excess of ions, are as yet not fully known. To gain further knowledge and better understanding of the nature of solution species, their specific interaction and participation in the gibbsite crystallization mechanisms, the role alkali ions play in the kinetic behaviour and mechanisms of nucleation, growth and aggregation/agglomeration from caustic aluminate solutions of industrial strength has been investigated.

No description available.

Effects of urban air pollution on health and environment have lead researchers to find economic air quality monitoring regulations. Since tin dioxide (SnO2) was demonstrated as a gas sensing device in 1962, tin oxide based thin film sensors have been widely studied due to their high sensitivity and fast response. The main advantages of using tin oxide sensors are their low cost, small size and low power consumption for mobile system applications. But, in order SnO2 based sensors to meet low concentration of gases they should be highly upgraded in sensitivity, selectivity and stability. This study was focused on the capacity of dopants in the SnO2 layer to increase the sensitivity of the sensor in detecting carbon monoxide. 1 wt. % Pd promoted and 0.1 wt. % Na-1 % Pd promoted SnO2 multilayer thin films were produced by sol-gel technique followed by spin coating route on soda-lime glass substrates. The EDX and SEM studies showed the surface composition and the surface structure is homogeneous throughout the films. The film thickness was determined app. 450 nm from the SEM image of the cross-section, after coating 8 layers. The experiments conducted at several temperatures namely 150, 175 and 200oC, in oxygen free and 1% oxygen containing atmospheres showed that the responses at higher temperatures in the presence of oxygen were much sharper with respect to others. Besides, Na promoted test sensors showed larger responses with shorter response time in oxygen free atmospheres at relatively lower temperatures. The results showed that the sensor signal is not directly correlated with the carbon dioxide production in oxygen free atmospheres.

The Bayer process for the production of alumina (A1203) from bauxite involves a perennial gibbsite (y-Al(OH)3) precipitation step, relating to an inherently slow crystal growth from supersaturated sodium aluminate solutions (pregnant Bayer liquors). The kinetics and mechanisms involved in the transformation of the tetrahydroxo, Al(III)-containing species in solution into octahedrally-coordinated Al(OH)3 crystals in the presence of NA+ and excess of ions, are as yet not fully known. To gain further knowledge and better understanding of the nature of solution species, their specific interaction and participation in the gibbsite crystallization mechanisms, the role alkali ions play in the kinetic behaviour and mechanisms of nucleation, growth and aggregation/agglomeration from caustic aluminate solutions of industrial strength has been investigated.

Atomic precision measurements provide a strong testing ground for new theoretical ideas and fundamental laws of physics. Measurement of the Lamb shift in the hydrogen atom is one of the best examples towards this -it resulted in the birth of QED in 1949 by Dyson, Feynman, Schwinger and Tomonaga. The precision measurements of the hyperfine structure in hydrogen and deuterium by Nafe, Nelson and Rabi indicated that the g-factor for the electron was not exactly 2 as predicted by Dirac, but slightly greater, due to QED effects. Thus the precision measurements are indispensable not only for developing new theory but also for the verification and fine-tuning of theoretical parameters. Precision measurement of hyperfine structure provide valuable information about the nucleus structure, which is helpful in fine tuning of atomic wave-functions used in theoretical calculations. The aim of the work reported in this thesis is the measurement of hyperfine frequency and the observation of hyperfine structure constant in alkali atoms and in Yb atom. This thesis is organized as follows. In Chapter 1, an introduction to the importance of Alkali atoms and Yb atom in the field of precision measurement will be discussed. The scope of this thesis is also discussed in this chapter. In Chapter 2, an introduction to hyperfine structure starting from the beginning of the atomic physics will be discussed. We have discussed about the LS-coupling, jj-coupling, and the influence of the atomic nucleus on atomic spectra. We have also discussed the Zeeman effect and Doppler broadening. In chapter 3, the detail of experimental technique used in this thesis as copropagating satabs, hyperfine frequency measurement using AOM scan, AOM lock and ring cavity has been discussed. Experimental technique to observe the EIT signal in two electron Yb system has been discussed, which can be improved the precision in frequency measurement because of the narrow line-width. In chapter 4, we describe the co-propagating saturated-absorption spectroscopy and its application in frequency measurement. Saturated-absorption spectroscopy (satabs) in a vapor cell is a standard technique used to stabilise the laser frequency. In normal satabs we are getting some extra peaks known as a crossover peaks because laser interact with different velocity group in a vapor cell. In satabs the crossover peaks are stronger and often swamp the true peaks. So we have developed a technique of co-propagating satabs to remove the spurious peak, which has several advantages over conventional satabs. The co-propagating satabs signal appears on a flat background (Doppler-free) with good signal-to-noise ratio and does not have the problem of crossover resonances in between hyperfine transitions. We have adapted this technique to make measurements of hyperfine intervals by using one laser along with an acousto-optic modulator (to produce the scanning pump beam). In chapter 5, we describe the measurement of the hyperfine interval in the 2P1/2 state of 7Li using the SAS technique in hot Li vapor. This technique produces spurious ground crossover resonances that are more prominent that the real peaks. So we have used this ground crossover to measure the hyperfine interval using AOM locking technique. We have developed a technique to measure the absolute frequencies of optical transitions by using an evacuated Rb-stabilized ring-cavity resonator as a transfer cavity. In chapter 6, we study the wavelength-dependent errors due to dispersion at the cavity mirrors by measuring the frequency of the same transition in the Cs D 2 line (at 852 nm) at three cavity lengths. The spread in the values shows that dispersion errors are below 30 kHz, corresponding to a relative precision of 10−10 . We give an explanation for reduced dispersion errors in the ring-cavity geometry by calculating errors due to the lateral shift and the phase shift at the mirrors, and show that they are roughly equal but occur with opposite signs. In chapter 7, we describe precision measurement of hyperfine structure in the 3P2 state of 171,173Yb, and see an unambiguous signature of the magnetic octupole coefficient C in 173Yb. The frequencies of the 3P23S1 transition at 770 nm → are measured using a Rb-stabilized ring-cavity resonator with an accuracy of 200 kHz. In 173Yb we obtain the hyperfine coefficients as A = − 742.11(2) MHz and B = 1339.2(2) MHz, which represent a two orders-of-magnitude improvement in precision, and C = 0.54(2) MHz. Using atomic-structure calculations for two-electron atoms, we extract the nuclear moments quadrupole Q =2.46(12)b and octupole Ω = 34.4(21)b × µN . The observation of nuclear octupole moment in two-electron atoms, to the best of our knowledge, was never reported before. In 171Yb we obtain the hyperfine coefficient A = 2678.49(8) MHz. Using this measurement as well as the previous measurement of A coefficient from our lab, we have compared the hyperfine anomalies for 1P1, 3P1 and 3P2 states. In chapter 8, we describe the EIT in two electron system of 174Yb from 1S0(Fg = 0) 3P1(Fe = 1). We have observed the EIT in degenerate two level system and → after lifting the degeneracy by applying the magnetic field we are getting five peaks. We have also observed the EIT in 173Yb. In 173Yb there are three degenerate two level system Fg =5/2 Fe =3/2, Fg =5/2 Fe =5/2, Fg =5/2 Fe =7/2. →→→ We have observed the same type of EIT signal for all the three transitions Fg = FFe = F, ±F + 1. → In Chapter 9, we give a broad conclusion to the work reported in this thesis and suggest future avenues of research to continue the work started here.

Abstract Carbon nanotubes are a promising material for various applications due to their unique collection of properties. However, carbon nanotube material as such is inert and insoluble, which hampers the true realization of its potential. In order to enhance the applicability of carbon nanotubes, their surface must be modified. This work concerned the chemical modification of single-walled carbon nanotubes (SWNT) by the Birch reduction, which is based on the reduction of the SWNT surface with the valence electron of alkali metal solvated in liquid ammonia. The reduction generates a SWNT anion, which reacts with electrophiles resulting in the covalent attachment of functional groups to the tube surface. In this work, aryl halides or alcohols were used as electrophiles to yield arylated or hydrogenated SWNTs, respectively. At first, the goal was to modify SWNTs as a filler material for polystyrene. The use of five halogenated ethenylphenyl derivatives as electrophiles revealed that the structure of electrophile affected the success of functionalization and the solubility of SWNTs in polystyrene-toluene solution. The most successful functionalization and solubilization of SWNTs were achieved with 1-chloro-4-ethenylbenzene. In the second part, liquid ammonia was replaced with a new solvent, 1-methoxy-2-(2-methoxyethoxy)ethane (diglyme) in order to avoid the restrictions, hazards and inconvenience of its handling. The work concentrated on the study of alkali metal reduction of SWNTs in diglyme by the use of arylation with 4-iodobenzoic acid or 4-chlorobenzoic acid and hydrogenation as model reactions. Li, Na or K was used as an alkali metal while naphthalene or 1-tert-butyl-4-(4-tert-butylphenyl)benzene was used in order to enhance the solvation of electrons. As a result, functionalization was simplified and enhanced. Electrophile affected the functionalization in such a way that arylation was significantly more successful than hydrogenation. The effect of alkali metal and electron carrier varied with electrophile. The most successful hydrogenation was achieved with the complex of Li and 1-tert-butyl-4-(4-tert-butylphenyl)benzene while arylation was the most successful with the complex of K and naphthalene. The solubility of SWNTs in water, ethanol, methanol and dimethylformamide was clearly improved by arylation whereas hydrogenation led to moderate improvement. / Tiivistelmä Hiilinanoputket ovat ainutlaatuisten ominaisuuksiensa vuoksi lupaava materiaali moniin sovelluksiin, mutta liukenemattomuus ja epäreaktiivisuus haittaavat niiden tehokasta hyödyntämistä. Käytettävyyttä voidaan parantaa kemiallisella modifioinnilla. Tässä työssä yksiseinäisiä hiilinanoputkia modifioitiin Birch-pelkistyksellä, joka perustuu putken pinnan pelkistykseen nestemäiseen ammoniakkiin solvatoituneella alkalimetallin valenssielektronilla. Pelkistyksessä hiilinanoputkesta muodostuu anioni, joka reagoi elektrofiilin kanssa johtaen funktionaalisten ryhmien kovalenttiseen sitoutumiseen putken pintaan. Tässä työssä hiilinanoputkia aryloitiin käyttämällä aryylihalideja elektrofiilinä tai vedytettiin käyttämällä alkoholia. Aluksi tavoitteena oli hiilinanoputkien modifiointi sellaiseen muotoon, että niitä voitaisiin käyttää polystyreenin täyteaineena. Viittä aryylihalidia käyttämällä havaittiin, että elektrofiilin rakenne vaikutti funktionalisoinnin määrään ja putkien liukoisuuteen polystyreeni-tolueeni-liuokseen. 1-Kloori-4-etenyylibentseenillä saavutettiin onnistunein arylointi ja paras liukoisuus. Työn toisessa osassa luovuttiin ammoniakin käytöstä siihen liittyvien rajoitteiden ja haittojen vuoksi. Keskityttiin hiilinanoputkien alkalimetallipelkistyksen tutkimiseen uudessa liuottimessa, 1-metoksi-2-(2-metoksietoksi)etaanissa (diglyymi). Mallireaktioina käytettiin arylointia 4-jodibentsoehapolla tai 4-klooribentsoehapolla ja vedytystä alkoholilla. Ammoniakin korvaaminen diglyymillä yksinkertaisti ja tehosti funktionalisointia. Reaktiot suoritettiin eri alkalimetalleilla (Li, Na tai K). Naftaleenia tai 1-tert-butyyli-4-(4-tert-butyylifenyyli)bentseeniä käytettiin elektronien solvatoinnin parantamiseksi. Elektrofiilin rakenne vaikutti funktionalisointiin siten, että aryylihalidi johti huomattavasti onnistuneempaan funktionalisointiin kuin alkoholi. Alkalimetallin ja elektroninkantajamolekyylin vaikutus vaihteli elektrofiilin mukaan. Litiumin käyttö 1-tert-butyyli-4-(4-tert-butyylifenyyli)bentseenin kanssa johti onnistuneimpaan vedytykseen. Kaliumin käyttö naftaleenin kanssa johti onnistuneimpaan arylointiin. Hiilinanoputkien liukoisuus vaihteli elektrofiilin mukaan. Arylointi paransi selkeästi hiilinanoputkien liukoisuutta veteen, etanoliin, metanoliin ja dimetyyliformamidiin. Vedytyksen vaikutus liukoisuuteen oli vähäisempi.

Abstract In this work, evolution of structural properties of anhydrous and hydrated alkali halide clusters are studied using synchrotron radiation based photoelectron spectroscopy. Alkali metal core level spectra of small anhydrous RbCl, RbBr, CsCl and CsBr clusters indicate a NaCl structure. For larger CsBr clusters a structural phase transition to CsCl structure is likely the case. Alkali halide core level spectra of mixed RbBr-water clusters indicate that at dilute concentration the salt is dissolved by the water cluster but ion pairing increases with concentration. Modeling of gas phase cluster formation and electronic structure calculations of core level chemical shifts are used to interpret the experimental spectra.

Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated.

No description available.

A new design AMTEC converter model was developed, and its effectiveness as a design tool was evaluated. To develop the model, requirements of the model were defined, several new design models were successively developed, and finally an optimal new design model was developed. The model was created within Sinda/Fluint, with its graphical interface, Thermal Desktop, a software package that can be used to conduct complex thermal and fluid analyses. Performance predictions were then correlated and compared with actual performance data from the Road Runner II AMTEC converter. Predicted performance results were within 10% of actual performance data for all operating conditions analyzed. This accuracy tended to increase within operating ranges that would be more likely encountered in AMTEC applications. Performance predictions and parametric design studies were then performed on a proposed new design converter model with a variety of annular condenser heights and with potassium as a working fluid to evaluate the effects of various design modifications. Results clearly indicated the effects of the converter design modifications on the converter's power and efficiency, thus simplifying the design optimization process. With the close correlation to actual data and the design information obtained from parametric studies, it was determined that the model could serve as an effective tool for the design of AMTEC converters.