The focus of the present research is to find the relative thermodynamic stability of ?-boron and ?-boron via heat capacity measurements. Efforts to synthesize ?-boron through the application of vapour-liquid-solid theory resulted in the discovery of a new chemical vapour deposition approach. The heat capacities of both synthesized ?-boron and commercial (99.5%) ?-boron were determined using relaxation calorimetry over the temperature range 0.2 K to 400 K. These data, in combination with literature information, allowed the calculation of the Gibbs energy of the ?-boron to ?-boron transition from 0 K to 1985 K. It was found that the transition from ?-boron to ?-boron was thermodynamically favourable at all temperatures up to 1985 K with a value of ?Gt(T = 300 K) = -10 kJ mol-1 ± 1 kJ mol-1 and ?Gt(T = 1985 K) = -15 kJ mol-1 ± 1 kJ mol-1.

Schwerpunkte der Arbeit waren die Synthese und in-situ Charakterisierung metastabiler Modifikationen der Elemente Silicium und Germanium, sowie die Darstellung binärer Silicide und Germanide der Erdalkali- und Seltenerdmetalle unter Druck (bis 20 GPa) und bei hoher Temperatur (bis 2200 K). Dabei konnten die Phasenbeziehungen von Allotropen des Germaniums näher beleuchtet werden und es gelang, eine neue Germaniummodifikation, Ge(hR8), in-situ strukturell zu charakterisieren. Die neu dargestellten metastabilen binären Silicide und Germanide unterteilen sich strukturell in solche, die clathratartige Tetrel-Netzwerke mit einer Koordinationszahl von drei und vier enthalten und in jene, bei denen die Anzahl benachbarter Tetrelatome vier übersteigt. So konnten beispielsweise Netzwerke dargestellt werden, die acht homonukleare Silicium oder Germanium Kontakte im Netzwerk aufweisen. Neben der strukturellen Charakterisierung standen die Bestimmungen der elektrischen Leitfähigkeit und des Magnetismus, sowie die Ermittlung der thermischen Eigenschaften im Focus der Arbeit. / Key aspects of the present work were the synthesis and in-situ characterization of metastable modifications of elemental silicon and germanium as well as the preparation of binary silicides and germanides of the alkaline earth and rare earth metals under pressure (up to 20 GPa) and at elevated temperatures (up to 2200 K). In that process the phase relations of germanium allotropes could be examined more closely and led to the preparation of a new germanium modification, Ge(hR8), which could be structurally characterized by in-situ experiments. The prepared silicides and germanides can be structurally separated in those containing clathrate-like networks with a coordination number of three and four and those which contain more neighbors in the network than four e.g., eight homonuclear silicon or germanium contacts in the network of CeSi5 and CeGe5. Beside the structural characterization the determination of the electrical resistivity and the magnetical properties as well as the analysis of the thermal behavior were in focus of the work.

abstract: New forms of carbon are being discovered at a rapid rate and prove to be on the frontier of cutting edge technology. Carbon possesses three energetically competitive forms of orbital hybridization, leading to exceptional blends of properties unseen in other materials. Fascinating properties found among carbon allotropes, such as, fullerenes, carbon nanotubes, and graphene have led to new and exciting advancement, with recent applications in defense, energy storage, construction, and electronics. Various combinations of extreme strength, high electrical and thermal conductivity, flexibility, and light weight have led to new durable and flexible display screens, optoelectronics, quantum computing, and strength enhancer coating. The quest for new carbon allotropes and future application persists. Despite the advances in carbon-based technology, researchers have been limited to sp3 and sp2 hybridizations. While sp3 and sp2 hybridizations of carbon are well established and understood, the simplest sp1 hybridized carbon allotrope, carbyne, has been impossible to synthesize and remains elusive. This dissertation presents recent results in characterizing a new sp1 carbon material produced from using pulsed laser ablation in liquid (PLAL) to ablate a gold surface that is immersed in a carbon rich liquid. The PLAL technique provides access to extremely non-thermal environmental conditions where unexplored chemical reactions occur and can be explored to access the production of new materials. A combination of experimental and theoretical results suggests gold clusters can act as stabilizing agents as they react and adsorb onto the surface of one dimensional carbon chains to form a new class of materials termed “pseudocarbynes”. Data from several characterization techniques, including Raman spectroscopy, UV/VIS spectroscopy, and transmission electron microscopy (TEM), provide evidence for the existence of pseudocarbyne. This completely new material may possess outstanding properties, a trend seen among carbon allotropes, that can further scientific advancements. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2018

Schwerpunkte der Arbeit waren die Synthese und in-situ Charakterisierung metastabiler Modifikationen der Elemente Silicium und Germanium, sowie die Darstellung binärer Silicide und Germanide der Erdalkali- und Seltenerdmetalle unter Druck (bis 20 GPa) und bei hoher Temperatur (bis 2200 K). Dabei konnten die Phasenbeziehungen von Allotropen des Germaniums näher beleuchtet werden und es gelang, eine neue Germaniummodifikation, Ge(hR8), in-situ strukturell zu charakterisieren. Die neu dargestellten metastabilen binären Silicide und Germanide unterteilen sich strukturell in solche, die clathratartige Tetrel-Netzwerke mit einer Koordinationszahl von drei und vier enthalten und in jene, bei denen die Anzahl benachbarter Tetrelatome vier übersteigt. So konnten beispielsweise Netzwerke dargestellt werden, die acht homonukleare Silicium oder Germanium Kontakte im Netzwerk aufweisen. Neben der strukturellen Charakterisierung standen die Bestimmungen der elektrischen Leitfähigkeit und des Magnetismus, sowie die Ermittlung der thermischen Eigenschaften im Focus der Arbeit. / Key aspects of the present work were the synthesis and in-situ characterization of metastable modifications of elemental silicon and germanium as well as the preparation of binary silicides and germanides of the alkaline earth and rare earth metals under pressure (up to 20 GPa) and at elevated temperatures (up to 2200 K). In that process the phase relations of germanium allotropes could be examined more closely and led to the preparation of a new germanium modification, Ge(hR8), which could be structurally characterized by in-situ experiments. The prepared silicides and germanides can be structurally separated in those containing clathrate-like networks with a coordination number of three and four and those which contain more neighbors in the network than four e.g., eight homonuclear silicon or germanium contacts in the network of CeSi5 and CeGe5. Beside the structural characterization the determination of the electrical resistivity and the magnetical properties as well as the analysis of the thermal behavior were in focus of the work.

No description available.

Die Vorhersage und Identifizierung von stabilen und metastabilen Stoffen ist ein wichtiges Instrument zur Bildung neuer Werkstoffe. Vor diesem Hintergrund gewinnen Konzepte einer rationalen Synthese zunehmend an Bedeutung: Die Berechnung der elektrochemischen Spannungsreihe für Festkörper und flüchtiger Phasen ermöglicht eine einfache Vorhersage der Reaktionswege. Unter Verwendung der elektrochemischen Spannungsreihe der Systeme As / P / O und As / P / X (X = F, Cl, Br, I) kann die Bildung von Elementallotropen über die Oxid- und Halogenidverbindungen in thermitischen Reaktionen abgeleitet werden. Die Analyse der Phasenbildung wird mit einer In-situ-Methode zur Überwachung von Gasphasenreaktionen gewonnen. Im Verlauf der Phasenformationen - zur Erreichung des Fest-Gas-Gleichgewichtes - können charakteristische Effekte beobachtet werden. / The prediction and identification of stable and metastable substances is an important tool to achieve new materials. With this objective in mind, concepts of a rational synthesis are gaining increasing importance: calculation of electromotive series of solids allows easy prediction of reaction pathways. Using the electromotive series of systems As/P/O and As/P/X (X = F, Cl, Br, I) the formation of element allotropes via the oxide and halide compounds in thermite type reactions can be deduced. The analysis of phase formation is acquired with an in situ method for monitoring gas-phase reactions. In the course of phase formations - attaining the solid-gas equilibrium state - characteristic effects can be observed.

Die Vorhersage und Identifizierung von stabilen und metastabilen Stoffen ist ein wichtiges Instrument zur Bildung neuer Werkstoffe. Vor diesem Hintergrund gewinnen Konzepte einer rationalen Synthese zunehmend an Bedeutung: Die Berechnung der elektrochemischen Spannungsreihe für Festkörper und flüchtiger Phasen ermöglicht eine einfache Vorhersage der Reaktionswege. Unter Verwendung der elektrochemischen Spannungsreihe der Systeme As / P / O und As / P / X (X = F, Cl, Br, I) kann die Bildung von Elementallotropen über die Oxid- und Halogenidverbindungen in thermitischen Reaktionen abgeleitet werden. Die Analyse der Phasenbildung wird mit einer In-situ-Methode zur Überwachung von Gasphasenreaktionen gewonnen. Im Verlauf der Phasenformationen - zur Erreichung des Fest-Gas-Gleichgewichtes - können charakteristische Effekte beobachtet werden. / The prediction and identification of stable and metastable substances is an important tool to achieve new materials. With this objective in mind, concepts of a rational synthesis are gaining increasing importance: calculation of electromotive series of solids allows easy prediction of reaction pathways. Using the electromotive series of systems As/P/O and As/P/X (X = F, Cl, Br, I) the formation of element allotropes via the oxide and halide compounds in thermite type reactions can be deduced. The analysis of phase formation is acquired with an in situ method for monitoring gas-phase reactions. In the course of phase formations - attaining the solid-gas equilibrium state - characteristic effects can be observed.

Measurement of all the mechanical properties of carbon nanotubes is extremely difficult because of its small size. In the present work, all the five transverse isotropic properties of single wall carbon nanotubes (SWCNTs) and double wall carbon nanotubes are estimated through molecular structural mechanics for different chirality, length and assumed thickness. Armchair, zigzag & chiral SWCNTs and polychiral DWCNTs are considered for the analysis. Longitudinal and lateral Young’s modulus; longitudinal and lateral Poisson’s ratio and shear modulus are estimated for 1080 SWCNTs and 1170 polychiral DWCNTs. Effect of temperature on all the properties of SWCNT are investigated. Modal characterization of SWCNT is carried out in base fixed condition and different mode shapes viz. axial, torsion and bending mode shapes are identified based on the effective mass. Once the transverse isotropic properties of SWCNTs are estimated, these are used to estimate the transverse isotropic properties of nanocomposites embedded with SWCNT agglomerates. During the manufacturing of nanocomposite, SWCNT agglomerates are formed due to sticking of number of SWCNTs. Parametric studies are carried out to see the effect of SWCNT length on the properties of nanocomposite. Empirical formulae for all the transverse isotropic properties of SWCNT at room temperature and elevated temperature; frequency of SWCNT are derived. Empirical formulae for polychiral DWCNT transverse isotropic properties are estimated. Input for these empirical formulae are the length, chirality and assumed thickness. Empirical formulae were also derived for nanocomposite embedded with different number of SWCNTs having different chirality. The derived empirical formulae were validated with available analytical and experimental results for some sample cases.

The major directions of this dissertation involve (1) the syntheses and characterization of molecular polygons incorporating sp1hybridized carbon linkers and L2Pt corners (L2 = cis-1,3-diphosphine), (2) the development of protected carbon chain complexes featuring fluorous phosphine ligands and (3) click reactions of metal terminal polyynyl complexes and further metallations of the resulting triazole rings. A brief overview is provided in Chapter I. Chapter II details the syntheses of molecular squares containing bidendate diphosphine ligands of the formula R2C(CH2PPh2)2 where R = Me, Et, n-Bu, n-Dec, Bn, and p-tolCH2 (general designation dppp*), in which the R2 groups are intended to circumvent the solubility issues encountered by others. Their syntheses involve double substitutions of the dimesylate compounds R2C(CH2OMs)2 using KPPh2. Building blocks of the formulae (dppp*)PtCl2 and (dppp*)Pt((C≡C)2H)2 are synthesized and characterized, including one crystal structure of the latter. The target complexes are accessed by reactions of (dppp*)PtCl2 with (dppp*)Pt((C≡C)2H)2 under Sonogashira type conditions. Six new squares of the formula [(R2C(CH2PPh2)2)Pt(C≡C)2]4 are characterized including two crystal structures. Further topics include approaches to higher homologues and cyclocarbon synthesis. Chapter III focuses on carbon chain complexes bearing fluorous phosphine ligands of the formula P((CH2)mRfn)3 (Rfn = (CF2)n-1CF3; m/n = 2/8, 3/8, and 3/10). Precursors of the formula trans-(C6F5)((Rfn(CH2)m)3P)2PtCl are synthesized and characterized, including one crystal structure, which reveals phase separation of the fluorous and non-fluorous domains. Reactions with butadiyne give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)2H. Oxidative homocouplings afford the target complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)4(C6F5)(P((CH2)mRfn)3)2Pt. Cyclic voltammetry indicates irreversible oxidations of the title compounds, in contrast to partially reversible oxidations of non-fluorous analogues. Chapter IV focuses on multimetallic complexes achieved by click reactions in metal coordination spheres. The copper catalyzed click reaction between trans-(C6F5)(p-tol3P)2Pt(C≡C)2H (1) and (η5-C5H4N3)Re(CO)3 affords the bimetallic 1,2,3-triazole trans-C6F5)(p1tol3P)2PtC≡CC=CHN((η51C5H4)Re(CO)3)N=N. Further reactions with Re(CO)5OTf and Re(CO)5Br give trimetallated adducts, which represent the first species of this type. An alternative route to a trimetallic complex involves the twofold cycloaddition of the diazide (η5-C5H4N3)2Fe and 1, giving (η5-C5H4NN=N-C(trans-(C≡C)Pt(Pp-tol3)2(C6F5)=CH)2Fe. The crystal structures of the di and trimetallic complexes are compared, but attempts to achieve a fourth metallation involving the =CH groups are unsuccessful. However, when the triazolium salt [trans-(C6F5)(p-tol3P)2PtC≡CC=CHN(CH2C6H5)N=N(Me)]+ I– is treated with Ag2O and [Rh(COD)Cl]2, a =CRh adduct is obtained. The success of =CH metallation is correlated to the 1H NMR chemical shift, indicative of an electronic effect.