Proefschrift--Utrecht. / Bibliography: p. [105]-108.

Proefschrift--Utrecht. / Bibliography: p. [105]-108.

No description available.

Cyclododecane (CDD) is a waxy, solid cyclic hydrocarbon (C12H24) that sublimes at room temperature and possesses strong hydrophobicity. In paper conservation CDD is used principally as a temporary fixative of water-soluble media during aqueous treatments. Hydrophobicity, ease of reversibility, low toxicity, and absence of residues are reasons often cited for its use over alternative materials although the latter two claims continue to be debated in the literature. The sublimation rate has important implications for treatment planning as well as health and safety considerations given the dearth of reliable information on its toxicity and exposure limits. This study examined how the rate of sublimation is affected by fiber type, sizing, and surface finish as well as delivery in the molten phase and as a saturated solution in low boiling petroleum ether. The effect of warming the paper prior to application was also evaluated. Sublimation was monitored using gravimetric analysis after which samples were tested for residues with gas chromatography-flame ionization detection (GC-FID) to confirm complete sublimation. Water absorbency tests were conducted to determine whether this property is fully reestablished. Results suggested that the sublimation rate of CDD is affected minimally by all of the paper characteristics and application methods examined in this study. The main factors influencing the rate appear to be the thickness and mass of the CDD over a given surface area as well as temperature and ventilation. The GC-FID results showed that most of the CDD sublimed within several days of its disappearance from the paper surface regardless of the application method. Minimal changes occurred in the water absorbency of the samples following complete sublimation. / Thesis (Master, Art Conservation) -- Queen's University, 2013-09-27 09:00:28.77

Sublimation epitaxy of SiC on low off-axis substrates was performed. The growth was performed at different temperatures, mainly under vacuum conditions or with an initial atmosphere of N2 at 0.5 mbar (RT). Some additional experiments under different conditions (Ar background, higher temperature, higher off-axis substrate) were performed in order to further investigate growth influencing factors. The samples were characterized by optical microscopy and atomic force microscopy. A dependence of 3C/6H growth on substrate off-axis, as well as on temperature, was clear to be seen. Favored growth of 6H in the presence of N2 was found.  An enlargement effect on the 3C domains grown in N2 ambient was observed. Additionally a correlation between step bunching and growth rate was found in step flow growth on low off-axis substrates. Suggestions for relevant growth mechanisms are made. Further work is discussed.

Thesis--University of California, Berkeley, 1963. / "UC-4 Chemsitry" -t.p. "TID-4500 (19th Ed.)" -t.p. Includes bibliographical references (p. 42-43).

Thesis (Ph.D.)--University of California, Berkeley, 1963. / "UC-4 Chemistry" -t.p. "TID-4500 (19th Ed.)" -t.p. Includes bibliographical references (p. 40).

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Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / Recently, the rare earth nitrides have received a considerable attention from theorists and experimentalists due to their potential applications in spintronic, piezoelectric, and thermoelectric devices. In this work, erbium nitride (ErN) and scandium nitride (ScN) crystals were grown and characterized experimentally, and the growth process was modeled and simulated. Erbium nitride (ErN) is a rare earth nitride notable for its magnetic and optical properties. Here we report on its growth on a non-native substrate, tungsten foil, via physical vapor transport, and its characterization. The source material was erbrium metal that was converted to ErN by heating in nitrogen. Subsequently, it was sublimed to form the ErN crystals. The operating conditions were 1620-1770 ⁰C and 150-330 Torr in pure nitrogen. The growth rate increased exponentially with temperature with an activation energy of 508 kJ/mol, and inversely with pressure. X-ray diffraction revealed the ErN preferentially adopted a (100) orientation, the same as the dominant orientation of the tungsten sheet. The lattice constant was 4.853 Å. The crystal shapes and sizes were dependent on the temperature, as revealed by SEM and optical microscopy. The ErN crystals were highly faceted, bound by (100) and (111) crystal planes. The ErN compound deviated from stoichiometry: the Er:N atomic ratio ranged from 1:1.15 to 1:1.2 according to EDX and XPS elemental analysis. Raman spectra was in good agreement with theoretical predictions. Scandium nitride single crystals (14–90 µm thick) were grown on tungsten (100) single crystal substrate by physical vapor transport in the temperature range of 1850-2000 ⁰C and pressure of 15-35 Torr. Epitaxial growth was confirmed using in-plane ɸ scan and out-of-plane x-ray diffraction techniques which revealed that ScN exhibited cube-on-cube growth with a plane relationship ScN (001) || W (001) and normal direction ScN [100] || W [110]. Atomic force microscopy revealed the surface roughness decreased from 83 nm to 18 nm as the growth temperature was increased. X-ray diffraction (XRD) rocking curves widths decreased indicating the crystal quality improved with increasing growth temperature. The lowest XRC FWHM was 821 arcsec, which is so far the lowest value reported for ScN. Scanning electron microscopy (SEM) exhibited the formation of macrosteps and cracks on the crystal surface with latter due to the mismatch of ScN’s and tungsten’s coefficients of thermal expansion . In general for crystal growth, material should deposit on the seed crystal and not on any adjacent supporting structures. This efficiently uses the source material and avoids the possibility of spurious polycrystals encroaching on, and interfering with the single crystal growth. To achieve this goal, a new crucible design with a cooling fin in contact with the seed was simulated and experimentally demonstrated on the physical vapor transport (PVT) crystal growth of scandium nitride. The heat transfer of the growth cavity for a conventional crucible and a modified crucible with the cooling fin were modeled theoretically via computational fluid dynamics (CFD) with FLUENT. The CFD results showed that the seed in the modified crucible was approximately 10 °C cooler than the crucible lid, while in the conventional crucible the temperature of the seed and lid were uniform. The experimental results showed that increasing the temperature gradient between the source and the seed by employing the cooling fin led to a dramatic increase in the growth rate of ScN on the seed and reduced growth on the lid. The relative growth rates were 80 % and 20 % on the seed and lid respectively, in the modified crucible, compared to 25% and 75% with the conventional crucible. Thus, the modified crucible improved the process by increasing the species transporting to the seed by sublimation.

Freeze-drying is the process of removal of water or organic solvent from a desired product by means of sublimation at a low temperature and low pressure. It is commonly employed for drying samples which are heat labile and require sensitive treatment, and is mainly used in the pharmaceutical and food industries. It is an expensive process, requiring vacuum, refrigeration and long cycle times, but does yield quality benefits due to the low temperatures involved and the porous nature of the product. Reducing drying times is important to manufacturers, and this depends on optimising rates of heat and mass transfer in the system without the sample losing its porous structure. However, freeze drying is difficult to study experimentally due to the low temperatures and pressures involved. The quality of the final product mainly depends on the sublimation rate and an optimum lyophilisation requires identification of the parameters which influence the process. The main aim of this study is to employ freeze drying microscopy (FDM) as a useful tool to identify these process parameters and help optimise primary drying phase of the freeze drying process for two systems: lactose (relevant to pharmaceuticals) and coffee (the most widely freeze-dried food product). This equipment allows the movement of sublimation fronts to be directly visualised in-situ under carefully controlled (and isothermal conditions), but has scarcely been used in the literature for this purpose. An image analysis method is developed to automatically track the movement of sublimation fronts, and the frontal data fitted to a simple mass transfer model employing surface and bulk resistances. Initial experiments with lactose solution show poor reproducibility in nucleation temperatures during the freezing step and thus primary drying rates. To improve reproducibility, a small amount of silver iodide (AgI) was added to samples which acts as a nucleating agent and increases the nucleation temperature. This addition of AgI also increases the mean ice crystal size in the samples and are easily visible under the freeze-drying microscope, and in many cases show a distinct orientation with respect to direction of sublimation front. Furthermore, the orientation greatly influences sublimation rates, being approximately factor of two faster when crystals are oriented in the direction of mass transfer. FDM experiments with coffee were less straightforward as nucleation temperatures could not be reliably controlled, even with AgI added. Nevertheless there was a clear decrease of bulk resistance with increasing nucleation temperature. An experimental programme was then undertaken to examine the impact of initial solid content, cooling rate, the addition of an annealing step, freeze drying temperature and aeration (for coffee samples). Frontal data were fitted to a simple mass transfer model comprising surface and bulk (per unit depth) resistances and good fits to data were obtained. FDM experiments with lactose and coffee clearly showed the presence of a surface resistance which could also be seen as a surface layer which was devoid of ice crystals (and hence not porous when sublimed). The edge resistance first increased and then decreased with solids content. The resistance per unit depth increased exponentially with solids content, so much so that there is an optimal solids content (around 10% solids) in relation of the rate of production of dried material. Cooling rates were mainly found to affect the surface resistance rather than bulk resistance and this may be due to different levels of surface drying when the samples are being cooled for different lengths of time. Annealing substantially changed the ice crystal sizes, and had a beneficial effect on freeze drying rates and had a similar effect to adding AgI. Freeze drying rates also increased with increasing temperature approximately in line with the saturated vapour pressure (SVP) of ice which is widely held to constitute the driving force for mass transfer. It was possible to make drying time calculations for conventional vial (lactose) and tray (coffee) drying using the frontal rate data obtained from FDM. For 10% lactose and 10% coffee (annealed) there was good agreement between the vial and tray data and predictions based on a microstructure oriented parallel to the direction of mass transfer. This was the only case where agreement was found, but also the only case where directionality was observed in FDM. The much faster drying times observed in the vial and tray experiments are thus attributed to directional solidification occurring in these systems, and this was borne out by SEM imaging. Aeration of the coffee samples was also found to substantially reduce drying times. The influence of microstructure on freeze drying rates is thus very clear.