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Investigation of interfacial microstructure of CrN coatings on HSS substrates pretreated by HIPIMS for adhesion enhancementJädernäs, Daniel January 2006 (has links)
<p>In this study, six dc Magnetron Sputtered (dcMS) CrN hard coatings were deposited on pretreated High Speed Steel (HSS) to achieve different interface architectures. The aim was to correlate the interfacial microstructure to the adhesion of the coatings. The substrates were pretreatment using the Ionized Physical Vapor Deposition (IPVD) method High Power Impulse Magnetron Sputtering (HIPIMS) using a Cr target in an inert atmosphere varying the substrate bias ($U_b$) between 0 V and 1100 V at ambient temperature as well as at a substrate temperature of 400$^\circ$C. The deposition parameters were chosen to show how kinetically induced diffusion, etching and implantation changes the interface chemistry and structure and to investigate their effect on the adhesion on the film. At elevated temperatures, the diffusion will be thermally driven. Annealing of the deposited samples were, therefore, performed at 900 K in an Ar atmosphere. The films were characterized employing XRD, HR-TEM, A-STEM and by scratch test measurements to see how the the interface microstructure can be correlated to the adhesion of the coating. The study shows that a sputter cleaned substrate surface with well preserved crystal structure of the substrate enhances the adhesion of the coating by promotion of local epitaxial growth. However, annealing was also shown to have a large effect on the adhesion enhancement by allowing for interdiffusion in the interface region and due to promotion of interface strain relaxation. Implantation of target material on the other hand had limited influence on the adhesion compared to the clean oxide free surfaces. The low adhesion improvement when gradually changing the chemical composition at the interface is assumed to stem from that the radiation induced defects and strain diminished the positive effect of this gradient.</p>
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Tablet shapes and in vitro evaluation of coated hydrophilic matrix tablets novel mupirocin formulations non-acidic enteric coating of omeprazole and novel hot-melt coating processLeung, Manshiu 14 May 2002 (has links)
This dissertation is comprised of four distinct formulation sections, which
are described below:
A novel solid dosage formulation was investigated for achieving zero-order
drug release profile by combining tablet shape design and tablet membrane film
coating. Verapmail (model drug) was compressed into hydrophilic matrix tablet
cores of flat-faced and bi-convex shape, which were encapsulated with membrane
controlling film. The hydrophilic tablet core contained hydroxypropyl
methylcellulose (HPMC) 15 LV, pectin, and Avecil��. The membrane film coating
solution was comprised of deionized water, Opadry��, Surelease�� and talc. The
combination of membrane film coating and tablet shape design was found to
influence in vitro verapamil release profile towards the zero-order release
demonstrated by the commercial Covera HS�� (Pharmacia).
An alternative formulation for the commercial Bactroban�� (Smithkline
Beacham) ointment 2% was developed. Both the texture and consistency of the
new ointment were comparable to the Bactroban�� ointment. The new and the
commercial formulations were found to be equivalent in drug release by the Bauer-Kirby test. Mupirocin remained unstable in the new formulation. Mg����� was added
to help stabilize mupirocin and was shown to complex with mupirocin by nuclear
magnetic resonance (NMR). The modified formulation including Mg����� however
failed to stabilize mupirocin. The stability assay results showed an average of
67.2% mupirocin recovery along with 25.2% degradation products.
A generic omeprazole formulation was developed, which was comprised of
nonpareil core, omeprazole matrix layer, and an enteric locating layer of
ammoniated hydroxypropyl methylcellulose phthalate (HPMCP) 55S. The new
formulation was gastro-resistant in protecting against omeprazole degradation for
up to 2 h, but failed to dissolve as rapidly as the commercial Prilosec�� (Astra
Merk) in simulated intestinal fluid. The addition of expotab�� to the enteric coating
layer failed to improve omeprazole dissolution rate.
A novel hot-melt coating methodology utilizing direct blending technique
has been developed. The processing steps for the direct blending hot-melt coating
are: (a) Hot-melt system preparation; (b) Dispersion/dissolution of the active
ingredient(s) in the hot-melt system; (c) Pre-heating of the coating substrate; and
(d) Cooling and congealing of the hot-melt on substrate surface. Immunogenic
effect was observed in mice administered with enteric-coated ragweed pollen
extract (RPE) alpha fraction by the hot-melt coating encapsulation with direct
blending method. The effect was not shown to be statistically significant. / Graduation date: 2003
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Self-Assembled Coatings for Controlling Biomolecular Adsorption on SurfacesSeong, Jiehyun, Lee, Seok-Won, Jun, Shinae, Choi, Hyun-Goo, Laibinis, Paul E. 01 1900 (has links)
We have investigated a series of molecular and polymeric approaches for generating adherent thin films that impart anti-fouling characteristics to oxide surfaces. These films incorporate oligo- or poly(ethylene glycol) moieties that are expressed in high density in the near-surface region. In our molecular approach, oligo(ethylene glycol)-terminated n-alkyl-trichlorosilanes, RO(CH₂CH₂O)₃(CH₂)₁₁SiCl₃, have been designed so to spontaneously adsorb onto oxide surfaces and produce densely packed films. Another strategy uses a surface initiated polymerization to generate reactive anchored polymer chains that are then chemically modified to incorporate oligo(ethylene glycol) units. Lastly, a comb copolymer comprising a poly(acrylic acid) backbone and different grafting ratios of a linear poly(ethylene oxide-r-propylene oxide) chain has been prepared that adsorbs onto surfaces and forms a poly(ethylene glycol)-exposing film in single step. These surface coatings provide varying levels of protein and cellular resistance that can be related to molecular-scale elements of their surface structure. / Singapore-MIT Alliance (SMA)
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Microstructural, Mechanical and Tribological Characterisation of CVD and PVD Coatings for Metal Cutting ApplicationsFallqvist, Mikael January 2012 (has links)
The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment. In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions. The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties. Through the deposition of well designed bonding and template layer structures the above problems may be eliminated. Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts. Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting. In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.
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Investigation of interfacial microstructure of CrN coatings on HSS substrates pretreated by HIPIMS for adhesion enhancementJädernäs, Daniel January 2006 (has links)
In this study, six dc Magnetron Sputtered (dcMS) CrN hard coatings were deposited on pretreated High Speed Steel (HSS) to achieve different interface architectures. The aim was to correlate the interfacial microstructure to the adhesion of the coatings. The substrates were pretreatment using the Ionized Physical Vapor Deposition (IPVD) method High Power Impulse Magnetron Sputtering (HIPIMS) using a Cr target in an inert atmosphere varying the substrate bias ($U_b$) between 0 V and 1100 V at ambient temperature as well as at a substrate temperature of 400$^\circ$C. The deposition parameters were chosen to show how kinetically induced diffusion, etching and implantation changes the interface chemistry and structure and to investigate their effect on the adhesion on the film. At elevated temperatures, the diffusion will be thermally driven. Annealing of the deposited samples were, therefore, performed at 900 K in an Ar atmosphere. The films were characterized employing XRD, HR-TEM, A-STEM and by scratch test measurements to see how the the interface microstructure can be correlated to the adhesion of the coating. The study shows that a sputter cleaned substrate surface with well preserved crystal structure of the substrate enhances the adhesion of the coating by promotion of local epitaxial growth. However, annealing was also shown to have a large effect on the adhesion enhancement by allowing for interdiffusion in the interface region and due to promotion of interface strain relaxation. Implantation of target material on the other hand had limited influence on the adhesion compared to the clean oxide free surfaces. The low adhesion improvement when gradually changing the chemical composition at the interface is assumed to stem from that the radiation induced defects and strain diminished the positive effect of this gradient.
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Design of low-friction PVD coating systems with enhanced running-in performance - carbon overcoats on TaC/aC coatingsNyberg, Harald, Tokoroyama, Takayuki, Wiklund, Urban, Jacobson, Staffan January 2013 (has links)
The widespread use of low friction PVD coatings on machine elements is limited by the high costs associated with fulfilling the demands on the surface quality of both the supporting substrate and the counter surface. In this work, an attempt is made at lowering these demands, by adding a sacrificial carbon overcoat to a TaC/aC low friction coating. Both coatings were deposited by planar magnetron DC sputtering, as separate steps in a single PVD-process. Coatings were deposited on substrates of two different surface roughnesses, in order to test the ability of this coating system to function on rougher substrates. Reciprocating ball on disc tests was performed, using balls with two different surface roughnesses. The worn surfaces were investigated using 3-D profilometry and SEM. The ability of the different overcoats to initially reduce the roughness of both the coated surface and the counter surface and to produce stable, low-friction conditions was examined for the different initial roughnesses. The implications for design of efficient run-in coatings for various systems are discussed.
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A study of the mechanism of film formation in the spray-coating of paper with nitrocellulose lacquers.Shick, Philip Edwin 01 January 1943 (has links)
No description available.
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Adhesion and the Surface Energy Components of Natural Minerals and AggregatesMiller, Clint Matthew 2010 August 1900 (has links)
A range of geochemical reactions are controlled by the interfacial characteristics
of rocks and minerals. Many engineered and natural systems are affected by
geochemical reactions that occur at interfaces. Asphalt-aggregate adhesion in road
construction is influenced by the interfacial characteristics of the aggregate. Likewise,
the remediation of nonaqueous-phase liquid contaminants, such as trichloroethylene or
methyl tert-butyl ether, is controlled by the interactions between mineral surfaces and
the organic liquid. Many natural systems are also influenced by reactions at interfaces.
The migration of petroleum in sedimentary basins is influenced by the wettability of the
surfaces of the basin pore space. Adhesion of organisms, such as bacteria or lichens, to
rock surfaces is controlled by the interactions of proteins and mineral surfaces.
Rock and mineral surfaces are described by surface energy. Surface energy is a
thermodynamic construct defined as the amount of work required to form more of a
surface. Surface energy can be divided into van der Waals, Lewis acid, and Lewis base
components. The ability to predict the magnitude of surface energy components is
valuable in understanding species behavior. Surface energy is controlled by three master
variables: surface chemistry, surface morphology, and surface coatings. While the
surface energy of a number of minerals and aggregates has been characterized, there has
not yet been a comprehensive study of the surface energies of a variety of the most
common minerals and aggregates using consistent methodology. In addition there has not yet been a study of the effect of these three master variables on surface energies of
natural minerals and rocks.
This study measured the surface energy of 22 common minerals and 7
aggregates. The samples’ bulk and surface chemistries were characterized with
wavelength and energy dispersive spectra analyses on an electron microprobe and x-ray
photoelectron spectroscopy. The XPS was also used to quantify the organic and
inorganic coatings on the surfaces. Results showed that van der Waals surface energy is
typically between 40 and 60 ergs/cm2. Polar surface energy varies by 1 to 3 orders of
magnitude, and thus is likely the most important component in accounting for changes
between natural minerals.
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Tungsten Inert Gas Arc Welding Fe-Mo-Ti-C Alloying Coatings Composites for High Temperature ApplicationsWen, Ching-San 09 July 2002 (has links)
none
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Coating studies and video imaging of the flow patterns of tablets in a semi-circular fluidized bedSubramanian, Ganeshkumar A. January 2001 (has links)
Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 159 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 118-122).
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