This work reports a novel approach to the assessment of the surface properties of compacts used in Surface Dissolution Imaging (SDI). SDI is useful for determining intrinsic dissolution rate (IDR), an important parameter in early stage drug development. Surface topography, post-compaction and post-SDI run, have been measured using a non-contact, optical, three-dimensional microscope based on focus variation, the Alicona Infinite Focus Microscope, with the aim of correlating the IDRs to the surface properties. Ibuprofen (IBU) was used as a model poorly-soluble drug. DSC and XRD were used to monitor possible polymorphic changes that may have occurred post-compaction and post-SDI run. IBUs IDR decreased from 0.033mg/min/cm to 0.022mg/min/cm from 10 to 20min, respectively, during the experiment. XRD and DSC showed no form changes during the SDI run. The surface topography images showed that a distinct imprint was embossed on the surfaces of some compacts which could affect IDRs. Surface parameter values were associated with the SDI experiments which showed strong correlations with the IDR values. The variable-focus microscope can be used as a complimentary tool in the determination of IDR values from the SDI.
Silver‐palladium alloys were electroplated as high quality coatings from a concentrated chloride bath. Adherent, uniform, and coherent deposits were obtained with thicknesses of up to 20 μm. The alloys were found to be homogenous, single‐phase solid solutions, with palladium content ranging from about 30% to 60%, depending on the operating variables. The microstructure of the plated Ag‐Pd alloys consists of very fine grains (100–300Å). These alloys have a fcc crystal structure, and the lattice parameter varies continuously with composition. The useful plating rate with moderate agitation was found to be about 0.44 μm/min at 10 mA/cm2, which is almost twice that of conventional cobalt‐hardened gold, due to the current efficiency of nearly 100%. Alloys containing about 40% Pd were obtained with these conditions. High speed plating of the Ag‐Pd alloy was achieved in a forced flow cell up to rates of about 9 μm/min. To achieve satisfactory deposits, it was generally necessary to use a thin (0.2–0.4 μm) soft gold underplating. Preliminary tests of electrical contact properties revealed that the Ag‐Pd coatings possessed low contact resistance (about 1 mΩ at 100g load). Other relevant properties include intermediate Knoop microhardness (about 200 kg/mm2 at 25g load) and an excellent resistance to formation of corrosion films in accelerated tests using flowers of sulfur. The present study indicates that the plated Ag‐Pd coatings are superior in contact resistance stability to the bulk wrought alloy R156 (40%Ag‐60%Pd). Finally, these coatings show satisfactory wear response in the selected tests provided a hydrocarbon lubricant is present.
Freeform surfaces are featured with superior optical and physical properties and are widely adopted in advanced optical systems. Slow tool servo (STS) ultra-precision machining is an enabling manufacturing technology for fabrication of non-rotationally symmetric surfaces. This work presents a theoretical and experimental study of surface topography generation in STS machining of freeform surfaces. To achieve the nanometric surface topography, a systematic approach for tool path generation was investigated, including tool path planning, tool geometry selection, and tool radius compensation. The tool radius compensation is performed only in one direction to ensure no high frequency motion is imposed on the non-dynamic axis. The development of the surface generation simulation allows the prediction of the surface topography under various tool and machining variables. Furthermore, it provides an important means for better understanding the surface generation mechanism without the need for costly trial and error tests. Machining and measurement experiments of a sinusoidal grid and microlens array sample validated the proposed tool path generation and demonstrated the effectiveness of the STS machining process to fabricate freeform surfaces with nanometric topography. The measurement results also show a uniform topography distribution over the entire surface and agree well with the simulated results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.