Effects of Section Size, Surface Cooling Conditions, and Crucible Material on Microstructure and As-Cast Properties of Investment Cast Co-Cr Biomedical Alloy

ASTM F75, a biomedical grade cobalt alloy, is commonly used for orthopedic implants manufactured using investment casting methods. The quality of the cast implants is paramount. Defects such as porosity, inclusions, or misruns are not tolerated and the mechanical properties have to conform to predetermined standards. Generally, castings are subjected to post-casting thermo-mechanical treatments to homogenize structure and improve mechanical properties. However, casting parameters have a significant effect on the as-cast properties of materials, and so if solidification and secondary phase precipitation can be controlled at this stage to limit defects and optimize properties, then the need for such expensive additional treatments may be reduced. The initial objective of this work was to determine the effect of section size and cooling rate on the microstructural characteristics and resultant mechanical properties of the investigated alloy. This was done by conducting a series of instrumented control experiments involving solidification of the alloy in typical investment shell molds, characterization of the as-cast micro/macrostructure, and a program of mechanical testing. In the process of conducting these experiments, unexpected microstructural features were observed that could not be found in the current literature. Through a series of tests conducted to ascertain the origin of this alternative microstructure, it was found that the crucible material used for melting the alloy was highly influential in defining the as-cast properties.     

Investigation of factors affecting the accumulation of vinyl chloride in polyvinyl chloride piping used in drinking water distribution systems

Plastic piping made of polyvinyl chloride (PVC), and chlorinated PVC (CPVC), is being increasingly used for drinking water distribution lines. Given the formulation of the material from vinyl chloride (VC), there has been concern that the VC (a confirmed human carcinogen) can leach from the plastic piping into drinking water. PVC/CPVC pipe reactors in the laboratory and tap samples collected from consumers homes (n = 15) revealed vinyl chloride accumulation in the tens of ng/L range after a few days and hundreds of ng/L after two years. While these levels did not exceed the EPA’s maximum contaminant level (MCL) of 2 μg/L, many readings that simulated stagnation times in homes (overnight) exceeded the MCL-Goal of 0 μg/L. Considerable differences in VC levels were seen across different manufacturers, while aging and biofilm effects were generally small. Preliminary evidence suggests that VC may accumulate not only via chemical leaching from the plastic piping, but also as a disinfection byproduct (DBP) via a chlorine-dependent reaction. This is supported from studies with CPVC pipe reactors where chlorinated reactors accumulated more VC than dechlorinated reactors, copper pipe reactors that accumulated VC in chlorinated reactors and not in dechlorinated reactors, and field samples where VC levels were the same before and after flushing the lines where PVC/CPVC fittings were contributing. Free chlorine residual tests suggest that VC may be formed as a secondary, rather than primary, DBP. Further research and additional studies need to be conducted in order to elucidate reaction mechanisms and tease apart relative contributions of VC accumulation from PVC/CPVC piping and chlorine-dependent reactions.     

The Effect of Informal Settlement Upgrading on Women’s Social Networks: Layout Versus Location

Informal settlements are prevalent in the South African urban landscape. Part of the attempt by the government to meet housing and infrastructure needs has been the in situ upgrading of these informal settlements. This paper explores the effect of in situ informal settlement upgrading on women’s social networks. Social networks are important as they allow access to various livelihood assets that are crucial for building sustainable livelihoods and resilient communities. The results of the research undertaken indicate that the newly upgraded informal settlements have not been conducive to the preservation or creation of women’s social networks due to poor layout planning and inadequate infrastructure provision. There is an assumption that if the informal settlements are upgraded in situ, social networks will not be disrupted. It is anticipated that, because the residents are in the same geographical area, they will be able to maintain their social networks. The paper makes the argument that, when it comes to sustaining social networks, settlement layout and infrastructure provision are just as important and geographical location.     

Deposition and retention of radiolabeled serum constituents in hair after systemic administration

We investigated the relationship between the changes in the pulmonary blood flow and histology during acute rejection following single lung transplantation. In single lung transplantation using adult mongrel dogs, immunosuppression with cyclosporine and azathioprine was discontinued after postoperative day 14 to induce rejection. Doppler flow probes were placed adjacent to the ascending aorta and the left pulmonary artery to measure the blood flow on a daily basis. In addition, chest roentgenograms were also examined daily. The pulmonary pressure was measured using a Swan-Ganz catheter prior to and following the induction of rejection. Open lung biopsies were performed when the left pulmonary artery flow decreased to half of the prerejection value. The pulmonary artery flow decreased to 14.3% of the aortic flow 5 days after the discontinuation of immunosuppression. The graft pulmonary vascular resistance increased significantly compared to the prerejection values (P < 0.001). This was not accompanied by any abnormalities on chest roentgenography. The histology was consistent, with marked perivascular lymphocytic infiltration with little alveolar or interstitial changes. During rejection, the increased pulmonary vascular resistance in the graft was probably the result of perivascular inflammatory cell infiltration, which was seen prior to changes on chest roentgenography. Changes in the left pulmonary artery flow and histology thus appear to be closely correlated in the early stages of acute rejection.