Sliding wear properties of HVOF thermally sprayed nylon-11 and nylon-11/ceramic composites on steel

Journal of Thermal Spray Technology, 16(5-6): pp. 927-932.Polymer and polymer/ceramic composite coatings were produced by ball-milling 60 μm Nylon- 11 together with nominal 10 vol.% of nano and multi-scale ceramic reinforcements and HVOF spraying these composite feedstocks onto steel substrates to produce semi-crystalline micron and nano-scale reinforced coatings polymer matrix composites. Room temperature dry sliding wear performance of pure Nylon-11, Nylon-11 reinforced with 7 nm silica, and multi-scale Nylon- 11/silica composite coatings incorporating 7-40 nm and 10 μm ceramic particles was characterized using a pin-on-disk tribometer. Coefficient of friction and wear rate were determined as a function of applied load and coating composition. Surface profilometry and scanning electron microscopy were used to characterize and analyze the coatings and wear scars. The pure Nylon-11 coating experienced less wear than the composites due to the occurrence of two additional wear mechanisms: abrasive and fatigue wear

Development of HVOF Sprayed Erosion/Oxidation Resistant Coatings for Composite Structural Components in Propulsion Systems

Thermally sprayed coatings are being studied and developed as methods of enabling lightweight composites to be used more extensively as structural components in propulsion applications in order to reduce costs and improve efficiency through weight reductions. The primary goal of this work is the development of functionally graded material [FGM] polymer/metal matrix composite coatings to provide improved erosion/oxidation resistance to polyimide-based polymer matrix composite [PMC] substrates. The goal is to grade the coating composition from pure polyimide, similar to the PMC substrate matrix on one side, to 100% WC-Co on the other. Both step-wise and continuous gradation of the loading of the WC-Co reinforcing phase are being investigated, Details of the coating parameter development will be presented, specifically the high velocity oxy-fuel [HVOF] combustion spraying of pure PMR-I1 matrix material and layers of various composition PMR-II/WC-Co blends onto steel and PMR-15 composite substrates. Results of the HVOF process optimization, microstructural characterization, and analysis will be presented. The sprayed coatings were evaluated using standard metallographic techniques - optical and scanning electron microscopy [SEMI. An SEM + electron dispersive spectroscopy [EDS] technique has also been used to confirm retention of the PMR-I1 component. Results of peel/butt adhesion testing to determine adhesion will also be presented

Transport properties of functionally graded materials

This paper presents a numerical method to predict the effective transport properties of multiphase functionally graded materials, accounting for the effects of random phase distribution and multiphase interactions. Firstly, the multiphase microstructures of such graded materials are reproduced by a random generation-growth algorithm, and then the corresponding transport governing equations are solved using a high-efficiency lattice Boltzmann method. The predicted effective electric and thermal conductivities agree well with the existing experimental data for both two- and three-phase functionally graded materials. Furthermore when the methodology is extended to other transport and even nontransport physical properties of multiphase composites, our simulated results still agree much better with the available experimental data than the existing theoretical models. This may exhibit the robusticity and wider applicability of the present approach. (c) 2007 American Institute of Physics

Mechanism and clinical importance of respiratory failure induced by anticholinesterases

© 2017, University of Kragujevac, Faculty of Science. All rights reserved. Respiratory failure is the predominant cause of death in humans and animals poisoned with anticholinesterases. Organophosphorus and carbamate anticholinesterases inhibit acetylcholinesterase irreversibly and reversibly, respectively. Some of them contain a quaternary atom that makes them lipophobic, limiting their action at the periphery, i.e. outside the central nervous system. They impair respiratory function primarily by inducing a desensitization block of nicotinic receptors in the neuromuscular synapse. Lipophilic anticholinesterases inhibit the acetylcholinesterase both in the brain and in other tissues, including respiratory muscles. Their doses needed for cessation of central respiratory drive are significantly less than doses needed for paralysis of the neuromuscular transmission. Antagonist of muscarinic receptors atropine blocks both the central and peripheral muscarinic receptors and effectively antagonizes the central respiratory depression produced by anticholinesterases. To manage the peripheral nicotinic receptor hyperstimulation phenomena, oximes as acetylcholinesterase reactivators are used. Addition of diazepam is useful for treatment of seizures, since they are cholinergic only in their initial phase and can contribute to the occurrence of central respiratory depression. Possible involvement of central nicotinic receptors as well as the other neurotransmitter systems - glutamatergic, opioidergic - necessitates further research of additional antidotes

Bochdalek hernia in adults – A case report

© 2018, Inst. Sci. inf., Univ. Defence in Belgrade. All rights reserved. Introduction. Asymptomatic Bochdalek hernia in adults is a rarity. The aim of this paper is to present a rare case of Bochdalek hernia among adults and to point out to significance of clinical suspicion and important role of imaging techniques in reaching the exact diagnosis of this abnormality. Case report. A patient, aged 68 years, came to the Clinic of Pulmonology complaining of constant dyspnea, coughing and fatigue. Computed tomography (CT) findings were dominated by the large rear right diaphragmatic hernia with the hernial sac that reached the carina trachea and urged the principal bronchi. The stomach, duodenum and proximal part of jejunal winds, as well as a greater amount of omental and mesenteric adipose tissue were localized in hernial sac. Radiography of gastroduodenum showed: entry of the esophagus into the cardia was in the level of the right main bronchus. Stomach was mainly located in the chest (cardia, upper corpus half - to the level of the right main bronchus). Operation was indicated. First, we made right thoracotomy and the hernia sac was separated from the right lung and then we performed median laparotomy and the contents of the hernia sac were returned to the abdominal cavity; diaphragm defect was reconstructed with prolen mesh. Conclusion. We presented a rare case of right sided Bochdalek hernia which was discovered at late age and surgically treated with success

Anatomical parameters of the acetabulum in heavy vehicle operators

© 2017, University of Kragujevac, Faculty of Science. All rights reserved. It has been suggested that long-term exposure by heavy vehicle operators to whole-body vibration (WBV) may be related to an increased risk of pathological changes in the anatomical parameters of the hip. The aim of this study was to explore the difference in anatomical parameters of acetabulum in drivers of heavy vehicles (experimental group; n=60) and subjects who have not been exposed to WBV (control group; n=60). The anteroposterior radiographic view of the hips was used to measure the following parameters: the vertical centre edge (VCE), the ‘horizontal toit externe’ angle (HTE), the neck shaft angle (NSA) and the acetabular depth (AD). Compared with the control group, the mean VCE angle values and AD were significantly lower, while the average HTE and NSA values were significantly higher in the experimental group. This study supports the hypothesis that exposure to whole-body vibration during operation of a vehicle causes an increased risk of acetabular dysplasia

Extramedullary involvement of lymph nodes in multiple myeloma

© 2017, University of Kragujevac, Faculty of Science. All rights reserved. Myeloma multiplex is a malignant disease of bone marrow plasma cells. It is usually confined to the bone marrow, but in rare cases, patients can develop extramedullary disease. The involvement of lymph nodes is rare and can be a diagnostic challenge. Here, we describe a 36-year-old male patient who presented with abdominal pain and discomfort initially. An abdominal ultrasound followed by computed tomography (CT) revealed retroperitoneal and mesenteric lymph node enlargement. Biopsies of the abdominal lymph node and infiltrated colon showed a plasma cell infiltrate positive for CD79α, CD38, CD138, kappa light chain and VEGF2. Multiple myeloma with extramedullary localization was diagnosed. After six cycles of chemotherapy consisting of doxorubicin, dexamethasone and thalidomide followed by autologous haematopoietic cell transplantation, the patient achieved complete remission. Specifically, a CT scan after therapy showed enlarged lymph nodes in the abdomen, but PET CT scans did not detect any metabolically active foci. Three years after the completion of therapy, the patient remains in remission. This case illustrates a rare presentation of extramedullary myeloma involving the abdominal lymph nodes, which could have been potentially mistaken for a lymphoid malignancy

Microstructure and Properties of Thermally Sprayed Functionally Graded Coatings for Polymeric Substrates

The use of polymer matrix composites (PMCs) in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance but their useful lifetime is limited by their poor erosion resistance. High velocity oxy-fuel (HVOF) sprayed polymer/cermet functionally graded (FGM) coatings are being investigated as a method to address this technology gap by providing erosion and oxidation protection to polymer matrix composites. The FGM coating structures are based on a polyimide matrix filled with varying volume fractions of WC-Co. The graded coating architecture was produced using a combination of internal and external feedstock injection, via two computer-controlled powder feeders and controlled substrate preheating. Porosity, coating thickness and volume fraction of the WC-Co filler retained in the coatings were determined using standard metallographic techniques and computer image analysis. The pull-off strength (often referred to as the adhesive strength) of the coatings was evaluated according to the ASTM D 4541 standard test method, which measured the greatest normal tensile force that the coating could withstand. Adhesive/cohesive strengths were determined for three different types of coating structures and compared based on the maximum indicated load and the surface area loaded. The nature and locus of the fractures were characterized according to the percent of adhesive and/or cohesive failure, and the tested interfaces and layers involved were analyzed by Scanning Electron Microscopy