Influence of Micro Glass Beads Added in a PBT Matrix on the Mechanical Properties of Composites

This paper presents the influence of adding materials (micros glass spheres) in a matrix of PBT on several mechanical properties: elasticity modulus, stress at break , elongation at break, energy at break. The mechanical properties of these composites depend on the glass beads concentration. The additivation of polybuthylen therephtalate with glass beads increases the values of the elasticity modulus, but reduces quite drastically the elongation at break. Using the SEM investigation, the authors pointed out the particular aspects of fracture surfaces: a ductile process at sample margins and a brittle one in the middle of the composite

Tribological Behavior of Polymers and Polymer Composites

This chapter means to explain the tribological behavior of polymer-based materials, to support a beneficial introducing of those materials in actual applications based on test campaigns and their results. Generally, the designers have to take into consideration a set of tribological parameters, not only one, including friction coefficient, wear, temperature in contact, contact durability related to application. Adding materials in polymers could improve especially wear with more than one order of magnitude, but when harder fillers are added (as glass beads, short fibers, minerals) the friction coefficient is slightly increased as compared to neat polymer. In this chapter, there are presented several research studies done by the authors, from which there is point out the importance of composite formulation based on experimental results. For instance, for PBT sliding on steel there was obtained a friction coefficient between 0.15 and 0.3, but for the composite with PBT + micro glass beads, the value of friction coefficient was greater. Adding a polymer playing the role of a solid lubricant (PTFE) in these composites and also only in PBT, decreased the friction coefficient till a maximum value of 0.25. The wear parameter, linear wear rate of the block (from block-on-ring tester) was reduced from 4.5 μm/(N⋅km) till bellow 1 μm/(N⋅km) for a dry sliding regime of 2.5…5 N, for all tested sliding velocities, for the composite PBT + 10% glass beads +10% PTFE, the most promising composite from this family of materials. This study emphasis the importance of polymer composite recipe and the test parameters. Also there are presented failure mechanisms within the tribolayer of polymer-based materials and their counterparts

The microbial picture in patients with oropharingeal diseases

Catedra Otorinolaringologie USMF “Nicolae Testemiţanu”Tonsils are a collection of lymphoid tissue, whose main aim is to provide immune protection of the organism. The important sign of abnormal tonsils is the presence of purulent or caseous content in the gaps. The constant mono- or polymicrobial palatine tonsils flora forms a complex and stable ecosystem, that sustains chronic inflammatory process. According to the modern literature, microflora spectrum is represented as pathogens and strains of the conditionally pathogenic microflora. Amigdalele palatine reprezintă o colecţie de ţesut limfoid, a căror scop principal este să asigure protecţia imună a organismului uman. Caracteristic pentru amigdalele palatine patologic schimbate este prezenţa conţinutului purulent sau a maselor cazeoase în cripte. Flora constantă a amigdalelor palatine mono- sau polimicrobiană formează o ecosistemă complexă şi stabilă, care susţine procesul inflamator cronic. Conform datelor literaturii contemporane spectrul microflorei este prezentat atît de către agenţii patogeni, cît şi de ştamele microflorei condiţionat patogene

REMOVAL OF DIVALENT IRON AND MANGANESE IONS AND HYDROGEN SULFIDE FROM GROUNDWATER

Processes of removal of divalent ions of iron and manganese and hydrogen sulfide from groundwater at various pH values and temperature were studied. Obtained results have been used in order to elaborate a process of groundwater purification from the mentioned pollutants. The use of elaborated process for natural water leads to the decrease of the content of iron, manganese and hydrogen sulfide below the maximum allowable concentrations

Tribological performance of the blend PBT and short aramid fibers

Polybutylene terephthalate (PBT) and its aramid fiber composite (10 wt.%) were investigated in order to measure their wear and frictional properties under variations of applied load (5 N, 10 N, 15N) and velocity (0.25 m/s, 0.5 m/s and 0.75 m/s), in dry regime. The tribological properties of the composite were evaluated using a block-on-ring tribotester. The worn surface was investigated with a scanning electronic microscope and the authors pointed out particular processes taking place into the superficial layers of the friction couple. During the tests, temperature was measured by an infrared camera near to the contact of bodies that are involved and the friction coefficient was monitored by the help of the tribometer UMT-2 (Brucker-CETR®)

The oxidation behavior of classical thermal barrier coatings exposed to extreme temperature

Thermal barrier coatings (TBC) are designed to protect metal surfaces from extreme temperatures and improve their resistance to oxidation during service. Currently, the most commonly used systems are those that have the TBC structure bond coat (BC) / top coat (TC) layers. The top coat layer is a ceramic layer. Oxidation tests are designed to identify the dynamics of the thermally oxide layer (TGO) growth at the interface of bond coat / top coat layers, delamination mechanism and the TBC structural changes induced by thermal conditions. This paper is a short study on the evolution of aluminum oxide protective layer along with prolonged exposure to the testing temperature. There have been tested rectangular specimens of metal super alloy with four surfaces coated with a duplex thermal barrier coating system. The specimens were microscopically and EDAX analyzed before and after the tests. In order to determine the oxide type, the samples were analyzed using X-ray diffraction. The results of the investigation are encouraging for future studies. The results show a direct relationship between the development of the oxide layer and long exposure to the test temperature. Future research will focus on changing the testing temperature to compare the results

Design, fabrication, and characterization of new materials based on zirconia doped with mixed rare earth oxides: review and first experimental results

Monazite is one of the most valuable natural resources for rare earth oxides (REOs) used as dopants with high added value in ceramic materials for extreme environments applications. The complexity of the separation process in individual REOs, due to their similar electronic configuration and physical–chemical properties, is reflected in products with high price and high environmental footprint. During last years, there was an increasing interest for using different mixtures of REOs as dopants for high temperature ceramics, in particular for ZrO2-based thermal barrier coatings (TBCs) used in aeronautics and energy co-generation. The use of mixed REOs may increase the working temperature of the TBCs due to the formation of tetragonal and cubic solid solutions with higher melting temperatures, avoiding grain size coarsening due to interface segregation, enhancing its ionic conductivity and sinterability. The thermal stability of the coatings may be further improved by using rare earth zirconates with perovskite or pyrochlore structures having no phase transitions before melting. Within this research framework, firstly we present a review analysis about results reported in the literature so far about the use of ZrO2 ceramics doped with mixed REOs for high temperature applications. Then, preliminary results about TBCs fabricated by electron beam evaporation starting from mixed REOs simulating the real composition as occurring in monazite source minerals are reported. This novel recipe for ZrO2-based TBCs, if optimized, may lead to better materials with lower costs and lower environmental impact, as a result of the elimination of REOs extraction and separation in individual lanthanides. Preliminary results on the compositional, microstructure, morphological, and thermal properties of the tested materials are reported

A review on differential scanning calorimetry as a tool for thermal assessment of nanostructured coatings

Nanostructured coatings and films play an important role in modern surface engineering due to their ability to improve and optimize materials behavior under different external constraints such as high/low temperatures, stress/strain, corrosive/oxidizing atmosphere, electromagnetic fields/fluxes etc., used practically in all industrial fields. Surface modification may be done using any type of materials: polymers, metals, ceramics, composites or hybrids on any type of substrate by different physical, chemical or combined technologies. Thermal characterization methods are one of the most accessible tools to study, model and predict the process parameters required to preserve the nanostructures during thermal treatment of different coatings, develop novel multi-material coating systems, study the complex correlations between material properties vs. synthesis and processing parameters in real environments. Differential Scanning Calorimetry (DSC) is often used as a standard method to put in evidence different thermal events such as phase transitions, decomposition, oxidation/reduction, nucleation and growth at the substrate/coating interfaces or in coating materials. The present paper aims to review some examples on how DSC may be used to assess the thermal behavior of coatings using standardization tools and developing novel application fields