1,720,975 research outputs found
Ant‐Nest Corrosion in Copper Pipes Triggered by Ethylene Vinyl Acetate‐Based Adhesive
Full text linkCorrosion of condenser circuits in refrigeration systems significantly impacts appliance reliability and longevity. This study investigates an unreported cause linked to changing adhesive materials during copper pipe assembly. Transitioning from a polyethylene‐based adhesive to one containing ethylene vinyl acetate caused unexpected perforation of copper coils within months. We hypothesized that even trace amounts of acetic acid, a byproduct of the latter adhesive, trigger a peculiar localized morphology known as “ant‐nest corrosion.” We propose using ethylene vinyl acetate‐free adhesives to prevent this issue in refrigeration systems
Raman spectroscopic study of bioactive silica based glasses: The role of the alkali/alkali earth ratio on the non-bridging oxygen/bridging oxygen (NBO/BO) ratio
Full text linkRaman spectra of bioactive glasses of the Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2 to be used in bone reconstruction systems have been collected from samples with three different concentrations of alkali and alkali earth elements. Compositions were chosen with a constant total amount of modifiers and formers, with only minor changes among the formers. The ratio of Non-Bridging Oxygens (NBO/BO) has been obtained from the Raman spectra and reported as a function of the alkali/alkali earth ratio, showing a linear increase. Dissolution tests indicate also a linear dependence of the amount of Na+, K+ and Ca++ ions leached in water has been obtained, thus demonstrating the sensitivity of the method, given that the changes from one glass composition tyo the other are of the order of some points in percentage among the glass modifiers
Failure investigation of a protective epoxy coating by means of crosscheck between infrared spectroscopy and thermal analysis
Full text linkThis paper reports the failure of an epoxy coating that was applied for corrosion prevention on the inner walls of a heat exchanger. The coating became brittle and detached from the walls of the exchanger after one year of service. An investigation was performed in order to evaluate the failure cause by means of thermal analysis, optical microscopy and infrared spectroscopy. Thermal analysis excluded an incomplete curing of the detached paint. Optical microscopy highlighted sediments, pores and cracks over the detached coating surface; infrared spectroscopy revealed vibrational bands associated with thermo-oxidative phenomena. A thermo-oxidative simulation was performed on fresh coating samples, pointing out that epoxy coating starts degrading around 100-120 °C. Taking into account the temporary malfunction of the cooling system reported by the user, the failure cause was identified in an overheating that induced a thermo-oxidative degradation of the coating and its subsequent embrittlement and detachment
Surface-enhanced Raman effect in hybrid metal–semiconductor nanoparticle assemblies
No full textHybrid metal–semiconductor nanoparticles consisting of silver nanoparticle cores (AgNPs) coated with a layer of CdSe quantum dots (QDs) have been studied by Raman spectroscopy. The hybrid nanoparticles were prepared via electrostatic interaction by mixing aqueous suspensions of QDs and AgNPs, where opposite charges on the AgNPs and QDs surfaces were induced by opportunely selected capping agents. Assemblies of such hybrid nanoparticles show an increased intensity of the Raman spectrum of up to 500 times, when compared to that of the sole QDs. This enhancement is attributed to the SERS effect (Surface-enhanced Raman scattering). Such enhancement of the Raman modes suggests several opportunities for further research, both in imaging and sensing applications
Scleroglucan-Based Foam Incorporating Recycled Rigid Polyurethane Waste for Novel Insulation Material Production
Full text linkThis study details the synthesis and performance evaluation of a novel lightweight thermal and acoustic insulation material, resulting from the combination of a scleroglucan-based hydrogel and recycled rigid polyurethane waste powder. Through a sublimation-driven water-removal process, a porous three-dimensional network structure is formed, showcasing notable thermal and acoustic insulation properties. Experimental data are presented to highlight the material’s performance, including comparisons with commercially available mineral wool and polymeric foams. This material versatility is demonstrated through tunable mechanical, thermal and acoustic characteristics, achieved by strategically adjusting the concentration of the biopolymer and additives. This adaptability positions the material as a promising candidate for different insulation applications. Addressing environmental concerns related to rigid polyurethane waste disposal, the study contributes to the circular economy
Impulse response method for defect detection in polymers: Description of the method and preliminary results
No full textThe major problem encountered in the application of polymer industrial products is the difficulty of effectively modelling and predicting material performance and service life according to applied loads and operating environmental conditions. Furthermore, the presence of defects such as voids or inclusions created during manufacturing may affect the final performance.
The aim of this study is to present and investigate the development of an innovative acoustic non-destructive technique (patent pending), able to verify defects into composite laminates.
The analysis was carried out in two steps: the first aims to verify if distinct phases can be recognized within a material, while the second has the purpose of testing the proposed method on defective materials ad hoc prepared
The effect of artificial weathering on PP coextruded tape and laminate
Full text linkThe aim of this work was to analyse the influence of artificial weathering on polypropylene (PP) selfreinforced
composite both as fabric constituent (tape) and as laminate. Particular attention has been
focused on the interaction between radiation and material microstructural characteristics, especially
for the selective action that the former causes in PP amorphous regions. The evaluation of carbonyl index
performed by Fourier Transform Infrared (FT-IR) spectroscopy has highlighted that tapes are more prone
to degradation since their drawn structure induces internal stress. Differential scanning calorimetry
(DSC) measurements have denoted a shift towards lower temperature of PP melting peak. While crystallinity
determination performed by DSC and FT-IR spectroscopy has underlined an increasing trend
for laminate over exposure time due to the higher amount of amorphous phase, Raman spectroscopy
has revealed that photo-degradation induces a rise of the isomeric defect fraction, limiting chemicrystallisation
both for tapes and laminates
Time-depending performance of resilient layers under floating floors
No full textIn the floating floor system the performance of resilient layers, in terms of impact sound pressure level
reduction, is of paramount importance. In the present study in order to evaluate the time-depending performances,
a comprehensive characterization of twenty different layers was carried out, evaluating
dynamic stiffness, compressibility and compressive creep. The aim of this work was to find out a possible
correlation among these parameters and the effect of service time on mechanical and acoustical properties.
Results indicated that a general rule couldn’t be defined. Furthermore, the presence of a coating, as
well as different density and/or contact shape, has proved to influence the final acoustical performances
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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