24 research outputs found
Phase composition and morphology as a function of depth for boride coatings grown on Fe-Ni alloys
No full textConsiderable R&D efforts are being carried out in order to produce materials with satisfactory resistance to wear, corrosion or both. In many applications, in fact, the in-service life of components is determined by the surface properties. In the important field of thermochemical treatments of steels, based on diffusion of species such as carbon, nitrogen or boron, boriding is in a peculiar position. Indeed, coatings constituted by iron borides generally display very high hardness, even in excess of 20 GPa, as well as good wear resistance under both sliding and abrasive conditions. Borided steel components display excellent performance in several tribological applications in the mechanical engineering and automotive industries. In spite of several researches performed since many years, some problems remain to be solved as, in particular, the role of alloying elements in the steel on growth and properties of the boride coating.
In the present work the attention has been addressed to the role of Ni, investigated by boronizing binary alloys in order to avoid any interference by other alloying elements. Five Fe-Ni alloys with a Ni contents in the range from 11 to 80 wt.% were borided by a pack-cementation process, using a high boron potential powder mixture constituted by amorphous boron activated with 10 wt.% of potassium fluoborate. The thermochemical treatments were carried out at 850°C for exposure times up to 8 h.
Phase composition and morphology of the boride coatings were characterized as a function of depth by the layer-by-layer removal technique as well as by observations carried out on metallographic cross-sections, using different and complementary techniques: X-ray diffraction (XRD), Mossbauer spectroscopy (MS), micro-Raman spectroscopy, optical (OM) and scanning electron microscopy (SEM), Vickers microhardness measurements (MHV)
Effetti allelopatici di Lavandula officinalis L. e Santureja montana L. su Matricaria chamomilla L.
No full textNew method to measure thermal shock resistance in ceramics using a piezo-spectroscopic technique
No full textA new method for assessing the critical temperature in thermally shocked ceramics is proposed. It is based on the measurement of stress relaxation of residual stresses as a consequence of thermal shock. The change in the stress-field is determined by piezo-spectroscopic technique. The technique is described and the results analyzed. The values obtained are compared with those obtained by the conventional method based on strength degradation measured on test pieces quenched at different temperatures. The agreement among the data is very good
Microscale computational simulation and experimental measurement of thermal residual stresses in glass-alumina functionally graded materials
No full textGlass-alumina functionally graded materials are new attractive composite materials, that can achieve peculiar mechanical properties due to their gradual compositional variation. Nevertheless, the difference between the coefficients of thermal expansion of the constituent phases may result in significant thermal residual stresses in service or during fabrication. A proper (glass formulation can minimize the mismatch in thermo-mechanical properties, thus relevantly reducing the mean value of the resultant thermal stresses. However, it is a crucial requirement to evaluate the effect of microstructural discreteness and randomness oil the actual stress distribution in functionally graded materials. With this aim,a computational model which applies the finite element method at the microscale is used. The careful modelling of the real microstructural details enables to accurately predict the local stress values and distribution. In order to verify the reliability of the computational simulations, the residual thermal stresses were also experimentally measured by means of a piezo-spectroscopic technique. The comparison between the numerical and the experimental results validate the microstructure-based model
Resa e composizione di oli essenziali estratti da piante officinali coltivate in agricoltura biodinamica
No full textEffect of Superficial Residual Stresses on Abrasive Wear Resistance of Al2O3/Al2O3 + 3Y-TZP multilayers
No full textMultilayered composite specimens consisting of Al2O3 / Al2O3+ 3Y-TZP (A/AZ) layers with different compositions and thicknesses were prepared starting from ceramic sheets obtained by tape casting. Residual stresses arisen from mismatch in thermal expansion coefficient during sintering were evaluated using luminescence piezo-spectroscopy. The stress in the superficial A layer was found to be compressive, and its value depended on the ratio between thickness of A and AZ layer. The influence of the superficial compressive stress on the abrasive wear resistance was investigated using microscale ball cratering test; results were correlated with the superficial compressive stress and compared with a specimen of pure unstressed Al2O3 prepared both by lamination and by cold isostatic pressing. Experiments show an improvement of performances in the samples containing compressive residual stress in the surfac
Nota editorial, diciembre 1966
No full textEsta sección recoge una diversidad de textos que dan cuenta de la contribución de expertos analistas que desde distintos enfoques se han referido sobre los acontecimientos financieros y económicos más relevantes ocurridos en Colombia y otros países. Se halla, en especial, noticias relativas a la producción y comercio del café dentro del panorama nacional y mundial; cifras de interés; también se rememora el contenido de revistas anteriores. En esta sección se compilan, además, reseñas, reflexiones, cartas y notas sobre la pluralidad de eventos académicos, sociales y culturales que han configurado el escenario económico nacional.En esta edición se tratan los siguientes temas:- La situación general; el costo vida; giros por importaciones; la banca y el mercado monetario; el mercado bursátil; el petróleo; el café; personal directivo- El mercado mundial del café- VIII Reunión de técnicos de bancos centrales del continente americano:Discurso pronunciado por el señor vicepresidente, doctor Antonio Micele, en la sesión inauguralRelatoría de la comisión IRelatoría de la comisión IIRelatoría de la comisión IIIInforme del relator general - Veinticinco años atrás (número 170, diciembre 1941
Isolation of n-humulone and its effect on the critical micelle concentration
No full textHmelj (Humulus lupulus L.) je trajnica vzpenjavka, ki se uporablja že stoletja ali celo tisočletje, predvsem kot sestavina piva, vendar so znane tudi nekatere zdravilne lastnosti hmeljevih spojin. Med te spojine spadajo tudi α-kisline, izmed katerih bomo v nalogi izolirali n-humulon. Ta deluje protibakterijsko saj je po svoji kemijski sestavi hidrofoben in se zato lahko vgradi v bakterijsko membrano in jo oslabi. Ker so površinsko aktivne snovi pomembna sestavina bakterijskih membran, smo želeli preveriti kakšne so interakcije med modelno površinsko aktivno snovjo in n-humulonom. Z uporabo izotermne titracijske kalorimetrije (ITC) smo želeli ugotoviti, kako dodatek n-humulona vpliva na kritično micelno koncentracijo (CMC) in termodinamčne parametre micelizacije. To nam lahko poda pomemben vpogled v njegove interakcije z fiziološkimi membranami.
V diplomski nalogi smo najprej ekstrahirali ekstrakt iz hmeljevih storžkov in nato s tehnikami hitre in preparativne kromatografije izolirali n-humulon. Sestavo frakcij smo sproti preverjali z reverznofazno kromatografijo visoke ločljivosti in na koncu potrdili istovetnost n-humulona z uporabo NMR spektroskopije. Dobili smo 0,6199 g izoliranega n-humulona. Nato smo s pomočjo izotermne titracijske kalorimetrije analizirali vpliv n-humulona na CMC in termodinamične parametre micelizacije DTAB pri različnih temperaturah.
Rezultati so pokazali, da prisotnost n-humulona v večini primerov znižuje CMC, kar nakazuje na njegovo vlogo pri spodbujanju nastanka micel. Poleg tega ima n-humulon izrazit vpliv na entalpijo micelizacije, saj povečuje eksotermnost procesa. Obenem rezultati nakazujejo pomembno vlogo hidrofobnih interakcij pri vključevanju n-humulone v micele, saj postane vrednost Δcp v prisotnosti n-humulona nekoliko bolj negativna.Hops (Humulus lupulus L.) are perennial climbing plants that have been used for centuries, or even millennia, primarily as an ingredient in beer, but some medicinal properties of hop compounds are also known. Among these compounds are the α-acids, from which n-humulone was isolated in this study. N-humulone exhibits antibacterial activity because it is hydrophobic mulecule, allowing it to embed itself into bacterial membranes and weaken them. Since surfactants are an important component of bacterial membranes, we wanted to examine the interactions between a model surfactant and n-humulone. Using isothermal titration calorimetry (ITC), we aimed to determine how the addition of n-humulone affects the critical micelle concentration (CMC) and the thermodynamic parameters of micellization. This can provide important insight into its interactions with physiological membranes.
In this thesis, we first extracted a crude extract from hop cones and then isolated n-humulone using flash and preparative chromatography techniques. The composition of the fractions was continuously monitored using reverse-phase high-performance liquid chromatography, and the identity of n-humulone was finally confirmed by NMR spectroscopy. We obtained 0,6199 g of isolated n-humulone. Subsequently, we used isothermal titration calorimetry to analyze the effect of n-humulone on the CMC and thermodynamic parameters of DTAB micellization at different temperatures.
The results showed that the presence of n-humulone generally decreases the CMC, suggesting its role in promoting micelle formation. N-humulone has a significant effect on enthalpy and specific heat of micellization, as it increases the exothermicity of the process
Relationship between fatigue limit and Vickers hardness in steels
No full textThe fatigue limit of steels can be correlated to hardness values of steel
