Plasma Plume Oscillations Monitoring during Laser Welding of Stainless Steel by Discrete Wavelet Transform Application

The plasma optical radiation emitted during CO2 laser welding of stainless steel samples has been detected with a Si-PIN photodiode and analyzed under different process conditions. The discrete wavelet transform (DWT) has been used to decompose the optical signal into various discrete series of sequences over different frequency bands. The results show that changes of the process settings may yield different signal features in the range of frequencies between 200 Hz and 30 kHz. Potential applications of this method to monitor in real time the laser welding processes are also discussed

A Real-Time Spectroscopic Sensor for Monitoring Laser Welding Processes

In this paper we report on the development of a sensor for real time monitoring of laser welding processes based on spectroscopic techniques. The system is based on the acquisition of the optical spectra emitted from the laser generated plasma plume and their use to implement an on-line algorithm for both the calculation of the plasma electron temperature and the analysis of the correlations between selected spectral lines. The sensor has been patented and it is currently available on the market

Synthesis of semicrystalline nanocapsular structures obtained by Thermally Induced Phase Separation in nanoconfinement

Phase separation of a polymer solution exhibits a peculiar behavior when induced in a nanoconfinement. The energetic constraints introduce additional interactions between the polymer segments that reduce the number of available configurations. In our work, this effect is exploited in a one-step strategy called nanoconfined-Thermally Induced Phase Separation (nc-TIPS) to promote the crystallization of polymer chains into nanocapsular structures of controlled size and shell thickness. This is accomplished by performing a quench step of a low-concentrated PLLA-dioxane-water solution included in emulsions of mean droplet size <500 nm acting as nanodomains. The control of nanoconfinement conditions enables not only the production of nanocapsules with a minimum mean particle diameter of 70 nm but also the tunability of shell thickness and its crystallinity degree. The specific properties of the developed nanocapsular architectures have important implications on release mechanism and loading capability of hydrophilic and lipophilic payload compounds

Process Control of Stainless Steel Laser Welding using an Optical Spectroscopic Sensor

The in-process monitoring and real-time control of the penetration depth during laser welding is evaluated. An optical collimator collects the optical emission for measurement with a fast spectrometer. The sensor data are used to calculate the electron temperature and subsequently to determine the weld quality of overlap welds in AISI 304 stainless steel sheets performed both with CW Nd:YAG and CO2 lasers. A PI-controller adjusts the laser power aiming at a constant penetration depth and has been tested for Nd:YAG laser welding. Optical inspection of the weld verifies the results obtained with the proposed closed-loop system of spectroscopic sensor and controller

Closed loop control of laserwelding using an optical spectroscopic sensor for Nd:Yag and CO2 lasers

Recent developments in laser joining show the applicability of spectral analysis of the plasma plume emission to monitor and control the quality of weld. The analysis of the complete spectra makes it possible to measure specific emission lines which reveal information about the welding process. The subsequent estimation of the electron temperature can be correlated with the quality of the corresponding weld seam. A typical quality parameter, for laser welds of stainless steel, is the achieved penetration depth of the weld. Furthermore adequate gas shielding of the welds has to be provided to avoid seam oxidation. In this paper monitoring and real-time control of the penetration depth during laser welding is demonstrated. Optical emissions in the range of 400nm and 560nm are collected by a fast spectrometer. The sensor data are used to determinethe weld quality of overlap welds in AISI 304 stainless steel sheets performed both with CW Nd:YAG and CO2 lasers. A PI-controller adjusts the laser power aiming at a constant penetration. Optical inspection of the weld surface and microscopic analysis of weld cross sections were used to verify the results obtained with the proposed closed-loop system of spectroscopic sensor and controller

Bombyx mori Silk Fibroin Regeneration in Solution of Lanthanide Ions: A Systematic Investigation

Silk Fibroin (SF) obtained from Bombyx mori is a very attractive biopolymer that can be useful for many technological applications, from optoelectronics and photonics to biomedicine. It can be processed from aqueous solutions to obtain many scaffolds. SF dissolution is possible only with the mediation of chaotropic salts that disrupt the secondary structure of the protein. As a consequence, recovered materials have disordered structures. In a previous paper, it was shown that, by modifying the standard Ajisawa’s method by using a lanthanide salt, CeCl3, as the chaotropic agent, it is possible to regenerate SF as a fibrous material with a very ordered structure, similar to that of the pristine fiber, and doped with Ce+3 ions. Since SF exhibits a moderate fluorescence which can be enhanced by the incorporation of organic molecules, ions and nanoparticles, the possibility of doping it with lanthanide ions could be an appealing approach for the development of new photonic systems. Here, a systematic investigation of the behavior of degummed SF in the presence of all lanthanide ions, Ln+3, is reported. It has been found that all lanthanide chlorides are chaotropic salts for solubilizing SF. Ln+3 ions at the beginning and the end of the series (La+3, Pr+3, Er+3, Tm+3, Yb+3, Lu+3) favor the reprecipitation of fibrous SF as already found for Ce+3. In most cases, the obtained fiber preserves the morphological and structural features of the pristine SF. With the exception of SF treated with La+3, Tm+3, and Lu+3, for all the fibers re-precipitated a concentration of Ln+3 between 0.2 and 0.4% at was measured, comparable to that measured for Ce+3-doped SF

Molecular interactions, characterization and photoactivity of Chlorophyll a/chitosan/2-HP-β-cyclodextrin composite films as functional and active surfaces for ROS production

Novel photosensitizing film based on the natural hybrid polymer Chitosan/2-hydroxy-propyl-β-Cyclodextrin (CH/CD) is synthesized introducing Chlorophyll a (CH/CD/Chla) as a photoactive agent for possible application in antimicrobial photodynamic therapy (PDT). The polymer absorbs visible light, in turn able to generate reactive oxygen species (ROS) and, therefore it can be used as environmental friendly and biodegradable polymeric photosensitizer (PS). The modified film is characterized by means of different spectroscopic, calorimetric, diffraction techniques and microscopic imaging methods including time-resolved absorption spectroscopy. UV–Vis, FTIR-ATR and X-ray Photoelectron Spectroscopy (XPS) analyses suggest that Chla shows a strong affinity toward Chitosan introducing interactions with amino groups present on the polymer chains. Nanosecond laser flash photolysis technique provides evidence for the population of the excited triplet state of Chla. Photogeneration of singlet oxygen is demonstrated by both direct detection by using infrared luminescence spectroscopy and chemical methods based on the use of suitable traps. Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Differential Scanning Calorimetry (DSC) analyses confirm also the occurrence of structural changes both on the film surface and within the film layer induced by the insertion of the pigment. Moreover, X-ray Diffraction data (XRD) shows the existence of an amorphous phase for the chitosan films in all the compared conditions

Study on the correlation between plasma electron temperature and penetration depth in laser welding processes

The plasma electron temperature has been estimated starting from the spectroscopic analysis of the optical emission of the laser-generated plasma plume during quite diverse stainless steel welding procedures (c.w. CO2 and pulsed Nd:YAG). Although the optical emissions present different spectral features, a discrete contribution of several iron lines can be highlighted in both types of welding. We have found that the electron temperature decreases as the laser power is enhanced, in static as well as dynamic conditions. Such a result could be useful to develop a closed loop control system of the weld penetration depth

Molecular interactions, characterization and photoactivity of Chlorophyll a/chitosan/2-HP-β-cyclodextrin composite films as functional and active surfaces for ROS production

Novel photosensitizing film based on the natural hybrid polymer Chitosan/2-hydroxy-propyl-β-Cyclodextrin (CH/CD) is synthesized introducing Chlorophyll a (CH/CD/Chla) as a photoactive agent for possible application in antimicrobial photodynamic therapy (PDT). The polymer absorbs visible light, in turn able to generate reactive oxygen species (ROS) and, therefore it can be used as environmental friendly and biodegradable polymeric photosensitizer (PS). The modified film is characterized by means of different spectroscopic, calorimetric, diffraction techniques and microscopic imaging methods including time-resolved absorption spectroscopy. UV–Vis, FTIR-ATR and X-ray Photoelectron Spectroscopy (XPS) analyses suggest that Chla shows a strong affinity toward Chitosan introducing interactions with amino groups present on the polymer chains. Nanosecond laser flash photolysis technique provides evidence for the population of the excited triplet state of Chla. Photogeneration of singlet oxygen is demonstrated by both direct detection by using infrared luminescence spectroscopy and chemical methods based on the use of suitable traps. Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Differential Scanning Calorimetry (DSC) analyses confirm also the occurrence of structural changes both on the film surface and within the film layer induced by the insertion of the pigment. Moreover, X-ray Diffraction data (XRD) shows the existence of an amorphous phase for the chitosan films in all the compared conditions

Assembled Nanostructured Architectures Studied By Grazing Incidence X-Ray Scattering

In this chapter, we will focus on a specific X‐ray-based technique among those employed in surface science and which is especially suitable for the study of self‐assembled nanocrystals: Grazing Incidence Small Angle X‐ray Scattering (GISAXS). We will first introduce the main field of investigation considered herein, with basic notions of X‐ray scattering from surfaces, and then address basic concepts about GISAXS. Finally, we will describe a few relevant examples of studies, of nanostructured architectures, through ex situ and in situ experiments of grazing incidence X‐ray scattering. This manuscript is focused on the former, showing that they can be performed by using laboratory instruments. In situ investigations still need synchrotron radiation sources in most cases; therefore, only a few examples selected from the literature are reported here, for the sake of completeness. The experiments described are mainly performed in the small angle range, providing information on the size and shape of nanocrystals, together with their spatial arrangement. Both 2D and 3D architectures are considered. In particular, GISAXS measurements of 2D superlattices of nano‐octapods, performed both at a third generation synchrotron beamline and with a table‐top set‐up, are compared; the employed table‐top set‐up is described in a dedicated paragraph. Further examples of grazing incidence studies as performed by the authors with a table‐top set‐up are reported: a GISAXS study of 3D iron oxide nanocrystal superlattices, showing the importance of modelling in order to obtain structural information from data; a combined small/wide angle scattering (GISAXS/GIWAXS) study of 3D PbS nanocrystal superlattices; and a GIWAXS study of P3HT nanofibres, showing how the ordering at the molecular and atomic length scales can be obtained by exploring different angular ranges in the same grazing incidence geometry. Finally, selected examples of in situ GISAXS studies, performed with synchrotron radiation sources, are described