Thermal Fields in Laser Cladding Processing: A “Fire Ball” Model. A Theoretical Computational Comparison, Laser Cladding versus Electron Beam Cladding

Laser cladding processing can be found in many industrial applications. A lot of different materials processing were studied in the last years. To improve the process, one may evaluate the phenomena behaviour from a theoretical and computational point of view. In our model, we consider that the phase transition to the melted pool is treated using an absorption coefficient which can underline liquid formation. In the present study, we propose a semi-analytical model. It supposes that melted pool is in first approximation a “sphere”, and in consequence, the heat equation is solved in spherical coordinates. Using the Laplace transform, we will solve the heat equation without the assumption that “time” parameter should be interpolated linearly. 3D thermal graphics of the Cu substrate are presented. Our model could be applied also for electron cladding of metals. We make as well a comparison of the cladding method using laser or electron beams. We study the process for different input powers and various beam velocities. The results proved to be in good agreement with data from literature

Composite Coatings Based on Renewable Resources Synthesized by Advanced Laser Techniques

This chapter reviews the progress and perspectives of composite materials in the form of thin films based on renewable resources for biofabrication of a new generation of medical implants with antibacterial properties. The chapter starts with an overview of the types of renewable materials that were currently studied and of the unique properties which make them perfect candidates for numerous bio‐related applications. A briefing of recent progresses in the field of advanced laser synthesis of composites from renewable and sustainable materials, as well as the relevant results in our researches is made. The discussion spans composite coatings based on renewable resources, [e.g., chitosan (CHT) and lignin (Lig)] as biomaterials intended for metallic implants. A particular attention is given to lignin synthesis in the form of thin films due to its ability to functionalize the medical implant surface while preserving the similar composition and the structural properties of the raw, renewable biomaterial. We focused on recent technological advancements (e.g., matrix‐assisted pulsed laser evaporation (MAPLE) and Combinatorial‐MAPLE) which have brought the spotlight onto renewable biomaterials, by detailing the relevant engineering data of processing. This chapter concludes that the extensions of advanced laser techniques are viable fabrication methods of a new generation of metallic implants

Laser Ablation of Biomaterials

Biomaterials, defined by high biocompatibility and biodegradability, are intensively used in medical applications, mainly to replace partial or total, damaged or destroyed hard or soft tissues. Most of them are used not only as coatings for implant coverage but also as parts for some medical devices. In the last decades, researchers sought to find the optimum processing methods and parameters to modify or deposit the biomaterial of interest. An important family of techniques, used to process a biomaterial, is represented by laser techniques, based upon laser ablation phenomenon. Laser ablation of biomaterials ensures the transference or modification with good precision and without or with minimal disruptions generated. To obtain thin coatings from biomaterials, one can use deposition techniques: pulsed laser deposition (PLD) or matrix-assisted pulsed laser evaporation (MAPLE). These techniques are chosen according to the selected biomaterial and desired performances of the obtained coating. Therefore, some sensitive biomaterials can be transferred only by MAPLE. Some results in the field of calcium phosphates deposited by PLD or MAPLE are presented, proving the usefulness of these biomaterials for medical applications

Biopolymer Thin Films Synthesized by Advanced Pulsed Laser Techniques

This chapter provides an overview of recent advances in the field of laser-based synthesis of biopolymer thin films for biomedical applications. The introduction addresses the importance of biopolymer thin films with respect to several applications like tissue engineering, cell instructive environments, and drug delivery systems. The next section is devoted to applications of the fabrication of organic and hybrid organic–inorganic coatings. Matrix-assisted pulsed laser evaporation (MAPLE) and Combinatorial-MAPLE are introduced and compared with other conventional methods of thin films assembling on solid substrates. Advantages and limitations of the methods are pointed out by focusing on the delicate transfer of bio-macromolecules, preservation of properties and on the prospect of combinatorial libraries’ synthesis in a single-step process. The following section provides a brief description of fundamental processes involved in the molecular transfer of delicate materials by MAPLE. Then, the chapter focuses on the laser synthesis of two polysaccharide thin films, namely Dextran doped with iron oxide nanoparticles and Levan, followed by an overview on the MAPLE synthesis of other biopolymers. The chapter ends with summary and perspectives of this fast-expanding research field, and a rich bibliographic database

Protected Laser Evaporation/Ablation and Deposition of Organic/Biological Materials: Thin Films Deposition for Nano- biomedical Applications

This chapter reviews the laser ablation of delicate organic/biological substances by matrix-assisted pulsed laser evaporation (MAPLE). It is shown that direct ablation in this case is possible but sometimes not workable at all in adverse conditions. The considered solution is the protection by a prevalent dissolving/suspending component that can allow for a “shielded” ablation by the frozen solvent followed by its gradual evaporation by melting, evaporation and evacuation by pumping system. We extend the study to the case of non-UV absorbing solvents, e.g., water, when the primary interaction between laser and solute ignites evaporation process at a lower ablation threshold due to reduced pressure inside irradiation chamber. We called this case as “generalized” MAPLE interaction. Relevant examples are provided and critically analyzed in view of potential applications for nanobiomedicine, biosensors, advanced implants and chemical technologies

Pulsed Laser-Deposited TiO2-based Films: Synthesis, Electronic Structure and Photocatalytic Activity

Active under visible light, photocatalysts based on doped titania were obtained via pulsed laser deposition (PLD) method. To find out the crystalline structure, optical properties, and electronic structure, the following techniques such as X-ray diffraction, electronic spectroscopy, electrical conductivity measurements, and X-ray photoelectron spectroscopy (XPS) are used. Photocatalytic activity is monitored by applying the photoreduction of dichromate ions under UV and visible light. The influence of zirconium ions and its content and synthesis conditions on the efficiency of nitrogen incorporation into titania structure that, in turn, determines the electronic structure and photocatalytic ability of the semiconductive materials are discussed. A substitutional nitrogen (Ti–N) rather than an interstitial one (Ti–O–N) is mainly responsible for the observed photoactivity. It is pointed that substitutional nitrogen is responsible for bandgap narrowing or formation of intragap localized states within semiconductor bandgap. The bandgap energy values are sharply decreased, while the relative intensity of substitutional nitrogen XPS peaks is increased. Pulsed laser synthesis of TiO2 films in N2/CH4 atmosphere not only leads to nitrogen incorporation but also to the formation of defects including oxygen vacancies and Ti3+ states which are all contributing to light absorption. An appropriate ratio of gas mixture, optimum zirconia content, suitable pressure, and temperature during synthesis was found for the synthesis of highly active semiconductive films. The highest photocatalytic conversion yields are obtained for nitrogen-doped 10% ZrO2/TiO2 synthesized in N2:CH4 = 5:1 at 100 Pa and at 450°C under both UV and visible light

A New Approach to Solve Non-Fourier Heat Equation via Empirical Methods Combined with the Integral Transform Technique in Finite Domains

This chapter deals with the validity/limits of the integral transform technique on finite domains. The integral transform technique based upon eigenvalues and eigenfunctions can serve as an appropriate tool for solving the Fourier heat equation, in the case of both laser and electron beam processing. The crux of the method consists in the fact that the solutions by mentioned technique demonstrate strong convergence after the 10 eigenvalues iterations, only. Nevertheless, the method meets with difficulties to extend to the case of non-Fourier equations. A solution is however possible, but it is bulky with a weak convergence and requires the use of extra-boundary conditions. To surpass this difficulty, a new mix approach is proposed with this chapter resorting to experimental data, in order to support a more appropriate solution. The proposed method opens in our opinion a beneficial prospective for either laser or electron beam processing

Efficient Microbial Decontamination of Translucent Liquids and Gases Using Optical Metamaterials

An effective way of decontamination using optical metamaterials like photonic crystals consisting of glass microspheres or granulated quartz with various geometries is proposed. The efficient decontamination using the evanescent zone of metamaterials opens a new perspective in pathogen decontamination. We propose different topological structures of metamaterials to enlarge the contact surface of ultraviolet radiation with polluted translucent fluids. The approach is based upon the increased transfer of UV radiation via evanescent waves of metamaterials into contaminated translucent fluids. A series of experimental estimations of the decontamination rate of this type of metamaterials have been made. For these investigations, a decontamination core filled up with metamaterials is used through which the contaminated fluid freely flows. Experiments have conclusively proved that evanescent zone of quartz and optical fiber metamaterials can effectively inactivate Coliform (including Escherichia coli), or Enterococcus bacteria, as well as yeast and Kombucha cultures