Powder Porosity Research Articles

A Machine Learning Framework for Melt-Pool Geometry Prediction and Process Parameter Optimization in the Laser Powder-Bed Fusion Process

Abstract This study presents a cost-effective and high-precision machine learning (ML) method for predicting the melt-pool geometry and optimizing the process parameters in the laser powder-bed fusion (LPBF) process with Ti-6Al-4V alloy. Unlike many ML models, the presented method incorporates five key features, including three process parameters (laser power, scanning speed, and spot size) and two material parameters (layer thickness and powder porosity). The target variables are the melt-pool width and depth that collectively define the melt-pool geometry and give insight into the melt-pool dynamics in LPBF. The dataset integrates information from an extensive literature survey, computational fluid dynamics (CFD) modeling, and laser melting experiments. Multiple ML regression methods are assessed to determine the best model to predict the melt-pool geometry. Tenfold cross-validation is applied to evaluate the model performance using five evaluation metrics. Several data pre-processing, augmentation, and feature engineering techniques are performed to improve the accuracy of the models. Results show that the “Extra Trees regression” and “Gaussian process regression” models yield the least errors for predicting melt-pool width and depth, respectively. The ML modeling results are compared with the experimental and CFD modeling results to validate the proposed ML models. The most influential parameter affecting the melt-pool geometry is also determined by the sensitivity analysis. The processing parameters are optimized using an iterative grid search method employing the trained ML models. The presented ML framework offers computational speed and simplicity, which can be implemented in other additive manufacturing techniques to comprehend the critical traits.

Effect of foaming and drying temperature on the physical, chemical, and functional properties of egg white powders produced using refractance window drying

This study investigated the effect of drying form (natural and foamed) and temperature (50–100 °C) on the physical, chemical, and functional properties of egg white powder produced using refractance window drying. The egg whites were dried in 4-55 min, depending on the drying conditions. On the one hand, the drying form was effective on the color properties, densities (bulk, tapped, or particle), Carr index, Hausner ratio, porosity, hygroscopicity, solubility, and foaming capacity of egg white powders. On the other hand, the drying temperature was effective for all analyzed properties except hygroscopicity, moisture content, and water activity of samples. The study demonstrated that foaming before refractance window drying enhances the color of the egg white powders and provides better solubility and foaming capacity. However, it has a detrimental effect on the flow properties of the powders evaluated according to the Carr index and Hausner ratio. Increasing the drying temperature until a certain extent (80 °C) generally provided better color, protein content, surface hydrophobicity, and functional properties. The study shows that egg powders suitable for different purposes (better foaming, low protein denaturation, better gelling, etc.) can be obtained if the drying form and temperature conditions are fine-tuned.

Porositas Serbuk Jahe Merah (Zingiber officinale Roscae var. Rubrum) terhadap Variasi Suhu dan Kadar Gula Pasir

Ginger is one of Indonesia's most abundant and widespread cultivated plants and is widely used in people's daily lives as a raw material and additive in the manufacture of food and beverages. One type of ginger that is in great demand in the herbal beverage industry is red ginger. The bioactive compounds found in ginger include 6-gingerol, 6-paradol, 6-methylshogaol, 8-methylshogaol, 8-gingerol, 10-gingerol and 6-shogaol. Red ginger contains various bioactive compounds with pharmacological effects such as analgesic, anti-inflammatory, anti-cancer, antioxidant and cardiotonic effects. Scanning Electron Microscopy (SEM) is a microscopy technique used to produce high-resolution images of the surface of an electron sample. This study aimed to analyze the porosity of red ginger powder against variations in temperature and sugar content. The temperatures were 80 and 90°C with a sugar content of 60 and 100%. The results showed that the increase and decrease in the percentage of porosity values were caused by differences in temperature variations applied to the crystallization process. The rate of red ginger powder's porosity that approaches the fresh red ginger rate is red ginger powder at 80°C and 60% crystallization agent. The research results contributed to the characteristics of the materials used and the development of red ginger drink powder products.

Compression behavior of nanoparticle powder considering fractal aggregate for additive manufacturing

Compression behavior of nanoparticle powder is still unclear, while it could largely affect its applications in additive manufacturing. Considering the fractal structure of aggregates in nanoparticle powder, from the van der Waal's state equation, the relation between porosity and compression pressure of nanoparticle powder was modeled theoretically, i.e. (P + c)(φ-a)=(1-a)c, here P is pressure, φ is porosity, a and c are parameters defined in main text. The model could capture the compression behavior of nanoparticle powders well. Under the same compression pressure, smaller nanoparticles will lead to larger porosity and thus lower thermal conductivity of nanoparticle packed beds, due to the easier aggregate of smaller nanoparticles. The compression behavior and the thermal conductivity of nanoparticle powders or packed beds are expected to supply information for powder spreading and sintering treatment respectively in additive manufacturing.

Exploring conventional and emerging dehydration technologies for slurry/liquid food matrices and their impact on porosity of powders: A comprehensive review.

The contribution of dehydration to the growing market of food powders from slurry/liquid matrices is inevitable. To overcome the challenges posed by conventional drying technologies, several innovative approaches have emerged. However, industrial implementation is limited due to insufficient information on the best-suited drying technologies for targeted products. Therefore, this review aimed to compare various conventional and emerging dehydration technologies (such as active freeze, supercritical, agitated thin-film, and vortex chamber drying) based on their fundamental principles, potential applications, and limitations. Additionally, this article reviewed the effects of drying technologies on porosity, which greatly influence the solubility, rehydration, and stability of powder. The comparison between different drying technologies enables informed decision-making in selecting the appropriate one. It was found that active freeze drying is effective in producing free-flowing powders, unlike conventional freeze drying. Vortex chamber drying could be considered a viable alternative to spray drying, requiring a compact chamber than the large tower needed for spray drying. Freeze-dried, spray freeze-dried, and foam mat-dried powders exhibit higher porosity than spray-dried ones, whereas supercritical drying produces nano-porous interconnected powders. Notably, several factors like glass transition temperature, drying technologies, particle aggregation, agglomeration, and sintering impact powder porosity. However, some binders, such as maltodextrin, sucrose, and lactose, could be applied in controlled agglomeration to enhance powder porosity. Further investigation on the effect of emerging technologies on powder properties and their commercial feasibility is required to discover their potential in liquid drying. Moreover, utilizing clean-label drying ingredients like dietary fibers, derived from agricultural waste, presents promising opportunities.

Effect of different reheating processes and conditions on the nutritional, functional, and microbiological properties of cow meat.

The objective of this study was to evaluate the effect of different reheating methods and conditions on the proximate composition, mineral content, oil quality, and functional and microbiological properties of cow meat. For this, a survey was carried out to identify the reheating methods used in the community. For this study, 8.6 kg of raw beef was used and group 1 (500 g) served as raw control. The remaining 8.1 kg was boiled for 30 min in 5 L of water. Four hundred grams of boiled beef was removed and served as cooked control (group 2). The remaining 3688 g was divided into four groups of 922 g, which were, respectively, divided into subgroups of 307 g. The four sets of subgroups were, respectively, reheated by boiling, frying, microwaving and oven roasting for 3 days. Reheating was done three times a day and samples were collected at the end of each day for further analysis. Changes in proximate composition, mineral content, oil quality, functional properties, and microbiological count were evaluated using standard methods. Results showed that frequent reheating of food was the most used preservation method of cooked food, and boiling and steaming were the most used methods. Reheating time significantly reduces the protein, mineral content, and oil quality of cow meat in general. For the functional properties, reheating methods/conditions generally increased the water-holding capacity, loose and packed bulk densities as well the pH of the meat. Reheating by frying increased the porosity and Hausner ratio of the meat powder while all the reheating treatments reduced the swelling capacity and titratable acidity of cow meat powder. Generally, the reheating methods and duration significantly reduced the bacterial count of cow meat powder. Cow meat should not be reheated for more than 2 days in order to preserve its physiochemical properties.

Visible Light Activation of Gold Nanoparticles Embedded into Titanium Dioxide Surface in Electrospun Polymeric Coatings

This work reports the development of a functional photocatalytic coating based on a combination of polymeric electrospun fibres and nanoparticles that is intended to be activated in the visible light range. In this sense, the resulting fibres can act as an effective matrix for the incorporation of titanium dioxide (TiO2) particles, which are covered by gold nanoparticles (AuNPs), in the outer surface of the metal oxide precursor. In the first step of the process, the optical properties of the nanoparticles were determined by UV-Vis spectroscopy. The extension of the visible absorption can be associated to the localized surface plasmon resonance (LSPR) of the metallic AuNPs. In addition, the resultant particle size distribution and average particle diameter was evaluated by dynamic light scattering (DLS) measurements. Furthermore, the phase composition and porosity of the functional particle powder were analysed by an XRD and N2 adsorption test. In the second step, these synthesized particles have been successfully immobilized into a PAA + β-CD electrospun fibre matrix by using the two different deposition methods of dip-coating and solution-casting, respectively. The morphological characterization of the samples was implemented by means of scanning electron microscopy (SEM), showing uniform and homogeneous, free-beaded fibres with a random distribution of the synthesized particles deposited onto the electrospun fibres. Then, the functional coatings were removed from the substrate, and a thermogravimetric (TGA) analysis was carried out for each sample in order to obtain the precursor mass immobilized in the coating. Once the overall mass of precursor was obtained, the percentage of TiO2 particles and AuNPs in the precursor was calculated by using inductively coupled plasma atomic emission spectrometry (ICP-AES). Finally, the photocatalytic activity of both functional solution and electrospun coatings were evaluated in terms of a gradual degradation of rhodamine B (RhB) dye after continuous exposition to a visible-light lamp.

Optimization of Highly Porous Mannitol Preparation using Ammonium bicarbonate and Citric acid as Templating Agents with Spray Drying Technique

This study investigated the effect of ammonium bicarbonate and citric acid as templating agents using spray drying technique to improve the porosity of D-mannitol powder. It has been shown that textural properties, such as surface area and pore volume produced, are affected by the type and concentration of templating agents, inlet temperature, and outlet temperature of spray drying. The structure of mannitol powder produced changes considerably due to the change in its textural properties to particle powder with high porosity, surface area, and pore volume. The results show that the ratio of D-mannitol to ammonium bicarbonate 10:5 w/w% with water solvent temperature of 30 oC, spray drying inlet temperature of 120 oC, and spray drying outlet temperature of 70 oC, resulting in the highest porosity, surface area, and pore volume. The surface area of mannitol increased from 1.167 m2/g to 3.571 m2/g, followed by an increase in pore volume from 0.0022 cc/g to 0.012 cc/g and pore diameter from 75.33 Å to 115.2 Å. The scanning electron microscope (SEM) results are consistent with the surface area measurement results using the Surface Area Analyzer (SAA). The resulting spray-dried mannitol powder with a high specific surface area allows it to be used as an excipient in solid formulations of oral preparations.

Flowability of plant based food powders: Almond, chestnut, chickpea, coconut, hazelnut and rice

This study presents bulk material characterization, especially powder flowability, of eight food powders from six different plants (almond, chestnut, chickpea, coconut, hazelnut and rice). The characterization of the bulk powders includes the particle size distributions, true densities, bulk and tapped densities, as well as the powder porosity and moisture content. The flowability is determined by means of Hausner ratio, Carr's index, flow function by an annular shear cell and dynamic angle of repose. The flowability characteristics are discussed in regard to the bulk powder properties and evaluated for their applicability as some methods could give misleading results for the flowability.

Evaluation of human amnion denuded derived mesenchymal stem cell on 3D porous hydroxyapatite composite scaffolds for osteogenic differentiation: Prolonged in vitro study

Recent studies using composite porous scaffolds have globally demonstrated the biocompatibility of mesenchymal stem cell sources. It is especially important in hard tissue bioengineering due to its desirable features and stemness effectivity. This study has emphasized primarily the evaluation of the morphological aspects of human amnion-denuded derived mesenchymal stem cells (hAMMSC) in combination with the fabrication of three-dimensional (3D) porous hydroxyapatite (Hap) composite scaffolds for bone tissue engineering based on the principal component of bone mineralization. We presented a novel combination of hAMMSC and nano-crystalline powder hydroxyapatite/bioactive glass (Hap/BG) composite scaffolds fabricated through the hydrothermal method via a novel formulation method from a previous study of stem cell in vitro prolonged culture. The 3D porous scaffold, 6 mm in size, was fabricated from 70 nm nanocrystalline powder and interacted with hAMMSC cultured in osteo-inductive conditions for 30 days. The characterization of 3D porous scaffolds was analyzed via Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) to explore the particle structure, morphology, bioactivity, and porosity of the composite powder and scaffolds in contact with hAMMSCs culture. Furthermore, biocompatibility was assessed using the PrestoBlueTM viability assay and scanning electron microscopy observation (SEM), which revealed the attachment, morphology, and spreading of hAMMSCs on the 3D porous scaffolds of Hap/BG by showing spindle-like morphology and forming the spreading filopodia bridge-like structure within the scaffolds. Subsequently, the secondary objective is the characterization of human AMMSC differentiation capacity assessed by early osteoblast differentiation and mineralization behaviour investigated by early detected assay via alkaline phosphatase activity (ALP) activity marker and energy dispersive X-ray (EDX) analysis simultaneously of the mineralization within bone matrix elements. It was comparatively evaluated via ALP and EDX for calcium quantification elements. Immunomodulatory properties were analyzed via ELISA kits. In conclusion, our findings indicate that 3D porous scaffolds made of Hap/BG composites could be great candidates for future regenerative medicine applications due to their support towards stem cell growth and enhancement of bone cell capacity.

Morphology and structure characterization of hollow granule mold powder for continuous casting

Characteristic parameters of granule morphology (granule diameter and sphericity) and structure (pore size, cross-sectional structure, and porosity) of mold powders were qualitatively and quantitatively analyzed. The results indicated that the granules had a rough surface, good sphericity, and a hollow structure; the internal pores had different diameters, location distributions, and irregular shapes; and the raw material powder particles were interwoven to form a cross-linked network. Energy-dispersive X-ray spectroscopy of the surface and cross-section of the mold powder granules revealed the internal structure and elemental distribution pattern, migration mechanism of the binder, and formation mechanism of the solid crust. The sphericity s values of the mold powder granules were mostly of class B (0.90–0.75 mm), accounting for 72.39%. The s values of more than 90% of granules exceeded 0.8. The porosity values, such as H and ε, increased as the internal pore diameter increased, reaching 0.92 and 0.96, respectively. The H and ε values of more than 90% of the granules were mainly concentrated in the 0.4–0.8 range, and the relationship between H and ε values as well as the variation in granule diameter and pore diameter were mainly consistent.

Comparative Analysis of Composition and Porosity of the Biogenic Powder Obtained from Wasted Crustacean Exoskeletonsafter Carotenoids Extraction for the Blue Bioeconomy

The recovery and recycling of wasted resources are at the forefront of contemporary global issues. Methods of addressing several different issues may go hand-in-hand with each other, such as linking food waste recycling into bio-based adsorbent materials and wastewater treatment. Crustacean exoskeletons are promising candidates for bio-friendly adsorbents; however, maximizing their efficiency requires the optimization of processing technology. Crustacean meat offers an (often luxury) culinary delicacy, while their waste exoskeletons offer opportunities for smart recycling of the magnesian calcite nanoporous biocomposite. Here, we conduct a structural characterization of the exoskeletons of three crustacean species to assess how the extraction of valuable carotenoids affects prospects for the further valorization of their porous powder. The exoskeleton powder’s composition and morphology were investigated by SEM, Raman spectroscopy, FTIR and XRD. The biomineral component magnesian calcite was recorded both in native and in post-extraction exoskeleton powder. Acetone extraction, however, partially removed organic matter from the exoskeletons, resulting in the porosity of the respective powder increasing significantly from below 10 m2 g−1 in the native powder to over 32 m2 g−1 in post-extraction samples of blue crab and spider crab exoskeletons—while the spiny lobster exoskeleton exhibited low porosity, as measured by the BET method. This new insight could improve exoskeleton processing in the sustainable circular economy and applied blue bioeconomy—most notably for adsorbent materials for pollutants dissolved in water or as ordered, nature-derived nanostructured templates.

Analytical solutions of surface porosity of waste brick powder specimens from different milling conditions: A path towards sustainability

Nowadays the replacement of cement with pozzolanic materials is becoming a very hot topic as a result of CO2 emission challenges during cement production. Pore structures of pozzolanic materials allow understanding of their effects on pore parameters of cement-based composites. In this study, analytical solutions of surface porosity of waste brick powder (WBP) specimens generated from varying milling conditions were constructed using segmentation, watershed, and threshold algorithms. Scanning electron microscopy was combined with simulations of pore structures from Gwyddion leading to multi-scale driven surface porosity solutions. These methods for surface porosity characterisation of pozzolans can be boiled down to calls for sustainable construction. By implementing analytical methods, the porosity properties of WBP subjected to various milling conditions are successfully observed for the first time. Overall, the presented simulations using all the three methods proved that increasing the mass of clay bricks fed in ball mill reduced the fineness levels of WBP and increased the surface porosity values. It was shown that the porosity values from all the three methods ranged from 17% to 51%. The watershed simulations were noticed to underestimate the surface porosity values in comparison with threshold and segmentation simulations. The results on mean pore areas, number of pores, pore densities, pore volumes and mean pore sizes of WBP specimens were quite different from surface porosity results as variations became more evident for all three methods. The results from this research have highlighted that the proposed analytical solutions are fast and efficient in evaluating the overall behaviour of WBP in cement-based composites and represent reference points for engineering researchers involved in studies on supplementary cementitious materials.

Study of Effect of Coil Movement on Growth Conditions of SiC Crystal.

SiC substrates have outstanding advantages over traditional materials in power device application, and are mainly prepared by a physical vapor transport method (PVT). Whether the PVT furnace works by resistance heating or induction heating, both face the problem of the deterioration of growth conditions during a long-term process. The relative position of the thermal field directly affects the crystal growth conditions, but the law of specific influence and the change in physical environment inside the thermal field have not been made sufficiently clear and lack systematic research. Therefore, SiC single crystal growth, with different directions and rates in the direction of movement of the heating module, was modeled using a simulation method, and the law of variation of the physical field, including heat flux, temperature, powder porosity and growth rate parameters under different schemes, was analyzed. The study indicates that the decay of raw materials is the primary reason why growth conditions cannot be maintained. The results verified that different coils' modes of movement have different effects on the improvement or adjustment of SiC crystals' growth conditions. Under the same temperature control conditions, the coils' movement rates of 200 μm/h, 0, -200 μm/h and -400 μm/h correspond to the average growth rates of 140, 152, 165 and 172 μm/h, respectively. The results show that downward displacement of the coils is beneficial in compensating for the deterioration of growth conditions, but it is easier to form convex surfaces and is not conducive to expanding diameter growth. This also verifies that the desired crystal growth state can be obtained by adjusting the position of the thermal field.

A novel particle engineering method for the production of inhalable cromolyn sodium powders by a combination of spray drier and nebulizer

Cromolyn sodium is a promising treatment for respiratory disease, especially asthma. Cromolyn sodium is mostly used in the form of a dry powder inhaler (DPI). Morphology of the powder, particle size, dispersibility, and stability are features that greatly influence the absorption efficiency of the given formulation and can be controlled through particle engineering. Although spray drying is the most common production method of cromolyn sodium, this method has some drawbacks including wide droplet size distribution, clogging risk, and lack of direct control over the mean droplet size. To enhance the aerosol performance of the powder, a new method known as a nebulizer-spray drier coupling (NSD) is proposed which affects the particle size distribution, surface features, and aerodynamic properties of the formulation. Ammonium bicarbonate and ethanol were added to assess the variation of produced powder porosity. The morphology, surface and crystallographic features of particles were analyzed with scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET, and X-ray diffraction (XRD) techniques respectively. Aerosol performance was measured with the next generation impactor (NGI). The results show that unlike the needle-like particle shape of the commercial (CS) cromolyn sodium and untreated (raw) cromolyn sodium, the NSD samples have a mushroom-like and spherical particle shape. In the same condition, NSD samples show higher fine particle fraction (FPF) and lower aerodynamic size distribution compared to their counterpart samples (spray-dried). The amorphous structure of the generated powder was confirmed through XRD and DSC analysis. Also, the addition of ammonium bicarbonate produced wider size distribution for particles, providing spherical, hollow, smooth-surface particles. Moreover, the influence of using ethanol (in spray drying process) as a solvent was explored, where the aerosolization performance was found to be improved when ethanol was added to the spray dried solutions. It was concluded that the newly developed powder preparation method (NSD method) could successfully provide cromolyn sodium powder for inhalation and can be introduced as a novel technique for particle engineering of DPIs.

Synthesis and CO2 adsorption kinetics of Aluminum Fumarate MOFs pellet with high recovery

As a promising CO2 adsorbent, Aluminum Fumarate (AlFu) metal organic frameworks (MOFs) were explored for pelletizing technology and CO2 adsorption characteristics. The effects of binder type (sodium carboxymethylcellulose (CMC), aluminum sol (AS)) and content (2.5 wt%-20 wt%), CO2 partial pressure (0.3 bar–1 bar) and temperature (35 °C–65 °C) on the mechanical performance and adsorption process were investigated. The results revealed that with the increase of binder mass, the pellet mechanical strength rose while the CO2 adsorption amount decreased. The AlFu pellet with 2.5 wt% CMC could retain the powder porosity and adsorption capacity. The mechanical strength of AlFu@CMC-2.5 wt% achieved 1.486 MPa, and the maximum adsorption capacity was 1.26 mmol/g at 35 °C and 1.0 bar. The CO2 adsorption capacity was increased with lower adsorption temperature and higher CO2 partial pressure. Compared with pseudo second order model and pseudo first order kinetic model, Avrami kinetic model could better describe the CO2 adsorption behavior of AlFu pellet. It indicated that the adsorption process was not a single physical or chemical adsorption. The rate-limiting kinetic analysis showed that the CO2 adsorption rate was determined by film diffusion and intraparticle diffusion rather than inter-particle diffusion.

Extraction and Characterization of Pharmaceutical Grade Microcrystalline Cellulose From Bambara Nut (Voandzeia Subterranean (L) Thousars) Husk

Microcrystalline cellulose is a vital ingredient in the food, pharmaceutical, and cosmetics industries. In this study, Bambara nutshell microcrystalline cellulose (BNS-MCC) was prepared by acid hydrolysis modification of Bambara nutshell alpha-cellulose pulp. The sample was subjected to sodium hydroxide pulping (2.0% and 17.5% NaOH respectively) and a multistage pulping treatment using 3.5% nitric acid. The analysis results showed that the pulping method was effective for substantial removal of lignin with a 14.416% yield of alpha-cellulose pulp. The organoleptic and physicochemical properties of BNS-MCC were examined. The prepared BNS-MCC powder was examined using a Scanning Electron Microscope (SEM), Fourier Transform Infrared spectroscopy (FTIR), and X-ray Diffractometer (XRD). The sample’s powder flow properties (true density, Hausner index, Carr’s index, angle of repose,powder porosity, loss on drying, and moisture sorption capacity) were (1.216g/mL, 1.34, 25.75%, 39.80o, 64.7%, and 46.81%). The results of the analysis of the BNS-MCC compared well with commercial grades and conformed to US Pharmacopeia (USP) and British Pharmacopeia specifications. This result shows that Bambara nutshells have potential application for pharmaceutical grade cellulose production used in direct compression tableting.

Effect of thermal-fluidic transport on the temperature distribution and the melt pool in laser powder bed fusion of Ti6Al4V

The thermal-fluidic transport affects the temperature distribution and melt pool size in laser powder bed fusion due to its large temperature gradient. A finite element model is established to predict the temperature and melt pool size with considering the thermal-fluidic transport effect. The enthalpy-porosity method is adopted to determine the solid-liquid interface with considering the momentum dissipation during the solidification of the melt pool. A parabolic optical penetration depth (POPD) volumetric heat source model is deduced based on the cylinder heat source model satisfying energy conservation. In the proposed model, the material properties are dependent on the temperature and the powder porosity. The proposed model is validated by comparing to published experimental data of melt pool size. Based on the validated finite element model, the thermal-fluidic transport effects on the temperature distribution and the melt pool are discussed. Results show that in terms of the melt pool width, the prediction accuracy of the surface heat source model is slightly higher than that of POPD volumetric heat source model. In terms of the melt pool depth, surface heat source model is appropriate for the low energy density, while POPD volumetric heat source model is suited for the medium energy density. The thermal-fluidic transport effect increases the melt pool width and length under the surface heat source model, and its effect on the melt pool depth is not obvious. While the thermal-fluidic transport effect decreases the melt pool length under POPD volumetric heat source model, and its effect of the melt pool width and depth is not significant.

3D Modeling of Polymer Selective Laser Sintering Process: Laser-Polymer Interaction Modeling

During selective laser sintering (SLS) process, the laser transmission in the polymer powder bed and solid polymer is different. The laser interaction with the powder bed splits into absorption, reflection and scattering three parts. The photon scattering between the polymer particles leads laser repeated absorption by particles, changes the photon’s traveling directions, and further influences the temperature distribution at the scanning laser area. New distribution and attenuation coefficients need to be introduced for correcting the results. For better simulating the photons travel ways, we introduce the modified Monte-Carlo method and Mie-Scattering theory to predict laser distribution in the polymer powder bed, by considering the scattering phenomenon. This paper analyses how the initial porosity influences the maximum temperature, laser attenuation rate and porosity change rate. The results show that lower porosity promoting the laser scattering phenomenon, decreasing the maximum temperature and the powder porosity change rate.

Evaluation of the impact of pH of the reaction mixture, type of the stirring, and the reagents' concentration in the wet precipitation method on physicochemical properties of hydroxyapatite so as to enhance its biomedical application potential.

Hydroxyapatite (HAp) constitutes a significant inorganic compound which due to its osteoinductivity, osteoconductivity as well as the ability to promote bone growth and regeneration is widely applied in development of biomaterials designed for bone tissue engineering. In this work, various synthesis methodologies of HAp based on the wet precipitation technique were applied, and the impact of pH of the reaction mixture, the concentration of individual reagents as well as the type of stirring applied (mechanical/magnetic) on the properties of final powders was discussed. Spectroscopic methods (Fourier transform infrared, Raman) and X-ray diffraction allowed to verify the synthesis parameters leading to obtaining calcium phosphate with 96% HAp in phase which indicated higher homogeneity of obtained powder (93.4%) than commercial HAp. Powders' morphology was evaluated using microscopic techniques while specific surface area was determined via Brunauer-Emmett-Teller analysis. Particle size distribution, porosity of powders, and stability of HAp suspensions were also characterized. It was proved that synthesis at pH=11.0 using mechanical stirring resulted in calcium phosphate with a high phase homogeneity and homogeneous pore size distribution (6-20 nm). Moreover, obtained HAp powder showed 71.8% more specific surface area than commercial material-that is, 110 m3 /g for synthetic HAp and 64 m3 /g in the case of commercial powder-which, in turn, is significant in terms of its potential application as carrier of active substances. Thus it was demonstrated that by applying appropriate conditions of HAp synthesis it is possible to obtain powder with properties enhancing its application potential for medical purposes.