Morphology Of Powders Research Articles

Highly stable and antifungal properties on the oilseed rape of Cu3(MoO4)2(OH)2 nanoflakes prepared by simple aqueous precipitation

In the last few decades, nanoparticles have been a prominent topic in various fields, particularly in agriculture, due to their unique physicochemical properties. Herein, molybdenum copper lindgrenite Cu3(MoO4)2(OH)2 (CM) nanoflakes (NFs) are synthesized by a one-step reaction involving α-MoO3 and CuCO3⋅Cu(OH)2⋅xH2O solution at low temperature for large scale industrial production and developed as an effective antifungal agent for the oilseed rape. This synthetic method demonstrates great potential for industrial applications. Infrared spectroscopy and X-ray diffraction (XRD) results reveal that CM samples exhibit a pure monoclinic structure. TG and DSC results show the thermal stable properties. It can undergo a phase transition form copper molybdate (Cu3Mo2O9) at about 300 °C. Then Cu3Mo2O9 nanoparticles decompose into at CuO and MoO3 at 791 °C. The morphology of CM powder is mainly composed of uniformly distributed parallelogram-shaped nanoflakes with an average thickness of about 30 nm. Moreover, the binding energy of CM NFs is measured to be 2.8 eV. To assess the antifungal properties of these materials, both laboratory and outdoor experiments are conducted. In the pour plate test, the minimum inhibitory concentration (MIC) of CM NFs against Sclerotinia sclerotiorum (S. sclerotiorum) is determined to be 100 ppm, and the zone of inhibiting S. sclerotiorum is 14 mm. When the concentration is above 100 nm, the change rate of the hyphae circle slows down a little and begins to decrease until to 200 ppm. According to the aforementioned findings, the antifungal effects of a nano CM NFs solution are assessed at different concentrations (0 ppm (clear water), 40 ppm, and 80 ppm) on the growth of oilseed rape in an outdoor setting. The results indicate that the application of CM NFs led to significant inhibition of S. sclerotiorum. Specifically, when the nano CM solution was sprayed once at the initial flowering stage at a concentration of 80 ppm, S. sclerotiorum growth was inhibited by approximately 34%. Similarly, when the solution was sprayed once at the initial flowering stage and once at the rape pod stage, using a concentration of 40 ppm, a similar level of inhibition was achieved. These outcomes show that CM NFs possess the ability to bind with more metal ions due to their larger specific surface area. Additionally, their semiconductor physical properties enable the generation of reactive oxygen species (ROS). Therefore, CM NFs hold great potential for widespread application in antifungal products.

Curcumin/Carrier Coprecipitation by Supercritical Antisolvent Route.

In this work, polyvinylpyrrolidone (PVP)- and β-cyclodextrin (β-CD)-based composite powders containing curcumin (CURC) were obtained through the supercritical antisolvent (SAS) technique. Pressure, total concentration of CURC/carrier in dimethylsulfoxide, and CURC/carrier ratio effects on the morphology and size of the precipitated powders were investigated. Using PVP as the carrier, spherical particles with a mean diameter of 1.72 μm were obtained at 12.0 MPa, 20 mg/mL, and a CURC/PVP molar ratio equal to 1/2 mol/mol; using β-CD as the carrier, the optimal operating conditions were 9.0 MPa and 200 mg/mL; well-defined micrometric particles with mean diameters equal to 2.98 and 3.69 μm were obtained at molar ratios of 1/2 and 1/1 mol/mol, respectively. FT-IR spectra of CURC/ β-CD inclusion complexes and coprecipitated CURC/PVP powders revealed the presence of some peaks of the active compounds. The stoichiometry of the complexes evaluated through the Job method revealed that β-CD formed inclusion complexes with CURC at a molar ratio equal to 1/1. Dissolution profiles revealed that in comparison with the curve of the pure ingredient, the SAS-processed powders obtained using both PVP and β-CD have an improved release rate.

Protein isolates made in the laboratory versus the factory: A case study with mung bean and chickpea

AbstractProtein isolates deliver functionalities such as gelling, emulsifying, and foaming, and many recent publications are reporting the functionality of new protein isolates produced in the laboratory. Laboratory protein isolation processes are quite different to industrial processes, and therefore isolate functionalities are likely to be different. We examined some of the differences between laboratory isolates and commercial isolates of mung bean and chickpea protein (MPBI and CPPI). We tested solubility as a function of pH, dispersibility by static light scattering, and viscosity enhancement in a rapid visco analyzer (RVA). Thermal transitions were evaluated with differential scanning calorimetry (DSC), and powder morphology was examined by scanning electron microscopy (SEM). Laboratory isolates were more soluble (e.g. 54%–57% vs. 5%–45% at pH 8) and dispersible than commercial isolates, with the largest DSC endotherms, indicating the least denaturation. Among commercial isolates, we found large differences in solubility, thermal properties, and viscosity enhancement, and minor differences in dispersibility and powder morphology. The hydration protocol had a strong effect on solubility and DSC results, and a moderate effect on RVA results. Comparisons between isolates produced in different laboratories are currently hampered by the use of nonstandard empirical methods for certain functionalities, and we highlight standardized methods for measuring dispersibility and viscosity enhancement. Protein isolation processes affect isolate functionality via effects on protein denaturation and aggregation, and via the morphology and surface chemistry of isolate powders. This means that findings with laboratory isolates cannot necessarily be extrapolated to commercial counterparts but also indicates the power of process design to modulate isolate functionality.

Regulation mechanism of morphology and particle size of ultrafine molybdenum powder prepared via hydrogen reduction of gaseous molybdenum trioxides

In this study, molybdenum powder with desired morphology and particle size was produced through hydrogen reduction of gaseous molybdenum trioxide by changing the hydrogen partial pressure, reaction temperature, hydrogen preheating temperature, and cooling gas flow rate. At the reaction temperature of 1000 °C, the reaction product was a mixture of MoO2 and Mo. The reduction rate reached 100% at 1100 °C, and a further increase in temperature from 1100 °C to 1200 °C caused the average particle size of molybdenum powder to increase from 26.2 nm to 63.1 nm. Both the hydrogen temperature and the cooling intensity during the reaction had a great influence on the nucleation and growth of the grains, respectively. The molybdenum powder obtained without hydrogen preheating exhibited higher nucleation rates and finer grains than those exposed to hydrogen preheating. The molybdenum powder particles evolved from irregular polyhedra to spheres as the cooling intensity decreased through the injection of cooling gas. Therefore, the results of this work provide theoretical guidance for tuning the morphology and particle size of molybdenum powder.

Fabrication of Ag-Bi Alloy Films from an Iodide-Tartrate Bath via Current Pulse Electrodeposition

Abstract Ag-Bi alloy films containing less than 1 mass% Bi were produced using an iodide-tartrate bath without cyanide ions by electrodeposition. Such films could have applications as electrical connectors in quick chargers intended for electric vehicles. The electrodeposition characteristics of these alloys were studied by electrochemical measurements in conjunction with both direct current (DC) and current pulse (CP) plating. The waveform associated with the CP plating incorporated both low and high current densities. The electrodeposition potential of Bi was found to be more negative than that of Ag and the electrodeposition of Bi on Ag was evidently inhibited compared with that on Bi. Aeration increased the limiting current density during the electrodeposition of the Ag-Bi alloys. Alloy specimens having powder morphologies could be electrodeposited using the DC plating process while CP plating generated films. Optimization of the waveform gave Ag-Bi alloy films containing less than 1 mass% Bi and having a maximum hardness of 102 HV.

Synergetic Effect of FeTi in Enhancing the Hydrogen-Storage Kinetics of Nanocrystalline MgH2

High-energy ball milling was applied to produce nanocrystalline MgH2-FeTi powder composites. In order to achieve a remarkable synergetic effect between the two materials, the amount of the FeTi catalyst was chosen to be 40 wt.%, 50 wt.% and 60 wt.%. The morphology and microstructure of the as-milled powders were characterized by scanning electron microscopy and X-ray diffraction, respectively. The evaluation of the diffraction profiles by the Convolutional Multiple Whole Profile fitting algorithm provided a detailed microstructural characterization of the coherently scattering α-MgH2 crystallites. Differential scanning calorimetry experiments revealed two overlapping endotherms corresponding to the dehydrogenation of metastable γ-MgH2 and stable α-MgH2 hydrides. Isothermal hydrogen-sorption experiments were carried out in a Sieverts-type apparatus. It was established that the MgH2-40 wt.% FeTi powder is capable of absorbing 5.8 wt.% hydrogen, while extraordinary absorption kinetics were observed for the MgH2-50 wt.% FeTi alloy, i.e., 3.3 wt.% H2 is absorbed after 100 s.

Influence of Selected Compositions of Wall Materials and Drying Techniques Used for Encapsulation of Linseed Oil and Its Ethyl Esters

The aim of the study was to compare the encapsulation of linseed oil and its ethyl esters using two coating materials (maltodextrin with whey protein concentrate (WPC) vs. maltodextrin with gum arabic) and two drying methods (spray-drying vs. freeze-drying) to obtain powders with the highest oxidative stability. A comparison was made based on the properties of emulsions (morphology, particle size distribution, and stability) and powders (morphology, physicochemical properties, fatty acid composition, and oxidative stability). The powder’s oxidative stability was determined based on the Rancimat protocol. The most uniform distribution of oil droplets in prepared emulsions was stated for ethyl esters in a mixture of maltodextrin and gum arabic. Emulsions with WPC had a bimodal character, while those with gum arabic had a monomodal character. Gum arabic promoted emulsion stability, while in samples containing WPC, sedimentation and creaming processes were more visible. Powders obtained using spray-drying had a spherical shape, while those obtained by freeze-drying were similar to flakes. Although encapsulation efficiency was the highest for freeze-dried powders made of linseed ethyl esters with gum arabic, the highest oxidative stability was stated for powders made by spray-drying with WPC as wall material (independently of linseed sample form). These powders can be easily applied to various food matrices, increasing the share of valuable α-linolenic acid.

Effects of gas pressure and catheter length on the breakup of discontinuous NiTi droplets in electrode induction melting gas atomization

NiTi powders used for selective laser melting have here been fabricated by the breakup of discontinuous droplets in electrode induction melting gas atomization (EIGA). The morphology, particle size distribution, and hollow ratio of the powder were characterized by scanning electron microscopy (SEM), laser particle size analyzer, and computed tomography (CT), respectively. The effects of gas pressure and catheter length on the particle size distribution and powder morphology were then studied. Furthermore, the effects of the classifier wheel speed on the particle size distribution and yield of the 15–53 μm powder in the classification process were also analyzed. The results showed that the average particle size (D50) of the NiTi powder first decreased and, thereafter, increased as the atomization gas pressure increased. This was also the situation with catheter length. Also, the yield of the 15–53 μm powder increased with an increase in the classifier wheel speed. The optimum parameters were a gas atomization pressure of 5 MPa, a tension length of 28 mm, and a classifier wheel speed of 660 r min−1. For this optimized condition, the D50 value and the yield of the NiTi powder were 57.54 μm and 46.4%. In addition, the flowability, hollow ratio, and oxygen content were 15.8 s/50 g, 0.31%, and 450 ppm, respectively.

Milling Processing, Morphology, and Optical Characterization of Powders from Natural Pigments as a Potential Sensitizing Material for Optical Sensors and Dye-Sensitized Solar Cells

Dye-Sensitized Solar Cells (DSSC) and optical fiber-based-sensors sensitized with organic dyes play a fundamental role in modern technology, particularly in the family of photovoltaic power generation devices and measurement of chemical variables. DSSC is low-cost, highly efficient, and easy to manufacture. Therefore, they are a suitable option for many engineering applications. This paper deals with natural pigment extraction (spirulina, carrots (beta-carotene), and beetroot) at different milling and temperature conditions. Nanoparticles were fabricated using an SPEX mill and a planetary ball mill. The particle size distribution, absorbance (UV-Vis), and powder morphology were obtained using Field Emission Scanning Electron Microscopy (FESEM). Herein, the optical characterization of modified TiO2 powder at different temperatures and milling conditions is performed. Results indicate that each natural dye is sensitive to operational temperature. In addition, the absorbance of the pigments is affected by milling conditions and particle size distribution. During SEM characterization, rounded particles were observed in the starting materials with average sizes of more than 15 microns in diameter until they were reduced to nanometer ranges close to 100 using SPEX milling. The observed absorption spectra range from 400nm to 642 nm for spirulina. Moreover, the experimental results show that the intensity of the absorption peaks is affected by the temperature, which indicates a degradation of the dye. Therefore, different combinations of natural dyes will be feasible to improve the wide range of light absorption of the visible spectra and stability of DSSCs and optical fiber-based sensors.

The effect of chemical composition and heat parameter on Nano-sized precipitate dispersion characterization in ODS steels

Oxide dispersion strengthened (ODS) supersaturated solid solution alloy powders with different Y/Ti atomic ratios were formed by mechanical alloying (MA) method and then heat treated under different conditions. The morphology, phase composition, and particle size distribution were researched. The precipitate distribution densities and hardness values of alloy powders after heat treatment were measured at the same time by the SAXS method and hard tester. The results show that the morphology of MA alloy powders is irregular in shape and only a small amount of MA alloy powders is bigger than 30 μm. During the MA process, alloy elements are solid solutions in the matrix. The work-harden effect of alloy powders formed in the MA process would be eliminated during the heat treatment process. The chemical composition and heat treatment parameters are crucial effects on nano-sized precipitate distribution characterization in ODS steels. The ODS sample with a Y/Ti atomic ratio of 0.99 has the highest distribution density of oxide precipitates at 1.89×1022/m3 resulting in the highest hardness value during the heat treatment process. The sample with a Y/Ti atomic ratio of 0.42 has the highest distribution density of nanoclusters 7.32×1023/m3.

Studies on activity and oxide shell thickness of micron-sized Mg-Al alloy powder

The empirical formula of average oxide thickness of atomized micron-sized aluminum - magnesium alloy powder was proposed. At the same time, the influence of particle size and the ratio of magnesium on samples’ activity was studied. The phase composition, morphology, and oxidation process of the alloy powders were studied by x-ray diffraction, scanning electron microscope/energy-dispersive x-ray, respectively. Study on the change of powder activity was achieved by standard gas volumn method. The results show that the oxide thickness of the atomized micron-sized aluminum - magnesium alloy powder is positively correlated with the particle size, and the activity decreases with the increase of the particle size and the magnesium content.

Powder degradation as a consequence of laser interaction: A study of SS 316L powder reuse on the laser directed energy deposition process

The feedstock capture efficiency on powder laser directed energy deposition (L-DED) is becoming a big challenge in the industrial use of the L-DED process for the manufacturing of large-scale AM parts. The powder capture efficiency is dependent on process optimization and the toolpath. The current literature presents a vast range of usual powder efficiency, between 3% and 32% and in some specific cases exceeding 90%. In L-DED, the powder-gas jet stream interacts with the laser beam adding material locally onto the substrate. Part of this material is captured by the melt pool. The not captured material that is affected by the laser beam suffers degradation. In the literature, there is a lack of studies related to powder reuse in the L-DED process. This paper presents a comprehensive study on the consequence of laser interaction with SS 316L metal powder particles during the L-DED process using a range of different powder characterization techniques to assess the powder morphology, size distribution, chemical composition, followability, and density. The study was conducted within eight powder reuse cycles, without adding virgin material to the powder batch. Reduction of particle size distribution range, increase in circularity, and improvement in the powder flowability were identified as consequences of powder reuse. The result of laser interaction with particles was further explored by scanning electron microscopy, presenting the continuous modification of the particles across the eight reuse cycles. The oxygen content on the particles was also measured to access the O2 pick-up as a consequence of particle heating.

High-performance thermoelectric properties of Cu2Se fabricated via cold sintering process

The concept of a ‘phonon-liquid electron-crystal’ has received significant interest in recent years, with copper selenide (Cu2Se) emerging as one of the high-performance thermoelectric materials within this framework. This study focuses on the fabrication of Cu2Se bulk pellets through a low-temperature sintering method known as cold sintering process (CSP). The introduction of a liquid phase (thiol-amine solution) in this process facilitates the dissolution and precipitation of ion/atom clusters, resulting in sample densification. Remarkably, a sample density of nearly 90 % is achieved at a low sintering temperature of only 473 K. Furthermore, this CSP approach preserves the morphology of the Cu2Se precursor powders and effectively inhibits grain growth. Consequently, the lattice thermal conductivity of the CSP samples is significantly reduced, attributed to enhanced grain boundary phonon scattering. This leads to a substantial improvement in the figure-of-merit (ZT), increasing from 0.65 at 800 K in the hot-pressed sample to 2.13 at 800 K in the CSP sample. The advantages of CSP can be extended beyond Cu2Se, as it holds promise for enhancing the performance of various high-performance thermoelectric materials.

Effect of Milling Time and Reinforcement Volume Fraction on Microstructure and Mechanical Properties of SiCp-Reinforced AA2017 Composite Powder Produced by High-Energy Ball Milling.

The influence of milling time and volume fraction of reinforcement on the morphology, microstructure, and mechanical behaviors of SiCp-reinforced AA2017 composite powder produced by high-energy ball milling (HEBM) was investigated. AA2017 + SiCp composite powder with different amounts of SiC particles (5, 10, and 15 vol%) was successfully prepared from gas-atomized AA2017 aluminum alloy powder with a particle size of <100 μm and silicon carbide (SiC) powder particles with an average particle size of <1 μm. An optical microscope (OM), X-ray diffraction (XRD), and scanning electron microscope (SEM) were utilized to characterize the microstructure of the milled composite powder at different milling periods. The results indicated that the SiC particles were homogeneously distributed in the AA2017 matrix after 5 h of HEBM time. The morphology of the particles transformed from a laminar to a nearly spherical shape, and the size of the milled powder particles reduced with increasing the content of SiC particles. The XRD analysis was carried out to characterize the phase constituents, crystallite size, and lattice strain of the composite powders at different milling periods. It was found that with increasing milling time and SiC volume fraction, the crystallite size of the aluminum alloy matrix decreased while the lattice strain increased. The average crystallite sizes were reduced from >300 nm to 68 nm, 64 nm, and 64 nm after 5 h of milling, corresponding to SiC contents of 5, 10, and 15 vol%, respectively. As a result, the lattice strain increased from 0.15% to 0.5%, which is due to significant plastic deformation during the ball milling process. XRD results showed a rapid decrease in crystallite size during the early milling phase, and the minimum grain size was achieved at a higher volume fraction of SiC particles. Microhardness tests revealed that the milling time has a greater influence on the hardness than the amount of SiC reinforcements. Therefore, the composite powder milled for 5 h showed an average microhardness three times higher than that of the unmilled powder particles.

Study on the Changes of Bone Calcium during the Fermentation of Bone Powders with Different Fermenters.

Two fermenters, Lactobacillus acidophilus (LA) and the active dry yellow wine yeast (HY), were utilized to ferment cattle bones in order to release calcium. The influences of fermenters and the fermentation process on the calcium release capacity, particle properties, morphology, and chemical composition of bone powders were assessed, and the underlying mechanism was discussed. The results showed that LA had a better capacity of acid production than yeast, and therefore released more calcium during the fermentation of bone powders. The released calcium in the fermentation broth mainly existed in the forms of free Ca2+ ions, organic acid-bound calcium and a small amount of calcium-peptide chelate. For bone powders, the fermentation induced swollen bone particles, increased particle size, and significant changes of the internal chemical structure. Therefore, fermentation has a great potential in the processing of bone-derived products, particularly to provide new ideas for the development of calcium supplement products.

Analysis of the Particle Size and Morphology of Tin Powder Synthesized by the Electrolytic Method.

This article discusses the effect of electrolysis parameters on the particle size and morphology of the tin powder synthesized by the electrolytic method. The electrolytic method is simple and can eliminate the risk of lead and arsenic gas emissions owing to the low temperature of the process. The effects of tin concentration in a sulfate-based electrolyte, a mass ratio of thiourea/gelatin as additives, current density, and electrolysis time on the particle size and morphology of the synthesized tin powder were examined. Pure tin and titanium plates were used as the anode and the cathode, respectively. After the electrolysis experiments were completed, the synthesized tin powders were analyzed by a particle size analyzer, a scanning electron microscope, and X-ray diffraction. The optimum condition of the experiment that resulted in the highest D90 was achieved at an initial concentration of SnSO4 = 3 g/L, a mass ratio of thiourea/gelatin = 1/4, a current density of 1 A/dm2, and a 10 min electrolysis time. Under this condition, 90% of the tin powder size obtained was smaller than 2.279 μm, showing a rounded morphology with a length-to-width ratio of 1.15. The current efficiency increased with increasing tin concentration, decreasing current density, and a shorter electrolysis time.

Effects of powder morphology on stereolithography additive manufactured Al2O3 ceramic

The digital light processing (DLP) for the preparation of alumina ceramics (Al2O3) is characterized by high molding accuracy and fast rates, making it show great promise for applications in high-end ceramic manufacturing. However, its forming process is greatly influenced by the photosensitive slurry. Although a large number of studies have been conducted to investigate the influence of different variables of the slurry on photo curing, the mechanism of the influence of the powder morphology of the Al2O3 raw material is still unclear. In this study, two kinds of slurry were prepared from spherical and laminated Al2O3 powders and DLP was carried out. The results showed that some of the spherical Al2O3 powder would break down after ball milling, resulting in a reduced flow-ability of the slurry. The relative density of the ceramic was 91.1 % and strength was 92.1 MPa. In contrast, the laminated Al2O3 could be oriented in the flow direction during flow, showing a lower viscosity. At the same time, the orientation allowed the lamellar powder to build up more tightly. The relative density of the ceramic was 93.2 % and strength was 165.5 MPa.

Effect of heat treatment on the particle size, shape and morphology of uranium deuteride powder

The influence of heat treatment on the geometric properties of UD3 powder (particles shape, size distribution and morphology) during hydriding-dehydriding were investigated. >95% of the UD3 particles synthesized by once hydriding of uranium were composed of primary particles not exceeding 38 μm. About 63% of primary particles had aspect ratios between 1.4–2.2. Particles prepared under heating conditions exhibited smooth surfaces and columnar structures on their sides. As the starting temperature of hydriding reaction decreased, the proportion of fine particles (<10 μm) in the powder increased. During the deuterium absorption-desorption, primary particles gradually broke down into small particles, which further adhered and aggregated into agglomerates by heat treatment. Agglomerates were consisted of cauliflower-like clusters, and their growth were random and non-oriented. The primary particles and/or agglomerates with aspect ratios between 1.4–2.2 always accounted for about 63%. Agglomerates exceeding 38 μm in multiple thermal cycles were very rare.

Synergetic effect of particle shape and multi-layer coating on the magnetic properties of FeSiAl-based soft magnetic composites

Gas atomization and multi-layer coating are widely used powder fabrication techniques to prepare soft magnetic composites (SMCs) utilized in high-power low-loss power electronics. However, the diverse morphologies of gas-atomized powders significantly impact coating effectiveness, subsequently influencing the soft magnetic properties of SMCs. Herein, FeSiAl-based SMCs with different particle shapes and a multi-layer coating of phosphate and heat-resistant silicone resin are prepared to explore the synergetic effects of particle shape and coating on magnetic performances. Compared with dumbbell-shaped powder, the spherical powder has a regular shape and strong flowability, resulting in a close-packing structure of the magnetic core. The spherical particle with a large specific surface area promotes efficient insulation coating effects. The dumbbell-shaped particles are potentially prone to cause pores and defects during the high-pressure compaction process, leading to poor dense packing and magnetic loss performance. With a similar average particle size, the magnetic core prepared by spherical powders exhibits a larger interface area, resulting in a greater demagnetizing field after phosphating passivation, thus significantly improving the DC-bias performance. The FeSiAl-based magnetic core prepared by spherical powders with 1.5 wt% phosphoric acid passivation has better magnetic loss and DC-bias properties than that by dumbbell-shaped powders, showing a stable permeability of 60.4, core loss of 286.2 mW/cm3 at 100 mT, 100 kHz, and DC bias characteristic of 49.1 % at a DC superposition field of 100 Oe.

Factors affecting particle characterization of powders used in additive manufacturing

The present study analyze the effects of sample preparation and data analysis techniques for different experimental methods of metal powder characterization. The aim is to propose a robust strategy for quantifying powder particle size distribution and morphology of relevance for metal additive manufacturing (MAM) processes, in particular for powders with nearly spherical particle shape. Laser diffraction (LD), scanning electron microscopy (SEM) and high-resolution X-ray computed tomography (XCT) are used to analyze three different stainless-steel 316L powders. The results obtained demonstrate that the powder sample itself and the sample preparation, both have a significant effect on the obtained values. For the imaging processing methods, the post-processing route is an important part of the characterization and strongly affects the results. However, proper sample preparation is shown to ease this post-processing. Given the high sphericity of the powders used, it is shown that 2D and 3D methods generally lead to the same result when the 2D data are properly transformed to 3D space. Guidelines to overcome the shortcomings of the different techniques are suggested.