Powder Chemistry Research Articles

Effects of phosphatization on the mineralogical and geochemical composition of marine ferromanganese crusts from the JiaXie Guyot in the Western Pacific: Constraints from high resolution analysis

The marine crusts comprise ferromanganese sediments formed through the precipitation of dissolved elements in seawater. These crusts serve as a record elements signal from paleo-ocean and are extensively utilized in paleo-oceanography. Previous researches have examined the chemical composition of the phosphatized crust layers using powder chemistry and leaching experiments. However, there exist divergent viewpoints regarding the influence of phosphatization on element behavior. In this study, we employed a combination of analytical techniques including scanning electron microscope (SEM), powder X-ray diffractometer (XRD), TESCAN Integrated Mineral Analyzer (TIMA), laser ablation and inductively coupled plasma time of flight mass spectrometry combined system (LA-ICP-TOF), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These methods were utilized to achieve mineral phase quantification, precise depiction of element distribution, and in-situ profile analysis of elements within the phosphatized crust layers from the JiaXie Guyot in the Western Pacific. The mineral phase analysis shows enormous carbonate fluorapatite (CFA) precipitate, which replace calcite in the old phosphatized layer. Additionally, vernadite experiences partial dissolution. Furthermore, a small amount of hematite, goethite, todorokite, zeolite, barite, as well as trace amounts chalcopyrite, sphalerite, galena, ilmenite, and pyrite are formed. The element distributions suggest potential outward migration of Fe, V, Zr, Zn and Cu, while Ce and Pb are locally enriched. In the phosphatized crust, some elements exhibit depletion in the old crust layer compared to the young crust layer, with Fe > Si > V>Zn > Ti ≥ Pb, while others are enriched in the order crust layer, such as Y>Pd > Ce > Pt. The study proposes that FeOOH·nH2O and associated adsorbed elements like Si, Ce, Y, V, Zn, Ti and Pb dissolve in vernadite and migrate outward during phosphatization, with weak phosphatization influence on Mn oxide. In addition, the phosphate-rich seawater might contribute additional elements such as Y, Ce and Pd to the crust layers. Thus, this study highlights the elemental distributions, migration patterns observed, and significance of presence for critical metals between old and young crust layers from the influence of phosphatization based on high resolution analysis. Particularly, it acknowledges the contribution of phosphate-rich seawater to the elemental composition of crust layers.

Reduction in Powder Wall Friction by an a-C:H:Si Film

The wall friction angle is an important parameter in powder flow. In a recent study for various powders, a reduction in the wall friction angle for steel was demonstrated by the application of an a-C:H:Si film on the steel surface. This work presents the results of a study of this effect in more detail regarding the influence of the powder material, the wall normal stress and the particle size of the powder for mass median diameters from 4 µm to approximately 150 µm. The wall friction angles were measured using a Schulze ring shear tester for three different powder materials: aluminum oxide, calcium carbonate and silicon carbide. The results showed little difference with respect to powder chemistry. For the coarser powders, the reduction in the wall friction angle due to the a-C:H:Si coating was highest (10° to 12°) and rather stress-independent, while for the fine and medium-size powders the reduction was lower and stress-dependent. With increasing wall normal stress, the reduction in the wall friction angle increased. These results can be explained by the friction reduction mechanism of a-C:H:Si, which requires a certain contact pressure for superficial graphitization.

Crystal size, a key character of lactose crystallization affecting microstructure, surface chemistry and reconstitution of milk powder

Lactose crystallization during storage deteriorates reconstitution performance of milk powders, but the relationship between lactose crystallization and reconstitution is inexplicit. The objective of this study is to characterize crystalline lactose in the context of formulation and elucidate the complex relationship between lactose crystallization and powder functionality. Lactose in Skim Milk Powder (SMP), Whole Milk Powder (WMP) and Fat-Filled Milk Powder (FFMP) stored under 23 %, 53 % and 75 % Relative Humidity (RH) at 25 ℃ for four months was compared. Lactose, surface chemistry and microstructure of FFMP stored at 25 ℃ and 40 ℃ at 23 % to 75 % RH for four months were also analyzed and interpreted. At the same RH, FFMP crystallized in the same pattern as WMP. At 53 % RH, FFMP and WMP differentiated from SMP in terms of lactose morphology as well as the ratio between anhydrous α-lactose and anhydrous β-lactose. Lactose remained amorphous at 23 % RH, crystallized predominantly to α/β-lactose (1:4) at 40 to 58 % RH and to α-lactose monohydrate at 75 % RH. The crystallinity index was similar for all powders containing crystalline lactose. The estimated crystallite size increased from approx. 0.1 to 20 µm with increasing RH and temperature. When amorphous lactose crystallized into crystals below approx. 0.1 µm at 25 °C and 43 % RH, the microstructure and surface lipid were comparable to that of the reference powder. This powder reconstituted into a stable suspension system comparable to that of reference (well performing) powders. These results demonstrate that crystallite size is the key property linking lactose crystallization and reconstitution. Our finding thus indicates limiting crystallite size is important for maintaining desired product quality.

Evaluation of a laser powder bed fusion designer Al-Mg-Zr-Si alloy for cold spray additive manufacturing

Metal additive manufacturing (AM) is a constantly developing approach utilized in many novel applications. Most metal AM techniques utilize alloys designed for traditional processing conditions, such as casting, whereas implementing alloys designed for AM may prove useful. Given the proven utility of the Al-Mg-Zr-Si Addalloy 5T® in melt-driven AM, this study investigated the use of this alloy in cold spray (CS), as minimal research has explored alloy design for use in solid-state processing. The as-atomized powder and CS samples were evaluated microstructurally and mechanically to determine suitability for CS. Premature brittle fracture were seen in the deposits, necessitating processing improvements for enhanced deposit performance. Feedstock thermal pre-processing was explored, guided by thermodynamic modeling, to improve spray-ability. Heat treatments resulted in generalized powder softening, suggesting improved processability using a CS gas-particle dynamics model. This model allowed for theoretical tuning of processing parameters, predicting improved deposition using a specific configuration with He gas. The through-process model-informed experimental approach emphasizes the potential of using Addalloy 5T® powder in CS when coupling heat treatment with processing parameter optimization. Results suggest that the CS community may benefit from alloy design specifically for solid-state processing, tailoring powder chemistry and microstructure for enhanced properties and processability.

Plasma spheroidization of gas-atomized 304L stainless steel powder for laser powder bed fusion process

Particles of AISI 304L stainless steel powder were spheroidized by the induction plasma spheroidization process (TekSphero-15 spheroidization system) to assess the effects of the spheroidization process on powder and part properties. The morphology of both as-received and spheroidized powders was characterized by measuring particle size and shape distribution. The chemistry of powders was studied using inductively coupled plasma optical emission spectroscopy for evaluation of composing elements, and the powder’s microstructure was assessed by X-ray diffraction for phase identification and by electron backscattered diffraction patterns for crystallography characterization. The Revolution Powder Analyzer was used to quantify powder flowability. The mechanical properties of parts fabricated with as-received and spheroidized powders using laser powder bed fusion process were measured and compared. Our experimental results showed that the fabricated parts with plasma spheroidized powder have lower tensile strength but higher ductility. Considerable changes in powder chemistry and microstructure were observed due to the change in solidification mode after the spheroidization process. The spheroidized powder solidified in the austenite-toferrite solidification mode due to the loss of carbon, nitrogen, and oxygen. In contrast, the as-received powder solidified in the ferrite-to-austenite solidification mode. This change in solidification mode impacted the components made with spheroidized powder to have lower tensile strength but higher ductility.

Chemical recovery of spent copper powder in laser powder bed fusion

In laser powder bed fusion (LPBF), recovered unfused powder from the powder bed often degrades upon sequential processing through mechanisms like thermal oxidation and particle satelliting from ejected weld spatters and particle-laser interactions. Given the sensitivity of LPBF performance and build quality to powder properties, spent powder is generally discarded after a few build cycles, especially for materials that are sensitive towards surface oxidation. This increases feedstock material costs, as well as costs associated with machine downtime during powder replacement. Here, a new method to chemically reprocess spent LPBF metal powder is demonstrated under ambient conditions, using a heavily oxidised Cu powder feedstock recovered from prior LPBF processing as a model material. This is compared to an equivalent virgin Cu powder. The near-surface powder chemistry has been analysed, and it is shown that surface oxide layers present on spent Cu powder can be effectively reset after rapid reprocessing (from 5 to 20 min). Diffuse reflectance changes on etching, reducing for gas-atomised virgin Cu powder due to the formation of anisotropic etch facets, and increasing for heavily oxidised spent Cu as the highly absorptive oxide layers are removed. The mechanism of powder degradation for moisture sensitive materials like Cu has been correlated to the degradation of LPBF deposits, which manifests as widespread and extensive porosity. This extensive porosity is largely eliminated after reprocessing the spent Cu powder. Chemically etched spent powder is therefore demonstrated as a practical feedstock in LPBF in which track density produced is comparable to virgin powder.

Copper-catalyzed decarboxylative Se insertion coupling of indoles and propiolic acids

A novel and efficient copper-catalyzed decarboxylative alkynylselenation of indoles with Se powder and propiolic acids has been developed. The outstanding advantages of this protocol not only nicely avoid the use of prefabricated arylselenation reagent and address the facile over-selention issues, but also enrich the chemistry of selenium powder. Importantly, this reaction could be extended to pyrrole, and the practical utility of this transformation has been demonstrated in gram-scale synthesis and late-stage indolylselenation of Clofibrate-derived propiolic acid.

Sintering anisotropy of binder jetted 316L stainless steel: part II – microstructure evolution during sintering

ABSTRACT Green density of binder jetted parts are typically equal or lower than the powder tap density. Also, anisotropic green porosity distribution is expected because of the characteristics of the binder jetting (BJ) printing process. In this study, the microstructure evolution in terms of phases and porosity characteristics was studied. A transition from irregular-shape interconnected porosity in pre-sintered samples to closed quasi-spherical porosity for samples sintered at 1370°C was observed. EBSD phase map showed ∼2.73% of δ-ferrite in sample sintered at 1370°C. The anisotropic porosity distribution was revealed by a higher area fraction of aligned large pores (>35 µm), within the cross-section perpendicular to the building direction. Chemical analysis showed an increase of C, O and N on the green sample, while a strong decrease was found after sintering when compared with the powder chemistry. δ-ferrite onset, from phase equilibrium calculations, varies from ∼1250°C (sintered sample chemistry) to ∼1350°C (powder chemistry).

Yttrium for the selective laser melting of Ti-45Al-8Nb intermetallic: Powder surface structure, laser absorptivity, and printability

High Nb-TiAl alloys are important materials to realize critical, light-weight parts of high-temperature applications. It has been challenging, however, to realize their laser-based additive manufacturing (AM) due to the materials’ high crack sensitivity. To mitigate the cracking problem particularly relating to oxygen, this study is designed to investigate the impact of introduced rare earth element (Y) on the microstructure, surface chemistry, and laser absorptivity of gas-atomized Ti-45Al-8Nb powder, and consequently on the printability of the alloy regarding its selective laser melting (SLM). It is observed that the Y addition significantly improves the SLM printability of the alloy and realizes samples that are free of macrocracks. The change in the surface structure of the powder is regarded as a critical factor contributing to improved printability. The corresponding chemical state and layer thickness of the oxide film covering the powder are determined by X-ray photoelectron spectroscopy (XPS) depth profile and transmission electron microscopy (TEM). It is further found that the surface structure of the powder leads to a higher laser absorption. As suggested by the study, modification of powder chemistry and powder surface structure by rare earth elements can be an effective means to improve the SLM formability of crack-sensitive materials.

Spatiotemporal and emission characteristics of laser-induced plasmas from aluminum-zirconium composite powders

Laser-induced plasmas and reactions therein depend on the ablated target's chemical composition and morphology. Recently, we have characterized plasma properties such as spatiotemporal morphology, electron density, species temperature within the plasma, ionization degree, etc. for pure Al under variations in morphology. Here, we utilize a bi-metal powder system to study similar characteristics as a function of powder chemistry. Micron-sized ball milled Al/Zr composites of three chemistries (3Al:2Zr, Al:Zr, and Al:3Zr) are compared to similarly-sized pure Al, pure Zr, and a mixture of Al + Zr powder. We find that the introduction of increasing concentrations of Zr has several interesting effects on the plasma compared to pure Al, including a dramatic increase in the electron density (to ~3–5 × 1020 cm−3), and the earlier onset of ZrO emission bands which have a higher disassociation energy and are thermodynamically preferred over AlO at high temperatures. Differences in plume morphology, the spatial distribution of molecular species, and the emission intensities of ZrO, Zr I and Al I were observed for Al + Zr and ball-milled Al:Zr samples, indicating the influence of microstructure on the chemical reactions. We measured plasma temperatures using the Saha-Boltzmann plot method; the composites demonstrate higher temperatures than pure Zr, Al + Zr mixtures, and pure Al. We observe only minor differences in temperature as a function of increasing Zr-content within the composites. This work continues to build on our understanding of the relationships between plasma properties and microsecond-timescale chemical reactions of reactive materials.

A process for fabrication of Li2TiO3 ceramic pebbles with high mechanical properties via non-hydrolytic sol-gel method

In this paper, the single-phase Li2TiO3 powder was successfully synthesized via non-hydrolytic sol-gel method (NHSG) using anhydrous lithium acetate (LiOAc) as lithium source and tetrabutyl titanate (TBOT) as titanium source. The effects of the temperature and the Li/Ti molar ratio on the synthesis of Li2TiO3 were investigated by XRD. FT-IR and XPS were used to characterize the synthesis mechanism and surface chemistry of Li2TiO3 powder heated at 650 °C for 2 h with 5 °C/min. Furthermore, the Li2TiO3 pebbles were successfully prepared using synthesized powder by indirect wet chemistry method. The results showed that the Li2TiO3 pebbles with diameter of 1.3mm–1.5 mm, crush load of 67 N, sphericity of 0.97, the relative density of 84.9%, the grain size of 2.85 μm and porosity of 19.84% were successfully fabricated when sintering temperature was 1050 °C for 2 h in air. Therefore，the NHSG method could provide a new efficient route for the production of Li2TiO3 ceramic pebbles.

Evolution of surface chemistry during sintering of water‐atomized iron and low‐alloyed steel powder

Water‐atomized iron and steel powder is commonly used as the base material for powder metallurgy (PM) of ferrous components. The powder surface chemistry is characterized by a thin surface oxide layer and more thermodynamically stable oxide particulates whose extent, distribution, and composition change during the sintering cycle due to a complex set of oxidation–reduction reactions. In this study, the surface chemistry of iron and steel powder was investigated by combined surface and thermal analysis. The progressive reduction of oxides was studied using model sintering cycles in hydrogen atmospheres in a thermogravimetric (TG) setup, with experiments ended at intermediate steps (500–1300°C) of the heating stage. The surface chemistry of the samples was then investigated by means of X‐ray photoelectron spectroscopy (XPS) to reveal changes that occurred during heating. The results show that reduction of the surface oxide layer occurs at relatively lower temperature for the steel powder, attributed to an influence of chromium, which is supported by a strong increase in Cr content immediately after oxide layer reduction. The reduction of the stable oxide particulates was shifted to higher temperatures, reflecting their higher thermodynamic stability. A complementary vacuum annealing treatment at 800°C was performed in a furnace directly connected to the XPS instrument allowing for sample transfer in vacuum. The results showed that Fe oxides were completely reduced, with segregation and growth of Cr and Mn oxides on the particle surfaces. This underlines the sequential reduction of oxides during sintering that reflects the thermodynamic stability and availability of oxide‐forming elements.

A Statistical Analysis of Powder Flowability in Metal Additive Manufacturing

The quality of parts fabricated with additive manufacturing is influenced by the flowability of the feedstock particles, which is the result of many factors, including chemistry (e.g., true density, the presence of surface oxides, and impurities), morphology (e.g., particle shape and the presence of satellites), and particle size distribution. This work investigates the relationship between powder characteristics and flow behavior of different powders using three flowability testing methods. Six powders of two compositions (316L stainless steel and AlSi10Mg), made using two different methods (gas‐ and water‐atomization), are investigated to rationalize the effect of powder chemistry and morphology on flow behavior. The results show that the true density of the powders can influence several flowability metrics. In addition, aspect ratio strongly influences the initiation of flow from a static condition, whereas average particle size strongly dictates the ease of maintaining that flow.

Baking Powder Chemistry

Baking Powder Chemistry

Mechanically activated combustion synthesis of Fe3Al composite powders reinforced with sub-micrometer TiC particles

The aim of this work was to develop a process to synthesize Fe3Al matrix composite reinforced with nano scale TiC particles from pure elemental powders as reactants, employing combustion synthesis. The effects of particle size, pre-milling time of precursors on ignition temperature and final powder microstructure were studied. The synthesized composite powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDX). The targeted powder chemistry, microstructure and optimum spatial distribution of TiC particles were obtained using a pre-milling time of 30 min and a furnace temperature of 1100 °C. Powders synthesized in this condition contained only Fe3Al and TiC phases. Because of its high hardness and the presence of nanosized reinforcements, this composite powder can be considered a good candidate for thermal spray applications in manufacturing wear resistant parts.

Powder chemistry effects on the sintering of MgO‐doped specialty Al2O3

AbstractIn this work, we investigate the effects of powder chemistry on the sintering of MgO‐doped specialty alumina. The stages at which MgO influences densification of Al2O3 were identified by comparing dilatometry measurements and the sintering kinetics of MgO‐free and MgO‐doped specialty alumina powders. MgO is observed to reduce the grain boundary thickness during densification using TEM. We show that MgO increases the solubility of SiO2 in alumina grains near the boundaries using EDS. First‐principles DFT calculations demonstrate that the co‐dissolution of MgO and SiO2 in alumina is thermodynamically favored over the dissolution of MgO or SiO2 individually in alumina. This study experimentally demonstrates for the first time that removal of SiO2 from the grain boundaries is a key process by which MgO enhances the sintering of alumina.

A critique of master sintering curve analysis

In this work, we explore factors affecting the accuracy of the master sintering curve (MSC) approach for analyzing the complete sintering profile of ceramic powders. We show that the instantaneous anisotropic shrinkage must be accounted for to develop an accurate MSC. The MSC diverges at >90% density because of basic assumptions that oversimplify the analysis of the densification process. We also show that powder chemistry and forming techniques can affect the fitting parameter Q. Q should not be interpreted as the sintering activation energy, or used to interpret mechanistic differences since it is comprised of several mechanisms that influence densification throughout the sintering cycle. Despite these limitations, the MSC is a useful and practical tool for predicting thermal load (i.e. time and temperature) effects on the densification of a ceramic part fabricated from a singular powder that is fabricated by a singular forming process.

Effect of chemistry on martensitic phase transformation kinetics and resulting properties of additively manufactured stainless steel

Here we investigate the effect of chemistry, including initial powder chemistry and spatial chemical variations due to vaporization during fabrication, on strain-induced martensitic phase transformation in 304L stainless steel components fabricated by directed energy deposition (DED) additive manufacturing (AM). The austenite stability was altered by mixing pre-alloyed 304L stainless steel powder with Fe powder, which promoted martensitic phase transformation and resulted in an increase in ultimate tensile strength and elongation to failure over pure 304L walls deposited by DED AM. The chemical composition variation with position, due to spatial variations in thermal history, was quantified, showing that austenite stabilizing elements Cr, Mn, and Ni were preferentially vaporized during deposition. We present a martensitic transformation kinetics equation that describes the evolution of martensite volume fraction with respect to plastic strain as a function of chemistry. This allows for the prediction of strain-induced martensite evolution as a function of strain, nominal chemistry, and heterogeneous chemistry due to vaporization within additively manufactured components.

Induction Plasma Technology Applied to Powder Manufacturing: Example of Titanium-Based Materials

Powder metallurgy technologies require specific powders to ensure a good quality to the manufactured parts. The critical properties are; the powder chemistry, flow ability, packing density, and the absence of porosity. This review highlights the capability of Tekna’s Inductively Coupled Plasma (ICP) technology for the production of high quality powders for the additive manufacturing industry.

Synthesis and Characterization of Hydrophilic and Semiconductor Cadmium Chromite Nanostructures

Cadmium chromite nanostructures were synthesized in high yield by a simple co-precipitation method. CdCr2O4 nanostructures have been achieved using cadmium nitrate tetrahydrate and CrCl3·6H2O as precursors by a co-precipitation method. The effects of various parameters including alkaline agent, pH value, reaction temperature, and surfactant type were investigated to discover the optimum conditions, and it was found that the size and morphology of products can be affected by these parameters. The structure, morphology and surface chemistry of CdCr2O4 powder were investigated by x-ray diffraction, scanning electron microscopy and energy dispersive x-ray spectroscopy. X-ray diffraction patterns indicated the chromite spinel phase with good crystallinity and an average crystallite size of approximately 20 nm. The hydrophilicity of the calcined oxides was investigated by wetting experiments and the sessile drop technique which were carried out at room temperature in air to determine the surface and interfacial interactions.