Influence Of Powder Properties Research Articles

Influence of powder properties and mixing technique under different conditions, on the densification and thermal conductivity of AlN for solar thermal applications

In this study, a novel approach is presented which can be utilized to enhance the thermal conductivity and densification of sintered AlN pellets. AlN pellets with a CaO additive were produced by spark plasma sintering. The influence of CaO powder properties such as particle size (micron-, submicron- and nano-scale), dispersion, flowability and structural characteristics, on the mixing behavior of AlN and CaO mixed powders, and on the porosity and thermal conductivity of AlN pellets, were investigated. Additionally, the influence of mixing conditions, including additive content and rotational speed in a novel high-shear mixer (Picomix), were studied and various mixing techniques were compared. The results indicate that when the CaO content of the AlN pellets is increased to 3 wt%, their thermal conductivity rises from 48.1 W/m·K to 112.9 W/m·K. This increase can be attributed to the formation of a liquid phase, and to a reduction in pellet porosity during sintering. Furthermore, when the rotational speed of the mixer is increased to 5000 rpm, the pellets’ thermal conductivity further rises to 126.2 W/m·K. This improvement is a result of the enhanced dispersion of CaO in the mixed powder. The shearing forces in the Picomix facilitate the coating of AlN particles with submicron- or nano-scale CaO particles, thereby improving the flowability of the mixed powder and narrowing the particle size distribution. This further improves the liquid phase distribution, thus enhancing the thermal conductivity of the AlN pellets (135.3 W/m·K). The novel high-shear mixer (Picomix) has demonstrated enhanced performance when compared with traditional mixing techniques (ball milling and manual mixing), since it involves a solvent-free process, is faster, has a lower energy consumption, causes less powder-oxidation and leads to a higher value of thermal conductivity, making it an excellent choice for the preparation of mixed powders for solar thermal applications.

Influence of Feedstock in the Formation Mechanism of Cold-Sprayed Copper Coatings

The aim of this article is to investigate the characterizations and formation mechanisms of cold-sprayed coatings using gas-atomized and electrolytic powders. The study highlights the importance of reaching the particles’ critical velocity for optimal deposition. The main findings reveal that the morphology and stacking conditions of the coatings have a significant impact on their mechanical properties. Coatings made with gas-atomized powders exhibited noticeable pores and higher plastic deformation, while electrolytic powder coatings had greater density and smoother interfaces with the substrate. Adhesion strength relied on the physical bonding resulting from the plastic deformation energy between the spraying powders and the substrate. Gas-atomized powders showed higher adhesion compared to electrolytic powders, with dendritic powders resulting in lower adhesion due to dispersed impact force. The interaction between thermal and kinetic energy during the cold spraying process facilitated plastic deformation and particle deposition by softening and eroding the substrate surface. Insufficient plastic deformation with dendritic powders led to incomplete overlap, pore formation at the interface, and the persistence of the oxide layer along powder boundaries. Overall, these findings provide valuable insights into the influence of powder properties on coating morphology, adhesion strength, and overall performance, contributing to the understanding and optimization of cold spray processes.

Finite Element Modeling of Powder Compaction: Mini-Tablets in Comparison with Conventionally Sized Tablets.

Mini-tablets are considered a promising solid dosage form in the pharmaceutical industry due to advantages such as dosing accuracy, efficiency as a drug delivery system, and alleged improvement in mechanical properties. Nevertheless, only a few experimental studies are available in the literature regarding this topic and technical aspects, such as punch's shape and size effect on the stress and density distribution in the compact mini-tablets, are still not fully investigated. In this paper, the influence of powder properties and process parameters, such as punch shape and size, on the evolution of mechanical properties during the tableting process and the potential occurrence of tablet defects are investigated using the mechanistic modeling approach, Finite Element Method (FEM). The numerical simulation cases consist of four different die sizes, mini-tablets of 2 mm, and 3 mm, and conventionally sized tablets of 8 mm and 11.28 mm. Each tablet size is simulated using four distinctive excipients, Avicel®PH-102, Kollidon®VA64, Pearlitol®100SD, and Supertab®11SD, and two different punch geometries, a flat-face punch, and a bevel edge punch. The model predictions in terms of stress and density distribution at different stages of the compaction process indicate similar behavior in terms of density and stress distribution profiles between the conventionally sized tablets and mini-tablets for a particular excipient. Based on tablet size, small localized differences are noted (e.g., low-density regions, high shear bands, and heterogeneous density profiles), suggesting a possible risk of tableting defects for conventionally sized tablets compared to mini-tablets. Furthermore, it is observed that bevel-edged tablets could facilitate the formation of cracks, leading to possible capping failure.

Influence of powder properties and processing gas on the microstructural evolution of Armstrong CP-titanium and Ti6Al4V powders processed by cold spray

This paper studies the microstructural evolution of commercially pure titanium (CP-Ti) and Ti6Al4V powders manufactured by the Armstrong process deposited by cold spray with nitrogen and helium. The unique, coral-like morphology of the powders resulted in high density deposits sprayed with both nitrogen and helium carrier gasses. The plastic deformation of the CP-Ti and Ti6Al4V particles upon impact leads to refinement of the equiaxed grains present in the starting powder. CP-Ti deposits sprayed with nitrogen result in a grain size of 1 ± 0.6 μm while deposit processed with helium results in a grain size of 0.7 ± 0.2 μm with no clear difference between the grain size at particle interiors and at prior particles boundaries. The low levels of intragranular misorientation in the CP-Ti helium deposit indicated the presence of recrystallized grains. The higher grain refinement when using helium as carrier gas resulted in a weak basal plane (0001) fiber texture. Regions of ultrafine grains are also identified in the microstructure of Ti6Al4V analyzed by SEM. Microhardness values of the deposits made with these coral-like morphology powders were similar to CP-Ti and Ti6Al4V cold sprayed deposits produced with spherical powders. • The microstructure was refined in both the cold sprayed CP-Ti and Ti6Al4V deposits. • Recrystallized grains were identified in the cold sprayed CP-Ti deposit sprayed with helium gas. • EBSD of CP-Ti sprayed with helium gas revealed a weak texture in the basal <0001> direction. • The vanadium-rich regions presented in the Ti6Al4V powder are retained in the cold spray deposit.

Influence of powder properties on residual stresses formed in high-pressure liquid fuel HVOF sprayed WC-CoCr coatings

This paper presents a systematic study of the effect of various WC-CoCr powders on the residual stresses of the high pressure HVOF sprayed coating. As the residual stresses are recognized to play a significant role in the mechanical and fatigue resistance of the coating, it is understandable that their management is important for damage tolerant coating design. Several studies have recently shown that processes, which produce high particle kinetic energy and lower particle temperature, such as Warm spray, HVAF and high-pressure HVOF processes, generate higher peening stresses and therefore final residual stresses is more compressive compared to lower kinetic energy HVOF systems. In addition to the spraying process, powder properties are known to be one of the most important variables in thermal spraying. Nevertheless, only few studies can be found on the effect of powder properties on residual stresses. The aim of this study was to understand the effect of different powder properties on the formation of residual stress. In situ monitoring was utilized to record curvature and temperature during spraying and to calculate coating residual stresses. This approach is a useful tool for understanding of residual stresses during the thermal spraying process enabling their manipulation. It was found that the powders, with only minor differences in density and particle size, produced a significant difference of about 350 MPa in the stress states of the coatings. The combined effect of spray powder properties and spray parameters on residual stress was almost 560 MPa.

Joint Impedance Spectroscopy and Fractography Data Analysis of Ceria Doped Scandia Stabilized Zirconia Solid Electrolyte modified by powder types and sintering temperature

Parameters of the non-Debye relaxation in the 10Sc1CeSZ solid electrolyte made of various types of ZrO2 powder stabilized with 10-mol.% Sc2O3 and 1-mol.% CeO2 were studied. The influence of powder properties and their sintering temperatures on the impedance spectra is analyzed. In regard to electrical response, the polycrystalline ceramic electrolytes may be considered as a single-phase or a two-phase material consisting of a grain bulk and a boundary. In many cases, the boundary resistance is independent practically on dopants and their distribution across the powders and sintering temperatures. The powder compositions suitable for an electrolyte and electrodes are specified.

Influence of powder properties on densification mechanism during spark plasma sintering

We report on the formulation of a factor, f, that when applied together with the activation energy for viscous flow (Q), can be used to provide important insight into the densification mechanism that are active during powder sintering. We ascertain the validity of this formulation by comparing the densification behaviour of atomized and milled powders for Ti-6Al-4V alloy and pure Ti during spark plasma sintering, and identifying the underlying mechanisms.

Magnesium-Silicon Substituted Carbonate Hydroxyapatite (Mg-Si CHA): Factors Affecting Sintering

Sintering has major effect on the final properties of materials such as density, porosity and microstructure. Sintering of Mg-Si CHA in particular is a complex process since changes could occur during sintering, which include phase formation, grain size, pore size and carbonate content, and this in turn affects the mechanical properties. Improved mechanical properties of Mg-Si CHA is critical in load bearing implant applications. Poor control of thermal treatment of Mg-Si CHA during sintering would cause carbonate loss, leading to partial or total decomposition of Mg-Si CHA, subsequently would affect the physical and mechanical properties. The influence of powder properties (particle size, porosity, morphology) and sintering parameters (heating rate, firing atmosphere) on the sintered Mg-Si CHA microstructure was studied using scanning electron microscopy (SEM) characterization technique. The SEM results showed that we are able to produce sintered Mg-Si CHA without cracking of the compacted pellets, while keeping the carbonate level in the amount required (2 – 8%). X-Ray diffraction (XRD) was also performed on the sintered samples and the results indicated that a single phase Mg-Si-CHA was obtained, while Fourier transform infra-red (FTIR) spectroscopy result confirmed that as-synthesized Mg-Si CHA powder was a B-type.

The influence of powder properties on the imbibation rate

Mixing of powders into liquids is a common unit operation. Mixing can be divided into several steps, imbibation of the powder into the liquid being the first. Under some circumstances, such as when the powder has poor wetting properties, imbibation can be the rate-determining step. The effects of different powder properties on the imbibation rate were evaluated using an experimental imbibation model based on the imbibing process employed in an industrial powder-in-liquid mixer. A multivariate analysis of the results suggests that bulk density and capillary penetration rate, and to some extent cohesivity, play an important role in determining the powder imbibation rate. The results also suggest that the capillary penetration rate is increasing on a large particle radius, slow solubilisation of the particles and a low ability of the particles to generate viscosity.

Influence of powder properties on compressibility of prealloyed atomised powders

The compressibility of metal powders depends on many factors, including morphological and mechanical properties of particles. Alloying elements increasing ferrite solid solution strengthening can influence the compressibility of prealloyed steel powders. The contribution deals with compressibility of Fe–Mn–Cr–[Mo–Ni] prealloyed and premixed powders with total alloying ∼2·0%. Quantification of powders compaction was performed using equation P=P0exp (−Kp11); proposed by Parilak et al. (1994), where P is the porosity at pressure p; P0 is apparent porosity; K and n are parameters related to morphology and plasticity of powder particles. The equation enables to study the compressibility in relation to geometry and mechanical properties of powder particles, through development of K and n parameters on pressing pressure p. The tested powders exhibited low varieties in the density at pressing pressures higher than ∼400 MPa, but some differences were identified during the first stage of compaction, at pressing pressures up to ∼200 MPa.

Mechanical Properties of WC/Co Coatings Prepared by Cold Spraying

Microstructure, hardness and wear resistance of WC/Co coatings prepared by cold spraying and influence of powder properties, such as powder size, WC particle size and cobalt content, on those properties have been investigated in this study. Both smaller WC particle and low cobalt content are found to be effective to produce dense, hard and highly wear resistant coating. Smaller powder size is also favorable to make a coating with high mechanical properties. The cold sprayed coating using WC (0.2μm) /12% Co with powder size of -20+0μm has best mechanical properties within this study. This coating has high density compared to conventional HVOF sprayed coatings. Its abrasive wear resistance has been almost comparable to HVOF coating. Strong correlation is also seen between hardness and wear resistance.

The Influence of Powder Properties and Tabletting Conditions on the Surface Roughness of Tablets

Tablets of five different compression formulations were investigated for their surface roughness using scanning electron microscopy and non-contact laser profilometry. It was found that the composition of a formulation not only influenced the tabletting properties of the powder mixtures, but also the surface properties of the final product. The addition of larger quantities of very brittle materials such as dibasic calcium phosphate dihydrate increased the surface roughness of tablets. An increase in tabletting pressure reduced the tablet surface roughness. Tablets were found to have smoother edges than faces, presumably due to the comparatively higher shear stress at the die walls and a polishing effect during tablet ejection. The assessment of surface roughness in three dimensions appeared more powerful than a simple line profile measurement.

Influence of powder properties on the performance of electrostatic coating process

Properties of powder, e.g. particle size distribution, chemical composition, triboand corona charging characteristics, electrical resistivity, hygroscopicity, fluidity and shape distribution play significant roles on the performance of powder coating such as transfer efficiency, film thickness, adhesion and appearance. Our focus in this paper is on particle size distribution, fluidity, charging characteristics and their effects on the first pass transfer efficiency. Even a minor difference in powder properties showed differences in the applications process illustrating the importance of characterizing physical parameters and control techniques to achieve desirable performance.

Characterization of SiC powders and the influence of powder properties on sintering (Technical Report)

Abstract

Compaction and sintering of ultrafine powders: R.A. Andievski (Russian Academy of Sciences, Moscow, Russia), Int. J. Powder Metallurgy, Vol 30, No 1, 1994, 59–66

The properties of many particulate materials can be improved through the application of ultrafine powders. There are, however, many peculiarities associated with the consolidation (i.e. compaction and sintering) of these powders. In this article, the following aspects of ultrafine powders are considered: the influence of powder properties on the interparticle friction characteristics; the content of adsorbed gases and storage problems; the effect of compaction pressure on the density of silicon nitride and nickel powders; the sintering parameters of these powders; and selected properties of consolidaled nanocrystalline materials

Mechanical properties of hot isostatically pressed zirconium nitride materials

The influence of powder properties on the sintering behaviour, the microstructural development and the mechanical properties of hot isostatically pressed (HIPed) zirconium nitrides were investigated. The results show that the densification behaviour is dependent on the powder characteristics, more precisely the grain morphology and size, and oxygen, carbon and metallic impurity contents. The mechanical properties are controlled mainly by the amount of porosity and the presence of a complex intergranular phase in direct relation to the purity of the starting powder. The differences in the fracture strength and toughness between the two grades are perceptible. On the other hand, the thermal shock resistance to fracture initiation, as well as the elastic parameters of both dense materials, are similar.

Studies on Sintering of Technical Grade Alumina—Part I: Characterization of Ground Alumina Powders

Characteristics of powders play an important role in the densification and grain growth during the sintering process of oxide ceramics. During the process of grinding for reduction of particle size, factors like impurity, hydration etc have to be controlled by the comminution period, ratio of material to grinding media (balls) as well as the use of proper liquid medium.In this investigation characterization of powders prepared by comminution of technical grade commercial alumina has been made with respect to wet grinding media and ratio of weight of balls to material. Powders thus obtained were examined by chemical analysis (purity), BET (surface area), SEM (shape and size), particle size distribution by X-ray (Sedigraph) methods. The influence of powder properties on the sintering behaviour of compacts was studied at 1400° and 1500°C for two hours.It was observed that an increased amount of balls reduced the particle size to a limiting stage with characteristic size distribution; a corresponding increase...

Influence of powder properties and processing conditions on microstructure and mechanical properties of sintered Si 3N 4

Influence of powder properties and processing conditions on microstructure and mechanical properties of sintered Si 3N 4

Influence of powder properties and processing conditions on microstructure and mechanical properties of sintered Si 3N 4

The influence of powder properties and the amount and ratio of Y 2O 3-Al 2O 3-additions on sintering behaviour, microstructural development and mechanical properties was investigated. The effect of applied pressure was studied by hot pressing and hot-isostatic-pressing exeriments with powder compacts and sintered materials. The results show a strong dependence of the densification behaviour on powder properties (specific surface area, grain morphology, oxygen and carbon content), amount and composition of sintering aids, and applied pressure. It was found that microstructure, characterized quantitatively by the mean length and the aspect ratio of the elogated β-grains, is strongly dependent on the amount and viscosity of the secondary phase. The mechanical properties, fracture strength and fracture toughness, are mainly controlled by the aspect ratio and grain size.

Microstructure in Sintered UO2Pellets

The influence of powder properties and sintering treatments on the development of microstructure in sintered UO2 pellets was studied. The nature and type of porosity and grain morphology are influenced by the calcination temperature and sintering treatment and these influences persist even at a high sintering temperature.