Fig 2 - uploaded by Ha-Neul Kim
Content may be subject to copyright.
Particle size distribution of the as-received raw powder and the ballmilled and microfluidized slurries. Microfluidization was repeated one time and 10 times, which produced a marginal difference in the distribution curves.
Source publication
In this study, a transparent magnesium aluminate (MgAl2O4) spinel prepared by homogeneous green compaction and sinter-HIP processes was investigated. The uniformity of the particle configuration in a green body could be improved by both a wet shaping via slip casting and a microfluidization process, which effectively disintegrates particle agglomer...
Contexts in source publication
Context 1
... particle size distribution of the MgAl 2 O 4 slurry after ball milling and microfluidization is shown in Fig. 2; for comparison, the particle size distribution of the as-received powder is also analyzed. As shown in Fig. 2, the as-received raw powder primarily consisted of several micron-sized agglomerates due to its high specific surface area and large van der Waals attraction. Pulverized by ball milling, the particles in the slurry showed a ...
Context 2
... particle size distribution of the MgAl 2 O 4 slurry after ball milling and microfluidization is shown in Fig. 2; for comparison, the particle size distribution of the as-received powder is also analyzed. As shown in Fig. 2, the as-received raw powder primarily consisted of several micron-sized agglomerates due to its high specific surface area and large van der Waals attraction. Pulverized by ball milling, the particles in the slurry showed a significant decrease in the mean particle size from 2.73 μm to 0.195 μm; however, the slurry still contained ...
Context 3
... the slurry still contained micron-sized agglomerates, which was exhibited in the particle size distribution curve as three peaks at 0.140 μm, 0.238 μm and 1.87 μm. Conversely, the micro- fluidized slurry showed a unimodal particle size distribution with a lower mean particle size (0.150 μm) without any micron-sized agglomerates. Additionally, Fig. 2 clearly shows that only 1 pass of the slurry through the microfluidizer is sufficient to fully disintegrate the agglomerates, which is accomplished within a few minutes. In this regard, micro- fluidization is shown to be a powerful process for the disintegration of large agglomerates in a nano-powder. The forces introduced for ...
Context 4
... increased with time for both slurries, but the viscosity of the ball-milled slurry increased more rapidly with a 58% steeper slope compared to the slope of the microfluidized slurry. While a lower viscosity indicates a weaker interparticle network and less flocculation in the as- milled or as-passed slurry, which agrees with the results of Fig. 2, the slower aging rate can be interpreted as a higher resistivity against re-flocculation and re-coagulation. Recently, Kadosh et al. reported the microstructure of a suspension directly observed by cryo-SEM and showed that a high level of flocculation and inhomogeneous void formations were pro- moted by aging for 30 min; this ...
Context 5
... particle size distribution of the MgAl 2 O 4 slurry after ball milling and microfluidization is shown in Fig. 2; for comparison, the particle size distribution of the as-received powder is also analyzed. As shown in Fig. 2, the as-received raw powder primarily consisted of several micron-sized agglomerates due to its high specific surface area and large van der Waals attraction. Pulverized by ball milling, the particles in the slurry showed a significant decrease in the mean particle size from 2.73 μm to 0.195 μm; however, the slurry still contained micron-sized agglomerates, which was exhibited in the particle size distribution curve as three peaks at 0.140 μm, 0.238 μm and 1.87 μm. Conversely, the micro- fluidized slurry showed a unimodal particle size distribution with a lower mean particle size (0.150 μm) without any micron-sized agglomerates. Additionally, Fig. 2 clearly shows that only 1 pass of the slurry through the microfluidizer is sufficient to fully disintegrate the agglomerates, which is accomplished within a few minutes. In this regard, micro- fluidization is shown to be a powerful process for the disintegration of large agglomerates in a nano-powder. The forces introduced for disintegration during microfluidization include a high shear stress applied through the narrow channel and also the cavitation phenomenon that can occur when the slurry passes out of the narrow channel into the connected wider tube. To et al. reported that the rapid expansion of a high-pressure suspension, such as cavitation, is effective at deagglomerating nanoparticle aggregates [25]. Therefore, it is reasonable to conclude that both the high shear stress and the strong cavitation in the proposed process improved the resulting deagglomeration of the MgAl 2 O 4 ...
Context 6
... particle size distribution of the MgAl 2 O 4 slurry after ball milling and microfluidization is shown in Fig. 2; for comparison, the particle size distribution of the as-received powder is also analyzed. As shown in Fig. 2, the as-received raw powder primarily consisted of several micron-sized agglomerates due to its high specific surface area and large van der Waals attraction. Pulverized by ball milling, the particles in the slurry showed a significant decrease in the mean particle size from 2.73 μm to 0.195 μm; however, the slurry still contained micron-sized agglomerates, which was exhibited in the particle size distribution curve as three peaks at 0.140 μm, 0.238 μm and 1.87 μm. Conversely, the micro- fluidized slurry showed a unimodal particle size distribution with a lower mean particle size (0.150 μm) without any micron-sized agglomerates. Additionally, Fig. 2 clearly shows that only 1 pass of the slurry through the microfluidizer is sufficient to fully disintegrate the agglomerates, which is accomplished within a few minutes. In this regard, micro- fluidization is shown to be a powerful process for the disintegration of large agglomerates in a nano-powder. The forces introduced for disintegration during microfluidization include a high shear stress applied through the narrow channel and also the cavitation phenomenon that can occur when the slurry passes out of the narrow channel into the connected wider tube. To et al. reported that the rapid expansion of a high-pressure suspension, such as cavitation, is effective at deagglomerating nanoparticle aggregates [25]. Therefore, it is reasonable to conclude that both the high shear stress and the strong cavitation in the proposed process improved the resulting deagglomeration of the MgAl 2 O 4 ...
Context 7
... particle size distribution of the MgAl 2 O 4 slurry after ball milling and microfluidization is shown in Fig. 2; for comparison, the particle size distribution of the as-received powder is also analyzed. As shown in Fig. 2, the as-received raw powder primarily consisted of several micron-sized agglomerates due to its high specific surface area and large van der Waals attraction. Pulverized by ball milling, the particles in the slurry showed a significant decrease in the mean particle size from 2.73 μm to 0.195 μm; however, the slurry still contained micron-sized agglomerates, which was exhibited in the particle size distribution curve as three peaks at 0.140 μm, 0.238 μm and 1.87 μm. Conversely, the micro- fluidized slurry showed a unimodal particle size distribution with a lower mean particle size (0.150 μm) without any micron-sized agglomerates. Additionally, Fig. 2 clearly shows that only 1 pass of the slurry through the microfluidizer is sufficient to fully disintegrate the agglomerates, which is accomplished within a few minutes. In this regard, micro- fluidization is shown to be a powerful process for the disintegration of large agglomerates in a nano-powder. The forces introduced for disintegration during microfluidization include a high shear stress applied through the narrow channel and also the cavitation phenomenon that can occur when the slurry passes out of the narrow channel into the connected wider tube. To et al. reported that the rapid expansion of a high-pressure suspension, such as cavitation, is effective at deagglomerating nanoparticle aggregates [25]. Therefore, it is reasonable to conclude that both the high shear stress and the strong cavitation in the proposed process improved the resulting deagglomeration of the MgAl 2 O 4 ...
Context 8
... analysis was conducted on the slurry that passed through the channel 10 times to check for any contamination created during microfluidization; these results are summarized in Table 1. It was found that no impurity inflow or contamina- tion from the fluidizing line had occurred comparing the ball- milled slurry to the microfluidized slurry. When deagglomera- tion is promoted by high-energy milling, impurity contamina- tion due to the abrasion of the milling media and the container is typically unavoidable; however, microfluidization is oper- ated without a milling media and only requires passing the slurry through a narrow channel made by single crystal diamond, allowing a high purity and the resulting composition of MgAl 2 O 4 to be maintained. Fig. 3 shows the rheological properties of the ball-milled and microfluidized slurries. The viscosity versus the shear rate profiles in Fig. 3(a) show that both slurries exhibited a non- Newtonian shear-thinning behavior, which decreases the viscosity as the shear rate increases; however, after reaching a steady viscosity at a sufficiently high shear rate, the viscosity of the microfluidized slurry showed was nearly half of that of the ball-milled slurry. In Fig. 3(b), the time-dependent viscosity profile of the slurries at a constant shear rate (30 s À 1 ) shows that the viscosity increased with time for both slurries, but the viscosity of the ball-milled slurry increased more rapidly with a 58% steeper slope compared to the slope of the microfluidized slurry. While a lower viscosity indicates a weaker interparticle network and less flocculation in the as- milled or as-passed slurry, which agrees with the results of Fig. 2, the slower aging rate can be interpreted as a higher resistivity against re-flocculation and re-coagulation. Recently, Kadosh et al. reported the microstructure of a suspension directly observed by cryo-SEM and showed that a high level of flocculation and inhomogeneous void formations were pro- moted by aging for 30 min; this phenomenon was shown to be caused by an increase of attractive force between particles with time [26]. It is thus inferred that the homogeneous, mono-sized particle distribution in the microfluidized slurry contributed to the higher stability of the slurry by maximizing the average interparticle distance and weakening the resistance of the flow of the suspension against the external shear force. In addition, Hotta et al. reported that microfluidization enhances the electrostatic repulsion between the particles without degrading the dispersant or the particle surface and enhances the steric repulsion by increasing the average polymer molecular weight and length, which increases the interparticle distance and slurry stability [20]. Fig. 4 shows the pore size distribution in the green compacts that were fabricated with varying slurry conditions and consolidation methods; the nomenclature and data of these conditions and methods are summarized in Table 2. The slip- casted body from the microfluidized slurry (MF) showed a narrower pore size distribution with the smaller mean pore size of 25.6 nm compared with the green body prepared from the ball-milled slurry (BM) which displayed a wider distribution with larger mean pore size (28.3 nm). In addition, the green density of MF was higher than that of BM, attributed to the smaller mean pore size in the green compact. It is considered that a narrower particle size distribution without micron-sized agglomerate of microfluidized slurry enabled more uniform and homogeneous particle coordination in the MF green body. Moreover, the higher stability of the microfluidized slurry against re-flocculation which was shown in Fig. 3 is thought to influence the narrow pore size formation during slip casting process that requires a prolonged casting time which may allow the particles to aggregate again. On the other hand, the green bodies fabricated by uniaxial dry pressing of freeze-granules prepared from the ball-milled slurry and microfluidized slurry (DP(BM) and DP(MF), respectively) followed by CIP at 200 MPa showed an overall larger and wider pore size distribution compared to that of the slip-casted specimen, resulting in lower green densities in Table 2. The conditions used here for pressing were not optimal so that the results do not represent the best values attainable by pressing. It was shown by Goldstein et al. [11] and Krell et al. [12] that dry pressing of granules with optimal conditions (i.e. solid loading, solvent, binder, granulation method and CIP schedule) can give a uniform green compact comparable to slip-casted bodies in this study. Nevertheless, it is interesting that when dry pressing was used as a consolida- tion method, the characteristics of the different slurry prepara- tions were shown to marginally affect the properties of the resulting green body; however, using a wet shaping process allowed prominent improvement to the homogeneity of the green compact with respect to different slurry preparation methods. It is inferred that the disintegrating effect of micro- fluidization was readily exploited in slip-casting in absence of a drying process which might cause flocculation or agglom- eration. Thus, the remaining part of the study will only discuss the slip-casted compacts, not dry pressed samples in order to observe the effects of microfluidization and pore size Table 2, and the cumulative distributions were found to fit the cumulative Gaussian distribution function well. distribution of the green body to sintering behavior and optical ...
Similar publications
In this study, acetaminophen was co-dried with microcrystalline cellulose (MCC) to produce a directly compressible formulation. The effects of co-drying were compared to wet granulation and physical mixing. Two MCC slurries with different particle morphologies and functionalities (bulk density, Carr's index, tensile strength, and rate constant of w...
Citations
... The fabricated ceramic membrane had a 475 L/h m 2 bar permeability. A number of factors, such as sintering temperature, casting time, suspension pH, particle size, etc., have an impact on the properties of slip casted ceramic membranes [96]. Fang et al. [97] investigated the effect of slip concentration, withdrawal speed and casting time on the preparation of coal fly ash ceramic membrane fabricated using the slip casting technique. ...
The continued increase in the global population has resulted in increased water demand for domestic, agricultural, and industrial purposes. These activities have led to the generation of high volumes of wastewater, which has an impact on water quality. Consequently, more practical solutions are needed to improve the current wastewater treatment systems. The use of improved ceramic membranes for wastewater treatment holds significant prospects for advancement in water treatment and sanitation. Hence, different studies have employed ceramic membranes in wastewater treatment and the search for low-cost and environmentally friendly starting materials has continued to engender research interests. This review focuses on the application of coal fly ash in membrane technology for wastewater treatment. The processes of membrane fabrication and the various limitations of the material. Several factors that influence the properties and performance of coal fly ash ceramic membranes in wastewater treatment are also presented. Some possible solutions to the limitations are also proposed, while cost analysis of coal fly ash-based membranes is explored to evaluate its potential for large-scale applications.
... A schematic diagram of the micro fluidization process[16]. ...
The exploration of nanocellulose has been aided by rapid nanotechnology and material science breakthroughs, resulting in their emergence as desired biomaterials. Nanocellulose has been thoroughly studied in various disciplines, including renewable energy, electronics, environment, food production, biomedicine, healthcare, and so on. Cellulose nanocrystal (CNC) is a part of the organic crystallization of macromolecular compounds found in bacteria’s capsular polysaccharides and plant fibers. Owing to numerous reactive chemical groups on its surface, physical adsorption, surface grating, and chemical vapor deposition can all be used to increase its performance, which is the key reason for its wide range of applications. Cellulose nanocrystals (CNCs) have much potential as suitable matrices and advanced materials, and they have been utilized so far, both in terms of modifying and inventing uses for them. This work reviews CNC’s synthesis, properties and various industrial applications. This review has also discussed the widespread applications of CNC as sensor, acoustic insulator, and fire retardant material.
... µm (D 10 : 0.26 µm, D 50 : 5.42 µm) for the ball-milled diatomite powders. The ball-milling process resulted in a narrowed particle size distribution and increased uniformity of the diatomite particles by reducing agglomerates [45,46]. According to the literature, this improved particle size distribution is beneficial for optimizing the viscosity of processing dispersions [46] and for enhancing the mechanical strength of the resultant ceramics [45] due to the formation of ordered particle domains. ...
... The ball-milling process resulted in a narrowed particle size distribution and increased uniformity of the diatomite particles by reducing agglomerates [45,46]. According to the literature, this improved particle size distribution is beneficial for optimizing the viscosity of processing dispersions [46] and for enhancing the mechanical strength of the resultant ceramics [45] due to the formation of ordered particle domains. The described trends were observed in our previous studies of reticulated porous ZrO 2 and ZrO 2 -toughened Al 2 O 3 ceramics [47,48], where ball-milling enabled the tailoring of the particle size distribution of the raw materials, resulting in the optimized viscosity of the processing slurries and improved compressive strength capabilities of the ceramic materials. ...
The proper application of millimeter-sized spherical porous ceramic supports in catalytic operations relies on their ease of handling, convenient separation, recyclability, high-catalyst-solid loading, and the optimum mass transfer of reactants and products. However, common granulation techniques of spherical carriers entail complex liquid-phase-based processes under severe conditions and the use of toxic or expensive reagents. The present study discusses the manufacturing of porous ceramic granules derived from an inexpensive silica source (diatomite, solid network) and a biopolymer cross-linked by ion exchange (sodium alginate, patterning structure). The results indicated that, with fixed granulation conditions, porous diatomite granules with a sphericity of approximately 0.9 could be successfully obtained by optimization of the diatomite/sodium alginate dispersion to a 30.07 wt.% solid content and 1560 mPa·s viscosity (at ~0.3 s−1). Moreover, the described manufacturing process was proven effective in developing hierarchically porous diatomite granules that were heat-treated at 1200 °C with high sphericity (~0.9), acceptable compressive strength (5.17 ± 0.31 MPa), and porosity features (total porosity: 69.0 ± 2.9%, macropore size: 2.777 μm, mesopore size: 35.34 nm), establishing them as well-matched support materials for either catalytic or adsorption applications.
... This results in good dispersion stability and low contamination. [30][31][32][33] Because ceramics with a homogeneous microstructure and no large defects are obtained using wet-jet milling, studies on using wet-jet milling to improve the mechanical properties and translucency of ceramics have been reported. 34,35 However, there are no reports that reveal the impact of wet-jet milling on the fabrication of c-axis-oriented HA ceramics under a strong magnetic field. ...
Controlling the crystal orientation of hydroxyapatite, an inorganic material that is a major component of human hard tissues is important to fabricate better artificial bones and artificial tooth roots. To obtain highly oriented hydroxyapatite ceramics under a strong magnetic field, a good dispersion of the raw materials in the slurry must be obtained. This study investigates the effect of wet‐jet milling of a slurry on the orientation of hydroxyapatite ceramics fabricated using a strong magnetic field. Although the prolonged ball milling with ZrO2 balls of the raw powder fractures the primary particles of hydroxyapatite, wet‐jet milling is used to successfully pulverize agglomerated hydroxyapatite raw powder without changing the morphology of the primary particles. Evidently, ceramics with a highly oriented c‐axis of hydroxyapatite are obtained by molding the wet‐jet milled slurry in a strong rotating magnetic field. They exhibit anisotropy in fracture toughness, and the fracture toughness calculated from the crack length perpendicular to the rotating axis is higher than that calculated from the crack length parallel to it. Furthermore, these values are higher than those of randomly oriented hydroxyapatite ceramics, which may be owing to the crystal orientation dependence of the fracture toughness of the hydroxyapatite grains and grain boundaries.
... The literature reports various approaches to develop transparent spinel. From the raw material point of view, commercial MgAl 2 O 4 powders are commonly used [18][19][20][21][22][23][24][25][26]. Some articles report the synthesis of the spinel powder from chloride or nitride [27][28][29]. ...
This study was devoted to the understanding of the influence of MgAl2O4 ceramic properties on their ballistic performances. By modifying the processing parameters, ceramics with different microstructures were obtained. Among them, a transparent MgAl2O4 spinel with an in-line transmission between 77% and 83% in the visible range, an average grain size of 8.6 μm and good mechanical properties (11.3 GPa in Knoop hardness and 2.5 MPa√m in fracture toughness) was produced. A thorough characterisation of the ceramics was accomplished in order to establish a link between microstructure, mechanical properties and ballistic protective performances against an armour piercing projectile of calibre 7.62x51 mm. The ballistic evaluation demonstrated the advantage of using a spinel layer as the strike face to stop a threat, while reducing drastically the thickness and the areal density of the transparent multilayer, compared to a simple glass armour. MgAl2O4 spinel with fine grains presented a better combination of mechanical properties compared to coarser microstructures, hence a better potential to damage a projectile at the impact.
... The increase in sintering temperature results in the reduction of grain size and membrane density, leading to a decrease in the mechanical strength of the membrane [84]. The slurry density and viscosity are dependent on particle size, morphology, thickness, suspension pH, and casting time [92]. One of the issues associated with the slip casting method is the weak strength and low toughness of the ceramic membrane due to the high porosity of the membrane [12]. ...
Nanomaterials have contributed significantly to the enhancement of technological and industrial development. The conventional membranes used in various separation processes are limited in their abilities, performances, and are prone to fouling or biofouling. Membranes fabricated with functionalized nanomaterials are sustainable, robust, and energy-efficient in membrane technology. The nanomaterials incorporate several properties into the membrane, such as antifouling, chemical resistance, high mechanical strength, and enhanced separation properties. In this chapter, the fabrication of sustainable membranes with FNMs is presented, discussing their performance, advantages, and drawbacks. Different fabrication techniques, including interfacial polymerization, surface coating, electrospinning, phase inversion, slip casting, extrusion, chemical vapor deposition, and more, have been detailed in this chapter. Various membranes such as thin-film nanocomposite, nanofibrous, ceramic, and carbon nanotube-based membranes can be fabricated using these techniques. Such membranes have enhanced properties that significantly improve the performance to overcome several challenges faced in the traditional membrane technology-based water treatment and desalination applications.
... The properties of ceramics strongly depend on the composition, nature of powders, impurities or additives, and fabrication methods [4]. Many different routes have been used to synthesize dense spinel-based ceramics such as hot pressing, pressureless methods, spark plasma, and microwave sintering utilizing spinel powder as the raw material, with or without sintering additives [5][6][7][8][9][10][11][12]. Some authors have reported on direct solid-state reactions of oxides, wet chemical precipitation, and mechanical activation [13][14][15][16][17][18][19]. ...
Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by a solid-state reaction between MgO and α-Al2O3 powders. Mechanical activation for 30 min in a planetary ball mill was used to increase the reactivity of powders. Yttrium oxide and graphene were added to prevent abnormal grain growth during sintering. Samples were sintered by hot pressing under vacuum at 1450 °C. Phase composition and microstructure of sintered specimens were characterized by X-ray powder diffraction and scanning electron microscopy. Rietveld analysis revealed 100% pure spinel phase in all sintered specimens, and a decrease in crystallite size with the addition of yttria or graphene. Density measurements indicated that the mechanically activated specimen reached 99.6% relative density. Furthermore, the highest solar absorbance and highest spectral selectivity as a function of temperature were detected for the mechanically activated specimen with graphene addition. Mechanical activation is an efficient method to improve densification of MgAl2O4 prepared from mixed oxide powders, while additives improve microstructure and optical properties.
... Nevertheless, most commercial productions of this ceramic occur through HP and HIP. Usage of these methods is costly, causes grain growth, causing diminished mechanical properties of the nal ceramics [3,12,19]. Various researchers have used spark plasma sintering methods for fabricating transparent ceramics. This is because by constraining the grain growth and obtaining a uniform distribution of the grain size, it is possible to achieve almost complete density within a short period of time [11,20]. ...
In this project, magnesia-alumina composite granules were prepared using spray drying method. Next, the synthesized powder was sintered at 1400°C for 15 min under 100 MPa pressure through spark plasma sintering without using any sintering aid. The effect of two sintering temperatures of 1400 °C and 1500 °C was explored on the phase formation, density, fracture toughness, and optical transmission within visible and IR ranges. SEM results indicated that the magnesia-alumina composite granules had spherical morphology with the mean particle size of 21 micrometers. The XRD pattern showed that after the spark plasma sintering stage at 1400 °C and 1500 °C, the spinel phase of magnesium aluminate was obtained as in situ. The disc sintered at 1400 °C had greater maximum transmission compared to the samples sintered at 1500 °C (47% vs. ~70%) within the middle IR region because of lower porosity of the sample. The magnesium aluminate spinel sintered at 1400 °C had a density 99.98% of the theoretical density, hardness 18 GPa, and fracture toughness 1.6 MPam1/2.
... Issaoui and Limousy (2019) and Mohammadi and Pak (2003) stated that several low-cost materials such as kaolin and fly ash can be used in the slip casting method to decrease the membrane fabrication cost. The slurry stability, density, and viscosity depend on the particle size, the morphology, solid load, suspension pH, casting time, and thickness (Kim et al. 2015;Kong et al. 2015;Tsetsekou et al. 2001). The main issue encountered in the slip casting method is the weak ceramic membrane strength due to the high porosity and the low toughness of the molds. ...
Membrane technologies are used intensively for desalination and wastewater treatment. Water filtration using ceramic membranes exhibited high performance compared with polymeric membranes due to various properties such as high resistance to fouling, permeability, rejection rate, and chemical stability. Recently, the performance of nanocomposite ceramic membranes was improved due to the development in nanotechnology. This article focusses on the development of porous ceramic membranes and nanomaterial functionalized ceramic membranes for water filtration applications. At the beginning, various fabrication methods of ceramic membranes were described, and the effect of surface modification techniques on the membrane intrinsic properties was reviewed. Then, the performance of nanoparticles functionalized ceramic membranes was evaluated in terms of physicochemical properties, rejection rate, and water permeability. This work can help new entrants and established researchers to become familiar with the current challenges and developments of nanoparticle-incorporated ceramic membranes for water filtration applications.
... Ces conditions douces au frittage évitent une croissance des grains, qui serait liée à des températures élevées et ne conservent que de la porosité intergranulaire[22,137]. Cependant, le post-traitement HIP combine une haute température à une forte pression isostatique afin d'éliminer la porosité fermée présente dans la céramique, tout en gardant une microstructure homogène (Figure I.30)[138,139]. Pour un post-traitement par HIP efficace, la porosité doit être fermée[111]. ...
... Ce résultat est cohérent avec la faible densité de l'échantillon (92%). Toutefois cette faible densité ainsi que la porosité ouverte (déterminée par pesée hydrostatique) seront sûrement des freins à l'utilité et l'efficacité d'un post-traitement par HIP[111]. Une hypothèse peut être établie quant à l'origine de cette large porosité. En effet, celle-ci est très probablement due à la présence des gros agglomérats denses dans la poudre lyophilisée. ...
... Chaque mise en forme possède ses propres avantages et inconvénients. La voie liquide comme le coulage en mouleporeux ou slip casting est plus avantageux dans la mise en forme d'un cru homogène, par la mise en place d'une suspension stable en cassant les agglomérats présents naturellement[106,109,111].La mise en forme par voie sèche, par pressage uniaxial permet de s'affranchir de cette étape supplémentaire mais un empilement granulaire compact de la poudre sera plus difficile à obtenir.Les microstructures obtenues sont plus hétérogènes et la poudre générera plus de porosité due aux agglomérats[109]. La Figure I.20 montre la différence d'empilement entre les deux mises en forme.La méthode de mise en forme par voie liquide présente plusieurs avantages non négligeables. ...
Ce travail d’élaboration de céramique transparente pour la protection balistique s’inscrit dansun contexte d’allégement de structure et d’amélioration des propriétés optiques et mécaniques.Le remplacement de la face avant en verre par une céramique polycristalline, telle que lespinelle MgAl2O4 permet d’optimiser considérablement les performances balistiques, touten diminuant la masse et le volume de la protection. Le principal objectif de ce travail a étél’obtention d’une céramique transparente type spinelle avec une microstructure à grains finspermettant d’obtenir de bonnes propriétés mécaniques et balistiques. Afin de contrôler lamicrostructure de la céramique, il est nécessaire d’adopter des conditions de frittage douces,c’est pourquoi l’utilisation d’une poudre très fine et réactive a été envisagée. Mais l’utilisationd’une telle poudre soulève souvent des problèmes de mise en forme et de frittage homogène,qui sont un frein à la transparence de la céramique. Cette étude s’est tout d’abord focaliséesur la poudre de spinelle en comparant quatre poudres de spinelle commerciales. Cette partiea permis de mettre en avant les particularités rhéologiques ou morphologiques nécessaires àla mise en forme des céramiques, influençant ainsi le frittage et donc la transparence finale,comme par exemple le réarrangement granulaire, la surface spécifique ou la perméabilité. Unefois la poudre de spinelle choisie, une étude de traitement a été menée sur cette dernièreen exploitant son agglomération afin d’obtenir une céramique transparente dans le visibleavec une microstructure fine. Le challenge a été d’optimiser sa mise en forme par différentstraitements et son frittage. Cette étude s’est soldée par l’obtention de céramique transparenteà fine microstructure (taille de grain de 4-5_m) et avec une transmission en ligne de 71%à 650nm, grâce à l’utilisation d’un spray dryer et d’un additif PEG. Une autre étude s’estconcentrée sur la possibilité de renforcer ce spinelle transparent par l’ajout de matériau dedifférentes natures (nanodiamant, alumine, zircone). L’objectif a été d’améliorer les propriétésmécaniques du spinelle, tout en gardant intactes ses propriétés optiques. L’ajout de phasesecondaire en tant que renfort soulève de nombreuses difficultés de par leurs tailles, l’indicede réfraction différent du spinelle et les éventuelles réactions qui peuvent se produire lors dufrittage. Une dernière étude a été menée sur la mise en forme de forme complexe, permettantainsi d’autres applications du spinelle en tant que protection. La voie classique par pressageuniaxial s’étant avéré peu concluante, une mise en forme par voie liquide s’est montrée êtreune solution envisageable. Elle a nécessité une étude complète de la mise en suspension duspinelle et son comportement lors de sa mise en forme. Chacune des études s’est appuyée surla morphologie de la poudre et son évolution lors de la mise en forme et le frittage, par lebiais d’études microstructurales et rhéologiques ainsi que l’évaluation des propriétés optiqueset mécaniques.
