A Study on the Density of Agglomerates Prepared from Cork Wastes

The density of black regranulate (BR) of cork and of black agglomerate (BA) and composite agglomerate (CA) prepared fromsuch a waste by different methods was investigated. The preparation of the agglomerates was undertaken by controlling thespecimen thickness for BA and the particle size for BR and the binder dosage for CA. The mass changes produced in theoven-drying treatment at 376.15 K of the agglomerates and in their subsequent stabilization under ambient conditions werealso analyzed. The density was determined by standard methods. For BR, the bulk density first decreased and then increasedwith decreasing particle size. It was much lower than the apparent density of the agglomeration products of cork. Although toa lesser extent, the density was also lower for BA than for CA. It was higher for the smaller thickness specimens of BA. In thecase of CA, the density followed the same variation trends as for BR. Furthermore it increased significantly with the increasein resin dosage. This resulted in a not     

Bending strength of black and composite agglomerates of cork

The bending strength of black and composite agglomerates of cork is investigated. In the preparation of the agglomerates, the raw material used was black regranulate (BR) of cork. Specimens of black agglomerate (BA) with a different thickness were obtained. In the case of the composite agglomerate (CA), both the particle size of BR and the resin dosage were varied. The bending strength increased with the increase in the specimen thickness for BA and in the particle size and the resin dosage for CA. This later parameter, in particular, greatly influenced such a mechanical property of this agglomeration product of cork.     

Agglomerating fluidization of group C particles: major factors of coalescence and breakup of agglomerates

An experimental study was carried out to determine the influence of different superficial gas velocities on the agglomerates of cohesive particles. The probability of agglomerate coalescence and breakup is proposed on the basis of the principle of force balance. Theoretical analysis shows that the higher superficial gas velocity and fluid density, the lower the particle cohesion, and that collisions between small and large agglomerates are advantageous for the agglomerating fluidization of cohesive particles. The average agglomerate size estimated by the model of force balance decreases with increasing superficial gas velocity, which is in agreement with experimental data.     

Rebound behavior of nanoparticle-agglomerates

In general, the rebound behavior of particles depends on the particle/substrate material combination and the particle size. In the present investigation the rebound behavior of nanoparticle agglomerates is investigated in a low pressure impactor and compared to single spherical particles. For agglomerates, their structure and mechanical strength will also affect the rebound behavior. The rebound of openly structured agglomerates (fractal dimension D_f < 2) is determined by the primary particle size and the particle-substrate combination. The impact velocity required for rebound (critical velocity) is independent of the agglomerate size and equal to the critical velocity of single spherical particles having the same size as the primary particles. In case of agglomerate fragmentation no rebound was observed for openly structured agglomerates. For denser agglomerates (D_f > 2), the critical impact velocity decreases with increasing agglomerate size, where the decrease is more accentuated for higher fractal dimensions, finally approaching the behavior of spheres.     

Cork agglomerates as an ideal core material in lightweight structures

The experiments carried out in this investigation were oriented in order to optimize the properties of cork-based agglomerates as an ideal core material for sandwich components of lightweight structures, such as those used in aerospace applications. Static bending tests were performed in order to characterize the mechanical strength of different types of cork agglomerates which were obtained considering distinct production variables. The ability to withstand dynamic loads was also evaluated from a set of impact tests using carbon-cork sandwich specimens. The results got from experimental tests revealed that cork agglomerates performance essentially depends on the cork granule size, its density and the bonding procedure used for the cohesion of granulates, and these parameters can be adjusted in function of the final application intended for the sandwich component. These results also allow inferring that optimized cork agglomerates have some specific properties that confirm their superior ability as a core material of sandwich components when compared with other conventional materials.     

Simulation of dispersion and collection process of agglomerated particles in collision with fibers using discrete element method

The behavior of agglomerates in collision with fibers was simulated using the three-dimensional modified discrete element method and the influences of several factors on the fraction of collected particles were examined. Furthermore the single fiber collection efficiency for agglomerated particles was also investigated. In the case where gas velocity is quite low, agglomerates are only deformed but barely dispersed and thus collected as a single deformable particle. By contrast above some critical gas velocity, constituent particles are dispersed and at the same time partly collected on fibers. The fraction of collected particles first increases then decreases as the van der Waals attractive force between particle and fiber increases. The reason for the decrease in fraction of collected particles in strong adhesion region is that the smooth deformation of agglomerates along the fiber surface is inhibited by too strong adhesion. It was also suggested that there exists an optimum size ratio between the agglomerate size and fiber radius for the collection fraction. This is also closely related to the deformation of agglomerate along the fiber surface. In case of non-agglomerated particle collision, all the particles entering within the collision region are collected by fiber. By contrast in case of agglomerate collision, the dispersion of agglomerates as well as collection occurs in the same process and all the particles colliding with the fiber are not necessarily collected. Consequently the single fiber collection efficiency considerably decreases comparing to that for non-agglomerated particle collision.     

3D printing of tuneable agglomerates: Strain distribution and effect of internal flaws

The current study presents a novel and reliable method for producing 3D printed agglomerates with different colour distributions and material properties with 2-fold aims: providing feasible and accurate control on compression of agglomerates under different compression angles, and better tracking of individual particle position after agglomerate breakage. Multi-coloured agglomerates in cubic tetrahedral and random sphere shapes were printed with both rigid and soft bonds. The printed agglomerates were analysed thoroughly of their surface and structural properties including surface roughness and printing accuracy. The agglomerate breakage behaviours under static compression were analysed as a function of bond strength, loading rate and loading directions, with strain distribution plotted over the random sphere agglomerate structure. In addition, agglomerate structures with designed internal macro-voids in different positions and sizes were also created for breakage study, in an effort to better understand parameters governing the mechanical properties of agglomerates with cavities and voids which is inevitable in particle industry but poorly understood at present.     

Agglomerate breakdown in fine alumina powder by multiple extrusion

Repeated extrusion through dies of various diameters and die entry angles was used to determine the rate of agglomerate breakdown in a paste consisting of a fine alumina powder, carbon black and a binder of hydroxyl propyl methyl cellulose in water. It was found that three extrusion passes were enough to break up all but 0.4% of the agglomerates. Dies with orifices of approximately 1 mm diameter and die entry angles of 45 to 90 (where the elongational strain and the deformation rates were highest) were the most efficient for disrupting and dispersing agglomerates and distributing the moisture evenly. This process of deagglomeration was studied by monitoring the load required to extrude and moisture distribution during five repeated extrusion passes of each test paste. The density, agglomerate area fraction and agglomerate circularity of dried extradates were quantified and plotted.     

Primary particle size and agglomerate size effects of amorphous silica in ultra-high performance concrete

Silica fume is widely used in ultra-high performance concrete (UHPC). However, it is a by-product in the industrial silicon production and therefore far from an optimized additive. Silica fume improves the compressive strength, but its detailed reaction mechanisms in concretes with low water/cement ratios are not yet fully understood. This study focuses on the influence of primary particle sizes and sizes of agglomerates of different amorphous silicas in UHPC. As a reference system, wet-chemically synthesized silica was used with very high purity, defined particle sizes, narrow primary particle size distributions and controllable agglomerate sizes. The obtained data were compared to silica fume. The results indicate that non-agglomerated silica particles produce the highest strength after 7 d, but a clear dependence on primary particle sizes, as suggested by calculations of packing density, was not confirmed. UHPC may be improved by incorporating an ameliorated dispersion of silica e.g. through commercial silica sols.     

Quantitative analysis of agglomerates levitated from particle layers in a strong electric field

The electrification, agglomeration, and levitation of particles in a strong electric field were analyzed experimentally and theoretically. Particle layers of glass, alumina, and ferrite were formed on a plate electrode and an external voltage was applied. Microscopic observations of the agglomerates levitated from the particle layers revealed that the number of primary particles constituting an agglomerate is affected by particle diameter and electrical resistance, but not by the applied electric field. The electric field distributions in the system were calculated by considering the charges and geometries of the agglomerates formed on the particle layers. The charges of the agglomerates were obtained experimentally. All forces acting on the agglomerates (i.e., gravitational forces, Coulomb forces, interaction forces between polarized particles, image forces, and gradient forces) were analyzed under different conditions, including various electric field distributions and charges of agglomerates. Furthermore, the critical conditions for the levitation of the agglomerates were evaluated using a force balance.     

Nanostructured La(Sr)CrO3 through gel combustion: sintering and electrical behavior

Nanostructured La(Sr)CrO3 (LSC) powders was prepared through glycine-nitrate gel combustion process. It was shown for the first time that the use of relatively inexpensive CrO3 as a starting material for chromium has a potential for the bulk preparation of sinter-active LSC powder. As-prepared powder when calcined at 700 degrees C resulted in LSC along with a small amount of SrCrO4 as a secondary phase. The powder was found to be composed of soft agglomerates with a particle size of approximately 70-270 nm. The average agglomerate size was found to be 0.95 microm. The cold pressing and sintering of the LSC powder at 1450 degrees C resulted in mono-phasic La0.8Sr0.2CrO3 with 94% of its theoretical density. This is the lowest sintering temperature ever reported for La0.8Sr0.2CrO3. The conductivity of the sintered La0.8Sr0.2CrO3 at 1000 degrees C was found to be approximately 18 S cm(-1).     

碳纳米管聚团弹性体的结构调变

为得到更加密实的碳纳米管聚团弹性体,使之成作为一种能量吸收材料,在化学气相沉积制备碳纳米管过程中,提出通水提高Co-Mo-Al2O3催化剂裂解乙烯的活性,以便在短时间内促进碳纳米管快速生长的方法,可将碳纳米管聚团密度由40~65 kg/m3提高至120~140 kg/m3。结果表明,所得碳纳米管聚团结构具有明显的二级聚团孔结构分布特征,二级聚团压缩响应特征,并具有明显的高密度压缩体的优点,能够在较小的体积吸收更多能量。     

Influence of temperature and aging time on HA synthesized by the hydrothermal method

The influence of temperature and aging time on the morphology and mechanical properties of nano-sized hydroxyapatite (HA) synthesized by a hydrothermal method is reported here. The pre-mixed reactants were poured into a stirred autoclave and reacted at temperatures between 25–250°C for 2–10 h. HA powders thus obtained were examined using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FESEM) and a particle size analyzer. It was found that the aspect ratio of the particles increased with the reaction temperature. The length of the HA particles increased with the reaction temperature below 170°C, but it decreased when the temperature was raised above 170°C. The agglomerates of HA particles were formed during synthesis, and their sizes were strongly dependent on reaction temperatures. As the reaction temperature increased, the agglomerate size decreased (p = 0.008). The density of the discs pressed from these samples reached 85–90% of the theoretical density after sintering at 1200°C for 1 h. No decomposition to other calcium phosphates was detected at this sintering temperature. A correlation existed (p = 0.05) between the agglomerate sizes of HA particles synthesized at various conditions and their sintered densities. With the increase of the agglomerate size, the sintered density of the HA compact decreased. It was found that both the sintered density and flexural strength increased with increasing aging time and reaction temperature. A maximum flexural strength of 78 MPa was observed for the samples synthesized at 170°C for 5 h with the predicted average at these conditions being 65 MPa. These samples attained an average sintered density of 88%.     

Effects of particle size and structure of carbon blacks on the abrasion of filled elastomer compounds

The effects of the particle size and structure of various carbon blacks on friction and abrasion behavior of filled natural rubber (NR), styrene–butadiene rubber (SBR) and polybutadiene (BR) compounds were investigated using a modified blade abrader. The effect of particle size and structure on abrasion resistance should be considered for the optimum design of desired wear properties. Characteristic parameters were introduced from the particle size and the structure of carbon blacks, with a linear relationship between the Young’s modulus and these characteristic parameters. The frictional coefficient depended not only on the particle size, but also on the structure of carbon black. The rates of abrasion were decreased with increasing surface area and developing structure of carbon blacks. Abrasion rates of the compounds were found to be proportional to a power n of the applied frictional work input. It was also observed that BR compounds caused much slower wear than NR and SBR compounds. The worn surfaces of the rubber compounds filled with carbon black having smaller particle size and a more developed structure showed narrower spaced ridges and better abrasion resistance. It means that smaller particle size and better structure development of carbon black resulted in improved abrasion resistance.     

Unified inversion scheme that uses light scattering for morphological parameters and optical properties of aggregated aerosols

A robust scheme for characterizing chainlike aggregated aerosols by use of nonintrusive light-scattering measurements is presented. This scheme entails the selection of suitable scattering quantities and their optimal measurement angles; the development of an inversion algorithm to yield the complex refractive index of agglomerates m = n + ik, the primary particle diameter d(p), the number of primary particles per agglomerate N(p), the number density of agglomerates n(A), and the volume fraction of agglomerates f(v); and evaluation of the uncertainties of the inferred parameters that correspond to measuring uncertainties. The data-inversion algorithm is based on the exact formulation of light scattering for agglomerates that consist of primary particles in the Rayleigh limit and therefore has solid theoretical foundations. In addition, this approach yields all the desired parameters of the aggregated aerosols by using in situ light-scattering measurements with a minimum of possible uncertainties. Furthermore, the methodology developed here can be extended to aerosols with other types of morphology and optical property.     

Effect of agglomerates in ZrO2 powder compacts on microstructural development

Ultrafine zirconia powders were prepared by a coprecipitation and spray-drying method. Agglomerates may be fragmented or present in green bodies after compaction. The effect of agglomerates on sintering and microstructural development was studied and it was found that the agglomerate content in compacts was a major factor affecting the microstructure development and the sintered densities. The interaction between agglomerates themselves, and between agglomerates and the primary particle matrix is discussed. It is argued that the hard agglomerates in the powder from the water-washed coprecipitates are formed by oxobridging between non-bridging hydroxyl groups present in the zirconium hydroxide structures due to the effect of hydrogen bonding in the aqueous system. The substitution of organic -OR groups for the non-bridging hydroxyl groups removes this hydrogen-bonding effect between the zirconium hydroxide units and thus eliminates the cause of agglomeration.     

Properties and uses of consolidated cork dust

Cork dust was consolidated without additives by heating under pressure. Four engineering properties of the compacted cork were measured: density, modulus, strength and fracture toughness. The thermal conductivity and the absorption of water by the compacted cork were also measured. The properties depend on the consolidation conditions, and (in a way which is not yet understood) on the origin of the cork dust itself, but not on particle size. The properties are compared with those of other common materials to identify possible uses.     

Deagglomeration of spray-dried submicron particles by low-power aqueous sonication

The resistance to deagglomeration of spray-dried agglomerated particles of submicron size was investigated using an ultrasonication system in water. Submicron agglomerates consisting of water-insoluble primary particles with size of 10 or 100 nm were prepared in different shapes by varying the heating profile during spray drying. Deagglomeration experiments were performed using a low-power sonication device. Spherical agglomerates were found to be more resistant to ultrasonic forces, while dent- or doughnut-shaped agglomerates tended to break down. The results show that the shape of the agglomerate plays an important role in the energy balance of the ultrasound operation. The energy produced from the collapse of cavitation bubbles in the ultrasound vessel may be used to promote motion of the agglomerates and deagglomeration.     

SIMS measurement of nano-sized Au agglomerates in Si

The conditions required for SIMS measurement, namely the detection depth of the SIMS signal and an appropriate measurement cycle, to obtain a reliable shape, size and atom number of nano-sized agglomerates in Si have been investigated. Au agglomerates in Si generated during annealing at 900 °C for 360 h are measured by an appropriate SIMS method and it is found that the Au agglomerate has a spherical shape with a concentration of 5.4 × 10²¹ Au atoms/cm³. The SIMS results agree well with the calculation of spherical agglomerates. The size of agglomerates larger than 20 nm and the Au atom number in agglomerates larger than several nm can be measured in a usual SIMS experiment.     

DYNAMICS OF AGGLOMERATE SIZE DISTRIBUTION IN LINEAR SHEAR FLOW FIELDS

ABSTRACT

A dispersive mixing model was developed and analyzed for the case when separation of the fragments following rupture of agglomerates primarily determines the dynamics of the mixing process. The model incorporates the effects of van der Waals forces within agglomerates and hydrodynamic interactions between fragments as they are convected apart from each other by the applied shear field. The essential features of the model are illustrated by examining the effect of shear on the breakage of parent agglomerates and their first five generations of fragments for a particular test case. In addition, the dynamics of the agglomerate size distribution produced by linear shear flow fields in gaps of various aspect ratios was analyzed for two types of initial conditions. These results provide insight to the design of the high shear zones in actual mixing equipment.