Particle-particle Bonds Research Articles

Intra and Extra-granular Disintegrant Properties of Modified Underutilised Red Lima Bean Starch in Paracetamol Tablet Formulation

Red lima bean (Phaseolus lunatus Linn) Family Fabaceae, has been modified by succinylation and annealing, and used as intra- and extra-granular disintegrants at concentrations of 5 and 10 %w/w in paracetamol tablet formulation in comparison with corn starch BP. The starches were characterised using FT-IR spectroscopy, SEM, proximate analysis, physicochemical and functional properties. FT-IR spectrometry revealed characteristic peaks at 1575.53 and 1713.99 cm-1 for the succinylated starch while the annealed showed no significant difference from the native starch. Modifications did not alter the ovoid shape of the native starch but reduced the particle size. Succinylation improved water absorption capacity, solubility and swelling of lima bean starch but annealing reduced the parameters. Tablets with disintegrants of lima bean starches generally had higher crushing strengths and lower friability than tablets with corn starch. Modifications reduced the disintegration time of the tablets when the starches were incorporated intra-granularly, which suggested particle-particle bond interruption and destruction of hydrogen bonds as mechanism of disintegration. Tablets containing 10 %w/w succinylated red lima bean starch incorporated intra-granularly had the highest disintegration efficiency ratio, DER, indicating a great balance between mechanical and disintegration properties. Modified red lima bean starches incorporated intra-granularly into paracetamol tablets led to faster disintegration and could efficiently substitute corn starch as disintegrant.

Direct measurements of the microstructural origin of shear-thinning in carbon black suspensions

Scientific questions surrounding the shear-dependent microstructure of carbon black suspensions are motivated by a desire to predict and control complex rheological and electrical properties encountered under shear. In this work, direct structural measurements over a hierarchy of length scales spanning from nanometers to tens of micrometers are used to determine the microstructural origin of the suspension viscosity measured at high shear rates. These experiments were performed on a series of dense suspensions consisting of high-structured carbon blacks from two commercial sources suspended in two Newtonian fluids, propylene carbonate and light mineral oil. The shear-induced microstructure was measured at a range of applied shear rates using Rheo-VSANS (very small angle neutron scattering) and Rheo-USANS (ultra-small angle neutron scattering) techniques. A shear-thinning viscosity is found to arise due to the self-similar break up of micrometer-sized agglomerates with increasing shear intensity. This self-similarity yields a master curve for the shear-dependent agglomerate size when plotted against the Mason number, which compares the shear force acting to break particle-particle bonds to the cohesive force holding bonds together. It is found that the agglomerate size scales as R g , agg ∼ M n − 1. Inclusion of the particle stress contribution extends the relevance of the Mason number to concentrated suspensions such as those relevant to the processing of carbon black suspensions for various applications.

A Novel Approach of Bulk Strength Enhancement through Microbially-Mediated Carbonate Cementation for Mylonitic Coal

Mylonite coal is known to be highly tectonically deformed coal and is a result of crushing original coal into fine-grained coal under multiple tectonic events. Because of its granular nature and the resultant inferior mechanical property, the borehole stability during both drilling and gas drainage is challenging due to unpredictable failures. This study explored a potential approach to enhance the bulk strength of mylonitic coal via microbiologically-mediated CaCO3 cementation which effectively increases the cohesion of the fine coal particles through the bio-cementation process. The experimental results indicated that the mechanical strength was significantly enhanced after a short period of biotreatment with 12 cycles of biotreatment yielding a maximum stiffness of 32 KN/mm and maximum uniaxial compressive strength of 9.3 MPa. The strength evolution behavior demonstrated that the macroscopic failure behavior of mylonite coal evolves from plastic failure to brittle failure as the increase of bio-treatments. The results from XRD indicated that the generated CaCO3 crystals mainly occurs in the form of calcite and vaterite. Imaging by SEM further indicated the cementation process for CaCO3. The generated CaCO3 precipitation first occurs on random spots on the particle surfaces, and then occupies the interstitial space until particle-particle bonds are generated.

Microstructure and yielding of capillary force induced gel

We have investigated the rheology and structure of a gel formed from a mixture of non-Brownian particles and two immiscible liquids. The suspension of particles in a liquid undergoes gelation upon the addition of a small content of second, wetting liquid which forms liquid bridges between particles leading to a sample spanning network. The rheology of this gel primarily exhibits a yield stress at low shear rates followed by a linear variation of shear stress at high shear rates. The apparent yield stress extracted from the flow curves increases rapidly with volume fraction of second liquid before saturation, while it exhibits a monotonic increase with increasing particle concentration. Rescaling of the yield stress curves using suitable shift factors results in an empirical expression for the yield stress showing squared dependence on liquid fraction and a rapid increase with particle fraction above a certain value, both combined in a highly nonlinear manner. The microstructural variations with changing secondary liquid content and particle fractions are captured using three dimensional X-ray tomography technique. The microstructure is observed to show increased local compactness with increased liquid content and increased spatial homogeneity with increased particle fractions. The images from X-ray tomography are analysed to obtain the distributions of particle-particle bonds (coordination number) in the system which serve to explain the observed yield stress behavior in a qualitative manner.

Micromechanical Characterization of Particle-Particle Bond in Biomass Assemblies Formed at Different Applied Pressure and Temperature

Micromechanical Characterization of Particle-Particle Bond in Biomass Assemblies Formed at Different Applied Pressure and Temperature

Strengthening mylonitized soft-coal reservoirs by microbial mineralization

Mylonitized-soft-coal is common throughout central China and results from the crushing of intact coal into fine particles under extreme tectonic stress. The fine particles result in very low permeability and hydraulic fracturing to recover natural gas is difficult due to the very low mechanical strength. Enhancing structural integrity and mechanical strength of these coals are the keys to efficiently extracting coalbed methane (CBM). The following explores using microbially-induced calcium carbonate cementation to strengthen and stiffen the coal – and therefore enable successful hydraulic fracturing. We explore the impact of this cementation on the mechanical properties and on microscopic mechanisms of failure for granular assemblages of four sizes. Results indicate significant strength gain after only short periods of biochemical reaction (hours to days) with four cycles of microbial injection (~2 days) yielding a maximum compressive strength (UCS) of ~12 MPa and a brittleness index of 0.17 exceeding that of hard coal. Notably, a higher calcium carbonate content does not automatically guarantee a higher strength- indicating that the distribution of the mineralization and the quality of the particle-particle bonding exerts key control. Also, for identical injection volumes, the resulting calcium carbonate content differs significantly with particle size – larger particle size samples can accommodate larger masses of calcium carbonate. Imaging by SEM indicates that precipitation first occurs on the particle surface, partially enveloping it, before creating particle-particle bonds – thus maintaining grain-pore and pore-pore fluid transport connectivity. As the void is occupied, the cementation process slows, halts, as bacteria and nutrient are expended, and further supply is limited. Therefore, for a fixed duration of supply, the interparticle space of the smaller particle-size will be the first to be bonded and the carbonate content of the smaller particle-size samples will be lower than that for larger particles.

Effects of Coalescence on Shear-Induced Gelation of Colloids.

Shearing lyophobic colloidal suspensions can lead to aggregation, followed by gelation, if the formed clusters grow to sizes large enough to percolate. If the temperature is set over the glass transition temperature of the suspended material, the particles embedded in the same aggregate start to coalesce with one another. Coalescence occurs to the finite viscosity of the particles' material, which leads to material diffusion from particle to particle. The driving force of this process is the reduction of the particle-dispersant interface and, as a consequence, the decrease the center-to-center separation of the particles. This leads to decreased cluster size, and hence a delayed gelation. Simultaneously, coalescence reinforces the particle-particle bonds formed upon aggregation, leading to clusters that are able to resist higher hydrodynamic forces before breaking up, hence leading to faster gelation. These two competing effects, combined with the natural complexity of colloidal aggregation makes it rather difficult to understand and predict which trend becomes dominant. In the present work, the shear-induced gelation of model polymeric colloidal systems with different glass transition temperatures has been studied. Starting with their interaction potential we investigate the impact of temperature on the gel time in concentrated suspensions (φ = 5%) under steady shear, followed by the effect of temperature on the stress-resistance of fully destabilized clusters under agitation. The results of the present work allow for a systematic view and deepened understanding of the factors governing shear-induced gelation in the presence of coalescence.

Tensile test simulation of high-carbon steel by discrete element method

Purpose – The tensile test is one of the fundamental experiments used to evaluate material properties. Simulating a tensile test can be a replacement of experiments to determine mechanical parameters of a continuous material. The paper aims to discuss these issues. Design/methodology/approach – This research uses a new approach to model a tensile test of a high-carbon steel on the basis of discrete element method (DEM). In this research, the tensile test specimen was created by using a DEM packing theory. The particle-particle bond model was used to establish the internal forces of the tensile test specimen. The particle-particle bond model was first tested by performing two-particle tensile test, then was adopted to simulate tensile tests of the high-carbon steel by using 3,678 particles. Findings – This research has successfully revealed the relationships between the DEM parameters and mechanical parameters by modelling a tensile test. The parametric study demonstrates that the particle physical radius, particle contact radius and bond disc radius can significantly influence ultimate stress and Young’s modulus of the specimen, whereas they slightly impact elongation at fracture. Increasing the normal and shear stiffness, the critical normal and shear stiffness can enable the increase of ultimate stress, however, up to maximum values. Research limitations/implications – To improve the particle-particle bond model to simulate a tensile test for high-carbon steel, the damping factors for compensating energy loss from transition of particle motions and failure of bonds are required. Practical implications – This work reinforces the knowledge of applying DEM to model continuous materials. Originality/value – This research illustrates a new approach to model a tensile test of a high-carbon steel on the basis of DEM.

Microstructure and nonlinear signatures of yielding in a heterogeneous colloidal gel under large amplitude oscillatory shear

We investigate yielding in a colloidal gel that forms a heterogeneous structure, consisting of a two-phase bicontinuous network of colloid-rich domains of fractal clusters and colloid-poor domains. Combining large amplitude oscillatory shear measurements with simultaneous small and ultra-small angle neutron scattering (rheo-SANS/USANS), we characterize both the nonlinear mechanical processes and strain amplitude-dependent microstructure underlying yielding. We observe a broad, three-stage yielding process that evolves over an order of magnitude in strain amplitude between the onset of nonlinearity and flow. Analyzing the intracycle response as a sequence of physical processes reveals a transition from elastic straining to elastoplastic thinning (which dominates in region I) and eventually yielding (which evolves through region II) and flow (which saturates in region III), and allows quantification of instantaneous nonlinear parameters associated with yielding. These measures exhibit significant strain rate amplitude dependence above a characteristic frequency, which we argue is governed by poroelastic effects. Correlating these results with time-averaged rheo-USANS measurements reveals that the material passes through a cascade of structural breakdown from large to progressively smaller length scales. In region I, compression of the fractal domains leads to the formation of large voids. In regions II and III, cluster-cluster correlations become increasingly homogeneous, suggesting breakage and eventually depercolation of intercluster bonds at the yield point. All significant structural changes occur on the micron-scale, suggesting that large-scale rearrangements of hundreds or thousands of particles, rather than the homogeneous rearrangement of particle-particle bonds, dominate the initial yielding of heterogeneous colloidal gels.

Understanding Disintegrant Action by Visualization

The aim of this study was to utilize high-speed video imaging for understanding the disintegrability of compacts and disintegrant action upon wetting. High-speed video imaging was used to visualize the disintegration of compacts and effect of wetting on free disintegrant particles. Acquired images were processed using MATLAB, and changes in the compact area and instantaneous motion of compacted particles on contact with water were analyzed. The capillary action of compacts was also determined for various disintegrants. Finally, the breakdown behavior of compacts prepared with selected disintegrants was analyzed at different compression forces to evaluate recovery of compaction strain. Water-insoluble inert diluent, dicalcium phosphate, was used as a comparator. The results from this visualization study provided an in-depth understanding of the disintegrant behavior of free and compacted disintegrant particles upon wetting. The mechanisms of swelling, capillary action, disruption of particle-particle bonds and strain recovery were successfully monitored by video imaging. The disintegration of compacts containing crospovidone appeared to be less influenced by swelling or wicking action. The influence of compression force on the disintegration of selected disintegrants confirmed that strain recovery is the dominant mechanism for the disintegrant action of crospovidone.

3D Simulation of Internal Tablet Strength During Tableting

This study presents a new approach to model powder compression during tableting. The purpose of this study is to introduce a new discrete element simulation model for particle-particle bond formation during tablet compression. This model served as the basis for calculating tablet strength distribution during a compression cycle. Simulated results were compared with real tablets compressed from microcrystalline cellulose/theophylline pellets with various compression forces. Simulated and experimental compression forces increased similarly. Tablet-breaking forces increased with the calculated strengths obtained from the simulations. The calculated bond strength distribution inside the tablets showed features similar to those of the density and pressure distributions in the literature. However, the bond strength distributions at the center of the tablets varied considerably between individual tablets.

Continuum percolation of long lifespan clusters in a simple fluid

We present results on the percolation loci for chemical clusters and physical clusters of long lifespan. Chemical clusters are defined as sets of particles connected through particle-particle bonds that last for a given time tau. Physical clusters are sets of particles that remain close together at every instant for a given period of time tau. By using molecular dynamics simulations of a Lennard-Jones system we obtain the percolation loci at different values of tau as the lines in the temperature-density plane at which the system presents a spanning cluster in 50% of the configurations. We find that the percolation loci for chemical clusters shifts rapidly toward high densities as tau is increased. For moderate values of tau this line converges to the low-density branch of the liquid-solid coexistence curve. This implies that no stable chemical clusters can be found in the fluid phase. In contrast, the percolation loci for physical clusters tend to a limiting line, as tau tends to infinity, which is far from the liquid-solid transition line.

Fluidization Behavior of Vibrated and Aerated Beds of Starch Powders.

Batch experimental work on the fluidization hydrodynamic and entrainment phenomena of cohesive starch powders was studied. Results show that fluidization can be realized as vibration break particleparticle bond in the bed. The higher Umf values compared to predictions indicate the formation of agglomerates in the bed. This has increased the residence time of fines to reduce material loss by entrainment. It was found that using starch powders as feed materials, entrainment was only in the range of 0.5-1.7% of the total fines (should be entrained) in the bed. As has also been found by other workers, the entrainment rate constants of group C decrease as particle size decreases. By adapting the criterion proposed by Rietema (1984) as well as Ma and Kato (1998), it was found in this case that the critical cohesion number, Ncoh* is 19.

A simple solid-on-solid model of epitaxial thin films growth: inhomogeneous multilayered sandwiches

In this work a simple solid-on-solid (SOS) model of inhomogeneous films epitaxial growth is presented. The results of the computer simulations based on the random deposition (RD) enriched by a local relaxation, which tends to maximize the number of a particle-particle lateral bonds (PPLB) against barriers blocking diffusion are presented. The influence of strength of the atoms interactions and barriers for diffusion on film roughness and possible bridges between the layers in trilayered sandwich system are considered. For magnetic layers with a non-magnetic spacer the bridging is responsible for direct magnetic coupling between layers. Also variation of the spacer thickness, when scanning the film surface is essential for uniformity of the magnetic coupling between the layers. Number of bridges for very thin spacer and variation of the spacer thickness are discussed in this work.

Erosion Properties and Dispersion-Flocculation Behavior of Bentonite Particles

AbstractExperimental and theoretical studies have been performed to clarify the ability of flowing groundwater in contact with bentonite to generate bentonite colloidal particles and disperse such colloids. This information is required to determine (a) the long-term stability of bentonite as a buffer material for borehole disposal of radioactive wastes in deep geologic media and (b) the potential influence of bentonite colloidal particles on radionuclide transport, specifically for use in scenario analyses in the performance assessment of waste disposal.In this study, the minimum groundwater velocity required to erode particles of Nabentonite or Ca-bentonite from a bentonite surface in contact with groundwater was derived from shear strengths of aqueous bentonite gel suspensions, as determined by viscometer tests. The shear strengths were used to estimate the corresponding shear force on bentonite particle-particle bonds, using an estimated value for the number of initial bentonite particle-particle bonds in the experimental systems studied. The derived shear force was converted to corresponding groundwater velocity by using Stokes' equation and simplifying assumptions. The results indicate that groundwater velocities in a range of about 10−5 to 10−4 m/s would be required to initiate bentonite erosion. This range is higher than the groundwater flow velocity generally found in deep geologic media in Japan. In addition, known groundwater electrolyte concentrations were compared with theoretical estimates of aqueous electrolyte concentrations required to flocculate colloidal bentonite particles (for example 1 × 10−3 mol/l Na+). The comparison indicates that, even if erosion of bentonite occurred, the colloidal bentonite particles formed would flocculate. As a result, this study has shown that the effect of bentonite colloids on radionuclide transport is likely to be negligible in the performance assessment of radioactive waste disposal in deep geologic media.

Predicting erosion resistance of muds

When measured or apparent yield stress of cohesive muds is assumed to reflect average particle-particle bond strength in network structures, critical bed shear stress required for grain-by-grain entrainment can be predicted from an analysis of the forces acting on component grains of geometrically-flat mud beds. Erosion resistance is then defined in terms of cohesive yield stress as well as nominal particle size, shape, relative density, and packing geometry. Predicted values of critical bed shear stress compare favorably with existing data from selected studies in which appropriate yield stress and hydrodynamic parameters have been reported.

The influence of moisture content on the consolidation and compaction properties of paracetamol

The influence of moisture content on the consolidation and compaction characteristics of paracetamol has been studied. Compression speed, mean yield pressure, relative powder density ( D 0), tablet crushing strength and capping pressure were used as the basis of the investigation. At all speeds of compression, mean yield pressure decreased with increasing moisture content especially up to 6% w/w, due to the plasticizing effect of moisture on the paracetamol powder. The relative density of the paracetamol tablets increased with moisture content due to interparticulate and die wall lubrication effects of the moisture forming surface films on the paracetamol particles, which smooth surface microirregularities and so reduce frictional forces and promote particle rearrangement and slippage. Increasing percentages of moisture up to 6% w/w increased tablet crushing strength, whilst higher moisture contents of 8% w/w significantly reduced compact strength. The initial increase in compact strength was likely to be due to the hydrodynamic lubrication effect of moisture, which promotes compaction force transmission and formation of strong hydrogen bonds. The subsequent decrease in tablet strength with moisture content above 6% w/w can be ascribed to hydrostatic resistance of excessive moisture in the void spaces, which reduces particle-particle contact area, surface energy and corresponding adhesive forces. The capping pressure of the paracetamol compacts increased with moisture content up to 6% w/w, probably due to the formation of strong interparticulate hydrogen bonding, which reduces particle-particle separation. The subsequent decrease in capping pressure at 8% w/w moisture content can be attributed to bond weakening as a result of the disruption of particle-particle bonds by an excess of moisture.

Rheology and particle interaction of thickened latex

The pseudoplastic rheological properties of concentrated monodisperse polystyrene latexes with known sodium lauryl sulfate and methylcellulose surface coverages have been studied. It was assumed that the flow units of a concentrated thickened latex subjected to mechanical shear are “flocs” which comprise many particles with immobilized medium in the interstices. During shearing, the particle-particle bonds within the flocs undergo compression and stretching, sometimes breaking and reforming, causing the energy dissipation measured as the yield stress. A model was developed to calculate the average number of bonds per floc and this model was applied to an empirical modification of Firth and Hunter's elastic floc model to correlate the yield stress with the particle-particle separation pressure (defined as a measure of the interaction strength). It was found that the yield stress of a thickened latex is affected by the particle-particle interaction and the morphology of the particle flocs. The particle-particle interaction is affected by the surface coverage of thickener and emulsifier, and their concentrations in the aqueous phase, as well as other factors. The morphology of the particle flocs is affected by the particle interaction and the mechanical treatment. The adsorption of emulsifier and thickener, the rheology of the thickened latexes, the morphology of the particle flocs, and the particle-particle interactions, as well as their interrelationships, are described.

A Comparison of Ag/W,Ag/WC, and Ag/Mo Electrical Contacts

Three Ag/R (where R = W, WC, or Mo) powder metal electrical contacts of 50/50 (volume percent) composition were prepared by an identical press-sinter-infiltrate process to have comparable microstructures. Their thermophysical, mechanical, and electrical performance properties were compared. Hardness, electrical conductivity, and thermal expansion are proportional to the refractory properties. Contact millivolt drop is highest in Ag/W followed by Ag/Mo and Ag/WC. Contact erosion at 30 A switch test is highest in Ag/W followed by Ag/WC and Ag/Mo. Arc affected zone microstructure explained the difference in millivolt drop properties. High current tests at 1600 A showed a different crack formation pattern and erosion mode among the three materials. The differences are explained in terms of particle-particle bond strength, silver wetting characteristic, and thermal shock resistance properties.

Flow behavior of coagulated colloidal sols. V. Dynamics of floc growth under shear

Further experiments on the “elastic floc” model, for the flow behavior of coagulated colloidal sols, are described. Previous theoretical and experimental work had shown that these systems could be adequately described by this model provided that certain assumptions could be made about the dependence of floc size, a, on shear rate D. In particular it was required that the quantity Z = ( λ′ Da 2 δ/ r 3) should be independent of the shear rate. It is shown in this paper that this is indeed the case, at least for particles of a given radius, r. It is also shown that the distance δ, through which particle-particle bonds in a floc are stretched, is essentially independent of shear rate and is of the order of a few angstroms at modest shear rates (300–3000 sec −1). (λ′ in the expression for Z is a dimensionless theoretical parameter which combines, among other things, the orthokinetic capture efficiency and a correction to the Stokes' equation for the frictional force on a sphere.)