ARR - Annual Report

Abstract

We report our recent results on the effect of impurities or ‘imposter molecules’ on the crystal growth process and developing mechanistic models describing the mechanisms by which impurities influence crystal growth. Impurities affect growth kinetics at the scale of kink attachment and detachment events, which are too fine to examine experimentally in real time. Thus, simulations are used to study the proposed mechanisms for growth inhibition/promotion and the results will be compared to experimental data available in the current literature. As a starting point, Kinetic Monte Carlo (KMC) simulations are utilized to simulate the time evolution of centrosymmetric organic crystal growth. Rare event rates are determined as functions of energetic barriers for desolvation and attachment/detachment works. Various mechanisms have been proposed to explain the growth-inhibiting effect of impurities, including step-pinning and spiral-pinning, which are described herein. These mechanisms will be incorporated into the KMC simulations, and compared to experimental values for validation. Once we have established effective working models, we will look to publish our results and ideally incorporate them into ADDICT3 (Advanced Design and Development of Industrial Crystallization Technology - version 3), an engineering tool which predicts relative growth rates and crystal morphology of solution-grown faceted crystals [1].

Additionally, we report on some new developments in ADDICT3 to improve the workflow during conceptual design of crystalline solid processes. ADDICT3 is capable of predicting the shape and morphology of crystalline particles using only the following input data, (1) crystal structure, (2) atom-atom force field, and (3) specified solvent and growth conditions. The key outputs are the steady-state growth shape and morphology of the crystals, and the “shape triangle” which gives graphical information about the influence of design variables (temperature, supersaturation, solvent) on the resulting shape and morphology of the crystal. More detailed outputs are also provided (e.g., periodic bond chain networks, growth spiral shapes, etc.) for use by the more sophisticated user. The tool can be used alone or in combination with other tools that have been developed recently to aid in the design of crystallization processes.

Executive Summary

Understanding and control of crystallographic polymorphism and crystal habit of organic compounds is scientifically and technologically important to several industries. Since a polymorph is determined at the early stages in crystallization, methods that lead to an advanced understanding of early crystal formation pathways and mechanisms are highly desirable. In this work, we have introduced time-resolved in situ wide-angle X-ray scattering (WAXS) at Cornell’s High Energy Synchrotron Source (CHESS) to study the early formation stages of the Form I and II crystallization events of a pharmaceutical compound, acetaminophen (ACM). Studies were informed by results from earlier investigations that both the surface chemistry of self-assembled monolayers (SAMs) as well as solvent conditions work together to control crystal polymorph. Studying crystallization of Form II by seeded nucleation, we verified that crystals grow faster at the substrate-solution interface than in the bulk above, and that the PTS (trichloro(phenyl) silane) SAM surface is taking over in controlling crystal growth by directing the (002) planes from slightly out-of-plane to a totally in-plane orientation. Studying crystallization of Form I by spontaneous nucleation, we identified unusual shifts along the scattering vector, q, of the earliest peak occurring in the in-situ scattering patterns. Further analysis and corroboration by other data sets pointed to the possible existence of structural transformations at these early crystal formation stages. Our results indicate that our methodologies are effective to gain insights into the earliest formation stages of the crystallization of ACM and are now being extended to other model compounds.

The reproducibility of flow measurement at low stresses is similar for the RST-XS.s shear cell and for the ball indentation method by sieve filling using an indentation attachment to the FT4 Powder Rheometer, however the measured values of unconfined yield stress do not agree. A small hopper will be designed based on the flow measurements of both instruments at low stresses. The critical outlet diameter for flow initiation will be experimentally determined and compared to the dimensions predicted by the flow measurements of these two instruments. To minimise the powder quantity, gypsum powder is proposed for this investigation due to its high bulk density and cohesive flow behaviour.

Shear cell measurements using the FT4 shear cell and Schulze RST-XS.s low stress shear cell agree at moderate stresses, however below 2 kPa the FT4 shear cell does not achieve the intended applied stresses for titania DT51, and therefore does not provide a reliable measurement in this range. The Schulze RST-XS.s provides unconfined yield stress measurements < 5% for the very cohesive titania at pre-shear stresses as low as 100 Pa, however the variability increaseses for more free-flowing powders.

Powder flow measurement at low stresses is more challenging due to (i) the required resolution of the force measurement and (ii) the reproducibity of the loose packing state. Shear cells pre-shear the sample in an effort to ensure a reproducible packing state, however the vertical consolidation applied in indentation and uniaxial compression approaches does not achieve this alone. Ball indentation measurements are assessed by pre-shearing and by blade conditioning, wire conditioning and sieve filling prior to vertical consolidation. At low stresses, pre-shearing is found to provide a large coefficient of variation in the bed hardness measurement by indentation, whereas sieve-filling is able to produce a coefficient of variation < 5% at low consolidation stresses. Uniaxial compression measurements correlate with ball indentation measurements at moderate stresses, allowing constraint factor to be determined and ultimately for unconfined yield stress to be inferred from indentation measurements. However, at lower stresses the uniaxial compression test underestimates the unconfined yield stress.

Measurement of powder flow behaviour is important for many powder handling operations. The most widely established method for measuring powder flow is by shear cell analysis, with procedures developed for designing hoppers based on mass or funnel flow behaviour using shear cell measurements. As the consolidation stress applied to the powder is reduced, the reliability and reproducibility of the measurement decreases. Powder flow measurement at low stresses is assessed here by ball indentation, uniaxial compression and shear cell methods.

Executive Summary

Figure 1. Take home message from the first year.

A first statistical classification was established for thirty powders. Four categories (green, yellow, orange and red) corresponding to various reconstituabilities were identified and summarized in the take home message (Figure 1). Long wetting time was associated to high particle surface hydrophobicity, small particle size, high protein and fat contents in the powder bulk. Long reconstitution time was linked to the powder manufacturing process (grinding) and low sugar content in the powder bulk.

• Green group: short reconstitution time and short wetting time,
• Yellow group: short reconstitution time and long wetting time,
• Orange group: long reconstitution time and short wetting time,
• Red group: long reconstitution time and long wetting time.

(3) First statistical correlations between the various powder characteristics and reconstituability ranking

(2) For selected powders: reconstitution kinetics in different conditions of temperature, stirring, etc.

(1) Powder classification according to their reconstitution behavior

Achieved deliverables:

The first year of the PhD work deals with the systemic physicochemical analysis of powders and their classification according to their reconstitution ability. It will be achieved at the end of January 2020. The PhD work has met the three stated deliverables for thirty powders.

(PhD duration: 1st February 2019 – 31th January 2022)

Executive Summary until the tenth month

EXECUTIVE SUMMARY

In the field of granular rheology, one of the most promising advances of the past decade has been the development of various nonlocal rheologies [1–7]. These constitutive models hold the promise of permitting the determination of a small number of empirical parameters for a particular set of particles, which then can be used to predict flow fields and stresses over a large range of intermittent, creeping, quasi-static, and intermediate flows. In order for these models to be useful, the aim is to make a set of flow measurements for a set of particles in one geometry, and then determine the constitutive parameters for use in predicting flows in other geometries (for the same particles). Doing this requires a quantitative understanding of which properties are set by both the particle properties, and the boundary conditions at the walls.

In Years 1-3, we established that NLR successfully models granular flows across different packing densities, particle sizes and shapes, and shear rates, using just 3 constitutive properties (A, b, µs), but that we must know the amount of slip at the wall from geometry-dependent measurements. In Years 4-6 of this project, we aim to address current shortcomings in how to calibrate and apply NLR to real granular systems. We aim to establish that, for a given set of particles, can we (1) make flow measurements in one geometry which determine the constitutive parameters and (2) use these parameters to predict flows in other geometries. Thus, our current work focuses on separating which flow properties are set by the particle properties, versus those set by the wall properties.

During this first year of the renewal grant, we have observed that boundary roughness strongly controls both the flow profile v(r) and shear rate profile γ˙ (r), particularly as measured at the outer wall. This is also the region of the flow most sensitive to nonlocal effects. We also observed that the pressure P , and therefore the stress ratio µ(r), are affected by the roughness of the wall. All of this is expected, and we can now begin a quantitative understanding of these effects during Year 5. We have done significant development work on photoelastic methods to prepare for these studies. In addition, we continued working on the IFPRI-funded collaboration with Nathalie Vriend.

This resulted in measurements taken at faster flow rates than are accessible in this apparatus (I 1), and resulted in a published paper [21] that included NCSU authors. Along with our other work during Years 1-3, this paper emphasizes the importance of understanding the timescales over which the force chains fluctuate. In performing the next year’s work, will utilize photoelastic methods (both statics and dynamics) as well as our older particle-tracking methods to meet the three aims.

Executive Summary

This project seeks to develop physically realistic models for spray-drying as used in industry with a focus on high viscosity and non-Newtonian fluid atomization. The goal of this work is to develop understanding and correlations for the accurate pilot-to-production scaleup of spray-drying. We divide the work to focus on two nozzle types: pressure-swirl, and two-fluid.

A testing facility is setup for experiments with swirl nozzle. Various types of pressure swirl nozzle with different scales are selected to be tested with different fluids at relatively high pressure. An imaging system is used to take near-nozzle images to analyze the atomization process. It is also used to measure the droplet size downstream and report number distribution and SMD at various radial positions. An atomization process is proposed by observing near-nozzle images. Physics model is being developed and its predictions will be compared with all the experiment results for further improvements.

Preliminary tests of two-fluid nozzles reveal the similarity to single-droplet breakup, thus detailed experimentation and analysis on single droplet atomization by an air jet was conducted. A working hypothesis that the rate of droplet deformation determines the mode of droplet breakup is being studied, and models for the underlying breakup processes have been compared to the experiments with reasonable agreement. The next phase for this branch of the project will be to apply the developed models for single-droplet breakup to the two-fluid atomization geometry.

Executive Summary

Segregation model development holds promise for translation of academic research into industrial practice. Two significant issues that hamper the applicability of models in industry, however, are (1) the inherent difficulty in measuring segregation rates (especially in an experimental setting) for validation purposes and (2) the significant dearth of validated scale-up studies for these models. In this project, we seek to alleviate these two shortcomings of segregation research through a combined theoretical, computational, and experimental program. One unique aspect of our work is that we use flow perturbations to establish an “equilibrium” between segregation and mixing in free surface granular flows in order to alter the steady-state distribution of particles. By achieving this balance between the rate of segregation and the perturbation rate, we can combine the model expressions that we are interested in testing with dramatically simplified experiments to ultimately deduce the segregation rate (and validate the expressions). Moreover, by exploring a novel view of the interplay between granular rheology and segregation, we aim to continue to develop a new way of structuring segregation rate models that make them inherently more scalable than any models previously reported. Thus far we have demonstrated which models from the literature may be considered state-of-the-art, but, more importantly, we developed several novel inherently scalable, theoretical models based on rheologically-relevant dimensionless groups that are applicable to density, size, shape, and cohesive segregation. We have experimentally validated some of these segregation models and plan to expand others, while incorporating the validated models into device-level transport equations in order to supply quantitative prediction of segregation at process scale.

Executive Summary

scale.

device-level transport equations in order to supply quantitative prediction of segregation at process

our ultimate aim is (experimentally) validated segregation models that can be incorporated into

applicable to density, size, shape, and cohesive segregation. As this project continues to mature

novel inherently-scalable models based on rheologically-relevant dimensionless groups that are

be considered state-of-the-art, but, more importantly, we have begun theoretical development of

previously reported. Thus far we have demonstrated which models from the literature may

way of structuring segregation rate models that make them inherently more scalable than any models

of the interplay between granular rheology and segregation, we aim to continue to develop a new

deduce the segregation rate (and validate the expressions). Moreover, by exploring a novel view

expressions that we are interested in testing with dramatically simplified experiments to ultimately

this balance between the rate of segregation and the perturbation rate, we can combine the model

free surface granular flows in order to alter the steady-state distribution of particles. By achieving

is that we use flow perturbations to establish an “equilibrium” between segregation and mixing in

combined theoretical, computational, and experimental program. One unique aspect of our work

In this project, we seek to alleviate these two shortcomings of segregation research through a

• for validation purposes
• the significant dearth of validated scale-up studies for these models.

are (1) the inherent difficulty in measuring segregation rates (especially in an experimental setting)

practice. Two significant issues that hamper the applicability of models in industry, however,

Segregation model development holds promise for translation of academic research into industrial

Executive Summary

2 and 3.

publication in Q1 2019. This report summarises the progress to date and the remaining work for years

of this work is included in this report, and the first “proof of principle” paper will be ready for

out for the first time which showed the layer by layer detail of the 3D printing process. A description

something which had not been previously observed. X-ray tomography of the agglomerate was carried

agglomerate bonds to determine the optimum bond material to prevent individual particle breakage,

more detail. Soft, rigid and a hybrid mixture of both soft and rigid materials were used for the

orientation, individual particles and observe the breakage behaviour with much more accuracy and in

agglomerates in colour. By dividing the agglomerate into coloured sections, it will be possible to track

of strength behaviour at different strain rates. A Stratasys Object 500 Connex 3 was used to print the

identical spherical agglomerates 3D printed in colour were carried out to investigate the distribution

ideas and implement them broadly. In year one of this project, quasi-static compression tests of

work from this project would enable the particle technology worldwide community to take up the

disintegration and powder flow and segregation using the newly developed approach. The published

The new IFPRI project contains three sub projects which focus on agglomerate breakage, agglomerate

successfully conducted and the results were highly reproducible.

structure. For the first time, experimental tests on “perfect” particles with tuneable properties were

and the breakage behaviour was compared with a DEM simulation of an agglomerate with an identical

techniques. In the previous IFPRI project, identical copies of agglomerates were designed and printed

orientations. To date, this has not been possible via experimental agglomeration production

under the same condition/orientation and then repeated for various other conditions and

3D printing technology allows mass fabrication of identical agglomerates that can be tested repeatedly

from a ‘single’ individual agglomerate can never be replicated.

possibility of reproducing the data under the same conditions. Therefore, experimental data produced

destructive nature of the experimental tests i.e. breakage, dissolution etc., which would eliminate the

inability to capture the true complexity of the agglomerate structures in simulations and 2) the

actual experimental measurements. The two key drawbacks of the current approach are 1) the

entered into a computer for imprecise estimates of the model simulations, then compared against the

measure the relevant properties of existing non-identical particles. These parameters are then

due to lack of suitable test particles. To date, the cumbersome approach has been to individually

Accurate and systematic validation of particle systems with a simulated model has not been possible

Executive Summary

size distribution, capillary pressure distribution.

• Generation (proof of concept) of characteristic data of the pore system, e.g. pore
• Image analysis of 3D-tomography data using VG Studio (expert software).
• Generation (proof. of concept) of tomography images of filter cakes
• Selection of compact and needle-shaped particle system
• Formation of filter cakes with different prose structure due to wetting effects.

proven:

The actual state of the project is that the methods have been developed and the concept is investigations.

method, it delivers precise and reproducible surface properties for the scientific (wet) coating with highly hydrophobic silanes. Even though this is a quite time consuming solution. The second one is the modification of the particle surface. For this case, we do a in which we change the wetting properties by changing the ethanol concentration in the shape two scenarios). The first approach is to change the composition of the mother liquid, in particle-particle interaction, we defined two main filtration scenarios (for each particle analyse the overall effect of wettability change in our system, which plays an essential role Particle-particle interaction during the filtration process was another scope of focus. To certain size range to fit to the voxel size of the measurements.

measurements, thus the solids need to have a certain X-ray adsorption as well as a sample. The material selection also was influenced by the specifications of the Xray filler and plastics. In the case of compact particles, we selected Al2O3 T60/46 alphaalumina we selected Wollastonite, which is widely used in ceramics, friction products, painting a fibrous behaviour when creation the filter cake structure. For the needle-like particles, progress, we applied compact and needle-like particles. The needle-like particles showed In order to analyse the effect of particle shape on the filter cake structure and filtration characteristics.

This study was done on two main particle shapes, which generated different filter cake comprehensive research by producing and interpreting laboratorial and micro-CT data.

Due to the complexity of the parameters affecting the cake filtration process, we do a