<p>Evidence exists for the airborne transmission of contagious pathogens such as SARS-CoV-2, influenza A virus and <i>Mycobacterium</i> <i>tuberculosis</i> in indoor environments. These pathogens are carried in the respiratory droplets and transmitted through airborne route to infect individuals. An important element in risk assessment for pathogenic bioaerosol exposure is a determination of the inhaled deposited dose rate – the number of deposited pathogenic particles per minute – received by each respiratory region and the fractional reduction of dose rate by different material facemasks. This paper presents an aerosol physics-based modeling framework to estimate the fractional reduction of regional dose rate in diverse indoor healthcare environments. The fractional reduction of dose rate is a useful metric to evaluate the facemask effectiveness in reducing the inhaled dose rate. Data extraction of pathogenic bioaerosol size distributions and size-dependent facemask filtration efficiency curve combined with deposition fraction model become the baseline to calculate the fractional reduction of dose rate by 10 different facemasks. Facemask leakage is also considered for the realistic representation of its impact on reduction fraction as current studies focus on mask material filtration efficiency. This analysis considers how the fractional reduction of dose rate is influenced by the pathogenic bioaerosol size distribution, age-dependent respiratory parameters, age-specific deposition fraction, facemask filtration efficiency and mask leakage. Different factors drove variations in the reduction fraction of various sized-pathogenic bioaerosols received by each respiratory region for each age group. This framework can be a useful tool for decision-makers in evaluating the mask’s effectiveness in reducing deposition of pathogenic bioaerosols.</p>

Metal additive manufacturing (AM) can produce complex parts that were once considered impossible or too costly to fabricate using conventional machining techniques, making AM machines an exceptional tool for rapid prototyping, one-off parts, and labor-intensive geometries. Due to the growing popularity of this technology, especially in the defense and medical industries, more researchers are looking into the physics and mechanics behind the AM process. Many factors and parameters contribute to the overall quality of a part, one of them being the powder bed itself. So far, little investigation has been dedicated to the behavior of the powder in the powder bed during the lasering process. A powder spreading machine that simulates the powder bed fusion process without the laser was designed by Lawrence Livermore National Laboratory and was built as a platform to observe powder characteristics. The focus for this project was surface roughness and particle size distribution (PSD), and how dose rate and coating speed affect the results. Images of the 316L stainless steel powder on the spreading device at multiple layers were taken and processed and analyzed in MATLAB to access surface quality of each region. Powder from nine regions of the build plate were also sampled and counted to determine regional particle size distribution. As a comparison, a simulation was developed to mimic the adhesive behavior of the powder, and to observe how powder distributes powder when spread.

Thermoporosimetry is a technique to determine small pore sizes based on melting and crystallization point depression. The temperature shift was measured by Differential Scanning Calorimetry (DSC). Development of thermoporosimetry was carried out on silica with a well-characterized narrow pore size distribution. Several parameters were studied, which a have a direct influence on melting and crystallization point depression (for example: a quality of the solvent, filling the pores with the solvent, time and frequency of centrifuging, superfluous solvent removal conditions, etc.). The optimum conditions for the thermoporosimetry method were developed using high porosity silica. The optimized experimental conditions found for silica were applied to polypropylene powder with much lower porosity. Several polypropylene powders were synthesized using different polymerization catalysts and their porosity determined. Polymer powder morphology and structure was characterized by standard methods. Powder porosity obtained by thermoporometry, gas sorption, and BET methods was compared.

Die Charakterisierung von Nanopartikeln erfordert eine Messung des Dispersitätszustandes bei allen Schritten der Herstellung - von der Synthese bis zum fertigen Produkt. Dafür ist eine leistungsfähige Partikelmesstechnik notwendig, deren Methoden bei der Beschreibung des komplexen Materialverhaltens helfen können. Die Ultraschalldämpfungsspektroskopie ist eine Messmethode, die zur prozessbegleitenden Charakterisierung hochdisperser Pulver und Suspensionen geeignet ist. Mit Vergleichen von Messungen und Modellrechungen wurde festgestellt, dass für die Ultraschalldämpfungs-Modellierung in Dispersionen homogener Partikel ein auf dem Phänomen der elastischen Streuung basierendes Modell praktisch relevant ist. Dies betrifft sowohl die Anwendung zur Messung in Suspensionen als auch in Emulsionen homogener Partikel. Bei einem Vergleich von Modellrechungen und Messungen für ein System poröser Partikel bzw. Aggregate wurde das Modell der Streuung an poroelastischen Kugeln als geeignet zur Beschreibung der Dämpfung disperser Systeme identifiziert. Bei Vorhandensein grober Partikel in Suspensionen nanoskaliger Systeme ist somit eine korrekte Auswertung der Partikelgröße möglich; der bislang übliche Messbereich wurde erweitert. Sekundärer Schwerpunkt der Arbeit ist die Diskussion der numerischen Modellanwendung. Es werden weiterhin Lösungsmöglichkeiten zur Dämpfungsberechnung und zur Berechnung der Größenverteilungen beschrieben. Des Weiteren wurden Anregungen für Entwickler von Ultraschallspektrometern abgeleitet.

NMR is gaining increasing interest in civil engineering for applications regarding microstructure characterization as e.g., to determine pore sizes or to monitor moisture transport in porous materials. This study reveals the capability of NMR as a tool for pore size characterization. Therefore, we measured floor screed and synthetic materials at partial and full saturation. For most examined materials, the pore size distribution was successfully determined using either a reference or a calibration method. Since diffusion effects were observed for some samples in single-sided NMR measurements, further tests employing an NMR core analyzer were carried out in a homogeneous magnetic field. The finally obtained surface relaxivity of floor screed (50 μm/s) resulted to be much higher than suggested by literature.

The master´s thesis deals with the volume changes of concrete during its concrete glow. These volume changes are generally more susceptible to high-strength concretes – HSC, which contain a bigger dose of binder. The theoretical section describes the possible reduction volume change especially in HSC, which are focused on the composition of concrete, especially on the type and particle size distribution of aggregate. Then attention is also paid to the different types of cements and their possible substitution. The part of the theoretical work describes the types of volume changes that may occur. In the experimental part are suggested the HSC by to secure informations. Different kinds of aggregates are used and a continuous or discontinuous grain curve and a different maximum grain size. Part of the sample was made only from CEM I 42,5 R and the second part of the sample from CEM I 42,5 R with the addition of very finely ground limestone. In terms of the part of the work were monitored volume changes of concrete with different composition and also their mechanical properties after 7, 28 and 90 days. Specifically, compressive strength, tensile strength, strength of the surface layers of concrete, water absorption and water-permeability test concrete. In conclusion, are listed all the results of tests.

The topic of the Ph.D. thesis was focused on the process of sintering alumina and zirconia ceramic materials with the aim to compare kinetics of sintering sub-micro and nanoparticle systems. Zirconia ceramic powders stabilized by different amount of yttria addition in the concentration range of 0 – 8 mol% were used. The different crystal structure (secured by yttria stabilization) of zirconia, as found, did not play statistically proven role in the process of zirconia sintering. The possible influence was covered by other major factors as particle size and green body structure, which does affect sintering in general. According to the Herrings law, the formula predicting sintering temperature of materials with different particle size was defined. The predicted sintering temperatures were in good correlation with the experimental data for zirconia ceramic materials prepared from both, coarser submicrometer, and also nanometer powders. In case of alumina ceramics the predicted and experimentally observed sintering temperature values did not match very well. Mainly the nanoparticle alumina materials real sintering temperature values were markedly higher than predicted. The reason was, as shown in the work, strong agglomeration of the powders and strong irregularities of particle shape. The major role of green body microstructure in the sintering process was confirmed. The final density of ceramic materials was growing in spite of sintering temperature, which was decreasing together with pore - particle size ratio (materials with similar particle size were compared). Sintering temperature was increasing together with growing size of pores trapped in the green body structure. Clear message received from the above mentioned results was the importance of elimination of stable pores with high coordination number out off the green body microstructure during shaping ceramic green parts. Same sintering kinetics model was successfully applied on the sintering process of submicro- and also nanometer zirconia ceramics. Activation energy of nanometer zirconia was notably lower in comparison to submicrometer material. For the sintering of nanoparticle zirconia was typical so called “zero stage” of sintering, clearly visible on kinetic curves. It was found out, that processes running in zirconia “green” material during zero stage of sintering are heat activated and their activation energy was determined. Pores of submicrometer zirconia were growing in an open porosity stage of sintering just a slightly (1.3 times) compared to the nanoparticle zirconia, where the growth was much higher (5.5 times of the initial pore diameter). This difference was most probably caused by preferential sintering of agglomerates within the green bodies and by particle rearrangement processes which appears in the zero stage of sintering of nanoparticular ceramics. The technology of preparation of bulk dense ytria stabilized zirconia nanomaterial with high relative density of 99.6 % t.d. and average grain size 65nm was developed within the thesis research.

A simple capillary flow porometer (CFP) was assembled for pore structure characterization of monolithic capillary liquid chromatography columns based on ASTM standard F316-86. Determination of differential pressures and flow rates through dry and wet samples provided the necessary information to determine the through-pore throat diameter, bubble point pore diameter, mean flow pore diameter, and pore distribution. Unlike measurements in bulk using traditional techniques to provide indirect information about the pore properties of monolithic columns, monoliths can be characterized in their original chromatographic forms with this system. The performance of the new CFP was first evaluated by characterizing the pore size distributions of capillary columns packed with 3, 5, and 7 µm spherical silica particles. The mean through-pore diameters of the three packed columns were measured to be 0.5, 1.0 and 1.4 µm, which are all smaller than the pore diameters calculated from a close-packed arrangement (i.e., 0.7, 1.1 and 1.6 µm), with distributions ranging from 0.1 - 0.7, 0.3 - 1.1 and 0.4 - 2.6 µm, respectively. This is reasonable, since visual inspection of SEM images of the particles showed relatively large fractions of smaller than specified particles in the samples. Typical silica monoliths were fabricated via phase separation by polymerization of tetramethoxysilane (TMOS) in the presence of poly(ethylene glycol) (PEG). The mean pore diameter and pore size distribution measured using the CFP system verified that a greater number of pores with small throat diameters were prepared in columns with higher PEG content in the prepolymer mixture. SEM images also showed that the pore diameters of monoliths fabricated in bulk were found to be smaller than those in monoliths synthesized by the same procedure, but confined in capillary tubes. The CFP system was also used to study the effects of column inner diameter and length on pore properties of polymeric monoliths. Typical monoliths based on butyl methacrylate (BMA) and poly(ethylene glycol) diacrylate (PEGDA) in capillary columns with different inner diameters (i.e., 50 to 250 µm) and lengths (i.e., 1.5 to 3.0 cm) were characterized. The mean pore diameters and the pore size distributions indicated that varying the inner diameter and/or the length of the column affected little the pore properties. The latter finding is especially important to substantiate the use of CFP for determination of monolithic pore structures in capillaries. The results indicate that the through-pores are highly interconnected and, therefore, pore structure determinations by CFP are independent of capillary length. A negatively charged polymer monolith based on BMA, ethylene glycol dimethacrylate (EDMA) and 2-acryloylamido-2-methylpropanesulfonic acid monomer (AMPS), was successfully prepared in silica sacrificial layer, planar (SLP) microchannels. Extraction of FITC (fluorescein 5-isothiocyanate) labeled phenylalanine and capillary electrochromatography (CEC) of FITC labeled glycine using this monolithic stationary phase were demonstrated.

Mesoporous γ-alumina is the most extensively used catalysts support in a wide range of catalytic processes. The usefulness of γ-alumina relies on its favorable combination of physical, textural, thermal, and chemical properties. Pore structure properties are among the most important properties, since high surface area and large pore volume enable higher loading of active catalytic phases, while design of pore size and pore size distribution is critical to optimize pore diffusional transport and product selectivity. In addition, accurate determination of surface area (SA), pore volume (PV) and pore size distribution (PSD) of porous supports, catalysts, and nanomaterials is vital to successful design and optimization of these materials and to the development of robust models of pore diffusional resistance and catalyst deactivation.In this dissertation, we report a simple, one-pot, solvent-deficient process to synthesize mesoporous γ-alumina without using external templates or surfactants. XRD, TEM, TGA and N2 adsorption techniques are used to characterize the morphologies and structures of the prepared alumina nanomaterials. By varying the aluminum salts or the water to aluminum molar ratio in the hydrolysis of aluminum alkoxides, γ-alumina with different morphologies and pore structures are synthesized. The obtained alumina nanomaterials have surface areas ranging from 210 m2/g to 340 m2/g, pore volumes ranging from 0.4 cm3/g to 1.7 cm3/g, and average pore widths from 4 to 18 nm. By varying the alcohols used in the rinsing and gelation of boehmite/bayerite precursors derived from a controlled hydrolysis of aluminum alkoxides, the average pore width of the γ-aluminas can be tuned from 7 to 37 nm. We also report improved calculations of PSD based on the Kelvin equation and a proposed Slit Pore Geometry model for slit-shaped mesopores of relatively large pore size (>10 nm). Two structural factors, α and β, are introduced to correct for non-ideal pore geometries. The volume density function for a log normal distribution is used to calculate the geometric mean pore diameter and standard deviation of the PSD. The Comparative Adsorption (αs) Method is also employed to independently assess mesopore surface area and volume.

This cumulative dissertation is a compendium of five peer-reviewed and published scientific papers on developing an advanced NMR Cryoporometry toolbox for pore architecture characterization. The dissertation contains five chapters. The first introduces porous materials, their types and applications. Chapter two describes the fundamentals of fluid phase equilibria in mesoporous solids and how modifications of the well-known Laplace equation describe various fluid phase equilibria. The basic principles of the Gas Sorption and NMR Cryoporometry techniques are discussed. In chapter three, different characterization techniques are amalgamated onto a common framework which can be used to compare fluid phase coexistence in porous materials of different pore sizes. Chapter four explains a completely new NMR Cryoporometry characterization methodology developed for cylindrical and spherical pore shapes. Chapter five concludes and crowns the present work by discussing the complementary benefits of the advanced technique in characterizing random porous materials and accounting for pore connectivity effects. All materials synthesized for the work in this dissertation have been obtained through collaborations with the groups of Profs. Dr. Michael Fröba and Simone Mascotto of the Hamburg University and Prof. Dr. Dirk Enke of the Leipzig University.:Table of Contents Thesis Summary ........................................................................................................1 List of publications ......................................................................................................2 Acknowledgements ...................................................................................................4 CHAPTER 1:.............................................................................................................10 Introduction ..............................................................................................................10 CHAPTER 2:.............................................................................................................12 Fluid Phase Equilibria in Mesoporous Solids ..........................................................12 2.1 Gas Sorption................................................................................................... 13 2.1.1 Adsorption Isotherms................................................................................ 15 2.1.2 Adsorption Hysteresis............................................................................... 18 2.1.3 Scanning Behavior.................................................................................... 23 2.2 NMR Cryoporometry ....................................................................................... 25 2.2.1 Pore Size Distribution (PSD)....................................................................... 28 2.3 Serially-Connected Pore Model (SCPM)......................................................... 29 2.4 Problem Statement ......................................................................................... 30 CHAPTER 3:..............................................................................................................32 Analogy between Characterization Techniques ......................................................32 • Publication 3. On the Comparative Analysis of Different Phase Coexistences in Mesoporous Materials CHAPTER 4:.............................................................................................................42 An Advanced NMR Cryoporometry Approach.........................................................42 • Publication 4.1. Nuclear Magnetic Resonance Cryoporometry Study of Solid−Liquid Equilibria in Interconnected Spherical Nanocages • Publication 4.2. A novel approach for advanced thermoporometry characterization of mesoporous solids: Transition kernels and the serially connected pore model CHAPTER 5:.............................................................................................................65 Characterizing Random Porous Materials................................................................65 • Publication 5.1. Comparative Gas Sorption and Cryoporometry Study of Mesoporous Glass Structure: Application of the Serially Connected Pore Model • Publication 5.2. Impact of Geometrical Disorder on Phase Equilibria of Fluids and Solids Confined in Mesoporous Materials Appendix A:.............................................................................................................100 Porous Solid Characterization Techniques............................................................100 A.1: Mercury Intrusion Porosimetry (MIP) ........................................................... 100 A.1.1. Experimental Set-up.............................................................................. 101 A.2: Gas Sorption................................................................................................ 103 A.2.1. Experimental Set-Up ............................................................................. 103 A.2: NMR Cryoporometry.................................................................................... 106 A.2.2. Experimental Set-Up ............................................................................. 106 Appendix B:..............................................................................................................109 Supporting information ............................................................................................109 Appendix C:.............................................................................................................115 Author contributions ................................................................................................115 Bibliography ............................................................................................................117