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The mechanical behaviour of bamboo is greatly influenced by its transverse properties, which are not easily measured by experiment. This study develops a framework and the computational tools required to evaluate the material and mechanical properties of bamboo in its full-culm form. A numerical model of bamboo as a transversely isotropic material with functionally graded material properties in the radial direction is developed. The random field method was introduced as a means of quantifying the measured uncertainty of bamboo with respect to the mechanical characterisation of its full-culm state. Four increasingly complex approaches to model circumferential compression tests of bamboo are presented: a theoretical evaluation using Castigliano’s theorem; an orthotropic model neglecting the graded nature of the culm wall; and, two models—one discrete and one continuum-based that define a transversely isotropic graded material. Output from each model is compared, calibrated and validated with experimental results. While the models developed were robust, their application has drawn into question the fundamental hypothesis that the functionally graded behaviour of bamboo can be captured using the rule of mixtures.

Hydroxyapatite (HA) is a well-known regenerative biomaterial. However, the slow degradation rate of HA is still an obstacle in clinical applications. In this study, we concentrated on investigating the degradation behavior of the calcium-rich HA foams, which had a demonstrated effect on blood differentiation in previous studies. The HA foams were processed by an emulsion method and were infiltrated with calcium nitrate to create a calcium carbonate second phase, heterogeneously distributed on and under the surface of the foam. During the 28-day solubility test, the calcium carbonate phase contributed to enhanced Ca2+ ion release into the saline compared to phase pure HA foams. Both types of foams were biocompatible as demonstrated by human endothelial cell culture on their surface. The release of calcium ions, the degradation behavior, and the endothelial cell differentiation behavior suggest this biphasic ceramic is a candidate for bone marrow in vitro culture and a possible bone substitute material.

In response to global climate change and resource limitations, nonconventional and vernacular, materials, or NOCMAT, are emerging as means to drive sustainable construction. Historically, vernacular materials derive from local customs and practices, rather than through formal scientific methodology, and despite being classified as “nonconventional”, they nevertheless constitute the majority of the built environment worldwide. When viewed not only as physical material, but also as integral to culture and communities, NOCMAT also have the potential to advance social equity and justice, so long as research, development, and education efforts are participatory and respectful of local conditions, rather than exploitative, paternalistic, or homogenizing. By understanding NOCMAT as a manifestation of Appropriate Technology, and drawing upon the literature from Engineering Education, recommendations are made for integrating NOCMAT into the engineering curriculum, ultimately arguing that the best approach requires some component of deep vernacular experience.

The materials genome project has proposed that computational modeling and materials informatics should be combined with the more commonly used experimental methodologies to speed the development of new materials technologies. Unfortunately the ability of materials informatics to contribute depends upon the ready availability of large amounts of appropriate information assembled into databases. In addition, the nature of current physics based materials modeling and simulation techniques are limited to short length scale and short timescale phenomena and systems of limited complexity. Such circumstances would suggest that this approach would have little utility in the development of non-conventional materials. However, it is possible to assemble databases specifically designed for certain material types and material structure-property relationships If this is done with generally accepted procedures and widely available tools, the process of assembling relatively large microstructural databases could be “democratized” to the point that non-conventional materials practitioners all around the world could participate. In this way, a systematic approach could be used to address the variability in the structure and property relationships for locally sourced non-conventional materials. This chapter will briefly introduce materials informatics before proceeding with a discussion of how they could be applied to non-conventional materials using a community based approach. This will be facilitated with one example, the structure-properties relationships of bamboo.

Long-term in vitro expansion of hematopoietic stem cells (HSCs), while maintaining their functionality and multilineage differentiation potential, is still challenging. In this study, three-dimensional (3D) high-porosity hydroxyapatite (HA) foams have been designed to closely mimic the chemistry and physical structure of cancellous bone. Furthermore, calcium oxide was distributed in the HA ceramics to provide surface calcium ion release, hypothesizing that a local surface calcium gradient supports HSC localization and maintenance. Primary human HSCs and osteoblasts were cocultured for 6 weeks. Controls were cultured in two-dimensional dishes, while scaffold cultures were performed with calcium nitrate-infiltrated HA scaffolds and untreated HA scaffolds. Cells were analyzed for surface markers by flow cytometry, metabolic activity, and hematopoietic multilineage differentiation potential. The release of calcium into culture medium was also determined. The implementation of HA scaffolds had a positive effect on erythrocyte colony formation capacity of HSCs, with an increased osteoblast fraction observed when compared to control cultures without scaffolds. The presentation of scaffolds did not affect metabolic turnover when compared to control cultures. In conclusion, 3D open-porous HA scaffolds provide a bone-like structure and enable the long-term maintenance of primary HSCs.

When compared to beam-based melting methods, binder jet 3D printing is less time consuming, and the printed material is less prone to residual stresses. However, binder jet printing often contains remnant porosity that survives pressureless sintering and limits the mechanical properties of metals including fatigue strength and ductility. In this work, gas atomized nickel-based superalloy 625 powders with three different particle size distributions are binder jet printed and subsequently isothermally sintered at subsolidus and supersolidus temperatures. Individual feature measurements were conducted on two-dimensional sections and pore size distribution frequencies were plotted to reveal the difference in microstructural evolution between subsolidus and supersolidus sintering. Supersolidus liquid phase sintering is thought to have facilitated particle rearrangement under the surface tension of the liquid phase, resulting in a homogeneous microstructure that favored subsequent densification and higher final density. Additionally, printed powder with a wide particle size distribution not only reached high green density of ~52%, but also achieved final densities above 99%.

Ceramic scaffolds are being developed to control both proliferation and differentiation of hematopoietic stem cells into desired cell products in bioreactors. These scaffolds mimic important aspects of the microenvironment or “niche” inside bone marrow. In particular, hematopoietic stem cell fate is thought to be effected by the architecture of trabecular bone and the presence of calcium. Here we report the effects of ceramics processing on the phase distribution and microstructure of biphasic ceramics used to culture hematopoietic stem cells. Processing of biphasic ceramics by powder mixing resulted in tetracalcium phosphate on the sintered surface. This correlated with observed surface deposits, weight gain, and the release of calcium ions in saline over 28 days. In contrast, impregnation of partially sintered hydroxyapatite with calcium nitrate resulted in calcium carbonate on the sintered surface. Impregnation correlated with the release of calcium ions into the saline, surface pitting, and weight loss.

Performance of full-culm bamboo structures is dominated by longitudinal splitting behaviour, often exacerbated by connection details. This behaviour is a function of the transverse properties of this highly orthotropic material. Considerable study of the longitudinal properties of bamboo is available in which it is often concluded that bamboo may be considered as a fibre-reinforced composite material and material properties may be assessed using rule-of-mixture methods. Nonetheless, few studies have addressed the transverse properties of the bamboo culm wall, despite these largely governing full-culm behaviour. This study investigated the transverse material property gradient through the culm wall and attempts to connect the mechanical results to physical observations and phenomena. Most importantly, the study demonstrates that the complex transverse behaviour of bamboo does not appear to behave as a classic fibre-reinforced composite material in the direction transverse to the fibres. In this study, five different bamboo species, Phyllostachys edulis, Phyllostachys bambusoides, Phyllostachys meyeri, Phyllostachys nigra, and Bambusa stenostachya were tested using a modification of the flat-ring flexure test to obtain a measure of the transverse tensile capacity of the bamboo. Microscopy analyses are used to qualitatively describe the culm wall architecture and to quantitatively assess the failure modes through the culm wall thickness.

Silver (Ag)-copper (Cu) bimetallic nanoparticles (NPs) were synthesized by the reduction of silver nitrate and copper (II) acetate monohydrate using ethylene glycol in a microwave (MW) heating system with controlled reaction times ranging from 5 min to 30 min. The molar ratio Ag/Cu was varied from 1:1 to 1:3. The effect of reaction conditions on the bimetallic NPs structures and compositions were characterized by x-ray photoelectron spectroscopy, x-ray diffraction and transmission electron microscopy. The average particle size was approximately 150 nm. The surface plasmon resonance (SPR) of Ag-Cu bimetallic NPs was investigated by monitoring the SPR band peak behavior via UV/Vis spectrophotometry. The resonance peak positions and peak widths varied due to the different structures of the bimetallic NPs created under the synthesis conditions. In the MW heating method, the reduction of Cu was increased and Cu was inhomogeneously deposited over the Ag cores. As the composition of Cu becoming higher in the Ag-Cu bimetallic NPs, the absorption between 400 nm to 600 nm was greatly enhanced.

The accumulation of bacteria in surface-attached biofilms can be detrimental to human health, dental hygiene, and many industrial processes. Natural biofilms are soft and often transparent, and they have heterogeneous biological composition and structure over micro- and macroscales. As a result, it is challenging to quantify the spatial distribution and overall intensity of biofilms. In this work, a new method was developed to enhance the visibility and quantification of bacterial biofilms. First, broad-spectrum biomolecular staining was used to enhance the visibility of the cells, nucleic acids, and proteins that make up biofilms. Then, an image analysis algorithm was developed to objectively and quantitatively measure biofilm accumulation from digital photographs and results were compared to independent measurements of cell density. This new method was used to quantify the growth intensity of Pseudomonas putida biofilms as they grew over time. This method is simple and fast, and can quantify biofilm growth over a large area with approximately the same precision as the more laborious cell counting method. Stained and processed images facilitate assessment of spatial heterogeneity of a biofilm across a surface. This new approach to biofilm analysis could be applied in studies of natural, industrial, and environmental biofilms. Graphical abstract A novel photographic method was developed to quantify bacterial biofilms. Broad spectrum biomolecular staining enhanced the visibility of the biofilms. Image analysis objectively and quantitatively measured biofilm accumulation from digital photographs. When compared to independent measurements of cell density the new method accurately quantified growth of Pseudomonas putida biofilms as they grew over time. The graph shows a comparison of biofilm quantification from cell density and image analysis. Error bars show standard deviation from three independent samples. Inset photographs show effect of staining Electronic supplementary material The online version of this article (doi:10.1007/s00216-015-9195-z) contains supplementary material, which is available to authorized users.

The construction and long-term maintenance of three-dimensional in vitro bone marrow models is of great interest but still quite challenging. Here we describe the use of a multi-compartment hollow-fiber membrane based three-dimensional perfusion bioreactor for long-term culture of whole human bone marrow mononuclear cells. We also investigated bioreactors with incorporated open-porous foamed hydroxyapatite scaffolds, mimicking the in vivo bone matrix. Cells in bioreactors with and without scaffolds were cultured to 6 weeks and compared to Petri dish controls. Cells were analyzed for gene expression, surface markers by flow cytometry, metabolic activity, hematopoietic potential, viability, and attachment by immunocytochemistry. Cells in bioreactors were metabolic active during long-term culture. The percentages of hematopoietic stem cell and mature endothelial cell fractions were maintained in bioreactors. The expression of most of the analyzed genes stabilized and increased after long-term culture of 6 weeks. Compared to Petri dish culture controls, bioreactor perfusion culture improved in both the short and long-term, the colony formation unit capacity of hematopoietic progenitors. Cells attached to the ample surface area provided by hydroxyapatite scaffolds. The implementation of a hydroxyapatite scaffold did not influence colony formation capacity, percentages of cell type specific fractions, gene expression, cell viability or metabolic turnover when compared to control cells cultured in bioreactors without scaffolds. In conclusion, three-dimensional perfusion bioreactor culture enables long-term maintenance of primary human bone marrow cells, with hydroxyapatite scaffolds providing an in vivo-like scaffold for three-dimensional culture.

Foamed hydroxyapatite offers a three-dimensional scaffold for the development of bone constructs, mimicking perfectly the in vivo bone structure. In vivo, calcium release at the surface is assumed to provide a locally increased gradient supporting the maintenance of the hematopoietic stem cells niche. We fabricated hydroxyapatite scaffolds with high surface calcium concentration by infiltration, and used human umbilical vein endothelial cells (HUVECs) as a model to study the effects on hematopoietic lineage direction. HUVECs are umbilical vein-derived and thus possess progenitor characteristics, with a prospective potential to give rise to hematopoietic lineages. HUVECs were cultured for long term on three-dimensional porous hydroxyapatite scaffolds, which were either infiltrated biphasic foams or untreated. Controls were cultured in two-dimensional dishes. The release of calcium into culture medium was determined, and cells were analyzed for typical hematopoietic and endothelial gene expressions, surface markers by flow cytometry, and hematopoietic potential using colony-forming unit assays. Our results indicate that the biphasic foams promoted a hematopoietic lineage direction of HUVECs, suggesting an improved in vivo-like scaffold for hematopoietic bone tissue engineering.

Soluble polymers are frequently used in freeze casting of ceramics to improve the structural integrity of the unfired ceramics. This study examined the effect of the molecular weight of polyethylene glycol (PEG) on the sintered microstructure of freeze-cast porous alumina ceramics. Increasing the molecular weight was shown to reduce the measured pore size from 10 μm to 5.5 μm, with the observed trend being qualitatively consistent with the effects of molecular weight on the diffusivity of PEG and constitutional supercooling.

Non-tuberculous mycobacteria are a threat to human health, gaining entry to the body through contaminated water systems, where they form persistent biofilms despite extensive attempts at disinfection. Silver is a natural antibacterial agent and in nanoparticle form activity is increased by a high surface area. Silver nanoparticles (AgNPs) have been used as alternative disinfectants in circulating water systems, washing machines and even clothing. However, nanoparticles, like any other antibiotic that has a pervasive durable presence, carry the risk of creating a resistant population. In this study Mycobacterium smegmatis strain mc(2)155 was cultured in AgNP enriched agar such that only a small population survived. Surviving cultures were isolated and re-exposed to AgNPs and AgNO3 and resistance to silver was compared to a negative control. After only a single exposure, mutant M. smegmatis populations were resistant to AgNPs and AgNO3. Further, the silver resistant mutants were exposed to antibiotics to determine if general resistance had been conferred. The minimum inhibitory concentration of isoniazid was four times higher for silver resistant mutants than for strain mc(2)155. However, core resistance was not conferred to other toxic metal ions. The mutants had lower resistance to CuSO4 and ZnSO4 than the mc(2)155 strain.

Environmental mycobacteria pose a significant health burden. Non-tuberculous mycobacteria infections have been traced to water treatment networks, where mycobacterial biofilms are ubiquitous. Filters that remove potential pathogens have significant medical applications. The purpose of this study is to demonstrate that an antibacterial silver nanoparticle (AgNP) coating can prevent colonization and growth of a mycobacterial biofilm on a filter material. The antibacterial efficacy of commercially available AgNPs was measured against Mycobacterium avium , Mycobacterium smegmatis , and Mycobacterium marinum after 48 h in liquid culture. Nanoparticles were deposited on micro-porous track etched polycarbonate membranes. The growth of biofilms on the membranes was observed by microscopy and counting colony forming units. M. smegmatis was most susceptible to AgNPs, with a 98.7% reduction at 100 μM AgNP concentration. M. avium was reduced by 97.3% at 539 μM AgNP after 48 h. Deposited nanoparticles inhibited colonization and growth for both M. smegmatis and M. avium on the membrane surface. Similar to the liquid culture, M. avium (84.2% survival) was more resistant than M. smegmatis (0.03% survival).

Microstructure mining aims to study material microstructures while embracing their complexity. The general steps in the microstructure mining method will be introduced in the context of ceramics processing and microstructure evolution in sintering. In particular, the methodology will be illustrated by the design of a new microstructural measurement called the effective diffusion distance. This parameter allows the experimental study of sintering microstructures using traditional kinetic models of sintering even when the microstructures are strongly aggregated. The limits of this approach will be discussed with respect to the scale of the aggregation relative to the size of the pores.

The microstructural evolution of hydroxyapatite (HAp) was quantified for isothermal sintering at 1100°C. The aggregated state of the powder particles is thought to be responsible for the relatively high value of the average pore separation throughout isothermal sintering. The measured grain size exponent of 6·7 is not compatible with the values expected for volume diffusion or grain boundary diffusion under the assumptions of the Combined Stage Sintering Model and hence the Master Sintering Curve. The measured exponent for a previously defined flux weighted effective diffusion distance gave a more reasonable value of 3·4. The theoretical exponent in the Combined Stage Sintering Model was then corrected to accommodate a non-linear relationship between the effective diffusion length and pore size. The results demonstrate how the effective lengthscale in the Combined Stage Sintering Model can be corrected to accommodate aggregation in the microstructure.

Hydroxyapatite pellets, partially densified in a low-temperature heat treatment, were infiltrated with calcium nitrate solution followed by in-situ precipitation of Ca(OH)2 and CaCO3. The infiltrated bodies were then densified to high relative density and the calcium carbonate transformed to calcium oxide during sintering and resulted in biphasic hydroxyapatite-CaO ceramics. This work investigated the influence of the infiltration on surface morphology, weight change, and microstructural-level degradation caused by exposure to saline at pH = 7.4 and a temperature of 20 °C. The CaO rendered the materials more susceptible to degradation, and released calcium into the saline faster than single phase, calcium deficient hydroxyapatite (HA) that were used as a control. In consequence, these ceramics could be used to release calcium into the culture microenvironments of bone tissue or bone marrow cells next to a scaffold surface.

Liver cell culture within three-dimensional structures provides an improved culture system for various applications in basic research, pharmacological screening, and implantable or extracorporeal liver support. Biodegradable calcium-based scaffolds in such systems could enhance liver cell functionality by providing endothelial and hepatic cell support through locally elevated calcium levels, increased surface area for cell attachment, and allowing three-dimensional tissue restructuring. Open-porous hydroxyapatite scaffolds were fabricated and seeded with primary adult human liver cells, which were embedded within or without gels of extracellular matrix protein collagen-1 or hyaluronan. Metabolic functions were assessed after 5, 15, and 28 days. Longer-term cultures exhibited highest cell numbers and liver specific gene expression when cultured on hydroxyapatite scaffolds in collagen-1. Endothelial gene expression was induced in cells cultured on scaffolds without extracellular matrix proteins. Hydroxyapatite induced gene expression for cytokeratin-19 when cells were cultured in collagen-1 gel while culture in hyaluronan increased cytokeratin-19 gene expression independent of the use of scaffold in long-term culture. The implementation of hydroxyapatite composites with extracellular matrices affected liver cell cultures and cell differentiation depending on the type of matrix protein and the presence of a scaffold. The hydroxyapatite scaffolds enable scale-up of hepatic three-dimensional culture models for regenerative medicine applications.

An emulsion casting method was chosen for the processing of highly porous hydroxyapatite (HAp) foams to be used for the in vitro culturing of primary human liver cells. The volume fraction of heptane added to the aqueous dispersion of HAp particles could be varied to achieve a wide range of porosities (10–90 vol.-%) and pore morphologies. The emulsion derived open foam has a distinctive morphology, including a continuous large pore phase and solid struts containing smaller isolated pores. The effect of the heptane content of the slip on this sintered structure was quantified using linear intercept measurement parameters. Additionally, macropores necessary for perfusion were created using polymer tubes placed in the casting mould. When the tube spacing approached the pore size in the foam, the pore morphology was strongly affected.

As an impregnated constituent in low-cost ceramic water filters, silver nanoparticles have a demonstrated antibacterial effect. The bactericidal mechanism is believed to be based on direct contact between silver and the cell wall of a contaminant organism. In this study microstructural analysis was used to examine the effect of the processing method on the distribution of silver nanoparticles in the filter material. Silver nanofluid was impregnated into fired clay ceramic samples by a low-cost soak-and-dry method. Analyses of filter samples by scanning electron microscopy, energy dispersive spectroscopy, and digital optical topological mapping showed that silver was concentrated in near surface pores, a condition that is not optimal for highest probability of silver contact. A simple experiment showed that segregation of silver occurs during the drying phase of impregnation. Drying curves showed that 90% of contained liquid evaporates from the external surface.

This study examined the effect of polyvinyl alcohol (PVA) on the microstructure and permeability of freeze-cast porous alumina. The PVA addition was shown to have a significant effect on the pore size, with the trends in microstructure morphology and scale being qualitatively consistent with the effects of PVA addition on constitutional supercooling. The measured Darcian permeabilities were between 10−10 m2 and 10−12 m2. The permeability decreased as the PVA content increased and a significant fraction of the flow could be attributed to inertial effects.

Suspensions of ZnO nanoparticles in water were prepared with the two-step powder dispersion process using several methods of ultrasonication. The dispersion of ZnO was found to proceed by a fragmentation process, with minimum achievable particle size in the range 50 to 300 nm. This is consistent with other oxide nanopowder systems, in which most primary particulates still remain in hardened aggregates that cannot be further reduced. A submersible accelerometer probe was developed and used to measure the relative ultrasonic energy field in the liquid for the various ultrasonication methods. Oscillation at the expected frequencies was identified in each case, with strong variability at different locations in the liquid volume.

The traditional models of sintering predict a pronounced dependence of densification rate on the scale of the microstructure as measured by the grain size. This study evaluates the grain size exponent for densification during isothermal sintering of an aggregated nanocrystalline zirconia powder, and for a submicrometer alumina powder. The results gave grain size exponents that are much higher than those anticipated for the expected sintering mechanisms. Furthermore, microstructural analysis showed that this overestimate of the exponent could be due to the spatial heterogeneity in the microstructure on the scale of the diffusion distance. To assess this issue, pore boundary tessellation was used to determine a new measurement of effective diffusion distance that takes into account the local spatial arrangement of pores. This measurement gives exponents much closer to those expected for the sintering of tetragonal zirconia by volume diffusion, and for the sintering of the alumina by grain-boundary diffusion.

Aqueous zinc oxide (ZnO) suspensions were prepared using a two-step preparation method in which an aggregated nanocrystalline ZnO powder was dispersed in water using a polyelectrolyte. The fluid showed anomalously high thermal conductivity when compared with the Maxwell and Hamilton-Crosser predictions. However, analysis of the particle size distribution showed that the fluid contained aggregated 20 nm crystallites of ZnO with a high volume fraction of particles larger than 100 nm. Sedimentation experiments revealed that particles settled out of the stationary fluid over times ranging from 0.1 hours to well over 10,000 hours. The size of the particles remaining in suspension agreed well with predictions made using Stoke's law, suggesting flocculation was not occurring in the fluids. Finally, a new concept of nanofluid stability is introduced based on the height of the fluid, sedimentation, Brownian motion and the kinetic energy of the particles.

Freeze casting has been used to process a range of ceramics with oriented pore structures, and soluble polymers are often used to improve the strength of the material before sintering. This study examined the effect of polyethylene glycol (PEG) on the three distinct microstructural scales, which include the colony size, the pore size, and the secondary dendrite spacing. The results showed that the trends in pore size and secondary dendrite spacing were consistent with the effect of constitutional supercooling on the growth of ice crystals. In contrast, the effect of PEG on colony size appeared to be more pronounced and may reflect preferential adsorption on the prism faces of the growing ice crystals. For both alumina and PEG content, the observed effects were very much dependent on the temperature of the chill surface used in casting.

This study used quantitative image analysis to examine the effect of powder forming method on a population of dense heterogeneities that could be imaged in partially sintered alumina using optical microscopy. Powder pressing resulted in a higher area fraction of dense heterogeneities than slip casting. Extreme value analysis was used to predict the size of the largest heterogeneity in the populations and assess the processing methods. Powder pressing resulted in the largest extreme value estimate. The results are interpreted in terms of the effect of the forming method on particle packing and the possible effect of the dense heterogeneities on mechanical strength.

Advanced ceramics are commonly manufactured by sintering high-purity powders. The design of ceramic elements is governed by its fracture strength, which is greatly influenced by microstructural flaws. Three ceramic powder preparation methods for ceramics manufacturing are considered in this paper—uniaxial pressing followed by isostatic pressing, flocculated slip casting, and dispersed slip casting. Their effects on the growth and characteristics of microstructure flaws and damage on the ceramic surface are investigated using a two-stage data-mining approach. In the first stage, digital microstructural images are mined to characterize the flaws and surface damage. In the second stage, an extreme value probability distribution is fitted using the information from stage 1. The extreme value distribution estimates large flaws which are highly correlated with subsequent fractures. Results of the two-stage data mining show that ceramic production method significantly affects flaw characteristics that, in turn, ...

Quantitative image analysis was used to study the effect of the powder forming method on the population of pull-out flaws for polished surfaces of dense alumina ceramics. By comparing the area fractions, the size distributions and the extreme values of the pull-out areas it was concluded that slip casting with dispersed slips resulted in significantly fewer and smaller pull-outs compared to slip casting with flocculated slips or powder pressing. The implications of these observations for the effect of the powder forming method on the strength of alumina ceramics are discussed.

The effect of slip dispersion on the consequent densification and microstructure evolution of alumina was studied for isothermal sintering. As expected, cast alumina bodies produced with flocculated slip required longer sintering time to reach high density. Quantitative microstructure analysis was used to study the relationships between the slip dispersion condition, the densification behavior, and microstructure evolution of cast alumina during sintering at 1350°C. A microstructural description based on pore boundary tessellation revealed a correlation between the degree of flocculation, tessellation cell properties, and densification rate. A conceptual understanding of the sintering of agglomerated powders was used to explain the observations.

Two computational intelligence approaches, a fuzzy logic algorithm and a neural network (NN) algorithm, for grain boundary detection in images of superalloy steel microstructure during sintering are presented in this paper. The images are obtained from an optical microscope and are quite noisy, which adversely affects the performance of common image processing tools. The only known way to accurately determine the grain boundaries is digitizing by hand. This is a very time-consuming process, causes operator fatigue, and it is prone to human errors and inconsistency. An automated system is therefore needed to complete as much work as possible and we consider a fuzzy approach and a neural approach. Both methods performed better than the widely available standard image processing tools with the neural approach superior on images similar to those trained while the fuzzy approach showed more tolerance of disparate images.

A new mesoscale description of sintering microstructures has been developed based on pore boundary tessellation. Evolution in the populations of tessellation cell properties suggests that intermediate stage sintering is characterized by the removal of relatively large pore sections thought to be associated with a low density network. The reduction in the area fraction associated with these larger pore sections was found to correlate with the change in densification rate during sintering, leading to speculation on the cause of the commonly observed logarithmic relationship between solid volume fraction and time. Sintering above a solid volume fraction of 0.9 appeared to be dominated by pore shrinkage and elimination consistent with the common perception of final stage sintering.

Information entropy was applied to size class selection for the unfolding of grain size distributions and the results were compared with traditional forward and inverse methods using arbitrarily selected size classes. This comparison shows that information entropy provides a better representation of the data.

Dimensionless parameters have been developed to study microstructural pathways for the sintering of powders. These parameters are designed to facilitate the comparison of microstructural paths for any sintering experiments, independent of the characteristic length scales in the microstructures. Microstructural pathways constructed with the dimensionless parameters are found to be similar for three different alumina ceramics. The systematic differences between the experimental results and the predictions of models based on simplifying geometric assumptions are explained in terms of the packing disruptions in the green microstructures.

The objective of this study was to provide quantitative information concerning the microstructural evolution of porous alumina derived from mixtures of a fine, active powder and a coarse powder with a wide size distribution. The coarse powder increased the green density and reduced the densification rate as expected. The addition of the coarse powder also increased the average grain and pore intercepts at any particular density. However, it was concluded that coarsening of the fine powder was not affected by 30% coarse powder when sintering time was considered rather than density. Coarsening did affect the average grain size when a higher fraction of the fine powder particles were in contact with the larger particles. This is expected to be particularly important for cases where coarse particles are bonded by a relatively small fraction of fine particles of the same phase.

The determination of a grain size distribution from one planar section requires a representative shape that allows the distribution in particle size to be estimated from the size distribution of the particle sections. In this work a simulation has been developed to randomly generate convex polyhedra and calculate the distributions in section properties needed to unfold the particle size distribution into three dimensions. Furthermore a new shape selection process based on a common shape factor is described. The relatively high symmetry polyhedra commonly used to unfold grain size distributions underestimate the grain size compared with the randomly generated polyhedra of the simulation. The latter are thought to be more representative of real grain shapes in that they do not commonly possess pairs of parallel faces.

The effect of slip casting condition and hence particle packing on densification and microstructural evolution was evaluated during isothermal sintering of a commercial alumina powder at 1350 °C. While there was significant effect of flocculation on solid volume fraction at short sintering times there appeared to be no inherent barrier to the eventual attainment of the same limiting solid volume fraction. Microstructural pathways based on average microstructural parameters and microstructural populations revealed no effect of casting condition on grain-scale pathways at this temperature. It is thought that microstructural pathways at higher length scales based on grain clusters will reveal the effect of slip casting independent of grain coarsening behavior.

Models of simultaneous coarsening and densification in final stage sintering commonly assume that the coarsening process results in microstructures that evolve self-similarly from a fixed microstructural geometry, differing only in scale. This assumption is experimentally tested for alumina in the solid volume fraction range of 0.97–1 using nondimensional microstructural parameters. The results clearly show that such models based on assumed geometries often underestimate the pore size relative to the grain size. The largest differences between the model and the experiments occur for lower firing temperatures and higher doping levels. It is concluded that the coarsening reflected in the effect of temperature and dopant level is not a self-similar process from a common microstructural geometry.

A neural network approach is presented for the estimation of shrinkage during a hot isostatic pressing (HIP) process of nickel-based superalloys for near net-shape manufacture. For the HIP process, the change in shape must be estimated accurately; otherwise, the finished piece will need excessive machining and expensive nickel-based alloy powder will be wasted (if shrinkage is overestimated) or the part will be scrapped (if shrinkage is underestimated). Estimating shape change has been a very difficult task in the powder metallurgy industry and approaches range from rules of thumb to sophisticated finite element models. However, the industry still lacks a reliable and general way to accurately estimate final shape. This paper demonstrates that the neural network approach is promising to estimate post-HIP dimensions from a combination of pre-HIP dimensions, powder characteristics and processing information. Compared to nonlinear regression models to estimate shrinkage, the neural network models perform very well. Furthermore, the models described in this paper can be used to find good HIP process settings, such as temperature and pressure, which can reduce operating costs.

The construction and long-term maintenance of three-dimensional in vitro bone marrow models is of great interest but still quite challenging. Here we describe the use of a multi-compartment hollow-fiber membrane based three-dimensional perfusion bioreactor for long-term culture of whole human bone marrow mononuclear cells. We also investigated bioreactors with incorporated open-porous foamed hydroxyapatite scaffolds, mimicking the in vivo bone matrix. Cells in bioreactors with and without scaffolds were cultured to 6 weeks and compared to Petri dish controls. Cells were analyzed for gene expression, surface markers by flow cytometry, metabolic activity, hematopoietic potential, viability, and attachment by immunocytochemistry. Cells in bioreactors were metabolic active during long-term culture. The percentages of hematopoietic stem cell and mature endothelial cell fractions were maintained in bioreactors. The expression of most of the analyzed genes stabilized and increased after long-term culture of 6 weeks. Compared to Petri dish culture controls, bioreactor perfusion culture improved in both the short and long-term, the colony formation unit capacity of hematopoietic progenitors. Cells attached to the ample surface area provided by hydroxyapatite scaffolds. The implementation of a hydroxyapatite scaffold did not influence colony formation capacity, percentages of cell type specific fractions, gene expression, cell viability or metabolic turnover when compared to control cells cultured in bioreactors without scaffolds. In conclusion, three-dimensional perfusion bioreactor culture enables long-term maintenance of primary human bone marrow cells, with hydroxyapatite scaffolds providing an in vivo-like scaffold for three-dimensional culture.

Alumina films were sintered on a rigid substrate to different densities. Stereological measurements suggest that microstructural anisotropy develops during the final stage of sintering, which can be interpreted in terms of the elimination of pore sections rather than anisotropic growth of isolated particle necks. Pore separation seems to be a better measure than grain intercept when compared with phenomenological models.

Simple geometric models of the three stages of sintering are used to predict the path of microstructural change—the evolution of the microstructure as a function of relative density—in terms of stereological parameters. The geometric assumptions in the models are based on those frequently used in other sintering models. Two nondimensional parameters, the ratio of the mean grain and mean void intercepts and the ratio of the solid/solid and solid/void surface areas, are introduced so that the model predictions can be compared quantitatively with experimental results, independent of the characteristic length scale. The comparison is made with two alumina powders. The results suggest that an important contributor to the inaccuracy of sintering models based on simple geometric assumptions is the failure to account for nonuniformity of particle packing.

Recent studies have compared particle-size analysis methods for soils containing fine clay particles. The results showed significant differences between the techniques. This study consisted of a series of hydrometer experiments designed to give greater understanding of the behavior of kaolinite clay during the ASTM 422-63 hydrometer test. The results were consistent with the aggregation of fine clay particles, possibly due to the known hydrolysis behavior of the sodium polyphosphate dispersants used in the experiment. To avoid a serious underestimation of the fraction of submicron clay particles in soils, dispersants that do not suffer from time-dependent hydrolysis should be evaluated for the hydrometer test.

Two methods were used to determine the in-plane orientation of Al2O2 platelets in slip-cast ceramic composites relative to the casting surface. The first used the ferrets applied to the platelets by an image analyzer, and the second involved a manually applied direction for the platelet axes. Most platelets were oriented more closely to the plane of the casting surface than to the casting direction. The manual method suggested much greater orientation of the platelets parallel to the casting surface. Further analysis of the image analysis results, in terms of aspect ratio, suggested that this was due to the fact that the manual method could not assign an orientation direction for platelet sections with small aspect ratios. This was further compounded by an aspect ratio dependence of platelet orientation.

Until recently, the processing of high surface area alumina ceramics has been restricted to transitional phases such as γ, δ, and θ. In this study, a nanocrystalline α-Al23 powder (100 m2/g) was processed into mesoporous α-Al23 ceramics with surface areas in the range 20 to 80 m2/g. Hence, the opportunity exists to study the effect of thermal treatment on the pore structure of a high surface area α-Al23 ceramic in the temperature range 600°C to 1000°C. The reduction in surface area was characterized as pure coarsening by surface diffusion. Examination of the pore structure showed both intraparticle pores and interparticle pores in the temperature range 600°C to 800°C and only interparticle pores above 800°C. The powder particles were dense and polycrystalline. However, much of their internal structure is lost in heat treatments above 1000°C.

Recently, the effect of solid inclusions on the sintering of ceramic powders has been explained in terms of a back-stress that opposes densification. Several analyses have been proposed to describe this problem. However, little quantitative information exists concerning the effect of reinforcement on microstructural evolution. This study compares the microstructural development of zirconia and mullite matrices in the presence of alumina platelets. The effect of platelet loading on density is similar for both composites. Quantitative stereological examinations reveal that the average grain size and pore size are finer for the zirconia-matrix composite. The platelet loading does not have any noticeable effect on the average grain size of the matrix in either composite. However, the average pore size increases as the volume fraction of platelets increases for both materials. Contiguity measurements have detected some aggregation of platelets in the zirconia-matrix composite.