bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Electrospun PBSU and PLGA Scaffolds Applied in Vascular Tissue Engineering
Authors: Zhao L. , He C. , Zhang Da Ming , Chang Jiang , Cui Lei
Published: September 2009

Poly(butylenes succinate) (PBSU) had good biocompatibility and biodegradability, but it is left unexplored for the possible application of PBSU in tissue engineering. The aim of this study was to compare PBSU and poly (lactide-co-glycolide) (PLGA) scaffolds prepared by electrospinning technique as vascular tissue engineering materials. Both scaffolds were characterized by fiber morphology, pore structure and mechanical properties. Smooth muscle cells (SMCs) and endothelial cells (ECs) were seeded on the electrospun PBSU and PLGA scaffolds and cultured for different time periods. Cell adhesion and proliferation on the scaffolds were measured by MTT assay, while SEM was used for observing cell morphology on the scaffolds. The results showed that fiber diameter of the electrospun scaffolds ranged from 300nm to 800nm and their porosities were higher than 90%. The electrospun PBSU scaffolds showed a high tensile strength of 2.06±0.11MPa, whereas the ultimate tensile strength of the electrospun PLGA scaffolds reached 14.31±5.24MPa. Cell adhesion efficacy had no significant difference between PBSU and PLGA scaffolds, but cell proliferation rate on PLGA scaffolds was significantly higher than that on PBSU scaffolds after 7 days of culture. Cell morphology was similar on both scaffolds with the polygonal shape for ECs and spindle-like shape for SMCs. From these results, the present in vitro study revealed that as compared to PLGA scaffolds, the electrospun PBSU scaffolds showed lower tensile strength and slower proliferation rate, but as regards the biocompatibility and pore structure, the electrospun PBSU scaffolds had a potential application in vascular tissue engineering.
Micropatterning of Poly (Ethylene Glycol)-Diacrylate (PEG-DA) Hydrogel by Soft-Photolithography for Analysis of Cell-Biomaterial Interactions
Authors: Subramani Karthikeyan , Birch M.A.
Published: September 2009

Poly (ethylene glycol) hydrogel (PEG) micropatterns fabricated by photolithography and various other microfabrication techniques have been used as a platform to analyze cell-biomaterial interactions in cell culture studies. Numerous innovative techniques have been described about photolithography and the use of Poly (dimethyl siloxane) stamp (PDMS) based pressure moulding technique for the microfabrication of PEG hydrogel micropatterns. We herein this literature describe a simple and a versatile method for fabricating Poly (ethylene glycol) hydrogel-diacrylate (PEG-DA) hydrogel micropatterns using the ‘Soft-photolithography’ technique which is a combination of pressure moulding using a PDMS stamp and photolithography. Using this simple technique, PEG-DA hydrogel micropatterns were fabricated on a silicon substrate of varying dimensions from 40μm to 10μm within the same substrate. Such a three-dimensional microenvironment with varying sizes can serve as an excellent platform to study cell behaviour in culture. These PEG-DA hydrogel micropatterns can further be functionalized by adding a variety of biomolecular cues within the PEG-DA hydrogel matrix or these biomolecules can be patterned on the PEG-DA micropatterns after photopolymerization using micro-contact printing for analysis of cell-biomaterial interactions and tissue engineering purposes.
A Micromechanical Model for Fibrous Biological Membranes at Finite Strain
Authors: Borri-Brunetto Mauro , Chiaia Bernardino , Deambrosi Marco
Published: September 2009

The mechanical model of a number of biological tissues is a membrane, i.e., a sheetlike
structure with small thickness, where deformation and stress can be described locally in two
dimensions. Many bio-membranes, particularly if subjected to large mechanical loads, present
a fibrous structure, with stiff fibers, sometimes with preferential orientations, embedded in a
more compliant matrix. Among this tissues are, e.g., the arterial walls, the amniotic membrane,
and the skin. The stiff fibers, typically made of collagen, are initially wrinkled and they follow
the deformation of the embedding matrix without contributing to the mechanical response until
they are fully distended. In this paper, the response of a fibrous membrane is described in the
framework of hyperelasticity, with aim to the implementation in an existing finite element code.
A micro-mechanical recruitment model, based on the statistical distribution of the activation
stretch of the collagen fibers is introduced, leading to the definition of a simple form of the
strain-energy function, depending on physically well-defined parameters. After some validation
tests performed in homogeneous strain conditions, an application to the study of the stress field
around circular holes in large deformation is presented, showing the capabilities of the proposed
model.
Preparation of Alginate/Poly(L-Arginine)-Chitosan Ternary Complex Microcapsules
Authors: Chen A.Z. , Wang Shi Bin , Weng L.J. , Chen M.Y.
Published: September 2009

Following a polyelectrolytical complex reaction, alginate/poly(L-Arginine)-chitosan ternary complex microcapsules were prepared by coating poly(L-Arginine) and chitosan as membrane materials on calcium alginate beads, which were produced by a high-voltage electrostatic droplet generator. The influences on the diameter and uniformity of the calcium alginate beads were studied, and the optimum operating parameters were selected to produce microcapsules. The in vitro drug release behavior and pH stimuli-response of alginate/poly(L-Arginine)-chitosan ternary complex microcapsules were investigated. In comparison with alginate/chitosan microcapsules, alginate/poly(L-Arginine) microcapsules and their corresponding double-membrane microcapsules, alginate/poly(L-Arginine)-chitosan microcapsules released the macromolecular drug in a more sustained and stable way. It was found that they released 85.7% of the bovine erythrocytes hemoglobin (Hb) in 85 hours by approximate first-order kinetics in pH 6.8 PBS. While in a pH 1.0 HCl solution, only 9.6 % of the Hb was released in the first half hour and then the drug release shifted to a flat stage, which indicated that the alginate/poly(L-Arginine)-chitosan microcapsules possessed a pH stimuli-response property. The results suggest that the alginate/poly(L-Arginine)-chitosan ternary complex microcapsules might be a potential colon-targeted drug delivery system for the encapsulation of proteins.
Biomimetic Functionally Graded Materials: Synthesis by Impeller-Dry-Blending
Authors: Chavara D.T. , Wang Cyndi X. , Ruys Andrew John
Published: September 2009

Functionally graded materials (FGMs) can be found naturally in many biological structures, for example bamboo and the mollusc shell. They are defined as having a compositional or microstructural gradient, for example the gradation in fibre content in bamboo stems. A continuous bulk functionally graded material has the potential to be an ideal orthopaedic implant for load bearing applications. Due to the fabrication complexities involved in the production of these continuous bulk functionally graded materials, commercialisation and fabrication are still proving to be a challenge to researchers worldwide. This paper presents an overview of the redesigned novel commercially viable process known as the Impeller-Dry-Blending (IDB) process. Results presented in this paper of fabricated functionally graded materials illustrate the potential of IDB to produce continuous bulk functionally graded materials consisting of either compositional or porosity concentration changes. The successful fabrication of these continuous bulk functionally graded materials at such a low cost clearly demonstrates the commercial viability of the IDB process.
Finite Element Analysis of the Membrane Used in a Novel BioMEMS
Authors: Sang Sheng Bo , Witte Hartmut
Published: September 2009

With new applications in the area of diagnostics, drug discovery and genetics, the need for Biological Micro-Electro-Mechanical Systems (BioMEMS) has increased tremendously in the last decade. Especially, surface stress-based BioMEMS has been investigated extensively in the recently years. In this paper, a new BioMEMS is proposed, which can be used to detect cells. It consists of microfluidics, square membrane and a fiber optic interferometer. The square membrane as the crucial and sensitive part includes three layers, self-assembled monolayer (SAM), gold and substrate material. Based on the BioMEMS, some fundamental study has been done, especially for the membrane due to its crucial role in the whole system. The finite element (FE) method has been used to study the membrane with different substrates. By the fundamental study, some important conclusions have been acquired: (1) The square membrane will reach maximal deflection at different ratio values (P: membrane size) to different substrates; (2) To a certain substrate, such as PDMS, the ratio making the membrane reach maximal deflection is different to dissimilar PDMS layer thickness; (3) If young’s modulus (E) of the substrate is too small, separation may happen between the gold layer and substrate layer when the gold size becomes smaller.
Nano-Sized and Nanocrystalline Calcium Orhophosphates in Biomedical Engineering
Authors: Dorozhkin Sergey V.
Published: September 2009

There has been much recent activity in the research area of nanoparticles and nanocrystalline materials, in many fields of science and technology. This is due to their outstanding and unique physical, mechanical, chemical and biological characteristics. Recent developments in biomineralization have demonstrated that nano-sized particles play an important role in the formation of the hard tissues of animals. It is well established that the basic inorganic building blocks of bones and teeth of mammals are nano-sized and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds of nanocrystals of biological apatite are found to combine into self-assembled structures under the control of bio-organic matrixes. It was also confirmed experimentally that the structure of both dental enamel and bones could be mimicked by an oriented aggregation of nano-sized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nano-sized and nanocrystalline calcium orthophosphates for clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various cells were detected on smaller crystals of calcium orthophosphates. Furthermore, studies revealed that the differentiation of various cells was promoted by nano-sized calcium orthophosphates. Thus, the nano-sized and nanocrystalline forms of calcium orthophosphates have the potential to revolutionize the field of hard tissue engineering, in areas ranging from bone repair and augmentation to controlled drug delivery devices. This paper reviews the current state of knowledge and recent developments of various nano-sized and nanocrystalline calcium orthophosphates, covering topics from the synthesis and characterization to biomedical and clinical applications. This review also provides possible directions of future research and development.
Silver-Polymer Nanohybrids Prepared by Microemulsion Polymerization
Authors: Donescu Dan , Nistor Cristina Lavinia , Purcar Violeta , Serban Sever , Radovici Constantin , Raditoiu Valentin , Petcu Christian , Ghiurea Marius
Published: September 2009

This work presents the preparation of some Ag°-polymer nanoparticles by emulsion polymerization of styrene (St), butyl acrylate (BuA) or methyl methacrylate (MMA), followed by the metal particles engendering. In order to increase the polymer-Ag° interaction, acrylic acid (AcrA), hydroxyethylmethacrylate (HEMA), sodium styrenesulfonate (StSO3Na) and vinyltriethoxysilane (VTES) coupled with tiopropyltrimethoxysilane (HSTMS) were subsequently used as comonomers when the polymeric latexes were prepared.
Comparing the two surfactants used in this study – nonylphenol ethoxylated with 25 moles of ethylene oxide (NPEO25) and sodiumdodecylsulfate (SDS) - one can notice that particle size was larger and zeta potential value decreased when, instead of the ionic surfactant SDS, the nonionic surfactant NPEO25 was added to the formulation. The latexes UV-Vis spectra shows absorptions at ~400 nm due to plasmon resonance adsorption assigned to Ag° nanoparticles. The value of λ caused by this phenomenon decreases in the following order: PSt>PBuA>PMMA, because of the increase of polarity. The reactive comonomers, mentioned above, cause the decrease of the maximum value, due to the increase of the polymer-metal interaction. Thermal stability of PSt is higher when silver nanoparticles are present and is lower after copolymerization. For HEMA and StSO3Na copolymers, the XRD studies point out the existence of a cubic crystalline phase, generated because of the maximum (high) concentration of Ag°. The UV-Vis reflexion spectra show maximum values of reflectance for the same two copolymers, proving that the crystalline phase of Ag° has a mirror effect.
Synthesis of ZnO Nanostructures by Hydrothermal Method
Authors: Georgiou Pantelitsa , Kolokotronis Konstantinos , Simitzis Johannis
Published: September 2009

ZnO was synthesized by the hydrothermal method using proper aqueous solutions of ZnCl2 and NaOH, as the main raw materials, corresponding to the molar ratio of Zn2+ : OH- = 1 : 20 (solution ‘A’), and a proper proportion of water as solvent, ethanol (EtOH) as non solvent and polyethylene glycol (PEG) as nonionic surfactant (solution ‘B’). The reaction takes place in an autoclave at 200 °C for a defined period of time (1-20 h). The solid ZnO products received after centrifugation, washing and drying were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The percentage of unreacted Zn present after the reaction in the liquid phase (incumbent solution) was determined by Atomic Absorption Spectroscopy. The parameters of processing (i.e., temperature, pressure, residence time) and the raw materials parameters (i.e. proportion of , amount of PEG) influence the morphology and the dimensions of the product. Increasing the residence time from 1 h → 3 h → 20 h, the amorphous regions illustrated in SEM images are decreased and the number and dimensions of the obtained single or branched rods of the final product are increased. Avoiding the use of additional water, i.e. the denominator in the aforementioned ratio, mL, water, is equal to zero, but simultaneously using ethanol, the ZnO material is mainly amorphous. Increasing the amount of the additional water without ethanol, no amorphous material is observed and single rods or flowerlike/starlike structures having ends of regular hexagonal pyramid structure, are formed. Increasing the proportion of PEG, many flowerlike or starlike branched structures having ends of regular hexagonal prismatic structure, are formed. The ZnO materials having much of amorphous regions do not show XRD peaks. On the other hand, the crystalline ZnO materials show many XRD peaks, which are indexed and they correspond to the wurtzite-structured (hexagonal) ZnO. Furthermore, the lattice constants  and c are determined.
Nano-Composites NiCrAl (MCrAl) Ternary Alloy Powder Synthesized by Mechanical Alloying
Authors: Hussain Mohammad Sakhawat , Ababtain M.A.
Published: September 2009

The purpose of this study was to explore an innovative method for producing nano-crystalline Ni, Cr and Al powders using high energy ball milling and brief secondary processes. Nano-crystalline powders were produced by using a planetary ball mill. The contaminations of the milled metal/alloy powders were carefully avoided by choosing appropriate lining of the vial and the alloy balls. Two approaches were investigated, namely attrition milling of pure metal powders (e.g. Al, Cr and Ni) and mechanical alloying of the elemental powders to form a ternary alloy of NiCrAl. Currently MCrAlY (M=Ni, Co or Fe) powders, up to 40µm in diameter are used in the production of thermal barrier coatings (TBC) on industrial gas turbine components. The powder samples synthesized were characterized by scanning electron microscope (SEM) and transmission microscope (TEM), the crystallite size was found to be less than 20nm; the powder particle size was in the range of 250-300nm; no undesirable particle contamination was detected. It is anticipated that these very fine particles will increase high temperature properties of the thermally sprayed MCrAlY overlay coatings.
Influence of Structural Imperfections and Doping on the Mechanical Properties of Single-Walled Carbon Nanotubes
Authors: Rahmandoust Moones , Öchsner Andreas
Published: September 2009

In This study, finite element models of Single-Walled Carbon Nanotube (SWCNT) in their perfect form were generated. Then, after deriving mechanical properties in agreement with existing literature values, different levels of perturbation and missing atoms in the structure were applied. In another approach, some of the Carbon atoms were replaced with Silicon to produce a Si-doped SWCNT. Mechanical properties of the three kinds of imperfect structures of SWCNT were then compared with the perfect structure results, for both fundamental Carbon Nanotubes, namely Zigzag and Armchair.The results show that with any kind of imperfection, the stiffness of the structure decreases compared to the perfect SWCNT.
Enhancement of Conductivity in Ceria-Carbonate Nanocomposites for LTSOFCs
Authors: Raze Rizwan , Wang Xiao Di , Ma Ying , Huang Yi Zhong , Zhu Bin
Published: September 2009

This work first explores high resolution transmission electron microscopy (TEM) to determine the interfacial regions and provide experimental evidences for interfaces between the SDC and carbonate constituent phases of the SD-carbonate two-phase composites to further investigate the superionic conduction mechanism in the ceria-carbonate composite systems and enhancement of conductivity. Schober first reported interfacial superionic conduction in ceria-based composites but without direct experimental proofs. Such superionic conduction mechanism remains unknown. Especially, in the nano-scale, this region is trifle to be detected.
An Advanced LOCOS-Process for the Sub-50 nm-Region Using Low-Stress PECVD-Silicon Nitrides
Authors: Kallis Klaus T. , Keller L.O. , Fiedler H.L.
Published: September 2009

The standard Local Oxidation of Silicon (LOCOS) technique uses different oxidation rates of silicon and Low Pressure Chemical Vapour Deposited (LPCVD) silicon nitride in steam ambient to structure the field oxide. Due to different coefficients of thermal expansion a pad oxide is needed at the boundary layer to prevent stress from the substrate. This leads to a lateral diffusion of oxygen, also known as “birds beak”, which limits the minimum structure size to a few 100 nm [1]. When scaling down to this dimension, the Shallow Trench Isolation (STI) has become the standard isolation technique for fabrication of high-performance semiconductors to allow a high package density. Unfortunately the STI-process uses Chemical Mechanical Polishing (CMP) which increases the process complexity and leads to high costs. Therefore a new method which uses a low stress Plasma Enhanced Chemical Vapour Deposited (PECVD) silicon nitride without a pad oxide at the boundary layer will be presented in this paper.
Investigation of Interrelation between Particle Size and Phase Transition in the Al2O3-ZrO2 System
Authors: Ivanov-Pavlov Denis A. , Konakov Vladimir G. , Solovieva Elena N. , Ushakov Viktor M. , Borisova Natalia V.
Published: September 2009

Powder precursors of the Al2O3-ZrO2 system were synthesized by the sol-gel method. Dispersity of the powders depended on synthesis and drying conditions. Differential Scanning Calorimetry, X-Ray diffraction, and method of adsorption–desorption isotherms were used to characterize the interrelations between particle size and phase transition in the Al2O3-ZrO2 system. It was revealed that azeotropic drying under overpressure is quite effective for obtaining well-dispersed powder precursors synthesized by the sol-gel method. In contrast to bulk materials, tetragonal, cubic, and monoclinic phases were found to exist in a wider temperature-composition range. It was shown that the existing phase symmetry in the well-dispersed powders correlates with the crystallite size.
Tuning of Titanium Oxide Morphology at Micro and Nano Scale by Alternating Current Anodising
Authors: Diamanti Maria Vittoria , Ormellese Marco , Pedeferri Maria Pia
Published: September 2009

High surface area TiO2 layers are particularly attractive for photocatalytic applications; suitable anodising processes can be used to produce the oxides and to tune their morphology and structure. In the presented research, an alternative technique to enhance the surface area of anodic oxides was identified. This was achieved with the implementation of an anodising treatment performed by supplying alternating current in diluted hydrochloric acid (feeding voltage ranging from 5 V to 10 V). Alternating current anodising caused the formation of a double texture of pits on the oxide surface, the bigger ones being some micrometres wide and formed by smaller pits hundreds of nanometres large; these holes distribution and dimensions can be modulated by varying electrolyte concentration, feeding voltage and anodising time.
Amorphous/Nanocrystalline Films Prepared by Magnetron Sputtering with Additional External Magnetic Field
Authors: Kalinnikov G.V. , Andrievski R.A. , Egorov V.K.
Published: September 2009

Combined amorphous and nanocrystalline films attract an attention due to possibility to improve toughness, wear resistance and other properties which are important in nanomaterials and processes in energy systems. One of the known film fabrication methods is the magnetron sputtering deposition in the presence of an additional external magnetic field with inductions of up to 0.3 T as it was demonstrated by an example of the B4C-TiB2 system. The induction effects on the amorphous films hardness, growth rate and nanocrystallization process were investigated and discussed. The deposition under an additional external magnetic field with induction more than 0.2 T leads to the of nc-inclusions formation as was determined by X-ray diffraction, microdiffraction and high resolution transmission electron microscopy methods. The target and film compositions were determined by energy disperse spectroscopy and Rutherford backscattering spectroscopy. Compared to the target composition, some enrichment by nonmetallic elements (carbon and boron) was fixed in films.
Formation of a Hollow Binary Alloy Nanosphere: A Kinetic Monte Carlo Study
Authors: Evteev Alexander V. , Levchenko Elena V. , Belova Irina V. , Murch Graeme E.
Published: September 2009

Results of kinetic Monte Carlo simulation of the formation of a hollow nanosphere by interdiffusion from a core-shell binary system are presented for the first time. The faster diffusing species is located in the core whilst the slower diffusing species form the shell. With its self-generated vacancy composition all stages of the hollow sphere formation process are observed in our model: interdiffusion, the supersaturation of the core of the nanosphere by vacancies, precipitation of pores and eventual void formation. Results of this simulation confirm the experimental conclusions that interdiffusion accompanied by the Kirkendall effect and Kirkendall porosity is one of the mechanisms responsible for the formation of hollow nano-objects.
Oxygen Isotope Exchange in Nanocrystal Oxide Powders
Authors: Fishman Anatoly Yakovlevich , Kurennykh Tatiana Eugenievna , Petrova S.A. , Vykhodets Vladimir Borisovich , Vykhodets V.B. , Zakharov Robert Grigorievich
Published: September 2009

It is shown that investigations of the isotope exchange kinetics in nanocrystalline oxides allows one not only to solve problems connected with determination of process parameters and characteristic scenarios, but also to substantially extend experimental opportunities in analysis of diffusion properties of oxides. A specific behavior of the oxygen isotope exchange was studied in nanocrystalline LaMnO3 and ZrO2:Y2O3 oxides. The former oxide is characterized by very small values of oxygen volume diffusion coefficients, while the latter one is, on the contrary, an ionic conductor. The study was carried out using powdered nanomaterials prepared from original ceramic materials by grinding in planetary mills or by laser evaporation. The study revealed future trends in the use of nanomaterials for analysis of the diffusion kinetics in oxides. It is demonstrated that in this case the sensitivity of traditional isotope methods increases considerably and fundamentally new opportunities are provided for analysis of processes on the "gas phase  solid state" interface as well as for the study of volume diffusion in polycrystals.
Considering a strong dependence of the isotope exchange rate on the particle size, it is also topical to conduct studies dealing, along with determination of kinetic parameters of the process, with the use of the obtained data for certification of dimensional characteristics of oxide nanopowders.
Non Parabolic Shift of Interfaces and Effect of Diffusion Asymmetry on Nanoscale Solid State Reactions
Authors: Beke Dezső L. , Erdélyi Z. , Balogh Z. , Cserháti Csaba , Katona G.L.
Published: September 2009

In a set of recent papers we have shown that the diffusion asymmetry in diffusion couples (the diffusion coefficient is orders of magnitude larger in one of the parent materials) leads to interesting phenomena: i) sharp interface remains sharp and shifts with non Fickian (anomalous) kinetics [1-5], ii) originally diffuse interface sharpens even in ideal (completely miscible) systems [6,7], iii) an initially existing thin AB phase in A/AB/B diffusion couple can be dissolved [8], iv) there exists a crossover thickness (typically between few nanometers and 1m) above which the interface shift turns back to the Fickian behaviour [9], v) the growth rate of a product of solid state reaction can be linear even if there is no any extra potential barrier present (which is the classical interpretation of the “interface reaction control” for linear kinetics) [10]. These latter results will be summarized and reformulated according to the usual expression for linear-parabolic law containing the interdiffusion coefficient, D, and interface transfer coefficient, K. Relation between the activation energies of D and K will be analyzed and compared with available experimental data.
Diffusion through Diatom Nanopores
Authors: Bhatta Hemant , Kong Tae Kyong , Rosengarten Gary
Published: September 2009

Microscopic diatoms, unicellular algae that are abundant in the earth’s waters, have been interesting to researchers because of their unique outer shell structure known as frustules. The frustules are composed of amorphous silica, naturally nano-fabricated, while displaying unparalleled diversity in structure and morphology. The nanoporous structures of the frustules allow them to be used for specialized filtration procedures. These diatom frustules however haven’t been fully characterized for fluid/particle flow. Each diatom frustule contains two to three porous layers. The inner layer of Coscinodiscus sp. for instance has holes of around 1.2 µm and the outer layer comprises holes of around 300 nm diameter. This research presents diffusion studies to characterize the flow of particles through these frustule pores. In order to successfully carry out the diffusion studies, a single frustule of diatom was stuck onto the end of a hollow capillary fibre with internal diameter of 15.5 µm. The capillary was then inserted into 500 µm glass tube filled with fluorescent dye, Rhodamine B, and the experiment carried out with Nikon epifluorescence microscopy. We observed that diffusion through the inner layer was affected by its porosity resulting in the reduction of the diffusivity i.e. D = 1.1×10-10 m2/s. The diffusion through both the inner and outer layer however resulted in diffusion coefficient (D = 3.1×10-11 m2/s) that was influenced not only by the porosity but also the tortuosity. Thus we notice that the intricate three dimensional structure of the diatom imposes different boundary conditions to the flow of the Rhodamine B molecules resulting in different diffusion rate.
Replicas as a Technique for Examining Fracture Surfaces of Ceramics
Authors: Varner James R.
Published: September 2009

This paper discusses reasons for using replicas of fracture surfaces of ceramics, describes several replicating methods and materials, and presents examples that compare replicas with actual fracture surfaces. Advantages of using replicas include being able (1) to examine large pieces without having to cut them down to size, (2) to provide convenient archiving of fracture surfaces, and (3) to eliminate sub-surface scattering of light. Many times, replicas provide clearer views of untreated (uncoated) fracture surfaces than can be obtained by direct observation. Replication using cellulose acetate tape and two types of silicone rubber (filled and unfilled) are described. Both methods are fast, relatively inexpensive, and non-destructive. Images of replicas of fracture surfaces of a glass and several ceramic materials (including electrical porcelain and several polycrystalline ceramics) are compared with images of actual fracture surfaces.
Machining and Wear of High-Alumina Ceramics for Structural Applications
Authors: Veskovic-Bukudur Stojana , Leban Tanja , Ambrozic Milan , Kosmač Tomaž
Published: September 2009

The wear resistances of four standard-grade high-alumina ceramics were evaluated and related to their machining ability. Three of the material grades contained 96% of alumina and 4% of either calcium silicate, or magnesium silicate, or manganese titanate in the starting-powder composition. The nominal alumina content in the fourth material was 99.7%. The specimens were fabricated using a low-pressure injection-molding forming technique, followed by thermal de-binding and sintering. After sintering the four materials differ significantly in their grain size, bending strength and Vickers hardness. No direct relationship between the microstructural parameters and the mechanical properties was found, but there was a grain-size dependence of the surface finish after grinding under industrial conditions. The two silicate-containing ceramics exhibited considerably higher wear resistances than the two silicate-free ceramics, but no direct relationship between the abrasive wear rate during grinding and the cutting time was observed. The cutting ability represents a valuable material characteristic for industrial practice, but it should not be directly used for predicting the wear rate during grinding. Quantitative differences in the cutting time and abrasive wear rate were manifested in the different topographies of the worn surfaces. Cutting resulted in relatively large area fractions of plastically deformed surfaces, whereas pullouts dominated the worn surfaces after grinding.
Fractality of Simulated Fracture
Authors: Frantík Petr , Keršner Zbyněk , Veselý Václav , Řoutil Ladislav
Published: September 2009

The paper is focussed on numerical simulations of the fracture of a quasi-brittle specimen due to its impact onto a fixed rigid elastic plate. The failure of the specimen after the impact is modelled in two ways based on the physical discretization of continuum: via physical discrete elements and pseudo-particles. Advantages and drawbacks of both used methods are discussed. The size distribution of the fragments of the broken specimen resulting from physical discrete element model simulation follows a power law, which indicates the ability of the numerical model to identify the fractal nature of the fracture. The pseudo-particle model, on the other side, can successfully predict the kinematics of the fragments of the specimen under impact failure.
Contact and Bending Strength Tests of Ceramics: What is the Difference?
Authors: Hegedűsová Lucia , Kovalčíková Alexandra , Kašiarová Monika , Dusza Ján
Published: September 2009

The paper deals with the determination of the characteristic strength and the Weibull modulus m of Si3N4 and SiC ceramic materials using conventional four-point bending and unconventional contact tests between opposite rollers and opposite spheres. Ceramographic and fractographic methods were used for the characterization of strength degrading defects represented by processing flaws and by cracks of different types arising during the loading. The processing flaws influenced the Weibull parameters mainly in the bending mode, and the strength and its scatter in contact modes was influenced by lateral, median and contact end cracks, originated during the contact test using rollers, and by cone cracks originated during the contact test using spheres.
Strength Tests on Silicon Nitride Balls
Authors: Supancic Peter , Danzer Robert , Harrer Walter , Wang Zhong Hua , Witschnig Stefan , Schöppl Oskar
Published: September 2009

For some years ceramic bearing balls based on silicon nitride have been routinely used in technical practice. An important property of bearing balls is their strength, but appropriate testing methods are still missing. In this paper four different methods for strength testing are applied to commercial bearing balls. Each of the tests needs a different type of specimen, their preparation needs a very different effort, and the stress state applied to the specimens is also very different. This causes pros and cons, which are discussed in detail. The conventional 4-point bending test characterises the material in the interior of the balls. The applied stress state is uniaxial. The machining of the bending bars out of the balls is time intensive and costly. The ball on three balls test also characterises interior of the balls. The stress state is biaxial. The machining of the disc shaped specimens out of the balls is less expensive than the production of bending bars, but the finish of the tensile loaded surface needs special care. The data of both types of tests can be converted into each other using Weibull theory. The specimens in the triple ball crush test are as-received bearing balls, which are squeezed together. This causes some kind of contact loading, as will also occur in service. Failure is caused by the creation and growth of contact cracks, followed by a collapse of the compressed and cracked material. A detailed analysis of test results is complicated. It can be speculated that the component’s behaviour is mainly influenced by the toughness of the material and that the flaws in the material or at the component’s surface are of less significance. In the newly developed notched ball test the highest stressed region is a part of the original surface of the balls. Machining of the notch is straightforward. The stress state is almost uniaxial. The strength depends on size of flaws in the surface region. Therefore the notched ball test is a relevant measure to characterize the quality of the bearing balls.
Fractographic Investigations of Ordinary Ceramic Refractory Materials with Reduced Brittleness
Authors: Harmuth Harald , Manhart Christian
Published: September 2009

A fractographic procedure was developed and applied for ordinary ceramic refractory materials with a rather large size of heterogeneities and defects. It is based on a stereooptical method for generation of digital surface profiles which are evaluated by an autocorrelation function. Furthermore, a lateral correlation length is derived. A group of seven refractory materials was characterised by mechanical and fracture mechanical investigations, and the same specimens had been characterized by the fractographic procedure. Correlations have been tested. The results show a relation between the lateral correlation length and two fracture mechanical characteristics which are significant for the material brittleness and the elastic strain energy stored at maximum load. These relations are contributed to the dependence of the crack path on brittleness. With decreasing brittleness the amount of the crack path proceeding along the grain/matrix boundary increases for the materials investigated.
Elimination of Oxygenation Cracking in YBCO Bulk Superconductors
Authors: Diko Pavel , Chaud Xavier , Antal Vitaliy , Kaňuchová Mária , Šefčíková Martina , Šuster Dušan , Kováč Jozef
Published: September 2009

The reasons for cracking of YBa2Cu3Oδ/Y2BaCuO5 (Y123/Y211 or YBCO) bulk single-grain superconductors are mechanical stresses, which arise in the sample during its fabrication. Two main sources of stresses appearing during fabrication were identified: the different thermal expansion coefficients of 123 and 211 phases and the dependence of 123 phase lattice parameters on the oxygen stoichiometry. As-grown YBCO bulks have low oxygen content, YBa2Cu3O6.3, are not superconducting, and must be oxygenated to form YBa2Cu3O7. During standard oxygenation at 400 °C the shortening of crystal lattice parameters causes intensive cracking. The created cracks allow oxygen penetration into the bulk and cause the oxygenation time to be technologically acceptable but reduce significantly the superconducting properties. Here we show that it is possible to eliminate the formation of oxygenation cracks and to reach a critical current density 2.5 times higher than in material bulk oxygenated in a standard way. The oxygenated crack-free samples were obtained by high pressure oxygenation with progressively increasing oxygen partial pressure.
Interfacial Characterisation in Transparent Spinel Matrix Reinforced by SiC Fibre
Authors: Chlup Zdeněk , Dlouhý Ivo , Gürbüz Selen , Dericioglu Arcan F. , Kozák Vladislav
Published: September 2009

The behaviour of a propagating crack when an interface is present is a key feature in composite materials. This interaction usually predetermines final fracture behaviour of the material. In case of ceramic based composites (particle, fibre reinforced, laminates etc.) knowledge about properties of the interface and/or interlayer is usually unknown due to difficulties associated with their experimental determination. The aim of this work is to indicate a possible way for the determination of interface characteristics suitable as inputs for numerical calculations. The introduced testing methodology was tested on spinel composite ceramics reinforced by unidirectional SiC fibre. The adopted method for fracture toughness determination is using a chevron notch technique. Additionally, fractographical techniques were used when interpreting the measured values.
The Influence of Corrosion in an Aqueous Solution of NaCl on Fracture and Strength of Various Structural Ceramics
Authors: Galusková Dagmar , Kašiarová Monika , Hnatko Miroslav , Galusek Dušan , Šajgalík Pavol , Dusza Ján
Published: September 2009

The present work studies the corrosion of three most widely used types of structural ceramics – silicon nitride, solid state sintered alumina and liquid phase sintered alumina – in 3 % aqueous solutions of sodium chloride at temperatures up to 290 °C and pressures up to 7 MPa. The corrosion of silicon nitride was controlled by attack of Si3N4 matrix grains, while yttrium oxynitride amorphous grain boundary phase was corrosion resistant. Corrosion of Si3N4 in reference media -distilled water - at 290 °C was characteristic by formation of passivation layer, which hindered further dissolution of silicon nitride matrix. The presence of sodium chloride resulted in formation of discontinuous layer of corrosion products, resulting in more severe corrosion than in distilled water. The corrosion of liquid phase sintered alumina was mainly attributed to congruent dissolution of SiO2 and CaO from grain-boundary amorphous film, which was accelerated at higher temperature, and accompanied by precipitation of siliceous phases from oversaturated solution at 200 °C. Pure polycrystalline alumina corroded by loss of alumina grains, which did not dissolve in the corrosion media. The corrosion impaired significantly the fracture strength of silicon nitride, creating new, corrosion related defects at the surface, while the influence of corrosion on fracture strength of polycrystalline aluminas was negligible.
Fracture Surface Development Coefficient and Sialon Ceramics’ Bending Strength
Authors: Stach Sebastian , Roskosz Stanisław , Cybo Jerzy , Cwajna Jan
Published: September 2009

Resistance to brittle cracking is one of the most important functional properties of sialon ceramics. Evaluation of the resistance requires an analysis of decohesion processes occuring in the material. Aiming at a comprehensive description of the morphology of typically brittle fractures, a quantitative characterization was made using different methods and techniques, regarding the surface of fractures formed in a three-point bending test. By using the parameter Sdr, determined via the surface stereometry method, the fracture surface development coefficient, RS, typical for fractography, was calculated. Analysis of the research results indicates a proportional relation between parameter RS and the sialon ceramics’ bending strength.
Fractography, Some Legal Aspects and Challenges
Authors: Bradt Richard C.
Published: September 2009

Evidence regarding a fracture event is absolutely and definitively recorded by Nature during the fracture process. That record is in the form of the general macrocrack pattern and the surface topological features of the newly formed fracture surface. In reality, it is the only perfect record of what actually occurred during a fracture. Whenever a conflict or controversy arises regarding a fracture, it is the moral and scientific responsibility of the fractographer to analyze and interpret the record of the fracture as it was created by Nature. It is further necessary for the fractographer to then inform and educate the members of the legal community (lawyer, judge and jury) as to exactly what happened during the failure. This educational process is necessary so that the legal community can collectively understand the history of the fracture and arrive at a just and fair decision regarding responsibility and potential liability for the failure. This paper describes the overall process from the beginning of the fracture examination of the failed artifact to the final appearance in court leading to a decision by the judge or a jury. Both the technical and the human factors are addressed with varying degrees of detail.
Corrosion of Alumina Ceramics in an Aqueous Solution of Sodium Chloride
Authors: Galusková Dagmar , Šajgalík Pavol , Galusek Dušan , Hnatko Miroslav
Published: September 2009

Two alumina based ceramics with 99.99 % and 95 % of Al2O3 were evaluated after dissolution in an aqueous solution containing 0.5 mol/l NaCl at temperatures of 150 and 200 °C. The weight loss of liquid phase sintered alumina was mainly attributed to congruent dissolution of SiO2 and CaO from grain-boundary amorphous film, which is accelerated at higher temperature, accompanied by precipitation of silicaceous phases from oversaturated solution at 200 °C. Pure polycrystalline alumina corroded by loss of alumina grains, which do not dissolve in the corrosion media.
Mechanical Behavior of Sintered Porous Two-Phase Titanium Nanolaminate-Composites at High Temperatures
Authors: Firstov Sergiy A. , Gorban Victor F. , Ivanova Inna I. , Pechkovsky Engel P.
Published: September 2009

Regularities, features and mechanisms of deformation and fracture processes of new ceramic materials – porous (=3-35 %) two-phase titanium nanolaminate-composites Ti3SiC2/TiC, Ti3AlC2/TiC, Ti4AlN3/TiN (content of TiC or TiN – 5-70 % vol.) at 20-1300 оС are established. Composites are made by reaction sintering. On increase in mechanical properties and resistance to deformation they settle down in the following sequence: Ti3AlC2/TiC–Ti4AlN3/TiN–Ti3SiC2/TiC. In porous nanolaminate-composites containing less than 20 % TiC the increase in porosity  results in decrease in high-temperature strength pl and increase of plasticity . Appreciable increase of strength of porous composites is marked at content TiC>25-30 % (vol.).
Failure Investigation of Forming Rolls Made of Si3N4
Authors: Morrell Roger , Harrer Walter , Danzer Robert , Berroth Karl
Published: September 2009

Tool surfaces for the forming of shaped steel strips are typically made from cemented carbides. Disadvantages of these tools are that they suffer from roughening of the surfaces and severe wear, which deteriorates the surface quality of the products and restricts the lifetime of the tool. Due to their high hardness and better high-temperature properties, improvements of tool behaviour can be expected by the use of silicon nitride. During a collaborative project between industrial partners, universities and research centres, forming rolls made of silicon nitride were tested at several positions in rolling mills. The suitability of Si3N4-rolls in rolling mills could be demonstrated at low and medium hard loaded positions. At Böhler-Profil in Waidhofen/Austria the rollers were used for the preparation of shaped steel strips from blank feedstock. During this very severely loaded application a pair of rollers failed. It could be shown that the rolls failed due to thermal stresses which can be reduced to a large extent by an improved design.
Investigation of γ-Alon Structural Evolution during Sintering and Hot-Pressing
Authors: Zientara Dariusz , Bućko Mirosław M. , Lis Jerzy
Published: September 2009

Dense polycrystalline aluminium oxynitride with spinel structure, -alon, is noted for its excellent thermal properties, high-temperature mechanical properties, low dielectric constant, thermal expansion coefficients and intrinsic transparency extending from ultraviolet to mid-infrared wavelengths. The dense materials were made by reactive pressureless sintering or hot-pressing of the SHS derived powders. Powders were synthesized from mixtures of aluminium and corundum powders of different proportions. The products of the SHS synthesis were composed mostly of -alon and in lesser extend of aluminium nitride. Ground powders were pressureless sintered at temperatures of 1800-2100°C for 2-6hs as well as hot-pressed at 1750-1950°C for 1 h under 25 MPa in nitrogen flow. The present work is focused on phase evolution of -alon materials during pressureless sintering and hot-pressing. The structural changes of -alon, a Al2O3 and AlN were also examined.
Fracture Properties of Basalt Fibre Composites with Cured or Pyrolysed Matrix
Authors: Černý Martin , Chlup Zdeněk , Sucharda Zbyněk , Glogar Petr
Published: September 2009

Composite materials based on polysiloxane matrix reinforced by basalt fibres were prepared in laboratories of the IRSM ASCR. The composite samples were pyrolysed at 400 ÷ 750 °C after moulding and curing at 250 °C. Measurement of several mechanical characteristics (flexural strength, fracture toughness, impact strength, and measurement of elasticity) demonstrates a favourable influence of pyrolysis in comparison with the cured-only composite material. Fracture toughness was measured by chevron-notch technique and fracture surfaces were investigated using a scanning electron microscopy.
Modification of the Density-Pressure Relationship due to the Internal Friction and Cohesion of a Powder Mass Undergoing Closed Die Compaction
Authors: Kupková Miriam
Published: September 2009

The existing density-pressure laws for a powder undergoing die compaction fit experimental data very well except for the low-pressure end of curves for some materials (SiC, Al2O3). To improve this, density - pressure relationship was modified by considering the internal friction and cohesion. For constant internal friction and vanishing cohesion, the modified relationship became mathematically equivalent to the existing one. For density-dependent friction, the modified and original relationships were able to provide nearly the same densities at medium and higher pressures but slightly different values at the low-pressure region.