Muhsin Çiftçioğlu

Determination of agglomerate strength distributions: Part 1. Calibration via ultrasonic forces

Abstract A characterization technique has been developed to quantitatively determine agglomerate strength distributions in bulk powders. This technique may be used throughout a powder processing procedure to determine the source of agglomeration, as well as an aid in the elimination of these agglomerates by helping the user to understand the nature of the interparticle bonds. Quantitative strength distributions are determined via exposure of a powder dispersion to a calibrated ultrasonic field and following the ensuing changes in the dispersion via particle size analysis. The ultrasonic field calibration method, developed by Ciftcioglu et al. , was examined to ascertain its quantitative ability. Difficulties encountered with the calibration method are discussed at length and suggestions made for its applicability and use.

Determination of agglomerate strength distributions Part 3. Application to titania processing

Abstract A quantitative agglomerate strength determination technique, consisting of exposing sample dispersion to a calibrated ultrasonic field and following the resultant changes via particle size analysis, was examined and developed in previous portions of this study. In the present part (Part 3) the use of this technique as a diagnostic tool in a powder processing scheme is demonstrated. Titanium dioxide was prepared by two different routes, thermal hydrolysis and base-induced precipitation, to obtain powders with distinctly different strength distributions. By the introduction of slight modifications in the processing schemes, a total of five different titania powders were produced. The agglomerate strength distributions of these powders (both precursor and the calcined oxide) were measured and related to chemical and other structural properties to show that slight changes in material properties could be detected and subsequently related to a particular processing step. Ultrasound-derived agglomerate strength distribution curves were also compared to uniaxial compaction tests.

Processing of Nanocrystalline Ceramics

Methods of preparing non-agglomerated powders for three systems -- yttria, titania, and yttria-stabilized zirconia -- are reviewed. The non-agglomerated nature of these powders should make it possible to sinter them into dense ceramic bodies with nanocrystalline grain sizes. Experiments with yttria-stabilized zirconia have shown that this is indeed the case, with mean linear intercept grain sizes of 60 nm resulting from original powder particle diameters of 13 nm. This ultrafine-grained zirconia is shown, in turn, to have superplastic forming rates 34 times faster than a 0.3 {mu}m-grained commercial zirconia of the same composition. 7 refs., 9 figs.

Monetite promoting effect of NaCl on brushite cement setting kinetics

Brushite forming calcium phosphate cements (CPCs) have received growing interest for scaffold applications due to their high surface area and high bioresorbability. The dehydrated form of brushite, monetite, has a finer microstructure with higher surface area, higher strength and bioresorbability comparable to brushite, making it a viable alternative phase in CPCs. The increase in monetite content of the β-tricalcium phosphate (β-TCP)-monocalcium phosphate monohydrate (MCPM) cement system due to the reduction in its supersaturation upon addition of NaCl to excess setting liquid was investigated kinetically. The relaxation period was monitored by pH-stat titration of the cement solution by 0.1 M NaOH. Monetite growth was achieved in shorter periods at higher NaCl concentrations where the supersaturation gap between brushite and monetite is thought to be narrowed due to high ionic strength in accord with Pitzers ion interaction model. The brushite/monetite ratio decreased consistently with increasing NaCl concentration in the 3-6 M range.

Mercury porosimetry of ordered sphere compacts: Investigation of intrusion and extrusion pore size distributions

Abstract Intrusion—extrusion hysteresis in mercury porosimetry is thought to be caused either by mercury contact angle hysteresis or by the domination of extrusion by pore bodies and intrusion by throats to the pore network. Mostly, only the information obtained during the intrusion of mercury has been used in the pore structure characterization of materials via mercury porosimetry. The use of the data obtained during extrusion has been the subject of several recent studies in an attempt to reach a more complete picture of pore structure. In this work, the possible use of both intrusion and extrusion for pore structure characterization have been investigated. Submicron monosize spherical particles of silica and yttrium hydroxycarbonate were synthesized and ordered compacts of these powders have been prepared. Mercury porosimetry tests on these high-density compacts (typically 68 – 70% of sphere density) have shown the presence of two pore peaks for intrusion and extrusion with the exception of one compact. Comparisons of intrusion pore sizes with the theoretical sizes of the constrictions for ordered sphere packings have shown reasonable agreements. Similar comparisons between the sizes of cavities in sphere packings and the extrusion pore sizes did not show the same agreement. Results for one sample did not show a distinct extrusion pore size even at very large pore sizes, most probably due to the domination of mercury extrusion by very few large pores present in the sample. For all other samples, the extrusion pore sizes were close to the actual sphere size and the extrusion was most probably dominated by a few vacant sphere sites in the ] ordered structures. The results of this work have shown that the possibility of using extrusion data for pore body size distribution determination is in serious doubt. The presence of very few larger pores in the porous body may dominate the whole extrusion process and can cause the extraction of inaccurate pore size information from the extrusion data.

Determination of agglomerate strength distributions: Part 2. Application to model agglomerates

Abstract To demonstrate the validity of the ultrasonic calibration technique (described in a previous paper of this series) for determining strength distributions in real agglomerates, a series of model agglomerates were synthesized. By using ordered packings of monosize (270 nm diameter) silica spheres which had been subjected to different heat treatment levels (800, 1 000, 1 050 °C) agglomerates with narrow strength distributions and known primary particle sizes were obtained. The model agglomerates were exposed to calibrated ultrasonic forces and agglomerate strength distribution curves prepared. Samples were also uniaxially compacted to compare the results obtained via the technique developed in this work with a traditional agglomerate strength testing method.

Preparation and Microstuructural Development of Nanocrystalline Titania and Alumina

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003

Preparation and Characterization of PolyLactide-Hydroxyapatite Biocomposites

In the present study, the preparation and characterization of polylactideHydroxyapatite(HA) composite films for biomedical applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical and microstructural properties of the composites were investigated. Poly-LLactide and 96/4 Poly(L-Lactide co D-Lactide) copolymer-HA composites containing 10-40 wt % HA particles have been prepared by solvent casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriethoxysilane (AMPTES) and 3mercaptopropyltrimethoxysilane (MPTMS) at three different concentrations(0.5-2 wt%). Silane treatment indicated improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for PLA composites containing 1 wt% aminofunctional silane treated HA and 0.5-wt % mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix. Introduction Bioabsorbable devices for load bearing applications, based on bioabsorbable polymer or composites can overcome some problems associated with metallic implants or devices applied in orthopaedics (1). These devices made of biodegradable polymers such as poly (L-lactide), poly (L-lactide co DL Lactide) copolymers are already in clinical use for the last twenty years [1-2]. Mechanical properties of these polymers gradually reduce as they degrade, allowing loads to be transferred to the bone, therefore reducing stress shield effect. Although they have many advantages over metallic implants, the major drawn back of such resorbable polymers is that they have weak mechanical properties especially for the load bearing applications [3]. Recently hydroxyapatite (HA) reinforced polylactide based composites have attracted great attention due to the favourable characteristics of HA which is expected to confer a bone bonding behaviour and to improve mechanical properties of these composites [4-5]. Many researchers have examined the preparation and characterization of hydroxyapatite/PLA composites in the last two decades [4-6]. In spite of the promising results obtained so far, nobody has studied the improvement of the interfacial interaction and adhesion between polylactide polymer and HA filler. The interaction and adhesion between filler and polymer matrix have a significant effect on the properties of the particulate filled reinforced materials, being essential to transfer the load between two phases and thus improve the mechanical properties. To improve the mechanical properties, it is necessary to render the surface of the filler and the polymer compatible, which can be achieved using several types of surface coupling agents. In the literature, there are many studies dealing with the characterization of interfaces and their influence on the mechanical Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1953-1956 doi:10.4028/www.scientific.net/KEM.264-268.1953

Mechanical Properties of Hydroxyapatite Composites Reinforced with Hydroxyapatite Whiskers

Abstract. Sintering and mechanical behavior of pure and hydroxyapatite (HA) whisker reinforced HA composites were investigated in this work. Pure and composite samples were prepared by using a commercial powder and whiskers prepared by molten salt synthesis. The dry-pressed samples were sintered in the 800 and 1300°C range. The effect of whisker-addition on the mechanical properties of HA was investigated through compression and hardness testing. Compressive strength and fracture strain were observed to increase by the addition of whiskers.

Low Temperature Synthesis of Spinel Powders by Mechanical Grinding

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003