2,112 research outputs found
Comparative sintering of zirconia and hydroxyapatite-zirconia composites
No full textHydroxyapatite [Ca10(PO4)6OH2, HA] is the major constituent of the mineral phase of bone and exhibits desirable properties as a bone graft, such as biocompatibility, bioactivity, osteoconductivity and direct bonding to bone tissue. However, due to its limited mechanical properties, in particular low fracture toughness (KIC) and tensile strength, HA is limited to non-load bearing applications and metal implant surface coatings. Zirconia (ZrO2) based materials exhibit high fracture toughness due to the stress induced martensitic transformation of tetragonal to monoclinic ZrO2. In theory, a composite material composed of HA and a reinforcing ZrO2 phase, combining the inherent bioactivity of HA with reinforcement from the ZrO2 is an attractive proposition in terms of load bearing bone replacement. The work contained herein attempts to improve the mechanical properties of HA through the addition of a ZrO2 phase and consolidation through two comparative sintering techniques, microwave and conventional sintering.
The first objective was to investigate the effect of microwave sintering on physical, mechanical and chemical properties of Y2O3 (2-5 mol%) doped ZrO2 compositions compared with conventional sintering. Y2O3 content was altered through the attrition milling of commercial undoped monoclinic ZrO2 powders with co-precipitated Y2O3-doped ZrO2 powders and these were characterized using X-ray diffraction (XRD), particle size analysis (PSA), transmission electron microscopy (TEM) and BET. Comparative sintering was performed at temperatures of 1100, 1200 and 1300°C. Post sintering characterization included phase analysis (XRD), microstructural analysis using scanning electron microscopy (SEM), density measurements and mechanical testing, which included Young?s modulus, biaxial flexural testing and microhardness. Compositions containing 2 mol% Y2O3 microwave sintered at a temperature of 1300°C exhibited the greatest improvement, due to retention of tetragonal ZrO2, with a 5% increase in relative density compared with conventional sintering. Grain size analysis indicated that there was significant grain growth in microwave sintered samples (to d = 353nm) compared to their conventionally sintered counterparts (d = 200nm). Associated with this was a 22% increase in Young?s modulus to 220GPa, a 77% increase in Vicker?s Hardness up to 11.5GPa and a 165% increase in biaxial flexural strength up to 800MPa. Based on these observations, a reinforcing ZrO2 phase containing 2 and 3 mol % Y2O3 was decided upon for addition to HA.
The second objective was to investigate the effect of microwave sintering on HA-ZrO2 composites containing a commercial HA powder and HA synthesized using a co-precipitation technique and ZrO2 with the optimum Y2O3 content for Y-TZP found in the initial stage. HA was precipitation synthesized at temperatures of 25 and 45°C and characterized using XRD, X-ray fluorescence (XRF), TEM and BET. Commercial HA composites containing 0, 5, 10, 20 & 40wt % ZrO2 additions and synthesized HA (S-HA) composites containing 0, 5 and 10 wt% ZrO2 were comparatively sintered. The post sintering characterization was similar to the previous step. In terms of phase stability it was found that the decomposition of HA to a and/or ß-TCP increased with increasing amounts of ZrO2 irrespective of the HA powder used. This decomposition increased with increasing temperature and was found to increase in microwave sintered samples at 1300°C. It was also found that CaO released through the decomposition of HA reacted with the ZrO2 reinforcing phase to form either a c-ZrO2 solid solution and/or CaZrO3 above temperatures of 1100°C. Microwave sintering resulted in increased densification at lower temperatures of 1000 & 1100°C. It was observed, however, that there was a reduction in the relative densities of ZrO2 composites compared to unfilled HA as the sintering temperatures increased to 1200°C. It was suggested that H2O formed through the decomposition of HA led to formation of pores and lower densities. The increase in porosity was observed to be detrimental to the mechanical properties of the HA-ZrO2 composites. The highest stiffness, biaxial flexural strengths and microhardness of 112 GPa, 164MPa and 5.7GPa were observed in unfilled HA conventionally sintered at a temperature of 1300°C with a corresponding relative density of 96.7%. Comparative values of 109GPa, 138MPa and 4.9GPa were achieved in microwave sintered samples sintered at 1200°C. Subsequent increases in ZrO2 reduced the mechanical properties. The addition of 2.5 wt % CaF2 to microwave sintered synthesized HA-ZrO2 composites resulted in a significant increase in the relative density. The substitution of F- for OH- resulted in the partial formation of Fluoro-HA, increasing the thermal stability, limiting the formation of H2O, and thus increasing density. While the addition of CaF2 increased the density of composites, CaO formed in this case from the substitution of F- for OH- reacts with t-ZrO2 again forming CaZrO3 and/or c-ZrO2. The increased density led to an increase in the Young?s modulus and the hardness. However, the biaxial flexural strengths of composites were not increased. While there was an increase in mechanical properties compared to HA-ZrO2 composites without CaF2, the Young?s modulus and the hardness only exhibited values comparable to unfilled HA. The strengths were inferior to unfilled HA.
The biocompatibilities of HA-ZrO2 composites were determined using In vivo & In vitro evaluation. In vitro evaluation indicated that the materials induced a favourable response in rat osteosarcoma cells. In vivo evaluation indicated that the material was osteoconductive and biocompatible in the rat tibia model
Hydroxyapatite-zirconia composites and strontium-hydroxyapatite for skeletal applications
No full textHydroxyapatite (HA) is inherently bioactive and is successfully used in non-load
bearing skeletal applications. However, its use in load-bearing applications is limited
due to its poor mechanical properties, particularly under tensional and torsional stresses.
For this reason HA is employed in non-load bearing clinical applications such as
implant coatings or as bone fillers. In the work contained herein, nano-sized zirconia
(ZrO2) is employed as a filler phase in an attempt to improve HA’s mechanical
properties. HA was synthesised at four temperatures: 6oC, 25oC, 45oC and 65oC. The
resultant powders were characterised in the green state using x-ray fluorescence (XRF),
dilatometry, x-ray-diffraction (XRD), BET and high-temperature XRD to determine the
synthesis temperature that offers the most suitable stoichiometry and resistance to
decomposition when sintering. ZrO2 (1, 2, 3, 4 and 5 wt%) was added to the most
promising laboratory synthesised HA. Although HA reinforcement by the incorporation of ZrO2 is reported in the literature, high temperatures of over 1400°C are commonly required to sinter these composites to high density; temperatures at which HA is thermally unstable. The literature reports that microwave sintering (MS) can increase both density and mechanical properties in ceramic bodies with shorter processing times and at lower sintering temperatures than conventional sintering regimes. On account of this, microwave sintering was employed in this study to sinter the HA-ZrO2 composites
at 700oC, 1000oC and 1200oC; in addition to comparative sintering in a conventional
(CS) furnace. The 700oC samples do not undergo any appreciable densification,
irrespective of sintering method. Increasing ZrO2 decreases density of both the CS and
MS samples from approximately 88% to 85% in the 1200oC samples. Increasing amounts of ZrO2 had no significant effect on the biaxial flexural strength (BFS) of the
composites. The BFS of the samples sintered at 1000oC ranged from 30-45MPa, while
the samples sintered at 1200oC ranged from 60-85MPa. Statistically the hardness of the
materials is not affected by ZrO2 incorporation, although the MS 1200oC samples do show increased maximum hardness values with added ZrO2. The hardness values for the CS and MS samples sintered at 1000oC range from 0.5 to 1.5GPa, while the samples
sintered at 1200oC range from 1.7 to 3GPa. The volume fraction porosity was
determined as the main controlling factor in both the BFS and hardness of the CS and
MS samples over the temperature range 700oC to 1200oC, however at specific sintering
temperatures other secondary controlling factors have increased control over BFS and
hardness. SEM analysis showed that the ZrO2 particles collected in the grain boundaries, thereby reducing grain boundary diffusion in both the CS and MS samples.
HA was subsequently doped with strontium (Sr2+) ions in an attempt to increase
bioactivity, as Sr positively influences bone remodelling. Successful synthesis of
strontium-hydroxyapatite (Sr-HA) was achieved, as determined by XRD, Fourier
transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS).
5% Sr incorporation resulted in stabilisation of a number of phases with an increase in BFS from 85MPa to 120MPa in the MS samples. A decrease in the maximum BFS
resulted in the CS samples, from 120MPa to 47MPa. The MS samples doped with 10%
Sr experienced approximately no change in BFS while the CS samples experienced an
increase in the maximum BFS from 47MPa to 73MPa. The maximum hardness for the
5% Sr-HA CS and MS samples increases from between 2GPa (MS) and 3GPa (CS) to
approximately 4.7GPa for both regimes. This remained unchanged for the 10% Sr-HA
samples. With 5% Sr dopant, the HA phase was stabilised in both sintering regimes,
however with increased 10% Sr dopant levels, decomposition increased. β-TCP is
stabilised in the CS samples with no α-TCP generation. This does not occur in the MS
samples due to destabilising effects of the microwave field. The 10% Sr-HA displayed
excellent bioactive properties in a successful animal trial
Esperienza ed evento della verità. Pratica filosofica e astrazione scientifica nel pensiero di A.N. Whitehead
No full textThis article analyzes the relationship between philosophy, experience and event in A.N. Whitehead’s thought. From the critics of the concept of object, the author retraces and describes the peculiar “abstract-concrete dialectic”, at the center of the researches concerning the perceptual experience.
Furthermore, according to Whitehead’s later works, she demonstrates how the philosophical practice is different from all other kinds of science, although it requires science itself because of the co-implication of object and event, abstraction and recognition
Il "Guerrin Meschino" di Gesualdo Bufalino : un'"opra" in versi
No full textGesualdo Bufalino first published Il Guerrin Meschino in 1991 in a non-commercial edition. In 1993, after a deep revision, he re-published his work with publisher Bompiani: the novel has a modified plot, and the author decided to insert three new poems in addition to the opening and closing poems, formerly present in 1991’s edition. This paper, in its entirety supported by handwritten material preserved at Fondazione Gesualdo Bufalino (Comiso), is divided in two parts: the first part illustrates the differences between the first and the second edition, the second part provides a critical edition of the five poems
A FEW WORDS ABOUT THE TEACHER. IN MEMORY OF THE EXCELLENT TEACHER AND SCIENTIST M.R. SAPIN
No full textM.R. Sapin (1925–2015) was a professor at I.M. Sechenov First Moscow State Medical University, honorary academician of Russian academy of medical sciences (1988), and an outstanding representative of the Moscow anatomical school of the middle of XX – early XXI century. From the very beginning of his medical training, Mikhail Romanovich got interested in anatomy, especially in angiology and lymphology, and later concentrated on its studying. The author of more than 30 text books and guidelines for schools, universities, and colleges, Mikhail Romanovich was the doctoral and thesis advisor of 51 Ph.D. and approximately 70 MD dissertations. M.R. Sapin made a significant contribution to the development of anatomical education providing the departments with a various range of dry and wet specimens. His stunning and effective work as a tutor was highly appreciated by his students and colleagues, Russian and foreign anatomists. M.R. Sapin was the leader of the Laboratory of Functional Anatomy since 1972, president of the International Association of Morphologists (1992–2006), chairman of the expert commission of Higher Attestation Commission (1959–1994), etc. A man of a great willpower, M.R. Sapin faced a lot of obstacles in his life and research work but overcame that all successfully. The article presents the most important facts of anatomist’s career and lifetime.</jats:p
Verslag van het voorgevallene tijdens het hooge opperwater op de Nederlandsche rivieren in den winter van 1919 op 1920
No full textNadat de Rijn op 20 December 1919 tot even beneden den middelbaren zomerstand 1901-1910 (M.R.) was gedaald vertoonde zich op die rivier een sterke en vrij snelle was, waardoor het water te Keulen tot 6m +M.R. bij het einde van het jaar steeg. In de daarop volgende 11 dagen daalde de waterstand tot 1.5m +M.R. om daarna in 5 dagen weder te rijzen tot den zeer hoogen stand van 7m +M.R. Door een aanvankelijk sterken later flauweren val liep de stand weder terug tot 1.5m +M.R. op 30 Januari. Ook op de Maas vertoonden zich twee dicht op elkaar volgende sterke wassen. Bij den aanvang van den eersten was op 19 december stond het water te Maastricht op ruim 1m +M.R. en steeg het in 6 dagen tot 4.37m +M.R.; in de daaropvolgende 9 dagen bleef de stand steeds hoger dan 4m +M.R. en daalde toen tot ongeveer 2m +M.R. op 10 Januari 1920. De tweede was trad op laatsgenoemde datum in waarbij het water oplied tot 4.94m +M.R. op 15 Januari. Het water daalde daarna dadelijk en was op 29 Januari tot ongeveer 2m +M.R. weggevallen. Bij den tweeden was op Rijn en Maas werden de hoogst bekende waterstanden bij open rivieren overtroffen te Keulen met 7 cm en te Maastricht met 2 cm. De rivieren waren ijsvrij.Hoogwaterversla
Seismic prevention and rahabilitation of nonstructural elements. Criteria to define a post-seismic damage analysis procedure
No full textIt reports very briefly the research work, developed by the author during her Doctorate course, about a post-seismic damage analysis procedure for nonstructural elements of framed structure building system
The Ontology of the Causal Basis of Man : To the Theory of Time
No full textIn 2014, Amirbegov Y.M.'s monograph titled "Mechanics of Thinking" or "Ontological Basis of the Subject" was published, which dealt with a philosophical question: the relationship of matter with consciousness and time of our being. But since the monograph duplicated the thesis conceived by the author and did not go beyond the material presented in it, on the advice of the consultant the author of the monograph is preparing its second edition in an expanded version with a new title: " Ontology of Causal Basis of Man", attracting his mentor, the author of "The Theory of Time or Principle of Formation of Matter Forms" Amirbegov M.R., as a co-author of this book,
Adhering to the opinion that matter between past and future temporal conti-nuity of eternity is reduced to nothing and in reality there remains only a causeless "Nothing", the authors of this book from a clean sheet, but with baggage of knowledge about objective forms of being and causeless reality with its possibili-ties, build an unparalleled theoretical model of human integrity, answering the question: what does a man, his sensorium, consciousness, his thinking apparatus and thought itself, why and how? The authors submit this book to the judgment of the reader
The application of intramolecular n-acyliminium cyclisation strategies towards biologically active heterocycles
No full textWe describe the application of N-acyliminium cyclisation strategies to access a range of heterocycles with potential for biological activity. We have described an asymmetric approach towards the anti-tumour pyrroloisoquinoline alkaloid (R)-(+)-crispine A. We have achieved a synthesis of the pyrrolo[2,1-a]benzazepine template which is a sub-unit of the Homoerythrina alkaloids, and the functionalised dodecahydrobenz[a]indolo[3,2-h]quinolizine template, which is a sub-unit of the manadomanzamine alkaloids. In addition, we have described an asymmetric synthesis of the α-hydrazino pyrroloisoquinoline ring system, towards the synthesis of conformationally restricted peptidomimetics
The Ontology of the Causal Basis of Man : To the Theory of Time
No full textIn 2014, Amirbegov Y.M.'s monograph titled "Mechanics of Thinking" or "Ontological Basis of the Subject" was published, which dealt with a philosophical question: the relationship of matter with consciousness and time of our being. But since the monograph duplicated the thesis conceived by the author and did not go beyond the material presented in it, on the advice of the consultant the author of the monograph is preparing its second edition in an expanded version with a new title: " Ontology of Causal Basis of Man", attracting his mentor, the author of "The Theory of Time or Principle of Formation of Matter Forms" Amirbegov M.R., as a co-author of this book,
Adhering to the opinion that matter between past and future temporal conti-nuity of eternity is reduced to nothing and in reality there remains only a causeless "Nothing", the authors of this book from a clean sheet, but with baggage of knowledge about objective forms of being and causeless reality with its possibili-ties, build an unparalleled theoretical model of human integrity, answering the question: what does a man, his sensorium, consciousness, his thinking apparatus and thought itself, why and how? The authors submit this book to the judgment of the reader
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