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1

Electronic Resource

Composition effects on the pH of a hydraulic calcium phosphate cement (1997)

BOHNER, M ; VAN LANDUYT, P ; MERKLE, H. P ; [et al.]

Springer

Journal of materials science 8 (1997), S. 675-681

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ISSN: 1573-4838

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Abstract The pH of a hydraulic calcium phosphate cement (HCPC) made of monocalcium phosphate monohydrate (Ca(H2PO4)2·H2O; MCPM), β-tricalcium phosphate (β-(Ca3(PO4)2; β-TCP) and water was measured as a function of reaction time and composition at room temperature. During setting, the cement pH varies from very acidic pH values, i.e., 2.5, to almost neutral pH values, i.e., 6. The cement pH profile significantly depends on the initial cement composition. However, all profiles are characterized by a sharp initial decrease of the pH due to the dissolution of MCPM crystals and the precipitation of dicalcium phosphate dihydrate (CaHPO4· 2H2O; DCPD) crystals. With an excess of MCPM, the final pH stays low, and its value can be predicted from the initial composition of the cement and solubility data. With an excess of β-TCP, the end pH is close to 5, which is much lower than 5.9, the value predicted by calculation. Results suggest that the difference may be due to the presence of impurities in the cement. Replacing MCPM by phosphoric acid renders the cement paste very acidic for the initial 30 s, but then the pH profile follows that obtained with MCPM. Adding pyrophosphate ions into the cement paste postpones the position of the pH minimum. The delay, which is proportional to the concentration of pyrophosphate ions, is thought to be due to the inhibiting action of pyrophosphate ions on the precipitation of DCPD crystals.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1018583706335

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2

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Effect of β-TCP granularity on setting time and strength of calcium phosphate hydraulic cements (1996)

Andrianjatovo, H. ; Jose, F. ; Lemaitre, J.

Springer

Journal of materials science 7 (1996), S. 34-39

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ISSN: 1573-4838

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: The effects of β-tricalcium phosphate (β-TCP) granularity on the properties of calcium phosphate hydraulic cements (CPHC) have been investigated. A model system based on mixtures of (β-TCP) and aqueous solution of orthophosphoric acid has been used. Powders with different shapes (irregular agglomerates or spheres) and sizes (d 50=7 to 130 μm) were prepared from two different calcium phosphate sources: Ca-deficient hydroxyapatite (DAP) or hydroxyapatite dicalcium phosphate mixtures (HAP-DCP). The cements exhibited setting times (ST) ranging from 65 to 510 s; they are mainly affected by the specific surface area (S BET) of the β-TCP powders, longer ST corresponding to lower S BET. In general, lower S BET and shorter ST values were obtained with HAP-DCP powders. Diametral tensile strengths (DTS) ranging from 3.5 to 10.4 MPa were obtained. The results show that DTS is affected in a complex way by the experimental variables. In general, DTS is higher with irregular agglomerates compared to spheres (+1.2 MPa), while better results are obtained with HAP-DCP powders (+0.9 MPa). The dependence of DTS on particle size is variable according to powder source and shape. The highest DTS (10.4 MPa) was obtained with irregular agglomerates prepared from HAP-DCP mixtures (d 50=16 μm), and the lowest (3.5 MPa), with irregular agglomerates prepared with DAP (d 50=123 μm). It can be concluded from this work that specific CPHC formulations can give quite different cement properties, such as setting time and ultimate mechanical strength, depending on the characteristics of the raw materials used. In the case of β-TCP based cements, the granularity of the starting cement powder, including particle size, shape and specific surface area, is of crucial importance and should be specified when the performances of different formulations are to be compared.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00121187

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3

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Synthesis, X-ray diffraction and solid-state 31P magic angle spinning NMR study of α-tricalcium orthophosphate (1996)

Bohner, M. ; LeMaître, J. ; LeGrand, A. P. ; [et al.]

Springer

Journal of materials science 7 (1996), S. 457-463

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ISSN: 1573-4838

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine , Technology

Notes: Abstract The effects of synthesis conditions on the quantitative preparation of α-tricalcium phosphate (α-TCP) have been investigated. The following parameters of the synthesis were considered: nature of the starting material-Ca-deficient hydroxyapatite, DAP, versus hydroxyapatite-anhydrous dicalcium phosphate mixtures (HAP-DCPA); Ca/P atomic ratio of the mixture, calcination temperature and time, and cooling rate. The yield and crystallinity of the final product have been estimated using X-ray diffraction (XRD) and solid state 31P magic angle spinning NMR (MAS-NMR) techniques. The results show that pure, well-crystallized α-TCP powders exhibiting nearly ideal MAS-NMR spectra, can be obtained by reactive sintering of HAP-DCPA (Ca/P=1.50...1.52) mixtures, at 1400°C for 8 h. The broadening of MAS-NMR spectra can be used as an indicator of structural order in the final product. The α-TCP yield with DAP was always less than 50%.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00122016

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4

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One damage law for different mechanisms (1997)

Lemaitre, J. ; Sermage, J. P.

Springer

Computational mechanics 20 (1997), S. 84-88

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ISSN: 1432-0924

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract We consider here a general three-dimensional kinetic damage law. It uses the thermodynamic of irreversible processes formalism and the phenomenological aspects of isotropic damage. It gives the damage rate as a function of its associated variable, the strain energy density release rate and the accumulated plastic strain rate. Associated with different plastic constitutive equations, this damage law takes into account brittle damage, ductile damage, low and high cycle fatigue and creep damage. In this paper we mainly focus on creep-fatigue interaction and high cycle fatigue. Associated to a viscoplastic constitutive equation having kinematic hardening, the damage law gives the non linear creep-fatigue interaction. The agreement with experiments is good. Associated to plastic constitutive equations also having kinematic hardening but introduced in a micromechanical two scale model based on the self-consistent scheme, it models the non linear accumulation of damage induced by a succession of sequences of different amplitudes as well as the effect of the mean stress and the influence of non proportional loading.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004660050221

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5

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Diffusive properties of motion on a bumpy plane (1998)

Samson, L. ; Ippolito, I. ; Batrouni, G.G. ; [et al.]

Springer

The European physical journal 3 (1998), S. 377-385

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ISSN: 1434-6036

Keywords: PACS. 05.20.-y Statistical mechanics[:AND:] 64.60.-i General studies of phase transitions

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract: We report on experiments studying the statistical properties of the motion of balls on a bumpy surface. This motion is found to be diffusive. In the direction of the mean flow, the coefficient of diffusion is found to attain a constant value, independent of the size of the ball and the inclination angle. The diffusion transverse to the mean flow is characterized by a coefficient which decreases with the inclination of the plane, and scales with the size of moving ball.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s100510050325

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6

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Reinitiation of a crack reaching an interface (1996)

Lemaitre, J. ; Desmorat, R. ; Vidonne, M. P. ; [et al.]

Springer

International journal of fracture 80 (1996), S. 257-276

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ISSN: 1573-2673

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract We consider here a bi-material made of two layers bonded together by an interface. The specimen is loaded in tension parallel to the interface and the existence of a mode I crack is assumed. The crack initiated in just one layer reaches the interface normally. We then study the second of the two possible cases: the crack crosses the interface and goes straight into the second layer, in mode I also; or the crack debonds the interface before reinitiating in the second layer at the debond tip. In the present study the conditions of the reinitiation of the crack in the second layer after debonding of the interface are presented. The maximum debond distance is calculated by means of a Shear Lag analysis associated with a damage constitutive equation. Qualitative rules for design are pointed out to make the interface a location of crack arrest or at least of crack growth delay. These rules are mainly: small thickness of the possibly cracked layer, strong interface and tough substrate.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00018507

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7

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A two scale damage concept applied to fatigue (1999)

Lemaitre, J. ; Sermage, J.P. ; Desmorat, R.

Springer

International journal of fracture 97 (1999), S. 67-81

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ISSN: 1573-2673

Keywords: Damage Mechanics ; high cycle fatigue ; nonlinear accumulation of damage ; mean stress effect ; nonproportional loading.

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The ductile type of damage is a phenomenon now well understood. Once the fully coupled set of constitutive equations is identified, Damage Mechanics is a powerful tool to predict failure. Brittle materials do not exhibit such a damageable macroscopic behavior. Nevertheless, they still fail. On the idea that damage is localized at the microscopic scale, a scale smaller than the mesoscopic one of the Representative Volume Element (RVE), we propose a three-dimensional failure modeling for monotonic as well as for fatigue loading. We develop a two scale model of what we shall call brittle damage: at the microscopic scale, micro-cracks or micro-voids exhibit a damageable plastic-like behavior with no effect on the global (mesoscopic) elastic behavior. Microscopic failure is assumed to coincide with the RVE failure. This model turns out to represent quite well physical phenomena related to high cycle fatigue such as the mean stress effect, the nonlinear accumulation of damage, initial strain hardening or damage effect and the nonproportional loading effect for bi-axial fatigue. The model has been implemented as a post-processor computer code. A simplified identification procedure for the determination of the material properties is given.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1018641414428

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8

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Synthesis of Y2Ba4(C2O4)7 · zH2O by aqueous precipitation (1995)

Rubattel, S. ; Jongen, N. ; Lemaitre, J. ; [et al.]

Springer

Journal of materials science 14 (1995), S. 1196-1198

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ISSN: 1573-4811

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00291804

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9

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Synthesis, sintering and expansion of Al0.8Mg0.6Ti1.6O5: a low-thermal-expansion material resistant to thermal decomposition (1997)

Buscaglia, V. ; Caracciolo, F. ; Leoni, M. ; [et al.]

Springer

Journal of materials science 32 (1997), S. 6525-6531

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract A low-thermal-expansion ceramic with the composition Al0.8Mg0.6Ti1.6O5 that is isostructural to aluminium titanate Al2TiO5, was prepared by solid-state reaction of a mixture of α-Al2O3, MgO and TiO2-rutile. The synthesized material does not decompose after annealing for 250 h in the temperature range of 900–1175°C. The ceramic sintered at 1350°C has a 97% relative density, a grain size of ≈5 μm and an average thermal expansion coefficient between 80 and 1000°C of ≈2×10−6 K−1. Materials with the same composition, but obtained by reaction sintering, have a higher thermal expansion coefficient (4×10−6 K−1) and showed the presence of secondary phases.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1018611311015

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