J. Muntasell

The effects of temperature on the behaviour of an apatitic calcium phosphate cement

An apatitic calcium phosphate cement is obtained by mixing α-tricalcium phosphate (α-TCP) and precipitated hydroxyapatite into a cement powder, and by then mixing this powder with an aqueous solution of Na2HPO4 as an accelerator. Setting times were reduced by about 30% by increasing the temperature from 22 to 37°C. Compressive strength reached higher intermediate and final values at 37 °C. Degrees of transformation of the α-TCP in the resulting calcium-deficient hydroxyapatite (CDHA) were much higher at 37 °C after 24 h of storage in Ringers solution according to X-ray diffraction. Differential scanning calorimetry indicated that the rate of reaction increased by a factor of about 5 when the temperature was increased from 25 to 37 °C. Scanning electron microscopy showed that the microstructure was more homogeneous and that a more tight entanglement of the precipitated CDHA crystals occurred after storage at 37 °C than at room temperature.

Poly(butylene terephthalate) poly(ethylene terephthalate) mixtures formed by ball milling

Mixtures of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) polymers were formed using ball milling technique and characterized by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). PET with different degrees of crystallinity was used in the solid-state mechanical milling process. Results suggest that PBT greatly influences the crystallization of amorphized PET by milling.

Thermomechanical cycling in Cu /Al /Ni-based melt-spun shape- memory ribbons

Temperature-induced transformations under constant tensile loads (thermomechanical cycling) have been performed on a set of Cu � /Al � /Ni-based shape-memory ribbons prepared by melt spinning. The rapidly solidified ribbons being already characterized in what concerns martensite and parent phase ageing and their effects on the thermal (stress free) martensitic transformation, the purpose of this study was to complete the characterization of the ribbons, particularly in their shape-memory effect. The results presented for a Cu */13.0 Al */4.0 Ni */0.3 Ti */0.05 B (wt.%) ribbon show larger recoverable strains in the strain � /temperature cycles (thus larger shape-memory effect) for ribbons aged at 200 8C than for the as-spun samples. The dependence of the transformation temperatures T on the applied load, quantified through the slope dT /ds , increases for aged alloys. Both results can be related to the recovery of internal stresses produced by the rapid solidification and some recovery of short-range disorder, both mechanisms favouring higher values of the effective transformation strain. This behaviour is in agreement with the evolution of transformation temperatures in stress free transformation and related microstructural changes produced by ageing the ribbons in parent phase. # 2003 Elsevier Science B.V. All rights reserved.

Amorphization of organic compounds by ball milling

We have applied the ball-milling technique to amorphize the organic compounds sucrose and poly(ethylene terephthalate). Differential scanning colorimetry and X-ray diffraction measurements show that the samples have been amorphized by milling. However, differential scanning colorimetry heating runs reveal some differences between the crystallization process of samples mechanically amorphized and those obtained by quenching.

Applicability for heat storage of binary systems of neopentylglycol, pentaglycerine and pentaerythritol: A comparative analysis

Abstract We have studied the solid-solid transitions of mixtures of the polyols neopentylglycol (NPG), pentaglycerine (PG) and pentaerythritol (PE). Values of temperatures and heat of transition for the PE/PG binary system are given. We have observed an increase of these values with the concentration of PE. Our calorimetric results show that PE/PG, PG/NPG and PE/NPG systems are suitable for heat storage. Depending on the transition temperatures, these systems are available for different applications (solar heat, industrial process heat, airborne and waterborne heat for space heating). We have also analysed the thermal hysteresis of the transitions and its influence on the utilization of these mixtures for energy storage.

Floor radiant system with heat storage by a solid-solid phase transition material

Abstract Heat storage by means of solid-solid phase transition has been used in a floor radiant system. Tests have been performed in order to establish a comparison between a system storing energy as latent heat with another one using sensible heat. The first system is much more efficient in temperature regulation, allowing an adequate utilization of the off-peak electricity for the charge period. Results obtained in this study show the promising perspectives of the solid-solid phase transition for thermal storage in building materials.

Influence of grain growth on the martensitic transformation in βCuZnAl memory alloys

Abstract The effect of grain size on martensitic transformation in CuZnAl shape memory alloys subjected to two thermal treatments in order to retain β phase has been studied by means of calorimetry and acoustic emission. The dependence of transformation temperatures and thermal hysteresis on grain size is interpreted from a thermodynamic model in terms of elastic enthalpy and frictional work contributions; these are non-chemical terms present in thermoelastic martensitic transformation.

Calorimetric study of the mixtures PE/NPG and PG/NPG

Abstract The polyalcohols neopentylglycol (NPG), pentaglycerine (PG) and pentaerythritol (PE) present reversible solid-solid transitions with properties (enthalpy change, temperature) that make them suitable for energy storage at relatively low temperatures (40–180°C). In this article we present a calorimetric study of the binary mixtures PE/NPG and PG/NPG. We have analyzed the dependence of the enthalpy changes and the transition temperatures on the concentration of the compounds, and the effect of cycling on the transition characteristics. Our results indicate that, when the concentration of the minoritary compound in the mixture is less than about 40% there is a total inhibition of the transition corresponding to this compound. We observe that the transition from crystalline solid to plastic crystal corresponding to NPG can be advanced in temperature by addition of PE or PG. This fact increases the possibilities of the utilization of these mixtures for solar energy storage.

Cold-crystallization of Poly(ether-ether-ketone) amorphized by ball milling

A partial amorphization of semicrystalline poly(ether-ether-ketone) has been induced mechanically by means of the ball-milling technique. The thermal behavior of the polymer has been studied using temperature-modulated differential scanning calorimetry. The cold crystallization of the amorphized material, taking place close to the glass transition temperature, can be detected on the nonreversing heat flow signal clearly separated from the glass transition effect.

Preliminary study of a heat storage unit using a solid-solid transition

A preliminary study for the design of a device for domestic water has been performed. A phase change material in solid state has been used to store solar energy. We have determined some characteristics physical parameters necessary to construct this device. The results obtained using a numerical simulation, considering an unidirectional model, have been verified with those obtained experimentally. The concordance between both experimentall and simulation results show that this model is available to study the heat transfer phenomenon in the PCM in order to optimize the design of the device.