José Luís Mier

Estimating the reversing and non‐reversing heat flow from standard DSC curves in the glass transition region

A mathematical model for the total heat flow obtained in differential scanning calorimetry (DSC) experiments from polymers with enthalpic relaxation is proposed. It is limited to the glass transition and enthalpic relaxation range of temperature and to the cases where the enthalpic relaxation is the only non‐reversing process taking place. The model consists of a mixture of functions representing the heat capacity heat flow of the glassy and non‐glassy fractions, the glass transition progress and the enthalpic relaxation heat flow.

DMTA study of a nickel-titanium wire

The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire were investigated by DMTA using cylindrical tension mode. The Youngs modulus, the maximum strain and residual deformation have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen for the temperature ramp dynamic experiments. A big change between 65 and 95°C is observed in the storage modulus. The values of E" at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different temperatures have been examined.

Oxidation stability of soy and palm based biodiesels evaluated by pressure differential scanning calorimetry.

The oxidation stabilizing effect of a substituted phenol on soy and palm based biodiesels was investigated according to the ASTM E2009 standard. Pressure differential scanning calorimetry (PDSC) measurements were used to evaluate the influence of oxygen pressure. A relationship was derived to describe the correlation between oxidation onset temperature and oxygen pressure. Additional standard differential scanning calorimetry (DSC) and thermogravimetric analysis tests were performed in order to evaluate other thermal effects of the additive. The different behavior of both fuels was explained on the basis of their different physical and chemical properties. PDSC results were compared with the values obtained by the Rancimat method and the crystallization temperature observed by standard DSC was compared with the cold filter plugging point obtained according to the EN 116 standard.

Study of the Degradation of a Polyesther-Polyurethane by TGA and the Logistic Mixture Model

The logistic mixture model was successfully studied previously in the separation of overlapping steps in some polymeric systems by the authors. In the present work, this method is applied to a polyesther-polyurethane degradation under air and inert atmospheres at several heat rates (5, 10, 15, 20 and 25 °C/min) in dynamic TGA. Every logistic component is fitted by reaction order, Johnson-Mehl-Avrami and Sestak-Berggren kinetics equations in order to calculate its kinetic parameters (activation energy, frequency factor and exponents). The reaction order model gives a good fitting and reproduces accurtelly the experimental curves. Johnson-Mehl-Avrami and Sestak- Berggren equations resulted to be not suitables because of the activation energy values obtained.

A study on wear of welded joins for pipelines

This study deals with the wear experienced in welded joins for pipelines. Its aim is to minimize the problems caused by this wear. An analysis is carried out on the tribological behaviour of three crucial areas within the welding: the base metal, the heat affected zone and the weld bead zone itself. The differences in mechanical properties between these areas are evaluated. Moreover, various alternatives in the welding process are proposed in an effort to improve the overall behaviour of the join.

Tribological Behaviour of an A355 Steel Pipe Welding

This work studies the behaviour of welding joints under abrasive wear in A355 Gr. P11 steel pipes carrying liquids at high temperatures. Various welding processes were tested on different joints in an effort to choose the one that gave the best wear response. For this purpose, a pin-on-disk tribometer was used at 200°C to simulate the service conditions of the pipes. The tests were carried out by pressing a hard chromium-plated steel pin, with a diameter of 4 mm and hardness of about 775 HV, on steel specimens in order to measure their mass loss and friction coefficient in the three welding zones: base metal (BM), heat affected zone (HAZ) and weld bead (WB). The tests conditions were 10 N of load, 200 rpm of rotation velocity and a radius of 3 mm. In addition, metallographic studies and hardness measurements of the three welding zones were done to complete this work.

Study of the Cure of a Diglycidyl-Ether of Bisphenol-a (DGEBA) / Triethylenetetramine (TETA) Epoxy System by Non-Isothermal Differential Scanning Calorimetry (DSC)

A diglycidyl-ether of bisphenol-A (DGEBA)/Triethylenetetramine (TETA) system was studied by non-isothermal differential scanning calorimetry (DSC) to establish its kinetics of cure. The DGEBA resin was Araldite GZ 601 X75 used in the marine coatings formulations. Previously, the optimum resin/hardener ratio was determined by the reaction heat measuring (.Hc) calculated from the curing exothermic peak. Tests at different heating rates (10, 15, 20, 25 and 30°C/min) under inert atmosphere were carried out in order to study the reaction kinetics. The activation energy of the cure (Ea) was obtained from these tests data by Borchardt-Daniels, autocatalytic, Duswalt and isoconversional Ozawa methods. Once the activation energy was determined, the master curves method was applied to find the kinetic model which best describes the measured DSC data. The Sestak-Berggren model SB (m,n) was found to be the most adequate for the system studied.

Comparative Study by Thermal Analysis of Four Different Kinds of Wood

Abstract. Knowledge of thermal behavior is needed when structural applications are concerned, and quick method of identifying species of wood is desirable in order to track the materials in industrial processes and in the life service. Samples of wood from four different species of trees (Castanea sativa, Quercus robur, Eucalyptus globulus, and Pinus sylvestris) have been studied by means of Simultaneous Thermal Analysis (STA). Dynamic scanning runs have been conducted under argon and air atmospheres. The simultaneous information of both weight and heat has been used in order to distinguish between species. Kinetic studies have been performed on the devolatilization processes. Similarities and differences have been pointed out and a quick and reliable procedure is suggested to distinguish among these four kinds of wood.