francisco franco - Academia.edu (original) (raw)

Uploads

Papers by francisco franco

Research paper thumbnail of The influence of ultrasound on the thermal behaviour of clay minerals

Journal of The European Ceramic Society, 2006

The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolin... more The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9 • C) while muscovite presents the largest (184 • C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area. The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied.

Research paper thumbnail of The influence of ultrasound on the thermal behaviour of a well ordered kaolinite

Thermochimica Acta, 2003

The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolin... more The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9 • C) while muscovite presents the largest (184 • C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area. The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied.

Research paper thumbnail of Phase transformation on heating of an aged cement paste

Thermochimica Acta, 2004

The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately aft... more The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 ]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating ( M versus the final mass). The sorbed water (EV), escaping at 110 • C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1-2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 • C into C 2 S and C 3 S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 • C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation M(700-800 • C) increased highly with ageing.

Research paper thumbnail of The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite

Journal of Colloid and Interface Science, 2004

The present study examined the effect of sonication on the particle size and structure of a well-... more The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m 2 /g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (−a/3 + b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers.

Research paper thumbnail of Polyhydroxylated pyrrolizidines. Part I: Short and highly stereocontrolled syntheses of hyacinthacines

Tetrahedron-asymmetry, 2001

Two short and highly stereocontrolled syntheses for 7a-epi-hyacinthacine A 2 (7-deoxyalexine) 3 a... more Two short and highly stereocontrolled syntheses for 7a-epi-hyacinthacine A 2 (7-deoxyalexine) 3 and 5,7a-diepihyacinthacine A 3 4 are, respectively, reported herein. An appropriately protected polyhydroxypyrrolidine, (2R,3R,4R,5S)-3,4dibenzyloxy-N-benzyloxycarbonyl-2%-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine 5, readily available from D-fructose, was chosen as the chiral starting material.

Research paper thumbnail of El acto de comunicar

El acto de comunicar es un proceso complejo en el que dos o más personas se relacionan y, a travé... more El acto de comunicar es un proceso complejo en el que dos o más personas se relacionan y, a través de un intercambio de mensajes con códigos similares, tratan de comprenderse e influirse de forma que sus objetivos sean aceptados en la forma prevista, utilizando un canal que actúa de soporte en la transmisión de la información.

Research paper thumbnail of The influence of ultrasound on the thermal behaviour of clay minerals

Journal of The European Ceramic Society, 2006

The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolin... more The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9 • C) while muscovite presents the largest (184 • C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area. The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied.

Research paper thumbnail of The influence of ultrasound on the thermal behaviour of a well ordered kaolinite

Thermochimica Acta, 2003

The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolin... more The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9 • C) while muscovite presents the largest (184 • C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area. The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied.

Research paper thumbnail of Phase transformation on heating of an aged cement paste

Thermochimica Acta, 2004

The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately aft... more The standard cement paste (C-43-St) was studied previously by static heating, SH, immediately after 1 month hydration at w/c = 0.4 [J. Therm. Anal. Calorim. 69 ]. This paste after 5-year ageing (unprotected from contact with air) was subject to thermal analysis in air and in argon (DTA, DTG and TG), to XRD at various temperatures, T, in a high temperature chamber, to mass spectroscopy (MS) and to IR spectroscopy. The aim of this study was to compare the results of SH (fresh paste) and of TG (the aged one), to verify the assumptions made on SH interpretation and to check the change in hydration products with ageing as measured by phase transformation on heating ( M versus the final mass). The sorbed water (EV), escaping at 110 • C from the fresh paste, was bound on ageing with a higher energy and escaped at higher temperatures. The joint water content of hydrates and of C-S-H gel increased on ageing by 1-2% in the dense paste C-43-St and did not change in the less compact one C-43-I. C-S-H gel transformed on heating above 600 • C into C 2 S and C 3 S. Portlandite content did not change on ageing. In the air atmosphere it became partly carbonated, which was accompanied by an increase in mass between 500 and 600 • C. Carbon dioxide and/or carbonate ions to form carbonates, were sorbed during ageing and were present in the aged paste in some form undetectable by XRD (amorphous or crypto-crystalline). Sensitivity to carbonation M(700-800 • C) increased highly with ageing.

Research paper thumbnail of The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite

Journal of Colloid and Interface Science, 2004

The present study examined the effect of sonication on the particle size and structure of a well-... more The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m 2 /g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (−a/3 + b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers.

Research paper thumbnail of Polyhydroxylated pyrrolizidines. Part I: Short and highly stereocontrolled syntheses of hyacinthacines

Tetrahedron-asymmetry, 2001

Two short and highly stereocontrolled syntheses for 7a-epi-hyacinthacine A 2 (7-deoxyalexine) 3 a... more Two short and highly stereocontrolled syntheses for 7a-epi-hyacinthacine A 2 (7-deoxyalexine) 3 and 5,7a-diepihyacinthacine A 3 4 are, respectively, reported herein. An appropriately protected polyhydroxypyrrolidine, (2R,3R,4R,5S)-3,4dibenzyloxy-N-benzyloxycarbonyl-2%-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine 5, readily available from D-fructose, was chosen as the chiral starting material.

Research paper thumbnail of El acto de comunicar

El acto de comunicar es un proceso complejo en el que dos o más personas se relacionan y, a travé... more El acto de comunicar es un proceso complejo en el que dos o más personas se relacionan y, a través de un intercambio de mensajes con códigos similares, tratan de comprenderse e influirse de forma que sus objetivos sean aceptados en la forma prevista, utilizando un canal que actúa de soporte en la transmisión de la información.