INTERACCIÓN DE AGLUTINANTES DE FLUORURO DE POLIVINILIDENO (PVDF) CON SOLUCIONES FUERTEMENTE ALCALINAS

Se propone una metodología para evaluar los fenómenos degradantes de aglutinantes en los medios alcalinos, información que debe de ser de gran ayuda para los expertos en el campo de la investigación y desarrollo de baterías, ya que se podría evaluar la estabilidad esperada de los aglutinantes fluorados antes de ser probados en células galvánica ensambladas. Por esto, se ahorra tiempo, esfuerzo y se agiliza el trabajo. Mientras que el poli (tetrafluoroetileno), PTFE, ha demostrado ser químicamente inerte, este plantea un desafío tecnológico severo, siendo difícil de procesar debido a su fibrilación. Los aglutinantes alternos son poli (1, 1-difluoroetileno), PVDF, y sus copolímeros, conocidos bajo el nombre comercial de Kynar R , que son significativamente más fáciles de usar. Sin embargo, cuando se mantiene en contacto con soluciones fuertemente alcalinas, la estabilidad química de Kynars se ve comprometida. Estos pueden someterse a reacciones de eliminación con la liberación de iones de fluoruro y la formación de enlaces dobles.Estos enlaces p pueden degradarse aún más por oxidación, en contacto con oxidantes incorporados en el cátodo. Estos procesos químicos no deseados pueden inhibir las propiedades aglutinantes y, en última instancia, pueden reducir la vida útil de las células galvánica, agotando el rendimiento de la batería. En este rol, se investigó la descomposición de la aglutinación de PVDF en medios alcalinos siguiendo dos pasos: (i) los aglutinantes puros fueron probados exponiéndolos a 32 wt % solución acuosa de KOH, a 60°C, temperatura que acelera los procesos degradantes, y (ii) se investigaron los aglutinantes incorporados en la pasta cátodo en condiciones similares. La degradación del aglutinante se evaluó determinando la concentración de iones de fluoruro liberados, monitoreando el cambio de color y la formación de precipitados y grabando e interpretando los espectros FT-IR.// A careful methodology to monitor binder degrading phenomena in alkaline media is proposed, which should assist experts in field of battery research and development, as it can evaluate the expected stability of fluorinated binders, prior to being tested in assembled galvanic cells. By this, it saves time, effort, and expedites work. While poly(tetrafluoroethylene), PTFE, has proven chemically inert, it poses a severe technological challenge, being difficult to process due to its fibrillation. Alternate binders are poly(1,1-difluoroethylene), PVDF, and its copolymers, known under the trade name of Kynar R , which are significantly easier to use. Nevertheless, when kept in contact with strongly alkaline solutions, the chemical stability of Kynars is compromised. They may undergo elimination reactions with the release of fluoride ions and the formation of double bonds. These p bonds may further degrade by oxidation, in contact with oxidizers incorporated in the cathode. Such undesired chemical processes may inhibit the binding properties and, ultimately, may reduce shelf life of galvanic cells, depleting battery performance. In this paper PVDF binder decomposition in alkaline media was investigated in two steps: (i) pure binders were tested by exposing them to 32 wt % aqueous KOH solution, at 60 C, a temperature that accelerates degrading processes, and next (ii) binders incorporated in cathode paste were investigated under similar conditions. Binder degrading was evaluated by determining the concentration of released fluoride ions, monitoring color change and precipitate formation and recording and interpreting FT-IR spectra

Radiocarbon investigation of the Superlative African Baobabs from Savé Valley Conservancy, Zimbabwe

Author Posting. © Studia Chemia, 2019. Studia Universitatis Babes-Bolyai Seria Chemia is an Open Access Journal (read, download, copy, distribute, print for research use, search, or link to the full texts of articles). The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia , 64(2), Tom II, (2019): 411-419, doi:10.24193/subbchem.2019.2.35.The article reports the radiocarbon investigation results of the superlative African baobabs from Savé Valley, Zimbabwe. Several wood samples collected from these baobab were analysed by AMS (accelerator mass spectrometry) radiocarbon dating. The radiocarbon dates of the oldest samples were 1529 ± 14 BP for Matendere Big baobab, 1179 ± 19 BP for Chishakwe Big tree and 1096 ± 35 BP for Mokore Giant baobab. The corresponding calibrated ages are 1430 ± 15, 1090 ± 40 and 1020 ± 25 calendar yr. The oldest tree from Savé Valley, which we described previously, is the Humani Bedford Old baobab. The radiocarbon date of its oldest sample, 1655 ± 14 BP, corresponds to a calibrated age of 1580 ± 30 calendar yr.Authors would like to acknowledge Léon and Judy Duplessis, the owners of the Matendere Rach, Lisa-Jane Campbell of Chishakwe Ranch, Roger Whittall, the owner of the Humani Ranch and his wife Anne Whittall, Greg and Melanie Duckworth of Mokore Ranch for granting access in the ranches and for authorising the investigation and sampling of the monumental baobabs. The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

Radiocarbon dating of the historic Livingstone Tree at Chiramba, Mozambique

Author Posting. © Studia Chemia, 2020. Studia Universitatis Babes-Bolyai Seria Chemia is an Open Access Journal (read, download, copy, distribute, print for research use, search, or link to the full texts of articles). The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 65, no. 3 (2020): 149-156, doi:10.24193/subbchem.2020.3.11.The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of the Livingstone Tree, a large African baobab on the right bank of the Zambezi, near Chiramba, Mozambique. In 1858, David Livingstone, who discovered the baobab, carved his monogram on the walls of its inner cavity. In 1996, the historic baobab was uprooted when a cyclone struck the area. Several wood fragments were extracted from the remains of the toppled tree. Five samples which originate from these fragments were subsequently dated by radiocarbon. The oldest sample had a radiocarbon date of 1598 ± 17 BP, that corresponded in 1996 to a calibrated age of 1490 ± 35 calendar years. According to this value, the Livingstone Tree at Chiramba becomes one of the oldest known African baobabs, with an age of over 1500 years. The Livingstone Tree had a closed ring-shaped structure, that consisted of 4 fused stems around a false cavity and also 2 additional stems outside the ring.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grants PN-II-ID-PCE-2013-76 and PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

Radiocarbon dating of the old ash of Aiton, Romania

Author Posting. © Studia Chemia, 2018. Studia Universitatis Babes-Bolyai Seria Chemia is an Open Access Journal (read, download, copy, distribute, print for research use, search, or link to the full texts of articles). The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 63, no. 3 (2018): 41-48, doi:10.24193/subbchem.2018.3.03.The article reports the AMS (accelerator mass spectrometry) radiocarbon investigation results of the old common ash of Aiton. Five wood samples were collected from the trunk of the tree. The deepest ends of the samples were analysed by AMS radiocarbon. We found radiocarbon dates between 165 ± 20 BP and 240 ± 18 BP, which correspond to calibrated ages of 230 – 360 years. These results, combined with a ring counting estimate, indicate an age of 330 ± 30 years for the ash of Aiton. By this value, the ash of Aiton becomes the oldest known common ash with accurate dating results.The research was funded by the Romanian Ministry of Research and Innovation CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

African baobabs with double closed ring-shaped structures and two separate false cavities : radiocarbon investigation of the baobab of Golconda Fort

Author Posting. © Studia Chemia, 2016. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Chemia 2016, no. 4 (2016): 21-30.The article discloses the results of radiocarbon investigation of the baobab of Golconda Fort, Hyderābād, India, which is the largest African baobab outside Africa. Two wood samples were collected from the large inner cavity; of these we extracted several segments for AMS (accelerator mass spectrometry) radiocarbon dating. The oldest sample segment had a radiocarbon date of 342 ± 22 BP, which corresponds to a calibrated age of 430 ± 20 yr. We estimate that the oldest part of the baobab has an age of 475 ± 50 yr. The investigation of the baobab of Golconda Fort revealed that it consists of 6 + 2 fused stems. Six stems build two rings that close two distinct false cavities, while two additional stems are located outside the rings. We called this new type of architecture double closed ring-shaped structure with two separate false cavities.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-II-ID-PCE-2013-76

Radiocarbon dating of Makuri Le boom, a very old African baobab from Nyae Nyae, Namibia

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Patrut, R. T., Patrut, A., Rakosy, D., Rakosy, L., Lowy, D. A., Von Redenf, K. F., & Bodis, J. Radiocarbon dating of Makuri Le boom, a very old African baobab from Nyae Nyae, Namibia. Studia Universitatis Babes-Bolyai Chemia, 65(2), (2020): 149-159, doi:10.24193/subbchem.2020.2.12.The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of Makuri Lê boom, a very large African baobab from Nyae Nyae Conservancy, Namibia. The investigation of this superlative baobab shows that it consists of 12 independent stems of different dimensions, which belong to three generations. Makuri Lê boom has an open ring-shaped structure, a type of architecture which allows baobabs to reach very large sizes and old ages. The oldest sample has a radiocarbon date of 1602 ± 17 BP, which corresponds to a calibrated age of 1520 ± 35 calendar yr. By this value, Makuri Lê boom becomes one of the oldest dated baobabs and angiosperms with accurate dating results.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-III-P4-ID-PCE-2016-0776, Nr. 90/2017

Radiocarbon dating of a very old African baobab from Savé Valley, Zimbabwe

Author Posting. © Studia Chemia, 2016. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Chemia 2016, no. 4 (2016): 7-20.The article reports the radiocarbon investigation results of the Humani Bedford baobab, an old African baobab from Savé Valley, Zimbabwe. Two wood samples were collected from the large inner cavity. Several segments were extracted from these samples and analysed by AMS (accelerator mass spectrometry) radiocarbon dating. We found that the age values of segments increase with the distance into the wood. This major anomaly is characteristic to multi-stemmed baobabs with a closed ring-shaped structure and a false cavity inside. The investigation of the Humani Bedford baobab evinced that the baobab consists of three fused stems. The fourth stem of the ring is missing. The oldest dated segment was found to have a radiocarbon date of 1655 ± 14 BP, which corresponds to a calibrated age of 1575 ± 30 yr. The dating results show that the stems which build the ring stopped growing toward the false cavity more than 600 yr ago. By considering the position of the oldest segment in the investigated stem, we concluded that the Humani Bedford baobab is around 1800 yr old. According to our dating results, the Humani Bedford baobab becomes the oldest living African baobab.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-II-ID-PCE-2013-76

Radiocarbon dating of a very large African baobab from Limpopo, South Africa : investigation of the Sagole Big Tree

Author Posting. © Studia Chemia, 2017. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 62, no. 2, Tom 2 (2017): 355-364, doi:10.24193/subbchem.2017.2.28.The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of Sagole Big tree, a giant African baobab from Limpopo, South Africa. Several wood samples were collected from the walls of its inner cavity and dated by radiocarbon. The age values along the cavity samples increase with the distance into the wood. This anomaly shows that the cavity is a false one. The oldest sample segment had a radiocarbon date of 781 ± 29 BP, which corresponds to a calibrated age of 740 ± 15 yr. We estimate that the oldest part of the Sagole baobab has an age of 800-900 yr. We determined that the tree has a closed ring-shaped structure, which consists of a large unit with six fused stems and of two additional leaning stems.The research was funded by the Romanian Ministry of Scientific Research CNCSUEFISCDI under grant PN-II-ID-PCE-2013-76

AMS radiocarbon dating of large za baobabs (Adansonia za) of Madagascar

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in PLoS One 11 (2016): e0146977, doi:10.1371/journal.pone.0146977 .The article reports the radiocarbon investigation of Anzapalivoro, the largest za baobab (Adansonia za) specimen of Madagascar and of another za, namely the Big cistern baobab. Several wood samples collected from the large inner cavity and from the outer part/exterior of the tree were investigated by AMS (accelerator mass spectrometry) radiocarbon dating. For samples collected from the cavity walls, the age values increase with the distance into the wood up to a point of maximum age, after which the values decrease toward the outer part. This anomaly of age sequences indicates that the inner cavity of Anzapalivoro is a false cavity, practically an empty space between several fused stems disposed in a ring-shaped structure. The radiocarbon date of the oldest sample was 780 ± 30 bp, which corresponds to a calibrated age of around 735 yr. Dating results indicate that Anzapalivoro has a closed ring-shaped structure, which consists of 5 fused stems that close a false cavity. The oldest part of the biggest za baobab has a calculated age of 900 years. We also disclose results of the investigation of a second za baobab, the Big cistern baobab, which was hollowed out for water storage. This specimen, which consists of 4 fused stems, was found to be around 260 years old

African baobabs with a very large number of stems and false stems : radiocarbon Investigation of the baobab of Warang

Author Posting. © Studia Chemia, 2017. This article is posted here by permission of Studia Chemia for personal use, not for redistribution. The definitive version was published in Studia Universitatis Babes-Bolyai, Seria Chemia 62, no. 1 (2017): 111-120, doi:10.24193/subbchem.2017.1.09.The article presents the AMS (accelerator mass spectrometry) radiocarbon dating results of the baobab of Warang, Senegal. The investigation of the baobab revealed that it consists of 18 partially fused stems, which represents the largest number of stems reported for an African baobab. Three stems build the ring that closes a false cavity, while 15 stems grow outside the ring. Seven wood samples were collected from the false cavity and from the outer part of other stems. The dating results evinced that the stems belong to four different generations, out of which the first generation is around 500 years old. We also documented the presence of false stems, which emerge from a large adjacent stem, are triangular in horizontal section and act as an anchor. The baobab of Warang possesses 12 ordinary stems and 6 false stems.The research was funded by the Romanian Ministry of National Education CNCS-UEFISCDI under grant PN-II-ID-PCE-2013-76