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Investigation of dissolution properties of Cd(OH)2 in alkaline solution

Mattsson, Joel LU (2016) KOO920 20161
Centre for Analysis and Synthesis
Abstract
In this project, the properties of Cd(OH)2 in alkaline solution were studied. The processes of oxidation and reduction for Cd(OH)2 in alkaline solution are very complex and even though many studies have been done on the subject, it is not completely understood yet. It is from a Ni-Cd battery point of view, important to understand these processes to prevent loss of active material. The Cd-electrode in the Ni-Cd battery consists of Cd-mass which is a mixture of Cd(OH)2, CdO and additives.
The properties of Cd(OH)2 which were studied were, dissolution rate, crystallite size and intactness of the samples. In addition, the composition of the samples was analysed
Three experiments were run in total. Tablets of Cd-compounds were produced and... (More)
In this project, the properties of Cd(OH)2 in alkaline solution were studied. The processes of oxidation and reduction for Cd(OH)2 in alkaline solution are very complex and even though many studies have been done on the subject, it is not completely understood yet. It is from a Ni-Cd battery point of view, important to understand these processes to prevent loss of active material. The Cd-electrode in the Ni-Cd battery consists of Cd-mass which is a mixture of Cd(OH)2, CdO and additives.
The properties of Cd(OH)2 which were studied were, dissolution rate, crystallite size and intactness of the samples. In addition, the composition of the samples was analysed
Three experiments were run in total. Tablets of Cd-compounds were produced and put into E22, an alkaline mixture. The solutions were run in water baths of 26, 40 and 60 °C for 14 days and samples were taken at day one, three, five, seven and 14. The composition of the tablets varied throughout the experiments. In experiment 1, Cd(OH)2 was used together with four different additives, HPMC, PVA, Ni(OH)2 and graphite, one additive per tablet. One tablet in each temperature was of pure Cd(OH)2. In experiment 2, the tablets were made of pure Cd(OH)2, pure CdO and pure Cd. Two different kinds of tablets were used in experiment 3. The tablets were made from Cd(OH)2 with one having Fe3O4 added. Four samples were run in each temperature, two of each in diluted E22 and two in normal E22. The samples of the experiments were analysed with powder XRD and ICP-OES.
The results show that the dissolution of cadmium increases with higher temperature. HPMC was the only additive which decreased the amount of dissolved cadmium species. The amount was significantly lower at 26 °C and slightly lower at 40 °C. The samples in diluted solution showed a considerably lower dissolution rate of cadmium than the samples in normal E22. The HPMC tablets together with the ones in diluted solution stayed the most intact throughout the experiments. For comparison the tablets of PVA and Ni(OH)2 disintegrated immediately when put into the solution. The crystallite generally decreased in size after being run in the experiment. Most of the samples showed the largest crystallites at 40 °C, exceptions being HPMC, Fe3O4 and Cd(OH)2 in diluted solution.
The conclusion was that HPMC is interesting due to decreasing the amount of dissolved cadmium species, but more research needs to be done to explore how large the impact it would have as an additive in the cadmium electrode. The accuracy of the results from the ICP-analysis was questionable due to a concentration gradient that is formed in the samples, which causes inconsistency in the sample taking. If similar experiments are to be conducted in the future, the problem with the gradient has to be solved. (Less)
Popular Abstract (Swedish)
De nickel-kadmiumbatterier som tillverkas vid Saft AB i Oskarshamn är uppladdningsbara och används vanligen som backup för strömförsörjning på sjukhus, flygplatser och till och med för hela städer. Ett problem för nickel-kadmiumbatterier är upplösning av kadmiumhydroxid, det aktiva materialet i kadmiumelektroden. Utöver förlust av aktivt material kan det upplösta materialet bilda ett tunt lager på elektroden som minskar kapaciteten hos batteriet. Det är därför viktigt att i så stor utsträckning som möjligt minska upplösningen av kadmiumhydroxid.
I denna studie undersöktes det om upplösningshastigheten av kadmiumhydroxid i alkalisk lösning kunde påverkas genom att tillsätta små mängder av andra föreningar, så kallade additiv, till... (More)
De nickel-kadmiumbatterier som tillverkas vid Saft AB i Oskarshamn är uppladdningsbara och används vanligen som backup för strömförsörjning på sjukhus, flygplatser och till och med för hela städer. Ett problem för nickel-kadmiumbatterier är upplösning av kadmiumhydroxid, det aktiva materialet i kadmiumelektroden. Utöver förlust av aktivt material kan det upplösta materialet bilda ett tunt lager på elektroden som minskar kapaciteten hos batteriet. Det är därför viktigt att i så stor utsträckning som möjligt minska upplösningen av kadmiumhydroxid.
I denna studie undersöktes det om upplösningshastigheten av kadmiumhydroxid i alkalisk lösning kunde påverkas genom att tillsätta små mängder av andra föreningar, så kallade additiv, till tabletter av kadmiumhydroxid. Tre olika försök utfördes där sammansättningen hos tabletterna varierades, totalt studerades fem olika additiv. Försöken utfördes genom att lägga tabletterna i E22, en basisk lösning som används i nickel-kadmiumbatterier. Lösningarna kördes sedan i vattenbad med tre olika temperaturer 26, 40 och 60 °C under 14 dagar. Prov på lösningarna togs med regelbundna mellanrum för att se hur mängden av upplöst kadmium varierade med tiden.
Av de additiv som undersöktes var det endast cellulosa-additivet HPMC som markant minskade mängden av upplöst kadmium. De andra additiven antingen ökade mängden kadmium i lösningen eller så var det ingen skillnad från tabletterna med ren kadmiumhydroxid. Tabletterna med HPMC var även de som höll sig mest intakta under försöken medan några av de andra additiven orsakade att tabletterna föll samman nästan omgående efter att de hade lagts i lösningen.
Tidigare studier inom området har visat att typer av cellulosa kan ha positiva effekter på kadmiumelektroden genom att hämma tillväxt av metalliskt kadmium och minska de kapacitetsförluster som påverkar batteriet under upprepade cykler av upp- och urladdning. Resultaten från denna studie tyder då på att det finns ytterligare en typ av cellulosa som, ur batterisynvinkel, påverkar systemet positivt.
Fler studier behöver utföras på HPMCs påverkan på upplösningsegenskaperna hos kadmiumhydroxid för att fastställa dess positiva effekt. Men resultaten skulle kunna leda till en förbättrad kadmiumelektrod som ökar livstiden och hållbarheten för nickel-kadmiumbatterier. (Less)
Please use this url to cite or link to this publication:
author
Mattsson, Joel LU
supervisor
organization
course
KOO920 20161
year
type
H2 - Master's Degree (Two Years)
subject
keywords
materials chemistry, materialkemi
language
English
id
8891681
date added to LUP
2016-09-30 09:30:53
date last changed
2016-09-30 09:30:53
@misc{8891681,
  abstract     = {In this project, the properties of Cd(OH)2 in alkaline solution were studied. The processes of oxidation and reduction for Cd(OH)2 in alkaline solution are very complex and even though many studies have been done on the subject, it is not completely understood yet. It is from a Ni-Cd battery point of view, important to understand these processes to prevent loss of active material. The Cd-electrode in the Ni-Cd battery consists of Cd-mass which is a mixture of Cd(OH)2, CdO and additives.
The properties of Cd(OH)2 which were studied were, dissolution rate, crystallite size and intactness of the samples. In addition, the composition of the samples was analysed
Three experiments were run in total. Tablets of Cd-compounds were produced and put into E22, an alkaline mixture. The solutions were run in water baths of 26, 40 and 60 °C for 14 days and samples were taken at day one, three, five, seven and 14. The composition of the tablets varied throughout the experiments. In experiment 1, Cd(OH)2 was used together with four different additives, HPMC, PVA, Ni(OH)2 and graphite, one additive per tablet. One tablet in each temperature was of pure Cd(OH)2. In experiment 2, the tablets were made of pure Cd(OH)2, pure CdO and pure Cd. Two different kinds of tablets were used in experiment 3. The tablets were made from Cd(OH)2 with one having Fe3O4 added. Four samples were run in each temperature, two of each in diluted E22 and two in normal E22. The samples of the experiments were analysed with powder XRD and ICP-OES.
The results show that the dissolution of cadmium increases with higher temperature. HPMC was the only additive which decreased the amount of dissolved cadmium species. The amount was significantly lower at 26 °C and slightly lower at 40 °C. The samples in diluted solution showed a considerably lower dissolution rate of cadmium than the samples in normal E22. The HPMC tablets together with the ones in diluted solution stayed the most intact throughout the experiments. For comparison the tablets of PVA and Ni(OH)2 disintegrated immediately when put into the solution. The crystallite generally decreased in size after being run in the experiment. Most of the samples showed the largest crystallites at 40 °C, exceptions being HPMC, Fe3O4 and Cd(OH)2 in diluted solution.
The conclusion was that HPMC is interesting due to decreasing the amount of dissolved cadmium species, but more research needs to be done to explore how large the impact it would have as an additive in the cadmium electrode. The accuracy of the results from the ICP-analysis was questionable due to a concentration gradient that is formed in the samples, which causes inconsistency in the sample taking. If similar experiments are to be conducted in the future, the problem with the gradient has to be solved.},
  author       = {Mattsson, Joel},
  keyword      = {materials chemistry,materialkemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Investigation of dissolution properties of Cd(OH)2 in alkaline solution},
  year         = {2016},
}