1,721,018 research outputs found
Content of aggressive CO2 in Celje water supply network
No full textVoda mora biti za potrebe ljudi optimalne kakovosti. V njej je raztopljenih veliko organskih in anorganskih snovi, ki lahko pod določenimi pogoji tvorijo spojine, ki povzročajo nezaželene spremembe, predvsem v vodovodnem omrežju. Med njih spada CO2, ki v vodo največ prehaja iz zraka, se v njej topi in tvori šibko ogljikovo kislino. Do neke mere je to optimalno za vzpostavitev karbonatnega ravnotežja. Voda, ki vsebuje preveč ogljikovega dioksida je agresivna in povzroči korozijo cevi, ventilov ter druge poškodbe vodovodnega omrežja. V diplomski nalogi sem s postopkom validacije metodo za določevanje agresivnega CO2 uvedla v laboratorijsko delo in jo preverila na realnih vzorcih pitne vode v celjskem vodovodnem omrežju.For human use, water needs to be optimal quality. It contains many organic and inorganic substances that can form harmful compounds under certain conditions. One of many is CO2, which passes into water from the air, dissolves in it and forms week carbonic acid. To some extent, this reaction is optimal for establishing carbonate equilibrium. Water that contains too much carbon dioxide is aggressive and causes corrosion of pipes, valves and other damage to the water supply network. In this research process I introduced the method for determining aggressive CO2 into laboratory work with the validation and tested it on real samples of drinking water in the Celje water supply network
Determination of gelatin in paper
No full textV raziskovalni nalogi bom napravil pregled literature za kvantitativno določanje beljakovin v vzorcih naravnega izvora. V ta namen se uporabljajo različne metode, od spektrofotometričnih do kromatografskih. Prve zahtevajo reakcijo, ki vodi do nastanka obarvane spojine, kromatografske metode pa večinoma zahtevajo razklop do aminokislin. Med beljakovinskimi dodatki v papirju najdemo izključno želatino, kot dodatek, ki naredi površino hidrofobno. V kolikor bodo pogoji to omogočali, bom opravil analizo vsebnosti želatine v vzorcih tibetanskega izvora.In this research, I will review the literature for the quantitative determination of proteins in samples of natural origin. Various methods are used for this purpose, from spectrophotometric to chromatographic. The former require a reaction leading to the formation of a colored compound, and chromatographic methods mostly require cleavage to amino acids. Among the protein additives in paper, we find exclusively gelatin, as an additive that makes the surface hydrophobic. If conditions allow, I will perform an analysis of the gelatin content in samples of Tibetan origin
Migration and loss of plasticizers in polyvinyl chloride
No full textPolivinil klorid je izjemno razširjen termoplastični polimer, ki ga najdemo povsod okoli nas. V čistem stanju je krhek material, zato se pri proizvodnji uporabljajo različni dodatki, da postane bolj primeren za obdelavo. Skupina najpomembnejših dodatkov so mehčala, ki mu znižajo temperaturo steklastega prehoda in ga naredijo mehkejšega. V življenjski dobi polivinil klorida poteka migracija mehčal, ki je poleg eliminacije HCl glavni proces njegove razgradnje. Migracijo sestavljata difuzija mehčala skozi matriko polimera do njegove površine in izhlapevanje v okoliški medij. Zaradi izgube mehčal postanejo predmeti krhki, lepljivi in porumenijo, medtem ko zaradi spremembe specifičnega volumna razpokajo. S temi težavami se spopadajo v muzejih in galerijah, ki hranijo veliko število predmetov iz polivinil klorida. Vendar pa ti procesi še niso dodobra raziskani in jasne smernice glede hrambe in ohranjanja teh predmetov ne obstajajo. V magistrskem delu sem se zato ukvarjala z migracijo in izgubo mehčal v polivinil kloridu. Vzorce, ki so vsebovali različna mehčala, sem podvrgla pospešeni razgradnji pri različnih pogojih, da sem lahko določila, kakšen je vpliv vlage, temperature in vrste mehčala. Vsebnosti mehčal v vzorcih sem določila s pomočjo ekstrakcije in plinske kromatografije. Ugotovila sem, da vlaga ne vpliva na izgubo mehčal, medtem ko so izgube večje pri višjih temperaturah, ki so jim vzorci izpostavljeni. Na migracijo vpliva tudi vrsta mehčala, kjer pomembno vlogo igra molekulska masa. Pri mehčalih z višjo molekulsko maso prihaja do počasnejše migracije. Med pospešeno razgradnjo sem spremljala tudi, ali lahko izgubo mase pripišem le izgubi mehčal. Dokazala sem, da je izguba mase vedno večja od izgube mehčala, torej se med izvedeno razgradnjo niso izgubljala le slednja.Polyvinyl chloride is nowadays one of the most widespread thermoplastic polymers. Pure PVC is solid brittle material, however it can be modified with additives which make it more prone to processing and moulding. Plasticizers represent the most important group of those additives and are used to soften it and reduce glass transition temperature. During the lifetime of PVC, the degradation processes take place, which include elimination of HCl and migration of plasticizers. Migration occurs through two processes: as diffusion through the polymer to its surface and evaporation to the surrounding gas phase. The loss of plasticizers results in yellowing, sweating and shrinking of PVC, while they crack because of changes in specific volume. Museums and galleries identified that as a problem as they want to conserve their PVC collections and artifacts in their original state. However, those processes are not thoroughly researched yet and clear guidelines on conservation of PVC objects don’t exist yet. That is why I studied migration and loss of plasticizers in PVC. I thermally degraded samples, which were plasticised by different plasticizers, at different conditions to determine the effects of temperature, relative humidity and type of plasticizer. I used extraction and GC-FID to determine the content of plasticizers in samples. I can conclude that relative humidity does not affect migration, while higher temperatures corelate with higher losses of plasticizers. Additionally, the type of plasticizer plays an important factor, as migration is slower if the molecular mass of plasticizer is higher. During my work I also researched if the detected mass loss can be attributed only to the loss of plasticizers. I concluded the mass loss is always higher than the loss of plasticizers, which means plasticizers are not the sole compound that was lost in the process of degradation
Determination of aldehyde pollutants in indoor air
No full textV diplomskem delu sem raziskal in predstavil hlapna aldehidna onesnaževala, njihove vire, vpliv na zdravje ter različne načine nižanja njihovih koncentracij v zraku. Nato sem napravil pregled literature za kvantitativno določanje formaldehida v zraku, kjer sem opisal različne tehnike vzorčenja in analiz. Najpogosteje so v uporabi pasivni vzorčevalniki na osnovi 2,4-dinitrofenilhidrazina, saj je za analizo potrebno le kvantitativno izpiranje reakcijskih produktov z vzorčevalnika ter kvantifikacija preko umeritvene krivulje s pomočjo HPLC. To metodo sem uporabil pri eksperimentalnem delu, kjer sem analiziral hlapna aldehidna onesnaževala z vzorčevalnikov, ki so bili sedem dni izpostavljeni zraku na različnih lokacijah muzeja Vasa v Stockholmu, na koncu pa sem svoje rezultate primerjal še z rezultati prvega opravljanja meritev izpred pol leta.In my thesis I researched and presented volatile aldehyde pollutants, their sources, health effects and different possibilities of reducing their concentration in the air. I reviewed the literature on quantitative determination of formaldehyde in indoor air and described several different techniques for sampling and analysis. The most widely used are passive samplers based on 2,4-dinitrophenylhydrazine, which require only quantitative washing of the reaction products from the sampler and quantification by HPLC. I used this method in my experiments, where I analysed different volatile aldehyde pollutants from samplers that had been exposed to air in several different locations of the Vasa museum in Stockholm for seven days. Finally, I compared my results to the ones taken from the first monitoring session six months ago
Acetic acid emission from cellulose acetate
No full textLjudje več kot 90 odstotkov našega časa preživimo v notranjih prostorih, bodisi na delovnem mestu bodisi v naših domovih. Ob tem pa se ne zavedamo, da smo stalno izpostavljeni hlapnim organskim spojinam, ki emitirajo iz različnih materialov vsakodnevne uporabe in lahko škodujejo našemu zdravju. Hlapne organske spojine (HOS) vključujejo spojine tako antropogenega kot tudi naravnega izvora. Vendar pa so tiste, ki jih je ustvaril človek, bolj zaskrbljujoče, saj so prisotne v zaprtih prostorih, kjer so njihove koncentracije višje in bolj nevarne. Glavni viri HOS v notranjih prostorih so gradbeni materiali, pohištvo iz lesa in materiali na osnovi polimerov. Eden od slednjih je tudi celuloza acetat, ki se je v preteklosti intenzivno uporabljal za izdelavo kinematografskih filmov in raznih umetnin, ter tako danes predstavlja pomemben del evropske dediščine. Vendar pa taki izdelki predstavljajo problem, saj so občutljivi in nestabilni, ob razgradnji pa emitirajo ocetno kislino, ki lahko škoduje zdravju ljudi in povzroči poškodbe različnih predmetov. Pomembni zgodovinski objekti tako sčasoma izgubljajo barvo, se zvijajo in upogibajo, filmi pa postanejo neuporabni. Zaradi preventive pred uničenjem dediščine so se razvile razne metode za oceno razgradnje, prav tako pa je vprašanje, kakšni so najboljši pogoji hrambe, tema precejšnjih raziskav. Mnogi materiali v notranjih prostorih lahko na primer adsorbirajo hlapne organske spojine in s tem privedejo do znižanja njihovih koncentracij. Vendar pa lahko taki materiali po adsorpciji delujejo tudi kot vir oddajanja, s čimer še podaljšajo čas zadrževanja teh spojin v zaprtih prostorih. Zaradi nevarnosti, ki jih HOS predstavljajo človeškemu zdravju, se je razvilo nekaj tehnik vzorčenja in določevanja teh spojin, poleg tega pa seveda mnogo strategij za znižanje koncentracij.People spend more than 90 percent of our time indoors, either at work or in our homes. At the same time, we are not aware that we are constantly exposed to volatile organic compounds, which are emitted from various materials of everyday use and can be harmful to our health. Volatile organic compounds (VOCs) include compounds of both anthropogenic and natural origin. However, those created by man cause more concern as they are present indoors where their concentrations are higher and more dangerous. The main sources of volatile organic compounds indoors are building materials, wood furniture and polymer-based materials. One of the latter is also cellulose acetate, which in the past was intensively used for the production of cinematographic films and various works of art, and thus today represents an important part of Europe\u27s heritage. However, such products pose a problem as they are sensitive and unstable and, when degraded, emit acetic acid, which can be harmful to human health and cause damage to various objects. Important historical objects thus lose color, twist and bend over time, and films become useless. To prevent the destruction of heritage, various methods for assessing decomposition have been developed, and the question of what the best storage conditions are is the subject of considerable research. For example, many indoor materials can adsorb volatile organic compounds, leading to a reduction in their concentrations. However, after adsorption, such materials can also act as a source of emission, thereby further extending the retention time of these compounds indoors. Due to the dangers that VOCs pose to human health, some techniques for sampling and determination of these compounds have been developed, as well as, of course, many strategies to reduce concentrations
Quantitative determination of metals in poly(vinyl chloride) by atomic spectroscopy
No full textPoli(vinilklorid) (PVC) je ekonomičen in vsestranski termoplastičen polimer, ki se uporablja v številnih običajnih potrošniških izdelkih. Je tretji najbolj razširjen sintetični plastični polimer na svetu za polietilenom in polipropilenom. Vendar pa PVC sam po sebi ni posebno uporabna snov, kar pomeni, da njegove številne različice potrebujejo različne dodatke, da pridobijo določene lastnosti. Bistveni dodatki za vse PVC materiale so stabilizatorji in maziva, v primeru fleksibilnega PVC-ja pa so vgrajena tudi mehčala. Ti dodatki največkrat temeljijo na različnih kovinskih spojinah, ki pa lahko v prevelikih koncentracijah škodljivo vplivajo na lastnosti materiala, prav tako pa lahko škodujejo okolju. V magistrski raziskavi sem raziskala izvor in pomen kovin v PVC ter ugotavljala, kakšna je njihova vloga pri razgradnji materiala. Prav tako sem raziskala metode za določanje kovin v PVC in jih primerjala. Tekom eksperimentalnega dela sem optimizirala mikrovalovni razklop PVC in naknadno določila kovine v 49 vzorcih s pomočjo ICP-OES. Vzorci so bili v večini PVC mape oz. folije, ki so se razlikovale glede na starost, prosojnost in obarvanost.
Pri pregledu rezultatov sem ugotovila, da so se najpogosteje v vzorcih pojavile kovine aluminij, barij, kalij, magnezij, natrij, kositer in cink. Na podlagi določenih masnih deležev kovin sem vsem vzorcem določila tudi stabilizatorje, pri čemer sem opazila, da se najpogosteje pojavljajo stabilizatorji, ki vsebujejo cink. Vzorce sem nato najprej primerjala z rezultati dveh standardov, pri čemer sem ugotovila, da standarda vsebujeta zelo malo kovin. To pomeni, da čist PVC ne vsebuje znatnih vsebnosti kovin in da so v večini kovine materialu dodane tekom industrijskega postopka. Vzorce sem nato primerjala tudi glede na prosojnost oz. obarvanost, glede na starost in glede na prisotne stabilizatorje. Poleg tega sem masne deleže kovin v treh vzorcih igrač primerjala tudi z mejnimi vrednostmi, ki jih določa Direktiva o varnosti igrač. Ugotovila sem, da obarvani vzorci zaradi dodanih polnil vsebujejo več kovin kot prozorni vzorci. Pri primerjavi starejših vzorcev z novejšimi se je izkazalo, da novejši vzorci v večini ne vsebujejo kadmija in svinca, vsebujejo pa kombinacijo barij – cink, kar nakazuje na pogostejšo uporabo barij – cink stabilizatorjev. Pri primerjavi učinkovitosti barij – cink in kositrovih stabilizatorjev so se kot bolj učinkoviti izkazali stabilizatorji barij – cink.Poly(vinyl chloride) (PVC) is an economical and versatile thermoplastic polymer used in many common consumer products. It is the third most widely used synthetic plastic polymer in the world after polyethylene and polypropylene. However, PVC itself is not a particularly useful substance, which means that its many variants require different additives to acquire certain properties. Essential additives for all PVC materials are stabilizers and lubricants, and in the case of flexible PVC, plasticizers are also incorporated. These additives are mostly based on various metal compounds, which, in excessive concentrations, can have a detrimental effect on the properties of the material, and can also harm the environment. In my master\u27s research, I investigated the origin and importance of metals in PVC and determined their role in the breakdown of the material. I also researched methods for determining metals in PVC and compared them. During the experimental work, I optimized the microwave decomposition of PVC and subsequently determined the metals in 49 samples using ICP-OES. Most of the samples were PVC folders or foils that differed in age, translucency and coloration.
When reviewing the results, I found that the metals aluminum, barium, potassium, magnesium, sodium, tin and zinc appeared most often in the samples. Based on certain mass proportions of metals, I also determined stabilizers for all samples, and I noticed that stabilizers containing zinc appear most often. I then first compared the samples with the results of two standards, and found that the standards contained very few metals. This means that pure PVC does not contain significant metal contents and that most of the metals are added to the material during the industrial process. I then compared the samples in terms of transparency or colouration, according to age and according to the stabilizers present. In addition, I also compared the mass proportions of metals in three toy samples with the limit values set by the Toy Safety Directive. I have found that the colored samples contain more metals than the clear samples due to the added fillers. When comparing older samples with newer ones, it turned out that the newer samples mostly do not contain cadmium and lead, but contain a combination of barium – zinc, which indicates a more frequent use of barium – zinc stabilizers. When comparing the effectiveness of barium – zinc and tin stabilizers, barium – zinc stabilizers proved to be more effective
Effect of water absorption in paper on reflectance spectra in the near-infrared region
No full textNamen dela je bil, da določim absorpcijske izoterme 58 vzorcem papirja ter ugotovim, kako vsebnost vode vpliva na NIR spektre.Rezultati meritev mase na mikrotehtnici MX/UMX oseminpetdesetih vzorcev pri različnih relativnih vlažnostih: 0%, 20%, 40%, 60%, 80% so, po pričakovanjih, pokazali, da se le-ta povečuje z vlažnostjo. Absorpcijski izotermi manj absorptivnega in bolj absorptivnega materiala sta se po pričakovanjih razlikovali po vsebnosti vode.Rezultati meritev v bližnjem infrardečem območju s spektrometrom Labspec so pokazali, da absorbanca vrha O-H vodikove vezi ni v premem ali obratnem sorazmerju z relativno vlažnostjo. Rezultati niso v skladu s pričakovanji, ker se iz pozicije vrhov določi strukturo molekul v vzorcu, medtem ko se iz višine vrhov določi koncentracije posameznih molekul v vzorcu. Pričakovali bi, da se bodo višine vrhov povečevale z vlažnostjo v nekakšni medsebojni odvisnosti. Vredno je poudariti, da vrhovi vode okoli 1900 nm predstavljajo vibracijo OH skupine, ki je prisotna v celulozi in beljakovinah, ki so gradniki papirja.The purpose of the work was to determine the absorption isotherms of 58 paper samples and to find out how the water content affects the NIR spectra. Results of mass measurements on the MX/UMX microbalance of fifty-eight samples at different relative humidities: 0%, 20%, 40%, 60%, 80% showed, as expected, that it increases with humidity. Absorption isotherms of less absorptive and more absorptive material differed according to water content, as expected. The results of measurements in the near infrared range with a Labspec spectrometer showed that the absorbance of the O-H hydrogen bond peak is not directly or inversely proportional to relative humidity. The results are not in line with expectations, because the structure of the molecules in the sample is determined from the position of the peaks, while the concentration of individual molecules in the sample is determined from the height of the peaks. We would expect the peak heights to increase with humidity in some kind of interdependence. It is worth emphasizing that the peaks of water around 1900 nm represent the vibration of the OH group, which is present in cellulose and proteins, which are the building blocks of paper
Monitoring of silk degradation using spectroscopic methods
No full textSvila je naravni polimer, sestavljen pretežno iz fibroina. Vlakna svile so zelo občutljiva na zunanje vplive, ki lahko preko reakcij oksidacije in hidrolize povzročijo nepopravljive poškodbe. Predmeti kulturne dediščine iz svile so neprecenljivi, zato sta razumevanje procesov razgradnje in iskanje načinov za spremljanje in vrednotenje stanja svile ključnega pomena za pravilno shranjevanje in omejitev nadaljnje razgradnje. V sklopu magistrske naloge sem raziskal procese, ki so glavni povzročitelji razgradnje svile in metode, ki se trenutno uporabljajo za določanje stanja svile. Ker za porušne analize ne moremo uporabljati zgodovinskih vzorcev, sem tekom eksperimentalnega dela iz sveže neobdelane in obtežene svile pripravil večjo količino vzorcev, ki sem jih nato v procesu umetno pospešene razgradnje izpostavil UV svetlobi, povišani temperaturi in različnim vrednostim relativne vlažnosti v kombinaciji s povišano temperaturo. Referenčne in pospešeno razgrajene vzorce sem analiziral z različnimi metodami, kot so kolorimetrija, ATR-FTIR, SEM-EDS in XRD. Ugotovil sem, da UV svetloba, povišana temperatura in relativna vlažnost vplivajo na stanje in razgradnjo vzorcev, zato je priporočljivo, da vzorce shranjujemo in razstavljamo pri nižjih temperaturah in zmernih relativnih vlažnostih ter osvetljenosti. Spremljanje in vrednotenje razgradnje predstavlja zelo kompleksen problem, ki omogoča veliko različnih možnosti za nadaljnje raziskave, tako pri uvedbi naprednih analiznih metod, kot tudi pri sami pripravi in pospešeni razgradnji vzorcev.Silk is a natural polymer consisting mainly of fibroin. Silk fibres are very sensitive to external influences, which can cause irreversible damage through reactions of oxidation and hydrolysis. Silk cultural heritage items are priceless, therefore understanding the processes of degradation and finding ways to monitor and evaluate the condition of silk is crucial for proper preservation and for limiting further degradation. In my master’s thesis I investigated the processes that are the main cause of silk degradation and analytical methods that are currently used to determine the condition of silk. Since we cannot use historical samples for destructive analysis, I prepared a large quantity of samples from fresh untreated and weighted silk, which I then exposed to UV light, elevated temperature and different relative humidities in connection with elevated temperatures. Afterwards I analysed reference and artificially aged samples using different methods, such as colorimetry, ATR-FTIR, SEM-EDS and XRD. I have found out that UV light, elevated temperature and relative humidity affect the condition and degradation of samples, therefore it is recommended that historical specimens are stored and exhibited at lower temperatures and moderate relative humidity and lighting. The monitoring and evaluation of silk degradation is a complex problem which provides us many different possibilities for further research, both in sample preparation, artificial aging and in the introduction of advanced analytical methods
The Use Of Microfadometer In Conservation-Restoration for Lightfastness Assessment Of Selected Materials
No full textDiplomska naloga obravnava uporabo mikrobledenjemera za oceno svetlobne stabilnosti predmetov kulturne dediščine, z namenom, da bi izdelali oceno svetlobne stabilnosti izbranega gradiva. To je bila tapeta datirana med 1750 in 1850, izdelana v tehniki lesoreza na papirju. Naloga je sestavljena iz treh večjih poglavij: uporaba mikrobledenjemera v konservatorstvu-restavratorstvu, meritve na izbranem gradivu in ocena svetlobne stabilnosti izbranega gradiva.
V prvem delu opišem mikrobledenjemer, njegovo uporabo, kako se interpretira podatke, ki jih dobimo z meritvami, in kakšna je uporaba teh meritev za namen izdelave priporočila osvetljenosti ob razstavljanju.
V drugem delu naloge predstavim meritve, ki sem jih opravila na izbranem gradivu in kako so meritve potekale, zakaj sem jih delala ter kakšne so bile ugotovitve. Poleg tapete so tu tudi meritve na papirnih vzorcih, vzorcu usnja, dveh različnih slik na platnu v akrilni in oljni tehniki ter meritve na barvni fotografiji.
V zadnjem delu sem izdelala oceno svetlobne stabilnosti in priporočila za razstavljanje tapete ter primerjala lastna priporočila s priporočili, ki so nastala pred meritvami.The bachelor’s thesis addresses the use of micro fadometer for lightfastness assessment of objects of cultural heritage with the aim of assessing the light stability of selected materials – a wallpaper dated between 1750 and 1850, made in the technique of linocut on paper. The thesis consists of three main parts: the use of microfadometer in conservation-restoration, measurments on selected material and assessment of light stability of selected material.
In the first part, I describe the microfadometer, its use, how to interpret the data obtained from measurements, and the application of these measurements in creation of lighting policy.
In the second part of the thesis, I present the measurements on selected material, the methodology and what the findings were. In addition to the wallpaper, there are also measurments on paper, leather, two different paintings on canvas made with acrylic and oil paints, and measurements on a color photograph.
In the last part of the thesis, I formulated a light fastness assessment and display policy and compared the new policy with the policy formulated before the use of microfadometer
Characterization of Corrosion Processes Under Electrolyte Droplet with Coupled Multielectrode Array
No full textAtmosferska korozija je kompleksen in dinamičen pojav, odvisen od številnih dejavnikov. Korozija pod kapljico je osnovni sestavni del omenjenih procesov. V magistrskem delu sem preučeval vpliv različnih koncentracij NaCl na prostorsko in časovno dinamiko korozijskih procesov pod kapljico elektrolita na površini ogljikovega jekla. Procese sem spremljal s pomočjo sklopljene mreže elektrod (ang. coupled multi-electrode array), s katero sem meril anodne in katodne tokove. Velikost in obliko kapljice sem vzporedno spremljal z dvema digitalnima kamerama: z vrha (tloris) in s strani (naris). Uporabil sem 4 različne koncentracije NaCl.
Rezultati so pokazali, da sta obseg in oblika korozijske poškodbe pri 1. kapljici v grobem podobni ne glede na koncentracijo NaCl. Istočasno je bilo iz tokov izmerjenih z mrežo sklopljenih elektrod razvidno, da so se prostorsko-časovne dinamike omenjenih procesov zelo razlikovale, vključno z njihovim trajanjem. Analiza slik zajetih s kamerama je pokazala t.i. »pripeto« vrsto kapljice (ang. sessile droplet), kjer stična površina s kovino ostaja enaka po velikosti in obliki. Za to vrsto kapljic sta značilna kapilarni in Marangonijev tok.
Največja kumulativna korozijska poškodba je bila izmerjena pod kapljico 0,5 % NaCl, največja trenutna korozijska hitrost v 0,1 % NaCl. Pri vseh meritvah sem opazil drugi vrh povečanja gostote električnega toka, pred posušitvijo kapljice. Vrhovi so bili relativno ozki, razen pri 3,5 % NaCl, kjer je bil omenjeni vrh bistveno širši. Pri vseh nanosih 2. in 3. kapljice so se pojavili izraziti, a kratki začetni vrhovi. Vrhovi pred posušitvijo kapljic so postali izrazitejši: višji in širši. V nekaterih primerih se je pojavilo celo več zaporednih vrhov. Omenjeni vrhovi so nakazali na daljšo življenjsko dobo 2. in 3. kapljice v primerjavi s 1. kapljico.
Eden glavnih ciljev mojega magistrskega dela je bil oceniti prostorsko-časovno dinamiko korozijskih procesov pri različnih kapljicah. Meritve s sklopljeno mrežo elektrod so pokazale, da so korozijski procesi v začetnem delu obstoja kapljice v grobem sledili Evansovemu modelu (anodni center v sredini s katodnim obročem). S tanjšanjem debeline sloja elektrolita so se pojavila odstopanja od omenjenega modela, pri čemer so se anodna mesta praviloma preselila bližje robu kapljice. Sicer so pri vseh koncentracijah NaCl nekatere elektrode ob sušenju kapljice spremenile predznak (določene tudi večkrat), pri čemer sam mehanizem prehajanja anod v katode in nasprotno, ni popolnoma jasen. Predvidevamo, da imata pomemben vpliv kapilarni in Marangonijev tok. Pri kapljici 3,5 % NaCl je slaba topnost kisika v kombinaciji z Marangonijevim tokom verjetno povzročila, da je večina začetnih katodnih področij proti koncu sušenja postala anodnih.Atmospheric corrosion is a complex and dynamic phenomenon influenced by multiple factors, where the fundamental part are electrochemical processes under an electrolyte droplet. In my MSc Thesis the evolution of corrosion process under droplet along with its evaporation on carbon steel was monitored by means of coupled multi-electrode array (CMEA). Simultaneously, digital imaging in vertical and horizontal directions was performed, in order to follow shape and volume of a droplet. Four different concentrations of NaCl were used.
It was indicated by CMEA that the cumulative corrosion damage and the corrosion pattern generated by the 1st droplets were roughly similar regardless of the concentration of NaCl. On the other hand, the spatio-temporal behaviour of corrosion processes and their duration differed significantly. Digitized imaging revealed sessile type of droplet evaporation, with the constant contact area and continuous reduction of the contact angle. It is known that an internal capillary flow and Marangoni flow occur within this type of droplets.
The highest cumulative corrosion damage was indicated in a droplet with 0.5 % NaCl concentration, whereas the highest corrosion rate was measured in a droplet with 0.1 % NaCl concentration. In all droplets a secondary corrosion current peak in the period before the final evaporation was observed. These peaks were generally relatively short, but in 3.5 % NaCl was considerably wider and contributed to the droplet duration. At the application of 2nd and 3rd successive droplets, initial short and high current transients were generated. The secondary peaks before the final evaporation of droplets became evident, not only higher, but also wider. In certain cases, a sequence of these peaks appeared. Due to these peaks, the durations of the 2nd and 3rd droplets were longer in comparison to the 1st ones.
One of my main interest was the spatio-temporal dynamics of anodic and cathodic sites during the evaporation of droplets. It was indicated by means of CMEA that the corrosion processes generally followed the Evans model (anodic centre and cathodic ring) in the first part of evaporation, but with thinning of the electrolyte film the anodic areas moved closely to the edge of a droplet. In all cases, some electrodes converted from anodes to cathodes, and vice versa (some even a few times). The mechanism of these changes is not quite clear, but it is assumed that the capillary and Marangoni flow played an important role. In 3.5 % NaCl droplets poor oxygen solubility in combination with Marangoni flow probably caused that most of initial cathodic sites changed to anodes before the end of evaporation
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