Mehanizem sinteze aluminijevih zlitin v elektrolizni celici

Salihagić Hrenko, Haris (author), Medved, Jože (mentor)

Potreba po izdelkih iz aluminija in aluminijevih zlitin se povečuje. Zato je treba poiskati nove postopke in pristope, s katerimi je mogoče izdelke iz aluminija proizvesti s čim manjšim ogljičnim odtisom. Sinteza aluminijevih zlitin v elektrolizni celici je eden izmed načinov, da se izognemo proizvodnji legirnih elementov in dolgim časom priprave zlitin v livarniških pečeh. Z dodajanjem TiO2 oziroma SiO2 je mogoče v elektroliznih celicah za proizvodnjo aluminija proizvesti zlitine Al-Ti in Al-Si. Da bi lahko določili vpliv dodatkov oksidov TiO2 in SiO2 na električno prevodnost elektrolitov, smo elektrolite analizirali z 0–6 mas. % dodanega oksida. Ugotovljeno je bilo, da ima TiO2 bistveno večji vpliv na zmanjšanje električne prevodnosti. Za sintezo Al zlitin v industrijskih elektroliznih celicah so primerni elektroliti, ki vsebujejo do 1 mas. % TiO2 oziroma SiO2. S sintezo zlitin Al-Ti in Al-Si v laboratorijski elektrolizni celici smo določili učinkovitost elektrolizne redukcije titana in silicija iz elektrolitov, ki vsebujejo 0,024 mas. % TiO2 oziroma 0,210 mas. % SiO2. Učinkovitost redukcije oksidov TiO2 in SiO2 iz elektrolitov v laboratorijski elektrolizni celici je 20- oziroma 25-odstotna, učinkovitost redukcije Al2O3 pa je bila 52,8–66,5-odstotna. Ugotovljeno je bilo, da se v laboratorijski elektrolizni celici večina titana in silicija sintetizira alumotermično. Da bi sintetizirali zlitini Al-Ti in Al-Si, smo v industrijsko celico tehnologije Aluminium Pechiney 18 dodajali TiO2 ali SiO2. Dodatki oksidov ne vplivajo na regulacijo temperature in prebitka AlF3. Pri sintezi zlitine Al-Ti je bilo ugotovljeno, da 75 % redukcije TiO2 poteče alumotermično, preostalih 25 % redukcije pa poteče elektrolizno. Pri redukciji SiO2 lahko redukcija poteka tako elektrolizno kakor tudi alumotermično. Delež alumotermične redukcije SiO2 v siliciju je pogojen z maso, ki je dodana v sistem elektrolita. Pri kontinuiranem dodajanju oksida v elektrolit se slednji reducira alumotermično, enaka količina oksida, dodanega v enkratni masi, pa se reducira alumotermično in elektrolizno. Med elektroliznim procesom povzročijo alumotermične reakcije nastanek Al2O3. Nastali Al2O3 vpliva na zmanjšanje upornosti elektrolizne celice in s tem na zmanjšanje količine dodanega Al2O3, katero regulira procesni računalnik. Zato smo izdelali model, po katerem izračunamo novo stopnjo dodajanja Al2O3 v elektrolizni proces ob kontinuiranem dodajanju TiO2 ali SiO2. Tako je v industrijskih celicah tehnologije Aluminium Pechiney 18 mogoča proizvodnja zlitin Al-Ti in Al-Si z minimalnimi spremembami procesnega vodenja ali celo brez njih.

• Language: Slovenian
• Keywords: elektrolizno pridobivanje aluminija, sinteza aluminijevih zlitin v elektrolizni celici, električna prevodnost
• Work type: Doctoral dissertation
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2020
• PID: 20.500.12556/RUL-116052
• COBISS.SI-ID: 15670275
• Publication date in RUL: 09.05.2020

Secondary language

• Language: English
• Title: Synthesis Mechanism of Aluminium Alloys in an Electrolysis Cell

Abstract

There has been an increase in the demand of aluminium products and aluminium alloys. Thus new procedures and approaches need to be developed in order to produce aluminium products with the lowest carbon footprint. Synthesis of aluminium alloys in electrolytic cell is one way to avoid production of alloying elements and long preparing times of alloys in foundry furnaces. Al-Ti and Al-Si alloys can be produced in electrolytic cells for aluminium production by adding TiO2 or SiO2. In order to determine the impact of TiO2 or SiO2 oxides on the electrical conductivity of electrolytes, the latter were analysed with 0–6 mass % of added oxide. Thereby it was determined that TiO2 has a significantly higher impact on the decrease in electrical conductivity. Suitable electrolytes for synthesis of Al alloys in industrial electrolytic cells contain up to 1 mass % of TiO2 or SiO2. From synthesis of Al-Ti and Al-Si alloys in a lab electrolytic cell we determined the efficiency of electrolytic reduction of titanium and silicon from electrolytes which contain 0.024 mass % of TiO2 or 0.210 mass % of SiO2. The reduction efficiency of TiO2 and SiO2 oxides from electrolytes in a lab electrolytic cell was 20 % or 25 % while the reduction efficiency of Al2O3 was 52.8–66.5 %. It was determined that in a lab electrolytic cell most of titanium and silicon is synthesised aluminothermically. In order to synthesise Al-Ti and Al-Si alloys, TiO2 or SiO2 were added into an industrial cell of the Aluminium Pechiney 18 technology. Addition of oxides has no impact on the regulation of temperature and the excess of AlF3. During Al-Ti alloy synthesis it was determined that 75 % of the TiO2 reduction occurs aluminothermically, while the remaining 25 % of the reduction occurs electrolitically. SiO2 reduction can occur both electrolitically as well as aluminothermically. The proportion of the aluminothermic reduction of SiO2 into silicon is conditioned by the mass, added into the electrolyte system. During continuous oxide addition to electrolyte, reduction of the latter occurs aluminothermically, while reduction of the same amount of oxide, added in a single amount, occurs aluminothermically and electrolitically. Aluminothermic reactions cause occurrence of Al2O3 during electrolysis. The obtained Al2O3 leads to decreased resistance of the electrolytic cell and thereby reduced number of Al2O3 kg doses, regulated by the process computer. Therefore we developed a model which calculates a new rate of Al2O3 addition to electrolysis process while continuously adding TiO2 or SiO2. Thereby Al-Ti and Al-Si alloy production without process control changes or with minimal process control changes can be achieved in industrial cells of the Aluminium Pechiney 18 technology.

• Keywords: electrolysis of aluminium, synthesis of aluminium alloys in electrolytic cell, electrical conductivity