Improving the environmental production of electrodes for solar panels 186 D O I: 1 0. 15 82 6/ ch im te ch .2 02 0. 7. 4. 09 Patianova A. O., Ivanova K. Yu., Rogozhina L. G., Kuzmin M. V., Semenov V. L. Chimica Techno Acta. 2020. Vol. 7, no. 4. P. 186–191. ISSN 2409–5613 Improving the environmental production of electrodes for solar panels A. O. Patianova*, K. Yu. Ivanova, L. G. Rogozhina, M. V. Kuzmin, V. L. Semenov Chuvash State University named after I. N. Ulyanov, 15 Moskovsky av., Cheboksary, 428015, Russia *email: alisa.patyanova@yandex.ru Abstract. Biodegradable aminosiloxanes have been synthesized by the interaction of 3-aminopropyltriethoxysilane with monoethanolamine in the presence of a binary antioxidant and an alkali metal alcoholate. The synthesized compounds were used to de- velop flux compositions for tinning copper wire and producing electrodes for solar panels. The wetting ability, fluxing activity and biodegradability of the flux were investigated. The possibility of using a flux for hot tinning of copper wire is shown, which makes it possible to increase the environmental friendliness of the production of electrodes for solar panels. Keywords: flux; lead-free solder; solar panels; electrode; tinning; copper wire; biodegrad- able aminosiloxanes Received: 29.10.2020. Accepted: 09.12.2020. Published:30.12.2020. © Patianova A. O., Ivanova K. Yu., Rogozhina L. G., Kuzmin M. V., Semenov V. L., 2020 Introduction Currently, the  most attrac- tive and promising of  renewable energy sources is the use of photovoltaic modules [1]. The quality of photovoltaic modules directly determines the  efficiency of  so- lar energy production, so the production of  photovoltaic modules becomes espe- cially important [2–5]. A relatively large number of  lead-free solders have been proposed for replacement of  lead-based ones. Most of these alloys contain metals such as Sn, In and Bi, with the dominant Sn content [6]. Long-term reliability data is extremely important for the successful application of these alloys, namely proper- ties such as the ability to withstand ther- mal fatigue, corrosion, changes in  me- chanical properties during thermal aging and the  ability to  withstand mechanical stress. Also the  cost, manufacturability, availability, melting point and the  effect of temperature on polymer components are important [7, 8]. The most promising sol- der is a low-melting lead-free one based on tin and indium of POIN-52 grade, which is used to impart high physical, mechanical and operational properties. The  product with high antifriction and wear-resistant properties to contacts with a low transient resistance and higher corrosive properties in  acidic and alkaline solutions, as  well as  mineral oils, which is  not typical for products made of pure metals is the result of  using such alloy. The  reason of  using indium is its ability to reduce the oxidiz- ability of alloys in the molten state, which is very important for increasing the reli- ability of final products. To ensure good 187 adhesion between the tin or tin alloy and the copper wire manufacturers need to use a suitable flux [8]. A significant drawback of such fluxes is  the  impossibility of  complete removal of  its components from the  brazed sur- face, which leads to its corrosion, as well as the inevitability of wastewater pollution with salts of heavy metals, amines and oth- er substances when washing products after soldering. This process is environmentally harmful. The  aim of  the  work was to  increase the environmentally friendly production of electrodes for solar modules by using harmless flux compositions that meet the existing requirements for solar mod- ules’ electrodes. It is  known that organosilicon com- pounds are biodegradable, they can in- crease the  intensity of  biological pro- cesses with oxidation of organic pollution of wastewater and thereby reduce the an- thropogenic load on environmental objects [9]. For this, we synthesized aminosilox- anes, organosilicon compounds, which can reduce the corrosivity of the flux, improve the solder spreading, ensure the required fluxing activity, increase the contact angle with the tinning surface, reduce the sur- face tension and eliminate the solder sur- face oxidation and the base material to be tinned. Experimental Aminoalkoxysilanes I–III were pre- pared by reacting 3-aminopropyltriethox- ysilane with monoethanolamine at differ- ent molar ratios in the presence of a binary antioxidant and an alkali metal alcoholate. To this end, (ν1, mol) 3-aminopropyltri- ethoxysilane, (ν2, mol) pre-distilled mo- noethanolamine are loaded into a reactor equipped with a stirrer, the reaction is car- ried out in the presence of an antioxidant Table 1 The structure and properties of aminosiloxanes Formula and name ν1 : ν2 Efficiency, % nD 20 IR spectrum, ν, cm–1: S i O-CH2-CH2-NH2 (O-CH2-CH3)2 H2N-H2C-H2C-H2C 3-aminopropyl- (2-aminoethoxy) diethoxysilane (I) 1:1 89.7 1.4440 3373, 3294 (NH2), 2974, 2927, 2883 (CH3, CH2), 1083 (Si-O-C) Si (O-CH2-CH2-NH2)2 O-CH2-CH3 H2N-H2C-H2C-H2C 3-aminopropyl-di- (2-aminoethoxy) ethoxysilane (II) 2:1 95.7 1.4521 3366, 3293 (NH2), 2971, 2927, 2875 (CH3, CH2), 1081 (Si-O-C) Si (O-CH2-CH2-NH2)3H2N-H2C-H2C-H2C 3-aminopropyl-tri- (2-aminoethoxy) silane (III) 3:1 97.6 1.4650 1590 (Si-O-C); 3362,3293 (NH2); 1083–1020 (Si-O) 188 and an alkali metal alcoholate. The mixture is kept at room temperature for 10 min- utes, then evacuated at  temperature up to 100 °C for 10–20 minutes, until the al- cohol is completely removed. Data on the  synthesis of  aminosilox- anes are given in Table 1. The process was monitored by IR spec- troscopy on an FT-801 Fourier spectropho- tometer. In the IR spectra of the obtained products, there are intense absorption bands at  1081–1085 cm–1, characteristic of  Si-O-C bonds. The  bands of  the  hy- droxyl group directly bonded to the sili- con atom are absent, and the bands cor- responding to the NH2-group are observed at  3275–3373 cm–1. Aminosiloxanes are clear to light yellow oily liquids. Further, with the  use of  synthesized aminosiloxanes, flux compositions were obtained. Citric acid is dissolved in an iso- propyl alcohol, glycerol is  added, and synthesized aminosiloxane of the general formula is  introduced into the  resulting mixture, Si (O-CH2-CH2-NH2)n (O-CH2-CH3)(3-n) H2N-H2C-H2C-H2C mixed well. Citric acid, isopropyl alcohol and glyc- erin are classified as  hazard class 4, are of  natural origin and biodegradable, so they have a minimal impact on the envi- ronment. The compositions of the flux for solder- ing and tinning are given in Table 2. The  viscosity of  the  flux for solder- ing and tinning copper wire, according to  the  compositions (Table  2) are deter- mined in accordance with GOST 6258–85. The activity of the flux (spreading coeffi- cient) of POIN-52 solder on copper plates at a temperature of 150±30 °C is calculated as the ratio of the spreading area of the sol- der under the action of the inventive flux to the spreading area of the solder under the action of the inventive flux in the form of  a  20% solution in  isopropyl alcohol. The absolute error in determining the ac- tivity of fluxes at a probability of 0.95 is ± 0.03, the error in measuring the tempera- ture of the solder is ±2 °C. Results and discussion The test results are shown in Table 3. According to above data the proposed flux compositions have good fluxing activ- ity, which provides a significant increase in  the  adhesion strength of  the  coating, improves the quality of tinning due to bet- Table 2 Compositions of flux for soldering and tinning copper wire Components, wt. % Flux 1 2 3 Citric acid 12 15 18 Glycerol 10 8 5 Aminosiloxane 1 3 - - Aminosiloxane 2 - 2 - Aminosiloxane 3 - - 1 Isopropyl alcohol others others others 189 ter spreading of  the  solder, that ensures continuous tinning of the copper plate and the absence of corrosion and are also easily biodegradable. The use of flux to obtain an electrode for the solar module showed that during the  production process, smoke does not accumulate over the tinning bath, splash- ing of tin and its alloys decreases. When the tinned copper wire is twisted, cracks and chips do not form, and the  coating does not peel off. Table 4 shows the test results of tinned copper wire using a flux. Table 3 Test results of flux for soldering and tinning copper wire Flux Test results of flux for soldering and tinning copper wire Biodegradation after 28 days, %Fluxing activity, mm Spread coefficient Wettability θ, o 1 95.56 2.86 14 72 2 99.16 2.91 12 64 3 110.47 2.97 10 60 Table 4 Tinned copper wire test results Indicator name, unit of measurement Tinned wire POIN-52 alloy Normalized value (ТТ) Test results Appearance smooth surface and continuous coating along the entire length of the wire the surface is smooth and clean, the coating is continuous the surface is smooth and clean, the coating is continuous the surface is smooth and clean, the coating is continuous Diameter, mm 0.0050.0050.25 + ‑ 0.249 0.254 0.252 Coating thickness, microns 0.001 0.0013.5 + ‑ 3.3 3.5 3.4 Density, g/cm3 8.9±0.2 9.0 9.0 9.0 Tensile strength of wire, N/mm2 200–290 240 244 244 Relative extension, % +5-1025 21 21 21 DC electrical resistance at 20 °C, Ohm/m. 0.35±0.03 0.35 0.35 0.35 Direct current electrical resistivity at 20 °C, Ohm mm2/m. 0.017±0.002 0.0176 0.0176 0.0176 190 Conclusions According to  the  above data, test re- sults show that the obtained data of the fin- ished tinned copper wire fully comply with the  standards, and the  flux can be used in the manufacture of electrodes for solar cells. In this way, 1. Biodegradable aminosiloxanes have been synthesized and used as active fluxing additives in the development of flux. 2. The qualitative and quantitative com- position of the flux for tinning copper wire and the production of electrodes for solar modules was selected, which is based on the use of environmentally friendly sub- stances based on natural, biodegradable raw materials. 3.  It has been found that the  synthe- sized aminosiloxanes increase the wetting ability, fluxing activity and also the biodeg- radability of the flux. 4.  As  a  result of  using the  developed compositions of fluxes, the gas contami- nation of  industrial premises decreases, the  likelihood of  injury and burns de- creases. 5.  Using the  developed flux for hot tinning of copper wire with low-melting lead-free solder POIN-52 allows obtaining an electrode for solar panels with high phys- ical, mechanical and operational properties. 6.  Improving the  environmental friendliness of  the  production of  elec- trodes for solar panels is achieved by a set of the above measures. 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