No. 3 / 2007 97 DEALKALIZATION of GLASS SURFACES by ACID
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Nonconventional Technologies Review – no. 3 / 2007 DEALKALIZATION OF GLASS SURFACES BY ACID GASES IN THE ELECTRIC FIELD Vasile SHARAGOV1 ABSTRACT: The influence of chemical composition of industrial glasses and the nature of active gases on rate of alkaline cations extraction under the effect of electric field is analyzed and integrated. The subjects of investigation were flat glass samples, bottles and jars of colorless glass, bottles of green glass, ampoules made from medicinal glass, illuminating glassware made from transparent colorless and milk glasses. Thermochemical treatments of samples were carried out using SO2, NO2, CO2, HCl, HF, CF2Cl2, CHF2Cl and gas mixtures. The reaction zone was subjected to electric field to intensify the glass dealkalization by gases. Main regimes of treatment: temperature between 300 and 600 oС, duration between 1 s and 2 h, quantity of gas reagent feeded into the camera between 0.01 and 1.00 mol. KEYWORDS: glass, active gas, treatment, dealkalization, rate, electric field. 1. INTRODUCTION: It was well-known by glass founders that comparison to other strengthening methods - glass annealing in presence of acid gases ion exchange, etching in hydrofluoric acid resulted in improvement of its properties [1]. and tempering [4, 6]. Due to the same Investigations aimed at thermochemical reason, while glass article maintaining this treatment of glassware by acid gases have layer is rapidly destroyed and strength been carried out for 100 years. The effect of degradation of glass takes place [4, 7]. acid gases on inorganic glasses leads to their Hence, the main direction of wide use of the dealkalization, reaction products being method lies in the increase of dealkalization occurred on the glass surface as a bloom. layer thickness. It is known that electric, The changes in structure and composition of magnetic and acoustic fields influence surface layer accompany the increase of significantly the chemical processes [8]. The glass chemical durability on 1-2 order of effect of physical fields on chemical magnitude, rise of mechanical strength on interaction between gases and glass has not 20-30 %, improvement of thermostability on been described in literature. 5-10 % [1-5]. The main disadvantage of gas The aim of the presented work is to study the treatment is in the low depth of dealkalization possibility of glass surfaces dealkalization layer (in case of industrial glasses - about 1 intensification using electric field. µm), so this effect is less than one in 2. EXPERIMENTAL: Thermochemical treatment in laboratory conditions was carried out in the following Experiments were held in laboratory and way. Samples of glass were inserted into the industrial conditions. The subjects of kiln at room temperature. Then the samples investigation were flat glass samples, bottles were heated to the designed temperature and and jars of colorless glass, bottles of green treated by gas reagent. After treatment glass, ampoules made from medicinal glass, samples were cooled in the kiln to the illuminating glassware made from transparent temperature below 100 0C.The samples of colorless and milk glasses. As a gas reagent flat glass were presented as plates with the 2 SO2, NO2, CO2, HCl, HF, CF2Cl2, CHF2Cl and area from 50 to 100 cm . To receive the mixtures of these gases were used. samples made from transparent colorless glass, the lumps from scatters with the area samples were received from bottles and jars. from 30 to 50 cm2 were cut out. Similar Besides, the plates with the thickness from 4 97 Nonconventional Technologies Review – no. 3 / 2007 to 6 mm were cast from illuminating glasses rotor glass forming machines (BB-7, BB-12). and container glass. Regimes of glass Experiments were also carried out at Glass- treatment are the following: temperature – manufacturing in the Ukraine and Russia. between 300 and 600 0C, duration – between Main conditions of treatment of glassware by 1s and 2 h, quantity of gas reagent feeded gaseous media: glass temperature – between into the camera between 0.01 and 1.00 mol. 500 and 800 °C; duration of reagent feed - Thermochemical treatment in industrial 1 s; volume fraction of gas (gas volume vs. conditions was carried out in the following container capacity) between 0.1 and 100 %. conditions. A part of these experiments Containers were treated in different places: have been carried out at Glass- final blowing of glassware, conveyor for manufacturing (Kishinau, Republic of transportation of containers towards Moldova), where a number of jars and annealing, lehr. The chemical compositions bottles is made using sectional glass-forming of industrial glasses are given in Table 1. machines (IS-8-2, IS-6-2, AL-106-2) and Table 1 Chemical compositions of industrial glasses Weight content of oxides, % Glass type SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 Other Flat 72.65 1.55 0.11 7.60 3.71 13.62 0.35 0.31 - Container 71.85 2.51 0.07 6.60 4.54 13.89 - 0.45 - Medicinal 72.81 4.52 0.05 6.05 0.82 8.15 1.64 - 6.11 B2O3 Transparent 73.31 1.80 0.04 6.95 - 16.46 1.15 0.24 - Milk 66.91 7.05 0.04 3.67 - 13.60 4.19 0.27 4.3 F- + + Four experimental series have been where νMe - dealkalization rate of Me from conducted simultaneously: glass by gases (µmol Me+/dm2 of glass 1. Samples were heated in tube oven up to surface); + + the given temperature, and then were CMe - Me concentration in solution after the treated by gas reagent. After the washing off the bloom by distilled water treatment glass was cooled in the oven (µmol Me+/l); turned off. V - solution volume (l); 2. The glass samples were subjected to S - sample surface square (dm2); electric field in line with the previous part τ - treatment duration (min). of thermal treatment but without active The majority of industrial glasses contain both gases. + + + + Na and K . So, separate rates νNa and νK 3. Simultaneous treatment by acid gases + as well as sum rate νMe was calculated [7]. and electric field. It should be pointed out that there are two 4. Repeat thermal treatment of glasses (as factors affecting the accuracy of the in part 1) but without gases and electric experiments. Firstly, the reaction products field. evaporate from sample surface (this process The main important criterion of dealkalization proceeds rapidly if the melting point is close process occurring is formation of bloom on to reaction temperature). So, the extraction the surface of glassware (the bloom consists rate can be higher than the calculated one. of products of reaction). In spite of the Hence, it is necessary to offset bloom lost by differences between the composition of evaporation. Secondly, in some cases the industrial and model glasses, treated by acid bloom burns fast to glass surface and isn't gases the data of bloom analysis were washed off by water. Moreover, non-soluble unambiguously found to certify the extraction compounds may occur in the reaction, for of cations from samples. The intensity of instance, fluorides of alkaline metals. The glass dealkalization by gases was estimated facts mentioned above should be taken into using the extraction rate of alkaline cations: account when extraction rate of cations from + + . -1 . -1 glass is determined. νMe = CMe V S τ , (1) In our experiments reaction products were washed off by distilled water and were 98 Nonconventional Technologies Review – no. 3 / 2007 analyzed by flame photometer. The maximum influence of temperature on dealkalization relative error of the calculation did not exceed rate of alkaline cations was studied. Regimes from 3 to 5 %. of glass treatment are the following: temperature – between 20 and 600 0C, 3. RESULTS AND DISCUSSION: duration – 15 min, quantity of gas reagent feeded into the camera - 1.00 mol. The Intensity of glass dealkalization by gases results obtained are shown in Table 2. depends on a lot of factors, the main of them are: temperature, chemical composition of glass and gas media [4]. In experiments the Table 2 Influence of temperature on the intensity of dealkalization of flat glass by gas media Dealkalization rate, µmol Me+/(dm2.min) o Temperature, C CO2 SO2 HCl CF2Cl2 SO2+ without CF2Cl2 gases 20 0.09 0.09 0.09 0.09 0.09 0.09 100 0.09 0.09 0.09 0.09 0.09 0.09 200 0.09 0.11 0.11 0.09 0.11 0.09 300 0.09 0.24 0.28 0.16 0.25 0.09 400 0.10 0.91 1.05 0.52 1.00 0.11 500 0.14 1.52 1.97 1.43 2.78 0.13 600 0.21 2.17 3.51 3.39 10.24 0.20 One can see from the Table 2 that while Electric field significantly accelerates the temperature rises the dealkalization rate reaction between glass and gases. Regimes increases significantly. In case of thermal of glass treatment are the following: treatment intensification of this process isn't temperature – between 20 and 600 0C, observed. Carbon dioxide is not active in duration – 15 min, voltage - between 0.5 and dealkalization. The mixture of sulfur dioxide 1.5 kV, quantity of gas reagent feeded into and CF2Cl2 (volume ratio 1:1) is the most the camera - 1.00 mol. The results are given active one in dealkalization of flat glass. in Table 3. Table 3 Influence of temperature on dealkalization of flat glass by CF2Cl2 in electric field Dealkalization rate, µmol Me+/(dm2⋅min) Temperature, oC U = 0 U = 0,5 kV U = 1,5 kV 20 0.09 0.09 0.09 100 0.09 0.09 0.09 200 0.09 0.10 0.11 300 0.16 0.25 0.34 400 0.52 0.87 1.15 500 1.43 2.20 3.12 600 3.39 5.03 9.83 Under the same conditions dealkalization rate Approximately the same results were by SO2 in presence of electric field is lower in obtained in case of container glass, colorless comparison to CF2Cl2.