Glass Means Health!

The glass industry is, as it is for the entire world, a critically important sector for Turkey, providing inputs to numerous industries such as construction, automotive, energy, white goods, food, beverages, pharmaceuticals, tourism, furniture, piping, electrical and electronics, as well as the household sector.

Overview of the Glass Industry

As is well known, the Turkish Glass Industry was established with the Paşabahçe Factory, which began production in 1935. Turkey ranks 12th in global glass production and 5th in European glass production. According to 2016 export figures, Turkey ranks 17th in glass exports. Glass exports totaled 678 thousand tons valued at USD 792 million. Sector exports grew 18.6% by volume compared to the same period of the previous year. This is an indicator of the sector's forward progress.

Glass Production

Soda-silica glass is produced through melting (heating/smelting) from furnace batch or cullet. The most important inputs used in glass production are sand, soda, dolomite, and quartz. Due to the richness of Turkey in these resources, Despite the availability of sufficient glass raw materials in Turkey, raw material reserves that meet the desired properties in terms of physical and chemical characteristics are gradually declining. Looking at the raw materials used in glass manufacturing, silica-quartz sand at 68-72% and sodium carbonate (soda) at 9-20% comprise the vast majority of glass. Other raw materials can be listed as follows: feldspar, dolomite, sodium sulfate, calcium carbonate, borax, sodium-potassium nitrate, zinc oxide, and barium carbonate. Materials such as sand, limestone, feldspar, dolomite, soda, and sodium sulfate, which are silica-based materials, are prepared for melting, cleaned, and stockpiled. Depending on the type of glass to be produced, the aforementioned materials are mixed according to specific formulas. The batch is heated to 1500°C–1600°C in special furnaces using natural gas, fuel oil, or electricity for melting. Depending on the product's properties, the molten glass is transferred to the shaping section. It is formed into the desired shape by one of the methods such as blowing, casting, drawing, floating, centrifuging, flowing, etc. Glass, being a naturally very fragile material, is reheated and cooled in a controlled manner to relieve internal stresses. This makes the material more durable.

Glass Raw Materials 1. Quartz Sand

Quartz sand, first used in glass production by the Romans, contains SiO2 and is found in the Earth's crust. Its color can vary depending on impurities contained within it, and quartz sand is fine-grained and white. If it contains iron oxide components, its color darkens. Colored quartzes can be used as gemstones. Quartz sand is formed as a result of the breakdown of quartz-rich rocks. Before sand obtained from these rocks can be used, it undergoes screening, then washing to remove foreign materials, and finally purification processes using flotation and magnetic separators. Sand used in glass production must contain impurities such as P2O5, MgO, and Fe2O3 at minimum levels and must contain a minimum of 99% SiO2. Such impurities cause defects in the color and appearance of glass. Iron oxide content and alkalies are undesirable in glass as they change its color. For crystal glass, iron content can be a maximum of 0.03%, while in green bottle production this ratio can reach up to 6%. In Turkey, it is found in places such as Istanbul, Şile, Tekirdağ, Zonguldak, Adapazarı, Sinop, and Adana.

2. Soda (Sodium Carbonate)

Sodium carbonate is a raw material found by the Egyptians in 3500 BCE as crude soda ash. Crystal soda is found as Na2CO3.H2O or Na2CO3.10H2O. The Na2O ratio in soda ranges between 44-58%. Turkey imported soda until 1975; thereafter, synthetic soda production began in Mersin.

3. Limestone

Also called limestone. Its composition is calcium carbonate (CaCO3). Marble is formed when calcites undergo transformation over long periods due to high temperature and pressure. Whether a substance contains limestone can be determined by its reaction with hydrochloric acid. CaCO3+2HCl → CaCl2+H2O+CO2 The carbon dioxide (CO2) produced in the resulting reaction causes effervescence. When limestone is heated, carbon dioxide is released. This process begins at 500°C. In glass production, when limestone is heated together with quartz, it readily melts and forms calcium silicate that vitrifies. CaCO3+SiO2 → CaO.SiO2+CO2 In the glass industry, limestone with low iron content that leaves no residue after calcination is used after grinding.

4. Sodium & Potassium Nitrate

Sodium Nitrate and Potassium Nitrate have low melting temperatures at 318°C and 500°C, respectively. Thus, they facilitate the melting of batch components accompanying them, and additionally, when used together with antimony oxides, they enable purification of the glass. In glass production, sodium nitrate may be preferred over potassium due to its lower cost. Due to its low decomposition temperature, sodium nitrate is used together with arsenic trioxide (As2O3) or antimony trioxide (Sb2O3) rather than alone. When sodium nitrate is used with arsenic, it provides free oxygen and introduces arsenic trioxide and arsenic pentoxide to the environment. These oxidized compounds combine with sodium and calcium, remaining in this form for extended periods and enabling purification.

5. Antimony Oxide

It serves as a refining agent, decolorizer, and facilitates metal separation in glass. It is oxidized by forming meta-antimonates (Na2Sb2O6, CaSb2O6) with sodium or calcium oxides.

6. Arsenic Oxide

In addition to its effect in purifying glass, it also enables coloring and homogenization of glass. In the early stages of glass melting, it is oxidized to pentoxide form by other oxidizing elements. Arsenic oxide, used at very low levels such as 0.5%, does not show volatilization at these levels.

7. Boric Acid

It is found in granular and powder form as a result of grinding colemanite ore, processing with sulfuric acid, filtering, and crystallization. In glass production, it prevents devitrification. It increases the resistance of glass against heat, chemicals, and mechanical effects.

8. Sodium Sulfate

It removes undissolved carbonates from the glass batch, preventing the formation of new bubbles. Additionally, part of it dissolves in the glass melt and increases surface tension, assisting in the removal of gases. Sodium sulfate is added to the initial batch at a ratio of 0.4-0.5%. Bilge Çalışkan - Chemical and Biology Engineer - Product and Service Development Specialist - Aleph Trade Sources [1] Turkish Statistical Institute Database. [2] TOBB Sector News Bulletins. [3] Turkey Glass and Glass Products Industry Council Sector Report.