What Is Borosilicate Glass

Widely used

Borosilicate glass has a wide range of applications due to its thermal shock resistance and low coefficient of thermal expansion. Borosilicate glass is manufactured using a variety of forming processes. It can be drawn into glass tubes and flat glass for pharmaceutical packaging, or it can be formed using the microfloat process. This results in a wide variety of glass shapes and thicknesses, thus providing unique geometries for many applications.

Is Borosilicate Glass More Expensive than Normal Glass?

If we compare two glass products – one made from soda-lime glass and the other made from borosilicate glass – the borosilicate product will most likely be more expensive. This comes down to the manufacturing process required to produce the material.

Higher Quality 

After an intense and complex production process, the final borosilicate glass objects are considered high-quality glassware and cost more than standard annealed glass.

What is the composition of high borosilicate glass？

What are the properties of borosilicate glass and what is its principle

Low thermal expansion rate

In materials physics, the thermal expansion coefficient of glass usually denoted α, is a numerical value that describes how the dimensions of a glass material change with temperature. The coefficient of thermal expansion is usually expressed in units of one degree Celsius (1/°C) or one degree Fahrenheit (1/°F). For most types of glass, α ranges from about 5×10−6 to 10×10−6/°C.

This property is critical for applications involving significant temperature changes, as it affects the material’s ability to withstand thermal stress without cracking. Glass is a non-crystalline or amorphous material usually made by rapidly cooling a melt of silicate components. This rapid cooling prevents the formation of regular crystal structures, causing the molecules to arrange themselves in a disordered manner. When glass is heated, its molecules begin to vibrate more vigorously, causing the distance between them to increase. This phenomenon causes the material to expand. High borosilicate glass is known for its extremely low thermal expansion rate (approximately 3 × 10 −6 K −1 at 20 °C) compared to other types of glass, such as soda-lime glass. This property is critical for applications that require stability under rapid temperature changes, such as laboratory glassware, cookware, and certain industrial applications.

As mentioned above, we already know that the low thermal expansion rate of high borosilicate glass can be attributed to its unique chemical composition and structure. The backbone of high borosilicate glass is its high content of silicon dioxide (SiO2), which forms a strong and stable silicon-oxygen tetrahedral network. The silicon-oxygen bonds are very strong and contribute to the glass’s rigidity and low thermal expansion. High borosilicate glasses typically have a higher SiO2 content than standard glass types, making the network stiffer and less prone to expansion. The main chemical reaction that forms the glass network involves converting silica and boron trioxide into a glassy matrix:
SiO2​+B2O3​→[SiO4​]4− and [BO4​]5− network

The addition of boron oxide (B2O3) causes B2O3 to interact with the silicon-oxygen network to form borosilicate glass, introducing boron-oxygen bonds into the structure. These bonds can form three- and four-membered rings, which contribute to the flexibility and stability of the glass network. The presence of B2O3 will therefore help reduce the thermal expansion of the glass by creating a more complex network that is less likely to expand under thermal stress. Compared to other types of glass, borosilicate glass contains lower amounts of alkali metals (such as sodium and potassium). This is because alkali metals weaken the glass network, making it more susceptible to thermal expansion. By minimizing these components, borosilicate glass maintains a more stable and rigid structure. The addition of aluminum oxide during the manufacturing process further enhances its thermal stability. Al2O3 is integrated into the glass network and connected with silicon to form a more complex and thermally stable structure. In this way, this big family can develop stably.

Thermal shock resistance

Due to the chemical structure of high borosilicate glass, in particular the dense Si-O network and the incorporation of boron, it is crucial for its low thermal expansion. The stiffness and stability of this network limit the movement of atoms and the expansion of the material when heated. Therefore, borosilicate glass can withstand sudden temperature changes without cracking, a property called thermal shock resistance.

Chemical resistance

Here we should praise the element boron, which plays a vital role here. It makes the structure of the glass more complex and tangled. This complexity makes it more difficult for water to penetrate the glass, thereby reducing the rate of corrosion that reacts with water.

In response, high borosilicate hydrochloric acid glass has gained durability in various environments. Corrosion resistance makes high borosilicate glass ideal for environments where there may be exposure to harsh chemicals or extreme conditions. This is why it is used in laboratory glassware as it may be exposed to corrosive substances for extended periods. And for it, this is also its unique ability.

High borosilicate glass is known for its excellent corrosion resistance, especially in acidic environments such as hydrochloric acid. This property is critical for applications requiring durability and longevity, such as chemical processing equipment and laboratory glassware. The mechanisms behind this resistance are complex and fascinating, with aspects of chemistry and materials science intertwined. What a wonderful fusion.

To sum up, the core of high borosilicate glass’s resistance to hydrochloric acid lies in its unique composition. High borosilicate glass typically contains silicon dioxide (SiO2), boron oxide (B2O3), and small amounts of alkali such as sodium oxide (Na2O) or potassium oxide (K2O). High levels of SiO2 provide a strong, stable network, while B2O₃ reduces the glass’s thermal expansion coefficient and enhances its resistance to thermal shock. The presence of B2O3 is also crucial to its acid resistance, as it forms a protective layer that blocks further reaction with the glass. When high borosilicate glass comes into contact with hydrochloric acid, the initial interaction occurs at the glass surface, where hydrogen ions (H⁺) from the acid attack the silica network. However, the boron oxide in the glass forms a hydration layer of boric acid (H₃BO₃), which significantly slows down the dissolution of the silica network. This layer acts as a barrier, reducing the rate at which the glass matrix is degraded by acids. A simplified chemical reaction of the interaction between high borosilicate glass and hydrochloric acid can be expressed as follows:
Initial acid attack SiO2+2HCl→SiCl2+2H2OSiO2+2HCl→SiCl2+2H2O
Formation of boric acid protective layer B2O3+3H2O→2H3BO3​

These reactions highlight the initial stages of the interaction, where the silica network is attacked and a protective layer of boronic acid forms. It should be noted that in actual processes the reaction is more complex and involves various intermediate steps and products, again depending on the glass composition and exposure to acid. Here are a few simple steps.
Step 1: Describe the acid attack on the SiO2 network, resulting in the formation of silicon chloride (SiCl2) and water.
Step 2: Explain how boron oxide reacts with water to form a boric acid protective layer.

Excellent optical transparency

High borosilicate glass is known for its excellent optical clarity. This property is critical for applications that require transparent materials that do not distort light, such as laboratory glassware, optical lenses, and certain types of windows. Optical transparency is a direct result of the material’s composition and its highly ordered structure.

(1) Low iron content
Borosilicate glass has a lower iron content. Iron impurities absorb light at the red end of the spectrum, causing the glass to appear green. High borosilicate glass maintains a clear, nearly colorless appearance by minimizing iron and other color-causing impurities, ensuring minimal light absorption and distortion. This is also a major innovation in our industrial technology.

(2) Uniform structure
The glass’s structure, characterized by a network of silicon-oxygen (Si-O) and boron-oxygen (B-O) bonds, is very homogeneous and free of crystalline inclusions that could scatter light. This uniformity allows light to be transmitted without significant scattering, thereby increasing its optical transparency.

(3) Chemical stability
High borosilicate glass’s resistance to chemical attack, including hydrochloric acid, means its surface remains smooth over time and does not etch. Rough or etched surfaces may scatter light, reducing clarity. The glass’s chemical stability ensures that its optical properties remain consistent even under harsh chemical exposure.

Why does borosilicate glass have so many advantages?

Among them, SiO2 (silica), is the main part of glass and provides the main network-forming agent for the glass structure. When B2O3 (boron trioxide) reaches 10%, this ingredient can change the glass network, lower the glass transition temperature, and enhance chemical resistance. It also helps reduce the thermal expansion coefficient of the glass. In addition to these, this family also includes some oxides such as Na2O (sodium oxide) and Al2O3 (aluminum oxide). These oxides constitute 8% and 3% respectively and act as intermediates in the glass network in the glass. Although the K2O (potassium oxide) content is only 1%, don’t underestimate it. It can further change the properties of the glass, similar to sodium oxide, and can also improve the waterproof and chemical resistance of the glass. Sodium oxide helps lower the melting temperature and improves the workability of the glass, while our aluminum oxide increases the mechanical strength and chemical durability of the glass. There are also other substances, this category accounting for 8% of the composition, containing various trace additives and impurities whose addition affects properties such as the color, transparency, and conductivity of the glass. During our glass-making process, we purify the glass by using hydrochloric acid (HCl) to remove impurities, but it does not remain as a component of the glass.

What is the production process of borosilicate glass?

Application Scenario

Conclusion

High borosilicate glass offers thermal stability, chemical durability, and mechanical strength unmatched by other glass types. Its manufacturing process involves the strategic introduction of hydrochloric acid, ensuring the removal of impurities and enhancing the structural properties of the glass. Its wide range of applications highlights its importance in daily and professional technical applications, making it a focus of materials chemistry research.

At this point, our introduction to borosilicate hydrochloric acid comes to an end. Thank you for reading so far, but our glass journey has just begun. BO-GLASS will continue to introduce you to high-quality content about glass. You can continue to Follow us and let glass become the bridge between us. BO-GLASS will continue to provide you with quality services.