Quartz rods, especially those made of high-purity fused silica, play a vital role in industry, laboratory and scientific research. Many users often ask when selecting, "What is the hardness of quartz rod? How many grades does it have?" This is a very important question, but the answer may be different from what you imagine. Strictly speaking, the Mohs hardness of the quartz rod itself is a fixed value, about Mohs 7, and it does not have a "hardness grade" classification like steel. Its scratch resistance and wear resistance mainly stem from its inherent material properties.

However, what users truly care about are often the mechanical strength, thermal shock resistance, deformation resistance, and surface treatment level exhibited by quartz rods in different application scenarios. The differences in performance levels are mainly reflected in the purity of quartz materials, manufacturing processes (such as electric melting or gas refining), and subsequent heat treatment.

1、Understanding the "hardness" of quartz rods: Mohs hardness level 7

1.1 What is Mohs hardness?

Mohs hardness is a standard for measuring the ability of minerals to resist scratches, expressed in numbers from 1 (softest, such as talc) to 10 (hardest, such as diamond).

1.2 Hardness positioning of quartz

The Mohs hardness of quartz (chemical composition of silicon dioxide, SiO ₂) is 7. This is a very high level, as a comparison:

The Mohs hardness of ordinary glass is about 5.5

The hardness of stainless steel knives is about 5.5

The hardness of tungsten carbide is about 9

The hardness of diamonds is 10

This means that quartz rods can easily scratch glass and metal surfaces, while also having good scratch resistance.

1.3 Reasons for Constant Hardness

As long as the quartz rod is made of pure silica, its Mohs hardness remains stable at around 7. The change in hardness usually means that the product contains a large amount of impurities or is not made of quartz material at all (such as ordinary soda lime glass).

2. Beyond hardness:

Although the hardness is fixed, there are significant differences in the performance of quartz rods of different grades, which directly determine what problems they can solve.

2.1 Purity level

Purity is the core "grade" indicator of quartz rods, which directly affects their temperature resistance and chemical stability.

Ordinary grade (>99.9%): containing a small amount of impurities, suitable for occasions with low temperature and requirements, such as certain observation windows and support rods.

High purity grade (>99.99%): With extremely low impurity content, it has superior high-temperature deformation resistance (higher softening point) and optical transmittance. Suitable for semiconductor industry, fiber preform, and high-end optical applications.

Ultra high purity/synthetic quartz grade (>99.999%): made through processes such as chemical vapor deposition, almost free of metal impurities and hydroxyl groups (OH -), with excellent optical uniformity and extremely low thermal expansion coefficient. Suitable for deep ultraviolet optics, lasers, and precision optical components.

2.2 Process and structural grade

The manufacturing process determines the intrinsic quality of the quartz rod, such as bubbles, impurity content, and uniformity.

Electric melting method: melting high-purity quartz sand with an electric arc in a vacuum or inert atmosphere. Capable of producing transparent quartz glass rods with low bubble content and good optical uniformity.

Gas refining method: Melting quartz sand in a hydrogen oxygen flame. High quality products can also be produced, and process control is crucial to their performance.

Continuous melting method: Continuous production, high efficiency, relatively low cost, suitable for large-scale industrial applications with less extreme optical performance requirements.

2.3 Thermal stability level

This is not a grade marked on the label, but a comprehensive performance indicator determined by purity and process.

Thermal shock resistance: Quartz rods have an extremely low coefficient of thermal expansion and can withstand drastic temperature changes without breaking. For example, quickly placing a high-temperature quartz rod into cold water usually does not explode. This feature solves the problem of device damage caused by rapid cooling and heating in high-temperature environments.

Softening point: The softening point of high-purity quartz rods is as high as about 1660 ° C, which means that they can still maintain their shape and strength at extreme high temperatures, solving the problem of easy softening and deformation of high-temperature carriers and supports.

2.4 Surface Quality Grade

The surface treatment level of quartz rods determines their mechanical strength and optical properties.

Fire polished surface: Smooth surface, good transparency, high mechanical strength, can effectively reduce stress concentration caused by surface microcracks.

Grinding and polishing surface: achieving extremely high surface smoothness and flatness, used for precision optical conduction, solving the problems of light scattering and energy loss.

Blank/cutting surface: The surface is relatively rough and may have microcracks, with relatively low mechanical strength. It is generally used for mechanical support applications that are not sensitive to the surface.

3. Practical problems that can be solved by quartz rods of different "grades"

Selecting the appropriate "grade" quartz rod based on the above indicators can solve the following industry problems in a targeted manner:

3.1 Addressing deformation and pollution issues in high-temperature environments

Application scenarios: Furnace tubes, carriers, and paddles for semiconductor monocrystalline silicon growth furnaces (pulling furnaces), diffusion furnaces, and oxidation furnaces.

Solution: Use high-purity, high softening point quartz rods as support and connection components. Its high-temperature non deformation characteristic ensures precise positioning of wafer transfer, and its high chemical purity avoids contaminating expensive silicon raw materials at high temperatures.

3.2 Solving the explosion problem under severe temperature changes

Application scenarios: Laboratory tube furnaces, vacuum coating equipment, lasers, UV lamp housings.

Solution: Utilize the extremely low thermal expansion coefficient and super strong thermal shock resistance of quartz rods as observation windows, lamp tube brackets, or reaction chamber skeletons to ensure stable operation of equipment in repeated temperature rise and fall cycles and extend its service life.

3.3 Addressing Loss Issues in Corrosive Environments

Application scenarios: chemical industry, acid washing process, special lighting system.

Solution: Quartz material itself has excellent acid and corrosion resistance (except for hydrofluoric acid and hot phosphoric acid). Using quartz rods as stirring rods, guide rods, or supports can withstand acidic and alkaline environments for a long time, replace metal parts, and solve the problems of corrosion loss and contaminated media.

3.4 Solving energy loss and distortion problems in precision optics

Application scenarios: UV lithography machines, spectrometers, high-power laser transmission systems.

Solution: Use ultra high purity synthetic quartz rods and undergo precision grinding and polishing to achieve extremely high transmittance and excellent optical uniformity in both ultraviolet and infrared bands. Solved problems such as light energy transmission loss, beam deformation, and thermal lens effect.

Although the hardness of quartz rods itself does not have a grade, their purity, manufacturing process, and surface treatment level constitute the actual "performance grade". When choosing, one should not only focus on the single indicator of "hardness", but also deeply understand whether its purity, thermal stability, and optical performance meet your specific application needs, so as to choose the "grade" of quartz rod product that can best solve your actual problem.

Luverre Quartz manufactures and sells a wide range of high quality quartz glass, including quartz tubes, quartz plates, quartz rods, quartz windows, quartz crucibles, quartz boats, quartz flanges, quartz beakers, quartz glass instruments, and more. We can meet all kinds of customized requirements for quartz glass products.