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Quartz Tube Proper Usage Guidelines

CLEANING

The cleaning of fused quartz is critical before it is used in any application. The fused quartz should be cleaned by placing it in a 7% maximum solution of Ammonium Bifluoride for no more than ten (10) minutes, or a 10% volume maximum solution of Hydrofloric Acid for no more than five (5) minutes. After cleaning, using the above method, the fused quartz should be rinsed in deionized or distilled water and then dried.

Tips:

  • To avoid water spotting, which may attract dirt and cause devitrification upon subsequent heating, fused quartz should be rinsed several times in deionized or distilled water and dried rapidly.
  • Use of clean, cotton gloves at all times is essential to reduce possibility of contamination.
  • Etching of the surface will remove a small amount of fused quartz material as well as any surface contaminants

RUNNING IN PROCEDURE

In order to increase resistance to devitrification and sag of your quartzware, an even layer of cristobalite must be formed on the O.D. of quartz tubes. Expose a new tube to a temperature of up to 1200° C and rotate it 90° every two (2) hours for the first 12 to 24 hours.

Tips:

  • If the working schedule does not permit adherence to this procedure, place the tube in a furnace at 1200°C and rotate it 90° every two hours for the first 8 hours, then reset the furnace to operating temperature.
  • This procedure helps minimize sag at high temperature to increase the lifetime of the diffusion tube, assuming sufficient mechanical support is designed into the furnace.

STORAGE

Space permitting, fused quartz should be stored in its original shipping container. If that is not practical, at least the wrapping should be retained. In the case of tubing, the end coverings should be kept in place until the product is used. This protects the ends from chipping and keeps out dirt and moisture which could compromise the purity and performance of the tubing.

SOLARIZATION

  1. Fused quartz made from natural raw material solarizes or discolors upon prolonged irradiation by high energy radiation (such as short UV, x-rays, gamma rays and neutrons)
  2. Resistance to this type of solarization increases with the purity of fused quartz
  3. Synthetic fused silica is highly resistant to solarization
  4. Solarization in fused quartz can be thermally bleached by heating it to high temperatures


BECAUSE THE PRODUCTS ARE ANNEALED

Both quartz and silica glass are annealed at approximately 1150° C. However, they reach a strain point at about 1120° C. These glass products, if rapidly cooled after use at temperatures above this strain point, will develop strain again. Special care should be taken when using large sized products.

Tips:

  • Elevate the temperature of the glass to point where the stress is relieved
  • Hold at this temperature until the entire body of the glass reaches temperature equilibrium
  • Cool the glass slowly to a temperature where the glass is rigid

Empirical Annealing Rates of Fused Quartz

The residual stress or design, depending on the application, may be in the range of 1.7 x 105 to 20.4 x 105 Pa (25 to 300 psi). As a general rule, it is possible to cool up to 100°C/hour for sections less than 25mm thick.

Cooling From One Side

Rate °C/minute = 2.867x10-2 x residual stress, PA

(2 x thickness, mm)2

Cooling From Two Sides

Rate °C/minute = 2.867x10-2 x residual stress, PA

(thickness, mm)2


WHEN JOINING FUSED QUARTZ AND OTHER MATERIALS

Quartz and silica glass only slightly expand with increases in temperature, in contrast with other materials. Care must be taken when these glass products are connected to other materials and the temperature rises, in order to avoid the development of cracks.

CARE MUST BE TAKEN DURING FURNACE INSERTION

Quartz and silica glass feature low thermal conductivity. If the glass product comes too close to a heating element, or is put in direct contact with a flame, it may become locally heated and develop cracks. Long glass tubes may also deform at temperatures of 1100° C or higher. Care should be taken to support both glass types, expecially large-sized products.

DEVITRIFICATION

Devitrification of quartz and silica glass means transition from a metastable (vitrified) state to a stable crystallized state of cristobalite. Devitrification occurs when the product is used at high temperatures over a long period of time, or it is heated while impurities adhere to its surface. Even very small impurities on the surface can have a major influence. Under such conditions, devitrification may even occur at temperatures of 1000° C or less. This hardly ever occurs at temperatures of 1150° C or less, if the glass surface is perfectly clean. Devitrification usually starts when the temperature rises to 1200° C or higher, then further develops as the temperature increases.