| High-temperature furnace or heating chamber | Transparent fused-quartz tube with a suitable wall thickness and an outside diameter matched to the furnace hardware. | Common continuous service: approximately 900–1,100 °C. Higher temperatures may be possible for limited periods when permitted by the design and supplier. | Air, vacuum, nitrogen, argon, or other controlled atmospheres, provided the atmosphere is compatible with the process and tube material. | Temperature profile, heating length, support spacing, wall thickness, thermal cycling, and furnace clearance. | Do not expose the hot tube to sudden cooling, direct water contact, or concentrated mechanical loads. Actual limits depend on geometry and mounting. |
| UV curing, photochemistry, or UV reactor | High-purity transparent quartz with a low-absorption surface and a wall thickness that provides the required optical transmission. | Often below 300 °C, although the process may operate at higher temperatures if the complete assembly is designed for it. | Air, oxygen, solvents, water, or process gases depending on the application. Confirm compatibility with the chemical mixture and UV wavelength. | Required wavelength range, optical clarity, tube diameter, path length, fouling resistance, and cleaning method. | Transmission decreases when the surface becomes contaminated, devitrified, or damaged. Some UV wavelengths are absorbed by quartz depending on purity and tube grade. |
| Laboratory reaction or process tube | Transparent fused-quartz tube with closed, open, flanged, or custom end geometry selected for the reactor and fittings. | Typically 20–1,000 °C, depending on the reaction, heating system, and thermal cycling rate. | Vacuum, inert gas, oxidizing gas, or selected chemical vapors. Review the compatibility of quartz with the specific reagents. | Internal volume, gas-flow pattern, seal arrangement, pressure differential, cleanability, and sample access. | Quartz is not universally resistant to all chemicals. Hydrofluoric acid and hot concentrated alkaline solutions can attack fused silica. |
| Semiconductor or high-purity thermal processing | High-purity fused-quartz tube with controlled dimensions, low particulate generation, and a surface finish suitable for the process. | Common process range: approximately 500–1,100 °C, with the exact limit set by the recipe and equipment. | High-purity nitrogen, argon, oxygen, hydrogen-containing mixtures, vacuum, or other qualified process atmospheres. | Metal contamination, particle control, dimensional stability, cleaning procedure, thermal uniformity, and service-life requirements. | Repeated thermal cycling can cause devitrification, distortion, or contamination buildup. Qualification should be based on the complete process, not temperature alone. |
| Thermocouple protection or sensor sheath | Small-diameter quartz sheath or tube with a closed end when electrical isolation and gas protection are required. | Frequently used below 1,000 °C; the allowable temperature depends on diameter, wall thickness, mounting, and thermal shock. | Air, inert gas, vacuum, or selected process gases. Check whether the process can react with the sensor, sheath, or sealing materials. | Probe diameter, insertion depth, response time, electrical insulation, vibration, and replacement method. | Thin tubes respond quickly but are more vulnerable to impact and thermal shock. Avoid bending loads and point contact with furnace parts. |
| Gas flow, sampling, or vacuum line | Quartz tube with suitable internal diameter, end connections, and wall thickness for the required flow and pressure conditions. | Usually selected according to the gas process temperature; many systems operate from ambient temperature to approximately 800 °C. | Dry gases, inert gases, oxidizing gases, vacuum, or process vapors after chemical compatibility review. | Internal diameter, pressure differential, leak-tight connections, flow resistance, dead volume, and cleaning requirements. | Quartz is rigid and brittle. It should not be treated as flexible tubing, and unsupported spans can increase breakage risk. |
| Optical viewing or inspection window | Optically clear quartz tube or window section with controlled surface quality and minimal contamination. | Ambient to high temperature, subject to the thermal gradient and mounting design. | Air, vacuum, inert gas, or process environments compatible with fused silica. | Viewing wavelength, clarity, surface finish, viewing angle, thermal gradient, and protection from deposits. | Localized heating, uneven cooling, scratches, and deposits can reduce optical performance and increase failure risk. |
| Chemical-resistant process containment | Quartz tube selected after reviewing the exact chemical concentration, temperature, exposure time, and flow conditions. | Often below 300 °C for wet chemical service; higher-temperature gas service requires a separate compatibility assessment. | Many acidic and aqueous environments are suitable, but compatibility must be checked for each chemical system. | Chemical concentration, temperature, exposure duration, stress condition, surface condition, and cleaning chemicals. | Hydrofluoric acid, hot phosphoric acid under some conditions, and hot concentrated alkalis may attack fused silica. Never assume universal chemical resistance. |
