High Temperature Quartz for Industrial Heat

Five properties explain why high temperature quartz is the default material for furnace tubes, heater envelopes and protection tubes in extreme heat.

Extreme Thermal Stability

Continuous service to 1200°C and short excursions to 1300°C. The softening point of fused silica lies above the melting point of aluminium — beyond borosilicate, polymers and many ceramics.

Thermal Shock Resistance

Near-zero thermal expansion means rapid heating and cooling — even direct flame impingement — does not crack the part. A quartz tube can go from a hot furnace to ambient air without failing.

Chemical Inertness at Heat

Resistant to most mineral acids, oxidants, halogens and process gases at high temperature. It does not leach metals into the process — vital for heat treatment and analytical work.

Infrared Transparency

Clear fused silica transmits IR from the near-UV to about 3.5 µm. This makes it the universal envelope for IR heaters — the element radiates straight through the wall to the workpiece.

Electrical Insulation at Temperature

Fused silica keeps excellent insulation where polymers fail. It serves as heating-element support rods, electrode sleeves in plasma systems and high-voltage vacuum feed-throughs.

Clear or Opaque Grades

Clear grade transmits IR for heating and observation; opaque grade scatters IR for thermal insulation and uniform furnace zones. Both come from the same fused silica family.

FGQuartz makes the core range of industrial high temperature quartz components. Standard dimensions ship from stock; custom dimensions and fabricated assemblies are made to drawing with no minimum order. For material and service-life guidance, see our high temperature quartz guide.

Clear and opaque fused silica furnace tubes for horizontal and vertical tube furnaces — heat treatment, CVD coating, catalyst testing, synthesis and annealing. Standard diameters for major platforms; custom lengths, walls and ends. Available with ground flat ends for O-ring sealing, flame-welded flanges and closed-end forms for sealed-atmosphere work.

Clear & opaque · Flanged / closed-end · OEM diameters

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Clear fused silica heater envelopes for short-wave and medium-wave infrared heating. The quartz heater tube transmits the element’s radiation through its wall to the workpiece for energy-efficient surface heating — curing, drying, forming and annealing in automotive, packaging, food and textile lines. Standard IR-heater diameters; twin-tube and custom forms.

Short / medium-wave IR · Twin-tube · OEM-compatible

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Single- and double-bore quartz protection tubes (thermocouple sheaths) for temperature measurement in corrosive, reactive or contamination-sensitive process gas. The quartz protection tube isolates the sensing junction from the atmosphere while conducting heat for accurate readings — where metal sheaths would be attacked or contaminate. Closed ends are flame-sealed; flanged thermowells machined from solid quartz.

Single / double bore · Flame-sealed · Thermowell option

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Fused silica sight windows for direct observation inside furnaces, combustion chambers and reactors. The window must take the temperature differential, the furnace IR, and sometimes corrosive atmospheres. Low thermal expansion minimises stress at the mount edge, preventing the edge cracking common with higher-expansion glass. Circular and rectangular; optical-grade polished for pyrometry.

Sight glasses · Pyrometry-grade · Round / rectangular

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Opaque fused silica tubes and liners for thermal insulation between the hot zone and the heating elements. Microscopic voids scatter and absorb IR instead of transmitting it, giving low surface emissivity — an effective radiant heat barrier. Opaque liners improve temperature uniformity along the tube by cutting radiant exchange with the elements. Single- and multi-zone, furnace-compatible diameters.

Low emissivity · Single / multi-zone · Furnace fit

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Complex assemblies that combine CNC-machined tube bodies, flame-welded side ports and flanges, and ground sealing faces — made to drawing. Plasma reactor electrode insulators, combustion-chamber liner systems, gas-sampling probe assemblies and multi-zone furnace tube sets are standard custom items. Drawings in DXF, STEP, IGES or PDF; prototype quantities from a single piece.

CNC + flame welding · DXF / STEP / IGES · Single-piece OK

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High temperature quartz serves more industrial sectors than any other glass. Here is the role it plays in each and why it beats the alternatives.

IR heater systems use quartz heater tubes to enclose resistive elements and transmit their radiation to the workpiece. Short-wave systems with filament temperatures above 2000°C need clear fused silica envelopes with peak transmission in the 0.7–2 µm band. Applications include automotive paint and powder-coat curing, plastic thermoforming, textile heat-setting, food surface treatment and PCB solder reflow. FGQuartz covers standard IR-heater diameters, with twin-tube and custom forms.

Industrial tube furnaces for metal heat treatment — bright annealing, hydrogen reduction, normalising and sintering — use quartz process tubes to contain the controlled atmosphere in the hot zone. Quartz is chosen because it seals gas-tight at both ends, takes the temperature, and does not react with the atmosphere or contaminate the workpiece with metallic impurities. Hydrogen bright annealing of precision parts, precious-metal annealing and ceramic sintering are common uses.

CVD of hard coatings on cutting tools, catalytic test reactors and high-temperature gas-phase systems use quartz reactor tubes because fused silica resists the halide and reactive-gas chemistries at reaction temperature. The chemical inertness of high temperature quartz keeps the reactor wall from catalysing side reactions that would distort selectivity and yield measurements in catalytic test work.

Atmospheric plasma jets, RF plasma torches in ICP-OES and ICP-MS instruments, and industrial plasma treatment systems use quartz chambers and torch tubes. Fused silica uniquely combines RF transparency for inductive coupling, chemical resistance to reactive plasma species, and thermal stability at the extreme periphery temperatures. ICP torch assemblies use high temperature quartz because it provides electrode insulation and plasma-energy resistance at once.

Food IR ovens use quartz heater tubes for browning, pasteurisation and dehydration where contact heating is not acceptable. Pharmaceutical manufacturing uses high temperature quartz in depyrogenation tunnels, dry-heat sterilisation ovens and API synthesis reactors, where contamination from equipment carries regulatory weight. The non-porous, inert surface of fused silica suits food- and pharma-grade hygiene needs for components close to the product.

Emissions monitoring and process gas analysers need probes that extract a representative sample from hot flue ducts without altering its composition by condensation, reaction or adsorption. High temperature quartz sampling probes are preferred because fused silica does not catalyse reactions between sample components and does not adsorb the polar molecules and water vapour that cause measurement errors in metal or polymer sampling systems.

A few material facts help engineers choose the right grade and keep components in service longer. For the full treatment, read our high temperature quartz guide.

Clear fused silica transmits infrared, so it suits IR heater envelopes, observation windows and any setup where radiation must pass through the wall. Opaque fused silica contains microscopic voids that scatter and absorb IR, giving low emissivity and good thermal insulation — ideal for furnace liners, baffles and radiant barriers. Many furnace builds combine both: clear where heat or light must pass, opaque where it must be contained.

Held around 1050–1200°C for long periods, fused silica can slowly crystallise into cristobalite — devitrification — which looks milky, weakens the part and generates particles. Alkali contamination accelerates it. Keep surfaces free of sodium, potassium and calcium (handle with clean gloves), avoid prolonged operation at the upper limit, and replace milky tubes proactively. High-purity fused silica resists devitrification far better than lower-purity quartz at the same temperature.

Fused silica serves continuously to about 1200°C and tolerates brief excursions to around 1300°C; its softening point is near 1680°C. Useful life at the top of this range depends on the atmosphere, the ramp rate and any devitrification-promoting contamination. For sustained work near 1200°C, high-purity high temp fused silica is strongly preferred over lower grades, which contain more impurities that accelerate failure.

High temperature quartz resists most mineral acids, oxidants, halogens and process gases even when hot. The key exceptions: hydrofluoric acid (HF) attacks and dissolves it; hot concentrated alkali (NaOH, KOH) dissolves the SiO₂ network above about 200°C; and very hot concentrated phosphoric acid can slowly etch the surface. For these, use PTFE or platinum instead. For nearly all other high-temperature chemistry, quartz is the most resistant practical material.

Tell us your operating temperature, process atmosphere, furnace type and component geometry. FGQuartz will confirm stock availability or provide a lead time and detailed quote within 24 hours. Explore related semiconductor quartz or the full application library.