Quartz Glass Technical FAQ

Quartz glass is amorphous, high-purity silicon dioxide (SiO₂ ≥ 99.99%) melted above 1700°C with no soda, lime or boron fluxes. It is the same family of material as fused silica and fused quartz: a non-crystalline SiO₄ network used for semiconductor furnaceware, UV optics and high-temperature laboratory ware. Unlike window glass or borosilicate, quartz glass contains essentially no network modifiers — trace metals are held below 20 ppm. Industry language: “fused silica” usually means synthetic material from SiCl₄; “fused quartz” usually means natural quartz crystal that has been melted; “quartz glass” is the umbrella term used in specifications and purchasing.

Yes — in industrial use, quartz glass, fused quartz and fused silica all mean amorphous high-purity SiO₂. The distinction is feedstock: fused silica is synthetic (SiCl₄), fused quartz is melted natural crystal. Synthetic material is purer and more homogeneous; natural fused quartz is the workhorse for tubes, boats and crucibles. Specify the grade, not the synonym — for deep-UV optics ask for JGS1/synthetic fused silica; for semiconductor process tubes, wafer boats and CZ crucibles, natural fused quartz with controlled alkali and OH is correct and more economical. Do not confuse either material with crystalline quartz (piezo crystals) or with “quartz” countertops, which are polymer-bound crushed stone.

Ordinary glass is made from silica sand plus soda and lime — it is not quartz glass. Quartz glass is made by melting nearly pure quartz crystal or synthetic SiO₂ with no fluxes, so it is a different material with a much higher working temperature and UV transmission. Silica sand is crystalline SiO₂, so in a geological sense most glass starts from quartz, but the fluxes drop the melting point from ~1700°C to ~1400°C and destroy UV transmission and high-temperature strength — that is why a borosilicate beaker and a fused-quartz process tube are not interchangeable.

Quartz glass is ≥99.99% SiO₂. Typical impurity budget: Al < 10 ppm, Fe < 5 ppm, Na+K < 5 ppm, total metals < 20 ppm. Hydroxyl (OH) is specified separately: optical IR grades are < 5–20 ppm OH; UV synthetic grades may contain 1000–2000 ppm OH. There are no intentional Na₂O, CaO or B₂O₃ additions — that is the entire chemical difference versus soda-lime and borosilicate glass, and it is why quartz glass costs more: the melt is hotter, the feedstock is purer, and diamond tooling is required to machine it.

Cost comes from high-purity feedstock, melt temperatures above 1700°C, diamond CNC tooling, and low-volume custom fabrication. You are paying for 1200°C service, UV transmission and semiconductor-level cleanliness — not for a commodity container. FGQuartz quotes from a drawing; prototype MOQ is one piece, and volume pricing follows geometry, grade and inspection level rather than a catalog list price.

The properties that drive specification are: continuous use at 1200°C, CTE of 5.5×10⁻⁷/°C, thermal conductivity 1.4 W/(m·K), density 2.2 g/cm³, refractive index 1.4585, UV–NIR transmission 185–2500 nm, dielectric constant 3.75, and chemical inertness to all acids except HF. Mechanically it is hard (Mohs 5.5–6.5) and strong in compression (~1100 MPa) but brittle in tension (~48 MPa) — design for compression, avoid point loads, and anneal after welding or heavy machining.

Quartz glass does not have a sharp melting point. Softening is ≈1680°C, annealing ≈1215°C, strain point ≈1120°C. Continuous service is 1200°C; short-term excursions to 1300°C are acceptable. Above that, sag and devitrification accelerate. For furnace tubes and CZ crucibles the practical limit is set by sag, not by melting — always confirm the thermal cycle with FGQuartz engineering, since wall thickness and span matter as much as the datasheet temperature.

The thermal conductivity of fused silica/quartz glass is 1.4 W/(m·K) at 20°C — much lower than metals and somewhat lower than alumina, which is why quartz tubes can hold steep radial gradients in diffusion furnaces without cracking. Specific heat is 670 J/(kg·K) and thermal diffusivity about 9.5×10⁻⁷ m²/s at 20°C. Combined with the near-zero CTE, this is the origin of quartz glass’s thermal-shock resistance.

The linear CTE of fused silica is 5.5×10⁻⁷/°C (0.55×10⁻⁶/K) between 20 and 300°C — about one-sixth of borosilicate and one-twelfth of soda-lime glass. That near-zero expansion is why a red-hot quartz tube can be set on a bench without shattering. Joints to metals or ceramics still need a designed transition — quartz-to-stainless usually uses a flange, clamp or bellows, not a rigid braze.

Fused silica and fused quartz have a density of 2.2 g/cm³ at 20°C. Crystalline alpha-quartz is about 2.65 g/cm³; the lower glass density reflects the open amorphous SiO₄ network. Use 2.2 g/cm³ for mass estimates of tubes, plates and boats — opaque (bubble) quartz is slightly lower because of closed voids.

Fused silica has nD = 1.4585 at 589 nm (20°C) and about 1.4496 at 1060 nm. The Abbe number is 67.8. These values are for amorphous quartz glass, not crystalline quartz (ne = 1.553, no = 1.544). For AR coatings and laser windows, specify wavelength and grade (JGS1/JGS2/JGS3).

The dielectric constant of fused silica is 3.75 at 1 MHz, 20°C. Volume resistivity exceeds 10¹⁸ Ω·cm at 20°C. Dielectric strength is 25–40 kV/mm and loss factor is under 1×10⁻⁴ at 1 MHz. These numbers make quartz glass a high-temperature electrical insulator for furnace feedthroughs, RF windows and semiconductor process hardware. Resistivity falls with temperature (about 7×10⁷ Ω·cm at 350°C) — still insulating, but design accordingly.

Yes, except for hydrofluoric acid (HF), hot phosphoric acid above ~150°C, and concentrated alkalis at high temperature. Quartz glass is inert to water, organics, and concentrated HCl, HNO₃ and H₂SO₄ — which is why it is used in wet benches and analytical labware. HF etches SiO₂ rapidly; even dilute HF or buffered oxide etch will frost and thin a quartz tank, so wall thickness and replacement interval need to be specified for HF service.

Regular soda-lime glass is ~70% SiO₂ plus soda and lime, max use ~300–400°C, no UV below 300 nm. Quartz glass is ≥99.99% SiO₂, 1200°C continuous, UV from 185 nm, with a CTE ten times lower. They share a name fragment, not a specification — if a drawing says “glass” and the process is a diffusion furnace, the buyer almost always means fused quartz.

Use borosilicate up to ~500°C for ordinary labware. Use quartz glass when you need >500°C, UV below 300 nm, semiconductor purity, or flame-welded custom geometry. Quartz costs more and machines only with diamond tools; borosilicate is cheaper and easier to blow. CTE: quartz 0.55×10⁻⁶/K vs borosilicate 3.3×10⁻⁶/K. UV at 254 nm (10 mm): quartz >90%, borosilicate <10%. For a muffle tube, wafer boat or CZ crucible, borosilicate is not a substitute.

JGS is the Chinese optical-quartz grade system. JGS1 is synthetic fused silica for deep UV (185–2500 nm, high OH). JGS2 is natural fused quartz for UV–visible (220–2500 nm). JGS3 is low-OH material for infrared (260–3500 nm). The number is a spectrum class, not a quality ranking. Pick by wavelength: below ~220 nm → JGS1; general 260–2500 nm → JGS2; beyond 2.5 µm or high-power IR → JGS3. Western analogues: JGS1 ≈ Suprasil/Corning 7980; JGS2 ≈ Homosil-type; JGS3 ≈ IR-grade fused quartz.

If the part must transmit below 220 nm, specify JGS1. If it is a general UV–visible window, sight glass or cuvette, specify JGS2. If it must work past 2.5 µm, specify JGS3 (low OH). Process tubes and wafer boats are usually non-optical fused quartz, not a JGS optical blank. Use the Grade Finder on this page, then send the clear aperture, thickness, scratch-dig and coating requirement with the drawing.

Yes. JGS1 synthetic fused silica transmits from 185 nm; a 10 mm path exceeds 90% at 254 nm. JGS2 is usable from ~220 nm. Ordinary glass and borosilicate do not transmit the 254 nm mercury line effectively. UV lamp envelopes, photochemical reactors and DUV laser windows are classic fused-silica applications — specify grade, thickness and whether solarization resistance is required.

FGQuartz draws and fabricates fused quartz tubes from 5 mm to 1000 mm OD, walls 0.5–20 mm+, lengths to 3000 mm (longer by welding). Types include clear, opaque, capillary, large-diameter furnace tubes, UV/IR grades, flanged, threaded, side-ported and bent welded assemblies. Typical uses: semiconductor diffusion/oxidation/LPCVD liners, solar POCl₃ tubes, fiber MCVD/VAD substrate tubes, IR heater envelopes and thermocouple sheaths. Concentricity and bow are held for automated loaders. Send OD, ID, length, grade, and whether you need flanges, ports or a bend.

FGQuartz fabricates large-diameter fused quartz furnace tubes up to 1000 mm outer diameter. Feasible wall, length and ovality depend on the drawing — send OD, ID and length for a manufacturing review. Large tubes are used as semiconductor and solar process chambers; heavy walls are available for vacuum, and ends can be fire-polished, ground, or welded to flanges.

Fused quartz tubes are rated 1200°C continuous and 1300°C short-term, with excellent thermal shock resistance. “High-pressure” tubes are heavy-wall custom parts; pressure rating is a function of OD, wall, temperature and end closures — it is calculated per drawing, not taken from a catalog. Quartz is a brittle glass, not a pressure-vessel steel, so FGQuartz will flag unsafe spans and recommend wall thickness or a different design.

Yes. FGQuartz oxy-hydrogen flame-welds flanges, side holes, tees, multi-port gas manifolds and bent routing tubes, then stress-relief anneals the assembly. CNC drilling, threading and grinding are combined with flame work on the same part — this is how custom furnace liners and gas injectors are made. Send STEP/DXF plus the process gas and temperature so weld placement and annealing can be planned.

In semiconductor and solar quartzware, a gas manifold is a fused-quartz tube assembly with welded tees, injectors and multi-port inlets that deliver process gas into a furnace or reactor — not an oil-and-gas steel manifold. FGQuartz flame-welds these from high-purity tube. If you need quartz injectors, shower heads or tee assemblies for a diffusion/LPCVD/PECVD tube, that is a custom quartz fabrication job — send the CAD.

A quartz wafer boat is a high-purity fused-silica carrier with precision-milled slots that holds silicon wafers in a diffusion, oxidation, LPCVD or annealing furnace. FGQuartz machines horizontal, vertical and half-shell boats for 2″–12″ (50–300 mm) wafers and M10/G12 solar formats, with custom slot pitch typically 2.0–6.0 mm at ±0.05 mm. Boats are CNC slot-milled (V-groove or U-groove), fire-polished to cut particle shedding, then annealed and CMM-checked for pitch, parallelism and bow. FGQuartz also reverse-engineers worn boats from a sample, photo or furnace model.

Yes. Slot count, pitch, groove profile (V or U), orientation (horizontal or vertical) and wafer diameter are all custom. Typical pitch is 2.0–6.0 mm. There is no minimum order quantity — a single replacement boat is a normal order. Send the furnace model, a DXF/STEP, or a worn sample, and FGQuartz matches rail geometry, handle and loadport so the new boat drops into the existing tube.

Use a fused-quartz boat for standard silicon diffusion, oxidation and LPCVD up to 1200°C where metallic contamination must stay extremely low. Use SiC when the process is hotter, more mechanically abusive, or when quartz sag life is the limiter. FGQuartz manufactures quartz boats; SiC is a different material system, and if you are replacing a quartz boat, send the drawing rather than assuming an SiC geometry is a drop-in.

Fused quartz crucibles hold molten silicon in Czochralski (CZ/MCZ) crystal growth for semiconductor and solar wafers, and they serve as high-purity lab and calcination vessels. FGQuartz makes CZ crucibles to 32″ (800 mm)+ diameter, clear lab crucibles from 10 ml to 2000 ml, and custom shapes with lids, spouts and flanges. CZ crucibles typically have a bubble-free inner surface and an opaque outer layer for thermal management; lab crucibles are clear fused silica for ashing, fusion and trace analysis.

Yes. Cylindrical fused-quartz crucibles — straight wall, flat or round bottom, with or without lid — are a standard FGQuartz custom item. They ship worldwide, including the USA, Australia and India, in export crates with clean, shock-safe packing. Send ID, height, wall and bottom type for a quote.

Yes. FGQuartz supplies fused-quartz crucibles for solar silicon CZ pulling as well as quartz tubes and boats for TOPCon, HJT and BC cell lines (POCl₃ diffusion, PECVD, wet process). Crucibles are specified for sag resistance and low alkali to protect crystal yield — solar and semiconductor CZ crucibles share the material family but differ in size, opaque-layer design and cost target.

Clear fused-silica lab crucibles are made from 10 ml to 2000 ml, flat or round bottom, with optional lids and pouring spouts. They take 1200°C, resist thermal shock, and stay clean for ashing and trace analysis. This is not the same product as a 32-inch CZ crucible — if you need a small analytical crucible, say so and the quote path is faster.

There is no single list price. Cost tracks diameter, wall, opaque vs. clear, OH/alkali spec, tooling and quantity — a 50 ml lab crucible and an 800 mm CZ crucible are different products. FGQuartz quotes from a drawing or a size table, usually within 24 business hours. To get a number, send ID/OD, height, wall, bottom type, grade, quantity and destination; prototype quantity can be one.

Yes. FGQuartz cuts, grinds, drills, chamfers and polishes fused-silica plates and windows in JGS1 (deep UV), JGS2 (UV–Vis) and JGS3 (IR). Custom shapes, mounting holes and fire-polished edges are routine, and anti-reflective coating is available when transmission must be maximized. Used as viewports, laser windows, substrates and furnace sight glasses — send length × width × thickness, grade, surface spec and any coating.

Yes. Optically polished windows, plates and selected custom optics in JGS1/JGS2/JGS3 for UV lithography, laser lines (193, 248, 266, 355, 532, 1064 nm) and spectroscopy. Homogeneity and bubble class follow the grade; JGS1 is the imaging/DUV choice. For a λ/10 laser window, put the optical spec on the drawing so the quote includes the right polishing path.

Yes. Solid fused-silica rods are drawn and then optionally centerless-ground, CNC-drilled, grooved or optically end-polished. They are used as fiber target rods, lab stirrers, supports, welding filler and custom fixtures. Specify diameter, length, ovality and whether the ends must be fire-polished or optically flat.

FGQuartz combines hot work (oxy-hydrogen welding, bending, blowing, fire polish) with cold work (multi-axis CNC milling, drilling, threading, grinding, optical polish) in one ISO 9001 plant. Custom tubes with flanges and ports, boats, crucibles, plates, tanks, injectors and multi-part assemblies are all in scope, with MOQ of one prototype. Accepted files: DXF, STEP, IGES, PDF, with a free design-for-manufacturability review before quote. Reverse engineering from a sample or photo is also available for replacement quartzware.

Yes, with diamond tooling on CNC mills, lathes and grinders. Quartz is hard (Mohs 5.5–6.5) and brittle, so feeds, coolant and fixturing are specialized. FGQuartz CNC-slots wafer boats, drills manifolds, threads flanges and grinds optical faces in house. After heavy machining the part is annealed to remove grinding stress, and edges are chamfered or fire-polished so they do not become crack starters.

Yes. High-purity fused silica is joined with an oxy-hydrogen flame to make vacuum-tight welds — flanges on tubes, crucible repairs, multi-port manifolds, and assembled boats — then annealed. This is a core FGQuartz process, not a subcontract. Quartz does not solder or TIG like metal, so geometry must allow torch access; a DFM pass will move a weld if the CAD puts it in an impossible corner.

Fused quartz is the only practical transparent, ultra-pure, 1200°C material that does not donate alkali or heavy-metal ions onto a silicon wafer. It is used for diffusion/oxidation/LPCVD process tubes, wafer boats, bell jars, liners, injectors and RTP windows. Clear quartz is chosen when pyrometry must look through the wall; opaque quartz when radiation shielding is wanted — FGQuartz supplies both, plus the boats that ride inside the tube.

Yes. FGQuartz fabricates quartz beakers, crucibles, flasks, reaction tubes, combustion boats, cuvettes and custom lab assemblies that survive 1200°C and aggressive acids (except HF). Custom labware from a sketch is common, with MOQ of one. Drawings in any language are fine; dimensioning in mm is preferred.

Quartz tanks are welded fused-silica baths for semiconductor and solar wet benches — cleaning, etch (non-HF or with designed life in dilute HF), and hot-acid process. FGQuartz builds seamless-weld tanks with overflow weirs, drains and custom flanges. HF service must be declared, since quartz dissolves in HF; for RCA-type cleans and hot sulfuric, quartz is the standard high-purity choice.

FGQuartz is a fused-silica manufacturer founded in 2005 in Lianyungang, Jiangsu, China. A 15,000 m² ISO 9001 plant melts, draws, CNC-machines and flame-welds quartz tubes, rods, plates, wafer boats, crucibles, tanks and custom assemblies for semiconductor, solar, fiber, optical and laboratory customers in 40+ countries. It is a factory, not a trading desk — melting and machining sit on one site, with material traceability and a certificate of compliance, and engineering replies to drawings within 24 business hours.

Send a DXF, STEP, IGES or PDF drawing, material grade, quantity and destination via our contact page. MOQ is one prototype. Standard catalog items ship in 7–14 days; custom work is typically 3–6 weeks. Engineering replies within 24 business hours. Include critical tolerances, surface finish, and whether the part is a reverse-engineered replacement — photos of a worn boat or crucible are enough to start a DFM review.

Yes. FGQuartz exports quartzware to 40+ countries, including the United States, EU, UK, India, Australia and East Asia. Parts are cleaned, vacuum-sealed and crate-packed from Lianyungang. Transit is typically several days by air freight after production; production itself is 7–14 days (stock-type) or 3–6 weeks (custom). Single-piece prototypes are accepted so you do not wait on a large MOQ.