Tungsten Crucible - Wholesale Tungsten Crucible
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What Is a Tungsten Crucible?
A tungsten crucible is a container manufactured from high-purity tungsten metal, typically 99.95% or higher purity, designed to hold molten metals, oxides and salts at very high temperatures. Tungsten has the highest melting point of all metals at 3422 C and a density of 19.3 g/cm3, which gives the crucible exceptional thermal stability, low vapor pressure and resistance to attack by many molten materials. Tungsten crucibles are produced by powder metallurgy routes, mainly pressing and sintering followed by forging or machining, and the finished product is used in crystal growth, smelting, coating and furnace applications where no other container material survives.
Manufacturing Process
Two production routes dominate commercial supply. The sintered route starts with isostatic pressing of high-purity tungsten powder into a green body, followed by sintering at temperatures above 2300 C in a hydrogen atmosphere to reach a density of more than 18.5 g/cm3, which corresponds to about 96% of theoretical density. The sintered blank is then forged, rolled or machined to the final dimensions, and large diameters are produced by welding segments. The chemical vapor deposition route deposits tungsten from tungsten hexafluoride or tungsten hexachloride vapor onto a rotating mandrel, producing very thin-walled, high-purity crucibles that are preferred for sapphire growth furnaces. All crucibles are finished by machining and verified by density measurement, ultrasonic inspection and dimensional control.
| Parameter | Typical Value |
|---|---|
| Purity | W 99.95% min |
| Density | 19.3 g/cm3 theoretical; sintered parts 18.5-19.2 g/cm3 |
| Melting point | 3422 C |
| Working temperature | Up to 2400 C in vacuum or inert atmosphere |
| Outer diameter | 10-600 mm |
| Height | 10-1200 mm |
| Wall thickness | 1-20 mm |
| Surface finish | Ground or polished, roughness Ra 1.6-3.2 |
Application Fields
Sapphire crystal growth: tungsten crucibles contain the alumina melt in Kyropoulos and heat exchanger method furnaces used to grow LED and optical sapphire boules.
Quartz glass and optical glass melting: the crucible withstands the high melting temperature of silica glass without contaminating the melt.
Rare earth smelting: tungsten containers are used for melting, distillation and refining of rare earth metals and their alloys.
Vacuum coating: tungsten boats, coils and crucibles serve as evaporation sources for metallizing films in the electronics and packaging industries.
High-temperature furnace components: susceptors, support tubes and thermal shields in vacuum furnaces and semiconductor processing equipment.
Quality Inspection and Packaging
Each crucible is inspected for density by the Archimedes method, for internal cracks by ultrasonic or dye penetrant testing, and for dimensions with calibrated gauges. Surface defects are removed by grinding and polishing to the specified roughness. Crucibles are packed individually in foam-lined wooden cases to prevent impact damage during sea or air freight, and export packing follows the dimensions and weight of each item.
How Silicon Metal Is Produced
Silicon metal is produced in a submerged electric arc furnace by carbothermic reduction of quartz and carbon reductants. The quartz is reduced at high temperature, and the molten silicon is tapped, cast and crushed to the required sizing, with the grade defined by the iron, aluminum and calcium content of the final product. Grades such as 1101, 3303, 411, 421, 441, 551 and 553 describe the maximum impurity levels in the designation, so a 553 grade, for example, allows up to 0.5 percent iron, 0.5 percent aluminum and 0.3 percent calcium. The same production route is used for silicon carbide, which is formed by reacting silica sand with petroleum coke at high temperature in an electric resistance furnace.
Quality Control and Certification
The acceptance of silicon metal and ferroalloy products is controlled by chemical analysis. Every lot is sampled and tested for the main impurities, and the analysis is recorded on the certificate together with the lot number, the size range and the packing details. In our inspection practice we verify the certificate analysis against the ordered grade before release, check the size distribution with sieves on a sample of each lot, and examine the material for contamination and oxide coating, because surface oxidation can change the effective analysis of fine fractions. Traceability from the production lot to the delivered package is maintained so that any question after delivery can be answered from the records.
Applications and Selection
Silicon metal is used as an alloying addition for aluminum casting, as a raw material for silicones and organosilicon chemistry, and as a semiconductor grade feedstock after further refining. Silicon carbide is used as an abrasive, a refractory raw material and a deoxidizer in steelmaking, and silicon briquettes and powders are supplied as convenient feed forms for foundries. The correct grade and size range are selected by the application and the furnace practice, and the analysis and sizing must be confirmed with the supplier before delivery so that the product matches the process.
Quality Control and Documentation
Every delivery of silicon metal and ferroalloy products should be supported by proper documentation that traces the material back to its production batch. In our inspection practice we verify the certificate against the order first, then check the critical dimensions, the surface condition and the marking on the goods themselves. The acceptance record is kept for each delivery, and third-party inspection can be arranged for projects that require independent verification. These documented checks are the difference between a delivery that runs smoothly through production and one that stops the line with a specification mismatch.
Selection Guidance
The correct silicon metal and ferroalloy products specification is selected by the service environment, the forming or fabrication operation and the required service life. Over-specification increases cost without benefit, while under-specification leads to premature failure, so the acceptance values should be fixed at ordering and confirmed on the certificate at delivery. In our experience, specifications that state the governing standard, the required property values and the acceptance tests are the ones that cause the fewest disputes, because every party knows exactly what will be verified.
Inspection Checklist
A practical incoming inspection for silicon metal and ferroalloy products covers the certificate check, the dimensional verification, the surface examination and the marking check. The certificate values are compared with the ordered limits, the dimensions are measured at the positions defined by the standard, and the surface is examined for the defects that matter for the intended application. Any deviation is recorded and agreed with the supplier before the material is released to production. This checklist takes minutes to run and prevents most downstream problems.
Common Misconceptions
Several misconceptions about silicon metal and ferroalloy products appear regularly in procurement discussions. The first is that a higher grade always means better value, when the correct grade is the one matched to the actual service. The second is that the certificate alone guarantees the quality, when the physical verification is equally important. The third is that storage and handling do not matter, when surface damage and corrosion at the storage stage are among the most common causes of rejected deliveries. Understanding these points helps buyers avoid both waste and failure.
Quality Control and Documentation
Every delivery of silicon metal and ferroalloy products should be supported by proper documentation that traces the material back to its production batch. In our inspection practice we verify the certificate against the order first, then check the critical dimensions, the surface condition and the marking on the goods themselves. The acceptance record is kept for each delivery, and third-party inspection can be arranged for projects that require independent verification. These documented checks are the difference between a delivery that runs smoothly through production and one that stops the line with a specification mismatch.
Selection Guidance
The correct silicon metal and ferroalloy products specification is selected by the service environment, the forming or fabrication operation and the required service life. Over-specification increases cost without benefit, while under-specification leads to premature failure, so the acceptance values should be fixed at ordering and confirmed on the certificate at delivery. In our experience, specifications that state the governing standard, the required property values and the acceptance tests are the ones that cause the fewest disputes, because every party knows exactly what will be verified.
FAQs
Q1: What is the maximum working temperature of a tungsten crucible?
In vacuum or inert gas atmospheres, tungsten crucibles are used up to about 2400 C. In oxidizing atmospheres tungsten oxidizes rapidly above roughly 500 C, so an inert or reducing environment is mandatory.
Q2: What is the difference between sintered and CVD tungsten crucibles?
Sintered crucibles are denser and stronger, with wall thicknesses from 1 mm upward, while CVD crucibles have very uniform thin walls and the highest purity, making them the standard choice for sapphire growth where melt contamination must be minimal.
Q3: Can tungsten crucibles be made to custom dimensions?
Yes. Diameter, height, wall thickness and bottom profile are produced to the customer drawing, and common tooling covers diameters from 10 mm to 600 mm and heights up to 1200 mm.
Q4: How long does a tungsten crucible last in sapphire growth service?
Service life depends on furnace atmosphere, temperature profile and handling, but properly operated sintered crucibles typically survive many growth cycles before wall thinning requires replacement.
Q5: Is a certificate of analysis supplied with each crucible?
Yes. Every batch is supplied with a material certificate stating tungsten purity, density and the results of the non-destructive inspection, and third-party inspection can be arranged on request.
