Mo1 vs Mo2 vs TZM: Choosing a Molybdenum Electrode Grade

For parts in contact with molten glass, a molybdenum electrode grade decision usually lands on Mo1: pure molybdenum at Mo ≥ 99.95%. Mo2 (Mo ≥ 99.9%) suits fixtures that do not touch the melt. TZM (Mo–0.5Ti–0.08Zr) is a strengthened alloy for loaded structural parts rather than glass-contact electrodes, and Mo-La with La₂O₃ dispersion serves long-time, creep-limited components. The grade sets both the duty envelope and the cost band.

How molybdenum electrode grades are divided

Within a drawing, a molybdenum electrode grade is a composition and process label, not a marketing name. Pure molybdenum grades are separated by purity; alloy grades are separated by the second phase or the solid solution element that raises high-temperature strength.

Pure molybdenum: two purity lines

Mo1 requires a molybdenum content of at least 99.95% and Mo2 at least 99.9%, the conventional industry reading applied under YS/T 1312-2019 for electrodes and GB/T 17792 for rod. The gap is five hundredths of a point, yet on iron, nickel and chromium it marks the boundary between a clean melt and a tinted one.

Alloyed molybdenum: a second phase

TZM is typically Mo–0.5Ti–0.08Zr with a trace of carbon, strengthened by carbides and solute elements. Mo-La uses La₂O₃ particles at roughly 0.3%–1%, a reference range, to pin grain boundaries. Neither changes the molybdenum matrix, but both change the recrystallization temperature and the machining difficulty.

Mo1, Mo2, TZM and Mo-La compared

The table places composition, purity or strengthening phase and typical use side by side. Values are typical figures or standard limits; the agreement governs.

The four grades reduce to two statements: Mo1 and Mo2 differ in total impurity, while TZM and Mo-La differ in strengthening mechanism. Purity governs cleanliness on the melt side; the second phase governs dimensional stability on the hot side. One does not substitute for the other.

Why Mo1 dominates glass-contact electrodes

Molten glass is sensitive to the metal it touches. Iron, nickel and chromium tint most glass families, and elevated carbon or oxygen can seed bubbles. For a molybdenum electrode grade in this position, lower total impurity means less interference with the melt, and Mo1 is the practical balance point.

Impurity elements and glass tint

Float, photovoltaic rolled and pharmaceutical glass each carry color and transmission requirements, and an element introduced by the electrode is hard to offset later through the batch recipe. Many glass lines therefore write Mo1 into the technical agreement and set separate limits on iron and nickel. High-purity and standard molybdenum electrodes compares the two purity classes in more detail.

Density and forged structure

Purity is only the entry threshold; density decides the working behaviour. A sintered billet that is forged or rolled has fewer pores and grain-boundary defects, which raises resistance to melt penetration. The effect of reduction ratio is covered in forging ratio and structural density. Two suppliers can both deliver Mo1 and still show different consumption if their forging and annealing schedules differ.

Three boundaries in a molybdenum electrode grade decision

A molybdenum electrode grade decision starts from three questions: does the part touch the melt, does it carry load for a long time, and does it sit in an oxidizing atmosphere at temperature.

Direct contact with the melt

Rods, plates and discs that sit in the glass are specified as Mo1, with the section sized by current density and cooling arranged through a water jacket. Related guidance sits in working current density for molybdenum electrodes. The grade settles only half the question at this position; the other half is structure and operating practice.

Structural parts away from the melt

Blocks, brackets and non-critical connections are not attacked by glass and can use Mo2 at lower cost. If such a part still sits hot in air, oxidation thinning and creep must be calculated, and the grade label alone will not answer it.

High-temperature load and creep

Clamp seats, connectors and furnace supports carry load for long periods, where TZM and Mo-La are the better fit. TZM holds more strength reserve, Mo-La holds better creep resistance over time, and the choice follows load and service duration. Process detail is described in TZM molybdenum alloy electrodes. Glass melt duties impose limited mechanical load, so placing TZM in a standard electrode position adds cost without a clear return.

Confirming the grade at goods-in

Drawing and technical agreement

A drawing should name the molybdenum electrode grade together with the standard number, the supply condition, dimensional tolerance and surface requirement. Writing only the grade, or only the word molybdenum, invites disagreement when suppliers follow different internal controls.

Incoming verification

Optical emission spectroscopy identifies the matrix elements and the main impurities, which separates the Mo1 and Mo2 purity bands and also detects titanium and zirconium in TZM or lanthanum in Mo-La. Sample by batch and keep a retention sample; the procedure is set out in sampling and judgment at goods-in. Standards for reference are YS/T 1312-2019, ASTM B387 and GB/T 17792 for rod, ASTM B386 and GB/T 3876 for plate, listed on the National Standards Information Public Service Platform and via openstd.samr.gov.cn and ASTM.

Frequently asked questions

Can TZM be used as a glass electrode?

It can, but with little return. TZM strength has limited effect in a glass melt duty, while alloying elements and cost are higher. Consider it only where the electrode also carries significant mechanical load.

Mo-La or TZM, which one fits?

Match the grade to the failure mode. Creep and sagging favor the dispersion strengthening of Mo-La; short-term load and joint deformation favor the strength reserve of TZM. Write the heat-treatment condition into the agreement either way.

How is the delivered molybdenum electrode grade confirmed against the contract?

Three pieces of evidence: the grade and standard number on the mill certificate, the spectroscopy result, and the batch traceability number. When all three agree the grade can be accepted; if one is missing, ask the supplier to explain before releasing the goods.

Summary

A molybdenum electrode grade decision compresses to one line: purity where the part meets the melt, strengthening where it carries load, and cost where it sits. Mo1 covers most glass and fiberglass electrodes, Mo2 carries non-contact structures, and TZM with Mo-La answers high-temperature load and creep. Writing grade, standard and supply condition into the drawing, then sampling at goods-in, closes the loop.