Unlocking the Power of Molybdenum: Applications, Benefits, and Future Prospects

Introduction

Molybdenum, atomic number 42, is a transition metal. It is the second member of Group 6 of the Periodic Table, between chromium and tungsten.

It has one of the highest melting temperatures of all the elements, yet unlike most other high-melting-point metals, its density is only 25% greater than iron’s. Its coefficient of thermal expansion is the lowest of the engineering materials, while its thermal conductivity exceeds that of all but a handful of elements.

Molybdenum properties

Atomic number	42
Atomic weight	95.96
Crystal structure	Body-centered cubic (BCC)
Lattice constant	a = 3.1470 Å
Density	10.22 g/cm3
Melting temperature	2623°C
Coefficient of thermal expansion	4.8 x 10-6 / K at 25°C
Thermal conductivity	138 W/m K at 20°C

Molybdenum metal and molybdenum-based alloys have a unique combination of properties, including:

• High strength at elevated temperatures
• High thermal and electrical conductivity
• Low thermal expansion

Molybdenum metal and its alloys are the first choice in many demanding specialized applications in electronics, heat treatment, and metal processing.

Nickel-based alloys

Molybdenum is an essential alloying element in high-performance nickel-based alloys. These alloys fall into two basic classes:

• Corrosion-resistant alloys
• High-temperature alloys. The high-temperature alloys can be further subdivided into two categories:

1. solid-solution strengthened
2. age-hardenable

Tables 1 and 2 provide the nominal compositions in weight percent of some commercially essential alloys of each type.

Corrosion-resistant nickel-based alloys

Alloy	UNS No	EN No	Ni	Cr	Fe	Mo	W	C	Cu
B-3®	N10675	2.46	65**	1.5	1.5	28.5	3*	0.01*	0.2*
C-276	N10276	2.4819	57	16	5	16	4	0.01*	0.5*
C-22®	N06022	2.4602	56	22	3	13	3	0.01*	0.5*
C-2000®	N06200	2.4675	59	23	3*	16	–	0.01*	1.6
G-30®	N06030	2.4603	43	30	15	5.5	2.5	0.03*	2
G-35®	N06035	2.4643	58	33.2	2*	8.1	0.6*	0.05*	0.3*
* Maximum ** Minimum

Table 1: Nominal compositions of some corrosion-resistant nickel-based alloys

High-temperature alloys

Alloy	UNS No	EN No	Ni	Co	Fe	Cr	Mo	W	Al	Ti	C
Solid-Solution Strengthened
X	N06002	2.4665	47	1.5	18	22	9	0.6	0.5*	0.15*	0.1
S	N06635	–	67	2*	3*	16	15	1*	0.25	–	0.02*
625	N06625	2.4856	62	1*	5*	21	9	–	0.4*	0.4*	0.10*
617	N06617	2.4663	54	12.5	1	22	9	–	1.2	0.3	0.07
230®	N06230	2.4733	57	5*	3*	22	2	14	0.5*	0.1*	0.1
Age-Hardenable
718	N07718	2.4668	52	1*	19	18	3	–	0.5	0.9	0.05
263	N07263	2.465	52	20	0.7*	20	6	–	0.6*	2.4*	0.06
282®	–	–	57	10	1.5*	20	8.5	–	1.5	2.1	0.06
Waspaloy	N07001	2.4654	58	13.5	2*	19	4.3	–	1.5	3	0.08
R-41	N07041	2.4973	52	11	5*	19	10	–	1.5	3.1	0.09
242®™	N10242	–	65	1*	2*	8	25	–	0.5*	–	0.03*
* Maximum

Table 2: Nominal compositions of some high-temperature alloys

Molybdenum Applications

In corrosion-resistant nickel-based alloys, molybdenum imparts resistance to nonoxidizing environments such as halide acids (HCl, HBr, and HF) and sulfuric acid, for example. Accordingly, the alloy most resistant to these environments is the B-3 alloy, which contains 28.5% Mo. Molybdenum also acts with chromium to resist localized corrosion attacks such as pitting and crevice. Alloys such as C-22 and C-2000 are particularly resistant to this attack.
The corrosion-resistant nickel-based alloys are found to be extensively used in the chemical processing, pharmaceutical, oil & gas, petrochemical, and pollution control industries, in which highly corrosive environments are ubiquitous.

In high-temperature alloys, molybdenum additions enhance resistance to damage caused by high-temperature creep. For solid-solution strengthened alloys, the slow diffusion of molybdenum in nickel provides an advantage. Since diffusion typically controls high-temperature creep, adding molybdenum effectively reduces creep rates. In the age-hardenable alloys that utilize the precipitation of gamma-prime, Ni 3(Al, Ti), molybdenum additions strengthen the matrix and reduce the lattice mismatch between the matrix and the gamma-prime particles, thereby improving the stability of the sediments. The effect of molybdenum in 242 alloys is unique. Its specific combination of molybdenum and chromium promotes the formation of long-range ordered Ni 2(Mo, Cr)-type particles, which impart significant strength without significantly reducing ductility. Molybdenum additions are also very effective in reducing the coefficient of thermal expansion.

High-temperature alloys such as S and 242, which contain large amounts of molybdenum, are used as seal rings in gas turbine engines to exploit this effect. Engineers extensively use high-temperature alloys in gas turbine engines to manufacture components such as turbine disks, combustors, transition ducts, turbine cases, seal rings, afterburner parts, and thrust reversers. They also apply these alloys in industrial heating, heat treatment, mineral processing, heat exchangers, and waste incineration.

Conclusion

Molybdenum’s versatile properties make it indispensable across various industries, from manufacturing to energy. Its unique combination of strength, corrosion resistance, and heat tolerance positions it as a critical material for the future, particularly in the face of emerging technological advancements. As demand grows, innovations in molybdenum’s applications are expected to expand further, reinforcing its importance in modern infrastructure and sustainable development. For more insights on molybdenum’s potential, please get in touch with Golden Sunbird Metals at [email protected].