Flake Vanadium Pentoxide: Grades, Properties and Uses

What Flake Vanadium Pentoxide Is

Vanadium pentoxide is the most widely traded vanadium chemical in the world, and the flake form is the physical shape in which a large share of that tonnage moves between producers and consumers. The compound is written V2O5, carries CAS registry number 1314-62-1, and appears as brittle, orange-yellow to dark red-brown platelets with a faint metallic lustre. The word "flake" describes how the material is solidified, not how it is chemically made: molten pentoxide leaving a melting furnace is poured onto a cooled surface, where it freezes rapidly into thin sheets that break into flat, irregular pieces.

Because the same declared chemistry can be delivered as flake, powder or granule, buyers should treat physical form and chemical specification as two independent purchasing variables. Flake is normally chosen where dust generation must be controlled, where material is charged into a furnace, converter or autoclave in bulk, and where a predictable, moderate dissolution rate matters more than instant dispersion. Powder is preferred where fast dissolution, slurry make-up or fine blending with other oxides is the priority. Two lots with identical V2O5 assay but different form can behave very differently in the same process.

Vanadium pentoxide sits at the top of the vanadium oxidation ladder: vanadium is present in the +5 state, which makes the solid a moderately strong oxidiser once it enters acidic solution. That single fact explains most of its industrial value, from steel alloying through sulfuric acid catalysis to redox flow battery electrolyte.

Chemical Identity and Molecular Composition

Formula: V2O5 (vanadium pentoxide, vanadic anhydride)

CAS registry number: 1314-62-1

Molar mass: 181.88 g/mol

Vanadium oxidation state: +5, the highest stable state

Character: amphoteric oxide; reacts with both acids and alkalis in solution

Appearance: orange-yellow to dark red-brown crystalline flake; colour shifts with frit size and cooling rate

The stoichiometry is fixed, so the vanadium delivered in a tonne of pure pentoxide can be calculated rather than estimated. Suppliers and buyers use the same arithmetic when converting between "V2O5 basis" and "V basis" in price comparisons, and getting this conversion wrong is one of the most common sources of commercial misunderstanding.

Element	Atoms per formula unit	Atomic mass (g/mol)	Mass share of V2O5
Vanadium (V)	2	50.94 each	56.03%
Oxygen (O)	5	16.00 each	43.97%
Total V2O5	7	181.88	100.00%

In practice, a 99.0% grade flake contains roughly 55.5% vanadium metal equivalent, while a 98.0% grade contains roughly 54.9%. When a downstream consumer is paid on contained vanadium, the difference between these two grades is a real tonnage difference, not a cosmetic one.

Physical and Thermal Properties

The properties that matter commercially are melting behaviour, density, solubility and oxidation behaviour. Flake pentoxide melts a little below 700 degrees Celsius, which is low enough for it to be fed directly into an electric arc furnace or an aluminothermic reaction vessel where it dissolves into the slag and provides vanadium to the metal bath.

Property	Typical value	Why it matters to a buyer
Molar mass	181.88 g/mol	Converts V2O5 assay into contained vanadium
Melting point	About 690 degrees C	Allows direct charging into molten metallurgical processes
Thermal behaviour at high temperature	Decomposes near 1750 degrees C with oxygen release	Volatilisation and fume losses in high-temperature furnaces
True density	Approximately 3.3 to 3.4 g/cm3	Slag and bath calculations
Bulk density of flake	Roughly 1.1 to 1.6 g/cm3 depending on frit size	Warehouse volume and bag payload planning
Solubility in water	Sparingly soluble, on the order of 1 g/L at 20 degrees C	Leaching, rinsing and effluent load
Solubility in acids and alkalis	Readily soluble in both	Wet chemical processing, electrolyte preparation
Oxidising behaviour	Oxidises organic matter and reduces to lower vanadium oxides	Incompatibility with combustible materials

The low water solubility is often overlooked. It means that spilled flake is not simply washed away by rain, and that dissolution for process use normally requires acid, alkali or elevated temperature rather than plain water at ambient conditions.

Typical Specification and Impurity Control

Commercial flake vanadium pentoxide is bought against a declared minimum V2O5 content together with maxima for the impurities that interfere with the intended use. Vanadium pentoxide for ferroalloy production tolerates more iron, silicon and alkali than pentoxide destined for catalysis or battery electrolyte, where trace arsenic, sulfur, sodium and potassium dominate the acceptance decision. GB/T 3283 is the widely referenced specification framework for vanadium pentoxide grades, and the exact declared limits for any contract must be read from the certificate of analysis issued against the ordered grade.

Parameter (dry basis)	98.0% grade	99.0% grade	99.5% grade
V2O5, minimum	98.0%	99.0%	99.5%
Vanadium equivalent, minimum	About 54.9%	About 55.5%	About 55.7%
Iron, maximum	0.30%	0.15%	0.05%
Silicon, maximum	0.20%	0.10%	0.05%
Sodium and potassium oxides, maximum	1.00%	0.50%	0.25%
Sulfur, maximum	0.05%	0.03%	0.02%
Phosphorus, maximum	0.03%	0.02%	0.01%
Arsenic, maximum	0.02%	0.010%	0.005%
Loss on ignition, typical	Below 1.0%	Below 0.5%	Below 0.3%

These are typical commercial bands rather than a substitute for the contracted grade sheet. Two further points deserve attention. First, loss on ignition is a quick indicator of hydration and residual ammonium salt; a high value usually points to incomplete calcination in the producer's conversion step. Second, alkali content is a leading indicator of the process route: material made by sodium salt roasting and water leaching tends to run higher in sodium unless the producer operates an effective ammonium metavanadate purification stage.

How V2O5 Flakes Are Produced

Almost all flake vanadium pentoxide is made by a conversion chain that begins with a vanadium-bearing feed and ends with a melting and casting step. The dominant feedstock worldwide is vanadium slag generated when vanadium-titanium magnetite is smelted for steel and the vanadium is deliberately oxidised into a separate slag phase. Vanadium-bearing stone coal and spent industrial catalysts are the other significant sources.

Roasting: the vanadium-bearing feed is roasted with a sodium salt such as sodium carbonate or sodium chloride, converting vanadium into water-soluble sodium vanadate.

Leaching and purification: the calcine is leached with water, and the pregnant liquor is purified to remove silicon, phosphorus and iron before vanadium is precipitated as ammonium metavanadate or a similar intermediate.

Calcination: the intermediate is calcined to drive off ammonia and water and to oxidise vanadium to the pentoxide.

Melting and casting: the dried pentoxide is melted in a furnace and cast onto a cooled plate or drum; the thin solidified sheet fractures into flake.

Sizing and packing: flake is screened to a nominal size band and packed, typically in lined drums, with sampling per the applicable ferrosilicon and ferroalloy sampling practice such as GB/T 4010 and ISO 3713.

Some producers bypass melting and deliver powder or technical granule directly from calcination. The chemistry can be equivalent, but the thermal history differs, and that is why a change of form in a supply contract is a technical change and not merely a packaging change.

Flake, Powder and Granule: Choosing the Right Form

Form selection follows the feed system of the plant that will consume the material.

Form	Typical size	Dust behaviour	Preferred use
Flake	Mostly 10 to 50 mm platelets	Low airborne dust	Furnace and converter charging, bulk metallurgical use
Granule	Roughly 1 to 10 mm	Moderate	Blending, continuous feed systems
Powder	Below 1 mm, often much finer	High, needs extraction	Catalyst manufacture, dissolution, electrolyte make-up

Flake dissolves more slowly than powder at the same temperature, which is an advantage when a controlled release of vanadium into a melt or a leaching circuit is wanted, and a disadvantage when a batch must be brought into solution quickly.

Metallurgical Applications

Steelmaking remains the largest outlet. Vanadium is added to steel as a microalloying element because vanadium carbonitride precipitates during hot rolling and cooling, raising yield strength and improving toughness without a heavy alloy addition. The pentoxide itself is not added to the steel bath directly; it is first reduced to an iron-vanadium master alloy.

Ferrovanadium: the classic route is aluminothermic reduction of V2O5 with aluminium, in the presence of iron, producing FeV50 (nominally 50% V grade) and FeV80 (nominally 80% V grade). Typical commercial ranges are 48 to 55% V for the 50 grade and 75 to 85% V for the 80 grade, with silicon, aluminium and carbon maxima set by GB/T 4139. Ferrovanadium is used for high-strength low-alloy steels, forging steels, tool steels and rails.

Vanadium-nitrogen alloy: a briquetted or sintered V-N product covered by GB/T 20567, typically carrying about 77 to 82% vanadium and 12 to 16% nitrogen. The nitrogen it introduces allows lower vanadium addition for a given strength target, which is why it is widely used in high-strength rebar and structural sections.

Titanium alloys: vanadium is a strong beta stabiliser, and the classic Ti-6Al-4V chemistry is normally introduced through a vanadium-aluminium master alloy made from pentoxide, not from the oxide itself.

In all three cases the acceptance logic is the same: contained vanadium, recovery in the melt, and impurity penalties, especially phosphorus and sulfur, which must be tightly limited in rail and forging grades.

Chemical and Energy Applications

Outside metallurgy, flake pentoxide serves two very different, specification-critical markets.

Catalysis: vanadium pentoxide is the active phase in the contact catalyst used for oxidising sulfur dioxide to sulfur trioxide in sulfuric acid plants, and in selective catalytic reduction catalysts used for nitrogen oxide abatement. Catalyst makers require low arsenic, low alkali and controlled surface area, and they usually receive vanadium in solution rather than as flake. Impurity limits at the 0.005% arsenic level are normal in this segment because alkaline metals and arsenic act as catalyst poisons.

Redox flow battery electrolyte: vanadium sulfate electrolytes for all-vanadium redox flow batteries are made from dissolved pentoxide, and the electrolyte specs demand very low levels of silicon, aluminium and other species that can precipitate and foul membranes. Purity here drives the selection of the 99.5% grade.

Other uses include glass and ceramic colouring, vanadium chemical intermediates such as ammonium metavanadate and vanadium oxalate, and specialty alloy additions.

Sampling, Testing and Acceptance

Vanadium pentoxide is a high-value material, so dispute resolution almost always turns on sampling and analytical method rather than on the nominal specification. The practical sequence below reflects common ferroalloy and oxide practice.

Mass and moisture: weigh and record gross, tare and net weight before sampling; moisture content determines whether the two parties are quoting a wet or dry basis.

Increment sampling: take increments from multiple positions in the lot in accordance with the applicable sampling standard for ferroalloys and their raw materials, such as GB/T 4010 and ISO 3713, then reduce to a laboratory sample.

Sample splitting: retain a sealed, labelled reserve sample for both parties; this is the single most cost-effective dispute control measure in vanadium trade.

Analysis: assay V2O5 by the titrimetric or instrumental methods referenced in the vanadium pentoxide specification, and determine impurities by inductively coupled plasma or atomic absorption techniques.

Size check: verify the flake size band by sieve analysis against the agreed nominal range.

A certificate of analysis that names the analytical method is worth considerably more than one that only quotes final numbers, because method differences explain most small disagreements between buyer and seller laboratories.

Packaging, Storage, Transport and Safety

Flake pentoxide is a toxic solid and an oxidiser, and both facts shape how it must be packed and stored.

Packaging: steel drums or heavy-duty bags with a sealed inner liner are standard; net weights of 25 kg, 50 kg and 200 to 250 kg are common. Ferroalloy packaging practice such as GB/T 3650 is a useful reference for marking retention, lot identification and handling instructions.

Storage: keep the material dry and under cover. Vanadium pentoxide is hygroscopic enough to take up moisture, and wet material both changes weight basis and increases corrosion of carbon steel equipment.

Segregation: store away from acids, alkalis, reducing agents, combustible and organic materials, and fine metal powders. Oxidiser plus fuel is the classic incompatibility.

Breathing protection: occupational limits for vanadium pentoxide dust are very low, typically around 0.05 mg/m3 of respirable dust. Local exhaust ventilation, dust-tight handling, protective clothing, eye protection and respiratory protection during cleaning operations are standard controls, together with washing facilities at the end of a shift.

Spills and waste: collect spilled material dry where possible, place it in labelled containers, and treat contaminated water as industrial effluent rather than discharging it.

Because vanadium pentoxide is a classified toxic substance in most jurisdictions, shipments normally travel with the appropriate hazard documentation. The documentation set, hazard class and labelling applied to a specific consignment should be confirmed against the regulations in force in the country of dispatch and destination at the time of shipment.

Common Misconceptions

"Flake and powder are the same product." The declared chemistry may be identical, but form changes dust behaviour, dissolution rate, bulk density and handling risk. Treat a form change as a technical change.

"Higher V2O5 always means better." A 99.5% grade is not automatically the right purchase. For ferrovanadium production, a well-run 98% grade with low phosphorus and sulfur may be the more economical and metallurgically cleaner choice.

"Vanadium pentoxide dissolves freely in water." It is only sparingly soluble in water; acid, alkali or heat is normally required to bring it into solution.

"Colour tells you the grade." Frit size, cooling rate and light scatter change the apparent colour considerably; only analysis establishes purity.

"Loss on ignition is irrelevant." Loss on ignition indicates residual ammonium salt and hydration, both of which reduce the vanadium actually delivered per tonne paid for.

FAQ

Q: What is the chemical formula and molar mass of flake vanadium pentoxide?
The formula is V2O5 with a molar mass of 181.88 g/mol, containing 56.03% vanadium and 43.97% oxygen by mass.

Q: Which purity grades of vanadium pentoxide flake are commonly traded?
Commercial material is normally bought at 98.0%, 99.0% and 99.5% minimum V2O5, with the higher grades used for catalysts and redox flow battery electrolyte and the lower grade used for vanadium master alloys.

Q: How is flake vanadium pentoxide made?
A vanadium-bearing feed such as vanadium slag is roasted with a sodium salt, leached, purified, precipitated as an ammonium vanadate intermediate, calcined to the pentoxide, melted, and cast onto a cooled surface where the solidified sheet breaks into flake.

Q: What is the melting point of vanadium pentoxide flake and why does it matter?
It melts at about 690 degrees C, low enough that flake can be charged directly into metallurgical furnaces and aluminothermic reduction vessels where it is reduced to ferrovanadium.

Q: How should vanadium pentoxide flake be stored and handled?
Keep it dry and under cover in sealed lined drums or bags, segregate it from acids, alkalis, reducing agents and combustible materials, and control dust with local exhaust ventilation and respiratory protection because occupational exposure limits for vanadium pentoxide are low, typically about 0.05 mg/m3 respirable dust.

Q: How is vanadium pentoxide content checked on receipt?
Weight and moisture are recorded first, increments are drawn from across the lot following ferroalloy sampling practice such as GB/T 4010 and ISO 3713, a reserve sample is sealed for each party, and the laboratory then assays V2O5 and impurity elements by the methods referenced in the applicable vanadium pentoxide specification.