Catamold 4605 is a Ni-Mo-alloyed low-alloy steel powder used in the Metal Injection Molding (MIM) process. The binder in this material is generally a polyacetal (POM)-based organic binder. During the debinding stage, nitric acid (HNO₃) vapor is used as a catalyst to decompose and remove the binder.
Nitric acid (HNO₃) is a volatile liquid even at room temperature.
Boiling point: ≈ 83 °C
Therefore, at around 80 °C, dense HNO₃ vapor begins to be released.
But here is the key point:
In the catalytic debinding furnaces used in MIM, nitric acid vapor is generally applied at temperatures of 120–160 °C.
Because in this temperature range, the polyacetal (POM) binder decomposes rapidly under acid catalysis and turns into formaldehyde / methanal (CH₂O) gas.
Chemical Reactions
1. Acid-catalyzed chain scission of the POM (polyacetal) structure:
(-CH₂-O-)_n → nCH₂O (formaldehyde / methanal)
2. Decomposition of formaldehyde / methanal with oxygen and temperature:
2HCHO + O₂ → 2HCOOH
HCOOH → CO + H₂O
HCOOH → CO₂ + H₂
3. By-products: CH₂O, CO, CO₂, H₂, H₂O
4. Oxides that can form on the metal surface: Fe₂O₃, Fe₃O₄, NiO
5. Reduction in a hydrogen atmosphere before sintering:
Fe₂O₃ + 3H₂ → 2Fe + 3H₂O
Chemical Properties of the Polyacetal (POM) in Catamold 4605
Catamold 4605 is a Ni-Mo-alloyed steel powder used in the MIM (Metal Injection Molding) process. The polyacetal (POM) binder in this steel powder holds the metal powders together during molding. The chemical and physical properties, reactivity and behavior of POM during debinding are given in detail below.
1. Basic Structure
- Chemical formula: [-CH₂-O-]_n
- Structure type: Linear polymer, repeating methylene oxide (–CH₂–O–) units
- Molecular weight: Typically 50,000–100,000 g/mol
2. Physical Properties
- Appearance: White, hard and waxy solid
- Density: ~1.41 g/cm³
- Melting point: 175–180 °C (crystalline regions)
- Glass transition temperature (Tg): ~-60 °C
- Thermal stability: Stable up to 200 °C; thermal decomposition begins above 200–220 °C.
3. Chemical Reactivity
- Acids / Bases: Resistant to most organic and inorganic acids and bases, but can depolymerize with strong oxidizing acids.
- Oxidation: Begins to oxidize with air above 200–220 °C.
- Catalytic decomposition: In an oxidizing environment such as nitric acid vapor, chain scission occurs and formaldehyde (CH₂O) and CO/CO₂ gases are released.
- Solubility: Insoluble in most organic solvents; limited solubility in polar aprotic solvents.
4. Mechanical Properties
- Hard and durable, low coefficient of friction
- High surface hardness and good dimensional stability
5. Properties Relevant to Debinding
- Acid-catalyzed depolymerization: HNO₃ or acid vapor breaks the chains → CH₂O and other gases are released.
- Temperature control is critical: At too high a temperature, excessive carbon residue or deformation of the part can occur.
Summary
The POM binder in Catamold 4605 is a polymer that is thermally hard, chemically inert in most environments, but can be decomposed by strong oxidizers. During debinding, chain scission is carried out with nitric acid vapor, exposing the metal powders and forming the brown part.
Why Does the Brown Part Form?
After the debinding process, the part is called the 'brown part'. The reason is that during binder removal the part becomes porous and a brownish color forms on the surface due to carbon and oxide residues.
References
1. Texas A&M University. (2022). Overview of Debinding Methods for Parts Manufactured Using Powder Material Extrusion. College Station, TX.
2. BASF AG. (2019). Catamold 4605 Technical Data Sheet. BASF Metal Systems Division, Germany.
3. Billmeyer, F. W. (1984). Textbook of Polymer Science (3rd ed.). Wiley.
4. Buchkremer, R. et al. (1998). Catalytic Debinding and Sintering of MIM Components. Journal of Materials Processing Technology, 77, 84-89.
5. German, R. M. (1990). Powder Injection Molding. Metal Powder Industries Federation.
6. Atkins, P., & Jones, L. (2013). Chemical Principles: The Quest for Insight (6th ed.). Freeman.
7. Reed-Hill, R. E., & Abbaschian, R. (1992). Physical Metallurgy Principles. PWS-Kent.