Analysis of Kitchen Aluminum Foil (2021)

Author: Dernocua (Kragen Javier Sitaker) | Date: 2021-05-24 (Updated 2021-09-11) | Read Time: $\approx 14$ minutes

Kitchen aluminum foil is a remarkably versatile and surprising material.

📐 Physical Dimensions and Properties

Standard kitchen foil is characterized by extreme aspect ratios. Typically, it is 10 μm thick and 400 mm wide, creating a dimensional ratio of $40,000:1$. When considering a standard ten-meter roll, the aspect ratio reaches a staggering $1,000,000:1$.

Material Specifications

🛠️ Metallurgical Characteristics

The foil is provided in a fully annealed state, meaning it is soft but work-hardens rapidly upon bending. This property, combined with its thinness, allows for the creation of metamaterials via deep submillimeter bends.

Chemical Composition & Alloys

Common alloys used in production include:

• 1100 & 1200: Often called "unalloyed" (1100 actually contains $0.05\% \text{--} 0.20\%$ copper and other impurities).
• 8111, 8015, and 8006.

Typical additive ranges:

• Silicon: $0.06\% \text{--} 0.6\%$
• Iron: $0.4\% \text{--} 1.6\%$
• Copper/Manganese: $< 0.5\%$

Mechanical Strength

The material exhibits the following properties:

• Young’s Modulus: $\approx 70\ \text{GPa}$
• Yield Strength: $30\text{--}170\ \text{MPa}$
• Ultimate Tensile Strength: $70\text{--}200\ \text{MPa}$

🌡️ Thermal and Chemical Behavior

Because aluminum possesses a face-centered cubic (fcc) crystal structure, it remains ductile even at absolute zero. In fact, its strength increases at cryogenic temperatures. While it loses strength as heat increases, it maintains structural integrity up to its melting point of approximately $650^\circ\text{C}$.

Oxidation and Energy

When oxidized (via anodization, electrical arcs, or soda solutions), it forms amorphous sapphire. If this is crystallized, it becomes a high-grade abrasive, refractory, or insulator.

The oxidation process is highly exothermic, making aluminum a high-energy-density fuel. This is utilized in amateur fuel cells, which typically oxidize aluminum into chloride rather than oxide or hydroxide.

☀️ Economic Application: Solar Concentration

Aluminum foil is an incredibly cheap alternative to traditional solar technology.

• Foil Cost: $50\text{¢}/\text{m}^2 \approx 0.05\text{¢}/\text{W}_p$ (as a solar concentrator).
• PV Cell Cost: $\approx 18\text{¢}/\text{W}_p$.
• Comparison: PV cells are roughly 360 times more expensive.

Note: If used for a PV concentrator with $21\%$ efficiency, the cost is $\approx 0.24\text{¢}/\text{W}_p$ electric.

Structural Stability

Large foil arrays are prone to deflection. To mitigate this, one can:

1. Mount small assemblies on stable surfaces (e.g., adobe walls or rocks).
2. Create a "corrugated cardboard" structure using the foil.
3. Use borax or aqueous boric acid (approx. \1.70/\text{kg}$) as an adhesive.
4. Leverage the surface tension of water to hold the foil in place during drying.

🔬 Experimental Work-Hardening

The author explored the possibility of using work-hardened aluminum foil as a tooling material to manipulate other pieces of foil.

Constructing a Foil Tool

To create a piercing cone:

• Fold foil to 16 layers thick.
• Form ribs that converge at a single point on the final fold.
• Roll the foil into a cone around that point.
• Reverse the final fold to ensure the outer edge (the most strained part) is the hardest.

Empirical Results

The author successfully used this cone to pierce an apple skin. The tool was constructed from a square of foil folded 256 layers thick.

Measurement Data:

Thickness: 2.57 mm
Dimensions: 27-29 mm per side
Mass: 1.8 g
Calculated Density: 0.8-1.0 g/cc (indicates >50% air)
Behavior: Sinks in water

Single-Point Incremental Forming (SPIF)

Using the cone to create ribs without tearing is difficult due to tip asperities. Two solutions were identified:

1. Smoothing: Remove asperities to allow the point to slide.
2. Chain-Drilling Method: Create a sequence of individual dents and then fill the gaps to form a continuous groove.

Observation: Tearing is minimized when the "workpiece" foil is backed by a hard surface, such as corrugated cardboard or a 256-layer foil square. These work-hardened ribs can then be used to imprint shapes onto annealed foil.

Final Achievement: The author successfully wrote a word in cursive on aluminum foil using a layered foil point.