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Ferrite Toroid Core: Wet-Process Copper-Zinc Ferrite with a Stepped Anneal Down to 310 °C (Snoek 1948)
The wet-process copper-zinc ferrite ring of Snoek's Example II, given a long stepped anneal in oxygen after its 600 °C hold: 19 hours at 510 °C, 34 hours at 410 °C and 12 hours at 310 °C. The initial permeability fell from 500 to 410.
Source: J. L. Snoek, US 2,452,529 (Philips, 1948), Example II, wet process. Picture: our diagram.
Advanced
3 days
Instructions
1
1
Dissolve the copper, zinc and iron salts
Dissolve the copper, zinc and iron salts
Make 1 litre of a purified solution of 0.2 mol copper sulphate, 0.3 mol zinc sulphate and 1 mol iron nitrate. Ours: 49.94 g copper sulphate pentahydrate; weigh the zinc sulphate and ferric nitrate for the hydrate you have.
Materials for this step:
Copper Sulfate Pentahydrate (CuSO₄·5H₂O)49.94 g
Zinc Sulfate0.3 mol
Ferric Nitrate1 mol
Distilled Water1 lTools needed:
Balance Scale
Borosilicate Beaker
Rubber Gloves2
2
Precipitate hot with 9 M caustic soda
Precipitate hot with 9 M caustic soda
Heat the solution and precipitate it with 0.5 litre of 9 molar caustic soda. Ours: 180 g sodium hydroxide in water to 0.5 litre. Strong alkali: goggles and gloves.
Materials for this step:
Sodium Hydroxide - Lab Grade180 gTools needed:
Borosilicate Beaker
Hot Plate
Chemical Splash GogglesRubber Gloves3
3
Wash, dry and pre-heat at 700 °C
Wash, dry and pre-heat at 700 °C
Wash out the deposit, dry it, and pre-heat it at 700 °C so it moulds better.
Tools needed:
Filter PaperDistilled Water
Drying Oven
Tube Furnace
Crucible with Lid (Porcelain)
Heat-Resistant Gloves4
4
Mould a ring at 4 tons per cm²
Mould a ring at 4 tons per cm²
Mould the powder at 4 tons per square centimetre into a ring 3 cm across with a 4 × 4 mm section.
Tools needed:
Hydraulic Press
Ring Pressing Die
Dust Mask5
5
Heat 3 hours at 900 °C, cool to 600 °C, hold 30 hours
Heat 3 hours at 900 °C, cool to 600 °C, hold 30 hours
Heat the ring for about 3 hours at 900 °C, cool it to 600 °C at 5 °C per minute, hold it there for 30 hours and let it cool to room temperature, all in a current of oxygen. Snoek's core: initial permeability 500.
Tools needed:
Tube Furnace
Oxygen
Pressure Gas Cylinder
Pyrometer
Crucible TongsHeat-Resistant Gloves6
6
Anneal 19 h at 510 °C, 34 h at 410 °C, 12 h at 310 °C
Anneal 19 h at 510 °C, 34 h at 410 °C, 12 h at 310 °C
After the 600 °C hold, keep the core for another 19 hours at 510 °C, 34 hours at 410 °C and 12 hours at 310 °C, all in oxygen. Snoek's core: initial permeability 410.
Tools needed:
Tube FurnaceOxygenPressure Gas CylinderPyrometerCrucible TongsHeat-Resistant GlovesMaterials
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