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Ferrite Toroid Core: Copper-Zinc Ferrite by the Wet Process, Precipitated with Caustic Soda (Snoek 1948)
Charlie

Created by

Charlie

28. October 2026DE
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Ferrite Toroid Core: Copper-Zinc Ferrite by the Wet Process, Precipitated with Caustic Soda (Snoek 1948)

Snoek's copper-zinc ferrite made the wet way: copper, zinc and iron salts thrown down together with hot caustic soda, so the particles are very fine and pure. The washed deposit is pre-heated, pressed into a ring and fired in oxygen, with a 30-hour hold at 600 °C. His core reached an initial permeability of 500. Source: J. L. Snoek, US 2,452,529 (Philips, 1948), Example II, wet process. Picture: our diagram.
Advanced
3 days

Instructions

1

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)Copper Sulfate Pentahydrate (CuSO₄·5H₂O)49.94 g
Zinc SulfateZinc Sulfate0.3 mol
Ferric NitrateFerric Nitrate1 mol
Distilled WaterDistilled Water1 l

Tools needed:

Balance ScaleBalance Scale
Borosilicate BeakerBorosilicate Beaker
Rubber GlovesRubber Gloves
2

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 GradeSodium Hydroxide - Lab Grade180 g

Tools needed:

Borosilicate BeakerBorosilicate Beaker
Hot PlateHot Plate
Chemical Splash GogglesChemical Splash Goggles
Rubber GlovesRubber Gloves
3

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 PaperFilter Paper
Distilled WaterDistilled Water
Drying OvenDrying Oven
Tube FurnaceTube Furnace
Crucible with Lid (Porcelain)Crucible with Lid (Porcelain)
Heat-Resistant GlovesHeat-Resistant Gloves
4

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 PressHydraulic Press
Ring Pressing DieRing Pressing Die
Dust MaskDust Mask
5

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 FurnaceTube Furnace
OxygenOxygen
Pressure Gas CylinderPressure Gas Cylinder
PyrometerPyrometer
Crucible TongsCrucible Tongs
Heat-Resistant GlovesHeat-Resistant Gloves

Materials

5

Tools Required

18

This blueprint makes

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Ferrite Toroid Core

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Ferric Nitrate: Scrap Iron Dissolved in Concentrated Nitric Acid (Thorpe 1912)
Hazardous

Ferric Nitrate: Scrap Iron Dissolved in Concentrated Nitric Acid (Thorpe 1912)

by CharlieDE

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