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Metal Oxide Varistor: Zinc Oxide with 0.2 % Bismuth Oxide, 750 °C, 1.0 mm (Masuyama 1972)
A non-linear resistor: the current through it rises far faster than the voltage across it. Masuyama, Matsuoka and Nishi made one from zinc oxide with a little bismuth oxide: pressed into a disc, sintered, lapped, and given metal electrodes. With 0.2 mole % bismuth oxide, sintered at 750 °C and lapped to 1.0 mm, the disc measured a C-value of 200 at 1 mA and a nonlinearity exponent n of 1.8.
Source: T. Masuyama, M. Matsuoka and T. Nishi (Matsushita), US 3,663,458 (1972), Example 1. Unknown: how the aluminium is sprayed on and what the silver paint is. The patent calls both well known, so they are linked to unknown heads. The 10 g batch is our arithmetic. Picture: the patent's drawing.
Advanced
1 day
Instructions
1
1
Weigh 99.8 : 0.2 and wet-mill 5 hours
Weigh 99.8 : 0.2 and wet-mill 5 hours
Mix zinc oxide and bismuth oxide 99.8 : 0.2 by moles. Ours, for 10 g: 9.887 g zinc oxide, 0.113 g bismuth oxide (our arithmetic). Mill wet for 5 hours, then dry. Unknown: the milling liquid.
Materials for this step:
Zinc Oxide Powder9.887 g
Bismuth Oxide0.113 gTools needed:
Balance Scale
Iron Ball Mill
Drying Oven2
2
Press discs 13 mm by 2.5 mm
Press discs 13 mm by 2.5 mm
Press the powder in a mould into discs 13 mm across and 2.5 mm thick at 340 kg/cm².
Tools needed:
Hydraulic Press
Disc Pressing Die
Vernier Caliper3
3
Sinter 1 hour at 750 °C and furnace-cool
Sinter 1 hour at 750 °C and furnace-cool
Sinter the discs in air for 1 hour at 750 °C, then let them cool in the furnace to room temperature (about 15-30 °C). Masuyama gives 800 to 1200 °C as the best range for zinc oxide with bismuth oxide.
Tools needed:
Muffle Furnace4
4
Lap both faces to 1.0 mm
Lap both faces to 1.0 mm
Lap both faces with 600-mesh silicon carbide until the disc is 1.0 mm thick.
Tools needed:
Silicon Carbide GritVernier Caliper5
5
Spray aluminium electrodes and attach leads
Spray aluminium electrodes and attach leads
Spray a metallised film of aluminium on both faces. Attach a lead wire to each with conductive silver paint. Unknown: the spraying method and the paint.
Materials for this step:
Aluminium Ingot1 as required
Silver Conductive Paint1 as required
Copper Wire2 piecesTools needed:
Unknown Metal Spraying MethodVernier CaliperMaterials
5- 9.887 gPlaceholder
- 0.113 gPlaceholder
- 1 as requiredPlaceholder
- 1 as requiredPlaceholder
- 2 piecesPlaceholder
Tools Required
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