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Metal Oxide Varistor: Zinc Oxide with 0.5 % Titanium Dioxide, Bismuth Oxide Paste Fired On (Masuyama 1972, Ex. 5)
A varistor with bismuth oxide fired on from a paste instead of mixed in: 99.5 % zinc oxide with 0.5 % titanium dioxide by moles, sintered at 1350 °C, coated with bismuth oxide paste and fired at 800 °C. The disc measured a C-value of 15 at 1 mA and a nonlinearity exponent n of 9.3.
Source: T. Masuyama, M. Matsuoka and T. Nishi (Matsushita), US 3,663,458 (1972), Example 5. Unknown: how the aluminium is sprayed on, what the silver paint is, and how strong the epoxy solution of the paste is. The 10 g batch is our arithmetic. Picture: the patent's drawing.
Advanced
2 days
Instructions
1
1
Weigh 99.5 : 0.5 and wet-mill 5 hours
Weigh 99.5 : 0.5 and wet-mill 5 hours
Mix zinc oxide and titanium dioxide 99.5 : 0.5 by moles. Ours, for 10 g: 9.951 g zinc oxide and 0.049 g titanium dioxide (our arithmetic). Mill wet for 5 hours, then dry, as in Example 1. Unknown: the milling liquid.
Materials for this step:
Zinc Oxide Powder9.951 g
Titanium Dioxide0.049 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 discs 13 mm across and 2.5 mm thick at 340 kg/cm², as in Example 1.
Tools needed:
Hydraulic Press
Disc Pressing Die
Vernier Caliper3
3
Sinter 1 hour at 1350 °C and furnace-cool
Sinter 1 hour at 1350 °C and furnace-cool
As in Example 2: sinter in air at 1350 °C for 1 hour and let the discs cool in the furnace.
Tools needed:
Muffle Furnace4
4
Lap both faces
Lap both faces
Lap both faces with silicon carbide abrasive. Example 5 gives no thickness.
Tools needed:
Silicon Carbide GritVernier Caliper5
5
Coat with bismuth oxide paste and fire at 800 °C
Coat with bismuth oxide paste and fire at 800 °C
Coat both lapped faces with a paste of 50 % by weight bismuth oxide in a solution of epoxy resin in butyl alcohol, and fire it in air at 800 °C for 30 minutes. The bismuth oxide diffuses into the zinc oxide. Not given: how much paste, or the strength of the epoxy solution.
Materials for this step:
Bismuth Oxide1 as requiredTools needed:
Epoxy Resin
n-ButanolMuffle Furnace6
6
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, as in Example 1. 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
6- 9.951 gPlaceholder
- 0.049 gPlaceholder
- 1 as requiredPlaceholder
- 1 as requiredPlaceholder
- 1 as requiredPlaceholder
- 2 piecesPlaceholder
Tools Required
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