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Metal Oxide Varistor: Pure Zinc Oxide, Bismuth-Manganese Oxide Paste Fired On (Masuyama 1972, Ex. 7)
A varistor whose bismuth oxide and manganese dioxide are both fired on from a paste: pure zinc oxide, sintered at 1350 °C, coated with a 70 : 30 bismuth oxide and manganese dioxide paste and fired at 800 °C. The disc measured a C-value of 200 at 1 mA and a nonlinearity exponent n of 12.7.
Source: T. Masuyama, M. Matsuoka and T. Nishi (Matsushita), US 3,663,458 (1972), Example 7. 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 zinc oxide and wet-mill 5 hours
Weigh zinc oxide and wet-mill 5 hours
Take pure zinc oxide (Table 9: 100 mole %). Mill wet for 5 hours, then dry, as in Example 1. Unknown: the milling liquid.
Materials for this step:
Zinc Oxide Powder10 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
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 7 gives no thickness.
Tools needed:
Silicon Carbide GritVernier Caliper5
5
Coat with bismuth and manganese oxide paste, fire at 800 °C
Coat with bismuth and manganese oxide paste, fire at 800 °C
Coat both lapped faces with a paste whose solids are 70 % bismuth oxide and 30 % manganese dioxide by weight, and fire it in air at 800 °C for 30 minutes. Example 7 does not name the paste's liquid; ours: the epoxy-resin butyl-alcohol solution of Example 4. Not given: how much paste.
Materials for this step:
Bismuth Oxide1 as required
Manganese Dioxide (Pyrolusite)1 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
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Tools Required
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