Method of making a capacitor by anodizing aluminum foil in a glycerine-phosphate electrolyte without a pre-anodizing hydration step
View Patent ↗A capacitor comprising an aluminum anode and a dielectric layer comprising phosphate doped aluminum oxide and process for making the capacitor. The capacitor has a CV Product of at least 9 μF−V/cm 2 at 250 volts. Furthermore, the capacitor is formed by the process of: forming an aluminum plate; contacting the plate with an anodizing solution comprising glycerine, 0.1 to 1.0%, by weight, water and 0.01 to 0.5%, by weight, orthophosphate; applying a voltage to the aluminum plate and determining an initial current; maintaining the first voltage until a first measured current is no more than 50% of the initial current; increasing the voltage and redetermining the initial current; maintaining the increased voltage until a second measured current is no more than 50% of the redetermined initial current, and continuing the increasing of the voltage and maintaining the increased voltage until a final voltage is achieved.
1. A process for preparing a capacitor comprising:
forming an aluminum plate;
without pre-hydration contacting said plate with an anodizing solution comprising glycerine, 0.1 to about 2.0%, by weight, water and 0.01 to about 0.5%, by weight, soluble orthophosphate;
applying a first voltage to said aluminum plate and determining an initial current;
maintaining said first voltage until a first measured current is no more than 50% of said initial current;
increasing said first voltage to a second voltage and redetermining an initial current at said second voltage;
maintaining said second voltage until a second measured current is no more than about 50% of said redetermined initial current, and
continuing said increasing said voltage and said maintaining said increased voltage until a final voltage is achieved,
wherein said capacitor has a capacitance above 9 μf−V/cm 2 at 250 volts.
2. The process for preparing a capacitor of claim 1 wherein said voltage is increased by no more than about 75 volts.
3. The process for preparing a capacitor of claim 2 wherein said voltage is increased by at least about 20 V to no more than about 50 V.
4. The process for preparing a capacitor of claim 1 wherein said first measured current or said second measured current is from about 1 to about 50% of said initial current.
5. The process for preparing a capacitor of claim 4 wherein said first measured current or said second measured current is from about 10 to about 30% of said initial current.
6. The process for preparing a capacitor of claim 5 wherein said first measured current or said second measured current is about 20% of said initial current.
7. The process for preparing a capacitor of claim 1 wherein said anodizing solution is at a temperature of about 25° C. to about 125° C.
8. The process for preparing a capacitor of claim 7 wherein said anodizing solution is at a temperature of about 80° C. to about 105° C.
9. The process for forming a capacitor of claim 1 wherein said anodizing solution comprises about 0.01 to about 0.1% soluble orthophosphate.
10. The process for forming a capacitor of claim 1 wherein said soluble orthophosphate is selected from a group consisting of ammonium phosphate, alkali metal phosphate, amine phosphate and mixtures thereof.
11. The process for forming a capacitor of claim 1 wherein said soluble orthophosphate is selected from a group consisting of mono-sodium phosphate, di-potassium phosphate, and sodium potassium phosphate.
12. The process for forming a capacitor of claim 1 wherein said soluble orthophosphate is selected from a group consisting of mono-ammonium phosphate and di-ammonium phosphate.