Ceramic, graded resistivity monolith using the ceramic, and method of making

1. A monolithic cassette comprising:

a first end having a first electrical resistivity;

a second end having a second electrical resistivity, wherein the second electrical resistivity is higher than the first electrical resistivity; and

a continuous grain structure between the first end and the second end; wherein electrical resistivity of the monolithic cassette is graded such that the resistance varies continuously from the first end to the second end.

2. The monolithic cassette of claim 1 , wherein the electrical resistivity is graded by up to 12 orders of magnitude between the first end and the second end.

3. The monolithic cassette of claim 1 , wherein the electrical resistivity is graded by at least 12 orders of magnitude between the first end and the second end.

4. The monolithic cassette of claim 1 , wherein the electrical resistivity is graded from 1 micro ohm meter to 1 mega ohm meter.

5. The monolithic cassette of claim 1 further comprising:

a ceramic composition and a conductive composition; wherein weight ratio of the ceramic composition to the conductive composition is graded between the first end and the second end.

6. The monolithic cassette of claim 5 , wherein the ceramic composition comprises zinc oxide, aluminum oxide, aluminum nitride, boron nitride, silicon dioxide, indium tin oxide, or combinations thereof.

7. The monolithic cassette of claim 5 , wherein the ceramic composition comprises 99.5 to 99.7 percent zinc oxide, and 0.3 to 0.5 percent aluminum oxide.

8. The monolithic cassette of claim 5 , wherein the conductive composition comprises silver, copper, gold, aluminum, indium, tin, gallium, nickel, titanium, zinc, lead, carbon, iron, tungsten, molybdenum, or combinations thereof.

9. The monolithic cassette of claim 5 , wherein each of the plurality of layers comprises:

45 to 58 percent by weight of the ceramic composition; and

42 to 55 percent by weight of silver.

10. The monolithic cassette of claim 5 , wherein percentage weight of silver is graded along the length of the monolith cassette.

11. The monolithic cassette of claim 1 , wherein the monolithic cassette exhibits at least one of the following properties:

Mohs harndess greater than 3;

root mean squared roughness less than 100 micron;

thermal stability greater than 300 degree Celsius; and

mechanical stability greater than 150 mega pascal.

12. A method of forming a monolithic cassette, the method comprising:

introducing a plurality of resistive powders into a die to form a stack of layers; wherein the plurality of resistive powders comprise a ceramic composition and a conductive composition, and wherein each layer comprises a distinct weight ratio of the ceramic composition and the conductive composition;

compacting the plurality of resistive powders into a green cassette at a pressure of 10 mega pascal and at ambient temperature; and

sintering the green cassette at a temperature below 925 degree Celsius for a duration of upto 24 hours.

13. The method of claim 12 , wherein introducing the plurality of resistive powders into a die further comprises:

introducing a first of the plurality of resistive powders into the die;

settling the first of the plurality of resistive powders to form a first layer of substantially uniform thickness; and

repeating the introducing and settling for each of the plurality of resistive powders to form successive layers of the stack.

14. The method of claim 12 , wherein:

the ceramic composition comprises zinc oxide, aluminum oxide, or combinations thereof;

the conductive composition comprises silver;

the compacting is performed at a pressure between 10 mega pascal and 60 mega pascal; and

the sintering is performed at a temperature between 850 degree Celsius and 950 degree Celsius in an atmosphere of air for a duration of 22 to 26 hours; wherein rate of change of temperature for sintering is between 1.5 and 2.5 degree Celsius per minute.

15. The method of claim 14 , wherein the ceramic composition comprises a substantially homogenous mixture of 99.5 to 99.7 percent zinc oxide powder, and 0.3 to 0.5 percent aluminum oxide powder.

16. The method of claim 14 , wherein each of the plurality of resistive powders comprises:

45 to 58 percent by weight of the ceramic composition; and

42 to 55 percent by weight of silver.