Methods of forming silicon carbide by spark plasma sintering
A method of forming silicon carbide by spark plasma sintering comprises loading a powder comprising silicon carbide into a die and exposing the powder to a pulsed current to heat the powder at a rate of between about 50° C./min and about 200° C./min to a peak temperature while applying a pressure to the powder. The powder is exposed to the peak temperature for between about 30 seconds and about 5 minutes to form a sintered silicon carbide material and the sintered silicon carbide material is cooled. Related structures and methods are disclosed.
1. A method of forming silicon carbide by spark plasma sintering, the method comprising:
loading a powder comprising silicon carbide into a die;
exposing the powder to a current to heat the powder at a rate of between about 50° C./min and about 200° C./min to a peak temperature while applying a pressure to the powder;
while the powder is exposed to the peak temperature, exposing the powder to a current density less than about 0.1 A/mm 2 for between about 30 seconds and about 5 minutes to form a sintered silicon carbide structure; and
cooling the sintered silicon carbide structure.
2. The method of claim 1 , further comprising, after cooling the sintered carbide structure, exposing the sintered silicon carbide structure to the peak temperature again to increase a density of the sintered silicon carbide structure.
3. The method of claim 1 , further comprising selecting the powder to comprise silicon carbide and a sintering aid.
4. The method of claim 3 , further comprising selecting the sintering aid to comprise boron carbide.
5. The method of claim 1 , further comprising selecting the powder such that silicon carbide constitutes at least about 98 weight percent of the powder.
6. The method of claim 1 , wherein cooling the sintered silicon carbide structure comprises cooling the sintered silicon carbide structure at a rate between about 100° C./min and about 500° C./min.
7. The method of claim 1 , further comprising selecting the peak temperature to be between about 2,000° C. and about 2,100° C.
8. The method of claim 1 , further comprising exposing the powder to the peak temperature for about 2 minutes.
9. The method of claim 1 , wherein forming a sintered silicon carbide structure comprises forming the sintered silicon carbide structure to have a density of at least about 3.178 g/cm 3 .
10. The method of claim 1 , wherein exposing the powder to a current to heat the powder at a rate of between about 50° C./min and about 200° C./min to a peak temperature comprises exposing the powder to a current density of about 0.1 A/mm 2 .
11. The method of claim 1 , further comprising selecting the die to comprise at least one tapered sidewall.
12. The method of claim 11 , further comprising selecting the taper to comprise about a 1° taper.
13. The method of claim 1 , further comprising selecting the die to comprise graphite exhibiting a coefficient of thermal expansion equal to about a coefficient of thermal expansion of the sintered silicon carbide structure between a temperature of about 1,950° C. and about 2,100° C.
14. The method of claim 1 , wherein forming a sintered silicon carbide structure comprises forming a silicon carbide structure having a density of about 3.21 g/cm 3 .
15. The method of claim 1 , wherein providing a silicon carbide powder into the die comprises providing the silicon carbide powder into the die substantially free of a lubricant.
16. The method of claim 1 , further comprising selecting the die to comprise isotropic graphite.
17. The method of claim 1 , wherein exposing the powder to a current comprises pulsing a direct current through the powder in cycles, each cycle comprising pulsing the direct current for about 12 milliseconds followed by applying substantially no current for about 6 milliseconds.
18. The method of claim 1 , further comprising, after cooling the sintered carbide structure, exposing the sintered silicon carbide structure to the peak temperature again to increase a density of the sintered silicon carbide structure by at least about 0.1 g/cm 3 .