Machinable ceramic

1. A machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–60 mass % of hexagonal boron nitride, 40–70 mass % of zirconia, and 0–20 mass % of silicon nitride, the ceramic having a strength of 240 MPa.

2. A machinable ceramic as claimed in claim 1 having a coefficient of thennal expansion of 3–5×10 −6 /° C. in the temperature range of 25–600° C.

3. A method of manufacturing a machinable ceramic comprising the steps of mixing a main constituent raw material powder which comprises 30–60 mass % of hexagonal boron nitride and 40–70 mass % of zirconia with a sintering aid in an amount of 1–15 mass % based on the main constituent raw material powder to obtain a raw material powder, and

sintering the raw material powder at a high temperature under pressure to obtain a sintered body.

4. A method as claimed in claim 3 wherein the main constituent raw material powder further comprises 0–20 mass % of silicon nitride.

5. A method of manufacturing a machinable ceramic as claimed in claim 4 wherein the zirconia has an average particle diameter of less than 1 micrometer.

6. A probe guide made of a machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–60 mass % of boron nitride, 40–70 mass % of zirconia, and 0–20 mass % of silicon nitride, the probe guide having a plurality of minute vacancies made by machining and having a form selected from slits and holes through which probes can pass.

7. A machinable ceramic as claimed in claim 1 , wherein the main constituent comprises 30–59.95 mass % of boron nitride, 40–69.95 mass % of zirconia, and 0–20 mass % of silicon nitride and wherein the ceramic has a blackish color.

8. A machinable ceramic as claimed in claim 7 wherein the main constituent further includes greater than 0 mass % of silicon nitride.

9. A probe guide comprising a blackish-colored machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–59.95 mass % of boron nitride, 40–69.96 mass % of zirconia, and 0–20 mass % of silicon nitride and wherein the ceramic has a blackish color, the probe guide having a plurality of minute vacancies made by machining and having a form selected from slits and holes through which probes can pass.

10. A machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–59.95 mass % of hexagonal boron nitride, 40–69.95 mass % of zirconia, 0–20 mass % of silicon nitride, and 0.05–2.5 mass % (calculated as an element) of at least one coloring additive selected from the group consisting of C, Si, elements of Groups IIIA–IVB in the fourth period, elements of Groups IVA–VB in the fifth period, elements of Groups IVA–VIB in the sixth period of the long form periodic table, and compounds of these elements.

11. A machinable ceramic as claimed in claim 10 having a coefficient of thermal expansion of 3–5×10 −6 /° C. in a temperature range of 25–600° C.

12. A machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–59.95 mass % of boron nitride, 40–69.95 mass % of zirconia, 0–20 mass % of silicon nitride, and 0.05–2.5 mass % (calculated as an element) of at least one coloring additive selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W metals and oxides of these metals.

13. A method of manufacturing a machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–59.95 mass % of boron nitride, 40–69.95 mass % of zirconia, and 0.05–2.5 mass % (calculated as an element) of at least one coloring additive selected from the group consisting of C, Si, elements of Groups IIIA–VIB in the fourth period, elements of Groups IVA–VB in the fifth period, elements of Groups IVA–VIB in the sixth period of the long form periodic table, and compounds of these elements including the steps of mixing a main constituent raw material powder comprising boron nitride, zirconia, and at least one coloring additive with a sintering aid in an amount of 1–15 mass % based on the main constituent raw material powder to obtain a raw material powder, and sintering the raw material powder at a high temperature under pressure to obtain a sintered body.

14. A method as claimed in claim 13 wherein the main constituent raw material powder further comprises 0–20 mass % of silicon nitride.

15. A probe guide comprising a machinable ceramic comprising a main constituent and a sintering aid, wherein the main constituent comprises 30–59.95 mass % of boron nitride, 40–69.95 mass % of zirconia, 0–20 mass % of silicon nitride, and 0.05–2.5 mass % (calculated as an element) of at least one coloring additive selected from the group consisting of C, Si, elements of Groups IIIA–IVB in the fourth period, elements of Groups IVA–VB in the fifth period, elements of Groups IVA–VIB in the sixth period of the long form periodic table, and compounds of these elements, the probe guide having a plurality of minute vacancies made by machining and having a shape selected from slits and holes through which probes can pass.

16. A probe guide comprising a machinable ceramic as claimed in claim 12 having a plurality of minute vacancies made by machining and having a shape selected from slits and holes through which probes can pass.

17. A machinable ceramic as claimed in claim 10 , wherein the coloring additive is selected from the group consisting of elements of Groups IIIA–IVB in the fourth period, elements of Groups IVA–VB in the fifth period, elements of Groups IVA–VIB in the sixth period of the long form periodic table, and compounds of these elements.

18. A method as claimed in claim 3 , wherein the sintered body has a strength of at least 240 MPa.