Spark plug

1. A spark plug comprising:

an insulator having a density of approximately greater than or equal to 3.95 g/cm 3, and

wherein said insulator is formed from at least 99.7% Al 2 O 3 and approximately 10-1000 ppm each of at least two materials selected from the group consisting of Y 2 O 3 , MgO, La 2 O 3 transition metal oxides and oxides of the Lanthanide Series and wherein said insulator has a porosity of 0.3% or less.

2. A spark plug comprising:

an insulator including at least 99% by weight Al 2 O 3 and having a density of 3.95 g/cm 3 or greater and wherein said insulator includes 10-1000 ppm La 2 O 3, and approximately 10-1000 ppm of at least one selected from the group consisting of Yb 2 O 3 , MgO, transition metal oxides from Group III B of the periodic table, and oxides of the Lanthanide Series.

3. The spark plug of claim 2 wherein said insulator includes approximately 99.9% by weight Al 2 O 3 .

4. The spark plug of claim 3 wherein said insulator contains less than 1000 ppm Y 2 O 3 .

5. The spark plug of claim 4 wherein said insulator contains approximately less than 500 ppm Y 2 O 3 .

6. The spark plug of claim 3 wherein said insulator contains greater than 10 ppm Y 2 O 3 .

7. The spark plug of claim 6 wherein said insulator contains greater than approximately 100 ppm Y 2 O 3 .

8. The spark plug of claim 3 wherein said insulator contains less than 1000 ppm of La 2 O 3 , Y 2 O 3 , MgO and the oxides of the Lanthanide Series.

9. The spark plug of claim 8 wherein said insulator contains approximately less than 500 ppm La 2 O 3 .

10. The spark plug of claim 3 wherein said insulator contains greater than 10 ppm La 2 O 3 and greater than 10 ppm of MgO.

11. The spark plug of claim 10 wherein said insulator contains greater than approximately 100 ppm La 2 O 3 .

12. The spark plug of claim 3 wherein said insulator contains 10-1000 ppm Yb 2 O 3 .

13. The spark plug of claim 12 wherein said insulator contains approximately less than 500 ppm Yb 2 O 3 .

14. The spark plug of claim 3 wherein said insulator contains greater than 10 ppm Yb 2 O 3 and greater than 10 ppm of an oxide from the Lanthanide Series.

15. The spark plug of claim 12 wherein said insulator contains greater than approximately 100 ppm Yb 2 O 3 .

16. The spark plug of claim 3 wherein said insulator contains 10-1000 ppm MgO.

17. The spark plug of claim 16 wherein said insulator contains approximately less than 500 ppm MgO.

18. The spark plug of claim 3 wherein said insulator contains greater than 10 ppm MgO, and greater than 10 ppm of an oxide of the Lanthanide Series.

19. The spark plug of claim 16 wherein said insulator contains greater than approximately 100 ppm MgO.

20. The spark plug of claim 3 wherein said insulator includes 10-1000 ppm MgO and 10-1000 ppm Y 2 O 3 .

21. The spark plug of claim 20 wherein said insulator includes approximately less than 500 ppm MgO and approximately less than 500 ppm Y 2 O 3 .

22. The spark plug of claim 21 wherein said insulator includes greater than 10 ppm MgO, greater than 10 ppm Y 2 O 3 and greater than 10 ppm of an oxide of the Lanthanide Series.

23. The spark plug of claim 21 wherein said insulator includes approximately greater than 100 ppm MgO and approximately greater than 10 ppm Y 2 O 3 .

24. The spark plug of claim 2 wherein said insulator includes approximately 99.94% by weight Al 2 O 3 .

25. The spark plug of claim 24 wherein said insulator includes approximately 100-500 ppm MgO.

26. The spark plug of claim 25 wherein said insulator includes approximately 300 ppm MgO.

27. The spark plug of claim 2 wherein said insulator includes approximately 99.97% by weight Al 2 O 3 .

28. The spark plug of claim 27 wherein said insulator includes approximately 100-500 ppm MgO.

29. The spark plug of claim 27 wherein said insulator includes approximately 300 ppm MgO.

30. The spark plug of claim 27 wherein said insulator includes approximately 120 ppm MgO.

31. The spark plug of claim 2 wherein said insulator includes approximately 99.99% by weight Al 2 O 3 .

32. The spark plug of claim 2 wherein said insulator further includes approximately 50-1000 ppm metal oxides selected from the group comprising MgO, transition metal oxides and oxides of the Lanthanide series.

33. The spark plug of claim 2 wherein said insulator further includes approximately 100-600 ppm metal oxides selected from the group comprising MgO, transition metal oxides and oxides of the Lanthanide series.

34. The spark plug of claim 32 wherein said insulator further includes approximately 50-1000 ppm metal oxides selected from the group consisting essentially of MgO, transition metal oxides and oxides of the Lanthanide series.

35. The spark plug of claim 33 wherein said insulator further includes approximately 100-600 ppm metal oxides selected from the group consisting essentially of MgO, transition metal oxides and oxides of the Lanthanide series.

36. The spark plug of claim 34 wherein said insulator further includes approximately 50-1000 ppm metal oxides selected from the group consisting of MgO, transition metal oxides and oxides of the Lanthanide series.

37. The spark plug of claim 35 wherein said insulator further includes approximately 100-600 ppm metal oxides selected from the group consisting of MgO, transition metal oxides and oxides of the Lanthanide series.

38. The spark plug of claim 32 wherein said transition metal oxides are selected from metal oxides of Group IIIB of the periodic table.

39. The spark plug of claim 32 wherein said transition metal oxides are selected from the group comprising Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 .

40. The spark plug of claim 32 wherein said transition metal oxides are selected from the group consisting essentially of Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 .

41. The spark plug of claim 32 wherein said transition metal oxides are selected from the group consisting of Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 .

42. The spark plug of claim 32 wherein said oxides of the Lanthanide Series are selected from the group of oxides comprising the oxides of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, and Lu.

43. The spark plug of claim 32 wherein said oxides further include aluminum.

44. The spark plug of claim 43 wherein said oxides including aluminum include MgAl 2 O 4 and M 3 Al 5 O 12 where M is selected from the group comprising Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, and Lu.

45. The spark plug of claim 43 wherein said oxides including aluminum include MgAl 2 O 4 and M x Al y O z where M is selected from the group comprising Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb, and Lu, and x is greater than or equal to 1, y is greater than or equal to 1, but less than or equal to 2 and z is greater than or equal to 3, but less than or equal to 4.

46. The spark plug of claim 2 wherein said insulator has a dielectric strength of at least 17 kilovolts (RMS) per millimeter.

47. The spark plug of claim 2 wherein said insulator has a dielectric strength of approximately greater than 17.5 kilovolts (RMS) per millimeter.

48. The spark plug of claim 2 wherein said insulator is transparent or translucent.

49. The spark plug of claim 2 wherein said insulator allows the passage of light from a core nose portion to a terminal portion.

50. The spark plug of claim 2 wherein said insulator is unglazed.

51. The spark plug of claim 50 wherein said unglazed insulator is sufficiently resistant to flash-over.

52. A spark plug comprising a polycrystalline insulator having a core nose and a terminal portion and wherein said insulator is capable of allowing passage of light from said core nose to said terminal portion, and wherein said insulator has a porosity of 0.3% or less and includes greater than 99.9% alumina and at least one material selected from the group consisting of MgO, Y 2 O 3 , La 2 O 3 and oxides of the Lanthanide series, and a density of 3.96 g/cm 3 or greater.

53. A spark plug of claim 52 comprising a translucent polycrystalline insulator.

54. The spark plug of claim 52 wherein said insulator includes a large shoulder and a small shoulder between said core nose and said terminal portion and wherein the thickness of the insulator at said small shoulder portion is less than 2.54 mm.

55. The spark plug of claim 52 wherein said insulator has a grain size of approximately less than 30 microns.

56. The spark plug of claim 52 wherein said insulator has an optical transmission rate of greater than 50% per millimeter in the visible light range.

57. The spark plug of claim 56 wherein said insulator has an optical transmission rate of greater than 70% per millimeter in the visible light range.

58. The spark plug of claim 56 wherein said insulator has an optical transmission rate of greater than 80% per millimeter in the visible light range.

59. The spark plug of claim 52 wherein said insulator has a grain size of approximately less than 20 microns.

60. The spark plug of claim 52 wherein said insulator has a grain size of approximately less than 10 microns.

61. The spark plug of claim 52 wherein said insulator has a grain size of approximately less than 5 microns.

62. The spark plug of claim 52 wherein said insulator has a grain size of approximately less than 2 microns.

63. The spark plug of claim 62 wherein said insulator has an in-line optical transmission of greater than 15%.

64. The spark plug of claim 52 wherein said insulator has a grain size of approximately 1 micron.

65. The spark plug of claim 64 wherein said insulator has an in-line optical transmission of greater than 40%.

66. A spark plug comprising an unglazed insulator, wherein said insulator has an outer surface and said outer surface has an average roughness of 0.40 micrometers or less, and a density of 3.95 g/cm 3 or greater, a dielectric strength of approximately 17 kilovolts (RMS) per millimeter, and wherein said insulator is capable of allowing the passage of light.

67. The spark plug of claim 66 wherein said insulator has a grain size of approximately less than 30 microns.

68. The spark plug of claim 66 wherein said insulator has a grain size of less than or equal to approximately 15 microns.

69. The spark plug of claim 66 wherein said insulator has a grain size of less than or equal to approximately 5 microns.

70. The spark plug of claim 69 wherein said insulator has an in-line optical transmission of greater than 5%.

71. The spark plug of claim 70 wherein said insulator has an in-line optical transmission of greater than or equal to 20%.

72. The spark plug of claim 71 wherein said insulator has a grain size is approximately less than or equal to 2 microns.

73. The spark plug of claim 72 wherein said insulator has an in-line optical light transmission of greater or equal to approximately 50%.

74. The spark plug of claim 73 wherein said insulator has a grain size of less than or equal to approximately 1 micron.

75. The spark plug of claim 52 wherein said insulator has a porosity of less than or equal to approximately 0.1%.

76. A spark plug comprising an insulator includes a large shoulder and a small shoulder between said core nose and a terminal portion and wherein the thickness of the insulator at said small shoulder portion is less than 2.54 mm, and a dielectric strength of 17 kilovolts (RMS) or greater per millimeter.

77. The spark plug of claim 76 wherein said thickness is approximately less than or equal to 1.9 mm.

78. The spark plug of claim 76 wherein said thickness is approximately less than or equal to 1.3 mm.

79. The spark plug of claim 76 wherein said insulator has a porosity of less than or equal to approximately 0.3%.

80. The spark plug of claim 79 wherein said insulator has a light transmission of greater than 5% per millimeter.

81. The spark plug of claim 76 wherein said insulator has a porosity of less than or equal to approximately 0.1%.

82. The spark plug of claim 81 wherein said insulator has light transmission of greater than 40% per millimeter.

83. The spark plug of claim 81 wherein said insulator has light transmission of greater than 60% per millimeter.

84. The spark plug of claim 81 wherein said insulator has light transmission of greater than 75% per millimeter.

85. The spark plug of claim 81 wherein said insulator has light transmission of greater than 80% per millimeter.

86. A spark plug comprising an unglazed insulator, wherein said insulator has an outer surface and said outer surface has an average roughness of 0.20 micrometers or less, a density of 3.95 g/cm 3 or greater, a porosity of 0.3% or less and is capable of allowing the transmission of light.

87. The spark plug of claim 1 wherein said insulator has an outer unglazed surface with a roughness of 0.20 micrometers or less.

88. The spark plug of claim 1 wherein said insulator has a grain size of less than or equal to 1 micron.

89. The spark plug of claim 1 wherein said insulator has a porosity of approximately 0.1% or less.

90. The spark plug of claim 52 wherein said insulator has a dielectric strength of 17.5 kilovolts (RMS) or greater.

91. The spark plug of claim 52 wherein said insulator includes an unglazed outer surface having an average roughness of 0.40 micrometers or less.