Glass ceramic with SiO2 as the main crystalline phase

Abstract

Glass ceramics having SiO.sub.2 as main crystal phase and precursors thereof are described which are characterized by very good mechanical and optical properties and in particular can be used as restoration material in dentistry.

Claims

1. Glass ceramic, which comprises the following components TABLE-US-00013 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 Al.sub.2O.sub.3 0 to 10.0 and comprises SiO.sub.2 as main crystal phase and comprises 5.0 to 50.0 wt.-% SiO.sub.2 as crystal phase.

2. Glass ceramic according to claim 1, which comprises 60.0 to 90.0 wt.-% SiO.sub.2.

3. Glass ceramic according to claim 1, which comprises 2.8 to 9.0 wt.-% Li.sub.2O.

4. Glass ceramic according to claim 1, which comprises 0 to 13.0 further alkali metal oxide Me.sup.I.sub.2O.

5. Glass ceramic according to claim 1, which comprises 0 to 11.0 wt.-% oxide of divalent elements Me.sup.IIO.

6. Glass ceramic according to claim 1, which comprises 0 to 10.0 wt.-% oxide of trivalent elements Me.sup.III.sub.2O.sub.3.

7. Glass ceramic according to claim 1, which comprises 0 to 21.0 wt.-% further oxide of tetravalent elements Me.sup.IVO.sub.2.

8. Glass ceramic according to claim 1, which comprises 0 to 7.0 wt.-% P.sub.2O.sub.5.

9. Glass ceramic according to claim 1, which comprises 0 to 6.0 wt.-% further oxide of pentavalent elements Me.sup.V.sub.2O.sub.5.

10. Glass ceramic according to claim 1, which comprises 0 to 6.0 wt.-% oxide of hexavalent elements Me.sup.VIO.sub.3.

11. Glass ceramic according to claim 1, which comprises 0 to 5.0 wt.-% fluorine.

12. Glass ceramic according to claim 1, which comprises at least one of the following components in the specified amounts: TABLE-US-00014 Component wt.-% SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 Me.sup.I.sub.2O 0 to 13.0 Me.sup.IIO 0 to 11.0 Me.sup.III.sub.2O.sub.3 0 to 10.0 Me.sup.IVO.sub.2 0 to 21.0 P.sub.2O.sub.5 0 to 7.0 Me.sup.V.sub.2O.sub.5 0 to 6.0 Me.sup.VIO.sub.3 0 to 6.0 fluorine 0 to 5.0.

13. Glass ceramic according to claim 1, which comprises low quartz, cristobalite or a mixture thereof as main crystal phase.

14. Glass ceramic according to claim 1, which comprises lithium phosphate and/or lithium silicate as further crystal phase.

15. Glass ceramic according to claim 1, wherein the glass ceramic is present in the form of a powder, a frit, a blank or a dental restoration.

16. Glass ceramic according to claim 13, which comprises low quartz as main crystal phase.

17. Glass ceramic according to claim 1, which comprises 10.0 to 30.0 wt.-% SiO.sub.2 as crystal phase.

18. Glass ceramic according to claim 4, wherein Me.sup.I.sub.2O is selected from Na.sub.2O, K.sub.2O, Rb.sub.2O and/or Cs.sub.2O.

19. Glass ceramic according to claim 5, wherein Me.sup.IIO is selected from MgO, CaO, SrO and/or ZnO.

20. Glass ceramic according to claim 6, wherein Me.sup.111.sub.20.sub.3 is selected from Al.sub.2O.sub.3, B.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3, Ga.sub.2O.sub.3 and/or In.sub.2O.sub.3.

21. Glass ceramic according to claim 7, wherein Me.sup.IVO.sub.2 is selected from ZrO.sub.2, GeO.sub.2, CeO.sub.2, TiO.sub.2 and/or SnO.sub.2.

22. Glass ceramic according to claim 9, wherein Me.sup.V.sub.2O.sub.5 is selected from V.sub.2O.sub.5, Ta.sub.2O.sub.5 and/or Nb.sub.2O.sub.5.

23. Glass ceramic according to claim 10, wherein Me.sup.VIO.sub.3 is selected from WO.sub.3 and/or MoO.sub.3.

24. Glass ceramic according to claim 1, which comprises at least one of the following components in the specified amounts: TABLE-US-00015 Component wt. % SiO.sub.2 70.0 to 83.0 Li.sub.2O 5.0 to 9.0 Me.sup.I.sub.2O 1.0 to 13.0 Me.sup.IIO 1.0 to 7.0 Me.sup.III.sub.2O.sub.3 2.0 to 9.0 Me.sup.IVO.sub.2 0 to 21.0 P.sub.2O.sub.5 1.0 to 6.5 Me.sup.V.sub.2O.sub.5 0 to 5.0 Me.sup.VIO.sub.3 0 to 6.0 fluorine 0 to 1.0.

25. Glass ceramic according to claim 1, which comprises 5.0 to 50.0 wt.-% low quartz, cristobalite or mixtures thereof as crystal phase.

26. Method for the preparation of the glass ceramic according to claim 1, comprising subjecting a starting glass comprising 58.0 to 92.0 wt.-% SiO.sub.2, 2.0 to 10.0 wt.-% Li.sub.2O and 0 to 10.0 wt.-% Al.sub.2O.sub.3 to at least one heat treatment at a temperature of from 700 to 950 C.

27. Method according to claim 26, in which (a) melt of the starting glass is shaped to form a glass blank, and (b) the glass blank is subjected to a heat treatment at a temperature of 700 to 900 C.

28. Method for the preparation of a glass ceramic, which comprises the following components TABLE-US-00016 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 Al.sub.2O.sub.3 0 to 10.0 and comprises SiO.sub.2 as main crystal phase, in which (a) powder of a starting glass comprising 58.0 to 92.0 wt.-% SiO.sub.2, 2.0 to 10.0 wt.-% Li.sub.2O and 0 to 10.0 wt.-% Al.sub.2O.sub.3, optionally after the addition of further components, is pressed to form a powder compact, and (b) the powder compact is subjected to a heat treatment at a temperature of 700 to 950 C.

29. Method for the preparation of a dental restoration comprising shaping a glass ceramic, which comprises the following components TABLE-US-00017 Component wt.-% SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 and comprises SiO.sub.2 as main crystal phase, into the desired dental restoration by pressing, sintering or milling.

30. Method according to claim 29, wherein the dental restoration comprises a bridge, inlay, onlay, veneer, abutment, partial crown, crown or facet.

31. Glass ceramic, which comprises the following components TABLE-US-00018 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 Al.sub.2O.sub.3 0 to 10.0 and comprises SiO.sub.2 as main crystal phase and comprises 5.0 to 30.0 wt.-% lithium disilicate as further crystal phase.

32. Method for the preparation of a glass ceramic, which comprises the following components TABLE-US-00019 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 Al.sub.2O.sub.3 0 to 10.0 and comprises SiO.sub.2 as main crystal phase, which comprises subjecting a starting glass comprising 58.0 to 92.0 wt.-% SiO.sub.2, 2.0 to 10.0 wt.-% Li.sub.2O and 0 to 10.0 wt.-% Al.sub.2O.sub.3 to at least one heat treatment at a temperature of from 700 to 950 C. for a period of 5 to 40 min.

33. Method for the preparation of a dental restoration comprising shaping a glass ceramic, which comprises the following components TABLE-US-00020 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 and comprises SiO.sub.2 as main crystal phase, into the desired dental restoration by pressing, sintering or milling, wherein said milling is carried out as part of a CAD/CAM method.

34. Method for the preparation of a dental restoration comprising shaping a glass ceramic, which comprises the following components TABLE-US-00021 Component wt. % SiO.sub.2 58.0 to 92.0 Li.sub.2O 2.0 to 10.0 and comprises SiO.sub.2 as main crystal phase, into the desired dental restoration by milling.

Description

EXAMPLES

Examples 1 to 35Composition and Crystal Phases

(1) A total of 35 glasses and glass ceramics having the composition given in Table I were prepared by melting corresponding starting glasses, optionally nucleation or stress relief, and then heat treatment for the crystallization.

(2) The following meanings apply in Table 1:

(3) TABLE-US-00011 T.sub.g glass transition temperature, determined by means of DSC T.sub.S and t.sub.S temperature and time used for melting the starting glass T.sub.Kb and t.sub.Kb temperature and time used for nucleation or stress relief of the starting glass T.sub.C and t.sub.C temperature and time used for crystallization of solid glass blocks T.sub.Sinter and t.sub.Sinter temperature and time used for crystallization of powder compacts T.sub.Press and t.sub.Press temperature and time used for crystallization of solid glass blocks by hot pressing CR value contrast value of the glass ceramic according to British Standard BS 5612 determined using: apparatus: CM-3700d spectrometer (Konica- Minolta) measurement parameters: measurement area: 7 mm 5 mm type of measurement: reflectance/ reflection measurement range: 400 nm-700 nm sample size: diameter: 15-20 mm thickness: 2 mm + 0.025 mm plane parallelism: +0.05 mm surface roughness: about 18 m. CTE coefficient of thermal expansion of the glass ceramic according to ISO 6872 (2008), measured in the range of from 100 to 500 C.

(4) In Examples 1 to 35 the starting glasses were first melted on a scale of 100 to 200 g from usual raw materials at the temperature T.sub.s for a period t.sub.s. Glass frits were prepared by pouring the melted starting glasses into water. For the further processing of the glass frits, the three method variants A), B) and C) specified below were used:

A) Solid Glass Blocks

(5) In examples for which T.sub.c and t.sub.c are specified in Table 1 (Examples 3-5, 7-12, 14, 16-24 and 26-35), the glass ceramics were prepared from solid glass blocks. For this, the obtained glass frits were melted again at the temperature T.sub.s for a period t.sub.s. The obtained melts of the starting glass were then poured into a graphite mould in order to produce solid glass blocks. These glass monoliths were then usually stress-relieved at the temperature T.sub.Kb for a period t.sub.Kb, whereby nucleation could take place. The nucleated starting glasses were then heated to a temperature T.sub.C for a period t.sub.c. Glass ceramics according to the invention comprising SiO.sub.2 as main crystal phase were thereby formed, as could be established by X-ray diffraction tests at room temperature.

(6) It is assumed that in this method variant a volume crystallization of the SiO.sub.2 crystal phase has taken place.

B) Powder Compacts

(7) In examples for which T.sub.Sinter and t.sub.Sinter are specified in Table 1 (1, 2, 6, 15 and 25), the glass ceramics were prepared from powder compacts. For this, the obtained glass frits were ground in a zirconium oxide mill to a particle size of <90 m. About g of these powders were then pressed to form cylindrical blanks and sintered in a sinter furnace (Programat from Ivoclar Vivadent AG) at a temperature T.sub.Sinter and a holding time of t.sub.Sinter to form dense glass ceramic bodies. Glass ceramics according to the invention comprising SiO.sub.2 as main crystal phase were formed by the sintering, as could be established by X-ray diffraction tests at room temperature.

(8) It is assumed that in this method variant a surface crystallization of the SiO.sub.2 crystal phase has taken place.

C) Hot Pressing of Solid Glass Blocks

(9) In Example 13, for which T.sub.press and t.sub.Press are specified, the glass ceramic was prepared by hot pressing of solid glass blocks.

(10) For this, the obtained glass frit was melted again at the temperature T.sub.s for a period t.sub.s. The obtained melt of the starting glass was then poured into a pre-heated steel mould in order to produce rods. These monolithic glass rods were then stress-relieved at a temperature T.sub.Kb for a period t.sub.Kb, whereby nucleation could take place. The rods were then sawn into blocks with a mass of about 4 to 6 g. These solid glass blocks were then pressed to form a shaped body in a hot-pressing furnace at the temperature T.sub.press and for a holding time of t.sub.press. Glass ceramic according to the invention comprising SiO.sub.2 as main crystal phase was formed by the hot pressing, as could be established by X-ray diffraction tests of the formed shaped body at room temperature.

(11) The glass ceramic blocks produced according to Examples 1 to 12 and 14 to 35 were machined in a CAD/CAM unit to form desired test pieces according to dental standard and to form dental restorations, such as crowns. For this, the crystallized blocks were provided with a suitable holder and then given the desired shape in an inLab MC XL grinding unit from Sirona Dental GmbH, Austria.

(12) For the glass ceramic according to Example 1, the colour values (L, a, b) were additionally determined according to DIN5033 and DIN6174 as follows: L: 90.68 a: 0.54 b: 4.82

(13) The examination of the chemical stability according to ISO 6872 (2008) of the glass ceramic according to Example 1 yielded an acid solubility of only 5 g/cm.sup.2.

(14) Further, glass ceramic blocks obtained according to Example 1 were provided with appropriate holders, and test pieces for determining the biaxial strength were ground out of them with an inLab grinding unit from Sirona Dental GmbH. The test pieces were polished to 15 m and then the biaxial strength was determined without further thermal treatment. The average strength of the thus-prepared test pieces was 247 MPa.

(15) TABLE-US-00012 TABLE I Example No. 1 2 3 4 5 6 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 80.1 60.0 77.5 77.1 80.1 80.1 Li.sub.2O 6.7 2.8 7.3 7.6 6.7 6.7 Na.sub.2O 1.0 K.sub.2O 3.0 3.3 3.2 2.1 3.0 3.0 Cs.sub.2O Rb.sub.2O MgO 1.5 3.0 1.7 1.6 4.3 CaO 2.8 2.5 4.3 SrO ZnO Al.sub.2O.sub.3 3.1 3.0 3.4 5.1 3.1 3.1 La.sub.2O.sub.3 0.8 B.sub.2O.sub.3 3.7 Y.sub.2O.sub.3 0.8 Ga.sub.2O.sub.3 0.8 In.sub.2O.sub.3 0.5 ZrO.sub.2 TiO.sub.2 SnO.sub.2 CeO.sub.2 GeO.sub.2 20.3 V.sub.2O.sub.5 Ta.sub.2O.sub.5 Nb.sub.2O.sub.5 P.sub.2O.sub.5 2.8 4.1 3.2 3.6 2.8 2.8 MoO.sub.3 WO.sub.3 F Tg/ C. 493 500 488 501 505 T.sub.s/ C., t.sub.s/min 1650, 150 1680, 60 1630, 150 1650, 60 1600, 60 1600, 60 T.sub.Kb/ C., t.sub.Kb/min 500, 10 540, 10 520, 90 540, 30 T.sub.c/ C., t.sub.c/min 780, 15 800, 10 800, 30 T.sub.Sinter/ C., t.sub.Sinter/min 860, 10 870, 15 910, 10 T.sub.Press/ C., t.sub.Press/min Main crystal phase low quartz low quartz low quartz low quartz low quartz low quartz Further crystal Li.sub.3PO.sub.4 Li.sub.3PO.sub.4; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.3PO.sub.4; phases cristobalite; Li.sub.3PO.sub.4 Li.sub.3PO.sub.4; Li.sub.3PO.sub.4 cristobalite diopside cristobalite CR value 57.3 68 CTE/10.sup.6K.sup.1 (100- 16.8 16 15.9 500 C.) Example No. 7 8 9 10 11 12 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 80.1 75.2 77.8 75.1 75.4 77.9 Li.sub.2O 6.7 6.7 6.7 7.1 7.6 7.7 Na.sub.2O K.sub.2O 3.0 3.1 2.1 2.1 Cs.sub.2O 9.2 Rb.sub.2O 6.6 MgO 3.3 3.3 1.6 1.6 1.6 CaO 1.7 SrO 4.3 ZnO Al.sub.2O.sub.3 3.1 2.8 2.8 3.3 5.1 5.2 La.sub.2O.sub.3 B.sub.2O.sub.3 Y.sub.2O.sub.3 1.9 Ga.sub.2O.sub.3 In.sub.2O.sub.3 ZrO.sub.2 TiO.sub.2 SnO.sub.2 CeO.sub.2 GeO.sub.2 V.sub.2O.sub.5 4.6 Ta.sub.2O.sub.5 Nb.sub.2O.sub.5 P.sub.2O.sub.5 2.8 2.8 2.8 3.1 3.6 3.6 MoO.sub.3 WO.sub.3 5.0 F Tg/ C. 518 523 516 501 573 498 T.sub.s/ C., t.sub.s/min 1600, 60 1600, 60 1600, 60 1650, 60 1650, 60 1650, 60 T.sub.Kb/ C., t.sub.Kb/min 550, 40 530, 80 520, 120 520, 10 590, 10 520, 10 T.sub.c/ C., t.sub.c/min 820, 10 800, 30 850, 15 780, 15 780, 15 800, 15 T.sub.Sinter/ C., t.sub.Sinter/min T.sub.Press/ C., t.sub.Press/min Main crystal phase low quartz low quartz low quartz low quartz low quartz low quartz Further crystal Li.sub.2Si.sub.2O.sub.5, Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5. Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.3PO.sub.4; phases cristobalite; Cs.sub.0.809AlSi.sub.6O.sub.12; Li.sub.3PO.sub.4 ' CaWO.sub.4; Li.sub.3PO.sub.4 cristobaliie, Li.sub.3PO.sub.4, Li.sub.3PO.sub.4 Li.sub.3PO.sub.4 Li.sub.2Si.sub.2O.sub.5 CaAl.sub.10SiO.sub.22 CR value 91.6 90.6 CTE/10.sup.6K.sup.1 (100- 15.7 16.4 14.5 15.6 16.9 500 C.) Example No. 13 14 15 16 17 18 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 79.2 77.6 79.6 78.4 79.0 90.0 Li.sub.2O 6.7 6.6 7.8 5.9 6.8 6.7 Na.sub.2O K.sub.2O 3.0 2.9 3.5 2.7 3.0 1.3 Cs.sub.2O Rb.sub.2O MgO 1.5 1.4 1.9 1.3 1.5 1.0 CaO 2.8 2.7 3.4 2.5 2.7 SrO 1.0 1.0 ZnO Al.sub.2O.sub.3 3.0 3.0 3.8 2.7 3.2 La.sub.2O.sub.3 B.sub.2O.sub.3 Y.sub.2O.sub.3 Ga.sub.2O.sub.3 In.sub.2O.sub.3 ZrO.sub.2 TiO.sub.2 SnO.sub.2 CeO.sub.2 2.0 GeO.sub.2 V.sub.2O.sub.5 0.1 Ta.sub.2O.sub.5 Nb.sub.2O.sub.5 P.sub.2O.sub.5 2.8 2.7 6.5 3.0 1.0 MoO.sub.3 WO.sub.3 F 0.8 Tg/ C. 501 582 440 470 T.sub.s/ C., t.sub.s/min 1650, 50 1600, 150 1650, 60 1640, 60 1650, 60 1700, 60 T.sub.Kb/ C., t.sub.Kb/min 510, 10 510, 10 600, 10 460, 10 480, 10 T.sub.c/ C., t.sub.c/min 780, 10 890, 10 780, 30 880, 10 T.sub.Sinter/ C., t.sub.Sinter/min 870, 15 T.sub.Press/ C., t.sub.Press/min 900, 25 Main crystal phase low quartz low quartz low quartz low quartz low quartz cristobalite Further crystal Li.sub.2SiO.sub.3; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; low quartz; phases Li.sub.3PO.sub.4; Li.sub.3PO.sub.4 Li.sub.3PO.sub.4 Ca.sub.2Al.sub.2SiO.sub.7 Ca(PO.sub.4).sub.3F Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5 Li.sub.3FO.sub.4; tridymite CR value 37.1 80.5 CTE/10.sup.6K.sup.1 (100- 15.9 13.7 500 C.) Example No. 19 20 21 22 23 24 Composition wt.-% wt.-% wt.-% wt.-% wt.-% wt.-% SiO.sub.2 78.5 73.2 72.4 75.4 75.8 75.1 Li.sub.2O 7.6 7.4 7.5 7.2 6.6 6.7 Na.sub.2O 2.2 0.7 K.sub.2O 3.8 2.5 4.0 3.3 Cs.sub.2O 12.1 Rb.sub.2O MgO 3.1 2.2 1.6 2.8 3.3 CaO 3.8 3.9 SrO ZnO 3.4 Al.sub.2O.sub.3 3.9 5.8 2.3 4.3 La.sub.2O.sub.3 B.sub.2O.sub.3 3.6 Y.sub.2O.sub.3 Ga.sub.2O.sub.3 In.sub.2O.sub.3 ZrO.sub.2 10.2 TiO.sub.2 SnO.sub.2 CeO.sub.2 GeO.sub.2 V.sub.2O.sub.5 Ta.sub.2O.sub.5 Nb.sub.2O.sub.5 P.sub.2O.sub.5 4.7 3.8 3.5 4.8 4.2 2.8 MoO.sub.3 WO.sub.3 F Tg/ C. 497 511 567 497 492 518 T.sub.s/ C., t.sub.s/min 1650, 120 1650, 60 1650, 60 1650, 120 1650, 120 1650, 60 T.sub.Kb/ C., t.sub.Kb/min 520, 10 530, 10 590, 10 510, 10 510, 10 540, 10 T.sub.c/ C., t.sub.c/min 740, 30 800, 15 850, 10 830, 30 820, 15 830, 15 T.sub.Sinter/ C., t.sub.Sinter/min T.sub.Press/ C., t.sub.Press/min Main crystal phase cristobalite cristobalite cristobalite cristobalite low quartz cristobalite Further crystal low high quartz; Li.sub.3PO.sub.4 low quartz; cristobalite; Li.sub.2Si2O.sub.5; phases quartz; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.3PO.sub.4; Li.sub.2Si.sub.2O.sub.5; Li.sub.3PO.sub.4 Li.sub.3PO.sub.4 Li.sub.3PO.sub.4; Li.sub.2SiO.sub.3; Li.sub.3PO.sub.4 diopside tridymite CR value 92.8 91 CTE/10.sup.6K.sup.1 (100- 15.9 500 C.) Example No. Composition 25 26 27 28 29 30 SiO.sub.2 79.7 74.2 74.2 74.2 74.2 79.2 Li.sub.2O 4.0 5.0 5.0 5.0 5.0 5.0 Na.sub.2O 1.0 1.0 1.0 1.0 1.0 1.0 K.sub.2O 2.7 2.7 2.7 2.7 2.7 2.7 Cs.sub.2O Rb.sub.2O MgO 3.0 6.0 6.0 6.0 6.0 3.0 CaO 2.5 SrO ZnO Al.sub.2O.sub.3 3.0 3.0 3.0 3.0 3.0 3.0 La.sub.2O.sub.3 B.sub.2O.sub.3 Y.sub.2O.sub.3 Ga.sub.2O.sub.3 In.sub.2O.sub.3 ZrO.sub.2 TiO.sub.2 4.0 SnO.sub.2 2.0 CeO.sub.2 GeO.sub.2 V.sub.2O.sub.5 Ta.sub.2O.sub.5 4.0 Nb.sub.2O.sub.5 4.0 P.sub.2O.sub.5 4.1 4.1 4.1 4.1 4.1 4.1 MoO.sub.3 4.0 WO.sub.3 F Tg/ C. 570 547.5 550 550 554 551 T.sub.s/ C., t.sub.s/min 1690, 60 1680, 60 1680, 60 1680, 60 1680, 60 1680, 60 T.sub.Kb/ C., t.sub.Kb/min 570, 10 570, 70 550, 10 570, 10 570, 10 T.sub.c/ C., t.sub.c/min 830, 15 820, 15 810, 15 830, 15 840, 15 T.sub.Sinter/ C., t.sub.Sinter/min 910, 10 T.sub.Press/ C., t.sub.Press/min Main crystal phase low quartz low quartz cristobalite cristobalite cristobalite cristobalite Further crystal Li.sub.3PO.sub.4; cristobalite; low quartz; Li.sub.3PO.sub.4; Li.sub.3PO.sub.4; Li.sub.3PO.sub.4; phases diopside; Li.sub.2SiO.sub.3; Li.sub.3PO.sub.4 low quartz; low quartz; tridymite cristobalite Li.sub.3PO.sub.4 TiO.sub.2; Li.sub.2SiO.sub.3 MgSiO.sub.3 CR value CTE/10.sup.6K.sup.1 (100- 17.3 500 C.) Example No. Composition 31 32 33 34 35 SiO.sub.2 77.0 76.1 78.3 72.2 86.0 Li.sub.2O 9.0 6.2 6.6 7.5 9.0 Na.sub.2O 2.2 K.sub.2O 3.2 3.0 3.2 Cs.sub.2O Rb.sub.2O MgO 3.1 1.6 1.5 1.8 CaO 2.9 2.8 1.9 SrO ZnO Al.sub.2O.sub.3 3.9 6.8 3.0 3.8 La.sub.2O.sub.3 B.sub.2O.sub.3 Y.sub.2O.sub.3 Ga.sub.2O.sub.3 In.sub.2O.sub.3 ZrO.sub.2 2.0 TiO.sub.2 1.8 SnO.sub.2 CeO.sub.2 1.8 GeO.sub.2 2.3 V.sub.2O.sub.5 Ta.sub.2O.sub.5 Nb.sub.2O.sub.5 P.sub.2O.sub.5 4.8 3.2 2.8 3.3 5.0 MoO.sub.3 WO.sub.3 F Er.sub.2O.sub.3 0.1 Tb.sub.4O.sub.7 0.3 Tg/ C. 483 523 513 494 445 T.sub.s/ C., t.sub.s/min 1650, 60 1640, 90 1640, 150 1650, 120 1700, 60 T.sub.Kb/ C., t.sub.Kb/min 500, 10 540, 10 530, 10 510, 10 T.sub.c/ C., t.sub.c/min 830, 10 800, 15 820, 15 780, 60 920, 15 T.sub.Sinter/ C., t.sub.Sinter/min T.sub.Press/ C., t.sub.Press/min Main crystal phase low quartz cristobalite low quartz low quartz low quartz Further crystal Li.sub.3PO.sub.4; Li.sub.3PO.sub.4 Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; Li.sub.2Si.sub.2O.sub.5; phases Li.sub.2Si.sub.2O.sub.5 Li.sub.3PO.sub.4 Li.sub.3PO.sub.4 Li.sub.3PO.sub.4; cristobalite CR value CTE/10.sup.6K.sup.1 (100- 16.9 500 C.)