Glass and glass ceramic

Abstract

An LAS-glass for producing a transparent glass-ceramic and an LAS-glass-ceramic having a predetermined chroma C* and a predetermined visually determinable scatter value (S) are provided. The LAS-glass and LAS-glass-ceramic has a process window as large as possible during the nucleus formation process with respect to the residence time in the relevant temperature range for the formation of nuclei.

Claims

1. An Li.sub.2OAl.sub.2O.sub.3SiO.sub.2 (LAS) glass for the production of a transparent glass ceramic, comprising: components, in wt. of: Al.sub.2O.sub.3 19-23, Fe.sub.2O.sub.3 0.01-0.02, Li.sub.2O 3.2-4.2, P.sub.2O.sub.5 0.01-<1.6, SiO.sub.2 64-68, SnO.sub.2 0.05-0.5, TiO.sub.2 1.6-2.5, ZnO 1.0-2.5, and ZrO.sub.2 1.2-2.0; and a condition B1, the condition B1 comprising 20<(Li.sub.2O+Al.sub.2O.sub.3+SiO.sub.2)/(SnO.sub.2+TiO.sub.2+ZrO.sub.2+Fe.sub.2O.sub.3)<25, a condition B2, the condition B2 comprising 22<(Li.sub.2O+Al.sub.2O.sub.3+SiO.sub.2+ZnO+P.sub.2O.sub.5)/(SnO.sub.2+TiO.sub.2+ZrO.sub.2+Fe.sub.2O.sub.3)<26.

2. The glass according to claim 1, wherein the components comprise: Al.sub.2O.sub.3 21.0-21.7, As.sub.2O.sub.3<0.05, BaO 0.2-0.8, CaO 0.1-0.4, Fe.sub.2O.sub.3 0.01-0.016, K.sub.2O 0.05-0.2, Li.sub.2O 3.6-3.9, MgO 0.5-0.8, Na.sub.2O 0.3-0.7, Nd.sub.2O.sub.3 0.02-0.07, P.sub.2O.sub.5 0.01-0.1, Sb.sub.2O.sub.3<0.05, SiO.sub.2 65.5-67.5, SnO.sub.2 0.08-0.16, TiO.sub.2 2.0-2.4, ZnO 1.6-1.9, ZrO.sub.2 1.6-1.9, and SrO 0.3-0.7.

3. The glass according to claim 1, wherein the composition further comprises 0.01 to 0.1 wt. % of Nd.sub.2O.sub.3.

4. The glass according to claim 1, wherein the composition further comprises 0.05-0.7 wt. % of SrO.

5. An Li.sub.2OAl.sub.2O.sub.3SiO.sub.2 (LAS) glass for the production of a transparent glass ceramic, comprising: components, in wt. %, of: Al.sub.2O.sub.3 19-23, Fe.sub.2O.sub.3 0.01-0.02, Li.sub.2O 3.2-4.2, P.sub.2O.sub.5 0.01-<1.6, SiO.sub.2 64-68, SnO.sub.2 0-0.5, TiO.sub.2 1.5-3.0, ZnO 1.0-2.5, ZrO.sub.2 1.2-2.0, MgO 0.5-0.8; and a condition B3, the condition B3 comprising 21<(Li.sub.2O+Al.sub.2O.sub.3+SiO.sub.2+ZnO+P.sub.2O.sub.5+MgO)/(SnO.sub.2+TiO.sub.2+ZrO.sub.2+Fe.sub.2O.sub.3)<26.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows C* as a function of t.sub.KBA for a glass according to the invention;

(2) FIG. 2 shows C* as a function of the constant heating rate for a glass according to the invention;

(3) FIG. 3 shows the scatter value S as a function of t.sub.KBA for a glass according to the invention;

(4) FIG. 4 shows the scatter value S as a function of the constant heating rate for a glass according to the invention;

(5) FIG. 5 shows a combined diagram with C* and S as a function of t.sub.KBA according to a first embodiment;

(6) FIG. 6 shows a combined diagram with C* and S as a function of t.sub.KBA according to a second embodiment;

(7) FIG. 7 shows C* as a function of t.sub.KBA for a comparative glass;

(8) FIG. 8 shows the scatter value S as a function of t.sub.KBA for a comparative glass; and

(9) FIG. 9 shows a combined diagram with C* and S as a function of t.sub.KBA for a comparative glass.

DETAILED DESCRIPTION

(10) A glass according to the invention (Example) and a comparative glass (Comparative Example) were investigated relative to their processing window.

(11) The compositions of the two glasses are listed in the following Table 1.

(12) TABLE-US-00001 TABLE 1 (data in wt. %) Example Comparative Example Al.sub.2O.sub.3 21.3 22 As.sub.2O.sub.3 <0.005 <0.005 BaO 0.52 1.19 CaO 0.24 0.035 Fe.sub.2O.sub.3 0.013 0.013 F <0.05 <0.05 K.sub.2O 0.11 0.29 Li.sub.2O 3.74 3.71 MgO 0.63 0.72 MnO.sub.2 <0.005 0.001 Na.sub.2O 0.52 0.38 Nd.sub.2O.sub.3 0.056 <0.01 P.sub.2O.sub.5 0.027 1.51 Sb.sub.2O.sub.3 <0.010 <0.010 SiO.sub.2 66.48 65.5 SnO.sub.2 0.11 0.31 TiO.sub.2 2.2 2.08 ZnO 1.79 <0.02 ZrO.sub.2 1.72 2.22 SrO 0.53 <0.002 Cl Not measured <0.02 HfO.sub.2 0.04 0.04

(13) The fluorine concentration was determined by flame spectroscopy, Li.sub.2O was determined wet chemically, and the other elements were determined with x-ray fluorescence spectroscopy.

(14) The impurities CoO, Cr.sub.2O.sub.3, Cs.sub.2O.sub.3, CuO, MoO.sub.3, NiO, PbO, Rb.sub.2O.sub.3, V.sub.2O.sub.5 in the glasses lie below the concentration of 0.005 wt. %. The measured HfO.sub.2 is entrained as an impurity via the ZrO.sub.2 raw material.

(15) The respective ratios for the sums of the components, corresponding to conditions B1 and B2, are listed in Table 2. The glass according to the invention complies with the conditions B1 and B2, whereas the comparative glass lies outside these ranges.

(16) TABLE-US-00002 TABLE 2 Example Comparative Example Li.sub.2O + Al.sub.2O.sub.3 + SiO.sub.2 91.55 91.21 SnO.sub.2 + TiO.sub.2 + ZrO.sub.2 + Fe.sub.2O.sub.3 4.043 4.623 Ratio B1 22.6 19.7 Li.sub.2O + Al.sub.2O.sub.3 + SiO.sub.2 + ZnO + 93.367 92.72 P.sub.2O.sub.5 SnO.sub.2 + TiO.sub.2 + ZrO.sub.2 + Fe.sub.2O.sub.3 4.043 4.623 Ratio B2 23.1 20.1 Li.sub.2O + Al.sub.2O.sub.3 + SiO.sub.2 + P.sub.2O.sub.5 + 94.0 93.44 MgO SnO.sub.2 + TiO.sub.2 + ZrO.sub.2 + Fe.sub.2O.sub.3 4.043 4.623 Ratio B3 23.25 20.21

(17) In FIG. 1, C* is presented as a function of t.sub.KBA for the Example according to the invention.

(18) The dependence of chromaticity C* on the residence time t.sub.KBA can be fitted by the approximation:

(19) $C^{*}\left(t_{\mathrm{KBA}}\right)=\frac{a}{\sqrt{t_{\mathrm{KBA}}}}+b.Math.\left(1-e^{-{\mathrm{ct}}_{\mathrm{KBA}}}\right)+d$

(20) The first term characterizes the reduction of the color value C* for short residence times t.sub.KBA; the second term quantifies the increase in the color value for long residence times t.sub.KBA.

(21) The parameter a is a measure for the change in color in the case of short residence times t.sub.KBA; the parameters b and c describe the steepness of the increase in color value for long residence times t.sub.KBA.

(22) The parameter d is an offset parameter and is decisive in determining the minimum color value that can be obtained.

(23) In order to determine the processing window B.sub.C*, e.g., for C*=5, the points of intersection of the constants at C*=5 and the function C*(t.sub.KBA) are determined or are calculated from the function C*(t.sub.KBA). A value of more than 200 min. results for the processing window B.sub.C* relative to C*=5.

(24) C* as a function of the constant heating rate r.sub.KBA belonging thereto is shown in the temperature range T1 to T2 in FIG. 2. In this Example, T1 amounts to 680 C. and T2 amounts to 880 C.

(25) Residence times t.sub.KBA can be calculated from the constant heating rates r.sub.KBA according to: t.sub.KBA=(T.sub.2T.sub.1)/r.sub.KBA.

(26) The use of different heating rates leads to the desired different residence times.

(27) The measurement curve of the constant heating rates can also be described by fitting:
C*(r.sub.KBA)=a.Math.{square root over (r.sub.KBA)}+b.Math.(1exp(c.Math.r.sub.KBA))+d

(28) In FIG. 3, the scatter value S is presented as a function of t.sub.KBA for the Example according to the invention.

(29) The dependence of the scatter value S on the residence time t.sub.KBA can be fitted by the approximation:

(30) $S\left(t_{\mathrm{KBA}}\right)=\frac{a}{\sqrt{t_{\mathrm{KBA}}}}+b.Math.t_{\mathrm{KBA}}+c$

(31) The first term characterizes the reduction in the scatter value S for short nucleation times; the second term quantifies the increase in the scatter value for long nucleation times. The parameter a is a measure of the change in color for short nucleation times; the parameter b describes the steepness of the increase in color value for long nucleation times.

(32) The parameter c is an offset parameter and is decisive in determining the minimum scatter value that can be obtained.

(33) In order to determine the processing window B.sub.S, e.g. for S=1.5, the points of intersection of the constants for S=1.5 are determined with the function S(t.sub.KBA) or calculated from the function S(t.sub.KBA). A value of more than 200 min. results for the processing window B.sub.S.

(34) In FIG. 4, S is presented as a function of the constant heating rate r.sub.KBA belonging thereto. This measurement curve can also be described by fitting:

(35) $S\left(r_{\mathrm{KBA}}\right)=a.Math.\sqrt{r_{\mathrm{KBA}}}+\frac{b}{r_{\mathrm{KBA}}}+c$

(36) In FIG. 5, the diagrams of FIGS. 1 and 3 are combined for the Example C*=4.5 and S=2, in order to determine the region of intersection (processing window B.sub.U), which is represented as cross hatching.

(37) Both C*=4.5 as well as S=2 are respected in the window B.sub.U. 44 min. results for B.sub.U.

(38) The processing windows B.sub.C*, B.sub.S and B.sub.U are shown for the values C*=5 and S=2 in FIG. 6. 55 min. results for B.sub.U.

(39) The corresponding diagrams for the comparative glass are shown in FIGS. 7 to 9.

(40) Evaluation of the processing window B.sub.C*.

(41) For the Comparative Example. small values result for a, and large values result for parameter b. The parameter c, which is a decisive factor via the decay behavior of the second term, is smaller for the Comparative Example. i.e., the second term has an effect for long t.sub.KBA times.

(42) The comparison of the curves/fits shows that clearly larger processing windows B.sub.C* with respect to the residence times t.sub.KBA are present for the glass according to the invention.

(43) For the glass according to the invention, for example, B.sub.C*=t.sub.KBAC*=5=200 min. results. For the Comparative Example, B.sub.C*=t.sub.KBAC*=5=7 min.

(44) For the glass according to the invention, for example, B.sub.C*=t.sub.KBAC*=4.8=100 min. results. For the Comparative Example, B.sub.C*=t.sub.KBAC*=4.8=1 min.

(45) Evaluation of the processing window B.sub.S:

(46) For the glass according to the invention, relatively large parameters a and very small values for b are characteristic. For the Comparative Example, in contrast, small values result for a, and large values result for parameter b. The parameter c, which is a decisive factor via the decay behavior of the second term, is smaller for the Comparative Example. i.e., the second term has an effect for long t.sub.KBA times.

(47) The comparison of the curves/fits shows that clearly larger processing windows B.sub.S with respect to the residence times t.sub.KBA are present for the glass according to the invention.

(48) For the glass according to the invention, for example, B.sub.S=t.sub.KBAS=2>200 min. results.

(49) For the Comparative Example, B.sub.S=t.sub.KBAS=2=16 min.

(50) For the glass according to the invention, for example, B.sub.S=t.sub.KBAS=1.5>200 min. results.

(51) For the Comparative Example, B.sub.S=t.sub.KBAS=1.5=5 min.

(52) In FIG. 9 the region of intersection (processing window B.sub.U) only amounts to 7 min. for C*=5 and S=2.