GB2120232A

GB2120232A - Glass composition

Info

Publication number: GB2120232A
Application number: GB08313476A
Authority: GB
Inventors: Thomas Joseph Loretz
Original assignee: Corning Netoptix Inc
Current assignee: Corning Netoptix Inc
Priority date: 1982-05-17
Filing date: 1983-05-16
Publication date: 1983-11-30
Also published as: FR2526784A1; DE3317778A1; GB8313476D0; JPS58208151A

Abstract

Glass useful in manufacturing microchannel plates has 63-72 mol % S02, 20-30 mol % PbO, 3-7 mol % alkali oxide components, 1-3.5 mol % alkaline earth oxide components and less than 1 mol% As2O3, Bi2O3, and Al2O3.

Description

SPECIFICATION Glass composition The invention relates to a glass composition suitable for use in manufacturing microchannel plates.

Alkali-lead-silicate glasses have often been used in the manufacture of microchannel plates, in which the current of electrons entering each of a plurality of parallel microchannels is multiplied, a plurality of electrons being emitted ("secondary emission") from a glass channel-defining wall for each electron that strikes it.

It has been discovered that microchannel plates manufactured from glasses having 63-72 mol % SiO2, 20-30 mol % PbO, 3-7 mol % alkali oxide components, 1-3.5 mol % alkaline earth oxide components and less than 1 mol % As203, Bi203, and Al203 have desirable secondary emission properties and gain stability.

Preferably the glass has more than 65 mol % SiO2, and has more K, Rb, and Cs alkali components than Li or Na components, to permit greater working temperatures. Preferably the glass transition temperature, Tg, of the glass is greater than 450"C, to provide thermal deformation resistance to the microchannel plates, and the sag temperature, Ts, above which material viscously deforms under its own weight) is more than 80"C greater than Tg to allow for process control flexibility in the manufacture of the microchannel plates.

In a preferred embodiment of glass particularly useful in microchannel plates in medical gamma ray cameras, there are low concentrations of alkali elements with substantial radioactive isotope content (e.g.

potassium oxide, which contains 19K40, and rubidium oxide, which contains 37Rb87), which would otherwise cause background noise, resulting in loss of image resolution and contrast.

The structure, composition and manufacture of a preferred embodiment of the invention will now be described, by way of example, with reference to the drawing, which is a diagrammatic vertical sectional view of a microchannel plate of glass according to the invention.

Microchannel plate 10 has plurality of parallel microchannels 12 formed by tubular channel defining walls 14 of glass having the composition described below.

The composition of the preferred embodiment of the invention is presented in the column under "Glass 6" in the following table.

GLASS COMPOSITION AND PROPERTIES Glass 7 Glass 2 Glass 3 Glass 4 Glass 5 Glass 6 Composition (dol Percent of Oxide) SiO2 68.00 69.90 64.40 69.00 71.2 65.72 PbO 24.00 21.15 28.06 23.18 21.55 27.91 Alkali Li2O 1.60 - - - 0.20 Na2O 2.80 - - - 0.45 K2O - - - 5.24 3.35 Rb2O - 1.38 2.20 1.10 1.20 2.12 Cs2O 0.30 4.77 2.05 0.18 - 0.97 Alkaline Earth SrO 3.00 - - - 1.63 BaO - 2.40 3.00 1.14 0.30 2.96 As203 0.06 0.09 0.07 0.13 0.08 0.10 Bi203 0.04 0.05 - 0.03 0.04 Al203 0.30 0.26 0.22 - - 0.22 Physical Properties Glass Transition (Tg,"C) 452 523 472 455 489 474 Glass Sag Point (Ts, 'C) 533 608 560 546 575 566 Index of Refraction (nd) 1.672 1.642 1.694 1.654 1.640 1.696 Thermal expansion coeff.

(a x 107/"C, 20-300"C) 80 76 84 86 82 77 The glass composition is prepared from appropriate raw materials in proportions to supply to specific amounts of listed compounds by standard melting practices in ceramic lined crucibles in a melting atmosphere rich in oxygen. Although the formulas are given in the table in the oxide mol percent, as is recognised in the art of glass science, carbonates, nitrates, sulphates, or halides are acceptable raw materials.

Glass tubing is prepared from the glass composition by extrusion, as is well known in the art. Glass 6 has a glass transition temperature, Tg, greater than 450"C, and a sag temperature, Ts, more than 80"C greater than Tg to provide process control flexibility, without a large risk of thermal deformation, during the manufacture of microchannel plates at high temperatures and pressure. High working temperatures are made possible by the large proportion of SiO2 and the absence of low atomic number alkali components, i.e., Li and Na.

In addition to the preferred glass composition identified as Glass 6 in the above tables, the compositions identified as Glasses 1-5 in the table and glasses having 63-72 mol % SiO2, 20-30 mol% PbO, 3-7 mol % alkali oxide components, 1-3.5 mol % alkaline earth oxide components and less than 1 mol % As203, By203, and Al203 are in accordance with the present invention. Preferably the glass has more than 65 mol % SiO2, and has more K, Rb, and Cs alkali components than Li or Na components, to permit greater working temperatures.

When the glass is to be used in microchannel plates in medical gamma ray cameras, it is desirable that the glass have low concentrations of alkali elements with substantial radioactive isotope content (e.g., potassium oxide, which contains 19K40 and rubidium oxide, which contains 37Rb87). This is because gamma ray cameras typically have exposure times of 5 to 10 minutes, and intrinsic noise from the microchannel plate detector results in loss of image resolution and contrast. Glass 1 is an example of an ultra-low noise glass having no detectable potassium oxide or rubidium oxide, and glasses 2,3 and 6 are low noise versions having small amounts of rubidium oxide and no detectable potassium oxide.

Claims

1. A glass composition comprising 63-72 moi % SiO2, 20-30 mol % PbO, 3-7 mol % alkali oxide components, and 1-3.5 mol % alkaline earth oxide components, wherein said glass composition has less than 1 mol % AS203, By203, and Al203.

2. A glass composition as claimed in claim 1 wherein said glass has a glass transition temperature greater than 450"C and a sag temperature of more than 80"C greater than the glass transition temperature.

3. A glass composition as claimed in claim 1 or 2 wherein there are low concentrations of alkali elements with substantial radioactive isotope content to reduce background noise.

4. A glass composition as claimed in any one of the preceding claims wherein said glass has more than 65 mol percent SiO2, and the sum, in mol %, of the K, Rb, and Cs alkali components is greater than the sum of the Li and Na alkali components.

5. A glass composition as claimed in any one of the preceding claims wherein said glass has 65.72 mol % SiO2, 2.12 mol % Rb2O and 0.97% Cs2O.

6. A glass composition as claimed in any one of claims 1 to 3 wherein said glass comprises 68.00 mol % SiO2, 1.60 mol % Li2O, 2.80 mol % Na2O, and 0.30 mol % Cs2O, and has no detectable K or Rb.

7. A glass composition as claimed in any one of claims 1 to 4 comprises 69.90 mol % SiO2, 1.38 mol % Rb2O, and 4.77 mol % Cs2O.

8. A glass composition as claimed in any one of claims 1 to 3 wherein said glass comprises 64.40 mol % SiO2, 2.20 mol % Rb2O, and 2.05 mol percent Cs2O.

9. A glass composition as claimed in any one of claims 1 to 4 wherein said glass comprises 69.00 mol % SiO2, 5.24 mol % K2O, 1.10 mol % Rb2O, and 0.18 mol % Cs2O.

10. A glass composition as claimed in any one of claims 1 to 4wherein said glass comprises 71.2 mol % SiO2, 0.20 mol % Li2O, 0.45 mol % Na2O, 3.35 mol % K2O, and 1.20 mol % Rb2O.

11. A microchannel plate made from glass comprising 63-72 mol % SiO2, 20-30 mol % PbO, 3-7 mol % alkali oxide components, and 1-3.5 mol % alkaline earth oxide components, wherein said glass has less than 1 mol % As203, By203, and Al203.

12. A plate as claimed in claim 11 wherein there are low concentrations of alkali elements with substantial radioactive isotope content to reduce background noise.