2,410,286 Patented Oct. 29, 1946 UNITED STATES PATENT OFFICE_ 2,410,286 GLASS HAVING LOW-POWER FACTOR Harrison P. Hood, Corning, N. Y., assignor to Corning Glass Works, Corning, N. Y., a corpo ration of New York No Drawing. Application November 12, 1943, Serial No. 510,033 6 Claims. (01. 106-54) 1 2 This invention relates to glass compositions and more particularly to glasses having characteristics which render them especially suitable for the fabrication of special parts in radio broadcasting and receiving apparatus for use at ultra high frequencies. In such apparatus power losses are of paramount importance and it is essential that Another object of this invention is to‘ provide glasses having power factors less than .0007 with silica contents less than 80%, expansion coe?i cients above 30x10"7 and softening points below the glass have a very low power factor. Moreover, of about 70%. 800° C. Another object is to provide a glass having a power factor of about .0004 with a silica content - I now have found that the substitution of po the expansion coe?icient must be high enough and the softening temperature low enough to 10 tassium, in percent by weight wholly or in part for sodium in the prior glasses, has an unexpected permit successful sealing to other glass and metal depressing effect on the power factor, whereby the parts. The power factor of fused silica glass is silica contents can be decreased to as little as - very low, but it is very di?icult to melt and fabri 70% or less and the power factor will not only cate and its use necessitates the use of special sealing glasses. Glasses having high silica con 15 remain below .0005 but actually can be further lowered to about .0004. Best results are depend tents also have correspondingly low power factors, ent also upon other factors. Sodium, if present, but such glasses are also hard to melt and have must be added as a ?uoride. The substitution low expansion coefficients. of lithium in equal percentages by weight for In my prior patent, No. 2,072,207, I have dis closed borosilicate glasses having relatively low 20 sodium or potassium raises the power factor re gardless of the presence of fluorine. The total power factors. The glasses of the patent contain alkali content should not exceed about 6% calcu 80% to 85% of silica and have low alkali contents lated as oxide. I have found that the introduc which areintroduced into the glass as sodium tion of alumina into the glass raises the power ?uoride or other fluorine compounds of sodium. With such high silica and low alkali contents the 25 factor, hence its presence is objectionable. Oxides of the metals of the second periodic group and prior glasses have unusually low expansion coeffi of lead should preferably be absent because they cients and high softening points. Decreasing tend to raise the power factor. The presence of their silica and increasing their alkali contents water or water containing compounds such as not only raises the expansions and lowers the boric acid, H3BO3, in the batch apparently tends softening points of the glasses, but also is accom to increase the power factor when no ?uorine is panied by a substantial increase in power factor. present. The latter is believed to eliminate water For example, in composition A of the patent a as HF and this behavior appears to be more effec minimum power factor of .0005 was obtained tive in the presence of potassium compounds. when the SiO2 was 85% and the alkali content, calculated‘ as NazO, was 2.2%, the glass then hav 35 Hence crystalline boric oxide, which contains no water, as distinguished from vitreous boric oxide, ing an expansion coe?lcient of 22><10-" and a is preferable as a source of boric-oxide when the softening point of 845° 0. However, in composi batch contains no ?uoride. Crystalline boric tion B the power factor was ?ve-fold greater or oxide may be prepared by the method disclosed .0025 when the $102 was lowered to 81.27% and the NazO was raised to 4.42%, the expansion then 40 in Patent 2,137,058. As examples of glasses illustrating my inven being 31><10-" and the softening point 800° C. tion, the following batches are given: In the glasses of the patent, therefore, it seems impossible to lower the silica below 80% without Table I too great sacri?ce in power factor nor to attain further lowering of the power factor without fur 45 ther sacri?ce in expansion coefficient and melt ability. Nevertheless, on account of the need for a better dielectric as an essential requirement for use in 350 235 the transmission and reception of unusually high frequencies, it is the primary object of this inven_ tion to provide a borosilicate glass having an extremely low power factor without the concomi tant high melting point and low expansion coe?i cient of prior glasses. 55 The compositions of the above batches in weight 2,410,286 3 percentage on the oxide basis and their respective power factors are as follows: Table II B103 ________ __ K20 _________ ... 24 6 35 4 26 4 24 6 26 4 27. 5 2. 5 Na2O_________ ________________________________________ _. Power factor. _ 00095 0005 . 00055 . 0006 00038 - 00033 00035 26. 5 1. 75 1.75 00042 4 2. A batch for a glass having ‘a, power factor less than .0005, which consists of sand, a ?uorine compound of an alkali metal and a compound of boron, and which amounts on the oxide basis approximately to 70% SiO2, 26% to 27.5% B203 and 2.5% to 4% total alkali metal oxide selected from the class consisting of NazOv and ‘K20, and comprising at least K20. 3. A batch for a glass having a power factor less than .0005, which consists of sand, a com pound of boron, a compound of potassium and a ?uorine compound of sodium, and which amounts Batches 4 to 8 contain ?uorine which is present on the oxide basis approximately to 70% $102, in the ?nal glasses although for convenience in 26.5% B203, 1.7% K20‘, and 1.7% NazO. calculating the ?nal compositions, it is omitted 15 4. A batch for a glass having a power factor from Table II. less than .0005, which consists of sand, crystalline Considering the above compositions, it will be boric oxide and at least one compound of an alkali noted that when the alkali consists of 4% or less metal including a ?uorine compound and which of potash, partly or entirely as ?uoride, the power amounts on the oxide basis approximately to 70% factor may be decreased to about .0004 or less, as S102, 26% to 27.5% B203, and 2.5% to 4% total shown by glasses 5, 6, and 7. In the absence of alkali metal oxide selected from the class consist ?uorine and/or with more than 4% K20 the ing of Na20 and K201, and comprising at least K20. power factor exceeds .0005 as shown by glasses 5. A borosilicate glass having a power factor 1, 2, 3, and 4. The values for power factor were less than .0005, which consists of approximately measured by the method known as A. S. T. M. D-150-42T set forth on page 1148 et seq., part III v25 70% SiOz, 26% to 27.5% B203, a small amount of fluorine, and 2.5% to 4% total alkali metal oxides of the A. S. T. M. Standards for 1942. selected from the class consisting of NazO and I claim: K20, and comprising at least K20. 1. The method of reducing the power factor of 6. A borosilicate glass having a power factor a borosilicate glass consisting of about 70% Si02, less than .0005 which consists of approximately 26% to 27.5% B203, 2.5% to 4% alkali metal oxide ‘ and ?uorine, which includes the step of intro 70% Si02, 26.5% 13203, 1.7% K20‘ and 1.7% Na20, ducing the boron content of the glass as crystal line boric oxide. and a small amount of ?uorine. HARRISON P. HOOD.