1、BRITISH STANDARD BS 4789:1972 Specification for Ceramic components for use in envelopes for electronic tubes UDC 621.385.032.7:621.315.612:666.3BS4789:1972 This British Standard, having been approved by the Telecommunication Industry Standards Committee, was published under the authority ofthe Execu
2、tive Board on 30March1972 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference TLE/5 Draft for comment 71/20608 ISBN 580 06699 1 Co-operating organizations The Telecommunication Industry Standards Committee, under whose supervision this British Standard w
3、as prepared, consists of representatives from the following Government departments and scientific and industrial organizations: British Broadcasting Corporation British Electrical and Allied Manufacturers Association British Radio Equipment Manufacturers Association British Radio Valve Manufacturers
4、 Association* British Railways Board Cable and Wireless Ltd. Crown Agents for Oversea Governments and Administrations Department of Employment and Productivity (H.M. Factory Inspectorate) Electrical Contractors Association (Incorporated) Electrical Research Association Electricity Council, the Centr
5、al Electricity Generating Board and the Area Boards in England and Wales Electronic Engineering Association* Electronic Valve and Semi-Conductor Manufacturers Association* Home Office Institution of Electrical Engineers Institution of Electronic and Radio Engineers* Institution of Production Enginee
6、rs Ministry of Defence, Army Department Ministry of Defence (Directorate of Standardization) Ministry of Defence, Navy Department* Ministry of Defence, Procurement Executive Post Office Radio and Electronic Component Manufacturers Federation Relay Services Association of Great Britain Science Resear
7、ch Council Radio and Space Research Station Scientific Instrument Manufacturers Association* Society of British Aerospace Companies Ltd. Telecommunication Engineering and Manufacturing Association The Government department and scientific and industrial organizations marked with an asterisk in the ab
8、ove list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: United Kingdom Atomic Energy Authority. British Ceramic Research Association. Individual experts. Amendments issued since publication Amd. No. Date CommentsBS478
9、9:1972 BSI 12-1999 i Contents Page Co-operating organizations Inside front cover Foreword iii 1 General 1 1.1 Scope 1 1.2 Definitions 1 1.3 General requirements 1 2 Properties and test methods 2 2.1 Test sample requirements 2 2.2 Electrical properties 2 2.2.1 Power factor (tan ) and permittivity (”)
10、 2 2.2.2 Temperature coefficient of permittivity 3 2.2.3 Volume resistivity 3 2.3 Mechanical properties 3 2.3.1 Determination of cross-breaking strength 3 2.3.2 Youngs modulus of elasticity 3 2.4 Thermal properties 4 2.4.1 Coefficient of linear expansion 4 2.4.2 Thermal conductivity 4 2.4.3 Maximum
11、thermal shock temperature 4 2.4.4 Deformation temperature 4 2.5 General properties 4 2.5.1 Cracks and porosity 4 2.5.2 Density 4 2.5.3 Grain size 4 2.5.4 Chemical stability 4 2.5.5 Vacuum tightness 4 3 Test schedules 4 3.1 Type testing 4 3.1.1 Selection of tests 4 3.1.2 Frequency of testing 4 3.2 Ba
12、tch testing 5 3.2.1 Selection of tests 5 3.2.2 Frequency of testing 5 3.3 Component testing 5 3.3.1 Selection of tests 5 3.3.2 Frequency of testing 5 3.3.3 Mechanical and visual tests 5 Appendix A Conditioning of samples 6 Appendix B Determination of cross-breaking strength 6 Appendix C Determinatio
13、n of deformation temperature 7 Appendix D Method of test for cracks and porosity 8 Appendix E Method of preparing a sample for grain size measurement 8 Appendix F Method of test for acid resistance 9 Appendix G Method of testing for vacuum tightness 9 Appendix H References 12 Figure 1 Test pieces 7
14、Figure 2 Determining the angle of bend 7BS4789:1972 ii BSI 12-1999 Page Figure 3 Apparatus for vacuum tightness test 10 Table 1 Samples required 2 Table 2 Loss factor 3 Table 3 Volume resistivity 3 Table 4 Thermal conductivity 4BS4789:1972 BSI 12-1999 iii Foreword This standard makes reference to th
15、e following British Standards: BS 784, Methods of test for chemical stoneware. BS 903, Methods of testing vulcanized rubber Part A26: Determination of hardness. BS 1598, Ceramic insulating materials for general electrical purposes. BS 4518, Metric dimensions of toroidal sealing rings and their housi
16、ngs (O-rings). This British Standard which has been prepared under the authority of the Telecommunication Industry Standards Committee is based on a draft prepared on behalf of the Department for Co-ordination of Valve Development, Ministry of Defence, by a working party drawn from government establ
17、ishments and from the tube industry. It has been discussed with the ceramic manufacturers, and the British Ceramic Research Association has tested a wide range of commercial materials to establish realistic limits (Ref. 1, Appendix H). The standard deals with three categories of materials as follows
18、: Category 1. A high grade material suitable for valve body parts. Category 2. A special grade suitable for high power microwave windows. Category 3. A special grade with high thermal conductivity. All categories are required to be vacuum tight. The standard does not deal with the ceramic materials
19、sometimes used for internal parts in valve construction. Although no explicit reference is made to any material, the properties called for in the standard for Categories1 and2 are those normally associated with high alumina content and those for Category3 with high beryllia content. Other materials
20、may, however, be accepted provided that allowance is made by the user for characteristic changes such as in the dielectric constant. The standard is closely related to BS1598:1964, “Ceramic insulating materials for general electrical purposes”. However, the uses to which the ceramics will be put in
21、tubes give rise to certain special requirements which involve either new limits or new tests. In the main these changes are as follows: 1) The ceramics must be vacuum tight. The standard includes details of a suitable test and the performance required. 2) High strength is required in order to give r
22、easonable latitude in the design of ceramic-metal seals, which usually involves some degree of mismatch in expansion coefficient over part of the working or processing temperature range. 3) High thermal conductivity is important both in increasing thermal shock resistance and in avoiding excessive t
23、emperature rise in high power applications. 4) The ceramics should be capable of being metallized consistently. This requires close reproducibility of microstructure. 5) They require to have a high stability under a variety of processing and user conditions, that include firing in vacuum and in hydr
24、ogen for which tests have been laid down. They may also have to withstand bombardment by X-rays, electrons or ions. Working temperatures of up to500 C may be encountered in use and the trend is towards still higher temperatures (up to1000 C) for some applications in the future. A wide variety of siz
25、es may be required, mainly in the form of tubes and discs. The guide to designers contained in BS1598 is also applicable to this standard. However, it should be noted that in addition to the fabrication methods mentioned in BS1598 isostatic pressing is often employed for tube components. This method
26、 results in greater uniformity of density.BS4789:1972 iv BSI 12-1999 Ceramics conforming to the standard shall be supplied either 1) already metallized on the surfaces requiring this treatment so that the whole process is under the control of the ceramic supplier or 2) unmetallized but capable of be
27、ing metallized. In conformity with BS1598:1964 the standard is confined to a description of the test to be applied, the number of specimens to be used for each test and the values defining pass or failure under the test. It covers type and batch testing, and also indicates tests to be applied to com
28、ponents. The main function of the tests laid down in this standard is the control of the ceramic as a material. It is emphasized, however, that results from test samples are affected by the forming method and this should, as far as possible, be the method used in the manufacture of production parts.
29、 Component tests agreed between user and supplier may, in addition to those recommended, bring out more specifically the suitability for the particular application. NOTEBeryllium oxide will be the material normally used for Category3. This material represents a toxic hazard and certain precautions w
30、hich have been published (Ref. 2, Appendix H) should be taken. In particular, it is essential to realize that inhalation of dust or of volatile compounds of beryllia is dangerous. Contamination of wounds by beryllia must be avoided. A British Standard does not purport to include all the necessary pr
31、ovisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1 to12 and
32、a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4789:1972 BSI 12-1999 1 1 General 1.1 Scope This British Standard covers the requirements for fabricated ceramic parts
33、 suitable for joining to metal to form the envelopes for electronic tubes (Category1) and for special materials (Categories2 and3) which are in addition suitable for high power microwave windows. It specifies the limits for values of properties for the different categories. For special applications
34、when a purchase order calls for a requirement different from this standard the purchase order shall prevail. This standard makes reference to and should be read in conjunction with BS1598:1964. NOTEThe titles of the British Standards referred to in this standard are listed on pageiii. 1.2 Definition
35、s For the purposes of this British Standard the following definitions apply: 1.2.1 type tests these are tests to demonstrate the suitability of the material for use as ceramic components for envelopes for electronic tubes and to provide design information. The tests are invoked in the initial produc
36、tion of a material 1.2.2 batch tests these are tests carried out as a continuous check on production to ensure that the material does not depart from the standards set in the type test. A batch is defined as the total material from a common source processed up to firing as a unit at one time in one
37、unit of equipment 1.2.3 component tests these are tests applied to fired components or to test pieces from the same batch of material fired with them and are usually the subject of a purchasing contract, since acceptance limits depend on the end-use of the components. However, some general tests are
38、 included in the specification 1.2.4 categories of material ceramic material is classified as: Category 1. A high grade material suitable for valve body parts. Category 2. A special grade suitable for high power microwave windows. Category 3. A special grade with high thermal conductivity. 1.3 Gener
39、al requirements The ceramic components shall be capable of being metallized and brazed to form parts of highly reliable vacuum-tight assemblies. Therefore, the material shall not significantly change in properties during normal processing (including metallizing). Close control of ceramic production
40、is necessary to ensure repeatability in performance between batches; in particular the microstructure shall be reproduced consistently. Unless otherwise specified, all the tests shall be carried out under “dry” conditions, i.e.an ambient temperature of20 5 C and a relative humidity (where significan
41、t) in the range of60% to70%.BS4789:1972 2 BSI 12-1999 2 Properties and test methods 2.1 Test sample requirements The followingTable 1 gives the subclause number of the test methods and the number of test pieces required. Table 1 Samples required 2.2 Electrical properties 2.2.1 Power factor (tan ) an
42、d permittivity (”). The material shall be tested at1MHz 1) , 70MHz and9400MHz at normal temperature (20 5 C). Categories2 and3 materials shall also be tested at9400MHz at200 C and400 C. The method of making the measurements at1MHz and70MHz shall be that described in BS1598, Appendix B. For the measu
43、rements at9400MHz any suitable method may be used but a convenient method is that described in Ref. 3 ofAppendix H. Six specimens shall be tested at1MHz and70MHz. Three specimens shall be tested at9400MHz. Frequencies shall be within10% of the nominal value. The losses shall be stated as the mean va
44、lue of loss factor (” tan ), and shall meet the requirements inTable 2. In the case of normal conditioning the coefficient of variation 2)of1) permittivity and2) loss factor at each frequency and temperature shall also be evaluated. The value of permittivity shall be stated by the manufacturer and t
45、he results shall lie within 5% of this nominal value for Category1 materials and within 2% for Categories2 and3 materials. Test Subclause Sample size Power factor and permittivity (1 MHz and 70 MHz) 2.2.1 6 Power factor and permittivity (9 400 MHz) 2.2.1 3 Temperature coefficient of permittivity 2.2
46、.2 3 Volume resistivity 2.2.3 6 Cross-breaking strength 2.3.1 6 Youngs modulus 2.3.2 2 Coefficient of linear expansion 2.4.1 3 Thermal conductivity 2.4.2 3 Maximum thermal shock temperatures 2.4.3 6 Deformation temperature 2.4.4 3 Cracks and porosity 2.5.1 6 a Density 2.5.2 3 Grain size 2.5.3 3 Chem
47、ical stability 2.5.4 6 Vacuum tightness 2.5.5 6 a See also3.3.2. 1) The test at this frequency is very sensitive to impurities in the material; this sensitivity reduces with increasing frequency. 2) Coefficient of variation = standard deviation mean -100 BS4789:1972 BSI 12-1999 3 Table 2 Loss factor
48、 Significant changes in appearance as a result of conditioning shall be recorded. 2.2.2 Temperature coefficient of permittivity. This test applies to Categories2 and3 materials only. The apparatus shall be the same as that used for the high-temperature permittivity tests at9400MHz. The temperature c
49、oefficient of permittivity is given in p.p.m./ C by: where ” t1and ” t2are the values of permittivity at9400MHz at the temperatures t 1and t 2respectively. The temperature t 1shall be between10 C and30 C and the temperature t 2between190 C and210 C. Three samples shall be measured and the results shall be stated as the mean value together with the coefficient of variation. The measurements at the two temperatures shall be carried out consecutively on each sample. The mean value shal
