BS 4789:1972

Cooperating organizations
Foreword
Specification
1. GENERAL
1.1 Scope
1.2 Definitions
1.3 General requirements
2. PROPERTIES AND TEST METHODS
2.1 Test sample requirements
2.2 Electrical properties
2.2.1 Power factor (tan delta) and permittivity
       (epsilon)
2.2.2 Temperature coefficient of permittivity
2.2.3 Volume resistivity
2.3 Mechanical properties
2.3.1 Determination of cross-breaking strength
2.3.2 Young's modulus of elasticity
2.4 Thermal properties
2.4.1 Coefficient of linear expansion
2.4.2 Thermal conductivity
2.4.3 Maximum thermal shock temperature
2.4.4 Deformation temperature
2.5 General properties
2.5.1 Cracks and porosity
2.5.2 Density
2.5.3 Grain size
2.5.4 Chemical stability
2.5.5 Vacuum tightness
3. TEST SCHEDULES
3.1 Type testing
3.1.1 Selection of tests
3.1.2 Frequency of testing
3.2 Batch testing
3.2.1 Selection of tests
3.2.2 Frequency of testing
3.3 Component testing
3.3.1 Selection of tests
3.3.2 Frequency of testing
3.3.3 Mechanical and visual tests
Appendices
A. Conditioning of samples
B. Determination of cross-breaking strength
C. Determination of deformation temperature
D. Method of test for cracks and porosity
E. Method of preparing a sample for grain size
    measurement
F. Method of test for acid resistance
G. Method of testing for vacuum tightness
H. References
Tables
1. Samples required
2. Loss factor
3. Volume resistivity
4. Thermal conductivity
Figures
1. Test pieces
2. Determining the angle of bend
3. Apparatus for vacuum tightness test

Lists the definitions, properties and test methods and gives the test schedules for type, batch and component testing of three categories of ceramic material suitable for use in electronic tube envelopes.

This British Standard covers the requirements for fabricated ceramic parts suitable for joining to metal to form the envelopes for electronic tubes (Category 1) and for special materials (Categories 2 and 3) 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 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 BS 1598:1964.

NOTE The titles of the British Standards referred to in this standard are listed on page iii.