For Thermal Electronic Emission
Lacquer spray and electrophotoretic coatings of emission carbonates (Ba-Sr-Ca) for oxide coated cathodes in electronic tube applications.
- Spray coating applications.
- High purity carbonates with isomorphous crystal structure.
- Controlled viscosity, uniformity, and particle size.
- Excellent emission characteristics.
- Long term stability
CATHODE COATINGS DESCRIPTION
Transene and triple carbonates are specially prepared electronic materials used for efficient thermal electron emission of cathode structures. These carbonates are compounds of Ba, Sr, and Ca, occurring as homogenous crystallites with an isomorphous crystal structure, carefully dispersed in a lacquer vehicle. Furthermore, the vehicle contains an improved binder to create a highly stable lacquer spray coating. These coatings can be applied to various geometric hot cathode structures.
- Filamentary, cylindrical, disk, hollow, etc.
Upon heating (breakdown), the carbonate coatings are converted to semiconductor oxides of Ba, Sr, and Ca. These oxides are characteristically n-type and exhibit high electron conductivity paralleling the high functional activity of the hot cathodes. In addition, the pore structures produced from these carbonate coatings are optimized to augment emission and conductivity.
Cathode Coating Types
|CATHODE COATING NO:||CARBONATES||VEHICLE||METHOS OF APPLICATION||COATING DENSITY|
|T-33C-118||BaSrCa 56/31/13%Ammonium. Carb, Spherulite Form||Nitrocellulose||Hand Spray||Very High|
|T-33C-334||BaSrCa 56/31/13%Ammonium. Carb, Spherulite Form||Methyl Methacrylate||Cataphoretic ctg. Filamentary wires||High|
|CATHODE COATING –100High calcium triple carbonate spray coating||(Ba-Sr-Ca) CO3 56-31-13%|
|CATHODE COATING –200High calcium, high density, triple carbonate spray coating||(Ba-Sr-Ca) CO3 56-31-13%|
Transene Cathode Coatings offer selection of materials to best satisfy requirements for electron emissive surface in radio tubes, TV and cathode ray tubes, power tubes, thyratrons, and other electron devices. Cathode Coating – 100 is for general-purpose applications. Cathode Coating – 200 is recommended where grid-to-cathode spacing must be held very closely.
Characteristics of Spray Cathode Coatings
|PERCENT COMPOSITION OF CARBONATES||VEHICLE
|DILUENT||ZAHN VISCSITY #1(SEC)|
|CATHODE COATING-100||HIGH CALCIUM TRIPLE CARBONATE SPRAY COATING||44% W/V||56% BaCO331% SrCO313% CaCO3||Ethyl Cellulose||85% Xylol-15% Butanol Mixture||32|
|CATHODE COATING-200||HIGH CALCIUM HIGH DENSITY TRIPLE CARBONATE SPRAY COATING||22% W/V||56% BaCO331% SrCO313% CaCO3||Ethyl Cellulose||85% Xylol-15% Butanol Mixture||32|
Process for Activation of Cathodes
(Triple Carbonates & Cathode Coatings)
The activation process described herein pertains to Transene Cathode Coatings, Types 100 and 200. The basic process is quite conventional and involves heating in vacuum to obtain the essential “breakdown” of cathodes. The process involves four operational steps as follows:
- Dissipation and removal of ethyl cellulose binder as volatile products.
- Conversion of the carbonates into the corresponding oxides by thermal degradation.
- Partial reduction of oxides by dissociation at the metal-coating interface to form free barium, with uniform dispersion of free barium resulting.
- Cathode stabilization.
The activation process begins by cathode heating to about 500 °C for a few minutes under vacuum (at least 10-5mm Hg.). The heat input is increased to raise the temperature close to 600 °C. The cathode coating will change in color during the heating process, becoming gray or black and finally pure white.
The temperature of the heated cathodes should then be increased to control the heater wattage. The temperature should rise to approximately 900 °C, to obtain complete conversion of the carbonates to oxide, e.g.:
BaCO3 ® BaO + CO2 (1)
CaCO3 ® CaO +CO2 (2)
SrCO3 ® SrO + CO2 (3)
Complete conversion of the carbonates to oxides will be indicated by the sharp drop in pressure to 10-6 mm Hg.
Final activation is then carried out by raising the cathode temperature to 1200 °C, but not higher. At this high temperature some barium is produced forming active cathode structures.
Stabilization is generally obtained by applying voltage to draw a cathode current of 25-50 ma/cm2 for a short time. The temperature is then reduced at 800 °C.
RCA EQUIVALENT MATERIALS
EMISSION CARBONATES POWDER
Subject to Availablility and Minimum Order Restrictions
BINDERS FOR CATHODE COATINGS
|Nitrocellulose Binder||Methacrylate Binders|