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SEARCH PRODUCTS
Cathode Coatings
Emission Carbonates Powder
Binders
Cathode Coatings
For Thermal Electronic Emission
Lacquer spray and electrophotoretic coatings of emission carbonates (Ba-Sr-Ca) for oxide coated cathodes in electronic tube applications.
SPECIAL FEATURES
- Spray and electrophoretic coating applications.
- High purity carbonates with isomorphous crystal structure.
- Controlled viscosity, uniformity, and particle size.
- Excellent emission characteristics.
- Long term stability
Cathode Coatings prepared to customer specifications are also offered. All items subject to minimum order quantities.
CATHODE COATINGS
DESCRIPTION
Transene double 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 ethyl cellulose binder to create a highly stable lacquer spray coating. An electrophoretic cathode coating is also offered. 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
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CATHODE COATING –100
High calcium triple carbonate spray coating |
(Ba-Sr-Ca) CO3 56-31-13% |
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CATHODE COATING –200
High calcium, high density, triple carbonate spray coating |
(Ba-Sr-Ca) CO3 56-31-13% |
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CATHODE COATING – 300
Low calcium, triple carbonate spray coating |
(Ba-Sr-Ca) CO3 56-39-4% |
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CATHODE COATING –400
Low calcium, high density, triple carbonate spray coating. |
(Ba-Sr-Ca) CO3 56-39-4% |
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CATHODE COATING – 700
High density, triple carbonate |
(Ba-Sr-Ca) 57-39-4% |
APPLICATIONS
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 Coatings - 200 and - 400 are recommended where grid-to-cathode spacing must be held very closely. Cathode Coating - 300 and - 400 permit cathodes to be operated at elevated temperatures; while tube transconductance shows excellent stability during life. Cathode Coating 700 is an electrophoretic type designed to achieve very high packing density of emission carbonates.
Special emission coatings are also available or can be developed for particular applications and requirements. These special products include coatings for cataphoresis, dip, and automatic or hand spray methods.
Electrophoretic Cathode Coating – Type 700 - Instructions
DESCRIPTION:
This product contains triple carbonates of barium and strontium suspended in an organic vehicle. The product includes an activator (Part B) which is added to Part A, containing the suspension of carbonates.
This mixture is suitable for electrophoretic coating after the addition of the activator (Part B). The suspended triple carbonate particles carry a negative charge. The charge is developed when the activator is added as a result of adsorption of hydroxyl ions. As a result, the carbonate particle will migrate to the positive terminal of the cell.
Procedure for Electrophoretic Coating
- Equipment needed:
- Stainless steel beaker
- Stirrer
- High voltage DC supply (0 to 400 volts and 0 to 200 ma)
- Room temperature 25 °C
- Voltage: 200 to 400 volts
- Polarity work – positive
- Mild agitation or stirring recommended.
The electrophoretic coat thickness is a function of temperature, time, voltage, and inter-electrode distance.
Characteristics of Spray Cathode Coatings
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TYPE |
PRODUCT
DESCRIPTION |
SOLIDS AS
CARBONATES |
PERCENT COMPOSITION OF CARBONATES |
VEHICLE
BINDER |
DILUENT |
ZAHN VISCSITY #1(SEC) |
|
CATHODE COATING-100 |
HIGH CALCIUM TRIPLE CARBONATE SPRAY COATING |
44% W/V |
56% BaCO3
31% SrCO3
13% CaCO3 |
Ethyl Cellulose |
85% Xylol-
15% Butanol Mixture |
32 |
|
CATHODE COATING-200 |
HIGH CALCIUM HIGH DENSITY TRIPLE CARBONATE SPRAY COATING |
22% W/V |
56% BaCO3
31% SrCO3
13% CaCO3 |
Ethyl Cellulose |
85% Xylol-
15% Butanol Mixture |
32 |
|
CATHODE COATING-
300 |
LOW CALCIUM TRIPLE CARBONATE SPRAY COATING |
44% W/V |
57% BaCO3
39% SrCO3
13% CaCO3 |
Ethyl Cellulose |
85% Xylol-
15% Butanol Mixture |
32 |
|
CATHODE COATING-
400 |
LOW CALCIUM HIGH DENSITY TRIPLE CARBONATE SPRAY COATING |
22% W/V |
57% BaCO3
39% SrCO3
4% CaCO3 |
Ethyl Cellulose |
85% Xylol-
15% Butanol Mixture |
32 |
Process for Activation of Cathodes
(Double and Triple Carbonates Cathode Coatings)
The activation process described herein pertains to Transene Cathode Coatings, Types-100,-200,-300,-400, and –500. 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.
CATHODE COATINGS RCA EQUIVALENT
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CATHODE COATING NO: |
CARBONATES |
VEHICLE |
METHOD OF APPLICATION |
COATING DENSITY |
|
T-33C-118 |
BaSrCa 56/31/13%
Ammonium. Carb, Spherulite Form |
Nitrocellulose |
Hand Spray |
Very High |
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T-33C-131
|
BaSrCa 57/39/4%
Sodium carb. Ppted.
Needle Form |
Nitrocellulose |
Hand Spray |
Medium to High |
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T-33C-132
|
BaSrCa 57/39/4%
Sodium carb.ppted.
Needle Form |
Nitrocellulose |
Hand Spray |
Medium |
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T-33C-138 |
BaSrCa 57/39/4%
Sodium carb. Ppted.
Needle Form |
Nitrocellulose |
Machine or Hand Spray |
Low to Medium |
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T-33C-185A |
BaSrCa 57/39/4%
Sodium carb. Ppted.
Needle Form
Low water solubles |
Nitrocellulose |
Hand Spray |
Medium to High |
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T-33C-304 |
BaSrCa 57/39/4%
Sodium carb. Ppted.
Needle Form |
Methyl Methacrylate |
Cataphoretic ctg. Filamentary wires |
High |
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T-33C-334 |
BaSrCa 56/31/13%
Ammonium. Carb, Spherulite Form |
Methyl Methacrylate |
Cataphoretic ctg. Filamentary wires |
High |
RCA EQUIVALENT MATERIALS
EMISSION CARBONATES POWDER
Subject to Availablility and Minimum Order Restrictions
|
PRODUCT # |
CARBONATE |
COMPOSITION |
FORM |
|
T-33-C-42 |
(BaSrCa)CO3 |
56/31/13% |
Spherulite Form |
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T-33-C-130 |
(BaSrCa)CO3 |
57/39/4% |
Needle Form |
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T-33-C-175A |
(BaSrCa)CO3 |
57/39/4% |
High Purity |
BINDERS FOR CATHODE COATINGS
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Nitrocellulose Binder |
Methacrylate Binders |
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T-33-B-10 |
T-33-B-207 |
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T-33-B-109 |
T-33-B-209 |
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T-33-B-110 |
T-33-B-610F |
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T-33-B-114 |
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T-33-B-608 |
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T-33-B-902 |
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