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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

CATHODE COATING 100

High calcium triple carbonate spray coating

(Ba-Sr-Ca) CO3 56-31-13%

CATHODE COATING 200

High calcium, high density, triple carbonate spray coating

(Ba-Sr-Ca) CO3 56-31-13%

CATHODE COATING 300

Low calcium, triple carbonate spray coating

(Ba-Sr-Ca) CO3 56-39-4%

CATHODE COATING 400

Low calcium, high density, triple carbonate spray coating.

(Ba-Sr-Ca) CO3 56-39-4%

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

  1. Equipment needed:
    1. Stainless steel beaker
    2. Stirrer
    3. High voltage DC supply (0 to 400 volts and 0 to 200 ma)
  2. Room temperature 25 C
  3. Voltage: 200 to 400 volts
  4. Polarity work positive
  5. 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

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:
  1. Dissipation and removal of ethyl cellulose binder as volatile products.
  2. Conversion of the carbonates into the corresponding oxides by thermal degradation.
  3. Partial reduction of oxides by dissociation at the metal-coating interface to form free barium, with uniform dispersion of free barium resulting.
  4. 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

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

T-33C-131

BaSrCa 57/39/4%

Sodium carb. Ppted.

Needle Form

Nitrocellulose

Hand Spray

Medium to High

T-33C-132

BaSrCa 57/39/4%

Sodium carb.ppted.

Needle Form

Nitrocellulose

Hand Spray

Medium

T-33C-138

BaSrCa 57/39/4%

Sodium carb. Ppted.

Needle Form

Nitrocellulose

Machine or Hand Spray

Low to Medium

T-33C-185A

BaSrCa 57/39/4%

Sodium carb. Ppted.

Needle Form

Low water solubles

Nitrocellulose

Hand Spray

Medium to High

T-33C-304

BaSrCa 57/39/4%

Sodium carb. Ppted.

Needle Form

Methyl Methacrylate

Cataphoretic ctg. Filamentary wires

High

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

T-33-C-130

(BaSrCa)CO3

57/39/4%

Needle Form

T-33-C-175A

(BaSrCa)CO3

57/39/4%

High Purity




BINDERS FOR CATHODE COATINGS

Nitrocellulose Binder

Methacrylate Binders

T-33-B-10

T-33-B-207

T-33-B-109

T-33-B-209

T-33-B-110

T-33-B-610F

T-33-B-114

 

T-33-B-608

 

T-33-B-902