Fluidized Bed Coats Refractory Metals Pfaudler successfully uses fluidized bed technique to coat molybdenum and niobium; long range goal is to coat tungsten and tantalum Research at the Pfaudler division of Pfaudler Permutit, Inc., Rochester, N.Y., has shown that a fluidized bed may be one of the answers to coating refractory metals. Pfaudler's research group has successfully coated molybdenum and niobium using fluidized bed technology. And one of the company's long range objectives is to use a fluidized bed to coat tungsten and tantalum. The refractory metals show useful structural properties at temperatures from 2000° to 4000° F., in an inert atmosphere. In the presence of oxygen, catastrophic oxidation of these metals at 1000° to 1200° F. destroys their high temperature usefulness. Protective coatings make it possible to use these materials to about 3000° F. Pfaudler has been working on the
fluidized bed process since 1957 and applied for a patent in 1960. Its lab scale fluidized bed reactor is a cylindrical vessel made of heat-resistant alloys. Direct heating is used to raise the temperature within the bed. A perforated ceramic plate inert to the coating materials and other products used in the process, is placed at the bottom of the reactor. The plate is separated from the bed material by a coarse layer of inert ceramic material, allowing even distribution of gases up through the bed. It also protects the ceramic plate from reactive bed materials. The bed material, Pfaudler says, can be a nonreactive material such as alumina, zirconia, or thoria; or made up of the coating material (silicon for a suicide coating). Pfaudler's re-
HOT FLAME. Uncoated molybdenum-titanium alloy at right burns through in 5 seconds in flame at 3125° F. Pfaudler silicide-coated sample at left is intact after one and a half hours exposure to this flame 46
C&EN
OCT.
8, 196 2
search group says the choice of either an inert or reactive bed material depends on what the desired coating may be. Fluidizing gases (a metal halide vapor, a halogen gas, argon, and hydrogen) come up through the bottom of the reactor separately or are mixed before entering the bed. These upward flowing gases react with each other or the bed material to form the coating. Excess chemical vapors and gaseous products pass out the top of the reactor and can be separated and recovered for reuse. In coating, for example molybdenum, the piece goes through a scrupulous cleaning procedure, since any amount of foreign matter will prevent proper formation of the coating. This procedure involves etching, sand blasting, vapor cleaning, and a final acetone or trichloroethylene wash. The part is then placed into the reactor. For a suicide coating, the bed material consists of silicon and alumina. Argon is used as the fluidizing gas and passes up into the reactor. Also, an iodine generator adjacent to the reactor passes iodine gas through the bed. The iodine and silicon react to form silicon tetraiodide. This reaction takes place at about 1800° .to 1900° F. After one to three hours, a strong molybdenum disilicide coating forms on the substrate material. Pfaudler says the coated molybdenum will withstand 3000° F. for one and a half to two hours. Niobium alloys coated by this method will withstand temperatures of 2600° F. for 10 to 12 hr. The temperature limits for these two refractory metals have already been reached by another coating m e t h o d pack cementation. But, Pfaudler says, the fluidized bed technique shows some advantages when compared to pack cementation. In coating a piece by pack cementation, the piece is placed in a retort along with the coating materialsalumina, ammonium chloride, urea, and silicon. The retort is sealed and brought up to about 2000° F. Temperature is held for 5 to 10 hr. During this time the ammonium chloride breaks down, reacts with the silicon to form silicon tetrachloride. This forms a disilicide coating on the refractory metal substrate. The retort is cooled and the part removed. The coated molybdenum piece, as the one produced by fluidized bed, withstands
8608
•
Aniline H y d r o g e n P h t h a l a t e
10 g. . . $ 3 . 3 0
C6H5NH2'HOCO-l-C6H4-2-COOH. . . MW 259 26 8572
l,3-Bis(2-methoxyethyl)urea
M P 68-70°
6362
1 - B r o m o p e n t a d e c a n e M P 17-19°
CH3OCH2CH2NHCONHCH2CH2OCH3. . .MW 176.22
3 - B r o m o q u i n o l i n e M P 13-15°
2 5 g. . .
1-Chlorononane B P 76-77°/7 m m
3.50
2 5 g. . .
4.65
1 0 0 g. . . 1 6 . 0 5
2-(o-Chlorophenoxy)propionic Acid M P 115-117° ClC 6 H 4 OCH(CH 3 )COOH. . . MW 200.62
8614
3.30
100 g. . . 11.45
CH 3 (CH 2 ) 8 C1. . .MW 162.70 8601
100 g. . . 15.15
25 g. . . 12.60
C 6 H 4 N:CHCBr:CH. . . MW 208.06 I I 8604
6.75 4.55
5 g. . .
CH 3 (CH 2 )i4Br. . . MW 291.32 5644
2 5 g. . . 2 5 g. . .
Cyclopentadienylsodium ( 1 8 % in T e t r a h y d r o f u r a n )
5 g. . .
2.80
2 5 g. . . 1 0 . 1 0 100 g. . .
9.40
5 g. . .
3.10
C 5 H 5 Na. . .MW 88.09 8547
2 , 2 - D i a l l y l o x y p r o p a n e B P 4 2 - 4 3 °/8 m m
8577
Ο,Ο-Diethyl
(CH 2 :CHCH 2 0) 2 C(CH3)2. . .MW 156.23 B P 134-13575 m m
5 g. . .
(C2H50)2POCH2COOC2H5. . . MW 224.19
May we suggest that after y o u ' v e s c a n n e d t h e s e latest a d d e n d a t o t h e b a s i c list o f 3 9 0 0 + Eastman Organic C h e m i c a l s , y o u tear o u t t h e p a g e a n d i n s e r t it i n y o u r c o p y of "Eastman O r g a n i c Chemi c a l s , List N o . 4 2 " ? T h i s w i l l increase your prospects of finding w h a t y o u w a n t w h e n y o u w a n t i t . Distillation Prod ucts Industries, Eastman Or ganic Chemicals Department, Rochester 3, Ν . Υ.
8611
2,4-Dinitrobenzenesulfonyl Chloride M P 102-104° (N0 2 ) 2 C 6 H 3 S0 2 C1. . .MW 266.62
8554
Ι , Ι ' - E t h y l e n e d i u r e a M P 190-191°
E t h y l p - N i t r o p h e n y l a c e t a t e M P 64-66°
F o r m y l h y d r a z i n e M P 59-61°
Hexaphenylbenzene
8569
4 - H y d r o x y - 3 - m e t h o x y c i n n a m i c Acid M P 173° d e c
2-Methyl-6-nitrobenzothiazole M P 167-169°
Eastman Organic Chemicals
8585
4.40
5 g. . .
4.90
1-Naphthalenesulfonyl
Chloride M P 67-69°
2 5 g. . . 2 0 . 1 5
P a r a b a n i c Acid M P 233° dec
5 g. . .
5.50
2 5 g. . . 23.60
l-Phenyl-lH-tetrazole-5-thiol Sodium Salt
Tetraethylammonium Perchlorate
10 g . . .
4.50
2 5 g. . .
9.75
10 g. . .
3.30
2 5 g.
2,3,4,5-Tetraphenylpyrrole M P 211-215°
p-Toluenesulfonhydrazide M P 110° dec
. .
6.75
5 g. . .
4.75
2 5 g. . . 19.80
2 5 g. . .
3.95
100 g. . . 13.05
Tris(2'-hydroxyacetophenono)chromium
5 g. . .
3.85
2 5 g. . . 15.40
Tris(l-phenyl-l,3-butadiono)chromium [c 6 H 5 C:0CH:C(CH 3 )0] 3 Cr. . .MW 535.54
Distillation Products Industries is a division
2 5 g. . .
9.35
(CH 3 COC 6 H 4 0) 3 Cr. . .MW 457.42 8583
6.30
4.35
CH3C6H4S02NHNH2. . .MW 186.23
ΘΡ^'
2 5 g. . .
1 0 0 g. . . 2 2 . 5 0
10 g. . .
NHC(C6H5):C(C6H5)C(C6H5):CC6H5. . . MW 371.48 I 1 6656
4.15
2 5 g. . .
( C 2 H O ) 4 N C 1 0 4 . . .MW 229.70
8609
1 g. . .
CH3NCOC6H4CO. . .MW 161.16 I I
C c H 5 NN:NN:CSNa. . .MW 200.20 I I 8617
13.75
N - M e t h y l p h t h a l i m i d e M P 132-135°
NHCONHCOCO. . . MW 114.07 I I 8602
4.10
. .
100 g. . . 14.90
C10H7SO2CI. . .MW 226.68 1734
5.30
5 g. . . 16.70
NO>C 6 H 3 N:C(CH 3 )S. . .MW 194.21 I I 8593
2 5 g. . .
2 5 g. . .
HO(CH 3 0)C 6 H 3 CH:CHCOOH. . . MW 194.19 3939
3.50
100 g. . . 11.00
100 g.
C 6 (C6H 5 )6. . -MW 534.70 8566
3.30
1 0 0 g. . . 1 8 . 1 5
N H 2 N H C H O . . .MW 60.06
8678
5 g. . .
2 5 g. . .
N02C6H4CH2COOC2H5. . . MW 209.20 8586
3.35
2 5 g. . . 10.40
2 5 g. . . 10.20
NH2CONHCH2CH2NHCONH2. . .MW 146.15 8119
2 5 g. . . 11.55
Ethoxycarbonylmethylphosphonate
5 g. . .
4.45
2 5 g. . . 18.25
of
Eastman Kodak Company
Prices
subject
to change
without
notice.
Inquiries
for larger quantities
will be
welcomed.
C&ΕΝ
47
temperatures of up to 3000° F. for one and a half to two hours. Probably the most important ad vantage of the fluidized bed process is that it takes from one to three hours to coat a part. Pack cementation, on the average, takes about 15 to 20 hr. and up to 50 hr. for large parts (more than 3 X 4 X 6 ft.). Pfaudler says other advantages over vapor deposi tion techniques include:
0// CVC CUSTOM HIGH-VACUUM DISTILLATION SERVICE
• Heat transfer rates are higher. • Continuous operation is feasible. • Concentration of reactants can be controlled to give desired reaction and coating growth rates.
- . , using the new CMS-15 Centrifugal Molecular Still on a 24-hour production basis Now you can enjoy the cost savings and improved quality and yield available through high vacuum molecular distil lation . . . with a custom service tailored to your needs. Here's how it works: 1. CVC technicians run a sam ple distillation of your ma terial (1 qt. liquid or 2 lbs. solid) to provide samples for evaluation. 2. A pilot distillation (drum quantities) is then made to determine optimum produc tion distillation conditions. 3. Re-run distillations are then available on a fixed or in definite schedule basis—no quantity limit if material is provided in drum units. This service is already helping manufacturers to upgrade their products to serve the premium market, both in development and production quantities, Typical recent runs have in cluded specialty chemicals, rubber additives, fatty acids, plasticizers, liquid epoxy res ins, and other heat-sensitive or viscous materials.
• It gives more consistent coating. • Irregular surface defects are elimi nated by the fluidizing action. Besides being able to coat refractory metals, Pfaudler says, the refractory metals themselves can be coated onto other metals with the fluidized bed method. Also, nonmetals (graphite,
Monsanto Adds New Plasticizer Blending Unit j
WRITE TODAY for complete de tails to: Frank Jossel, Consoli dated Vacuum Corporation, Rochester 3, Ν . Υ.
Consolidated Yacuum R O C H E S T E R 3, N E W Y O R K A SUBSIDIARY OF BELL & HOWELL
48
C&EN
OCT. 8, 1962
carbides, nitrides, borides, and oxides) and other metals (rhenium, cobalt, nickel, ruthenium, rhodium, osmium, platinum, and their alloys) can be coated onto metallic or nonmetallic parts using fluidized bed technology. For now the big interest in refrac tory metals is in forming aerospace components. Although reentry of present orbital-type flights do not re quire such heat resistant components (ablative shields are used), future space probes, such as Dyna Soar (X-20) will need such protective coat ings. Pfaudler says its research pro gram is primarily aimed at aerospace needs but adds that there is a definite potential for high temperature coat ings in electrodes, turbines, and some heat exchangers. Pfaudler foresees a bright future for coating via fluidized bed. But with the variety of coatings and substrate materials, it seems reasonable that a number of methods and coatings will prevail for specific end uses.
Monsanto Chemical has installed a new plasticizer blending facility at its Dela ware River plant near Bridgeport, N J . The move brings to four the number of these units for Monsanto, each near its plasticizer manufacturing plants. Mon santo has thus enhanced its leading position in the highly competitive plas ticizer market. Monsanto offers bulk customers a wide variety of blends, mostly two-component systems, but some go as high as five. Plasticizers most widely used in the blends include dioctyl phthalate (DOP), Santicizer 160 (butylbenzyl phthalate), diisodecyl phthalate, HB-141 (hydrogenated terphenyl), tricresyl phosphate, Santicizer 141 (octyldiphenyl phosphate), and Santicizer 165 (butyloctyl phthalate).
The Delaware River plant consists of six 25,000-gal. storage tanks, two 5000-gal. blending tanks equipped with agitators, and two filling lines. Plasticizer is pumped to the blending tanks through volumetric meters, which are accurate within plus or minus 1.0%. Batch size varies from 1000 to 4000 gal. To en sure complete uniformity, components are agitated for at least an hour. And they are circulated through filters to re move any possible contaminants, Mon santo says. After thorough blending, the material is pumped into a tank car or truck. By far the biggest customers for blends are floor tile makers. Other large uses are in plastisols and ex trusions. Custom blending for the plastics industry is expected to reach 40 million lb. this year, up from less than 5 million lb. in 1955.
