PARR General Purpose Asid Digestion Bombs

PARR General Purpose Asid Digestion Bombs

Acid Digestion Bombs

Speed Analytical Procedures

Parr acid digestion bombs have added a new alternative to the task of preparing analytical samples for analysis. By combining the unique chemical inertness of PTFE with the advantages of a sealed pressure vessel, these convenient bombs offer a rapid procedure for sample dissolution or digestion that has several important advantages over more traditional methods of sample preparation. By providing a convenient means for holding strong mineral acids or alkalis at temperatures well above normal boiling points, these sturdy digestion bombs will:

Accelerate digestions which otherwise would proceed slowly if conducted in an open container at atmospheric pressure.
Permit the use of strong acids, such as HF or aqua regia, which will attack most other conventional containers.
Dissolve analytical samples without losing trace elements and without adding unwanted contaminants from the container itself.
Generate a vigorous chemical action that is a great time saver in analytical procedures.
Obtain complete digestion or dissolution of samples that react slowly or incompletely when treated by other methods.

Chemists who have worked with sealed glass tubes and other cumbersome digestion devices will recognize the attractiveness of these convenient digestion vessels.

Dissolve Inorganic Samples

Ores, rock samples, glass and other inorganic materials can be dissolved rapidly in Parr acid digestion bombs using strong mineral acids: HF, HCI, H2SO4, HN03, Aqua Regia and others. Other chemicals and manufactured products can be leached or dissolved as well, all without introducing unwanted ions and with complete sample recovery. Using reaction temperatures well above normal boiling points, samples can be dissolved or digested rapidly for all types of chemical analyses, particularly for AA and ICP spectroscopy, and for other instrumental methods in which trace elements must be identified.

Digest Organic Materials

Organic samples can be treated with nitric acid and other oxidizing acids in these bombs with no difficulty, provided certain safety precautions are observed. Alkaline or acid hydrolysis reactions can also be handled equally well.

Other Reactions

In addition to their normal uses for sample digestion and dissolution, these bombs serve as excellent general purpose reactors for procedures requiring a small, PTFE lined vessel for use within prescribed pressure and temperature limits. Agitation can be produced with a magnetic stir bar or by shaking or rolling the bomb.

Metal Jacketed and Microwave Styles

Parr PTFE lined acid digestion bombs are made in two different styles: There is a line of metal- jacketed bombs that can be heated in an oven, sand bath, oil or water bath and in other conventional ways, and a new line of digestion bombs developed specifically for rapid heating in a microwave oven. Both styles are made in several sizes, offering a broad selection of bombs ranging from economical models for routine tests to massive styles for procedures involving extreme conditions or potentially hazardous samples. Each of these bombs has a thick walled PTFE liner that completely isolates the charge from the supporting body. These liners are removable and can be charged or emptied while outside of the bomb to eliminate any possible contamination from acid contact with metal parts. They can be replaced if they become damaged or contaminated.

Unique Closures

Several designs are used to keep Parr acid digestion bombs tightly sealed during consecutive heating and cooling cycles when conventional seals might leak. One of these designs uses a tapered closure between the PTFE cup and cover with an unusually long sealing face that tends to become self-sealing. This long path also minimizes the tendency for acid migration through the joint. Bombs using this design can be sealed by simply turning down a knurled cap by hand without using a wrench or spanner. For applications requiring higher temperatures and pressures, the PTFE liners are made with a broad, flanged closure and sealed by tightening the bomb cap with a spanner or, in a larger design, by using cap screws to develop the sealing force. Tight closures for the PTFE cup in Parr microwave bombs are developed and maintained with self- sealing PTFE O-rings.

Spring-Loaded Seals

Since PTFE has a much larger coefficient of thermal expansion than the materials within which a liner is enclosed, a PTFE liner will expand and contract more than its enclosure when these bombs are heated and cooled. To compensate for this difference and to maintain a constant loading on the PTFE seal, all Parr acid digestion bombs have spring-loaded closures which will continue to maintain pressure on the liner seal throughout the operating cycle, and particularly during cooling when PTFE parts would otherwise relax and leak.

Safety Rupture Discs

Safety rupture discs are provided in most Parr acid digestion bombs to protect the bomb and the operator from the hazards of unexpected or dangerously high internal pressures. The burst pressure in each installation is established by a frangible metal disc installed as a sandwich with a matching inner disc which serves as a corrosion barrier to protect the rupture disc from corrosive vapor.

The Nature of PTFE

The use of PTFE for the sample cup in these bombs is an obvious choice, not only because of its unique inertness to strong acids and high temperatures, but also because it is transparent to microwave energy, allowing energy to flow directly to the sample while serving also as an insulator to restrict heat flow from the reaction zone. PTFE does, however, have two characteristics which make it somewhat less than perfect for this application, and the user who understands these deficiencies will be able to minimize their effect upon his work.

First, PTFE has a tendency to creep or flow under pressure or load. This tendency is present even at room temperature and it is accentuated at higher temperatures. At temperatures below 150°C the tendency to creep will be negligible. But as temperatures rise above 150° the creep effect will become more pronounced, making it more difficult to maintain tight seals and resulting in deformation and shorter life for the PTFE components. The extent of the creep effect will be roughly proportional to the maximum operating temperature.

Secondly, PTFE is a porous material. Although the materials and designs used in Parr acid digestion bombs minimize the effects of this porosity, users of these bombs can expect to see evidence of vapor migration across the cover seal and through the wall of the liner itself. Parr is able to minimize these problems by machining these parts from virgin PTFE that has been molded at an optimum pressure selected to reduce any porosity to an absolute minimum. The thick walls and effective seals used in these bombs also help to overcome these undesirable properties. Experiments have shown that the amount of solute lost in this manner during a normal digestion is negligible, but vapor migration into the walls of the PTFE cup will occur and cannot be avoided.

Bomb Selection Guide

Bomb No.	4745	4749	4744	4746	4748
Size, mL	23	23	45	23	125
Maximum charge, grams, Inorganic sample	1.0	1.0	2.0	1.0	5.0
Organic sample	0.1	0.1	0.2	0.1	0.5
Recommended Maximum Temperature, °C	150	250	250	275	250
Absolute Maximum Temperature, °C	250	250	250	275	250
Absolute Maximum pressure, psig	1200	1800	1800	5000	1900
Body Material	SS	SS	SS	SS	SS
Cup seal	Tapered	Flanged	Flanged	Tapered	Flanged
Rupture disc	No	Yes	Yes	Yes	Yes
Closure style	Hand Tighten	Spanner Wrench	Spanner Wrench	Hand Tighten	Six Cap Screws
Bomb dimensions, centimeters, Height overall	8.45	8.45	13.53	12.70	15.2
Maximum O.D.	6.05	6.35	6.35	8.41	9.52
Cup dimensions, centimeters, Inside diameter	3.10	2.64	2.64	3.10	4.45
Inside depth	3.09	4.37	9.50	3.09	8.25
Bomb weight, grams	965	1020	1430	3700	3750

4745 General Purpose Bomb

23 mL, 150°C, 1200 psig

This is the original acid digestion bomb introduced by Parr in 1969 to provide a PTFE lined metal bomb of simple design and minimum cost that can be used safely for routine sample preparation purposes. Its wide acceptance over the intervening years has proved it to be an excellent design for general digestion procedures in which temperatures and pressures are held below 150°C and 1200 psig. It can be used occasionally above 150°, but at elevated temperatures it becomes increasingly difficult to maintain a tight seal.

This bomb does not have a safety rupture disc, but it is designed so that the bottom plate will shear out and release the charge if the bomb pressure should exceed 7000 psig. This 'weak link' design, while effective in preventing a lateral burst which might injure a bystander, is not an adequate substitute for a frangible rupture disc as provided in other Parr designs. For this reason, the 4745 bomb is not recommended for experimental procedures in which explosive pressures may be generated.

Ordering Guide

4745 Acid digestion bomb, 23 mL
A255AC Replacement PTFE cup with cover, 23 mL

4749 General Purpose Bomb

23 mL, 250°C, 1800 psig

This is a 23 mL, general purpose acid digestion bomb, similar to the original 4745 model but modified for use at higher temperatures and pressures, and provided with safety blowout protection as well. Operating temperatures and pressures up to a maximum of 250°C and 1800 psig are permitted in this bomb using a thick-walled PTFE liner with a broad, flanged seal. The forces required to seal the liner are developed by tightening the bomb cap with a spanner while holding the bomb in a special fixture. A safety rupture disc in the bomb head is designed to blow out and release the pressure through an opening in the cover at approximately 3500 psig. With its high temperature capability and safety rupture disc this is an excellent bomb for all general digestion purposes, and particularly for experimental procedures in which the behavior of the reactants has not been well established.

One of the original applications for this bomb, which continues to be one of its principal uses, is for digesting alumina samples at temperatures to 250°C. For this and other difficult digestions, Parr offers an optional tumbling ring that can be attached to the bomb body. With this ring in place, the bomb will roll smoothly when placed on a powered roller, thus providing a convenient means for agitating the charge during long digestion procedures.

Accessories such as the spanner wrench, holding fixture and tumbling ring are not included with the bomb and must be ordered separately.

Ordering Guide

4749 Acid digestion bomb, 23 mL
A280AC Replacement PTFE cup with cover, 23 mL
286AC Corrosion disc, .00211, T347SS
287AC Rupture disc, .003

4744 General Purpose Bomb

45 mL, 250 °C, 1800 psig

This is a 45 mL modification of the 23 mL, 4749 PTFE lined bomb for users who want additional capacity in this popular model. It is made with the same closure as the 23 mL bomb, using a similar thick-walled PTFE cup, 3-3/4 inches deep inside, with a broad flanged seal. Safety blow out protection is provided with a rupture disc that will release pressure through an opening in the cover. Its maximum temperature and pressure ratings, 250°C and 1800 psig, are the same as for the 4749 model. The 4744 bomb is sealed by turning the screw cap down until it is hand tight, then tightening the cap not more than one- eighth turn with a hook spanner. The spanner and holding fixture required for this operation are the same as used with the 4749 bomb. These accessories must be ordered separately.

Ordering Guide

4744 Acid digestion bomb, 45 mL
A280AC2 Replacement PTFE cup with cover, 45 mL
286AC Corrosion disc, .002 inch, T347SS
287AC Rupture disc, .003 inch, lnconel
264AC2 Hook spanner wrench
A285AC Holding fixture
A284AC Tumbling ring

4746 and 4747 High Pressure Bombs

23 mL, 250 °C, 5000 & 3300 psig

This is a high strength acid digestion bomb with a 23 mL, A255AC PTFE cup and cover in a strong outer body which can be made either of stainless steel or nickel. The 4746 stainless bomb is intended for use with nitric, sulfuric or other oxidizing acids, offering best resistance to any acid vapors which might migrate through the PTFE cup under high pressures. The 4747 bomb with a nickel body is to be used with HCI, HF and other reducing acids. Working pressures up to 5000 psi and temperatures to 275°C can be handled in the 4746 stainless bomb, but pressures in the 4747 nickel bomb must be limited to 3000 psi due to the lower physical strength of nickel. The 4746 stainless bomb has a safety rupture disc that will release through a passage in the bottom of the bomb. The nickel bomb does not have a blow- out passage since reactions with reducing acids are not potentially explosive.

These bombs were developed initially for dissolving nuclear fuel samples but many other applications with refractory or highly active materials are indicated. Their heavy construction will be reassuring when working with mixtures which are potentially explosive or whose behavior is unknown and therefore must be handled with care.

The extreme pressures developed in these bombs will tend to deform the PTFE cup, making it difficult to remove the cup from the bomb. To overcome this problem, Parr offers an A263AC spanner jack that will push the cup out of the bomb with a smooth, uniform pressure without damaging the cup. This spanner jack is not included with the bomb and must be ordered separately.

Ordering Guide

4746 Acid digestion bomb, high pressure, stainless steel
4747 Acid digestion bomb, high pressure, nickel
A255AC Replacement PTFE cup with cover, 23 mL
252AC Corrosion disc, .002 inch, T347SS
253AC Rupture disc, .010 inch, T347SS
A263AC Spanner jack assembly with 264AC face spanner
264AC Face spanner only

4748 Large Capacity Bomb

125 mL, 250°C, 1900 psig

The 4748 bomb is the largest of all Parr acid digestion bombs. It has a 125 mL, removable PTFE cup in a stainless steel body with six cap screws in the screw cap to seal the flanged PTFE cup. An expandable wave spring maintains continuous pressure on the seal during the cooling cycle when PTFE parts might otherwise relax and leak. Stirring can be provided with a magnetic stir bar.

A safety rupture disc above the PTFE cup will blow out through an opening in the bomb head if pressure should accidentally reach the 3500 psi range. But for safe operation, pressures in this bomb should never exceed 1900 psi and temperatures must not exceed 250°C. Operations should be conducted well below these limits whenever possible due to the potential destructive forces in a large bomb charge. It also is advisable to test any new procedures for safety in one of the smaller bombs before scaling up to this size. A wrench for the cap screws is furnished with the bomb. No other accessories are required.

Ordering Guide

4748 Acid digestion bomb, 125 mL
A305AC Replacement PTFE cup with cover, 125 mL
310AC Corrosion disc, .00211, T347SS
311AC Rupture disc, .00311, lnconel

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