APIEZON OILS

Apiezon oils consist of esters or specially selected hydrocarbon fractions. They have very low vapor pressures and are very stable. They were developed for, and are ideally suited as, vapor-diffusion pump fluids.

Apiezon oils have advantages over other types of vacuum pump oils in many high vacuum applications particularly with electrical and electronic equipment. The main thermal degradation product of Apiezon oils is carbon which forms conducting layers, as distinct from the insulating layers formed by silicones and their degradation products. This is of particular importance; for example, in vacuum operations with systems containing electrical relays where a minute trace of silicone can effectively open-circuit the relay. Similarly, in apparatus involving the movement of charged particles, as in electron microscopes, mass spectrographs, or pumped X-ray machines, minute traces of silicone or silicate deposits can seriously affect the operation of the equipment. Apiezon oils are extremely efficient pumping oils for this type of equipment and deposits of degradation products have little or no harmful effect.

Apiezon oils are unaffected by traces of water in the vapor being pumped and will not liberate corrosive acids.

Other special advantages of the Apiezon oils over other vapor diffusion pump fluids include their resistance to many different chemical vapors likely to be pumped and good pumping speeds to give low fine side pressures without the disadvantage of very low critical backing pressures.

Apiezon oils are highly refined, specially manufactured products, and as such are tools of the specialist in high vacuum work. To obtain maximum efficiency with the equipment, the oils must be used in the proper manner according to the technique developed in this highly specialized field. Thus vapor diffusion pumps employing Apiezon oils should not be opened to the atmosphere when the oil is hot if the life of the oil is to be utilized to the maximum. Similarly the diffusion pump heaters should not be energized when the backing pressure of the pump is in excess of 0.4 torr. Increases of pressure over short periods will not harm the oil provided the pump is of suitable design.

Table 1 - Properties of Diffusion Pump Oils

(a) over 20oc to 30oC (ASTM D 1903/61T)
(a) over 10oc to 40oC 
(c)  ASTM D 1807-62T Sodium Line

Table 2 - Physical properties of Lubricating and Sealing Oils

Certain Apiezon oils are available which have been treated with a suitable anti-oxidant. These are known as the Apiezon AP series and will withstand a considerable number (500-1,000) of atmospheric exposures while hot. Apiezon Oil AP 201 is an inhibited oil for use in booster diffusion pumps. Oil AP 301 is a synthetic ester with added inhibitors and passivators.

Apiezon oils have found several interesting uses in recent years outside the original high vacuum applications for which they were formulated. To assist research workers in evaluating Apiezon oils for new applications, a comprehensive list of physical properties is given in Table 1. Figure 1 shows the vapor pressure curves for the oils.

One vapor-diffusion pump oil cannot meet all the requirements of the various pumps in use. For example, for largescale pumps a robust, medium high vacuum oil is required; for high vacuum work a high quality, stable, very low vapor pressure fluid is needed; for general laboratory use there is a need for a relatively inexpensive low vapor-pressure fluid. To cover these various requirements, several grades of Apiezon vapor-diff usion pump oils are available.

APIEZON OIL A

This oil is intended for use in small vapor diffusion pumps where an ultimate pressure of 10-4 to 10-5 torr is all that is desired, but where it is required to operate the pump against a higher backing pressure than may be used with Apiezon Oils B and C; with a typical 3-inch pump a maximum backing pressure of 0.4 torr may be used.

Apiezon Oil A is suggested for educational institutions where it is desirable to use a reasonably priced robust oil because of the danger of loss by accident by inexperienced users, and where a moderately high vacuum is usually sufficient.

APIEZON OIL B

Oil B is a good, general purpose fluid for large or small vapor diffusion pumps required to obtain baffled ultimate pressures of 10-6 torr. A good pumping speed may be obtained and the critical backing pressure for Apiezon Oil B is higher than that for Oil C. Although Oil C has the lowest vapor pressure of the Apiezon oils, where a cold trap is used it is possible to obtain a higher vacuum using Oil B. Also the lower boiler temperature required for Oil B results in decreased thermal decomposition.

APIEZON OIL BW

Oil BW is a water-white oil with similar general characteristics of Oil B, though it enables slightly higher pumping speeds to be achieved.  The extremely high level of purity of Apiezon Oil BW makes it suitable for use in the evacuation of mass spectrometers where very minute traces of impurities in the vacuum pump oil can interfere with the accuracy of the spectrometer determinations.

APIEZON OIL C

Apiezon Oil C gives the highest vacuum, without cold trap, of the Apiezon Oils, baffled ultimate pressures of 1 0-7 torr or better being attainable. If a cold trap is used, however, Oil B is preferred.

Oil C is particularly favored by research workers, notably in the field of nuclear physics, since it produces the best possible vacuum of any oil in the Apiezon range when operating with a vapor diffusion pump (without trap).

APIEZON OIL G

Apiezon Oil G is for use in large vapor diffusion pumps required to achieve baffled ultimate pressures of 10-5 torr. It is of particular advantage in equipment frequently open to the atmosphere and where large quantities of air are being pumped since, operating at a lower temperature than many oils, there is less possibility of decomposition.

APIEZON OIL AP 201

AP 201 "booster" pump oil is based on a hydrocarbon oil but, unlike other Apiezon hydrocarbon oils, it is strongly resistant to oxidation. This has been achieved by incorporating an efficient antioxidant which is non-toxic and thermally very stable. The anti-oxidant was selected to have the same vapor pressure characteristics as the base oil so that it does not concentrate in either the liquid or the vapor phase when the oil is distilled.

This fluid is a hydrocarbon oil and as such can be inflammable if used carelessly.   At normal atmospheric pressure and temperature it is completely safe having a flash point of 196'C (PM.C.C.). AP 201 should be used at a boiler temperature not over 250'C, and should be allowed to cool below the flash point before removal from the pump.

APIEZON OIL AP 301

AP 301 consists of a precisely formulated mixture of synthetic organic hindered esters of the type used in supersonic aircraft engine lubrication, together with inhibitors and passivators, all of which have been carefully selected with special attention to their vapor pressure characteristics. This new fluid possesses fire and autoignition characteristics superior to those of conventions hydrocarbon oils or esters and presents none of the surface contamination problems associated with silicone products. It has a high boiling point, low viscosity, can be poured at extremely low temperatures, and as shown in Table 1, has good fire resistance properties which are superior to an equivalent silicone fluid and are comparable with phosphate esters.

The hindered esters used in the manufacture of AP 301 inherently have; better oxidation stability than conventional esters and, as combined with new low vapor pressure and thermally stable inhibitors, give a markedly improved oxidation stability when compared with conventional esters previously used as vacuum fluids.

AP 301 is particularly suitable for systems where electric discharge, filament-emitters or contactor switching systems are involved. Being a non-silicone and non-corrosive material, it will not deposit insulating silicious films or form highly corrosive acids which can damage delicate components. In addition to use as a diffusion pump fluid, the excellent lubricating properties of these inhibited esters make AP 301 an excellent rotary vacuum pump oil.

APIEZON OILS FOR LUBRICATING AND SEALING

Apiezon Oil J and Apiezon Oil K are not vapor diffusion pump oils but are lubricating oils intended for use in rotating gland seals and similar equipment where a good, moderately viscous oil and low vapor pressure are required. These oils are excellent lubricants, as are the Apiezon greases.

Apiezon Oil J is moderately viscous with an estimated vapor pressure at 20'Cof 10-8 torr.

Apiezon Oil K is extremely viscous with an estimated vapor pressure at 20'C of 10-9 to 1 0-10 torr.

See Table 1 for Physical Properties of Apiezon Oils.

PRECAUTIONS: Apiezon Products - Health and Safety

Apiezon products have been widely and safely used in vacuum distillation apparatus in both industry and laboratories for a number of years.  As a result they should not present a health hazard assuming normal standards of industrial hygiene and safety are followed in their handling.

All Apiezon products are bases on petroleum products of a low order of acute toxicity. However, certain individual develop a rash after repeated contact. Therefore, it is recommended that gloves be worn to handle Apiezon. If Apiezon material is inadvertently in contact with the skin, wipe the area carefully, then cleanse thoroughly using a mild soap. Should any Apiezon products be heated for application, vent the fumes and avoid breathing the warm vapors.

In terms of explosion and fire, Apiezon products are considered non-hazardous.

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