ASTM D7094 for flash point by modified continuously closed cup (MCCCFP) tester
6. Apparatus
6.1 Flash Point Apparatus, Continuously Closed Cup Operation - The type of apparatus suitable for use in this test method employs a lid of solid brass, the temperature of which is controlled electrically. Two temperature sensors for the specimen and the lid temperatures, respectively, two arc pins for a high voltage arc, and a connecting tube for the pressure monitoring and the air introduction are incorporated in the lid. Associated equipment for electrically controlling the chamber temperature is used, and a digital readout of the specimen temperature is provided. The apparatus and its critical elements are shown in Figs. A1.1 and A1.2.
6.1.1 Test Chamber - The test chamber is formed by the sample cup and the temperature controlled lid and shall have an overall volume of 7 +/- 0.3 mL. A metal to metal contact between the lid and the sample cup shall provide good heat contact but allow ambient barometric pressure to be maintained inside the test chamber during the test. Critical dimensions are shown in Fig. A1.2. The pressure inside the measuring chamber during the temperature increase is monitored. A seal that is too tight results in a pressure increase above ambient due to the temperature and the vapor pressure of the sample. A poor heat contact results in a bigger temperature difference between the sample and the heated lid.
6.1.2 Sample Cup - The sample cup shall be made of nickel-plated aluminum or other material with similar heat conductivity. It shall have an overall volume of 7 +/- 0.3 mL and shall be capable of containing 2 +/- 0.2 mL of sample. The critical dimensions and requirements are shown in Fig. A1.2.
6.1.3 Specimen Temperature Sensor - The specimen temperature sensor (Fig. A1.1) shall be a thermocouple (NiCr-Ni or similar) in stainless steel of 1 mm diameter with a response time of t (90) = 3 s. It shall be immersed to a depth of at least 2 mm into the specimen. It shall have a resolution of 0.1°C and a minimum accuracy of +/- 0.2°C, preferably with a digital readout.
6.1.4 Magnetic Stirring - The apparatus shall have provisions for stirring of the sample. A rotating magnet outside the sample cup shall drive a small stirring magnet which is inserted into the sample cup after sample introduction. The stirring magnet shall have a diameter of 3 +/- 0.2 mm and a length of 12 +/- 1 mm. The rotation speed of the driving magnet shall be between 250 and 270 rev/min.
6.1.5 Air Introduction - The apparatus shall have provisions for introduction of air immediately after each flash test. The air shall be introduced by a short air pulse from a small membrane compressor by means of a T-inlet in the connecting tube to the pressure transducer. The volume of the introduced air, from 0.5 to 2 mL, is dependent on the sample temperature (see Table 1).
6.1.6 Electrical heating and thermoelectric cooling of the lid (see the Peltier element shown in Fig. A1.1) shall be used to regulate the temperature of the test chamber for the duration of the test. The temperature regulation shall have a minimum accuracy of +/- 0.2°C.
6.1.7 A high voltage electric arc shall be used for the ignition of the flammable vapor. The energy of the arc shall be 1.3 +/- 0.3 J (1.3 +/- 0.3 Ws) per arc and the energy shall be applied within 19 +/- 2 m/s. (Warning - Because samples containing low flash material or having a flash point below the preset initial temperature can oversaturate the vapor inside the chamber and hence prohibit the detection of a flash point in the chosen range, a precautionary arc set at 5°C intervals is required while the lid and sample cup temperatures are equalizing.)
6.1.8 The pressure transducer for the flash point detection shall be connected to the connecting tube in the lid and shall have a minimum operational range from 80 to 177 kPa with a minimum resolution of 0.1 kPa and a minimum accuracy of +/- 0.5 kPa. It shall be capable of detecting an instantaneous pressure increase above barometric pressure of a minimum of 20 kPa within 100 m/s.
NOTE 3 - The monitoring of the instantaneous pressure increase above barometric pressure is one of several methods to determine a flash inside the test chamber. A pressure increase of 20 kPa corresponds to a flame volume of approximately 2.5 mL.
NOTE 4 - An automatic barometric correction, which is performed according to the procedure described in 12.1, can be installed in the tester. The absolute pressure reading of the pressure transducer described in 6.1.8 may be used for the correction.
6.1.9 The introduction of a test specimen of 2.0 +/- 0.2 mL shall be accomplished by the use of a pipette or syringe of the required accuracy.
7. Reagents and Materials
7.1 Purity of Reagents - Use only chemicals of purity specified in Table X1.1. Unless otherwise indicated, it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficient purity to permit its use without lessening the accuracy of the determination.
7.1.1 Anisole - (Warning - See 7.2.)
7.1.2 Dodecane - (Warning - See 7.2.)
7.2 Cleaning Solvents - Use only noncorrosive solvents capable of cleaning the sample cup and the lid. Two commonly used solvents are toluene and acetone. (Warning - Anisole, dodecane, toluene, acetone, and many solvents are flammable and are health hazards. Dispose of solvents and waste material in accordance with local regulations.)
8. Sampling
8.1 Obtain at least a 50 mL sample from a bulk test site in accordance with the instructions given in Practice D4057, D4177, or E300. Store the sample in a clean, tightly sealed container at a low temperature.
8.2 Do not store samples for an extended period of time in gas permeable containers, such as plastic, because volatile material may diffuse through the walls of the container. Discard samples in leaky containers and obtain new samples.
8.3 Erroneously high flash points can be obtained when precautions are not taken to avoid loss of volatile material. Do not open containers unnecessarily. Do not make a transfer unless the sample temperature is at least 18°C below the expected flash point. When possible, perform the flash point as the first test.
8.4 Samples of very viscous materials may be warmed until they are reasonably fluid before they are tested. However, do not heat the unsealed sample above a temperature of 18°C below its expected flash point.
8.5 Samples containing dissolved or free water may be dehydrated with calcium chloride or by filtering through a qualitative filter paper or a loose plug of dry absorbent cotton. Warming the sample is permitted, but it should not be heated above a temperature of 18°C below its expected flash point. (Warning - Because samples containing volatile material will lose volatiles and then yield incorrectly high flash points, the treatment described in 8.4 and 8.5 is not suitable for such samples.)
