Oxygen Bomb Test Research Articles

Ignition and combustion properties of NGO coated AlH3

AlH3 is a highly promising additive for energetic materials and has gained considerable attention as a substitute fuel for aluminum in solid propellants. In order to improve its compatibility with energetic materials and oxidants, carbon coating materials are often used. Nitrated graphene oxide (NGO) was prepared and used as a surface modifier of α-AlH3 in our study. Various analytical techniques were utilized to examine its structure and morphology, including Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), particle size distribution (PSD) and X-ray diffraction (XRD). The oxidization, ignition characteristics, flame propagation behavior and heat of combustion of AlH3 and AlH3/NGO powder were investigated using differential thermal analysis (DTA), a laser igniter, a high-speed camera and an oxygen bomb calorimetry. Results show that NGO coating agent catalyzes the thermal decomposition and hydrogenation process of AlH3, and accelerates the oxidation process of AlH3. The addition of 4 % NGO decreases the oxidation activation energy of AlH3 by about 8.94 %. The laser ignition energy of AlH3/NGO is much lower than that of AlH3, and the ignition energy decreases linearly as NGO is added from 1 % to 10 %. The flame development process supports the good thermal conductivity assistance effect of an appropriate amount of NGO in the combustion process of AlH3 in air, which is consistent with the result of oxygen bomb test, indicating that the addition of NGO leads to an improvement in the combustion efficiency of AlH3.This may provide valuable insights for the development of new high-energy solid propellants.

Effect of the natural antioxidant ferulic acid and its ester derivatives on the oxidative stability of ester-based lubricants: Experimental and molecular simulation investigations

Pentaerythritol oleate, as one of the ester-based lubricants, has excellent lubricity and low temperature properties, but is susceptible to oxidation due to the susceptible α-H of isolated double bonds in the molecular structure. Ferulate natural antioxidants, including the ferulic acid and its two ester derivatives were selected, focusing on exploring mechanisms, especially the effect of physical factors on the antioxidant properties. The chemical activity, dispersion, mobility and oxygen resistance of antioxidants were studied by molecular simulation. These combined results of the simulations show that the sequence of the antioxidation were isooctyl ferulate > ethyl ferulate > ferulic acid. Then the rotational oxygen bomb test and the pressure differential scanning calorimetry results confirmed the antioxidant activities of the three species. According to the Rancimat test, the oxidation induction time of the isooctyl ferulate/PETO was increased by 300% compared to the control.

Enhanced decomposition of laminated ammonium perchlorate composite

In order to improve the thermal decomposition performances of ammonium perchlorate (AP), the laminated AP composite was prepared by ice-template induced self-assembly method. In this study, Iron-Konjac glucomannan (Fe3+-KGM) hydrosol rich in AP was selected as the freezing precursor. Through directional freezing of precursor and recrystallization of AP molecules, the laminated AP composite was obtained. The results showed that the thickness of the lamellar composite structure is about 10 to 30 μm, and the recrystallized AP particles are uniformly dispersed in the gel system. The oxygen bomb test results show that the micro-/nano-layered structure can significantly improve the sample’s combustion heat value. Thermal analyses indicated that with the increasing Fe3+ content, the peak exothermic temperature of lamellar AP composite at different heating rates both showed a decreasing trend. With 10 wt% Fe(NO3)3·9H2O added, the decomposition peak temperature decreased from 433.0 to 336.2 °C at a heating rate of 5 °C/min, and the apparent activation energy (Ea) decreased dramatically from 334.1 kJ/mol to 255.4 kJ/mol. A possible catalytic thermal decomposition mechanism of lamellar AP composite catalyzed by Fe3+ was proposed. This work is beneficial to the structural design of other energetic materials.

Synthesizing Hindered Structure Poly (p‐Phenylenediamine) by Enzymatic Catalysis and Evaluating Its Antioxidation Mechanism in Biodegradable Castor Oils

AbstractIn this study, poly(p‐phenylenediamine) (PPDA) was synthesized by an enzymatic polymerization method using p‐phenylenediamine as the monomer in the water phase. The PPDA structure was characterized by infrared (IR), gel permeation chromatography, and elemental analysis. The antioxidation behavior of the as‐synthesized PPDA in biodegradable castor oil was investigated using a rotary oxygen bomb test and pressurized differential scanning calorimetry. A theoretical calculation was conducted to investigate its antioxidation mechanism. PPDA was found to exhibit excellent oxidation resistance in castor oil at 150 °C, which effectively prolonged the oxidation induction time of the oil. The results obtained herein suggest that as with phenolic antioxidants, PPDA with a hindered structure effectively improves the antioxidation performance of the oil by enhancing the stability of nitrogen free radicals.

DBHP-Functionalized ZnO Nanoparticles with Improved Antioxidant Properties as Lubricant Additives.

In this article, 3-(3,5-di- tert-butyl-4-hydroxyphenyl) propionic acid (DBHP)-functionalized ZnO (DBHP-ZnO) nanoparticles were synthesized by decomposing the organometallic precursor Zn(DBHP)2 under alkaline conditions. This in situ surface modification method can induce small-sized ZnO nanoparticles (5 nm) and form strong linkage between DBHP and ZnO nanoparticles. DBHP as an organic compound hindered phenol antioxidant that not only improved the dispersion stability of the prepared DBHP-ZnO nanoparticles in the lubrication oil but also scavenged free radicals produced during the oxidation process of oil. Compared with DBHP, the thermal stability of the prepared composite antioxidant was greatly enhanced by introducing inorganic ZnO nanoparticles, which was proved by the results of the thermogravimetric analysis test. A rotary oxygen bomb test, pressurized differential scanning calorimetry, and free-radical-scavenging method all showed that DBHP-ZnO nanoparticles had better antioxidant properties than DBHP under high temperature in the base oil of di- iso-octylsebacate (DIOS). The activation energy of the oxidation process was used to analyze this result by the model-free methods, including the Flynn-Wall-Ozawa method and the Kissinger equation. The calculated results showed that DIOS containing DBHP-ZnO nanoparticles have the lowest reaction constant and the longest half-life period compared to those of individual DBHP and ZnO nanoparticles, which is attributed to the combined action of the organic-inorganic composites. Besides, DBHP-ZnO nanoparticles as the additive are able to improve the antiwear ability of DIOS to some extent. Therefore, the as-prepared DBHP-ZnO nanoparticles with desired dispersibility as well as better thermal stability and antioxidant ability than DBHP in the DIOS base oil could be a potential high-performance nanocomposite additive for a synthetic lubricant base oil like DIOS.

The Oxidation and Combustion Properties of Gas Atomized Aluminum−Boron−Europium Alloy Powders

AbstractIn this paper, the Aluminum−boron−europium ternary alloy fuels with boron content of 1.5∼4.85 wt. % and europium content of 3 wt. % were prepared by the close‐coupled gas atomization. XRD, SEM, TG‐DTA and oxygen bomb test were used to analyze the phase constituents, morphology, thermal oxidation behavior and combustion exothermic property of powders, respectively. The functions of boron and europium on the combustion of metal fuels were studied, and a reasonable oxidation model of the alloy particles was proposed. The results show that there are Al, AlB2, Al4Eu and B6Eu in the alloy. When the europium content is constant, the combustion enthalpy of the Al−B−Eu alloy powder firstly increases and then decreases as the boron content increases. Additionally, at oxygen pressure of 3.0 MPa, the Al−3.5B−3Eu ternary alloy powder burned completely with the maximum combustion enthalpy of 33324.5 J g−1. This increases by 11 % compared with theoretical combustion enthalpy of aluminum powder (31.1 kJ g−1). Al−3.5B−3Eu undergoes a dramatic oxidation exothermal phenomenon at 1110 °C with the weight increase efficiency of 53.66 %, which is 1.7 times that of aluminum. Due to the synergistic effects between the phase of B6Eu and AlB2 inside the alloy particles, the Al−3.5B−3Eu alloy powder shows excellent exothermic performance.

Synthesis of Styrenated Sulfur- and Phosphorus-Free Organic Titanate and Evaluation of Its Tribological and Antioxidant Properties as an Additive in Poly-α-olefin

The styrenated sulfur- and phosphorus-free organic titanate (STAE) was synthesized via an in situ method with soybean oil, diethanolamine, and isopropyl titanate. The tribological and antioxidant behavior of the as-synthesized STAE as an additive in PAO was evaluated by a four-ball test, a rotary oxygen bomb test (ROBT), and differential scanning calorimetry (DSC), and its oxidative stability was estimated through thermogravimetric analysis (TGA). The as-synthesized STAE exhibits excellent antiwear and load-carrying capacities as well as good antiwear synergism with zinc dialkyldithiophosphate (ZDDP) in poly-α-olefin (PAO). STAE in PAO also showed good synergistic antioxidation effects with the traditional additive p,p-(dioctyldiphenylamine (DODPA). This is because STAE can effectively reduce the oxidation rate of DODPA, which was confirmed by the results of Fourier transform infrared spectroscopy (FTIR) and gas chromatography-tandem mass spectrometry (GC/MS).

Preparation and characterization of sintered B/MgB2 as heat release material

Sintered B/MgB2 (S-B/MgB2) was originally prepared by introducing Mg to B and sintering the system under appropriate temperature and atmosphere. During the sintering process, B2O3 layer was depleted by Mg reduction and the product was characterized by XRD and SEM methods. The XRD results show that the constituents of S-B/MgB2 are B, B6O, MgB2 and MgO. Coupled with EDS, it is noticed that Mg has a desirable distribution in the particles, indicating a uniform configuration of S-B/MgB2. TG-DSC method was applied to verify the microstructure and study the oxidation processes of S-B/MgB2. It is noticed that S-B/MgB2 enjoys a high thermal stability due to the protection from MgB2/MgO shell. In addition to that, because of the absence of B2O3 layer and increased active B content, the length and rate of the oxidation reaction increase, resulting in a boost of reaction ratio and heat release in TG-DSC. Accompanied with theoretical calculation and oxygen bomb test results, it appears that S-B/MgB2 also enjoys a heat release which is not evidently affected by external conditions. Therefore, S-B/MgB2 has a promising future as heat release material.

Enzymatic Oligomerization of p-Methoxyphenol and Phenylamine Providing Poly(p-methoxyphenol-phenylamine) with Improved Antioxidant Performance in Ester Oils

Poly(p-methoxyphenol-phenylamine), denoted as P(MOP-PA), was synthesized via the enzymatic oligomerization of p-methoxyphenol and phenylamine monomers in the presence of horseradish. The structure of the as-synthesized product was confirmed by Fourier transform infrared spectrometry, time-of-flight mass spectrometry, and elemental analysis, and the oligomerization process was studied by high-performance liquid chromatography. Moreover, the antioxidation behavior of P(MOP-PA) as an antioxidant in several ester oils was evaluated by rotary oxygen bomb test and pressurized differential scanning calorimetry, and its antioxidant mechanism was discussed. It was found that, as the antioxidant in various base oils, P(MOP-PA) exhibits excellent antioxidation ability at elevated temperatures of 150 and 210 °C. In addition, P(MOP-PA) has an antioxidant ability that is better than that of poly(p-methoxyphenol), and it exhibits an antioxidation ability in synthetic ester oil, such as di-iso-octyl sebacate, that is muc...

The development of a model for the prediction of polymer spontaneous ignition temperatures in high pressure enriched oxygen across a range of pressures and concentrations

High pressure enriched oxygen is used in a wide number of areas, including aircraft, medical breathing apparatus, diving, mining and mountaineering operations. It is also used for a number of industrial processes, but is most commonly used for combustion. Where the pressure or concentration of oxygen is increased well above that of atmospheric, oxidation reactions occur more readily, and at a faster rate, relative to those under atmospheric conditions. Thus the criteria used for polymer selection is key to preventing, or at least limiting, the possibility of a catastrophic oxygen incident which endangers both property and human life. In this work spontaneous ignition temperature (SIT) data obtained in high pressure enriched oxygen from both differential scanning calorimetry and oxygen bomb testing are compared. A model is derived to enable the calculation of a SIT of a non-metal at any pressure and oxygen concentration using existing test data from other pressures. This has been shown to work with reasonable success for most materials tested, being validated using the comparison of test data from the oxygen bomb test and Pressurised Differential Scanning Calorimetry (PDSC) testing. These results may indicate the suitability of a PDSC for safety testing in the future. Further work is needed to increase the data base of ignition test data from PDSCs, and thermodynamic constants to allow for the direct comparison, and to assess the suitability of this apparatus for safety testing of more materials.

Synthesis of 1,3,5-Tris(phenylamino) Benzene Derivatives and Experimental and Theoretical Investigations of Their Antioxidation Mechanism

1,3,5-Tris(phenylamino) benzene and a series of its substitution derivatives were synthesized. The structure of the as-synthesized products was confirmed by nuclear magnetic resonance spectroscopy and high resolution mass spectra. Moreover, the antioxidation behavior of 1,3,5-tris(phenylamino) benzene and its substitution derivatives as antioxidants in several ester oils was evaluated by a rotary oxygen bomb test and pressurized differential scanning calorimetry, while theoretical calculations were conducted to examine their antioxidation mechanism. It was found that 1,3,5-tris(phenylamino) benzene exhibits better antioxidation ability at elevated temperature (150 and 210 °C) than commonly used commercial antioxidant diphenylamine. In the meantime, the substitution groups exhibit significant effects on the antioxidation behavior of 1,3,5-tris(phenylamino) benzene and its derivatives. This is because the substituents result in changes in the molecular structure and electronic effect of the as-synthesized p...

Synthesis of ploy(p-methoxyphenol) and evaluation of its antioxidation behavior as an antioxidant in several ester oils

Ploy(p-methoxyphenol), denoted as PMOP, was synthesized via an enzymatic polymerization method with p-methoxyphenol as the monomer. The corrosion resistance, tribological properties and thermal stability of as-synthesized PMOP were examined. The antioxidation behavior of as-synthesized PMOP as an antioxidant in ester oils was evaluated by rotary oxygen bomb test and pressurized differential scanning calorimetry. It was found that PMOP exhibits excellent antioxidation ability at 150°C and 210°C in various base oils. Besides, PMOP has much better antioxidation ability in synthetic ester oil like di-iso-octyl sebacate than several commonly used commercial hindered phenolic antioxidants.

Natural and Synthetic Antioxidant Additives for Improving the Performance of New Biolubricant Formulations

Knowledge of the oxidative stability of vegetable oils for lubricant applications is a key point, because vegetable oil oxidation potential is the main disadvantage for its use as a lubricant. Oil degradation after an oxidation process can seriously affect its lubricating function and increase wear. In this work, two different methods for evaluating the oxidation stability of lubricating vegetable oils, the oxidation onset temperature, characterized through DSC measurements (ASTM E 2009-08), and the pressure drop in the oxygen pressure vessel (ASTM D 942-02), have been used. Additionally, thermogravimetric analysis and FTIR studies have also been carried out. High-oleic sunflower (HOSO) and castor (CO) oils were selected and blended with natural ((+)-α-tocopherol (TCP), propyl gallate (PG), l-ascorbic acid 6-palmitate (AP)) or synthetic antioxidants (4,4'-methylenebis(2,6-di-tert-butylphenol) (MBP)), with the aim of formulating biodegradable vegetable-based lubricants according to REACH regulation. (1) The results showed that the most effective biodegradable antioxidant is PG, comparable to MBP, whereas lower effectiveness was obtained for TCP and AP. In relation to the methods tested, DSC measurements achieve accurate data more quickly for evaluating the oxidation stability of these basestocks, showing a linear correlation with the traditional method based on the oxygen bomb test. The empirical equation obtained depends on the mechanism involved in the antioxidant activity.

Comparison of four accelerated stability methods for lard and tallow with and without antioxidants

AbstractThe oxidative stability of lard and tallow with and without antioxidants was evaluated by four accelerated stability methods, the active oxygen method (AOM), the oxygen bomb test, the Rancimat method, and the Schaal oven test. The results indicated that the oxidative stability of animal fats and the relative effectiveness of an antioxidant in the fats could have different mechanisms. When the protective index was used to demonstrate the relative effectiveness of the antioxidants, the results suggested that the Rancimat Method may be the least reliable method compared with AOM, oxygen bomb test, and Schaal oven test. More than one accelerated stability method is recommended for evaluating the effectiveness of an antioxidant or the oxidative stability of fats.

The combined effect of tocopherols, L-ascorbyl palmitate and L-ascorbic acid on the development of warmed-over flavour in cooked, minced turkey

The combined effect of a natural mixture of tocopherols (extracted from soybean oil), L-ascorbyl palmitate and L-ascorbic acid on oxidation of cooked, minced turkey meat, measured as 2-thiobarbituric acid reactive substances (TBARS) after reheating, was studied for three concentrations of each additive in a total of 19 combinations plus two control batches, each at two different oxygen pressures (21 and 1% O 2), during 9 days of chilled storage (5 °C), and compared with an accelerated oxygen-bomb test at 90 °C. For initial screening of antioxidative activity, the latter test has been found to be a valuable analytical tool. The effect of the additives from the storage experiment could be measured by two parameters; (i) M, the maximal level of TBARS, and (ii) r, a first-order rate constant for development of TBARS. Tocopherols reduced M most significantly, L-ascorbyl palmitate to a lesser degree, and L-ascorbic acid increased M, in effect acting as a prooxidant. For 21% O 2 packaging, the effect on M of the three additives and their concentrations was multiplicative and could be quantified by a protection factor, P (i-x,j-y,k-z), obtained by multiplication of the relative protection obtained by each additive at the lowest concentration used. In contrast to M, r was reduced more by L-ascorbyl palmitate than by tocopherols, while L-ascorbic acid had only a small effect on r. The combined use of tocopherols and L-ascorbyl palmitate in cooked, minced turkey meat products, optimises oxidative protection as a result of indirect synergism, i.e. tocopherols reduced mainly the maximum level of oxidation, while L-ascorbyl palmitate reduced the rate at which the maximum level of oxidation is approached.

An improved apparatus for oxygen bomb testing

AbstractAn improved oxygen bomb apparatus has been developed. The increased precision and readability of the continuous pressure recording allows a new method of end‐point measurement. It was possible to use smaller test samples than any previously reported. Sample size and oxygen pressure were shown to be relatively unimportant variables. Temperature is the most useful variable for controlling test time. This is preferable over sample dispersion or addition of catalysts in terms of simplifying the procedure. Peroxide formation at the oxygen bomb test end point is three to four times the value at the end point of the Active Oxygen Method.

The properties and performance of Poly AOTM -79; a nonabsorbable, polymeric antioxidant intended for use in foods.

Abstract and SummaryThe physical, chemical, and biological characteristics of Poly AO™‐79, a composition selected from a class of polymers prepared by the polycondensation of divinylbenzene and a blend of various sterically hindered phenols and hydroquinone, are discussed. Data are presented indicating that Poly AO™‐79 demonstrates excellent antioxidant activity in stabilizing vegetable oils when compared to monomeric food grade antioxidants [butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), and tertiary butylhydroquinone (TBHQ)] as measured by the active oxygen method (AOM) and oxygen bomb test. Stability tests using thermogravimetric analysis indicate that the material is not depolymerized in the presence of air at temperatures up to 300 C while BHT, BHA, and TBHQ are completely volatilized at 150–170 C. Using14C‐radiolabeled antioxidants, the physical losses of Poly AO™‐79 from frying oil heated to 190 C is nil while 65% and 80% losses are incurred with BHA after 1 and 2 hr holding time, respectively. The physical carry‐through of Poly AO™‐79 onto potatoes from frying oil at 190 C is quantitative as compared to ca. 20% losses with BHA and TBHQ. Sensory panel tests reflect that the carry‐through of Poly AO™‐79 is in an active form as evidenced by the prolonged shelf‐life of chips fried in oil containing Poly AO™‐79 as compared to BHA and TBHQ. Rats and mice orally dosed with14C‐radiolabeled antioxidants indicate that Poly AO™‐79 is virtually not absorbed from the gastrointestinal tract (ca. 0.2–0.6%) while monomeric antioxidants are readily transported (80–100%). Acute oral and intraperitoneal toxicity tests indicate that Poly AO™‐79 is without effect at the highest dose tested (10 g/kg body weight).

Volumetric Oxygen-Absorption Test for Rubber Aging

Abstract A volumetric oxygen-absorption test for aging of rubber has been investigated from the point of view of the effect of cure and the effect of mercapto-benzimidazole on the aging behavior. The test has also been evaluated by comparison with conventional air oven and oxygen bomb aging. A compounded but uncured Hevea black stock is more resistant to oxidation than the vulcanized material, but after a reasonable cure is obtained, further heating produces only a small change in the rate of oxygen absorption. The change in physical properties corresponding to a given amount of oxygen absorbed varies somewhat with time of cure in the initial stages, but after the absorption of 4 or 5 cc. of oxygen per gram of rubber, the changes in most physical properties are a direct function of the amount of oxygen absorbed. Neither time of cure nor the presence or absence of inhibitor has any significant effect on the subsequent rate of change in such properties as tensile strength and ultimate elongation for a given amount of oxygen absorbed. Oven aging data on identical time cures confirm the reported superiority of a combination of mercaptobenzimidazole with a conventional type of anti-oxidant. Oxygen absorption data reveal, however, that mercaptobenzimidazole causes a significant decrease in the rate of oxidation of a Hevea black stock, and thus it clearly functions at least in part as an antioxidant in the usually accepted sense. The deterioration of properties is, in general, proportional to the oxygen absorbed, except in the early stages of oxidation where the mercaptobenzimidazole stocks change somewhat less than the controls for a given amount of oxygen absorbed. When the cures are selected to give comparable initial properties, however, the change in tensile strength of the mercaptobenzimidazole stocks with amount of oxygen absorbed is essentially the same as for the controls, even in the initial stages. These data suggest that the observed protection imparted by mercaptobenzimidazole results from a combination of two factors: (1) the normal antioxidant activity of mercaptobenzimidazole, which reduces the amount of oxygen absorbed; and (2) an effect on the nature of the cure attained when mercaptobenzimidazole is present, such that the absorption of a given amount of oxygen in the early stages is not accompanied by as great a change in properties. Thus, it appears that the deactivating effect may be the result of the effect of this material on the vulcanization process rather than a direct effect on the oxidation process. A comparison of the effect of oxygen absorption, air oven, and oxygen bomb aging methods on changes in physical properties of Hevea black stocks shows that the results obtained by oxygen absorption and air oven methods (both at 100° C) are similar, but that the higher oxygen concentration of the oxygen bomb test (70° C and 300 pounds per square inch) apparently results in a higher proportion of chain scission when compared to cross-linking of the polymer chains.

Aging of Rubber in the Oxygen Bomb at Room Temperature

Abstract The work described below was carried out as a first step in determining whether an oxygen-bomb test at room temperature could be used as an accelerated aging test for unvulcanized rubber compositions, e.g., as used on surgical and adhesive plasters and for combining shoe fabrics, because a high-temperature test is unsatisfactory in such cases, owing to the melting of the compositions. The only infallible way of assessing the value of an accelerated test for such compositions is by comparison with natural aging, but as this is a very lengthy process and as the deterioration is difficult to measure quantitatively, it was decided to make preliminary tests on the effect of high oxygen concentration at room temperature by using vulcanized rubber. Although the results proved to be negative so far as the original purpose of the work was concerned, it is considered of interest to place them on record in view of the prominence given in some papers on aging to the relationship between oxygen concentration and rate of oxidation and deterioration of rubber. A mix composed of rubber 100, sulfur 3, zinc oxide 5, stearic acid 1, and diphenylguanidine 0.75, was vulcanized for 30 minutes at 153° C. Tensile tests, using standard ring-specimens and the Schopper machine, were made on unaged specimens and on specimens that had been aged (1) in an oxygen bomb at 300 lb. per sq. in. oxygen pressure and at room temperature (about 10° C), (2) in a Geer oven at 70° C. Four rings were used for each test, the tensile strength and breaking elongation figures quoted being the average for the two rings giving the highest tensile strength, and the figures for the elongations at constant loads the average of all four rings.

The Effect of Specimen Thickness on Rate of Artificial Aging

Abstract From time to time the question of the effect of thickness on the rate of deterioration of rubber samples subjected to accelerated aging tests, particularly the oxygen-bomb test, is raised. Apparently little experimental work has been done, and no satisfactory answer has yet been given. According to the well-known laws of mass action, the rate of deterioration should slow up with increasing thickness of rubber, and one might expect thin articles to deteriorate further, in a given bomb-aging period, than similar articles of heavier gage. Nevertheless, it is tacitly assumed that variations in thickness have practically no effect—and for small variations this assumption is reasonable considering the oxygen concentration used; or possibly no assumption is made, and the aging tests are just performed mechanically without regard for theoretical considerations and possibilities. The fact that the oxygen-bomb is used largely for comparing the aging quality of similar articles, usually of comparable gage, has doubtless tended to keep the question of the influence of thickness dormant. Again, in the testing of laboratory compounds, most laboratories have standardized on a uniform thickness of cured slabs (0.075″), so that the question of thickness in this type of work does not come into the picture. Occasionally, however, it may be desirable to compare the bomb-aging behavior of articles of quite different types, and when in such cases there is a large difference in thickness, the validity of the comparison may be called in question.