A N EXPERIMENTAL STUDY OF THE OXIDATION OF GRAPHITE IN HIGH-TEMPERATURE SUPERSONIC AND

by Iruin

LangZey Langley

HYPERSONIC ENVIRONMENTS

M. Miller and Kenneth Satton 9": 6 - -

https://ntrs.nasa.gov/search.jsp?R=19660019918 2020-04-25T04:09:07+00:00Z

TECH LIBRARY KAFB, "I

AN EXPERIMENTAL STUDY OF STHE OXIDATION OF GRAPHITE

IN HIGH-TEMPERATURE SUPERSONIC AND HYPERSONIC ENVIRONMENTS

By I r v i n M. Mi l l e r a n d Kenneth Sutton

Langley R e s e a r c h C e n t e r Langley Station, Hampton, Va.

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

For s a l e by the Clearinghouse for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price $2.00

AN EXPERIMENTAL STUDY OF THE OXIDATION OF GRAPHITE

IN HIGH-TEMPERATURE SUPERSONIC AND HYPERSONIC ENVIRONMENTS

By Irvin M. Miller and Kenneth Sutton Langley Research Center

SUMMARY

An experimental study was made of the oxidation of graphite exposed to high- temperature supersonic and hypersonic tes t s t reams of air and air-nitrogen mixtures. Oxidation-rate data were obtained on hemispherical-shaped models of three grades of graphite over wide ranges of aerothermal parameters t o define the oxidation behavior of graphite and to compare this behavior with diffusion-controlled theory.

Models of ATJ graphite maintained a smooth shape and oxidized in a consistent manner at a rate below the maximum theoretical rate for diffusion-controlled reactions over a wide range of test conditions. However, most of the models of AHDG and AGSX graphite became distorted at oxygen-mass-flux levels above 0.03 lbm/ftZ-sec (0.146 kg/mZ-s) and at stagnation pressures behind the shock wave above 5.17 atmos- pheres. Because of equipment limitations, the stagnation pressure and oxygen-mass-flux levels at which this phenomenon begins was not determined. Furthermore, the distorted models of these two grades lost mass in an unpredictable and catastrophic manner at rates ranging up to 2L times the maximum rate for diffusion-controlled theory. At pres- ent, the factors which could explain the distortion effect in AHDG and AGSX graphites are not known.

2

INTRODUCTION

Graphite is being considered for use in hyperthermal environments because of its superior strength-weight ratio at temperatures above 3500' R (1940O K), relatively low cost, high thermal conductivity, high resistance to thermal shock, high emissivity, and ease in machining. A serious disadvantage to the use of graphite is that it begins to oxidize to a gaseous product at temperatures below 1000° R (560' K) with a consequent loss of material. In order t o predict the performance of graphite for various flight mis- sions, it is necessary to have an understanding of its oxidation behavior over a wide range of aerothermal parameters (such as pressure and oxygen concentration). Furthermore, an understanding of this oxidation behavior may result in an improved comprehension of

i

the oxidation behavior of carbonaceous chars which a r e formed on charring ablators, a class of materials being considered for reentry heat-shield applications.

The reaction of graphite with oxygen in a flowing airstream is either chemically controlled, diffusion controlled, or a combination of these, depending on the surface tem- perature. (See ref. 1.) A chemically controlled reaction occurs at lower surface tem- peratures where an excess of oxygen is present at the graphite surface, and the reaction rate depends only on the chemical kinetics of graphite and oxygen. At higher surface temperatures the oxygen supply at the surface becomes rapidly depleted, and the reaction rate becomes limited by the rate at which oxygen diffuses to the reacting surface. The rate of this diffusion-controlled reaction is therefore a function of the oxygen mass flux to the surface.

Numerous papers have been published on the chemically controlled oxidation of carbon and graphite in static or low-flow-rate oxidizing environments. (For example, see refs. 2 and 3.) The results of such studies, which a r e usually given in some form of the Arrhenius equation, have shown a wide variation in reaction rates which is generally thought t o be due to differences in the materials tested. Some theoretical papers have shown that the diffusion-controlled oxidation of graphite should be influenced by the aero- dynamic characteristics of the airstream and body shape (see ref. 3); however, data on the oxidation behavior of graphite have not been adequate to allow a prediction of this behavior over a range of environmental conditions. One experimental study conducted in a hypersonic environment (ref. 4) yielded a limited amount of data for defining the effect of aerothermal parameters on oxidation rates.

Most aerothermal structural applications being considered for graphite and charring ablators involve high surface temperatures between 2800° R (1560' K) and 5000' R (2780O K) at which diffusion-controlled reactions a r e expected. (See ref. 5.) Therefore, the primary purpose of the present experimental study was to investigate the oxidation behavior of graphite at surface temperatures above 2800° R (1560' K) as a function of aerothermal parameters in high-temperature supersonic and hypersonic environments and to compare this behavior with existing theory.

The experimental program was carried out with three grades of graphite to deter- mine whether a variation in physical properties would affect oxidation behavior. Wide ranges of aerothermal parameters were included in the program by exposing hemispher- ical graphite models with diameters between 0.375 and 1 inch (0.953 and 2.54 cm) to the jets of three test facilities: the Langley 11-inch ceramic-heated tunnel, the arc-heated materials jet at the Langley Research Center, and the Langley 20-inch hypersonic arc- heated tunnel. The oxygen content in the jets of the latter two facilities was varied to increase the range of oxygen mass flux. The stagnation pressure behind the shock wave was varied from 0.06 to 8.28 atmospheres, the stagnation enthalpy was varied from

2

d 595 to 4080 Btu/lbm (1.38 to 9.47 MJ/kg), and the oxygen mass fraction was varied from 0.059 to 0.232.

SYMBOLS

The units used for the physical quantities defined in this paper are given both in the U S . Customary Units and in the International System of Units (SI). (See ref. 6.) Appendix A is included for the purpose of explaining the relationships between these two systems of units.

C mass fraction of oxygen

H enthalpy, Btu/lbm (MJ/kg)

k specific reaction rate, lbm/ft 2-sec-atma (kg/mZ-s - (N/m2)a)

M Mach number

I5 mass -transfer rate, lbm/f t 2- s e c (kg/m 2- s)

Prandtl number Npr

P pressure, atm (1 atm = 101325 N/m2)

q heat-transfer rate, Btu/ft2-sec (MW/m2)

r model radius, in. (cm)

T temperature, ?R (OK)

t time, sec (s)

X mole fraction of oxygen

a order of the reaction

P blowing coefficient

x mass of carbon reacted per unit mass of oxygen consumed

Subscripts :

C carbon

e at the outer edge of the thermal or concentration boundary layer

3

0

t ,2

W

stagnation condition behind the shock wave

at the wall

METHODS AND TESTS

Models and Techniques

The hemispherical-shaped models used in the present study were machined to 0.375-inch (0.953-cm), 0.5-inch (1.27-cm), and 1-inch (2.54-cm) diameters, as shown by the drawing in figure 1. This range in model size was included t o aid in varying the heat- transfer rate to the stagnation point. Three grades of graphite were used: AHDG, AGSX, and ATJ. These grades were selected to determine whether different graphite grades would have different oxidation rates under diffusion-controlled conditions. Some proper- ties of the different graphite grades, as given by each manufacturer, are summarized in table I.

Test conditions were chosen to obtain a wide variation in the important aerothermal parameters expected to influence the oxidation of graphite. These parameters were stag- nation pressure, stagnation enthalpy, and s t ream mass fraction of oxygen. Stagnation pressure in the present report always refers to the stagnation pressure behind the shock wave. In order t o obtain a wide variation of test conditions, models were tested in three different facilities at the Langley Research Center: the Langley 11-inch ceramic-heated tunnel, the arc-heated materials jet at the Langley Research Center, and the Langley 20-inch hypersonic arc-heated tunnel. Test conditions used in the study are shown for each facility in table II.

The Langley 11-inch ceramic-heated tunnel, described in reference 7, was adapted with a Mach 2 nozzle having an exit diameter of 1.332 inches (3.38 cm). This arrangement provided airstreams in which the model size and/or stagnation pressure were varied (see table 11) to obtain a range of oxygen mass flux at high stagnation-pressure levels. This range of oxygen mass flux at high stagnation-pressure levels was extended by the use of the arc-heated materials jet, described in reference 8, which was equipped with a Mach 2 nozzle having a 0.738-inch (1.874-cm) exit diameter and an air-nitrogen mixing system. A broad range of oxygen mass flux was obtained by varying the volume ratio of air to nitro- gen in the test stream. The Langley 20-inch hypersonic arc-heated tunnel described in reference 9 and shown in figure 2 was used to provide air and air-nitrogen test s t reams in which the stagnation pressure and air-nitrogen volume ratio were varied at low stagnation- pressure levels to extend further the range of oxygen mass flux. A Mach 6 nozzle with an exit diameter of 6.6 inches (16.76 cm) was used in this tunnel.

4

The test streams for all these facilities had low contamination levels. The arc- heated jet and arc-heated tunnel utilize water-cooled copper electrodes and, as reported in reference 8, produce airs t reams with less than 0.1 percent contamination. The ceramic-heated tunnel had a low-mass-flow airstream with a large ceramic pebble bed, and tests of graphite models in a cold airstream from this system indicated no significant erosion of graphite models due to dust contamination.

The models were held in the test stream by water-cooled stings. Models, model holders, and sting assemblies are shown in figure 3 for the 0.375-inch-diameter (0.953-cm) and l-inch-diameter (2.54-cm) models. The assembly for the 0.5-inch- diameter (1.27-cm) model is similar in appearance to that for the 0.375-inch-diameter (0.953-cm) model. The four-model holder shown in figure 3(c) was used only in the hypersonic arc-heated facility where four 0.375-inch-diameter (0.953-cm) models could be tested simultaneously because of the large size of the nozzle exit.

In all three facilities the test procedure was generally the same. The test facility and instrumentation were programed for a specific run time. After flow stabilization was obtained in the test stream of the facility, movie cameras and a photographic pyrometer were turned on, and the model was inserted into the center of the test stream. The model was removed from the test stream at the specific test time or earlier if it appeared to oxidize rapidly. Movie cameras and a photographic pyrometer were used to record the recession of the model, and the photographic pyrometer was used to record model surface temperatures. In many of the runs an optical pyrometer w a s also used to measure the surface temperature at the stagnation point and to aid in observing the model under test. For most of the runs made in the supersonic arc-heated materials jet only the optical pyrometer was used to measure surface temperature.

Instrumentation and Data Reduction

The surface temperature of the model at the stagnation point was measured in most of the runs by a photographic pyrometer described in reference 10. This instrument was chosen because it provided a permanent measurement record of the model surface tem- perature at and near the stagnation point with a measurement e r r o r under the conditions of the tes t of about &4 percent. Data were recorded every second for shorter runs and every other second for longer runs. The optical pyrometer, used either with the photo- graphic pyrometer or alone, was calibrated with a standard lamp source and was found to have an e r ro r of less than &2 percent. Measured surface temperatures were corrected for emissivity with a value of 0.77. (See ref. 11.)

Model recession and shape change were recorded by 16-mm black and white and color film in cameras operated at 64 or 400 frames per second and also by 35-mm film in the photographic pyrometer operated at 20 frames per second. Data reduction of the

9 %

5

I I 1 1 1 I I

receded model length on the 16-mm film was accomplished with the aid of a movie pro- jector equipped with a still frame device and a frame counter. The projected length of the image was measured by a linear scale within an accuracy of about 1.5 percent. The elapsed time was determined, within an accuracy of a fraction of a second, by dividing the number of elapsed frames by the predetermined framing rate. Data reduction of the receded model length on the 35-mm film was accomplished with the aid of a contour pro- jector equipped with a mechanical stage and micrometer dials. The projected length of this image was measured with an e r ro r of about 1.5 percent.

In order t o determine the recession rate of the model, the model length was plotted as a function of time, and a straight line was drawn through the data representing a linear decrease of model length with time. This rate was converted to mass loss rate by multi- plication by the nominal density of the graphite. The accuracy of the nominal density of the graphite was checked by measuring the density of about three models of each graphite grade and was found to be within 14 percent of the measured density. Mass loss rates were considered to be accurate within 1 5 percent.

Oxygen mass flux, the parameter influencing diffusion-controlled reactions, was not measured; it was computed from a known value, the stream mass fraction of oxygen, and a computed value, the heat-transfer coefficient. Values of oxygen mass flux s o com- puted a r e valid at the stagnation point of smooth surfaces and a r e based on the initial shape of the model; hence, they are listed as reference oxygen mass f lux on the figures to be presented. The equations used to compute oxygen mass flux are discussed in appendix B.

Since the purpose of the present study was to define the oxidation behavior of graph- ite at surface temperatures above 2800° R (1560O K) where diffusion-controlled reactions are expected, the data for surface temperatures below 2800' R (1560' K) were excluded from the analysis and results.

RESULTS AND DISCUSSION

A marked difference in oxidation behavior was observed between ATJ graphite and the other two graphite grades tested (AHDG and AGSX). Models of ATJ graphite main- tained a round shape and surface integrity over wide ranges of stagnation pressure and oxygen mass flux for extended time periods, as shown in figures 4 and 5. This type of behavior was observed for AHDG and AGSX graphite models at low stagnation pressures from 0.0606 to 0.197 atm, as shown in figures 6(a) and 7(a). At stagnation pressures above 5.17 a tmand an oxygen mass flux exceeding 0.03 lbm/ft2-sec (0.146 kg/mz-s), however, many of the models became grossly distorted and revealed a highly irregular surface. An example of this phenomenon can be seen in figures 6(b) and 7(b). The

6

movies showed that the AHDG and AGSX graphite models became initially distorted in the a rea surrounding the stagnation region. If the models were kept in the test stream for longer periods of time, the distorted area expanded to consume the stagnation region. Models 3 and 4 of figure 6(b) are AHDG graphite models which were removed with the stagnation region intact, whereas model 5 is an AHDG graphite model which became com- pletely distorted. Most of the AGSX graphite models became completely distorted, as shown by models 4 and 5 in figure 7(b). The distorted model shapes observed for 0.5-inch- diameter (1.27-cm) models of AHDG and AGSX graphite were also observed for l-inch- diameter (2.54-cm) models of the same grades, an indication that the distortion effect is not influenced by model size. parameters and observed results for all models.

(See figs. 8 and 9.) Tables III, IV, and V show the test

In addition to the marked difference found in model shape behavior between ATJ graphite and the other two graphite grades tested, a difference was also found in the mass loss rate, as shown in figures 10, 11, and 12. These three figures show the oxidation rate plotted as a function of oxygen mass flux, which is considered to be the primary variable controlling diffusion-controlled reactions. (See ref. 1.) For comparison, all three fig- ures show a theoretical carbon monoxide (CO) curve (the upper limit for diffusion- controlled reactions) and a theoretical carbon dioxide (C02) curve (the lower limit for diffusion-controlled reactions). The latter curve is based on the assumption that C02 is the predominant effective product for diffusion-controlled reactions (see ref. 12). These curves are defined by equations and supporting references in appendix B.

Figure 10 shows that the oxidation-rate data for ATJ graphite in all test environ- ments followed a linear relationship with oxygen mass flux and fell between the theoreti- cal CO and C02 curves. The data obtained in the arc-heated jet and the ceramic-heated tunnel indicated agreement over the range of oxygen mass flux common to both facilities.

Figures 11 and 1 2 show that at low levels of stagnation pressure and oxygen mass flux AHDG and AGSX graphite models maintained a smooth shape and oxidation rates were below the theoretical CO curve. However, at stagnation pressures above 5.17 atm and oxygen mass flux exceeding 0.03 lbm/ft2-sec (0.146 kg/ma-s), many of the graphite models became grossly distorted in shape, as previously noted, and mass loss rates for these models were highly erratic and unpredictable, ranging up to 22 times the theoreti- cal maximum rate. Many of the models were removed from the stream with the stagna- tion region intact, and the oxidation rates for these models followed a pattern similar to the oxidation rates for ATJ graphite. This result suggests that if other graphite grades are tested under the same environmental conditions without becoming distorted, their oxidation rates would be similar to those for ATJ graphite. However, oxidation rates cannot presently be predicted for AHDG and AGSX graphite grades for stagnation pres- sures greater than 5.17 atm and for oxygen mass flux greater than 0.03 lbm/fta-sec

1

7

(0.146 kg/mZ-s). Because of the limitations of the test facilities, no data were available for stagnation pressures between 0.2 and 5.17 atm. Thus, the stagnation pressure at which model distortion and erratic oxidation rates become significant for AHDG and AGSX graphite grades was not determined.

Figures 10, 11, and 12 show a scattering of the oxidation-rate data for those models which did not become grossly distorted, and some of this scattering is believed to be due to variations in surface temperature. The importance of surface temperature is shown in figure 13, in which normalized rate data for the three grades of graphite tested are plotted as a function of this parameter. The normalized oxidation rate, a ratio of the experimental rate to the diffusion-limited rate for a CO product, was used to compare all data on the same basis. The plotted data show a surface-temperature effect between 2800° R (1560O K) and 3400' R (1890O K). When the data of figure 13 were separated into low- and high-stagnation-pressure ranges, as shown in figures 14 and 15, the surface- temperature effect was pronounced at low stagnation pressures up to 3800' R (2110O K) but was indeterminant at high stagnation pressures probably because of the narrow tem- perature range for most of the data. The results indicate that the scattering of the data in figures 10, 11, and 1 2 for those models which did not become grossly distorted is largely due to variations in surface temperature at low stagnation pressures, but is not understood at high stagnation pressures.

In order to help determine the oxidation mechanism at low stagnation pressures, pseudo activation energies were computed from the data at these low pressures. Values of pseudo activation energy from 10 to 13 kcal/g-mole (41.8 to 54.4 MJ/kg-mole) were found for the three grades of graphite for temperatures between 2800' R (1560' K) and 38000 R (21100 K). These values are intermediate between that found for diffusion- controlled reactions (4 kcal/g-mole (16.7 MJ/kg-mole); see ref. 2) and those found for chemically controlled reactions (17 to 44 kcal/g-mole (71 to 184 MJ/kg-mole); see ref. 3). These results indicate that for the range of surface temperatures between 2800° R (1560O K) and 3800' R (2110' K), oxidation may be occurring in a transition region between chemically controlled and diffusion- controlled reactions.

An analysis of oxidation data for surface temperatures between 3600' R (2000' K) and 3800' R (2110' K) suggested that the oxidation mechanism at this temperature level was nearly diffusion limited. This analysis was based on the theoretical prediction that if graphite is oxidized in air or air-nitrogen mixtures, the oxidation rate will depend upon both oxygen mass fraction and stagnation pressure in a unique manner, depending upon the oxidation mechanism. In a chemically controlled reaction, the oxidation rate depends on both variables raised to the same power; in a diffusion-controlled reaction, the oxidation rate depends on oxygen mass fraction raised to the first power and on stagnation pressure raised to the one-half power. (See appendix C.) If the theory is correct, log-log plots of

8

oxidation rate as a function of each variable would yield linear curves, the slope of each curve representing the power of the variable. Figures 16 and 17 show, for all three graphite grades, that the power of the oxygen mass fraction is about 1 and the power of the stagnation pressure is about 0.4.

Although the mechanism for initiating and maintaining the observed unpredictable and catastrophic oxidation behavior of AHDG and AGSX graphite is not known, it is of interest to point out the general conditions which appear t o influence this behavior. Since the surface of the ATJ graphite models did not become rough and that of the AHDG and AGSX models did, the initiation of a rough surface appears to depend on the differences between graphite grades. These differences can be divided into three classes: (1) Chem- ical composition, such as impurities that may act as inhibitors or accelerators influencing the oxidation reaction; (2) physical properties, such as maximum grain size; and (3) proc- essing technique, such as an extrusion or molding process. included in these three classes, and the relation of these properties to oxidation behavior should be investigated in order t o gain a better understanding of recession rate mechanisms.

Many basic properties are

Once the graphite surface has been initially roughened, the diffusion-controlled theory does not apply because the theory assumes a laminar boundary layer, and a rough- ened surface can be expected to produce turbulence with consequent higher rates of heat and mass transfer. One form of turbulence which can cause an accelerated transfer of oxygen t o the surface is a horseshoe-shaped vortex which has been found to occur in the pits and cavities of a roughened surface. (See ref. 13.) Many of the tested models showed surface irregularities which appeared similar to those reported in this reference.

CONCLUSIONS

As a result of an experimental study of the oxidation behavior of graphite in high- temperature supersonic and hypersonic environments, the following conclusions a r e drawn:

1. Models of AHDG and AGSX graphite became grossly distorted in many cases at oxygen-mass-flux levels above 0.03 lbm/ftZ-sec (0.146 kg/m2-s) and at stagnation pres- su res behind the shock wave above 5.17 atmospheres, whereas models of ATJ graphite maintained a smooth shape over a wide range of test conditions. Because of equipment limitations, the stagnation pressure and oxygen-mass-flux levels at which this phenom- enon begins were not determined.

2. The oxidation rates of models of ATJ graphite followed a linear relation with oxygen mass flux between the theoretical CO and C02 curves over a wide range of oxygen flux, indicating that the oxidation of ATJ graphite is predictable for a wide range of

9

environments. The models of AHDG and AGSX graphite which became grossly distorted lost mass in an unpredictable manner at rates ranging up to 21- times the theoretical maximum rate.

2

3. The mechanism responsible for the distortion of AHDG and AGSX graphite and the mass loss rate behavior of these two graphites are not presently understood.

4. The oxidation-rate data for the models of AHDG and AGSX graphite with the stagnation region intact followed a pattern similar t o that for ATJ graphite; these results indicate that if other graphite grades are tested under the same environmental conditions without becoming distorted their oxidation rates would be similar to those for ATJ graphite.

5. Since the factors accounting for the difference in oxidation behavior between the graphite grades studied are not known, the behavior of other graphite grades or carbo- naceous chars in like environments cannot be predicted until such factors. a r e determined.

6. The normalized oxidation rates for all three grades of graphite tested appeared to be temperature dependent at low stagnation pressures (0.06 to 0.20 atm) for surface temperatures between 2800' R (1560' K) and 3400° R (1890O K). This temperature range may represent a transition region between chemically controlled and diffusion-controlled reactions.

7. An anlysis of the data for surface temperatures above 3600° R (2000' K) showed evidence of a diffusion-controlled reaction for all three grades of graphite.

Langley Research Center, National Aeronautics and Space Administration,

Langley Station, Hampton, Va., January 19, 1966.

10

APPENDIX A

CONVERSION OF U.S. CUSTOMARY UNJTS TO SI UNITS

The International System of Units (SI) was adopted in 1960 by the Eleventh General Conference on Weights and Measures held in Paris, France. Conversion factors required for units used herein are given in the following table:

Physical quantity

Activation energy Density Enthalpy Heat-transfer rate Length Mass-transf er rate Mass-transfer rate X square

Pressure Temperature

root of nose radius

U.S. Customary Unit

kcal/g-mole

Btu/lbm Btu/f t2- se c in. lbm/f t 2 - s ec lbm/ft3/2-sec

g/cm3

atm OR

Conversion factor

( *)

2.32 x 10-3

4.18 1000

0.01 13 5 2.54 4.88 2.70

1.01325 X lo5 5/9

SI Unit

MJ/kg- mole kg/m3 MJ/kg m / m 2 cm kg/m2- s kg/m3/2- s

N/m2 OK

* Multiply value given in U.S. Customary Unit by conversion factor to obtain equivalent value in SI unit.

Prefixes to indicate multiples of units are:

Prefix

mega (MI centi (c) milli (m)

Multiple

11

APPENDIX B

EQUATION FOR DIFFUSION-CONTROLLED OXIDATION OF GRAPHITE

Numerous investigators have made theoretical analyses of a diffusion-controlled oxidation process in an aerothermal environment. (See refs. 14, 15, and 16.) While the resulting theoretical equations are different, they lead to the same equation if the Lewis number is assumed to be unity. In reference 16, the Lewis number is assumed to be unity for chemical reactions between a surface and a chemical species outside a laminar boundary layer. Reference 14 gives a theoretical equation in a readily usable form, and with a Lewis number of unity and the rate of formation of pyrolysis products equal to zero, this equation becomes

where fiC is the mass loss rate of carbon, h is the mass of carbon oxidized per unit mass of oxygen consumed, p is the blowing coefficient, q is the heat-transfer rate, and He and a r e the enthalpy at the edge of the thermal boundary layer and at the wall, respectively. For the reaction

ce is the mass fraction of oxygen at the boundary-layer edge,

h = 3/4; hence, equation (Bl) becomes

m = 0 . 7 5 ~ ~ q O C 1 + 0.75pce(He - ILly)

or

rile= 0.75 q -+ ce 0.75p(He - .w)

In reference 17, p is evaluated for the case of air injected into a boundary layer of air. For the purpose of the present study it was assumed that the molecular weight of carbon monoxide injected into the boundary layer was sufficiently similar to air to war- rant the use of p as evaluated in reference 17:

12

I

APPENDIX B

where NprYw is the Prandtl number at wall conditions. For the present study it was assumed that NprYw = 0.71; hence

Inserting this value of p in equation (B2) results in the following equation for the mass loss rate of graphite:

Now

where ho is the oxygen mass flux. Inserting this value of into equation (B5) results in the equation for oxygen mass flux used in the present study:

C

1 q Ao = 1 C e + 0.44.2ke %)

The heat-transfer coefficient was computed from reference 18. He - Hw

If C 0 2 instead of CO were assumed as the product of the reaction (see ref. 12), then

and x = 3/8. Equation (B7) is applicable because the Prandtl number for carbon dioxide is close to that for air, and therefore, equation (B3) for carbon monoxide is valid for car- bon dioxide. Theoretical mass loss rates for equation (B8) would be half of those com- puted by using equation (B6). In this case, the value of ho computed by using equa- tion (B7), in which it was assumed that h = 3/4, would be 4.5 percent in e r ro r for a i rs t reams, and the e r r o r decreases t o 1.5 percent as the mass fraction of oxygen in air-nitrogen s t reams decreases from 0.232 to 0.059.

13

i

APPENDIX C

ANALYSISOFDATATODETERMINETHERATE

CONTROLLING MECHANISM

In a chemically controlled reaction, the oxidation rate is (ref. 1)

a! 'C = @o,e

O,e where mc is the mass loss rate of carbon, k is the specific reaction rate, and p is the partial pressure of oxygen at the outer edge of the concentration boundary layer. Also

where xe is the mole fraction of oxygen at the outer edge of the concentration boundary layer and p is the total pressure at the outer edge of the concentration boundary layer. The mass fraction of oxygen at the outer edge of the boundary layer can be approx- imated by

t,2

ce =xe

where ce is the mass fraction of oxygen at the outer edge of the concentration boundary layer. Equation (C3) is valid since the molecular weights of oxygen and air are similar. Combining equations (C3), (C2), and (Cl) yields

The e r ro r introduced by using C e for xe ranges from about 10 percent for air to about 13 percent for an air-nitrogen mixture containing 25 percent air by volume. There- fore, it is seen that for a chemically controlled reaction tional t o ce and pt,2 raised to the same power.

Ac is approximately propor-

In a diffusion-controlled reaction, the oxidation rate is (see eq. (B5), appendix B)

14

.

I

APPENDIX C

where is the heat-transfer coefficient. Since ce 5 0.232 for the test condi-

tions of this study,

i i

He - Hw

q It can be shown from reference 18 that, for a modified Newtonian flow, H e - Hw

is a weak function of temperature and can be expressed by the following equation:

q =Constant x He - Hw

Therefore, equation (C 6) becomes

AC = Constant x ce 2 2 y

The er ror introduced in the approximations of equation (C6) ranges from about 10 percent for air to about 2 percent for an air-nitrogen mixture containing 25 percent air by volume. Therefore, it is seen that for a diffusion-controlled reaction rhc is approximately proportional to ce raised to the first power and p raised to the one-half power.

t ,2

15

REFERENCES

1. Frank-Kamenetskii, D. A. (N. Thon, trans.): Diffusion and Heat Exchange in Chemical Kinetics. Princeton Univ. Press, 1955.

2. Gulbransen, E. A.; Andrew, K. F.; and Brassart , F. A.: The Oxidation of Graphite at Temperatures of 600° to 1500° C and at Pressures of 2 to 76 Torr of Oxygen. J. Electrochem. SOC., vol. 110, no. 6, June 1963, pp. 476-483.

3. Scala, Sinclaire M.: The Ablation of Graphite in Dissociated Air. Part I: Theory, R62SD72, Missile and Space Div., Gen. Elec. Co., Sept. 1962.

4. Diaconis, N. S.; Gorsuch, P. D.; and Sheridan, R. A,: The Ablation of Graphite in Dissociated Air - Part 11: Experiment. Paper No. 62-155, Inst. Aerospace Sei., June 1962.

5. Scala, S. M.; and Gilbert, L. M.: Aerothermochemical Behavior of Graphite at Ele- vated Temperatures. R63SD89, Missile and Space Div., Gen. Elec. Co., Nov. 1963.

6. Mechtly, E. A.: The International System of Units - Physical Constants and Conver- sion Factors. NASA SP-7012, 1964.

7. Trout, Otto F., Jr.: Design, Operation, and Testing Capabilities of the Langley ll-Inch Ceramic-Heated Tunnel. NASA TN D-1598, 1963.

8. Mayo, Robert F.; Wells, William L.; and Wallio, Milton A.: A Magnetically Rotated Electric Arc Air Heater Employing a Strong Magnetic Field and Copper Electrodes. NASA TN D-2032, 1963.

9. Schaefer, William T., Jr.: Characteristics of Major Active Wind Tunnels at the Langley Research Center. NASA TM X-1130, 1965.

10. Exton, Reginald J.: Theory and Operation of a Variable Exposure Photographic Pyrom- eter Over the Temperature Range 1800° to 3600' F (1255' to 2255' K). NASA TN D-2660, 1965.

11. Anon.: The Industrial Graphite Engineering Handbook. Union Carbide Corp., c.1964.

12. Welsh, W. E., Jr.; and Chung, P. M.: A Modified Theory for the Effect of Surface Tem- perature on the Combustion Rate of Carbon Surfaces in Air. Proc. Heat Transfer Fluid Mech. Inst., Stanford Univ. Press , 1963, pp. 146-159.

13. Williams, David T.: Flow in Pits of Fluid-Dynamic Origin. A M J., vol. 1, no. 10, Oct. 1963, pp. 2384-2385.

14. Dow, Marvin B.; and Swann, Robert T.: Determination of Effects of Oxidation on Per- formance of Charring Ablators. NASA TR R-196, 1964.

16

. . . ... . _. . . .

15. Eckert, E. R. G. (With Pt. A and Appendix by Robert M. Drake, Jr.): Heat and Mass Transfer. Second ed. of Introduction to the Transfer of Heat and Mass, McGraw- Hill Book Co., Inc., 1959.

16. Lees, Lester: Convective Heat Transfer With Mass Addition and Chemical Reactions. Combustion and Propulsion - Third AGARD Colloquium, M. W. Thring, 0. Lutz, J. Fabri, and A. H. Lefebvre, eds., Pergamon Press, 1958, pp. 451-498.

17. Roberts, Leonard: Mass Transfer Cooling Near the Stagnation Point. NASA TR R-8, 1959. (Supersedes NACA TN 4391.)

18. Fay, J. A.; and Riddell, F. R.: Theory of Stagnation Point Heat Transfer in Dissoci- ated Air. J. Aeron. Sci., vol. 25, no. 2, Feb. 1958, pp. 73-85, 121.

17

TABLE I.- GRAPHITE PROPERTIES

_ _ - -

Density Grade

AGSX AHDG ATJ 1.73 1730

_ _ _

I

Maximum grain size _ _

in. r - m m

0.016 0.407 .033 1 .838 .006 .152

__ -

_.

- - - -

Ash, percent

0.13 .05 .20

- .~ -

Forming method

Extruded Extruded Molded

18

TABLE IL- TEST CONDITIONS

(a) U.S. Customary Units

Model iiafneter,

111.

0.375

0.37 5, 1

0.375

Nomina Mach

number M

6

6

6

~

Mass fraction

of oxygen, C e

Stagnatiin- pressure,

a tm

1.0606 t o 0.197

1.0606 t o 0.197

pt,29

1.0606 to 0.197

Stagnation enthalpy,

H Btufibm

Cold wall eating rate,

9, Btu/ftz-sec

Test facility

Sraphite grade

ATJ

AHDG

AGSX

flux, mch lbm/ftz-sec

I

1809 to 4080

1809 to 4080

1809 to 4080

237 to 430

237 to 430

>angley 20-inch hypersonic a rc- heated tunnel

.117 to 0.232

.117 to 0.232

.117 to 0.232

0.0127 to 0.0248

255 to 430 0.0167 to 0.0248

Lrc-heated mate- rials jet at the Langley Research Center

AT3

AHDG

AGSX

ATJ

AHDG

AGSX

Graphite grade

ATJ

AHDG

AGSX

ATJ

AHDG

AGSX

ATJ

AHDG

AGSX

0.375, .5

0.375, .5

0.5

0.375, .5

0.375, .5,

1

0.5, 1

6.38

~~

6.38 t o 8.28

6.38

5.17 t o 7.42

5.17 to 7.50

5.17 to 7.50

.059 to 0.232

.059 to 0.232 910 to 1063 653 to 812

1.059 to 0.232

0.119 to 0.143 7 ~~

643 to 1078

729 to 1078

595 to 1079

~

0.232 .angley ll-inch ceramic -heated tunnel

352 to 695

303 to 810 I

0.232 0.086 to 0.171 I

291 to 745 0.232 O.O8l3 to 0.143 I

I

(b) SI Units I

Model iameter,

cm

Jominal Mach

lumber, M

6

6

Stagnation enthalpy,

H, M J h

4.20 to 9.47

4.20 to 9.47

4.20 to 9.47

2.11 to 2.47

1.49 to 2.50

~ ~ ~ _ _ 1.69 to 2.50

Cold wall ieating rate,

e m / m 2

2.69 to 4.88 ~

Mass fraction

of oxygen, C e

Stagnation pressure,

N/m2 9 , 2 ,

3.12t019.9x103

3.12 to 19.9 x 103

3.12 to 19.9 x lo3 6 . 5 0 ~ 105

6.50to8.39x10’

6.5OX1o5

5.22 to7.50X 10’

5.22to7.60X10!

5.22to7.60X 10’

Test facility

Langley 20-inch hypersonic a r c - heated tunnel

0.953

0.953, 2.54

0.953

0.953, 1.27

0.953, 1.27

1.27

0.953, 1.27

0.953, 1.27, 2.54

1.27, 2.54

-. .

,117 to 0.232 1.0815 to 0.1210 I 1.0620 to 0.1210 2.69 to 4.88

2.89 to 4.88

7.41 to 9.22

.117 to 0.232

,117 to 0.232 6

2

1.0815 to 0.1210

Irc-heated mate- rials jet at the Langley Research Center

.059 to 0.232

0.1557 to 0.811 I .059 to 0.232 2

.059 to 0.232 0.1557 to 0.623 I 2

2 4.00 to 7.93 0.232 0.581 to 0.698 Langley ll-inch ceramic-heated tunnel 3.44 to 9.19 0.232 0.420 to 0.834 2

1.38 to 2.50 3.32 to 8.49 0.232 0.420 to 0.698 2

19

TABLE m.- TEST PARAMETFEE AND RESULTS FOR ATJ GRAPHITE MODEIS

(4 us. cvstomary units

Langley 20-inch hypersonic arc- heated h e 1 (Mach number = 6)

Cold w d heating rate

,rU/rt2:s

371 340 282 237 255 400 428 412 430 328

315

400 352 400 580 580 695

0.375

Cbrygen mass flu

Ihm/ft2-s,

0.0167 .ON7 .0210 ,0248 .0248

.0iB.i

.0171

.0171

.0204

.0224

0.0319

1 1

,0636

,0970

1

O'lr

.1276

1 .148

.119

.I19 ,143

I m s 10s

rake of

I b 3 - 2

0.0113 .0117 8 0 7 5 .0126 ,0106 .0102 .0115 3 0 9 6 .ow8 ,0077 .0076 ,0091

0,0154 .Or53 .0199 .0351 .0324 ,0343 .0468 ,0414 .0579 ,0526 ,0616 .OH9 ,0580 ,0737 ,0723 ,0745

0.0627 ,0702 ,0735 .0620 ,0605 ,0679

Surface temperature .tagnation poi

OR f ide l shap

-

:zz 't,29 at

0.0601 .mol ,101 .197 ,197

'i" I .128f

6.38

I

'I 1.42

-ti' !nthalpg BhJjlbU

1809 1809 2605 4080 4080

T

709 643 709

3710 3760 3210 3200 3250 3840 3790 3650 3600 3220 3245 3280

3840 3410 3690 3545 3610 3220 3835 3470 3430 3640 3710 4000 3975 3680 3675 4130

3670 3610 3460 3800

rlaLs jet a t the langley Research center (Mach number = 2)

ceramic-heated h e 1 (Mach n u h e r = 2)

(b) SI Units ~

old w a l heating

$$A2

4.21 3.86 3.20 2.69 2.89 4.54 4.86 4.66 4.66 3.72

3.58 ~

4.54 4.00 4.54 6.61 6.61 7.93

~

Oxygen lass flur ;g/mZ-s

0.0815 ,0815 .IO25 ,1210 ,1210

'Or5 ,0834 .0634 .W96 .1w3

0.1557

1 1

,3113

.4734

1 .6227

i .7222

0.6832

I ,5807 ,5807 ,6978

______

Test facility Made1

M a e h y k b e r 1 em

diameter surface

emperature ai tagnation p i n

OK

2060 2090 1790 1780 1810 2140 2110 2030 2000 1790 1800 1820

2140 1904 2050 1970 2010 1790 2130 1930 1910 2020 2060 2220 2210 2050 2040 2300

2040 2010 1920 2110

RW .MI Be<

12c

1

75 89 101 120

30

t 27

i' 60 30 60 41

113 92 158 30 60 30

~

6.12 X 10 6.12 0.20 9.90 9.90

0.0551 .0571 .0366 ,0615 ,0517 .W98 ,0561 ,0468 ,0476 .0376 ,0371 ,0444

0.0752 .0747 ,0971 ,1713 ,1581 .I674 ,2284 ,2020 ,2826 2567 .SO06 ,2533 .a30 3597 ,3528 ,3636

0.3060 3426 .3587 ,3026 ,2952 3314

~

4.20 4.20 6.04 9.47 9.47 4.20

hypersonic arc- heated h e 1

3'01 re-heated mate- 1 rials jet at the langley Research Center (Mach number = 2)

,.22 x 10:

1 1.64 1.49 1.64

ceramic-heated

"i" %he letter R dendes r-d model shape.

TABLE IV.- TEST PARAMETERS AND RESULTS FOR AHDG GRAPHITE MODELS

Test facility and

Mach number

Langley 20-inch hypersonic arc- heated tunnel (Mach number = 6

4rc-heated mate- - rials jet at the

Langley Research Center (Mach number = 2

Langley 11-inch ceramic-heated tunnel (Mach number = 2'

Model iameter

in.

15

1

0.

1

.375

I

'i .375 .375

tagnation vessure, 't,2, atm

0.0606 .0606 .lo1 .197 .197 .Of306

1 .1285

I .171

6.:

8.28 7.78 8.26 7.83

5.17 5.17 7.50 7.50 5.17

6.05

tagnatior mthalpy Btu/lbm'

1809 1809 2605 4080 4080

lr

3700

1063 9 58 987 910

837 1078 1078 837

l o r 729

837 837

'T 837 837

1078

(a) U.S. Customary Units

Cold wall heating rate

,tu/ftfsec

371

282 237 255 400 412 428 430 328

315 240

812 691 74 2 653

303 416 497 362 680 580 580 630 305 362 362 497 704 704 514 592 810

Mass ractior of

0.232 mygen

1

.117

.117

.170

.232

.232

0.059 I .117 .117 .170

1 .232 I .059 .117 .170 .232 .059 .117 .170

0. 3

oxygen nass flux, ,m/ft 2-sec

0.0167 .0167 .0210 .0248 .0248 .0167

1 .0171 .0171 .0204 .0224 .0127

0.0319

I .0638 .0638 .0970

1 .1276

1 .0471 .0900 .1357 .1662 .0369 .0739 .1108

0.0860 .om0 .lo50 .lo30 .1430 .1190 .1190 .1290 .lo20 .lo30 .lo30 .lo50 .I460

1 .1680 .1710

mass loss rate of

graphite, im/fta-sec

0.0124 .0108 .0093 .0087 .0111 .0112 .0099 .0099 .0094 .0052 .0064 .0086 .0089

0.0158 .0261 .0180 .0210 .0511 .0406 .0641 .0527 .0548 .0760 .OB15 .0914 .0623 .0666 .0171 .0325 .0510 .0660 .0177 .0370 .0492

0.0362 .0433 .0477 .0756 .0620 .0631 .0596 .0603 .1930 .lo40 .0842 .0600 .1420 .loo0 .1670 .1620 .0760

Surface emperature at tagnation point,

OR

3710 3760 3160 3000 3110 3840 3670 3280 3350 2770 3140 2975 3430

3470 3500 3770 3370 3660 3520 3700 3700 3535

3585 3640

2845 3110 3250 3840 3660 3770 3860

3570 3430 3685 3780 3695

4060 3630 3780 3930 3990 3975 3650 3860 3925

~

( *) R

1

1

R R S

i S

t D S S R D R S

S

S R S

?

D D S D

1

- Zun h e , 3ec

89 101 120 180

30 30 60 90

-

20

60 30

- 102 53 55 60 37

30

106

i' 50 25 54 43 20 -

*The letter R denotes round model shape, the letter S denotes stagnation region intact, and the letter D denotes distorted model shape.

21

TABLE IV.- TEST PARAMETERS AND RESULTS FOR AHDG GRAPHITE MODELS - Concluded

v

Test facility and

Mach number

f

Model iiameter

cm

Langley 20-inch hypersonic arc- heated tunnel (Mach number = 6

a

~-

irc-heated mate- rials jet at the Langley Research Center (Mach number = 2

~.

angley 11-inch ceramic-heated tunnel (Mach number = 2:

5

2.54

1 1

.95

2.54

.95

2.54

I 1.27

.95

.95

6.11

itagnatio enthalpy, MJbg

4.20 4.20 6.04 9.47 9.47 4.20

1

8.58

2.47 2.22 2.29 2.11

1.94 2.50 2.50 1.94 2.50

I 1.69 1.94 1.94 2.50

1 1.94 1.94 2.50

(b) SI Units

:old wal heating rate,

W/mB

4.21

3.20 2.69 2.89 4.54 4.68 4.86 4.88 3.72

3.58 2.74

9.22 7.84 8.42 7.41

3.44 4.72 5.64 4.11 7.72 6.61 6.61 7.18 3.46 4.11 4.11 5.64 7.99

5.83 6.72 9.19

5.99

3. 12

Oxygen nass flu: kg/mz-r:

0.0815 .0815 .lo25 .1210 -1210 .0815

I .0834 .0834 .0996 .lo93 .0620

0.1557

I .3113 .3113 .4734

1 .6227

1 .2298 .4392 .6622 31 1 1 .la01 .3606 .5407

0.4197 .4294 .5124 .5026 .6978 .5807 .5807 .6295 .4978 .5026 .5026 .5124 .7125

1 .a198 .a345

m s s lor: rate of

graphitr W m 2 -

0.0605 -0527 .0454 .0425 .0542 .0547 .0483 .0483 .0459 .0254 .0312 .0420 .0434

0.0771 .1274 .08 78 .lo25 .2494 .1981 .3128 .2572 .2674 .3709 .3977 .4460 .3040 .3250 .0834 .1586 .2489 .3221 .08 64 .la06 .2401

0.1767 .2113 .2328 .3689 .3026 .3079 .2908 .2943 .9418 .5075 .4109 .2928 .6930 .4880 .I3150 .7906 .3709

Surface temperature ai ;tagnation poin

OK

2060 2090 1760 1670 1730 2140 2040 1820 1860 1540 1750 1650 1910

1930 1950 2100 1870 2040 1960 2060 2060 1970

1990 2020

1580 1730 1810 2140 2040 2100 21 50

1990 1910 2050 2100 2050

2260 2020 2100 2190 2220 2210 2030 21 50 2180

vIodel sha~

%he letter R denotes round model shape, the letter S denotes stagnation region intact, and the letter D denotes distorted model shape.

22

TABLE V.- TEST PAFlAMETERS AND RESULTS FOR ACSX GRAPHITE MODEIS

Test facility and

Mnchnvmber

ingley 20-inch hypersonic are- heated tvnnel (Mach number = 6)

Model diameter,

in

0.375

rc-heated mate-

Langley Research center (Mach number = 2)

rials jet a t the

angley 11-inch ceramic-heated tunnel (Mach number = 2)

I

0

Test facility and

Mach number

ingley 20-inch hypersollie arc- heated b e l (Mach number = 61

:c-heated. mate- rials jet at the Langley Research Center (Mach number = 2)

rngley 11-inch ceramic-heated tUNIe1 (Mach mmber = 2

a nation

M J b g

4.20 4.20 6.04 9.47 4.20

1

.LW,

1.95 1.38 1.59 1.70 1.95 2.50

Model amete, cm

Cold wall

s7&2

4.21 3.86 3.20 2.89 4.54 4.68 4.86 4.88 3.72

3.58

heating

5.40 3.32 4.78 5.21 6.20 8.49 6.61

i 1.27

I

agnatia

i,23 -essure

0.0606 .0606 ,101 ,197 ,0606

1 .I285

I 6.:

5.63 5.c3

5.17 6.05 7.42

Ragnation

>t,2, N/d: 1res8"re

6.12 X 10: 6.12 0.20 9.90

7 '"1 6.50 X 10:

5.69 X 105 5.69 7.60

1 5.22 6.11 7.49

1809 1809 2605 4080 I809

1

842 595 685 732 842

1079

'i"

Cold w a l l heatlng

rate

371 340 282 255 400 412 428 430 328

315

tu/ft2:see

473 29 1 419 457 543 745 580 630 695

VLVis aetior of

1.232

wgen

I

.I17

.I17

.I70

.232

1.059 ,059 ,117

I 1

,170

,232

1 1.232

I

(b) SI UnitE

Mass attic

f x y w

1.232

,117 ,117 ,170 ,232

1.059 ,059 ,117

1 1

,170

,232

1 1.232

Orlw laaS flux m/itz-shc

0.0167 ,0167 ,0210 ,0248 ,0167

1 ,0171 ,0171 ,0204 .0224

0.0319 ,0319

' O r ,0970

I ,1276

1 0.0660 ,0860 ,1020 ,1020 ,1030 .IO50 ,1190 ,1290 ,1430

%:Yux .g/m2-e

0.0615 ,0815 .IO25 ,1210 ,0815

I .0835 ,0835 ,0496 ,1093

0.1557 ,1557

.i" ,4134

1 ,6227 I

0.4197 ,4197 ,4978 ,4978 ,5026 SI24 ,5807 ,6295 ,6978

cas* 1088 rate af "pz?

m ft see

0.0110 ,0112 ,0078 ,0065 ,0109 ,0094 ,0103 ,0086 ,0047 ,0063 ,0069

0.0186 .0226 ,0432 ,0423 ,0515 .0623 ,0751 .0808 .I240 ,0427 ,0695 ,0673 .0661

0.1397 ,0800 ,1910 ,1850 ,1570 .1270 .0569 ,0671 ,0726

Lam losf rate Of ;r;P; 0.0537

,0547 ,0361 ,0317 ,0532 ,0459 ,0503 ,0420 ,0229 ,0307 .0337

0,0408 ,1103 ,2108 .2064 ,2513 3 0 4 0 ,3665 ,3943 ,6051 ,4524 ,3392 ,3284 ,3226

0.6817 ,3904 ,9321 3028 .7682 3198 ,2777 3214 3543

Surface

aR 3660 3760 3160 2950 3730 3600 3420 3110 2710 2900 2940

3595 3460 3990 3800 3625 3740

,mperature a t agnation point

3660 3b10

3730 3640 3670

4190 4100 4000 4010 3725 3860

2035 2090 1760 1640 2070 2000 I900 1730 1510 1610 1640

2000 1920 2220 2110 2020 2080

2050 2020

2070 2020 2040

2330 2260 2210 2230 2070 2150

lode1 sham

lode1 sham

( 4 R

S R D

R R I I

- 78 26 60 64 60 60 30

- "" ec me,

- 20

01 20

30 -

. - 78

~ 2 6 60 64 60 60

- iD .The letter R denotes rmnd made1 shape. the tetter S dendes s t a p t i o n region intact, and the letter D denotes distorted male1

shape.

23

I

tB-i

I ! A B I in. cm in. cm

0.375 0.953 0.563 I .429

(a\ Models of AHDG and AGSX graphite.

in. cm in. c m ,_0.375 0.953 0.750 1.905 0.500 1.270 0.750 1,905

(b) Models of ATJ graphite.

Figure 1.- Construction details of hemispherical graphite models.

L-64-14808 Figure 2.- Photograph of Langley 20-inch hypersonic arc-heated tunnel.

(a) 0.375-inch-diameter (0.953-cm) model.

Figure 3.- Photographs of model, model holders, and water-cooled sting assemblies.

L-64-799.1

(b) 1-inch-diameter (2.54-cm) model.

Figure 3.- Continued.

L-64-798.1

(c ) Four-model holder for 0.375-inch-diameter (0.953-cm) models.

Figure 3.- Concluded.

L-65-4673.1

2 Untested 0.0167 0.0167 0.0210 0.0248 (0.0815) (0.0815) (0.1025) (0.12 10)

3760 3745 3210 3250 (2090) (2080) (1785) ( I 8 IO) 0.0606 0.0606 0.101 0.197

mo, Ibm/ft -sec ( kq/m2- s)

t ,see 120 240 I20 120

T, ,OR

P t , 2 ,atm

( O K 1

(a) 0.375-inch-diameter (0.953-cm) models exposed to low stagnation pressures; oxygen mass fraction c, = 0.232.

mo,lbm/ftil-sec Untested 0.0319 0.0638 0.1276 0. I276

t , s e c ( kg /m2-s ) ( 0.1558) (0.312) (0.6 22 ) (0 .622)

30 30 30 60 Tw ,"R 3840 38 35 4000 3975

( O K ) (2130) (2130) (2220) (2210 1 ce 0,059 0.117 0.232 0.232

(b) 0.5-inch-diameter (1.27-cm) models exposed to h igh stagnation pressure of 6.4 atm. L-66- 1094

Figure 4.- Models of ATJ graphite exposed to wide range of oxygen mass flux.

w 0

11111 0 I/ 2 I

Centimeter

- 0 1/8 2/8 3/8

Inch

(a ) t = 2 5 sec I

A i r f l o w ( b ) t = 5 0 sec I

( c ) t = 75 sec L-66-1093

Figure 5.- Typical effect of exposing 0.375-inch-diameter (0.953-cm) ATJ graphite model to h igh oxygen mass f lux for a long run time. m,, = 0.140 Ibm/ft2-sec (0.683 kg/m2-s); pt,2 = 5.17 atm; Total exposure time = 113 sec; ce = 0.232; Equil ibr ium T, = 3890° R (21600 KI.

0.0248 0.0167 0.0210 m0,1bm/ft2 -sec Untested 0.0 I67 ( k d m 2 - s ) (0.0815) (0.0 815) (0.10 25 1 (0.12 I O )

t , sec 120 I40 I20 120 T, ,OR 3 760 3755 31 60 3110

(OK 1 (2090) (2085) (1760) ( 1730) 0. I97 0.101 0.0606 0.0606 Pt,2, atm

(a) 0.375-inch-diameter (0.953-cmJ models exposed to low stagnation pressures; oxygen mass fraction ce = 0.232.

0.1276 m Ibm/ft2- sec Untested N i t rogen 0.03 19 0.0638

t , sec 30 60 59 60 (0 .1558) (0.312) (0.622)

0' ( k g /m2-s)

Tw , OR 3490 3770 3835 ( O K ( I 940 1 (2095) (2 130)

Ce 0 0 .059 0.117 0.232 Model I 2 3 4 5

(b) 0.5-inch-diameter (1.27-cmJ models exposed to h igh stagnation pressure of 6.4 atm. L-66-1092

Figure 6.- Models of AHDG graphite exposed to wide range of oxygen mass flux.

0.01 67 0.0167 0.0210 0.0248 (0.12 IO)

* , Ibm/ft2 - sec Untested mo ( k g / m 2 - s ) (0.0815 1 0.0815 (0 . IO 25)

T, O R 3760 3665 3 I60 31 10

Pt,2 t otm 0.0 606 0.0606 0.101 0,197

t , s e c 120 240 120 120

( O K 1 (2090) (20 30) (1760) ( 1730)

la) 0.375-inch-diameter (0.953-cm) models exDosed to low staqnation pressures; oxygen mass fract ion cp = 0.232.

0.1276 mo , Ibm/ft2- sec Untested 0.0319 0.0 638 0. I 2 76

30 60 t , sec 30 30 Tw ,OR 3595 3800 3 740 3710

(0.1558) (0.312) (0,622) (0.622) ( k g /m * - s 1

( O K ) (2 000) (2110) (2080) (2060) 0,170 0.232 Ce 0.059 0.117

Model I 2 3 4 5

(b) 0.5-inch-diameter (1.27-cm) models exposed to h igh stagnation pressure of 6.4 atm.

Figure 7.- Models of AGSX graphite exposed to wide range of oxygen mass flux.

L-66-1091

m ,lbm/ft2- sec Untested 0

( k g /m2- s )

0.088 0.103 0.105

60 60 6 0 3430 (1910) 3780 (2100) 3 9 30 (2185)

5.17 7.50 7 -50

( 0 . 5 0 2 ) (0.512) ( 0.4 29)

0.232 0 .232 0 ,232

Figure 8.- 1-inch-diameter 12.54-cm) AHDG graphite models exposed to h igh stagnation pressures and h igh oxygen mass flux. L-66-1090.1

W W

Untested r;lo Ibm/ f t2 - sec 0.102 0.103 0.1 0 5

(0.497) ( 0 3 0 2 ) (0.512) ( k g /m2 - s )

t sec 6 0 6 0 60

T, ,OR (OK) 4000 (2220) 3 7 2 5 (2 070 ) 3 8 6 0 ( 2 145)

p t 1 2 a t m 7.50 7.50 7.50 c e 0 . 2 3 2 0 . 2 3 2 0 .232

Figure 9.- 1-inch-diameter (2.54-cm) AGSX graphite models exposed to h igh stagnation pressure and h igh oxygen mass flux. L-64-803.1

0 Q) m I

(u t 'c \

E f! ,.

.I2

.IC

,08 0 -E

c

I= 0

0 ,06 0

0 a,

rc

c z * m .04 0

m cn

-

s .o 2

0

n 0

0

Tes t faci l i ty

20 -inch hypersonic arc -heated tunnel

Arc -heated materials jet

I I - inch ceramic -heated tunnel

/

t o P t 2 ~5.17 to -'-*' -7- ' 7.42 atm

.02 .04 .O 6 -0 8 .IO .I2 .I4 .I6

Reference oxygen mass flux, mot Ibm/ft2- sec

6

5

4

m I

(u

E 3 ' 0 Y

0 L

.E

2

I

,O

W en

Figure 10.- Comparison of oxidation rates of ATJ graphite with theoretical curves.

.2oL-

.I 8 -

.I6 -

0 a,

I * .I4 -

% \ 0 e o Arc-heated materials jet E e W 0 0 1 1 - inch ceramic-heated tunnel

.l-

Test facility

20 -inch hypersonic arc-heated tunnel

8

8

/

- , I /// * ," /?be"'-

I

.L 0 .02 .04 .O 6 .08 .IO

Reference oxygen mass f lux,mO, Ibm/ftZ- sec

Figure 11.- Comparison of oxidation rates of AHDG graphite wi th theoretical curves.

.36

.2(

.I€

. IC

N' - I L 4- Lc

\

E 0

,E" .li

c 0

0 0 e 0 .IC 2 e

u) .08

+

ln ln 0 - ln

.OE

.OL

.02

0

0 r .I

mo,kg /m2-s .5 ? I

.6 I

A 20- inch arc-heated tunnel

0 0 0 Arc-heated materials je t

0 0 II- inch ceramic-heated tunnel

I 1 . 1 I - ~I I I 1 .02 .04 .O 6 .08 . IO .I2 .I4 .I6 .I8

Reference oxygen mass f l ux , mo, I bm/ f t2 - sec

Figure 12.- Comparison of oxidation rates of AGSX graphite with theoretical curves.

37

w 00 Surface temperature

I .c

.8

.6 in C, ex D . . m C , theory

0

- - -yo 1250 I500 I750 2000 2250 --- ___ --_ .

T 0

T O o

--T ---,- ~ -- _- -,-- Graphite

grade 0 A H D G 0 AGSX

ATJ

Pt,2 = 0.06 to 8.28 atm

Ce ~0.059 to0.232

0 0 0

QJ 0

m 0

0

n o 45 8 0 0 . 0 n 0

2 0

n n

3500 4000 4500 2000 2500 3000

Surface temperature, T, ,OR

Figure 13.- Normalized graphite oxidation rate as a function of surface temperature.

p

W (D

-

.6 .- m ~ l exp

m C ,theory

.2 '-

Pt12=0.06 t o 0.20 a tm Ce = 0.117 to 0.232

0 0

n 0

OO\ n

0

17

Figure 14.- Normalized graphite oxidation rates as a function of surface temperature and graphite grade at low stagnation pressures.

I .c

.E

.6 mc, exp

"C, theory

.2

Surface temperature , OK 1750 2000.. ,. _.._ 2250 -. 2-5 00

~~ ~~ 1 - - - - - - - i 0 - 0

1 - ~-

I250 I500

I U

Gra phi t e grade

0 AHDG AGSX

A ATJ

0

Pt,2 = 5.17to 8.28 atm

Ce = 0.059 t o 0.232

n

0 0

n A A

I.. J , - I 0 2000 2500 3000 3500 4000

Surface temperature T,,, ,OR

Figure 15.- Normalized graphite oxidation rate as a funct ion of surface temperature at h igh stagnation pressures.

40

I .- . 4500

C 0 n v 5:

I

u - I ON

grade in

' 2

I - + N 0 AHDG

0 AGSX

Model diameter = 1/2 inch

E

- ATJ A

.E

(1.27cm)

c

0

1 -,lo- - - - - -

1 1 1 .. _ _ 111b5

Mass fraction of oxygen, Ce

Figure 16.- Graphite oxidation rate as a function of mass fraction of oxygen.

tb N

I-. W

ol m

10-1

5

c Y- \ I E n -

c 0

-E

Graphite grade

0 AHDG

0 AGSX ATJ

Tw = 3600 - 3800 O R (2000-2110 O K )

Cd = 0.232

Stagnation pressure , p t , 2 ,atm

Figure 17.2 Graphite oxidation rate X (model radius)'/'as a function of stagnation pressure.

v, I

N \ m

E \ Ol Y

“The aeronautical aiid space activities of the United States shall be conducted so as to contribirte . . . to the expansioii o f himan knowl- edge of phenomena i n the atmosphere and space. The Admiiiistratioii shall provide f o r the widest practicable and appropriate dissemination of information concerning its activities and the results there0 f .”

-NATIONAL AERONAUTICS AND SPACE ACT OF 1958

NASA SCIENTIFIC A N D TECHNICAL PUBLICATIONS

TECHNICAL REPORTS: important, complete, and a lasting contribution to existing knowledge.

TECHNICAL NOTES: of importance as a contribution to existing knowledge.

TECHNICAL MEMORANDUMS: Information receiving limited distri- bution because of preliminary data, security classification, or other reasons.

CONTRACTOR REPORTS: Technical information generated in con- nection with a NASA contract or grant and released under NASA auspices.

TECHNICAL TRANSLATIONS: Information published in a foreign language considered to merit NASA distribution in English.

TECHNICAL REPRINTS: Information derived from NASA activities and initially published in the form of journal articles.

SPECIAL PUBLICATIONS: Information derived from or of value to NASA activities but not necessarily reporting the results of individual NASA-programmed scientific efforts. Publications ihclude conference proceedings, monographs, data compilations, handbooks, sourcebooks, and special bibliographies.

Scientific and technical information considered

Information less broad in scope but nevertheless

Details on the availability of these publications may be obtained from:

SCIENTIFIC AND TECHNICAL INFORMATION DIVISION

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

Washington, D.C. 20546