Narottam P. Bansal

Glenn Research Center, Cleveland, Ohio

Sung R. Choi

Naval Air Systems Command, Patuxent River, Maryland

Properties of Desert Sand and CMAS Glass

NASA/TM—2014-218365

August 2014
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Narottam P. Bansal

Glenn Research Center, Cleveland, Ohio

Sung R. Choi

Naval Air Systems Command, Patuxent River, Maryland

Properties of Desert Sand and CMAS Glass

NASA/TM—2014-218365

August 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

Desert sand was supplied by NAVAIR. Thanks are due to Dr. Paul Angel, Dr. Richard Rogers, Dr. Valerie Wiesner, Doug Doza, 

Ralph Pawlik, Derek Johnson, Bob Angus, and Ray Babuder for technical assistance during this work. This research was supported 

by NASA’s Aeronautical Sciences Project as well as by NAVAIR through a space act agreement (SAA3-1260).

Available from

NASA Center for Aerospace Information

7115 Standard Drive

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Available electronically at http://www.sti.nasa.gov

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2014-218365 1 

Properties of Desert Sand and CMAS Glass 

Narottam P. Bansal 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Sung R. Choi 

Naval Air Systems Command 

Patuxent River, Maryland 20670 

Abstract 

As-received desert sand from a Middle East country has been characterized for its phase composition 

and thermal stability. X-ray diffraction analysis showed the presence of quartz (SiO2), calcite (CaCO3), 

gypsum (CaSO4.2H2O), and NaAlSi3O8 phases in as-received desert sand and showed weight loss of 

~35 percent due to decomposition of CaCO3 and CaSO4.2H2O when heated to 1400 °C. A batch of asreceived desert sand was melted into calcium magnesium aluminosilicate (CMAS) glass at ~1500 °C. 

From inductively coupled plasma-atomic emission spectrometry, chemical composition of the CMAS 

glass was analyzed to be 27.8CaO-4MgO-5Al2O3-61.6SiO2-0.6Fe2O3-1K2O (mole %). Various physical, 

thermal and mechanical properties of the glass have been evaluated. Bulk density of CMAS glass was 

2.69 g/cm3

, Young’s modulus 92 GPa, Shear modulus 36 GPa, Poisson’s ratio 0.28, dilatometric glass 

transition temperature (Tg) 706 °C, softening point (Td) 764 °C, Vickers microhardness 6.30.4 GPa, 

indentation fracture toughness 0.750.15 MPa.m

1/2

, and coefficient of thermal expansion (CTE) 

9.810–6/°C in the temperature range 25 to 700 °C. Temperature dependence of viscosity has also been 

estimated from various reference points of the CMAS glass using the Vogel-Fulcher-Tamman (VFT) 

equation. The glass remained amorphous after heat treating at 850 °C for 10 hr but crystallized into 

CaSiO3 and Ca-Mg-Al silicate phases at 900 °C or higher temperatures. Crystallization kinetics of the 

CMAS glass has also been investigated by differential thermal analysis (DTA). Activation energies for 

the crystallization of two different phases in the glass were calculated to be 403 and 483 kJ/mol, 

respectively. 

1.0 Introduction 

Ingested particulate materials such as sand, fly ash, and volcanic ash may cause serious damage by 

erosion as it passes through the jet engine or by plugging the cooling holes of the combustor liner and the 

blades resulting in premature failure. To improve efficiency, future jet engines will operate at much 

higher temperatures than the current engines. At these elevated operating temperatures, desert sand or 

runway dust ingested into turbine engines will melt into a viscous and corrosive slag-like material of 

calcium magnesium aluminosilicate (CMAS) composition. Sand and molten CMAS may chemically 

interact and/or infiltrate into the pores of thermal and environmental barrier coatings (TBC/EBC) and may 

deposit on the surfaces of various engine components (Refs. 1 to 6). These processes could adversely 

affect the performance and life of jet engines. To help understand the effects of CMAS on durability and 

life of TBCs and EBCs, it would be beneficial if various properties of the desert sand glass are available. 

The objective of the current study was to characterize the as-received desert sand from a Middle East 

country for its composition and thermal stability and also to evaluate the various physical, thermal, and 

mechanical properties of the CMAS glass resulting from melting of the desert sand. 
NASA/TM—2014-218365 2 

2.0 Experimental Methods 

2.1 Glass Melting 

Desert sand from a Middle East country was melted into glass in a Pt crucible using a programmable 

box furnace. As-received sand was heated at a rate of 10 °C/minute with isothermal holds of 30 min each 

at 150, 790, and 1275 °C. After holding at 1500 °C for about an hour for homogenization of the melt, it 

was quenched in water. The resulting glass frit was ground to powder in a Fritsch Planetary Mill 

(Model# LC 106-A) using corundum grinding bowl and zirconia milling media. 

2.2 Chemical Analysis 

Chemical composition of the glass powder was analyzed by inductively coupled plasma-atomic 

emission spectrometry (ICP-AES) using a Varian Vista Pro model in the axial configuration. About 

100 mg of glass powder was fused with 1 g of sodium carbonate to convert it into soluble form. A reagent 

blank was carried through the procedure to subtract out impurities from sodium carbonate, particularly the 

alkali metals. A qualitative scan was done to determine the major and minor constituents. This was 

followed by a quantitative analysis by comparison with standards of known concentration to create 

calibration curves for each of the desired elements. 

2.3 Hot Pressing 

The glass powder was loaded into a graphite die and hot pressed in vacuum at ~800 °C under 17 MPa 

(2.5 ksi) for 10 to 15 min into discs and bars using a Centorr mini hot press. The applied pressure was 

released before onset of cooling. Grafoil was used as spacers between the samples and the punches. 

Surfaces of hot pressed samples were ground and polished to remove residual grafoil. The final 

finishing was completed with a #500 diamond grinding wheel under the specified condition in accordance 

with ASTM standard C1161 (Ref. 7). 

2.4 X-ray Diffraction 

X-ray diffraction (XRD) patterns of the as-received desert sand, CMAS glass powder, hot pressed 

samples, and glass powder heat-treated at different temperatures were recorded at ambient temperature 

using a step scan procedure (0.02°/2 step, count time 0.4 s) on a Bruker D8 Advanced diffractometer 

equipped with a crystal monochromator employing copper K radiation. 

2.5 Thermal Analysis 

Simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were 

carried out using Netzsch STA 409 C system interfaced with a computerized data acquisition and analysis 

system at heating/cooling rates of 5 or 10 °C/minute in flowing air. The test samples were contained in 

alumina cups. Glass transition and crystallization peak maximum temperatures were obtained from the 

DTA scans. To evaluate crystallization kinetics of the glass, DTA scans were recorded at various heating 

rates of 2 to 40 °C/minute. 

2.6 Dilatometry 

Glass transition temperature, softening point and coefficient of thermal expansion (CTE) were 

measured on a 2.5 cm long hot pressed glass bar using a Netzsch differential dilatometer model 402-C 

interfaced with a computerized data acquisition and analysis system at a heating rate of 5 °C/minute in 

air. Alumina was used as the standard material. 
NASA/TM—2014-218365 3 

2.7 Density, Elastic Modulus, Microhardness, and Indentation Fracture Toughness 

Density was measured from the bulk mass and volume of the hot pressed disc. Young’s modulus, 

shear modulus, and Poisson’s ratio were determined at ambient temperature by the impulse excitation 

method defined in ASTM C 1259 (Ref. 8) using the hot pressed glass disc. The test setup records the 

natural frequency of the disc when excited mechanically in the desired mode. An Audio Technica 

ATM350 condenser microphone amplified with an M-Audio DMP preamplifier was used to acoustically 

detect and amplify the natural frequency. A computer system instrumented with National Instruments 

acoustic signal acquisition hardware and Sound & Vibration Toolset software was used to determine the 

natural frequency. 

Vickers microhardness was evaluated at ambient temperature using hot pressed glass disc with 

polished surfaces in accordance with ASTM C 1327 (Ref. 9). A Zwick model 3212 Hardness Tester was 

used for the Vickers diamond indent application. The Zwick hardness tester incorporates a dampening 

mechanism used to lower the indenter which remains in full load contact with the specimen for 15 sec. 

Four different indentation loads of 1.96, 2.9, 4.9, and 9.8 N were used for each series of tests. An upper 

limit of 9.8 N (1 kg) load was set by the indent exhibiting the start of extreme spalling. A number of 

indentations were made on the polished specimen using each load. Indentation diagonal length (2a) and 

crack length (2c) were measured using the integral optical micrometer for each impression. Values of 

microhardness and fracture toughness were determined from indentation length and crack length as 

described earlier (Refs. 10 to 12). 

3.0 Results and Discussion 

3.1 Desert Sand 

3.1.1 Phase Composition 

The XRD pattern (Fig. 1) of the as-received desert sand showed the presence of SiO2 (Quartz), 

CaSO4.2H2O (Gypsum), CaCO3 (Calcite), NaAlSi3O8 (Albite), and Mg-Al silicate phases. Approximate 

composition of the desert sand was calculated to be 34 percent SiO2 (Quartz), 41 percent CaSO4.2H2O 

(Gypsum), 11 percent CaCO3 (Calcite), 7 percent NaAlSi3O8 (Albite), and 5 percent Mg-Al silicate 

phases from semi-quantitative analysis of XRD results. 

Figure 1.—X-ray diffraction of as-received desert sand from the Middle East showing the presence of CaSO4.2H2O 

(Gypsum), SiO2 (Quartz), CaCO3 (Calcite), NaAlSi3O8 (Albite), and Mg-Al Silicate phases. 
NASA/TM—2014-218365 4 

Figure 2.—Simultaneous DTA and TGA of as-received desert sand from the Middle East at a 

heating rate of 5 K/minute in air. 

3.1.2 Thermal Stability 

Simultaneous DTA/TGA scans of the as-received desert sand at a heating rate of 5 °C/minute in air 

from room temperature to 1420 °C are shown in Figure 2. Several thermal events are present. The 

endothermic peak in DTA at ~155 °C that is accompanied by a weight loss of ~9.68 percent is due to the 

dehydration of CaSO4.2H2O into CaSO4. The next endothermic DTA event at ~797 °C along with a 

weight loss of ~6.4 percent in TGA is ascribed to the decomposition reaction: CaCO3  CaO + CO2. 

Endothermic DTA peaks at 1214 and 1282 °C and corresponding weight loss of ~18 percent in TGA are 

probably due to the stepwise decomposition of CaSO4 according to the reactions: CaSO4  CaSO3 + 1⁄2 O2

followed by CaSO3  CaO + SO2. The exothermic peak at 1344 °C may be due to the formation of 

CaSiO3 and/or CaAl2Si2O8 phases via solid state reaction(s) between the constituents. 

3.2 Glass 

3.2.1 Composition 

From inductively coupled plasma-atomic emission spectrometry (ICP-AES), chemical composition of 

the CMAS glass powder was analyzed to be 25.2CaO-2.6MgO-8.2Al2O3-59.8SiO2-1.6Fe2O3-1.5K2O 

(weight %) or 27.8CaO-4MgO-5Al2O3-61.6SiO2-0.6Fe2O3-1K2O (mole %). Composition of the desert 

sand glass of the current study is richer in silica but contains lower amounts of CaO, MgO, and Al2O3 than 

the composition 35CaO-10MgO-7Al2O3-48SiO2 (mole %) of the synthesized model CMAS used by other 

researchers (Refs. 1 to 4). 

3.2.2 Crystallization 

Simultaneous DTA/TGA scans of the CMAS glass powder recorded at a heating rate of 10 °C/minute 

in air are given in Figure 3. The DTA shows a glass transition inflection at 734 °C and a couple of 

exothermic peaks at 878 and 982 °C due to crystallization of glass. The crystallization onset temperature, 

Tx, for this glass is found to be ~880 °C from the DTA curve. No thermal event is observed during the 

cooling cycle. A large value of 146 °C for (Tx-Tg) indicates this glass to be highly stable. 
NASA/TM—2014-218365 5 

Figure 3.—Simultaneous DTA and TGA of sand CMAS glass powder at a heating rate of 

10 K/minute in air. 

To evaluate crystallization kinetics of the CMAS glass, DTA scans were recorded at various heating 

rates of 2 to 40 K/minute. A typical DTA scan recorded at a heating rate of 20 K/minute from room 

temperature to 1100 °C in air is shown in Figure 4. Values of peak maximum temperatures (Tp) for the 

two crystallization peaks at various scan rates are given in Table 1. Duplicate DTA runs were made at the 

scan rate of 5 K/minute. Values of Tp1 and Tp2 for the two runs at heating rate of 5 K/minute in Table 1 

indicate very good reproducibility. Values of Tp are seen to increase with increase in heating rate. The 

crystallization peak maximum in the DTA or DSC scans corresponds to the temperature at which the rate of 

transformation of the viscous liquid into crystals becomes maximum. When the crystalline phase has the 

same composition as the liquid, the transformation rate will depend on the density of crystallization sites. 

However, when the composition of the crystalline phase is different from that of the liquid, as in the present 

case, the rate of transformation will be controlled by the rate of diffusion through the viscous liquid and the 

number of crystallization sites to which diffusion can occur. If the number of nucleation sites is increased, 

e.g., by using slower heating rates, the peak maximum will occur at a temperature at which the melt viscosity 

is higher, i.e., at a lower temperature. This explains the increase in Tp with the heating rate (Table 1) observed 

in the present study. 

It has been shown earlier that the temperature Tp of the crystallization peak changes with heating rate 

 according to the relation (Refs. 13 to 18): 

ln(Tp

2

/) = ln(Ec/R) + E/RTp (1) 

where Ec is the effective overall activation energy for the crystallization process,  is an effective 

frequency factor which is a measure of the probability that a molecule having energy E participates in the 

transformation, and R is the gas constant. According to Equation (1), a plot of ln(Tp

2

/) versus 1/Tp should 

be linear with a slope of Ec/R and an intercept [ln(Ec/R) - ln ]. 
NASA/TM—2014-218365 6 

Figure 4.—DTA of desert sand CMAS glass powder at a heating rate of 20 K/ 

minute in air. 

TABLE 1.—EFFECT OF HEATING RATE ON DTA CRYSTALLIZATION 

PEAK MAXIMUM TEMPERATURES (Tp) FOR DESERT SAND GLASS

Scan rate 

(K/min) 

Peak 1 (Tp1) 

(K) 

Peak 2 (Tp2) 

(K) 

2 1121 1209.8 

5 1136 1234.7 

5 1136 1234.7 

10 1148 1254.9 

20 1172 1271.2 

30 1188 1280.1 

40 1196 1285.9 

Plots of ln(T / ) 2

p  versus Tp 1 for crystallization of the CMAS glass are shown in Figure 5. A linear /

plot indicates validity of the kinetic model of Bansal et al. (Refs. 13 to 18) and validity of the assumptions 

made in this model. Values of kinetic parameters E and  obtained from linear least squares fitting of the 

experimental data are listed in Table 2. The crystallization activation energies of 403 and 483 kJ/mol for 

CMAS glass are in the same range as reported earlier for barium aluminosilicate (BAS) (Refs. 16 and 17) 

and magnesium aluminosilicate (MAS) (Ref. 19) glasses. 

The XRD pattern of the glass powder is shown in Figure 6. It contains only a large halo indicating the 

glass powder to be amorphous, as expected. XRD patterns of CMAS glass powder heat treated at various 

temperatures from 700 to 980 °C for 10 h in air are presented in Figure 7. The results for the development 

of crystalline phases in the CMAS glass after heat treatments at different temperatures are summarized in 

Table 3. The glass powder remains amorphous at temperatures up to 850 °C. However, two very minor 

peaks are present in the XRD of glass heated at 850 °C indicating the initiation of crystallization of 

CaSiO3. Glass heated at 870 °C is mostly amorphous but contains small crystallization peaks due to the 

formation of minor amounts of Ca2Mg0.5AlSi1.5O7 as well as trace amount of CaSiO3 phase. Strong 

crystallization peaks are observed in the XRD patterns of glass heated at 900 or 980 °C. Glass heated at 

900 °C shows the formation of Ca2Mg0.5AlSi1.5O7 as major phase and CaSiO3 minor crystalline phase 

whereas CaSiO3 is the major crystalline phase and Ca-Mg-Al silicate minor phase in the glass after 

heating at 980 °C. X-ray diffraction pattern from the surface of a glass disc hot pressed at 

800 °C is shown in Figure 6. The sample is amorphous. The two low intensity peaks are from the 

presence of residual grafoil on the sample surface. 
NASA/TM—2014-218365 7 

Figure 5.—Plots of ln(T p

 2/) versus reciprocal of peak temperature for the two 

crystallization exotherms for desert sand CMAS glass powder. 

TABLE 2.—KINETIC PARAMETERS FOR CRYSTALLIZATION 

OF DESERT SAND GLASS 

Crystallization process Activation energy, Ec

(kJ/mol) 

Frequency factor,  

(sec–1) 

Peak 1 403 9.51015

Peak 2 483 9.51017

Figure 6.—X-ray diffraction of desert sand CMAS glass powder and glass disc hot pressed 

at 800 C for 10 min under 2.5 ksi in vacuum. 

 
NASA/TM—2014-218365 8 

Figure 7.—X-ray diffraction of desert sand CMAS glass powder heat treated at various temperatures 

for 10 h in air. 

3.2.3 Dilatometry 

Dilatometric thermal expansion curve for a hot pressed one inch long glass bar, measured from room 

temperature to 820 °C at a scan rate of 5 °C per minute, is shown in Figure 8. This shows a glass 

transition temperature (Tg) of 706 °C and dilatometric softening point (Td) of 764 °C. The average linear 

coefficient of thermal expansion (CTE), , was calculated to be 9.810–6/°C in the temperature range 

from 25 to 700 °C. 

3.2.4 Temperature Dependence of Glass Viscosity 

Temperature dependence of glass viscosity () is expressed by the Vogel-Fulcher-Tamman (VFT) 

Equation (20): 

 log  = A + B/(T-To) (2) 

where A, B, and T0 are constants. Melting point Tm of glass is estimated from Bemann Equation (21): 

 Tg/Tm = 2/3 (3) 

 

TABLE 3.—DEVELOPMENT OF CRYSTALLINE PHASES 

IN DESERT SAND GLASS AFTER HEAT TREATMENTS 

AT VARIOUS TEMPERATURES FOR 10 h IN AIR 

SampleTemperature(°C)PhasesfromXRD

SG700 700 Amorphous

SG800 800 Amorphous

SG850 850 Amorphous

SG870 870 Ca2Mg0.5AlSi1.5O7,CaSiO3

SG900 900 Ca2Mg0.5AlSi1.5O7,CaSiO3

SG980 980 CaSiO3,Ca2Mg0.5AlSi1.5O7
NASA/TM—2014-218365 9 

Figure 8.—Dilatometric thermal expansion scan of hot pressed desert sand CMAS glass 

at a heating rate of 5 C/minute in air. 

Figure 9.—Temperature dependence of viscosity of desert 

sand CMAS glass. 

For silicate glasses, a number of specific viscosity values have been assigned as reference points 

corresponding to various temperatures. For silicate glasses, viscosity values at reference temperatures Tg, 

Td, and Tm are designated as 1013.6, 1011.3, and 106

 dPaS, respectively (Ref. 22). For the sand glass of the 

present study, values of Tg, Td, and Tm are 979, 1037, and 1468.5 K. Values of constants A, B, and T0 of 

VFT Equation (1) are determined from three equations by substituting  values corresponding to Tg, Td, 

and Tm in Equation (2). For sand glass, values of these constants are calculated to be: A = 2.6 kPa.s, 

B = 2418 kPa.s.K, and T0 = 759 K. 

The VFT equation for the desert sand glass becomes: 

 log  = 2.6 + 2418/(T-759) (4) 

Temperature dependence of viscosity of the desert sand glass is shown in Figure 9. 
NASA/TM—2014-218365 10 

3.2.5 Density, Elastic Modulus, Microhardness, and Indentation Fracture Toughness 

Bulk density of CMAS glass was determined to be 2.69 g/cm3 from weight and volume 

measurements. Values of Young’s modulus (E), Shear modulus (G), and Poisson’s ratio (	) were 

measured to be 92.3 GPa, 36 GPa, and 0.28, respectively. 

For Vickers microhardness measurements, a number of indentations were made on the surface of a 

hot pressed polished specimen using indentation loads of 1.96, 2.9, 4.9, and 9.8 N. Typical indentations 

on the glass specimen at various loads are shown in Figure 10. An upper limit of 9.8 N (1 kg) load was set 

by the indent exhibiting the start of extreme spalling. Indentation diagonal length (2a) and crack length 

(2c) were measured for each impression as shown in Figure 11. Results for an indentation were not 

included if value of c/a was less than 2.3 or if crack branching was present. Vickers microhardness was 

calculated using the equation: 

 Hv = 1.854 [P/(2a)2

] (5) 

where Hv is the Vickers microhardness in Pascal, P is the applied load in Newton, and 2a is the indent 

diagonal length in meter. Values of Hv at various loads are shown in Figure 12 and Table 4. Average 

value of Hv for the desert sand glass was found to be 6.30.4 GPa. This value of Vickers microhardness 

for desert sand glass falls in the same range as found for other silicate glasses. 

A number of mathematical equations are available for determination of indentation fracture toughness 

(Refs. 23 to 27). Miyoshi et al. (Ref. 23) provided the relation: 

 Kc = 0.0264 E0.5 P0.5 a/c-1.5 (6) 

where Kc is the indentation fracture toughness in MPa.m1⁄2, E is the Young’s modulus in GPa, P is the 

indentation load in Newton, a is the half indent length in meter, and c is the half crack length in meter. 

Marshall and Evans (Ref. 24) reported the following relation: 

 Kc = 0.036 E0.4 P0.6 a

0.8 c-1.5 (7) 

for evaluation of Kc. According to Anstis et al. (Ref. 25), Kc may be obtained from the equation: 

 Kc = 
 P (E/Hv)

1⁄2 c-1.5 (8) 

where 
 is an empirical constant. Based on a fit to experimental data using independent fracture toughness 

measurements, Anstis et al. (Ref. 25) determined the value of 
 as 0.016±0.004. Values of Kc evaluated at 

various indentation loads from Equation (6) of Miyoshi et al. are shown in Figure 13. Values of Kc

determined using various Equations (6) to (8) are listed in Table 4 which are found to be in good 

agreement with each other. For desert sand glass an average value of indentation fracture toughness was 

found to be 0.75±0.15 MPa.m1⁄2 which is typical as found for other silicate glasses. It will be interesting to 

compare these values with those obtained from the single edge V-notch beam (SEVNB) method. 

 
NASA/TM—2014-218365 11 

Figure 10.—Optical micrographs showing Vickers indentations on CMAS 

glass at applied loads of (a) 1.96 N, (b) 2.9 N, (c) 4.9 N, and (d) 9.8 N. 

Figure 11.—Vickers indentation on CMAS glass at an applied 

load of 9.8 N showing indentation diagonal length (2a) and 

crack length (2c). 
NASA/TM—2014-218365 12 

Figure 12.—Values of Vickers microhardness for desert sand CMAS glass at various 

indentation loads. 

Figure 13.—Values of indentation fracture toughness evaluated using equation of 

Miyoshi et al. (Ref. 23) at various indentation loads for desert sand CMAS glass. 

TABLE 4.—VICKERS HARDNESS AND INDENTATION FRACTURE TOUGHNESS 

OF DESERT SAND GLASS 

Indent load 

(N) 

Crack length 

(2c)/Indent 

length (2a) 

Vickers hardness, 

Hv (GPa) 

Indentation fracture toughness, Kc (MPa.m1⁄2), from various 

equations 

Eq. (6) Miyoshi 

et al. 

Eq. (7) 

Marshall & 

Evans 

Eq. (8) Anstis et al. 

1.96 2.9 5.90.1 0.7 0.7 0.6 

2.94 2.80.1 6.60.1 0.8 0.9 0.7 

4.9 3.20.1 6.40.1 0.750.05 0.80.1 0.650.05 

9.8 3.80.2 6.20.1 0.650.05 0.70.1 0.60.1 
NASA/TM—2014-218365 13 

4.0 Summary and Conclusions 

As-received desert sand from the Middle east consisted of quartz (SiO2), calcite (CaCO3), gypsum 

(CaSO4.2H2O) and NaAlSi3O8 phases and showed weight loss of ~35 percent due to decomposition of 

CaCO3 and CaSO4.2H2O when heated to 1400 °C. Chemical composition of the glass, obtained by 

melting of desert sand at ~1500 °C, was analyzed to be 27.8CaO-4MgO-5Al2O3-61.6SiO2-0.6Fe2O3-1K2O 

(mole %) using inductively coupled plasma-atomic emission spectrometry. The glass remained 

amorphous after heat treating at 850 °C for 10 hr but crystallized into CaSiO3 and Ca-Mg-Al silicate 

phases at 900 °C or higher temperatures. Various physical, thermal and mechanical properties of the glass 

have been evaluated. The glass showed bulk density 2.69 g/cm3

, Young’s modulus 92 GPa, Shear 

modulus 36 GPa, Poisson’s ratio 0.28, dilatometric glass transition temperature (Tg) 706 °C, softening 

point (Td) 764 °C, Vickers microhardness 6.30.4 GPa, indentation fracture toughness 0.750.15 

MPa.m

1/2

, and coefficient of thermal expansion (CTE) 9.810–6/°C in the temperature range 25 to 700 °C. 

Temperature dependence of viscosity of the CMAS glass has been estimated from viscosity values at 

various reference points. Crystallization kinetics of the CMAS glass was also investigated by differential 

thermal analysis (DTA). Activation energies for crystallization of two different phases in the glass were 

calculated to be 403 and 483 kJ/mol, respectively. 

5.0 Future Work 

Future research will involve the determination of strength of desert sand glass in 4-point bend as well 

as its fracture toughness by single edge v-notch beam (SEVNB) method. Interactions of this CMAS glass 

will also be investigated with various environmental barrier coating (EBC) and thermal barrier coating 

(TBC) materials at elevated temperatures of 1200 to 1500 °C. Effects of sand glass exposures on stability 

of EBC and TBC coatings as well as SiCf/SiC composites will also be studied. 

References 

1. K. M. Grant, S. Kramer, G. G. E. Seward, and C. G. Levi, Calcium-Magnesium Alumino-Silicate 

Interaction with Yttrium Monosilicate Environmental Barrier Coatings, J. Am. Ceram. Soc., 93 [10], 

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