exergy consumption through the life cycle of ceramic parts

Exergy Consumption Through the Life Cycle of CeramicParts

Hideki Kita,* Hideki Hyuga, Naoki Kondo, and Tatsuki Ohji

National Institute of Advanced Industrial Science and Technology (AIST), 2266-98 Shimo-Shidami,Moriyama-ku, Nagoya 463-8560, Japan

Exergy is a measure that can commonly deal with the quantification of a variety of resources, products, and energy comingin and going out of the manufacturing systems. In this study, exergy analysis was conducted on a ceramic tube and a steelheater protection tube used in aluminum casting, and the amount of exergies consumed through their life cycle were cal-culated. In the production stage, the ceramic heater tube consumes much higher exergy than the steel one; however, analysisthrough the life cycle in seven years shows that exergy consumptions for the ceramic and steel tubes were 1223 and 1585 GJ,respectively. These results reveal that ceramics are effective in the reduction of environmental burden.

Introduction

Although structural ceramics have excellent prop-erties compared with other metals, they are not in wide-spread use because of the higher initial cost. However, inaddition to the financial costs, it is also important toconsider the value of reducing the impact of a productin terms of natural resource consumption and environ-mental problems throughout its life cycle. In order toachieve this, we need a method for the quantitativeevaluation of natural resource consumption that is sim-ilar to measurements of economic cost. In this regard,we believe that exergy analysis could be an effectiveapproach.

Because the modes of the energy and resourcescoming in and going out of the ‘‘systems’’ during eachprocess in a product’s life cycle are varying, this makes it

difficult to evaluate the overall consumption and rate ofeffective utilization of natural resources. In order to de-sign products that are highly energy efficient throughouttheir life cycles, a measurement index that can quanti-tatively and integrally express natural material and en-ergy resources is important. Exergy could be an effectivemeasurement index that can be used for this purpose.

Examples of exergy analysis that have been carriedout to date for artificial products include research intoexergy consumption in the usage stage of electrical light-ing, in the production and consumption of reinforcedconcrete, and in the life cycle of aluminum and steelcans; among natural products, analysis of exergy con-sumption in plants during photosynthesis has beencarried out.1–6 Studies using exergy analysis on ceramic-related issues have not been found.

Based on these considerations, we carried out ex-ergy analysis for ceramics in order to clarify the valueof environmental impact reduction throughout theirlife cycles and to develop a design policy for a highly

Int. J. Appl. Ceram. Technol., 5 [4] 373–381 (2008)DOI:10.1111/j.1744-7402.2008.02235.x

Ceramic Product Development and Commercialization

*[email protected]

r 2008 The American Ceramic Society

efficient ceramics production process. In our previousreport, analysis was conducted based on the manufac-turing process of ceramic parts, and the process effi-ciency was evaluated.7 In this report, we calculated theexergies for natural resources and energies in the pro-duction and usage stages when ceramic heater protec-tion tubes were used, compared with conventional steelheater protection tubes, to estimate the reduction inenvironmental impact.

Experimental Procedure

The Object for Analysis

In the melting and casting production of alumi-num, silicon nitride ceramics are now being used asmany components exposed into molten aluminumbecause of their superior corrosion and thermal shockresistances. One of these applications is a heater protec-tion tube, which contains heat sources such as gasburners or electrically heated wires inside to keep thetemperature of molten aluminum constant. It is saidthat use of a highly durable silicon nitride heater pro-tection tube provides great improvement in thermalefficiency.8

Figure 1 shows the structure of an aluminum melt-ing furnace and the mounting location of heater pro-tection tubes. Stainless steel tubes have been mainlyused; however, the high corrosion rate due to the reac-tion between molten aluminum requires frequentexchanges, and then, this inevitably leads to theexchangeable vertical soaking type heater.

On the contrary, silicon nitride, which is extremelystable in molten aluminum, changed the furnace struc-ture. A horizontal soaking-type heater mounted at thebottom of the furnace was designed, which reduced heatloss drastically8 and provided higher efficiency whencompared with the vertical soaking type.

Figure 2 shows the schematic of heater protectiontubes studied in this report. The tube measures1346.5 mm in length, 155 mm in outer diameter, and19 kg in weight for both types of steel and ceramics.Initial thicknesses of the tubes are 3 and 8 mm for steeland ceramics, respectively.

We conducted exergy analyses on the production ofheater protection tubes. Data for its production (quan-tities of raw material, fuel, waste, waste gas, water, etc.),which were necessary for analyzing exergy, were ob-tained from companies.8 Some data were unavailable,and they were supplemented with the authors’ knowl-edge of ceramic processing.

Exergy Calculations

Chemical Exergy Calculations for Metal and InorganicCompounds9: Referential species of inorganic com-pounds are denoted as Xx, Aa, Bb, and so on. They areformed according to the following reaction formula:

xX þ aAþ bB þ � � � ! XxAaBb � � � ð1ÞUsing DG0 for the Gibbs free energy change, the

chemical exergy of the inorganic compound can be cal-culated using the following formula:

Ex0 ¼ 1

x½�DG0 � aEx

0ðAÞ � bEx0ðBÞ � � � �� ð2Þ

As a reference, the exergy value of a substance isdefined as zero if it does not react in a temperature en-vironment of 251C (298.15 K). References for some ar-tificial materials are published in Japanese Industrial

Heater

(A) Vertical Soaking Type

Molten Aluminum

(B) Horizontal Soaking Type

Heat Insulation Material

Fig. 1. Heater mounting location in an aluminum meltingfurnace.8

Thickness:

· Steel:3mmt

· Ceramics :8mmt

77.5 mm 1100mm 169mm

1346.5mm

�15

5mm

�19

5mm

Fig. 2. Dimension of a heater protection tube.8

374 International Journal of Applied Ceramic Technology—Kita, et al. Vol. 5, No. 4, 2008

Standards (JIS),10 but for those not mentioned in JIS,the reference is the smallest free energy value. The valuesfor thermo-chemical data used in the calculations areshown in Appendix A.11

Chemical Exergy Calculation for Organic Com-pounds: The chemical exergy equation for organiccompounds is derived based on chemical exergy valuesfor the individual hydrocarbon compounds that act asthe building blocks of petroleum. Although the formu-las of Rant12 and Szargut13 are known to be statisticallydependent on elemental composition, in this report werevised the Rant formula for solid fuels, and Nobusawa’sequation14 was used for practical application:

Ex ¼ mHl

1:0064þ 0:1519fH

fC

þ 0:0616fO

fC

þ 0:0429fN

fC

� �

ð3Þ

Here, Ex is chemical exergy of organic compounds,m and Hl are dry weight (kg) and lower heating value(kJ/mol), respectively, and jC, jH, jO, and jN are theweight fractions of carbon, hydrogen, oxygen, andnitrogen contained in the compounds.

Exergy Calculation for Input Energy: The input energyused in this study was from electric power and LPG(liquefied petroleum gas). The exergy value for electricalpower was the same as the electrical energy value,because electrical power has extremely low entropy. Thecalculation for LPG exergy was based on Nobusawa’sequation,14 as used in the previous section. The distri-bution was obtained for a mixed mole rate of the exergyvalues of C3H8 and C4H10 (0.2 and 0.8, respectively),and the mixed entropy was calculated based on thedifference between LPG exergy and the lower heatingvalue:

ExðmixÞ ¼ HðmixÞ þ T0 � DSðmixÞ ð4Þ

H ðmixÞ ¼XðXi � HiÞ þ R � T0

�X

Xi � lnðXiÞ��

ð5Þ

DSðmixÞ ¼ ðExðmixÞ �HxðmixÞÞ=T0 ð6Þ

Here, Ex(mix) is the chemical exergy of mixed gas (kJ/mol), H(mix) the lower heating value of mixed gas (kJ/mol), T0 environmental temperature (K), R the gas con-

stant ( 5 8.314 J/mol), DS(mix) entropy of mixed gas(J/K �mol), Xi the volume fraction of each component,and Hi the lower heating value of each component(kJ/mol).

Production Subsystems: For the calculation of exergyinput, consumption, and waste, the production systemwas assumed to be an assembly of subsystems, andquantification was performed for the input/output ex-ergy of each production subsystem. The purpose of per-forming the analysis in subprocess units was not only forthe sake of orderliness, but also for clarifying the loca-tion of problems with a view to improving the processefficiency and production method; an example is shownin Fig. 3. For each subsystem, raw materials, fossil fuels(including electric power and steam), etc. containingexergy were inserted (input), and waste, waste heat, etc.as well as a product or an intermediate product con-taining exergy were generated (output). The obtainedintermediate product was used as the starting materialfor the next subsystem.

The final product was obtained by going throughthese subsystems and calculating the exergy values thatenter or exit the respective subsystems. In principle,processes and items such as mining for the raw mate-rials, construction, dismantlement, transportation, facili-ties, packing material for transportation, and palletingshould also be included. The focal point of this study,however, is the production of a heater protection tube;thus, the above-mentioned processes were regarded tobe outside the scope of the present study.

Process Efficiency: In this report, the ratio between theexergy fixed in the product and the total input exergy

• Materials

Step 1• Energy• Water• Gas

• Waste• Heat• Water• Gas

• (Intermediate) Products

INPUTOUTPUT

Step 2

Step N

• (Final) Products

Sub system

Fig. 3. Assembly of subsystems for the process.

www.ceramics.org/ACT Exergy Consumption Through the Life Cycle of Ceramic Parts 375

was determined by the above calculation (rate of exergyfixation), and this rate was regarded as the processefficiency:

Z ¼ ExðpÞ=ExðinÞ ð7ÞHere, Z is the rate of exergy fixation, Ex(p) is the

exergy fixed in the product, and Ex(in) is the actual in-put exergy.

Results and Discussion

Exergy in Production

The exergy balance for the production of a steelprotection tube is shown in Table I. The productionprocess of the steel protection tube consists of sintering,reduction, transfer, decarbonization, and metal rolling.5

Table I. Materials and Exergy Balance for the Production of Steel Protection Tube�,5

Raw materials Intermediate products Disposal

Weight(kg)

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Sintering Ironstone 27.1 0.0 Sinteredore

26.8 0.0 Wastage 4.3 0.0

Limestone 4.0 0.0Fuel 48.5 Waste exergy 48.5Sum 31.1 48.5 Sum 26.8 0.0 Sum 4.3 48.5

Reduction Sinteredore

26.8 0.0 Pig iron 19.9 163.8 Wastage 17.4 30.4

Ironstone 6.0 0.0Coke 4.5 150.9Fuel 211.1 Waste exergy 193.8Water(m3)

0.3 26.0 Water vapor(m3)

0.3 0.0

Sum 37.2 388.0 Sum 19.9 163.8 Sum 17.4 224.2Transfer Pig iron 19.9 163.8 Pig iron 19.9 160.4 Heat waste 3.4Decarbon Pig iron 19.9 160.4 Steel 25.5 173.6 Wastage 6.1 28.3

Scrap 9.7 64.4Oxygen 2.1 3.8Fuel 58.1 Waste exergy 93.9Water(m3)


0.0 0.0

Sum 31.6 295.8 Sum 25.5 173.6 Sum 6.1 122.2Transfer Steel 25.5 173.6 Steel 25.5 169.7 Heat waste 4.0Metalrolling

Steel 25.5 169.7 Steel 19.0 126.0 Wastage 6.5 42.8

Fuel 43.3 Waste exergy 50.0Water(m3)


0.0 0.0

Sum 25.5 218.7 Sum 19.0 126.0 Sum 6.5 92.7Totalprocess

Materials 53.3 260.0 Steel 19.0 126.0 Wastage 34.3 101.4

Fuel 361.0 Waste exergy 393.6Sum 621.0 126.0 495.0�Each exergy values were calculated.


Based on the incoming and outgoing materials and en-ergies for the respective processes, the exergy input forone tube was calculated to be 621.0 MJ. Of this exergyinput, 126.0 MJ was fixed in the product; thus, the re-mainder of 495.0 MJ is considered to be disposed of aswaste or heat. Then, the process efficiency of steel wasapproximately 20%.

Table II shows the exergy balance for the produc-tion of a ceramic heater protection tube.7 The processinvolves mixing, granulation, CIPing and green ma-chining, dewaxing, and sintering. As the input energy,LPG was used for drying in granulation, and electricpower was used in dewaxing and sintering. Most of thematerial removed by green machining is supposed to bereused; thus, the raw material powder is not wasted.When the same weight of silicon nitride as the abovewas produced, the total input exergy of 4175.3 MJ,which is the sum for raw materials, electric power, andgas (312.2 MJ, 1616.6 MJ, and 2246.5 MJ, respec-tively), was necessary. The exergy fixed in the productwas 229.4 MJ, and the remaining 3779.7 MJ was dis-charged into the environment as waste or heat. Theprocess efficiency of ceramics was calculated to be ap-proximately 5.5%. The details were studied in a previ-ous report.7

Exergy Consumption During Operation

Dissolution of Heater Protection Tube and Its Dis-posal: The ceramic protection tube is chemically stablein molten aluminum. In the case of the steel protectiontube, corrosion and dissolution occur because of the

chemical reaction with molten aluminum. Therefore,once a predefined thickness has been reached, it is nec-essary to replace it, and its lifespan is about 6 months.The loss due to dissolution is assumed to proceedaccording to the following equation:

D ¼ Do� ð22expðktÞÞ ð8Þ

Here, D is the thickness (mm) of the heater pro-tection tube, Do is its initial thickness (mm), and k is theapparent reaction rate constant. In the above equation,Do was set to 3 mm, and the thickness of the heaterprotection tube at the time of replacement was denotedby Di. The condition for replacement was set to whenthe thickness is half the initial thickness (Di/Do 5 0.5).The lifespan for replacement (t) is 6 months; thus, thereaction rate (corresponding to constant k) was calcu-lated to be 0.067578 mm per month by substitutingthese values.

On the other hand, in the case of the ceramic pro-tection tube, the tube is replaced after 7 years, which isthe same as the lifespan of the entire furnace. However,the reaction of the ceramic itself hardly progressed, andthe details are not known. In this study, the value of Di/Do was assumed to be 0.8, and the lifespan was assumedto be 200 months. The reaction rate constant was cal-culated in a similar way as above, and the reaction ratewas determined to be 0.000912 mm per month. Thecalculated thickness change according to elapsed time isshown in Fig. 4.

The exergy is consumed by dissolution loss. The con-sumed exergy was calculated according to the followingequation using the obtained reaction rate constant and

Table II. Materials and Exergy Balance for the Production of Ceramic Protection Tube�

Process

Input resources Products Disposal

Electric power(MJ)

LPG Raw materials Products Materials

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Weight(kg)

Exergy(MJ)

Mixing 266.8 30.9 291.1 30.9 291.1 0.0 0.0 266.8Spraydryng

300.1 46.4 2246.5 197.4 311.7 20.3 291.1 223.6 103.9 2463.2

Forming 175.0 20.3 291.1 20.3 291.1 0.0 0.0 175.0Dewaxing 98.4 20.3 291.1 19.0 229.4 1.4 61.8 98.4Sintering 776.3 42.7 229.9 19.0 229.4 23.7 0.6 776.3Sum 1616.6 46.4 2246.5 202.1 312.2 19.0 229.4 248.7 166.2 3779.7�Each exergy values were calculated.


the results shown in Fig. 4:

E ¼ Eo� expðktÞ ð9Þ

Here, E is the consumed exergy, Eo the initial ex-ergy, and t the elapsed time. In the case of the steelprotection tube, one tube (19 kg) has an exergy of126.0 MJ (see Table I); thus, the exergy per unit weightis 6.6 MJ/kg. The consumed exergy was calculated in asimilar way for the silicon nitride protection tube. Inthis case, the exergy per unit weight is 12.1 MJ/kg basedon the data in Table II.

The change in consumed exergy with time is shownin Fig. 5. A steel heater protection tube needs exchangeevery 6 months; on the contrary, a ceramic tube can beused continuously for 7 years.

The value of the completed ceramic heater protectiontube is its high conservation stability (no diffusion).That is to say, while the steel tube consumes exergy as aresult of the chemical reaction during operation, the

ceramic tube hardly consumes any exergy. Because thesteel tube is replaced every 6 months, 14 steel tubes areused in 7 years. On the other hand, only one ceramictube is used in 7 years. Therefore, the respective con-sumed exergies are as follows:� when a steel tube is used:

126:0 ðMJ=tubeÞ � 14 ðtubesÞ ¼ 1764MJ

� when a silicon nitride tube is used:

229:4 ðMJ=tubeÞ � 1 ðtubeÞ ¼ 229:4MJ

Steel diffuses in molten aluminum and becomes animpurity, whereas the chemically stable ceramic doesnot diffuse in molten aluminum. As a result, the qualityof the ceramic is excellent and the aluminum product iseasily recyclable. An additional advantage of the ceramicis that its operation period can be shortened.

Exergy Necessary for Furnace Operation: Table III showsa comparison of the electric power consumed duringoperation and that consumed during down-time.8

When a steel tube is used, it would be a vertical soak-ing type. In the case of a ceramic tube, a horizontalsoaking type is possible (Fig. 1). For the vertical soakingtype, 9.4 kW is necessary during operation and 4.0 kWis necessary during down-time. The thermal efficiencyof the horizontal soaking type, in which the ceramictube is used, can be improved. The consumed electricpowers during operation and during down-time are6.8 kW and 3.8 kW, respectively. If the operation timeis assumed to be 60% of a day (i.e., 40% down-time)and the equipment is assumed to be operated for 360days per year, the total consumed electric power (exergy)in 7 years will be as follows:� when a steel tube is used:

ð9:4� 0:6� 24þ 4:0� 0:4� 24Þ � 360� 7� 3:6=1000¼ 1576GJ

0

2

4

6

8

10

0 12 24 36 48 60 72 84

Thi

ckne

ss o

f H

eate

r T

ube

/ mm

Ceramic tube

Steel tube

Elapsed Time / months

Waste

Solution

Fig. 4. Thickness change of tubes according to elapsed time.

0

500

1000

1500

2000

0 12 24 36 48 60 72 84

Ceramic tube

Steel tube

Waste

Solution

Elapsed Time / months

Exe

rgy

Con

sum

ptio

n / M

J

Fig. 5. Calculated lost exergy of tubes according to elapsed time.

Table III. Electric Power Consumption for Verticaland Horizontal Soaking Type

Stage

(A) Verticalsoaking type(steel tube)

(B) Horizontalsoaking type

(ceramic tube)

Running 9.4 kW 6.8 kWDown–time 4.0 kW 3.8 kW


� when a silicon nitride tube is used:

ð6:8� 0:6� 24þ 3:8� 0:4� 24Þ � 360� 7� 3:6=1000¼ 1219GJ

That is, for the vertical soaking type, the consumedexergy is 1576 GJ. On the other hand, the consumedexergy is 1219 GJ for the horizontal soaking type when asilicon nitride tube is used.

Comparison of Exergy Consumptions for Production,Operation, and Disposal

As mentioned above, when a furnace is operated for7 years, 14 steel protection tubes are necessary becauseof dissolution loss. On the other hand, only one siliconnitride tube is required for the same period. The ce-ramic tube does not have to be changed for 7 years;however, it is replaced because of wearing by the furnacematerial.

As mentioned above, the disposal exergy in theproduction process is 495.0 and 3779.7 MJ for one steeltube and for one silicon nitride tube, respectively (referto Tables I and II). Therefore, the total exergy can becalculated, as shown below, by multiplying the numberof tubes used in 7 years:

�When a steel tube is used:495:0 ðMJ=tubeÞ � 14ðtubesÞ ¼ 6930:0MJ�When a silicon nitride tube is used:

3779:7 ðMJ=tubeÞ � 1ðtubeÞ ¼ 3779:7MJ

ð10Þ

In the following, the disposed exergy as a result ofoperational wear is also shown.

�When a steel tube is used:126:0 ðMJ=tubeÞ � 14ðtubesÞ ¼ 1764MJ�When a silicon nitride tube is used:

229:4 ðMJ=tubeÞ � 1ðtubeÞ ¼ 229:4MJ

ð11Þ

As shown in ‘‘Exergy Necessary for Furnace Oper-ation,’’ the consumed electric powers during usage for thesteel tube and the silicon nitride tube are 1576 and1219 GJ, respectively. By adding (10) and (11) to theconsumed electric power, the consumed exergies whenusing the steel tube and the silicon nitride tube are cal-culated to be 1585 and 1223 GJ, respectively. Thus,when a silicon nitride tube is used, the consumed exergyis 362 GJ less than when a steel tube is used. In otherwords, the silicon nitride tube consumes a larger exergyper tube during the production process; however, it isreplaced less frequently and its consumption of electricpower can be smaller than the steel tube because the sil-icon nitride tube has a high conservation stability. As aresult, the total exergy consumption through a life cycleof production, operation, and disposal is smaller thanthat of the steel tube. Silicon nitride is hard-to-recyclematerial. Therefore, when the silicon nitride parts reachthe end of its usefulness, in many cases, they will be dis-carded and buried in the ground. The disposal of siliconnitride could have a very low impact on environmentbecause they are extremely stable in the earth (Table IV).

Conclusions

Exergy analysis was conducted on ceramic and steelheater protection tube used in aluminum casting, andthe amount of exergy consumed through the life cyclewas calculated.

(1) In the production stage, a ceramic heater con-sumes much higher exergy than the steel one, 495 and3780 MJ for one piece, respectively.

(2) Analysis through the life cycle in 7 years showsthat exergy consumptions for the ceramic tube and steeltube are 1223 and 1585 GJ, respectively. These resultsreveal that ceramics are effective in the reduction of en-vironmental burden.

Table IV. Comparison of Consumed Exergy for Steel and Ceramic Tubes Through Life

Stage Steel tube Ceramic tube

[1] Production stage 6930 MJ 5 495(MJ/P)� 14(P) 3780 MJ 5 3780(MJ/P)� 1(P)[2] Usage stage (A)w 1764 MJ 5 126(MJ/P)� 14(P) 229 MJ 5 229(MJ/P)� 1(P)[3] Usage stage (B)z 1576 GJ 5 (9.4� 0.6� 2414.0� 0.4� 24)

� 360� 7� 3.6/10001219 GJ 5 (6.8� 0.6� 2413.8� 0.4� 24)

� 360� 7� 3.6/1000Total ([1]1[2]1[3]) 1585 GJ 1223 GJwLost exergy by reaction with molten aluminum plus disposal.zInput energy for running the furnace.


References

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5. T. Morihana, I. Takahashi, and M. Shukuya, ‘‘Exergy Consumption of Re-inforced Concrete Walls in the Courses of Production and Use,’’ J. Archit.Plann. Environ. Eng., 520 99–105 (1999) (in Japanese).

6. Y. Soeno, T. Akashi, H. Ino, K. Shiratori, K. Nakajima, and K. Harada,‘‘Exergy Analysis for the Integrated Evaluation of Environmental Impacts,’’J. Japan Inst. Metals, 66 [9] 885–888 (2002) (in Japanese).

7. H. Kita, et al. ‘‘Exergy Analysis on the Ceramic Manufacturing Process,’’ J. Ceram. Soc. Jpn., 115 12 987–992.

8. Tounetsu Corporation, ‘‘Ceramic Heater Protection Tube,’’ http://www.tounetsu.co.jp/index-j.html (in Japanese).

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Appendix A

Table A1. Thermo-Chemical Data

T Cp S H–H (T) (gef ) DfH DfGK J/kmol J/kmol kJ/mol J/kmol kJ/mol kJ/mol

Si (sl)298.15 4.767 4.5 0 �4.5 0 0

N2 (g)298.15 29.129 191.5 0 �191.5 0 0

Si3N4 (s)298.15 92.685 66.07 0 �66.07 �787.8 �676.46

SiO2 (sl)298.15 44.966 43.4 0 �43.4 �908.346 �854.542

O2 (g)298.15 29.486 205.029 0 �205.029 0 0

C (s)298.15 8.541 5.74 0 �5.74 0 0

CO2 (g)298.15 36.861 213.63 0 �213.63 �393.509 �394.359

Y2O3 (sl)298.15 101.697 99.08 0 �99.08 �1905.31 �1816.65

Y3Fe5O12 (s)298.15 430.493 406.6 0 �406.6 �4976.8 �4650.8

Fe2O3 (s)298.15 103.711 87.4 0 �87.4 �824.2 �742.2


T DrH DrS DrGlog (Kp) Kp Dr (GEF)K kJ/mol J/kmol kJ/mol

1.6667Fe2O3(s)1Y2O3(sl) 5 0.6667Y3Fe5O12(s)298.15 �39.028 26.331 �47.014 8.236 1.72E108 �26.331

0.6667N2(g)1Si(sl) 5 0.3333Si3N4(s)298.15 �262.574 �124.482 �225.464 39.5 124.482

SiO2(sl)1C(s) 5 CO2(g)1Si(sl)298.15 514.837 183.32 460.183 �80.621 �183.32

O2(g)1Si(sl) 5 SiO2(sl)298.15 �908.346 �180.459 �854.542 149.71 180.459

C(s)1O2(g) 5 CO2(g)298.15 �393.509 2.861 �394.359 69.089 �2.861

Table A1. Continued


exergy consumption through the life cycle of ceramic parts

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