Commercial Phase Change Material for Thermal Energy Storage Applications with only PCM and Metal Foam Infiltrated PCM in a Latent Heat Thermal Energy Storage System

Abstract

Introduction

Problem Modeled

Mathematical Model and Governing Equations

Boundary Conditions

Results and Discussion

Conclusions

References

Phase Change Thermal Energy Storage and Recovery in a Complex-Shaped Double Pipe Heat Exchanger

Abstract

Introduction

Problem Modeled

Model Assumptions

Mathematical Formulation

Boundary Conditions

Solution Procedure

Results and Discussion

Conclusions

References

Encapsulating Battery Components with Melting Gels

Abstract

Introduction

Battery Requirements

Melting Gels as Sealing Glasses

Evaluating Melting Gels as Seals

Temperature Dependence of Gas Transport in Melting Gels

Effect of Electrolytes

Summary

References

Nanotechnology for Energy, Healthcare and Industry

Preparation and Characterization of Zinc Substituted Cobalt Ferrite Nano-Particles by Citrate Gel Method

Abstract

1. Introduction:

2. Experimental Procedure:

3. Results and Discussion:

4. Conclusion:

Acknowledgements:

References:

Effect of Drying Time and Temperature on the In-Plane and Thru-Plane Electrical Properties of Multiwalled Carbon Nanotube Films Deposited on Paper Substrates Using a Unidirectional Drying Method

Abstract

Introduction

Materials and Methods

Results and Discussion

Conclusions

Acknowledgements

References

The Effect of Additive on NOx Emission During Thermal Decomposition of Nano-Recrystallised Nitrate Salts

Abstract

Introduction

Experimental

Discussion

Conclusions

Acknowledgments

Footnotes

References

Author Index

Advances in Materials Science for Environmental and Energy Technologies III

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.

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ISBN: 978-1-118-99668-3

ISSN: 1042-1122

Preface

The Materials Science and Technology 2013 Conference and Exhibition (MS&T’13) was held October 27–31, 2013 at the Palais des congress, in Montreal, Quebec, Canada. One of the major themes of the conference was Environmental and Energy Issues. Twenty six papers from six symposia held in this theme are included in this volume. These symposia included Green Technologies for Materials Manufacturing and Processing V; Materials Issues in Nuclear Waste Management in the 21st Century; Materials Development and Degradation Management in Nuclear Applications; Energy Storage III: Materials, Systems and Applications; Nanotechnology for Energy, Healthcare and Industry; and Hybrid Organic — Inorganic Materials for Alternative Energy.

The success of these symposia and the publication of the proceedings could not have been possible without the support of The American Ceramic Society and other organizers of the program. The program organizers for the above symposia are appreciated. Their assistance, along with that of the session chairs, was invaluable in ensuring the creation of this volume.

TATSUKI OHJI, AIST, JapanJOSEF MATYÁŠ, Pacific Northwest National Laboratory, USANAVIN JOSE MANJOORAN, Siemens AG, USAGARY PICKRELL, Virginia Polytechnic Institute and State University, USAANDREI JITIANU, Lehman College, USA

Green Technologies for Materials Manufacturing and Processing

COMPARISON OF THE NANOSECOND PULSE AND DIRECT CURRENT CHARGING TO DEVELOP THE STRONGLY CHARGED ELECTRET

Keishi Awaya, Masaya Mitsuhashi, Tsubasa Sakashita, Hong Byungjin, Tadachika Nakayama, Weihua Jiang, Akira Tokuchi, Tsuneo Suzuki, Hisayuki Suematsu and Koichi Niihara

Extreme Energy-Density Research Institute, Nagaoka University of Technology, Nagaoka, Japan

ABSTRACT

Recently, micro power generation using electrets has attracted much attention due to its large power output at a low frequency range. Since the theoretical power output is proportional to the square of the surface charge density of the electret, the development of a high-performance electret is required. Conventionally, electrets have been mainly manufactured by corona discharge generated using a direct current (DC) source. However, dielectric breakdown usually occurs when high voltage is applied to a material due to the increased surface charge density of the electret. Here, we focus on the nanosecond pulse (70 ns pulse width) that has ability to apply higher voltages to materials than when DC is used. A series of measurements of surface potential and thermally stimulated discharge current (TSDC) spectra is made for various polytetrafluoroethylene (PTFE) electrets, which were manufactured by DC and nanosecond pulses. It is found that the surface charge density and thermal resistibility of electric charges are improved by using nanosecond pulses. A surface charge density using a nanosecond pulse of 0.59 mC/m2 is larger than that of using DC by 59%. In addition, the thermal stability of the electret manufactured by nanosecond pulses is superior to that of by DC. Moreover, discharge energy of nanosecond pulse generator is greater than that of DC power source. Therefore, we conclude that nanosecond pulse will be more useful for manufacturing electrets than DC.

INTRODUCTION

In recent years, energy harvesting attracts much attention all over the world1. Especially, micro power generator using electret is studied actively2, 3 Since the theoretical power output of generator is proportional to the square of the surface charge density of the electret4, the development of a high-performance electret is required. Conventionally, electrets are manufactured by corona discharge using DC power source. However, dielectric breakdown usually occurs when a high voltage is applied to materials due to the increased surface charge density of electrets. Here, we focus on the nanosecond pulse (70 ns pulse width) that has ability to apply higher voltages to materials without inducing dielectric breakdown. Nanosecond pulse has a potential to produce more strongly charged electret than DC, because it can apply higher voltage than DC to materials.

The objective of the present study is to develop a fabrication method for a new electret using nanosecond pulse for higher surface charge density and thermal stability.

EXPERIMENTAL

Nanosecond pulse power source

Figure 1 shows output wave pattern of a nanosecond pulse generator. Nanosecond pulse discharge generates an extremely short pulse width and because the voltage falls before the generation of insulation breakdown, which is induced by the application of a high voltage, it is possible to apply the higher voltages than when DC is used.

Figure 1. Output wave pattern of nanosecond pulses

Electret manufacture

Electrets were manufactured by applying a high voltage to a needle and injecting ions using a corona discharge under condition given in Table I. Polytetrafluoroethylene (PTFE or Teflon) was used as an electret material because PTFE is highly insulating and is a typical electret material. A 6 × 6 cm2 of 50-μm-thick PTFE was installed on an earth electrode, and electrification was performed using a corona discharge by applying a high voltage to a needle electrode at a fixed distance from the earth electrode. Fabrication conditions are shown in Table II. −6 kV DC is the maximum voltage that can be applied to the sample without being damaged.

Table I. Capacity of nanosecond pulse generator

Pulse width

70 ns

Output voltage(max)

-30 kV

Pulse risetime

10 ns

Repetition frequency(max)

500 Hz

Output current(max)

-30 A

Input voltage

24 V

Table II. Electret fabrication conditions

Nanosecond Pulse

Output voltage

−6 kV

−20 kV

−15 kV

−10 kV

Pulse repetition frequency

−

200 Hz

Distance between electrode

10 mm

Discharge time

30 min

Heat temperature

250 °C

Figure 2. Electret fabrication by corona discharge

Measurement of surface potential and thermally stimulated discharge current

In order to evaluate the performance of nanosecond pulses as a new fabrication method for electret, the temporal change of the surface potential was examined. The samples were stored at 23°C with 75% of humidity. The surface potential was measured with a surface voltmeter (Statiron DS3H, Shishido Electrostatic, Lid).

Thermally stimulated discharge current (TSDC) was measured while applying heat to the electret, as shown in Figure 3 (a). By measuring the TSDC, it is possible to estimate parameters such as the trapped charge concentration, the depth of charge injection, and the electret lifetime. Conditions for temperature increase is shown in Figure 3 (b).

Figure 3. Measurement of TSDC

Measurement of discharge energy

The discharge energy was measured by observing the voltage and current waveforms. Figure 4 (a) & (b) show the measurement systems used for DC and nanosecond pulses.

Figure 4. Schematics of measurement system of discharge energy

Discharge energy of DC power source was calculated as described below.

Discharge energy of a nanosecond pulse generator was calculated as described below.

RESULTS AND DISCUSSION

Comparison of surface potential

Figure 5 shows the surface potential as a function of discharging time under application of electrets −6 kV DC and −20 kV nanosecond pulses (repetition frequency: 200 Hz). It shows that surface potential of −2500 V (equal to surface charge density of 0.59 mC/m2) by nanosecond pulses is higher than that of DC by 59 % after discharge for 200h. This is mainly considered to be because the high voltage nanosecond pulses inject more charge into the electret.

Figure 5. Surface potential of electret

Figure 6 shows the surface potential measured after 150 h since they have been charged for 5 and 30 minutes. Comparison of the results for the DC and the nanosecond pulses reveals that by increasing the discharge times from 5 to 30 minutes for nanosecond pulses, the sample was charged at least 500 V higher. This is thought to occur due to the voltage application time being intermittent in the case of nanosecond pulse discharge so that it takes time to inject sufficient ions into the electret.

Figure 6. Surface potential of electret (after 150 h)

Comparison of thermal stability of electret

Figure 7 shows the results of TSDC measurement of PTFE made into an electret by applying −6 kV DC and −20 kV nanosecond pulses (repetition frequency: 200 Hz). It shows that a peak appears at near 175°C after application of DC and at around 210°C after application of nanosecond pulses. It is conjectured that when the current peak occurs at a high temperature, the thermal stability goes high, ions are injected deeply, and which results in the longer lifetime of the electret. With application of nanosecond pulses, it is believed that because a high voltage was used, ions were deeply injected and the thermal stability was high.

Figure 7. TSDC spectra of electret

Figure 8 shows the TSDC of electrets charged at various output voltages using nanosecond pulses. It has been previously reported that, in the case of DC, the TSDC increased with increasing output voltage. The same trend, in which current peaks increase and the amount of injected charge increases, was also observed during application of nanosecond pulses. Since nanosecond pulse generator has ability to apply the higher voltage than DC without generating dielectric breakdown to applied materials, it can be expected that the electrets, manufactured by nanosecond pulse would be more strongly charged according to the increased voltage by nanosecond pulse power generator.

Figure 8. TSDC spectra of electret

Comparison of discharge energy

Figure 9 shows the discharge energy per second for DC and the discharge energy per pulse for nanosecond pulses. The product of the discharge energy per pulse and the pulse repetition frequency equals the discharge energy per second. The discharge energy using nanosecond pulses at −20 kV was higher than the discharge energy at −8 kV, which is near the limit for DC (when the repetition frequency was 50 Hz or greater). It suggests that nanosecond pulse generator has ability to produce larger amount of ions than the DC power source.

Figure 9. Discharge energy of power source

Varying the distance between the needle and earth electrodes for DC and nanosecond pulses and measuring the discharge energy revealed that, whereas the discharge energy varied greatly with the distance between the electrodes for DC, the variation was small for nanosecond pulses. This demonstrates that nanosecond pulses enable stabilizing the discharge without being affected by the distance variation between the electrodes.

CONCLUSION

In order to evaluate the performance of nanosecond pulses as a new fabrication method of electret, the surface potential and thermal stability of electrets charged by nanosecond pulse and DC, discharge energies of nanosecond pulse generator and DC were examined and compared. As for the surface potential, we have found that surface potential of −2500 V(equal to surface charge density of 0.59 mC/m2) by nanosecond pulses is higher than that of by DC after 200h from discharge by 59 %. This is mainly considered to be because the high voltage nanosecond pulses inject more charge into the electret. For the thermal stability, we have found that a peak of TSDC appears near at 175°C in the case of DC and at around 210°C in the case of nanosecond pulses. It would imply that in the case of nanosecond pulses, ions were deeply injected and the thermal stability of electret was high, because a high voltage was used. In terms of the discharge energy, we have found that the discharge energy using nanosecond pulses at −20 kV was higher than that using DC at −8 kV (when the repetition frequency was 50 Hz or greater). Moreover, variation of discharge energy depending on the distance between the electrodes of nanosecond pulse generator was smaller than that of DC. These demonstrate that nanosecond pulse generator produce more ions than DC and stable discharge is possible by using nanosecond pulses without being greatly affected by the distance between the electrodes.

Therefore, we conclude that nanosecond pulse will be more useful for manufacturing electrets than DC.

REFERENCES

1R.J.M. Vullers, R.van Schaijk, I.Doms, C.Van Hoof, R.Mertens: Micropower energy harvesting, Solid-State Electronics, 53, 684–693 (2009)

2Hua-Bin Fanga, Jing-Quan Liua, Zheng-Yi Xub, Lu Donga, Li Wangb, Di Chena, Bing-Chu Caia, Yue Liub: Fabrication and performance of MEMS-based piezoelectric powergenerator for vibration energy harvesting, Microelectronics Journal, 37, 1280–1284 (2006)

3M. Nifuku, Y. Zhou, A. Kisiel, T. Kobayashi, H. Katoh: Charging characteristics for electret filter Materials, Journal of Electrostatics, 51–52, 200–205 (2001)

4Boland J, Chao C-H, Suzuki Y and Tai Y-C: Micro electret power generator, 16th IEEE Int. Conf. MEMS(Kyoto) 538–41 (2003)

PROPORTIONING CONTROLLED LOW STRENGTH MATERIALS USING FLY ASH AND GROUND GRANULATED BLAST FURNACE SLAG

Dr. Udayashankar B C

Professor & Head, R.V.College of Engineering Bangalore, Karnataka, India.And

Raghavendra T

Assistant Professor, R.V.College of Engineering Bangalore, Karnataka, India.

ABSTRACT

As the construction industry continues to recognize the importance of sustainable development, technologies such as controlled low-strength material (CLSM) have come to the forefront as viable means of safely & efficiently using by-product & waste materials in infrastructure applications. CLSM is defined by ACI (American Concrete Institute) Committee-229 as a self-compacting, cementitious material used primarily as a backfill in-lieu of compacted fill. In this paper two industrial by-products, namely fly ash & ground granulated blast furnace slag, are used as constituent materials in CLSM. Mixture proportions developed for CLSM containing these waste materials were tested in the laboratory for properties such as flow & un-confined compressive strength. The cardinal aim is to analyze the experimental data generated to formulate a phenomenological model to arrive at the combinations of the ingredients to produce CLSM to meet the strength development desired at the specified age irrespective of the age & proportion of the mix.

INTRODUCTION

CLSM is defined by ACI Committee-229 [1] as a material that results in a compressive strength of 8.3MPa or less. Currently CLSM applications require unconfined compressive strengths in the range of 2 MPa or less, so as to allow future excavation of previously laid surfaces for alterations as the need arises. The upper limit of 8.3MPa allows using this material for structural fill under buildings where future excavation is unlikely. Besides CLSM should not be confused with compacted soil - cement, because CLSM requires no compaction (consolidation) or curing to achieve the desired strength unlike soil cement. These class of materials offer a direct means to utilize wide spectrum of waste materials which otherwise pose a problem in their safe disposal.

CLSM is also regarded as flowable fills since they are liquid like materials that harden to the consistency of stiff clay. It is a combination of sand, fly ash and small percent of cement, water and admixtures. Sand is the major component of most of these flowable fills. Other benefits of processing flowable fills are limited labor component, accelerated construction, ready placement in inaccessible zones and the ability to manually re-excavate for relaying utilities if required.

MATERIALS AND METHODS

In our present experimental study, two industrial by-products, namely fly ash and ground granulated blast furnace slag, are used as constituent materials in CLSM. Mixture proportions were developed for CLSM containing these industrial by-products and tested in the laboratory for various properties, such as flowability and un-confined compressive strength (UCS). This project deals with the technology of proportioning CLSM with Low-Calcium (Class F) dry Fly ash procured from Raichur Thermal Power Plant, Karnataka and Ground granulated blast furnace slag procured from Jindal Steel Works, Karnataka, as the base materials.

The present investigation aims to generalize the two basic principles namely Abrams law and Lyse’s rule for proportioning the cement based controlled low strength materials.

Fly ash is the finely divided residue resulting from the combustion of pulverized coal, which is transported from the fire box through the boiler by flue gases. Since fly ash has pozzolanic properties like natural pozzolana, it is considered to have some self-cementitious properties. The term fly ash is also described as any fine particulate material which precipitated from the stack gases of industrial furnaces burning solid fuels. The solid and fine-grained materials were collected by mechanical or electrical separators. The specific gravity of the fly ash was found to be 2.4, the results of the chemical analysis are tabulated in Table I, Chemical analysis conducted on the ash indicated that the ash conforms to the requirements of IS: 3812 (Part-I)-2002. It can be seen that the content of SiO2+Al2O3 is 88.10% for the ash against minimum of 70% stipulated in IS: 3812(9) (Part-I)-1981.

Table I. Chemical Composition of flyash

Ground granulated blast furnace slag (GGBS) is a mineral admixture and could be used as cement replacing materials in concrete composites. As per ASTM C 989-99 blast–furnace slag is defined as the non metallic product, consisting essentially of silicates and alumino–silicates of calcium and other bases that are developed in a molten condition simultaneously with iron in a blast furnace. Unlike pozzolonic materials like silica fume, fly ash, high reactivity metakaolin, GGBS is a latent hydraulic material. It produces C-S-H gel after reacting with water. The reaction is accelerated in the presence of CaOH that is produced from the primary hydration of OPC. Table II, gives the physical and chemical properties of GGBS used for the experiment.

Table II. Physical and Chemical properties of GGBS

Constituents

Test results

IS code provision

SiO

percent

37.21

−

percent

13.24

−

percent

1.0

−

Ca O percent

37.23

−

Mg O percent

8.65

17.0 (max)

percent

1.5

5.5 (max)

Sulphide sulphur

0.65

2.0 (max)

S O

percent

0.55

Inslouble residue percent

0.90

5.0 (max)

CaO + Mg) + 1/3Al

O3 Si O

+ 2/3A

1.05

1.0

CaO + MgO + Al

Si O

1.85

1.0

Blaine’s fineness, m

/kg (permeability method)

373

−

Specifice gravity

2.80

−

Flowability

The workability of the mix is determined by spread flow test. The apparatus for this test consists of a mould in the form of a frustum of a cone, 60mm high with 70 mm top diameter and 100mm at the base. Since the mixes does not contain coarse aggregate this test is in order to assess workability. The cone placed on a base plate of about a meter in diameter is filled with the mix of combinations of solid constituents at different water content is filled without any air entrapment and lifted. Due to its own weight the mix spreads whose diameter in mutually perpendicular directions is measured and averaged.

The relative flow area, RFA is calculated from the relation:

Where D is the average diameter of the spread mix in mm

It has been observed that the spread increases with increase in water content and the relative flow area is in the range of 5 to 15 which is of self flowing and self leveling consistency as needed for controlled low strength materials

AIM AND SCOPE OF INVESTIGATION

Our aim is use of industrial by-products namely flyash and ground granulated blast furnace slag, as constituent materials in CLSM, to generate a set of experimental data, analyze them and formulate a phenomenological model i.e. a kind of ready to use equation. The use of such an equation would be to proportion CLSM mixes for desired strength (at specified age and binder/water ratio) and flow (at specified water content). Du. L et al. [6] made efforts to develop predictive models for the compressive strength of CLSM, various models and statistical approaches were considered but no single model was found to work well for the entire range of materials and mixture proportions. The various combinations of materials involved in the generation of CLSM mixes would involve multiple iterations to achieve desired flow and strength. With the help of phenomenological model it is required to make a single trial and determine its flow and strength values respectively. Further this trial mix value would enable us to predict flow and strength of other mixes within no time and without much time consuming effort. TR & BCU [2] have formulated phenomenological model for CLSM mixes constituting cement, GGBS and sand. Their experimental values fairly matched with the predicted values and hence reinforcing confidence in the application of these phenomenological models, formulated for a specific set of constituent materials. However, if the constituents are changed, as in the case of our investigation to proportion CLSM mixes constituting cement, flyash, GGBS and Sand, then it becomes necessary to formulate a fresh phenomenological model out of newly generated set of experimental data.

Materials used

The following materials and variable parameters are used.

Binders:

For each series 40 specimens were casted i.e. 10 specimens were casted for each (Water Content / Binder) ratio and testing of five specimens in each set after age of 7 and 28 days was performed. Tables III & IV, gives the material calculations for different combinations at 1:1.5 Mortars.

Table III. Material calculation for different combinations of cement and flyash 1:1.5 Mortars

Table IV. Material calculation for different combinations of cement, flyash and GGBS 1:1.5 Mortars

PHENOMENOLOGICAL MODEL FOR FLOW & STRENGTH DATA

Generalized Abrams’ Law has been used for the purpose of development of phenomenological model. For this a reference value i.e. B/W ratio of 1.81 has been identified. It implies that a trial test done at this ratio would take care of synergy between all the ingredients. These strength values are normalized with respect to their respective reference value. In figures – 3, 4, 5 & 6, the linear fit of the data is done since according to Bolemey’s Law the consideration of inverse of W/B ratio is done to transform the data into linear form in all other investigations dealing with cement based composites. The linear relationships are obtained for the combinations given in Tables III & IV. The equation of the trend line itself is the phenomenological model generated. The left hand side of phenomenological model represents normalized values of strength.

In the development of phenomenological model for flow assessment also, a reference value of RFA at water content of 24 percent (since no segregation and bleeding, also optimum RFA range from 5 to 15) for 1:1.5 mortar series has been identified. The flow lines of these data points are normalized with respect to their respective reference value. Thus normalized values of all the series are plotted to a scale along the ordinate against the water content values which are plotted along the abscissa, as shown in figures 1 & 2. To use this phenomenological model one set of data with a known combination of ingredients at reference value has to be generated. The tests conducted for any given set of ingredients at these reference values would take of material properties and associated synergy between interacting and non—interacting constituents with water. This is needed to use the phenomenological model as input parameter in the denominator of the left hand expression in the equations formulated.

Figure 1: Generalization for flow of (C+F) mortar

Figure 2: Generalization for flow of (C+F+G) mortar

Figure 3: Generalization for 7-day strength of (C+F) mortar

Figure 4: Generalization for 7-day strength of (C+F+G) mortar

Figure 5: Generalization for 28-day strength of (C+F) mortar

Figure 6: Generalization for 28-day strength of (C+F+G) mortar

With this data the RFA at other water content can be assessed and vice versa. The validation of this model for an independent set of data is also examined.

RESULTS AND DISCUSSIONS

The strength and flow data has been synthesized in Table V. cement+flyash and cement+flyash+GGBS, for a particular ratio with corresponding sand mixed with specified water content forms one set. For such a set the strength does not vary beyond the range of experimental discrepancy as seen in figures – 3, 4, 5 & 6. This is in accordance with the Bolemy’s consideration of Abrams’ Law. As the F/C ratio changed to 3.5, 2.8, 2.0 and 1.75 and and (F+G)/C ratio changed to 8, 2.66 the strength changes since the set of cementing material changes & Pozzolanic nature of flyash, flyash+GGBS has a role to play. The increase in strength takes place as the ratio of F/C, (F+G)/C decreases due to cement playing the dominant role in strength development lessening the Pozzolanic nature of the flyash, flyash+GGBS. Water–cementitious ratio, W/(C+F) & W/(C+F+G), (0.50, 0.55, 0.60 & 0.65) is the main variable. The variation of F/C (3.5, 2.8, 2.0 and 1.75 for cement + flyash mortars) and (F+G)/C (8,4 and 2.66 for cement + flyash + GGBS mortars) forms six combinations of cementing materials. They have to be considered separately since they are equivalent to six types of cementing materials. The strength development with age (7 and 28 days) is also a variable.

Table V. Average flow & strength results for cement+flyash & cement+flyash+GGBS Mortars

The flow data has been converted to relative flow area of spread (RFA), calculated from the relation (D/100)2-1, and is tabulated in Table V. It is clear that the flow increases with increase in water content and increases with F/C and (F+G)/C ratios irrespective of W/(C+F) and W/(C+F+G) ratios. This is in conformity with Lyse’s rule. For a given set of materials, represented by its F/C ratios, as the water content increases the spread also increases. It is not possible to examine the generalization to arrive at generalized Lyse’s rule since at water content of 45% there appears to be sudden transition in the relative flow area, because of inevitable bleeding. To circumvent this it would be necessary to examine the flow behavior from altogether different consideration such as flow time through a flow cone akin to vee-bee time. This has not been done in this investigation due to the need of fabrication of such a facility. This forms proposed future investigation.

Average flow and strength results

It can be seen that in the above case (cement + flyash mortars and cement + flyash + GGBS mortars) the relative flow area increases with increase in water content. This is in accordance with Lyse rule. Likewise even the strength decreases with decrease in binder/fluid ratios in accordance with Abrams law. Since binder/fluid ratio is considered in figures it can be seen that trend in variation can be represented linearly with a high degree of correlation coefficient.

Even with the age, the strength gain also follows the same pattern. It is interesting to note that when flow or strength data is superposed as water content or binder/fluid ratio increases, relative flow area lines plotted against varying water content and strength lines plotted against varying binder/fluid ratios are all converging lines towards decrease in the binder - fluid ratio i.e. corresponding increase in fluid/binder ratio. The range of RFA and Strength development is quite considerable implying that number of trials would be involved in arriving at suitable combinations. It is to be examined as to how the properties of a given set of materials and their combinations can be brought about into the fold of a functional relation.

Figures 7 to 10 show the predicted path for strength & flow generated from phenomenological models. Combined series graphs are generated by using four series (F/C=3.5 + F/C=2.8 + F/C=2 + F/C=1.75) RFA and Strength values for cement + flyash 1:1.5 mortars and using two series ([F+G]/C=8 + [F+G]/C=2.66) RFA and Strength values for cement + flyash + GGBS 1:1.5 mortars.

Figure 7: Predicted path for flow of F/C=2.33 mortar, from combined generalized equation

Figure 8: Predicted path for flow of (F+G)/C=4 mortar, from combined generalized equation

Figure 9: Predicted path for 28-day strength of F/C=2.33 mortar, from combined generalized equation

Figure 10: Predicted path for 28-day strength of (F+G)/C=4 mortar, from combined generalized equation

Examination of experimental values for an independent series {F/C=2.33; cement + flyash 1:1.5 mortar and (F+G)/C=4; cement + flyash + GGBS 1:1.5 mortar} and predicted values reveal that, in general the trend is followed and in few cases there is considerable discrepancy. There are two reasons for this. In the case of experimental RFA values for certain combinations due to bleeding taking place it is difficult to identify the exact water content responsible for flow. In the case of experimental strength values one factor was observed like in the cases where bleeding took place at higher water content, the cylindrical samples made showed some dewatering leaving some water standing on the top of samples before final setting takes place, which makes it difficult to exactly link the strength developed with the corresponding B/W ratio. In cases where these did not happen the experimental values are closer to the predicted paths.

CONCLUSION

For the combinations of ingredients with varying range of water content and binder /fluid ratios the interpretations of experimental data and subsequent analysis permit to make the following conclusions.

1. The workability measured by relative flow area (RFA), follows LYSE RULE which categorically states that flow is a linear function of water content. For every combination there is limiting water content beyond which bleeding takes place. This makes exact assessment of flow. The strength development with age increases as B/W ratio increases (i.e., decrease in W/B ratio). This is in accordance with ABRAMS’ LAW. The increase in strength is linear with increase in B/W ratio in accordance with Bolemy’s Law.

2. A single trial mix flow and strength data is required as input in the ‘phenomenological Models’ to arrive at the required water content for specified flow and Binder – Fluid ratio for the level of strength required.

3. The validation has been examined with respect to independent set of data i.e. for F/C=2.33 ratio and (F+G)/C=4 ratio. The Predictions are within the limits of accuracy needed at engineering level.

4. With minimum laboratory trials for proportioning CLSM, the phenomenological models enhance the rapidity in taking engineering decisions.

5. The combination of flyash and GGBS has resulted in relatively higher strengths which may make it possible to use such CLSM mixes for structural fills where future excavation is unlikely.

6. Use of industrial by-product such as flyash and ground granulated blast furnace slag, into the production of CLSM will enable sustainable growth of concrete industry and hence will therefore add points towards Leadership in Energy and Environmental Design (LEED) certification.

REFERENCES

1ACI 229R-94 “Controlled Low Strength Materials (CLSM)”, American Concrete Institute Report, Concrete International, V 16, No.7, pp55–64, USA.

2Raghavendra T and Udayashankar B C, Study on flow & strength characteristics of CLSM using ground granulated blast furnace slag, J. Mater. Civ. Eng., 10.1061/ (ASCE) MT.1943–5533.0000927 (Aug. 27, 2013).

3Du L, Laboratory Investigations of Controlled Low Strength Material, Ph.D dissertation, The University of Texas at Austin (2008).

4Lianxiang Du, Migual Arellano and Keith Folliard, Rapid setting CLSM for bridge approach repair, ACI Materials Journal, V 103, No.5 (October 2006).

5Charles E pierce, Sarah L Grassman and Tracey M Richards, Long term strength development of CLSM, ACI Materials Journal, V 99 (April 2002).

6Lianxiang Du, Kevin J. Folliard and David Trejo, Effects of Constituent Materials and Quantities on Water Demand and Compressive Strength of Controlled Low-Strength Material, J. Mater. Civ. Eng., Volume 14, Issue 6, pp. 485–495 (November/December 2002)

7Nagaraj T.S and Zahida Banu, Generalization of Abram’s Law, Cement and Concrete Research, Elsevier Science, 26 (6), pp.933–942 (1996).

TENSILE AND FATIGUE TESTING OF 304 STAINLESS STEEL AFTER GASEOUS HYDROGEN EXPOSURE

P. Ferro, A. Anderson, M. Beckett, K. Davidson, J. Marciniak, A. Obenberger

Gonzaga University, 502 E Boone Ave., Spokane WA

ABSTRACT

Samples of 304 stainless steel were subjected to a range of hydrogen exposure conditions including 1 week at 1 atm, and up to 3 weeks at 138 MPa. Samples were tested in bending fatigue and tensile testing. Increased hydrogen exposure correlated with loss of fatigue life for bending fatigue. Tensile test data appears to show increased strain rate sensitivity after exposure to gaseous hydrogen at one atm pressure for one week.

INTRODUCTION

One of the objectives of the current investigations is to contribute to the design database for components that will be subjected to hydrogen exposure and cyclic stresses. Previous investigations at Gonzaga have shown that the bending fatigue life of 304 stainless decreased after supersaturation levels of hydrogen exposure (e.g. up to 138 MPa hydrogen at 300C for 21 days) [1–3]. Supersaturation hydrogen exposure appears to reduce the fatigue life of 304 stainless bending fatigue specimens from 75,070 cycles (sx=27840, n=15) cycles to 9,460 cycles (sx=1960, n=5) at an estimated maximum stress level of 183 MPa. Statistically significant changes in fatigue life for specimens subjected to 1 atmosphere of hydrogen pressure for one day have not been found. Intermittent hydrogen exposure (e.g. re-exposing after each subsequent 6000 bending fatigue cycles) does not appear to correlate with reduced fatigue life for preliminary tests that have been run to date [3].

Proposed mechanisms to explain the reduced fatigue life may be based on surface adsorption, decohesion or on a dislocation interaction. For example, if surface adsorption is the mechanism, hydrogen ahead of the propagating crack tip in fatigue possibly reduces the energy for creating new surfaces, thereby lowering the threshold requirements for crack tip advancement [4].

The preliminary results reported here are for fatigue and tensile experimentation on flat samples of a nominal grade of 304 stainless steel exposed to a range of hydrogen conditions.

PROCEDURE

Bending Fatigue

The bending fatigue tests were performed using a VSS-40H bending fatigue testing machine (Fatigue Dynamics, Walled Lake MI). The cycling frequency was between 300 and 350 cycles per minute. After the specimen failed, it was removed and the location of the failure was identified by measuring the distance from the start of the specimen radius to the middle of the failure location on specimen. Bending fatigue specimens were plasma cut from 0.9 mm thick sheets of nominally type 304 stainless steel. The plasma-cut specimens were belt-ground along the periphery to remove slag. The specimens were hand sanded and polished, with a final sand paper application of 600 grit. Hydrogen exposure conditions included no exposure, one week at 1 atm hydrogen and 138 MPa at temperatures as high as 375°C for 15 days (‘supersaturation conditions’). The typical hydrogen concentration in 300 series stainless steels after similar conditions is approximately 140 ppm, by weight [5]. Other hydrogen charging protocols are described by Mine et al. [6] The bending fatigue experimental equipment and procedures may be found in previous papers [1–3].

Tensile testing

Tensile tests were performed on a MTS tensile testing machine using a 2.5 kN load cell. Strain rates of 3.81 mm min−1 and 0.41 mm min−1 were used to test specimens that were exposed to hydrogen ranging from no exposure to supersaturation levels. The specimens were plasma cut from 304 stainless sheet, and sanded and polished with a final application of 600 grit sand paper. The hydrogen exposure conditions were the same as that described for the bending fatigue specimens.

RESULTS

Figure 1. Bending fatigue results for 304 stainless at a calculated maximum stress of 189 MPa. The data preliminarily indicates that supersaturation hydrogen exposure conditions may reduce bending fatigue life.

Fig. 2 shows a bar chart of the ultimate force to failure of 304 samples at two different strain rates and two different hydrogen exposure conditions. Each bar represents the mean and plus or minus one standard deviation for a data population of twenty five samples. The data in fig. 2 appears to preliminarily indicate that lower strain rates reduce the ultimate force to failure. The data also shows that exposure to one week of hydrogen accentuates the strain rate effect. T tests that were run on the four populations for the data bars shown in fig. 2 only indicate a statistically significant difference between the two populations that were exposed to hydrogen, each pulled at different strain rates. In other words, the strain rate effect on ultimate force to failure appears to be increased by one week exposure to hydrogen.

Figure. 2. Bar graph of tensile test results for 304 stainless steel. Each bar represents tensile test results for 25 samples. The data is for ultimate force to failure for combinations of strain rate and hydrogen. The populations that were exposed to one atmosphere hydrogen for one week (‘low hydrogen’) are significantly different, indicating an enhanced strain rate effect from low hydrogen exposure.

Fig. 3 shows a bar chart of the elongation of the 304 tensile samples for four data populations, representing two different strain rates and two different hydrogen exposure conditions. Each bar represents the mean and plus or minus one standard deviation for a data population of twenty five samples.

Figure. 3. Bar graph of tensile test results for 304 stainless steel. Each bar represents tensile test results for 25 samples. The data is for elongation for combinations of strain rate and hydrogen.

The axes shown in figs. 2 and 3 indicate the strain rate and hydrogen exposure conditions for the different sample populations, where ‘HSR’ and ‘LSR’ indicate high strain rate and low strain rate respectively. ‘LH’ and ‘NH’ indicate one week of one atm hydrogen exposure compared to no hydrogen exposure, respectively.

Table 1 shows t-tests results for the tensile test sample populations. Each population represents twenty five samples. The t-tests that were run were paired homoscedastic. Statistical significance was determined if the populations were different at a 95% level of confidence. The t-tests indicate that the high strain rate ultimate force to failure population is statistically significanlty different than the low strain rate ultimate force to failure population, for both populations’ samples exposed to one atmosphere hydrogen for one week.

Table 1. T-test results for ultimate force to failure data

Compared Populations

T-test Result

Different?

high strain rate (no H

) v. low strain rate (1 atm H

)

0.1536

low strain rate (no H

) v. low strain rate (1 atm H

)

0.1971

low strain rate (no H

) v. high strain rate (no H

)

0.3096

low strain rate (1 atm H

) v. high strain rate (1 atm H

)

0.0016

YES

DISCUSSION

The overall objective of the hydrogen embrittlement testing at Gonzaga is to contribute to the design database for future hydrogen designs. With widespread and increasing development of hydrogen fuel cell powered devices, mechanical designers will benefit from greater knowledge of hydrogen’s possible medium- to long-term effects on mechanical properties. The work at Gonzaga focuses on mechanical testing of materials that have been exposed to hydrogen, and has an added benefit of providing a hands-on educational experience for undergraduate engineering students.

The bending fatigue results presented here agree with the predicted trend of higher hydrogen levels leads to worsening mechanical properties, in this case lower fatigue life. Supersaturation levels of hydrogen appeared to have the lowest fatigue life, possibly because dissolved hydrogen reduces the stress required for crack growth ahead of the advancing crack tip. The population of samples that were exposed to one atmosphere of hydrogen for one week did not appear to have reduced fatigue life, compared to unexposed samples. However, continued testing may reveal a slight difference if a sufficient number of samples are tested.

Future bending fatigue work at Gonzaga will focus on higher levels of bending stress for the same exposure conditions as that reported here. Additionally, an investigation of the failed surfaces may show different fractographic appearances based on hydrogen exposure level.

The tensile data presented shows that the strain rate effect appears to be accentuated by low hydrogen exposure levels. The possible accentuated effect was only observed, at a statistically significant level, for ultimate force to failure. The literature suggests that strain rate effects are more likely to be seen for elongation rather than for ultimate force [4]. Future testing includes tensile tests on supersaturated samples, at the high and low strain rates used in the present work. Future tensile testing may also include other strain rates.

The conclusion reached that the strain rate appears to be accentuated by one week hydrogen exposure appears to be valid for the two strain rates tested, which are approximately an order of magnitude different. Future testing may include a more detailed study of varying strain rates to see if there is a threshold strain rate difference below which no effect is significantly observed.

Another noteworthy observation from the tensile test data is that the standard deviations of the populations for all of the low strain rate data appear to be larger than that of the high strain rate data. This observation includes the ultimate force as well as the elongation data.

CONCLUSIONS

Supersaturation of hydrogen in 304 stainless appears to reduce the fatigue life of bending fatigue samples. After one week of exposure to one atmosphere of hydrogen gas, the data does not show a fatigue life difference although testing is continuing to increase the sample size, and to test other stress levels.

Tensile data for 304 stainless exposed to one atmosphere hydrogen for one week appears to have an accentuated strain rate effect on ultimate force to failure. Samples that were tested at two different strain rates after two different hydrogen exposure conditions preliminarily indicate the low levels of hydrogen exposure may acccentuate the strain rate effect. Higher strain rates appear to correlate with higher force to failure. After one week of hydrogen exposure, the difference in force to failure was significantly different for the two strain rates tested.

ACKNOWLEDGMENTS

The authors acknowledge the support provided by Gonzaga University, and by the faculty, staff and students of the School of Engineering and Applied Sciences (SEAS). The authors particularly acknowledge the help of Floyd Grillo, Steve Klemp, James Moody, Jackie Davis, Cameron Davis, Jason Ross and others in the shop for helping generate test samples.

REFERENCES

1. P. Ferro, “Effect of Hydrogen on Bending Fatigue Life for Materials Used in Hydrogen Containment Systems”, Advances in Materials Science for Environmental and Nuclear Technology II, ed. S.K. Sundaram, T. Ohji, K. Fox, E. Hoffman, Ceramic Transactions, v. 227, pp. 39–49, American Ceramic Society Publication, Wiley ISBN 978-1-118-06000-1 (2011).

2. P. Ferro et al., “Fatigue Testing of Hydrogen-exposed Austenitic Stainless Steel”, Advances in Materials Science for Environmental and Energy Technologies, Ceramic Volumes (2012).

3. P. Ferro, R. Miresmaeili, R. Mitra, J. Ross, W. Tiedemann, C. Hebert, D. Howard, “Hydrogen-exposed Austenitic Stainless Steel Welded Specimens in Bending and Rotational Bending Fatigue”, MS&T 2012 Conference, Pittsburgh PA, October 2012, Ceramic Volumes (2013).

4. H.G. Nelson, “Hydrogen Embrittlement”, Treatise on Materials Science and Technology, v. 25, Academic Press, ISBN 0-12-341825-9 (1983).

5. C. San Marchi, B.P. Somerday, X. Tang, G.H. Schiroky, Effects of Alloy Composition and Strain Hardening on Tensile Fracture of Hydrogen-precharged Type 316 Stainless Steels, Int’l J. Hydrogen Energy, 33, 889–904, (2008).

6. Y. Mine, K. Tachibana, Z. Horita, Effect of High-Pressure Torsion Processing and Annealing on Hydrogen Embrittlement of Type 304 Metastable Austenitic Stainless Steel, Met. and Mat. Trans. A, 41A (2010).

LARGE POROUS IRON OXIDE PARTICLES SYNTHESIZED FROM HYDRATED IRON PHOSPHATE PARTICLES OF STRENGITE

S. Fujieda, K. Shinoda, S. Suzuki

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan

ABSTRACT

To obtain large porous iron oxide particles for application to arsenic adsorbents, hydrated iron phosphate particles of strengite (FePO4·2H2O) were synthesized from a solution containing ferrous (Fe(II)) ions and then treated using an alkaline solution. As the size of each alkaline-treated particle is several tens of micrometers, the water filterability of these particles is high. In addition, alkaline-treated particles have a large specific surface, because each particle consists of agglomerated fine maghemite (γ-Fe2O3) particles of several nanometers in diameter. It is concluded that hydrated iron phosphate particles synthesized from a solution containing Fe(II) ions are appropriate precursors.

INTRODUCTION

Arsenic contamination of drinking water is a serious problem because of its toxicity.1 The ion adsorption technique is useful to remove arsenic from contaminated water,2 and great effort has been dedicated to the development of arsenic adsorbents based on iron oxides and iron oxihydrooxides.3–5 The synthesis of these fine particles with large specific surface is effective for obtaining a large arsenic adsorption capacity. However, their filterability is likely low. It is required to obtain arsenic adsorbents with both large specific surface and high water filterability.

Recently, porous iron oxide particles of about 20 μm in size have been obtained by a novel method using an alkaline solution.6 In this method, hydrated iron phosphate particles of about 20 μm in size are synthesized as precursors from a solution containing ferrous (Fe(II)) ions by the injection of oxygen gas at 368 K. Then, these particles are immersed in the alkaline solution. As the phosphorous in hydrated iron phosphate particles is removed to the alkaline solution, porous iron oxide particles are obtained. The particle size after immersion is almost the same as that before immersion. Thus, such particles exhibit a large arsenic adsorption capacity and high water filterability.6 The investigation mentioned above focused on the hydrated iron phosphate of metastrengite with the space group P21/n. However, it has been reported that hydrated iron phosphate of strengite with the space group Pbca is synthesized from an aqueous solution containing ferric (Fe(III)) ions by adjusting reaction conditions.7 In this investigation, hydrated iron phosphate particles of strengite were synthesized from a solution containing Fe(II) ions and these particles were treated using an alkaline solution. The cross section of an alkaline-treated particle was observed. In addition, the adsorption property in aqueous solution containing arsenic was investigated for the application to arsenic adsorbents.

EXPERIMENTAL

Hydrated iron phosphate particles were synthesized from ferrous sulfate (Fe(II)SO4) hydrate and aqueous phosphoric acid (H3PO4). First, an iron sulfate solution was prepared by using deaerated water. Subsequently, aqueous phosphoric acid was added to the iron sulfate solution in a reaction vessel with continuous bubbling of nitrogen gas. The iron concentration in the solution was 1 mol/L. The initial molar ratio of Fe(II) and P was set at 1.5 to 1. Oxygen gas was injected into the solution at approximately 368 K for 3 hours. A suspension containing precipitated particles was obtained by the above-mentioned procedure. The precipitated particles were separated by filtering and then washed with distilled water several times. In order to obtain porous iron oxide particles without phosphorus, as-precipitated particles were immersed in 1 M NaOH solution for 1 hour. The remaining particles, that is, alkaline-treated particles were separated from the solution by the filtering and then washed with distilled water several times.

The morphology of as-precipitated particles and alkaline-treated particles was observed by a scanning electron microscopy (SEM). The crystal structure of these particles was identified by X-ray diffraction measurements. The cross section of an alkaline-treated particle was observed by transmission electron microscopy (TEM). An electron beam 1 nm in diameter was used for a electron diffraction measurement. To investigate the adsorption property, 200 ml of arsenic solution with about 100 As-mg/L was prepared using aqueous arsenic acid (H3AsO4), and then 40 mg of alkaline-treated particles was immersed in such solution for 240 minutes. The arsenic concentration change in the solution after immersion of alkaline-treated particles was analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

RESULTS AND DISCUSSION

Figure 1(a) shows an SEM image of as-precipitated particles obtained from a solution containing Fe(II) ions by the injection of oxygen gas. The size of each as-precipitated particle is several tens of micrometers. Such large particles size is maintained after the treatment using an alkaline solution, as shown in Fig. 1(b). Therefore, the water filterability of alkaline-treated paticles is high.

Figure 1 SEM images of (a) as-precipitated particles and (b) alkaline-treated particles.

To evaluate the phosphorous concentration, about 50 mg of alkaline-treated particles was dissolved in 50 ml hydrochloric acid and the solution was analyzed by ICP-AES. The result of ICP-AES analysis showed that the phosphorous concentration in the solution was less than the detection limit under the present experimental conditions, indicating that alkaline-treated particles are iron oxides or iron oxyhydroxides.

X-ray diffraction patterns of as-precipitated particles and alkaline-treated particles are presented in Fig. 2. The reference diffraction patterns of strengite, metastrengite, maghemite and magnetite are also given in the same figure. The diffraction peaks of as-precipitated particles are assigned to those of strengite, although small peaks assigned to those of metastrengite are also observed. Note that such particles were synthesized by the reaction for 180 minutes, though hydrated iron phosphate particles of strengite have been synthesized from a solution contain Fe(III) ions by the reaction for 2 days at boiling temperature.7 On the other hand, alkaline-treated particles exhibit broad diffraction peaks. A similar X-ray diffraction pattern has been observed in porous iron oxide particles obtained from metastrengite.6 These peaks seem to be assigned to a spinel-type structure such as magnetite (Fe3O4), composed of Fe(II) and Fe(III) ions, and maghemite (γ-Fe2O3), composed of Fe(III) ions. It is likely that alkaline-treated particles are composed of Fe(III) ions, because strengite and metastrengite are composed of such ions. In addition, porous iron oxide particles obtained from metastrengite have been identified as maghemite by extended X-ray adsorption fine structure (EXAFS) measurement at the Fe K adsorption edge.6 Hence, alkaline-treated particles are reasonably identified as maghemite.

Figure 2 X-ray diffraction patterns of as-precipitated particles and alkaline-treated particles. The reference diffraction patterns of strengite, metastrengite, maghemite and magnetite are also indicated.

In order to characterize the inside of an alkaline-treated particle, it was cut by a focused ion beam (FIB) apparatus with gallium ions. The cross section images of an alkaline-treated particle are presented in Fig. 3. As shown in Fig. 3(a), a certain amount of pores is observed among particles with diameters of several tens of nanometers. In addition, each particle is composed of agglomerated fine particles of a few nanometers in diameter as shown in Fig. 3(b). It is likely that iron porous particles obtained from iron phosphate particles of strengite have both high filterability and a large specific surface.

Figure 3 (a) TEM image of the cross section of an alkaline-treated particle and (b) a high magnification image of the same particle.

The electron diffraction pattern of alkaline-treated particles is presented in Fig. 4. A clear diffraction pattern is observed in Fig. 4(a). All diffraction spots can be assigned to those of maghemite, as shown in Fig. 4(b). The result of electron diffraction is consistent with that of X-ray diffraction as shown in Fig. 2. In the crystal structure of strengite, Fe ions form FeO6 octahedral units, which are linked with PO4 tetrahedral units. On the other hand, magnetite is composed of both FeO6 octahedral units and FeO4 tetrahedral units. Thus, the local structure of Fe and the network of Fe-O units in alkaline-treated particles are different from those of as-precipitated particles. It is suggested that iron porous particles are formed by the dissolution of strengite in the alkaline solution and the precipitation of maghemite. Such reactions initially occur on the surface of as-precipitated particles in the alkaline solution. Hence, the surface part of as-precipitated particles changes from strengite to porous iron oxide identified as maghemite. As the alkaline solution can penetrate into pores, the interface between strengite and maghemite proceeds to the inside of as-precipitated particles. It is highly probable that the reaction process described above leads to the formation of large porous iron oxide particles.

Figure 4 (a) Electron diffraction pattern of an alkaline-treated particle and (b) a schematic of indexed diffraction spots.

To evaluate the arsenic adsorption property, alkaline-treated particles obtained from strengite were immersed in an aqueous solution containing arsenic. Figure 5

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