Developments in Strategic Materials and Computational Design IV, Volume 34, Issue 10 E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Ceramic Engineering and Science Proceedings
• Sprache: Englisch

Seitenzahl: 522

Veröffentlichungsjahr: 2013

Beschreibung

Ceramic Engineering and Science Proceedings Volume 34, Issue 10 - Developments in Strategic Materials and Computational Design IV A collection of 25 papers from The American Ceramic Society's 37th International Conference on Advanced Ceramics and Composites, held in Daytona Beach, Florida, January 27-February 1, 2013. This issue includes papers presented in the Geopolymers and Chemically Bonded Ceramics (Focused Session 1); Thermal Management Materials and Technologies (Focused Sessoin 2); and Materials for Extreme Environments: Ultrahigh Temperature Ceramics and Nano-laminated Ternary Carbides and Nitrides (MAX Phases) (Symposium 12).

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Introduction

Geopolymers and Chemically Bonded Ceramics

Importance of Metakaolin Impurities for Geopolymer Based Synthesis

Abstract

I. Introduction

II. Experimental Part

III Results and Discussion

IV. Evidence for the Presence of Crystallized Phase

V. Conclusion

Acknowledgements

References

Mechanical Strength Development of Geopolymer Binder and the Effect of Quartz Content

Abstract

Introduction

Experimental

Results and Discussion

Summary and Conclusions

Acknowledgments

References

The Role of SiO2 & Al2O3 on the Properties of Geopolymers with and without Calcium

Abstract

Introduction

Materials and Methods

Results

Discussion

Conclusion

References

Synthesis of Thermostable Geopolymer-Type Material from Waste Glass

Abstract

Introduction

Experimental

Results and Discussion

Conclusion

Acknowledgement

References

The Effect of Curing Conditions on Compression Strength and Porosity of Metakaolin-Based Geopolymers

Abstract

Introduction

Experimental

Results and Discussion

Conclusions

References

Chemically Bonded Phosphate Ceramics Subject to Temperatures Up to 1000° C

Abstract

Introduction

Experimental Procedure

Analysis and Results

Discussion

Conclusion

Acknowledgements

References

Mechanical Properties of Geopolymer Composite Reinforced by Organic or Inorganic Additives

Abstract

1. Introduction

2. Experimental Part

3. Result and Discussion

4. Conclusion

6. References

Evaluation of Geopolymer Concretes at Elevated Temperature

Abstract

Introduction

Experimental Procedure

Results and Discussion

Conclusions

References

Basic Research on Geopolymer Gels for Production of Green Binders and Hydrogen Storage

Abstract

Introduction

Experimental

Results and Discussion

Conclusion

Acknowledgements

References

Mechanical Characteristics of Cotton Fibre Reinforced Geopolymer Composites

Abstract

Introduction

Experimental Methods

Results and Discussion

Conclusions

Acknowledgements

References

Green Composite: Sodium-Based Geopolymer Reinforced with Chemically Extracted Corn Husk Fibers

Abstract

Introduction

Experimental Procedures

Results and Discussion

Conclusions

Acknowledgements

References

Optimization and Characterization of Geopolymer Mortars Using Response Surface Methodology

Abstract

Introduction

Model Determination

Experimental Procedure

Results and Discussion

Conclusions

References

Evaluation of Graphitic Foam In Thermal Energy Storage Applications

Abstract

Introduction

Method

Results and Conclusions

Acknowledgements

References

Thermal Management Materials and Technologies

Q-State Monte Carlo Simulations of Anisotropic Grain Growth in Single Phase Materials

Abstract

Introduction

The Model

Results

Practical Application

Conclusions

Acknowledgments

References

Virtual Materials (Computational) Design and Ceramic Genome

Numerical Calculations of Dynamic Behavior of a Rotating Ceramic Composite with a Self-Healing Fluid

Abstract

Introduction

Modeling and Computer Simulation for Two-Phase Flow

Static Wetting: Deposition of Drops on Horizontal Surfaces

Physical Validation Impact of the Drop on an Inclined Surface

Coalescence of Micrometer Droplet:

Presentation of the Experiments

Preparation of Samples

Experimental Results

6. Conclusion

References and Citations

Explicit Modelling of Crack Initiation and Propagation in the Microstructure of a Ceramic Material Generated with Voronoi Tessellation

Abstract

Introduction

Generation of Polycrystals

Modelling of the Polycrystalline Microstructure

Evaluation of the Macroscopic Elastic Constants

Simulation of the Failure of a Micro-Cantilever Beam

Conclusions

Acknowledgements

References

Kinetic Monte Carlo Simulation of Cation Diffusion in Low-K Ceramics

Abstract

Introduction

Kinetic Monte Carlo Method

Energy Barriers

Results and Discussion

Conclusion

References

Effective, Thermoelastic Properties of C/C Composites Calculated using 3D Unit Cell Presentation of the Microstructure

Abstract

Introduction

Studies on Composite Architecture

Material Modeling

3D Unit Cell Presentation of the Microstructure

Mori-Tanaka Method

Cca Model

Numerical Results

Conclusion

Acknowledgements

References

Inelastic Design of MMCS with Lamellar Microstructure

Abstract

Introduction

Inelastic Material Homogenization: Secant Method

Inelastic Material Homogenization: Tangent Operator

Damage of the Ceramic Phase

Calculation of the Damage Variable

Calculation of the Tangent Operator for the Damage Model

Numerical Modeling of the Inelastic Material Behavior of the Single Domain

Inelastic Material Optimization: Direct Differential Method

Inelastic Material Optimization: Sensitivity Analysis.

Inelastic Material Optimization: Numerical Results.

Summary

Acknowledgements

References

Multi-Scale Modeling of Textile Reinforced Ceramic Composites

Abstract

Introduction

Laboratory Measurements

Numerical Calculations

Results and Discussions

Acknowledgments

References

Numerical Estimation of the Infiltrability of Woven CMC Preforms

Abstract

Introduction

Simulation Tools and Strategy

Materials

Results and Discussion

Conclusion

Acknowledgements

References

Multiscale Extraction of Morphological Features in Woven CMCs

Abstract

Introduction

Input Data

Yarn Segmentation Algorithm

Fiber Segmentation Algorithm

Results

Conclusion

Acknowledgements

References

Materials for Extreme Environments: Ultrahigh Temperature Ceramics and Nanolaminated Ternary Carbides and Nitrides

Influence of Precursors Stoichiometry on SHS Synthesis of Ti2AlC Powders

Abstract

Introduction

Preparation

Results and Discussion

Conclusion

Acknowledgments

References

XRD and TG-DSC Analysis of the Silicon Carbide-Palladium Reaction

Abstract

Introduction

Experimental Work

Results

Discussion

Conclusions

References

Modelling Damage and Failure in Structural Ceramics at Ultra-High Temperatures

Abstract

Introduction

Background for Fracture Mechanics Methods Under Creep Conditions

Failure Mechanisms in Zrb2 in the Ultra High Temperature Range

Finite Element Modelling

Creep Crack Growth Prediction Models

Finite Element Framework for UHTC Materials

Conclusions

Acknowledgements

Nomenclature

References

Influence of Precursor Zirconium Carbide Powders on the Properties of the Spark Plasma Sintered Ceramic Composite Materials

Abstract

Introduction

Experimental

Results and Discussion

Conclusion

Acknowledgements

References

Second Annual Global Young Investigator Forum

Dielectric and Piezoelectric Properties of Sr and La CO-Doped PZT Ceramics

Abstract

Introduction

Experimental

Results and Discussion

Conclusions

Acknowledgement

References

Author Index

Developments in Strategic Materials and Computational Design IV

Copyright © 2014 by The American Ceramic Society. All rights reserved.

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Preface

Contributions from two Symposia, two Focused Sessions, and the Annual Global Young Investigator Forum that were part of the 36th International Conference on Advanced Ceramics and Composites (ICACC), in Daytona Beach, FL, January 27–February 1, 2013 are presented in this volume. The broad range of topics is captured by the Symposia and Focused Session titles, which are listed as follows: Focused Session 1—Geopolymers and Chemically Bonded Ceramics; Focused Session 2—Thermal Management Materials and Technologies; Symposium 10—Virtual Materials (Computational) Design and Ceramic Genome; and, Symposium 12—Materials for Extreme Environments: Ultrahigh Temperature Ceramics and Nanolaminated Ternary Carbides and Nitrides.

This was the 11th consecutive year for the topic covered by Focused Session 1 concerning Geopolymers and Chemically Bonded Ceramics. As in years past, it continued to attract attention from international researchers as well as new application domains. Twelve papers are included in this year’s proceedings. The studies focus on processing as well as the associated microstructural and mechanical properties in relevant environments. Such studies are critical in the pursuit of sustainable and environmentally friendly ceramic composites. Focus Session 2 emphasizes new materials and the associated technologies related to thermal management. The topic includes innovations in ceramic or carbon based materials tailored for either high conductivity applications (e.g., graphite foams) or insulation (e.g., ceramic aerogels); heat transfer nanofluids; thermal energy storage devices; phase change materials; and a slew of technologies that are required for system integration. One paper is included here addressing the relatively new application of high conductivity graphite foams for thermal energy storage.

Symposium 10 is dedicated to the modeling of ceramics and composites. This includes property prediction, innovative simulation methods, modeling defects and diffusion in ceramics as well as the study of virtual materials with the aim of further optimizing the behavior to facilitate the design of new ceramics and composites with tailored properties. Nine papers are available within this volume discussing subjects such as stochastic crystal growth, crack modeling, numerical assessment of self-healing composites, multi-scale modeling of CMCs, and laminate property predictions using 3D unit cells. Symposium 12 addresses the many facets related to materials for extreme environments. This includes the relationship between material structures and properties, structural stability under extreme environments, novel characterization methods, and life predictions. Four papers from this symposium are included within this collection. Lastly, a single study is included from the Second Annual Global Young Investigators Forum. The paper is focused on the dielectric and piezoelectric properties of a novel PZT ceramic.

The editors wish to thank the symposium organizers for their time and labor, the authors and presenters for their contributions; and the reviewers for their valuable comments and suggestions. In addition, acknowledgments are due to the officers of the Engineering Ceramics Division of The American Ceramic Society and the 2013 ICACC program chair, Dr. Sujanto Widjaja, for their support. It is the hope that this volume becomes a useful resource for academic, governmental, and industrial efforts.

WALTRAUD M. KRIVEN, University of Illinois at Urbana-Champaign, USA

JINGYANG WANG, Institute of Metal Research, Chinese Academy of Sciences, China

YANCHUN ZHOU, Aerospace Research Institute of Materials & Processing Technology, China

ANDREW L. GYEKENYESI, NASA Glenn Research Center, USA

Introduction

This issue of the Ceramic Engineering and Science Proceedings (CESP) is one of nine issues that has been published based on manuscripts submitted and approved for the proceedings of the 37th International Conference on Advanced Ceramics and Composites (ICACC), held January 27–February 1, 2013 in Daytona Beach, Florida. ICACC is the most prominent international meeting in the area of advanced structural, functional, and nanoscopic ceramics, composites, and other emerging ceramic materials and technologies. This prestigious conference has been organized by The American Ceramic Society’s (ACerS) Engineering Ceramics Division (ECD) since 1977.

The 37th ICACC hosted more than 1,000 attendees from 40 countries and approximately 800 presentations. The topics ranged from ceramic nanomaterials to structural reliability of ceramic components which demonstrated the linkage between materials science developments at the atomic level and macro level structural applications. Papers addressed material, model, and component development and investigated the interrelations between the processing, properties, and microstructure of ceramic materials.

The conference was organized into the following 19 symposia and sessions:

Symposium 1

Mechanical Behavior and Performance of Ceramics and Composites

Symposium 2

Advanced Ceramic Coatings for Structural, Environmental, and Functional Applications

Symposium 3

10th International Symposium on Solid Oxide Fuel Cells (SOFC): Materials, Science, and Technology

Symposium 4

Armor Ceramics

Symposium 5

Next Generation Bioceramics

Symposium 6

International Symposium on Ceramics for Electric Energy Generation, Storage, and Distribution

Symposium 7

7th International Symposium on Nanostructured Materials and Nanocomposites: Development and Applications

Symposium 8

7th International Symposium on Advanced Processing & Manufacturing Technologies for Structural & Multifunctional Materials and Systems (APMT)

Symposium 9

Porous Ceramics: Novel Developments and Applications

Symposium 10

Virtual Materials (Computational) Design and Ceramic Genome

Symposium 11

Next Generation Technologies for Innovative Surface Coatings

Symposium 12

Materials for Extreme Environments: Ultrahigh Temperature Ceramics (UHTCs) and Nanolaminated Ternary Carbides and Nitrides (MAX Phases)

Symposium 13

Advanced Ceramics and Composites for Sustainable Nuclear Energy and Fusion Energy

Focused Session 1

Geopolymers and Chemically Bonded Ceramics

Focused Session 2

Thermal Management Materials and Technologies

Focused Session 3

Nanomaterials for Sensing Applications

Focused Session 4

Advanced Ceramic Materials and Processing for Photonics and Energy

Special Session

Engineering Ceramics Summit of the Americas

Special Session

2nd Global Young Investigators Forum

The proceedings papers from this conference are published in the below nine issues of the 2013 CESP; Volume 34, Issues 2–10:

Mechanical Properties and Performance of Engineering Ceramics and Composites VIII, CESP Volume 34, Issue 2 (includes papers from Symposium 1)

Advanced Ceramic Coatings and Materials for Extreme Environments III, Volume 34, Issue 3 (includes papers from Symposia 2 and 11)

Advances in Solid Oxide Fuel Cells IX, CESP Volume 34, Issue 4 (includes papers from Symposium 3)

Advances in Ceramic Armor IX, CESP Volume 34, Issue 5 (includes papers from Symposium 4)

Advances in Bioceramics and Porous Ceramics VI, CESP Volume 34, Issue 6 (includes papers from Symposia 5 and 9)

Nanostructured Materials and Nanotechnology VII, CESP Volume 34, Issue 7 (includes papers from Symposium 7 and FS3)

Advanced Processing and Manufacturing Technologies for Structural and Multi functional Materials VII, CESP Volume 34, Issue 8 (includes papers from Symposium 8)

Ceramic Materials for Energy Applications III, CESP Volume 34, Issue 9 (includes papers from Symposia 6, 13, and FS4)

Developments in Strategic Materials and Computational Design IV, CESP Volume 34, Issue 10 (includes papers from Symposium 10 and 12 and from Focused Sessions 1 and 2)

The organization of the Daytona Beach meeting and the publication of these proceedings were possible thanks to the professional staff of ACerS and the tireless dedication of many ECD members. We would especially like to express our sincere thanks to the symposia organizers, session chairs, presenters and conference attendees, for their efforts and enthusiastic participation in the vibrant and cutting-edge conference.

ACerS and the ECD invite you to attend the 38th International Conference on Advanced Ceramics and Composites (http://www.ceramics.org/daytona2014) January 26-31, 2014 in Daytona Beach, Florida.

To purchase additional CESP issues as well as other ceramic publications, visit the ACerS-Wiley Publications home page at www.wiley.com/go/ceramics.

SOSHU KIRIHARA, Osaka University, Japan

SUJANTO WIDJAJA, Corning Incorporated, USA

Volume Editors

August 2013

Geopolymers and Chemically Bonded Ceramics

IMPORTANCE OF METAKAOLIN IMPURITIES FOR GEOPOLYMER BASED SYNTHESIS

A. Autef1, E. Joussein2, G. Gasgnier3 and S. Rossignol1

1 Groupe d’Etude des Matériaux Hétérogènes (GEMH-ENSCI) Ecole Nationale Supérieure de Céramique Industrielle, 12 rue Atlantis, 87068 Limoges Cedex, France.

2 Université de Limoges, GRESE EA 4330, 123 avenue Albert Thomas, 87060 Limoges, France.

3 Imerys Ceramic Centre, 8 rue de Soyouz, 87000 Limoges, France.

corresponding author: [email protected]

ABSTRACT

Geopolymers are the object of numerous studies because of their low environmental impact. The synthesis of these geomaterials is achieved by the alkaline activation of aluminosilicates. Alkaline activation is typically accomplished by the activation of potassium or sodium silicate. Since these alkaline silicate solutions are relatively expensive. It is imperative to understand all of the phenomena and reactions involved during geopolymer synthesis. We thus attempted to study the role played by siliceous species in the alkaline silicate solutions.

During the setting of the materials, the reactive mixture forms at least two phases: (i) a solid phase and (ii) a gelified liquid which recovered it. The quantity of gel varies with the Si/Al, Si/K and Si/H2O molar ratios. Several exchanges take place at the gel-solid interface and involve composition and pH variations. Moreover, the nature and the number of networks depend on the alkaline solution used.

I. INTRODUCTION

The alkaline silicate solutions (waterglass) necessary for the synthesis of geopolymer materials are solutions containing a dissolved glass with an aspect similar to water. Alkaline silicate solutions are widely used in the industry as binders, emulsifying agents, deflocculants or in the paper industry. These sodium or potassium-based solutions, present complex structures, composed of diverse monomeric and polymeric species [1,2,3]. Their composition evolves according to various variables, such as the value of pH [4] or the SiO2/M2O molar ratio (where M=Na or K). These parameters allow control of the various species in the mixture which confer variable properties of the solutions, in particular in terms of reactivity. Important differences are also noted between potassium and sodium elements; these differences can be at the origin of variations, both in terms of structure and stability, within geopolymer materials.

Several studies were recently realized in these alkaline silicate solutions [5] and on their role during geopolymer formation [6,7,8]. These various studies allowed highlighting the existence of two phases within the consolidated material [7]: a geopolymer phase and a gel phase, present in more or less high quantity according to the source of silica used during the manufacture of the alkaline silicate solution. Indeed, the use of sand as a substitute for the amorphous silica leads to a decrease of the Si / Al ratio and of the quantity of geopolymeric phase [7].

The consolidation of the material is then possible thanks to the important presence of gel but leads to a decrease in the mechanical properties. These materials, synthesized from a commercial metakaolin, also contain impurities initially present in the raw material (e.g. anatase, muscovite, quartz).

The objective of this study is to understand the role played by the siliceous species from the activation solution during the formation of geopolymers. Hence, the role of the alkaline silicate solution was studied by comparing a commercial solution with a laboratory prepared solution with the same Si / K molar ratio. To eliminate the effect of impurities within the consolidated materials, a high purity metakaolin (99 %) was used for both activating solutions.

II. EXPERIMENTAL PART

1. Sample preparation

Geopolymer materials were synthesized according to two ways as described by Figure 1.

Figure 1 : Synthesis protocol of geopolymer compounds.

Table 1 Characteristics and nomenclature of raw materials used.

Nature

Amorphous silica

Metakaolin MI

Nomenclacture

S

MI

d

50

(μm)

0.14

7.54

BET value (m

2

/g)

202

~ 7

Chemical analysis (wt. %)

99.9 SiO

2

50 SiO

2

50Al

2

O

3

In the case of geopolymers A [6], the KOH pellets were first dissolved in water at room temperature to form an alkaline solution (pH=14). An amorphous silica, being very fine and highly reactive (denoted S; purity of 99.9%) and supplied by SIGMA ALDRICH was dissolved in the alkaline solution. The continuation of the protocol is similar to what was previously described. Nomenclatures and molar ratios are presented in the Table 2.

Table 2 Nomenclature and compositions of compounds.

2. Characterization

The FTIR spectra were obtained using a Thermo Fisher Scientific 380 infrared spectrometer (Nicolet). The IR spectra were gathered over a wave number range of 400 to 4000 cm−1 with a resolution of 4 cm−1. The atmospheric CO2 contribution was removed with a straight line between 2400 and 2280 cm−1. To follow the evolution of the involved bonds within the sample in time, a computer algorithm was used to acquire a spectrum every 10 minutes for 13 hours, producing 64 scans. To allow comparisons of the various spectra, the spectra were corrected with the baseline and then normalized. The characterization of the powders and gels was also conducted by FTIR.

Differential thermal analysis (DTA) and thermo gravimetric analysis (TGA) were performed on a SDT Q600 apparatus from TA Instruments in an atmosphere of flowing dry air (100 mL/min) in platinum crucibles. Signals were measured with Pt/Pt-10%Rh thermocouples. Some milligrams of material are placed in a platinum crucible and the analysis is made from 30 °C to 800 °C, at 10 °C / min.

The chemical analyses were obtained by XRF investigations using a XMET 5500 X from Oxford. Samples are analyzed from pressed pellet.

III RESULTS AND DISCUSSION

1. Synthesis of materials

In the way to study the influence of the alkaline solution only one sort of metakaolin highly pure (MI metakaolin) was used. Therefore, the influence of the impurities was eliminated. It was chosen to maintain constant the Si / K and Si / H2O ratios, what leads to a decrease in the Si / Al ratio from 1.62 to 1.40 compared to the previous study from an other type of metakaolin raw material [10]. Whatever the composition, (i) a consolidated geopolymer-like material was synthesized, and (ii) a demixing brought in the reactive mixture from the first hour after the synthesis: a fine coat of transparent liquid appeared slowly at the surface. The polycondensation phase is effective in 6 at 10 hours. The viscosity of the supernatant liquid increased until to form a gel, 5 to 8 days after the synthesis. Afterward, the supernatant phase will be named “gel” and the solid phase “solid”. As an example, the reactive mixture E gave a sample consisting of the “solid E” recovered from the “gel E”. The same results were observed for A samples.

According to previous results the variations of the various molar ratios during the substitution of the other metakaolin by the MI metakaolin led to the formation of a more important quantity of gel on the solids surface. This increase seemed to be inversely proportional to the Si / H2O ratio leading to an extension of the gelation time. The quantity of gel formed also increased with the Si/Al ratio. This observation highlighted the role of the aluminum as a networking agent. The variation of these molar ratios influenced the formed gel quantity and the gelation speed without affecting the local structure of the gel. There was thus no modification of the formation mechanisms but only an influence on their kinetics.

2. Comparison of A and E compounds (open mold)

The difference between both A and E solutions was in the nature of the Qn species in solution [6]. Indeed, studies by 29Si NMR revealed a quantity of Q0 species superior to Q1 in the laboratory prepared solution while the opposite was observed in the commercial solution [8]. The silicon availability compared with the aluminum thus differs, what led to variations of reactivity and thus to the formation of the various networks. However, whatever was the alkaline solution used all the prepared samples within the framework of the present study led to the formation of a solid phase and a gel. To characterize the obtained materials, all of them were analyzed by infrared spectroscopy and thermal analysis. The mass variations were different between these two compounds (Figure 2 (a)). The 24 % weight loss noticed in the case of the solid is characteristic of this type of material [11]. Whatever the composition (A or E) the behavior in temperature was similar. The Figure 2 (b) presents the heat flow profiles (endothermic peak) for each of the materials characteristic of the elimination of the water.

Figure 2 : Curves of thermal analyses of gels E (—) and A (—) and solids E (—) and A (—), 20 days of synthesis (a) weight loss and (b) heat flow as a function of temperature.

For geopolymer compounds the loss of water intervened for nearby temperatures of 100°C [10]. The gel appeared as a compound very rich in water with a 93 % weight loss, characteristic of a silica gel [12]. In that case, the water elimination intervened in a temperature domain vaster than for the solid and went on until neighboring temperatures of 200°C. The very similar weight loss behavior for temperatures lower than 100°C showed that a part of the gel behaved as a “solid”. There would be in that case a common interface which would make the interpretations difficult.

The results obtained by infrared spectroscopy on drops of reactive mixture at various times are grouped on the Figure 3 (a and b). The absorption band shift due to the siliceous species is similar in the case of mixtures E and A which consolidates the idea that a polycondensation reaction intervened at the beginning.

Figure 3 : Variation in time of the Si-O-M band (a) and of the I (Q) / I(H2O) (b) ratio during the formation of E () and A () solids in open mold.

3. Focus on the composition E

a. Characterization of the supernatant liquid

To determine the gel and solid formation mechanisms, FTIR spectroscopy studies and chemical analyses were realized on materials E synthesized with the commercial potassium silicate solution. This supernatant liquid found on the solid surface was expelled during the consolidation of the latter. As previously observed, the quantity of liquid formed above the solid compound was stable with time until the gelation moment which intervened at the end of 7 days. To follow this transformation in the gel, the supernatant phase was punctually analyzed by infrared spectroscopy (Figure 4).

Figure 4 : Variation in time of the (a) Si-O-M band and (b) I(Q2) / I(H2O) ratio in the supernatant liquid 1 () and 2 (Δ) produced by sample E, in open mold during the gelation.

The observed absorption bands were attributed to the changes of vibrational and rotational states of the various bonds from the literature [13, 14, 15]. The drift of the absorption peak position caused by the siliceous species (denoted Q2) was raised (Figure 4 (a)) because it was defined as one of the characteristics of the polycondensation phenomena [16]. Indeed, a polycondensation reaction was characterized by an evolution of the position of the vibration band relative to the bond Q2. An increase of the intensity of this vibration band was also noted.

The I(Q2) / I(H2O) ratio of the absorbed intensities by the change of vibrational states of the siliceous and aqueous species was also determined (Figure 4 (b)) by considering the maxima of absorption situated respectively between 1660-1630 cm−1 and 1100-970 cm−1. Whatever was the considered sample (gel 1 or 2) issue from two preparations, the same evolutions were noticed, evidencing the reproducibility of the synthesis. The increase of the wavenumber corresponding to the Si-O-M peak, due to a replacement of the Si-O-Al bound by the Si-O-Si bound, suggests that the reactions were essentially made between siliceous species [10]. The decrease of the I(Q) / I(H2O) ratio (Figure 4 (b)) resulted mainly in the increase of the H2O vibration band compared with that attributed to Si-O-M which decreased very slowly. This phenomenon is in agreement with the hypothesis of local reorganizations between the siliceous species which polycondensate to form a gel [5]. From approximately 70 hours of reaction, stabilization was observed; it could be explained by a ripening of the gel [5].

b. Influence of the reactivity (comparison between open and closed molds)

In the case of the solid, acquisitions were not any more made in a punctual way but by automated follow-up during polycondensation. The acquisitions were realized on a drop of reactive mixture in an open mold. The variations of the Si-O-M vibration band position as well as the I(Q) / I(H2O) are represented in the Figure 5A. The Si-O-M band shift with time towards lower wavenumbers (Figure 5A (a)) was due to the polycondensation reactions which began for the formation of the geopolymer, as shown in previous works [17]. The sudden evolution of its position towards the high wavenumber which arose beyond the first 3 hours following the synthesis could result from the formation of Si-O-Si recombination between the various Qn species within the network to form a second network or a crystallized compound. Indeed, during such a formation, there was gradually consumption of the species Q2 for the benefit of the Q3 and Q4 formation [18]. This evolution would thus be characteristic of the formation of a compound for which the nature was not identified. This compound was formed from the available species in solution; it could also be a potassium aluminosilicate or a potassium silicate. It would seem that this phenomenon is comparable to that observed for the supernatant liquid but according to different reaction kinetics. According to this hypothesis, the formation of this compound would contribute to enrich the supernatant liquid, until led to saturation in the middle causing the gel formation. The increase in the I(Q) / I(H2O) ratio (Figure 5A (b)) at the beginning of the reaction resulted from the decrease in the water contribution. This revealed that the solid network formation led to an elimination of water which was necessary for the polycondensation reaction. The small decrease which then appeared translates a weak increase of the vibration band attributed to H2O which suggests that the formation of the compound revealed by the shift of the Si-O-M vibration band is accompanied by a weak water discharge. These first results being obtained in a drop of mixture in an open mold not allowing observation of the demixing phenomenon.

Figure 5 : (A) Variation in time of the (a) Si-O-M band and (b) I(Q2) / I(H2O) ratio during the formation of solids E1() and E2 (Δ) in open mold. (B) Variation in time of the (a) Si-O-M band and (b) 1(Q2) / I(H2O) the formation of solids E1 () and E2 (Δ) in closed mold.

To reproduce the conditions of formation of a geopolymer material, an in situ analysis in a closed mold was realized by infrared spectroscopy (cf. experimental part). The obtained results are given on the Figure 5B. The observed differences between both samples can be understood by temperature variations, around 5°C, during the acquisitions which modified the reaction kinetics. The observed wavenumber diminution (Figure 5B (a)) is characteristic of a polymerization reaction during geopolymer formation [10]. Nevertheless, for the solid E the evolution of the wavenumber seemed to be disturbed near 10 hours of reaction. Indeed, the band position increased during a few hours before starting its decrease again. This means that another phenomenon disrupted the polycondensation reactions introduced during the first 10 hours following the synthesis. This disturbance could correspond to the formation of a crystallized phase or to a silica gel [5]. A silicate network could form very quickly, and then siliceous species would react to form a siliceous compound. Once this compound formed, the charged species in the middle can again govern and lead to the formation of a solid geopolymer. On the other hand, the slowing down and/or the inversion of the progressive variation of the I(Q) / I(H2O) ratio can again be characteristic of the formation of a compound (Figure 5B (b)). Indeed, the I(Q) / I(H2O) ratio presents a non linear behavior: a rough fall of the I(Q)/I(H2O) ratio is observed approximately ten hours after the synthesis. The siliceous species contribution being constant in time, it is the water contribution that imposes the observed evolution. There is first water consumption which corresponds to the formation of the solid network. Then the water production (decrease of the I(Q) / I(H2O) ratio) translates the formation of a compound. This phenomenon corresponds to the formation of a gel. Finally, when the gel is totally formed the polycondensation of the solid network continues and consumes some water during its nucleation.

IV. EVIDENCE FOR THE PRESENCE OF CRYSTALLIZED PHASE

To determine the presence of a possible crystallized compound, XRD studies were realized on the gels (dried at 110°C) and on solids. Figure 6 presents the patterns obtained.

Figure 6 : XRD patterns obtained on E and A gels and solids (PDF files: * K2Si2O5 (00-026-1331); # K2SiO3 (04-013-3814); ° K2Si4O9 (00-039-0212).

The gels and solids being amorphous, it is difficult to determine exactly their nature; however the appearance of certain shoulder can translates the implementation of particular local orders within these materials. XRD patterns obtained on the various solids were similar and corresponded to amorphous materials. Their diffraction dome was centered on 28°(2θ). However, for a 24°(2θ) value a shoulder was observed for all the compounds. This shoulder could be attributed to the presence of the K2Si2O5 compound. Indeed, this compound has already been identified in geopolymer materials prepared from a commercial alkaline silicate [19]. Besides, in the case of dried gels, the maximum diffracted intensity corresponded to superior values of 2θ. Furthermore, there was an appearance of a diffraction peak badly defined at 32°(2θ). The latter, particularly visible in the gel E, could be attributed to a network with K2Si4O9. In the gels, there would thus be existence of one or several alkaline silicates and a siliceous amorphous network.

Figure 7 : Recalculated molar compositions from XRF analyses performed on E and A compounds.

V. CONCLUSION

Geopolymers present a growing interest because of their low environmental impact. These materials are obtained by alkaline activation of alumino-silicate. The high cost of the necessary alkaline solutions constitutes a break in the development of these innovative binders. It is thus indispensable today to understand all the phenomena and the reactions occurring during their synthesis to promote the development of these materials. The present research work ensues from this imperative: its objective was to study the role played by the siliceous species within the activating solution in the presence of pure metakaolin.

The results highlighted the formation of a gel phase during the synthesis of geopolymers from pure metakaolin.

From these studies, it is possible to provide that (i) the variations of Si / Al, Si / K and Si / H2O molar ratios influence the quantity of gel formed and the gelation kinetics in the presence of a very pure metakaolin and (ii) the change in the initial alkaline solution does not lead to modification of the phenomena but the nature and the number of existing networks differ.

ACKNOWLEDGEMENTS

The authors thank the IMERYS Ceramic Centre for the metakaolin samples.

REFERENCES

[1] J. G. Vail, Soluble silicate: Their properties and uses. Reinhold, New York, 1952.

[2] G. Lagerström, Equilibrium studies of polyanions. III. Silicate ions in NaCl04 medium, Acta Chemica Scandinavica, 13, 722–736 (1959).

[3] G. Engelhardt, D. Zeigan, H. Jancke, D. Hoebbel, W. Wieker, 29Si NMR spectroscopy of silicate solutions. II. On the dependence of structure of silicate anions in water solutions from the Na/Si ratio, Zeitschrift für anorganische Chemie, 418, 17–28 (1975).

[4] M. Dietzel, Dissolution of silicates and the stability of polysilicic acid, Geochim. Cosmochim. Acta, 64, 19, 3275 (2000).

[5] M. Tohoue Tognonvi, S. Rossignol, J. P. Bonnet, Effect of alkali cation on irreversible gel formation in basic medium, Journal of Non-Crystalline Solids, 357, 43–49 (2011).

[6] A. Autef, E. Joussein, G. Gasgnier, S. Rossignol, Parameters that influence silica dissolution in alkaline. 35th International Conference on Advanced Ceramics and Composites, accepted.

[7] A. Autef, E. Joussein, G. Gasgnier, S. Rossignol, Role of the silica source on the geopolymerization rate, Journal of Non-crystalline solids, 358, 2886–2893 (2012).

[8] E. Prud’homme, A. Autef, N. Essaidi, P. Michaud, B. Samet, E. Joussein, S. Rossignol, Defining existence domains in geopolymers through their physicochemical properties, Applied Clay Science, http://dx.doi.org/10.1016/j.clay.2012.10.013 (2012).

[9] E. Prud’homme, P. Michaud, E. Joussein, C. Peyratout, A. Smith, S. Arrii-Clacens, J. M. Clacens, S. Rossignol, Silica fume as porogent agent in geo-materials at low temperature, Journal of the European Ceramic Society, 30, 1641–1648 (2010).

[10] E. Prud’homme, Rles du cation alcalin et des renforts minéraux et végétaux sur les mécanismes de formation de géopolymères poreux ou denses, thèse de doctorat. Université de Limoges, France, 2011.

[11] P. Duxson, G. C. Lukey, J. S. J. van Deventer, Physical evolution of Na-geopotymer derived from metakaolin up to 1000 °C, Journal of Materials Science, 42, 3044–3054 (2007).

[12] M. Tohoue Tognonvi, J. Soro, S. Rossignol, Physical-chemistry of silica/alkaline silicate interactions during consolidation. Part1: Effect of cation size, Journal of Non-Crystalline Solids, 358 (1) 81-87 (2012).

[13] J. R. Marinez, Infrared spectroscopy analysis of the local atomic structure in silica prepared by sol-gel, Journal of Chemical Physics, 109 (17), 7511–7517 (1998).

[14] W. K. W. Lee, J. S. J. Van Deventer, Use of Infrared Spectroscopy to Study Geopolymerization of Heterogeneous Amorphous Aluminosilicate, Langmuir, 19 (21), 8726–8734 (2003).

[15] P. Innocenzi, Infrared spectroscopy of sol-gel derived silica-based films: a spectra microstructure overview, Journal of Non-Crystalline Solids, 316, 309–319 (2003).

[16] C. A. Rees, J. L. Provis, G. C. Luckey, J. S. J. Van Deventer, Attenuated Total Reflectance Fourier Transform Infrared Analysis of Fly Ash Geopolymeer Gel Aging, Langmuir, 23 (15), 8170–8179 (2007).

[17] E. Prud’homme, P. Michaud, E. Joussein, C. Peyratout, A. Smith, S. Rossignol, Consolidated geo-materials from sand or industrial waste, Ceramic Engineering and Science Proceedings, 30 (2), 313–324 (2010).

[18] S. Puyam, P. S. Singh, M. Trigg’ I. Burgar, T. Bastow, Geopolymer formation processes at room temperature studied by 29Si and 27Al MAS-NMR, Materials Science Engineering A, 396, 392–402 (2005).

[19] S. Delair, E. Prud’homme, C. Peyratout, A. Smith, P. Michaud, L. Eloy, E. Joussein, S. Rossignol, Durability of inorganic foam in solution: The role of alkali elements in the geopolymer network, Corrosion Science, 59, 213–221 (2012).

MECHANICAL STRENGTH DEVELOPMENT OF GEOPOLYMER BINDER AND THE EFFECT OF QUARTZ CONTENT

C. H. Rüscher1, A. Schulz1, M. H. Gougazeh2, A. Ritzmann3

1Institut für Mineralogie, Leibniz Universität Hannover

2Natural Resources and Chemical Engineering Department, Tafila Technical University

3GNF Berlin Adlershof e.V.

ABSTRACT

The development of compressive strength of alkali activated metakaolin in dependence of waterglass to metakaolin ratios and quartz additions were investigated during ageing at room temperature. The compressive strength could be optimized for maximal strength for nominal Si/Al ratios of about 1.8-2 of the binder for ageing between 7 and 10 days. However this composition invariably leads to weakening for longer ageing time (weakening effect). Moreover, the optimum in strength for Si/Al ≈ 1.9 could be seen as a shoulder or weaker peak in an extended field of Si/Al and alkali/Al ratios. Additions of quartz, either as “sand” for mortars or as fine grained quartz or as significant virgin contents in the kaolin source could avoid the weakening effect and improve, therefore, the geopolymer property.

INTRODUCTION

“Binder formation” of alkali-waterglass activated metakaolin may follow always the same mechanism for waterglass/metakaolin compositions 7-10. Hardening occurs generally completely inhomogeneous due to condensation of polysiloxo chains from the waterglass solution from that moment when hydroxide is consumed by the solution of metakaolin. The amount of available hydroxide solution may govern how much Al3+ could be transferred into the waterglass and how the initial waterglass condensate becomes modified. Accordingly the more or less rapid increase in strength is just a consequence of the reaction kinetics of crosslinking the long chains via sialate bondings (-Si-O-Al-O-). Unfortunatelly by the same time long polysiloxo chains become more and more shortened due to the strong increase of sialate bonds during polycondensation. It has been shown that a protection of the long polysiloxo chains, could become available in the presence of high amounts of unreacted metakaolin or also by the presence of Ca-ions 10. Here the compressive strength development is discussed in some details considering some additional results in the field of Si/Al and alkali/Al ratios. Additionally the development of compressive strength in the presence of quartz, either as addition or virgin in the kaolinite source, will be considered.

EXPERIMENTAL

All these series of cements (A-D) were prepared by hand mixing the different metakaolin powders in the alkaline solution of potassium waterglass for about 10 min, forming homogeneous slurry. The slurry was then filled to cylindrical PE-containers (18 mm in diameter and 12 mm in height), which were closed. These containers were held under laboratory conditions (22+/-1°C) during ageing. The containers were opened just before the compressive force measurements. These samples were then used for other characterizations (XRD, IR). For the compressive strength measurements the size of the sample could be used as given by the size of the boxes in a manually driven testing machine (ENERPAC P392, USA). The compressive force was monitored digitally (HBM, Scout 55 and U3 force transducer).

Thermogravimetric analysis were carried out using a Setaram equipment (Setsys Evolution). The measurements were done by heating to 1000°C, holding for 30 minutes and cooling with a flow of 20 ml/min of technical air. For heating and cooling a rate of 5°C/min were used. XRD pattern were recorded on a Broker AXS D4 ENDEAVOR diffractometer (Ni filtered Cu-Kα radiation). The measurements were carried out with a step width of 0.03° (2θ) and 1 second per step. The powder data were analysed with the Stoe WinXPOW software package. FTIR analysis was performed on a Broker IFS66v FTIR spectrometer by using KBr pellet techniques in the 370–4000 cm−1 range, with a resolution 2 cm−1 (1 mg sample diluted in 200 mg of KBr). SEM/EDX investigations were carried out on a JEOL machine (JSM-6390A) equipped with Broker XFlash 410-11-200.

RESULTS AND DISCUSSION

Nominal compositions of metakaolins and geopolymers

Figure 1. XRD pattern of metakaolin samples as used in this study showing some impurity phases as denoted. MKFqz is with the addition of 30 wt% Qz, whereas MKF is nearly free of Qz.

Fig. 2 Compressive strength development of geopolymer cements of series M as a function of a.) nominal molar ration Si/Al at 7, 14 and 28 days of ageing and b.) ageing time. Data given by Duxson et al. 4 and Tsitouras et al5 are included.

Fig. 3 Contour plot of compressive strength data in the field of Si/Al and Na/Al ratio taken from Rowles and O’Connor 1. Included are points of composition M1-M6 from this work. Thick solid line marks the systematic variation in composition obtained by KWG/MKM ratios (Tab. 1, for i). Thinner solid line denoted [3, 4, 5] corresponds to series of nominal constant Na/Al ratio worked on by Duxson et al. 2, 3 and Tsitouras et al.4.

Table 1. Geopolymer-cements of series M as described in the text. KWG/MK: used mass ratios waterglass/metakaolin, MK: used nominal compositions of MK (by wt%) as given by i, ii for calculations of nominal molar ratios of the geopolymer: Si/Al, K/Al, K/Si, H2O/Si. (*Note: For M1 1.0 denotes only the ratio of 50%-KOH solution/MK)

Using as usual about 1 mg sample in 200 mg KBr IR spectra of MKF and MKM do not show any significant quartz content. However the amount detected in XRD indicates about up to 4% in both cases. For MKMph a quartz content of about 10-15% could be estimated from IR spectra. According to Rietveld phase analysis the crystalline contribution could be about 19% which could be separated as about 13.5% and 5.5% to be due to quartz and alumina, respectively. This implies that not more than about 81% of the MKMph sample could be activated. Corresponding Si/Al, K/Al, K/Si, H2O/Si ratios are given in Tab. 2 in comparison to values obtained using results of large area bulk EDX analysis (54.06 SiO2, 43.64 Al2O3, 0.57 K2O, 0.81 Fe2O3).

Table 2. Geopolymer-cements of series A, C and D, notations as described in Tab. 1.

For determination of the nominal molar ratios of Si/Al, K/Al, K/Si, H2O/Si ratios of the MKF and MKFqz related geopolymer (Tab. 2) results of thermogravimetric analysis of Fluka kaolinite could be used. A mass loss of 12.71% were obtained to be compared to an expected mass loss due to dehydration of ideal kaolinite Al2Si2O5(OH)4 of 13.9%. This implies that only 91% of the sample could be activated for geopolymerisation ignoring a possible weight loss related to muscovite and other phases which could be dehydrated. A cross check of the quality of TG data could be given considering the mass loss of about 8.98% obtained for the Fluka kaolinite with the addition of quartz, i.e. 29.3% loss in good agreement with the amount of quartz added.

Compressive strength data of alkali activated metakaolin, series M1-M7.

The compressive strength of a series of alkali activation of metakaolin of nominal compositions as given in Tab. 1 (M1,..,M7) aged for 7, 14, and 28 days show highest strength at Si/Al ratio of 1.85 (Fig. 2 a). These data were obtained during ageing shown in Fig. 2 b. There is a relative steep increase in strength within the first 7 days of ageing and than a rather flat behavior for further ageing. For the cement M5 with the highest strength a gradual weakening is observed, which becomes more pronounced with further ageing as will be discussed further below (compare Fig. 4). It is interesting to note that a compressive strength of about 8 MPA is also obtained for metakaolin activated just with KOH solution without the addition of waterglass. As mentioned in the introduction in the presence of waterglass quasi instantaneous formation of polysiloxo chains occur during the solution process of metakaolin. This effect could be seen using the “molybdate method”. This method is able to distinct between the content of polymeric silicate units, and shorter ones and were used for series of samples where all the metakaolin could be consumed during binder formation 7-9. Since a maximum in the concentration of polymeric silicate units occurs always at much shorter time compared to the time required for reaching maximal strength this condensation effect can be distinct from further network formation which just encloses the preformed chains. Notably during network formation the concentration of polymeric silicate units decreases leading finally to an even complete loss of strength initially gained. In the absence of waterglass this “waterglass effect” is absent. Conclusively it may be argued that using mixtures of alkali-hydroxide solution and metakaolin just the basic strength of an aluminosilicate network is attained.

Figure 4. Compressive strength development during ageing of test bodies as denoted (see text).

Using scanning electron microscopy and energy dispersive analysis (SEM/EDX) Rowles and O’Connor 2 obtained a separation into two phases concerning the Si/Al and Na/Al ratios in all cases of their cements. In particular regions of higher and lower Si/Al ratios with respect to the nominal Si/Al content was observed on a micrometer scale. Those regions with lower Si/Al were identified as “grains” relating it to metakaolin in its origin, being still strongly altered in compositions. The matrix possess always higher Si/Al ratios. These observations could well support the mechanism described above concerning the initial condensation of waterglass, followed by a transport of Al3+ ions from the metakaolin to the waterglass condensates. In MAS NMR investigations Rowles et al. 11 also observed residual unreacted metakaolin for series of composition with Si:Al/Na:Al ratios 1.1/0.6, 1.5/0.8, 2.0/1.0, 2.5/1.3 and 3.0/1.5 as 42%, 28 %, 18%, 0%, 25%, respectively. A similar effect of decreasing contents of unreacted metakaolin is also indicated along the series of samples M2 to M5 considering earlier XRD and IR investigations 8, 9. This could also imply that the amount of unreacted metakaolin could not be influenced significantly by temperature, i.e. 75°C compared to 25°C. Instead the constitution of the initial waterglass (degree of condensation, water and hydroxide content) and the waterglass to metakaolin ratio sensitively govern the reaction volume whereas the temperature strongly influences the reaction kinetics 8.

The effect of quartz in the binder

Significant differences in the development of compressive strength of the geo-cement M5, the geo-mortar (M5 plus sand) and ordinary Portland cement (OPC) and its mortar counterpart are observed during ageing (Fig. 4