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Structural and solid state EMF studies of phases in the CaO–K2O–P2O5 system with relevance for biomass combustion
Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

Fosfaters reaktioner i energiomvandlingsprocesser är kritisk för den generella processen som helhet, för askrelaterade problem, emissioner liksom för en effektiv och hållbar användning av askan.

Denna avhandling är en sammanställning och diskussion med utgångspunkt i åtta artiklar som behandlar strukturella och termodynamiska studier på faser i CaO-K2O-P2O5-systemet, vilka är av relevans inom förbränning av biomassa. Målsättningen med denna avhandling var: i) att sammanställa och granska tillgängliga strukturella och termodynamiska data i CaO-K2O-P2O5-systemet samt att identifiera avsaknad av data, ii) att fylla i dessa luckor med grundläggande termodynamiska, strukturella och fasstabilitets studier samt iii) att visa på användning samt fördelarna med dessa nya data vid praktisk tillämpning.

En initial litteraturundersökning i CaO-K2O-P2O5-systemet visade att det saknades både strukturella och termodynamiska data. När det gällde tillgängliga termodynamiska data var situationen särskilt otillfredsställande. Det fanns endast data för några kalcium– och kaliumfosfater med varierande tillförlitlighet. Situationen beträffande pulverröntgen för fasidentifiering var bättre, fast fördunklad av det faktum att strukturellt liknande fasövergångar ofta förekommer i det undersökta systemet. Däremot fattades det tillfredställande enkristallstrukturdata för ternära faser i det undersökta systemet.

Enkristallröntgendiffraktion användes för att bestämma strukturerna för CaK2P2O7, CaKP3O9, Ca10K(PO4)7 och CaKPO4. Faserna CaK2P2O7 and CaKPO4 tillsammans med Ca3(PO4)2, KPO3 och K4P2O7 studerades med pulverröntgendiffraktion och termiska analysmetoder för att klargöra fasmodifikationer och övergångstemperaturer. Gibbs bildningsenergi bestämdes för Ca(PO3)2, Ca2P2O7, Ca3(PO4)2, Ca10K(PO4)7, CaK2P2O7, CaKPO4 och CaK4(PO4)2 med ems-metodik och yttriastabiliserad zirkonia som fast elektrolyt och Ni/Ni3P som hjälpsystem. Både de strukturella och termodynamiska data användes sedan vid analyser i ett förbrännningexperiment av olika sädesslag. Framtagna data användes både vid identifiering och även vid kvantifiering av bildade faser i biomassaresterna.

Abstract [en]

The behaviour of phosphates in thermochemical biomass conversion processes are critical for the general process chemistry, for ash related problems, for emissions as well as for an efficient, sustainable and beneficial use of the ash residues.

This thesis is a summary and a discussion of eight papers dealing with structural and thermodynamical studies of phases in the CaO-K2O-P2O5 system, with relevance for biomass combustion. The objectives were: i) to compile and review the available structural and thermodynamical data of phases in the CaO-K2O-P2O5 system as well as to identify existing gaps in the field of these data, ii) to fill in as many as possible of the gaps by fundamental thermodynamic, structural and phase stability studies and iii) to demonstrate the uses and the benefits of the new data in practical applications.

An initial review of the CaO-K2O-P2O5 system showed that both structural information and thermodynamic data were lacking. The situation regarding the available thermodynamic data was especially unsatisfactory, data could only be found for some few calcium phosphates and a few potassium phosphates with varying reliability. Concerning powder X-ray diffraction patterns for phase identification the situation was better, though obscured by the fact that structurally close related phase transitions often occur in the studied system. However, adequate single crystal structural data of ternary phases in the system was completely missing.

Crystal structures of CaK2P2O7, CaKP3O9, Ca10K(PO4)7 and CaKPO4 were determined by single-crystal X-ray diffraction. The phases CaK2P2O7 and CaKPO4 were together with Ca3(PO4)2, KPO3 and K4P2O7, investigated by powder X-ray diffraction and thermal analysis to elucidate phase modifications and transitions temperatures. Gibbs standard energy of formation was determined for Ca(PO3)2, Ca2P2O7, Ca3(PO4)2, Ca10K(PO4)7, CaK2P2O7, CaKPO4 and CaK4(PO4)2 by solid state emf measurements with yttria stabilised zirconia as solid electrolyte and Ni/Ni3P as auxiliary solid couple. Both the structural and thermodynamical data were subsequently utilised in analysis of a combustion experiment of cereal grains. The data were also used to both identify and quantify the phases formed in biomass combustion residues.

Place, publisher, year, edition, pages
Umeå: Energiteknik och termisk processkemi , 2006. , 45 p.
Series
ETPC Report, ISSN 1653-0551 ; 06-06
Keyword [en]
calcium potassium phosphates, structural studies, Gibbs standard energy of formation, EMF measurements, biomass, combustion, chemical equilibrium model calculations
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-858ISBN: 91-7264-149-5 (print)OAI: oai:DiVA.org:umu-858DiVA: diva2:144759
Public defence
2006-09-29, KB3A9, KBC-huset, Linnaeus väg 6, Umeå, 13:00
Opponent
Supervisors
Available from: 2006-09-07 Created: 2006-09-07Bibliographically approved
List of papers
1. Phases of relevance for ash formation during thermal processing of biomass and sludge´s: review of thermodynamic data, phase transition and crystal structures in the system CaO-K2O-P2O5
Open this publication in new window or tab >>Phases of relevance for ash formation during thermal processing of biomass and sludge´s: review of thermodynamic data, phase transition and crystal structures in the system CaO-K2O-P2O5
2004 In: 2nd World Conference on Biomass for Energy, Industry and Climate protection, 10-14 May, Rome, 1454-1457 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-5280 (URN)
Available from: 2006-09-07 Created: 2006-09-07Bibliographically approved
2. CaK2P2O7
Open this publication in new window or tab >>CaK2P2O7
2003 (English)In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. E59, no part 11, i139-i141 p.Article in journal (Refereed) Published
Abstract [en]

Crystals of the title compound, calcium dipotassium diphosphate, have been synthesized from a melt and structurally characterized using single-crystal X-ray diffraction. The CaK2P2O7 structure can be described as a layer structure, with alternating [K2P2O72-] and [Ca2+] layers parallel to the ab plane. Ca2+ is coordinated by six O atoms in a distorted octahedron. K+ is coordinated by nine O atoms in two different polyhedra.

Place, publisher, year, edition, pages
International Union of Crystallography, 2003
Identifiers
urn:nbn:se:umu:diva-5281 (URN)10.1107/S1600536803021287 (DOI)000186318900001 ()
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved
3. Calcium potassium cyclo-triphosphate
Open this publication in new window or tab >>Calcium potassium cyclo-triphosphate
2004 (English)In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. E60, no 2, i15-i17 p.Article in journal (Refereed) Published
Abstract [en]

Crystals of calcium potassium cyclo-triphosphate, CaKP3O9, have been synthesized from a melt and structurally characterized using single-crystal X-ray diffraction. The compound is isostructural with the mineral benitoite (BaTiSi3O9).

Place, publisher, year, edition, pages
International Union of Crystallography, 2004
Identifiers
urn:nbn:se:umu:diva-5282 (URN)10.1107/S1600536804000303 (DOI)000188555500004 ()
Note
Part 2, FEB 2004Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved
4. Single crystal structure determination of Ca10K(PO4)7
Open this publication in new window or tab >>Single crystal structure determination of Ca10K(PO4)7
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-5283 (URN)
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2010-01-13Bibliographically approved
5. Ca10K(PO4)7 from single-crystal data
Open this publication in new window or tab >>Ca10K(PO4)7 from single-crystal data
2006 (English)In: Acta Crystallographica Section E: Structure Reports Online, ISSN 1600-5368, E-ISSN 1600-5368, Vol. 62, no 12, 253-255 p.Article in journal (Refereed) Published
Abstract [en]

 Crystals of decacalcium potassium heptakis(orthophosphate), Ca10K(PO4)7, were obtained from a melt. The structure of Ca10K(PO4)7 is isostructural with β-Ca3(PO4)2 and has been determined previously [Morozov, Presnyakov, Belik, Khasanov & Lazoryak (2000). Crystallogr. Rep. 45, 19-26]. The present investigation confirms the previous study, but with higher precision and with all displacement parameters refined anisotropically. The structure contains four Ca, one K, three P and ten unique O atoms, of which the K, one Ca, one P and one O atom are located on threefold rotation axes.

Place, publisher, year, edition, pages
Munksgaard: Blackwell, 2006
Identifiers
urn:nbn:se:umu:diva-5284 (URN)doi:10.1107/S1600536806047003 (DOI)
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved
6. Determination of standard Gibbs free energy of formation for Ca2P2O7 and Ca(PO3)2 from solid state EMF measurements using yttria stabilised zirconia as solid electrolyte
Open this publication in new window or tab >>Determination of standard Gibbs free energy of formation for Ca2P2O7 and Ca(PO3)2 from solid state EMF measurements using yttria stabilised zirconia as solid electrolyte
2006 (English)In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 38, no 11, 1371-1376 p.Article in journal (Refereed) Published
Abstract [en]

The equilibrium reactions: 3Ca2P2O7(s) + 6Ni(s) reversible arrow 2Ca3(PO4)2(s) + 2Ni3P(s) + 5/O-2(g) and 2Ca(PO3)2(s) + 6Ni(s) reversible arrow Ca2P2O7(s) + 2Ni3P(s) +/- 5/2O2(g) were studied in the temperature range 890 K to 1140 K. The oxygen equilibrium pressures were determined using galvanic cells incorporating yttria stabilized zirconia as solid electrolyte. From the measured data and using the literature values of standard Gibbs free energy of formation for Ca3(PO4)2 and Ni3P, the following relationship of the standard Gibbs free energy of formation for Ca2P2O7 and Ca(PO3)(2) were calculated:

ΔfG° (Ca2P2O7) +/- 11/(kJ · mol-1)=-3475.9 + 1.5441 (T/K) -0.1051 (T/K) · 1n(T/K) and

ΔfG° (Ca(PO3)2) +/- 12/(kJ · mol-1)= -3334.8 + 6.1561 (T/K) -0.6950(T/K) · 1n(T/K).

Keyword
EMF measurements, gibbs free energy of formation, solid electrolyte, uxiliary solid couple, calcium phosphates
Identifiers
urn:nbn:se:umu:diva-5285 (URN)10.1016/j.jct.2006.01.018 (DOI)000242435400016 ()
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved
7. Determination of standard Gibbs energy of formation for CaKPO4, CaK4(PO4)2, CaK2P2O7 and Ca10K(PO4)7 from solid state EMF measurements using yttria stabilised zirconia as solid electrolyte
Open this publication in new window or tab >>Determination of standard Gibbs energy of formation for CaKPO4, CaK4(PO4)2, CaK2P2O7 and Ca10K(PO4)7 from solid state EMF measurements using yttria stabilised zirconia as solid electrolyte
2008 (English)In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 40, no 1, 40-46 p.Article in journal (Refereed) Published
Abstract [en]

The equilibrium reactions: 4CaKPO4(s) + 6Ni(s)  CaK4(PO4)2(s) + 3CaO + 2Ni3P(s) + 5/2O2(g), 4CaKPO4(s) + 3K4P2O7(s) + 6Ni(s)  4CaK4(PO4)2(s) + 2Ni3P(s) + 5/2O2(g), 4CaK2P2O7(s) + 6Ni(s)  4CaKPO4(s) + K4P2O7(s) + 2Ni3P(s) + 5/2O2(g) and Ca10K(PO4)7(s) + 9CaK2P2O7(s) + 18Ni(s)  19CaKPO4(s) + 6Ni3P(s) + 15/2O2(g) were studied in the temperature range from 880 to 1125 K. The oxygen equilibrium pressures were determined using galvanic cells incorporating yttria stabilised zirconia as solid electrolyte. From the measured data and using literature values of standard Gibbs free energy of formation for CaO, Ni3P and K4P2O7, the following relationship of the standard Gibbs free energy of formation for CaKPO4, CaK4(PO4)2, CaK2P2O7, and Ca10K(PO4)7 were calculated:

ΔfG(CaKPO4) ± 5.2/(kJ · mol−1) = −1506.6 − 3.2933(T/K) + 0.4603(T/K) · ln(T/K) 890 < (T/K) < 1125

 

ΔfG(CaK4(PO4)2) ± 8.9/(kJ · mol−1) = −3498.2 − 2.1339(T/K) + 0.3661(T/K) · ln(T/K) 930 < (T/K) < 1125

ΔfG(CaK2P2O7) ± 7.2/(kJ · mol−1) = −2690.0 − 3.7820(T/K) + 0.5599(T/K) · ln(T/K) 940 < (T/K) < 1100

ΔfG(Ca10K(PO4)7) ± 133/(kJ · mol−1) = −5988.3 − 57.063(T/K) + 7.4407(T/K) · ln(T/K) 880 < (T/K) < 1015.

Place, publisher, year, edition, pages
Elsevier Ltd., 2008
Identifiers
urn:nbn:se:umu:diva-5286 (URN)10.1016/j.jct.2007.06.006 (DOI)
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved
8. Slagging characteristics during combustion of cereal grains rich in phosphorous
Open this publication in new window or tab >>Slagging characteristics during combustion of cereal grains rich in phosphorous
2007 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 2, 710-717 p.Article in journal (Refereed) Published
Abstract [en]

A residential cereal burner (20 kW) was used to study the slagging characteristics of cereal grains with and without lime addition. The deposited bottom ash and slag were analyzed using X-ray diffraction (XRD), to identify the crystalline phases, and environmental scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (ESEM/EDS), to study the morphology and elemental composition. Phase-diagram information was utilized to extract qualitative information about the behavior of cereal grain ashes under combustion conditions. Chemical equilibrium model calculations were used to interpret the experimental results. In addition, investigations of the melting behavior of the produced slags were conducted. The results showed significant differences in slagging characteristics between the fuels that were used. The slags consisted of high-temperature melting crystalline phases (calcium/magnesium potassium phosphates) and a potassium-rich phosphate melt for all cereal grains. For oat and barley, cristobalite was also identified in the slag. Furthermore, in these cases, the slags most probably contained a potassium-rich silica melt. The differences in the melting behaviors of the slags had a considerable effect on the performance of the burner. The addition of lime reduced the formation of slag for barley and totally eliminated it for rye and wheat. This occurs because lime contributes to the formation of high-temperature melting calcium potassium phosphates.

Place, publisher, year, edition, pages
American Chemistry Society, 2007
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-5287 (URN)10.1021/ef060429x (DOI)
Available from: 2006-09-07 Created: 2006-09-07 Last updated: 2017-12-14Bibliographically approved

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