M. Drábik

Changes of thermal events of macrodefect-free (MDF) cements due to the deterioration in the moist atmosphere ☆

Sulfoaluminate ferrite belite (SAFB) clinker premixed with Portland cement in mass ratio 85:15 was combined with hydroxypropylmethyl cellulose (HPMC) or sodium poly-phosphate (poly-P) for the macrodefect-free (MDF) process and subsequent moisture treatment. Mass changes as the measure of the moisture resistance and thermoanalytical traces of MDF cements gave useful information. The mass change depends more on the humidity than on the composition (polymer and inorganic constituents) of the MDF cement or duration of the original MDF cement synthesis. The values of mass changes at 100% relative humidity (RH) and at ambient conditions are affected by the nature of the polymer, poly-P being highly advantageous. Attack by environmental water and carbon dioxide increases the contents of C4(A,F)SH12(AFm) and CaCO3, represented by thermogravimetry (TG) effects at 250°C and differential thermal analysis (DTA) peaks at 600–700°, respectively. In contrast, the quantity of cross-linking, where the decomposition of Al(Fe)–O–C(P) bonds typically produces TG–DTA effects at 250–550°C, remains intact during the moisture attack.

Macrodefect-Free Materials: Modification of Interfaces in Cement Composites by Polymer Grafting

MDF materials are chemically bonded ceramic materials free of the macrodefects typical of hydraulic cement-based materials. MDF materials arising through reactions of sulfo-aluminate-ferrite belitic (SAFB) clinkers and/or Portland cements (PC) with two types of water-soluble polymer (hydroxy-propylmethyl cellulose {HPMC}, polyphosphate glass {poly-P}) are discussed. Mixes of low energy SAFB clinkers with Portland cement, HPMC and, especially poly-P comprise promising cross-linked compositions additional to the better known MDF materials formed from high alumina cement with polyvinylalcohol/acetate. The principles of co-ordination of P and C atoms (of the polymer) with Al and Fe atoms (originating from the cement) are highlighted from spectroscopic information on next-nearest-neighbour interactions, along with the effects of second co-ordination spheres. Polymers modify the interface through functional bonding/grafting of polymer chains onto the surfaces of cement grains. Both the cross-linked atomic structure and the interface coincide well with the model of functional polymers and represent a new type of atomic-level structure in polymer-modified cements. Interpretation is based on previous magnetic resonance and thermal analysis studies. The compactness of Al(Fe)-O-P cross-links reduces transport through the interfaces, increasing the interfacial interactions and resisting the unfavourable uptake of moisture and carbonation.

Attack by Moisture on Advanced Cement-Based Macroscopic Defect-free Materials A Thermoanalytical Study

When exposed to attack by moisture, macroscopic defect-free materials (MDFs) undergo mass and phase changes. The nature of such changes was studied thermoanalytically. Attacked samples differ from non-attacked samples in the degradation of classical cement hydrates (TG, below 200°C) and calcium carbonate (TG, DTA, 550-650°C). Quantitative assessment favours the hypothesis of the impregnation/barrier effect due to the incorporation of polyphosphate glass into the structure of the MDFs. The identity of the thermal decomposition of attacked and non-attacked samples in the range 250-400°C demonstrates the resistance of cross-linked sections of polymer and clinker constituents to the effects of moisture.

Thermal reactivity and1H NMR spectroscopy of Sr1−xH2xV6O16 · aq

The results of study of the thermal reactivity and1H NMR spectroscopy of solid polyvanadates of general formula Sr1−xH2xV6O16 · aq are presented. Compounds withx=0 (a),x ∈ (0.3–0.6) (b) andx=1 (c) were studied. The protons are bonded in V - OH (b, c) and V - O ... H (a, b, c) groups, in H2O molecules (a, b, c) and in H2O ... H2O systems (a, b, c). Dehydration of the studied compounds proceeds stepwise. Total dehydration causes decomposition of the original structures and Sr(VO3)2, SrV12O30 and V2O5 are formed. The results confirm the role of crystal water in stabilizing the structures of the studied compounds.ZusammenfassungDie Ergebnisse einer1H-NMR-spektroskopischen Untersuchung der thermischen Reaktivität von festen Polyvanadaten der allgemeinen Formel Sr1−xH2xV6O16 · H2O werden dargelegt, bei denenx=0 (a),x=0.3–0.6 (b) andx=1 (c) ist. Die Protonen sind in V - OH-Gruppen (b, c) und V - O ... H-Gruppen (a, b, c), H2O molekulen sowie in H2O ... H2O-Systemen (a, b, c) gebunden. Die Dehydratisierung der untersuchten Verbindungen erfolgt stufenweise. Vollständige Dehydratisierung führt zur Zersetzung der ursprünglichen Strukturen und zur Bildung von Sr(VO3)2, SrV12O30 und V2O5. Die Ergebnisse bestätigen die Rolle des Kristallwassers bei der Stabilisierung der Strukturen der untersuchten Verbindungen.РезюмеПредставлены резулт аты исследования термической реакцио нной способности твердых поливанадат ов общей формулы Sr1− xH2xV6O16· вода и их ПМР спектрос копия. Были изучены соедине ния сx=0 (а),x=0.3– 0.6 (б) их=1 (в). Протоны связаны в V-OH (группа соединений б, в) и V-O ... H (соединения а, б, в), в молекулы H2O (соединени я а, б, в) и в системы H2O ... H2O (со единения а, б, в). Дегидратация исслед ованных протекает ступенчат о. Полная дегидратаци я вызывает разложение исходных вещуств с образованием Sr(VO3)2, SrV12O30 и V2O5. Результаты подтверждают роль кр исталлизационной воды в стабилизации с труктур исследованн ых соединений.

Studies of model macroscopic-defect-free materials. Part 1.—Investigations of the system 4CaO · Al2O3· Fe2O3–4CaO · 3Al2O3· SO3–hpmc–H2O by X-ray, thermoanalytical and NMR techniques

Model macroscopic-defect-free (MDF) materials representing selected compositions in the system 4CaO · Al2O3· Fe2O3–4CaO · 3Al2O3· SO3–hpmc–H2O have been prepared, with a variety of water-to-solid ratios and reactions quenched at varying times. Product mixtures were examined by analytical X-ray powder diffraction, thermal analyses and 27Al MAS NMR spectroscopy. Inhibition of crystallisation of hydrated products and elevated temperatures for thermal transformations of those products occur in materials prepared under MDF processing conditions, which incorporate organopolymer (hpmc, hydroxypropylmethylcellulose) into an amorphous hydrated product. Al–O–C crosslinks can be invoked to explain the 27Al spectra, and also the elevation in temperatures of thermal events.

Contribution of materials chemistry to the knowledge of macro-defect-free (MDF) materials*

The latest studies on the reactivity of inorganic-polymeric networks in selected cement-based materials and the focus toward nano- and atomic levels of grafting of polymers on interfaces represent some of the success stories of materials chemistry. Recent developments are reviewed and discussed, with particular emphasis on macro-defect-free (MDF) materials. Experimental evidence of next-nearest-neighbor (NNN) interactions has led to the definition of the scope and model of Al(Fe)–O–P cross-linking under mechanochemical synthesis conditions, in a system combining the most common (Portland) cement and commercially available polyphosphates. Current approaches to synthesis of MDF materials, together with the atomic-level interpretations of both the formed functional interfaces and the adverse influence of moisture, are discussed.

Chemistry for the design and better understanding of cement-based materials and composites

Macrodefect-free (MDF) materials are one example of “hot topics” in the field of cement-based materials and composites exerting new possibilities of the exploitation of added value. These are formed through cross-linking reactions of atoms at the interfaces of cement grains and functional polymers, when medium pressure and twin-rolling procedure are applied. The MDF-relevance of the system of Portland cement + polyphosphate is reported, together with optimal synthesis conditions and limiting rules. The chemistry knowledge about MDF materials has been shown critical for both procedure design and exploitation. Chemical shifts in both 27Al and 31P MAS NMR spectra confirm Al(6)—O—P(4) cross-linking in virgin probes and indicate secondary hydrolysis during moisture uptake in domains free of cross-links. Thermogravimetric identification of the contents of hydrated and cross-linked phases in virgin and in moisture-attacked MDF probes displays that moisture uptake is accompanied by an increase in content of cementitious hydrates and CaCO3. The key phenomena governing the moisture sensitivity/resistance are the density and compactness of interfacial Al(6)—O—P(4) cross-links vs. the access of the moist environment to the unreacted cement residue.

Conversion and heat evolution during hydration of aluminium and iron-containing clinker phases in presence of sulphates

The progress of the reactions of water with brownmillerite (C4AF+) and its mixtures with gypsum (C¯SH2) and calcium sulphoaluminate (C4A3¯S) was investigated by means of calorimetric measurements in situ and X-ray diffractometry to determine the reaction heat and the conversion of the solid reactants as functions of time up to 50 h. The rapid reaction of C4AF with water and the modifying effect of sulphates on the composition of the hydrated phases were confirmed. The presence of sulphates causes the induction period during the reactions of aluminium and iron-containing clinker phases with water. These phenomena are important technologically too, especially in cements with increased contents of C4AF and of sulphate-yielding phases (C¯SH2 and C4A3¯S).ZusammenfassungDer Verlauf der Hydratation von Brownmillerit Ca4AF* bzw. seinen Mischungen mit Gips (C¯SH2) und Calcium-sulfat-aluminat (C4A3¯S) wurde durch kalorimetrische Messungen in situ und Röntgendiffraktometrie verfolgt, um die Abhängigkeit der Reaktionswärme und des Umsatzes der festen Reaktanden von der Zeit (bis 50 h) zu bestimmen. Die schnelle Reaktion von C4AF mit Wasser und der modifizierende Effekt der Sulfate auf die Zusammensetzung der hydratisierten Phase wird bestätigt. Die Anwesenheit von Sulfat bewirkt eine Induktionsperiode bei der Reaktion von alumimum- und eisenhaltigen Klinkerphasen mit Wasser. Diese Erscheinungen sind von technischer Bedeutung, insbesondere für Zemente mit erhöhtem Gehalt an C4AF und sulfatbildenden Phasen wie C¯SH2 und C4A3¯S.РезюмеХод реакций черного м иллерита (4СаО · Аl2О3 · Fe2O3) и его смесей с гипсом и кальцийсульфоалюми натом (4СаО · 3Аl2О3 · SO3) с вод ой был изучен с помощью к алориметрии и рентгеновской диффр актометрии с целью оп ределения теплоты реакции и сте пени превращения твердых реагентов в з ависимости от времен и (до 50 часов). Подтверждены быстра я реакция миллерита с водой и ви доизмененное влияни е сульфатов на состав гидратиров анных фаз. Присутствие сульфат ов вызывает индукцио нный период реакций алюминий- и железосодержащих кл инкерных фаз с водой. Установленные явлен ия являются также технологически важн ыми, особенно, для цеме нтов с увеличенным содержа нием миллерита и сульфат-содержащих ф аз.

Interaction between chiral ions: synthesis and characterization of tartratovanadates(V) with tris(2,2′-bipyridine) complexes of iron(II) and nickel(II) as cations

Four new compounds composed of chiral complex cations and anions: Δ-[Fe(bpy)3] Λ-[Fe(bpy)3][V4O8((2R,3R)-tart)2]·12H2O (1), Δ-[Fe(bpy)3]2Λ-[Fe(bpy)3]2[V4O8((2R,3R)-tart)2][V4O8((2S,3S)-tart)2]·24H2O (2), Δ-[Ni(bpy)3]Λ-[Ni(bpy)3][V4O8((2R,3R)-tart)2]·12H2O (3) and Δ-[Ni(bpy)3]2Λ-[Ni(bpy)3]2[V4O8((2R,3R)-tart)2][V4O8((2S,3S)-tart)2]·24H2O (4) have been prepared. The compounds have been characterized by spectral methods, and their thermal decomposition was studied by simultaneous DTA, TG measurements. The final products after dynamic decomposition and additional heating were Fe2V4O13 for 1 and 2 and Ni(VO3)2 for 3 and 4. The crystal structures determined for 1, 2 and 4 have evidenced that 1 is “hemiracemic” and 2 and 4 are “fully racemic” compounds.

Cross-linking of atoms and thermal stability of new MDF compositions

We have summarized Al, Fe, C and P atoms incorporations within cross-linking interaction and location of those after MDF procedure of sulphobelitic clinker — hydroxypropylmethyl cellulose (hpmc) — sodium salt of polyphosphates (poly-P) compositions. Design of Al/Fe-O-C/P cross links is given and discussed. Thermoanalytical patterns (i) give the evidence of the presence of polymers in the reaction products and (ii) confirm the linkages of solidified polymers throughX=C or P of Al/Fe-O-X cross links in interphase regions with decomposition temperature interval higher than this in classical hydraulic materials. Designed local structure of interphase regions gives atomic level explanation of the densification of a bulk, its microstructure and exceptional technological properties. Similar phenomenon has been reported for the high aluminium — polyvinylalcohol/acetate MDF compositions. Moreover, variant clinker as well as polymers employed in syntheses represent one of the proposals aimed to the increase of the moisture resistence; our results are in the power of the above alternative for phases of sulphobelitic clinker.