Magdalena Szumera

Influence of surface-modified montmorillonites on properties of silicone rubber-based ceramizable composites

Ceramizable (ceramifiable) silicone rubber-based composites are modern elastomeric materials for fire protection application. The most important sector of economy using such materials is cable industry because there are special types of electric circuits that have to keep working in the case of fire. These kinds of composites can create ceramic phase protecting copper wire from melting under high temperature. When temperature increases, polymer matrix degrades (creating silica residue as one of the products) and mineral particles dispersed in silicone rubber matrix stick together creating stiff, durable, insulating and porous ceramic skin. In this paper, the influence of surface modification of montmorillonite with quaternary ammonium salts on ceramization of their silicone rubber composites is presented. Filler modification was studied, determining changes to its surface energy and thermal stability. Mechanical properties, flammability and thermal stability of composites were determined. Ceramization of the composites was discussed from the point of view of their mechanical properties and structure of ceramic phase after heat treatment, determined by compression stress tests, porosimetry and scanning electron microscopy adequately. Results show that type of modifier applied strongly affects properties of silicone rubber-based ceramizable composites before and after ceramization. Samples containing surface-modified montmorillonite produce significantly less heat during their thermal decomposition than composite filled with unmodified montmorillonite. Moreover, incorporation of montmorillonite modified with ammonium salt of linear organic chain causes the creation of nano-porous structure after ceramization. On the one hand, it facilitates heat insulation, but on the other hand, high total volume of pores adversely affects mechanical endurance of the ceramic phase.

Effect of carbon fibers on thermal properties and mechanical strength of ceramizable composites based on silicone rubber

Ceramizable (ceramifiable) silicone composites are one of the most important elastic technical materials produced industrially. These composites are commonly used to increase flame retardancy of electrical cables and to ensure integrity of electricity network during fire by their ability to create a continuous ceramic structure. In this paper, ceramizable silicone composites filled with different contents of carbon fibers were tested. The research was focused on the characterization of ceramic structure created during heat treatment of the composites and thermal properties of the composites. For this purpose, morphology (SEM) and compression strength of the ceramic structures were studied. To describe process of ceramic structures creation, TG/DSC analysis was done. These tests have demonstrated that, the increase in carbon fibers amount improves the mechanical properties of ceramic structure regardless of heat treatment conditions.

Comparative study of zinc addition effect on thermal properties of silicate and phosphate glasses

The aim of the study was an analysis of two groups of glasses from the SiO2–P2O5–K2O–CaO–MgO system with various content of network formers in the form of P2O5 and SiO2, modified by the addition of ZnO. Their effect on glass-forming ability, glass transition effect, crystallization process and the kind of crystallizing phases was examined using DSC and XRD methods. It was observed that in both matrixes, the addition of ZnO decreases the glass transition temperature (Tg). The lower Tg values observed in the phosphate matrix glasses and the accompanying higher values of the changes in molar heat capacity (Δcp) in contrast to the silicate matrix glasses may be considered an indicator of the degree of the reconstruction of their amorphous structure, which facilitates the process of their crystallization. It was found that the crystallizing products of the silicate matrix glasses were silicates and phosphates whose structure contained zinc. In the phosphate matrix glasses, it was observed that zinc inhibited the crystallization of silicate phases.

Effect of copper addition on glass transition of silicate–phosphate glasses

Glass transformation effect of mixed SiO2–P2O5–K2O–MgO–CaO–CuO glasses was studied by DSC, XRD, SEM, and Raman spectroscopy methods. The relationship between the parameters characterizing glass transformation effect and an amount of phosphorous and copper forming the glassy structure was discussed. It was shown that an increasing content of phosphorous increased solubility of copper in the structure of the studied glasses which was the result of P–O–Cu bonds formation. Degree of changes of Tg, ∆cp, and time of relaxation values were higher in glasses with higher content of P2O5 and CuO. The observed relations were explained on the basis of the local atomic interactions in the structure of glass.

Direct crystallization of silicate–phosphate glasses of NaCaPO4–SiO2 system

The subject of the study was silicate–phosphate glasses of NaCaPO4–SiO2 system which are precursors of glass–crystalline materials. Glass–crystalline materials of NaCaPO4–SiO2 system obtained via crystallization of glasses belong to a group of the so-called bioactive materials. In order to obtain glass–crystalline materials with pre-established parameters, it is necessary to conduct crystallization of glasses at specific conditions. In order to design direct crystallization process properly, it is necessary to know the structure and microstructure of the glassy precursor. Microscopic investigation showed that liquation takes place in all the studied glasses. Based on DSC examinations, it has been found out that crystallization of the glasses of NaCaPO4–SiO2 system is a multistep process. The presence of several clearly separated exothermic peaks in DSC curves of investigated glasses makes it possible to crystallize only the separated phase with the matrix remaining amorphous or vice versa. Conducted detailed X-ray and spectroscopic studies of the materials obtained by heating in a gradient furnace (in the temperature specified on the basis of DSC) showed that separated phase and matrix crystallizes separately. Therefore, bioactive glass–crystalline materials can be obtained due to the existence of the phase separation phenomenon and pre-established sizes of the crystalline phase.

Characterization of thermally induced of crystalline phases in CuO-containing silicate–phosphate glasses

The DSC, XRD, FTIR, and 31P MAS-NMR methods were applied to study complex crystallization processes occurring during the thermal treatment of multicomponent SiO2–P2O5–K2O–CaO–MgO glasses modified by the addition of variable amount of copper. The crystallization temperatures were found to decrease with the increasing copper content. The products of multistage crystallization identified by XRD and characterized by FTIR and NMR are the Ca9KMg(PO4)7 and Ca19Cu2(PO4)14 phosphates of whitlockite-type, and the CaMgSi2O6 and Cu0.69Mg1.31Si2O6 silicates of diopside type.

Structural role of Fe in the soil active glasses.

Glasses of the SiO(2)-P(2)O(5)-K(2)O-MgO-CaO-Fe(2)O(3) system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of iron addition on the structure of glasses was evaluated by FTIR spectroscopy (with spectra decomposition) and (57)Fe Mössbauer spectroscopy. The chemical activity of glasses in the 2 mass% citric acid solutions was measured by the ICP-AES method. It has been found that the formation of domains with structure similar to phosphates with chemically stable P-O-Fe(3+) and P-O-Fe(2+) bonds decreases the glass solubility under conditions simulating the soil environment.

Thermal analysis of glasses for proecological applications

Thermal behaviour and biochemical activity of potassium-silicate-phosphate glasses modified by addition of Ca, Mg, acting as ecological fertilisers of controlled release rate of the nutrients for plants were studied. It has been found that the biochemical activity of silicate-phosphate glasses depends on the nature and the number of components forming the glassy framework and is related to the thermal stability of glass demonstrated by the formation of new compounds during the process of crystallisation. It is proved that these seemingly different properties are determined by the same parameters which are the strengths bonds of glass network-formers and modifiers as well as their chemical affinity.

Molybdenum modified phosphate glasses studied by 31P MAS NMR and Raman spectroscopy

Glasses have been synthesized in the system P2O5-SiO2-K2O-MgO-CaO modified by addition of MoO3. Glasses were prepared by conventional fusion method from 40 g batches. The influence of Mo-cations on the analysed glass structure was investigated by means of Raman and (31)P MAS-NMR techniques. It has been found that molybdate units can form Mo[MoO4/MoO6]-O-P and/or Mo[MoO4/MoO6]-O-Si bonds with non-bridging oxygens atoms of Q2 methaphosphate units, resulting in the transformation of chain methaphosphate structure into pyrophosphate and finally into orthophosphate structure. It has been also found that increasing amount of MoO3 in the structure of investigated glasses causes their gradual depolymerization and molybdenum ions in the analysed glass matrix act as modifying cations.

Bioactivity of Fibrous Polymer Based Nanocomposites for Application in Regenerative Medicine

Aim of the work was production of nanocomposite polymer fibres containing ceramic particles using the electrospinning method and characterisation of morphology and bioactivity of the produced materials. The first stage of investigations consisted in preparation of a series of poly-L-lactide (PLA) solutions in various solvents mixtures in order to reach viscosity which would allow formation of fibres by the electrospinning method. Ceramic nanoparticles such as tricalcium phosphate (TCP) and silica (SiO2) were used as nanofillers of the polymer matrix. Their particle size distribution in the solvent solution as well as in the polymer suspension was determined by dynamic light scattering method (DLS). Morphology of the nanoparticles was observed using transmission electron microscopy (TEM). Distribution of the nanofillers in the nanocomposite fibres as well as diameter and morphology of the fibres was assessed using scanning electron microscopy with energy dispersive spectroscopy method (SEM/EDS). Effect of the nanofillers addition and the shaping method on the structure of the PLA matrix was investigated on the basis of the thermal analysis methods (TG/DSC) on the nanocomposite foils prepared by casting. It was revealed that the nanocomposite fibres showed apatite nucleation in in vitro conditions i.e. after incubation in SBF (37°C/ 3 days).