Filler influence on microstructure of Fe/resin composites M. Strečková, R. Bureš, M. Fáberová, T. Sopčák Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, Košice, Slovak Republic Acknowledgement This work was financially supported by Slovak Research and Development Agency under the contract no APVV 0222/10
Outline of my presentation is as follows Theoretical background and motivation Aim of the present work Experimental procedure Results and discussions Conclusions
Theoretical background The phenol-formaldehyde resin (PFR) belong to the oldest thermosetting polymers with a wide range of usage, because of their low cost, aging endurance, undemanding preparation and grate modification with regard for further use. The appropriate design of composite powder materials with desirable mechanical and physical-chemical properties is a very difficult task, because their chemical modification should simultaneously improve various properties such as dimensional and shape stability, hardness and flexural strength, electric and magnetic properties. Soft magnetic composites (SMC), which are used in electromagnetic applications, can be produced from ferromagnetic powder particles coated by an electrical insulating film.
Theoretical background PFR is a possible insulating organic coating for preparation of SMC, but conservation of dimensional stability after curing is a limiting factor of overall sample preparation. The evolution of water and other volatile by-products is a undesirable part of crosslinking process during curing and causes formation of micro- and macrovoids in the sample (foaming of resin at the surface as shown in both figures below).
Aim of the present work Preparation of resol type phenol – formaldehyde resin suitable as a organic coating on Fe powder particle. Modification of PFR by two different inorganic additives SiO2 and ZnSO4, with the aim to prepare Fe-PFR, Fe-PFR-SiO2 and Fe-PFR-ZnSO4 microcomposite materials. The analysis of thermal degradation process of pure and modified PFR by TG and DSC analysis. The observation of morphology and microstructure with respect to the additives. The study of mechanical hardness, flexural strength, electric resistivity and magnetic properties.
phenol catalyst 26% NH3 formaldehyde 37%Water solution heating 85°C Experimental Preparation of PFR Reflux 45 min The reaction molar ratio of phenol/formaldehyde/ammonia – 1.0/1.5/0.35
Experimental Preparation of PFR After removal water under vacuum PREPOLYMER with honey – like viscosity The structure was identified by IR and 13C-NMR spectroscopy.
Experimental Preparation of modified PFR The dried additives SiO2 and ZnSO4 were added to PFR in the fortieth minute of water removing under vacuum. The two type of modified resins were prepared PFR-SiO2 PFR-ZnSO4 Coating The pure and modified resins were dissolved in acetone, the Fe particles were added to those solutions and mechanically mixed after a complete evaporation of acetone was achieved from the suspension. In order to prepare the microcomposites Fe-PFR-SiO2 and Fe-PFR-ZnSO4, the coated powder was pressed into required shape for mechanical testing at 800 MPa.
Experimental Curing Curing schedule applied for each sample. Thermal analysis Simultaneous DSC and TG analysis were performed by difference scanning calorimeter, samples were heated up to 700°C at heating rate of 10°C/min in air. SEM, mechanical testing The microstructure and morphology were analyzed by scanning electron microscopy equipped with EDX analysis. Vickers hardness and flexural strength were measured according to standards.
Results The rapid evolution of water at 175°C from PFR The higher mass loss, slow and easier evolution in the PFR-SiO2 Small mass loss corresponds to release of chemically weakly bonded water in Fe microcomposite powder The opposite situation in the case of Fe microcomposite powder in comparison with resins without Fe can be observed The highest mass loss in the Fe-PFR-ZnSO4 because of different structure of PFR-ZnSO4 after coating process. Two significant regions in DSC traces. First 125 °C-225 °C Second 400 °C- 600 °C
Results – SEM characterisation The negative effect of evolution of water –foaming of PFR on the surface – destabilization of dimensional shape –formation of micro- and macrovoids The positive effect of additives – act against surface deformation – act against separation of PFR from bulk
Results The morphology of modified PFR-SiO2 coating on Fe powder before curing. – uniform –smooth – adhesive – the native agglomerates of SiO2 The zoom of SiO2 agglomerates sticked on Fe particles – the size of SiO2 is around 1 μm – SiO2 agglomerates are composed of fine 100nm nanoparticles and they did not disaggregated during the composite preparation
Results The morphology of modified PFR-ZnSO4 coating on Fe powder before curing. –addition of ZnSO4 causes a significant change in the polymer structure, which is constituted by nano-fibers linking Fe particles – formation of fibrillar structure The zoom on fibrillar structure –fiber is around 10 μm long, 100 nm thick – very small ZnSO4 particles are located on their surface – incorporation of ZnSO4 to the PFR structure was confirmed by EDX analysis
Results The morphology of modified PFR-SiO2 coating on Fe powder after curing. – homogeneous –smooth – adhesive – incorporated SiO2particles in the coating The morphology of modified PFR-ZnSO4 coating on Fe powder after curing. – more rough but still compact coating – the different morphology arises because of the breakdown of PFR fibers during polymer melting at the curing temperature
Results SEM image on microstructure –PFR creates macroscopically continuous phase around Fe particles – uniform network – resin clusters are occasionally evident – overall microstructure exhibits insignificant porosity Detail on the coating – the resin coating is uniform without any visible exfoliation
Results Composition of microcomposites, Vickers hardness and flexural strength – the hardness of sintered Fe at 1100 °C is 115 HV/10 – the microcomposite material Fe-PFR-ZnSO4, shows much higher hardness than the pure sintered Feat the expense of smaller flexural strength – the growth in resistivity comes from the higher amount of electroinsulating component – the highest resistivity in the sample F can be attributed to incorporation of chemically inert SiO2 fine particles into the PFR coating.
DC hysteresis loop of Fe-PFR-ZnSO4 (95% - 4,5% PFR - 0,5%ZnSO4) DC hysteresis loop of Fe-PFR (95% Fe - 5% PFR)
Concluding remarks The iron powder coated by PFR as a thin electrical insulating layer was prepared with aim to design a new class of prospective soft magnetic composite. The elimination of undesirable foaming and destabilization of the sample was achieved by modification of PFR coating by two inorganic additives SiO2 and ZnSO4 and proposed curing schedule. The results of TG and DSC analysis showed that both additives are suitable water absorbents. The addition of ZnSO4 caused a significant change in the polymer structure, which consist of nano-fibers linking Fe particle in final composite. The mechanical hardness test has confirmed that the fibrillar structure of Fe-PFR-ZnSO4 microcomposite results in a more stable material with significantly higher hardness The pure and modified PFR coating form an excellent insulating spacer in between Fe microparticles, which consequently leads to enormous increase of the specific resistivity.
Syntéza PFR-SiO2 (s teosom) pre prípravu mikrokompozitného materiálu Fe-PFR-SiO2 • Možné výhody: • samotná syntéza SiO2 priamo v PFR by mohla spevniť PFR a zvýšiť mechanickú pevnosť materiálu. • príprava nano SiO2 sol-gel procesom in-situ je jednoduchšia a rýchlejšia • dôkaz o veľkosti takto pripravených SiO2 bol robený TEM-kou, syntetizujú sa častice s veľkosťou 180nm a 50nm • IR analýzy potvrdzujú prítomnosť Si v polymérnej matrici • TG a DSC analýzy (ešte vyhodnotím) SEM, TEM
Mólový pomer fenol-formaldehyd-amoniak-teos (ďalej Ph:F:NH3:TEOS) Ph:F:NH3:TEOS 1:1,5:0,35: (0,17 0,085 0,064) Príprava PFR-SiO2 podľa postupu zaužívanom pri príprave samotnej PFR. Postuptné znižovanie SiO2 v PFR (podľa potreby a výsledkov mechanickej tvrddosti). Stanovenie SiO2 v PFR spektrofotometricky. Povlakovanie (snaha znižovať hmotnostné percento PFR na Fe časticach) Vytvrdzovanie (vytvrdzovací cyklus). Lisovanie Mechanické skúšky Elektrický odpor a Magnetické merania
Syntéza PFR-B (s H3BO3) pre prípravu mikrokompozitného materiálu Fe-PFR-B Možné výhody: - priame naviazanie bóru do štruktúry PFR, fenolové jadrá sa premosťujú O-B-O mostíkmy čo by malo viesť k výraznej mechanickej tvrddosti a termálnej stabilite pripravejej modifikovanej živice. - analýzy ktoré mám urobené sú: IR spektrofotometria PFR-B, kde mám dôkaz priameho naviazania B do polymérnej štruktúry. - TG a DSC analýza PFR-B (ešte musím vyhodnotiť)
. Mólový pomer Ph:F:NH3:B3BO3 1:1,5:0,35:0,3 Príprava PFR-H3BO3 podľa postupu zaužívanom pri príprave samotnej PFR. Stanovenie B v pripravenej PFR-B spektrofotometricky s chinalizarínom Daná PFR-B sa rozúšťa v etanole Povlakovanie Vytvrdzovanie Lisovanie Mechanické skúšky. SEM,TEM, elektrický odpor, magnetické merania.