POLYSIALATE BINDERS - International PhD Foundry Conference

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POLYSIALATE BINDERS - International PhD Foundry Conference Powered By Docstoc
					     Brno University of Technology
    Czech Foundrymen Society – CFS




International PhD Foundry Conference
                   3rd June 2009



    Polysialate Binders - a Way
       to Solve Shakeout of
    Foundry Sand Mixtures with
         Alkaline Silicates




                                                            Fridrich R., Jelínek.P
         Faculty of metallurgy and materials engineering, Department of Foundry
1.          Introduction

Nowadays we can see better interest on inorganic binders, mainly on the alkaline silicates base. Previously used foundry
sand mixtures composed of colloidal sodium silicates solutions and opening-material had some disadvantages as worse
shakeout of foundry cores after heat exposition. Also higher adhesive bonds of silicate melt to quartz opening-material make
more difficult reclaming process. One of the way to solve these problems is to use polysialates. Polysialates increase primary
strengths of cores, that can solve the shakeout by lower concetration of binder (Na+ ions), also reduce adhesive bonds and
that helps mechanical shakeout of opening-material. One of the most common application tends to „ST-mixtures“, hardened
by using liquid organic ester, p.e. on the acetatic acid or carbonate base. The achievement of this solving way depends on
setting optimal ratio Si/Al (>3:1) to obtain geopolymeric resin in liquid form, with similar properties to colloidal solutions of
alkaline silicates. This paper is focused on influence of aluminium of polysialate liquid binder to strengths after heat exposition
of ST-mixtures (shakeout).


2.          Principle of polysialate binder generation

Polysialates are inorganic polymeric amorphous as far as semi-crystalline compounds. Basic polysialate construction units are
tetrahedron shapes AlO4 and SiO4 [1]. For polysialates preparation can be used different especially natural aluminium-silicon
materials (p.e. kaolin). From next clay material for the preparation can be also used metakaolinite, that is ground, thermal
tidy washed clay (kaolin) [2]. Principle of the preparation is heating-up till dehydroxylation temperature, about 550-650°C
[3], when get desintegration of origin kaolinite structure and making unstable, metakaolinite, beyond change of coordination
number of Al-atom from 6 on to 4 or 5. Both forms are very reactive and ready for hydration. The changes can be described
[4]:

                                                    AlO2(OH)4 = AlO4 + 2H2O

By alkaline activation create amorphous 3 dimensional inorganic polymers like zeolites concerning general formula:

                                                    Mn [-(Si-O)2-Al-O]n.xH2O

Important is the manner of polymerization and ratio Si/Al in the final product [5]. Characteristic sign of binders is low level of
polymerization. That support even the results of 29SiNMR (tab.1) spectrums.

                                                                  29
                                              Tab.1: Results of        SiNMR spectrums.

CHEMICAL SHIFTS (ppm)


sample         Q0                        Q1          Q2                               Q2+3      Q3         Q4


WG-21          -72.31     -75-77,5       -80-81      -82,0-82,5             -83-85    -86-92    -93-99     -106


WG-RG          -72.31     -75-77,5       -80-81      -82,1-82,4             -83-85    -86-91    -93-99     -


INTEGRALS [%]


WG-21          2,9        0,3            15,8        7,9                    0,8       46,8      25,5       0


WG-RG          4,6        1              18.9        10                     4         45.5      16         0


With the mark WG-RG is commercially produced binder RUDAL (Sand team, l.t.d. Brno) and WS-31 is water-glass with similar
physiochemical properties (module, coagulating treshold, density). As from tab.1 by binder RUDAL is the level of
polycondenzation of silicate anions strongly reduced to lower structures Q2+Q3 and Q1 and totally are lost colloidal parts Q4.

Only after reaction with ester hydrolysates and conversion sol-gel can be imagine creation of higher polymeric structure of
high strength. Beside silicon opening-material can be polysialate binders combine with zirconsilicate, chromite or andalusite
and harden with thermic conversion (200°C, Hot-Box), also with gas or liquid esters (without thermic conversion) [6].




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3.          Preparation of ST foundry sand mixtures from polysialates binders

By selected commercially produced polysialate binders was watched the influence of aluminium amount on strength after heat
exposition of foundry sand mixtures.

Polysialate binders were divided into 2 groups:



     1.   BINDERS WITH LOW CONTAIN OF ALUMINIUM

     2.   POLYSIALATE BINDERS WITH HIGH AMOUNT OF ALUMINIUM

In representative of polysialates binders with high amount of aluminium belongs commercially produced binder, by which was
changed the amount of Al. Together were prepared 3 samples almost the same parametres. It was the sample 1,2,3. From
binders with low contain of aluminium was chose DORSIL V2 – binder VŠB-TU Ostrava, Department of Foundry. The
preparation was in long – lasting intensive dissolution of metakaolinite with high specific surface (d50 = 5,987 µm) in
concentrated solution of NaOH (10M) and in mixture with water-glass of standard contain, to have reached parameters
(tab.2). These groups were compared with standard, that had 0 mg/l of Al. Parameters of these binders are in the next tab.2,
physiochemical characteristic of polysialate binders:

                                 Tab.2: Physiochemical characteristic of polysialate binders.
                                                                              Dry
                                                                  SiO2       matter
                               Sample             Na2O[%]         [%]         [%]           MP
                              Binder 1               12,98        28,26       41,24        2,25
                              Binder 2               13,18        26,40       39,58        2,07
                              Binder 3               13,75        26,23       39,58        1,97
                              Standard               12,25        29,71       41,96        2,50
                            DORSIL V2                12,38        28,45       41,18        2,37

                                               KP                                  *amount Al
                          Sample            [% Na2O]             density             [mg/l]
                         Binder 1                 5,20             1490                 8868
                         Binder 2                 3,39             1484                14041
                         Binder 3                 3,35             1494                15814
                         Standard                 5,32             1474                   0
                       DORSIL V2                  5,65             1458                 525

*metodics of assesment: ICP-AES

The mentioned binders were used for preparation of laboratory cores prepared from ST-mixtures.

                                                  Tab.3: Contain of ST-mixtures.

                    Opening-material (Šajdíkovy Humence
                    Š35 ŠH)                                                  100 hm.d.

                    Binder                                                   1,8 hm.d.
                                                                             14 % on
                    Hardener (SA 71:SA 74 = 1:1)                             binder




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4.         Strengths after heat exposition and influence of aluminium contain

     A) In the first case the samples were let to thermal exposition after 2 hours of ST-hardening on
        air (24°C; 41% relative moisture) - pic.1.

                                Pic.1: Measuring strengths after heat exposition.




     B) In the second case the samples were let to thermal exposition after 24 hours of ST-hardening
        on fresh air (24°C; 41% relative moisture) – pic.2.




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                                         Pic.2: Measuring strengths after heat exposition.




Values of shear strengths after heat exposition are average of 15 measurements. For higher reproduction of the results were
by samples (Ø50x50±1mm) measured volume weights.


5.            Analyse of the results

There were made a system to analyse strengths after heat exposition for particular temperatures. Tables 4, 5 keep changes
of strengths after heat exposition by samples after 2hours of ST-hardening and tables 6,7 keep changes of strengths after
heat exposition by samples after 24 hour of ST-hardening.

      Tab.4: Shear strengths after heat exposition (samples were exposed to heat exposition for 2 hours of self hardening).
                           Shear strengths after heat
                           exposition [N/cm2]
                                     Binder Binder Binder                  Dorsil
                           Standard 1       2       3                      V2
                                    12         33         27          25          21         2hod./ST
                                    52         23         23          26          38           200°C
                                     9           7        13          17          10           400°C
                                     8         57         61          53          11           800°C

     Tab.5: Differences of shear strengths after heat exposition (samples were exposed to heat exposition for 2 hours of self
                                                           hardening).
Differences of shear
strengths after heat
exposition
[± Δ N/cm2]
Standard             Binder1 Binder2    Binder3    Dorsil V2
                                                                                       2h
                 +40     -10         -4        +1        +17                                   200°C
                                                                                       200°C
                 -43     -16       -10          -9        -28                                    400°C
                                                                                       400°C
                  -1    +50        +48        +36          +1                                    800°C




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     Tab.6: Shear strengths after heat exposition (samples were exposed to heat exposition for 24 hours of self hardening).
                   Shear strengths after heat
                   exposition [N/cm2]
                             Binder Binder Binder                 Binder
                   Standard 1       2       3                     V2
                           63         36          34         35          65    24hod./ST
                           20         16          19         20          35         200°C
                           11         13          19         20            7        400°C
                             6        57          40         44            6        800°C

  Tab.7: Differences of shear strengths after heat exposition (samples were exposed to heat exposition for 24 hours of self
                                                         hardening).
             Differences of shear
             strengths after heat
             exposition
             [± Δ N/cm2]
             Standard             Binder1 Binder2   Binder3   Dorsil V2
                                                                                                 24 h
                              -43     -20       -15       -15        -30                                 200°C
                                                                                                 200°C
                               -9      -3         0         0        -28                                  400°C
                                                                                                 400°C
                                      -5       +44           +21           +24              -1            800°C


1) Binders Standard a Dorsil V2 have extremely high amounts of shear strengths after 24 hours of ST-hardening (2x higher in
comparison with binders 1-3). Opposite is after 2 hours of hardening.

2) High primary strengths admit even decrease amount of binder to ST-mixtures under 1,8 weight parts still having good
manipulation strengths.

3) Binder Dorsil V2 have the most decrease (absolutely) by change on temperature 200°C and also on temperature 400°C.

4) All of polysialates binders 1, 2 and 3 in the area of the II.maximum (800°C) extremely harden.


6.           Discussion of achieved results

     Selected standard has the highest value of module (2,50).
     Very closed density of binders made possible to dose the same volume of binder to ST-mixture (1,8 weight part).
     Extremely amounts of ST-mixtures after 24 hours keeping on fresh-air by standard and Dorsil V2 show on low part of
     conversion sol-gel by esters (SA 71 and 74) (14%, low reactivity), ran out additional dehydratation.
     Effect of binders 1-3 on strengths after heat exposition by 200°C/2h was very favourable.
     Extremely high amounts by 200°C/2h for standard and Dorsil V2 only after 2 hours of hardening on fresh air point on
     sufficient dehydratation of both binders.
     In the area 400°C/2h are the amounts of strengths after heat exposition of all binders almost stable.
     Essential changes can be seen in the area of the II.maximum. Extreme hardening by polysialate binders 1-3 is by
     800°C/2h.
     By 800°C very low strengths after heat exposition show binder standard and also Dorsil V2, that can put together in
     connection with higher module (higher KP).
     The influence of different aluminium concentration in the area of the II.maximum by the polysialate binders 1-3 is not
     apparent. It shows only the dependance on temperatures 200°C and 400°C and on contain of aluminium. With increasing
     amount of aluminium grow up shear strengths after heat exposition.


7.           Conclusions

There were verified effects of polysialate binders 1,2,3 with different concentration of aluminium. Typical behaviour of these
binders is better shakeout to temperatures 400°C. By high temperatures (II.maximum-800°C) on the other hand to worse
shakeout and extreme increase of strength after heat exposition.




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The dependance of strengths after heat exposition on the aluminium contain in binders 1,2,3 in high temperatures was not
proved. Using the binder Dorsil V2 even low amount of Al, the strengths after heat exposition were however in the area of the
II.maximum much lower. The influence of the Al took a positive effect mainly increasing of its primary strengths, that makes
possible to work with lower amount of the binder (under 1,8%).


8.          References

[1]         SCHMÜCKER, M., MACKENZIE, K. J. D.: Microstructure of sodium polysialate siloxo geopolymer. Ceramics
            International. 2005, vol. 31, is. 3, s. 433-437.
[2]         Metakaolin      KM      40,      KM       60     [online]. [cit.    2008-01-15].     Dostupný       z     WWW:
            <http://www.keramost.cz/cs/produkty/kaolin/metakaolin/>.
[3]         HLAVÁČ, J.: Základy technologie silikátů. Praha, SNTL / ALFA, 1988. 516 s.
[4]         HANZLÍČEK ,T., STEINEROVÁ ,M.: Investigation of dissolucion of aluminosilicates in aques alkaline solution under
            laboratory conditions, Ceramics – Silikáty 46, 2002.
[5]         BURIAN A., ANTOŠ P., KAJZAROVÁ M., NOVOTNÝ J., HRAZDĚRA M., VYKOUKAL, M.: Geopolymerní pojivový
            systém a vlastnosti pojivové obálky zrn. In Sborník Výzkum a vývoj ve slévárenství, mezinárodní konference, s.
            200-203. Hotel Relax, Rožnov pod Radhoštěm, 6.-7.9 2005.
[6]         BERTHELET,M. – VARGAS,M.: Systéme liant polysialate. Hommes-Fonderie. Octobre 1999,no 297, s.22-25.




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