Effectofliquid-to-solidratiosonthepropertiesofmagnesiumphosphatechemicallybondedceramicsWangAijuan,WangYao【推荐论文】.doc

精品论文effect of liquid-to-solid ratios on the properties of magnesium phosphate chemically bonded ceramics wang aijuan, wang yao5(school of material science and engineering, xian university of technology, xian 710048) abstract: the temperature variation, setting time, phase compositions and compressive strength of magnesium phosphate chemically bonded ceramics were important for its application in biomedical field. different amount of liquid were added into the premixed acid phosphates and oxides powders in order to study the effect of liquid-to-solid ratios on the properties of magnesium phosphate chemically10bonded ceramics. the results indicated that the setting time increased and the maximum temperature decreased as the increase of liquid-to-solid ratio. the hydrated product was mainly composed bymagnesium potassium phosphate hexahydrate, which was not affected by the liquid-to-solid ratios. besides, magnesia was also found because it was obvious excess for the hydrated reaction. the compressive strength decreased as the increase of liquid-to-solid ratios possibly because of the higher15porosity caused by the superfluous liquid. according to the performed study, results indicated that the properties of mpcbc could be adjusted by changing the liquid-to-solid ratios.keywords: inorganic material; magnesium phosphate chemically bonded ceramics; chemical preparation; liquid-to-solid ratios; biomedical applications200introductionbecause of the excellent adhesive strength and higher early compressive strength, magnesium phosphate chemically bonded ceramics (mpcbc) attracted much attention in the field of hard tissue repair, especially for the use of artificial joints fixation, screw fixation as well as comminuted fracture fixation, etc 1-4. the solidifying process of mpcbc including the25dissolution of acid phosphates (such as nh4h2po4, nah2po4, kh2po4, etc), the release of cations (mg2+), and then po43- reacted with the newly released mg2+ ions. subsequently, themain reaction product of magnesium potassium phosphate hexahydrate (mgkpo46h2o), alsowas called k-struvite, appeared. after that, a coordinated network was formed and consolidated into mpcbc 5-8. obviously, it was necessary of the simultaneous presence of mg2+ and po43-30ions to form the coordinated network. the reaction equation was described as follows 9:- 9 -4mg2+ + po 3-+ k+ 6h2o mgkpo46h2oeq(1)which could be also expressed as follows 10,11:mgo(s) + kh2po4(s) + 5h2o mgkpo46h2o(s)eq(2)it was clear that factors influencing the hydrated process and hydrated products involved35many aspects, such as the raw materials properties, liquid-to-solid (h2o/(mgo+kh2po4) ratios, kinds of liquid, etc. many studies on the influencing factors have been carried out by many researchers 4, 8, 12-14. for example, g. mestres, et al.4 selected nah2po4, nh4h2po4, and the equimolar mixture of both as the raw materials, and studied the change of phase compositions with different raw materials. the results indicated the nh4+-containing mpcbc resulted in40struvite (mgnh4po46h2o) as the major reaction product, whereas mpcbc prepared with nah2po4 resulted in an amorphous product. the effect of water content on the mechanical properties of mpcbc, including compressive strength and elastic modulus were investigated by z. ding, et al 12. the results showed that the mechanical properties of mpcbc were mainlycontrolled by the total porosity which was determined by water content. f. qiao, et al. 8 studiedfoundations: doctoral fund of ministry of education of china (no. 20106118120013)；the natural sciencefoundation of shaanxi province(2012jq6009)brief author introduction:wang ai-juan, (1981-), female, lecture, biomedical materials. e-mail:45the properties of mpcbc with different magnesium to phosphate (m/p) molar ratio. the experimental results showed that the m/p ratio had large influence on the setting time and mechanical properties of mpcbc. the setting time decreased with the raised m/p ratios. besides, as the increase of m/p ratio, the compressive strength of mpcbc increased at first and then decreased. in our previous work, the effect of raw materials properties on the solidifying process50has been carried out13. the results indicated that the setting time increased and the maximum temperature decreased as the decrease of the chemical activity of mgo. besides, the phasecompositions were similar with each other, and mainly composed of mgo and mgkpo46h2o.from above, it could be found that many studies have been carried out on the influencing factors on the properties of mpcbc. as we all known, the temperature variation, setting time,55phase compositions and compressive strength of magnesium phosphate chemically bonded ceramics were important for its application in biomedical field. however, there are relatively few studies on the above properties of mpcbc when it was used as biomedical materials. unlike in construction cements, the cost of the end product is not a major issue when it was used as biomedical materials, but purity and performance of the final product is very important 7.60therefore, the effect of liquid-to-solid ratios on the setting time, temperature variation curves, microstructures, phase compositions and compressive strength of mpcbc were characterized systematically in this article.1material and methodsmedical grade mgo particles (zehui chemical industry group, china) were calcined at 1100,651200, 1300, 1400, 1500 for 3h. chemical reagent kh2po4 particles (beijing kang pu hui wei technology co., ltd, china) were used as the acid compound. deionized water was employed as the solidifying liquid. mgo-to-kh2po4 weight ratio of 1:1 (molar ratio of about 3.4:1) was employed.mgo and kh2po4 particles were mixed by milling for 3h firstly. after that, different amount70of deionized water were added into the premixed powders. stirring was kept all the time untilmpcbc solidified. when the liquid (milliliter)-to-solid (gram) ratio was below than the value of1:4 (that is 1ml liquid and 4g solid), it was difficult to shape. besides, when the liquid-to-solid ratio was higher than the value of 2:3, the solidifying process was carried out slowly and thus caused the flow of the slurry. therefore, based on the workability of mpcbc as chemical bonded75ceramics, the liquid-to-solid ratio was controlled with the value of 1:4, 1:3, 2:5, 1:2, 3:5, 2:3, respectively.all of the samples used to test the setting time and temperature variation were fabricated withthe mixing powders (mgo and kh2po4) weight of 3g. the setting time of mpcbc was determined according to astm c 191 method b with modification using an automatic vicat80apparatus, which was described particularly in ref.15. the temperature variation on the surface of mpcbc was tested using infrared radiation thermometer (irt, fluke 561) in order to indicate the heat release of the reacting process. the surface morphology and microstructure of mpcbc were observed using scanning electron microscope (sem, jsm-6700f) after gold sputtering. the phase compositions of the samples were characterized by x-ray diffraction (xrd, 7000s) using85cu k radiation. the compressive strength was tested with the sample of 611mm usingmechanical tester (ht-2402). the fabricating process of the samples was described as follows. different amount of deionized water were added into the previous mixed powders with the designated liquid-to-solid ratio to form a paste, which was then placed in a glass tube. thesamples were stored at 37 in a 100% humidity box for setting. after 24h, the compressive9095100105110115120125strength was tested. at least 10 samples were used in the mechanical test. the porosity of mpcbc with different liquid-to-solid ratios was tested according to ref. 16, and at least 3 samples were used to detect the porosity.2results2.1 temperature variationirt was used to test the temperature variation of mpcbc, and only the relative changing trends were tested because the influencing factors of absolute temperature were various 7. in order to insure the reliability of the temperature changing trend, 9 samples with different liquid-to-solid ratios and different calcining temperatures of mgo particles were tested. the temperature changing curves were shown in fig. 1. it was obvious that despite of different liquid-to-solid ratios, similar changing trends could be found. all of the temperature changing curves increased firstly, and then decreased gradually. the lower the liquid-to-solid ratio, the higher the maximum temperature was. besides, the time of reaching the maximum temperature value was different from each other. the maximum temperature appeared early for the sample with lower liquid-to-solid ratio.figure 1 temperature changing curves of mpcbc with different liquid-to-solid ratios and mgo calcining temperatures (a) 1100; (b) 1300; (c) 1500.2.2 setting timebesides reacting temperature, the setting time was also key for the application of mpcbc in biomedical field. it should not harden too fast to allow moulding or injection and not harden too slow to allow the surgeon to close the defect shortly after placement 17. for mpcbc, the initial and final setting times are very close 4, and thus only the final setting time was tested in this work. fig. 2 showed the changing curves of setting time. 30 samples with different fabricating process parameters were also tested. it was clear that the setting time increased as the increase of liquid-to-solid ratio. the sample fabricated with the liquid-to-solid ratio of 2:3 and mgo particlescalcined at 1500 had the longest setting time.2.3 phase compositionsfig.3 showed the xrd patterns of mpcbc with different liquid-to-solid ratios. from which, it was clear that the xrd pattern does not contain any peaks other than those of mgkpo46h2o and mgo. this possibly indicated that all of kh2po4 particles took part in the hydrated reaction. the appearance of mgkpo46h2o diffraction patterns indicated that the hydrated product was formed, and it was comparatively phase pure. because of the obvious excess of mgo for the hydrated reaction, the diffraction peaks of mgo were also tested. besides, the diffraction peaks intensity decreased and the peaks width of mgkpo46h2o increased gradually with the decrease of liquid-to-solid ratio, but those of mgo were similar.figure 2 setting time of mpcbc with different liquid-to-solid ratios and mgo calcining temperatures.1301351401452.4 microstructurefig.4 showed the sem micrographs of mpcbc with the liquid-to-solid ratio of 1:3. it was clear that the hydrated reaction was inhomogeneous. a carpet consists of sheet-like protruding structures was found (fig. 4c). studies indicated that the sheet-like products were mainly composed of the crystallized mgkpo46h2o 7, and indicated the relatively complete hydrated reaction. however, the structure with particles dispersed in the based materials could be found in fig. 4a, b obviously. in order to study the reason that caused the difference of the structure, eds of fig. 4 a, b, c were shown in fig. 4 d, e, f, respectively, and the interested fields were also pointed out. it was clear that the atomic ratio (at.%) were similar with each other despite of the difference of the microstructure. compositions of o, mg, p, and k distribute evenly. this possibly implied that the homogeneously mixing of mgo and kh2po4 particles. it still need a further study in order to study the reason caused the difference of the microstructure. besides, numerous cracks were also observed in fig. 4, which were presumably during drying of the hydrated gel-like phase.figure 3 xrd patterns of mpcbc with different liquid-to-solid ratios (a) 1:3; (b) 2:5; (c) 2:3.figure 4 sem micrographs and eds of mpcbc with the liquid-to-solid ratio of (a,d) 1:3; (b,e) 2:5; (c,f) 2:3.1501552.5 compressive strengthfigure 5 showed the compressive strength of mpcbc after solidifying for 24h with different liquid-to-solid ratios. the results indicated that the compressive strength decreased with the increase of liquid-to-solid ratios, which was in accordance with that of f. qiao, 8 and zhu ding, et al 12.3discussionas is known, the dissociation of raw materials is essential in the solidifying process ofmpcbc. it is considered that the ternary system of mgo-kh2po4-h2o is kicked off by the dissociation of kh2po4 when it comes into contact with water during the mixing stage, and thenreleased k+, h+, po4, hpo4and h2po4ions. the resultant acidic environment induced the3-2-160165dissociation of mgo. subsequently, the principal reaction product, mgkpo46h2o, was formed with po43-, k+ and mg2+ ions, and then developed a struvite network 18,19.according to the main hydrate reaction of mpcbc as shown in eq. (1) and (2), the theoretical molar ratio of mgo and kh2po4 for complete mgo consumption was 1:1. an obvious excess of mgo (mgo-to-kh2po4 molar ratio of about 3.4:1) than the required was used in this experiment. however, despite of the excess of mgo particles, the eds results (fig. 4 d, e, f) indicated that the atom ratios were similar with each other (fig. 4 a,b,c). this possibly implied the hydrated product and the excessive mgo distributed evenly. besides, g. mestres, etc. pointed out3-that only the outer rim of mgo could possibly react with po4ions in a very short time because of170the low solubility of mgo during the solidifying process 4. the residual mgo particles were covered by the hydrated products. as a result, the element distributed evenly. the schematic illustration of the forming process of mpcbc is shown in fig.6.figure 5 porosity (a) and compressive strength (b) of mpcbc with different liquid-to-solid ratios (measurementsare expressed as meansd)175180185190195figure 6 schematic illustration of the forming process of mpcbc.the reaction process of mpcbc involved the mixing of mgo and kh2po4, the mixing of the added liquid and previous mixed solid. if mgo and kh2po4 distributed evenly, it could be possible deduced that the difference of the microstructure (fig. 4 a, b, c) was considered to be the unequally mixing between the added liquid phase and the previous mixed powders. if liquid was enough, the hydrated reaction was possibly carried out completely and thus crystallized mgkpo46h2o appeared. on the contrary, amorphous gel appeared. therefore, the decrease of mgkpo46h2o diffraction peak intensity and the increase of peak width (shown in fig. 3) possibly implied the poorly crystallized of the hydrated product fabricated with lower liquid-to-solid ratio.besides, studies indicated that the solidifying process of mpcbc was connected directly with the concentration of mg2+ ions 7. increasing the amount of mgo could raise the ph value of the reaction environment because of the release of oh- ions, and then accelerated the reaction between mgo and kh2po4. much mgo particles caused the rapid reaction rate. there was not enough time for the hydrated product to crystallize before mpcbc solidified. this also caused the structure of mpcbc was inhomogeneous.according eq. (1) and (2), the added liquid was much more than that of joining the hydrated reaction. it was clear that the setting time reduced as the decrease of liquid-to-solid ratio, as shown in fig. 2. as is known the chemical reaction was an exothermic reaction. the superfluous liquid volatilization would take the heat away and thus decreased the hydrate reactive rate. the short setting time implied the rapid hydrated reaction. the hydrated reaction heat released quickly200205210215220225230235240because of the rapid reaction rate, and thus the maximum temperature value was high and the appearing time was short for the sample fabricated with low liquid-to-solid ratio (as shown in fig.1). besides, the net rate of heating of the slurry will depend on the amount of heat dissipated during the ceramic formation. the superfluous liquid volatilization would bring a part of the generated heat out. this also caused the small temperature change.as the bone substitute materials, it is required to provide adequate mechanical support for the defect site. clearly, the liquid-to-solid ratio plays an important role on the compressive strength of mpcbc from fig. 5. the larger the liquid-to-solid ratio, the lower the compressive strength was. this phenomenon was similar with the report of z. ding, et al 12. mpcbc are formed in an aqueous solution, the stability of water is an important consideration. water will decompose andproduce either h2 or o2(eq(3)eq(5), which will result in formation of porous and weak mpcbc 7. besides, the volatilization of excessive water also brought a lot of pores into the solidified mpcbc. therefore, when the liquid was enough to ensure the completely wetted of mgo andkh2po4 powders, the porosity of mpcbc would increase as the increase of liquid-to-s