Keramičko inženjerstvo — разлика између измена

=== Mikrostrukturna uniformnost ===
 
InPri the processing ofobradi fine ceramicskeramike, theneregularne irregularveličine particlečestica sizesi andoblici shapesu intipičnom aprahu typicalčesto powderdovode oftendo leadnejednakih tomorfologija non-uniformpakovanja packingšto morphologiesrezultira that result in packingpromenom [[densitygustina|gustine]] variationspakovanja inu thekompaktiranom powder compactprahu. UncontrolledNekontrolirana [[Flocculation|agglomerationaglomeracija]] ofpraha powderszbog due to attractiveatraktivnih [[van der Waals forces]]|van cander alsoValsovih sila]] givetakođe risemože toda instvori microstructuralmikrostrukturne inhomogeneitiesnehomogenosti.<ref name="A">{{cite book
|editor1=Onoda, G.Y. Jr. |editor2=Hench, L.L. |title= Ceramic Processing Before Firing|publisher=Wiley & Sons|place=New York
|year=1979
}}</ref>
 
Diferencijalni naponi koji nastaju kao rezultat neravnomernog skupljanja tokom sušenja direktno su povezani sa brzinom kojom se [[rastvarač]] može ukloniti i stoga zavise od distribucije poroznosti. Takvi naponi su povezani sa prelaskom iz plastičnog u krhko stanje u konsolidovanim telima<ref name="C">{{cite journal
Differential stresses that develop as a result of non-uniform drying shrinkage are directly related to the rate at which the [[solvent]] can be removed, and thus highly dependent upon the distribution of porosity. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies,<ref name="C">{{cite journal
|author1=Franks, G.V. |author2=Lange, F.F.
|title=Plastic-to-Brittle Transition of Saturated, Alumina Powder Compacts
|doi=10.1111/j.1151-2916.1996.tb08091.x
|issue=12
}}</ref> i mogu dovesti do širenja pukotina u nerastopljenom telu, ako se ne otklone.
}}</ref>
and can yield to [[crack propagation]] in the unfired body if not relieved.
 
InPored additiontoga, anybilo fluctuationskakve influktuacije packingu densitygustini inpakovanja theu compactkompaktima asdok itse ispripremaju preparedza forpeć thečesto kilnse arepojačavaju oftentokom amplifiedprocesa duringsinterovanja, the sintering process,što yieldingrezultira inhomogeneousnehomogenim densificationzgušnjavanjem.<ref name="D">{{cite journal
|author=Evans, A.G. |author2= Davidge, R.W.
|title=Strength and fracture of fully dense polycrystalline magnesium oxide
|year=1970
|bibcode = 1970JMatS...5..314E |doi = 10.1007/BF02397783
|issue=4 }}</ref> Pokazano je da neke pore, i drugi strukturni [[Crystallographic defect|defekti]] povezani sa varijacijama gustine, imaju štetnu ulogu u procesu sinterovanja tako što rastu i na taj način ograničavaju gustinu krajnjih tačaka.<ref name="F">{{cite journal
|issue=4 }}</ref>
Some pores and other structural [[Crystallographic defect|defect]]s associated with density variations have been shown to play a detrimental role in the sintering process by growing and thus limiting end-point densities.<ref name="F">{{cite journal
|author=Lange, F.F.|author2=Metcalf, M.
|title=Processing-Related Fracture Origins in Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> Composites II: Agglomerate Motion and Crack-like Internal Surfaces Caused by Differential Sintering
|doi=10.1111/j.1151-2916.1983.tb10069.x
|issue=6
Differential}}</ref> stressesZa arisingdiferencijalne fromnapone inhomogeneouskoji densificationnastaju havepri alsonehomogenom beenzgušnjavanju showntakođe toje resultpokazano inda therezultiraju propagationu ofširenju internalunutrašnjih crackspukotina, thustako becomingda thepostaju strength-controllingnedostaci flawskoji ograničavaju jačinu.<ref name="G">{{cite journal|author=Evans, A.G.|journal=J. Am. Ceram. Soc.|volume=65|page=497|year=1987|doi=10.1111/j.1151-2916.1982.tb10340.x|title=Considerations of Inhomogeneity Effects in Sintering|issue=10}}</ref>
}}</ref>
Differential stresses arising from inhomogeneous densification have also been shown to result in the propagation of internal cracks, thus becoming the strength-controlling flaws.<ref name="G">{{cite journal|author=Evans, A.G.|journal=J. Am. Ceram. Soc.|volume=65|page=497|year=1987|doi=10.1111/j.1151-2916.1982.tb10340.x|title=Considerations of Inhomogeneity Effects in Sintering|issue=10}}</ref>
 
Stoga je poželjno da se materijal obrađuje na takav način da je fizički ujednačen u pogledu raspodele komponenati i poroznosti, pre nego da se koristi raspodela veličina čestica koje će maksimizirati gustinu. Sadržaj ravnomerno dispergovanog sklopa čestica koje imaju snažne interakcije u suspenziji zahteva potpunu kontrolu nad interakcijama među česticama. [[Dispersity|Monodisperzni]] [[koloid]]i pružaju tu mogućnost.<ref name="J">{{cite journal
It would therefore appear desirable to process a material in such a way that it is physically uniform with regard to the distribution of components and porosity, rather than using particle size distributions which will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over particle-particle interactions. [[Monodisperse]] [[colloid]]s provide this potential.<ref name="J">{{cite journal
|author=Mangels, J.A. |author2= Messing, G.L.
|title=Microstructural Control Through Colloidal Consolidation
}}</ref>
 
MonodisperseNa powdersprimer, monodisperzni ofpraškovi colloidalkoloidnog [[silica|silike]], forse example,mogu maydovoljno thereforestabilizovati beda stabilizedse sufficientlyobezbedi tovisok ensurestepen auređenosti high degree of order in theu [[colloidalColloidal crystal|koloidnom kristalnom]] orili polycrystallinepolikristalnom colloidalkoloidnom solidčvrstom whichmaterijalu resultskoji fromnastaje aggregationagregacijom. The degree of order appears toStepen beuređenosti limitedje byograničen thevremenom timei andprostorom spacekoji allowedsu fordozvoljeni longer-rangeza correlationsuspostavljanje tokorelacija bevećeg establisheddometa.<ref name="K">{{cite journal|author=Whitesides, G.M.
|title=Molecular Self-Assembly and Nanochemistry: A Chemical Strategy for the Synthesis of Nanostructures
|journal=Science
}}</ref><ref name="L">{{cite journal|author=Dubbs D. M |author2= Aksay I.A.|title=Self-Assembled Ceramics|journal=Annu. Rev. Phys. Chem.|volume=51|year=2000|doi=10.1146/annurev.physchem.51.1.601|pmid=11031294|bibcode=2000ARPC...51..601D|pages=601–22 }}</ref>
 
Takve defektivne polikristalne koloidne strukture su osnovni elementi submikrometarske koloidne [[materials science|nauke o materijalima]], i samim tim, pružaju prvi korak u razvoju rigoroznijeg razumevanja mehanizama koji su uključeni u mikrostrukturnu evoluciju u neorganskim sistemima kao što je polikristalna keramika.
Such defective polycrystalline colloidal structures would appear to be the basic elements of submicrometer colloidal [[materials science]], and, therefore, provide the first step in developing a more rigorous understanding of the mechanisms involved in microstructural evolution in inorganic systems such as polycrystalline ceramics.
 
== Reference ==