كليدواژه :
مواد تاريخي بر پايه‌ي گچ , بلورشناسي , فن شناسي , آسيب شناسي , XRD , SEM
چكيده فارسي :
پژوهش و شناخت آثار تاريخي گچي در ايران دو مشكل فني و واژه شناسي دارد. مشكل فني موضوع اين مقاله، عموماً ناشي از شناخت خصوصيات بلور گچ، هم چون تغييرات حلاليت يا شكل بلوري در اثر حضور مواد افزودني يا تغييرات محيطي است. در اين مقاله 3 نمونه‌ي تاريخي جمع آوري شده از كوه خواجه‌ي سيستان، قلعه الموت قزوين و شادياخ نيشابور، و 3 نمونه‌ي مدلسازي شده‌ي جديد با توجه به ريزساختار بلوري آن ها بررسي مي‌شود. آزمايش XRD حضور فاز غالب انيدريت (CaSO4) را براي هر دو لايه‌ي گچ بري كوه خواجه نشان مي‌دهد؛ در حالي كه ملات مربوط به شادياخ داراي فاز غالب ژيپس (CaSO4.2H2O) است. پس از تشخيص عدم حضور ماده‌ي افزودني آلي در نمونه هاي تاريخي با روش سوختن تر، از هر نمونه تصاوير SEM تهيه شد. اين تصاوير در تشخيص كيفي شكل بلورهاي گچ، كنارهم نشيني آ ن ها در ريزساختار نمونه هاي مختلف و سنجش فشردگي ريزساختار بلوري آن ها به كمك نرم‌افزار پردازش تصوير به‌صورت كمّي كمك مي‌كنند. در تصاوير SEM تهيه شده از دو لايه‌ي گچ بري كوه خواجه، بلورهاي منوكلنيك ژيپس ديده نمي‌شوند و ملات هاي گچ شادياخ و قلعه الموت نيز فقط ساختاري فشرده را نشان مي‌دهند؛ در حالي كه در نمونه‌هاي مدلسازي شده، بلورهاي گچ به‌وضوح قابل شناسايي هستند. نتيجه‌ي اين مشاهدات بيان مي‌كند كه هرچند استفاده از تصاوير SEM و تحليل بصري يا پردازش تصويري آن ها، نتايج ارزشمندي در بررسي و شناسايي ريزساختار مواد تاريخي گچي دارند، اما نتايج آن ها بايد در كنار آزمايش XRD و پس از تشخيص حضور يا عدم حضور ماده ي افزودني آلي، تفسير و بررسي شوند.
چكيده لاتين :
Investigation of gypsum-based historical materials has two main problems: philological problems and
technical issues. Technical issues, the main topic of this article, are normally consequences of
physicochemical complexity of gypsum crystals in different conditions and variety of additives or
mixed materials. Neglecting this technical problem, leads researchers to misunderstand or misinterpret
these materials. Moreover, exclusively use of one analytical method, such as scanning electron
microscope or X-ray fluorescence, provides an incomplete picture of samples that regularly produces
further misunderstanding of specimen or its history. The methodology of this study is a multianalytical
approach via XRD, SEM and using image analysis software on electron photomicrographs
to estimate amount of free spaces in microstructure of samples. A group of three experimental
samples were made from traditional recipes of craftsmen in Iran, in order to make a connection
between philological problems came from tradition, and technical problems came from mineralogical
property of gypsum. Gach-e Tiz, or quick setting mortar shows a very dense microstructure in SEM
micrographs. Variety sizes of monoclinic crystals of gypsum are present in it, and moreover some
shapeless and bulky regions are also visible. Gach-e Kam-Mayeh, or low setting mortar reveals a much
more open microstructure than the former one, filled with needle like crystals and a lot of micro
porosity between crystals. There is no evidence of bulky forms area in Gach-e Kam-Mayeh. Gach-e
Koshteh, or mechanical low-setting mortar which is a traditional Iranian recipe, shows a parallel layers
of laminar gypsum crystals setting upon each other. This form also demonstrates no evidence of
bulky regions. Historical samples were collected from a stucco decoration belong to Kuh-e Khwaja of
Sistan; a gypsum mortar fragment from Shadyakh, Neyshabur and a piece of gypsum mortar from
Alamut castle of Qazvin. The results of XRD show that both layers of Kuh-e Khwaja stucco contain
anhydrite as the major phase and the sample of Shadiyakh mostly composed of Gypsum. Organic
materials extractions represent no evidence of organic additive to this historical materials. Therefore
the images of their microstructure are comparable with experimental samples that made without any
additive. Lower layer of Kuh-e Khwaja’s stucco shows a lot of tiny crystals that are not very look like
gypsum, but precipitated on the surface of bigger and deformed crystals. The microstructure of it is
very open and include big amount of micro porosity in compare with other samples. Upper layer of
this stucco shows not any form of gypsum crystals but very disturbed flaked shapes, supposedly
gypsum crystals transformed to anhydrate. The micrographs of Shadiyakh’s mortar also reveal not any
clear form of gypsum crystals but base on XRD result it still as gypsum materials. This sample
contains mostly from that bulky and dense structure which shows the usage of low amount of water
for its paste. The results of image analysis on electron micrographs at magnification of ×250 and
×500 provide a good and comparable estimation for free space evaluation in the micro structure of
gypsum based materials. The combination of these techniques and methods lead to better
understanding of gypsum based historical materials.
