10.6092/issn.1973-9494/10674
The experimental work described in this paper is aimed at evaluating the possibility of applying microwave heating to a restoration project. The technique involves the application of microwaves to stone surfaces affected by biodeterioration. Results showed that the pests were completely devitalised. The materials chosen for the survey were yellow and grey tuff. Samples of both tuffs were taken in the area of agro nocerino-sarnese and samples of lime mortar and brick were taken from a ruin located in Saint Eustachio (AV). The methodology consists of two phases: in the first, samples of material are placed in a reverberation chamber and treated by varying the parameters of power and exposure time; in the second, they underwent chemical-physical analysis aimed at establishing whether the treatment had induced aesthetic and/or structural alterations. The procedure was performed both on intact samples and on powdered samples for further analysis. Specifically selected and treated samples were subjected to colorimetric analysis, thermogravimetric analysis, of x-ray diffraction, infrared spectroscopy, SEM, and analysis of transport properties and compressive strength. Results from the chemical and structural analyses relating to the samples treated with the protocol showed no differences between the treated and untreated material. The only difference between the two types of material used related to the absorption capacity of water after treatment. From this, it can be deduced that the heating of stone materials using microwaves devitalizes pests, while leaving the substrate unaltered and the microstructure unaffected by any change.
application/pdf
1973-9494
10674
en
Bruno Bisceglia
Conservation Science in Cultural Heritage
structural analysis
Microwave Treatment of Stone Surfaces for the Devitalization of Biodeteriogens
Text.Serial.Journal
https://conservation-science.unibo.it/
19
Articles
2020-03-18
2020-03-17
2020-03-18
2020-04-03
267-282
CSCH
Bruno Bisceglia
2019
10.6092/issn.1973-9494/10674
267
Department of Industrial Engineering, University of Salerno
1973-9494
structural analysis
en
282
Microwave Treatment of Stone Surfaces for the Devitalization of Biodeteriogens
https://conservation-science.unibo.it/article/download/10674/10600
19
M     ICROWAVE TREATMENT OF STONE SURFACES FOR
      THE DEVITALIZATION OF BIODETERIOGENS


   Luigi Guerriero, Margherita Cicala1LFROD&KLDFFKLR       1

   Department of Architecture and Industrial Design
   University of Campania “Luigi Vanvitelli”, Naples, Italy

   Bruno Bisceglia
   Department of Industrial Engineering
   University of Salerno, Italy
   
   
   &RUUHFWHGLQGDWHVHHWKHHUUDWXP
   KWWSVGRLRUJLVVQ
   
   
   
   




   Keywords: disinfestation, pyroclastic lithotypes, stone materials, structural analysis


   1. Introduction

   The state of cultural heritage is increasingly exposed to a continuous risk of bio-
logical degradation caused by the attacks of photosynthetic biodeteriogenic agents
or heterotrophic organisms. The damage caused is both aesthetic and structural,
and requires an innovative, non-invasive cleaning method. Through the controlled
use of microwave (MW) irradiation on stone materials disinfestation is obtained
without altering the original state of conservation and greatly reduces risks for the
operators [1]. This protocol, already proven to be effective on paper, cloth and
wood, was executed on the building materials typical of the architectural tradition
found in the region of Campania. The materials included yellow and gray tuff sam-
ples taken from a natural quarry in the geographical area of the Agro Nocerino-
Sarnese, together with samples of cotto and lime mortar taken from an abandoned
and unused ruin located in Sant’ Eustachio in the area of Avellino (AV) (Figure 1
and 2). The experimentation consisted of exposing portions of pyroclastic litho-
types, infested with biodeteriogens such as molds, mosses, lichens and herba-
ceous vegetation, to microwaves for different lengths of time and using different
power outputs. Analyses were carried out on each individual sample, before and
after exposure, and again after powdering, to ensure uniformity [2].

*1 Corresponding author: nicola.chiacchio@hotmail.it
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       Figure 1. Example of “bozzette” (smaller-sized blocks) masonry of Neapolitan yellow tuff (18th
                                                                                                       century).




                                                                                                                Figure.2. Example of “block” masonry of gray Campanian tuff (19th century).



                                                                                                          This procedure allowed us to establish the basis of a new protocol that included
                                                                                                       colorimetric analysis, thermal analysis, spectroscopic analysis, X-ray diffraction,
                                                                                                       SEM, evaluation of transport properties and compressive strength, so as to guar-
                                                                                                       antee the chromatic and microstructural integrity of the material at the end of the
                                                                                                       cleaning process [3].
                                                                                                          Preserving the authenticity of historical materials is one of the main objectives of
                                                                                                       restoration. It is therefore necessary to ensure their proper conservation using increas-
                                                                                                       ingly innovative methods.
                                                                                                          The aggressiveness of the substances used, treatment times, penetration depth,
                                                                                                       and risks to operators are the limits of the currently available techniques for cleaning
                                                                                                       stone surfaces affected by biodeteriogens, it is therefore necessary to experiment with
                                                                                                       a new protocol that is able to overcome these issues [4].

                                                                                                 268
   The new protocol to which reference is made is microwave cleaning (MW), which
guarantees the cleaning of the material (yellow and gray tuff) without altering the mi-
crostructure of the stone and avoiding direct interaction with the material.
   The tests were carried out on the untreated yellow and gray tuffs from a natural
quarry of the Agro Nocerino-Sarnese, performing the microwave treatment only on
a part of the collected material, so as to be able to compare the material treated with
microwaves with the untreated material.
   The use of this technique on the wall portions of the architectural assets, in general
in stone affected by infestation, proved to be effective thanks to the selective micro-
wave heating based on the dielectric characteristics of the materials, and to act only
on the biological infesting organisms due to the fact they consist mainly of water [5].


  2. Materials and methods

   The methodology used for experimentation on the stone materials consists of two
phases: in the first phase the samples are placed in the reverberating chamber of
the microwave laboratory of the University of Salerno, in the second phase they are
subjected to chemical-physical analyses. This procedure is carried out first on an
intact sample of material, placed in the reverberation chamber and subjected to the
isotropic exposure process. The chamber is an aluminum cube (120 cm in length)
equipped with two stirrers, with rotation modes that work at different speeds (0.4 and
1.1 rps); a magnetron powered by 2.45 GHz, 2 kW CW with a switching power sup-
ply. The system is completed by data acquisition software that measures the incident
and reflected power at the entrance of the chamber. With the obtained data, it was
possible to establish a range of values for the power and exposure time parameters,
which were modified in order to establish whether there are threshold values beyond
which changes in the structure of the stone material are found. This system allows




                                                                                                  CONSERVATION SCIENCE IN CULTURAL HERITAGE
the magnetron to operate at different power levels, from a few watts to 2 kW. Meas-
urement of the incident and reflected power at the input of the reverberation chamber
is performed using a directional coupler. The samples are treated with an incident
power of 400 ÷ 900 W for 60 ÷ 180 s (Figure 3) [6].




                             Figure 3. MW exposure system.


                                                                                            269
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                                                   Figure 4. Grinding of yellow tuff.



                                                                                                          In order to evaluate the chemical composition and the effect of the treatment
                                                                                                       with MW, FT-IR diffraction and X-ray diffraction analyses were performed on both
                                                                                                       the treated and untreated tuff samples, followed by colorimetric analysis to verify
                                                                                                       possible aesthetic alterations, and a water absorption test through full immersion
                                                                                                       and capillary ascent, and uniaxial compression resistance to verify both the trans-
                                                                                                       port properties and the durability of the tuff samples [7].
                                                                                                          The same analyses were then carried out on samples of material reduced to
                                                                                                       a powder form by manual grinding in a mortar and subsequently homogenized to
                                                                                                       guarantee uniformity between the samples (Figure 4).
                                                                                                          The material was then divided into 36 vials and subjected to 4 levels of expo-
                                                                                                       sure cycles of microwave treatment by increasing the power output as follows:
                                                                                                       400W, 500W, 600W, 700W. For each passage at the respective temperatures, 9
                                                                                                       samples were exposed, of which 3 with an exposure time of 60 seconds, 3 with
                                                                                                       an exposure time of 90 seconds and 3 with an exposure time of 120 seconds. The
                                                                                                       samples to be subjected to the irradiation consisted of glass tubes with a total
                                                                                                       weight of 13.5gr, which were labeled and then filled with just over one gram of tuff
                                                                                                       powder (Figure 5).
                                                                                                          The samples were weighed with precision scales to one thousandth of a gram
                                                                                                       before and after the treatment to evaluate the percentage of weight loss. The data
                                                                                                       acquired by the software show the incident and reflected power, evaluated at the
                                                                                                       input of the camera (in correspondence with the waveguide); by comparing these
                                                                                                       data with the previously acquired data, the absorbed power is obtained. After per-
                                                                                                       forming microwave treatment on all the samples, each one was then analyzed
                                                                                                       chemically and physically, to evaluate the triggering of any alteration processes.
                                                                                                       The following investigations were carried out: thermogravimetric analysis (tGa),
                                                                                                       X-ray diffraction, infrared spectrophotometry and differential scanning calorimetry
                                                                                                       (DSC) (Figure 6).




                                                                                                 270
  Figure 5. Reverberating chamber used for the exposure of the tuff samples to microwaves.



    More specifically, the tests performed for both treatments, that is, on the whole
tuff sample and on the powdered tuff sample were:
    X-ray diffraction, which is used to verify the detection of “collapses” of the crys-
talline phases in amorphous phases; this is a process in which an X-ray beam,




                                                                                                   CONSERVATION SCIENCE IN CULTURAL HERITAGE
incident on a crystal sample, is diffused by the electrons of the latter (scattering
process). From the study of the angular distribution of the diffracted radiation we
go back to the shape, the size and the orientation of the elementary cell.
    X-ray diffraction is commonly realized with samples consisting of microcrystal-
line powder of the material, in which the image produced by X-ray diffraction is
recorded and analyzed to reveal information on the nature of the lattice and on
any components in a mixture of polycrystals. The ground sample is placed on
the support and inserted into the diffractometer. This instrument consists of two
arms: on one arm is the source from which the x-ray beam is sent; on the other is
mounted the counter which, by rotating, reveals the diffracted rays. These rays,
once captured, are processed by a computer. The image returned by the software
is a diffractogram characterized by a series of peaks, each of which represents the
diffraction event. The height of the peaks is directly proportional to the intensity of
the diffracted radiation. The analyses were carried out using a Bruker D8 advance
diffractometer and then comparing the results of the untreated tuff with those of
the same material subjected to the various treatments.




                                                                                             271
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       Figure 6. a) Gray tuff infested with lichens before the treatment with MW; b) gray tuff infested with
                                                                                                       lichens after the treatment with MW.



                                                                                                           Thermogravimetric analysis, which is useful to evaluate the processes resulting
                                                                                                       from the heating suffered by an element for which the mass variation is constantly
                                                                                                       recorded. Depending on the temperature of the sample under examination it is
                                                                                                       possible to identify the chemical-physical processes it has undergone. In fact, for
                                                                                                       each element, by virtue of the weight loss and the corresponding temperature, it
                                                                                                       is possible to identify the transformation it has undergone (evaporation of water,
                                                                                                       dissociation of compounds, oxidation processes, etc.). These data are expressed
                                                                                                       by a thermogram (tGa curve) which shows the temperature or time on the x-axis,
                                                                                                       and the weight variation on the y-axis (Figure 7).
                                                                                                           For tuff, as in general for inorganic materials, the water present can be clas-
                                                                                                       sified in relation to the interaction with the structure: free water, hydration water,
                                                                                                       crystallization water or strongly bound water. The instrument used for thermal
                                                                                                       analysis consists of a microbalance, a gas purge system that guarantees an inert
                                                                                                       environment, the furnace that can be heated up to 1000 °C, and a data acquisition
                                                                                                       and processing system. The gas usually used to control the atmosphere around
                                                                                                       the sample is nitrogen, which prevents oxidation processes (which could cause a
                                                                                                       weight variation). Before carrying out the analyses, the capsules are previously
                                                                                                       cleaned in a flask at 1000 °C, then inserted into the thermo-gravimetric cell and the
                                                                                                       calibration process is carried out. The analyses were performed using a Netzsch
                                                                                                       thermal analyzer, and nitrogen was used as purge gas. During the test the sample
                                                                                                       was equilibrated at a temperature of 20 °C and heated to a final temperature of
                                                                                                       600 °C, with a heating rate of 10 °C per minute [8].




                                                                                                 272
Figure 7. a) Overlap of thermogravimetric profiles of yellow tuff samples treated and not treated
with microwaves at the power of 400 W with corresponding magnification; b) exposure times are
shown in brackets.



   Infrared spectrophotometry, which is an analytical technique used for the identi-
fication of organic and, in some cases, inorganic materials; it allows information to
be obtained on the functional groups of the molecules of the analyzed substance
[9]. The FTIR technique (Fourier Transform Infrared Spectroscopy) measures the
wavelength range of the infrared spectrum that is absorbed by the material. The
absorption of the infrared radiation produces in the molecules some characteristic
vibrational motions, defined as stretching and bending. The stretching is the result
of the continuous variation of the bond distances between two atoms and can be
symmetric or asymmetric; the bending, on the other hand, refers to the modifica-




                                                                                                          CONSERVATION SCIENCE IN CULTURAL HERITAGE
tion of the binding angle on the same plane or outside the plane on which the
angles are considered. The amount of energy needed to produce each vibrational
motion depends directly on the strength and polarity of the bonds between the
atoms of the analyzed molecule. The test consists in subjecting the sample to an
electromagnetic radiation that interacts with the matter. In the case of solid sub-
stances, it is necessary to reduce the material to a powder and arrange a quantity
equal to about 5 mg in a small mortar; the sample is then homogenized with KBr
up to an amount of 100 mg. The resulting sample is placed in a special holder,
which must then be pressed to obtain a disk with a thickness of a few μm. To be
analyzed, it is inserted into a metal support with a suitable hole. Before testing the
material, the empty support must be inserted as a reference for the analysis. The
recognition of substances by analysis is often based on the comparison of the test
spectrum with that of known substances or with spectra reported in the literature
(Figure 8) [10].




                                                                                                    273
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       Figure 8. Superimposition of WAXD diffractograms of yellow tuff samples treated with microwaves
                                                                                                       at the power of 400 Watt; exposure times of the samples are shown in parentheses (LEGEND:
                                                                                                       deg= Temperature degrees; a.u.= Arbitrary Unit; s= Seconds).

                                                                                                          Differential scanning calorimetry is a thermal analysis which, together with thermo-
                                                                                                       gravimetric analysis, provides information on some physical properties of a sample
                                                                                                       subjected to a controlled thermal cycle. Differential scanning calorimetry (DSC) allows
                                                                                                       information to be obtained on some physical properties of a sample subjected to a con-
                                                                                                       trolled thermal cycle, providing information on the heat reaction of the material. This in-
                                                                                                       formation is taken from a differential measurement of the thermal flux between the test
                                                                                                       sample and a reference sample. In fact, when the sample undergoes an endothermic
                                                                                                       process (heat absorption), the system must provide a higher quantity of heat in order to
                                                                                                       maintain the same temperature, equal to that of the reference sample. Before carrying
                                                                                                       out the test, the sample is placed in a crucible, net weighed up to the fourth decimal
                                                                                                       digit, and closed using a small press. It is then inserted into the analysis instrument
                                                                                                       together with an empty crucible that will serve as a reference for the differential meas-
                                                                                                       urement. Three “lids” then allow to hermetically insulate the test cell from the outside.




                                                                                                       Figure 9. Overlap of IR spectra of yellow tuff samples treated and not treated with MW. The
                                                                                                       power of the treatment is 400 Watt; the exposure times are shown in parentheses (LEGEND:
                                                                                                       Wave number= intensity of the waves expressed in cm; Absorbency= absorbency of the material
                                                                                                       expressed in arbitrary unit; s= Seconds).


                                                                                                 274
   A continuous and uniform flow of nitrogen is created inside the furnace, which avoids
any oxidation which could distort the result. During the test, the heat given off by the
furnace heats both the sample and the reference crucible in the same way, therefore
any variation in temperature between the two is due to phenomena that arise in the
material to be analyzed: there will be a rise in temperature due to exothermic reactions
or a lowering due to endothermic reactions.
   Throughout the whole experiment, a thermocouple-based system collects the tem-
perature data and sends it to a computer where it is processed, generating output us-
ing a special software (Figure 9-10) [11].


  3. Results and discussion

    The results of the analyses obtained by comparing the treated and the untreated
material, in the form of “pieces” and “powder”, showed that in both cases there were
no changes in the structure of the material as a result of the microwave treatment. For
the experimentation, several treatment cycles were carried out, progressively increas-
ing the incident power and the exposure time. In this way we tried to show whether by
making the treatment more “aggressive” there were structural alterations in the mate-
rial. The results of the analysis obtained from the comparison between the treated
and the untreated material showed that after the microwave treatment there were no
changes in the structure (Table 1) [12].




                                                                                                 CONSERVATION SCIENCE IN CULTURAL HERITAGE




Figure 10. Overlap of DSC thermograms of treated and non-microwaved tuff samples with a
power of 400 W (exposure times are shown in parentheses).




                                                                                           275
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       Figure 11. a) Curves of water capillary rise vs square root of time relative to yellow tuff; b) grey tuff.



                                                                                                       Table 1. Comparative analysis (grey and yellow tuff).




                                                                                                           In particular:
                                                                                                           − the thermogravimetric analysis showed that when the parameters increase, the
                                                                                                       tuff loses a certain amount of water, mostly free and weakly bound water that does not
                                                                                                       influence the part linked to the structure of the material (Figure 11);
                                                                                                           − the differential scanning calorimetry, used to complete the results of the TGA,
                                                                                                       confirms that water loss corresponds to those of free and weakly bound molecules;
                                                                                                       the colorimetric analysis shows that no perceptible chromatic alterations or aesthetic
                                                                                                       modifications occurred;


                                                                                                 276
    − the X-ray diffraction showed perfectly overlapping spectra and therefore no altera-
tion of crystalline phases; the infrared spectrophotometry confirmed that there is no
alteration of the structure;
    − the transport properties relative to the treated gray tuff presents an increase in
water transport properties, but not to a significant extent as in the case of the yellow
tuff (Table 2-3);


Table 2. Power-Time Parameters graphic (700 W-180 s).




                                                                                                  CONSERVATION SCIENCE IN CULTURAL HERITAGE
Table 3. Power-Time Parameters graphic (500 W-600 s).




                                                                                            277
                                                                                                           It can be observed that, according to the results of the previous experiments,
                                                                                                       there are no effects that lead us to believe that microwaves damage the tuff (Figure
                                                                                                       12). It is important to underline the difference in the “state” of the material exposed
                                                                                                       in the chamber: in the first case, “pieces” of stone were treated, while in the second
                                                                                                       case, samples of tuff dust were exposed inside vials. This could lead one to think
                                                                                                       that, given the porous nature of the material, there may be different responses to
                                                                                                       increasing power outputs. Although temperature readings were taken during the
                                                                                                       control of the MW material, due to the limits of the instrumentation it is not possible
                                                                                                       to arrive at an accurate treatment; thus, the temperature reached during the inter-
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       vention is not known. This data could have better defined the possible transforma-
                                                                                                       tions suffered by the material, because at certain temperatures some components
                                                                                                       of the tuff collapse [13].




                                                                                                       Figure 12. FT IR spectra of tuff sample: a) Gray tuff: 700 W, 9 min; b) Yellow tuff: 500 W, 3 min.




                                                                                                 278
      4. Conclusion

    The present paper has examined a detailed range of analyses that supports the
fact that the absence of structural changes in the yellow and gray tuff show that mi-
crowaves do not cause any damage. It can be concluded that the heat treatment of
stone materials with microwaves effectively devitalizes pests, while the substrate of
the material in question remains unchanged. This technique therefore avoids direct
interaction with the tuff and does not modify its microstructure.
    It would therefore be interesting to consider this technique as a possible solution in
the disinfestation of architectural assets, as it aims to verify the feasibility of the method
for disinfesting biodeteriogens from stone cladding (yellow tuff, gray tuff) both to pre-
serve the chemical-structural integrity of the material, and to reduce exposure times
and risks associated with the use of toxic substances. It also guarantees complete
control of all operations by the operator. It is evident that the results obtained change in
virtue of the material subjected to irradiation, therefore this arises as a first study from
which an interesting research field for architectural restoration could develop.


      Acknowledgements

   E. Avallone M.D. and E. Caliendo M.D. Department of Industrial Engineering, Uni-
versity of Salerno, Italy, for support in reengagement of surveys; F. Chiadini M.D. and
A. Scaglione M.D Department of Industrial Engineering, University of Salerno, Italy, for
support in the microwave treatment; A. Fondacaro M.D. and L. Incarnato M.D. Depart-
ment of Industrial Engineering, University of Salerno, Italy, for their scientific contribu-
tion in the surveys.




                                                                                                       CONSERVATION SCIENCE IN CULTURAL HERITAGE
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                                                                                                             Biographical notes

                                                                                                          Luigi Guerriero graduated in Architecture; he has a Ph.D. in Conservation of Ar-
                                                                                                       chitectural Heritage. Since 2000 he has been an associate professor of Restoration
                                                                                                       at the Faculty of Architecture of the II University of Naples. He has organized and
                                                                                                       directed research groups and coordinated national scientific initiatives. He has been
                                                                                                       a member on the scientific council for national meetings and exhibitions. His research
                                                                                                       concerns the theories and history of restoration, particularly regarding the protagonists
                                                                                                       and interventions of the mid-twentieth century, the mensiochronologic characterization
                                                                                                       of traditional constructive elements, with the related protocols for the analysis of de-
                                                                                                       terioration and of structural modeling and urban restoration methods and techniques.

                                                                                                           Margherita Cicala obtained a magna cum laude for the title of doctor at the Univer-
                                                                                                       sity of Architecture of the II University of Naples.

                                                                                                          Nicola Chiacchio obtained the title of doctor at the University of Architecture of
                                                                                                       the II University of Naples. He collaborates on research projects for Snecs (Social
                                                                                                       Network of the Historical Center Entities) and Chis (Cultural Heritage Information


                                                                                                 280
System) of the Consortium Databenc Research Unit ICAR19-restoration active at
the ICT center in the University of Salerno. He also collaborates with numerous pro-
fessional firms, specializing in the field of architectural restoration and the recovery
of historical centers and rural areas, especially in the 3D modeling of buildings of
historical and artistic value.

   Bruno Bisceglia graduated in Electronic Engineering in 1984 and was appointed
Assistant Professor of Electromagnetics in 1988. In 1989 he joined the Society of
Jesus, and in 1996 was ordained priest. After graduating in Fundamental Theology
in 1996, he defended his Doctoral thesis in Theology in 2002. He has been Adjunct
Professor of Bioelectromagnetic Interaction in the University of Sannio at Benevento
and Adjunct Professor of Electromagnetic Pollution and Risk Management and Mobile
Communication in the University of Salerno.


    Summary
    The experimental work described in this paper is aimed at evaluating the possibility
of applying microwave heating to a restoration project. The technique involves the ap-
plication of microwaves to stone surfaces affected by biodeterioration. Results showed
that the pests were completely devitalised. The materials chosen for the survey were
yellow and grey tuff. Samples of both tuffs were taken in the area of agro nocerino-
sarnese and samples of lime mortar and brick were taken from a ruin located in Saint
Eustachio (AV). The methodology consists of two phases: in the first, samples of mate-
rial are placed in a reverberation chamber and treated by varying the parameters of
power and exposure time; in the second, they underwent chemical-physical analysis
aimed at establishing whether the treatment had induced aesthetic and/or structural
alterations. The procedure was performed both on intact samples and on powdered
samples for further analysis. Specifically selected and treated samples were subjected




                                                                                                    CONSERVATION SCIENCE IN CULTURAL HERITAGE
to colorimetric analysis, thermogravimetric analysis, of x-ray diffraction, infrared spec-
troscopy, SEM, and analysis of transport properties and compressive strength. Results
from the chemical and structural analyses relating to the samples treated with the
protocol showed no differences between the treated and untreated material. The only
difference between the two types of material used related to the absorption capacity
of water after treatment. From this, it can be deduced that the heating of stone materi-
als using microwaves devitalizes pests, while leaving the substrate unaltered and the
microstructure unaffected by any change.


   Riassunto
   Il lavoro di sperimentazione illustrato è atto a valutare la possibilità di applicare il
riscaldamento a microonde, nel progetto di restauro. La tecnica consiste nell’applica-
zione delle microonde di superfici lapidee interessate da biodeteriogeni. Tale metodo,
ha mostrato come vi sia una completa devitalizzazione dell’infestante. I materiali scelti
per l’indagine sono campioni di tufo giallo e tufo grigio prelevati nell’area geografica
dell’agro nocerino-sarnese e campioni di malta di calce e cotto prelevati da un rudere
ubicato a S. Eustachio (AV). La metodologia consta di due fasi: nella prima i campioni
di materiale vengono posti nella cavità riverberante e trattati variando i parametri po-
tenza e tempo di esposizione; nella seconda gli stessi vengono sottoposti ad analisi


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                                                                                                       di natura chimico-fisica, volte a stabilire se il trattamento avesse indotto alterazioni
                                                                                                       estetiche e strutturali. Tali processi sono stati eseguiti sia su campioni integri che su
                                                                                                       campioni ridotti in polvere per un’analisi più capillare. Nello specifico i campioni sele-
                                                                                                       zionati e trattati, sono stati sottoposti ad analisi colorimetrica, termogravimetrica, ana-
                                                                                                       lisi di diffrazione di raggi X, spettroscopia infrarossa, SEM, e l’analisi delle proprietà di
                                                                                                       trasporto e della resistenza a compressione.
                                                                                                           Dalle analisi chimico-strutturali relative ai campioni trattati con il protocollo non
                                                                                                       emergono differenze del materiale trattato rispetto al materiale tal quale, l’unica dif-
                                                                                                       ferenza sostanziale tra le due tipologie di materiale adoperato è relativa alla capacità
N. Chiacchio et al. - Microwave treatment of stone surfaces for the devitalization of biodeteriogens




                                                                                                       di assorbimento d’acqua dopo il trattamento. Se ne deduce che il riscaldamento me-
                                                                                                       diante esposizione a microonde di materiali lapidei devitalizza l’infestante, lasciando
                                                                                                       inalterato il substrato e non apportando modifiche della microstruttura.




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