Endodontide kullanılan nikel–titanyum esaslı kullanılmış döner diş eğelerinden metalik değerlerin geri kazanımı
Recovery of metallic values from disposed nickel–titanium rotary endodontic files
Yazar: MUHAMMED İHSAN ÖZGÜN
Danışman: PROF. DR. MAHMUT ERCAN AÇMA ; DR. ÖĞR. ÜYESİ YASİN RAMAZAN EKER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Hidrometalurji = Hydrometallurgy ; Malzeme üretimi = Material production ; Üretim metalurjisi = Production metallurgy

Özet:
Nikel – titanium esaslı alaşımlar, endodontide diş kanal tedavisinde kanal eğesi
olarak yaygın bir şekilde kullanılmaktadır. Diş kanal tedavisinde Ni – Ti
alaşımlarının tercih edilmesinin başlıca sebepleri; yüksek mukavemet göstermeleri,
biyo uyumlu olmaları, yüksek korozyon dayanımına sahip olmaları, süper elastiklik
gösterebilmeleri ve şekil hafızalı özellik kazandırılarak tekrarlı kullanılabilen bir
ürün haline getirilebilmeleridir. Ülkemizde ve dünyada, endodontide Ni – Ti alaşımı
döner diş eğeleri ile tedavi sistemleşmiş bir hal almıştır. Tek bir dişin tedavisi bile
farklı tip ve boylarda Ni – Ti alaşımı eğeler yardımı ile gerçekleştirilmektedir. Diş
kanal tedavisinde Ni – Ti alaşımının her bir eğe için bir veya iki kullanımlık olması
önerilmektedir. Ancak sterilizasyon yapılsa bile eğelerde meydana gelen aşınma,
eğenin aşındırma kabiliyetini kaybetmesine sebep olmakta ve tekrarlı kullanımı
sınırlandırmaktadır. Ni – Ti alaşımı döner diş eğeleri sınırlı kullanımlarından sonra
tıbbi atıklarla birlikte toplanmakta ve bilinen bir metalurjik kazanım sürecine tabi
tutulmamaktadır.
Ülkemizde yılda iki milyona yakın kanal tedavisi yapılmakta olup, bu kanal
tedavilerinin % 80'inde Ni – Ti alaşımı döner diş eğelerinin kullanıldığı Türkiye
Cumhuriyeti Sağlık Bakanlığı'nca rapor edilmiştir. Bu eğeler, ağırlıkça % 55 – 60
nikel ile % 40 – 45 titanyum içermektedir. Tutucu kısımları, çok defa pirinç
alaşımdan imal edilmekte olup ağız florasında korozyona maruz kalmaması için altın
ile kaplanmıştır. Ni – Ti alaşımı uç kısımlar nikel ve titanyum kaynağı olarak
değerlendirilebilecek niteliktedir. Altın ve nikel kaplamalı pirinç alaşımı tutucu
kısmın geri kazanımı da dahil edildiğinde, bu işlemin geri kazanım maliyetini
düşürmesi beklenebilir.
Bu tez kapsamında döner diş eğesi olan, nikel ve titanyum esaslı uç kısmının, derişik
asitte çözme, sülfürik asitte pişirme ve karıştırmasız otoklav ortamında derişik
sülfürik asitte çözme gibi yüksek korozif ortamlarda, farklı liç teknikleri ile
hidrometalurjik olarak geri kazanımı sağlanmaya çalışılmıştır. Liç işlemlerinde asit
konsantrasyonu, sıcaklık ve süre parametreleri incelenmiştir. Bu yöntemler
içerisinden tam çözünme veriminin sağlandığı, otoklav ortamında derişik sülfürik
asitte liç işlemi için optimizasyon yapılmıştır. Geri kazanım sonunda kostik soda
(NaOH) ile pH ayarlaması yapılarak Ti(OH)4 ve Ni(OH)2 elde edilmiş, dehidratasyon
ile birlikte NiO ve TiO2 (anatas) fazlarına ulaşılmıştır.
Altın ve nikel kaplamalı pirinç alaşımından imal edilen tutucu kısım ise nitrik asit
ortamında ısıtılarak liç edilmiş, altından gayrı metallerin tamamına yakını çözelti
ortamına alınarak altın kaplama, alaşımdan ayrılmıştır. Altından gayrı metaller,
kostik soda ile pH ayarlaması yapılarak çöktürülmüş ve çöken metal hidroksitlerin
katı / sıvı ayrımı yapıldıktan sonra dehidratasyon ile su molekülleri yapıdanxxii
uzaklaştırılarak, CuO, ZnO elde edilmiştir. Altın ve nikel kaplamalı pirinç alaşımı
tutucu kısmın Ni – Ti alaşımı uç ile beraber geri kazanımı, bu konuda tasarlanacak
geri kazanım sürecini daha da cazip hale getirilmiştir.

Abstract:
Endodontics is a branch of dental medicine that deal with dental problems that
advanced to tooth pulp. The first aim of endodontic treatment is prevent tooth losses.
Whatever tooth disease, endodontic treatment can be result in tooth saving. Before
the widespread use of nickel-titanium alloys in endodontics, stainless steel rotary
files are used for endodontic root canal treatment. Stainless steel rotary file is not
elasticity as Ni – Ti rotary file in curved tooth root canal. However, 20 percent of
rotary files is made of stainless steel. Nickel – titanium based alloys are used for
endodontic root channel treatment as rotary files. Due to their flexibility, strength
and bio-compatibility nickel- titanium based superalloys are widely used for dental
canal treatment. Moreover, these alloys are high corrosion resistance materials. and
show super elasticity and shape memory behavior.
In a tooth canal treatment, one endodontic Ni – Ti rotary file may be used several
times. It is suggested that Ni – Ti rotary files should be used just once by endodontic
authorities. Although, after adequate sterilization, Ni – Ti rotary files use several
times, abrasion loss of these files obstacle to further use. Nickel – titanium based
endodontic rotary files are disposed together with medical wastes. Ni – Ti rotary file
disposes are not recovered metallugically. In Turkey, number of endodontic root
canal treatments is done around 2 million per year, among them % 80 used Ni – Ti
rotary files.
Elimination of oxides is necessary for titanium melting and elemental accumulation
changes nickel –titanium based alloys' properties. Nickel – titanium based alloys are
produced with very pure raw materials and also production methods, like Vacuum
Arc Remelting (VAR) or Vacuum Induction Melting (VIM) is expensive. Due to
their reduced size the volume / surface ratio of Ni – Ti rotary files are suitable for
oxidation. The oxide layer, disposed Ni – Ti rotary files melting is result in material
losses.
In industry, nickel containing scrap is used as a nickel source in steel production. The
use of nickel containing scrap for steel production is 14 % while the use of metallic
nickel is 65 %. The majority of the primary nickel output is directed to the
production of ferronickel for stainless steel production.
As in the recycling of nickel, mixed titanium alloy scrap types are converted to
ferrotitanium for producing titanium alloyed steel as a titanium source. The amount
of titanium alloys scrap which converted to ferrotitanium is 50 percent
approximately. High quality titanium alloys are used in very small scale and
recycling procedure of high quality titanium alloys are also very small scale.
Recycled from titanium containing scrap as a very pure oxide can be appropriate for
titanium production. Pure titanium oxides (Anatase, Rutil) are used as a pigment or
photocatalytic materials that more valuable than ferrotitanium.xxiv
In this work, a recycling process is suggested for disposed endodontic Ni – Ti rotary
files. Ni – Ti alloy part was separated from holder and rubber. Specified
metallurgical recycling process of disposed Ni – Ti rotary files is not known,
hydrometallurgical methods are prefered as an effective recycling of Ni – Ti rotary.
Due to the high corrosion resistance of nickel – titanium alloys, conventional
leaching methods are not effective. Corrosion resistance behavior is caused by
compact oxidation layer of nickel – titanium based alloys. Oxidation layer of Ni – Ti
rotary files was characterized by SEM – EDX characterization method. Acid baking
process and autoclave leaching techniques , that are non – conventional but effective
leaching techniques are used for recycling process design. In preliminary studies,
sulphuric acid, hydrochloric acid and nitric acid had been tried at different
concentration and temperature. Dissolving of Ni – Ti rotary files within sulphuric
acid is more effective than the other two acids. High temperature and high sulphuric
acid concentration increased the dissolution effect, the highest dissolution rate is
observed with 14 % wt hot sulphuric acid solution.
Leaching capabilities of sulphuric acid was enhanced by acid baking process. In this
process, Ni – Ti rotary file sample was heated with concentrated sulfuric acid for two
hours. After that few water drops added to hot sample – acid mixture. Dissolution of
Ni – Ti rotary file became very quickly. Sample / acid weight ratio in acid baking
experiments has been selected as 1/3, 1/5, 1/7 and 1/9. Increasing acid the amount is
improving the metal dissolution but, the dissolution is not efficient when acid weight
ratio is above 7. In addition, high acid ratio inhibited nickel dissolution from Ni – Ti
rotary file.
Ni – Ti rotary files totaly dissolved under pressure via autoclave leaching process.
Autoclave has been manufactured by 316 L type quality stainless steel containing
teflon cup which prevents acid attack to stainless steel. The effect of temperature,
concentration an leaching time has been evaluated. Autoclave leaching solution was
prepared as 2,5 M and 5 M sulphuric acid solution. Dissolving time parameters have
determined as 30, 60, 90, 120 minutes. Temperature parameters have also selected as
150, 175, 200, 225, 250 oC degrees. 150 oC, 120 minutes, 1/5 sample / acid ratio
parameters and 250 oC, 30 minutes, 1/5 sample / acid ratio parameters are border
conditions for 100 % dissolving. Hence, furnace energy consumption during heating
has measured with power analyzer. At these temperature parameters, power values
are so closed. Heating time is decisive for energy consumption at these conditions
that are work for total dissolution. After leaching parameter optimization, all of Ni – Ti rotary files was dissolved at 250 oC, 30 minutes, 1/5 sample / acid ratio conditions and solution named "black
liqueur"containing nickel and titanium ion was obtained. Titanium and nickel ions were precipitated by pH adjustment with NaOH. At pH 1, titanium ions was precipitated as Ti(OH)4, while Nickel ions were precipitated at pH 10 as Ni(OH)2. In order to prevent the formation of rutile phase, titanium hydroxide was dehydrated at 300 oC. The anatase was characterized with XRD and Raman spectroscopy. Nickel
hydroxide was dehydrated at 600 oC to convert as nickel oxide that was characterized
with XRD. Ni – Ti rotary files' holder is gold and nickel coated brass that gold content of holder
is 0.6 percent. Gold is biocompatible metal. Nickel coating has been made for
inhibition of gold – copper diffusion. The reason of choosing brass for holder
manufacturing is high torsion yield. In consequence of containing high valuable
metals, holders were recycled. Metal out of gold were dissolved in 63 % hot nitric
acid solutions. Dissolving time parameters were selected as 6, 8, 10, 12, 18 hours.
The undissolved metal part was characterized with XRF. 12 hour treatment time was
optimum enrichment condition for which gold containing of undissolved part is 76
percent.
The solution obtained from holder recycling, contains copper, zinc and nickel ions.
These ions were precipitated by pH adjustment with NaOH. Copper ion was
precipitated as Cu(OH)2 at pH 8 value and zinc ion was precipitated as Zn(OH)2 at
pH 10 value. Zinc was precipitated with together nickel ions at pH 10. Like nickel
hydroxide precipitated from "black liqueur", Cu(OH)2 and Zn(OH)2 were dehydrated
at 600 oC. At the end of the dehydration process, CuO and ZnO were obtained. These
oxide was characterized with XRD. NiO peaks have not detected with XRD analysis
of dehydrated ZnO particles.
Leaching with acid baking process was not work efficiently. Experimental studies
were showed that disposed Ni – Ti rotary files can be recycled by autoclave leaching
and pH adjustment with caustic soda and all of the products are considered as a raw
material.