Kolloidale Verarbeitung und Sintern von nanoskaligem TiN-Pulver

Ein nanoskaliges TiN Pulver mit einer spezifischen Oberfläche von 54m2/g wurde oberflächenmodifiziert, wobei die auf der Pulveroberfläche lokalisierten Ti-OH Gruppen als Kopplungszentren dienten. Durch die dadurch etablierten abstoßenden Wechselwirkungskräfte wurde dieses Pulver bis auf seine Primärteilchengröße von 40 nm redispergiert und daraus stabile, nanodisperse TiN-Suspensionen mit hohen Feststoffgehalten bis 40 Gew.- hergestellt. Sinterexperimente an den aus diesen Suspensionen über Schlickerdruckguß hergestellten Formkörpern mit Gründichten um 52 ergaben, dass über druckloses Sintern eine vollständige Verdichtung bei Temperaturen bei 1400°C erfolgt und bis zu relativen Dichten von 95 nur ein geringfügiges Kornwachstum (mittlere Korngröße < 70nm) stattfindet. Der Zusammenhang zwischen der Härte und der Korngröße der verdichteten TiN-Proben mit mittleren Korngrößen unter 200 nm ist durch die Hall-Petch-Beziehung beschreibbar. Im weiteren wurde festgestellt, dass die stabile, nanodisperse TIN-Suspensionen auch für die Herstellung von TiN-Grünschichten verschiedener Dicke über Verfahren wie z.B. Tauchbeschichtung geeignet sind, die über eine nachträgliche Sinterbehandlung bei Temperaturen um 1300°C verdichtet werden können. Als eine weitere Einsatzmöglichkeit dieser TiN-Suspensionen wurde die Herstellung von Kompositen erarbeitet, wo TiN als Verstärkungsphase in nanodisperser Form eingebracht werden muß.Nano scaled TiN with a specific surface area of 54 m2/g was surface modified by using of Ti-OH groups localized on the powder surface as coupling center for the organic modifier. Due to the repulsive forces introduced by this way, the powder were redispersed in aqueous medium down to the primary particle size of 40 nm. Further on, stable aqueous slurries of solid contents up to 40 wt.- with nanodispersed TiN which were used for the preparation of green bodies by pressure slip casting. Sintering experiments on the green samples with relative densities around 52 revealed that a full densification takes place by pressureless sintering at 1400°C in nitorgen atmosphere. It was observed that up to relative densities around 52 revealed that a full densification takes place by pressureless sintering at 1400°C in nitrogen atmosphere. It was observed that up to relative densities of 95 no significant grain growth occured (Average grain size < 70nm). At relative densities above 95 an accelerated grain growth takes place. The relation between the hardness and grain size obeyed to a Hall-Petch law in the grain wize area under 200 nm. Using TiN slurries were green TiN coatings of different thickness on different substrates were prepared by dip coating and subsequent densification at around 1300°C. another application field for the TiN slurries was the composite materials in which a homogeneous TiN distribution was archived by using colloidal methods and TiN slurries from surface modified starting powder

Kolloidale Verarbeitung und Sintern von nanoskaligem TiN-Pulver

Ein nanoskaliges TiN Pulver mit einer spezifischen Oberfläche von 54m2/g wurde oberflächenmodifiziert, wobei die auf der Pulveroberfläche lokalisierten Ti-OH Gruppen als Kopplungszentren dienten. Durch die dadurch etablierten abstoßenden Wechselwirkungskräfte wurde dieses Pulver bis auf seine Primärteilchengröße von 40 nm redispergiert und daraus stabile, nanodisperse TiN-Suspensionen mit hohen Feststoffgehalten bis 40 Gew.- hergestellt. Sinterexperimente an den aus diesen Suspensionen über Schlickerdruckguß hergestellten Formkörpern mit Gründichten um 52 ergaben, dass über druckloses Sintern eine vollständige Verdichtung bei Temperaturen bei 1400°C erfolgt und bis zu relativen Dichten von 95 nur ein geringfügiges Kornwachstum (mittlere Korngröße < 70nm) stattfindet. Der Zusammenhang zwischen der Härte und der Korngröße der verdichteten TiN-Proben mit mittleren Korngrößen unter 200 nm ist durch die Hall-Petch-Beziehung beschreibbar. Im weiteren wurde festgestellt, dass die stabile, nanodisperse TIN-Suspensionen auch für die Herstellung von TiN-Grünschichten verschiedener Dicke über Verfahren wie z.B. Tauchbeschichtung geeignet sind, die über eine nachträgliche Sinterbehandlung bei Temperaturen um 1300°C verdichtet werden können. Als eine weitere Einsatzmöglichkeit dieser TiN-Suspensionen wurde die Herstellung von Kompositen erarbeitet, wo TiN als Verstärkungsphase in nanodisperser Form eingebracht werden muß.Nano scaled TiN with a specific surface area of 54 m2/g was surface modified by using of Ti-OH groups localized on the powder surface as coupling center for the organic modifier. Due to the repulsive forces introduced by this way, the powder were redispersed in aqueous medium down to the primary particle size of 40 nm. Further on, stable aqueous slurries of solid contents up to 40 wt.- with nanodispersed TiN which were used for the preparation of green bodies by pressure slip casting. Sintering experiments on the green samples with relative densities around 52 revealed that a full densification takes place by pressureless sintering at 1400°C in nitorgen atmosphere. It was observed that up to relative densities around 52 revealed that a full densification takes place by pressureless sintering at 1400°C in nitrogen atmosphere. It was observed that up to relative densities of 95 no significant grain growth occured (Average grain size < 70nm). At relative densities above 95 an accelerated grain growth takes place. The relation between the hardness and grain size obeyed to a Hall-Petch law in the grain wize area under 200 nm. Using TiN slurries were green TiN coatings of different thickness on different substrates were prepared by dip coating and subsequent densification at around 1300°C. another application field for the TiN slurries was the composite materials in which a homogeneous TiN distribution was archived by using colloidal methods and TiN slurries from surface modified starting powder

Synthesis and processing of nanoscaled ceramics by chemical routes

Nanocrystalline boehmite and TiN powders have been used as model systems for testing the conception of small-molecule surface modification for the preparation of processable nanoscaled slips and pastes with a high solid content. It was found that after surface modification of boehmite with carboxylic acids like acetic or propionic acid and the addition of 5 to 6 vol.-% of organic processing additives pastes with a solid content of about 45 vol.-% can be prepared. The nanocrystalline pastes have been extruded to tubes which after drying exhibit green densities of about 55 to 60 % of the theory. In the case of TiN it was shown that deagglomeration with short-chained organic bases gives low viscous slips with a solid content of 40 wt.-%. Green bodies with a green density of about 50 % of the theory have been prepared by vacuum-assisted pressure filtration. The nanocrystalline material exhibits a very high sintering activity so that a density above 96 % of the theory could be achieved at 1150°C leading to a microstructure consisting of an average grain size of about 50 nm. This clearly demonstrates the potential of nanosized starting material for separating the densification regime from the grain growth regime in the sintering step

Sol-gel derived nanocomposite materials for corrosion protection of aluminium alloys

Thermally curable nanocomposite coating materials have been developed to seal and protect copper-containing aluminium alloys against corrosion. The coating material was prepared via the sol-gel-process starting from epoxy functionalised silanes, nanoscaled silica and organic diole crosslinker. This coating matrix was additionally supplied with a varying content of cerium oxide (1-20 wt.%). The corrosion protective efficiency of these coatings was investigated on aluminium alloys Al 6013-T6 and AlCu4MgSi by salt spray test and electrochemical impedance spectroscopy (EIS), both on coatings with an artificial damage. Here, the pure coating matrix showed first corrosion attack by filiform corrosion and pitting after 10 days on Al 6013, and after 2 days on AlCu4MgSi. By additional incorporation of cerium oxide, on Al 6013 filiform corrosion and pitting could be effectively suppressed with a content of at least 20 wt.% CeO2 (related to solid content of the coating) and no corrosion attack (Ri=0, Wb=0= was observed over a period of 60 days (1440 h) of salt spray test. For AlCu4MgSi, which has a higher copper content and thus a higher corrosion sensitivity, the addition of cerium oxide in the coating matrix provided efficient protection against filiform and pitting corrosion on the artificial damage during a salt spray exposition of 14 days (336 h). EIS studies on the damaged coatings confirmed these results

Colloidal processing and sintering of nano-scale TiN

Surface modification of nano-scale TiN powder with guanidine propionic acid was used for the preparation of well dispersed slurries. The starting powder could be completely deagglomerated for modifier concentrations exeeding 7.5 wt.-% at pH = 9. Such slurries (<40 wt.-% solid content) behave like an ideal Netwonian liquid. Green compacts with relative densities around 50 % were prepared by pressure filtration. The specimen are characterized by a homogeneous green microstructure with pore sizes in the range of 3 to 10 nm, which could be sintered to high density (>96%) below 1400°C up to densities of 96% grain coarsening can be neglected, but further densification was accompainied by an exaggregated grain growth

Processing and sintering of nanosized TiN

The concept of surface modification of nano-scale particles with short-chained organic molecules has been used for the preparation of deagglomerated slurries of n-TiN using guanidine propionic acid as surface modifier, the strongly agglomerated powder could be redispersed to its primary particle size of 30 to 40 nm. From such suspensions green specimens with densities of 50% could be prepared by pressure filtration, which could be sintered to high densities (>96%) at temperatures below 1400°C without significant grain growth

Processing and sintering of nanosized TiN

The concept of surface modification of nano-scale particles with short-chained organic molecules has been used for the preparation of deagglomerated slurries of n-TiN using guanidine propionic acid as surface modifier, the strongly agglomerated powder could be redispersed to its primary particle size of 30 to 40 nm. From such suspensions green specimens with densities of 50% could be prepared by pressure filtration, which could be sintered to high densities (>96%) at temperatures below 1400°C without significant grain growth

Biochemically and histopathologically comparative review of thiamine's and thiamine pyrophosphate's oxidative stress effects generated with methotrexate in rat liver

PubMed: 23197226Background: Oxidative liver injury occurring with methotrexate restricts its use in the desired dose. Therefore, whether or not thiamine and thiamine pyrophosphate, whose antioxidant activity is known, have protective effects on oxidative liver injury generated with methotrexate was comparatively researched in rats using biochemical and histopathological approaches. Material/Methods: Thiamine pyrophosphate+methotrexate, thiamine+methotrexate, and methotrexate were injected intraperitoneally in rats for 7 days. After this period, all animals' livers were excised, killing them with high-dose anesthesia, and histopathologic and biochemical investigations were made. Result: Biochemical results demonstrated a significant elevation in level of oxidant parameters such as MDA and MPO, and a reduction in antioxidant parameters such as GSH and SOD in the liver tissue of the methotrexate group. Also, the quantity of 8-OHdG/dG, a DNA injury product, was higher in the methotrexate group with high oxidant levels and low antioxidant levels, and the quantity of 8-OHdG/dG was in the thiamine pyrophosphate group with low oxidant levels and high antioxidant levels. In the thiamine and control groups, the 8-OHdG/dG rate was 1.48±0.35 pmol/L (P>0.05) and 0.55±0.1 pmol/L (P<0.0001). Thiamine pyrophosphate significantly decreased blood AST, ALT and LDH, but methotrexate and thiamine did not decrease the blood levels of AST, ALT and LDH. Histopathologically, although centrilobular necrosis, apoptotic bodies and inflammation were monitored in the methotrexate group, the findings in the thiamine pyrophosphate group were almost the same as in the control group. Conclusions: Thiamine pyrophosphate was found to be effective in methotrexate hepatotoxicity, but thiamine was ineffective. © Med Sci Monit, 2012

Retrograde Intrarenal Surgery versus Percutaneous Lithotripsy to Treat Renal Stones 2-3 cm in Diameter

Objective. Retrograde intrarenal surgery (RIRS) performed using a flexible ureterorenoscope marked the beginning of a new era in urology. Today, even staghorn stones are successfully treated via RIRS. The recommended treatment for larger stones is percutaneous nephrolithotomy (PNL). However, the question of whether PNL or RIRS should be the first-line treatment option for larger stones remains controversial. In this study, we contribute to the debate by comparing the success and complication rates of PNL and RIRS that were used to treat renal pelvis stones 2-3 cm in diameter. Materials and Methods. The medical records of 154 patients (74 PNL, 80 RIRS) were retrospectively evaluated. PNL patients were placed in Group 1 and RIRS patients in Group 2. Results. The complete stone-free rates were 95.5% in the PNL group and 80.6% in the RIRS group 1 month postoperatively (P=0.061). The respective complication rates (evaluated using the Clavien system) were 13.5% and 8.8% (P=0.520). Conclusions. RIRS affords a comparable success rate, causes fewer complications than PNL, and seems to be a promising alternative to PNL when larger stones are to be treated. Prospective randomized controlled trials are needed to confirm these findings