Grzegorz Adamek

Nanostructured Titanium-10 wt% 45S5 Bioglass-Ag Composite Foams for Medical Applications

The article presents an investigation on the effectiveness of nanostructured titanium-10 wt% 45S5 Bioglass-1 wt% Ag composite foams as a novel class of antibacterial materials for medical applications. The Ti-based composite foams were prepared by the combination of mechanical alloying and a “space-holder” sintering process. In the first step, the Ti-10 wt% 45S5 Bioglass-1 wt% Ag powder synthesized by mechanical alloying and annealing mixed with 1.0 mm diameter of saccharose crystals was finally compacted in the form of pellets. In the next step, the saccharose crystals were dissolved in water, leaving open spaces surrounded by metallic-bioceramic scaffold. The sintering of the scaffold leads to foam formation. It was found that 1:1 Ti-10 wt% 45S5 Bioglass-1 wt% Ag/sugar ratio leads to porosities of about 70% with pore diameter of about 0.3–1.1 mm. The microstructure, corrosion resistance in Ringer’s solution of the produced foams were investigated. The value of the compression strength for the Ti-10 wt% 45S5 Bioglass-1 wt% Ag foam with 70% porosity was 1.5 MPa and the Young’s modulus was 34 MPa. Silver modified Ti-10 wt% 45S5 Bioglass composites possess excellent antibacterial activities against Staphylococcus aureus. Porous Ti-10 wt% 45S5 Bioglass-1 wt% foam could be a possible candidate for medical implants applications.

Saccharose Particles as a Space Holder for Ti-Void Composite Preparation

In this work a new method of Ti-void composites (foam, scaffold) preparation is shown. In this process as a space holder particles we have applied a saccharose crystals (table sugar) with size up to 1.3 mm. After Ti and saccharose particles mixing and pressing, a green compacts composed of sugar and Ti grains were produced. Then, the sugar crystals were removed by its dissolution in water, which lead to open spaces (pores) formation in the green compacts. Then the compacts were sintered at 1250 °C. Alternatively, a sugar was evaporated during sintering without water dissolution. The foams were investigated by SEM, XRD and computed tomography. Such prepared void metal composites have porosity of about 72% and average pore size of about 0.7 mm. The pores have cubical shape corresponding to sugar crystals shape. The method is very promising in foams preparation and the made Ti-void composites can be applied for hard tissue implants, for example.

Microstructure and Interconnections Characteristics of Titanium Foam

Titanium foams are widely used as biomaterials and potentially as a twin skinned, sandwich, structures for aerospace structures, filter or a catalyst or catalysts carrier for chemical reactions. The porosity is particularly important for tissues ingrowth and vascularity. Open porosity is essential in the case of flow-on machines. The distribution and size of pores is significant to achieve a uniform material effort and ensure to receive an appropriate hydraulic properties.The aim of this study was to determine the effect of titanium particle size and the amount of porogen on the microstructure and the size of pore interconnections in titanium foams made using saccharose as the space holder material.The paper characterizes titanium foam, made from the Grade 1 Ti powders (Alfa Aesar) with a particle sizes of 0.150 mm and 0.044 mm (separately) and spherical particles of saccharose (Pfeifer & Langen) having an average size of 0.7 ÷ 0.9 mm, as a porogen. There was prepared a mixture of powders of the proposed porosity of 50, 60 and 70%. Summarizing 6 mixtures were prepared. After sintering there were received specimens having a diameter of 8 mm and a height of 5 mm. Microstructure analysis was performed using the microtomography Skyscan 1172 (Bruker microCT) and the CTAn software (Bruker microCT).The results indicate the uniform pore distribution and size of the interconnections allowing high permeability.

Electrochemical Deposition of the Ca-P Coatings on the Porous Nanocrystalline Ti-6Al-4V Alloy

The formation mechanism of the Ca–P coating on the porous nanocrystalline Ti-6Al-4V alloy is presented. The Ca–P compounds were cathodically deposited at different potential (from –0.5 to –10 V vs. open circuit potential), using a solution mixture of Ca (NO3)2 + (NH4)2HPO4 + HCl. Depending of the deposition potential, the atomic ratio of Ca/P in deposits is in the range from 0.25 to 1.71, which indicates that the coating composition corresponds in some cases to hydroxyapatite. The Ca–P particles penetrate preferentially the pores inside, which improve bonding of the bioceramic layer to the metallic substrate. Increasing the cathodic deposition potential results in changes of the Ca–P morphology from thin porous, through cracked up to thick 90 μm continous coating. The porosity of the Ca–P decreases with increasing cathodic deposition potential. It is proposed the electric field enhancement mechanism of the electrolytic ions flow and Ca–P growth on the surface irregularities, such as pores and surrounding hillocks.

Microstructure and Electrochemical Properties of Refractory Nanocrystalline Tantalum-based Alloys

The nanocrystalline refractory tantalum alloys were made using mechanical alloying. The tantalum alloys were modified by niobium, molybdenum and tungsten in the concentration of 5, 10, 20 and 40 wt.%. The nanocrystalline powders were consolidated (hot-pressed) using the pulse plasma sintering mode. The hot pressing at the temperature of 1300 o C results in an increase of the grain size, in comparison to mechanically alloyed powders. However, the lowest grain size (significantly below 100 nm) was achieved for Ta-W alloys (approximately 40-60nm). The grain size was confirmed by XRD, TEM and AFM. The most uniform microstructure is also exhibited by the Ta-W alloys. The corrosion resistance was measured using the potentiodynamic mode in a chloride solution. The nanocrystalline Ta-Mo and Ta-W alloys achieved the same level of corrosion resistance as microcrystalline pure tantalum and 3 orders of magnitude better than pure nanocrystalline tantalum. Among all the prepared nanocrystalline tantalum alloys, the most promising properties exhibit those having 10% of the tungsten addition.

Corrosion Properties of Ti Scaffolds Prepared with Sucrose as a Space Holder

In this work we shows procedure for new biomaterial - void metal composite (VMC) formation. We used a quasi-spherical sucrose crystals as a space holder material. In the process, titanium powder (different particle sizes) and sucrose were mixed together and uniaxially pressed to make a green compacts. In the next step the sucrose crystals were dissolved in water, leaving open spaces surrounded by metallic scaffold with different porosity (50 – 70%). Such prepared titanium scaffold was dried and sintered in vacuum. The foams morphology was investigated by SEM and CT. The corrosion tests of the as prepared materials were performed in Ringer`s solution using cyclic polarization measurements. We shows that Ti scaffolds prepared by using sucrose as a space holder have corrosion resistance comparable to bulk microcrystalline titanium.

Formation and Properties of the Ta-Y2O3, Ta-ZrO2, and Ta-TaC Nanocomposites

The nanocrystalline tantalum-ceramic composites were made using mechanical alloying followed by pulse plasma sintering (PPS). The tantalum acts as a matrix, to which the ceramic reinforced phase in the concentration of 5, 10, 20, and 40 wt.% was introduced. Oxides (Y2O3 and ZrO2) and carbides (TaC) were used as the ceramic phase. The mechanical alloying results in the formation of nanocrystalline grains. The subsequent hot pressing in the mode of PPS results in the consolidation of powders and formation of bulk nanocomposites. All the bulk composites have the average grain size from 40 nm to 100 nm, whereas, for comparison, the bulk nanocrystalline pure tantalum has the average grain size of approximately 170 nm. The ceramic phase refines the grain size in the Ta nanocomposites. The mechanical properties were studied using the nanoindentation tests. The nanocomposites exhibit uniform load-displacement curves indicating good integrity and homogeneity of the samples. Out of the investigated components, the Ta-10 wt.% TaC one has the highest hardness and a very high Young’s modulus (1398 HV and 336 GPa, resp.). For the Ta-oxide composites, Ta-20 wt.% Y2O3 has the highest mechanical properties (1165 HV hardness and 231 GPa Young’s modulus).

Characterization of High-Energy Ball-Milled and Hot-Pressed Nanocrystalline Tantalum

The paper shows a comparison of nanocrystalline and microcrystalline tantalum sinters. The nanocrystalline tantalum was made using high-energy ball milling. The sinters were made using hot pressing with high frequency induction heating. The structure and microstructure of the powders and sinters were investigated. After 48 hour milling, the microcrystalline tantalum transformed into nanocrystalline powder. The hot pressing resulted in a formation of bulk tantalum with ultrafine grains and hardness as high as 1067 HV. The nanostructure supports the densification process at lower sintering temperature in comparison to microcrystalline tantalum. The average crystallite size in nanocrystalline bulk materials reached 170 nm.

Hot pressing of nanocrystalline tantalum using high frequency induction heating and pulse plasma sintering

The paper presents the results of nanocrystalline powder tantalum consolidation using hot pressing. The authors used two different heating techniques during hot pressing: high-frequency induction heating (HFIH) and pulse plasma sintering (PPS). A comparison of the structure, microstructure, mechanical properties and corrosion resistance of the bulk nanocrystalline tantalum obtained in both techniques was performed. The nanocrystalline powder was made to start from the microcrystalline one using the high-energy ball milling process. The nanocrystalline powder was hot-pressed at 1000 °C, whereas, for comparison, the microcrystalline powder was hot pressed up to 1500 °C for proper consolidation. The authors found that during hot pressing, the powder partially reacts with the graphite die covered by boron nitride, which facilitated punches and powder displacement in the die during densification. Tantalum carbide and boride in the nanocrystalline material was found, which can improve the mechanical properties. The hardness of the HFIH and PPS nanocrystalline tantalum was as high as 625 and 615 HV, respectively. The microstructure was more uniform in the PPS nanomaterial. The corrosion resistance in both cases deteriorated, in comparison to the microcrystalline material, while the PPS material corrosion resistance was slightly better than that of the HFIH one.