Jens Klimke

• Dr. rer. nat.
• CEO at POLYCRYSTAL design GmbH, Dresden, Germany

The correlation between grain size, optical birefringence, and transparency is discussed for tetragonal zirconia (ZrO2) ceramics using the Mie, Rayleigh, and Rayleigh–Gans–Debye scattering models. Our results demonstrate that at the degree of mean birefringence in the range (0.03–0.04) expected for tetragonal ZrO2, only the Mie theory provides reas...

A quantitative assessment of the homogeneity of particle coordination in green bodies is achieved by addressing pore structures. Avoiding a coarser tail of the pore size distribution is important but insufficient for optimum sintering. Instead, the steepest slope of the main body of the distribution is responsible for a maximum density at lowest te...

The overview focuses on inherent optical properties, governed by composition and the state of the crystal lattice, and on the interference of these properties with the microstructural optimization of transparent ceramics (e.g. the dependence of the tolerable pore size or grain size on the refractive index). Starting with the general difference betw...

The differences of translucency and transparency request special conditions for a right photographic presentation and for correct transmission measurements. These differences also influence the materials design of products because of the effect of thickness. Prerequisites of a clear transparency of ceramics are derived for inherent materials proper...

Translucent and transparent polycrystalline (PX) functional ceramic materials have been gaining a high degree of interest in recent years for substituting single crystal (SX) optical ceramics in a whole range of application fields such as transparent armor, infrared windows, laser host materials, scintillator host materials and medical and ortho...

Targeting higher toughness transparent ceramics, tetragonal (3 mol % yttria) and cubic (8 mol % yttria) ZrO2 starting powder mixtures were densified by spark plasma sintering (SPS) in vacuum at 1100 °C and post hot isostatic pressing (HIP) in argon at 1100 °C. The influence of the ultra-fine microstructure and phase composition on the fracture resi...

In order to increase the in-line transmission of fine transparent alumina in visible light the grain growth during sintering of alumina ceramics was supressed using a combined densification process. This process combines presintering of a green body by spark plasma sintering with final hot isostatic pressing. The presintering by spark plasma sinter...

Contrary to the moderate ballistic advantage of Al2O3ceramics over MgAl2O4 polycrystals, the present study shows a reverse ratio of the ballistic strength of alumina and spinel single crystals: Spinel single crystals outperform sapphire and exhibit a similarly high stability as submicrometer Al2O3 ceramics. The results correlate with different clea...

An injection molding feedstock was developed containing the high purity and highly sinter active alumina powder TM-DAR. The selected binder system allowed a volume loading of 57 vol-%. For minimizing metal contamination during feedstock compounding a shear roller was equipped with wear resistant machine components. The produced alumina samples were...

The kinetic of sintering of alumina was studied using Kinetic Field of Response, Master Curve and Thermokinetic method. Sintering was modelled by each method and predictions of the density evolution for various temperature- time- profiles including rate controlled sintering were carried out and compared to experiments. Additionally microstructure e...

It is demonstrated that a complete elimination of pores on sintering is governed not only by the size of the ceramic powder particles and by the homogeneity of their mutual coordination but similarly strongly by the state of the crystal lattice: with different cation disorder at fixed stoichiometry (n = 1) the sintering temperatures may differ by a...

The transmission of transparent colored ceramics based on Al(2)O(3) doped with light transition metals is measured in the visible and infrared range. To clarify the role of the dopands we perform ab initio calculations. We discuss the electronic structure and present optical spectra obtained in the independent particle approximation. We argue that...

MgAl2O4 is a candidate for sintered windows, domes and lenses for UV, visible, and IR applications. However, exact Mie calculation shows that for imaging uses with a window thickness of e.g. 5 mm even IR transmission will not tolerate smallest amounts of 0.01% of 50-100 nm small pores, and the impact of such pores is even worse at shorter wave leng...

Introduction: Targets of Transparent Armor Development - Microstructural und Technological ConsequencesPowder and Green Body CharacterizationSintering and Transmission ResultsDiscussion and Conclusions Acknowledgement

The study investigated the deagglomeration of spinel nanopowders (MgO·nAl2O3, n≈1) from different syntheses in correlation with their resulting performance on green processing and sintering. Transmission results are addressed as a means of evaluating the degree of last pore elimination. As a result, clear transparent components with a thickness of...

Tools made of sub-μm-grain Al2O3 ceramics have already been successfully tested in the machining of hardened steels (since they have good technological characteristics), but there is no scientific and technological experience in machining wood-based materials. The aim of the present study was to examine the cutting properties of the edges made of s...

Hardness is important for a high ballistic strength, and with HV10=20–22GPa sintered sub-μm Al2O3 is the hardest of all transparent materials for compact windows. However, light transmission through polycrystalline Al2O3 is limited by birefringent scattering losses: high transmissions are known at larger IR wavelengths for grain sizes of about 0.5μ...

New sub-μm Al2O3-ceramics exhibit much better mechanical and tribological characteristics than commercially available grades. Previously, the sub-μm-ceramics have been successfully tested for machining hardened steels, but there is not any scientific experience with machining wood-based materials. The aim of the presented study was to examine how t...

Manufacturing strategies for the different types of transparent ceramics were derived from a general understanding of the physics of light transmission in the first part of this dual publication. This second part addresses present and future applications. With the exception of few small transparent optical components the past development was focuse...

Starting with an overview of the different classes of transparent inorganic materials and of the microstructural essentials of clear transparency, this first part of a dual publication summarizes fundamental conditions for the manufacture of different transparent ceramics, for right characterization and testing and for materials selection. A second...

Sintered sub-micrometer alumina (alpha-Al2O3) is the hardest transparent armor. However, its trigonal structure gives rise to a strong thickness effect that makes thicker components translucent. Cubic ceramics (no birefringence!), on the other hand, are less hard but may exhibit an improved transmission. Known cubic armor ceramics are manufactured...

Titanium films, deposited at 3.6 kW and 5.5 kW in a hollow cathode arc evaporator, were investigated by in-situ GIXRD and GIXR. At RT an angle shift of the of the titanium (002) reflection up to Δ2⊖ = 1.0° was observed. The shifts increase during annealing in vacuum up to 350°C. These large shifts can be explained with an incorporation of silicon,...

Calculations of the mean amplitude of the vibrations by means of the Debye-theory show that grazing incidence x-ray reflectometry (GIXR) can be used as in situ technique for thermally induced processes in thin films and multi layers. In situ grazing incidence x-ray reflectometry and grazing incidence x-ray diffractometry (GIXRD) were carried out al...

The grazing incidence asymmetric Bragg diffraction technique (GIABD) makes it possible to obtain information from the sample surface down to deeper layers of the sample by increasing the incidence angle of the X-ray beam. Unfortunately the intensities of different penetration depths are difficult to compare because the irradiated sample volume vari...

The influence of the oxidic boundary layer on the electrode potential behaviour of gold electrodes with the solid electrolyte Zr0.86Y0.14O1.93 (YSZ) at temperatures ≤ 700 °C in gases containing oxygen and combustible components was investigated. The interface between gold and the solid electrolyte was chemically modified with TiO2 which was produce...

The grazing incidence asymmetric Bragg diffraction technique (GIABD) makes it possible to obtain information from the sample surface down to deeper layers of the sample by increasing the incidence angle of the X-ray beam. Unfortunately the intensities of different penetration depths are difficult to compare because the irradiated sample volume vari...

When titanium is deposited on silicon 〈100〉 at different discharge powers in a hollow cathode arc evaporator device the chemical, physical and structural properties of the thin films depend strongly on the discharge power. α-Ti with small gradients of structure parameters is observed at a discharge power >4.0 kW. Lower discharge powers produce film...

Magnesium oxide thin films were deposited at an average evaporation rate of 1.8 nm s−1 onto different crystalline alumina substrates and amorphous float glass. The deposits were made in an electron-beam evaporator at substrate temperatures between 25°C and 190°C under different oxygen partial pressures. Films of 0.1, 0.5 and 1 μm thickness were dep...

Ex situ x-ray diffraction measurements and in situ ellipsometry results were combined in order to get information about the layer growth from Ti on Si. Ti-films were deposited at different deposition rates in a hollow cathode arc deposition device on silicon wafers 〈100〉. The thin film analyses were made mainly in grazing incidence configuration wi...

Combining X-ray powder diffraction with fluorescence measurements is an efficient way to determine the optimum activator concentration of inorganic phosphors. La1-xEuxAlO3 samples (perowskite structure), prepared by solid state reactions with 0.55D0-7F1 and 5D0-7D2 transitions and fluorescence intensity reaches a maximum at 1 mol% Eu3+. X-ray diffr...