Static and dynamic degradation of sintered calcium phosphate ceramics

The chemical compositions of calcium phosphate materials are similar to that of bone making them very attractive for use in the repair of critical size bone defects. The bioresorption of calcium phosphate occurs principally by dissolution. To determine the impact of composition and flow conditions on dissolution rates, calcium phosphate tablets were prepared by slip casting of ceramic slips with different ratios of hydroxyapatite (HA) and ß-tricalcium phosphate (ß-TCP). Dissolution was evaluated at pH4 using both a static and dynamic flow regime. Both the composition of the HA:ß-TCP tablet and flow regime noticeably influenced the rate of dissolution; the 50:50 HA:ß-TCP composition demonstrating the greatest level of dissolution, and, exposure of the ceramic specimens to dynamic conditions producing the highest rate of dissolution. Understanding the impact of phase composition and flow condition with respect to the dissolution of calcium phosphate will aid in the development and improvement of materials for bone substitution.

Rotary moulding of ceramic hollow wares

A novel processing method for the fast and economic production of hollow ceramic components has been developed by combining in situ coagulation moulding with a modified version of the technique of rotary moulding[Binner, J. G. P., Al-Dawery, I. A., Tari, G. and Yan, Y., Rotary casting technique. UK Patent application No. 0506349.0, March 2005], the latter being adapted from the polymer industry. The process was found to require a high solids content suspension, hence development work was performed in this direction though in the end a new, commercial suspension was utilised. Of the three forming routes of gel casting, direct coagulation casting and in situ coagulation moulding, the latter was found to be the most promising for the new process of rotary moulding of ceramics. Due to the low value of clay-based ceramics, a new low cost coagulant was identified and the effect of lactone concentration and temperature on setting time determined. Following substantial optimisation work, it was found that a two-speed approach to multi-axial rotation was the most successful; medium sized cream jugs could be produced in just 7 min. With respect to mould materials, the porous resin normally used for pressure casting of sanitary ware was found to be the best option, though since this is quite expensive conventional plaster-of-paris moulds were found to be a suitable material to enable companies, particularly SMEs, to become familiar with the technology whilst avoiding high costs for trials. The processed articles could be successfully fired and glazed using gas-fired kilns with no sign of any black cores. Major advantages of the process include the ability to precisely calculate the amount of ceramic slip required, eliminating either slip wastage or the need to pour used slip back into the virgin material as currently happens with slip casting. In addition, since the precursor suspension has a very high solids content, the time and energy required to dry the green product and associated moulds has been considerably reduced. © 2008 Elsevier Ltd. All rights reserved.

Casting of Self-Compacting Concrete

Increased productivity and improved working environment have had high priority in the development of concrete construction over the last decade. Development of a material not needing vibration for compaction—i.e. selfcompacting concrete (SCC)—has successfully met the challenge and is now increasingly being used in routine practice. The key to the improvement of fresh concrete performance has been nanoscale tailoring of molecules for surface active admixtures, as well as improved understanding of particle packing and of the role of mineral surfaces in cementitious matrixes. Fundamental studies of rheological behaviour of cementitious particle suspensions were soon expanded to extensive innovation programmes incorporating applied research, site experiments, instrumented full scale applications supporting technology, standards and guides, information efforts as well as training programmes. The major impact of the introduction of SCC is connected to the production process. The choice and handling of constituents are modified as well as mix design, batching, mixing and transporting. The productivity is drastically improved through elimination of vibration compaction and process reorganisation. The working environment is significantly enhanced through avoidance of vibration induced damages, reduced noise and improved safety. Additionally, the technology is improving performance in terms of hardened material properties like surface quality, strength and durability.

Le 'bon Allemand' dans le roman français de l'immédiat après-Seconde Guerre mondiale: une erreur de casting?

The end of the Occupation, which was much more violent than its beginning, dramatically affected the overall perception of Germans and Germany for many years in post-WWII France. This vision is of course reflected to a large extent in French literature. Yet, paradoxically, many novels—including the ‘best-sellers’ E ´ ducation europe´enne (1945) by Romain Gary, Mon Village a` l’heure allemande (1945) by Jean-Louis Bory or Les Foreˆts de la nuit (1947) by Jean-Louis Curtis—contain a ‘good German’ character. Firstly, this article will give an overview of the dominant representations of Germans in post-WWII France, before suggesting that the ‘good German’ character follows both a literary tradition and the humanist values of the French Resistance, to which these writers claim to subscribe. Finally, it will show how this character, far from blurring the Manichean ideology of the novel in which he appears, actually reinforces it.