Materials Chemistry and Physics 77 (2002) 711–718 Characterisation of solar-synthesised TiC x (x = 0.50, 0.625, 0.75, 0.85, 0.90 and 1.0) by X-ray diffraction, density and Vickers microhardness Jorge Cruz Fernandes a , Carlos Anjinho a , Pedro Miguel Amaral a , Lu´ ıs Guerra Rosa a , José Rodr´ ıguez b , Diego Mart´ ınez b , Fernando Almeida Costa Oliveira c , Nobumitsu Shohoji c,∗ a Departamento de Engenharia de Materiais, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal b Plataforma Solar de Almer´ ıa, Centro Europeo de Ensayos de Energ´ ıa Solar, Centro de Investigaciones EnergeticasMedioambientales y Tecnologicas, P.O. Box 22, 04200 Tabernas, Spain c Departamento de Materiais e Tecnologias de Produção, Instituto Nacional de Engenharia e Tecnologia Industrial, Estrada do Paço do Lumiar, 1649-038 Lisbon, Portugal Received 3 October 2001; received in revised form 8 February 2002; accepted 22 February 2002 Abstract Homogeneous single-phase hypo-stoichiometric carbide TiC x of titanium with known stoichiometric ratio x (0.50, 0.625, 0.75, 0.85, 0.90 and 1.0) was prepared from mixed powders of Ti metal and graphite through 30 min solar heating in inert Ar atmosphere and characterised by X-ray diffraction (XRD), density ρ and Vickers microhardness Hv. In spite of short radiation period at relatively low temperature (no higher than 1600 ◦ C), formed TiC x specimens were all with relatively high degree of crystallinity judging from good separation between K1 and K2 peaks of XRD patterns at high (hkl) index. Measured density of prepared TiC x powders was practically identical to the calculated value from the measured lattice parameter for respective x implying that f.c.c. (face centred cubic) Ti lattice was with no defect and 100x% of the O-sites (octahedral interstitial sites) were filled with C atoms leaving the rest 100(1 - x)% of O-sites vacant. Reflecting polycrystalline nature of the prepared TiC x compact, measured Hv scattered over range of ±400 around 1100. Application of 50 h heat treatment at 600 ◦ C appeared to realise C atoms ordering re-configuration over O-sites leading to slight extent of tetragonal distortion for TiC x specimens with x = 0.50 and 0.625. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Titanium carbide; Non-stoichiometry; Powder density; Vickers microhardness; Solar furnace 1. Introduction In our preceding work [1], we reported that single-phase titanium mono-carbide TiC x being in equilibrium with ex- cess free carbon (either graphite or amorphous carbon) was formed through 30 min irradiation to concentrated solar beam at PSA (Plataforma Solar de Almer´ ıa). This solar irra- diation led to measured temperature 1600 ◦ C. The observed degree of progress of the carbide formation reaction for Ti in this solar synthesis appeared to be more advanced than the one observed by the carbide forming experiment un- dertaken in a laboratory electric furnace under comparable temperature and reaction duration. This carbide formation acceleration observed for Ti might be some photochemical effect. We observed evidences in- dicative of some types of photochemical effects for certain ∗ Corresponding author. Tel.: +351-21-716-5181x2303; fax: +351-21-716-6568. E-mail address: nobumitsu.shohoji@ineti.pt (N. Shohoji). other d-group transition metals in our series of solar car- bide synthesis experiments, e.g. accelerated graphitisation of amorphous carbon during carburising W with excess amorphous carbon under solar radiation [2,3]: formation of high-temperature Mo mono-carbide phase, MoC 1-x , from reaction of Mo with graphite under solar radiation at relatively low temperature [4]: unexpected formation of Ta sub-carbide, Ta 2 C, besides mono-carbide TaC from re- action of Ta with amorphous carbon under solar radiation [5]. These aspects were recently compiled in the compre- hensive review article [6]. We believe that these reported consequences observed during solar carbide synthesis were photochemical equilibrium effects [2–6]. On the other hand, the observed distinction in lattice parameter a(TiC x ) between the Ti mono-carbide being in equilibrium with excess free carbon prepared under the solar radiation and that prepared in a standard laboratory electric furnace might also be a result of photochemical equilibrium effect but it might represent merely the difference in stage of progress of the carbide formation process before being 0254-0584/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0254-0584(02)00131-1