Particle refinement of ZrB2 by the combination of borothermal reduction and solid solution

Flexible synthesis of ultra‐fine ZrB₂ powders was achieved by borothermal reduction in a mixture of ZrO₂, boron, and TiO₂. Without TiO₂ additive, coarse ZrB₂ powders with particle size of 0.81 μm were obtained, presumably due to good wettability and solubility of ZrB₂ in the byproduct B₂O₃. It was found that the particle growth of ZrB₂ was effectively inhibited by the solid solution of TiB₂ (≥1 mol%). The refinement mechanism was that the solid solution of in situ formed TiB₂ presumably lowered the wettability and solubility of ZrB₂ in the B₂O₃ liquid and significantly inhibited the coarsening of ZrB₂. The average particle size of resulting powders decreased to 0.37 μm with the addition of 10 mol% TiO₂.     

Synthesis and characterization of ceramic nanoparticles reinforced lead-free solder

Sn-0.7Cu is among the least expensive types of lead-free solders available. However, its poor mechanical properties have limited its application. In this study, Sn-Cu lead-free solder reinforced with amorphous silica (SiO₂) nanoparticles was synthesized through powder metallurgy route. Desired mixtures of raw materials was mechanically milled, compressed, sintered and extruded to prepare bulk solder samples. The samples were characterized by optical and electron microscopy as well as mechanical tests. The results showed that mechanical properties were increased by addition of SiO₂ nanoparticles to the solder matrix. Addition of 1.5 wt% ceramic reinforcement to the composite increased tensile, yield and compressive strengths up to 27%, 23% and 41%, respectively, compared to those of the monolithic sample. In addition, the ceramic nanoparticles caused an up to 50% decrease in the wetting angle between the substrate and the nanocomposite solder.     

Suppression of carbon contamination in SPSed CaF2 transparent ceramics by Mo foil

Transparent calcium fluoride (CaF₂) ceramics were fabricated by spark plasma sintering (SPS) using Mo foil to separate from graphite die, and the effect of Mo foil on transparency, microstructure and carbon contamination was investigated. The discoloration was removed and the transmittance increased from 8% to 54% at the wavelength of 300 nm and 63% to 86% at 1100 nm by using Mo foil. The average grain size of CaF₂ ceramics SPSed at 1100 °C was 16 μm by using graphite sheet, whereas it was 260 μm by using Mo foil, indicating that ceramics with large grain size are possible to reach high transmittance. Raman spectroscopy and X-ray photoelectron spectroscopy revealed that carbon contamination in the CaF₂ ceramics using Mo foil decreased 78% than that shielded by graphite sheet.     

Effect of magnetic CoFe2O4 component on sintering densification process of Bi3.15Nd0.85Ti3O12 ceramics

Sintering densification processes of the composite ceramics (Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT)/CoFe₂O₄ (CFO)) have been investigated using dilatometric experiments combining with the TG-DTA, density measurements and microstructure studies. Microstructures analyses and quantitative calculations show that the composite ceramics achieve densification at low temperatures (<1150 °C). The formation of coherent-lattice interfaces between (200)/(020)_BNdT and (310)_CFO are considered to play an important role on such densification. The intrinsic preferred orientation of BNdT grains is suppressed by CFO phase because of this coherent relationship. Although the sintering activation energies of 0.8BNdT-0.2CFO are about 2.7 times larger than those of pure BNdT due to the pinning effect, the composite ceramic could still be densified, indicating the formation energy of coherent-lattices provided the extra sintering force. The even coercive electric fields of the resulting pure BNdT and 0.8BNdT-0.2CFO ceramic are approximately 89 and 97 kV/cm, respectively, at 250 kV/cm. The polarization of 0.8BNdT-0.2CFO reaches saturation around 430 kV/cm.     

Using Barkhausen noise to measure coating depth of coated high<Emphasis Type="Bold">-</Emphasis>speed steel

Coated high-speed steel tools are widely used in machining processes as they offer an excellent tool life to cost ratio, but they quickly need replacing once the coated layer is worn away. It would be therefore useful to be able to measure the tool life remaining non-destructively and cheaply. To achieve this, the work presented here aims to measure the thickness of the coated layer of high-speed cutting tools by using Barkhausen noise (BHN) techniques. Coated high-speed steel specimens coated with two different materials (chromium nitride (CrN), titanium nitride (TiN)) were tested using a cost-effective measuring system developed for this study. Sensory features were extracted from the signal received from a pick-up coil and the signal features, Root mean square, peak count, and signal energy, were successfully correlated with the thickness of the coating layer on high-speed steel (HSS) specimens. The results suggest that the Barkhausen noise measuring system developed in this study can successfully indicate the different thickness of the coating layer on CrN/TiN coated HSS specimens.     

Influence of Different Application of Lubricants on Wear and Pre-existing Rolling Contact Fatigue Cracks of Rail Materials

Rolling contact fatigue (RCF) of rail can be a significant problem affecting safety and maintenance. Rail materials have been optimized to reduce it, but not enough is known about how friction management products applied to the rail affect crack growth. This study presents experimental results carried out to explore the influence of different lubricants and application orders on wear and pre-existing RCF cracks in rail materials. The results indicate that the types or properties of lubricants have a vital role in the wear rate and fatigue crack growth characteristics of rail materials after conditioning with 5000 dry cycles to initiate cracks. Using a different application order of two lubricants has a significant influence on the crack growth angles in the rail rollers.     

Affordable housing and planning gain,linkage fees and the rational nexus: Using the land use planning system in England and the USA to deliver housing subsidies

The paper examines how the English planning system is being used to reduce land prices for social housing schemes at a time when government subsidies to social rented housing producers are being cut and compares and contrasts this with practice within the USA. The paper describes the key characteristics of the English planning system, recent trends in English housing policy, the role the planning system plays in meeting overall housing requirements and how it has been adapted to meet specific needs. It explains the new arrangements the government has put into place to lower land prices for social housing and argues that this represents a specific tax on development values to provide subsidies for social housing and that the government has had to significantly modify the land use planning system in order to achieve its housing policy aims. The paper compares these changes with practices in the USA, particularly in relation to the ‘rational nexus’ argument. It finds significant parallels and argues that the use of the planning system to help provide affordable housing through de facto and site specific taxes on land values can be justified and does not need to be restricted to cases where the rational nexus argument applies, but that practice in each country reflects underlying differences in attitudes to development rights, market provision of housing and the role of local governments.     

Intra‐Urban migration and housing submarkets: theory and evidence

In the 1950s and 1960s a group of housing economists at Columbia University developed a framework for the analyses of urban housing markets which was based around the concept of housing submarkets and household migration. There is now widespread agreement amongst housing economists that submarkets should be adopted as a working hypothesis but the concept has been reformulated in terms of intra‐urban relative house price differentials. The accepted test for submarket existence uses a hedonic model of house prices which assumes market equilibrium. This paper returns to an analysis of submarkets which focuses on spatial migration patterns. By examining household intra‐urban mobility patterns in the Glasgow housing market it is possible to demonstrate that submarkets tend to be self‐contained. The analysis also suggests that the current standard statistical tests may be incomplete and in the case of Glasgow underestimate the number of submarkets.     

Book reviews

Managing Cities. The New Urban Context. P. Healey, S. Cameron, S. Davoudi, S. Graham & A. Madani‐Pour (Eds) Chichester, John Wiley and Sons, 1995, £14.95 pb, ISBN 0–471–95533–7

Industrial Property: Policy and Economic Development. Rick Ball & Andy Pratt (Eds). London, Routledge, 1994, £45.00 hb, ISBN 0–415–09152–7

Grassroots Environmental Action: People's Participation in Sustainable Development. Dharam P. Ghai & Jessica M. Vivian (Eds). London and New York, Routledge, 1995 (pb), 347 pp., ISBN 0–415–12703–3

Services and Space: Key Aspects of Urban and Regional Development. N. Marshall & P. Wood. Essex, Longman Scientific and Technical, 1995, 294 pp., £17.99 pb, ISBN 0–582–25162–1

Servicing The Middle Classes: Class, Gender and Waged Domestic Labour in Contemporary Britain. Nicky Gregson & Michelle Lowe. Routledge, 1994, vii + 327 pp., £13.99 pb, ISBN 0–419–08531–4

Urban Development Planning: Lessons for the Economic Reconstruction of South Africa's Cities. Richard Tomlinson. Johannesburg, Witwatersrand University Press, 1994, 277 pp., £14.95 pb, ISBN 1–868–14258–2     

The affordability of “affordable” housing in England: conditionality and exclusion in a context of welfare reform

Abstract

Contemporary debates around affordability have largely focused on homeownership and private renting. This article considers the affordable social rented sector in England, in which reforms to social welfare assistance, reduced security of tenure, and a shift towards mid-market rents, are changing access to ‘affordable’ housing for those on the lowest incomes. Drawing on in-depth interviews with housing associations and stakeholders, the article highlights the increasing use of affordability assessments for prospective tenants. These assessments interact with mid-market rental products to increase the potential for exclusion from affordable housing on the grounds of ability to pay. This conditionality is applied not only at the point of tenancy access, but also at renewal of fixed-term tenancies. The research highlights that the combination of welfare and housing policies, in the context of a financialising housing association sector, has the potential to erode access to social housing for those who are perceived as a financial risk, reshaping the focus of social housing.