arXiv subjects

Hans Brouwer

Publications and source records attributed to Hans Brouwer.

3 recordsLinked to original sources

arXiv2025

Unraveling the thermodynamics and mechanism behind the lowering of reduction temperatures in oxide mixtures

Hydrogen-based direct reduction offers a sustainable pathway to decarbonize the metal production industry. However, stable metal oxides, like Cr$_2$O$_3$, are notoriously difficult to reduce, requiring extremely high temperatures (above 1300 $^\circ$C). Herein, we show how reducing mixed oxides can be leveraged to lower hydrogen-based reduction temperatures of stable oxides and produce alloys in a single process. Using a newly developed thermodynamic framework, we predict the precise conditions (oxygen partial pressure, temperature, and oxide composition) needed for co-reduction. We showcase this approach by reducing Cr$_2$O$_3$ mixed with Fe$_2$O$_3$ at 1100 $^\circ$C, significantly lowering reduction temperatures (by $\geq$200 $^\circ$C). Our model and post-reduction atom probe tomography analysis elucidate that the temperature-lowering effect is driven by the lower chemical activity of Cr in the metallic phase. This strategy achieves low-temperature co-reduction of mixed oxides, dramatically reducing energy consumption and CO$_2$ emissions, while unlocking transformative pathways toward sustainable alloy design.

cond-mat.mtrl-sci↗

arXiv2024

SiloFuse: Cross-silo Synthetic Data Generation with Latent Tabular Diffusion Models

Synthetic tabular data is crucial for sharing and augmenting data across silos, especially for enterprises with proprietary data. However, existing synthesizers are designed for centrally stored data. Hence, they struggle with real-world scenarios where features are distributed across multiple silos, necessitating on-premise data storage. We introduce SiloFuse, a novel generative framework for high-quality synthesis from cross-silo tabular data. To ensure privacy, SiloFuse utilizes a distributed latent tabular diffusion architecture. Through autoencoders, latent representations are learned for each client's features, masking their actual values. We employ stacked distributed training to improve communication efficiency, reducing the number of rounds to a single step. Under SiloFuse, we prove the impossibility of data reconstruction for vertically partitioned synthesis and quantify privacy risks through three attacks using our benchmark framework. Experimental results on nine datasets showcase SiloFuse's competence against centralized diffusion-based synthesizers. Notably, SiloFuse achieves 43.8 and 29.8 higher percentage points over GANs in resemblance and utility. Experiments on communication show stacked training's fixed cost compared to the growing costs of end-to-end training as the number of training iterations increases. Additionally, SiloFuse proves robust to feature permutations and varying numbers of clients.

cs.LG↗

arXiv2022

Influence of Bismuth Oxide as a Sintering Aid on the Densification of Cold Sintering of Zirconia

Zirconia (ZrO2) has emerged as a promising technical ceramic, both as high temperature structural material and thermal barrier coating material, etc. The traditional synthesis of ZrO2 with spark plasma sintering (SPS) usually requires a sintering temperature as high as 1200C. General interest in lowering the sintering temperature to reduce energy consumption and thermal stresses has led to research on two promising routes, cold sintering via temperature-dependent chemical reactivity and sintering aids, which facilitates mass transport and improves densification. Here we combine both by developing a single-step sintering process benefitting from both water vapor through the in-situ conversion of Zr(OH)4 to ZrO2 and liquid phase Bi2O3 as a sintering aid. The resultant ZrO2 has a relative density above 80 percent with a sintering temperature as low as 900C.

cond-mat.mtrl-sci↗